OR/15/026 Introduction - Revision history

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	[[Image:OR15026fig1.jpg\|thumb\|400px\| '''Figure 1''' Simplified bedrock geology map of the Huntly and Turriff districts. ]]~~Read 1923~~		[[Image:OR15026fig1.jpg\|thumb\|400px\| '''Figure 1''' Simplified bedrock geology map of the Huntly and Turriff districts. ]]
	The Huntly and Turriff districts lie in the central and western parts of Buchan in north-east Scotland. The economy of the region is based largely on agriculture and forestry, with tourism and whisky production also important. The scenery is typically gently rolling, with the Turriff district forming part of the Buchan plateau, lying between 100 m and 200 m above OD. The districts are drained by the River Deveron and its tributaries, notably the rivers Bogie and Isla, except for their south-eastern part, which is drained by the River Ythan. The drainage pattern in part reflects the routes followed by glacial meltwaters across the districts as they moved generally from west to east. Higher hill ground occurs mainly within the Huntly district, particularly in the west and south, culminating in the Tap o’Noth (563 m), a prominent sentinel overlooking Strathbogie. These higher areas are given over largely to forestry and hill farming.		The Huntly and Turriff districts lie in the central and western parts of Buchan in north-east Scotland. The economy of the region is based largely on agriculture and forestry, with tourism and whisky production also important. The scenery is typically gently rolling, with the Turriff district forming part of the Buchan plateau, lying between 100 m and 200 m above OD. The districts are drained by the River Deveron and its tributaries, notably the rivers Bogie and Isla, except for their south-eastern part, which is drained by the River Ythan. The drainage pattern in part reflects the routes followed by glacial meltwaters across the districts as they moved generally from west to east. Higher hill ground occurs mainly within the Huntly district, particularly in the west and south, culminating in the Tap o’Noth (563 m), a prominent sentinel overlooking Strathbogie. These higher areas are given over largely to forestry and hill farming.

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	The conditions prevailing during regional metamorphism in the wider Buchan region have been the subject of a number of studies since the 1960s. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985"></ref>) used a range of geobarometers and geothermometers to demonstrate an increase in pressure and temperature westwards from the central part of the Turriff Syncline to Portsoy. Subsequent work has further constrained general pressure conditions throughout the region (Baker, 1985<ref name="Baker 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76. </ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transfor- mation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14.</ref>). Chinner (1966)<ref name="Chinner 1966">CHINNER, G A. 1966. The distribution of pressure and temperature during Dalradian metamorphism. Quarterly Journal of the Geological Society of London, Vol. 122, 159–186.</ref> interpreted sillimanite to result from a thermal overprint on the regional metamorphic pattern that related to depth of burial. Subsequently, Fettes (1970)<ref name="Fettes 1970"></ref>, Pankhurst (1970)<ref name="Pankhurst 1970">PANKHURST, R J. 1970. The geochronology of the basic igneous complexes. Scottish Journal of Geology, Vol. 6, 83–107.</ref>, and Ashworth (1975)<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. Geological Magazine, Vol. 112, 113–136. </ref> suggested that the high temperature metamorphic effects, manifest as sillimanite, resulted from the high heat flow associated with intrusion of the mafic-ultramafic plutons. They postulated that their emplacement was approximately coeval with the peak of regional metamorphism. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76.</ref>) delineated two stages of sillimanite growth, one related to the regional metamorphism and the other associated with the basic masses. However, they believed that development of the ‘regional’ and ‘contact’ sillimanite occurred at approximately the same time.		The conditions prevailing during regional metamorphism in the wider Buchan region have been the subject of a number of studies since the 1960s. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985"></ref>) used a range of geobarometers and geothermometers to demonstrate an increase in pressure and temperature westwards from the central part of the Turriff Syncline to Portsoy. Subsequent work has further constrained general pressure conditions throughout the region (Baker, 1985<ref name="Baker 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76. </ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transfor- mation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14.</ref>). Chinner (1966)<ref name="Chinner 1966">CHINNER, G A. 1966. The distribution of pressure and temperature during Dalradian metamorphism. Quarterly Journal of the Geological Society of London, Vol. 122, 159–186.</ref> interpreted sillimanite to result from a thermal overprint on the regional metamorphic pattern that related to depth of burial. Subsequently, Fettes (1970)<ref name="Fettes 1970"></ref>, Pankhurst (1970)<ref name="Pankhurst 1970">PANKHURST, R J. 1970. The geochronology of the basic igneous complexes. Scottish Journal of Geology, Vol. 6, 83–107.</ref>, and Ashworth (1975)<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. Geological Magazine, Vol. 112, 113–136. </ref> suggested that the high temperature metamorphic effects, manifest as sillimanite, resulted from the high heat flow associated with intrusion of the mafic-ultramafic plutons. They postulated that their emplacement was approximately coeval with the peak of regional metamorphism. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76.</ref>) delineated two stages of sillimanite growth, one related to the regional metamorphism and the other associated with the basic masses. However, they believed that development of the ‘regional’ and ‘contact’ sillimanite occurred at approximately the same time.

	The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">~~BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14.~~ </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.		The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990"></ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.

	The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986"></ref>, 1991<ref name="Fettes 1991"></ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).		The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986"></ref>, 1991<ref name="Fettes 1991"></ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).

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History of geological research

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	The relationships between the intrusions of the North-east Grampians Basic Subsuite and the adjacent Dalradian metasedimentary rocks have also been the subject of considerable work. Fettes (1968<ref name="Fettes 1968">FETTES, D J. 1968. Metamorphic structures of Dalradian rocks in north-east Scotland. Unpublished PhD thesis, University of Edinburgh.</ref>, 1970<ref name="Fettes 1970">FETTES, D J. 1970. The structural and metamorphic state of the Dalradian rocks and their bearing on the age of emplacement of the basic sheet. Scottish Journal of Geology, Vol. 6, 108–118.</ref>) showed that in Southern Highland Group arenites and pelites lying north of the Insch Pluton the hornfels mineralogy and texture overprinted an early penetrative fabric, but were in turn overprinted by a secondary deformation and metamorphism. Droop and Charnley (1985)<ref name="Droop 1985">DROOP, G T R, and CHARNLEY, N. 1985. Comparative geobarometry of pelitic hornfelses associated with the newer gabbros: a preliminary study. Journal of the Geological Society of London, Vol. 142, 53–62. </ref> estimated pressure (P) and temperature (T) conditions from metamorphic assemblages in pelitic rocks in the inner hornfels of the Morven–Cabrach, Huntly, Knock and Belhelvie plutons. Using several geobarometers they obtained pressures of 4 to 5 kb and temperatures of 700°C to 850°C, implying that the plutons were all intruded at about the same crustal level (15 to 18.5 km). Later work by Droop et al. (2003)<ref name="Droop 2003">DROOP, G T R, CLEMENS, J D, and DALRYMPLE, D J. 2003. Processes and conditions during contact anatexis, melt escape and restite formation: the Huntly Gabbro Complex, NE Scotland. Journal of Petrology, Vol. 44, 995–1029. </ref> used more modern thermodynamic datasets to assess P-T conditions of the partially melted migmatitic rocks associated with the Huntly Pluton and the surrounding pelitic rocks. Their results corroborated the earlier work giving P values of 5 kb but higher T values for the migmatites of about 900°C.		The relationships between the intrusions of the North-east Grampians Basic Subsuite and the adjacent Dalradian metasedimentary rocks have also been the subject of considerable work. Fettes (1968<ref name="Fettes 1968">FETTES, D J. 1968. Metamorphic structures of Dalradian rocks in north-east Scotland. Unpublished PhD thesis, University of Edinburgh.</ref>, 1970<ref name="Fettes 1970">FETTES, D J. 1970. The structural and metamorphic state of the Dalradian rocks and their bearing on the age of emplacement of the basic sheet. Scottish Journal of Geology, Vol. 6, 108–118.</ref>) showed that in Southern Highland Group arenites and pelites lying north of the Insch Pluton the hornfels mineralogy and texture overprinted an early penetrative fabric, but were in turn overprinted by a secondary deformation and metamorphism. Droop and Charnley (1985)<ref name="Droop 1985">DROOP, G T R, and CHARNLEY, N. 1985. Comparative geobarometry of pelitic hornfelses associated with the newer gabbros: a preliminary study. Journal of the Geological Society of London, Vol. 142, 53–62. </ref> estimated pressure (P) and temperature (T) conditions from metamorphic assemblages in pelitic rocks in the inner hornfels of the Morven–Cabrach, Huntly, Knock and Belhelvie plutons. Using several geobarometers they obtained pressures of 4 to 5 kb and temperatures of 700°C to 850°C, implying that the plutons were all intruded at about the same crustal level (15 to 18.5 km). Later work by Droop et al. (2003)<ref name="Droop 2003">DROOP, G T R, CLEMENS, J D, and DALRYMPLE, D J. 2003. Processes and conditions during contact anatexis, melt escape and restite formation: the Huntly Gabbro Complex, NE Scotland. Journal of Petrology, Vol. 44, 995–1029. </ref> used more modern thermodynamic datasets to assess P-T conditions of the partially melted migmatitic rocks associated with the Huntly Pluton and the surrounding pelitic rocks. Their results corroborated the earlier work giving P values of 5 kb but higher T values for the migmatites of about 900°C.

	The conditions prevailing during regional metamorphism in the wider Buchan region have been the subject of a number of studies since the 1960s. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985">~~HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76.~~ </ref>) used a range of geobarometers and geothermometers to demonstrate an increase in pressure and temperature westwards from the central part of the Turriff Syncline to Portsoy. Subsequent work has further constrained general pressure conditions throughout the region (Baker, 1985<ref name="Baker 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76. </ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transfor- mation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14.</ref>). Chinner (1966)<ref name="Chinner 1966">CHINNER, G A. 1966. The distribution of pressure and temperature during Dalradian metamorphism. Quarterly Journal of the Geological Society of London, Vol. 122, 159–186.</ref> interpreted sillimanite to result from a thermal overprint on the regional metamorphic pattern that related to depth of burial. Subsequently, Fettes (1970)<ref name="Fettes 1970"></ref>, Pankhurst (1970)<ref name="Pankhurst 1970">PANKHURST, R J. 1970. The geochronology of the basic igneous complexes. Scottish Journal of Geology, Vol. 6, 83–107.</ref>, and Ashworth (1975)<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. Geological Magazine, Vol. 112, 113–136. </ref> suggested that the high temperature metamorphic effects, manifest as sillimanite, resulted from the high heat flow associated with intrusion of the mafic-ultramafic plutons. They postulated that their emplacement was approximately coeval with the peak of regional metamorphism. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76.</ref>) delineated two stages of sillimanite growth, one related to the regional metamorphism and the other associated with the basic masses. However, they believed that development of the ‘regional’ and ‘contact’ sillimanite occurred at approximately the same time.		The conditions prevailing during regional metamorphism in the wider Buchan region have been the subject of a number of studies since the 1960s. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985"></ref>) used a range of geobarometers and geothermometers to demonstrate an increase in pressure and temperature westwards from the central part of the Turriff Syncline to Portsoy. Subsequent work has further constrained general pressure conditions throughout the region (Baker, 1985<ref name="Baker 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76. </ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transfor- mation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14.</ref>). Chinner (1966)<ref name="Chinner 1966">CHINNER, G A. 1966. The distribution of pressure and temperature during Dalradian metamorphism. Quarterly Journal of the Geological Society of London, Vol. 122, 159–186.</ref> interpreted sillimanite to result from a thermal overprint on the regional metamorphic pattern that related to depth of burial. Subsequently, Fettes (1970)<ref name="Fettes 1970"></ref>, Pankhurst (1970)<ref name="Pankhurst 1970">PANKHURST, R J. 1970. The geochronology of the basic igneous complexes. Scottish Journal of Geology, Vol. 6, 83–107.</ref>, and Ashworth (1975)<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. Geological Magazine, Vol. 112, 113–136. </ref> suggested that the high temperature metamorphic effects, manifest as sillimanite, resulted from the high heat flow associated with intrusion of the mafic-ultramafic plutons. They postulated that their emplacement was approximately coeval with the peak of regional metamorphism. Hudson (1980<ref name="Hudson 1980">HUDSON, N F C. 1980. Regional metamorphism of some Dalradian pelites in the Buchan area, NE Scotland. Contributions to Mineralogy and Petrology, Vol. 73, 39–51. </ref>, 1985<ref name="Hudson 1985">HUDSON, N F C. 1985. Conditions of Dalradian metamorphism in the Buchan area, NE Scotland. Journal of the Geological Society of London, Vol. 142, 63–76.</ref>) delineated two stages of sillimanite growth, one related to the regional metamorphism and the other associated with the basic masses. However, they believed that development of the ‘regional’ and ‘contact’ sillimanite occurred at approximately the same time.

	The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.		The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.

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	The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.		The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.

	The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986"></ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).		The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986"></ref>, 1991<ref name="Fettes 1991"></ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).

	There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923"></ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.		There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923"></ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.
Line 303:		Line 303:
	</ref>). The patterns of major and trace element abundances derived from the stream-sediment samples in the Huntly and Turriff districts generally reflect the underlying rock units, despite the extensive cover of superficial glacial deposits (mainly till). Hence Ca, Mg, Fe, V, Cr, Ni and Co concentrations are enhanced over the mafic-ultramafic plutons, and K and Ga depleted. In contrast, the Southern Highland Group rocks show enhanced B, Li, Ti and Ga concentrations but low Zr and Ca values. Granitic rocks show enhanced concentrations of K, Rb, Be and Li. The correspondence of stream-sediment and hence till geochemistry with the underlying bedrock suggests that the subglacial till was formed largely in situ.		</ref>). The patterns of major and trace element abundances derived from the stream-sediment samples in the Huntly and Turriff districts generally reflect the underlying rock units, despite the extensive cover of superficial glacial deposits (mainly till). Hence Ca, Mg, Fe, V, Cr, Ni and Co concentrations are enhanced over the mafic-ultramafic plutons, and K and Ga depleted. In contrast, the Southern Highland Group rocks show enhanced B, Li, Ti and Ga concentrations but low Zr and Ca values. Granitic rocks show enhanced concentrations of K, Rb, Be and Li. The correspondence of stream-sediment and hence till geochemistry with the underlying bedrock suggests that the subglacial till was formed largely in situ.

	Both geophysical and geochemical data have been employed to facilitate the delineation of geological boundaries and the nature and extent of units in the poorly exposed Huntly and Turriff districts. Bouguer gravity modelling was used to provide some estimates of the thickness of both the Devonian sequence in the Turriff Outlier (Ashcroft and Wilson, 1976<ref name="Ashcroft 1976">ASHCROFT, W A, and WILSON, C D V. 1976. A geophysical survey of the Turriff basin of Old Red Sandstone, Aberdeen- shire. ''Journal of the Geological Society of London'', Vol. 132, 27–43.</ref>). Leslie (1984)<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. Scottish Journal of Geology, Vol. 20, 215–235. </ref> used ground magnetic surveys and pitting to model the north-eastern contact of the Insch Pluton and its aureole. Similarly Fettes et al. (1991)<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. Scottish Journal of Geology, Vol. 27, 57–73.</ref> combined geological and geophysical methods (mainly detailed ground magnetic surveys) to delineate the nature of the PSZ and the Dalradian stratigraphy to the south-west of Huntly. Gunn et al. (1996)<ref name="Gunn 1996"></ref> combined detailed ground magnetic surveys, and limited new gravity data with borehole information to elucidate the nature of the Succoth–Brown Hill Ultramafic intrusion. This last work linked to an assessment of the amount and nature of platinum group elements associated with the ultramafic and mafic intrusions. The potential for economic quantities of platinum group and other elements has attracted several mineral companies to north-east Scotland, commencing in the 1970s. The companies undertook extensive geophysical surveys, notably of magnetic susceptibility, and drilled considerable numbers of boreholes in the Huntly and Knock Plutons and adjacent migmatitic rocks. Fletcher used material from prospective boreholes to study the mineralogy of the Huntly and Knock plutons and associated mineralisation (Fletcher, 1989<ref name"Fletcher 1989">FLETCHER, T A. 1989. The geology, mineralisation (Ni-Cu-PGE) and stable isotope systematics of Caledonian mafic intrusions near Huntly, NE Scotland. Unpublished Ph D thesis, University of Aberdeen. </ref>; Fletcher and Rice, 1989<ref name="Fletcher & Rice 1989">FLETCHER, T A, and RICE, C M. 1989. Geology, mineralisation (Ni-Cu) and precious - metal geochemistry of Caledonian mafic and ultramafic intrusions near Huntly, north-east Scotland. Transactions of the Institution of Mining and Metallurgy (Sec- tion. B: Applied Earth Science), Vol. 98, B185–200. </ref>). However, to date, no economic deposits have been found.		Both geophysical and geochemical data have been employed to facilitate the delineation of geological boundaries and the nature and extent of units in the poorly exposed Huntly and Turriff districts. Bouguer gravity modelling was used to provide some estimates of the thickness of both the Devonian sequence in the Turriff Outlier (Ashcroft and Wilson, 1976<ref name="Ashcroft 1976">ASHCROFT, W A, and WILSON, C D V. 1976. A geophysical survey of the Turriff basin of Old Red Sandstone, Aberdeen- shire. ''Journal of the Geological Society of London'', Vol. 132, 27–43.</ref>). Leslie (1984)<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. Scottish Journal of Geology, Vol. 20, 215–235. </ref> used ground magnetic surveys and pitting to model the north-eastern contact of the Insch Pluton and its aureole. Similarly Fettes et al. (1991)<ref name="Fettes 1991"></ref> combined geological and geophysical methods (mainly detailed ground magnetic surveys) to delineate the nature of the PSZ and the Dalradian stratigraphy to the south-west of Huntly. Gunn et al. (1996)<ref name="Gunn 1996"></ref> combined detailed ground magnetic surveys, and limited new gravity data with borehole information to elucidate the nature of the Succoth–Brown Hill Ultramafic intrusion. This last work linked to an assessment of the amount and nature of platinum group elements associated with the ultramafic and mafic intrusions. The potential for economic quantities of platinum group and other elements has attracted several mineral companies to north-east Scotland, commencing in the 1970s. The companies undertook extensive geophysical surveys, notably of magnetic susceptibility, and drilled considerable numbers of boreholes in the Huntly and Knock Plutons and adjacent migmatitic rocks. Fletcher used material from prospective boreholes to study the mineralogy of the Huntly and Knock plutons and associated mineralisation (Fletcher, 1989<ref name"Fletcher 1989">FLETCHER, T A. 1989. The geology, mineralisation (Ni-Cu-PGE) and stable isotope systematics of Caledonian mafic intrusions near Huntly, NE Scotland. Unpublished Ph D thesis, University of Aberdeen. </ref>; Fletcher and Rice, 1989<ref name="Fletcher & Rice 1989">FLETCHER, T A, and RICE, C M. 1989. Geology, mineralisation (Ni-Cu) and precious - metal geochemistry of Caledonian mafic and ultramafic intrusions near Huntly, north-east Scotland. Transactions of the Institution of Mining and Metallurgy (Sec- tion. B: Applied Earth Science), Vol. 98, B185–200. </ref>). However, to date, no economic deposits have been found.

	The Quaternary deposits and features of north-east Scotland have been studied for over 150 years, commencing with the pioneering work of Thomas Jamieson who reconstructed the glacial history of the region based mainly on the stratigraphical record (e.g. Jamieson, 1858<ref name="Jamieson 1858">JAMIESON, T F. 1858. On the Pleistocene deposits of Aberdeenshire. Quarterly Journal of the Geological Society of London, Vol.14, 509–532.</ref>, 1906<ref name="Jamieson 1906">JAMIESON, T F. 1906. The glacial period in Aberdeenshire and the southern border of the Moray Firth. Quarterly Journal of the Geological Society of London, Vol. 62, p. 13–39.</ref>). Jamieson’s mantle was taken over by Alexander Bremner who published numerous papers in the early 1900s focussed particularly on the glacial meltwater channels formed during ice retreat (e.g. Bremner, 1934<ref name="Bremner 1934">BREMNER, A. 1934. The glaciation of Moray and ice movements in the north of Scotland. Transactions of the Geological Soci- ety of Edinburgh, Vol. 13, 17–56. </ref>, 1942<ref name="Bremner 1942">BREMNER, A. 1942. The origins of the Scottish river system. Scottish Geographical Magazine, Vol. 58, 15–20, 54–59, 99–103. </ref>). The significant early work by Jamieson and Bremner, their models of Late Devensian glaciation, and the work of later workers on the Quaternary geology of north-east Scotland were summarised in Merritt et al. (2003)<ref name="Merritt 2003">MERRITT, J W, AUTON, C A, CONNELL, E R., HALL, A M, and PEACOCK, J D. 2003. Cenozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, Sheets 66E, 67, 76E, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland). </ref>, who provided a comprehensive account of the Cenozoic geology and landscape evolution of north-east Scotland.		The Quaternary deposits and features of north-east Scotland have been studied for over 150 years, commencing with the pioneering work of Thomas Jamieson who reconstructed the glacial history of the region based mainly on the stratigraphical record (e.g. Jamieson, 1858<ref name="Jamieson 1858">JAMIESON, T F. 1858. On the Pleistocene deposits of Aberdeenshire. Quarterly Journal of the Geological Society of London, Vol.14, 509–532.</ref>, 1906<ref name="Jamieson 1906">JAMIESON, T F. 1906. The glacial period in Aberdeenshire and the southern border of the Moray Firth. Quarterly Journal of the Geological Society of London, Vol. 62, p. 13–39.</ref>). Jamieson’s mantle was taken over by Alexander Bremner who published numerous papers in the early 1900s focussed particularly on the glacial meltwater channels formed during ice retreat (e.g. Bremner, 1934<ref name="Bremner 1934">BREMNER, A. 1934. The glaciation of Moray and ice movements in the north of Scotland. Transactions of the Geological Soci- ety of Edinburgh, Vol. 13, 17–56. </ref>, 1942<ref name="Bremner 1942">BREMNER, A. 1942. The origins of the Scottish river system. Scottish Geographical Magazine, Vol. 58, 15–20, 54–59, 99–103. </ref>). The significant early work by Jamieson and Bremner, their models of Late Devensian glaciation, and the work of later workers on the Quaternary geology of north-east Scotland were summarised in Merritt et al. (2003)<ref name="Merritt 2003">MERRITT, J W, AUTON, C A, CONNELL, E R., HALL, A M, and PEACOCK, J D. 2003. Cenozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, Sheets 66E, 67, 76E, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland). </ref>, who provided a comprehensive account of the Cenozoic geology and landscape evolution of north-east Scotland.

Ajhil: /* History of geological research */

2019-12-03T10:31:03Z

History of geological research

← Older revision		Revision as of 11:31, 3 December 2019
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	The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.		The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.

	The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">~~FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.~~</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).		The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986"></ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).

	There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923"></ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.		There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923"></ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.

Ajhil at 10:30, 3 December 2019

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	The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).		The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).

	There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeen- shire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.		There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923"></ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.

	A more conventional model views the unit as an integral part of the Dalradian succession (Crinan Subgroup) that has undergone Caledonian deformation and high grade metamorphism largely as a result of its structural position in the immediate hangingwall of the PSZ (e.g. Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>). The British Geological Survey published the regional Bouguer gravity and aeromagnetic survey maps in 1978 (Institute of Geological Sciences, 1978a<ref name="IGS 1978a">INSTITUTE OF GEOLOGICAL SCIENCES. 1978a. Moray–Buchan sheet 57°N-04°W 1:250 000 series, Bouguer gravity anomaly map. </ref>, b<ref name="IGS 1978b">INSTITUTE OF GEOLOGICAL SCIENCES. 1978b. Moray–Buchan sheet 57°N-04°W 1:250 000 series, Aeromagnetic anomaly map.</ref> respectively). The results of a regional stream-sediment survey are summarised in the East Grampians geochemical atlas (British Geological Survey, 1991<ref name="BGS 1991">		A more conventional model views the unit as an integral part of the Dalradian succession (Crinan Subgroup) that has undergone Caledonian deformation and high grade metamorphism largely as a result of its structural position in the immediate hangingwall of the PSZ (e.g. Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>). The British Geological Survey published the regional Bouguer gravity and aeromagnetic survey maps in 1978 (Institute of Geological Sciences, 1978a<ref name="IGS 1978a">INSTITUTE OF GEOLOGICAL SCIENCES. 1978a. Moray–Buchan sheet 57°N-04°W 1:250 000 series, Bouguer gravity anomaly map. </ref>, b<ref name="IGS 1978b">INSTITUTE OF GEOLOGICAL SCIENCES. 1978b. Moray–Buchan sheet 57°N-04°W 1:250 000 series, Aeromagnetic anomaly map.</ref> respectively). The results of a regional stream-sediment survey are summarised in the East Grampians geochemical atlas (British Geological Survey, 1991<ref name="BGS 1991">

Ajhil at 10:29, 3 December 2019

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	__NOTOC__		__NOTOC__
	{{OR/15/026}}		{{OR/15/026}}
	[[Image:OR15026fig1.jpg\|thumb\|400px\| '''Figure 1''' Simplified bedrock geology map of the Huntly and Turriff districts. ]]		[[Image:OR15026fig1.jpg\|thumb\|400px\| '''Figure 1''' Simplified bedrock geology map of the Huntly and Turriff districts. ]]Read 1923
	The Huntly and Turriff districts lie in the central and western parts of Buchan in north-east Scotland. The economy of the region is based largely on agriculture and forestry, with tourism and whisky production also important. The scenery is typically gently rolling, with the Turriff district forming part of the Buchan plateau, lying between 100 m and 200 m above OD. The districts are drained by the River Deveron and its tributaries, notably the rivers Bogie and Isla, except for their south-eastern part, which is drained by the River Ythan. The drainage pattern in part reflects the routes followed by glacial meltwaters across the districts as they moved generally from west to east. Higher hill ground occurs mainly within the Huntly district, particularly in the west and south, culminating in the Tap o’Noth (563 m), a prominent sentinel overlooking Strathbogie. These higher areas are given over largely to forestry and hill farming.		The Huntly and Turriff districts lie in the central and western parts of Buchan in north-east Scotland. The economy of the region is based largely on agriculture and forestry, with tourism and whisky production also important. The scenery is typically gently rolling, with the Turriff district forming part of the Buchan plateau, lying between 100 m and 200 m above OD. The districts are drained by the River Deveron and its tributaries, notably the rivers Bogie and Isla, except for their south-eastern part, which is drained by the River Ythan. The drainage pattern in part reflects the routes followed by glacial meltwaters across the districts as they moved generally from west to east. Higher hill ground occurs mainly within the Huntly district, particularly in the west and south, culminating in the Tap o’Noth (563 m), a prominent sentinel overlooking Strathbogie. These higher areas are given over largely to forestry and hill farming.

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	The superficial deposits are dominated by widespread but commonly thin and even patchy tills and locally developed spreads of glaciofluvial sand and gravel. Glacial meltwater channels were developed extensively and have strongly modified the former river pattern. There is only sparse evidence of features and deposits that resulted from the pre-Late Devensian ice sheets. Early in the Dimlington Stadial, the Moray Firth ice sheet transported dark grey, clay-rich till containing rafts of Jurassic mudstones and Quaternary marine sediments onshore to the south and south-east as far as Turriff. This ice stream also diverted the inland ice sourced in the Grampian Highlands eastwards and southwards, as shown by recorded striations and distribution of both local and far-travelled erratics. A later phase of north to north-eastward movement by this East Grampians ice sheet is indicated by north-trending striae and the distribution of troctolite and gabbro erratics from the Huntly intrusion (Read, 1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>; Merritt et al., 2003<ref name="Merritt 2003">MERRITT, J W, AUTON, C A, CONNELL, E R., HALL, A M, and PEACOCK, J D. 2003. Cenozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, Sheets 66E, 67, 76E, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland). </ref>). Till resulting from the East Grampians ice sheet occurs mainly to the north in the Portsoy and Banff districts (Sheets 96W and 96E respectively). The presence of ice in the Moray Firth during deglaciation resulted in the formation of marginal lakes and as a result the bulk of meltwater was diverted eastwards via a series of glacial meltwater channels. Classic examples include the Fyvie Gorge, occupied now by the River Ythan, and the valley of the Idoch Water. The courses of the Deveron and Ythan rivers and their tributaries were also considerably modified by the glacial meltwaters. Recent superficial deposits comprise river alluvium in the valleys of the rivers and larger streams, and patches of peat locally developed to the north and west of the River Deveron and to the east of Fyvie and Cuminestown.		The superficial deposits are dominated by widespread but commonly thin and even patchy tills and locally developed spreads of glaciofluvial sand and gravel. Glacial meltwater channels were developed extensively and have strongly modified the former river pattern. There is only sparse evidence of features and deposits that resulted from the pre-Late Devensian ice sheets. Early in the Dimlington Stadial, the Moray Firth ice sheet transported dark grey, clay-rich till containing rafts of Jurassic mudstones and Quaternary marine sediments onshore to the south and south-east as far as Turriff. This ice stream also diverted the inland ice sourced in the Grampian Highlands eastwards and southwards, as shown by recorded striations and distribution of both local and far-travelled erratics. A later phase of north to north-eastward movement by this East Grampians ice sheet is indicated by north-trending striae and the distribution of troctolite and gabbro erratics from the Huntly intrusion (Read, 1923<ref name="Read 1923"></ref>; Merritt et al., 2003<ref name="Merritt 2003">MERRITT, J W, AUTON, C A, CONNELL, E R., HALL, A M, and PEACOCK, J D. 2003. Cenozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, Sheets 66E, 67, 76E, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland). </ref>). Till resulting from the East Grampians ice sheet occurs mainly to the north in the Portsoy and Banff districts (Sheets 96W and 96E respectively). The presence of ice in the Moray Firth during deglaciation resulted in the formation of marginal lakes and as a result the bulk of meltwater was diverted eastwards via a series of glacial meltwater channels. Classic examples include the Fyvie Gorge, occupied now by the River Ythan, and the valley of the Idoch Water. The courses of the Deveron and Ythan rivers and their tributaries were also considerably modified by the glacial meltwaters. Recent superficial deposits comprise river alluvium in the valleys of the rivers and larger streams, and patches of peat locally developed to the north and west of the River Deveron and to the east of Fyvie and Cuminestown.

	===Structure and metamorphism===		===Structure and metamorphism===

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	The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.		The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.

	The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995">~~STEPHENSON, D, and GOULD, D. 1995. The Grampian Highlands: British Regional Geology. (Keyworth, Nottingham: British Geological Survey.) ISBN 0 11 884521 7~~ </ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).		The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995"></ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).

	There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeen- shire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.		There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeen- shire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.

Ajhil: /* History of geological research */

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History of geological research

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	</ref>). The patterns of major and trace element abundances derived from the stream-sediment samples in the Huntly and Turriff districts generally reflect the underlying rock units, despite the extensive cover of superficial glacial deposits (mainly till). Hence Ca, Mg, Fe, V, Cr, Ni and Co concentrations are enhanced over the mafic-ultramafic plutons, and K and Ga depleted. In contrast, the Southern Highland Group rocks show enhanced B, Li, Ti and Ga concentrations but low Zr and Ca values. Granitic rocks show enhanced concentrations of K, Rb, Be and Li. The correspondence of stream-sediment and hence till geochemistry with the underlying bedrock suggests that the subglacial till was formed largely in situ.		</ref>). The patterns of major and trace element abundances derived from the stream-sediment samples in the Huntly and Turriff districts generally reflect the underlying rock units, despite the extensive cover of superficial glacial deposits (mainly till). Hence Ca, Mg, Fe, V, Cr, Ni and Co concentrations are enhanced over the mafic-ultramafic plutons, and K and Ga depleted. In contrast, the Southern Highland Group rocks show enhanced B, Li, Ti and Ga concentrations but low Zr and Ca values. Granitic rocks show enhanced concentrations of K, Rb, Be and Li. The correspondence of stream-sediment and hence till geochemistry with the underlying bedrock suggests that the subglacial till was formed largely in situ.

	Both geophysical and geochemical data have been employed to facilitate the delineation of geological boundaries and the nature and extent of units in the poorly exposed Huntly and Turriff districts. Bouguer gravity modelling was used to provide some estimates of the thickness of both the Devonian sequence in the Turriff Outlier (Ashcroft and Wilson, 1976<ref name="Ashcroft 1976">ASHCROFT, W A, and WILSON, C D V. 1976. A geophysical survey of the Turriff basin of Old Red Sandstone, Aberdeen- shire. ''Journal of the Geological Society of London'', Vol. 132, 27–43.</ref>). Leslie (1984)<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. Scottish Journal of Geology, Vol. 20, 215–235. </ref> used ground magnetic surveys and pitting to model the north-eastern contact of the Insch Pluton and its aureole. Similarly Fettes et al. (1991)<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. Scottish Journal of Geology, Vol. 27, 57–73.</ref> combined geological and geophysical methods (mainly detailed ground magnetic surveys) to delineate the nature of the PSZ and the Dalradian stratigraphy to the south-west of Huntly. Gunn et al. (1996)<ref name="Gunn 1996">GUNN, A G, STYLES, M T, ROLLIN, K E, and STEPHENSON, D. 1996. The geology of the Succoth–Brown Hill mafic-ultramafic intrusive complex, near Huntly, Aberdeenshire. ''Scottish Journal of Geology, ''Vol. 32, 33–49.</ref> combined detailed ground magnetic surveys, and limited new gravity data with borehole information to elucidate the nature of the Succoth–Brown Hill Ultramafic intrusion. This last work linked to an assessment of the amount and nature of platinum group elements associated with the ultramafic and mafic intrusions. The potential for economic quantities of platinum group and other elements has attracted several mineral companies to north-east Scotland, commencing in the 1970s. The companies undertook extensive geophysical surveys, notably of magnetic susceptibility, and drilled considerable numbers of boreholes in the Huntly and Knock Plutons and adjacent migmatitic rocks. Fletcher used material from prospective boreholes to study the mineralogy of the Huntly and Knock plutons and associated mineralisation (Fletcher, 1989<ref name"Fletcher 1989">FLETCHER, T A. 1989. The geology, mineralisation (Ni-Cu-PGE) and stable isotope systematics of Caledonian mafic intrusions near Huntly, NE Scotland. Unpublished Ph D thesis, University of Aberdeen. </ref>; Fletcher and Rice, 1989<ref name="Fletcher & Rice 1989">FLETCHER, T A, and RICE, C M. 1989. Geology, mineralisation (Ni-Cu) and precious - metal geochemistry of Caledonian mafic and ultramafic intrusions near Huntly, north-east Scotland. Transactions of the Institution of Mining and Metallurgy (Sec- tion. B: Applied Earth Science), Vol. 98, B185–200. </ref>). However, to date, no economic deposits have been found.		Both geophysical and geochemical data have been employed to facilitate the delineation of geological boundaries and the nature and extent of units in the poorly exposed Huntly and Turriff districts. Bouguer gravity modelling was used to provide some estimates of the thickness of both the Devonian sequence in the Turriff Outlier (Ashcroft and Wilson, 1976<ref name="Ashcroft 1976">ASHCROFT, W A, and WILSON, C D V. 1976. A geophysical survey of the Turriff basin of Old Red Sandstone, Aberdeen- shire. ''Journal of the Geological Society of London'', Vol. 132, 27–43.</ref>). Leslie (1984)<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. Scottish Journal of Geology, Vol. 20, 215–235. </ref> used ground magnetic surveys and pitting to model the north-eastern contact of the Insch Pluton and its aureole. Similarly Fettes et al. (1991)<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. Scottish Journal of Geology, Vol. 27, 57–73.</ref> combined geological and geophysical methods (mainly detailed ground magnetic surveys) to delineate the nature of the PSZ and the Dalradian stratigraphy to the south-west of Huntly. Gunn et al. (1996)<ref name="Gunn 1996"></ref> combined detailed ground magnetic surveys, and limited new gravity data with borehole information to elucidate the nature of the Succoth–Brown Hill Ultramafic intrusion. This last work linked to an assessment of the amount and nature of platinum group elements associated with the ultramafic and mafic intrusions. The potential for economic quantities of platinum group and other elements has attracted several mineral companies to north-east Scotland, commencing in the 1970s. The companies undertook extensive geophysical surveys, notably of magnetic susceptibility, and drilled considerable numbers of boreholes in the Huntly and Knock Plutons and adjacent migmatitic rocks. Fletcher used material from prospective boreholes to study the mineralogy of the Huntly and Knock plutons and associated mineralisation (Fletcher, 1989<ref name"Fletcher 1989">FLETCHER, T A. 1989. The geology, mineralisation (Ni-Cu-PGE) and stable isotope systematics of Caledonian mafic intrusions near Huntly, NE Scotland. Unpublished Ph D thesis, University of Aberdeen. </ref>; Fletcher and Rice, 1989<ref name="Fletcher & Rice 1989">FLETCHER, T A, and RICE, C M. 1989. Geology, mineralisation (Ni-Cu) and precious - metal geochemistry of Caledonian mafic and ultramafic intrusions near Huntly, north-east Scotland. Transactions of the Institution of Mining and Metallurgy (Sec- tion. B: Applied Earth Science), Vol. 98, B185–200. </ref>). However, to date, no economic deposits have been found.

	The Quaternary deposits and features of north-east Scotland have been studied for over 150 years, commencing with the pioneering work of Thomas Jamieson who reconstructed the glacial history of the region based mainly on the stratigraphical record (e.g. Jamieson, 1858<ref name="Jamieson 1858">JAMIESON, T F. 1858. On the Pleistocene deposits of Aberdeenshire. Quarterly Journal of the Geological Society of London, Vol.14, 509–532.</ref>, 1906<ref name="Jamieson 1906">JAMIESON, T F. 1906. The glacial period in Aberdeenshire and the southern border of the Moray Firth. Quarterly Journal of the Geological Society of London, Vol. 62, p. 13–39.</ref>). Jamieson’s mantle was taken over by Alexander Bremner who published numerous papers in the early 1900s focussed particularly on the glacial meltwater channels formed during ice retreat (e.g. Bremner, 1934<ref name="Bremner 1934">BREMNER, A. 1934. The glaciation of Moray and ice movements in the north of Scotland. Transactions of the Geological Soci- ety of Edinburgh, Vol. 13, 17–56. </ref>, 1942<ref name="Bremner 1942">BREMNER, A. 1942. The origins of the Scottish river system. Scottish Geographical Magazine, Vol. 58, 15–20, 54–59, 99–103. </ref>). The significant early work by Jamieson and Bremner, their models of Late Devensian glaciation, and the work of later workers on the Quaternary geology of north-east Scotland were summarised in Merritt et al. (2003)<ref name="Merritt 2003">MERRITT, J W, AUTON, C A, CONNELL, E R., HALL, A M, and PEACOCK, J D. 2003. Cenozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, Sheets 66E, 67, 76E, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland). </ref>, who provided a comprehensive account of the Cenozoic geology and landscape evolution of north-east Scotland.		The Quaternary deposits and features of north-east Scotland have been studied for over 150 years, commencing with the pioneering work of Thomas Jamieson who reconstructed the glacial history of the region based mainly on the stratigraphical record (e.g. Jamieson, 1858<ref name="Jamieson 1858">JAMIESON, T F. 1858. On the Pleistocene deposits of Aberdeenshire. Quarterly Journal of the Geological Society of London, Vol.14, 509–532.</ref>, 1906<ref name="Jamieson 1906">JAMIESON, T F. 1906. The glacial period in Aberdeenshire and the southern border of the Moray Firth. Quarterly Journal of the Geological Society of London, Vol. 62, p. 13–39.</ref>). Jamieson’s mantle was taken over by Alexander Bremner who published numerous papers in the early 1900s focussed particularly on the glacial meltwater channels formed during ice retreat (e.g. Bremner, 1934<ref name="Bremner 1934">BREMNER, A. 1934. The glaciation of Moray and ice movements in the north of Scotland. Transactions of the Geological Soci- ety of Edinburgh, Vol. 13, 17–56. </ref>, 1942<ref name="Bremner 1942">BREMNER, A. 1942. The origins of the Scottish river system. Scottish Geographical Magazine, Vol. 58, 15–20, 54–59, 99–103. </ref>). The significant early work by Jamieson and Bremner, their models of Late Devensian glaciation, and the work of later workers on the Quaternary geology of north-east Scotland were summarised in Merritt et al. (2003)<ref name="Merritt 2003">MERRITT, J W, AUTON, C A, CONNELL, E R., HALL, A M, and PEACOCK, J D. 2003. Cenozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, Sheets 66E, 67, 76E, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland). </ref>, who provided a comprehensive account of the Cenozoic geology and landscape evolution of north-east Scotland.

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← Older revision		Revision as of 11:27, 3 December 2019
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	The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.		The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.

	The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995">STEPHENSON, D, and GOULD, D. 1995. The Grampian Highlands: British Regional Geology. (Keyworth, Nottingham: British Geological Survey.) ISBN 0 11 884521 7 </ref>; Carty, 2001<ref name="Carty 2001"> </ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).		The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995">STEPHENSON, D, and GOULD, D. 1995. The Grampian Highlands: British Regional Geology. (Keyworth, Nottingham: British Geological Survey.) ISBN 0 11 884521 7 </ref>; Carty, 2001<ref name="Carty 2001"></ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).

	There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeen- shire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.		There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeen- shire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.

Ajhil: /* History of geological research */

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History of geological research

← Older revision		Revision as of 11:26, 3 December 2019
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	The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.		The pseudomorphing of andalusite by kyanite west of the PSZ was first noted by Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> and subsequently studied by Chinner (1980)<ref name="Chinner 1980">CHINNER, G A. 1980. Kyanite isograds of Grampian metamorphism. Journal of the Geological Society of London, Vol. 137, 35–39. </ref>, Chinner and Heseltine (1979)<ref name="Chinner 1979">CHINNER, G A, and HESELTINE, F J. 1979. The Grampide andalusite/kyanite isograd. Scottish Journal of Geology, Vol. 15, 117–127. </ref> and Beddoe-Stephens (1990)<ref name="Beddoe 1990">BEDDOE-STEPHENS, B. 1990. Pressures and temperatures of Dalradian metamorphism and the andalusite-kyanite transformation in the north-east Grampians. Scottish Journal of Geology, Vol. 26, 3–14. </ref>. Beddoe-Stephens used several geothermometers to elucidate the pressure and temperature conditions under which the inversion from andalusite to kyanite occurred. He showed that there was an increase in pressure of about 2 kb across the PSZ and interpreted this in terms of westerly directed thrusting across this structure as postulated by Baker (1987)<ref name="Baker 1987">BAKER, A J. 1987. Models for the tectonothermal evolution of the eastern Dalradian of Scotland. Journal of Metamorphic Ge- ology, Vol. 5, 101–118.</ref>. In contrast, Dempster et al. (1995)<ref name="Dempster 1995">DEMPSTER, T J, HUDSON, N F, and ROGERS, G. 1995. Metamorphism and cooling of the NE Dalradian. Journal of the Geological Society of London, Vol. 152, 383–390. </ref> suggested that the superimcumbent load imposed by the emplacement of the mafic-ultramafic intrusions may have been responsible for this pressure increase.

	The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34. </ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.		The role of the Portsoy Lineament and Shear Zone was not recognised during the original surveys. Read (1923)<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeenshire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref> placed the main dislocation, the Boyne Line, farther east and interpolated its extension southwards into the Huntly district where it was position was defined by sparse exposures of gneissose and schistose lithologies. Elles (1931)<ref name="Elles 1931">ELLES, G L. 1931. Notes on the Portsoy coastal district. Geological Magazine, Vol. 68, 24–34.</ref> first recognised a major dislocation in the Dalradian succession farther west at the junction of the Portsoy Limestone Formation and Cowhythe Psammite Formation in Links Bay by Portsoy. She termed this structure the Portsoy Thrust. Subsequent work has shown that there is a major shear zone, the Portsoy Shear Zone (PSZ), some 1.5 km wide, exposed on the Banffshire coast at Portsoy. Its role in the geological history of north-east Scotland has been variously interpreted but most authors agree that it is a regionally significant structure with a long history of movement (Fettes et al., 1986<ref name="Fettes 1986">FETTES, D J, GRAHAM, C M, HARTE, B, and PLANT, J A. 1986. Lineaments and basement domains: an alternative view of Dalradian evolution. Journal of the Geological Society of London, Vol.143, 453–464.</ref>, 1991<ref name="Fettes 1991">FETTES, D J, LESLIE, A G, STEPHENSON, D, and KIMBELL, S F. 1991. Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys. ''Scottish Journal of Geology'', Vol. 27, 57–73.</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995">STEPHENSON, D, and GOULD, D. 1995. The Grampian Highlands: British Regional Geology. (Keyworth, Nottingham: British Geological Survey.) ISBN 0 11 884521 7 </ref>; Carty, 2001<ref name="Carty 2001"> </ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).
	</ref>; Goodman, 1994<ref name=Goodman 1994">GOODMAN, S. 1994. The Portsoy–Duchray Hill Lineament: a review of the evidence. Geological Magazine, Vol. 131, 407– 415. </ref>; Stephenson and Gould, 1995<ref name="Stephenson 1995">STEPHENSON, D, and GOULD, D. 1995. The Grampian Highlands: British Regional Geology. (Keyworth, Nottingham: British Geological Survey.) ISBN 0 11 884521 7 </ref>; Carty, 2001<ref name="Carty 2001">~~CARTY, J. 2001. Deformation, magmatism and metamorphism in the Portsoy Shear Zone, North East Scotland. Unpublished PhD thesis, University of Derby.~~ </ref>; Viete et al., 2010<ref name="Viete 2010">VIETE, D R, RICHARDS, S W, LISTER, G S, OLIVER, G J H, and BANKS, G J. 2010. Lithospheric-scale extension during Grampian orogenesis in Scotland. 121–160 in Continental tectonics and mountain building: the legacy of Peach and Horne. LAW, R D, HOLDSWORTH, R E, KRABBENDAM, M, and STRACHAN, R A (editors). Special Publication of the Geological Society of London, No. 335. ISBN 978-1-86239-300-4 </ref>). Ashcroft et al. (1984)<ref name="Ashcroft 1984"></ref> showed that the PSZ was part of a network of steeply inclined shear zones that bounded and transected the Buchan area of north-east Scotland, approximately coeval with emplacement of the North-east Grampian Basic Subsuite. Although the PSZ now dips steeply eastwards authors differ as to whether formerly it dipped more gently and was the site of regional westward thrusting (Baker, 1987<ref name="Baker 1987"></ref>; Beddoe-Stephens, 1990<ref name="Beddoe 1990"></ref>; Viete et al., 2010<ref name="Viete 2010"></ref>).

	There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeen- shire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.		There have been widely differing interpretations of the nature of the protoliths and geological history of the Cowhythe Psammite Formation (‘Cowhythe Gneiss’). Read (1923<ref name="Read 1923">READ, H H. 1923. The geology of the country around Banff, Huntly and Turriff (Lower Banffshire and North-west Aberdeen- shire) Explanation of Sheets 86 and 96. Memoir of the Geological Survey, Scotland. (Edinburgh: HMSO).</ref>, 1955<ref name="Read 1955">READ, H H. 1955. The Banff Nappe: an interpretation of the structure of the Dalradian rocks of north-east Scotland. Proceedings of the Geologists’ Association, Vol. 66, 1–29. </ref>) interpreted this unit as part of his Keith Division — older gneissose metasedimentary rocks with a more complex structural and metamorphic history that formed the autochthonous basement to the Banff Nappe. Ramsay and Sturt (1979)<ref name="Ramsay 1979">RAMSAY, D M, and STURT, B A. 1979. The status of the Banff Nappe. 145–151 in The Caledonides of the British Isles– reviewed. HARRIS, A L, HOLLAND, C H, and LEAKE, B E (editors). Special Publication of the Geological Society of London, No. 8. </ref> emphasised this structural and metamorphic complexity, and in combination with Rb-Sr isotopic data from the Inzie Head and Ellon gneisses that gave Neoproterozoic ages (Sturt et al., 1977<ref name="Sturt 1977">STURT, B A, RAMSAY, D M, PRINGLE, I R, and TEGGIN, D E. 1977. Precambrian gneisses in the Dalradian sequence of north-east Scotland. Journal of the Geological Society of London, Vol. 134, 41–44. </ref>), they suggested that this unit represented allochthonous pre-Caledonian basement, thrust westwards along the Portsoy Thrust. Oliver (in Viete et al., 2010 <ref name="Viete 2010"></ref>) obtained a U-Pb SHRIMP age of 1012 ± 10 Ma from zircon overgrowths in a migmatitic leucosome from the western part of the Cowhythe Psammite Formation, suggesting that Grenvillean basement is present. Viete et al. (2014)<ref name="Viete 2014">VIETE, D R, OLIVER, G J H, and WILDE, S A. 2014. Discussion of ‘Metamorphic P-T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogeny, Scotland’. ''Geological Magazine'', Vol. 151, 755–763.</ref> obtained more detailed U-Pb SHRIMP ages from 55 small euhedral zircons, typically with prominent oscillatory zoning, sampled from both the leucosome and mesosome of the migmatitic pelite. The zircons gave concordant ages between 1025 and 975 Ma, with a mean 206Pb/238U age of 1003± 6 Ma age, interpreted as dating the migmatisation. Inherited ages ranged from 3000 Ma to 1000 Ma.