OR/15/026 Intrusive igneous rocks - Revision history

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	Mineral chemistry data indicate that the majority of the cumulate rocks in the Huntly and Knock intrusions belong to the Lower and Middle Zones of Clarke and Wadsworth (1970)<ref name="Clarke 1970"></ref>. However, in contrast to the Insch Pluton, there is no overall coherent igneous ‘stratigraphy’ within the Huntly mass. In the West Huntly body both cryptic variation patterns and way-up indicators in the layered rocks suggest that the base of the intrusion now corresponds to the western margin with younging upwards towards the east. However at Bridges, similar rocks that also show relatively primitive compositions, young towards the west. Hay (2002)<ref name="Hay 2002"></ref> has suggested that these layered cumulate rocks in the eastern part of the Huntly Pluton may represent roof cumulates. Alternatively they may be indicative of large scale folding within the intrusion (Fletcher, 1989)<ref name="Fletcher 1989"></ref>. In the Knock Pluton microchemical data for plagioclase suggests that the base of the intrusion lies along the western contact, similar to Huntly. However borehole evidence from Drumnagorrach demonstrates the complex nature of the western margin of the Knock body with numerous mafic sheets and contaminated mafic rocks juxtaposed with highly foliated amphibolitised metabasic rocks, probably derived from the gabbros.		Mineral chemistry data indicate that the majority of the cumulate rocks in the Huntly and Knock intrusions belong to the Lower and Middle Zones of Clarke and Wadsworth (1970)<ref name="Clarke 1970"></ref>. However, in contrast to the Insch Pluton, there is no overall coherent igneous ‘stratigraphy’ within the Huntly mass. In the West Huntly body both cryptic variation patterns and way-up indicators in the layered rocks suggest that the base of the intrusion now corresponds to the western margin with younging upwards towards the east. However at Bridges, similar rocks that also show relatively primitive compositions, young towards the west. Hay (2002)<ref name="Hay 2002"></ref> has suggested that these layered cumulate rocks in the eastern part of the Huntly Pluton may represent roof cumulates. Alternatively they may be indicative of large scale folding within the intrusion (Fletcher, 1989)<ref name="Fletcher 1989"></ref>. In the Knock Pluton microchemical data for plagioclase suggests that the base of the intrusion lies along the western contact, similar to Huntly. However borehole evidence from Drumnagorrach demonstrates the complex nature of the western margin of the Knock body with numerous mafic sheets and contaminated mafic rocks juxtaposed with highly foliated amphibolitised metabasic rocks, probably derived from the gabbros.

	Major areas of the Huntly Pluton are underlain by cumulate rocks in which the primary igneous textures have been partially or wholly eliminated as a result of recrystallisation to finer grained granular lithologies. In some zones a pervasive planar foliation or cleavage has also been superimposed. These rocks are separated from the layered cumulate sequences by narrow belts of transitional rocks, mostly glomeroporphyritic olivine-gabbros or ophitic gabbros, which have been less strongly recrystallised. The origin of the granular gabbroic rocks in the ‘Younger Basic’ intrusions has been discussed by several workers (Read and Haq, 1965<ref name="Read 1963">READ, H H, and HAQ, B T. 1965. Notes, mainly geochemical, on the granite-diorite complex of the Insch igneous mass, with an addendum on the Aberdeenshire quartz-dolerites. ''Proceedings of the Geologists’ Association'', Vol. 76, 13–19. </ref>; Clarke and Wadsworth, 1970<ref name="Clarke 1970"></ref>; Wadsworth, 1988<ref name="Wadsworth 1988">~~WADSWORTH, W J. 1988. Silicate mineralogy of the Middle Zone cumulates and associated gabbroic rocks from the Insch Intrusion, NE Scotland. ''Mineralogical Magazine'', Vol. 52, 309–322.~~</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 (Section. B: Applied Earth Science), Vol. 98, B185–200.</ref>; Gillespie et al., 1994<ref name="Gillespie 1994">GILLESPIE, M R, STYLES, M T, HENNEY, P J, WETTON, P, SULLIVAN, M A, and PEREZ-ALVAREZ, M S. 1994. A new approach to map production and petrogenetic interpretation using petrological databases: an example from the Huntly–Knock intrusions of Aberdeenshire. ''British Geological Survey Technical Report'', WG/94/14. </ref>; Hay, 2002<ref name="Hay 2002"></ref>). Various mechanisms for their formation have been proposed, but in the Huntly and Knock plutons we attribute the recrystallisation to shear-related deformation of the hot, ductile rock either immediately following or during the later stages of magma crystallisation.		Major areas of the Huntly Pluton are underlain by cumulate rocks in which the primary igneous textures have been partially or wholly eliminated as a result of recrystallisation to finer grained granular lithologies. In some zones a pervasive planar foliation or cleavage has also been superimposed. These rocks are separated from the layered cumulate sequences by narrow belts of transitional rocks, mostly glomeroporphyritic olivine-gabbros or ophitic gabbros, which have been less strongly recrystallised. The origin of the granular gabbroic rocks in the ‘Younger Basic’ intrusions has been discussed by several workers (Read and Haq, 1965<ref name="Read 1963">READ, H H, and HAQ, B T. 1965. Notes, mainly geochemical, on the granite-diorite complex of the Insch igneous mass, with an addendum on the Aberdeenshire quartz-dolerites. ''Proceedings of the Geologists’ Association'', Vol. 76, 13–19. </ref>; Clarke and Wadsworth, 1970<ref name="Clarke 1970"></ref>; Wadsworth, 1988<ref name="Wadsworth 1988"></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 (Section. B: Applied Earth Science), Vol. 98, B185–200.</ref>; Gillespie et al., 1994<ref name="Gillespie 1994">GILLESPIE, M R, STYLES, M T, HENNEY, P J, WETTON, P, SULLIVAN, M A, and PEREZ-ALVAREZ, M S. 1994. A new approach to map production and petrogenetic interpretation using petrological databases: an example from the Huntly–Knock intrusions of Aberdeenshire. ''British Geological Survey Technical Report'', WG/94/14. </ref>; Hay, 2002<ref name="Hay 2002"></ref>). Various mechanisms for their formation have been proposed, but in the Huntly and Knock plutons we attribute the recrystallisation to shear-related deformation of the hot, ductile rock either immediately following or during the later stages of magma crystallisation.

	Contaminated gabbroic rocks are widespread in both the Huntly and Knock plutons, with large areas of xenolithic rocks predominant towards their eastern margins. These rocks are derived from the assimilation of large quantities of metasedimentary rocks, preserved on a large scale either marking the roof zone of the intrusion or as a result of an emplacement mechanism that led to incorporation of a large amount of sedimentary material along this boundary. Elsewhere, for example in the central part of the Huntly Pluton, slow cooling of the magma allowed relatively complete digestion of the sedimentary xenoliths leading to the development of contaminated gabbros.		Contaminated gabbroic rocks are widespread in both the Huntly and Knock plutons, with large areas of xenolithic rocks predominant towards their eastern margins. These rocks are derived from the assimilation of large quantities of metasedimentary rocks, preserved on a large scale either marking the roof zone of the intrusion or as a result of an emplacement mechanism that led to incorporation of a large amount of sedimentary material along this boundary. Elsewhere, for example in the central part of the Huntly Pluton, slow cooling of the magma allowed relatively complete digestion of the sedimentary xenoliths leading to the development of contaminated gabbros.

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Modified cumulate rocks

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	Extensive, but poorly exposed areas of the Huntly and Knock plutons appear not to be underlain by cumulate rocks, but such rocks have received little attention prior to the work of 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>. Subsequently, field mapping, BGS Mineral Reconnaissance Programme surveys, and reevaluation of EVL borehole data, show that these ‘non-cumulate' rocks consist of a variety of rock types including modified cumulates and contaminated gabbroic rocks (Figures 6b, c). Each type commonly has textural affinities with adjacent units and irregular or gradational contacts.		Extensive, but poorly exposed areas of the Huntly and Knock plutons appear not to be underlain by cumulate rocks, but such rocks have received little attention prior to the work of 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>. Subsequently, field mapping, BGS Mineral Reconnaissance Programme surveys, and reevaluation of EVL borehole data, show that these ‘non-cumulate' rocks consist of a variety of rock types including modified cumulates and contaminated gabbroic rocks (Figures 6b, c). Each type commonly has textural affinities with adjacent units and irregular or gradational contacts.

	''West Huntly'': the relationships between modified and unmodified cumulate lithologies are best seen in the West Huntly body. Cumulate rocks that display a range of igneous textures pass eastwards in the Bin Forest into rocks, firstly with an anhedral granular character and then through a range of intermediate types. This transition is best observed on the eastern flanks of the Bin between the Bin Quarry and the summit, but is also discernible in the eastern part of Dubenan Wood. Towards the east orthopyroxene appears as a cumulus phase, accompanied by an increase in olivine grain size. Aggregates of olivine crystals, up to 2 cm across, give rise to a glomeroporphyritic olivine-gabbro with a distinctive spotted appearance that can be mapped as a discontinuous band up to 50 m wide. Farther east these rocks become increasingly fine grained and develop an anhedral granular texture (Plate 3). Orthopyroxene becomes an increasingly important constituent and olivine gradually disappears. These rocks, termed granular gabbros, outcrop in a band about 1 km wide on the eastern flank of the Bin Forest. They comprise a heterogeneous group, composed mostly of fine-grained gabbroic and leucocratic noritic rocks. They are commonly partly or wholly recrystallised and show amphibolite-facies mineralogies. Although relict primary igneous textures are found locally, a foliation is widely developed and mylonitic fabrics are seen sporadically.		''West Huntly'': the relationships between modified and unmodified cumulate lithologies are best seen in the West Huntly body. Cumulate rocks that display a range of igneous textures pass eastwards in the Bin Forest into rocks, firstly with an anhedral granular character and then through a range of intermediate types. This transition is best observed on the eastern flanks of the Bin between the Bin Quarry and the summit, but is also discernible in the eastern part of Dubenan Wood. Towards the east orthopyroxene appears as a cumulus phase, accompanied by an increase in olivine grain size. Aggregates of olivine crystals, up to 2 cm across, give rise to a glomeroporphyritic olivine-gabbro with a distinctive spotted appearance that can be mapped as a discontinuous band up to 50 m wide. Farther east these rocks become increasingly fine grained and develop an anhedral granular texture (Plate 3). Orthopyroxene becomes an increasingly important constituent and olivine gradually disappears. These rocks, termed granular gabbros, outcrop in a band about 1 km wide on the eastern flank of the Bin Forest. They comprise a heterogeneous group, composed mostly of fine-grained gabbroic and leucocratic noritic rocks. They are commonly partly or wholly recrystallised and show amphibolite-facies mineralogies. Although relict primary igneous textures are found locally, a foliation is widely developed and mylonitic fabrics are seen sporadically.

	[[Image:OR15026plate3.jpg\|thumb\|center\|500px\| '''Plate 3''' Photomicrographs of rocks from pre- and syntectonic mafic–ultramafic intrusions in the Huntly district.<br>		[[Image:OR15026plate3.jpg\|thumb\|center\|500px\| '''Plate 3''' Photomicrographs of rocks from pre- and syntectonic mafic–ultramafic intrusions in the Huntly district.<br>

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Modified cumulate rocks

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	[[Image:OR15026plate3.jpg\|thumb\|center\|500px\| '''Plate 3''' Photomicrographs of rocks from pre- and syntectonic mafic–ultramafic intrusions in the Huntly district.<br>		[[Image:OR15026plate3.jpg\|thumb\|center\|500px\| '''Plate 3''' Photomicrographs of rocks from pre- and syntectonic mafic–ultramafic intrusions in the Huntly district.<br>
	1.Cumulate, West Huntly ([[Media:~~P808811_~~.jpg\|P808811]])<br>		1.Cumulate, West Huntly ([[Media:P808811.jpg\|P808811]])<br>
	2.Glomeroporphyritic olivine-gabbro, west Huntly ([[Media:~~P808813_~~.jpg\|P808813]])<br>		2.Glomeroporphyritic olivine-gabbro, west Huntly ([[Media:P808813.jpg\|P808813]])<br>
	3.Granular/schistose gabbro, central Huntly ([[Media:~~P808812_~~.jpg\|P808812]])<br>		3.Granular/schistose gabbro, central Huntly ([[Media:P808812.jpg\|P808812]])<br>
	4.Contaminated gabbro, central Huntly ([[Media:~~P808814_~~.jpg\|P808814]])<br>		4.Contaminated gabbro, central Huntly ([[Media:P808814.jpg\|P808814]])<br>
	5.Clinopyroxenite/wehrlite, Succoth–Brown Hill ([[Media:~~P808815_~~.jpg\|P808815]])<br>		5.Clinopyroxenite/wehrlite, Succoth–Brown Hill ([[Media:P808815.jpg\|P808815]])<br>
	6.Sheared metagabbro, Succoth–Brown Hill ([[Media:~~P808810_~~.jpg\|P808810]])]]		6.Sheared metagabbro, Succoth–Brown Hill ([[Media:P808810.jpg\|P808810]])]]
	A large area underlain by granular gabbroic rocks extends from the east side of Dunbennan Hill eastwards under the town of Huntly and northwards from there in a band less than 1 km wide towards Haddoch [NJ 534 447]. In this area sporadic exposures of heterogeneous, fine- to medium-grained noritic rocks with minor clinopyroxene are found. Biotite is a common constituent, locally forming abundant coarse plates.		A large area underlain by granular gabbroic rocks extends from the east side of Dunbennan Hill eastwards under the town of Huntly and northwards from there in a band less than 1 km wide towards Haddoch [NJ 534 447]. In this area sporadic exposures of heterogeneous, fine- to medium-grained noritic rocks with minor clinopyroxene are found. Biotite is a common constituent, locally forming abundant coarse plates.

Dbk: /* Cumulate rocks */

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Cumulate rocks

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	The cumulate rocks crop out over approximately 7 km<sup>2</sup>, mainly in Dunbennan Wood [NJ 495 415] and the Bin Forest [NJ 510 430], where they are cut by a number of faults. Boreholes through a narrow north–south band of ultramafic cumulate rocks close to the western margin of the body intersected a sheared contact, although local hornfelsing of the country rocks is evident. Olivine-gabbro is the dominant rock type of the West Huntly body with subordinate troctolite, melatroctolite, mela-olivine-gabbro and rare thin bands of anorthosite. Olivine-orthopyroxene-gabbro occurs in the eastern parts of its outcrop.		The cumulate rocks crop out over approximately 7 km<sup>2</sup>, mainly in Dunbennan Wood [NJ 495 415] and the Bin Forest [NJ 510 430], where they are cut by a number of faults. Boreholes through a narrow north–south band of ultramafic cumulate rocks close to the western margin of the body intersected a sheared contact, although local hornfelsing of the country rocks is evident. Olivine-gabbro is the dominant rock type of the West Huntly body with subordinate troctolite, melatroctolite, mela-olivine-gabbro and rare thin bands of anorthosite. Olivine-orthopyroxene-gabbro occurs in the eastern parts of its outcrop.

	[[Image:~~P008624_~~.jpg\|thumb\|400px\| '''Plate 2''' Magmatic layering in olivine-gabbro cumulates, Bin Quarry, Huntly Pluton (P008624). ]]		[[Image:P008624.jpg\|thumb\|400px\| '''Plate 2''' Magmatic layering in olivine-gabbro cumulates, Bin Quarry, Huntly Pluton (P008624). ]]
	Crystal lamination and igneous layering are common. The layering ranging from less than a centimetre up to several metres thick, and generally trends between north and north-north-east and dips steeply or near vertically (Plate 2). In the northern part of the body in the Bin Forest the layering dips to the west, whereas in its southern part around Dunbennan Hill, it dips to the east. Modal layering, reflecting the variations in the proportion of plagioclase to the mafic constituents, is the most widespread form, but grain size, phase and textural layering are also locally developed. Pseudosedimentary structures are locally preserved in the layered sequences. These include scour features, current bedding, and rip-up clasts. These features, together with the cryptic variation in mineral compositions and graded layering, all indicate a younging direction to the east. The northern section, in the Bin Forest, is thus interpreted as being overturned. Cyclic units, marked by repetitive phase layering with the onset of olivine crystallisation, are present on the metre scale, but larger scale cyclic units cannot be identified with confidence.		Crystal lamination and igneous layering are common. The layering ranging from less than a centimetre up to several metres thick, and generally trends between north and north-north-east and dips steeply or near vertically (Plate 2). In the northern part of the body in the Bin Forest the layering dips to the west, whereas in its southern part around Dunbennan Hill, it dips to the east. Modal layering, reflecting the variations in the proportion of plagioclase to the mafic constituents, is the most widespread form, but grain size, phase and textural layering are also locally developed. Pseudosedimentary structures are locally preserved in the layered sequences. These include scour features, current bedding, and rip-up clasts. These features, together with the cryptic variation in mineral compositions and graded layering, all indicate a younging direction to the east. The northern section, in the Bin Forest, is thus interpreted as being overturned. Cyclic units, marked by repetitive phase layering with the onset of olivine crystallisation, are present on the metre scale, but larger scale cyclic units cannot be identified with confidence.

Dbk: /* Succoth–Brown Hill type */

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Succoth–Brown Hill type

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	The Succoth–Brown Hill mafic-ultramafic intrusion forms a poorly exposed elongate pod underlying an area of approximately 14 km<sup>2</sup> (Gunn et al., 1990<ref name="Gunn 1990">GUNN, A G, STYLES, M T, STEPHENSON, D, SHAW, M H, and ROLLIN, K E. 1990. Platinum-group elements in ultramafic rocks of the Upper Deveron Valley, near Huntly, Aberdeenshire. ''British Geological Survey Technical Report'', WF/90/09.</ref>, 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>). The boundaries of the intrusion are not exposed, but are interpreted as probably shear zones or faults. About 70 per cent of the complex is composed of metagabbroic rocks. The remainder consists of ultramafic rocks disposed in two belts along the northern and southern margins, the rocks along the latter being largely serpentinised.		The Succoth–Brown Hill mafic-ultramafic intrusion forms a poorly exposed elongate pod underlying an area of approximately 14 km<sup>2</sup> (Gunn et al., 1990<ref name="Gunn 1990">GUNN, A G, STYLES, M T, STEPHENSON, D, SHAW, M H, and ROLLIN, K E. 1990. Platinum-group elements in ultramafic rocks of the Upper Deveron Valley, near Huntly, Aberdeenshire. ''British Geological Survey Technical Report'', WF/90/09.</ref>, 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>). The boundaries of the intrusion are not exposed, but are interpreted as probably shear zones or faults. About 70 per cent of the complex is composed of metagabbroic rocks. The remainder consists of ultramafic rocks disposed in two belts along the northern and southern margins, the rocks along the latter being largely serpentinised.

	[[Image:~~P808816_~~.jpg\|thumb\|400px\| '''Plate 1''' Complex banding in metagabbroic rocks in the Succoth–Brown Hill pluton (P808816). ]]		[[Image:P808816.jpg\|thumb\|400px\| '''Plate 1''' Complex banding in metagabbroic rocks in the Succoth–Brown Hill pluton (P808816). ]]
	The metagabbroic rocks exhibit wide textural variation and include highly deformed, heterogeneous types, homogeneous, medium-grained variants with gabbroic texture and fine-grained, foliated mafic types (Plate 1 (P808816)). Penetrative foliations and mylonitic fabrics have mostly near vertical or steep east or south-east dipping orientations, probably reflecting the margins of the intrusion. Coarse-grained ultramafic intrusive rocks comprise variably altered and recrystallised clinopyroxene-rich and olivine-rich lithologies. Primary igneous features are poorly preserved as a result of later deformation, metamorphism and alteration. However, relatively undeformed modal layering that dips south-east at 30 to 40° is present in pyroxene-rich rocks in exposures near Red Burn [NJ 3448 8382].		The metagabbroic rocks exhibit wide textural variation and include highly deformed, heterogeneous types, homogeneous, medium-grained variants with gabbroic texture and fine-grained, foliated mafic types (Plate 1 (P808816)). Penetrative foliations and mylonitic fabrics have mostly near vertical or steep east or south-east dipping orientations, probably reflecting the margins of the intrusion. Coarse-grained ultramafic intrusive rocks comprise variably altered and recrystallised clinopyroxene-rich and olivine-rich lithologies. Primary igneous features are poorly preserved as a result of later deformation, metamorphism and alteration. However, relatively undeformed modal layering that dips south-east at 30 to 40° is present in pyroxene-rich rocks in exposures near Red Burn [NJ 3448 8382].

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Dbk: /* Keith–Portsoy Granite */

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Keith–Portsoy Granite

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	[[Image:OR15026plate3.jpg\|thumb\|center\|500px\| '''Plate 3''' Photomicrographs of rocks from pre- and syntectonic mafic–ultramafic intrusions in the Huntly district.<br>		[[Image:OR15026plate3.jpg\|thumb\|center\|500px\| '''Plate 3''' Photomicrographs of rocks from pre- and syntectonic mafic–ultramafic intrusions in the Huntly district.<br>
	1.Cumulate, West Huntly ([[Media:~~P808811_~~.jpg\|P808811]])<br>		1.Cumulate, West Huntly ([[Media:P808811.jpg\|P808811]])<br>
	2.Glomeroporphyritic olivine-gabbro, west Huntly ([[Media:~~P808813_~~.jpg\|P808813]])<br>		2.Glomeroporphyritic olivine-gabbro, west Huntly ([[Media:P808813.jpg\|P808813]])<br>
	3.Granular/schistose gabbro, central Huntly ([[Media:~~P808812_~~.jpg\|P808812]])<br>		3.Granular/schistose gabbro, central Huntly ([[Media:P808812.jpg\|P808812]])<br>
	4.Contaminated gabbro, central Huntly ([[Media:~~P808814_~~.jpg\|P808814]])<br>		4.Contaminated gabbro, central Huntly ([[Media:P808814.jpg\|P808814]])<br>
	5.Clinopyroxenite/wehrlite, Succoth–Brown Hill ([[Media:~~P808815_~~.jpg\|P808815]])<br>		5.Clinopyroxenite/wehrlite, Succoth–Brown Hill ([[Media:P808815.jpg\|P808815]])<br>
	6.Sheared metagabbro, Succoth–Brown Hill ([[Media:~~P808810_~~.jpg\|P808810]])]]		6.Sheared metagabbro, Succoth–Brown Hill ([[Media:P808810.jpg\|P808810]])]]
	A large area underlain by granular gabbroic rocks extends from the east side of Dunbennan Hill eastwards under the town of Huntly and northwards from there in a band less than 1 km wide towards Haddoch [NJ 534 447]. In this area sporadic exposures of heterogeneous, fine- to medium-grained noritic rocks with minor clinopyroxene are found. Biotite is a common constituent, locally forming abundant coarse plates.		A large area underlain by granular gabbroic rocks extends from the east side of Dunbennan Hill eastwards under the town of Huntly and northwards from there in a band less than 1 km wide towards Haddoch [NJ 534 447]. In this area sporadic exposures of heterogeneous, fine- to medium-grained noritic rocks with minor clinopyroxene are found. Biotite is a common constituent, locally forming abundant coarse plates.