File:EGS Ballachulish Fig 04.jpg

Pressure-temperature grid of reactions In the chemical system K₂O-FeO - MgO-Al₂O₃-SiO₂-H₂O for typical mineral compositions In quartz-bearing pelitic rocks from Ballachulish (Pattison Harte, 1997). Dehydration reactions below the initial melting reaction (Pl+Kfs+Qtz+H₂O = L) are shown In solid lines. Higher grade reactions up-temperature of the initial melting reaction are shown In dashed lines. Als = andalusite or sillimanite. V = hydrous vapour, The short dashed line numbered 3 is the metastable extension of Ms+Qtz = Als+Kfs+V The dot-dashed reaction 5, Ms=Crn+Kfs+V, only occurs In quartz-absent rocks. The And=Sil curve is from Pattison (1992). H − And=Sil curve and triple point of Holdaway (1971); RGB − And=Sil curve and triple point of Richardson Et Al. (1969). Roman numerals − contact metamorphic zones referred to In the text. Zone IV comprises two different assemblages IVa and IVb that occur At the same grade In rocks of different composition. In quartz-absent rocks, Zone V can Be divided into lower grade (Va) and higher grade (Vb) subzones based on the presence of muscovite (Va) and corundum (Vb), respectively. Reaction numbering In Arabic numerals follows the text except that the ‘P’ prefix is omitted. Isopleths are of (100x Mg/(Mg+Fe)) In cordierite.

Figure 4. From: Pattison, D.R.M. and Harte, B. The Ballachulish Igneous Complex and aureole: a field guide. Edinburgh : Edinburgh Geological Society, 2001.