November 22, 2005 AFM Diagram – represents metamorphic reactions in pelites, JBT Assumes muscovite always present. Projects from aluminosilicate (Al2O5) through FeO and MgO Isograds in pelites depend on the bulk composition of the rock! Scotland – Barrovian metamorphism – chlorite, biotite, garnet, staurolite X marks typical pelite composition 2 important minerals, chloritoid and staurolite, only coexist in very aluminous bulk rock compositions1. Chloritoid appears 2. Chlorite stability decreases3. Staurolite appears 4. Garnet appears (ctd + bio + H2O = gt + chl) … see how compositions change mineral assemblage!5. Chloritoid disappears, biotite full solid solution 6. Tie line switch (gt + chl = str + bt) 7. Tie line switch (str + chl = ky + bt) brings out kyaniteComplication: MnO is an additional component in many pelites Spessartine garnet
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