Journal
JOURNAL OF PETROLOGY
Volume 45, Issue 1, Pages 183-202Publisher
OXFORD UNIV PRESS
DOI: 10.1093/petrology/egg085
Keywords
phase relations; HP metapelite; NKFMASH; THERMOCALC; phengite geobarometry
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Using an internally consistent thermodynamic dataset and updated models of activity-composition relation for solid solutions, petrogenetic grids in the system NKFMASH (Na2O-K2O-FeO-MgO-Al2O3-SiO2-H2O) and the subsystems NKMASH and NKFASH have been calculated with the software THERMOCALC 3.1 in the P-T range 5-36 kbar and 400-810degreesC, involving garnet, chloritoid, biotite, carpholite, talc, chlorite, kyanite/sillimanite, staurolite, phengite, paragonite, albite, glaucophane, jadeite, with quartz/coesite and H2O in excess. These grids, together with calculated AFM compatibility diagrams and P-T pseudosections, are shown to be powerful tools for delineating the phase equilibria and P-T conditions of Na-bearing pelitic assemblages for a variety of bulk compositions from high-P terranes around the world. These calculated equilibria are in good agreement with petrological studies. Moreover, contours of the calculated phengite Si isopleths in P-T pseudosections for different bulk compositions confirm that phengite barometry is highly dependent on mineral assemblage.
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