Abstract

Archean rocks, Superior Province, Kapuskasing structural zone. In migmatitic mafic gneiss, paragneiss, dioritic and tonalitic rocks, a lower-grade garnet-clinopyroxene-plagioclase (Gt-Cpx-Pl) zone and patchy, higher-grade orthopyroxene zones are distinguished. Based on mineral-melt equilibria, minimum conditions for the Gt-Cpx-Pl zone are 750 degrees C, 6 kbar, a H 2 O = 0.5-0.7 and for the orthopyroxene zone, 770 degrees C, 6 kbar, a H 2 O < 0.5. Garnet-biotite and garnet-pyroxene geothermometers and geobarometers yield temperatures ranging from <600 degrees C in the west to locally >800 degrees C. Pressure values are 5.4-8.4 kbar and define a NNE-trending area of relatively high P in the Kapuskasing Zone, supporting the interpretation of a tilted crustal section.--Modified journal abstract.

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