Abstract

Sapphirine in the granulitie terrane of the Eastern Ghats, near Kakanuru, India, has three modes of occurrence: (1) as a dominant mineral in a rock of possible regolithic origin, (2) generally as rims around spinel and magnetite in khondalite, and (3) replacing spinel in pyroxenites. All three types have distinct compositional characteristics; the XMg [Mg/(Mg + Fe2+)] value increases from 0.770 to 0.964 from type 1 to type 3. The parageneses of various types are discussed.

Temperature and pressure estimates based on suitable mineral pairs and calibrated geothermometers and geobarometers indicate extremely high grade metamorphic conditions. The temperature estimate, based on two-pyroxene and two-feldspar geothermometers, ranges from 840 to 1050 °C. The estimated pressure is about 7.3 kbar. These P-T conditions are in accordance with the sapphirine paragenesis. The temperature estimate from the garnet-biotite geothermometer yields a lower value (≃600 °C) that can be attributed to a subsequent metamorphic event accompanied by hydration and metasomatism.

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