U–Cr-rich high Mg-Al granulites from Karimnagar Granulite Belt, India: implications for Neoarchean-Paleoproterozoic events in southern India

摘要: High Mg-Al granulite occurs as enclave within granite gneisses at Karimnagar, southern India, and it contains coarse granoblastic aggregates of orthopyroxene sapphirine with minor amount cordierite, spinel phlogopite. An important chemical characteristic these minerals is their extremely high MgO content the Cr2O3 in spinel. Textural analysis shows + cordierite peak-metamorphic assemblage that possibly evolved though breakdown a spinel-bearing assemblage. Cation exchange geothermometers involving orthopyroxene, yield temperatures 600–800 °C maximum 860 implying an event temperature (HT) metamorphism. Pseudosection FeO–MgO–Al2O3–SiO2 system stability peak- below 6.2 kbar. Subsequently, rock underwent hydration cooling appearance phlogopite Chromium enrichment inherited from protolith its presence presumably stabilized high-temperature field. The recorded Rb–Sr age ca. 2,500 Ma host gneiss marks upper limit HT Presence patchy, lobate grains well veinlets uraninite brannerite also feature rock. Uranium mineralization took place during post peak metamorphic stage, sulfide represented by tiny pyrite, millerite pentlandite coincided with, outlasted uranium mineralization. U–Th–Pb ages suggest 2,200 ± 12 for granulite. Based on field relations, surmised metamorphism study area older than comparable other parts Eastern Dharwar Craton. It can be conceived widespread India.