Occurrence of kornerupine-bearing granulite from Karimnagar, Andhra Pradesh

摘要

Here, we report the occurrence of kornerupine–bearing, quartz-free granulite from the Malial area of Karimnagar district, Andhra Pradesh. It occurs as small enclaves and pods within the granite-gneiss, associated with garnet–orthopyroxene–cordierite–biotite-gneiss. Its mineral assemblage includes kornerupine–cordierite–biotite–spinel, K-feldspar, ilmenite and magnetite. Kornerupine, a hydrated magnesium–aluminium silicate plots on the 4MgO–3Al_2O_3–4SiO_2 (4 : 3 : 4) composition along the solid solution join between 4 : 3 : 4 and 1 : 1 : 1 (3.5MgO.3.5Al_2O_3.3.5SiO_2) compositions. The relative XMg values among various minerals are as follows: cordierite biotite kornerupine spinel. The deduced post-peak metamorphic pressure–temperature conditions of 5–6 kbar and 650–750°C for the kornerupine –spinel–bearing quartz-free granulites are consistent with the experimental work on stability of kornerupine in the MgO–Al_2O_3–SiO_2–H_2O system.