Petrochemistry of a Hornblende Porphyrite from Chityal, Andhra Pradesh

An isolated oval body of hornblende porphyrite occurring three km SE of Chityal, Nalgonda District, A.P. shows typical porphyritic texture both megascopically and microscopically. Euhedral primary hornblende occurs as pnenocrysts in a mesostasis of secondary actinolite and altered plagioclase. With the development of diopside at the expense of hornblende, the rock has acquired a granulitic texture while retaining the porphyritic habit.

Chemically the rock is characterised by low alumina and high magnesia and calcium. Among the trace elements, the high concentration of Cr, Cu, V and Co are in sympathetic relation with the major elements. The somewhat high values of Li, Sr and Rb, are thought to be partly due to introduction through water-enriched magmatic fluids which have metamorphosed the primary members of the rock. Tne rock appears to have suffered first a retrograde and then a prograde metamorphism.