Evidence of superposed metamorphism from the Gokavaram area, Eastern GhatsBelt, and its relation with the Kemp Land Coast, East Antarctica

In this paper, we compare the petrological histories of the Kemp Land Coast (east Antarctica) and Gokavaram area (Eastern Ghats), that were supposed t o have been juxtaposed. The area around Gokavaram is dominated by different varieties of paragneisses (pelitic, quartzofeldspathic and calcareous comp osition) with relatively minor amounts of orthogneisses (mafic, enderbitic and granitic composition). The rocks were involved in three major phases of deformation and were finally affected by localised shear movement. On the basis of reaction textures, well preserved in high Mg-Al granulites and cal c-silicate granulites, and geothermobarometric data we deduce a polymetamor phic evolution of the rocks. Following an early M-1 metamorphism culminatin g at 9.2-9.4 kbar, > 950 degrees C, the rocks cooled nearly isobarically do wn to 850 degrees C. During a subsequent M-2 metamorphism, near isothermal decompression to 5-6 kbar occurred. This was followed by near isobaric cool ing down to 600-650 degrees C. M-3 is a weak amphibolite facies overprint, largely restricted to late shears, which involved hydration as well. Availa ble radiometric data from this area can be interpreted in terms of partial resetting of U-Pb systematics in older sphenes due to M-3 metamorphism at c a. 550 Ma. Despite the absence of sufficient isotopic data on the Eastern C hats granulites, we document a remarkable similarity in the petrological hi story of the two supposedly erstwhile neighbours.