Petrology of basic granulites from Maruturu near Anakapalle in the Eastern Ghats Granulite Belt
Rao AT., Srinivasa Rao K., Srinivas S.
Basic granulites frequently occur in garnetiferous quartzo-feldspathic gneisses and rarely in garnetiferous sillimanite gneisses, calc-silicate rocks and quartzites in the entire Eastern Ghats Granulite Belt (EGGB). Commonly these basic layers are parallel to the foliation and are occasionally boudinaged. These share a common tectonic and metamorphic history with those of the associated litho-units. There are also unusual basic granulite dykes which crosscut the foliation in quartzo-feldspathic gneisses, folded calc-silicate rocks and basic granulites at Maruturu near Anakapalle in the EGGB. The two generations of basic granulites are even grained with a polygonal annealed mosaic and characterised by the mineral assemblage: coexisting pyroxenes and plagioclase. The mineral composition data of coexisting pyroxenes indicate large scale equilibrium at granulite facies conditions. Both types of basic granulites have almost similar bulk composition and have tholeiitic affinity. The basic granulite dykes have low contents of REE with a smooth distribution pattern and a general decrease from LREE to HREE. The revival of basic magmatism during post D1 and D2 at Maruturu reveals that extensional set-up recurs in the EGGB. The basic granulites of Maruturu are correlated with Proterozoic metabasic dykes in East Antarctica and Western Australia. The 1300 Ma basic granulites reported in Maruturu and Rayagada in the vicinity of Maruturu indicate that these intrusive basic bodies are coeval with the dyking events in Eastern Albany Mobile Belt in Western Australia and Vestfold Hill Block in Prydz Bay region in East Anatarctica.