Restoration of Late Neoarchean–Early Cambrian tectonics in the Rengali orogen and its environs (eastern India): The Antarctic connection

Abstract

Geological mapping and P–T path reconstructions are combined with monazite chemical age and Secondary Ion Mass Spectrometric (SIMS) U–Pb zircon age determinations to identify crustal domains with distinctive evolutionary histories in the Rengali orogen sandwiched between two Grenvillian-age metamorphic belts, i.e. the Eastern Ghats Granulite Belt (EGGB) in the south, and the amphibolite facies Gangpur Schist Belt (GSB) in the north, which in turn forms a collar along the NW/W margins of the Paleo/Mesoarchean Singhbhum Craton (SC) north of the Rengali orogen. Anatectic gneisses in the orogen core exhibit multi-phase Neoarchean/Paleoproterozoic deformation, metamorphic P–T histories and juvenile magma emplacement events. The high-grade belt is inferred to be a septum of the Bastar Craton (BC). The flanking supracrustal belt in the orogen — dominated by quartz-muscovite schists (±staurolite, kyanite, garnet pyrophyllite), inter-bedded with poorly-sorted and polymict meta-conglomerate, and meta-ultramafic/amphibolite bands — evolved along P–T paths characterized by sub-greenschist to amphibolite facies peak P–T conditions in closely-spaced samples. The supracrustal rocks and the anatectic gneisses of contrasting metamorphic P–T histories experienced D1, D2 and D3 fabric-forming events, but the high-angle obliquity between the steeply-plunging D3 folds in the anatectic gneisses and the gently-plunging D3 folds in the supracrustal unit suggests the two lithodemic units were tectonically accreted post-S2. The supracrustal belt is inferred to be a tectonic mélange formed in an accretionary wedge at the tri-junction of the Bastar Craton, the Eastern Ghats Granulite Belt and the Singhbhum Craton; the basin closure synchronous with the assembly of EGGB and the Singhbhum Craton–Gangpur Schist belt composite occurred between 510 and 610Ma. Based on the available evidence across the facing coastlines of the Greater India landmass and the Australo–Antarctic blocks at ~500Ma, it is suggested that the EGGB welded with the Greater India landmass during the Pan African along an accretion zone, of which the Rengali orogen is a part, synchronous with the final assembly of the Gondwanaland.