First Paleoproterozoic ophiolite from Gondwana: Geochronologic-geochemical documentation of ancient oceanic crust from Kandra, SE India

SHRIMP-RG zircon U-Pb ages confirm the 1.85 Ga age of oceanic crust generated along the SE margin of India. This Paleoproterozoic ophiolite was accreted along a NE-trending suture that juxtaposes the outboard Proterozoic Eastern Ghats Granulite Belt (EGGB) against the inboard Archean Nellore Schist Belt of the Dharwar craton. Collision between the EGGB arc crust and India apparently was highly oblique, involving SW thrusting of oceanic crust and a trailing arc onto the Dharwar craton. Although deformed and dismembered, the original lithologic sequence of the Kandra Ophiolite Complex (KOC) has been largely retained. From SW to NE, the complex consists of layered + isotropic gabbros, sheeted dolerite dikes and amygdaloidal pillow basalts. Ultramafic units are intercalated within the gabbroic rocks, and plagiogranite veins + patches occur within the dolerites. Metacherty layers cap the basalts. The KOC exhibits EMORB geochemistry overprinted by subduction-zone metasomatism. Mafic magmas show high LILE/HFSE, positive Ba and Pb anomalies and negative anomalies for Nb, Zr and Hf in spidergrams - typical of a suprasubduction-zone setting. Its structure and geochemistry suggest that the KOC represents a Chilean-type continental backarc ophiolite. This is the first unequivocal Paleoproterozoic ophiolite reported from India, and probably the first from Gondwana. The 1.85 Ga KOC represents an important Gondwana example in the cascade of arc-continent collisions that assembled the Paleoproterozoic supercontinent Columbia. (C) 2010 Elsevier B.V. All rights reserved.