GEOCHRONOLOGIC-GEOCHEMICAL DOCUMENTATION OF A PALEOPROTEROZOIC OPHIOLITE FROM SE INDIA

SHRIMP-RG zircon U-Pb ages demonstrate the presence of extensive 1.9 Ga continental rift-related magmatism along the SE margin of India. Early-stage lithospheric stretching produced rift-zone mafic magmas such as the Cuddapah traps and the Bastar dikes, whereas advanced stages of rifting produced new oceanic crust. This Paleoproterozoic ophiolite is preserved at Kandra in the NE-trending suture juxtaposing the tectonically contrasting Proterozoic Eastern Ghats Granulite Belt with the Archean Nellore Schist Belt. The Kandra Ophiolite Complex (KOC) defines an arcuate belt ~19 km long and 3.5-5 km wide. The WNW-ESE trending KOC shows a discordant relationship with the Nellore Schist Belt, and the southeastern contact of the complex against granites is sheared. We infer that collision between the western Dharwar craton and the eastern arc crust was highly oblique, involving SW thrusting of oceanic crust onto the Dharwar craton. Although deformed and dismembered, the original zonal arrangement of the KOC has been largely retained. From SW to NE the complex consists of layered + isotropic gabbros, sheeted dolerites and amygdaloidal pillow basalts. Ultramafic units are scattered within the gabbroic rocks, and plagiogranite occurs as veins + patches within dolerite dikes. Quartzites + cherty layers cap the complex. Gabbros show cumulate textures and dikes exhibit ophitic, subophitic and porphyritic textures with plagioclase phenocrysts. The entire complex underwent epidote-amphibolite facies metamorphism at 1.6 and 1.0 Ga. Unambiguous cumulate gabbros, sheeted dikes and oceanic plagiogranite in the Kandra complex provide robust evidence for Paleoproterozoic sea-floor spreading along the southeastern margin of the Indian subcontinent. The KOC exhibits MORB geochemistry overprinted by a subduction-zone metasomatic signature. The Kandra ophiolite is the first unequivocal Paleoproterozoic ophiolite reported from India, and to our knowledge, is the first even from Gondwana. Its existence has relevance for the assembly of the Paleoproterozoic supercontinent Columbia.