Dismembered ophiolites in Paleoproterozoic nappe complexes of Kandra and Gurramkonda, South India

The constitution and structural architecture of ophiolites is important in the understanding of cratonic growth through subduction-collision-accretion history in the Precambrian terrains. The Nellore schist belt (NSB), sandwiched between the Eastern Ghats belt (EGB) and the Eastern Dharwar craton, South India is known to have deformed remnants of 'ocean-plate stratigraphy' (OPS) as at Kanigiri and Kandra suggesting multiple cycle of ocean opening and closure in the Paleoproterozoic-Mesoproterozic interval. The outcrop details and structural architecture of the Paleoproterozoic Kandra complex with geochemical character of subduction-related ophiolites is described and analyzed to better constrain the accretion-collision history along the southeastern margin of the Indian craton. Imbricate thrust slices between Kandra and Arimanupadu host slivers of hornblende metagabbro, thick massive to pillowed metabasalt sheets, sheeted meta-dolerite dykes and thin metapsammite and metapelite interstratified with metabasalt, comparable to Layer 2A of oceanic crust. Contractional deformation in interlayered metabasalt and quartzite around Kandra is accommodated by south dipping imbricate thrust systems and N(NE) vergent folds. The WNW trending thrust system with dominant tectonic transport toward northeast, is oblique to overall N-S trend of the NSB or the EGB. Further east, intercalated metabasalts, deep water turbidites and thin metacherts around Gurramkonda are deformed into SW vergent imbricate thrust system. Here, occurrence of metabasalt sheets along individual thrusts, suggest syntectonic emplacement of some basalts as the subducted and scraped upper oceanic crust was incorporated in the acrcetionary prism. The rock sequences around Kandra and Gurramkonda comprising incomplete OPS are tectonically stacked over granites of the Eastern Dharwar craton margin. Bivergent thrust systems around Kandra possibly root into a detachment separating Layers 1-2 from more rigid deeper layers (cf. Layer 3 of oceanic crust), as indicated by absence of significant volume of ultramafic rocks at the current outcrop level. (C) 2011 Elsevier Ltd. All rights reserved.