Tectonic Evolution of the Ramagiri Schist Belt: Parallel Shallow Platformal and Deepwater Facies Association in the Eastern Dharwar Craton, South India

ABSTRACT In the Ramagiri Schist Belt (RSB) of Eastern Dharwar Craton (EDC), the assemblages of cross-bedded quartzite-pelitic sediments, massive metabasalt/amphibolite, and differentiated volcanics of massive-pillowed-pyroclastic character with co-magmatic basic and acidic intrusives with thin volcaniclastic and nonclastic sediment intercalation are delineated as the discontinuous Western and continuous Eastern arms, respectively. The sediment accumulation in the Western arm is interpreted as bed-load lateral accretion on a gentle basin floor of shallow platform, and as the dump- vertical accretion deposits on the steep floor of a linear rifted trough with a subduction mechanism is interpreted. A linear continuous gravity high over the Eastern arm supports the existence of high-density materials in a linear rifted trough of eastern RSB. Thus, this study proposes an initial shallow platformal sedimentation and the conversion of the same depositional site as a linear rifted trough for the accumulation of thick high-density materials with an E-W convergence and subduction-abduction mechanisms in the overall RSB. The unusual occurrence of spinifex textured-pillowed ultramafic slices within the shallow platformal Western arm is interpreted as the allochthonous ophiolitic fragments with their derivation from the Eastern arm’s subduction zone, and transfer-accumulation of these towards the continental margin by abduction mechanism is envisaged. The syn-tectonic Ramagiri, Anantapur-Bukkapatnam alkali-feldspar granites along the margins of RSB’s rifted trough, in the zones of ductile shear mark the later stage of greenstone development in the RSB. Thus, the overall RSB evolution suggests a late Archaean plate tectonic setting analogous to Meso-Cenozoic processes.