Structure and tectonics of a Mesoproterozoic ophiolite – Insight from Kanigiri Ophiolite with a mélange zone, southern India

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Research Article

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The ~1334 Ma Kanigiri Ophiolite (KO) occurring within the Nellore Schist Belt (NSB) at the Eastern Dharwar Craton (EDC) margin, India provides clues to tectonics of the paleo-ocean outboard of Mesoproterozoic Indian craton. The KO shows a diverse assemblage of fragmentary remains of the then oceanic crust including massive gabbro-anorthosite from the lower part, through a tectonic mélange, to 2–3 km thick slivers of upper oceanic crust with vesicular to pillowed basalt, mafic agglomerate, and mafic to felsic tuff with thin sedimentary intercalation. The mélange consists of up to meter size blocks of mafic igneous rocks and larger rafts of pelagic chert set in a fine grained, weakly foliated mafic matrix showing low grade metamorphism and hydrothermal alteration. The volcanic components of the KO are ultrapotassic to potassic, while the gabbroic rocks show high Ti/V, high Th/Nb ratios, high Y, and enrichment in Th compared to Hf and Ta, suggesting suprasubduction zone oceanic arc setting. Restricted to N-S elongated fault bounded block, the KO shows internal deformation with two sets of folds and tectonic foliation in the upper part and common block-in-matrix structure with gabbroic blocks in the middle part, possibly representing an accretionary wedge. The KO is tectonically juxtaposed against multiply deformed shallow marine succession of the Udaigiri Group (NSB), where second generation folds and crenulation cleavage compare with those in the KO metavolcanics. Post- tectonic granitic stocks of ~1284 Ma age intrude the ophiolitic melange and adjoining rocks of the NSB, suggesting ocean closure and accretionary growth of the EDC margin during the Mesoproterozoic. Components of the EDC margin were fused together during the 1100–900 Ma Rodinia amalgamation with collisional suturing between India and Antarctica. The earlier supercontinent build-up namely Columbia (or Nuna), probably left traces of an archipelago like paleogeographic scenario outboard of the EDC.

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