A Neoarchean dismembered ophiolite complex from southern India: Geochemical and geochronological constraints on its suprasubduction origin

Ophiolites, the remnants of ancient oceanic lithosphere, have been described from collisional sutures of various ages with only few examples from Archean terranes. Here we report the discovery of a Neoarchean ophiolite suite from the southern margin of the Dharwar Craton in India, tectonically intercalated within a Neoproterozoic suture zone. The metamorphosed and variably dismembered ophiolite suite, exposed around Devanur, comprises altered ultramafic units, websterite, gabbros, mafic dykes, amphibolites, trondhjemites and pegmatites associated with ferruginous metachert. Structural and petrographic studies indicate that the rocks represent a highly sheared and metamorphosed suite emplaced as a thrust sheet. The major and trace element geochemistry of the mafic dykes indicate derivation from basaltic–andesitic magmas with tholeiitic to calc-alkaline characteristics. The rocks display negative Nb anomalies with enrichment of LILE (K, Rb, Ba, Th) and depletion in HFSE (Ti, Nb, Hf, Tb). The tectonic discrimination of these rocks based on various geochemical plots suggests that they were generated in a suprasubduction zone setting. We present new SHRIMP zircon U–Pb data for two trondhjemite samples from this complex, which yield 238U–206Pb ages of 2528 ± 61 and 2545 ± 56 Ma. The Neoarchean age from the trondhjemites obtained in our study is closely comparable to similar ages obtained in recent studies from magmatic zircons in charnockites and orthogneisses in the area. The suprasubduction zone assemblages and arc magmas suggest a Neoarchean ocean closure along the southern margin of the Dharwar Craton.

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► Discovery of a Neoarchean suprasubduction ophiolite from southern India.
► U–Pb dating of zircons from trondhjemites yield ~ 2.5 Ga.
► Neoarchean ocean closure along the southern margin of the Dharwar Craton.