Subduction-accretion-collision history along the Gondwana suture in southern India: A laser ablation ICP-MS study of zircon chronology

摘要

We report the petrological characteristics and preliminary zircon geochronology based on laser ablation ICP mass spectrometry of the various units in an accretionary belt within the Palghat-Cauvery Shear/ Suture Zone in southern India, a trace of the Cambrian Gondwana suture. Zircons extracted from a plagio-granite in association with an ophiolite suite within this suture possess internal structure that suggests magmatic crystallization, and yield mid Neoproterozoic ~(206)Pb/~(238)U age of 817 ± 16 Ma (error: 1σ) constraining the approximate timing of birth of the Mozambique Ocean floor. Compiled age data on zircons separated from a quartzite and metamorphosed banded iron formation within the accretionary belt yields a younger intercept age of 759 ±41 Ma (error: la) which we relate to a mid Neoproteozoic magmatic arc. Detrital zircons extracted from the quartzite yield ~(207)Pb/~(206)Pb age peaks of about 1.9-2.6 Ga suggesting that they were sourced from multiple protolithis of Neoarchean and Paleoproterozoic. Meta-morphic overgrowths on some zircon grains record ca. 500-550 Ma ages which are in good harmony with the known ages for the timing of high-grade metamorphism in this zone during the final stage of continent collision associated with the birth of the Gondwana supercontinent in the latest Neoproterozoic-Cambrian. The preliminary geochronological results documented in our study correlate with the subduction-accretion-collision history associated with the closure of the Mozambique Ocean and the final amalgamation of the Gondwana supercontinent.