Meso/Neoarchean crustal domains along the north Konkan coast, western India: The Western Dharwar Craton and the Antongil-Masora Block (NE Madagascar) connection

Abstract

Synthesis of mesoscopic structures and microscopic analyses of fabric superposition and deformation microstructures are combined with Th–U–Pb (total) ages in monazites to constrain the Meso/Neoarchean crustal domains in the Western Dharwar Craton (WDC) along the western coast of India; the domains are correlated with those in NE Madagascar to configure the assembly of crustal domains in the East Gondwanaland prior to the Mesozoic break up. In the WDC, para-schists and phyllites of the Shimoga schist belt, SSB (unmixed age components, 3067±26 and 3158±110Ma) and the Peninsular gneisses (3138±35Ma) are intruded by granitoid plutons (2924±50Ma) deformed at low-T. Five generations of deformation events are identified in the SSB and Peninsular gneisses. But the two early tectonic fabrics in Peninsular gneisses formed at anatectic amphibolite facies conditions are in sharp contrast to fabrics in SSB formed at greenschist facies. The two lithodemic units are inferred to share a pre-3.2Ga tectonic contact.By contrast, in the Goa schist belt (GSB), phyllites/schists (unmixed ages – 2436±34, 2543±66 and 2625±36Ma) and polymict conglomerates (unmixed ages – 2458±34 and 2566±53Ma) possess two generations of tectonic fabrics and are the youngest dated metamorphic unit in the WDC. The deformed Quepem granitoid pluton located along the axial zone of the regional-scale N-trending gently plunging upright folds in GSB yields comparable chemical age (2565±33Ma). Angular to sub-rounded and boulder to granule sized polymict clasts of Peninsular gneisses (3128±60Ma), foliated granitoids, amphibolites, BIFs and low-grade quartzite/chlorite-muscovite schists in GSB para-conglomerates suggest the sediments deposited in shallow basin were derived from neighboring sources, e.g. the Peninsular gneisses and SSB supracrustals. The Neoarchean deformation-metamorphism marks the closure of the Goa basin synchronous with the 2.4–2.6Ga accretion of the West and the East Dharwar Cratons.Based on the results of this study, the following correlation among Mesoarchean–Neoarchean crystallites in the Western Dharwar Craton and the Antongil-Masora Block, NE Madagascar (in italics below) appears realistic, e.g. 2.4–2.6Ga Goa schist belt≈Mananara Group; 2.5Ga Quepem granitoid≈Masoala Suite; 3.1Ga Shimoga schist belt≈Fenerivo Group; 3.1Ga Peninsular gneiss suite≈Nosy Boraha suite.