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 plus or minus 26 and 3158 plus or minus 110 Ma) and the Peninsular gneisses (3138 plus or minus 35 Ma) are intruded by granitoid plutons (2924 plus or minus 50 Ma) 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-3.2 Ga tectonic contact. By contrast, in the Goa schist belt (GSB), phyllites/schists (unmixed ages - 2436 plus or minus 34, 2543 plus or minus 66 and 2625 plus or minus 36 Ma) and polymict conglomerates (unmixed ages - 2458 plus or minus 34 and 2566 plus or minus 53 Ma) 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 plus or minus 33 Ma). Angular to sub-rounded and boulder to granule sized polymict clasts of Peninsular gneisses (3128 plus or minus 60 Ma), 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 2.4-2.6 Ga 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. 2.4-2.6 Ga Goa schist belt approx equal to Mananara Group; 2.5 Ga Quepem granitoid approx equal to Masoala Suite; 3.1 Ga Shimoga schist belt approx equal to Fenerivo Group; 3.1 Ga Peninsular gneiss suite approx equal to Nosy Boraha suite.
