Paleoproterozoic/Mesoproterozoic tectonism in the northern fringe of the Western Dharwar Craton (India): Its relevance to Gondwanaland and Columbia supercontinent reconstructions

A newly discovered suite of Paleoproterozoic/Mesoproterozoic amphibolite facies supracrustals and foliated granitoids between Pernem and Phonda along the northern Konkan coast of western India limits the northern boundary of the Archean Western Dharwar Craton (WDC). Top-to-the south transport of the suite is associated with progressively southward tightening of folds with down-dip stretching lineation, obliteration of pre-existing fabrics, and widespread stabilization of garnet (lacking in the WDC) along a mid-crustal counterclockwise pressure-temperature path. Th-U-total Pb ages in metamorphic monazites in the WDC supracrustals are 2.5Ga; chemical ages of metamorphic monazites (2.3Ga, 2.2Ga, 1.9Ga, and 1.7Ga) in the WDC-limiting Pernem-Phonda tectonic zone decreases northwards. Based on the finding, we suggest that the southern boundary of the Central Indian Tectonic Zone (CITZ)the accretion zone between the North and the South Indian Blocksshould be relocated similar to 550km south from its perceived location near the Gulf of Cambay. In spite of the apparent geometric fit, we suggest the CITZ and the Trans North China Orogen may not be continuous as has been suggested in some Paleoproterozoic reconstructions of the Columbia supercontinent. The monazite ages in the footwall schists are similar to 2.5, 2.25, and 2.10Ga Pb-Pb ages in detrital zircon in the Sahantaha Group located north of the Paleoarchean Antongil-Masora Block in Madagascar. We suggest that the Paleoproterozoic/Mesoproterozoic shear zone system extended westward into Madagascar north of the Antongil Block in East Gondwanaland, and this may clarify the unexplained source of zircon in the Sahantaha quartzites.