Geochronological constraints on Meso- and Neoarchean regional metamorphism and magmatism in the Dharwar craton, southern India

Abstract

This contribution addresses the time framework of the regional metamorphism in the three crustal provinces making the Archean Dharwar craton. We present results of texturally controlled in situ EPMA chemical dating of monazites, chemical dating of monazite separates, as well as Sm–Nd garnet–whole rock isochrons and SHRIMP U–Pb zircon ages for pelites, amphibolites and granitoids over target areas typical of the various crustal levels of the provinces. The Western Dharwar craton has undergone a major thermal pulse at 2.52 Ga followed by slow cooling to ca. 2.4 Ga and recorded earlier thermal events around 3.0 Ga and 3.1 Ga. The Central Dharwar craton records a major high-grade thermal imprint at ca. 2.55–2.51 Ga followed by cooling up to 2.45 Ga and earlier thermal events at ca. 2.62 and 3.20 Ga. In the Eastern Dharwar craton the widespread thermal pulse between 2.55 and 2.52 Ga is best recorded. From 2.52 Ga on, the entire craton ultimately and contemporaneously undergoes the main event of regional HT–LP metamorphism. The contrasted thermal records of the three provinces reflect their accretion age(s) and their degree of involvement in a wide Latest Archean hot orogen, which sets the capacity of these lithospheric segments to be impact by deformation and mantle fluxes. The tectonic setting of Latest Archean hot orogeny is compatible with active plate margin processes having interacted with mantle instabilities (i.e., plumes?). The tectonic setting of pre-2.5 Ga thermal pulses is difficult to assess, but considering their systematic links with documented magmatic pulses, they may have been generated in contexts comparable that of Latest Archean hot orogeny where lateral constrictional flow of hot orogenic crust achieves gravity driven flow, 3D mass redistribution of viscous lower crust submitted to convergence.