Tectono-magmatic evolution of the Archean Dharwar craton: A synthesis based on the geochemistry and emplacement history of the greenstone belt rocks of the craton

The roots of the tectonically uplifted Archean continental crustal blocks containing various greenstone-granite terranes are the preserved crustal lithologies exposed in various Archean cratons of the world. The trace element geochemical signatures of some of the preserved lithologies of these magmatic belts reflect the primary melt compositions in the mantle which help in understanding the petrogenesis of the rocks and the involvement of subduction zone processes, if recognized, in the generation of these melts. The Dharwar craton (DC), one of the major cratons of the world located in the Indian subcontinent, is made up of different tectonic blocks amal-gamated along various suture zones. Here we review the current understanding about the division of the DC, the polarity of subduction of the different blocks and the petrogenesis of the magmatic rocks of the greenstone belts, and present a synthesis based on the trace element characteristics of the primary basalts. Our study validates the heterogeneous nature of the Archean mantle during the Dharwar crustal evolution. Collation of geophysical, structural, lithological, geochemical and geochronological data imply that the Dharwar craton was accreted by the juxtaposition of at least three major cratonic blocks with noticeably distinct tectonic and magmatic histories. The continued preservation of siliciclastic sedimentary rocks in the greenstone belts of the western Dharwar craton combined with the dominant presence of the >3.0 Ga old gneissic crust, as compared to the central and eastern cratons, could be significant in constraining the involvement of continental crustal detritus in the gen-eration of the magmatic rocks of the greenstone belts. In the central and eastern Dharwar cratons, granitoid crust older than 3.0 Ga was probably destroyed to different extents for the generation of magmatic rocks. The existence of such an older crust is implied by the available Nd model ages. The scattered records of bimodality in the greenstone belt rocks of the central and eastern Dharwar cratons attest for the presence of heterogeneous mantle during Neoarchean. Subduction processes had become predominant by Neoarchean as evidenced from the chemical composition of primary basalts of the greenstone belts of the Dharwar craton. In all likelihood, the polarity of subduction was directed westward with the WDC acting as the foreland and the amalgamation of distinct cratonic blocks were along suture zones represented scatteredly by and as greenstone belts.