THE GEOLOGICAL EVOLUTION OF THE ARCHEAN DHARWAR-CRATON

Although the Archean Dharwar craton (3.5 to 2.5 Ga) has an interesting geological evolutionary history, the depositional environment and the stratigraphic status of the Sargur Group and the stratigraphic relationship between the Bababudan and the Chitradurga Groups of the Dharwar Supergroup is ambiguous (Sunder Raju and Mazumder, 2020).The Dharwar Craton comprises the western (WDC) and the eastern (EDC) subdivisions (possibly separated by the Closepet granite), predicated on lithological contrasts and inferred metamorphic and magmatic evolution. A postulated genesis of the WDC comprises early, c. 3.5 Ga protocrust, which possibly formed as basement to the c. 3.35–3.2 Ga Sargur Group and equivalent greenstone belts. The later are thought to have formed through accretion of plume-related ocean plateaux. The broadly coeval Peninsular Gneiss Complex possibly originated from beneath plateau remnants, leading to metamorphism of the Sargur Group at c. 3.13–2.96 Ga. At c. 2.9–2.6 Ga, the Dharwar Supergroup, comprising lower Bababudan (mainly braided fluvial-nearshore facies association, glaciomarine and subaerial volcanic strata) and upper Chitradurga (relatively deeper marine clastic, chemical sedimentary and subaqueous volcanic rocks) groups formed. The Dharwar Supergroup constitute the younger greenstone belt characterized by two distinct magmatic events, at 2.7–2.6 and 2.58–2.54 Ga; the latter was approximately coeval with c. 2.6–2.5 Ga granitic magmatism, which marked final cratonization of the WDC. The EDC consists of 2.7–2.55 Ga tonalite–trondhjemite–granodiorite gneisses and migmatites, essentially coeval greenstone belts (mainly volcanic lithologies), with minor inferred remnants of an older, c. 3.38–3.0 Ga crust, and voluminous 2.56–2.5 Ga granitoids (including the Closepet). An east–west accretion of EDC island arcs (or possibly of an assembled arc-granitic terrane) on to the WDC is postulated, and the Closepet granite perhaps accreted earlier on to the WDC to form a ‘central Dharwar’ terrane. The sedimentary succession of the Sargur Group requires an in depth study to decode the mysteries of early earth surface processes and crust-mantle interactions.