The Dharwar craton, southern India, interpreted as the result of Late Archaean oblique convergence

The Dharwar craton comprises two distinct parts separated by a steep N-S sinistral shear zone. In the western part a pre-2900 Ma complex of orthogneisses, granodiorites and narrow tracts of supracrustal rocks (Sargur Group) forms the basement to volcanic and sedimentary basins of the Dharwar Supergroup (ca. 2800-2550 Ma). Late Archaean deformation is characterised by NE-SW crustal shortening and steep N-S sinistral shear zones. The eastern part is underlain by parallel, steep N-S or NW-SE linear belts of calc-alkaline, anatectic and juvenile granites and granodiorites (Dharwar batholith, ca, 2750-2510 Ma) with intervening volcanic and sedimentary schist belts (ca. 2800-2550 Ma). The plutonic belts are 15-25 km wide, up to 150 km long, and bounded by steep NW-SE high-strain zones up to 2 km wide with sinistral shear sense (except one which is dextral). Magmatic-state fabrics and structures in the plutonic rocks are parallel to solid-state sinistral shear fabrics in the high-strain zones, but diffuse magmatic banding is commonly oblique to these zones and coincides with the plane of instantaneous shortening in sinistral shear. Magmatic-state structures, swarms of vertical NW-SE dykes of granite, and the vertical wedge shape of the linear belts are consistent with emplacement of the batholith during sinistral shear when magma pressure exceeded regional horizontal compressive stress. Upright folds and schistosity, steep reverse faults and effects of regional HT/LP metamorphism show that deformation was partitioned into NE-SW shortening in the schist belts during emplacement of the plutonic belts in the sinistral shear regime. The western part of the craton is interpreted as the foreland to an accretionary are represented by the batholith and schist belts (intra-arc basins) in the east. NE-SW shortening and sinistral transcurrent displacements in the foreland and are are consistent with are-normal and are-parallel displacements during oblique convergence analogous to Mesozoic-Cenozoic convergent settings. (C) 2000 Elsevier Science B.V. All rights reserved.