B. Chadwick et al., The Dharwar craton, southern India, interpreted as the result of Late Archaean oblique convergence, PRECAMB RES, 99(1-2), 2000, pp. 91-111
The Dharwar craton comprises two distinct parts separated by a steep N-S si
nistral shear zone. In the western part a pre-2900 Ma complex of orthogneis
ses, granodiorites and narrow tracts of supracrustal rocks (Sargur Group) f
orms the basement to volcanic and sedimentary basins of the Dharwar Supergr
oup (ca. 2800-2550 Ma). Late Archaean deformation is characterised by NE-SW
crustal shortening and steep N-S sinistral shear zones. The eastern part i
s underlain by parallel, steep N-S or NW-SE linear belts of calc-alkaline,
anatectic and juvenile granites and granodiorites (Dharwar batholith, ca, 2
750-2510 Ma) with intervening volcanic and sedimentary schist belts (ca. 28
00-2550 Ma). The plutonic belts are 15-25 km wide, up to 150 km long, and b
ounded by steep NW-SE high-strain zones up to 2 km wide with sinistral shea
r sense (except one which is dextral). Magmatic-state fabrics and structure
s 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 consisten
t with emplacement of the batholith during sinistral shear when magma press
ure exceeded regional horizontal compressive stress. Upright folds and schi
stosity, steep reverse faults and effects of regional HT/LP metamorphism sh
ow that deformation was partitioned into NE-SW shortening in the schist bel
ts during emplacement of the plutonic belts in the sinistral shear regime.
The western part of the craton is interpreted as the foreland to an accreti
onary are represented by the batholith and schist belts (intra-arc basins)
in the east. NE-SW shortening and sinistral transcurrent displacements in t
he foreland and are are consistent with are-normal and are-parallel displac
ements during oblique convergence analogous to Mesozoic-Cenozoic convergent
settings. (C) 2000 Elsevier Science B.V. All rights reserved.