AN ARCHEAN TECTONIC MODEL OF THE DHARWAR CRATON, SOUTHERN INDIA - THEORIGIN OF THE HOLENARASIPUR GREENSTONE-BELT (HUSSAN DISTRICT, KARNATAKA) AND REINTERPRETATION OF THE SARGUR-DHARWAR RELATIONSHIP

The occurrence of the Holenarasipur greenstone belt is explained by ac cretionary process at a trench. A sequence of amphibolite (MORE), cher t, and banded iron formation associated with komatiitic amphibolite (o ceanic island material) is an Archaean analogue to the modern oceanic crust grown through the migration from an active ridge to a trench. At a trench, slices of such a sequence mixed with or became covered by t urbidite from land mass (quartzite and conglomerate) to form an accret ionary complex. Available SHRIMP data suggest the synchronous formatio n of nearby tonalite-trondhjemite-granodiorite (TTG) with the greensto ne belt by melting of subducting oceanic plate. The Dharwar craton has been built up stepwise: (1) Sargur stage--ocean-ocean collision to fo rm oceanic island are with TTG and an accretionary complex (older gree nstone belt), followed by the collision of such arcs to form mini-cont inents at the early to middle Archaean (until 3.0 Ga); (2) Dharwar sta ge--the amalgamation of mini-continents with newer accretionary comple xes (younger greenstone belt) under the same subduction polarity cause d by the change from two layered to whole mantle convection with the p rogressive cooling of the earth (3.0-2.5 Ga). The cessation of TTG act ivity was also due to the cooling of the earth. Tectospheric peridotit e keel formed with TTG has acted as a thermal insulator to stabilize t he Dharwar craton after the Archaean. Copyright (C) 1996 Elsevier Scie nce Ltd