THE SANDUR SCHIST BELT AND ITS ADJACENT PLUTONIC ROCKS IMPLICATIONS FOR LATE ARCHEAN CRUSTAL EVOLUTION IN KARNATAKA

Six formations are defined in a new lithostratigraphy of the volcanic and sedimentary rocks of the schist belt. The formations (Yeshwantnaga r, Deogiri, Raman Mala, Donimalai, Taluru, Vibhuti Gudda) young consis tently northeast, except for a parr of the Taluru Formation in the nor theast of the belt. We propose the new term Sandur Group to include th ese formations. Their combined thickness of c.35 km is in part an effe ct of thrust thickening The Sandur Group was deposited in mainly shall ow marine environments in a setting comparable with that of unstable m ixed-made basins. An incomplete, upright, synclinal sheath fold domina tes the structure in the east of the schist belt, and another incomple te synclinal sheath fold occurs in the west, its hinge areas and north eastern limb having been cutout by a steepened thrust (the Sandur vall ey discontinuity). The margins of the belt were intruded by syntectoni c, multipulse granites with magmatic and crystal-plastic solid-state l inear and planar fabrics and the granite emplacement outlasted deforma tion. HT/LP metamorphism of the schist belt was contemporaneous with d eformation and granite emplacement. The granites are an integral part of the Late Archaean polyphase granite complex in eastern Karnataka an d contiguous parts of Andhra Pradesh and Tamil Nadu, For which we prop ose the term Dharwar batholith. Published isotopic age data show that its western part includes anatectic granites and relies of Peninsular Gneiss (>2900 Ma), but the eastern part is dominated by juvenile grani tes. The batholith accreted onto the Archaean foreland to the west com prising Late Archaean marginal basins of the Dharwar Supergroup (Kudre mukh, Bababudan-Ranibennur, Chitradurga-Gadag) and their basement of P eninsular Gneiss (>3000 Ma) during Late Archaean plate convergence wit h NE-SW shortening and sinistral transcurrent displacements. The steep linear belts (Kolar, Ramagiri, Kushtagi, etc.) and irregular tracts ( Sandur, Hutti) of volcanic and sedimentary rocks in eastern Kamataka f ormed as intra-arc basins above the evolving Dharwar batholith.