Abstract
Abstract Chitradurga schist belt is a 450 km long linear feature of Archaean age and composed of several types of volcanic and sedimentary rocks. It has been deformed by 3-phases of folding rendering elucidation of stratigraphic sequence complicated. The volcanic rocks range in composition from Spinifix Textured Peridotitic Komatiite (STPK) to rhyolite. Volcanism appears to have occurred, at least at two diflerent stratigraphic levels in the belt. The STPK, basalt and rhyolite suites are not genetically related with each other, except in Gadag, where basalt-rhyolite may be cogenetic phases of the same suite. Chemogenic sediments have a higher order contribution and enrichment from volcanogenic exhalative component. Graywacke sedimentation is recognized at two stratigraphic levels. The graywackes of the central part of the belt and those from the Gadag part of the belt differ very much from each other in their abundance of rock fragments, plagioclase/K-feldspar and Na2O/K2O ratios, Fe2O3, MgO, Cr, Ni, Zr, Rb and Sr abundances. Detrital mineral content and REE pattern of the graywackes of the central part are similar to those from other areas of the world of the same period and appear to have been derived from mixed, but predominantly tonalitic source. Gadag graywackes, on the other hand, appear to have had a predominantly volcanic source. Folded BIF horizons too are inferred to form a significant part of the source areas. Gadag part of the belt is the youngest as the Bagewadi-Kodkal conglomerate contains porphyritic granite pebbles along with rhyolites. This progressive younging and widening of the belt to the north is governed by the attitude of the axial plane foliation and plunge of the fold axes. It also probably reflects the style of the opening of a rift in the Archaean continental crust. Gravity data support such a rift origin. Horizontal EW compression is an essential feature of the Chitradurga schist pointing to its being a probable late Archaean suture.
Published Version
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