Geochemical characterization and petrogenesis of Proterozoic Khairagarh volcanics: implication for Precambrian crustal evolution


T. Ahmad, Department of Geology, Centre of Advance Studies, University of Delhi, Delhi, India.



The Khairagarh volcano-sedimentary sequence is exposed along the Kotri–Dongargarh Belt towards the north-eastern part of the Bastar Craton. This sequence is exposed south of the Central Indian Shear (CIS) and east of the Sakoli Group rocks. The Khairagarh volcanic sequence is represented by low-Ti, intermediate-Ti and high-Ti basalt–basaltic andesite series that probably represent varying degrees of partial melting of an enriched mantle source, thus they appear to be consanguineous. These rocks are associated with a sequence of high magnesium andesitic (HMA) rocks that follow a separate evolutionary trend, thus they appear not to be related to the basalt–basaltic andesite sequence. The presence of the two contrasting sequences probably indicates generation in a hot Andean-type subduction zone for the HMA, and Andean-type back-arc rifting for the basalt–basaltic andesite samples. The possibility of a relatively thick crust around 3.6 Ga in the Bastar Craton and the Amgaon Gneissic Complex, basement for the Khairagarh–Sakoli sequence, probably indicates that it was part of the Supercontinent Ur. The mantle extraction age of about 2.9 to 2.5 Ga, based on the Nd-model ages for the Khairagarh–Sakoli sequence, probably indicate that this part of the Central Indian Shield became part of the Supercontinent Columbia subsequently. Copyright © 2011 John Wiley & Sons, Ltd.