Identification of paleosols in the Precambrian metapelitic assemblages of peninsular Indi - a major element geochemical approach

Abstract

AI₂O₃ greater than 20%, positive correlation between AI₂O₃ and Ti0₂, plot towards the AI₂O₃ corner in the Al₂0₃-K₂0-Fe₂O₃ (T) diagram and high chemical indices of alteration and weathering (CIA, CIW) distinguish the paleosols (fossil residual soils) from transported and deposited pelitic rocks like shales. Submarine weathering products are characterized by high MgO whereas the subaerial ones are not. Application of these criteria shows that majority of the khondalites of Orissa, Andhra Pradesh and Kerala are metamorphosed paleosols. They were probably formed from bauxite type lateritic soils. The protoliths of khondalites of Madras were, however, shales. Except for the biotite schists, other high alumina metapelites of Holenarasipur greenstone belt could also have been formed from paleosols. These latter being characterized by higher MgO content could represent metamorphosed submarine weathering products. The metapelites occurring at the base of the Aravalli Supergroup in Rajasthan also have chemical characters similar to residual soils. The Dharwar and Cuddapah shales stand apart from such metamorphosed probable paleosols.