Provenance and Tectonic Setting of the late Paleoproterozoic Clastic Sedimentary Rocks of the Cuddapah Basin, South India

摘要

A geochemical study on mudstone from sandstone-mudstone heterolith of Paleoproterozoic Gulcheru Formation of the Cuddapah Supergroup reveals two simultaneous sources, contributing sediments to the basin, one is a weathered source and the other is juvenile input as indicated by the CIA (average 67) values ranging from 53 to 90. A weak to moderate positive correlation between Fe2O3 + MgO and Al2O3 (r=0.4) contents indicate the dominance of mafic rock fragments, clay minerals and/or micas. The trace element ratios like Th/U of 4 were recycled sediments with some degree of weathering. The REE patterns of the shales (normalized to chondrite) are LREE enriched with a flat HREE, lacking strong Eu deficiency while some of the samples show pronounced positive Eu anomaly indicating both felsic and mafic derivation. This mixed source is also indicated by a wide range in the La/Th ratios (avg., 3.4; range 0.9-7.1) and high positive correlation (r = 0.8) between Cr and Ni. These observations imply that sediments were mainly derived from dissected arc-systems and mixed with continental derived sediments. Thus the involvement of the arc systems place constraints on the nature of plate boundary in eastern part of the Cuddapah basin and relate it to the supercontinent episodes during the Proterozoic thus involving a more complex paleogeodynamic evolution of the Cuddapah basin.