Provenance and source area weathering of Siwalik foreland basin rocks in NW Himalayas: insights from hydrochemistry, petrography and geochemical signature

摘要

The geochemical characteristics of stream/slopewash sediments, modal composition and petrography of the clastic units from the Siwalik Group has been investigated to determine the provenance and tectonic setting of these rocks, as well as to appraise the influence of the weathering and recycling processes upon source rock signatures. The higher CIA index indicates that the source area underwent moderate to intense chemical weathering processes, possibly due to climatic and/or tectonic variations. Alternatively, modal analyses show that the source area of the Siwalik rocks may have been composed of recycled sedimentary materials. The La/Th ratios and Hf discriminant plot show that they originally come from a differentiated silicic source. This has been further supported by Hiscott Diagram (Cr/V vs. Y/Ni) and Th-Hf-Co discrimination diagram which supports a primitive silicic source for these rocks indicating a higher proportion of felsic material in their primitive source area. The Eu/Eu* versus (Gd/Yb)_N diagram for the samples of the Siwalik sediments indicates that the source rocks are mainly influenced by post-Archean felsic rocks.