Analysis of Provenance of Siwalik Group in Western Nepal Himalaya Using Petrography and U-Pb Geochronology

Abstract:

The east-west trending southernmost litho-tectonic unit, Siwalik, is about 5 Km thick fluvial coarsening upward sequence, which was deposited during middle Miocene to early Pleistocene. This fluvial sediment is excellent archives of the Himalayan exhumation, tectonic events and mountain building processes. This paper deals with the possible provenance of the middle Miocene to early Pleistocene fluvial sediments along the Karnali River section as well as added some knowledge of the Himalayan orogeny by the means of petrography and detrital zircon U-Pb dating under LA-ICP-MS. The petrographic studies shows the detritus grain of sandstones from the Karnali River section falls on ‘recycled orogeny’ field on QFL plots. The detrital zircon U-Pb geochronological study shows that the sediments were mostly derived from entire three litho units ;Tethys, Higher, and Lesser Himalaya during the time of deposition of Siwalik whereas the erosion process of Lesser Himalayan sediment increased after ~10 Ma. Overall, the combined studies show the mixed type of provenance as seen in the western Himalaya of India.

Key words: U-Pb geochronology, Provenance, Siwalik Group