Abstract

Foreland basin deposits of the Tansen Group of Lesser Himalayan association in central Nepal record passive margin sedimentation of the Indian continent with direct deposition onto eroded Precambrian rocks, succeeded by detritus from orogenesis as the Indian continent collided with Asia on a north-dipping subduction zone. Samples collected from Tansen Basin (Amile, Bhainskati, and Dumri formations), Higher and Tethys Himalaya were examined detrital zircon U-Pb dating and through petrographically. The Cretaceous-Paleocene Amile Formation is dominated by a broad detrital zircon U-Pb~1830Ma age peak with hosts a significant proportion (23%) of syndepositional Cretaceous zircons (121 to 105Ma) would be contributions from the Lower Lesser Himalayan volcanosedimentary arc, Gangdese batholith (including Xigazeforearc). The Bhainskati and Dumri Formation of the Tansen Group are more similar to Tethyan units than to Higher Himalaya Crystalline (HHC). The presence of ~23+/-1Ma zircons from the Higher Himalaya unit suggests that they could not have been exposed until the earliest Miocene time. Petrographic results indicate their “Quartzose recycled” and “recycled orogenic” suggesting Indian cratonic and Lower Lesser Himalayan (LLH) sediments as the likely source of sediments for the Amile Formation, the Tethyan Himalaya (TH) and Upper Lesser Himalaya (ULH) as the source for the Bhainskati Formation, and both the Tethyanand Higher Himalaya as the major sources for the Dumri Formation.

Keywords:Foreland basin; U-Pb Zircon ages; Petrographic results; Provenance analysis