尼泊尔低喜马拉雅带Lakharpata群沉积时限与沉积环境限定:来自顶部凝灰岩的年代学和地球化学证据OA

The Lakharpata Group,a sedimentary sequence exceeding 5 000 m in thickness,is exposed in the Nepal Lesser Himalayan belt and preserves a key record of Precambrian tectono-sedimentary evolution along the northern margin of the Indian continent.However,its precise depositional age and tectonic setting remain poorly constrained.This study presents zircon U-Pb ages and geochemical data from newly identified tuff interlayers at the top of the Aru Formation,the uppermost unit of the Lakharpata Group in the Tansen area of central Nepal.Dating results indicate a volcanic eruption age of 1 569 Ma.Integrating with previously published detrital zircon ages from the underlying quartzite units,the depositional age of the Lakharpata Group in the Nepal Lesser Himalayan belt is constrained to approximately 1 680～1 569 Ma,corresponding to the Late Paleoproterozoic to Early Mesoproterozoic,rather than the previously assumed Mesoproterozoic to Early Paleozoic age.Geochemical analyses reveal that the tuffaceous rocks originated from a high-K subalkaline rhyolitic magma source,characterized by enrichment in K2O,Al2O3,MgO,and CaO,and depletion in Na2O.Their trace element compositions show enrichments in Th,U,and LREEs,with pronounced depletions in Ba,Sr,and Eu.Chondrite-normalized REE patterns display a distinctive right-inclined"V"-shape,implying an intraplate volcanic setting.Combined with sedimentary facies analysis,the Lakharpata Group is interpreted to have been deposited in a passive continental margin basin during the breakup of the Columbia supercontinent.