Detrital zircon U-Pb geochronology of the Lunpola basin strata constrains the Cenozoic tectonic evolution of central Tibet

Abstract

The Cenozoic tectonic evolution of central Tibet plays an important role in the growth of the Tibetan plateau. Paleoelevation studies show that the central Tibetan plateau hosted an east-west trending belt of basins in the Paleogene, but how they relate to the regions uplift history remains unclear. This study addresses the uplift history of the central Tibetan plateau by focusing on Lunpola basin strata deposited in the Cenozoic through detrital zircon basin provenance and zircon geochemical indicators for crustal-thickening. U-Pb dating of detrital zircon demonstrates that the Lunpola basin was mainly derived from mixed sources composed of Paleozoic–Mesozoic sedimentary rocks of the Lhasa terrane, the Cretaceous igneous rocks of the northern Lhasa terrane, and the Paleozoic–Mesozoic sedimentary rocks of southern Qiangtang terrane. The modal framework-grain composition of sandstone samples from the basin strata indicates a recycled orogen as the source. Sandstone composition analysis reveals an increase in the volcanic component with time associated with a pulse of quartz grains in the middle Eocene. We interpret such observations to indicate input from early Cretaceous clastic sediments belonging to the Duba Formation and the Baingoin Plutonic Complex, which imply passive exhumation along the hanging wall of the Gerze-Siling Co thrust. Trace element geochemistry of zircon grains demonstrates an increase in europium anomaly (Eu/Eu*), which we interpret to reflect ∼20 km crustal thickening in central Tibet from the Eocene to Oligocene, as well as an increase of >3 km surface elevation which partly was induced by the Cenozoic sedimentary accumulation. This significant uplift event may have been associated with convective removal of a thickened Tibetan lithosphere that in turn led to magmatic inflation of the Tibetan crust.