Provenance And Paleogeography Of The Cretaceous Strata In The Muang Xai Basin,northern Laos: Petrology,whole-rock Geochemistry,and U-Pb Geochronology Constraints

The Muang Xai Basin,located in northern Laos,is associated with the Simao,Vientiane and Khorat Basins.The paleogeographic link of these basins has not been investigated in great detail,thus the investigation presented here is a comprehensive analysis of petrology,whole-rock geochemistry and detrital zircon U-Pb chronology used to characterize the provenance of the Muang Xai Basin.Results suggest that the sedimentary source includes felsic rocks from an active continental margin or continental arc with minor amounts of recycled passive continental margin sediments.Sandstones of the Muang Xai Basin contain detrital zircons with varying U-Pb peak ages: 2.50–2.47 Ga,1.85–1.83 Ga,858–730 Ma,466–416 Ma,308–219 Ma,175–149 Ma and 110–101 Ma.The youngest age peak of all the zircons is 103 Ma,which limits the age of the Mesozoic strata to the Late Cretaceous.Detrital zircon U-Pb and trace element data,combined with geochemical result,reveals that the pre-Ordovician zircons were derived from recycled sediments of the Yangtze Block,originally sourced from the Qinling Orogenic belt.This provenance is shared with coeval sediments in the Simao and Khorat Basins,while magmatic rocks of the Ailaoshan,Truong Son Belt,and Lincang terrane are responsible for zircons of 416–466 Ma and 219–308 Ma in age.Zircons of 101–110 Ma and 149–175 Ma in age were sourced from magmatic rocks of the southwestern South China Block and northern Vietnam.Thus,the Muang Xai Basin sediments might have originated from a reactivation event that affected a mature hinterland and not an active orogenic belt.The provenance of Muang Xai basin originates from the reactivation of orogenic belt rather than from the uplift of regional orogenic belt.These provenance results suggest that sediment flow into the Khorat red beds was likely from the Great Simao Basin and northern Vietnam,and not directly from the Yangtze Block.