Provenance analysis and structural implications of Gequ Formation at the Buqingshan area in the eastern segment of the East Kunlun region

Detailed statistics of gravel composition, gravel granulometry and the LA-ICP-MS U-Pb dating of detrital zircons from conglomerate bed in Delisitan of Buqingshan show that this conglomerate was derived from the nearby place with rapid accumulation. This conglomerate consists mainly of quartzite and granite and subordinately of siliceous rocks and basic rocks, with minor sandstone and limestone. The coefficients of dispersion are 1.54~2.02 for the gravel of conglomerate. The detrital zircon age spectra can be divided into three groups:①Early Ordovician-Late Silurian age group, 499~409Ma, with the peak value being 426Ma, corresponding to the tectono-magmatic events associated with Proto-Tethys northward subduction and collision at the end of Early Paleozoic; ②Neoproterozoic age group, 744~619Ma, with the peak value being 744Ma, corresponding to the breakup of Rodinia supercontinent; ③Paleoproterozoic age group, 2443Ma, corresponding to the tectono-magmatic hydrothermal event of East Kunlun in Paleoproterozoic. An integrated analysis of the U-Pb detrital zircon ages and sedimentology characteristics show that the granite gravel was derived from magmatic arc in Caledonian in northern East Kunlun Orogen, the gravel of quartzite and metamorphic rocks was from the East Kunlun metamorphic rock series in basement, and the gravel of sedimentary rocks might have come from the early sedimentary formation in the orogenic belt. A comprehensive analysis reveals that the Gequ Formation is a mollasse formation of the littoral-shallow facie which deposited on anactive continental margin. It represents both the beginning of the Paleo-Tethys northward subduction and the sedimentary responding of tectonics at the beginning of the subduction.