碎屑锆石对班公湖地区晚侏罗世-早白垩世沉积物源的制约

本文对班公湖地区中生代沙木罗组（J3—K1s）和日松组（J3r）地层的碎屑锆石进行了形态学及U-Pb年代学的研究。结果表明：锆石颗粒粒径约为100～150 μm，内部结构清晰，晶体为长柱状，自形程度较高，多数锆石不含暗色包体及浑圆形内核； 有些锆石颗粒有扇型分带结构。Th/U比值较大，多数大于0.1，均值约为0.86，说明岩浆的成因以锆石为主体，部分颗粒或晶体可能为变质成因； 锆石年龄主要分布在6个区间范围内： 1）180～100 Ma， 2）350～180 Ma， 3）600～450 Ma， 4）1100～600 Ma， 5）1800～1400 Ma， 6）2200～1800 Ma。锆石U-Pb年龄谱对应了羌塘地块经历的几次构造热事件，验证了晚侏罗世—早白垩世班公湖地区的物源主要来自其北部的羌塘地块。

Constraints of provenance from detrital zircon of Upper Jurassic-Lower Cretaceous Formation in Bangong Co area

The Bangong Co area is located between the Qiangtang block and the Risong magmatic arc zone during the Upper Jurassic Lower Cretaceous.The sedimentary environment of the Bangong Co area is residual sea basin as the Tethyan oceanic basins northward subduction.The sediment is Shamuluo Formation and Risong Formation.Based on the research of Tethyan oceanics evolution，Qiangtang block maybe the provenance of the Bangong Co area.We did some research on morphology and U Pb geochronology of detrital zircon.The grain diameter of detrital zircon is 100～150 μm.The crystal is elongated and high euhedral.There have no dark inclusion and round shaped kernel.Some detrital zircon has fan sub band structure.The value of Th/U is high and the typical value is 086.So the magmatic zircon is dominant.The distribution of U Pb age of zircon is： 1)180～100 Ma； 2)350～180 Ma； 3)600～450 Ma； 4)1 100～600 Ma； 5)1 800～1 400 Ma； 6)2 200～1 800 Ma.The U Pb age of zircon corresponds with the tectonic event of Qiangtang.So the provenance of Upper Jurassic Lower Cretaceous Formation in Bangong Co area is Qiangtang block.