西藏洞错地区多尼组砂岩碎屑锆石U-Pb年龄及其地质意义

Detrital zircon U-Pb age of the Duoni Formation sandstone in Dongcuo area, Tibet, and its geological significance

摘要: 对洞错地区早白垩世多尼组砂岩的碎屑锆石进行了U-Pb测年研究。结果表明，锆石颗粒粒径为50~180μm，Th/U值大，约51颗锆石的比值大于0.4，平均值约为0.64，说明锆石大部分为岩浆成因，部分可能为变质成因；锆石年龄主要分布在7个区间范围（或峰值）：3261Ma、2739~2335Ma、1880~1750Ma、1006~657Ma、577~510Ma、456~409Ma和252~202Ma。3261Ma的最老碎屑锆石颗粒说明，其物源区存在古太古代古老地壳的残留。锆石U-Pb年龄谱对应羌塘地块经历的几次构造热事件，验证了洞错地区早白垩世沉积物的物源可能来自北部的南羌塘地块。

Abstract: In this paper, the authors conducted some researches on U-Pb geochronology of detrital zircon of the Duoni Formation in Dongcuo area, Tibet. The grain diameter of detrital zircon is 50~180μm. The Th/U ratio is high. The Th/U ratio of 51 zircon samples is greater than 0.4, with the typical value being 0.64. So the magmatic zircon is dominant. The distribution of U-Pb age of zircon is 3261Ma, 2739~2335Ma, 1880~1750Ma, 1006~657Ma, 577~510Ma, 456~409Ma and 252~202Ma. The oldest detrital zircon age is 3261Ma. The provenance of the sediments contained residues of the earth's crust in Archean.The U-Pb age of zircon corresponds to the tectonic event of Qiangtang. So the provenance of Lower Cretaceous Formation in Dongcuo area should be Qiangtang block.