拉萨地块晚古生代沉积源区转变——来自措勤地区永珠组碎屑锆石的证据

    Evolution of Late Paleozoic sedimentary provenance of Lhasa block: Detrital zircons from Yongzhu Formation in Cuoqin area, Tibet

    • 摘要: 晚古生代是拉萨地块地质演化的重要转折期,一些关键地质问题存在争论,如拉萨地块来源问题。选择西藏措勤地区上石炭统永珠组为研究对象,石英砂岩中碎屑锆石U-Pb测年数据显示523Ma、920Ma两个年龄峰值。通过与拉萨地块及其周缘晚石炭世冰期之前地层碎屑锆石对比,认为拉萨地块永珠组920Ma年龄峰值更具有冈瓦纳大陆靠印度一侧的物源特征,其与南羌塘、拉萨、喜马拉雅微陆块在裂离之前具有显著的亲缘关系。而含有冰筏碎屑的拉嘎组和来姑组中包含的西澳大利亚物源信息(约1180Ma年龄峰值),暗示来自西澳大利亚的冰筏可能通过洋流作用漂移至拉萨地块而后沉积冰筏碎屑。

       

      Abstract: The Late Paleozoic is an important transition period for the geological evolution of the Lhasa block, so there are some disputes on key geological issues, such as the origin of the Lhasa block. In this paper, the Upper Carboniferous Yongzhu Formation in the Cuoqin region of Tibet was selected as the study object. The U-Pb dating data of detrital zircons in quartz sandstone show the peak ages of 523Ma and 920Ma. Based on a comparison with the Lhasa block and the detrital zircons formed before the Lhasa blockin the Late Carboniferous glacial period, the authors hold that the 920Ma agepeak of the Yongzhu Formation in the Lhasa block is more characteristic of the provenance on the Indian side of the Gondwana opening, and that the Nanqiangtang, Lhasa and Himalayan microlandmasses were significantly related before splitting. The source information of western Australia (about 1180Ma age peak) in the Laga and Laigu groups containing ice raft debris suggests that ice rafts from western Australia might have drifted to the Lhasa block through ocean currents and then deposited ice raft debris.

       

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