保山地体新元古代——早古生代沉积岩碎屑锆石年代学及其构造意义

滇西潞西地区位于青藏高原东南缘,大地构造位置上属于保山地体。由于新生代强烈的陆内变形作用,保山地体与青藏高原腹地体的对应关系难以确定。野外观察及LA-ICP-MS锆石U-Pb测年结果表明,潞西新元古代—早古生代地层(震旦系—寒武系蒲满哨群及下奥陶统大矿山组)大部分碎屑锆石Th/U0.1,说明其大多为岩浆成因。U-Pb年龄跨度较大,太古宙—早古生代都有分布,且具有明显的562Ma、892Ma及2265Ma年龄峰,以及较弱的1680Ma和2550Ma年龄峰。保山地体潞西地区沉积岩碎屑锆石年龄分布特征与特提斯喜马拉雅、南羌塘沉积地层碎屑锆石年龄分布特征相似,说明其具有相同的物源——冈瓦纳大陆北部的印度大陆。在新元古代晚期—早古生代,保山地体位于印度大陆北缘,与南羌塘、喜马拉雅地体相邻。伴随着俯冲相关的增生造山过程,保山地体形成相应的新元古代末期—早古生代沉积地层。

Detrital zircon geochronology of Neoproterozoic-Early Paleozoic sedimentary rocks in Baoshan terrane and its tectonic significance

The Luxi area of west Yun''nan which belongs to Baoshan terrane is located on the southeastern margin of the Tibetan Plateau. It is difficult to confirm the relationship between Baoshan terrane and Tibetan Plateau due to the strong deformation in Cenozoic. Based on the field study and LA-ICP-MS U-Pb dating, the authors hold that most detrital zircons of Neoproterozoic to early Paleozoic strata in Luxi area have high Th/U ratios (>0.1), which corresponds to the features of magmatic zircons. Zircon UPb ages are distributed from Archean to Early Paleozoic, with age peaks showing strong peaks of Cambrian (562Ma), Neoproterozoic (890Ma), Paleoproterozoic (2292Ma), and some weaker age peaks of Mesoproterozoic (1676Ma) and Neoproterozoic (2500Ma). The detrital zircon age distribution pattern in Baoshan terrane is similiar to that in South Qiangtang and Tethys Himalayan sedimentary strata, indicating that they were all derived from the Indian block located on the northern margin of Gondwanaland. From late Neoproterozoic to Early Paleozoic, Baoshen terrane was located on the northern margin of India block, adjacent to the north Qiangtang and Himalayan terrane. During the accretionary orogenic process related to the subduction, the late Newproterozoic to Early Paleozoic sedimentary strata were formed in the Baoshan terrane.