藏北南羌塘盆地二叠纪曲地组碎屑锆石LA-ICP-MS U-Pb年龄及其地质意义

摘要

南羌塘盆地是特提斯大洋俯冲削减而产生的一套构造增生地质体,也是研究青藏高原早期构造演化的关键地区,盆地内出露的石炭纪地层极少.对晚古生代曲地组2个砂岩样品进行全岩主量、微量、稀土元素的研究,并采用LA-ICP-MS同位素测定技术对其中的碎屑锆石进行U-Pb同位素测定,结果表明,碎屑锆石年龄具有6个峰值:330~270Ma、560~480Ma、880~720Ma、1750~1650Ma、2400~2000Ma和2800Ma;地球化学特征表明,曲地组源区的大地构造环境主要为被动大陆边缘及大陆岛弧环境;沉积物物源具有多源性,但仍需进一步研究.推测其物源主要为晚古生代二叠纪之前的冈瓦纳大陆北缘相关地体.%The southern Qiangtang basin is a set of tectonic accretionary geological bodies produced by Tethys subduction, and is al-so the key area for the study of early tectonic evolution in the Tibetan Plateau. In this basin, Carboniferous strata are rarely exposed. In this paper, the major compositions elements, trace elements and rare earth elements were studied by using two samples collected from the Late Paleozoic Qudi Formation. Zircon U-Pb dating through LA-ICP-MS isotope measurement shows that the ages have six peaks, i.e., 330~270Ma, 560~480Ma, 880~720Ma, 1750~1650Ma, 2400~2000Ma and 2800Ma. An analysis of geochemical charac-teristics suggests that the geotectonic background for the source region of Qudi Formation was passive continental margin and land arc, and the provenance of sediments had multi-source character, which, however, needs further research. It is inferred that the mate-rial source might have come from the northern Gondwana during Permian.