柴达木盆地北缘西段下石炭统物源和构造背景：来自碎屑岩U- Pb年代学与地球化学的约束

为查明柴达木盆地北缘西段早石炭世沉积物来源和构造背景,本次研究采集小赛什腾山怀头他拉组沉积岩进行碎屑岩锆石U- Pb年代学和全岩微量元素地球化学分析。研究表明：测试样品微量元素蛛网图呈平坦型,富Th、U、Hf,贫Co、Sc、Ni、V元素;砂岩轻重稀土元素分馏明显,属轻稀土富集型,具有中等负Eu异常;Cr/Zr、Sm/Nd、Th/Sc及Th/U等微量元素比值和判别图版显示研究区怀头他拉组为上地壳长英质物源区。沉积岩微量元素、稀土元素含量及特征比值显示,研究区样品与大陆弧环境砂岩具有极为相似的地球化学特征,相关构造环境投图同样表明怀头他拉组沉积环境以大陆弧为主,兼有主动大陆边缘特征。怀头他拉组碎屑锆石U- Pb年龄可划分出3个年龄区间,480～402 Ma,1493～900 Ma和1908～1803 Ma。年龄谱呈早古生代单峰值特征,峰值年龄为414 Ma,反映物源区与柴北缘加里东期构造带内早古生代晚期的岩浆作用关系密切。结合前人区域上古地理、古水流证据,综合分析认为小赛什腾山下石炭统怀头他拉组物源主要来自于柴北缘高压—超高压变质带。

Provenance and tectonic setting of the Lower Carboniferous in the west section of the North Qaidam basin: Constraints from detrital zircon U- Pb geochronology and geochemistry

In this study,we aimed to determine the material source and tectonic background of the Early Carboniferous strata in the west section of the northern Qaidam basin. To achieve this, we collected clastic rocks from the Huaitoutala Formation in the Xiaosaishiteng Mountain area for geochemical and zircon U- Pb geochronological analysis. The results of our analysis showed that the UCC- normalized trace element spider diagram of the clastic sedimentary rocks exhibited a flat shape. Additionally, we observed enrichment of Th, U, and Hf while Co, Sc, Ni, and V showed depletion. The rare earth elements of the sandstones displayed an obvious fractionation of light and heavy REEs, with a notable enrichment of light REEs with a medium- negative Eu anomaly. Furthermore, the ratios of Cr/Zr, Sm/Nd, Th/Sc, and Th/U, as well as discrimination diagrams, indicated that most of the sediments were derived from the upper crust source area, with felsic- intermediate rocks as dominant contributors. Multiple geochemical parameters revealed that the geochemical characteristics of these samples closely resemble those of continental arc sandstone. The interrelated tectonic environment discrimination also verified that the Huaitoutala Formation was developed in a continental arc and active continental margin tectonic settings. The U- Pb ages of the detrital zircons in the Huaitoutala Formation revealed three distinct populations: 480~402 Ma, 1493~900 Ma, and 1908~1803 Ma. These populations collectively yielded a single peak at 414 Ma in the histogram, indicating significant tectonomagmatism episodes during the late Early Paleozoic in the north Qaidam Caledonian Orogenic Belt. Based on previous paleogeographical and paleocurrent evidence, we can infer that the provenance of the Early Carboniferous Huaitoutala Formation is derived from the north Qaidam Caledonian Orogenic Belt.