Institute of Geomechanics, Chinese Academy of Geological Sciences
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，研究区样品与大陆岛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于大陆岛弧为主，兼有主动大陆边缘特征的构造背景。怀头他拉组碎屑锆石U-Pb年龄可划分出三个年龄区间，401～480 Ma，900～1493 Ma和1803～1908 Ma。年龄谱呈早古生代单峰值特征，峰值年龄分别为414 Ma，反映物源区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。
Aiming at finding out the material source and tectonic background of Early Carboniferous strata in west section of northern Qaidam Basin. In this study, the Huaitoutala Formation clastic rocks from Xiaosaishiteng Mountain area were collected for geochemical and detrital zircon U-Pb geochronology analysis. The results show that UCC-normalized trace element spider diagram of clastic sedimentary rocks is flat shaped, with the enrichment of Th, U, Hf and the loss of Co, Sc, Ni, V. The rare earth elements of the sandstones display obvious fractionation in light and heavy REE, strong enrichment in light REEs with medium negative Eu anomaly. The Cr/Zr, Sm/Nd, Th/Sc and Th/U ratios and discrimination diagrams indicating that most sediments were derived from upper crust source area with felsic- intermediate rocks as dominant contributors. Multiple geochemical parameters revealed the geochemical characteristics of test samples are close to the continental island arc sandstone. Interrelated tectonic environment discrimination also verified that Huaitoutala Formation was developed in continental island arc and active continental margin tectonic settings. The U-Pb ages of detrital zircons in Huaitoutala Formation can be divided into three populations: 401～480 Ma, 900～1493 Ma and 1803～1908 Ma, which yield a single Early Paleozoic peak (414 Ma) in histogram, indicating key tectonomagmatism episodes of the north Qaidam Caledonian Orogenic Belt during late Early Paleozoic. Based on previous research conclusions of paleogeography and paleocurrent evidence, it is inferred that the provenance of the Early Carboniferous Huaitoutala Formation have come from the north Qaidam Caledonian Orogenic Belt.