【摘要】 华北克拉通西南缘相邻的秦–祁–贺交联区早古生代以来的洋陆格局、沉积构造演化及其相邻块体之间的亲缘关系是近年来学界重点关注的热点课题。笔者采取LA-ICP-MS锆石UPb年代学方法，选取北祁连构造带东北缘南华山地区香黄沟剖面出露的一套原先认为属于志留系—泥盆系但缺少化石记录的粗碎屑磨拉石沉积岩系，进行了碎屑岩样品采集与碎屑锆石U-Pb定年分析，探讨其地层时代、碎屑物质来源及其地质构造意义。测试结果表明，该磨拉石建造所含最年轻锆石U-Pb谐和年龄为（230.2±2.6）Ma，还有几个年轻锆石谐和年龄分别为（232±5）Ma、（232±3）Ma和（236.7±2.4）Ma，样品最年轻组分锆石U-Pb加权年龄为（233.2±5.1）Ma，由此限定其宿主地层的最早沉积时代为晚三叠世；结合周邻相近地层单元的碎屑锆石年龄谱对比分析认为，研究区该套磨拉石沉积层系主体应属上三叠统沉积地层单元，不支持过去将其归为志留系—泥盆系的传统认识。区域年龄谱对比分析认为，南华山香黄沟剖面这套晚三叠世的粗碎屑磨拉石沉积岩系早中生代组分碎屑物质来源主要为北秦岭地区和阿拉善地区，早古生代碎屑物质来源主要为祁连–北秦岭地区，前寒武纪碎屑物质来源具有华北板块与祁连–北秦岭造山带的双向混合物源特征。该砾岩沉积主要受控于印支期秦–祁碰撞造山带的构造作用，属于印支期秦–祁海槽最终碰撞闭合过程的沉积构造响应，指示印支期秦–祁碰撞造山事件以后，鄂尔多斯盆地西南部及其相邻秦–祁造山带地区全面进入了陆内或板内构造环境。更多还原

【Abstract】 The ocean-continent pattern, sedimentary tectonic evolution and the relationship between adjacent blocks in the Qin-Qi-He crosslinking area on the southwest margin of the North China Craton since the Early Paleozoic have been the focus of research in recent years. In this paper, LA-ICP-MS zircon U-Pb geochronological analysis is used to analyze a set of coarse clastic molarite sedimentary rocks, which were previously thought to belong to Silurian and Devonian but lack of fossil records, from Xianghuanggou section in Nanhuashan area,northeastern margin of the North Qilian tectonic belt. Clastic rock samples were collected and detrital zircon UPb dating analysis was performed. The results show that the U-Pb concordant age of the youngest zircon is230.2±2.6 Ma, and the concordant age of several younger zircons is 232±5 Ma, 232±3 Ma and 236.7±2.4 Ma,respectively. U-Pb weighted age of the youngest zircon is 233.2±5.1 Ma, and the earliest depositional age of the host strata is the Late Triassic. Combined with the age spectrum of detrital zircons from the adjacent stratigraphic units, it is concluded that the main body of the molarite sedimentary strata in the study area belongs to the Upper Triassic sedimentary stratigraphic units. It does not support the traditional understanding of the Silurian Devonian system in the past. According to the comparative analysis of regional age spectrum, the Late Triassic coarse clastic molarite sedimentary rocks in Xianghuanggou section of Nanhuashan Mountain are mainly derived from the North Qinling and Alxa areas in the Early Mesozoic, and the Qilian-North Qinling areas in the Early Paleozoic. The source of Precambrian detrital material is a bidirectional mixture source between the North China plate and the Qilian-North Qinling orogenic belt. The conglomerate deposits were mainly controlled by the tectonism of the Qin-Qi collisional orogenic belt in the Indosinian period, and should belong to the sedimentary tectonic response of the final collisional closure process of the Qin-Qi trough in the Indosinian period.更多还原