鄂尔多斯盆地西北缘早—中侏罗世延安期碎屑锆石LA-ICP-MS定年及其物源意义  

LA-ICP-MS detrital zircon dating and its provenance significance in Yan'an Formation of the Early-Middle Jurassic in the northwestern margin of Ordos Basin

作　　者：赵红格[1,2] 刘池洋[1,2] 王海然[1] 高少华[1] 李蒙[1] 卓鱼周 乔建新[1] 张孙玄琦 蒋盛[1] 

机构地区：[1]西北大学地质学系,陕西西安710069 [2]西北大学大陆动力学国家重点实验室,陕西西安710069

出　　处：《地学前缘》2015年第3期184-193,共10页Earth Science Frontiers

基　　金：西北大学大陆动力学国家重点实验室科技部专项项目(BJ08133-14;BJ081334-2);国家自然科学基金项目(41330315;40902032);国家科技油气重大专项项目(2011ZX05023-001-002)

摘　　要：鄂尔多斯盆地西北部延安期地层分布广泛,其周缘同期地层分布零星,不同地区岩性具有一定的相似性,对该时期的盆地沉积边界和物源属性还存在争议。文中利用锆石LA-ICP-MS U-Pb测年和地球化学分析方法,探讨了西北部不同地区延安期的物源时代和性质。本次在贺兰山和桌子山地区共测试锆石年龄210个,获得193个有效的单颗粒碎屑锆石年龄。贺兰山地区大部分碎屑锆石阴极发光图像具有环带结构,且具左倾式稀土元素分布模式,大部分Th/U值大于0.4,表明锆石来源以岩浆为主,变质为次。锆石年龄绝大部分为古生代(集中于二叠纪),其次为元古宙。桌子山地区碎屑锆石具有与贺兰山相似的阴极发光和稀土元素分布特征,但碎屑锆石年龄分布差别较大。其中大部分锆石年龄(66.7%)分布于新太古代—元古宙(集中于元古宙),其次为二叠纪(22.7%)和早—中三叠世(10.6%)。通过与周缘古老地层的年龄对比认为,鄂尔多斯盆地西北部早中侏罗世延安期的沉积物源,贺兰山地区可能主要来自其西侧的阿拉善地块海西期岩浆岩,其次为西北部元古宙岩浆岩和变质岩(贺兰山群);桌子山地区可能主要为其西北部元古宙岩浆岩和变质岩,其次为海西期岩浆岩和早—中三叠世岩浆岩。早—中侏罗世延安期西缘贺兰山地区和桌子山、磁窑堡等地区的物源年龄具有一定的相似性,但仍然存在差异,需要借助于岩石学和沉积学方面的证据进一步精细刻画其物源属性。The Early-Middle Jurassic Yan＇an Formation widely distributed in the northwestern margin of Ordos Basin, and the outcrops scattered limitedly with similar lithological features. Many disputes still exist about the source areas of Yan＇an Formation due to the tremendous geological reformation since the Late Cretaceous. The zircon Laser-Ablation Inductively Cotlpied Plasma Mass Spectrometry （LA-ICP-MS） U-Pb dating was used to determine the ages of the source areas of the Yan＇an Formation in the region. There are three samples selected from the sandstone of Yan＇an Formation in two areas, altogether 210 grains were dated, and 193 valid zircon ages were obtained. Most zircons from the samples of Helan Mountain showed circular belt images under the cathodoluminescence microscope and displayed the left-oblique distribution pattern of rare earth elements. Most of those zircons have the Th/U larger than 0. 4 indicating the magmatic origin, and a few zircons were from the metamorphic rock in the area. Most zircon U-Pb dating ages are mainly of the Paleozoic with the maior peak in the Permian. The secondary ages are of the Proterozoie. The zircons from Z!auozi Mountain area are with the similar characteristics both in the images under the cathodoluminescence microscope and in the rare earth dement distribution pattern. There exists much difference in the zircon ages between the two areas. The old ages in Zhuozi Mountain possess great proportions; 66. 7% are of the Late Archean- Proterozoic （mainly the Proterozoic） ; only 22.70//00 of the total ages belong to the Permian, and 10. 6% are of the Early-Middle Triassic. Compared with the ages of surrounding ancient rocks, it is concluded that the main sources of the Early-Middle Jurassic in the northwest margin of Ordos Basin were the Proterozoic magmatic and metamorphic rocks in the Alashan Paleo-Biock; for the north of Ordos Basin, the main source was the Hercynian granite in the Alashan Paleo-Block. The main provenance in Helan Mountain was the Hercynian

关 键 词：早—中侏罗世延安期 碎屑锆石年龄分布 沉积物源 元古宙岩浆岩变质岩 海西期岩浆岩 

分 类 号：P597[天文地球—地球化学]