鄂尔多斯盆地北部中生代中晚期地层碎屑锆石U-Pb定年与物源示踪

发布时间：2018-03-03 05:01

本文选题：中侏罗统直罗组　切入点：下白垩统志丹群　出处：《地质学报》2017年07期 　论文类型：期刊论文

【摘要】：本文采用LA-ICP-MS碎屑锆石原位微区测年方法,对鄂尔多斯盆地北部杭锦旗地区中侏罗统直罗组和下白垩统志丹群进行了砂岩碎屑锆石U-Pb年龄分布及其变化特征研究,统计和对比了前人对该区周缘岩体的同位素年代学结果,结合区域构造背景,系统地研究了盆地北部直罗组及志丹群地层物源及其演变。结果表明:(1)4个直罗组样品和2个志丹群样品锆石年龄总体呈现出270~280Ma、320~340Ma、1800~2000Ma、2300~2500Ma 4个峰值年龄段,在志丹群样品中出现有少量230~240Ma锆石年龄;(2)杭锦旗地区上述砂岩的物源主要来自阴山、大青山—乌拉山的片麻岩、麻粒岩、孔兹岩以及形成于海西期的中酸性侵入岩,同时也有狼山地区岩体、集宁地区孔兹岩的一部分贡献;(3)1800~2000Ma、2300~2500Ma峰值年龄均为华北克拉通基底构造热事件的反映,270~280Ma、320~340Ma两个峰值年龄可能记录了早石炭世—中二叠世古亚洲洋向华北板块北缘的两次快速俯冲事件;(4)下白垩统志丹群样品中出现的230~240Ma的锆石,指示晚侏罗世的燕山运动在盆地北缘引起的强烈逆冲推覆造山作用使得印支期侵入岩被抬升至地表并遭受剥蚀,从而为研究区地层进一步增加了来自蚀源区印支期侵入岩的物源;(5)与中侏罗统直罗组样品相比,下白垩统志丹群样品在2300~2500Ma峰值测点所占比例明显增加,这可能是由于早白垩世时期盆地北部沉积边界较中侏罗世相对扩展,使来自阴山的物源比例增加。
[Abstract]:In this paper, the zircon U-Pb age distribution and its variation characteristics of the Middle Jurassic Zhiluo formation and the Lower Cretaceous Zhidan Group in the Hangjinqi area, northern Ordos Basin, have been studied by LA-ICP-MS in situ zircon dating method. The isotopic geochronology of the surrounding rock bodies in this area is statistically analyzed and compared, combining with the regional tectonic background. The stratigraphic source and evolution of the Zhiluo formation and Zhidan group in the northern part of the basin have been systematically studied. The results show that the zircon ages of 4 Zhiluo formation samples and 2 Zhidan group samples generally show four peak ages of 270 ~ 280 Ma ~ 320 Ma ~ (180) Ma ~ (1) 2000 Ma-2300 ~ (2 300) Ma ~ (2 500) Ma. A small amount of 230- 240 Ma zircon age was found in the samples of the Zhidan Group. The source of the above sandstone in the Hangzhou Jinqi area is mainly from the gneiss, granulite, khondite and intermediate-acid intrusive rocks formed in the Hercynian epoch, from the gneiss, granulite and kongzite formed in the Yingshan, Daqingshan-Ula Mountains. There is also a rock mass in the Langshan area. Part of the contribution of the Kongzi rocks in the Jining area is the peak age of 2300 ~ 2500Ma in 2000 Mai, 2300 and 2500Ma, both reflecting the tectonic thermal events of the North China Craton basement, reflecting the two peak ages of 270-280 Ma-320 Ma and 340 Ma, which may record two peak ages of the early Carboniferous and the Middle Permian Paleo-Asian Ocean toward the northern margin of the North China plate. Zircon from the lower Cretaceous Zhidan Group samples of 230 ~ 240 Ma, The strong thrust-nappe orogeny caused by the Yanshanian movement of the late Jurassic in the northern margin of the basin caused the Indosinian intrusive rocks to be uplifted to the surface and eroded. Thus, the formation of the study area further increased the provenance of the Indosinian intrusive rocks from the etched source area. Compared with the samples of the Zhiluo formation of the Middle Jurassic, the percentage of the samples of the Lower Cretaceous Zhidan Group at the peak value of 2300 ~ 2500Ma increased obviously. This may be due to the relatively expansion of the northern boundary of the basin during the early Cretaceous period compared with the Middle Jurassic period, resulting in an increase in the source ratio from the Yinshan Mountains.
【作者单位】：大陆动力学国家重点实验室西北大学地质学系;陕西延长石油(集团)油气勘探公司延长气田采气一厂;
【基金】：国家自然科学重点基金项目(编号41330315) 西北大学大陆动力学国家重点实验室科技部专项经费中国地质调查局工作项目(编号12120114009201)联合资助成果
【分类号】：P534.4;P597.3

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