摘要
采用LA-ICP-MS碎屑锆石原位微区测年方法,对鄂尔多斯盆地南部黄陵地区及彬县地区中侏罗统直罗组砂岩进行了碎屑锆石U-Pb年龄分布特征研究,统计和对比盆地周缘岩体的同位素年代学结果,结合盆地南部直罗组地层典型露头实测古水流数据,综合研究了盆地南部直罗组沉积物源。结果表明:(1)黄陵地区直罗组样品总体呈169~438 Ma、1 435~2 083 Ma、2 300~2 767 Ma三个年龄组,对应峰值分别为274 Ma、1 851 Ma和2 366 Ma。彬县地区直罗组样品总体呈213~485 Ma、802~974 Ma、1 633~1 894 Ma和2 143~2 739 Ma 4个年龄组,对应峰值分别为430Ma、450Ma、1 720Ma和2 254Ma。(2)黄陵地区直罗组地层物源主体来自西北部阿拉善地块的中酸性侵入岩及变质岩。彬县地区直罗组地层物源主体来自西部的北、中祁连造山带,源岩为中酸性侵入岩、基性侵入岩及变质岩,同时存在火山岩、碎屑岩及变质碎屑岩的部分贡献。(3)盆地南部直罗组下段地层各典型露头古水流优势方向集中于110°~140°,表明古流向以向东和东南为主,即该时期物源主要来自盆地西、西北方向,这与碎屑锆石年代学对比所指示的物源区相一致,这些物源分析结果对于进一步认识侏罗纪时期盆地原型及古地理格局具有较重要的参考价值。
Based on LA-ICP-MS in situ isotopic dating, the distribution features of U-Pb ages have been comprehensively analyzed in detrital zircons from the sandstones of Zhiluo Formation of the Middle Jurassic, in the Huangling-Binxian area of the southern Ordos Basin. Meanwhile, we collected geochronology data of previous researchers obtained from rocks around the basin and compared them with our data from local samples. Together with our palaeocurrent direction data measured from the typical outcrops of the lower member of Zhiluo Formation we performed a systematic analysis of the sedimentary provenance of Zhiluo Formation. The main conclusions drawn from this analysis are as follows： （1） zircon ages of the sandstones in Huangling can be clearly divided into three groups at 169 - 438 Ma, 1435 - 2083 Ma and 2300 - 2767 Ma, and their corresponding age peaks were at 274 Ma, 1851 Ma and 2366 Ma; similarly, the ages of the sandstones in Binxian can be divided into four groups at 213 - 485 Ma, 802 - 974 Ma, 1633 - 1894 Ma and 2143 - 2739 Ma with corresponding age peaks at 430 Ma, 450 Ma, 1720 Ma and 2254 Ma; （2） the provenance of Zhiluo Formation in the Huangling area came mainly from intermediate-acid intrusive and metamorphic rocks of the Alxa Block, while the provenance of sandstones in Binxian primarily came from the intermediate-acid and basic intrusive rocks and metamorphic rocks of the north and central Qilian orogenic belts; the volcanic, detrital and meta-detrital rocks from the source area also provided part of the source; and （3） the dominant palaeocurrent direction ranged between 110~ and 140~ and pointed to the east and southeast, suggesting that the direction of provenance came mainly from west and northwest, consistent with the direction of the source area identified by contrastive analysis of detrital zircon geochronology. These conclusions can provide some theoretical perspectives for a better understanding of the prototype and paleogeographie characteristics of the Ordos Basin in the Jurassic period.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2017年第6期254-276,共23页
Earth Science Frontiers
基金
国家自然科学重点基金项目(41330315)
中国地质调查局工作项目(12120114009201)
西北大学大陆动力学国家重点实验室科学技术部专项经费资助项目
关键词
中侏罗统直罗组
古流向
碎屑锆石U-Pb定年
沉积物源
鄂尔多斯盆地南部
Zhiluo Formation of Middle Jurassic
palaeocurrent direction
detrital zircon U-Pb dating
sedimentary provenance
southern Ordos Basin
