鄂尔多斯盆地南部下白垩统宜君组碎屑锆石U-Pb年龄及物源意义  

Detrital Zircon U-Pb Dating and Provenance Significance of the LowerCretaceous Yijun Formation in the Southern Ordos Basin

作　　者：李姣莉 王建强[1] 彭恒 李科亮 丰孝林 张东东[1] LI JiaoLi;WANG JianQiang;PENG Heng;LI KeLiang;FENG XiaoLin;ZHANG DongDong(Geology Department/State Key Laboratory of Continental Dynamics,Northwest University,Xi'an 710069,China;Department of Geoscience,University of Padova,Padova 35131,Italy)

机构地区：[1]西北大学地质学系大陆动力学国家重点实验室,西安710069 [2]帕多瓦大学地球科学系,意大利帕多瓦35131

出　　处：《沉积学报》2023年第5期1609-1623,共15页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41972153);陕西省教育厅科学研究计划项目资助(22JP086)。

摘　　要：早白垩世为中生代鄂尔多斯盆地演化的最晚阶段,构造环境与沉积物源体系发生了明显的改变,对盆地演化及多能源矿藏(产)赋存具有重要影响。以鄂尔多斯盆地南部下白垩统宜君组为主要研究对象,利用碎屑锆石定年方法,结合周邻地质体锆石U-Pb年龄谱峰及构造演化特征,示踪了宜君组沉积物质来源并探讨了其地质意义。结果表明,宜君组砂岩碎屑锆石U-Pb年龄主要集中分布于早中生代(195~250 Ma)和早古生代(400~500 Ma)时期,峰值年龄分别为218 Ma和450 Ma,与今北秦岭地区广泛出露岩体的时代具明显的时空一致性,而元古宙—太古宙锆石年龄不但数量少且较为分散。经区域对比,指出宜君组物源主要来自秦岭造山带,秦岭造山带早中生代岩体侵位后,最晚在早白垩世初已抬升剥露至地表,并开始向盆地南部提供大量物源。本研究在一定程度上间接约束了秦岭晚中生代隆升剥露及渭北隆起发育的时限,对明确盆地南部中生代砂岩型铀矿铀源及成矿分布具有一定的指示意义。The Early Cretaceous was the latest evolution period of the Mesozoic Ordos Basin.The tectonic environ⁃ment and sedimentary provenance system have undergone significant changes since then that are of great significance to the evolution of the basin and the exploration of multi-energy mineral reservoirs and/or mineralization.This study takes the Lower Cretaceous Yijun Formation in the southern Ordos Basin as the main research object,uses the detri⁃tal zircon laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)uranium-lead(U-Pb)dating method,and analyses the characteristics of zircon U-Pb age spectrum peaks and structural evolution characteristics of surrounding blocks to trace the provenance of the Yijun Formation and discuss its geological significance.The results show that the detrital zircons U-Pb ages from the Yijun Formation are distributed in the Early Mesozoic(ca.195⁃250 Ma)and Early Paleozoic(ca.400⁃500 Ma)periods,with peak ages of ca.218 Ma and ca.450 Ma,respectively,which are consistent with the age of the widely exposed rock masses in the North Qinling area today.The Proterozoic-Archaean zircon ages are not only small in number,but have no obvious age peaks.Based on comparison of the re⁃gional geological background,the provenance comes from the North Qinling orogenic belt.It was uplifted and ex⁃posed to the surface at the beginning of the Cretaceous,providing a large amount of material to the southern Ordos Ba⁃sin.This study restrained the uplift and exhumation of Qinling in the Late Mesozoic to a certain extent and restricts the time limit for the development of the Weibei uplift.The research has a certain guiding role in determining the ura⁃nium ore sources and ore-forming distribution of Mesozoic sandstone-type uranium deposits in the southern part of the basin.

关 键 词：鄂尔多斯盆地南部 下白垩统宜君组 碎屑锆石U-Pb定年 物源分析 地质意义 

分 类 号：P618.13[天文地球—矿床学]