摘要
为查明鄂尔多斯盆地北部上古生界石盒子组沉积物源及构造背景,通过常规薄片统计、重矿物及其组合特征、石英颗粒阴极发光、全岩主量及微量元素分析以及锆石U-Pb测年(LA-ICP-MS)等方法对研究区物源进行系统研究。结果显示,碎屑组成、重矿物、石英颗粒阴极发光等矿物、岩石学特征均表明研究区石盒子组盒8段沉积物源来自北部,且自东向西平面分区明显,指示存在多个并列的古水系提供物源。球粒陨石标准化的稀土配分模式图显示,北部露头区和盆地内样品二者REE配分曲线形态一致,均显示轻稀土略富集、中等负Eu异常的右倾模式,反映二者物质组成的继承性,与矿物岩石学揭示的物源来自北部蚀源区相吻合。主量元素SiO_(2)-K_(2)O/Na_(2)O、K_(2)O/Na_(2)O-SiO_(2)/Al_(2)O_(3)、TFe_(2)O_(3)+MgO-TiO_(2)判别图及微量元素Th/Sc、Th/U等比值及构造背景判别图显示物源区兼具活动陆缘、被动陆缘和岛弧构造背景,这种复杂的构造背景与鄂尔多斯陆块北缘与阴山陆块碰撞对接时所表现出的复杂构造背景相一致。北缘隆起带的多次旋回性抬升,形成北部再旋回造山带物源。北部露头区变质岩和火成岩的锆石年龄及盆地内石盒子组砂岩碎屑锆石U-Pb测年显示,二者峰值年龄为2.0~1.8 Ga,2.4~2.2 Ga,都集中在元古宙。碎屑锆石最年轻年龄为295.8±3.6 Ma,这一年龄说明沉积作用发生在早二叠世之后,即北缘古亚洲洋关闭后的隆起剥蚀阶段。锆石测年结果2.0~1.8 Ga和2.4~2.2 Ga峰值年龄与近年来对西部陆块孔兹岩系的同位素测年结果相吻合。综合以上分析,显示各个方面互相印证,重建出当时有多个并列古水系,从北部蚀源区向盆地盒8段提供物源。
This study investigates the provenance and tectonic setting of the Upper Paleozoic Shihezi Formation in the northern Ordos basin using a comprehensive suite of analytical techniques.These include thin section petrography,heavy minerals analysis,cathodoluminescence imaging of quartz grains,geochemical analysis of major and trace elements,and zircon U-Pb geochronology(LA-ICP-MS).Our results show that the detrital composition,heavy mineral assemblages,and cathodoluminescence characteristics of quartz grains from the He8 Member of the Shihezi Formation point to a northern provenance.These characteristics display distinct west-to-east variations with obvious zoning on the plane,suggesting the presence of multiple parallel ancient water systems transporting sediment.Chondrite-normalized REE patterns from both the northern outcrop areas and basin samples are consistent,further supporting a northern source.The REEs patterns displayed an obvious fractionation of light and heavy REEs,with a notable light REE enrichment and a moderate negative Eu anomaly.Furthermore,major elements(SiO_(2)-K_(2)O/Na_(2)O,K_(2)O/Na_(2)O-SiO_(2)/Al_(2)O_(3),TFe_(2)O_(3)+MgO-TiO_(2))and trace element ratios(Th/Sc,Th/U),as well as the geochemical discrimination diagram of the tectonic settings,indicated a complex tectonic setting for the source area,encompassing active continental margin,passive continental margin,and island arc.This aligns with the tectonic history of the northern Ordos basin margin during its collision with Yinshan block.Subsequent cyclic uplifts in the northern uplift zone(Yinshan and Daqingshan)generated a distinct cyclic source,explaining the multi-cyclic characteristics observed in the detrital component discrimination patterns.Zircon U-Pb dating of metamorphic and igneous rocks in the northern outcrop area,as well as detrital zircons from basin sandstones,reveals two distinct age populations:2.0~1.8 Ga and 2.4~2.2 Ga,both within the Proterozoic.The youngest detrital zircon age of 295.8±3.6 Ma indicates sedimentation occu
作者
马艳萍
刘池洋
赵靖舟
刘桂珍
郭艳琴
陈建军
侯宾东
MA Yanping;LIU Chiyang;ZHAO Jingzhou;LIU Guizhen;GUO Yanqin;CHEN Jianjun;HOU Bindong(School of Earth Sciences and Engineering,Xi’an Shiyou University,Xi’an,Shaanxi 710065,China;Shaanxi Provincial Key Laboratory of Oil and Gas Accumulation,Xi'an Shiyou University,Xi’an,Shaanxi 710065,China;State Key Laboratory of Continental Dynamics(Northwest University),Xi’an,Shaanxi 710069,China;Department of Geology,Northwest University,Xi’an,Shaanxi 710069,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2024年第12期3567-3587,共21页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号40902042,90814005,42230815,42272148,42202124)
国家科技重大专项课题(编号2008ZX05007-005)
国家重点基础研究发展规划(973)项目(编号2003CB214607)
陕西省教育厅基金项目(编号Z12039)联合资助的成果。
