鄂尔多斯盆地奥陶系凝灰岩锆石U-Pb年代学、地球化学特征及其地质意义  

The zircon U-Pb geochronology and geochemical characteristics of the Ordovician tuff in the Ordos basin and their geological significances

作　　者：汪建 赵红格[1] 雷琳琳 曹红霞 王建强[1] 王世哲 魏柳斌 李俊[1] WANG Jian;ZHAO Hong-ge;LEI Lin-lin;CAO Hong-xia;WANG Jian-qiang;WANG Shi-zhe;WEI Liu-bin;LI Jun(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069,China;Geological Research Institute of CNPC Logging Co.,Ltd,Xi'an 710076,China;Research Institute of Shaanxi Yanchang Petroleum(Group)Co.,Ltd,Xi'an 710065,China;Exploration and Development Research Institute of CNPC Changqing Oilfield,Xi'an 710016,China)

机构地区：[1]西北大学地质系,大陆动力学国家重点实验室,西安710069 [2]中国石油集团测井有限公司地质研究院,西安710076 [3]陕西延长石油(集团)有限责任公司研究院,西安710065 [4]中石油天然气股份有限公司长庆油田勘探开发研究院,西安710016

出　　处：《矿物岩石地球化学通报》2023年第6期1359-1371,共13页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金资助项目(42072170,41972153);大陆动力学国家重点实验室基金资助项目(201210132);长庆油田勘探开发研究院项目(技2018-131)。

摘　　要：鄂尔多斯盆地奥陶系凝灰岩多出露于盆地西南边缘,盆地内部露头少,钻井取心资料有限,研究较少,而盆地内部凝灰岩的分布规律、年代及地球化学特征分析对于地层时代及区域构造环境的确定具有重要指示作用。本文以鄂尔多斯盆地内部钻井取心和测井资料为基础,结合野外露头、岩石薄片、锆石U-Pb年代学和主、微量元素等分析方法,对奥陶系凝灰岩平面展布、年龄及地球化学特征进行了研究。结果显示,盆地内奥陶系马家沟组典型层段凝灰岩具有南厚北薄的特点,总体厚度具有从盆地西南边缘向内部(东北方向)减薄的趋势,指示凝灰物质主要来源于盆地西南部。盆地内、外奥陶系凝灰岩的锆石U-Pb年龄均为晚奥陶世(445.0~449.9 Ma)。在Zr/TiO_(2)-Nb/Y图解上凝灰岩样品点落入流纹/英安岩、粗面安山岩系列,说明凝灰物质来源于中酸性岩浆;在Th-Ta-Hf和Rb-(Y+Nb)图解上样品点均落入火山弧系列;在锆石微量元素Th/Nb-Hf/Th图解中,绝大部分样品都落入岩浆弧/造山带环境,反映凝灰岩与火山弧活动密切相关。结合区域构造背景及前人研究结果,本文认为鄂尔多斯盆地奥陶系凝灰岩所代表的沉积事件与北秦岭-北祁连造山带加里东期的岩浆弧活动具有很好的地质响应关系。The Ordovician tuffs in the Ordos basin are mostly exposed in the southwestern margin of the Ordos basin and occaionally outcropped in the internal part of the basin.Because of limited drilling core data,relatively limited researches of the tuffs have been undertaken.However,the research on the distribution regularity,age and geochemical characteristics of the tuffs in the Ordos basin plays an important indicative role for determining the stratigraphic age and regional tectonic environment.Based on the analysis of sampling and logging data of drilling cores in the Ordos Basin,combined with field outcrops,rock slices,zircon U-Pb chronology and analyses of major and trace elements,in this paper,we have studied the distribution,age and geochemical characteristics of Ordovician tuffs in the Ordos Basin.The results show that the thickness of typical Ordovician tuff in the Majiagou Formation is characterized with relatively thick in south and relatively thin in north,with the decreasing trend from the southwest margin to the central part(northeastward)of the basin,indicating that the tuff was mainly sourced from the southwest of the basin.Zircon U-Pb ages of Ordovician tuffs in inner and outer zones of the basin are all of Late Ordovician(445.0~449.9 Ma).Data of tuff samples are plotted into fields of rhyolite/dacite and trachyandesite series in the Zr/TiO_(2)-Nb/Y diagram,indicating that the tuff was formed from intermediate-acidic magma.In addition,data of tuff samples are all plotted into the field of the volcanic arc series in the Th-Ta-Hf and Rb-(Y+Nb)diagrams,and are mostly plotted into the magmatic arc/orogenic environment.in the tectonic environment discrimination diagram of Th/Nb-Hf/Th for trace elements of zircons,indicating that the tuff was closely related to volcanic arc activity.Combined with the regional tectonic background and previous research results,it is considered that the sedimentary event represented by the Ordovician tuff in the Ordos Basin had a good geological response relationship with the Ca

关 键 词：凝灰岩 锆石U-PB定年 地球化学 晚奥陶世 岩浆弧环境 鄂尔多斯盆地 

分 类 号：P597[天文地球—地球化学]