鄂尔多斯盆地西南部早中生代侵入岩脉的形成时代及成因  

Age and petrogenetic implication of the Early Mesozoic dykes in the southwestern Ordos Basin

作　　者：侯云东[1] 蒋子文 刘新社[1] 罗静兰[3] 范立勇[1] 胡新友 杜一凡 HOU Yundong;JIANG Ziwen;LIU Xinshe;LUO Jinglan;FAN Liyong;HU Xinyou;DU Yifan(Research Institute of Exploration and Development,Changqing Oil Field Company,PetroChina,Xi’an 710021,Shaanxi,China;Department of Geological Engineering/Key Laboratory of Cenozoic Resource and Environment in North Margin of the Tibetan Plateau,Qinghai University,Xining 810016,Qinghai,China;Department of Geology/State Key Laboratory of Continental Dynamics,Northwest University,Xi'an 710069,Shaanxi,China)

机构地区：[1]中国石油长庆油田分公司勘探开发研究院,陕西西安710021 [2]青海大学地质工程系/青藏高原北缘新生代资源环境重点实验室,青海西宁810016 [3]西北大学地质学系/大陆动力学国家重点实验室,陕西西安710069

出　　处：《地质通报》2023年第7期1098-1117,共20页Geological Bulletin of China

基　　金：国家自然科学基金项目《鄂尔多斯盆地基底岩石的地质记录及构造意义——来自探井基底岩芯片麻岩和盖层砂岩研究的证据》(批准号:41772189);国家科技重大专项子课题项目《碎屑岩输导层结构模型中成岩演化过程与流体流动特征》(编号:2017ZX05008-004-004-001);中国石油天然气股份公司重大科技专项项目《鄂尔多斯盆地南部上古生界物源分析及砂体展布规律研究》(编号:2016E-05-02);青海大学青年科研基金项目《北秦岭造山带~320~260 Ma构造热事件及其构造背景》(编号:2021-QGY-8)。

摘　　要：鄂尔多斯盆地西南部龙门地区早中生代侵入岩是盆地内少有的岩浆活动记录,为探讨盆地早中生代形成构造背景提供了理想的研究对象。对鄂尔多斯盆地龙门地区早中生代侵入岩开展岩相学、岩石地球化学及年代学研究。结果表明,侵入岩为钙碱性—高钾钙碱性闪长玢岩和二长玢岩,二者均呈低Mg^(#)、Cr、Ni和Co含量,富集REE和LILE,贫HFSE,亏损Nb、Ta、Ti和P的特征,锆石ε_(Hf)(t)=-33.89~-9.73,t_(DM2)=1564~2780 Ma,主要为古元古代和部分新太古代陆壳物质部分熔融的产物。二长玢岩的轻、重稀土元素分馏略低于闪长玢岩,具有更低的Yb、Y和高的Sr、Sr/Y值,指示其为压力较高条件下盆地基底较深陆壳物质部分熔融的产物;闪长玢岩则为较低压力下的较浅基底陆壳物质熔融的产物。两类岩石均获得242 Ma的形成年龄,与盆地以南秦岭造山带早中生代洋盆俯冲闭合、陆—陆碰撞挤压初期的岩浆活动一致,表明秦岭造山带早中生代以来的构造岩浆活动影响到鄂尔多斯盆地西南部地区,盆地内早中生代侵入岩的出现是秦岭勉略洋盆向北俯冲汇聚挤压环境背景下,鄂尔多斯盆地基底不同深度陆壳物质部分熔融侵入的结果。2类岩石的形成年龄与盆地南缘秦岭造山带中生代构造转折时期相对应,即从晚三叠世长7段沉积开始,鄂尔多斯盆地由之前的挤压环境开始向伸展环境转变。The Early Mesozoic dykes in Longmen area,the southwestern Ordos Basin are infrequent records of magmatism,which provides an ideal object for discussing the tectonic setting of the Early Mesozoic in the Ordos Basin.Petrography,petrogeochemistry and zircon U-Pb dating as well as Lu-Hf isotope for the Early Mesozoic dykes in the Longmen area of the southwestern Ordos Basin are studied.The result shows that these dykes are calc-alkaline to high poassium calc-alkaline dioritic porphyrite and monzonitic porphyrite characterized by low Mg^(#),Cr,Ni and Co contents.They are relatively rich in REE and LILE,poor in HFSE and depleted in Nb,Ta,Ti and P.However,the LREE/HREE ratios of monzonitic porphyrite are slightly lower and with much lower Yb,Y and higher Sr,Sr/Y ratios than those of the dioritic porphyrite,indicating that the former was formed by partial melting of deeper crustal materials under relatively high pressure,while the later was the product of melting of shallow crust material under lower pressure.Both of the dioritic and monzonitic porphyrite yield 242 Ma,consisting with those magmatism during the initial compression after the Early Mesozoic ocean basin closure in the Qinling orogenic belt.Their zirconε_(Hf)(t)=-33.89~-9.73,t_(DM2)=1564~2780 Ma,which implies that the tectonic and magmatic activity occurred in Qinling orogenic belt since the Early Mesozoic has affected the southwestern Ordos Basin.All suggested that these dykes are resulted from the partial melting of Neoarchean and Paleoproterozoic basement of the Ordos Basin at different depths under the background of northward subduction of the Mianlue ocean basin in Qinling orogenic belt,which were roughly corresponding to the early Mesozoic tectonic transition from compression to extension in the Qinling orogenic belt.Consequently,the Ordos Basin has entered into a tectonic setting from the compression to the extension at the initiation of Chang 7 Member deposition during the Late Triassic.

关 键 词：锆石U-PB年龄 岩石地球化学 侵入岩脉 鄂尔多斯盆地 

分 类 号：P534.5[天文地球—古生物学与地层学] P588.12[天文地球—地质学] P597.3