摘要
鄂尔多斯盆地西南缘广泛出露中元古代岩浆岩,相关研究对揭示Columbia超大陆裂解过程具有重要意义。为厘清岩浆成因及该时代构造演化特征,本文对鄂尔多斯盆地西南缘骑安沟地区的双峰式火成岩开展了系统的岩石学、锆石U-Pb年代学与地球化学研究。锆石U-Pb定年结果显示,花岗斑岩和玄武安山岩的年龄分别为1794±10 Ma和1803±21 Ma,指示其形成于中元古代。地球化学特征表明,花岗斑岩为过铝质A_(2)型花岗岩,富集大离子亲石元素(LILE)且亏损高场强元素(HFSE),具有较高的Rb/Sr值(2.95~3.55),反映其源于地壳熔融。玄武安山岩属钙碱性系列,具有LILE选择性富集、HFSE显著亏损的岛弧型配分特征,稀土元素配分曲线右倾,较大陆地壳具高La/Nb(3.83~4.01)、La/Ta(342~355)值,指示其来源于富集岩石圈地幔,且受地壳物质混染影响,Nb/Ta=17.8~18.6,Rb、Th明显富集,Eu异常不明显(δEu=0.96~0.97)表明岩浆演化过程中未经历明显的斜长石分离结晶作用。根据构造判别图解及区域构造背景综合分析,认为该套双峰式火成岩形成于中元古代造山后大陆板内伸展环境,反映了华北克拉通约1.80 Ga期间的裂解事件。
Mesoproterozoic magmatic rocks are extensively exposed along the southwestern margin of the Ordos Basin.Relevant studies are of great significance for revealing the breakup process of the Columbia Supercontinent.To clarify the magmatic genesis and the tectonic evolution characteristics of this era,this paper conducts systematic petrological,zircon U-Pb geochronological,and geochemical studies on the bimodal igneous rocks in the Qi'angou area of the southwestern Ordos Basin.Zircon U-Pb dating results show that the ages of the granite porphyry and basaltic andesite are 1794±10 Ma and 1803±21 Ma,respectively,indicating their formation in the Mesoproterozoic.Geochemical characteristics reveal that the granite porphyry is a peraluminous A_(2)-type granite,enriched in largeion lithophile elements(LILE)and depleted in high field strength elements(HFSE),with relatively high Rb/Sr ratios(2.95~3.55),reflecting its origin from crustal melting.The basaltic andesite belongs to the calc-alkaline series,exhibiting island arc-type distribution characteristics of selective LILE enrichment and significant HFSE depletion,with right-inclined rare earth element(REE)distribution patterns.Compared with the continental crust,it has higher La/Nb(3.83~4.01)and La/Ta(342~355)ratios,indicating its derivation from the enriched lithospheric mantle and influence of crustal material contamination(Nb/Ta=17.8~18.6,obvious Rb-Th enrichment).The insignificant Eu anomaly(δEu=0.96~0.97)suggests that the magma did not undergo obvious plagioclase fractional crystallization during its evolution.Comprehensive analysis based on tectonic discrimination diagrams and regional tectonic settings indicates that this set of bimodal igneous rocks formed in a post-orogenic intracontinental extensional environment during the Mesoproterozoic,reflecting the breakup event of the North China Craton around 1.80 Ga.
作者
郭伟
任军峰
崔军平
任战利
王红伟
宋昊昱
刘国庆
GUO Wei;REN Jun-feng;CUI Jun-ping;REN Zhan-li;WANG Hong-wei;SONG Hao-yu;LIU Guo-qing(Department of Geology,Northwest University,Xi'an 710069,China;Exploration and Development Research Institute of PetroChina Changqing Oilfield Company,Xi'an 710018,China;State Key Laboratory of Continental Evolution and Early Life,Northwest University,Xi'an 710069,China)
出处
《岩石矿物学杂志》
北大核心
2026年第2期223-244,共22页
Acta Petrologica et Mineralogica
基金
长庆油田科技重大专项(2024D1JC06)。
关键词
鄂尔多斯盆地西南缘
骑安沟双峰式火成岩
中元古代
造山后伸展
southwestern margin of the Ordos Basin
Qi'angou bimodal igneous rocks
Mesoproterozoic
postorogenic extension
