摘要
基性岩墙(岩脉)产生的地球动力学环境多样,如大陆内部的裂谷带、地幔柱活动相关的大火成岩省、增生造山带的弧前或弧后局部引张带、后碰撞区域性伸展部位等。本文旨在通过对天山中段干沟公路沿线基性岩墙的地质、地球化学、同位素年代学综合研究,结合区域地质研究的最新进展,探讨其形成的构造环境。基性岩墙侵位于古生代沉积岩地层和花岗质岩体之中,具NNW~340°、NE~25°和NE~65°三组延伸方向,并以NNW~340°向优势展布。2个岩墙样品分别获得磷灰石U-Pb年龄302±6Ma和310±9Ma;此外,寄主二云母花岗岩获得锆石U-Pb年龄399±3Ma和403±3Ma。基性岩墙球粒陨石标准化稀土元素配分曲线近平坦、轻重稀土分馏不强、Eu异常不明显,微量元素蛛网图呈现Nb、Ta、Ti和Sr的负异常,(87 Sr/^(86)Sr)初始比值介于0.7058~0.7066、εNd(t)值变化于+4.3~+4.7之间。造就基性岩墙的岩浆可能由受俯冲流体改造的岩石圈地幔部分熔融(1%~5%)产物与软流圈地幔物质相混合而形成。天山造山带后碰撞造山期,区域性大规模伸展作用促使造山带加厚下地壳和岩石圈地幔发生减薄,导致软流圈地幔物质上涌,为基性岩浆的形成提供了深部前提条件;而中-上地壳层次,不同构造单元的边界断裂发生大规模右行走滑运动,产生一系列破裂面,为基性岩浆侵位提供了有效储存空间。
The geodynamic environment associated with mafic dikes is various,including the rift belt within a continent,the large igneous province related to a mantle plume,the extensional belt at a fore-arc or back-arc setting of accretionary orogens,the post-collisional regional extension setting,etc.This paper is aimed to explore the genetic tectonic environment of mafic dikes exposed along the Gangou Highway across the middle segment of Tianshan orogen on the basis of the comprehensive studies on their geological characteristic,geochemistry and isotopic chronology and the newest progresses on the regional geology.The mafic dike intruded into the Paleozoic sedimentary strata and granitic plutons and extended to the NNW~340°,NE~25°and NE~65°,among which the NNW~340°is a dominant tendency.Two dike samples yielded apatite U-Pb ages of 302±6Ma and 310±9Ma,respectively.Additionally,the host two-mica granite yielded zircon U-Pb ages of 399±3Ma and 403±3Ma.The chondrite-normalized rare earth element(REE)pattern of mafic dikes is characterized by an almost flat curve,displaying no strong fractionation and no obvious Eu anomaly.Their primitive mantle-normalized spidergram patterns show negative Nb,Ta,Ti and Sr anomalies.And,their initial 87 Sr/^(86)Sr values vary from 0.7058 to 0.7066 andεNd(t)values from+4.3 to+4.7.The parent magma of mafic dikes was likely produced by the minglement of the asthenospheric materials and the products resulted from a low-degree(1%~5%)partial melting of sub-continental lithospheric mantle(SCLM)fertilized by subduction-related fluids.During the post-collisional stage of the Tianshan orogen,the regional large-scale extension had triggered the thinning of thickened lower orogenic crusts and lithospheric mantles,resulted in the upwelling of asthenospheric materials and provided the prerequisite for the genesis of mafic magmas.Meanwhile,a series of fractures,which were produced by the large-scale dextral strike-slip movement of border faults among different tectonic units,had supplied an available storing space for mafic magmas in the middle to upper crustal level.
作者
江拓
高俊
李继磊
王钟瑞
王信水
马智佩
JIANG Tuo;GAO Jun;LI JiLei;WANG ZhongRui;WANG XinShui;MA ZhiPei(Wuhan Center of China Geological Survey(Geosciences Innovation Center of Central South China),Wuhan 430205,China;State Key Laboratory of Lithospheric and Environmental Coevolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences,China University of Geosciences,Wuhan 430074,China)
出处
《岩石学报》
北大核心
2025年第9期3053-3080,共28页
Acta Petrologica Sinica
基金
国家自然科学基金项目(42172234、41902232、42122011、42072079)资助.
