西天山新源南部二叠纪辉绿岩墙群地球化学特征、锆石U-Pb年龄及其地质意义  

Geochemistry and zircon U-Pb age of the Permian radial diabase dyke from southern Xinyuan area, Western Tianshan Mountains, Xinjiang, and their geological significance

作　　者：冯博[1] 薛春纪[2] 赵晓波[2] 汪冰[1] 张恩[1] FENG Bo;XUE Chunji;ZHAO Xiaobo;WANG Bing;ZHANG En(Airborne Survey and Remote Sensing Center of Nuclear Industry,Shijiazhuang 050002,Hebei,China;State Key Laboratory of Geological Processes and Mineral Resources/School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]核工业航测遥感中心,河北石家庄050002 [2]地质过程与矿产资源国家重点实验室/中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地质通报》2019年第6期1028-1039,共12页Geological Bulletin of China

基　　金：国家重点研发计划深地资源勘查开采项目《北方增生造山成矿系统的深部结构与成矿过程》(编号:2017YFC0601202)

摘　　要：南天山古洋盆闭合、碰撞造山时限等洋-陆格局的演化过程是西天山备受关注的地球动力学问题,紧邻那拉提北缘断裂的新源地区二叠纪放射状辉绿岩墙提供了解决这个问题的良好机会。新源地区辉绿岩具辉绿结构,斑晶为斜长石和普通辉石,基质主要由斜长石、辉石、绿泥石等副矿物组成。岩石为富钠贫钾、过铝质、钙碱性岩浆系列。辉绿岩岩墙富集Rb、Th和La等元素,明显亏损Nb、Ta等元素,显示εNd(t)为正值(+3.3^+3.8)和低的初始锶比值((87Sr/86Sr)i=0.70479~0.70548),幔源物质明显。与该区石炭纪玄武岩地球化学性质相似,岩浆可能为二叠纪软流圈和岩石圈相互作用的产物,其起源与软流圈上涌有关。辉绿岩岩墙LA-ICP-MS锆石U-Pb年龄为280.4±3.6Ma,被解释为岩脉成岩年龄,即岩脉形成于二叠纪。结合区域构造背景,推测辉绿岩岩脉形成于塔里木地块与中天山-伊犁地块碰撞闭合后的板内伸展环境,并与南天山洋洋壳岩石圈板块断离密切相关。The accretionary processes of the Western Tianshan Mountains is a hot topic but there is no consensus on the final closure of the Paleo-South Tianshan Ocean basin and subsequent post-collision process. The Permian radial diabase dyke exposed near the North Nalati Fault provides an opportunity for understanding these problems. The dyke shows a typical ophitic texture. The phenocryst is composed of plagioclase and pyroxene, and the substrate is mainly composed of plagioclase, pyroxene, chlorite and some other accessory minerals. The diabase dyke hassodium-rich, potassium-poor and peraluminous characteristics, and hence belongs to the calc-alkaline series. The dyke is characterized by depletion of Nb and Ta and enrichment of Rb, Th and La, and has mantle source material with positive εNd(t) values (+ 3.3^+ 3.8) and low initial Sr((879Sr/86Sr)i=0.70479~0.70548)). These geochemical characteristics are similar to those of the Carboniferous basalt of the study area, suggesting that the parental magma was formed by the interaction of asthenosphere and lithosphere. Zircon U-Pb dating of the dyke yielded an age of 280.4 ±3.6Ma. Combined with regional tectonic background, the authors hold that these Permian diabaseswere formed fromintraplate extension after the collision stage which was closely related to the oceanic lithosphere break-off.

关 键 词：辉绿岩岩墙 二叠纪 岩石成因 LA-ICP-MS锆石U-PB年龄 新疆西天山 

分 类 号：P534.46[天文地球—古生物学与地层学] P588.12[天文地球—地质学]