阿尔金山喀腊大湾地区堆晶辉长岩地球化学、年代学:洋壳演化证据  

Geochemistry and geochronology of cumulated gabbro from Kaladawan area,Altun Mountains,NW China:Evidence for oceanic crust evolution

作　　者：陈柏林[1,2] 李松彬 王永[1,2] 陈正乐 周永贵[1,2] 郝瑞祥 刘牧[1,2] CHEN Bailin;LI Songbin;WANG Yong;CHEN Zhengle;ZHOU Yonggui;HAO Ruixiang;LIU Mu(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Natural Resources,Beijing 100081,China)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081

出　　处：《中国地质》2023年第5期1557-1572,共16页Geology in China

基　　金：“十二五”、“十一五”国家科技支撑计划重点项目(2011BAB06B08-04,2006BAB07B02-04);中国地质科学院院所长基金项目(JYYWF20180602);中国地质调查局项目(1212011085043)联合资助。

摘　　要：【研究目的】喀腊大湾地区地处阿尔金走滑断裂北侧与东西向阿尔金北缘断裂所夹持的区域;堆晶辉长岩呈近东西向带状断续出露于阿尔金北缘断裂以南4 km,南北两侧与枕状玄武岩等基性海相火山岩共生产出。作为洋壳的主要组成岩石类型,堆晶辉长岩的研究将进一步揭示早古生代阿尔金洋洋壳的演化特征。【研究方法】本文对喀腊大湾地区堆晶辉长岩开展了岩石学、矿物学、地球化学及锆石SHRIMP U-Pb年代学测试和研究。【研究结果】研究显示,喀腊大湾堆晶辉长岩分为伟晶结构和粗晶结构两种类型,并具渐变过渡特点,其地球化学特征具有低K_(2)O含量(平均为0.44%)、平坦的稀土元素配分曲线(LREE/HREE平均值为2.54)、Eu正异常(δEu平均为1.05)、Nb和Ta的负异常(Nb平均2.31×10^(-6)、Ta平均0.16×10^(-6))等特征,反映其产于弧后盆地构造环境。锆石SHRIMP U-Pb年龄为514~516 Ma,与相邻产出的中基性火山岩517 Ma非常接近,表明堆晶辉长岩形成于早古生代晚寒武世。【结论】研究结果显示喀腊大湾地区晚寒武世存在明显的洋壳扩张,该结果与喀腊大湾地区岛弧型中酸性火山岩478~485 Ma和同碰撞中酸性侵入岩477~488 Ma共同构成了区域构造演化的一个完整序列,进一步确定了北阿尔金地区早古生代洋壳扩张、板块俯冲到陆块碰撞的演化历史。This paper is the result of geological survey engineering.[Objective]The Kaladawan area is located within the area defined by the NE-striking Altun strike-slip fault to the north and EWstriking northern Altun fault.The cumulated gabbro is exposed to the north Altun Fault 4 km to the south,basic marine volcanic rocks such as occipital basalt occur in both north and south.As the main component rock type of oceanic crust,the study of cumulate gabbro will further reveal the evolution characteristics of early Paleozoic Altun oceanic crust.[Methods]In this paper,petrology,mineralogy,geochemistry and zircon SHRIMP U-Pb dating of cumulate gabbro in the Kaladawan area have been studied.[Results]The study shows that the cumulate gabbro in Kaladawan can be divided into two types:pegmatite and coarse-grained,and has the characteristics of gradual transition.The geochemistry features include low K_(2)O content(average is 0.44%),flat REE partition curves(the average LREE/HREE value is 2.54),positive Eu anomalies(the averageδEu value is 1.05),and negative Nb and Ta anomalies(the average Nb and Ta content is 2.31×10^(-6)and 0.16×10^(-6),respectively),which indicates that it occurs in the tectonic environment of the back-arc basin.The zircon SHRIMP U-Pb age of 514-516 Ma is very close to that of the adjacent intermediate-basic volcanic rocks of 517 Ma,indicating that the cumulate gabbro was formed in late Cambrian of the early Paleozoic.[Conclusions]The results show that there was an obvious oceanic crust spreading during the late Cambrian in the Kaladawan area.This result,together with island arc intermediate-acid volcanic rocks 478-485 Ma and co-collisional intermediate-acid intrusive rocks 477-488 Ma,constitutes a complete sequence of regional tectonic evolution,and an evolutionary history of the early Paleozoic oceanic crust spreading and plate subduction to continental collision in the North Altun region is further determined.

关 键 词：堆晶辉长岩 地球化学 锆石SHRIMP年龄 蛇绿混杂岩带 地质调查工程 喀腊大湾地区 阿尔金山 

分 类 号：P618.51[天文地球—矿床学]