东昆中构造混杂岩带清泉沟弧前玄武岩地质、地球化学特征及构造环境  

Geochemistry and Tectonic Setting of Qingquangou Forearc Basalts in Central Tectonic Mélange of East Kunlun Orogen

作　　者：李瑞保[1,2] 裴先治[1,2] 李佐臣[1,2] 裴磊[1] 陈国超[1] 李小兵[1] 陈有炘[1] 刘成军[1] 魏博[1] Li Ruibao;Pei Xianzhi;Li Zuochen;Chen Youxin;Liu Chengjun;Wei Bo;Pei Lei;Chen Guochao;Li Xiaobing(School of Earth Science and Resources,Chang'an University,Xi'an 710054,China;Key Laboratory of Western Mineral Resources and Geological Engineering ,Mimstry of Education,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,Ministry of Natural Resources,Chang'an University,Xi'an 710054,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]长安大学西部矿产资源与地质工程教育部重点实验室,自然资源部岩浆作用成矿与找矿重点实验室,陕西西安710054

出　　处：《地球科学》2018年第12期4521-4535,共15页Earth Science

基　　金：国家自然科学基金项目(Nos.41502191,41472191,41172186);中央高校基本科研业务费专项资金项目(Nos.CHD2011TD020,2013G1271091,2013G1271092,310827161002,310827161006,310827173702);青海省国土资源厅-中国铝业公司公益性区域地质矿产调查基金项目(No.200801)

摘　　要：东昆中构造混杂岩带东段清泉沟玄武岩岩石源区及构造环境研究具有重要意义.通过对清泉沟玄武岩进行详细的地质、地球化学和构造环境研究,结果表明,该套玄武岩属于亚碱性拉斑玄武岩系列,球粒陨石标准化稀土元素配分图呈现轻稀土元素弱亏损-弱富集的特征,与正常大洋中脊玄武岩(NMORB)和西太平洋IBM弧前玄武岩(FAB)配分特征相似.岩石成因研究表明其源区具亏损地幔特征,且地幔熔融程度比NMORB源区熔融程度较高.构造环境研究表明该套玄武岩形成于大洋初始俯冲阶段的弧前环境.综合区域地质资料,认为东昆中古洋盆至少于中寒武世(510Ma)之前开始向北俯冲,在俯冲初期形成了清泉沟弧前玄武岩,构成了俯冲带初始弧壳或不成熟洋内岛弧.The research on magmatic source and tectonic setting of Qingquangou basalts in eastern section of East Kunlun is important for discussion of the tectonic evolution of East Kunlun ocean. This paper presents a systematic field geology, geochemistry, and tectonic setting research. The results show that the SiO2 contents of Qingquangou basalts range from 48.60% to 49.28%, MgO contents range from 7.72%-8.00%, TiO2 contents range from 1.07%-1.10% (average values, 1.09%), which are similar to the values of Izu-Bonin-Mariana forearc basalt, West Pacific. The basalts are classified into the tholeiitic basalt of subalkaline series based on the major elements feature. Qingquangou basalts are characterized by the ∑LREEs range from 22.64×10^-6-33.31×10^-6, ∑HREEs range from 13.13×10^-6-18.37×10^-6, ∑REEs range from 36.02×10^-6-51.68×10^-6, and (La/Yb)N range from 0.88-1.10. The chondrite normalized REE patterns show the widely enriched-depleted feature of LREE, resembling the feature of NMORB basalts and IBM forearc basalts, West Pacific. Moreover, the samples have low ratios of Ti/Y (312) and Ti/V (<20), also indicative of the forearc basalt feature. The primitive mantle normalized trace element spider diagram shows enriched LILEs and undifferentiated HFSEs (e.g., Nb, Ta, Zr, Hf, etc.) features. Petrogenesis research shows that its source was derived from the depleted mantle, and further proves that its partial melting degree is higher than that of NMORB-type basalts. Additionally, the tectonic discrimination diagram suggests that the basalts formed in forearc tectonic setting. Combined with the previous data, it is concluded that East Kunlun ocean began to subduct northward at Middle Cambrian (ca.510 Ma), and that Qingquangou forearc basalts were generated meanwhile, forming the nascent island arc crust.

关 键 词：东昆仑 蛇绿岩 清泉沟 弧前玄武岩 地球化学 

分 类 号：P548[天文地球—构造地质学]