Geochemical characteristics and tectonic implications of HP-UHP eclogites and blueschists in southwestern Tianshan, China  

作　　者：AI Yongliang ZHANG Lifei LI Xuping QU Junfeng 

机构地区：[1]MOE Key Laboratory of Orogenic Belt and Crust Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China [2]School of Geosciences and Resources, China University of Geosciences, Beijing 100083, China

出　　处：《Progress in Natural Science:Materials International》2006年第6期624-632,共9页自然科学进展·国际材料（英文版）

基　　金：Supported by National Natural Science Foundation of China (Grant Nos. 40325005, 40228003, 40272031)MOE Young University Teachers Award Program and partly by Peking University Analysis Fund

摘　　要：Four rock assemblages in correspondence with two different tectonic settings have been recognized in the NEE-SWW extending HP UHP metamorphic belt in southwestern Tianshan, northwest China. Eclogite assemblage EC1 is geochemically akin to alkaline within-plate oceanic island basalt （OIB）, EC2 shows affinity to enriched mid oceanic ridge basalt （EMORB）. Rare earth element （REE） and other immobile trace element characteristics of blueschist assemblage BS1 resemble those of normal mid-oceanic ridge basalt （NMORB）. These three assemblages are likely formed on a seamount setting, and the prevalent presence of carbonate minerals and omphacite quartzite stripes/gobbets suggests ancient pelagic sediments including marls are probably developed upon the basaltic seamount, Whereas the geochemical characteristics of BS2 assemblage are of volcanic arc basalt type. The seamount with the pelagic sediments on it is brought into the subduction zone, and volcanic arc basalts formed on the active continental margin and trench sediments are eroded and enwrapped in the subducting mass, they are altogether subjected to high to ultrahigh pressure metamorphism and subsequent exhumation towards surface. The HP UHP metamorphic belt is thus interpreted as a subduetion-accretionary complex formed by tectonic juxtaposition and imbrication of seamount, seafloor, trench and volcanic arc sequences during oceanic crust subduction.在与的通讯的四个岩石集合拖引不同 tectionic 背景在在西南的 Tianshan 扩大 HP-UHP metarmorphic 带的 NEE-SWW 被认出了，西北中国， Eclogite 集合 ECI 与碱的在内板 geochemically 类似海洋的岛暗岩(OIB ) 。EC2 显示出亲密关系到充实的中间海洋的山脉暗岩(EMORB ) 。稀土元素元素(REE ) 和蓝片岩集合 BSI 的另外的不动的踪迹元素特征正常中间海洋的山脉暗岩(NMORB ) 类似于那些。这三个集合多半在一个海底山背景，和碳酸盐矿物质和 omphacite 的流行存在上被形成石英岩条纹 / 团块包括泥土建议古老的远洋的沉积可能在玄武岩的海底山之上被开发。而 BS2 集合的 geochemical 特征具有暴烈的弧暗岩类型。有它上的远洋的沉积的海底山在潜水艇 ducting 团中被带进 subduction 地区，和在活跃大陆人边缘上形成的暴烈的弧暗岩，沟沉积被侵蚀并且包，他们完全受到高度到超离频压力变态和随后的发掘向出现。HP-UHP 变形的带因此作为海底山的构造并排和 imbrication 形成的 subduction-accretionary 建筑群被解释，海地板，沟并且暴烈在海洋的外壳 subduction 期间是序列。

关 键 词：southwestern Tianshan HP-UHP metamorphic belt subduction-accretion complex trace element geochemistry. 

分 类 号：P595[天文地球—地球化学]