西藏丁青宗白蛇绿混杂岩地球化学特征及其洋中脊叠加洋岛的成因  

Geochemical Characteristics and Its Origin for Mid-Ocean Ridge Superposing Oceanic Island of Chongbe Ophiolitic Mélange,Dingqing,Xizang(Tibet)

作　　者：韦振权[1] 夏斌[1] 周国庆[2] 钟立峰[1] 王冉[1] 胡敬仁 陈国结 

机构地区：[1]中国科学院边缘海地质重点实验室中国科学院广州地球化学研究所 [2]南京大学地球科学系,南京210093 [3]西藏自治区地质调查院,拉萨850000

出　　处：《地质论评》2007年第2期187-197,共11页Geological Review

基　　金：国家自然科学基金重点项目(编号40534019)的成果。

摘　　要：宗白蛇绿混杂岩位于班公湖—怒江缝合带东段丁青地区,是丁青蛇绿岩的重要组成部分。为确定该蛇绿混杂岩的构造属性,探讨其成因,对其进行了岩石学和全岩地球化学研究。结果表明,宗白蛇绿混杂岩存在两套成因不同的岩石。混杂岩中的玄武岩和辉长岩具有与洋岛玄武岩(OIB)相似的地球化学特征,其成因可能与来自地幔深部的“热点”作用有关。而混杂岩中的辉绿岩的地球化学特征与MORB相似,形成于洋中脊(洋内弧后盆地扩张中心)环境,并有受“热点”作用影响的印记;具有强烈亏损的地球化学特征的方辉橄榄岩则代表了洋内岛弧的基底残片,是已经亏损的地幔再次熔融产生玄武质岩浆后的残留物。这两套不同成因的岩石在板块汇聚过程中一起构造侵位于班公湖—怒江缝合带中。Chongbe ophiolitic mélange is located in the east segment of the Bangong Co-Nujiang ophiolite belt in eastern Xizang （Tibet）. It is an important member of the Dingqing ophiolite. In order to acquire the tectonic property of the mélange and discuss its petrogenesis, the petrography and whole rock geochemistry are carefully studied. The results show that there are two suits of rocks which have different origins in Chongbe ophiolitic melange. The geochemical characteristics of the basalts and gabbros from Chongbe ophiolitic mélange are similar to that of oceanic island basalt （OIB）. Their origin may be related to the ＂hotspot＂. The geochemical characteristics of the diabases from Chongbe ophiolitic mélange are quite different to that of the basalts and gabbros while similar to that of MORB. It may be formed in midocean ridge （intra-oceanic back-arc basin spreading center） and affected by ＂hotspot＂. The Harzbergites with highly depletion of geochemical characteristic are the relic of the basement of intra-oceanic island arc, which were partial melted again and fractionate the basaltic magma. Two suits of rocks which has different origin emplaced together in the Bangong Co-Nujiang suture in the course of the collision of the plates.

关 键 词：宗白蛇绿混杂岩 地球化学 洋岛玄武岩 洋中脊 丁青 西藏 

分 类 号：P588.3[天文地球—岩石学]