青藏高原北羌塘盆地多彩地区蛇绿岩地球化学特征及构造环境  

Geochemistry of the Duocai ophiolite in north Qiangtang Basin,Qinghai-Tibet plateau: environments for tectonics

作　　者：李善平[1,2] 潘彤 李永祥 王磊 温得银[2] 王树林[2] 常有英[2] 黄青华[2] 王钦元 

机构地区：[1]青海省地质矿产研究所青海省青藏高原北部地质过程与矿产资源重点实验室,青海西宁810012 [2]青海省地质调查院,青海西宁810012 [3]青海省第八矿产勘查院,青海西宁810001 [4]青海省第五矿产勘查院,青海西宁810001

出　　处：《中国地质》2010年第6期1592-1606,共15页Geology in China

基　　金：青海省重大科技专项(2010-J-A1);中国地质调查局"1:25万治多;杂多幅区域地质调查"项目(I46C003004;I46C004004)资助

摘　　要：多彩蛇绿岩是通天河蛇绿混杂岩的组成部分,区域上隶属西金乌兰—金沙江缝合带北延部分。多彩蛇绿岩各岩石组分呈构造岩块、岩片产出,出露零星,面积小,但岩石组分较齐全,主要由异剥橄榄岩、单斜辉石岩、辉长岩、玄武岩、辉绿岩及硅质岩等组成,缺乏地幔橄榄岩,蛇绿岩组分均与围岩呈构造接触关系。异剥橄榄岩以富MgO、贫TiO2、贫P2O5为特征,Eu不显异常或显弱负异常,是具有SSZ型蛇绿岩的重要岩石组分;辉长岩具高TiO2、Al2O3;玄武岩与辉绿岩具相似的特性,玄武岩Th/Ta平均为1.78,Ta/Hf>0.15,而Ta/Hf=0.15～0.2,与大洋板内玄武岩相似;硅质岩Al2O3/(Al2O3+Fe2O3)比值为0.9,(La/Ce)N值为1.81,可能具有陆源海特性。由上述特征并结合蛇绿岩形成时代及构造环境判别图解,推测多彩蛇绿岩形成于俯冲带构造环境。Duocai ophiolite is a component part of mélange ophiolite in Tongtian River area,and regionally belongs to the northward extension part of Xijinwulan-Jinsha River suture zone.Each Duocai ophiolite occurs in the form of tectonite and rock chips exposed as small and scattered outcrops,but has fairly complete kinds of rocks,mainly composed of diallage-peridotite,pyroxenite monoclinic pyroxinite,gabbro,basalt,diabase and siliceous rocks,with no mantle peridotite.Ophiolite components assume tectonic contact with wall rocks.Diallage-peridotite is characterized by rich MgO,poor TiO2 and P2O5,with no or only weak negative Eu anomaly.Diallage-peridotite is an important rock of SSZ type.Gabbro has high TiO2 and Al2O3 content;basalt and diabase have similar characteristics.Th/Ta of basalt has an average value of 1.78,Ta/Hf0.15,and Ta/Hf=0.15-0.2,and characteristics of these elements are similar to those of oceanic intraplate basalts.Al2O3/（Al2O3＋Fe2O3） ratio of siliceous rocks is 0.9,（La/Ce）N is 1.81,showing characteristics of a land-based sea.Based on the above-mentioned characteristics in combination with the age of ophiolite as well as tectonic setting discrimination diagrams of basalt and diabase,the authors hold that Duocai ophiolite was formed in a subduction zone tectonic setting.

关 键 词：青藏高原 北羌塘盆地 蛇绿岩 西金乌兰—金沙江缝合带 俯冲带 

分 类 号：P588.125[天文地球—岩石学]