地球学报
地毬學報
지구학보
ACTA GEOSCIENTIA SINICA
2015年
1期
30-39
,共10页
熊发挥%杨经绥%李源%刘钊%郭国林%周文达%陈松永%李毅兵%徐向珍%牛晓露
熊髮揮%楊經綏%李源%劉釗%郭國林%週文達%陳鬆永%李毅兵%徐嚮珍%牛曉露
웅발휘%양경수%리원%류쇠%곽국림%주문체%진송영%리의병%서향진%우효로
洋岛玄武岩%洋中脊%东波蛇绿岩%雅鲁藏布江缝合带
洋島玄武巖%洋中脊%東波蛇綠巖%雅魯藏佈江縫閤帶
양도현무암%양중척%동파사록암%아로장포강봉합대
OIB basalt%mid-ocean ridge%Dongbo ophiolite%Yarlung Zangbo Suture
西藏东波蛇绿岩位于雅鲁藏布江缝合带西段,由地幔橄榄岩、辉石岩和辉长岩等组成。地幔橄榄岩主要为方辉橄榄岩、纯橄岩和少量二辉橄榄岩。岩体的边界出露玄武岩和硅质岩等。地幔橄榄岩中有少量辉石岩和辉长岩的脉岩,宽约1 m,走向北西,与岩体的构造线方向基本一致。各岩相岩石地球化学研究结果表明,东波蛇绿岩的岩相存在较大的差异,玄武岩具有与洋岛玄武岩(OIB)相似的地球化学特征,而地幔橄榄岩中辉石岩、辉长岩脉与洋中脊玄武岩(MORB)相似,形成于洋中脊环境,并受后期俯冲流体作用的改造。东波岩体中二辉橄榄岩具有与深海地幔橄榄岩较一致的轻稀土亏损特征,而方辉橄榄岩和纯橄岩的地球化学特征显示出岩体形成于 MOR 环境,后受到 SSZ 环境的改造。东波蛇绿岩的岩石地球化学特征显示其洋中脊叠加洋岛的构造背景。
西藏東波蛇綠巖位于雅魯藏佈江縫閤帶西段,由地幔橄欖巖、輝石巖和輝長巖等組成。地幔橄欖巖主要為方輝橄欖巖、純橄巖和少量二輝橄欖巖。巖體的邊界齣露玄武巖和硅質巖等。地幔橄欖巖中有少量輝石巖和輝長巖的脈巖,寬約1 m,走嚮北西,與巖體的構造線方嚮基本一緻。各巖相巖石地毬化學研究結果錶明,東波蛇綠巖的巖相存在較大的差異,玄武巖具有與洋島玄武巖(OIB)相似的地毬化學特徵,而地幔橄欖巖中輝石巖、輝長巖脈與洋中脊玄武巖(MORB)相似,形成于洋中脊環境,併受後期俯遲流體作用的改造。東波巖體中二輝橄欖巖具有與深海地幔橄欖巖較一緻的輕稀土虧損特徵,而方輝橄欖巖和純橄巖的地毬化學特徵顯示齣巖體形成于 MOR 環境,後受到 SSZ 環境的改造。東波蛇綠巖的巖石地毬化學特徵顯示其洋中脊疊加洋島的構造揹景。
서장동파사록암위우아로장포강봉합대서단,유지만감람암、휘석암화휘장암등조성。지만감람암주요위방휘감람암、순감암화소량이휘감람암。암체적변계출로현무암화규질암등。지만감람암중유소량휘석암화휘장암적맥암,관약1 m,주향북서,여암체적구조선방향기본일치。각암상암석지구화학연구결과표명,동파사록암적암상존재교대적차이,현무암구유여양도현무암(OIB)상사적지구화학특정,이지만감람암중휘석암、휘장암맥여양중척현무암(MORB)상사,형성우양중척배경,병수후기부충류체작용적개조。동파암체중이휘감람암구유여심해지만감람암교일치적경희토우손특정,이방휘감람암화순감암적지구화학특정현시출암체형성우 MOR 배경,후수도 SSZ 배경적개조。동파사록암적암석지구화학특정현시기양중척첩가양도적구조배경。
Located in the western part of the Yarlung Zangbo Suture Zone (YZSZ) of southern Tibet, the Dongbo ophiolite is composed of mantle peridotite, pyroxenite, gabbro and some other kinds of rocks, with harzburgite, dunite and a small amount of lherzolite constituting dominant lithologies. Basalts and siliceous rocks were found at the edge of the mantle tectonites. Occasionally, a small amount of pyroxenite and gabbro dikes with a width of about one meter crosscut the mantle tectonites in NW direction, which resembles the tectonic line of mantle tectonites. Geochemical characteristics of the different lithofacies in Dongbo ophiolite show remarkable differences, and geochemical characteristics of basalt are similar to features of ocean island basalt (OIB); however, pyroxenite and gabbro dikes in the peridotite are similar to MORB in geochemical characteristics, suggesting that they were derived from mid-ocean ridge (MOR) but affected by the subduction fluids at the second stage. The lherzolite in Dongbo ophiolite is consistent with the abyssal peridotite in the feature of LREE depletion; however, geochemical characteristics of harzburgite and dunite show that they were formed at the mid-ocean ridge (MOR) and reformed in a subduction zone setting. The lithogeochemical characteristics of Dongbo ophiolite indicate a tectonic setting of ocean island overlaid with ocean ridge.
