【摘要】 弯岛湖蛇绿混杂岩带是金沙江缝合带西段的重要组成部分。蛇绿岩混杂于上三叠统变质碎屑岩夹变质火山岩中,成份主要为镁铁质-超镁铁质杂岩,岩石类型有变质橄榄岩、变质堆晶质辉长岩及其伴生的岛弧型花岗岩系。岩石化学及地球化学特征表明:蛇绿岩主要为低Ti(岛弧-弧后)型、富集型洋中脊(E-MORB)拉斑玄武岩;与之共(伴)生的基性喷出岩、辉绿岩脉属板内洋岛型裂谷型碱性玄武岩及其过渡类型系列。在变质辉长岩获得全岩Sm-Nd等时线年龄值为232±11Ma,代表了镁铁质-超镁铁质杂岩的形成年龄,可能为洋壳初始俯冲变质的时间。在蛇绿岩上覆的硅质岩中发现有中三叠世拉丁晚期至晚三叠世卡宁早期的放射虫化石,表明弯岛湖镁铁质-超镁铁质杂岩可能形成于中三叠世多岛洋盆或弧后盆地构造环境。更多还原

【Abstract】 The Wandaohu ophiolitic mélange is an essential component of the western part of Jinshajiang suture zone,The ophiolites are mixed in the Upper Triassic metaclastic rocks which interlayered by metavolcanic rocks,The main components of ophiolites are mafic-ultramafic complexes,in which metaperidotites,metacrystal-stacking gabbros and concomitant island-arc granites are included,Geochemical data indicate that most of the ophiolitic mélange are tholeiites of low-Ti(island arc-back arc) type and enriched middle-ridge type(E-MORB),The basic extrusive rocks,diabase veins accompanied with above mentioned ophiolites could be classified as interplate rift-type alkaline basalts and other transitional series,Metagabbro,dated at 232±11Ma with Sm-Nd isochron,represents the formation age of the mafic-ultramafic complexes and initial metamorphic age of the subduction of oceanic crust,The radiolarites were found in the sillcalites which overlained ophiolite,The age of the radiolarites is between Late Latin stage of Middle Triassic and Early Kaning stage of Late Triassic,indicating that the Wandaohu mafic-ultramafic complexes may form in the Middle-Triassic poly-islands oceanic basin or back-arc basin tectonic setting.更多还原