文档介绍：第22卷第5期现代地质 VoL22 2008年lO月 GEOSCIENCE 中祁连北缘奥陶纪岩浆弧地层王永和1”,焦养泉1,李建星2,雷桂侠2 (,湖北武汉430074;,陕西西安710054) 摘要:奥陶纪是祁连山加里东期构造带俯冲一碰撞格局奠定时期。通过区域填图和沉积环境分析及岩石地球化学研究, 系统分析了沉积及岩浆作用过程,认为在肃北县野牛台地区的晚奥陶世地层是中祁连地块西段北缘岩浆弧的组成部分。该地层为一套浅变质的基性一中性火山岩、碎屑岩及少量含化石灰岩组合,由下部海相安静深水还原环境向上部近岸水下河道一滨岸过渡,上部夹有冲积扇一河流相沉积,物源区为近源的岩浆弧和古老结晶基底,反映出自下向上水体变浅、盆地收缩的进积序列。其中的火山岩自下向上由基性向中性转变、由岛弧拉斑—钠质碱性玄武岩向钾质碱性玄武岩过渡, 反映出与挤压构造环境相关的成熟岩浆弧火山岩组合特点。晚奥陶世岩浆弧地层、侵入岩与其北的同期构造蛇绿混杂岩带的相伴产出,暗示北祁连西段该时期洋壳在北部向北俯冲的同时,南部还向南俯冲并形成汇聚大陆边缘。关键词:中祁连地块北缘;野牛台;晚奥陶世;岩浆弧;沉积一火山岩地层;俯冲一碰撞中图分类号:; 文献标志码:A 文章编号:1000—8527(2008)05—0r724—09 Ordovician Magmatic Arc Stratum oftheMiddleQilian Block WANG Yong—hel·2,JIAO Yang—quanl,LI ,LEI (,Earth Resources,China of ,Wuhan,Hubei 430074,China; ofGeology andMineral Resources,Xi'an,Shaaxi 710054,Ch/na) Abstract: oftheCaledonian tectonic beltintheQilian unitformed intheOrdovician period. Bygeologic mapping,analysis ofenvironment ofsedimentation and study ofrock geochemistry,it considered thatthe rockformation of LateOrdovician epoch inYeniutai,Subei County theimportant part ofmagmatic arc ofthenorthern margin inthe western part ofthemiddle Qilian panied with theintermediate-acid intrusiverocks ofLateOrdovician volcanic arcs,this stratum posed ofsliishfly metamorphosed bas- icandintermediate volcanic rocksandconglomerate,sandstone,slate and afewfossil—bearing limestones from bottom ofpeaceful and deep water reducing environment of maline facies totheupper ofalongshore underwater river-estuarine environment withalluvial—fluvialsedimentary sandwiched intheupper source the magmatic arc intrusive rock,volcano—sedimentary rock and antiquity crystalline basement intheneighbor area, which reflects aprogradational sequence inascending orderwith lower water and shrinkage of transformations of volcanic rock inascending order are from basic tomiddle volcanic rock,from tholeiiteof land arcsodium alkali