地质通报2025，Vol.44Issue(2)：493-510,18.DOI:10.12097/gbc.2023.01.027
甘肃大道尔吉蛇绿岩岩石成因及其对南祁连早古生代构造演化的约束
Petrogenesis of the Dadaoerji ophiolite from the Gansu Province,NW China:Constraints on the Early Paleozoic tectonic evolution of the South Qilian Orogen
摘要
Abstract
[Objective]The Dadaoerji region in the South Qilian Orogen hosts medium-sized ophiolite-type chromite deposits.However,the formation age,petrogenesis and tectonic evolution of the Dadaoerji ophiolite suite are still unclear.[Methods]Hence,in this study,we conducted systematic LA-ICP-MS zircon U-Pb for pyroxene peridotive dating and whole-rock geochemical studies of both pyroxene peridotite and gabbros within the upper part of this ophiolite suite.[Results]Zircon U-Pb dating show 206Pb/238U spot ages that are concordant with the main concentration range of 471～420 Ma,and also yielded a weighted mean age of 460±15 Ma(MSWD=3.8),suggesting that the timing of formation of the Dadaoerji ophiolite suite could be constrained in the Late Middle Ordovician.These gabbros belong to low potassium tholeiitic series,both pyroxene peridotites and gabbros are enriched in large ion lithophile elements(e.g.,Rb,Ba,U,Sr)and depleted in high field strength elements(e.g.,Nb,Ta,Zr,Hf),with Th negative anomalies.Moreover,these gabbros also display a near flat and slightly right pattern((La/Yb)N=1.54～2.43)and slight Eu positive anomalies.These together indicate that the magma of gabbros was derived from a depleted spinel Lherzolite mantle via metasomatism of subduction fluids,and evolved by partial melting of 20%～30%.Furthermore,the magma source of gabbros might have underwent crustal contamination.Accordingly,we also infer that the older zircons in pyroxene peridotite likely inherited from magma source.[Conclusions]In combination with the regional geological settings,this study suggests that the Dadaoerji ophiolite suite formed under the extensional environment of the back-arc basin caused by the subduction of the North Qaidam Ocean during the late Middle Ordovician.The Dadaoerji ophiolite was also classified as a subduction zone type(SSZ)ophiolite,which provides new evidence for the subduction evolution of the South Qilian Orogen during the early Paleozoic.关键词
早古生代/蛇绿岩/辉橄岩/辉长岩/锆石U-Pb年龄/地球化学/大道尔吉/南祁连造山带Key words
Early Paleozoic/ophiolite suite/pyroxene peridotite/gabbro/zircon U-Pb geochronology/geochemistry/Dadaoerji/South Qilian Orogen分类
地质学引用本文复制引用
冯鹏宇,任文秀,谢奋全,丁仨平,黄增保,郝丽荣..甘肃大道尔吉蛇绿岩岩石成因及其对南祁连早古生代构造演化的约束[J].地质通报,2025,44(2):493-510,18.基金项目
中国地质调查局项目《甘肃省区域地质调查片区总结与服务产品开发》(编号:12120113013500)、国家自然科学基金项目《甘肃中口子盆地早白垩世植物多样性与古环境演变》(批准号:42362003)及甘肃省自然科学基金《甘肃北山罗雅楚山地区沉积-变质型铁矿成矿规律与隐伏矿床预测》(批准号:22JR5RA820) （编号:12120113013500）
