华北板块北缘东段三叠纪构造演化——来自辽北开原岩浆岩年代学、地球化学的证据  

Evolution of the eastern segment of the northern margin of the North China Craton in the Triassic:Evidence from the geochronology and geochemistry of magmatic rocks in Kaiyuan area,North Liaoning

作　　者：陈井胜[1,2] 李崴崴 时溢 李斌[1,2] 赵春强 张立东[1,2] CHEN JingSheng;LI WeiWei;SHI Yi;LI Bin;ZHAO ChunQiang;ZHANG LiDong(Shenyang Center of Geological Survey,China Geological Survey,Shenyang 110034,China;Northeast Geological S&T Innovation Center of China Geological Survey,Shenyang 110034,China;Liaoning Institute of Geology and Mineral Resources,Shenyang 110029,China)

机构地区：[1]中国地质调查局沈阳地质调查中心,沈阳110034 [2]东北地质科技创新中心,沈阳110034 [3]辽宁省地质矿产研究院有限责任公司,沈阳110029

出　　处：《岩石学报》2022年第8期2216-2248,共33页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41902234、41872203);中国地质调查局地调项目(DD20190042、DD20221632)联合资助。

摘　　要：本文对华北板块北缘东段辽北开原地区辉长岩和流纹岩进行了岩相学、锆石U-Pb年代学和地球化学研究,结合前人资料探讨古亚洲洋东段三叠纪演化过程。锆石测年结果显示,辉长岩及流纹岩形成时代均为三叠纪(分别为246±2Ma、241±2Ma、226±3Ma及241±2Ma)。三期三叠纪辉长岩具有相似的地球化学特征,起源于地幔,并且在上升就位过程中均受到地壳物质的混染。其中,早三叠世辉长岩(246Ma)起源于受流体改造的富集型岩石圈地幔,由石榴石尖晶石二辉橄榄岩1%部分熔融形成,形成于俯冲板片断离导致的伸展环境;中三叠世辉长岩(241Ma)起源于受流体和熔体双重改造的过渡型岩石圈地幔,由石榴石尖晶石二辉橄榄岩1%~2%部分熔融形成;晚三叠世辉长岩(226Ma)起源于受流体和熔体双重改造的过渡型岩石圈地幔,由石榴石尖晶石二辉橄榄岩3%~4%部分熔融形成,形成于造山后的伸展拉张环境。中三叠世流纹岩(241Ma)富集轻稀土元素和大离子亲石元素,亏损高场强元素,亏损Nb、Ti、P、Sr元素等特征,属于后碰撞I型花岗岩,其低Sr低Yb特征暗示其源区深度为30~40km之间,其与中三叠世辉长岩构成“双峰式”火成岩,二者形成于岩石圈底部残余洋壳脱离导致的伸展环境。综合前人发表数据,根据年代学、岩石组合及地球化学特征可将华北板块北缘东段三叠纪岩浆活动划分为5期:252~246Ma、246~242Ma、242~240Ma、240~230Ma和230~215Ma。结合区域磨拉石建造、变质作用及蛇绿岩等资料,认为本区三叠纪经历了如下演化过程:(1)活动大陆边缘向同碰撞转换,古亚洲洋完成最终闭合(252~246Ma);(2)持续挤压隆升造山(246~242Ma);(3)南北挤压背景下,残余俯冲洋壳脱落导致的伸展(242~240Ma);(4)持续挤压作用下快速隆升,地壳加厚(240~230Ma);(5)造山后的伸展拉张环境(230~215Ma)。To constrain the evolution of the eastern segment of the Paleo-Asian Ocean(PAO),petrography,geochemistry and zircon U-Pb dating analyses were conducted over the gabbro and rhyolite in the Kaiyuan area,North Liaoning,in the eastern segment of the northern margin of the North China Craton(NCC).Zircon dating results indicate that the gabbros and rhyolite were formed in the Trassic(246±2 Ma,241±2 Ma,226±3 Ma and 241±2 Ma).The three gabbros of Triassic have similar geochemical characteristics,originated from the mantle,and were contaminated by crust materials in the process of ascending and emplacement.The Early Triassic gabbro(246 Ma)originated from the enriched mantle source metasomatized by fluid.It was formed by 1%partial melting of garnet spinel lherzolite in the extensional environment caused by breaking off slab.The Middle Triassic gabbro(241 Ma)was derived from a transitional mantle metasomatized by fluid and melt,and was formed by 1%to 2%partial melting of garnet spinel peridotite.The Late Triassic gabbro(226 Ma)was derived from a transitional mantle metasomatized by fluid and melt,and was formed by 3%~4%partial melting of garnet spinel lherzolite in the post-orogenic extensional environment.The Middle Triassic rhyolite(241 Ma)has the characteristic of post collisional I-type granite,that enriched in light rare earth elements and large ion lithophile elements,depleted in high field strength elements,and negative Nb,Ti,P and Sr anomaly.The low content of Sr and Yb suggested a 30~40 km depth source.The Middle Trassic“bimodal”igneous rocks implied an extensional environment caused by the remainder oceanic crust breaked away at the bottom of the crust.Based on the lithologic association,regional strata information and the chronological data in this paper and published by predecessors,the Triassic magmatism in the eastern segment of the northern margin of the NCC can be divided into five stages:252~246 Ma,246~242 Ma,242~240 Ma,240~230 Ma and 230~215 Ma.These five magmatic events were the results of the sou

关 键 词：华北板块北缘东段 三叠纪 辉长岩 锆石U-PB年代学 构造演化 

分 类 号：P588.124[天文地球—岩石学] P588.141[天文地球—地质学] P597.3