早古生代北阿尔金HP/LT混杂岩片--一个“化石”俯冲隧道  

Early Paleozoic North Altun HP/LT mélange slice:A fossil subduction channel.

作　　者：毛小红[1] 林宜慧 张建新[1] MAO XiaoHong;LIN YiHui;ZHANG JianXin(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Department of Geography,Hanshan Normal University,Guangzhou 521041,China)

机构地区：[1]自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100037 [2]韩山师范学院地理科学与旅游学院,广州521041

出　　处：《岩石学报》2023年第12期3533-3554,共22页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42202058);中国地质科学院基本科研业务费项目(JKYZD202310);中国地质调查局地质调查项目(DD20221649)联合资助。

摘　　要：北阿尔金高压/低温(HP/LT)变质岩呈构造岩片分布在俯冲-增生杂岩中,主要由强变形的变质沉积岩(泥质片岩、钙质片岩和石英片岩)和少量呈透镜状分布在变沉积岩中的蓝片岩和榴辉岩组成,与相邻的蛇绿混杂岩呈断层接触。榴辉岩主要矿物为绿辉石、石榴子石、多硅白云母、石英、冻蓝闪石,含少量蓝闪石、绿泥石、方解石、钠长石、榍石。蓝片岩主要矿物为蓝闪石、石榴子石、碳酸盐类矿物、阳起石、绿帘石、钠云母、绿泥石、钠长石和石英,偶见多硅白云母,其中在部分蓝片岩的石榴子石中有少量硬柱石和绿辉石包体。本文对蓝片岩(样品A06-16-7)和榴辉岩(样品A03-3-5.3)开展了岩石学和相平衡模拟研究,得到它们形成的压力峰期的温压条件分别是:T=~524℃、P=~2.1GPa和T=~527℃、P=~2.2GPa,并均经历了后期蓝片岩相的退变质叠加。结合区域上已有的研究表明,北阿尔金HP/LT混杂岩片中不同类型岩石可能经历了不同的变质演化历史,反映了古俯冲隧道的不均匀性,并在俯冲隧道的较浅部混杂在一起,共同经历了蓝片岩相或蓝片岩-绿片岩过渡相条件下的透入性变形作用。High-pressure/low temperature(HP/LT)metamorphic rocks in the North Altun occur as a tectonic slice in subduction-accretion complex.It is mainly composed of strongly deformed metamorphic sedimentary rocks(argillaceous schist,calcareous schist and quartz schist)and a small number of pods of blueschists and eclogites within meta-sedimentary rocks,and contacted with adjacent ophiolitic mélange by faults.Eclogite consists of omphacite,garnet,phengite,barroisite and quartz with varying amounts of glaucophane,chlorite,calcite,albite and titanite.Blueschist consists of garnet,glaucophane,carbonate,actinolite,chlorite,albite,quartz and epidote with varying amounts of phengite,and with or without omphacite and lawsonite inclusions in garnet.Phase equilibrium modelling constrain the P-T conditions of blueschist(Sample A06-16-7)and eclogite(Sample A03-3-5.3),respectively.It shows that the P-T conditions of the peak pressure are T=~524℃,P=~2.1GPa and T=~527℃,P=~2.2GPa,and both of them have underwent isothermal decompression from eclogite facies to blueschist(blueschist-greenschist)facies conditions during exhumation.Combined with previous data,it shows that different types of rocks in the HP/LT metamorphic terrane in North Altun may have undergone different metamorphic evolutionary histories,reflecting the inhomogeneity of the paleo-subduction channel,and juxtaposed at relatively shallow level within subduction channel,which have experienced penetrative deformation under blueschist or blueschist-greenschist facies conditions.

关 键 词：北阿尔金 榴辉岩 蓝片岩 相平衡模拟 

分 类 号：P588.34[天文地球—岩石学]