大陆造山带深熔垮塌的岩石学、地球化学证据:以北大别深熔混合岩为例  

Petrological and Geochemical Evidence of Anatexis Collapse in Continental Orogenic Belt:Taking Anatectite of North Dabie Terrain as an Example

作　　者：王德远 续海金[2] 王攀 贾敏 高占冬 Wang Deyuan;Xu Haijin;Wang Pan;Jia Min;Gao Zhandong(Guizhou Instiute of Mounlain Resourrces,Guriyung 55000,China;School of Earh Se iemces,China Unisersity of Greosciences,Wshan 430074,Chima)

机构地区：[1]贵州省山地资源研究所,贵阳550001 [2]中国地质大学地球科学学院,武汉430074

出　　处：《吉林大学学报（地球科学版）》2020年第3期675-693,共19页Journal of Jilin University：Earth Science Edition

基　　金：国家“十三五”重点研发计划项目(2016YFC0502606);贵州科学院创新人才团队能力提升工程(黔科院人才[2019]08);贵州科学院青年基金项目(黔科院J字[2019]09号)。

摘　　要：北大别位于大别造山带的核部,分布着大量的造山带垮塌时期形成的混合岩,其于理解大别造山带的形成和演化有着重要的意义。北大别混合岩的原岩为TTG(D)岩石,因黑云母和角闪石的脱水熔融诱发深熔作用产生。顺层产出的为富斜长石浅色体,主要矿物组成为斜长石+石英+黑云母±钾长石±角闪石。伟晶岩脉或团块为富钾长石浅色体,主要矿物组成为钾长石+石英±斜长石±黑云母±角闪石。暗色体为变晶结构,主要矿物组成为角闪石+黑云母+斜长石+石英±单斜辉石;其中,暗色矿物角闪石和黑云母常常定向排列,具有明显的溶蚀结构;暗色体中浅色矿物颗粒较小,以斜长石和石英为主,指示部分熔融的残余产物。全岩地球化学特征表明,碱金属元素(Na、K等)、大离子亲石元素(Ba、K、La等)和LREE等优先进入酸性熔体,而相容元素和中-重稀土元素等残留在残余体中。浅色体与本区花岗岩相比,二者都有右倾的稀土配分模式,富集LREE,亏损HREE。但浅色体具有明显的Eu正异常,δEu值为2.48~6.55,而花岗岩则有弱的Eu负异常,并且浅色体中大颗粒斜长石相互构成框架结构,含量明显高于正常花岗岩熔体,表明浅色体更可能是熔体早期结晶的产物。North Dabie terrain(NDT)is located in the core of Dabie orogenic belt,where a large number of migmatites were formed during the collapse of orogen.It is of great significance to understand the formation and evolution of Dabie orogenic belt.The protolith of NDT migmatites are TTG(D)rocks generated from the anatexis induced by dehydration and melting of biotite and amphibolite.The plagioclase-rich leucosome produced in the bedding with Pl+Qtz+Bi±Kfs±Hbl is its major mineral composition.The pegmatite veins or block masses are rich in K-feldspar-rich leucosome with Kfs+Qtz±Pl±Bi±Hbl as its major mineral composition.The melanosome is a crystalloblastic structure with Hbl+Bi+Pl+Qtz±Cpx as its major mineral composition.The amphibolite and biotite in melanosome usually have directional alignment and distinct melting corrosion structures.The main leucocratic minerals in the melanosome are plagioclase and quartzes,indicating the residual products of partial melting.The whole-rock geochemistry shows that alkali metal elements Na,K,large ion lithophile elements Ba,K,La,and LREE etc.have the priority of entering into the acid melt;however,the compatible elements and middle-high rare earth elements remain in the restite minerals.The leucosomes have the same right deviation REE patterns as that of the granitoids,rich in LREE and loss of HREE,but have a large positive Eu anomaly with the ratios ofδEu ranging from 2.48 to 6.55;while the granite is on the contrary,the content of the frame structure composed of the large-grain plagioclases is apparently higher than the normal granite melt,which indicates that the leucosomes are more likely the product of the early crystallization of the melts.

关 键 词：北大别 混合岩 深熔作用 造山带垮塌 岩石学 地球化学 

分 类 号：P588.12[天文地球—岩石学]