甘肃余石山铌钽矿化变粒岩原岩成岩年龄及构造背景  

Genetic Age and Tectonic Setting of Parent Rocks of Nb-Ta Mineralized Leptynites in Yushishan,Gansu Province

作　　者：陈威 曹晓峰[2] 吕新彪[2] 杨文[2] 卢友月 李通国[3] 吴义布[3] CHEN Wei;CAO Xiaofeng;LÜXinbiao;YANG Wen;LU Youyue;LI Tongguo;WU Yibu(Wuhan Center,China Geological Survey,Wuhan 430205,Hubei,China;School of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,Hubei,China;Geological Survey of Gansu Province,Lanzhou 730020,Gansu,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]中国地质大学(武汉)资源学院,湖北武汉430074 [3]甘肃省地质调查院,甘肃兰州730020

出　　处：《大地构造与成矿学》2022年第4期755-772,共18页Geotectonica et Metallogenia

基　　金：国家重点研发计划项目(2017YFC0602404);中国地质调查局地质调查项目(DD20190154、DD20221689)联合资助。

摘　　要：与已报道的岩浆型和沉积型铌钽矿床含矿岩石特征不同,甘肃余石山铌钽矿化体呈层状产在熬油沟组变粒岩中,为探讨该铌钽矿化变粒岩的原岩岩性、原岩成岩年龄及形成构造背景,本文运用矿物学、岩石学、矿床学、地质年代学及岩石地球化学等手段进行研究。镜下观察及EDS元素分析结果显示,矿化变粒岩和浅粒岩中含铌钽的独立矿物主要为铌铁矿、褐钇铌矿、烧绿石、铌钽金红石、铌钇矿及锆英石等。不活动元素指标和图解显示变粒岩和浅粒岩原岩为中酸性火成岩,结合变粒岩的变余火山碎屑结构,指示变粒岩和浅粒岩原岩为粗面岩或碱流岩。微量和稀土元素分析结果显示变粒岩与浅粒岩都富集Th、U、Rb等大离子亲石元素,亏损Ba和Sr;富集Nb、Ta、Zr、Hf等高场强元素,亏损P和Ti。变粒岩和浅粒岩LA-ICP-MS锆石U-Pb年龄分别为812±5 Ma和814±3 Ma,指示变粒岩原岩形成年龄为812~814 Ma。在构造环境判别图解中,变粒岩和浅粒岩样品都投在板内构造花岗岩区域,结合前人对该区域构造背景的研究,推测变粒岩原岩应喷发于陆内裂谷环境,其形成与Rodinia超大陆的裂解有关。The Yushishan Nb-Ta mineralized bodies are strata-like,hosted in the leptynites of the Aoyougou Formation which are different from the ore-bearing rocks of the known magmatic and sedimentary Nb-Ta deposits.In order to delineate the lithology,genetic age and tectonic setting of the primary rocks of the Yushishan Nb-Ta mineralized leptynites,we carried out petrological,mineralogical,geochronological,and geochemical analyses of the ore-bearing leptynites.The results of microscopic observation and EDS analysis show that the niobium and tantalum bearing minerals in the Yushishan letynites are mainly columbite,fergusonite,pyrochlorite,Nb-Ta rutile,samarskite,and zircon.Inactive element indicators indicate that the leptynites were originally intermediate-acid igneous rocks.Combined with the metamorphic residual pyroclastic structure of the leptynites,it is likely that the leptynites derived from trachyte or pantellerite.The trace element results show that the leptynites are rich in REE,especially LREE.The primitive mantle-normalized spider diagrams show that the leptynites are enriched in large iron lithophile elements(LILE)such as Th,U and Rb and depleted in Ba and Sr,enriched in high field strength element(HFSE)like Nb,Ta,Zr and Hf,but depleted in P and Ti.LA-ICP-MS U-Pb dating of magmatic zircon from two leptynite samples provided weighted mean 206Pb/238U ages of 812±5 Ma and 814±3 Ma,indicating the parent rocks of the leptynites were crystallized at ca.812-814 Ma.In the tectonic discrimination diagrams,the leptynite samples all fall in the within-plate granite field.Combined with the previous research results,the parent rocks of the Yushishan leptynites were likely formed in a rift setting,possibly related to the break-up of the Rodinia supercontinent.

关 键 词：余石山 变粒岩 铌钽矿化 地球化学 地质年代学 

分 类 号：P595[天文地球—地球化学] P612[天文地球—地质学]