辽宁本溪歪头山条带状铁矿的成因类型、形成时代及构造背景  

Genetic type,formation age and tectonic setting of the Waitoushan banded iron formation, Benxi,Liaoning Province

作　　者：代堰锫[1,2] 张连昌[1] 王长乐[1,2] 刘利[1,2] 崔敏利[1] 朱明田[1] 相鹏[1,2] 

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院矿产资源研究重点实验室,北京100029 [2]中国科学院研究生院,北京100049

出　　处：《岩石学报》2012年第11期3574-3594,共21页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划973项目(2012CB416601);中国科学院知识创新工程重要方向项目群(KZCX-2YW-Q04-07)联合资助

摘　　要：辽宁鞍本地区位于华北克拉通东北缘,分布有诸多大型-特大型条带状铁矿床。本文对该区歪头山铁矿进行了岩石学、矿物学及年代学研究。歪头山铁建造以条带状铁矿石为主,兼含有少量的块状矿石,其顶底板围岩及矿体夹层主要为太古界鞍山群斜长角闪岩。元素地球化学分析表明,铁矿石富集重稀土[(La/Yb)PAAS=0.24～0.33],具La正异常(La/La*=1.43～1.61)、Eu正异常(Eu/Eu*=2.40～4.54)及Y正异常(Y/Y*=1.10～1.30),Y/Ho值平均30.59,Sr/Ba值平均17.62,Ti/V值平均19.45,反映成矿物质可能来源于由海底火山活动带来的高温热液与海水的混合溶液。铁矿石无明显Ce负异常(Ce/Ce*=0.92～1.06),暗示BIF沉积时海水处于缺氧环境。除Fe2O3T与SiO2外,铁矿石中其它氧化物含量均非常低,且贫Th、U、Zr等具有陆源性质的元素,表明大陆碎屑物质对BIF贡献极少。斜长角闪岩稀土元素配分型式近于平坦[(La/Yb)N=0.80～1.10],无明显Ce异常(Ce/Ce*=0.95～0.99)与Eu异常(Eu/Eu*=0.88～1.16);其大离子亲石元素富集,高场强元素无明显亏损。地球化学分析表明,斜长角闪岩原岩可能为产于弧后盆地的玄武质火山岩。锆石形态与微量元素分析显示,斜长角闪岩中的锆石均属岩浆成因。SIMS锆石U-Pb定年显示斜长角闪岩原岩形成于2533±11Ma,代表了歪头山BIF的成矿年龄;在玄武质岩浆喷发过程中,还捕获了一组年龄为2610±5Ma的锆石。电子探针分析显示磁铁矿成分纯净(FeOT=92.04%～93.05%),其标型组分特征暗示歪头山BIF属沉积变质型铁矿。综合分析认为,歪头山铁矿属Algoma型BIF,成矿与弧后盆地岩浆活动密切相关,指示了新太古代末华北克拉通普遍发育的一期BIF成矿事件。Anshan-Benxi area in Liaoning Province, where plenty of large-superlarge banded iron formations are distributed, is located at the northeastern part of the North China craton. Petrology, mineralogy and geochronology of the Waitoushan iron deposit in Anshan-Benxi area are studied in this paper. Iron ores in the Waitoushan deposit are predominantly banded, with a scrap of massive. The Archean amphibolites in the Anshan Group were developed as main wall rocks and interlayer among the orebodies. Geochemical analyses show the iron ores are enriched in HREE [（La/Yb）PAAS=0.24～0.33], and characterized by positive La anomaly （La/La＊=1.43～1.61）, positive Eu anomaly （Eu/Eu＊=2.40～4.54） and positive Y anomaly （Y/Y＊=1.10～1.30） with Y/Ho=30.59, Sr/Ba=17.62, Ti/V=19.45, indicating the ore-forming materials were derived from the intermixture of high temperature hydrotherm and seawater. There is no distinct negative Ce anomaly （Ce/Ce＊=0.92～1.06）, imlying the seawater was under anoxic condition during the deposition of the Waitoushan BIF. Apart from Fe2OT3 and SiO2, the contents of other oxides are rather low, with depletion in continental origin elements （such as Tu, U, Zr）, implying the continental detrital materials contributed little to the metallogenic process of the Waitoushan BIF. The chondrite-normalized REE pattern of amphibolites is flat [（La/Yb）N=0.80～1.10] with no distinct Ce anomalies （Ce/Ce＊=0.95～0.99） and Eu anomalies （Eu/Eu＊=0.88～1.16）, while the N-MORB-normalized trace element pattern shows enrichment in LILE without pronounced depletion in HFSE. Geochemical analyses show the protolith of amphibolites was probably basic volcanics originating in back-arc basin setting. Morphology and trace element analyses of zircon grains indicate the zircons selected from amphibolites were all magmatic. SIMS zircon U-Pb dating shows the protolith of amphibolites was formed at 2533±11Ma, standing for the formation age of the Waitoushan iron deposit. During the eruptio

关 键 词：条带状铁建造 斜长角闪岩 新太古代 弧后盆地玄武岩 歪头山铁矿 鞍本地区 

分 类 号：P588.345[天文地球—岩石学]