摘要
早前寒武纪条带状铁建造(BIF)型铁矿是中国最重要的铁来源,占全国铁储量的60%以上,其中以华北地区新太古代晚期BIF型铁矿最为典型。通过对华北克拉通东北部辽宁清原地区小莱河BIF及围岩进行了详细的岩石学、地球化学和同位素研究,旨在对物源区和构造环境提供制约。小莱河BIF主要由磁铁矿、石英和硅酸盐(如铁紫苏辉石等)等组成,样品SiO_(2)和全铁(FeO^(T))含量变化范围较大。少量小莱河BIF样品的Al_(2)O_(3)含量(质量分数,下同)较高(>1%),指示在沉积过程中存在陆源碎屑物质的输入。而未受碎屑物质混染的BIF样品显示典型的海水特征,包括Al_(2)O_(3)、高场强元素和过渡金属元素含量较低,轻稀土元素相对亏损及重稀土元素富集和Eu正异常等特征。模拟结果显示,样品与海底高温热液、海水1∶100混合溶液的PAAS标准化稀土元素配分模式吻合,指示海底热液活动为BIF提供了热量和物质。小莱河BIF成矿物质来源于高温热液淋滤的清原绿岩带底部基性—超基性岩。小莱河BIF的围岩主要为石棚子组变质火山岩及少量变质碎屑沉积岩。碎屑沉积岩地球化学特征受控于岛弧体制下中—低程度风化的复杂物源区组成(如奥长花岗岩、英云闪长岩及少量基性岩等),与小莱河BIF的物源区类似。综合矿床地质、地球化学、同位素、年代学等特征,认为小莱河BIF系形成于弧后盆地内的阿尔戈马型BIF。
Early Precambrian banded iron formation(BIF)is the most important source of iron in China,accounting for more than 60%of the national iron reserves,among which the Late Neoarchean BIF in North China Craton is the most typical.The petrological,geochemical and isotopic data of Xiaolaihe BIF and its wall rock in Qingyuan area of Liaoning,North China Craton were combined to constrain their provenance and tectonic setting.The Xiaolaihe BIF is composed of magnetite,quartz and silicates(e.g.,ferrohypersthene),and is characterized by variable SiO_(2) and FeO^(T) contents.The higher Al_(2)O_(3) contents(>1%)of subordinate amounts of Xiaolaihe BIF indicate some terrigenous input during deposition.Other detrital-free Xiaolaihe BIF samples have low abundances of Al_(2)O_(3),HFSE,and transition metals,normalized REE patterns enriched in HREE and depleted in LREE,and positive Eu anomalies,which is reflective of seawater.Modeling reveals that the REE patterns of Xiaolaihe BIF well match that of mixture from the high-temperature hydrothermal fluids and ambient seawater with the ratio of 1∶100,suggesting that heat and mass from the seafloor hydrothermal activity contribute to Xiaolaihe BIF.Xiaolaihe BIF preserved in Shipengzi Formation is commonly found to be interbedded with metamorphosed volcanic rocks,and minor metamorphosed clastic sedimentary rocks.The chemical characteristics of the clastic sedimentary rocks associated with Xiaolaihe BIF are mainly controlled by complex source compositions(tonalite and trondhjemite,and minor mafic rocks)within an island arc setting,although they have undergone low-intermediate source weathering,which is consistent with the provenance of BIF.Combined with recent studies on geology,geochemistry,isotope and geochronology of the BIF,it is revealed that Xiaolaihe BIF is classified as Algoma-type one deposited in a back-arc basin within an oceanic island arc system.
作者
杨帆
张伟
李壮
张茜
崔莹
YANG Fan;ZHANG Wei;LI Zhuang;ZHANG Xi;CUI Ying(College of Geosciences,China University of Petroleum,Beijing 102249,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)
出处
《地球科学与环境学报》
CAS
北大核心
2022年第3期481-498,共18页
Journal of Earth Sciences and Environment
基金
国家自然科学基金项目(42002238,41804045)
中国石油大学(北京)科研基金项目(2462017YJRC032,2462021YXZZ004)
自然资源部东北亚矿产资源评价重点实验室开放课题基金项目(DBY-KF-19-03)。
