鞍山-本溪地区条带状铁矿的Fe同位素特征及其对成矿机理和地球早期海洋环境的制约  

Fe isotope compositions of banded iron formation from Anshan-Benxi area:Constraints on the formation mechanism and Archean ocean environment

作　　者：李志红[1] 朱祥坤[1] 唐索寒[1] 

机构地区：[1]中国地质科学院地质研究所,国土资源部同位素地质重点实验室,大陆构造与动力学国家重点实验室,北京100037

出　　处：《岩石学报》2012年第11期3545-3558,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40973037;41003005);地调项目(1212011120295;1212011121069)联合资助

摘　　要：本文报道了鞍山-本溪地区晚太古代条带状铁建造的主量元素、微量元素、稀土元素和Fe同位素的分析结果。结果显示:铁矿主要由Fe2O3T和SiO2组成,具有较低的Al2O3和TiO2含量;微量元素含量和稀土总量均较低;经页岩标准化的稀土元素配分模式呈现轻稀土亏损、重稀土富集;具有明显的La、Eu、Y的正异常;较高的Y/Ho比值。这些特征均表明鞍山-本溪地区条带状铁矿是由极少碎屑物质加入的化学沉积岩,成矿物质主要来源于海底热液的贡献。相对于标准物质IRMM-014,条带状铁矿石的Fe同位素组成最突出的特征是均为正值,这是由于二价铁溶液经部分氧化和沉淀形成富集重铁同位素的三价铁氧化物或氢氧化物的结果,且沉淀程度的不同是控制Fe同位素组成变化的重要因素。条带状铁矿无明显的Ce负异常和Fe同位素组成为正值的特征暗示了铁矿沉淀时的海水为低氧逸度环境。The results of elemental and Fe isotopic composition of BIF from Anshan-Benxi area are reported. The average bulk compositions of iron ore are characterized by higher total Fe2O3 and SiO2, and low contents of Al2O3 and TiO2. The overall contents of trace elements and ∑REE are very low. The Shale-normalized REE patterns display LREE depletion, distinct positive anomalies of La, Eu, Y and high Y/Ho values.These features show that BIFs are chemical sediments devoid of detrital input and originated from hydrothermal fluids. Relative to IRMM-014, BIFs show heavy Fe isotope enrichment, implying that the Fe from hydrothermal source was only partially oxidized. The variations in Fe isotope compositions may be explained in terms of different degree of precipitation. The lack of Ce negative anomalies and the heavy Fe isotope enrichment of BIF demonstrate that the oxygen fugacity in the depositional environment was very low.

关 键 词：BIF FE同位素 物质来源 成矿机理 古环境 鞍山-本溪地区 

分 类 号：P618.51[天文地球—矿床学]