西太平洋卡罗琳洋脊CM4海山铁锰结壳矿物学和地球化学特征

MINERALOGY AND GEOCHEMISTRY OF FERROMANGANESE CRUSTS OF CAROLINE RIDGE CM4 GUYOT IN THE WESTERN PACIFIC

2017年8月中国科学院海洋研究所在西太平洋低纬度海区的卡罗琳洋脊CM4海山开展了多学科综合调查,发现该海山山体表面分布着大量的铁锰结壳。本文对该海山的5个铁锰结壳样品进行了矿物学和地球化学研究,利用X射线衍射(XRD)、电感耦合等离子光谱及质谱(ICP-OES、ICP-MS)等测试技术分析了铁锰结壳的矿物组成、主微量元素和稀土元素含量,并进一步探讨了铁锰结壳的成因类型。结果表明,该海山铁锰结壳的矿物组成以水羟锰矿为主,含有少量钡镁锰矿、水钠锰矿、针铁矿、纤铁矿、石英和方解石。该海山铁锰结壳的Mn、Fe、Co、Ni、Cu元素平均含量分别为24.24%、15.14%、0.16%、0.34%、0.01%。与全球各大洋海山区铁锰结壳相比,该海山样品的Cu含量很低。该海山铁锰结壳的稀土元素(REY)含量相对偏低,总体为轻稀土(LREE)富集;稀土(REY)配分模式显示相对平坦的特征,呈明显的Ce正异常,轻微的Y负异常和Ho正异常。样品的矿物组成、元素比值、元素组合等都表明该海山铁锰结壳属于水成成因,未受明显的成岩作用影响。

In August 2017,a multidisciplinary comprehensive survey of the Caroline ridge CM4 guyot in the low latitudes of the western Pacific Ocean was conducted,in which a large number of ferromanganese crusts were found distributed on the mountain surface.Five ferromanganese crust samples collected from Caroline CM4 guyot were studied in mineralogy and geochemistry.By using XRD,ICP-OES and ICP-MS,mineral composition and the contents of major elements,trace elements,and rare earth elements of the samples were analyzed,and the geochemical characteristics and genesis were preliminarily discussed.Results show that the ferromanganese crusts are dominated by vernadite with a small amount of todorokite,birnessite,goethite,quartz,and calcite.The average concentration of Mn,Fe,Co,Ni,and Cu of the samples is 24.24%,15.14%,0.16%,0.34%,0.01%,respectively.Compared with that of ferromanganese crusts in Pacific,Atlantic,and Indian Ocean,the Cu content of the samples is relatively lower.The samples are relatively enriched in LREE.The REE diagram shows a positive anomaly of Ce,Ho and negative anomaly of Y.Meanwhile,the mineral composition,element ratios,and element groups indicate that the samples are hydrogenetic in origin and have not undergone obvious diagenesis.