中太平洋海区富钴结壳地球化学特征及成因机制

本文利用ICP-AES、EPMA、X-ray衍射等测试技术以及聚类分析和因子分析等多种数理统计方法，系统地对中太平洋海区富钴结壳的元素地球化学特征、矿物组成和微观组构进行了研究，并探讨了其成因机制，获得以下主要认识： 1中太平洋海区富钴结壳类型多样，均为水成成因，其矿物相主要由锰矿物相、铁矿物相和非金属矿物相组成；富钴结壳壳层发育多种原生和次生构造类型。 2磷酸盐化作用不仅强烈改变富钴结壳元素初始含量，而且造成富钴结壳某些元素间的相关性发生改变，这些敏感型元素对可用于指示富钴结壳是否发生磷酸盐化。在不同水深段内，未磷酸盐化型富钴结壳的主要元素随经向、纬向的变化趋势相似，表明其受水体化学障、表面生产力和物质来源等环境参数控制；而随水深的变化则具有区域一致性，表明水体化学具有区域成层性。 3未磷酸盐化富钴结壳稀土元素含量和轻重稀土分馏程度随水深发生规律变化，这种变化不仅与它们在海洋中的含量和行为有关，也与海洋背景颗粒的吸附有关；铈(Ce)在富钴结壳中基本上呈4价，且动力学因素控制了其富集过程，因此Ce异常不能用于指示富钴结壳形成环境的氧化程度。 4基于富钴结壳微层呈锯齿状且同一微层生长速率不同，提出了富钴结壳在各种基底表面生长以及后继发育过程受固液界面双电层控制的发育模式。在富钴结壳整个发育过程中，经历了从贫氧环境向富氧环境的转变，但微环境则呈富氧-低氧过程的交替。 关键词： 富钴结壳；中太平洋；元素地球化学；界面双电层

In this paper, the mineralogy, the micro-textures and the elemental geochemistry of the cobalt-rich crusts from the Central Pacific Ocean were analyzed systematically using the ICP-AES, the EPMA, and the X-ray diffraction combined with mathematical statistics such as factor analysis and cluster analysis, and so on. And then, the formation mechanism of the cobalt-rich crusts was discussed. The main conclusions of this study are: 1 The types of the cobalt-rich crusts from the Central Pacific Ocean are the hydrogenous. The mineralogies of them are vernadite, iron oxyhydroxide and minor non-metal phases. Many kinds of primary and secondary structures formed in the layers of cobalt-rich crusts. 2 Phosphorization changes not only the original element contents in the cobalt-rich crusts, but also the correlationships between the elements. Thus these sensitive element pairs could be used as the indicators of phosphorization. The variations of major elements in the non-phosphatized cobalt-rich crusts to the longitude, latitude in different water intervals is similare each other, and thus these can be explained by the physicochemistry bars in seawater, surface-water bio-productivity and material sources, and so on. That the change of major elements with water depth in different areas is similare, which illustrates that the regional stratification of ocean water chemistry. 3 The REE contents and LREE/HREE ratios in the non-phosphatized cobalt-rich crusts take regular variations with waterdepth, while these variations could be elucidated by two processes: one is the adsorption of setting particulates in ocean column, another is the contents and behaviors of the REE in ocean. The Ce in the cobalt-rich crusts occurs as the Ce(Ⅳ), and its enrichment is a kinetic process, thus the Ce anomalies could not used as the redox proxy of the formation environment of the cobalt-rich crusts. 4 Based on the investigation into the microlayers which showing the crenulated and having the different growth rates, one interface electric double layer model was suggested to describe that the precipitation of the cobalt-rich crusts on the surfaces of the various substrates. Although the environment of them change from a early lower oxidizing condition to a higher later generally, the microenvironment alter alternatively from the higher oxygen level to the lower. Key words: cobalt-rich crusts; Central Pacific Ocean; elemental geochemistry; interface electric double layer