| 太平洋调查区多金属结核的地球化学特征和成因 |
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| 引用本文： | 任江波,邓义楠,赖佩欣,何高文,王汾连,姚会强,邓希光,刘永刚.太平洋调查区多金属结核的地球化学特征和成因[J].地学前缘,2021,28(2):412-425. |
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| 作者姓名： | 任江波 邓义楠 赖佩欣 何高文 王汾连 姚会强 邓希光 刘永刚 |
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| 作者单位： | 广州海洋地质调查局自然资源部海底矿产资源重点实验室,广东广州510075;南方海洋科学与工程广东省实验室(广州),广东广州511458 |
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| 基金项目： | 南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(GML2019ZD0106);国家自然科学基金项目(41702096);国家自然科学基金项目(41803026);国际海域资源调查与开发“十三五”课题(DY135-R2-1-05);中国地质调查局项目(DD20191009) |
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| 摘 要： | 东太结核主要为半埋藏和埋藏型,发育于以黏土和硅质组分为主的沉积环境。东太结核的锰相矿物主要有水羟锰矿和钡镁锰矿,具有较高的REY、Cu、Ni含量和Mn/Fe比值,显示遭受间隙水的影响,落入水成成因和成岩成因两个区间范围。西太结核主体暴露在海水中,周围沉积物主要由深海黏土组成。西太结核的锰相矿物几乎只有水羟锰矿,具有较高的REY、Co含量和低Mn/Fe比值,属于典型的水成成因型。两个区域的多金属结核的稀土北美页岩标准化模式均显示Ce正异常、Y负异常和无或弱Eu异常,与海水稀土特征构成良好的耦合关系,是多金属结核对海水稀土选择性富集的结果。西太结核相对东太结核具有更高的Ce含量和δCe,Co、Ti与Ce具有良好的正相关关系。研究认为海水中溶解氧并不一定是控制结核Ce正异常程度的关键因素,Co、Ti等元素及其相关组分能够引起Ce与其他稀土元素的强烈分馏,也可能是影响多金属结核Ce正异常程度的控制因素。研究区多金属结核和富钴结壳表层样的εNd范围为-6.6~-2.5,是全球最富放射性成因Nd的海洋铁锰壳层。结合稀土模式以及Eu异常特征,本研究认为多金属结核的稀土主要来自εNd相对较高的周围陆壳,可以通过河流或者大气沉降等方式输送到大洋,而研究区广泛分布的海山玄武岩释放的放射性成因Nd同位素对海水的影响微弱。
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| 关 键 词： | 多金属结核 富钴结壳 稀土元素 西太平洋海山区 CC区 |
| 收稿时间： | 2019-04-15 |
Geochemical characteristics and genesis of the polymetallic nodules in the Pacific survey area |
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| REN Jiangbo,DENG Yinan,LAI Peixin,HE Gaowen,WANG Fenlian,YAO Huiqiang,DENG Xiguang,LIU Yonggang.Geochemical characteristics and genesis of the polymetallic nodules in the Pacific survey area[J].Earth Science Frontiers,2021,28(2):412-425. |
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| Authors: | REN Jiangbo DENG Yinan LAI Peixin HE Gaowen WANG Fenlian YAO Huiqiang DENG Xiguang LIU Yonggang |
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| Institution: | 1. Ministry of Natural Resources Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Guangzhou 510075, China2. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China |
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| Abstract: | The polymetallic nodules in China’s polymetallic nodules exploration contract area in the East Pacific Basin (EP nodules) are largely buried or semi-buried in a sedimentary environment dominated by clay and siliceous components. The manganese mineral phases of the EP nodules mainly include vernadite and todorokite, with high REY and high Cu and Ni contents and Mn/Fe ratio. These characteristics indicate the nodules are affected by interstitial water thus falling into the range of diagenesis and hydrogenesis. In comparison, the polymetallic nodules in the Northwest Pacific Basin (WP nodules) are mostly exposed to seawater, and the surrounding sediments are mainly deep-sea clay. The manganese mineral phases of the WP nodules are almost all vernadite, with high REY, high Co content and low Mn/Fe ratio. It shows that the WP nodules are of typical hydrogenic form. The NASC-normalized REY patterns of the polymetallic nodules in both regions show positive Ce and negative Y anomalies and no/weak Eu anomaly, while the REY patterns of ambient seawater show obvious negative Ce and positive Y anomalies and no obvious Eu anomaly. This inverse coupling relationship implies that the REY patterns of the polymetallic nodules are the result of selective enrichment from seawater. The WP nodules have higher Ce content and δCe than the EP nodules. Both Co and Ti correlate positively with Ce, which may collectively affect the selection of Ce and Y in seawater by polymetallic nodules. In this study, dissolved oxygen in seawater was not a factor controlling the level of positive Ce anomaly observed in the polymetallic nodules. Rather, elements such as Co and Ti and their related components can cause strong fractionation of Ce and other REY, which may be the controlling factor. The surface samples of polymetallic nodules and cobalt-rich crusts in the study area, with εNd values ranging from -6.6 to -2.5, represent the most radioactive ferromanganese samples of Nd in the global sea area. Combining the εNd result with REY patterns and Eu anomaly, we suggest that REY in polymetallic nodules mainly come from the surrounding continental crust with relatively high εNd and can be transported to the ocean via rivers or atmospheric deposition. However, the radioactive Nd isotopes released from basalt in the Northwest Pacific Basin have only weak effect on the seawater. |
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| Keywords: | polymetallic nodules Co-rich crusts rare earth elements seamounts in western Pacific Ocean Clarion-Clipperton region |
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