| 中国富钴结壳合同区海水的稀土元素特征及其意义 |
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| 引用本文： | 任江波,邓希光,邓义楠,何高文,王汾连,姚会强.中国富钴结壳合同区海水的稀土元素特征及其意义[J].地球科学,2019,44(10):3529-3540. |
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| 作者姓名： | 任江波 邓希光 邓义楠 何高文 王汾连 姚会强 |
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| 作者单位： | 广州海洋地质调查局国土资源部海底矿产资源重点实验室, 广东广州 510075 |
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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）项目GML2019ZD0106自然资源部海底矿产资源重点实验室开放基金KLMMR-2017-A-01中国地质调查局项目DD20191009国际海域资源调查与开发"十三五"课题DY135-C1-1-04国际海域资源调查与开发"十三五"课题DY135-R2-1-05国家自然科学基金41803026 |
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| 摘 要： | 通过对西太平洋34件海水样品的稀土元素（REY:REE+Y）测试及其与研究区富钴结壳稀土耦合特征分析，揭示了海水稀土特征及其成因.海水的稀土含量随水深呈现逐渐增加的趋势，∑ REY范围为14.0×10-12~65.5×10-12，平均值为31.9×10-12，其中Y的绝对值（均值为6.0×10-12~24.1×10-12）和相对值（（Y/Ho）N均值为1.98）均较高，La含量次之（均值为1.8×10-12~11.6×10-12），Ce含量相对较低（均值为2.4×10-12~8.8×10-12），δCe范围为0.33~1.03（均值为0.66），（La/Yb）N平均值为0.71.海水稀土元素北美页岩标准化后显示左倾模式，具有显著的Ce负异常、Y正异常和无明显的Eu异常特征.研究区普遍发育水成成因的富钴结壳，即其稀土元素和其他组分均源自海水.富钴结壳的稀土含量相对海水富集6~7个数量级，其Ce正异常和Y负异常的稀土模式与海水构成良好的耦合关系，指示富钴结壳类组分对海水稀土清扫具有选择性，是造成海水稀土模式的重要因素.海山上发育的磷块岩以及周围盆地深海泥中的磷酸盐组分，它们具有较高的稀土含量和类似于海水的稀土模式，指示海洋磷酸盐消耗稀土时并未分馏而是继承海水模式.海水独特的稀土模式特征是补给与消耗平衡作用的结果，铁锰氧化物和海洋磷酸盐是两种典型的海洋自生组分，它们对海水稀土特征的形成至关重要.
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| 关 键 词： | 稀土元素 海水 富钴结壳 海洋磷酸盐 麦哲伦海山区 地球化学 |
| 收稿时间： | 2018-12-28 |
Rare Earth Element Characteristics and Its Geological Implications for Seawater from Cobalt-Rich Ferromanganese Crust Exploration Contract Area of China |
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| Abstract: | The contents of rare earth elements and yttrium (REY) are determined using ICP-MS spectrometry in 34 seawater samples obtained from various depths from Caiwei Guyot and Weijia Guyot in western Pacific. Based on the data, the vertical profile of ∑REY content of seawater column are established in cobalt-rich ferromanganese crust exploration contract area of China. The contents of rare earth element in seawater increase gradually with the water depth. The ∑ REY contents range from 14.0×10-12 to 65.5×10-12, with an average of 31.94×10-12. Both the absolute content and relative content of Y are high, ranging from 6.0×10-12 to 24.1×10-12, with mean (Y/Ho)N value of 1.98, followed by La, with content ranging from 1.8×10-12 to 11.6×10-12. Ce is relatively low, with contents ranging from 2.4×10-12 to 8.8×10-12. And the δCe is from 0.33 to 1.03, with mean value of 0.66. The NASC-normalized REY patterns show left mode, with mean (La/Yb)N value of 0.71, obvious negative Ce anomalies, positive Y anomaly and no obvious Eu anomaly. Aqueous cobalt-rich ferromanganese crust is widely distributed in the study area, whose rare earth elements and other components are derived from seawater. The rare earth content of cobalt-rich crusts is 6-7 orders of magnitude higher than that of seawater, while NASC-normalized REY patterns of cobalt-rich ferromanganese crust show remarkable positive Ce and negative Y anomaly. This coupling relationship indicates that cobalt-rich ferromanganese crust components are selective for the cleaning rare earth elements of sea water, causing seawater rare earth anomaly. Both the phosphate rock developed on the seamounts and the phosphate components in the deep mud of the surrounding basin have high rare earth contents and a rare earth pattern similar to that of seawater. These phenomena indicate that the marine phosphate is not fractionated but inherited the REE patterns of seawater. The unique characteristics of REE patterns of seawater are the result of the balance between supply and consumption. Ferromanganese oxide and marine phosphate are two typical marine autogenic components, which are essential for the formation of REE patterns of seawater. |
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