Geochemistry of rare earth elements in cobalt-rich crusts from the Mid-Pacific M seamount

Rare earth elements（REEs） and major elements of 25 cobalt-rich crusts obtained from different depths of Mid-Pacific M seamount were analyzed using inductively coupled plasma-atomic emission spectrometer and gravimetric method.The results showed that they were hydrogenous crusts with average ∑REE content of 2084.69 μg/g and the light REE（LREE）/heavy REE（HREE） ratio of 4.84.The shale-normalized REE patterns showed positive Ce anomalies.The total content of strictly trivalent REEs increased with water depth.The Ce content and LREE/HREE ratios in Fe-Mn crusts above 2000 m were lower than those below 2000 m.The change in REE with water depth could be explained by two processes：adsorptive scavenging by setting matters and behaviors of REE in seawater.However, the Ce abundance took no obvious correlation with water depth reflects the constant Ce flux.The Ce in crusts existed mainly as Ce（IV）, implying that the oxidative-enriching process was controlled by kinetic factors.

中太平洋M海山富钴结壳稀土元素地球化学

用ICP-AES和重量法测试了中太平洋M海山不同水深范围内（1300~3000 m）25个富钴结壳样品的稀土元素和常量元素。结果显示M海山富钴结壳为水成结壳,稀土元素总量平均为2084.69μg.g-1,LREE/HREE平均为4.84,具有正的Ce异常。ΣREE（不含Ce）随水深增加而增加,而Ce和LREE/HREE比值则以文石溶跃面为界（水深2000 m）呈现不同的变化,稀土元素这些变化除了与海洋背景颗粒的吸附清扫有关外,还与稀土元素在海水中的行为有关。富钴结壳Ce虽随水深变化,但与水深关系不明显,可能反映其通量恒定。富钴结壳中Ce基本全为Ce（Ⅳ）,表明氧化富集过程,这一过程受动力学因素控制。