中太平洋富钴结壳稀土元素的地球化学特征

Rare earth elements geochemistry in Co-rich crust

利用"大洋一号"调查船在中太平洋不同海区调查时获取的18个富钴结壳样品,采用化学分析及ICP-AES分析法,对中太平洋海区富钴结壳稀土元素的含量、分布特征、配分模式以及来源进行了分析和研究,结果表明:(1)中太平洋海区富钴结壳中稀土元素含量异常高,总量为1703×10-6～2879×10-6,约为正常深海沉积物、有孔虫核壳和海水中稀土元素含量的10～100倍,与莱恩群岛和夏威夷群岛海区结壳中稀土元素的含量接近,且明显高于约翰斯顿岛、马绍尔群岛和南中国海等海区结壳中稀土元素的含量;(2)中太平洋海区富钴结壳中稀土元素的配分模式基本相同,轻稀土元素富集,尤其是Ce元素相当富集,呈较为明显的正异常,而重稀土元素则普遍亏损;(3)中太平洋海区富钴结壳中稀土元素与海水中稀土元素的配分模式为明显的镜像关系;(4)中太平洋海区富钴结壳中稀土元素总量与Mn呈显著正相关,与Mn/Fe相关不明显,反映出研究区结壳中的稀土元素主要来自于海水和上覆水的缓慢沉积以及火山喷发、洋底玄武岩风化淋漓和生物化学沉积。

The rare\|earth elements (REE) concentration of Co\|rich crust from the central Pacific Ocean was determined using chemical\|digest ICP\|AES method. This paper discusses the REE abundance, distribution features in different layers, REE participation patterns and sources of Co\|rich crust. Our research results suggest that:(1)The REE concentrations in Co\|rich crusts of the central Pacific are distinctively high, and REE is remarkably enriched relative to normal pelagic sediments and multimetallic nodules. Its content varied between 1 7206×10\+\{-6\} and 2 879×10\+\{-6\}, was higher than the REE concentration of crusts from Johnston Islands, Marshall Islands and the South China Sea, and closed to the concentration of crusts from Line Islands and Hawaiian Achipelago. Perhaps they have similar sedimentation environment. (2)The REE participation patterns of research area are similar. The LREE is relatively enriched. Especially Ce is distinctively enriched, and displays remarkably positive Ce anomalies. The HREE is relatively in depletion. The reason perhaps is that the HREE easily forms relative stable complex compounds in seawater and is relatively difficult to enter the lattice of minerals.(3)The REE participation patterns in crusts displays mirror\|like relationship with the REE patterns in seawater.(4)The REE concentrations of crusts display remarkably positive correlation with the Mn contents and Mn/Fe ratios, but are not in the distinctive correlation with iron.(5)The origin of REE in crusts is similar to the other elements in crusts, perhaps comes from the seawater and overlying water, volcanic eruption, seabed basalt weathering, biochemical sedimentation. Its concentration and distribution are from results of sedimentation environment evolution, controlled by hydrogenous mineralization.