太平洋多金属结核和富钴结壳稀土元素地球化学对比及其地质意义

摘要

多金属结核和富钴结壳是大洋两类典型的铁锰产物.为探讨不同海区多金属结核和富钴结壳之间稀土元素特点及其揭示的地质意义,利用近年中国在太平洋获取的样品进行对比,采用ICP-AES对稀土元素测试.结果表明,结壳具有正Ce异常明显、LREE富集、∑REE高的特点,而结核表现为HREE相对富集、∑REE相对较低,因成因类型不同,Ce异常或表现为正异常、负异常或异常不明显.结核形成后受到成岩作用的影响,而结壳则为水成作用形成;结核和结壳中REE的存在形式比较复杂,不同海区各不相同,中太平洋东部产出的结壳和位于东太平洋的结核中REE可能主要赋存于铁矿物相,而西太平洋结壳REE可能主要赋存于锰矿物相;结核和结壳REE可能分别来自海水和海山蚀变玄武岩,热液作用影响有限.%Polymetallic nodules and cobalt-rich crusts are two types of ferro-manganese deposits in the ocean.In order to probe into their REE geochemical characteristics in different oceanic areas of the Pacific Ocean, the authors collected samples from eastern Pacific basin, central Pacific Ocean and western Pacific Ocean and examined REE characteristics by means of ICP-AES.There are obvious positive Ce anomalies, rich LREE (light REE) and high total REE (∑REE) in the crusts.In contrast, there are rich HREE (heave REE) and relatively low ∑REE in the nodules.Ce anomalies have different styles, such as positive, negative and indistinct anomalies caused by different genetic types of nodules.The "M" type tetrad effects of nodules indicate that the nodules have suffered diagenesis, while the crusts have not been subjected to this effect.There exist different modes of occurrence of REE in nodules and crusts in different oceanic areas.REE in the crusts from central Pacific Ocean and in the nodules from eastern Pacific Ocean probably exist in the Fe-mineral phase, whereas REE in the crusts from western Pacific Ocean might exist in the Mn-mineral phase.REE in the nodules and crusts might have been mainly derived from seawater and seamount altered basalt respectively, with limited hydrothermal contribution.