太平洋中部多金属结核稀土元素地球化学

RARE EARTH ELEMENT GEOCHEMISTRY OF POLYMETALLIC NODULES FROM THE CENTRAL PACIFIC

用“海洋四号”调查船于1986—1988年在太平洋中部进行了3个航次调查,对所取样品运用仪器中子活化方法进行了REE分析。结果表明:多金属结核作为一种特殊类型的深海沉积物,特别富含REE。太平洋中部多金属结核大多具有Ce正异常。海山结壳∑REE最高,早期成岩型结核最低,水成型结核介于二者之间。早期成岩型结核Ce的正异常明显弱于水成型结核,甚至出现Ce的负异常。海山、丘陵区结核的∑REE高于平原、凹地区结核,且前者Ce异常强于后者。单个结核从下向上∑REE增大,Ce正异常增强。REE与Fe和δ—MnO_2呈明显的正相关,在氧化条件下富集。影响多金属结核中REE分布最直接的因素是水-沉积物(或岩石)界面的氧化还原条件,而导致环境氧化还原条件变化的地质因素则有早期成岩作用、热液作用、南极底层流等等。

Based on the rare earth element contents determined by instrumental neutron activition method in the polymetallic nodules collected from the Central and Eastern Pacific by R/V Hai-yang 4 during her 861, 871 and 881 cruised of 1986-1988, the following conclusions are suggested. Polymetallic nodules, as a particular type of deep sea sediments, are very rich in rare earth elements (REE). Most of the nodules from the Central Pacific (CP area) and Eastern Pacific (CC area) have positive Ce anomalies. ΣREE is highest in polymetallic crusts from seamount, lowest in early digenetic nodules, and between tht above two values in hydrogenetic nodules. The positive Ce anomalies of early diagenetic nodules are obviously lower than those of hydro-genetic nodules. Sometimes, the early diagenetic nodules have negative Ce anomalies. ΣREE in polymetallic nodules from seamount and hill at the seafloor is higher than that of polymetallic nodules from abyssal plain and depression. The positive Ce anomalies of the former are higher also. In an individual nodule, the REE and positive Ce anomalies increase from the bottom to the top. There is a positive correlation between REE, Fe and δ-MnO2 in polymetallic nodules. REE are concentrated in polymeallic nodules at oxidaion condition. The main factor controlling REE distribution in polymttallic nodules is the Eh value at the water-sediments interface, and geological factors which can lead to variation of the Eh value are early dia-genesis, hydrothermal activity, AABW, and others.