Chemical composition of East Pacific Rise basal sediments

Analyses by atomic absorption spectrophotometry and spark-source mass spectrography of 25 basal metalliferous sediment units from widely spaced locations on the western flank of the East Pacific Rise show that the deposits are enriched relative to normal pelagic sediment in Fe, Mn, Ni, Cu, Pb, Zn, and many trace elements. The elements are partitioned differently between the various mineralogic constituents of the sediment, with Fe and Mn largely in separate phases and many of the remaining elements primarily associated with reducible ferromanganese oxide minerals but also with iron minerals and other phases. Most of the iron in the deposits is probably of volcanic origin, and much of the manganese and minor elements is derived from sea water. The bulk composition of the deposits varies with age; this is thought to be due to variations in the incidence of volcanic activity at the East Pacific Rise crest where the deposits were formed.采用原子吸收分光光度法（atomic absorption spectrophotometry）与火花源质谱法（spark-source mass spectrography），对东太平洋海隆（East Pacific Rise）西翼分布于不同间距站位的25个基底含金属沉积单元开展分析，结果表明：相较于常规远洋沉积物（pelagic sediment），该类沉积中铁（Fe）、锰（Mn）、镍（Ni）、铜（Cu）、铅（Pb）、锌（Zn）及多种微量元素均发生富集。 各类元素在沉积物的不同矿物组分间呈现差异化分异特征：铁与锰主要赋存于相互独立的物相中，其余多数元素主要与可还原铁锰氧化物矿物（ferromanganese oxide minerals）结合，同时也可与铁矿物及其他物相共存。 沉积中的绝大部分铁大概率源自火山作用，而大部分锰及微量元素则来源于海水。该类沉积的整体化学成分随沉积年代发生变化，这一现象被认为是由沉积形成区域——东太平洋海隆轴部的火山活动频次变化所导致。