COMPARISON BETWEEN NORTHWESTERN CONTINENTAL MARGIN OF THE SOUTH CHINA SEA AND OTHER OCEANS OF GEOCHEMICAL CHARACTERISTICS OF POLYMETALLIC NODULES

Geochemical characteristics of polymetallic nodules can reflect differences of their growth environments, and can show origins of their dominative factors. In this study, different samples of polymetallic nodules collected from the South China Sea, the Pacific and the Indian Ocean were analyzed using ICPMS(AES). Their geochemical compositions and characteristics were compared among samples from different regions. According to the data, samples collected from the northwestern continental margin of the South China Sea were rich in Fe, Si, and ∑REE, while poor in Mn, Cu, Co and Ni. Heavy REE (HREE) was depleted relative to light REE (LREE) very obviously, the latter being 19.54 times less than the former. The ratio of Mn/Fe and element correlation of w(Mn)-w(Fe)-w(Cu+Ni) suggested that the origins of samples from the northwestern continental margin of the South China Sea and from a seamount of the Pacific may be of hydrogenic. Samples from sea basins of the Pacific may be diagenetic in origin, and the Indian Ocean samples were both hydrogenic and diagenetic in formation. Different from ocean samples, polymetallic nodules from the northwestern continental margin of the South China Sea have typical characteristics of a marginal sea which were marked by terrigenous sediments including rich elements of Fe,Si,Al and REE. These characteristics showed that the unique terrigenous sedimentary conditions and the changeful paleoceanic environment have an important effect on the growth of nodules in the South China Sea.