南海尖峰海山多金属结壳地球化学

南海尖峰海山多金属结壳富含30多种元素,其锰铁矿物主要由钡镁锰矿,δ-MnO_2和FeOOH·xH_2O组成。与其它海区的结壳相比,尖峰海山结壳富含Cu、Ni、Ba、Zn、Pb等元素,而Co、Ti、稀土元素(REE)、Sr等元素相对较贫。研究表明,HREE亏损,具明显的Ce正异常,较明显的Tb正异常和Yb负异常。这是氧化弱碱性海洋环境所致。结壳是水成作用的产物,它的形成受南海独特的古海洋环境所控制,海底火山热液作用,可能也是影响因素之一。

GEOCHEMISTRY OF POLYMETALLIC CRUST FROM JIANFENG SEAMOUNT, SOUTH CHINA SEA

Polymetallic crusts cover most hard substrates on seafloor volcanic edifices (basalt?) in South China Sea Basin. Crust samples from Jiangfeng Seamount are discussed. The thickness of the crusts is 1 to 3 cm generally and might reach 5 cm in maximum. The dominant crystalline phases in our samples are toderokite and (3-MnO2(vernadite). Compared with those in other earas, South China Sea crusts have higher metallic concentration of Cu, Ni, Ba, Zn, Pb and lower Co, Ti, REE, Sr. Shale-nomalized REE patterns of the crust show a depletion in HREE, a large positive Ce anomaly, a positive Tb anomaly and a negative Yb anomaly. Crust mineralogy, geochemistry indicate the crust is formed in a week oxidizing and alkalic environment. Polymetallic crusts are hydrogenetic, and the metals and REE (except for minor contributions from detrital phases) are derived from seawater. The formation of the crust is dependent on the local paleoceanographic environment influnced by volcanic hydrothemal activity.