东太平洋CC区WPC1101柱样沉积环境及埋藏多金属结核成因

WPC1101重力活塞柱样取自东太平洋CC区西部,其顶部见有水成多金属结核,3.4~3.5 m发育埋藏多金属结核层。对该柱样的沉积物成分、磁性地层、黏土矿物及元素地球化学结果进行综合分析,以探讨柱样的沉积环境变迁;对埋藏多金属结核进行地球化学元素分析,探讨其形成环境。结果表明:该柱样成分以硅质黏土为主;蒙/伊比表明晚渐新世时期研究区海底火山、热液活动较强,自生黏土组分较高;而上新世以后则相对减弱。柱样自下而上生物成因SiO2含量逐渐增多,代表陆源碎屑物质的Al2O3含量相对稳定,P2O5、CaO、Cu、Co、Ni则由于生物SiO2含量的增加而稀释,含量降低。埋藏多金属结核发育于生物生产力旺盛、沉积间断发育期,其内稀土元素(Ce元素除外)由于受后期成岩作用发生清扫作用,转移至沉积物中,而Ce元素不参与后期成岩过程,持续在多金属结核内富集。

DEPOSITIONAL ENVIRONMENT AND ORIGIN OF BURIED POLLYMETALLIC NODULES: AN INTERPRETATION OF PISTON CORE WPC1101 FROM CC ZONE OF EASTERN PACIFIC

The Piston Core WPC1101 was taken from the Clarion-Clipperton Fracture Zone, Equatorial Pacific in 2011. Polymetallic nodules have been discovered both on the top and in the sediment sequence 3.4-3.5 m deep. This paper summarized the results of sedimentology, magneto-stratigraphy, clay mineralogy and element geochemistry for interpretation of its depositional environment. The main component of the core consists of siliceous clay; the values of M/I show that the volcanic and hydrothermal activities occurred on the ocean floor were stronger in late Oligocene than in Pliocene. From the bottom to the top, the content of biogenetic SiO2 increases, while Al2O3, which represents terrigenous components, remains relatively constant in content. Contents of P2O5, CaO, Cu, Co, Ni are diluted attributing to the increment of biogenetic SiO2. The buried polymetallic nodules are developed together with a depositional hiatus, when the primary productivity was high. Processes which favor the enrichment of transitional metals in buried nodules cause the depletion of REE3+ in nodules and the enrichment of REE3+ in associated sediments. In contrast, Ce appears to be enriched in nodules, but not involved in diagenetic reactions.