马里亚纳海沟“挑战者”深渊沉积物地球化学特征及成因机制

Geochemical Characteristics and Formation Mechanism of Sediments from the Challenger Deep in the Southern Mariana Trench

【目的】为探究马里亚纳海沟“挑战者”深渊沉积物的主要类型、地球化学特征和成因机制。【方法】以马里亚纳海沟“挑战者”深渊从北坡(上覆板块)、轴部到南坡(俯冲板块)16个站位的沉积物和蚀变基岩开展矿物学及地球化学分析。【结果与结论】“挑战者”深渊沉积物分为褐红色深海黏土质沉积物、硅质生物软泥、自生沉积物(富锰微结核)和钙质生物软泥四种主要类型。其中,褐红色深海黏土质沉积物为深渊沉积物的主要类型,对深渊沉积物的成分贡献最大,其主量、微量元素地球化学特征与洋壳蚀变基岩具有相似性。提出了褐红色深海黏土质沉积物成因主要源于俯冲板块和上覆板块玄武质基岩蚀变的观点。此外,深渊底部活跃的有机质早期成岩作用,对沉积物地球化学性质产生了重要影响,是导致“挑战者”深渊沉积物相比邻近深海沉积物具有较低稀土元素含量和富集微锰结核的主要原因。

[Objective]To investigate the hadal sediments main type,geochemical characteristics and formation in the Challenger Deep of the southern Mariana Trench,[Methods]the mineralogical and geochemical analysis were uesd to study the sediments and altered basalt from north slope(overlying plate)and axis to the south slope(subduction plate)at the Challenger Deep of the Mariana Trench.[Results and Conclusions]The hadal sediments can be divided into four types:red deep-sea clay,siliceous sediments,micromanganese-rich sediments,and calcareous sediments.The red deep-sea clay is the most common type of hadal sediment,which contribute the most to subducted sediments.Major and trace element geochemical characteristics are similar to those of altered basalt of the oceanic crust,which imply that red clay is mainly derived from the basalt alteration of the subducted and overlying plates,rather than the volcanic and terrestrial inputs.Moreover,intensified organic matter diagenesis has an important influence on the geochemical properties of the hadal sediments,which is the main reason the Challenger Deep sediments have lower rare earth elements and enrich more micromanganese nodules than the adjacent deep-sea sediments.