马里亚纳海沟沉积物Hf-Nd同位素解耦成因研究

海洋沉积物Hf、Nd同位素组成对于理解俯冲带物质循环以及探讨地球系统中岩石圈、水圈、生物圈和大气圈的相互作用具有重要的指示意义。前期工作表明马里亚纳海沟沉积物具有明显的Hf-Nd同位素解耦特征，但目前缺乏对该深渊环境下沉积物及其单矿物原位微区元素-同位素的系统研究，制约了我们揭示沉积物物质组成、来源和沉积环境与Hf-Nd同位素解耦的成因联系。因此，本项目拟以马里亚纳深渊沉积物为研究对象，开展矿物组成分析，重点开展Pb同位素以及锆石U-Pb定年、磷灰石REE-Hf-Nd同位素分析，结合已有的主微量元素和Sr-Nd-Hf同位素数据，试图揭示沉积物物质组成、来源和沉积环境，从而探讨沉积物Hf-Nd同位素解耦的成因机制。结合已有的成果，本研究将为理解海沟沉积物Hf-Nd同位素解耦的成因及其对俯冲带物质循环的指示作用提供新的资料，为进一步探讨地球系统不同圈层相互作用提供独特的视角。

It has been well documented that Hf and Nd isotopic composition of global marine sediment is an important indicator for understanding material cycling in subduction zone and bear key information for the interactions between lithosphere, hydrosphere, biosphere and atmosphere of the Earth System. Previous investigation demonstrated that sediments in the Mariana Hadal Trench with a water depth of larger than 7000 m have much higher Hf isotopic composition than that of the Seawater Array in a given Nd isotopic composition, showing an typical Hf-Nd isotopic decoupling. However, due to the lack of the elemental and isotopic (Sr-Hf-Nd-Pb) analyses of sediments and their minerals deposited in such environment, the genetic link between Hf-Nd isotopic decoupling and the composition, provenance and sedimentary environment of sediments is poor constrained. Here, this study will carry out mineral and isotopic (Pb) analyses of the bulk sediment, and apply in-situ techniques to analyze detrital zircon U-Pb age and conduct element (REE) and isotopes (Hf-Nd) of apatite to decipher the composition, provenance and sedimentary environment of sediments. This result will be integrated with detailed mineral examination and major, trace elemental and Sr-Nd-Hf isotopic data to constrain the origin of Hf-Nd decoupling in the Mariana Hadal Trench sediments. Together with available data, the outcomes of this study will provide an independent constraint on the origin of Hf-Nd decoupling of trench sediments and its implication for material cycling in subductine zone. Combined with elemental and isotopic (Sr-Hf-Nd-Pb) data from seawater, eolian dust and river sediment, this study will help to provide new perspectives into the interactions between the various spheres of the Earth system.