Phase relations and partial melting of C-bearing sediment under mantle conditions

沉积岩的俯冲作用被认为是地幔中挥发分和微量元素再循环的重要过程。实验和理论研究表明，碳酸盐和含水矿物可能在俯冲过程中幸存下来。它们能产生深部交代流体，对地幔中富集域的形成具有重要意义。在含有CO2或H2O或CO2和H2O的系统中获得了可用的实验数据。在这两个水和CO2轴承实验，氧势可能是相当高的，而许多天然沉积物减少。H2O、CO2和还原挥发性物质（CH 4、H2等）比例的变化可能影响熔体/流体相的组成和性质。实验将在7-12 GPa和~800-1400°C下使用多砧压机进行。这个压力范围是特别感兴趣的，因为发生了许多反应，控制泥质系统中含水相的稳定性，包括多硅白云母和硬柱石的分解，黄玉的脱水和高压相EGG的形成。起始材料将是合成混合物，其对应于平均沉积物组成[全球俯冲沉积物（GLOSS）]，H2O、CO2、K/Na比和石墨添加量存在变化，以实现还原条件。本体组合物还将掺杂有一系列微量元素（包括REE、LILE和HFSE）。

Subduction of sedimentary rocks is believed to be an important process for volatile and trace element recycling in the Earth's mantle. Experimental and theoretical investigations show that carbonates and hydrous minerals may survive subduction. They can produce deep metasomatizing fluids which are important for the formation of enriched domains in the mantle. Available experimental data were obtained in systems with either CO2 or H2O or both CO2 and H2O. In both water- and CO2-bearing experiments, the oxygen potential was probably rather high, whereas many natural sediments are reduced. Changes in the proportions of H2O, CO2 and reduced volatile species (CH4, H2, etc.) may affect both the composition and the properties of the melt/fluid phase. Experiments will be carried out at 7-12 GPa and ~800-1400°C using a multianvil press. This pressure range is of special interest because a number of reactions occur that control the stability of hydrous phases in pelitic systems including decomposition of phengite and lawsonite, dehydration of topaz and formation of high-pressure phase EGG. Starting materials will be synthetic mixtures corresponding to average sediment compositions [Global Subducted Sediment (GLOSS)] with variations in H2O, CO2, the K/Na ratio, and the addition of graphite to achieve reducing conditions. The bulk compositions will also be doped with a range of trace elements (including REE, LILE and HFSE).