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性和微量元素循环的重要过程。实验和理论研究表明，碳酸盐和含水矿物可能在俯冲中幸存下来。它们可以产生深部交代流体，这对地幔中富集域的形成是重要的。可用的实验数据是在含有CO2或H2O或同时含有CO2和H2O的体系中获得的。在含水和含二氧化碳的实验中，氧势可能相当高，而许多自然沉积物的氧势却降低了。H2O、CO2和减少的挥发性物质(CH4、H2等)比例的变化可能会影响熔体/流体相的组成和性质。实验将在7-12 Gpa和~800-1400°C的条件下使用多顶锤压力机进行。这一压力范围特别重要，因为在泥质体系中发生了许多控制水合相稳定性的反应，包括多硅白云母和钠铝石的分解、黄玉的脱水和高压相鸡蛋的形成。起始材料将是与平均沉积物组成[全球俯冲沉积物(光泽度)]相对应的合成混合物，其中H2O、CO2、K/Na比和添加石墨以实现还原条件的变化。块状成分还将掺入一系列微量元素(包括稀土、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).