Influence of H2O and CO2 on deep melting beneath ridges

摘要0623550(赫希曼)学术价值：这项工作确定了水和二氧化碳对洋脊下深部熔融的影响，从而对亚脊流变学、动力学、地球化学和观测地球物理具有重要意义。讨论的问题包括：(1)大洋中脊下挥发分诱导的熔融开始于什么深度，产生熔融的比例是多少；(2)洋脊下熔融和脱水之间的关系是什么；(3)二氧化碳对激发海脊下碳酸盐硅酸盐部分熔融和脱水有什么影响。这项工作将包括高压和高温多个砧板实验，以确定少量H2O和CO2对深度熔化和脱水的影响。实验对象是在3、4和5 GPa时加入少量H2O的橄榄岩的固相线；在3 GPa时微含水橄榄岩的熔融程度和残留脱水程度；以及在3和4 GPa时二氧化碳对微含水橄榄岩熔融和残留脱水的影响。RUN产物将用电子显微镜、振动光谱和二次离子质谱仪(SIMS)进行分析。将特别注意对名义上的无水矿物中的H和H/Ce进行SIMS分析，提供部分熔融过程中矿物脱水的直接证据，并监测实验中潜在的H2O损失。实验结果将对挥发分与海脊下熔融之间的关系提供强有力的约束，这对于研究熔融制度与产生的熔体的体积和组成之间的关系的地球化学家、表征海脊下的熔融和温度异常的地球物理学家以及寻求模拟地幔流动、熔融和大洋岩石圈发展之间的关系的地球动力学家来说，应该是有用的。更广泛的影响：实验结果将被纳入目前由PI汇编的实验矿物/熔体相平衡的LEPER(实验相关系库)数据库，并将提供熔融算法的关键数据，以研究H2O和CO2对地幔熔融的影响，目前可用限制条件很少。这项拟议的研究将支持明尼苏达大学的一名教职员工，为研究生提供培训，并将有助于本科生的教育。特别是，研究活动将通过NSF资助的REU网站(从地表到地心的地球流体)纳入本科教育机会，并将雇用本科生研究助理。

ABSTRACT 0623550 (HIRSCHMANN)Intellectual Merit: This works determines the influence of H2O and CO2 on deep melting beneath ocean ridges, with consequent importance to sub-ridge rheology, dynamics, geochemistry, and observational geophysics, is well recognized. Questions addressed include: (1) at what depth does volatile-induced melting begin beneath mid-ocean ridges, and what proportions of melt are generated, (2) what the relationship between melting and dehydration beneath ridges is, and (3) what influence does CO2 have in inciting carbonated silicate partial melting and dehydration deep beneath ridges. Work will involve high pressure and temperature multi-anvil experiments to determine the influence of small amounts of H2O and CO2 on deep melting and dehydration. Experimental targets are the solidus of peridotite with small amounts of added H2O at 3, 4, and 5 Gpa; the extent of melting and the extent of residue dehydration of slightly hydrous peridotite at 3 Gpa; and the effect of CO2 on melting and residue dehydration of slightly hydrous peridotite at 3 and 4 GPa. Run products will be analyzed with electron microscopy, vibrational spectroscopy, and secondary ion mass spectrometry (SIMS). Special attention will be paid to SIMS analysis of H and H/Ce in nominally anhydrous minerals, providing direct evidence of mineral dehydration during partial melting as well as monitoring for potential H2O loss from experiments. The experimental results will provide strong constraints on the relationship between volatiles and melting beneath ridges that should prove useful to geochemists investigating the relationship between melting regime and the volume and composition of melts produced, to geophysicists characterizing melting and temperature anomalies beneath ridges, and to geodynamicists seeking to model the relationship between mantle flow, melting, and development of the oceanic lithosphere. Broader Impacts: The experimental results will be incorporated into the LEPER (Library of Experimental PhasE Relations) database of experimental mineral/melt phase equilibria presently being compiled by the PI and will provide key data of the MELTS algorithm for the effect of H2O and CO2 on mantle melting, for which available constraints are presently sparse. The proposed research will support a faculty member at the University of Minnesota, provide training for a graduate student, and will aid education of undergraduates. In particular, the research activities will be integrated into opportunities for undergraduate education through an NSF-funded REU site (Fluids in the Earth from Surface to Core) and will employ undergraduate research assistants.