Melting of Carbonated MORB-like Eclogite and Genesis of Ocean Island Basalts

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的，海洋岛屿玄武岩（OIB）的化学反映了地球地幔成分和过程的复杂性。同位素和微量元素地球化学研究表明，地幔中OIB的母岩是不均匀的。然而，在OIBs的主要元素不均匀性的情况下，并没有完全理解的OIBs的主要元素组成的全谱迄今为止还没有产生的实验室实验。特别是，携带再生地壳同位素特征的OIB的主要元素组成不能与现有的俯冲洋壳熔融实验相协调。这个建议是为了测试是否熔融俯冲洋壳，在富CO2流体或碳酸盐的存在下，产生岩浆（部分熔融的地幔）的主要元素组成类似于碱性OIB。其目的是约束的主要和微量元素组成的碳酸盐玄武岩榴辉岩的硅酸盐部分熔体，以及通过与地幔橄榄岩反应，这种熔体的成分演化。实验将在2至4 GPa的压力范围内进行。特别是，实验将进行解决以下基本问题：（1）在CO2的存在下，硅过剩榴辉岩的硅酸盐部分熔体的组成是什么，碳酸盐地壳可以作为碱性OIB的根源？(2)如何榴辉岩+CO2衍生的熔体组成的变化，由于与浅地幔，亏损辉橄榄岩的相互作用？(3)在板内玄武岩的成因中，再循环碳酸盐结壳的贡献是什么？(4)产生碱性OIB的合理条件（深度/温度/源成分）是什么？在这项工作中，将进行实验室实验，以模拟高压，高温条件下的岩浆生成过程的海洋岛屿。将使用光学和电子显微镜、电子探针显微分析和质谱分析等成熟技术对部分熔融淬火岩石进行分析。这些结果将进一步加深对玄武岩（构成洋底的主要岩石）成因的理解，并将增加非均质地幔岩石熔融与深部碳循环的联系。其结果将与固体地球科学广泛领域的其他姐妹学科相结合，这些学科试图捕捉地球地幔中的复杂过程，特别是玄武岩源区的复杂过程。这项工作将支持莱斯大学新成立的实验岩石学实验室和一名新教师。研究还将涉及研究生和本科生研究人员的教育和培训。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)Chemistry of oceanic island basalts (OIBs) reflects the complexity of compositions and processes in the Earth's mantle. Isotope and trace element geochemistry have established that parent lithologies of OIBs in the Earth's mantle are heterogeneous. However, the case of major element heterogeneity in OIBs is not completely understood as the full spectrum of major element compositions of OIBs have so far not been produced by laboratory experiments. Especially, the major element compositions of OIBs that carry isotopic signatures of recycled crust cannot be reconciled with existing melting experiments on subducted oceanic crust. This proposal is to test whether melting of subducted oceanic crust, in the presence of CO2-rich fluids or carbonates, produces magmas (partial melts of the Earth's mantle) with major element compositions similar to alkalic OIBs. The aim is to constrain the major and trace element compositions of silicate partial melts derived from carbonated basaltic eclogite, and the compositional evolution of such melts through reaction with mantle peridotite. The experiments will be performed at a pressure range of 2 to 4 GPa. In particular, the experiments will be performed to address the following fundamental questions: (1) What are the compositions of silicate partial melts of silica-excess eclogite in the presence of CO2 and can carbonated crust act as a root source of alkalic OIBs? (2) How do eclogite+CO2-derived melt compositions change owing to interaction with shallow mantle, depleted harzburgite? (3) What is the contribution of recycled carbonated crust in the origin of intraplate basalts? (4) What are the plausible conditions (depths/temperatures/source compositions) of generation of alkali OIBs? In this work, laboratory experiments will be conducted to simulate high pressure, high temperature conditions relevant for magma generation processes beneath oceanic islands. Analysis of the partially molten quenched rocks will be carried out using well established techniques of optical and electron microscopy, electron probe microanalysis, and mass spectrometry. The obtained results will further the understanding of genesis of basalts (the dominant rock that makes up the ocean floor) and will add to link melting of heterogeneous mantle rocks and deep carbon cycle. The results will be integrated with other sister-disciplines in the broad field of solid Earth science that seek to capture the complex processes in the Earth's mantle in general and in the source regions of basalts in particular. The work will support a newly established experimental petrology laboratory and a starting faculty member at Rice University. The research will also involve education and training of graduate and undergraduate researchers.