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，大洋岛玄武岩化学(OIB)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，地幔中大洋钻探的母岩性质是非均质的。然而，由于到目前为止还没有通过实验室实验获得海洋石油储备的主要元素组成的全谱，因此对海洋石油储备中主要元素的不均一性的情况还没有完全了解。特别是，具有再循环地壳同位素特征的OIBs的主要元素组成与现有的俯冲洋壳熔融实验不相符。这项提议是为了测试俯冲洋壳在富含二氧化碳的流体或碳酸盐存在的情况下熔融是否会产生主要元素成分类似于碱性OIB的岩浆(地球地幔的部分熔融)。目的是通过与地幔橄榄岩的反应，控制碳酸盐化玄武岩榴辉岩硅酸盐部分熔体的主量元素和微量元素组成，以及此类熔体的成分演化。实验将在2到4 Gpa的压力范围内进行。具体来说，这些实验将被用来解决以下基本问题：(1)在CO2存在的情况下，硅酸盐过量榴辉岩的硅酸盐部分熔体的组成是什么，碳化地壳是否可以作为碱性OIB的根源？(2)榴辉岩+CO2衍生的熔体成分是如何变化的，因为与浅地幔、亏损方辉橄榄岩的相互作用？(3)再生碳酸盐结壳在板内玄武岩成因中的贡献是什么？(4)碱性OIB生成的可能条件(深度/温度/源成分)是什么？在这项工作中，将进行实验室实验，以模拟与大洋岛屿下岩浆生成过程相关的高压、高温条件。对部分熔融的岩石进行分析将使用成熟的光学和电子显微镜、电子探针显微分析和质谱分析技术。这些结果将进一步加深对玄武岩(构成洋底的主要岩石)成因的认识，并将不均匀地幔岩石的熔融与深层碳循环联系起来。这些成果将与固体地球科学这一广泛领域的其他姊妹学科结合起来，力求捕捉地球地幔中的复杂过程，特别是玄武岩源区的过程。这项工作将支持一个新成立的实验岩石学实验室和赖斯大学的一名初任教员。这项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.