Experimental Investigation of Magma Generation in Subduction Zones: Hydrous Liquidus Phase Relations of Primitive Magmas from the Trans-Mexican Volcanic Belt

俯冲带岩浆生成的实验研究：跨墨西哥火山带原始岩浆的含水液相相关系

• 批准号: 0739065
• 负责人: Paul Wallace
• 金额: $ 30万
• 依托单位: University of Oregon Eugene
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-01 至 2012-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0739065&HistoricalAwards=false
• 关键词: Experimental; Investigation; Magma; Generation; Subduction

Intellectual Merit. There is strong evidence from experimental petrology and olivine-hosted melt inclusions that H2O is important in the formation of supra-subduction zone mafic magmas. However, despite the increasing sophistication of geochemical and geodynamic models based in part upon these data, there is still a major gap in our knowledge of the P-T-XH2O conditions of magma generation in mantle wedges above subducting slabs. This project will test some fundamental ideas about arc magma generation by addressing the following questions:1. Do primitive magmas from the TMVB saturate with a lherzolite, harzburgite or pyroxenite assemblage at mantle pressures under hydrous conditions?2. Are there differences in the pressures at which H2O-rich magmas (probably formed by flux melting) and H2O-poor magmas (probably formed by decompression melting) last equilibrated with a mantle assemblage? Such differences could relate to transport and storage of subduction derived components within the wedge (e.g. do H2O-rich melts derive from closer to the slab).3. Are mantle equilibration temperatures and pressures for the H2O-poor primitive magmas consistent with advection and upwelling of hotter mantle from behind the arc?4. How do equilibration temperatures and pressures compare with predictions for the thermal structure of the mantle wedge based on 2D and 3D geodynamic models?This project will provide important constraints for evaluating the relative roles of fluid-flux and decompression melting in arcs and for testing geodynamic models of subduction systems by providing data on temperatures and H2O contents at various depths within the mantle wedge.Liquidus phase relations will be determined for five primitive melt compositions from the Trans-Mexican Volcanic Belt (TMVB) as a function of H2O content at mantle wedge pressures. Starting compositions span much of the global range of K2O and H2O for primitive arc magmas. Compositional effects of deep crustal fractional crystallization such parental basalts will be evaluated to test whether more evolved compositions can be "back-corrected" to primary melt compositions.Broader Impacts. This project will integrate research and education through the involvement of a Ph.D. student at the University of Oregon. The student will participate in all aspects of the experimental research and will learn a spectrum of modern analytical and imaging techniques (FTIR, electron probe, SEM). An undergraduate student will also be involved in a senior thesis project. The interpretation of results will involve collaboration with a young scientist in Mexico, Dr. Vlad Manea (UNAM, Juriquilla, Mexico and Caltech), who is working on geodynamic modeling of subduction zones. John Donovan, a highly regarded electron beam instrument operator, will be involved in developing robust methods for analyzing hydrous run products.

智力优势。有强有力的证据，从实验岩石学和橄榄石为宿主的熔融包裹体，H2O是重要的形成超俯冲带镁铁质岩浆。然而，尽管越来越复杂的地球化学和地球动力学模型的基础上，这些数据的一部分，仍然有一个主要的差距，在我们的知识的P-T-XH 2 O的条件下，岩浆生成的地幔楔俯冲板。本计画将借由解决下列问题来验证一些关于弧岩浆生成的基本观念：1。原始岩浆从TMVB饱和与二辉橄榄岩，辉橄榄岩或辉石岩组合在地幔压力下的含水条件？2.富H2O岩浆（可能由熔剂熔融形成）和贫H2O岩浆（可能由减压熔融形成）最后与地幔组合平衡的压力是否存在差异？这种差异可能与俯冲衍生成分在楔内的运输和储存有关（例如，富H2O熔体是否来自更靠近板片的地方）。贫H2O原始岩浆的地幔平衡温度和压力是否与弧后较热地幔的平流和上涌一致？4.平衡温度和压力与基于二维和三维地球动力学模型的地幔楔热结构预测相比如何？通过提供地幔楔内不同深度的温度和H2O含量的数据，该项目将为评价弧中流体通量和减压熔融的相对作用以及测试俯冲系统的地球动力学模型提供重要的约束条件，将确定跨墨西哥火山带（TMVB）五种原始熔体成分的液相线相位关系，作为地幔楔压力下H2O含量的函数。原始弧岩浆的起始成分跨越了K2 O和H2O的全球范围。将评估深地壳分离结晶的成分效应，例如母玄武岩，以测试是否可以将更多演化的成分“反向校正”为原始熔体成分。该项目将通过一名博士的参与，将研究和教育结合起来。俄勒冈州大学的学生。学生将参与实验研究的各个方面，并将学习现代分析和成像技术（FTIR，电子探针，SEM）的光谱。一名本科生也将参与一个高级论文项目。对结果的解释将涉及与墨西哥年轻科学家Vlad Manea博士（墨西哥国立自治大学、墨西哥Juriquilla和加州理工学院）的合作，他正在研究俯冲带的地球动力学建模。约翰多诺万，一个高度重视的电子束仪器操作员，将参与开发强大的方法分析含水运行产品。