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.

智力优点。实验岩石学和橄榄石熔体包裹体强有力的证据表明，H2O 在超俯冲带镁铁质岩浆的形成中发挥着重要作用。然而，尽管部分基于这些数据的地球化学和地球动力学模型日益复杂，但我们对俯冲板块上方地幔楔中岩浆生成的 P-T-XH2O 条件的了解仍然存在重大差距。该项目将通过解决以下问题来测试有关弧岩浆生成的一些基本想法：1。在含水条件下的地幔压力下，TMVB 的原始岩浆是否会饱和二辉橄榄石、方辉橄榄岩或辉石岩组合？2．富水岩浆（可能由熔剂熔化形成）和贫水岩浆（可能由减压熔化形成）最后与地幔组合达到平衡的压力是否存在差异？这种差异可能与楔内俯冲衍生成分的运输和储存有关（例如，富含 H2O 的熔体是否来自靠近板片的地方）3。贫水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相一致？4。平衡温度和压力如何与基于 2D 和 3D 地球动力学模型的地幔楔热结构预测进行比较？该项目将为评估弧中流体通量和减压熔融的相对作用以及测试地球动力学模型提供重要约束通过提供地幔楔内不同深度的温度和 H2O 含量数据来研究俯冲系统。将确定来自跨墨西哥火山带的五种原始熔体成分的液相线相关系（TMVB）作为地幔楔压力下 H2O 含量的函数。原始弧岩浆的初始成分涵盖了 K2O 和 H2O 的大部分全球范围。将评估深部地壳分步结晶（例如母体玄武岩）的成分影响，以测试更多演化的成分是否可以“反向校正”为初级熔体成分。更广泛的影响。该项目将通过博士的参与将研究和教育结合起来。俄勒冈大学的学生。学生将参与实验研究的各个方面，并将学习一系列现代分析和成像技术（FTIR、电子探针、SEM）。本科生还将参与高级论文项目。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、墨西哥朱里基拉和加州理工学院）的合作，他正在研究俯冲带的地球动力学模型。约翰·多诺万 (John Donovan) 是一位备受推崇的电子束仪器操作员，他将参与开发用于分析含水运行产物的可靠方法。