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。实验性岩石学和橄榄石托管熔体包含物中有强有力的证据表明，H2O在形成上毛岩浆的形成中很重要。然而，尽管基于这些数据的一部分地球化学和地球动力学模型的复杂性越来越高，但我们对俯冲板上高于俯冲楔形的地幔楔的P-T-XH2O条件的了解仍然存在一个主要差距。该项目将通过解决以下问题：1。来自TMVB的原始岩浆是否在含水条件下的地幔压力下用lherzolite，Harzburgite或辉石集合饱和？2。在最终用地幔组合的最终平衡的压力上，富含H2O的岩浆（可能是由减压熔化形成）的压力是否存在差异？这种差异可能与楔块内的俯冲衍生成分的运输和存储有关（例如，富含H2O的熔体从靠近板的靠近）.3。 H2O贫穷原始岩浆的地幔平衡温度和压力是否与弧线后面的较热地幔的对流和上升相一致。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的热结构进行比较？该项目将提供重要的约束，以评估流体 - 流通量和减压融化的相对作用，并在ARC中以及通过在温度下和H2O中的多种俯冲模型中的测试模型在ARC中的地球动力学模型进行测试，楔形相关关系将确定来自跨墨西哥火山带（TMVB）的五个原始熔体组合物（TMVB）的五个原始熔体组合物，这是地幔楔形压力下H2O含量的函数。对于原始弧岩浆而言，启动构图涵盖了K2O和H2O的大部分范围。将评估深层地壳分数结晶的组成效应，以测试是否可以将更多进化的成分“反校正”到主要的熔体成分。该项目将通过博士参与来整合研究和教育。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，Electron Probe，SEM）。一名本科生也将参与一个高级论文项目。结果的解释将涉及与墨西哥的一位年轻科学家Vlad Manea博士（UNAM，Juriquilla，Mexico和Caltech），他正在研究俯冲区的地球动力学建模。备受推崇的电子束仪器操作员约翰·多诺万（John Donovan）将参与开发可靠的方法来分析液压运行产品。