New Insights into Granite Petrogenesis From Experimental Studies of Hydrous Melting, Water Solubility, and Supercritical Fluids

从含水熔融、水溶性和超临界流体的实验研究对花岗岩岩石成因的新见解

• 批准号: 1347987
• 负责人: Craig Manning
• 金额: $ 43.47万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-04-01 至 2017-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1347987&HistoricalAwards=false
• 关键词: New; Insights; into; Granite; Petrogenesis

Granites are one of our planet's most important rocks. They are a central component of the continental crust, which carries nearly all information in the geologic record older than the most recent 200 million years of earth history. These rocks help identify past sites of plate convergence. And they may have been among the first rocks to form during earth?s early evolution, perhaps as early as within 300 million years of Earth's origin. Yet despite their importance, there remains surprising controversy about the origin of granitic rocks. We know that water is required to create granitic magmas. But petrologists do not agree on the source of this water ? the widely accepted model is that water is delivered by hydrous minerals that become unstable in the melting region; however, this fails to explain key aspects of granite genesis and is inconsistent with more general models of convergent-margin magmatism in the continental crust. An alternative is that granites are generated during open-system melting in the continental crust, and that migrating deep-crustal fluids facilitate granite creation. However, the basic chemical properties of such fluids are poorly understood, hindering proper testing of the alternative hypothesis. This project seeks to address this problem through new experimental constraints on the role of water-rich fluids in the genesis of granites.The work will exploit hydrothermal piston-cylinder methods developed at UCLA, in which large volumes of H2O can be sealed and retained in noble metal capsules. Preliminary investigations demonstrate that textures diagnostic of each phase region in simple mineral-H2O or rock-H2O binaries can reproducibly be obtained. Where ambiguous, the textural interpretations can be checked with simple trace-element monitors that independently identify liquid, vapor, or liquid+vapor fields. When deployed together, accurate and precise isobaric phase relations across full T-XH2O binaries can now be obtained. Three lines of investigation will be pursued. The first will determine phase relations in albite-H2O and related binaries. We will first complete preliminary studies of albite-H2O described herein. The work maps isobaric temperature-composition relations across the full binary, including solidus, liquids, crystal solubility in H2O, and the liquid+vapor miscibility gap and its closure. When binaries at different pressures are combined, the critical curve and second critical end point can be established to previously unobtainable precision and accuracy. The studies will be expanded to the jadeite-H2O and nepheline-H2O binaries, forming a foundation for modeling liquid-H2O interactions in key parts of the system NaAlSiO4-SiO2-H2O. In the second experimental program, we will build on the mineral-H2O binaries by investigating the haplogranite-H2O system. Finally, we will examine the change in phase relations when H2O activity is reduced by addition of CO2 or alkali halides. Data from each set of experiments will be used as the basis for thermodynamic models of H2O-silicate mixing to establish a theoretical foundation for understanding, for the first time, the topologies of liquid-vapor miscibility gaps, their links to hydrous melting, and the thermodynamics of supercritical silicate melt-H2O fluid in granitic systems. When complete, the work will lead to new understanding of the role of aqueous fluids in granite petrogenesis, which will inform models of convergent margin magmatism and evolution of the continental crust.

花岗岩是地球上最重要的岩石之一。它们是大陆地壳的核心组成部分，承载着比最近2亿年地球历史更古老的地质记录中的几乎所有信息。这些岩石有助于确定过去板块聚合的地点。它们可能是地球上最早形成的岩石之一？地球的早期演化，也许早在地球起源的3亿年内。然而，尽管它们很重要，但关于花岗岩的起源仍然存在令人惊讶的争议。我们知道花岗岩岩浆的形成需要水。但岩石学家对这些水的来源意见不一？普遍接受的模型是，水是由在熔融区变得不稳定的含水矿物输送的;然而，这无法解释花岗岩成因的关键方面，也与大陆地壳会聚边缘岩浆活动的更一般模型不一致。另一种解释是花岗岩是在大陆地壳开放系统熔融过程中生成的，迁移的地壳深部流体促进了花岗岩的生成。然而，这些流体的基本化学性质知之甚少，阻碍了备择假设的正确检验。该项目旨在通过对富水流体在花岗岩成因中的作用的新实验限制来解决这一问题。这项工作将利用加州大学洛杉矶分校开发的热液活塞缸方法，其中大量的H2O可以密封并保留在贵金属胶囊中。初步研究表明，在简单的矿物-水或岩石-水二元系统中，可以重复地获得每个相区的纹理诊断。在不明确的地方，可以用简单的示踪元素监测器来检查纹理解释，这些监测器独立地识别液体、蒸汽或液体+蒸汽场。当一起部署时，现在可以获得整个T-XH 2 O双星的准确和精确的等压相位关系。将进行三方面的调查。第一个将确定在钠长石-H2O和相关的双星的相位关系。我们将首先完成本文所述的钠长石-H2O的初步研究。这项工作绘制了整个二元系的等压温度-组成关系，包括固相线、液体、晶体在H2O中的溶解度，以及液体+蒸汽的溶解度间隙及其闭合。当不同压力下的二元化合物组合时，临界曲线和第二临界终点可以建立到以前无法获得的精确度和准确度。这些研究将扩展到硬玉-H2O和霞石-H2O双星，为模拟NaAlSiO 4-SiO2-H2O系统关键部分的液体-H2O相互作用奠定基础。在第二个实验计划中，我们将建立在矿物-H2O双星通过调查的haplogranite-H2O系统。最后，我们将研究当H2O活性通过加入CO2或碱金属卤化物而降低时相关系的变化。从每一组实验的数据将被用来作为水-硅酸盐混合的热力学模型的基础，建立一个理论基础，为理解，第一次，液体-蒸汽的可渗透性差距的拓扑结构，它们的联系，含水熔融，超临界硅酸盐熔体-H2O流体在花岗岩系统的热力学。完成后，这项工作将导致对花岗岩岩石成因中含水流体作用的新认识，这将为会聚边缘岩浆作用和大陆地壳演化的模型提供信息。