Collaborative Research: Solution Thermodynamics of Igneous Pyroxenes and Garnets

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。火山是熔岩在地球表面喷发的地方；它们既是主要的自然灾害，也是令人着迷的科学研究目标，因为它们是来自地球内部的信使，那里发生了岩石融化。然而，他们的信息被编码在熔岩的化学中，为了读取这个代码，我们需要将源区的化学和物理组成与产生的岩浆的数量和组成联系起来的工具。计算热力学(CT)已被证明是预测这些联系的重要工具，并已成为现代岩石学熔融和岩浆运移模拟的必要组成部分。数以千计的研究人员和学生利用CT(熔体、pMELTS和phMELTS软件包以及大量关于矿物和熔体热力学的工作)的主要研究人员以前的工作，他们的兴趣范围从火山喷发到从地球内部到大气和海洋的挥发物运输，再到矿床的形成。该项目资助加州理工学院和OFM Research的研究人员合作，改进和扩展石榴石和辉石的热力学模型，这两种矿物都存在于类地行星的地幔中。这项工作的动机是希望完成xMELTS软件包，这是一个CT工具，将允许在~40 Gpa的压力下模拟类地行星的部分融化。一旦完成，这一工具将使科学家能够定量评估地球上部1200公里以及月球、火星和木卫二等其他陆地天体中岩浆产生的化学成分。这一评估将帮助我们了解这些行星从形成到现在是如何在化学上进化的。根据这笔赠款开发的热力学模型和软件工具将迅速传播给研究界；它们将被纳入xMELTS和phMELTS，它们将被编程为网络服务，以便从OFM网站进行分布式计算访问，并将在基于Excel的应用程序中使用。人们期待拟议的工作将产生有助于计算基础设施的热力学模型，该基础设施在本科生和研究生的课堂上都得到了很好的利用，并将支持广泛的科学家社区的研究努力。此外，拟议的工作将支持研究生教育和培训。将石榴石和辉石模型纳入xMELTS对于橄榄岩和辉石岩主体成分的部分熔融的现实正演模拟至关重要。所提出的石榴石固溶体模型适用于含有少量Cr3+、Na、Fe3+和Ti4+的(Ca，Mg，Fe2+)3Al2Si3O12-(Mg，Fe2+)4Si4O12体系的成分，其中含有马来石。辉石模型将扩展SACK和Ghiorso模型[通式为(Na，Ca，Mg，Fe2+)(Mg，Fe2+，Ti4+，Fe3+)(Si，Al，Fe3+)2O6]，以包括CaCrAlSiO6和KAlSi2O6。石榴石模型将基于以前发表的石榴石热力学的低压模型，并将主要通过评估石榴石与尖晶石、石榴石-橄榄石和石榴石-辉石之间的交换平衡而扩展到更高的压力。辉石模型的扩展将主要根据辉石-尖晶石的交换平衡进行校准。在这两种情况下，文献数据都将根据需要补充新的实验。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Volcanoes are places where molten rock erupts on the surface of the Earth; they are both major natural hazards and fascinating targets for scientific study because they are messengers from the interior of our planet, where melting of rocks takes place. Their message, however, is encoded in the chemistry of lavas and in order to read that code we need tools that relate the chemical and physical make-up of the source region to the quantity and composition of magma generated. Computational thermodynamics (CT) has proven to be an essential tool for predicting these connections and has become a necessary component of modern petrologic modeling of melting and magma transport. Previous work by the lead investigators in CT (the MELTS, pMELTS, and phMELTS software packages and a substantial body of work on mineral and melt thermodynamics) is utilized by thousands of researchers and students whose interests range from volcanic eruptions, to the transport of volatiles from the Earth's interior to its atmosphere and oceans, to the formation of ore deposits. This project funds collaboration between researchers at Caltech and OFM Research to improve and extend thermodynamic models of the minerals garnet and pyroxene, both of which occur in the mantles of terrestrial planets. The motivation for this effort is the desire to complete the xMELTS software package, a CT tool that will permit modeling of partial melting of terrestrial planets to pressures of ~40 GPa. Once completed, this tool will allow scientists to quantitatively assess the chemistry of magma production in the upper 1200 km of the Earth and throughout other terrestrial bodies like the Moon, Mars and Europa. This assessment will help us understand how these planets have evolved chemically since their formation to the present day. The thermodynamic models and software tools developed under this grant will be rapidly disseminated to the research community; they will be incorporated into xMELTS and phMELTS, they will be programmed into web services for distributed computing access from the OFM website, and they will be made available for use in Excel-based applications. There is every expectation that the proposed work will result in thermodynamic models that contribute to a computational infrastructure that is well utilized in the classroom at both the undergraduate and graduate level, and will support the research efforts of a broad community of scientists. In addition, the proposed work will support graduate education and training.Incorporation of both the garnet and pyroxene models into xMELTS is essential for realistic forward modeling of partial melting in peridotite and pyroxenite bulk compositions. The proposed garnet solid solutions model will apply to compositions in the system (Ca,Mg,Fe2+)3Al2Si3O12-(Mg,Fe2+)4Si4O12 containing minor amounts of Cr3+, Na, Fe3+, and Ti4+, which is inclusive of majorite. The pyroxene model will extend the Sack and Ghiorso model [with general formula (Na,Ca,Mg,Fe2+)(Mg,Fe2+,Ti4+,Fe3+)(Si,Al,Fe3+)2O6] to include the components CaCrAlSiO6 and KAlSi2O6. The garnet model will be based on previously published low-pressure models of pyralspite garnet thermodynamics and will be extended to higher-pressures principally by evaluation of exchange equilibria between garnet and spinel, garnet-olivine, and garnet-pyroxene. The pyroxene model extension will be calibrated mainly from exchange equilibria involving pyroxene-spinel. In both cases, literature data will be supplemented with new experiments as required.