Collaborative Research: Partial Melting of the Shallow Mantle from Thermodynamic Modeling of Minerals and Melt

这项拨款是为了完善和改进MELTS计划，以应用于与地幔部分熔融有关的问题。 MELTS是一个通用的热力学算法包，允许岩浆过程的正演模拟。 MELTS地幔熔融问题的应用产生了相当多的新的洞察过程中的部分熔融和熔体输送，特别是有关的子脊过程，但在MELTS的不完善阻碍了这些问题的应用。 在拟议的补助金期间，我们将解决这些缺陷，通过增加复杂的硅酸盐液体和辉石的热力学模型，并通过绑定产生的模型更强烈的高压矿物熔体相平衡。我们还将扩展MELTS的能力，使其能够应用于与地幔熔融过程相关的重要突出问题仍然存在的深度和条件。 其中包括（1）洋脊下较深的区域（4-6 GPa），在那里少量的挥发分被认为产生了对次洋脊过程的地球动力学和爆发的MORB的地球化学具有重要意义的小程度熔融;（2）俯冲带上方的地幔楔，在那里H2O和/或H2O+CO2在确定熔融的地点和样式方面起着重要作用。以及熔体的组成和体积。 MELTS中提出的改进将包括（1）将用于液体混合熵的模型从类矿物组分的分子混合之一改变为温度、压力和可变化学计量的组成依赖性聚合物单元的混合之一。(2)完成了我们已经开始的工作，即扩大辉石以纳入Cr，并重新校准辉石的热力学模型，重点是匹配高压辉石-液相平衡。（3）添加复杂的C-O-H流体，作为一个独立的相，溶解在硅酸盐液体中，以及相关的碳质矿物（碳酸盐，石墨，金刚石）。(4)用于校准的矿物-熔体相平衡实验数据库的持续扩展。(5)进行“地面实况”相平衡实验，以测试和改进原型模型。

This grant is to refine and improve the MELTS program for application to problems related to partial melting of the mantle. MELTS is a versatile package of thermodynamic algorithms that allows forward modeling of magmatic processes. Application of MELTS to mantle melting problems has yielded considerable new insight into processes of partial melting and melt transport, particularly related to sub-ridge processes, but imperfections in MELTS have hampered applications to these problems. During the proposed grant period, we will address these defects by increasing the sophistication of the thermodynamic models of silicate liquids and pyroxenes and by binding the resulting model more strongly to high pressure mineral-melt phase equilibria. We will also extend MELTS' capabilities to allow application to depths and conditions where important outstanding problems related to mantle melting processes remain. These include (1) the deeper regions beneath ridges (4-6 GPa), where small quantities of volatiles are believed to generate small-degree melts that have great significance to the geodynamics of sub-ridge processes and to the geochemistry of erupted MORB, and (2) the mantle wedge above subduction zones, where H2O and/or H2O+CO2 play a significant role in determining the locus and style of melting, and the composition and volume of melts. Proposed improvements in MELTS will include (1) changing the model for the entropy of mixing of the liquid from one of molecular mixing of mineral-like components to one of mixing of temperature, pressure and compositionally dependent polymeric units of variable stoichiometry. (2) Completing our already-initiated work of expanding pyroxenes to incorporate Cr and recalibrating the thermodynamic model for pyroxenes with an emphasis on matching high pressure pyroxene-liquid phase equilibria (3) Adding complex C-O-H fluids, both as a distinct phase and dissolved in silicate liquids, as well as associated carbonaceous minerals (carbonates, graphite, diamond). (4) Continuing expansion of the database of mineral-melt phase equilibria experiments used in calibration. (5) Conducting "ground-truthing" phase equilibria experiments to test and improve prototype models.