Defining the Hydrous Petrogenetic Grid: Experimental Constraints on Primitive Hydrous Magmas

对火山的研究，包括地球上产生火山的过程，是地球科学的一个重要组成部分。这种令人敬畏的地质过程经常扰乱人类活动，如航空航班，有时威胁到生活在火山中心附近的数百万人的生命。因此，我们对这一潜在致命现象的认识和理解关系重大。发生在破坏性板块边界（即俯冲带）的弧形地带的火山的一个重要方面是，水和二氧化碳等挥发性成分在高压和高温下岩石的原始熔化中所起的作用。这种熔融过程形成了岩浆（熔融岩石和晶体的混合物），最终在地表喷发成为熔岩。众所周知，H2O和CO2影响火山源岩的初始熔化温度，决定所产生岩浆的物理性质（如密度和粘度），并为爆炸性喷发（气体膨胀）提供燃料。这个项目的重点是研究这些挥发性成分对地幔熔融过程的化学影响。从这个项目中收集到的知识将有助于限制形成火山弧的岩浆的起源，它们最初的H2O和CO2含量，并将有助于我们对火山形成过程的全面理解。本实验研究将解决的具体问题是H2O对地幔条件下熔体二氧化硅活性的影响。虽然实验观察到，在含水条件下形成的地幔熔体含有明显较高的二氧化硅含量，并且在明显较低的温度下熔化，但基本关系仍然受到实验数据的限制。作为对现有限制的补充，本研究将使用一系列成分（基性到中间体）的实验来系统地测量P、T和可变流体（H2O-CO2）成分如何影响二氧化硅活性。所得数据将使热力学分析能够显示可能与上地幔处于平衡状态的含水熔体的范围，从而澄清H2O在原始熔体产生中的作用（或缺乏作用）。

The study of volcanoes, including the processes in the earth that give rise to them, is an important part of earth sciences. This often awe-inspiring geologic process often disrupts human activity such as airline flights, and sometimes threatens the lives of the millions of people that live near volcanic centers. Therefore, there is much at stake that depends on our knowledge and understanding of this potentially deadly phenomenon. One important aspect of volcanoes that occur in arcs at destructive plate boundaries (known as subduction zones) is the role that volatile components such as H2O and CO2 play in the original melting of rock at high pressure and temperature. This melting process forms the magmas (molten rock and crystal mixtures) that are eventually erupted at the surface as lavas. It is well known that H2O and CO2 influence the initial melting temperature of the source rocks of volcanoes, determine the physical properties of the resulting magma (such as its density and viscosity), and fuel explosive eruptions (gas expansion). This project is focused on the influence of these volatile components on the chemistry of the melting process in the Earth's mantle. The knowledge gleaned from this project will help constrain the origins of the magmas that form volcanic arcs, their initial H2O and CO2 contents, and will contribute to our overall understanding of the processes that create volcanoes.The particular question that will be addressed by this experimental study is the influence of H2O on the silica activity of melts at mantle conditions. While it has been experimentally observed that mantle melts formed under hydrous conditions contain significantly higher silica contents, and melt at significantly lower temperatures, the fundamental relationships remain poorly constrained by experimental data. As a complement to existing constraints, this study will use experiments over a range of compositions (mafic to intermediate) to systematically measure how P, T, and variable fluid (H2O-CO2) composition influence the silica activity. The resulting data will enable a thermodynamic analysis showing the range of hydrous melts that could have been in equilibrium with the upper mantle, and thus will clarify the role (or the lack thereof) of H2O in the generation of primitive melts.