Experimental investigation of deep fluids of the lower crust and subduction zones

我们作为一个社会所面临的最大的地质灾害之一是与俯冲带有关的大地震和火山爆发，在俯冲带中，两个构造板块发生碰撞。这两种灾害类型都受到深层富水流体的存在和流动的强烈影响。在俯冲带地震的情况下，当岩石下降到地幔中时，这些流体被释放出来，它们大大改变了引起地震的变形的速率和类型。在火山爆发的情况下，同样的流体在覆盖的板块中运作，引发熔化，并最终在地表产生大规模的爆炸性喷发。然而，这些流体及其产生的熔体的化学性质仍然知之甚少，主要是因为它们必须在实验室中进行研究的条件非常具有挑战性。该项目将利用加州大学洛杉矶分校开发的方法来表征这些深层流体和熔体，以及它们如何溶解和运输物质。这些数据和新模型将为这些深部流体的化学和性质提供前所未有的见解，这些流体在俯冲系统造成的危害中占据如此突出的地位。作为该项目的一部分，两名研究生将接受指导，加州大学洛杉矶分校的实验实验室将在加州大学洛杉矶分校的大型科学推广活动中举办实践演示。这项工作的所有结果将通过纳入实验相关系图书馆而提供给地球科学界的其他人。所产生的数据和模型将为国际科学家提供服务，以研究流体在高压地质和地球物理过程中的作用。这项工作将涉及三项旨在提高对深部流体-岩石相互作用的理解的实验研究。第一个将围绕NaAlSi3O8-H2O系统构建，有和没有NaCl。该化学体系是深部富硅酸盐流体的一个有用模型。实验将侧重于相关系和热力学数据，允许表征这些流体的稳定性，它们共存的矿物质，以及是什么触发它们分解成单独的流体。第二个项目的目的是提供实验的限制，在深层流体中发现的个别溶解的物种。我们将使用一个新的实验设计，调查矿物饱和面的组成范围很广。该项目将侧重于溶解的镁和钙，这是最相关的流体地幔在俯冲带的相互作用。第三个项目将联合收割机实验与新的建模相结合，以研究含盐深层流体中的含水二氧化硅。基于H2O-NaCl溶液密度的石英溶解度修正模型将扩展到其他盐-H2O体系。石英溶解度的新实验将进行沿着水-盐二元系，并在H2O-NaCl-CO2三元系。这些数据提供了强大的约束解决方案密度，并可用于约束状态方程的含盐深部流体，从简单的二进制与H2O，更复杂的多组分系统，预计在地壳深部和上地幔。这些研究的最终结果将是为更广泛的地球科学界提供新的数据和模型。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Among the greatest geologic hazards we face as a society are the large earthquakes and volcanic eruptions associated with subduction zones, where two tectonic plates collide. Both hazard types are strongly influenced by the presence and movement of water-rich fluids at great depth. In the case of subduction-zone earthquakes, such fluids are liberated as rocks descend into the mantle, and they substantially modify the rates and style of the deformation that give rise to earthquakes. In the case of volcanic eruptions, the same fluids operate in the overriding plate to trigger melting, and ultimately to power massive, explosive eruptions at the surface. Yet the chemical properties of these fluids and the melts they produce remains very poorly understood, chiefly because the conditions at which they must be studied are quite challenging to generate in the laboratory. This project will exploit methods developed at UCLA for characterizing these deep fluids and melts, and how they dissolve and transport matter. The data and new models will provide unprecedented insights into the chemistry and properties of these deep fluids that figure so prominently in the hazards posed by subduction systems. Two graduate students will be mentored as part of this project, and the experimental laboratory at UCLA will host hands-on demonstrations during large UCLA science outreach events. All results of this work will be available to the rest of the geoscience community via incorporation in the Library for Experimental Phase Relations. The data and models produced will serve an international community of scientists investigating the role of fluids in high pressure geologic and geophysical processes.The work will involve three experimental investigations aimed at improving understanding of deep fluid-rock interaction. The first will be built around the system NaAlSi3O8-H2O, with and without NaCl. This chemical system is a useful model for silicate-rich fluids at depth. Experiments will focus on phase relations and thermodynamic data, allowing characterization of the stability of these fluids, their coexisting minerals, and what triggers their unmixing into separate fluids. The aim of the second project is to provide experimental constraints on the individual dissolved species found in deep fluids. We will use a new experimental design to investigate a wide compositional range of mineral saturation surfaces. The project will focus on dissolved Mg and Ca, which are most relevant to fluid-mantle interactions in subduction zones. The third project will combine experiments with new modeling to investigate aqueous silica in salty deep fluids. A modified model of quartz solubility based the densities of H2O-NaCl solutions will be extended to additional salt-H2O systems. New experiments on quartz solubility will be conducted along H2O-salt binaries, and in the H2O-NaCl-CO2 ternary. The data offers robust constraints on solution density, and can be used to constrain equations of state of salt-bearing deep fluids ranging from simple binaries with H2O, to more complex multicomponent systems expected in the deep crust and upper mantle. The end result of these investigations will be new data and models available to the broader geoscience community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.