Aqueous Aluminosilicate Complexing in Deep-Crustal and Upper-Mantle Fluids

流体对地球上固体矿物的作用强烈影响着高压、高温火成岩和变质环境的地球化学演化。这些效应的证据可以在矿物中的流体包裹体、元素和同位素位移以及深部环境样品中的矿脉和交代特征中找到，其中包括地幔包体、钻石、弧状岩浆和与俯冲有关的岩石，以及广泛的区域变质地体。不幸的是，高压流体-岩石相互作用的建模是困难的，因为深层、稠密流体的物理化学仍然高度不确定。该项目将支持一系列实验研究，目标是地球内部稠密流体的络合假说。预计这项研究的结果将为稠密水相流体的新型化学提供新的见解，同时有助于支持本科生和研究生的指导、持续的国际合作以及将结果纳入加州大学洛杉矶分校的高级岩石学课程。一个关键的问题是，在富含H2O的高压流体中，有越来越多的证据表明形成了聚合氧配位的多核络合物。例子包括H6Si2O7二聚体、H5AlSiO6和类钠长石分子。对这种物种的了解很少，主要是因为它们的浓度在大多数上到中地壳的热液环境中可以忽略不计；然而，在高P和T时，聚合物种可能要丰富得多。多核配合物具有潜在的重要性，因为它们提高了所有元素的溶解度。特别是，它们提供了配位环境，允许溶解原本在H2O中相对不溶解的元素(例如，Al、Ti、Zr)。该项目将支持对假设复杂的关键方面进行实验研究。热液活塞-圆柱体实验研究将针对硅、铝和碱之间的相互作用。这些组分在稠密流体中的浓度最高。高压(5-20kbar)和高温(600-900℃)的实验工作将包括：(1)使用锆石-斜晶石二氧化硅缓冲液校准极低硅浓度下的硅聚合；(2)基于刚玉的溶解度作为pH的函数，确定铝水合物在水中的形态；(3)通过测量刚玉的溶解度随硅水浓度的变化来研究铝-硅的络合作用；(4)表征钾长花岗石-水体系中的流体组成；以及(5)测定金红石在Na-Al-Si-H2O溶液中的溶解度。

The geochemical evolution of high-pressure, high-temperature igneous and metamorphic environments is strongly influenced by the effects of fluids on solid minerals in the Earth. Evidence for these effects can be found in fluid inclusions in minerals, elemental and isotopic shifts, and veins and metasomatic features in samples from deep settings, including mantle xenoliths, diamonds, arc magmas, and rocks associated with subduction that are exhumed, as well as a wide range of regional metamorphic terranes. Unfortunately, modeling of high-pressure fluid-rock interaction is difficult because the physical chemistry of deep, dense fluids remains highly uncertain. This project will support a set of experimental studies that target a complexing hypothesis for dense fluids in the interior of the Earth. It is expected that the results from this study will provide new insights into the novel chemistry of dense aqueous fluids, while helping support the mentoring of undergraduate and graduate students, continued international collaboration and incorporation of the results into the UCLA's Advanced Petrology class. A key problem is that in H2O-rich high-pressure fluids there is growing evidence for formation of polymerized oxygen coordinated polynuclear complexes. Examples include H6Si2O7 dimers, H5AlSiO6, and albite-like molecules. Such species are poorly understood, chiefly because their concentrations are negligible in most upper- to mid-crustal hydrothermal settings; however, at high P and T, polymerized species may be much more abundant. Polynuclear complexes are potentially important because they elevate solubility of all elements. In particular, they provide coordination environments that permit dissolution of elements that are otherwise relatively insoluble in H2O (e.g., Al, Ti, Zr). This project will support an experimental investigation into key aspects of the hypothesized complexing. Hydrothermal piston-cylinder experimental studies will target interactions between Si, Al, and alkalis. These components are present at the highest concentrations in dense fluids. The high-pressure (5-20 kbar) and high-temperature (600-900°C) experimental work will include: (1) calibration of Si polymerization at very low Si concentration using the zircon-baddeleyite silica buffer; (2) determination of Al hydrate speciation in H2O based on corundum solubility as a function of pH; (3) investigation of Al-Si complexing through measurement of corundum solubility changes with aqueous Si concentration; (4) characterization of fluid compositions in the haplogranite-H2O system; and (5) determination of rutile solubility in Na-Al-Si-H2O solutions.