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

高压、高温火成岩和变质环境的地球化学演化受到流体对地球固体矿物作用的强烈影响。这些影响的证据可以在矿物中的流体包裹体、元素和同位素移动、深部样品中的脉体和交代特征中找到，包括地幔捕虏体、钻石、弧岩浆、与被发掘的俯冲有关的岩石，以及范围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，因为深层致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，以地球内部致密流体的复杂假设为目标。预计这项研究的结果将为致密含水流体的新化学提供新的见解，同时有助于支持本科生和研究生的指导，继续进行国际合作，并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，在富水高压流体中，有越来越多的证据表明形成了聚合氧配位多核配合物。例子包括H6Si2O7二聚体、H5AlSiO6和类钠长石分子。人们对这些物种知之甚少，主要是因为它们的浓度在大多数上至中地壳热液环境中可以忽略不计；然而，在高P和高T下，聚合的物种可能更加丰富。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，允许溶解相对不溶于水的元素（例如，Al, Ti, Zr）。该项目将支持对假设络合的关键方面进行实验研究。热液活塞缸实验研究将针对硅，铝和碱之间的相互作用。这些成分在致密流体中浓度最高。高压（5- 20kbar）和高温（600-900°C）实验工作将包括：(1)使用锆-baddeleyite二氧化硅缓冲液校准极低硅浓度下的硅聚合；(2)基于刚玉溶解度随pH的函数测定H2O中水合铝形态；(3)通过测定刚玉溶解度随水溶液Si浓度的变化来研究Al-Si络合；(4)单长花岗岩- h2o体系流体组成表征；(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.