Thermodynamic, Petrologic, Geochemical and Isotopic Constraints on Metal (Re, Pt, Pd, Ir, Ru, Os and Other Metals) Mobility During Hydrothermal Serpentinization of Ultramafics

金属的热力学、岩石学、地球化学和同位素制约超镁铁岩热液循环系统中蛇纹石化作用过程中（Re、Pt、Pd、Ir、Ru、Os等金属）的活动性研究超镁铁岩热液蚀变过程中金属的活动性对地球科学中许多悬而未决的问题具有重要意义，如定量分析微量金属进出海洋的热液通量，量化俯冲和地幔交代过程中金属的溶解度和迁移过程，最终了解贱金属矿床的成因。 这里测试的假设是，蛇纹化热液流体可以导致显着的金属浸出超镁铁岩。 本文提出了一项为期三年的研究计划，其中结合理论和观测数据来研究超镁铁岩（400度）蛇纹石化过程中微量金属的地球化学行为。 特别强调的是获得高质量的数据，铂族元素（PGEs）和其他亲硫元素。 利用北方加州一个连续的方辉橄榄岩-蛇纹岩过渡露头研究了超镁铁岩热液蚀变过程中微量金属的活动性和迁移途径。详细的实地测绘，岩相学，同位素（Os，Sr和O）和地球化学数据相结合，估计金属动员的程度，变质温度和水岩比在蛇纹石化。相对金属迁移率的确定通过直接比较的金属含量之间的蛇纹方辉橄榄岩和新鲜的方辉橄榄岩和数量级的绝对估计的金属溶解度计算使用的水岩比的估计，作为约束的散装岩石的Os，Sr，或O同位素系统学。 的fO2，pH值，和主要和次要元素的组成和形态的蛇纹状热液流体推断相结合的热力学模型的非均相水平衡与基于场的限制平衡固相。 微量金属，特别是Re和PGEs的理论溶解度和形态，也计算使用适当的各种配合物的缔合常数，如果已知的。 这种观察和理论的结合提供了对热液流体的性质（例如，盐度、fO2、pH和温度）促进金属迁移。

AbstractThermodynamic, petrologic, geochemical, and isotopic constraints on metal (Re, Pt, Pd, Ir, Ru, Os, and other metals) mobility during serpentinization in ultramafic-hosted hydrothermal circulation systemsUnderstanding metal mobility during hydrothermal alteration of ultramafic rocks bears importance to a number of outstanding problems in the earth sciences, such as quantifying hydrothermal fluxes of trace-metals into or out of the ocean, quantifying the solubilities and transport processes of metals during subduction and mantle metasomatism, and finally, understanding the genesis of base metal ore deposits. The hypothesis that is tested here is that serpentinizing hydrothermal fluids can result in significant leaching of metals from ultramafic lithologies. A three-year study, in which theoretical and observational data are combined to investigate the geochemical behavior of trace metals during the serpentinization of ultramafic lithologies (at temperatures 400 o), is proposed. Particular emphasis is placed on obtaining high quality data for the platinum group elements (PGEs) and other chalcophile elements. The mobility and transport pathways of trace metals during hydrothermal alteration of ultramafic rocks are investigated using a continuous harzburgite to serpentinite transition outcrop in northern California. Detailed field mapping, petrography, and isotopic (Os, Sr, and O) and geochemical data are combined to estimate the degree of metal mobilization, metamorphic temperatures, and water-rock ratios during serpentinization. Relative metal mobilities are determined by direct comparison of the metal contents between serpentinized harzburgites and fresh harzburgites and order-of-magnitude absolute estimates of metal solubilities are calculated using estimates of the water-rock ratio, as constrained by bulk-rock Os, Sr, or O isotopic systematics. The fO2, pH, and major- and minor-element composition and speciation in the serpentinizing hydrothermal fluids are inferred by combining thermodynamic modeling of heterogeneous aqueous equilibria with field-based constraints on equilibrium solid phases. The theoretical solubilities and speciations of trace metals, particularly of Re and the PGEs, are also calculated using appropriate association constants for various complexes, if known. This integration of observation and theory provides a better understanding of what properties of hydrothermal fluids (e.g., salinity, fO2, pH, and temperature) facilitate metal transport.