Aqueous Aluminosilicate Polymers: Transport Agents in Crustal and Mantle Fluids?

地壳和地幔中流体的运动改变了岩石的成分。地质学家在各种尺度上看到了这些变化的证据，从充满矿物的微裂缝到圣海伦斯火山等火山。然而，要评估需要多少流量才能产生观察到的变化是极其困难的，主要是因为我们对形成岩石的矿物如何在高压和高温下溶解在地质流体中知之甚少。这个项目将使用新的实验方法来量化矿物在地质流体中的溶解度。完成这项工作的关键是最近认识到水中的二氧化硅是地质流体中的主要溶质，并且溶解的二氧化硅在高压和温度下显著聚合。铝很容易被结合到这些结构中，大大提高了它的溶解度。钛也表现出类似的行为。显然，这些元素的溶解得益于聚合物物种中结构环境的可获得性，这些环境在能量上比纯H2O提供的环境更有利。这些观察结果提出了一个简单的假设，即铝硅酸盐聚合物溶质可能是理解深部交代环境中元素活动性的关键。研究小组将进行的实验针对这一假设的三个组成部分。第一部分将通过研究地幔矿物(顽辉石+镁橄榄岩)在Na2O-Al_2O_3-SiO_2-H_2O流体中的溶解来研究当它们遇到新的化学环境时，这种结构的演化及其输运能力。第二条线将利用独居石和磷钨矿探索稀土元素在含聚合物流体中的溶解性。最后，该团队将通过重点研究方解石来研究聚合物溶质在地球挥发性循环中所起的作用。实验研究完成后，将测试一种控制地球深部交代环境中元素转移的新机制。

The movement of fluids in the Earth's crust and mantle changes rock composition. Geologists see evidence for these changes on a variety of scales, ranging from mineral-filled microcracks to volcanoes such as Mount St. Helens. However, it is extremely difficult to assess how much flow is required to produce the observed changes, chiefly because we know little about how the rock-forming minerals dissolve in geofluids at high pressures and temperatures. This project will quantify the solubility of minerals in geofluids using novel experimental approaches.Key to the completion of the work is the recent recognition that aqueous silica is a dominant solute in geofluids, and that dissolved silica polymerizes significantly at high pressures and temperatures. Aluminum is readily incorporated in these structures, dramatically raising its solubility. Titanium exhibits similar behavior. Evidently, dissolution of these elements is aided by the availability of structural environments in the polymeric species that are more energetically favorable than those offered by pure H2O. These observations suggest the simple hypothesis that the aluminosilicate polymeric solutes may hold the key to understanding element mobility in deep metasomatic settings. The experiments to be carried out by the research team target three components of this hypothesis. The first will address the evolution of such structures, and their transport capacity, when they encounter new chemical environments by studying dissolution of mantle minerals (enstatite + forsterite) in Na2O-Al2O3-SiO2-H2O fluids. A second line of investigation will explore the solubility rare-earth elements in polymer-bearing fluid, using the minerals monazite and xenotime. Finally, the team will investigate the role played by polymeric solutes in Earth's volatile cycling by focusing on calcite. When complete, the experimental research will offer a test of a new mechanism for controlling element transfer in Earth's deep metasomatic environments.