Experimental Investigation of H2O, Cl, CO2 and SO2 Solubilities in Rhyolite and Andesite Melts at Shallow Crustal Conditions

为了更好地了解岩浆脱气如何影响火山爆发和地球上许多金属矿床的生成，将通过实验测定挥发物水、二氧化碳、硫和氯在硅酸盐岩浆中的溶解度。像这样的挥发物对于地球地幔、地壳、大气和海洋储集层的演化；通过流体和岩浆在这些储集层内部和之间的化学流动性；以及与火山喷发和矿藏生成有关的岩浆脱气过程，具有根本的重要意义。岩浆输送挥发分的能力是挥发分在硅酸盐熔体中溶解度的直接函数，一旦超过这些挥发分溶解度，就有一个或多个流体相从熔体中逸出。目前对岩浆流体出溶的了解仅限于含有其中一种或两种挥发物的体系，因此拟议的研究将系统地研究：(1)(水、二氧化碳和氯)和(水、二氧化硫和氯)在流纹岩和安山岩熔体中的溶解度；(2)氯如何在这些具有重要地质意义的熔体和含有这些挥发物的流体之间分配。氯在硅酸盐熔体和流体之间的分配程度是特别令人感兴趣的，因为这种挥发物是岩浆的常见成分，它对成矿过程很重要，它的行为对岩浆脱气过程提供了关键限制，而且因为大气中的氯破坏了臭氧的稳定，并影响了其他大气过程。溶解度数据将通过在代表地壳浅层岩浆脱气的压力和温度条件下进行的水热实验产生，实验结果将用成熟的方法进行分析。这项拟议调查的学术价值来自于实验数据，这些数据涉及：(1)对硅酸盐熔体中挥发分溶解机理的解释，(2)允许计算挥发分溶解度和预测岩浆脱气过程的模型，以及(3)基于硅酸盐熔体包裹体(硅酸盐熔体包裹体是硅酸盐玻璃的微观样品，代表被困的硅酸盐熔体)的正在进行的岩浆脱气行为的地球化学调查。这些数据也将有助于研究氯对地球大气和气候的影响的模型。拟议中的调查也具有更广泛的意义，因为这些数据、它们与科学的相关性以及它们与社会的相关性将通过美国自然历史博物馆的展品和公共项目共享。科学研究的成果和重要性通过博物馆永久展厅的标本、电子媒体和其他媒体向公众展示；专注于地质过程的系列讲座；以及通过与参加NSF支持的本科生研究体验计划的暑期实习生的互动。

AbstractTo better understand how magmatic degassing influences explosive volcanic eruptions and the generation of many of Earth's metallic mineral deposits, the solubilities of the volatiles water, carbon dioxide, sulfur, and chlorine in silicate magmas will be determined experimentally. Volatiles like these are fundamentally important to the evolution of the Earth's mantle, crust, atmosphere, and ocean reservoirs; chemical mobility, via fluids and magmas, within and between these reservoirs; and magmatic degassing processes related to volcanic eruption and the generation of mineral deposits. The capacity of magmas to transport volatiles is a direct function of volatile solubilities in silicate melts, and once these volatile solubilities are exceeded one or more fluid phases exsolve from melts. Current understanding of magmatic fluid exsolution is limited to systems containing just one or two of these volatiles, thus the proposed study will investigate systematically: (1) the solubilities of (water, carbon dioxide, and chlorine) and (water, sulfur dioxide, and chlorine) in rhyolite and andesite melts, and (2) how chlorine is distributed between these geologically important melts and fluids containing these volatiles. The extent to which chlorine is distributed between silicate melt and fluids is of particular interest, because this volatile is a common component of magmas, it is important to mineralizing processes, its behavior provides key constraints on processes of magmatic degassing, and because chlorine in the atmosphere destabilizes ozone and affects other atmospheric processes.The solubility data will be generated through hydrothermal experiments conducted at pressure and temperature conditions that are representative of magmas that degas in the shallow crust, and the products of the experiments will be analyzed by well-established methodologies. The intellectual merit of the proposed investigation springs from the experimental data which are relevant to: (1) the interpretation of volatile solubility mechanisms in silicate melts, (2) models that allow computation of volatile solubilities and predict processes of magmatic degassing, and (3) ongoing geochemical investigations of magmatic degassing behavior based on studies of silicate melt inclusions (which are microscopic samples of silicate glass that are representative of trapped silicate melt). These data will also be useful for models addressing the impact of chlorine on Earth's atmosphere and climate.The proposed investigation also has broader significance because the data, their relevance to science, and their relevance to society will be shared through exhibits and public programs at the American Museum of Natural History. The results and importance of scientific research are presented to the general public through specimens, electronic media, and other media in the museum's permanent exhibition halls; lecture series focused on geologic processes; and through interactions with summer interns participating in an NSF-supported Research Experiences for Undergraduate Students program.