In situ spectroscopic study of the thermodynamic properties of water-bearing magmas

含水岩浆热力学性质的原位光谱研究

• 批准号: 11640480
• 负责人: YAMASHITA Shigeru
• 金额: $ 2.24万
• 依托单位: Okayama University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640480/
• 关键词: magma; water; silicate melt; thermodynamics; infrared spectroscopy; 高温高圧実験; 反応エネルギー; 含水マグマ; 相平衡; 溶解反応エネルギー

The goal of this research was to quantify the thermodynamic properties of water dissolved in silicate melts. Water is a major volatile component dissolved in magma at depth, and is capable of nearly complete exsolution from the melt (but being sustained in the melt as vapor bubbles) when the magma rises to near the surface. This causes a progressive increase of the volume per unit mass of the rising magma and a modification of the cooling path. Knowledge of the thermodynamic properties of water in silicate melts is critical for modeling these effects, and thus fundamental for understanding the dynamics of magma migration and eruption. Two major advances in the quantification of the thermodynamic properties of water in silicate melts have been achieved through this research: (1) High temperature infrared absorption peaks due to OH group and H2O molecule were measured in two basalt glasses (one containing 1.3 wt% water, one containing 2.9 wt% water; the anhydrous composition remains unch … More anged) as a function of temperature between 〜 25℃ and 575℃. The concentrations of OH group and H2O molecule were determined using the room-temperature calibrations of the molar absorption coefficients. The results show that both OH group and H2O molecule are equilibrium species in the melts, which is consistent with the idea that water is incorporated in a silicate melt through homogeneous reaction H2O molecule + O = 2OH. The product is favored by increase of temperature above the glass transition, and the homogeneous reaction equilibria in these two melts show a good agreement with each other; an equation 1n K = -4070(±470)/T + 3.68(±0.60) reproduces both. The 1n K values obtained in the melts are not distinguishable from those obtained by previous studies in rhyolitic melts within experimental uncertainty. This suggests that there is little influence of composition on the calorimetric properties of the homogeneous reaction equilibria in natural magmatic melts. (2) Heat of solution of water in rhyolite melts was thermodynamically modeled, on the basis of the temperature dependence of water solubility in the melts obtained from infrared spectroscopy of the quenched glasses. In the model developed here, water was assumed to be dissoleved through a coupled reaction H2O molecule melt + O melt = 2OH melt (homogeneous reaction) and H2O vapor = H2O molecule melt (heterogeneous reaction), and ideal mixing of these melt components was assumed. A non-linear multiple regression to the solubility dataset converged upon ΔH° homo (P, T) = 25.8±11.8 kJ, ΔS° homo (P, T) = 6.0±8.7 J/K, and, ΔH° hetero (1bar, T) = -25.3±4.8 kJ/mol. From these optimum values, the following interpretations can be made: The heat of solution is approximately zero at 0.1 MPa, and increases with pressure below 〜 20 MPa, where the absolute value of the heat is negative. At pressures between 〜 20 MPa and 100 MPa, the heat of solution roughly levels out (〜 -7±6 kJ/mol at 850℃) as a result of the balance of the exothermic heterogeneous reaction and endothermic homogeneous reaction. Although error of estimation is large, the present results suggest that at pressures of 10 to 100 MPa (the pressure range important to closed system magma bubbling), the calorimetric effect of bubbling causes a temperature drop of only <10℃. Less

这项研究的目的是量化溶解在硅酸盐熔体中的水的热力学性质。水是溶解在深层岩浆中的主要挥发性成分，并且能够几乎完全从熔体中溶出（但以蒸气泡的形式维持在熔体中）。 ）当岩浆上升到接近地表时，这会导致上升岩浆的每单位质量的体积逐渐增加，并且冷却路径的改变对于模拟这些效应至关重要，和因此，通过这项研究，在定量硅酸盐熔体中水的热力学性质方面取得了两个重大进展，对于理解岩浆迁移和喷发的动力学具有重要意义：（1）由OH基团和H2O分子产生的高温红外吸收峰。在两种玄武岩玻璃（一种含有 1.3 wt% 水，一种含有 2.9 wt% 水；无水组合物保持未老化）中测量，作为温度的函数〜利用室温摩尔吸光系数校准测定了25℃和575℃下OH基团和H2O分子的浓度，结果表明OH基团和H2O分子在熔体中均为平衡态，这与熔体中的OH基团和H2O分子浓度一致。认为水通过均相反应 H2O 分子 + O = 2OH 结合到硅酸盐熔体中，通过将温度升高到玻璃化转变温度以上以及均相反应，有利于产物的产生。这两种熔体中的平衡显示出良好的一致性；方程 1n K = -4070(±470)/T + 3.68(±0.60) 再现了这两种熔体中获得的 1n K 值。先前对流纹岩熔体的研究在实验不确定性范围内获得了这一结果，这表明成分对天然岩浆熔体均相反应平衡的量热特性影响很小。 (2) 根据从淬火玻璃的红外光谱中获得的熔体中水溶解度的温度依赖性，对水在流纹岩熔体中的溶解热进行热力学建模。在此开发的模型中，假设水通过溶解。耦合反应 H2O 分子熔体 + O 熔体 = 2OH 熔体（均相反应）和 H2O 蒸气 = H2O 分子熔体（非均相反应），以及这些的理想混合假设溶解度数据集的非线性多元回归收敛于 ΔH° 均值 (P, T) = 25.8±11.8 kJ、ΔS° 均值 (P, T) = 6.0±8.7 J/K 和 ΔH。 ° hetero (1bar, T) = -25.3±4.8 kJ/mol 根据这些最佳值，可以做出以下解释： 溶解热大约为零。 0.1 MPa，并且随着压力低于~ 20 MPa而增加，其中热量的绝对值为负。在~ 20 MPa和100 MPa之间的压力下，溶解热大致持平（850℃时~ -7±6 kJ/mol）。 ℃）是放热非均相反应和吸热均相反应平衡的结果，尽管估计误差很大，但目前的结果表明，在10至10℃的压力下。 100 MPa（对封闭系统岩浆鼓泡重要的压力范围），鼓泡的量热效应仅导致温度下降<10℃以下。

项目成果

Yamashita, S: "Heat of solution of water in rhyolite melt : constraints from water solubility measurements"EOS. 81. S433-S433 (2000)

Yamashita，S：“流纹岩熔体中水的溶解热：水溶性测量的限制”EOS。

Yamashita, S.: "Heat of solution of water in rhyolite melt: constraints from water solubility measurements."EOS. 81. S433 (2000)

Yamashita, S.：“流纹岩熔体中水的溶解热：水溶性测量的限制。”EOS。

山下 茂: "珪酸塩ガラス中の水の顕微赤外分光分析〜マグマ研究への応用"Jasco Report. 41・2. 15-18 (1999)

Shigeru Yamashita：“硅酸盐玻璃中水的微红外光谱分析 - 在岩浆研究中的应用”Jasco Report 41・2（1999）。

Yamashita, S: "Experiment study of the effect of temperature on water solubility in natural rhyolite melt to 100 MPa"Journal of Petrology. 40. 1497-1507 (1999)

Yamashita，S：“温度对 100 MPa 天然流纹岩熔体中水溶性影响的实验研究”岩石学杂志。

Yamashita, S.: "Micro-IR spectroscopy of water-bearing silicate glasses: an application to experimental petrology."Jasco Report. 41(in Japanese). 15-18 (1999)

Yamashita, S.：“含水硅酸盐玻璃的微红外光谱：在实验岩石学中的应用。”Jasco 报告。