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有机硅熔体中的水的热力学特性。水是深度溶解在岩浆中的主要挥发性成分，当岩浆升至表面附近时，熔体几乎可以从熔体中几乎完全实现。这会导致岩浆上升岩浆的每单位质量的逐渐增加和冷却路径的修改。了解硅酸盐熔体中水的热力学特性对于对这些作用进行建模至关重要，因此对于理解岩浆迁移和喷发的动力学基础。通过这项研究实现了硅熔体中水热力学特性的两个主要进步：（1）在两个玄武岩玻璃中测量了由OH组和H2O分子引起的高温红外吸收峰（一种含有1.3 wt％水）（一种包含1.3 wt％的水，一个含有2.9 wt％的水；另一个含量为25 wt; andry ardros Inder andros Inshife and andros Inshife and a，AS的功能〜A AS 〜A，AS 〜A AS 〜A AS 〜A，AS 〜A AS 〜A AS 〜A 〜A 575℃。使用摩尔吸收系数的室温校准确定OH组和H2O分子的浓度。结果表明，OH组和H2O分子都是熔体中的等效物种，这与通过均匀反应H2O分子 + O = 2OH掺入水融合到有机硅中的想法是一致的。该产物受到玻璃过渡高于温度的升高，并且这两种熔体中的均质反应平衡彼此吻合良好。方程1N k = -4070（±470）/t + 3.68（±0.60）都重现了这两者。在熔体中获得的1NK值与先前在实验不确定性内的节奏融化的研究中获得的1N K值无法区分。这表明组成对天然岩浆熔体中均质反应的cal含量特性几乎没有影响。 （2）根据节奏熔体中水溶液在节奏熔体中的热量，基于从淬火玻璃的红外光谱中获得的水溶液的温度依赖性。在此处开发的模型中，假定水通过偶联反应H2O分子熔体 + O熔体= 2OH熔体（均质反应）和H2O蒸气= H2O分子熔体（异源反应）（异源反应），并假定这些熔体成分的理想混合。对ΔH°homo（p，t）收集到溶液数据集的非线性多重回归= 25.8±11.8 kJ，ΔS°homo（p，t）= 6.0±8.7 j/k和，ΔH°Hetero（1bar，t）= -25.3±4.8 kj/mol。从这些最佳值可以做出以下解释：溶液的热量在0.1 MPa时大约为零，并且随压力低于20 MPa而增加，其中热量的绝对值为负。在约20 mPa至100 mPa之间的压力下，由于放热异质反应和吸热性均质反应的平衡，溶液的热量大致降低（〜 -7±6 kJ/mol，850℃）。尽管估计的误差很大，但目前的结果表明，在10至100 MPa的压力下（对封闭系统岩浆气泡很重要的压力范围），气泡的量热效应导致温度下降仅<10℃。较少的

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。