Experimental calibration of the effect of H2O on plagioclase crystallization in basaltic melt at 200 MPa
Experimental calibration of the effect of H2O on plagioclase crystallization in basaltic melt at 200 MPa
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DOI：
10.2138/am.2012.4100
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发表时间：
2012-07
影响因子：
3.1
通讯作者：
R. Almeev;F. Holtz;J. Koepke;F. Parat
中科院分区：
文献类型：
--
作者：
R. Almeev;F. Holtz;J. Koepke;F. Parat
摘要在200 MPa下进行了少量水对以斜长石为液相的玄武质熔体液相线温度的影响的结晶实验。通过红外光谱法和卡尔-费歇尔滴定法测定的淬火玻璃中的H2O浓度范围为0.02至4.2重量% H2O。在200 MPa下的干液相线温度估计从实验在1大气压（H2O-自由）和从已知的压力依赖性的斜长石结晶温度。斜长石液相线温度上的水（表示为重量% H2O）的效果是非线性的，并随着熔体H2O浓度的增加而减少。根据我们的新的实验数据，可以经验地用以下公式预测：（TDRY-TWET）= 76.99·CH 0.71H·O其中CH·O是熔体中的水浓度（wt%），TDRY和TWET分别是无水和含水体系中斜长石的结晶温度。在这项研究中计算出的CH = O和液相线温度之间的关系对于从高铝玄武岩到玄武安山岩的一系列玄武岩成分都是有效的。预测的斜长石的液相线凹陷与以前的模型预测的橄榄石液相线曲线的经验方程的组合是有用的，以确定液相线温度在各种含H2O的玄武岩系统中，斜长石或橄榄石是液相线相。
Abstract Crystallization experiments were conducted at 200 MPa to determine the effect of small amounts of H2O on the liquidus temperature of basaltic melts in which plagioclase is the liquidus phase. The H2O concentrations in the quenched glasses, determined by infrared spectroscopy and Karl-Fischer titration, ranged from 0.02 to 4.2 wt% H2O. The dry liquidus temperature at 200 MPa was estimated from experiments at 1 atm (H2O-free) and from the known pressure dependence of plagioclase crystallization temperature. The effect of water (expressed as wt% H2O) on the plagioclase liquidus temperature is nonlinear and diminishing with increasing melt H2O concentrations. According to our new experimental data, it can be empirically predicted with following equation: (TDRY-TWET) = 76.99·CH0.71H₂O where CH₂O is the water concentration in the melt (wt%), TDRY, and TWET are plagioclase crystallization temperatures in water-free and water-bearing systems, respectively. The relationship between CH₂O and liquidus temperature worked out in this study is valid for a range of basaltic compositions, ranging from high-alumina basalts to basaltic andesites. The combination of the empirical equation predicting the liquidus depression of plagioclase with previous models predicting the olivine liquidus curve is useful to determine the liquidus temperature in various H2O-bearing basaltic systems in which either plagioclase or olivine is the liquidus phase.