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首页> 外文期刊>Contributions to Mineralogy and Petrology >The rate of water loss from olivine-hosted melt inclusions
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The rate of water loss from olivine-hosted melt inclusions

机译：橄榄石熔体包裹体的失水速率

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Diffusive water loss from olivine-hosted melt inclusions has been reported previously. This process must be considered when interpreting melt inclusion data. This study measured the rate of water loss from olivine-hosted melt inclusions during heating-stage experiments to test a previous diffusive reequilibration model and the hydrogen diffusion mechanism that controls the rate. Olivine-hosted melt inclusions were heated to a constant temperature in reduced Ar gas in a heating stage for a few hours, and unpolarized Fourier transform infrared spectra were repeatedly measured through the inclusions. Water loss occurred rapidly in the experiments. Within a few hours, the water absorbance at 3,500 cm~(-1) wavenumber decreased by half. The observed water loss rate can be explained by the diffusive reequilibration model and hydrogen diffusion in olivine coupled with metal vacancy. The beginning of water loss was different in the low- and high-temperature experiments. At low temperatures (1,423 and 1,437 K), water loss did not occur in the initial 1 or 2 h. At high temperatures (1,471-1,561 K), water loss began immediately. The initial time period without water loss at low temperatures may be explained by a hydrogen fugacity barrier in the hostolivine. At low temperatures, the internal pressure may be lower than the equilibrium pressure of melt inclusion and olivine, causing lower hydrogen fugacity in the melt inclusion than in the olivine, which will delay the water loss from the melt inclusion. The tested model and diffusivity were used to estimate the rate of water loss during homogenization experiments and magma eruption and cooling. For 1-h homogenization experiment, the model shows that large inclusions (50 urn radius) in large olivines (500 urn radius) are robust against water loss, while large or small inclusions (50-10 urn radius) in small olivines (150 μm radius) may suffer 30-100% water loss. For natural samples, the correlation between water concentration and melt inclusion and olivine sizes may be helpful to infer the initial water concentration, degree of diffusive reequilibration, and magma cooling rate.
机译：先前已经报道了橄榄石包裹的熔体夹杂物造成的扩散性水损失。解释熔体夹杂物数据时必须考虑该过程。这项研究在加热阶段的实验中测量了橄榄石型熔体包裹体失水的速率，以测试先前的扩散再平衡模型和控制该速率的氢扩散机制。在加热阶段中，将橄榄石型熔体夹杂物在还原的Ar气中加热至恒温几个小时，然后通过夹杂物重复测量非偏振傅立叶变换红外光谱。在实验中失水迅速发生。在几个小时内，在3500 cm〜（-1）波数下的吸水率下降了一半。观察到的失水率可以通过扩散再平衡模型和橄榄石中的氢扩散以及金属空位来解释。在低温和高温实验中失水的开始是不同的。在低温（1,423和1,437 K）下，在最初的1或2小时内没有发生水分流失。在高温（1,471-1,561 K）下，水分立即流失。低温下没有水分流失的初始时间段可以通过在橄榄石中的氢逸度障碍来解释。在低温下，内部压力可能低于熔体夹杂物和橄榄石的平衡压力，从而导致熔体夹杂物中的氢逸度低于橄榄石中的氢逸度，这将延迟熔体夹杂物的水分流失。测试的模型和扩散率用于估计均质化实验，岩浆喷发和冷却过程中的失水率。对于1小时均质化实验，模型显示，大型橄榄石（半径500微米）中的大包裹体（半径50微米）对失水具有较强的抵抗力，而小型橄榄石（150微米）中的大或小的夹杂物（半径50-10微米）半径）可能会损失30-100％的水分。对于天然样品，水浓度与熔体夹杂物和橄榄石尺寸之间的相关性可能有助于推断初始水浓度，扩散再平衡程度和岩浆冷却速率。

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