Volatiles H2O, CO2, and Cl in a subduction related basalt
Volatiles H2O, CO2, and Cl in a subduction related basalt
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俯冲相关玄武岩中的挥发物 H2O、CO2 和 Cl
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发表时间：
1984
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通讯作者：
A. T. Anderson
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作者：
D. M. Harris;A. T. Anderson
通过对橄榄石中硅酸盐熔体包裹体的研究，对危地马拉俯冲带火山Fuego 1974年喷发产物进行了研究。熔融包裹体在橄榄石、斜长石、磁铁矿和普通辉石沉淀的区域取样。喷发的火山灰，基块和熔融包裹体成分的比较表明，包裹体代表的样品中存在的岩浆体的热边界层的液体。H2O和CO2在玻璃夹杂物的浓度进行了测定的真空熔融测压技术，使用个别橄榄石晶体（Fo 77至Fo 71）与玻璃夹杂物的组合物，范围从高铝玄武岩玄武安山岩。水、Cl和K2 O浓度随着橄榄石晶体变得更富铁（Fo 77至Fo 71）和玻璃夹杂物中SiO2从51重量%增加至54重量%而增加两倍二氧化硅。熔体中的H2O浓度从1.6重量%增加到1.5重量%。在最小分化的液体中为约3.5%，在更分化的液体中为约3.5%。这些包裹体中二氧化碳的含量比H2O低大约一个数量级。纯H2O与熔体夹杂物平衡时的气体饱和压力（使用Burnham（1979）的溶解度模型从玻璃夹杂物组成计算得出）近似为P（H2O）（Pa）=（SiO2 - 48.5 wt.%）× 1.45 × 107。在喷发前结晶过程中，熔体中水的浓度和气体饱和压力分别从约1.5%增加到3.5%和从300巴增加到850巴。
The products of the 1974 eruption of Fuego, a subduction zone volcano in Guatemala, have been investigated through study of silicate melt inclusions in olivine. The melt inclusions sampled liquids in regions where olivine, plagioclase, magnetite, and augite were precipitating. Comparisons of the erupted ash, groundmass, and melt inclusion compositions suggest that the inclusions represent samples of liquids present in a thermal boundary layer of the magma body. The concentrations of H2O and CO2 in glass inclusions were determined by a vacuum fusion manometric technique using individual olivine crystals (Fo77 to Fo71) with glass inclusion compositions that ranged from high-alumina basalt to basaltic andesite. Water, Cl, and K2O concentrations increased by a factor of two as the olivine crystals became more iron-rich (Fo77 to Fo71) and as the glass inclusions increased in SiO2 from 51 to 54 wt.% SiO2. The concentration of H2O in the melt increased from 1.6 wt.% in the least differentiated liquid to about 3.5% in a more differentiated liquid. Carbon dioxide is about an order of magnitude less abundant than H2O in these inclusions. The gas saturation pressures for pure H2O in equilibrium with the melt inclusions, which were calculated from the glass inclusion compositions using the solubility model of Burnham (1979), are given approximately by P(H2O)(Pa)=(SiO2−48.5 wt.%) × 1.45 × 107. The concentrations of water in the melt and the gas saturation pressures increased from about 1.5% to 3.5% and from 300 to 850 bars, respectively, during pre-eruption crystallization.