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首页> 外文期刊>Contributions to Mineralogy and Petrology >Storage conditions of Bezymianny Volcano parental magmas: results of phase equilibria experiments at 100 and 700 MPa
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Storage conditions of Bezymianny Volcano parental magmas: results of phase equilibria experiments at 100 and 700 MPa

机译：Bezymianny火山亲本岩浆的储存条件：100和700 MPa时相平衡实验的结果

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摘要

The crystallization sequence of a basaltic andesite from Bezymianny Volcano, Kamchatka, Russia, was simulated experimentally at 100 and 700 MPa at various water activities (aH_2O) to investigate the compositional evolution of residual liquids. The temperature (7) range of the experiments was 950-1,150℃, aH_2O varied between 0.1 and 1, and the log of oxygen fugacity (FO_2) varied between quartz-fayalite-magnetite (QFM) and QFM + 4.1. The comparison of the experimentally produced liquids and natural samples was used to constrain the pressure (P)-T-aH_2O-f0_2 conditions of the Bezymianny parental magma in the intra-crustal magma plumbing system. The phase equilibria constraints suggest that parental basaltic andesite magmas should contain ~2-2.5 wt% H_2O; they can be stored in upper crustal levels at a depth of ~ 15 km, and at this depth they start to crystallize at ~ 1,110℃. The subsequent chemical evolution of this parental magma most probably proceeded as decompressional crystallization occurred during magma ascent. The final depths at which crystallization products accumulated prior to eruption are not well constrained experimentally but should not be shallower than 3-4 km because amphibole is present in natural magmas (> 150 MPa). Thus, the major volume of Bezymianny andesites was produced in a mid-crustal magma chamber as a result of decompressional crystallization of parental basaltic andesites, accompanied by mixing with silicic products from the earlier stages of magma fractionation. In addition, these processes are complicated by the release of volatiles due to magma degassing, which occurs at various stages during magma ascent.
机译：在各种水分活度（aH_2O）下，分别在100和700 MPa下模拟了俄罗斯堪察加半岛Bezymianny火山的玄武质安山岩的结晶序列，以研究残余液体的成分演化。实验的温度（7）范围为950-1,150℃，aH_2O在0.1和1之间变化，并且氧逸度（FO_2）的对数在石英-铁橄榄石-磁铁矿（QFM）和QFM + 4.1之间变化。通过对实验产生的液体和天然样品的比较，来限制壳内岩浆管道系统中Bezymianny父母岩浆的压力（P）-T-aH_2O-f0_2条件。相平衡约束条件表明，父母玄武质安山岩岩浆中应含有约2-2.5 wt％的H_2O。可以将它们存储在约15 km深度的上地壳层中，并且在此深度下它们会在约1,110℃开始结晶。该母岩浆随后的化学演化很可能是在岩浆上升过程中发生减压结晶而进行的。在喷发前积累结晶产物的最终深度在实验上没有受到很好的限制，但不应浅于3-4 km，因为天然岩浆中存在闪石（> 150 MPa）。因此，由于母体玄武质安山岩的减压结晶作用，并伴随着来自岩浆分馏早期阶段的硅酸盐产物的混合，在中壳岩浆室内产生了大量的Bezymianny安山岩。另外，由于岩浆脱气导致的挥发物的释放使这些过程变得复杂，该过程在岩浆上升期间的各个阶段发生。

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