Rhyolite-MELTS: a Modified Calibration of MELTS Optimized for Silica-rich, Fluid-bearing Magmatic Systems
Rhyolite-MELTS: a Modified Calibration of MELTS Optimized for Silica-rich, Fluid-bearing Magmatic Systems
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DOI：
10.1093/petrology/egr080
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发表时间：
2012-05-01
影响因子：
3.9
通讯作者：
Carley, Tamara L.
中科院分区：
文献类型：
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作者：
Gualda, Guilherme A. R.;Ghiorso, Mark S.;Carley, Tamara L.
硅质岩浆系统具有重大的科学意义和社会重要性，因为它们在地壳演化和火山爆发造成的危害中发挥作用。熔体是一个强大的和广泛使用的工具来研究岩浆系统的演化在广泛的组成和条件。然而，目前的MELTS校准无法正确预测石英+长石饱和面在温度，压力和成分空间中的位置，使其不适合研究石英-长石体系。我们创建了一个修改后的校准MELTS优化的流纹岩系统，称为MELTS，使用早期爆发的主教浮石作为参考。小的调整量热法确定的石英和碱长石的钾端元在MELTS校准的形成焓导致大大改善预测的石英+长石饱和表面作为压力的函数。应用流纹岩熔体的高地范围火山序列（内华达州），桃泉凝灰岩（亚利桑那州-内华达州-加州），和晚喷发的主教凝灰岩（加州），使用的组成，从粗面英安岩到高硅流纹岩，表明校准是适合于各种流体轴承凝灰岩系统。一些重要的意见包括以下几点。(1)模拟的演化路径是一致的岩相观察和玻璃成分，需要进一步的工作来比较预测和观察到的矿物成分。(2)流纹岩熔体很好地捕捉了岩浆的几乎不变的性质;在广泛的伪不变结晶后观察到不寻常的行为，这表明新的校准最适合相对较小（即< 50重量%）的结晶间隔，与火山岩中观察到的情况相当。(3)我们的成功与流纹岩熔体表明，含水相不起关键作用的含水系统可以适当处理;模拟是敏感的初始水浓度，虽然只有一个纯H2O流体建模，适量的水可以添加或减去模拟CO2在流体溶解度的影响。我们对自然系统的持续研究表明，流纹岩熔体在限制结晶条件方面非常有用，特别适合于探索岩浆的喷发潜力。我们发现，使用晚爆发的主教凝灰岩全岩和熔体包裹体组合物的流纹岩熔体模拟放置的限制是不一致的垂直分层岩浆体。
Silicic magma systems are of great scientific interest and societal importance owing to their role in the evolution of the crust and the hazards posed by volcanic eruptions. MELTS is a powerful and widely used tool to study the evolution of magmatic systems over a wide spectrum of compositions and conditions. However, the current calibration of MELTS fails to correctly predict the position of the quartz + feldspar saturation surface in temperature, pressure and composition space, making it unsuitable to study silicic systems. We create a modified calibration of MELTS optimized for silicic systems, dubbed rhyolite-MELTS, using early erupted Bishop pumice as a reference. Small adjustments to the calorimetrically determined enthalpy of formation of quartz and of the potassium end-member of alkali feldspar in the MELTS calibration lead to much improved predictions of the quartz + feldspar saturation surface as a function of pressure. Application of rhyolite-MELTS to the Highland Range Volcanic Sequence (Nevada), the Peach Spring Tuff (Arizona-Nevada-California), and the late-erupted Bishop Tuff (California), using compositions that vary from trachydacite to high-silica rhyolite, shows that the calibration is appropriate for a variety of fluid-bearing silicic systems. Some key observations include the following. (1) The simulated evolutionary paths are consistent with petrographic observations and glass compositions; further work is needed to compare predicted and observed mineral compositions. (2) The nearly invariant nature of silicic magmas is well captured by rhyolite-MELTS; unusual behavior is observed after extensive pseudo-invariant crystallization, suggesting that the new calibration works best for relatively small (i.e. < 50 wt %) crystallization intervals, comparable with what is observed in volcanic rocks. (3) Our success with rhyolite-MELTS shows that water-bearing systems in which hydrous phases do not play a critical role can be appropriately handled; simulations are sensitive to initial water concentration, and although only a pure-H2O fluid is modeled, suitable amounts of water can be added or subtracted to mimic the effect of CO2 in fluid solubility. Our continuing work on natural systems shows that rhyolite-MELTS is very useful in constraining crystallization conditions, and is particularly well suited to explore the eruptive potential of silicic magmas. We show that constraints placed by rhyolite-MELTS simulations using late-erupted Bishop Tuff whole-rock and melt inclusion compositions are inconsistent with a vertically stratified magma body.