A Physical Model for Three‐Phase Compaction in Silicic Magma Reservoirs
A Physical Model for Three‐Phase Compaction in Silicic Magma Reservoirs
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DOI：
10.1002/2017jb015224
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发表时间：
2018-03
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影响因子：
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通讯作者：
C. Huber;A. Parmigiani
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作者：
C. Huber;A. Parmigiani
我们开发了一个包含硅酸盐熔体、晶体和流体(挥发分)混合物的岩浆储集层中的相分离模型。这三个相之间的相互作用控制了相分离的动力学，从而控制了岩浆储集层的化学和物理演化。我们提出的模型是基于Bercovici等人的两阶段损伤理论方法。(2001年，https://doi.org/10.1029/2000JB900430)和Bercovici和Ricard(2003年，https://doi.org/10.1046/j.1365-246X.2003.01854.x))，因为它提供了考虑相之间的界面(在宏观范围内)的杠杆作用，这些相之间的界面可以根据岩浆中局部发生的机械功和相变而变形。损伤模型还提供了这样的优势，即压力对于每个阶段都是唯一定义的，并且不需要在不同阶段相等，这将使我们能够在未来的研究中考虑在成熟的、富含晶体的岩浆体中流体被动员时的巨大毛细压力。在三相压实的第一次分析中，我们数值求解了一个简单的一维问题的三相压实方程，其中我们只考虑粘性应力和浮力应力之间的竞争，重点讨论了流体对熔体-晶体分离效率的影响。我们对比了三组模拟来探索三相压实的行为，熔体-晶体参考压实情景(两相压实)，没有相变的三相情景，以及具有参数化二次沸腾(结晶诱导的出溶)的三相情景。模拟结果表明，两相(熔融结晶)和三相(熔融结晶-挥发分)压实驱动相分离的差别很大。我们发现，更轻、粘性显著降低的流体的存在阻碍了熔体-晶体的分离。
We develop a model for phase separation in magma reservoirs containing a mixture of silicate melt, crystals, and fluids (exsolved volatiles). The interplay between the three phases controls the dynamics of phase separation and consequently the chemical and physical evolution of magma reservoirs. The model we propose is based on the two‐phase damage theory approach of Bercovici et al. (2001, https://doi.org/10.1029/2000JB900430) and Bercovici and Ricard (2003, https://doi.org/10.1046/j.1365-246X.2003.01854.x) because it offers the leverage of considering interface (in the macroscopic limit) between phases that can deform depending on the mechanical work and phase changes taking place locally in the magma. Damage models also offer the advantage that pressure is defined uniquely to each phase and does not need to be equal among phases, which will enable us to consider, in future studies, the large capillary pressure at which fluids are mobilized in mature, crystal‐rich, magma bodies. In this first analysis of three‐phase compaction, we solve the three‐phase compaction equations numerically for a simple 1‐D problem where we focus on the effect of fluids on the efficiency of melt‐crystal separation considering the competition between viscous and buoyancy stresses only. We contrast three sets of simulations to explore the behavior of three‐phase compaction, a melt‐crystal reference compaction scenario (two‐phase compaction), a three‐phase scenario without phase changes, and finally a three‐phase scenario with a parameterized second boiling (crystallization‐induced exsolution). The simulations show a dramatic difference between two‐phase (melt crystals) and three‐phase (melt‐crystals‐exsolved volatiles) compaction‐driven phase separation. We find that the presence of a lighter, significantly less viscous fluid hinders melt‐crystal separation.