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Vibro-agitation of chambered magma

机译：房室岩浆的振动搅动

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We present the results of a novel set of calculations into the effect of in situ pressure reduction of a crystal-rich, basaltic magma layer by propagating seismic (P) waves. Three stages in the process are identified. Critically, an instability can arise such that a low pressure melt layer develops close to the floor in initially densely packed magma (with mean crystal volume fraction φ = 0.6) on near-instantaneous timescales. The role of particle pressure, p(z), a newly identified force arising from interactions between adjacent crystals in the magma, is fundamental to the development of the instability, which will not arise in crystal-free liquids. Key variables governing the instability are identified and include the mean particle diameter, the excitation frequency (1-10 Hz), interstitial melt viscosity and melt compressibility. The quasi-static particle pressure that develops as a result of the spatiallydecaying oscillations leads to two effects: (1) a rapid reduction in interstitial melt pressure (c. 10 to 20% ambient pressure) leading to bubble formation, and (2) contraction of a thin magma layer at the base of the magma chamber. Where the basalt layer is overlain by silicic magma, the resulting gas phase may promote local gravitational interaction leading to chamber unrest. The proposed mechanism has implications for the timescales of crystal-liquid separation in magmas, which during the seismic event could be on the order of seconds.
机译：我们介绍了一组新的计算结果，这些结果通过传播地震波（P）来原位降低富含晶体的玄武岩浆层的压力。确定了过程中的三个阶段。至关重要的是，可能会出现不稳定现象，从而在接近瞬时的时间尺度上，在最初密集堆积的岩浆（平均晶体体积分数φ= 0.6）中，低压熔体层会靠近地面发展。粒子压力p（z）的作用是岩浆中相邻晶体之间相互作用产生的新发现的力，它是不稳定现象发展的基础，而在无晶体液体中则不会出现这种现象。确定了控制不稳定性的关键变量，包括平均粒径，激发频率（1-10 Hz），间隙熔体粘度和熔体可压缩性。由于空间衰减振荡而产生的准静态粒子压力会导致两个效果：（1）间隙熔体压力迅速降低（环境压力约为10％到20％），从而导致气泡形成；（2）收缩岩浆室底部的一层薄岩浆层。在玄武岩层被硅质岩浆覆盖的地方，所产生的气相可能会促进局部重力相互作用，从而导致室内动荡。所提出的机制对岩浆中液-液分离的时间尺度有影响，在地震事件中该时间尺度可能约为秒。

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