Abstract Magmatic reservoirs located in the upper crust have been shown to result from the repeated intrusions of new magmas, and spend much of the time as a crystal-rich mush. The geometry of the intrusion of new magmas may greatly affect the thermal and compositional evolution of the reservoir. Despite advances in our understanding of the physical processes that may occur in a magmatic reservoir, the resulting architecture of the composite system remains poorly constrained. Here we performed numerical simulations coupling a computational fluid dynamics and a discrete element method in order to illuminate the geometry and emplacement dynamics of a new intrusion into mush and the relevant physical parameters controlling it. Our results show that the geometry of the intrusion is to first order controlled by the density contrast that exists between the melt phases of the intrusion and resident mush rather than the bulk density contrast as is usually assumed. When the intruded melt is denser than the host melt, the intrusion pounds at the base of the mush and emplaced as a horizontal layer. The occurrence of Rayleigh-Taylor instability leading to the rapid ascent of the intruded material through the mush was observed when the intruded melt was lighter than the host one and was also unrelated to the bulk density contrast. In the absence of density contrasts between the two melt phases, the intrusion may fluidize the host crystal network and slowly ascend through the mush. The effect of the viscosity contrast between the intruded and host materials was found to have a lesser importance on the architecture of intrusions in a mush. Analyzing the eruptive sequence of well documented eruptions involving an intrusion as the trigger shows a good agreement with our modeling results, highlighting the importance of specifically considering granular dynamics when evaluating magmas and mush physical processes.

中文翻译：

---

岩浆糊中侵入体的结构

摘要 位于上地壳的岩浆储层已被证明是新岩浆反复侵入的结果，并且大部分时间都以富含晶体的糊状物形式存在。新岩浆侵入的几何形状可能会极大地影响储层的热演化和成分演化。尽管我们对岩浆储层中可能发生的物理过程的理解有所进步，但由此产生的复合系统结构仍然受到很大限制。在这里，我们进行了结合计算流体动力学和离散元方法的数值模拟，以阐明新侵入糊状物的几何和就位动力学以及控制它的相关物理参数。我们的结果表明，侵入的几何形状是由侵入的熔融相和常驻糊状物之间存在的密度对比控制的一阶控制，而不是通常假设的体积密度对比。当侵入的熔体比主体熔体更致密时，侵入体在糊状物的底部撞击并形成水平层。当侵入的熔体比主体熔体轻并且与体积密度对比无关时，观察到瑞利-泰勒不稳定性的发生导致侵入材料通过糊状物快速上升。在两个熔体相之间没有密度对比的情况下，侵入可能使主体晶体网络流化并缓慢上升穿过糊状物。发现侵入材料和主体材料之间的粘度对比的影响对糊状侵入结构的重要性较小。分析涉及入侵作为触发器的有据可查的喷发的喷发序列显示出与我们的建模结果非常吻合，突出了在评估岩浆和糊状物物理过程时特别考虑颗粒动力学的重要性。