Mafic magmatic enclaves as tracer of protracted mixing and hybridization

火山喷发是一种主要的自然灾害。了解导致火山喷发的过程有助于改进对个别岩浆系统的灾害预测和长期评估。热岩浆从深处上升，在浅层岩浆储存区内补充和混合，被认为是引发火山动荡的重要机制。在某些情况下，这种补给可能是火山喷发的直接触发机制。补给的证据以镁铁质包体的形式存在--成分不同的岩浆碎片分散在厘米到分米尺度上。炽热的岩浆提供热能，使岩浆流动，并驱动搅拌和混合。利用补给岩浆中晶体中的化学特征，该项目将探索热中断在哪些空间和时间尺度上进行。这些信息为岩浆混合的洞室规模动力学模型提供了独特的约束，以及这些热瞬变事件是短暂的还是扰乱了岩浆系统数年至数十年。这项研究将对拉森火山国家公园内持续数十年的混沌岩全新世喷发进行研究。该项目的第二个组成部分使用一种新的数值模拟技术来约束富含晶体的镁铁质包体的机械完整性，这些包体提供了关于这些包体在混合和混合过程中可以存活多长时间的独立信息，从而真实地记录了那段热历史。该团队将采用斜长石分带和多相流数值模拟的双重方法，研究在镁铁质岩浆包体中记录的岩浆混合动力学。镁铁质包体是混合动力学的独特记录器，因为它们既是混合的档案，也是推动混合的媒介。其目的是跟踪混合的新出现的热瞬变和潜在的返回到新的均匀存储条件。之所以可以捕捉到这种热演化，是因为研究地点加利福尼亚州的混沌岩穹顶在六个不同的事件中喷发，整个动乱时期持续了几年到几十年。热瞬变将使用矿物-矿物平衡和元素扩散方法进行记录。为了评估这些包体的生存时间和力学完整性，我们将使用一种新的数值方法来研究寄主英安岩浆中镁铁质包体的机械侵蚀。研究人员将使用离散单元法和格子Boltzmann方法(DEM-LBM)数值模拟，直接模拟宿主熔体对包体的机械侵蚀过程中的流固相互作用，以限制由于混沌混合而经历剥离/侵蚀的镁铁质包体的生存时间。通过他们的耦合方法，他们将能够评估通过宿主岩浆的粘度捕获的温度以及晶体的形状和相对堆积如何影响富含晶体的集合体的机械侵蚀。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Volcanic eruptions are a major natural hazard. Understanding the processes leading up to volcanic eruption help greatly to improve hazard forecasting and the long-term assessment of individual magmatic systems. Hot magma rising from depth that recharges and mixes within a shallow magma storage region is considered an important mechanism to start volcanic unrest. In some cases, such recharge may be the direct triggering mechanism for an eruption. Evidence for recharge exists in the form of mafic enclaves–compositionally distinct pieces of magma dispersed at the centimeter to decimeter scale. The hot magma provides thermal energy that mobilizes the magma and drives stirring and mingling. Using chemical signatures in crystals from the recharge magmas, this project will explore over which spatial and temporal scales the thermal disruption operates. Such information provides unique constraints for chamber-scale dynamic models of magma mixing and whether these thermal transient episodes are short-lived or disrupt a magmatic system for years to decades. This research will be conducted on the Holocene eruptions of the Chaos Crags in Lassen Volcanic National Park that lasted for several decades. A second component of this project uses a novel numerical modeling technique to constrain the mechanical integrity of the crystal-rich mafic enclaves, which provide independent information on how long these enclaves can survive during mixing and mingling and therefore represent faithful records of that thermal history. This team will study the dynamics of magma mixing recorded in mafic magmatic enclaves using a dual approach of plagioclase zoning and numerical modeling of multiphase flow. Mafic enclaves are unique recorders of the mixing dynamics as they are both the archive and the agent that drives mixing. The objective is to track the emerging thermal transients of mixing and the potential return to a new uniform storage condition. This thermal evolution can be captured because the study site, the Chaos Crags domes, CA, erupted in six separate events and the entire unrest period lasted years to decades. The thermal transients will be documented using mineral-mineral based equilibria and elemental diffusion methods. In order to assess the survival times and mechanical integrity of such enclaves, we will employ a novel numerical approach for investigating mechanical erosion of mafic enclaves in a host dacitic magma. Researchers will use coupled Discrete Element Method and Lattice Boltzmann Method (DEM-LBM) numerical simulations to directly simulate the fluid-solid interaction during mechanical erosion of the enclaves by the host melt to constrain the survival time of mafic enclaves experiencing plucking/erosion in response to chaotic mixing. With their coupled approach, they will be able to assess how the temperature, captured through the viscosity, of the host magma as well as the shape and relative packing of crystals influences the mechanical erosion of the crystal-rich aggregate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.