Mafic magmatic enclaves as tracer of protracted mixing and hybridization

镁铁质岩浆包体作为长期混合和杂交的示踪剂

• 批准号: 2122789
• 负责人: Philipp Ruprecht
• 金额: $ 32.04万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2122789&HistoricalAwards=false
• 关键词: Mafic; magmatic; enclaves; tracer; protracted

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.

火山爆发是一种主要的自然灾害。了解导致火山爆发的过程将大大有助于改进灾害预测和对个别岩浆系统的长期评估。从深处上升的热岩浆在浅岩浆储存区内重新充电和混合，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爆发的直接触发机制。镁铁质包体是以厘米到分米尺度分散的成分不同的岩浆块，这是补给的证据。炽热的岩浆提供了热能，使岩浆流动，并驱动搅拌和混合。利用补给岩浆晶体中的化学特征，该项目将探索热破裂在哪个空间和时间尺度上运作。这些信息提供了独特的限制，岩浆混合室规模的动态模型，这些热瞬变事件是短暂的，还是破坏岩浆系统数年至数十年。本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了一种新的数值模拟技术来限制富含晶体的镁铁质包体的机械完整性，这提供了关于这些包体在混合和混合过程中可以存活多久的独立信息，因此代表了该热历史的忠实记录。该小组将使用斜长石分带和多相流数值模拟的双重方法研究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者，因为它们既是档案，也是驱动混合的媒介。其目的是跟踪出现的热瞬态混合和潜在的返回到一个新的统一的存储条件。这种热演化可以被捕获，因为研究地点，混沌岩圆顶，加利福尼亚州，爆发了六个独立的事件，整个动荡时期持续了几年到几十年。将使用基于矿物-矿物的平衡和元素扩散方法记录热瞬变。为了评估这些包体的生存时间和机械完整性，我们将采用一种新的数值方法来研究主机英安质岩浆中的镁铁质包体的机械侵蚀。研究人员将使用耦合离散元方法和格子玻尔兹曼方法（DEM-LBM）数值模拟来直接模拟主熔体对包体的机械侵蚀过程中的流体-固体相互作用，以限制镁铁质包体的生存时间。通过他们的耦合方法，他们将能够评估温度，通过粘度捕获，主岩浆以及晶体的形状和相对包装如何影响富含晶体的聚集体的机械侵蚀。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。