MELTING, MELT MIGRATION, AND VOLCANISM AT CONVERGENT PLATE BOUNDARIES

智力优势：地球上地幔在会聚板块边界的熔融（岩浆）的产生被认为是由两个过程中的一个或两个引起的：通量熔融，因为下行板块脱水释放的水上升到地幔楔的热中心;和热地幔上升到楔的减压熔融。该项目旨在研究这两个熔体生成过程的相对贡献，因为它们被认为控制了一些至关重要的地质条件。将开发一个数值模型，其中包括熔体迁移的物理学，这将被用来预测收敛边缘的地质变化。据推测，火山系统内的地球化学成分的空间变化在收敛的边缘可能是由于变量混合的岩浆起源于流量和绝热减压熔融过程。这一假设将通过检查观察到的会聚边缘火山活动和比较的化学成分的范围，其地理分布，以2D和3D的数值模型输出确定的流量和减压熔体的变量贡献进行测试。将研究减压边界层内的积水岩浆的通道可能局部化以形成不同的火山中心的机制。为什么火山会像现在这样间隔开？是什么决定了不同火山中心之间的分离？这个过程可以用指法不稳定性的研究来解释吗？如果不同的熔体混合的解压缩通道内的指状不稳定性将探讨使用分析和数值模型。或者，通过考虑板片脱水对橄榄石-辉石地幔和溶解熔体不稳定性的影响，研究在底辟上涌环境中由于局部湿熔融导致的较小熔体的浮力渗流。该项目包括本科生和研究生的研究和培训经验，通过布朗大学的谢里丹教学中心为研究生提供教学机会，并为高年级本科生提供研究活动。参与该项目的研究生和本科生将参加当地学校的四年级外联活动。更广泛的科学影响包括在各种收敛边缘与众多地震和理论研究的协同作用，以及将建立计算地球动力学研究基础设施的数值模拟代码的开发。所开发的方法也将对各种领域中粘性压实固体中的多孔流动的研究产生影响，可能包括石油开采和勘探。

Intellectual Merit: The production of melt (magma) in the Earth's upper mantle at convergent plate boundaries is believed to arise from one or both of two processes: flux melting, as the water released by dehydration of the down-going plate rises into the hot center of the mantle wedge; and decompression melting of the hot mantle as it rises into the wedge. The project aims to study the relative contributions of these two melt-generation processes, since they are believed to govern a number of critically-important geological conditions. A numerical model will be developed that incorporates the physics of melt migration, and this will be used to predict the varying geology at convergent margins. It is hypothesized that the spatial variation in geochemical composition within volcanic systems at convergent margins may be attributable to the variable mixing of magmas originating from both flux and adiabatic decompression melt processes. This hypothesis will be tested by examining observed convergent margin volcanism and comparing the range of chemical compositions, and their geographic distribution, to 2D and 3D numerical model outputs determined by the variable contribution of flux and decompression melts. The mechanisms by which channeling of ponded magma within the decompaction boundary layer may be localized to form distinct volcanic centers will be investigated. Why are volcanoes spaced apart as they are? What governs the separation between distinct volcanic centers? Might this process be explained by studies of fingering instabilities? Fingering instabilities within the decompaction channel if disparate melts are mixed will be explored using analytical and numerical models. Alternatively, the buoyant percolation of smaller bodies of melt due to localized wet melting within an otherwise diapiric upwelling setting will be investigated by considering the impact of slab dehydration on an olivine-pyroxene mantle and dissolution melt instabilities.Broader Impacts: The project includes research and training experiences for undergraduate and graduate students, with graduate student teaching opportunities via the Sheridan Center for Teaching and Learning at Brown, and research activities for upper division undergraduates. The graduate and undergraduate students involved in the project will participate in 4th grade outreach activities in local schools. Wider scientific impacts include synergies with numerous seismic and theoretical studies at a variety of convergent margins, and the development of numerical modeling codes that will build the research infrastructure for computational geodynamics. The methods developed will also have a bearing on studies of porous flow in viscous compacting solids in a variety of fields, potentially including petroleum recovery and exploration.