MELTING, MELT MIGRATION, AND VOLCANISM AT CONVERGENT PLATE BOUNDARIES

智力价值：地球上地幔在汇聚的板块边界产生熔融(岩浆)被认为是由两个过程中的一个或两个引起的：熔剂熔化，因为下行板块脱水释放的水上升到地幔楔形的热中心；以及热地幔上升到楔形时的减压熔融。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。将开发一个结合了熔体迁移物理的数值模型，并将用于预测收敛边缘的不同地质情况。推测汇聚边缘火山系统内地球化学成分的空间差异可能归因于熔融过程和绝热减压熔融过程中岩浆的不同混合。这一假设将通过检验观测到的汇聚边缘火山作用，并将化学成分范围及其地理分布与由通量和减压熔体的可变贡献确定的2D和3D数值模型输出进行比较来验证。解压作用边界层内滞留的岩浆的沟道作用可能局部形成不同的火山中心的机制将被研究。为什么火山会像现在这样隔开？是什么支配着不同火山中心之间的分离？这个过程可以通过对指法不稳定性的研究来解释吗？如果混合了不同的熔体，将使用解析和数值模型来探索分解通道内的指进不稳定性。或者，将通过考虑板岩脱水对橄榄石-辉石地幔的影响和溶解熔体的不稳定性来研究在其他底辟上升环境中由于局部湿熔而导致的较小熔体的浮力渗流。广泛的影响：该项目包括本科生和研究生的研究和培训经验，以及通过布朗大学谢里登教学中心的研究生教学机会，以及针对高年级本科生的研究活动。参与该项目的研究生和本科生将参加当地学校四年级的外展活动。更广泛的科学影响包括与各种汇聚边缘的许多地震和理论研究的协同作用，以及开发将为计算地球动力学建立研究基础设施的数值建模代码。开发的方法还将对各种领域的粘性压实固体中多孔流的研究产生影响，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.