MELTING, MELT MIGRATION, AND VOLCANISM AT CONVERGENT PLATE BOUNDARIES

理论价值：地球上地幔中熔体（岩浆）的产生被认为是由两个过程中的一个或两个过程产生的：通量熔融，即下行板块脱水释放的水上升到地幔楔的热中心；热地幔上升到楔状时的减压融化。该项目的目的是研究这两种融冰产生过程的相对贡献，因为它们被认为控制着一些至关重要的地质条件。将开发一个结合熔体迁移物理的数值模型，并将用于预测汇聚边缘的变化地质。本文认为，汇聚边缘火山系统地球化学组成的空间变化可能是由通量和绝热减压熔融过程产生的岩浆的不同混合引起的。这一假设将通过检查观测到的会聚边缘火山活动，并将化学成分的范围及其地理分布与由通量和减压熔体的可变贡献决定的2D和3D数值模型输出进行比较来检验。在分解边界层内的池状岩浆通道可能被定位形成不同火山中心的机制将被研究。为什么火山之间的间隔是这样的？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，将使用解析和数值模型探索分解通道内的指法不稳定性。另外，考虑到板块脱水对橄榄石-辉石地幔和溶蚀熔体不稳定性的影响，将研究较小的熔融体的浮力渗透，这是由于局部湿熔融在其他底辟上涌环境中造成的。更广泛的影响：该项目包括本科生和研究生的研究和培训经验，研究生通过布朗大学谢里登教学中心的教学机会，以及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的四年级外展活动。更广泛的科学影响包括与各种收敛边缘的众多地震和理论研究的协同作用，以及将为计算地球动力学建立研究基础设施的数值模拟代码的发展。所开发的方法也将对各种领域的粘性压实固体的多孔流动研究产生影响，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.