MELTING, MELT MIGRATION, AND VOLCANISM AT CONVERGENT PLATE BOUNDARIES

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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.