The exchange of heat and chemical species between the surface and interior of the Earth are controlled by plate tectonics. Specifically, the Earth?s plates are recycled back into the mantle at subduction zones, where one tectonic plate is forced beneath another. During subduction some of the material from the descending plate is returned to surface forming the Earth?s crust. Much of this transport occurs via melting of the subducted material and subsequent volcanism at the surface, however, buoyant material can also return to the surface via solid-state flow in ?diapirs?. The goal of this project is to study the rise of these buoyant diapirs using a combination of laboratory experiments and numerical models. We will use these models to ascertain where and when diapirs form and to determine the relationship between diapir characteristics (volume/buoyancy) and ascent paths from the descending slab to the surface. Because buoyant diapirs will have different chemical signatures than the melts generated directly from the subducting plate, understanding the efficiency of this process is critical for determining chemical evolution of the Earth. This project will also support the education of a PhD student and a post-doctoral research fellow.
While many previous studies have investigated mantle flow driven by the subducting slab, relatively few have focused on the ascent of buoyant material from the slab back to the surface. In this project we will characterize the 3 stages of diapir evolution: formation stage, rise stage, and arrival stage, and determine how each is influenced by the plate-driven mantle wedge flow field. The laboratory experiments will be used to model the pathways and interaction of ascending diapirs in three dimensions as a function of specific aspects of the plate-driven flow field, including slab rollback, along-strike variations in slab geometry (e.g., slab edges, gaps, changes in dip), and deformation of the overriding plate. Diapirs will be initiated assuming different buoyancy sources including a point source, line source, and sheet of buoyant material on the surface of the down-going slab. We expect that diapir ascent paths will be strongly influenced by diapir volume (buoyancy) flux and the pattern of flow in the mantle wedge?potentially resulting in large horizontal net transport of buoyant slab-derived material to the surface. High-resolution numerical models will then be used to study melting and melt-matrix interaction within the spectrum of ascending diapirs based upon density contrast, diapir size, path shape and transit time. Such models are important for characterizing chemical differentiation within diapirs. Combining the laboratory experiments with the numerical models, we will be able to place important new constraints on how chemical signals can be transported from the slab to the surface in subduction zones.
