Collaborative Research: Voyage to the bottom of Arcs: interplay between water, deformation, and lower crustal stability

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The formation of continents is intimately linked to plate tectonics on Earth. Subduction zones are tectonic boundaries where oceanic plates sink back into the Earth's deep interior. This process triggers melting in the deep Earth, the formation of volcanic island arcs, and the building of continental crust over time. Arc volcanos are well-studied due to their exposure at the Earth's surface. However, the roots of island arcs are difficult to access and therefore, remain poorly studied. Deep arc roots play a critical role in controlling the evolution of continental crust and the Earth system as a whole. Due to their high density, arc roots are hypothesized to regularly detach (delaminate) from the shallow and less dense parts of the arc, and sink back into the Earth, modifying the composition of the bulk continental crust over time. Importantly, the viscous nature of deep arc roots, and hence their likelihood of being detached, depends on their composition, particularly water. This study will provide new constraints on how material is delaminated, or removed, from volcanic arc roots. The team will combine state-of-the-art volatile analyses with rheological measurements on natural samples, which will be integrated into numerical models. The formation and evolution of continents, without which no life on land could have developed, is an active topic of interest for the broad scientific community.The processes by which the Earth's crust, and in particular the continental crust, has been constructed over time have been debated since the observation that bulk continental crust is andesitic in composition, but mantle-derived parental melts are mostly basaltic. A number of studies have suggested that delamination, a process by which dense mafic rocks at the base of arcs regularly sink back into the mantle, could account for the chemical gap between bulk continental crust and mantle melts. Other studies have proposed that delamination alone is not sufficient to explain the discrepancy. Currently, numerical simulations of this process have two major limitations: (1) viscosities used in current models are not linked to water measurements on natural arc cumulates because these in-situ analyses have never been performed; and (2) it is assumed that the material that detaches is initially isotropic although natural cumulate samples show a wide range of textures and internal deformation. This is a novel interdisciplinary project that is focused on the chemical and rheological role of water in lower crustal cumulates from four arc settings. The goal is to examine the interplay between water, deformation, and lower crustal stability in subduction zones, using a unique combination of geochemical, rheological, and numerical approaches. This collaborative project will support two Ph.D. students and the training of a postdoctoral investigator. In addition, the PIs will design a tectonics class tailored for K-12 students at the Perkins School for the Blind (MA). They will also offer undergraduate internship opportunities and make an active effort to recruit promising minority students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.