MARGINS: Collaborative Research: Origins of Local Variations in Subduction-Related Fluids: Evidence from Olivine-Hosted Melt Inclusions from the Central American Subduction Zone

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One of the most important processes that occurs at subduction zones is the fluid-mediated transfer of material from subducting lithosphere into overlying mantle. The sources of fluid for this important mass transfer remain controversial. Along the Central American subduction zone erupted basaltic magmas display systematic geochemical variations along the volcanic front which have been linked to changes in intensity and the agents of slab-to-wedge mass transfer (e.g., Eiler et al., 2006). In the Nicaraguan portion of the Central American subduction zone there are also local (i.e., intravolcano) geochemical variations in basaltic magmatism that can rival the much-ballyhooed along-arc differences (e.g., Patino et al., 2000). These local variations in the chemistry of erupted basalts have also been linked to variations in fluid transfer from the subducting Cocos plate (Patino et al., 2000; Walker et al., 2001). They may also reflect local variability in melt generation and/or mantle wedge depletion (Carr et al., 1990; Feigenson and Carr, 1993; Reagan et al., 1994; Walker et al., 2007). We propose to critically evaluate the origin of the local geochemical variations in Nicaragua through major, volatile and trace element analyses of olivine-hosted melt inclusions in basaltic tephras.Intellectual Merit. A full major, volatile and trace element characterization of the melt inclusion population in Nicaraguan basaltic tephras will allow us to determine the range in primitive compositions feeding Nicaraguan volcanoes. We can then test whether the range in primitive compositions is caused by local variations in fluid input from the subducting Cocos plate; in the melting history of the mantle wedge; or in the melting dynamics in the mantle wedge. The volatile and trace element contents of the melt inclusions will also permit further characterization of the slab signals imprinted on Nicaraguan magmas and, when combined with existing whole-rock data, help us to identify the fluid bearers of these slab signals, a question that remains unresolved both on local and regional scales. Better constraints on the variety of slab-related fluids contributing to magmatism are integral to identifying which tectonic parameters (slab dip, slab hydration, crustal thickness) are most instrumental in creating an environment conducive to maximizing heterogeneity in erupted magma compositions in Nicaragua (e.g., Abers et al., 2003; Ranero et al., 2003) and along other subduction zones. The volatile element analyses of the melt inclusions will include the determinations of H2O, CO2, Cl and S. This will allow us to evaluate all of the magmatic processes that can affect the volatile concentrations of magmas (e.g. Hauri, 2002; Wade et al., 2006). Thus, we will be able to determine the degassing histories of magmas at individual volcanoes, which exerts a critical control on the explosivity of eruption (Roggensack et al., 1997; Cervantes and Wallace, 2003b; Spilliaert et al., 2006).Broader Impacts. The proposed project will provide continued support for programs at both Northern Illinois University and Arizona State University involving research experience for undergraduate students, particularly female students. In addition, it will permit continued transfer of scientific knowledge to Central American colleagues to help enhance community-level understanding about the workings of active and dormant volcanoes. For instance, knowledge of the degassing and eruptive processes learned from melt inclusions will provide important information on potential volcanic hazards.