EAGER: Collaborative Research: Continental Subduction and Deep Crustal Melting

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Subducted continental crust can attain pressure-temperature conditions that are above the solidus for many crustal lithologies, but the conditions, timing, and consequences of deep crustal melting are largely unexplored. Although there have been experimental investigations of ultrahigh-pressure (UHP) melting, there are very few field-based studies of natural examples; existing work has focused largely on the age and chemical characteristics of granitoid bodies that are associated with UHP terrains and not on migmatites that commonly host UHP rocks. The generation of large amounts of partially molten crust during subduction has implications for mass and heat transfer from the mantle to the crust, orogenic growth by the addition of partially molten material generated at depth, and evolution of orogenic landscapes (e.g. development of plateaux). Moreover, the role of partially molten crust must be considered in understanding the mechanisms by which (U)HP rocks are overprinted during exhumation and subsequent orogenic processes. This proposed Early Grant for Exploratory Research (EAGER) project is designed to obtain U/Pb zircon ages from magma bodies (leucosomes, pegmatites) spatially associated with eclogite to determine if zircon crystallized and thus melting occurred at UHP conditions. If this exploratory study is successful, it will set up the background canvas for a larger scale project with the ultimate goal of testing the hypothesis that, in some orogens, partial melting of continental crust occurs during continental subduction and is dynamically linked to the thermal-mechanical evolution of orogens and the exhumation of UHP rocks. The pursuit for adequate sample material will take place in the Western Gneiss Region (Norway) because it is an accessible locale with abundant exposure of UHP rocks that are hosted by migmatite; some eclogite bodies are themselves migmatitic.