Eclogite pod in migmatite, Western Gneiss

Region, Norway

2-D thermomechanical modeling of partial melting

in continental subduction (from Whitney et al., 2009)

Partial melting and continental subduction

The generation of large amounts of partially molten crust during continental 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 landscapes (e.g. development of plateaux). Moreover, the role of partially molten crust must be considered in understanding the mechanisms by which (ultra)high-pressure (UHP) rocks are overprinted during exhumation. We are conducting a pilot project 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 (U)HP conditions.

Our ultimate goal is to test 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 ultrahigh-pressure rocks.       

The Western Gneiss Region, Norway, was selected for this investigation because it is an accessible locale with abundant exposure of UHP rocks that are hosted by migmatite, and some eclogite bodies are themselves migmatitic. The migmatites have not been adequately studied for their petrology, geochemistry, structures, or age, but, owing to the large number of studies of the eclogite and the regional tectonic evolution, there is a framework in which to understand new data from the migmatites. An important outcome of the research is integration of UHP processes into an understanding of orogeny by incorporating a new mechanism (i.e., melting at UHP conditions) for production of the large amounts of partially molten crust observed in active and ancient mountain systems.

People: Christian Teyssier, Donna Whitney, Roxanne Renedo, Stacia Gordon (U Nevada-Reno), Patrice Rey (U Sydney), Haakon Fossen (U Bergen)