Seismic Study of Deep Eclogitic-Granulitic Crust and Moho in the Bergen Arcs, Norway

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This study involves seismic imaging of eclogite at one of the world's classic localities. Eclogite is a unique rock type because of its physical properties such as high density, which is a response to abnormally high pressure. Eclogite is related to processes of mountain building and associated subduction. Yet we know little about the subsurface distribution of eclogites. The classic eclogite localities that we study are in the Bergen Arcs of western Norway where eclogitization is related to fluid flow along fault zones and regionally in the associated gneisses. The eclogites are formed at such high pressures that they correspond to a depth of up to 100 km. Another presumed role of eclogites is as a trigger for recycling of crustal material back down into the mantle because of their high density. What is the nature of continental crust and crust-mantle boundary beneath an eclogite terrane, where do the eclogites come from and how do they get there? What was the role of deep fluids in eclogite formation? These are the problems that we propose to clarify. With an NSF Small Grant for Exploratory Research, the investigators were able to utilize the University of Bergen research vessel for a combined land-marine seismic recording experiment to image the deep structure of the eclogite terrane. Seismic energy from marine airguns was recorded on 16 ocean bottom seismometers and 15 seismic recorders on land using new IRIS land seismic recorders to yield 250 km long profiles. Because of their unique seismic characteristics, the researchers expect to image eclogite bodies throughout the crust, deep fluid passageways that promoted eclogitization, and faults that brought eclogites up to the surface. Results should provide new information on mountain building and crustal formation, specifically how crust in mountain belts over-thickens and subsequently how deepest crust comes back up to the surface.