Collaborative Research: Northwestern Canada Seismic Experiment

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Gaherty-EAR0003404Revenaugh-0003746Garnero-0003745The Canadian Northwest Experiment (CANOE hereafter) will employ a Y-shaped, 48-station broadband seismic array to address two of the great unsolved problems in the evolution of the solid Earth: the assembly and stabilization of the continents, and the importance of the Earth's core-mantle boundary (CMB) as the birthplace of mantle plumes and the graveyard of subducted slabs. Constructed via a sequence of collisional events associated with subduction, continents grow outwards from nuclei that stabilize quickly, experiencing little deformation over the subsequent billions of years. This stability is presumably due to dynamic processes associated with craton construction, but is poorly understood. The best locale in the world for mapping continent construction is the northwestern corner of the Canadian shield, which is characterized by a progression from the 2.5-4 billion-year-old Slave province (home to the oldest known rocks on Earth) to the recently uplifted Northern Cordillera of the great Rocky Mountain system. The investigators will deploy broadband seismometers across this transition, with a western arm following the Alaskan highway from Whitehorse, BC to Edmonton, AB, and an eastern arm reaching from Fort Nelson, BC to Yellowknife, NWT. Using records of local, regional, and distant earthquakes, the investigators will construct detailed images of the mantle and crust associated with this cordillera-to-craton transition.By recording earthquakes from the far reaches of the Pacific basin, the CANOE deployment will also provide unsurpassed sampling of the seismic structure of the lowermost mantle. The 90's witnessed a parade of new and unusual discoveries about the Earth's lower mantle and CMB, including evidence for compositional heterogeneity, partial melting, and anisotropic mantle fabric that have strong implications for mantle dynamic processes. CANOE, situated within 120o of the vast majority of the world's deep seismicity, provides a remarkable opportunity to examine the lower mantle in greater detail. This includes unsurpassed coverage of the CMB beneath Hawaii, providing an excellent opportunity to test models of the genesis of this hotspot archetype.Following the experiment, all data will be made available to the community through the IRIS Data Management Center (www.iris.washington.edu). Seismic instrumentation will be provided by the IRIS PASSCAL program. A portion of the experiment is funded by the Canadian Lithoprobe program via a grant to the University of British Columbia.--