Collaborative Research: Active Tectonics at the Aleutian-Kamchatka Corner: A Lithospheric Perspective

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01-36103RitzwollerThis is a collaborative proposal between Principal Investigators at the University of Colorado and Yale University. Arctic tectonics is dominated by the interaction of the North American, Eurasian,and Pacific plates. In oceanic areas, the boundaries between these plates are relatively well known, but much of the North American-Eurasian plate boundary is defined by a broad zone of intra-continental deformation. The driving mechanisms for this deformation are poorly understood.Newly acquired seismic data makes it possible to decipher plate motion at the Aleutian-Kamchatka junction. This junction connects the strike-slip Bering fault along the western Aleutians with an active subduction zone beneath southern Kamchatka, where plate convergence is accompanied by vigorous arc-volcanics. The Okhotsk Sea lies in the back-arc region of the Kamchatka subduction zone, and its unresolved deformation is critical to understanding present-day North America-Eurasia plate interaction. The evolution of the Kamchatka-Aleutian junction is a critical component of the Cenozoic evolution of the Pacific-Eurasian plate boundary, and thus of Arctic tectonics as a whole. The principal goal of this project to characterize the temperature and the texture of the lithosphere and the asthenosphere near the Aleutian-Kamchatka junction region. Temperature is related to seismic velocity anomalies, and deformation texture to seismic anisotropy. Temperature and texture will reveal the role of the upper mantle in the interplay between the plates, particularly 1) how mantle processes facilitate the vigorous subduction-related volcanism near the Aleutian-Kamchatka junction, and 2) whether and how past extensional tectonics in the Okhotsk Sea have influenced the Cenozoic development of the North America-Eurasia boundary. The Yale Principal Investigators acquired seismic data in Kamchatka by operating a portable network of broadband seismometers in 1998 -1999. Recordings from this network combined with data from permanent seismological stations will for the primary data set for this study. They bring expertise in regional tectonics, receiver function analysis, and characterizing lithospheric dynamics using seismic anisotropy. The Colorado Principal Investigators are experts in surface wave tomography inversion for models of the crust and the upper mantle and the inference of mantle temperature from seismic models. This collaboration is designed to generate accurate and more sharply focused images of isotropic and anisotropic seismic features near the Kamchatka-Aleutian corner. From these images the temperature and texture of the upper mantle that constrains lithospheric dynamics will be inferred.