Measuring the depth extent of processes driving the tectonic evolution of North America

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The accretion of rifted continental margin fragments, island arcs, and oceanic plateaus onto the western margin of North America has contributed to its growth since the Mesozoic. However, Precambrian ages of the upper mantle underlying these terranes in the Canadian Cordillera indicate that they are underlain by older lithosphere. It would therefore appear that the orogenic processes associated with the growth of this portion of North America were limited to the shallow crust. Contrasting ages between terranes at the surface and deeper structures represent a clear departure in tectonic style from other orogenic systems where the crust and its underlying mantle possess a similar evolutionary history. The research program proposed here seeks to understand the mechanisms by which terranes combine to form continents and will accomplish this goal by surveying the crust and upper mantle of the western margin of North America. Determining the present-day structure of the crust and upper mantle within suture zones that juxtapose formerly disparate terranes, and comparing their structures to stable continental regions, will clarify the process of continental growth. The short-term objectives of this program will be to systematically map the structure of the crust and upper mantle within and across terranes utilizing existing datasets from the northern cordillera of North America. ******This program will additionally collect new broadband seismic data along a profile spanning from the Canadian Cordillera into the interior of North America. New broadband seismic data recorded by arrays located at this sharp lateral gradient in surface deformation will help characterize how the lithosphere changes at this structural boundary at the surface. Integrating observations from new and already available seismic datasets will yield insights into the properties that characterize portions of the crust and upper mantle that have been deformed and how those differ from regions that resist deformation. These observations will address the long-term objective of this study to identify the factors responsible for intraplate deformation in western North America. This long-term goal will be accomplished by answering the following questions: (1) How do the combined contributions from gravitational potential energy and boundary forces cause deformation within the interior of continents? (2) In what ways do the structures of terranes change as they are integrated into continents? And (3) What structures or processes in the lower crust and upper mantle influence surface tectonics? This program will benefit the geoscience community by increasing our understanding of a fundamental aspect of continental evolution. Additionally, the population in and around the Canadian Cordillera will benefit from improved understanding of crustal and upper mantle structures that can be responsible for regional seismic hazards.