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TitleRegional variations of mantle anisotropy across the Canadian Cordillera from teleseismic shear-wave splitting
AuthorZandt, G; Frassetto, A M; Cassidy, J F; Bostock, M G
SourceAmerican Geophysical Union, Fall Meeting 2009, abstract volume; 2009, 1 pages
Alt SeriesEarth Sciences Sector, Contribution Series 20090238
MeetingAmerican Geophysical Union Annual Fall Meeting 2009; San Francisco, California; US; December 14-18, 2009
Mediaon-line; digital
ProvinceBritish Columbia
Subjectstectonics; geophysics; mantle; anisotropy; seismic interpretations; seismic waves; deformation; Denali Fault; Queen Charlotte Fault; Cenozoic
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
LinksOnline - En ligne
AbstractThe Canadian Cordillera overlies a slab window developed after the cessation of ocean-continent subduction during the mid-Cenozoic. Widespread basaltic volcanism occurring over the last 20 million years throughout the Cordillera appears geochemically depleted when compared to magmas generated within continental lithosphere. Characterizing seismic anisotropy constrains ongoing deformation in the upper mantle beneath the Cordillera and provides an opportunity to investigate the potential source of these magmas. We use the rotation correlation, eigenvalue minimization, and energy minimization methods through the Splitlab software package to analyze teleseismic SKS phases recorded by seismometers deployed as part of the Batholiths and Nechako Experiments and increased regional monitoring. Splitting measurements collected across the central British Columbia, southeastern Alaska, and the southern Yukon reveal regional patterns in seismic anisotropy. Stations closest to the southern Denali and Queen Charlotte faults show large splitting times (1.5-2.0 s) along orientations consistent with the dextral transform between the North American and Pacific plates. Stations within the coastal region show generally null patterns. A robust pattern of east-west oriented splitting across the central Coast Mountains Batholith and Interior Plateau cannot be easily explained in terms of lithospheric structural fabric, and its regional coherency and magnitude (up to 1.5 s) indicates that a significant amount of anisotropy occurs within asthenospheric mantle. When combined with other geophysical and geochemical constraints, the pattern of anisotropy suggests upwelling and lateral flow of asthenosphere around the northern edge of the subducting Juan de Fuca slab. Asthenospheric flow into a complex slab window north of the Juan de Fuca plate would explain the lack of splitting seen in certain regions of the Cordillera and provide a mechanism for fueling the post-subduction volcanism observed across the interior of British Columbia.