Strain transfer and partitioning across the Yakutat collision in SW Yukon – SE Alaska: Indentor corner dynamics

English Abstract:

SW Yukon - SE Alaska is the site of present-day orogeny and accretion of the Yakutat Terrane to the Northern Cordillera. The transpressive Yakutat–North America relative motion results in strong strain-partitioning tectonics that link the Aleutian subduction to the west to Fairweather transform to the south. GPS, geomorphology, and seismicity data are integrated to quantify strain distribution between strike-slip and shortening deformation. In particular, new GPS data straddling the main faults show a diffuse indentor-like deformation, with strong along-strike variations of the main fault slip rates and high strain concentration in a “strain knot” at the indentor syntaxis. A detailed regional geomorphology study gives further information about the deformation pattern along the Denali and Totschunda Fault. Ongoing datation of geomorphological markers will give us new slip-rate estimates along thes faults. Our results suggest that the present-day reactivation of the old, inherited lithospheric-scale faults that structure the SW Yukon – SE Alaska cordillera (Fairweather, Denali, Totschunda Faults) is strongly controlled by their geometrical relation with the stress pattern generated by the collision indentor corner.