BETWEEN TWO FAULTS: STRUCTURALLY CONTROLLED EXHUMATION PATTERNS ALONG THE DENALI FAULT SYSTEM

Variations in exhumation along strike-slip faults are commonly linked to restraining bends or an increase in converging plate obliquity as a fault changes strike. We document how two different fault pairs with varying dips and obliquity along the Denali fault system have contrasting spatial and temporal exhumation patterns. Detrital apatite fission track thermochronology (DAFT) documents differences in exhumation patterns between two fault bounded blocks and demonstrates how the distinct geometry and lithospheric scales of the bounding faults lead to different scales and styles of exhumation. In the western block, between the sub-vertical lithospheric Denali and Hines Creek faults, unimodal Late Miocene age populations document rapid exhumation in the narrow (~20 km width) block of crust between the two faults. In the second region, in a broader, more distributed zone of deformation (~45 km width) between the lithospheric Denali fault and low-angle, shallow-crustal Granite Mountain fault, dominantly bi- and tri-modal age populations document Late Miocene and older Paleogene rock cooling. Convergence obliquity increases systematically to the west along strike of the Denali fault as it curves, but the region with the greatest obliquity has the lowest topography and minimal exhumation signal in our study area. We therefore suggest that the scale and dip of the subsidiary second fault (lithospheric or shallow crustal and steep or shallow angle) rather than the strike of the primary fault (Denali fault) with respect to the convergence direction of the converging plate plays a controlling role in the patterns of exhumation and topographic development in the Eastern Alaska Range.