DENALI DAMAGE: BEDROCK DEFORMATION, KINEMATICS, AND FLUID FLOW IN THE BRITTLE REGIME ALONG THE DENALI FAULT ZONE, KLUANE LAKE, YUKON TERRITORY, CANADA

Stream incised and road cut exposures provide rare evidence for bedrock damage associated with the Denali fault zone. The exposures lie within several hundred meters of the mapped NW trace of the dextral strike slip Denali fault and an apparent surficial mountain front fault scarp. Wrangellian Paleozoic and Triassic volcanic rocks are juxtaposed with Jura-Cretaceous metasedimentary rocks along the fault. The volcanic rocks are intensely deformed by myriad polished and striated slip surfaces.

The slip surfaces can be grouped by distinct slip regimes and associated mineralogy. Chlorite, hematite, and quartz surfaces show reverse dip slip to reverse oblique slip. These are systematically overprinted by calcite surfaces dominated by dextral and sinistral strike slip. A small but tantalizing dataset shows that the faults strike sub-parallel to the mapped trace of the Denali and are steeply dipping (mean plane ~ 324/82, n=26). The mean slip vector for reverse faults is 73/102 and for strike slip faults 16/320, both falling nearly on the mean plane for the fault population. Calcite slip surfaces resemble low temperature ‘mylonites’ (Kennedy and White, 2001) and may reflect a component of aseismic creep. In contrast, many such surfaces locally cut opening mode calcite veins possibly formed by seismogenic hydrofracturing.

Although deformation is regionally distributed along numerous major and minor faults mapped subparallel to Denali, little is known about the relative ages or detailed kinematics of the fault network as a whole. Strain partitioning likely occurs at a variety of scales. However, the overprinting of strike slip on reverse slip suggests reactivation and progressive strain associated with more recent deformation adjacent to the principal slip zone of the Denali fault. Oblique slip may reflect transitional or localized stress states as regional transpression evolved during progressive exhumation. An alternate hypothesis for overprinting includes complex, multi-stage slip during single events (e.g., Denali [Haeussler et al., 2004] and Wenchuan earthquakes [Pan et al., 2013]). In sum, the extensive network of variably mineralized slip surfaces at Kluane Lake suggests a heterogeneous damage zone with reactivated preexisting weaknesses kinematically associated with the evolution of the Denali fault.