Horizontal-slip along restraining bends of strike-slip faults is often partitioned into a vertical component via splay faults. The active Susitna Glacier Thrust Fault (SGTF), as shown by its initiation of the 2002 M7.9 Denali Fault earthquake, lies south of, and intersects the dextral strike-slip Denali Fault. Geochronology and thermochronology data from samples across the SGTF constrain the region's tectonic history and the role of thrusting in the formation of the eastern Alaska Range south of the Denali fault. U-Pb zircon ages indicate intrusion of plutons in the footwall (~57 Ma) and hanging wall (~98 Ma). These U-Pb zircon ages correlate to those from the Ruby Batholith/Kluane Terrane~400 km east along the Denali Fault, supporting geologic correlations and hence constraints on long-term slip rates. Ar mica and K-feldspar data from footwall and hanging wall samples (~54 to~46 Ma) reflect cooling following magmatism and/or regional Eocene metamorphism related to ridge subduction. Combined with apatite fission track data (ages 43-28 Ma) and thermal models, both sides of the SGTF acted as a coherent block during the Eocene and early Oligocene. Contrasting apatite (U-Th)/He ages across the Susitna Glacier (~25 Ma footwall,~15 Ma hanging wall) suggest initiation of faulting during the middle Miocene. Episodic cooling and exhumation is related to thrusting on known or hypothesized faults that progressively activate due to varying partition of strain along the Denali Fault associated with changing kinematics and plate interaction (Yakutat microplate collision, flat-slab subduction and relative plate motion change) at the southern Alaskan plate margin.
Contrasting lithospheric strength between terranes often results in the concentration of strain and deformation within the weaker material. Dramatic alternating asymmetric topography of the central and eastern Alaska Range along the active Denali fault is due to contrasting lithospheric strength between terranes and a suture zone, controlled by fault location with respect to the irregular boundary of a relatively stronger terrane backstop. Highest topography and greatest Neogene exhumation in the central Alaska Range occur on the concave side of the arcuate Denali fault, yet to the north and on the convex side of the fault in the eastern Alaska Range. The Denali fault largely lies along a Mesozoic suture zone between two large composite terranes (Yukon and Wrangellia composite terranes: YCT and WCT), but the McKinley strand of the fault cuts across an embayment of weaker suture-zone rocks (Alaska Range suture-zone, ARSZ) within the irregular southern boundary of the YCT (Hines Creek fault). Deformation (and uplift of the Alaska Range) is driven by slip and partitioning of strain along the Denali fault, occurring preferentially in weaker rocks of the ARSZ against the stronger YCT. Where the YCT lies well north of the McKinley strand, deformation is primarily to the north of the fault (eastern Alaska Range). Where the YCT is close to the fault, deformation is primarily to the south (central Alaska Range). While the trace of the McKinley strand approximates a small circle, two restraining bends (McKinley and Hayes) pinned equidistant from the ends of this strand localize uplift and exhumation.
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