The role of thrust faulting in the formation of the eastern Alaska Range: Thermochronological constraints from the Susitna Glacier Thrust Fault region of the intracontinental strike-slip Denali Fault system

Abstract

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.

Changing exhumation patterns during Cenozoic growth and glaciation of the Alaska Range: Insights from detrital thermochronology and geochronology

“…ZUPb ages of 90–110 Ma are minor (<8%) or absent in most samples with three exceptions (Figure ). Significant 100 Ma and 93 Ma ZUPb age peaks in the Beluga (#5) and Susitna (#12) catchments, respectively, are likely derived from Late Cretaceous plutons dated within these catchments [ Riccio et al , ; Jones et al , ]. The large component of 90–110 Ma ZUPb ages in the Chulitna catchment (#11) and the minor component in other catchments may be derived from second‐cycle zircons of the Mesozoic Kahiltna flysch [ Hults et al , ] or first‐cycle zircons from unmapped Late Cretaceous plutons.…”

“…There is a reasonable match between detrital river and bedrock cooling ages within the same catchments; catchments #4 and #5: 45–49 Ma detrital AFT, 40–55 Ma bedrock feldspar 40 Ar/ 39 Ar minimum ages and AHe [ Benowitz et al , ; R. O. Lease, unpublished bedrock thermochronology data, 2016]; catchment #6: 46 Ma detrital AFT, 35–50 Ma bedrock AFT [ Ward et al , ]; catchments #8 and #9: 51–53 Ma detrital ZFT; 39–52 Ma bedrock ZFT [ Plafker et al , ]; and catchment #12: 37–45 Ma detrital ZFT and AFT, 30–50 Ma bedrock feldspar 40 Ar/ 39 Ar and AFT [ Riccio et al , ]. Detrital cooling age peaks that are coeval with 50–70 or 25–40 Ma magmatism have an uncertain origin, because it is unclear whether these cooling ages reflect postemplacement pluton cooling or erosional exhumation.…”

Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

“…In the central Alaska Range, rapid cooling at ~6 Ma is documented by apatite FT data from the Denali massif and potentially indicates a change in Pacific Plate convergence direction (Fitzgerald et al, ). Other workers suggest that rapid Neogene cooling of rocks along the CDFZ and other structures is the result of advection of crust through the large restraining bend that characterizes the CDFZ and attendant large‐scale contractional deformation and vertical rock uplift (Figure , inset; Fitzgerald et al, ; Riccio et al, ; Lease et al, ). Bedrock apatite He and detrital apatite FT dates from high‐relief, glaciated catchments adjacent to the CDFZ record accelerated Pleistocene cooling and exhumation as the result of glacial erosion (Benowitz et al, ; Lease, ; Lease et al, ).…”

“…Phase II kinematics of the EDFZ may have been dominantly strike‐slip relative to Phase I contraction‐dominated deformation, as has been suggested for the CDFZ (Cole et al, ). The bulk of separation measured along the EDFZ is inferred to have occurred ~post‐55 Ma, further suggesting continuing dextral slip along the EDFZ over Phase II (Eisbacher, ; Lanphere, ; Riccio et al, ). Second, the locus of contractional strain and attendant exhumation may have been concentrated elsewhere during Phase II slow cooling in the Kluane Ranges.…”

Basinga: A cell‐by‐cell GIS toolbox for computing basin average scaling factors, cosmogenic production rates and denudation rates

“…Riccio et al, 2014).3 Wittmann et al, 2011).4 Puchol et al, 2016).5 Molliex et al, 2016). 6(Hippe et al, 2012).7 Carretier et al, 2015).8 Lupker et al, 2012).…”