Late Miocene to Quaternary evolution of the McCallum Creek thrust system, Alaska: Insights for range-boundary thrusts in transpressional orogens

Abstract

Thrust systems are a primary mechanism for accommodating the convergent component of oblique plate motion and are therefore key players in the structural development of transpressional orogens. In southern Alaska, the Denali fault system is a highly partitioned dextral-convergent fault system spatially coincident with Alaska Range topography and thus offers an opportunity to evaluate the evolution of range-bounding thrust systems in orogens resulting from oblique plate motion. Our analysis is focused on the late Miocene-Present McCallum Creek thrust system, which consists of the McCallum Creek reverse fault and a kinematically linked foreland thrust system south of the Denali fault in the eastern Alaska Range. Apatite fission-track cooling ages, tephrachronology, and balanced cross sections indicate that convergence partitioned to the McCallum Creek thrust system has accommodated ~4 km of rock exhumation and ~5.5 km of south-vergent shortening since hanging wall rocks passed through the apatite fission-track partial annealing zone at ca. 6 Ma. A blind foreland thrust system developed after ca. 3.8 Ma and was subsequently overtaken by out-of-sequence slip on the main McCallum Creek fault. Incised segments of modern streams, perched terraces, and tilted Quaternary deposits suggest that foreland structures are active in the Quaternary. Shortening on the McCallum Creek thrust system is oriented at a high angle to the Denali fault, making the McCallum Creek thrust system one of the only known structures south of the Denali fault in the Alaska Range to accommodate the collisional mode of active deformation in southern Alaska. The late Miocene reactivation of faults in the McCallum Creek area likely records evolution of the Denali fault system in response to modification of the southern Alaska convergent plate boundary.

Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

“…Recent bedrock and detrital thermochronologic studies document rapid and persistent exhumation of the entire Alaska Range starting ca. 30-25 Ma (Benowitz et al, 2011, 2012a, 2012cFitzgerald et al, 2014;Riccio et al, 2014;Lease et al, 2016) coincident with and locally proceeding Oligocene fluvial sedimentation in the Tanana foreland basin north of the Range (Ridgway et al, 2007) and the McCallum and Colorado Creek basins south of the range (Allen, 2016;Waldien et al, 2018; this study) as well as arc-related dike swarm emplacement along the Denali fault (this study). Exhumation in the Alaska Range also impacted sedimentary basins positioned farther south of the range.…”

“…2; Ridgway et al, 2007). Along the south flank of the central and eastern Alaska Range, Oligocene-Miocene fluvial-lacustrine sedimentary strata record strike-slip basin development and deformation related to dextral slip along the Denali fault (Colorado Creek and McCallum basins, Trop et al, 2004;Allen, 2016;Waldien et al, 2018). In the central and eastern Alaska Range and northern Talkeetna Mountains, ca.…”

“…Hence, the often-cited Foraker-McGonagall same-pluton piercing point may be incorrect, and these plutons may not be genetically related. The observed westward decreases in displacement and slip rates, in conjunction with fault geometry and topography, indicate partitioning of fault-normal convergence along the Denali fault in a zone of transpression resulting from increasing obliquity between the fault and plate convergence (Hauessler, 2008;Fitzgerald et al, 2014;Bemis et al, 2015;Waldien et al, 2018 Changes in basin character along the Denali fault illuminate the overall tectonic setting. Strike-slip basin development along the eastern Denali-Duke River fault (Ridgway and DeCelles, 1993) occurs where "strong" terranes collide and plate motion is oblique to the fault (Fitzgerald et al, 2014).…”

A river runs through it both ways across time: 40Ar/39Ar detrital and bedrock muscovite geochronology constraints on the Neogene paleodrainage history of the Nenana River system, Alaska Range

“…In summary, during earliest Miocene times, the ancestral Nenana River system flowed to the south into Cook Inlet as the Alaska Range was rising (Fig. 13A), but the Alaska Range was less extensive than today (Bill et al, 2018;Waldien et al, 2018). By the early Miocene (ca.…”

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

“…Alternatively, exhumation in the Kluane Ranges may reflect other factors such as changing plate convergence angle with respect to EDFZ orientation (e.g., DeMets & Merkouriev, 2016). Oligocene-Miocene cooling and (or) deformation is documented along the broader Denali fault system, although variable in timing, and also attributed to flat-slab subduction of the Yakutat microplate (Figure 9b; Benowitz et al, 2011;Benowitz et al, 2014;Lease et al, 2016;Trop et al, 2004;Waldien et al, 2018). Our data imply EDFZ activity triggered by far-field plate boundary processes over timescales beyond the resolution of our thermochronometric data.…”