Tectonic Underplating and Dismemberment of the Maclaren‐Kluane Schist Records Late Cretaceous Terrane Accretion Polarity and ~480 km of Post‐52 Ma Dextral Displacement on the Denali Fault

Abstract

Terrane accretion introduces irregular geometry and allochthonous material to obliquely convergent margins, which create opportunities to quantify strike-slip displacement along otherwise margin-parallel fault systems. We present new bedrock geologic mapping and U-Pb and 40 Ar/ 39 Ar geochronology from the Alaska Range suture zone in the eastern Alaska Range, which confirm a longhypothesized correlation between the Maclaren Glacier metamorphic belt (Alaska, USA) and the Kluane metamorphic assemblage (Yukon Territory, Canada) across the right-lateral Denali fault. The new data inform a palinspastic reconstruction showing that the dissected metamorphic belts and associated plutons record ~480 km of dextral displacement along the Denali fault since ca. 52 Ma. Before strike-slip separation, the Maclaren-Kluane schist formed by west-vergent forearc underplating in the waning stage of the ca. 100-90 Ma arc built upon the Yukon-Tanana terrane. The prograde structural and metamorphic evolution of the Maclaren-Kluane schist records the final collision of the Wrangellia composite terrane at ca. 75-65 Ma along a set of east-dipping thrust shear zones, which we infer to record the polarity of the Late Cretaceous plate boundary between the composite terrane and North America. Paleogene extension partially exhumed the schists to the upper crust and may be a consequence of regionally distributed strike-slip faulting at that time. Localization of the modern Denali fault after ca. 52 Ma dismembered the schists and four neighboring belts of plutonic, metasedimentary, and volcanic rocks. The transition to Yakutat oblique flat slab subduction at ca. 30-25 Ma marks the onset of transpressional deformation in the Denali fault system, which reactivated Late Cretaceous collisional structures bounding the Maclaren schist. Neogene reactivation of the Totschunda fault reduced strike-slip motion on the Denali fault east of the Denali-Totschunda intersection and continues to transfer residual plate boundary slip onto the Denali fault west of the intersection. Key outcomes of our synthesis include: (a) Much of the ~480 km of displacement on the Denali fault accumulated after strike-slip on the neighboring Tintina and Border Ranges fault systems had largely shut down; (b) The modern Denali fault system should not be grouped with strike-slip faults credited with large-scale margin-parallel transport of Cordilleran terranes in the Cretaceous. Instead, a poorly understood proto-Denali fault system may be a candidate for large-scale Cretaceous translation; and (c) the longevity (≥33 Myr) of the highly localized Denali fault master strand (≤1 km wide) implies that it occupies a major mechanical boundary that penetrates the lithosphere.Plain Language Summary Many of the rocks that make up present-day western Canada and southern Alaska did not form as part of North America. Instead, most formed as coherent island chains (called terranes), collided with North America, and then slid northward along fault systems to their present location. The timing of...

Large-scale, crustal-block vertical extrusion between the Hines Creek and Denali faults coeval with slip localization on the Denali fault since ca. 45 Ma, Hayes Range, Alaska, USA

“…30-25 Ma (Benowitz et al, 2011a(Benowitz et al, , 2012(Benowitz et al, , 2014(Benowitz et al, , 2019Riccio et al, 2014;Burkett et al, 2016;Lease et al, 2016;McDermott et al, 2019McDermott et al, , 2021Waldien et al, 2021bWaldien et al, , 2022). Together, these thermochronological studies outline a history of asymmetrical uplift and unroofing of the Alaska Range through time and space along the Denali fault system, with juxtaposed crustal blocks being translated hundreds of kilometers and at times in and out of geometric complexities (Waldien et al, 2021a). Hence, counter to what has been suggested (Lease et al, 2016), there is no systematic evidence of orogen-scale, west-to-east deformation expansion in the Alaska Range.…”

“…The extent of Neogene vs. early Cenozoic shortening (e.g., Trop et al, 2019) and the composition of the current basement to these strata is a subject of debate (Romero et al, 2020;Keough and Ridgway, 2021). More recent work has led to the conclusion that labeling all of the continentally derived rocks to the north as North American affinity and considering the Kahiltna as one basin oversimplifies regions with complex geologic histories (Hults et al, 2013;Dusel-Bacon et al, 2017;Dumoulin et al, 2018, Box et al, 2019, Waldien et al, 2021a. In this paper, these vestigial terms are used for simplicity and because the true geologic complexity inherited from the Mesozoic holds no sway on the scope of this work.…”

“…The 2000-km-long, dextral strike-slip Denali fault traverses the Alaska Range suture zone and has been active since at least ca. 65 Ma (Miller et al, 2002 Benowitz et al, 2014;Waldien et al, 2021a). The modern trace of the Denali fault is arcuate, with an azimuth that varies by over 50° (Fig.…”

Why is Denali (6,194 m) so big? Caught inside the tectonic wake of a migrating restraining bend

“…This period of orogenesis is part of the late Miocene southern Alaska tectonic event that reflects a change in Pacific plate convergence angle (Waldien et al., 2018). This event also led to the partitioning of slip from the eastern Denali Fault onto the Totschunda Fault and a resultant change in the geometry of the southern Alaska block (Figure 1; Waldien et al., 2021b). We postulate and investigate if the ~6 Ma launch of the extreme topographic relief in the Denali area is related to the formation and evolution of the MMRB at this time.…”

Long distance plutonic relationships demonstrate 33 million years of strain partitioning along the Denali fault

“…The Denali fault system is a long-lived (>100 My ;Trop et al, 2020) and active dextral fault system responsible for the highest topography in North America (Burkett et al, 2016). Late Pleistocene-Holocene slip rates along the Denali fault in Alaska decrease from east (12.9 mm/year) to west (5.3 mm/year; Figure 1; Haeussler et al, 2017) with partitioned strain accommodated in part via thrust fault splays on both sides of the fault (Bemis et al, 2015;Waldien et al, 2018Waldien et al, , 2021. It currently accommodates ~20% of the active convergence between the Yakutat plate and North America (Elliott & Freymueller, 2020), has experienced at least 400 km of total slip since 57 Ma (e.g.…”