Tectonic Growth of the Late Paleozoic‐Middle Mesozoic Northwestern Margin of Laurentia and Implications for the Farewell Terrane: Stratigraphic, Structural, and Provenance Records From the Central Alaska Range

Abstract

The late Paleozoic-Jurassic paleogeography of the northwestern margin of Laurentia remains a less-studied aspect of the tectonic development of the North American Cordillera. To date, the better-studied tectonic events in the northern Cordillera are related to the later Mesozoic and Cenozoic accretion of allochthonous terranes, such as the Insular superterrane (Wrangellia composite terrane; e.g.,

High-Latitude Depositional Systems, Provenance, and Basinal Setting of the Late Cretaceous Cantwell Basin, Denali National Park and Preserve, Alaska: A Stratigraphic Framework for Paleontological and Paleoclimatic Studies

“…(2) the oceanic Wrangellia composite terrane (WCT) to the south (Figure 1), which is thought to have collided obliquely from south to north along the continental margin [38,42,43]; and (3) deformed and metamorphosed sedimentary basin assemblages that represent the Jurassic-Cretaceous ocean basin between the ancestral North American margin and the WCT that was subsequently segmented and eventually fully closed in the collisional zone (e.g., Kahiltna basin) [43,44]. The part of the Cantwell basin exposed in our study area also overlaps a slightly older, Late Jurassic-Early Cretaceous accretionary zone associated with the interpreted collision of the allochthonous Farewell terrane with the ancestral North American margin [45]. Much of the Cantwell Formation in our study area was deposited unconformably atop Upper Triassic basalt interpreted as part of the Farewell terrane (unit TRbd in Figure 2) e.g., Refs.…”

“…Much of the Cantwell Formation in our study area was deposited unconformably atop Upper Triassic basalt interpreted as part of the Farewell terrane (unit TRbd in Figure 2) e.g., Refs. [35,36,45], whereas along the northern basin margin, the Cantwell Formation overlies deformed Mesozoic marine strata interpreted to be associated with the ancestral North American margin (unit TRcs in Figure 2) [45].…”

“…U-Pb detrital zircon ages from these strata include late Mesoproterozoic, Neoproterozoic, and Silurian-Ordovician populations that are extremely uncommon in rocks of the YCT or Wrangellia composite terrane [45]. Note that while unit KJf in the study area has been interpreted by regional mapping studies as part of the Kahiltna assemblage [34], recent U-Pb detrital zircon analyses from unit KJf along the northern basin margin yielded age spectra that are distinct from strata of the Kahiltna assemblage exposed south of the Denali fault [45]. Direct sediment input from basin-bounding thrust systems during the deposition of the Cantwell basin is also consistent with conglomerate clast compositions in alluvial fan strata along both margins documented in previous studies [2,81].…”

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

“…1B), which are composed principally of Late Jurassic to Late Cretaceous marine sedimentary strata and metamorphic equivalents (Ridgway et al, 2002;Trop et al, 2020). 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.…”

“…The metamorphosed North American crust is ~26-30 km thick north of the Hines Creek fault, whereas the Wrangellia composite terrane crust has been imaged to be ~30-48 km thick south of the Denali fault and possibly increases in thickness from west to east (Veenstra et al, 2006;Fuis et al, 2008;Brennan et al, 2011;Allam et al, 2017;Miller et al, 2018). Between the continental margin and the Wrangellia composite terrane is the dissected and imbricate Mesozoic Kahiltna marine basin with a generally undetermined basement (Romero et al, 2020;Keough and Ridgway, 2021), resulting in a total crustal thickness of ~41 km thick, as shown by P receiver functions (Miller et al, 2018).…”