Cenozoic tectono‐thermal history of the Tordrillo Mountains, Alaska: Paleocene‐Eocene ridge subduction, decreasing relief, and late Neogene faulting

Abstract

[1] Topographic development inboard of the continental margin is a predicted response to ridge subduction. New thermochronology results from the western Alaska Range document ridge subduction related orogenesis. K-feldspar thermochronology (KFAT) of bedrock samples from the Tordrillo Mountains in the western Alaska Range complement existing U-Pb, 40 Ar/ 39 Ar and AFT (apatite fission track) data to provide constraints on Paleocene pluton emplacement, and cooling as well as Late Eocene to Miocene vertical movements and exhumation along fault-bounded blocks. Based on the KFAT analysis we infer rapid exhumation-related cooling during the Eocene in the Tordrillo Mountains. Our KFAT cooling ages are coeval with deposition of clastic sediments in the Cook Inlet, Matanuska Valley and Tanana basins, which reflect high-energy depositional environments. The Tordrillo Mountains KFAT cooling ages are also the same as cooling ages in the Iliamna Lake region, the Kichatna Mountains of the western Alaska Range, and Mt. Logan in the Wrangell-St. Elias Mountains, thus rapid cooling at this time encompasses a broad region inboard of, and parallel to, the continental margin extending for several hundred kilometers. We infer these cooling events and deposition of clastic rocks are related to thermal effects that track the eastward passage of a slab window in Paleocene-Eocene time related to the subduction of the proposed Resurrection-Kula spreading ridge. In addition, we conclude that the reconstructed KFAT max negative age-elevation relationship is likely related to a long period of decreasing relief in the Tordrillo Mountains.

Persistent long-term ( c. 24 Ma) exhumation in the Eastern Alaska Range constrained by stacked thermochronology

“…1), and the rocks preserve evidence of rapid exhumation at approximately 23 and 6 Ma based on apatite fission track (AFT) thermochronology and an earlier Eocene exhumation event based on 40 Ar/ 39 Ar K-feldspar thermochronology Benowitz et al 2012a). The approximately 23 Ma exhumation pulse is thought to be controlled by regional uplift and is corroborated by the highenergy depositional environment of the early Miocene Tyonek Formation of Cook Inlet (Stricker & Flores 1996).…”

“…Recent AFT work in SW Alaska indicates rapid cooling in both plutonic and meta-sedimentary samples between approximately 24 and 20 Ma, implying regional cooling due to exhumation during this time period (Fig. 1) (O'Sullivan et al 2010;Benowitz et al 2012a). Deformation and metamorphism was occurring on part of the eastern Denali Fault by about 25 Ma at the Cottonwood complex ( Fig.…”

Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

“…This process often results in significant lithospheric thinning through physical erosion of the mantle lithosphere from beneath the overriding plate and thermal erosion from upwelling asthenosphere (Cole and Stewart, 2009;Jacobson et al, 2011;Ling et al, 2013). The net effect of this event upon the forearc region is typically short-term isostatic uplift of as much as several kilometers, followed by rapid subsidence to near original elevations after the ridge passes (Cloos, 1993;Madsen et al, 2006;Breitsprecher and Thorkelson, 2009;Groome and Thorkelson, 2009;Benowitz et al, 2012a). Furthermore, development of a slab window due to ridge subduction can lead to temporary cessation of the volcanic arc (e.g., Dickinson and Snyder, 1979;Thorkelson, 1996;Gorring and Kay, 2001).…”

Focused rock uplift above the subduction décollement at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

“…12-10 Ma (Plafker, 1987;Zellers, 1995;Ferris et al, 2003;Eberhart-Phillips et al, 2006;Enkelmann et al, 2008Enkelmann et al, , 2009 and as early as ca. 30-18 Ma (Plafker et al, 1994b;Enkelmann et al, 2008;Haeussler, 2008;Finzel et al, 2011;Benowitz et al, 2011Benowitz et al, , 2012Arkle et al, 2013). As the collision of this relatively buoyant material progressed, a fold-thrust belt developed, leading to high topography in the eastern Chugach-Saint Elias Mountains, and a marked transition between shallow subduction beneath the Prince William Sound and relatively steeper subduction of dense oceanic Pacifi c plate to the southwest (Fig.…”

“…Numerous studies using lowtemperature thermochronology have focused on exhumational patterns across major fault systems associated with fl at-slab subduction in southern Alaska, including studies in the Alaska Range (e.g., Fitzgerald et al, 1995;Haeussler et al, 2008Haeussler et al, , 2011Benowitz et al, 2011Benowitz et al, , 2012Benowitz et al, , 2013, Chugach Mountains (Little and Naeser , 1989;Buscher et al, 2008;Arkle et al, 2013), and Saint Elias Mountains (e.g., Berger et al, 2008aBerger et al, , 2008bBerger and Spotila, 2008;Meigs et al, 2008;Enkelmann et al, 2008Enkelmann et al, , 2009Spotila and Berger, 2010). Some of these studies detected loci of rapid exhumation, particularly in the Saint Elias and western Chugach Mountains, which may be the result of crustalscale lithologic backstops to upper crustal rock deformation above the subducting Yakutat microplate.…”