Alaska Range and Environs

Research Paper THEMED ISSUE: Geologic Evolution of the Alaska Range and Environs GEOSPHERE Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western GEOSPHERE, v. 16, no. 1 North America and initiation of the Totschunda fault https://doi.org/10.1130/GES02127.1 Jeffrey M. Trop1, Jeffrey A. Benowitz2, Donald Q. Koepp1, David Sunderlin3, Matthew E. Brueseke4, Paul W. Layer2, and Paul G. Fitzgerald5 18 figures; 3 tables; 1 set of supplemental files 1Department of Geology and Environmental Geosciences, Bucknell University, 701 Moore Avenue, Lewisburg, Pennsylvania 17837, USA 2Geophysical Institute and Geochronology Laboratory, University of Alaska–Fairbanks, Fairbanks, Alaska 99775, USA 3 CORRESPONDENCE: [email protected] Department of Geology and Environmental Geosciences, Lafayette College, Easton, Pennsylvania 18042, USA 4Department of Geology, Kansas State University, Manhattan, Kansas 66506, USA 5Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA CITATION: Trop, J.M., Benowitz, J.A., Koepp, D.Q., Sunderlin, D., Brueseke, M.E., Layer, P.W., and Fitzgerald, P.G., 2020, Stitch in the ditch: Nutzotin ABSTRACT clasts. Deposition was occurring by ca. 117 Ma and following the subduction of intervening oceanic Mountains (Alaska) fluvial strata and a dike record ceased by ca. 98 Ma, judging from palynomorphs, lithosphere is a fundamental process in plate ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda The Nutzotin basin of eastern Alaska consists the youngest detrital ages, and ages of crosscut- dynamics and the growth of Earth’s continents. The fault: Geosphere, v. 16, no. 1, p. 82–110, https://doi. of Upper Jurassic through Lower Cretaceous ting intrusions and underlying lavas of the Chisana suturing process itself results in changes in plate org /10.1130 /GES02127.1. siliciclastic sedimentary and volcanic rocks that Formation. Following deposition, the basin fill was dynamics, creates Earth’s largest mountain belts, depositionally overlie the inboard margin of deformed, partly eroded, and displaced laterally by and changes global climate dynamics by closing Science Editor: Andrea Hampel Wrangellia, an accreted oceanic plateau. We pres- dextral displacement along the Totschunda fault, ocean basins and forming high topography (e.g., Guest Associate Editor: Graham D.M. Andrews ent igneous geochronologic data from volcanic which bisects the Nutzotin basin. The Totschunda Coney et al., 1980; Raymo et al., 1988; Zhu et al., Received 17 February 2019 rocks and detrital geochronologic and paleonto- fault initiated by ca. 114 Ma, as constrained by the 2005; Najman et al., 2010). Although a fundamental Revision received 6 August 2019 logical data from nonmarine sedimentary strata injection of an alkali feldspar syenite dike into the and global tectonic process, details of this process Accepted 9 October 2019 that provide constraints on the timing of depo- Totschunda fault zone. remain poorly understood. Well-exposed geologic sition and sediment provenance. We also report These results support previous interpretations records of past suturing events await detailed inves- Published online 21 November 2019 geochronologic data from a dike injected into the that upper Jurassic to lower Cretaceous strata in tigation using modern analytical techniques (e.g., Totschunda fault zone, which provides constraints the Nutzotin basin accumulated along the inboard Finzel et al., 2011; Benowitz et al., 2014, 2019; Orme on the timing of intra–suture zone basinal defor- margin of Wrangellia in a marine basin that was et al., 2015). Ancient suture zones crop out across mation. The Beaver Lake formation is an important deformed during mid-Cretaceous time. The shift Earth’s continents in regional structural, sedimen- sedimentary succession in the northwestern Cor- to terrestrial sedimentation overlapped with crust- tary, and petrologic trends that extend hundreds to dillera because it provides an exceptionally rare al-scale intrabasinal deformation of Wrangellia, thousands of kilometers along strike. Such zones stratigraphic record of the transition from marine based on previous studies along the Lost Creek of deformation are rarely characterized by simple, to nonmarine depositional conditions along the fault and our new data from the Totschunda fault. single, easily recognizable lines but instead may be inboard margin of the Insular terranes during Together, the geologic evidence for shortening zones of deformation hundreds of kilometers wide mid-Cretaceous time. Conglomerate, volca- and terrestrial deposition is interpreted to reflect (Dewey, 1977). Suture zones are syncollisional fea- nic-lithic sandstone, and carbonaceous mudstone/ accretion/suturing of the Insular terranes against tures but often also serve as postcollisional zones shale accumulated in fluvial channel-bar com- inboard terranes. Our results also constrain the of crustal weakness prone to reactivation (Dewey, plexes and vegetated overbank areas, as evidenced age of previously reported dinosaur footprints to 1977; Hendrix et al., 1996; Holdsworth et al., 2001; by lithofacies data, the terrestrial nature of recov- ca. 117 Ma to ca. 98 Ma, which represent the only Cavazza et al., 2017; Laskowski et al., 2017; Trop et ered kerogen and palynomorph assemblages, and dinosaur fossils reported from eastern Alaska. al., 2019). These high-strain zones are often reac- terrestrial macrofossil remains of ferns and coni- tivated as strike-slip faults that laterally shuffle fers. Sediment was eroded mainly from proximal the upper plate (e.g., the Denali fault system; Fitz- sources of upper Jurassic to lower Cretaceous ■ INTRODUCTION gerald et al., 2014). The timing of fault initiation igneous rocks, given the dominance of detrital can provide independent controls on the timing This paper is published under the terms of the zircon and amphibole grains of that age, plus Suturing of fragments of continental crust, of accretion (Duvall et al., 2011). Geologic records CC-BY-NC license. conglomerate with chiefly volcanic and plutonic island arcs, and overthickened oceanic crust preserved within suture zones provide an archive © 2019 The Authors GEOSPHERE | Volume 16 | Number 1 Trop et al. | Suturing of the Wrangellia terrane with western North America and initiation of the Totschunda fault Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/16/1/82/4925052/82.pdf 82 by guest on 28 September 2021 Research Paper of the evolution of tectonic processes during and 148°W 141°W Canada Alaska Tintina fault following welding of crustal fragments, including AK YT deformation, magmatism, and sedimentation. North The northern Cordillera of western North Amer- Nutzotin basin BC Denali fault Dezadeash basin 64°N ica is an archetypal example of continental growth Fig. 3 Fig.1 through accretionary tectonic processes. It is a Kahiltna basin Totshunda WR Duke River IT fault fault complex collage of allochthonous terranes, sedi- AX PE Gravina basin mentary basins, magmatic belts, and subduction CP YA complex strata accreted to the continental margin, AX Gulf of Alaska CPC especially during Mesozoic to recent time (Coney et IT al., 1980; Plafker and Berg, 1994; Trop and Ridgway, AX 60°N 2007; Colpron et al., 2007; Gehrels et al., 2009). The Pacificplate Alexander, Wrangellia, and Peninsular terranes 0 200 km AX amalgamated during Paleozoic time, collided with IT Intermontane terrane and Ancestral NA (mainly Pz.-Precambrian rocks) the continental margin, and shuffled laterally along CPC Coast Plutonic Complex (Mesozoic-Cenozoic plutonic and metamorphic rocks) strike-slip faults, including the Denali, Totschunda, Mesozoic marine basins along inboard margin of Insular terranes and Duke River faults (Fig. 1; Plafker and Berg, 1994; Insular terranes (AX-Alexander terrane, PE-Peninsular terrane, WR-Wrangellia) Cowan et al., 1997; Stamatakos et al., 2001; Roe- CP Chugach and Prince William terranes (Mesozoic-Cenozoic accretionary prism) YA Yakutat terrane ske et al., 2003; Gabrielse et al., 2006; Wyld et al., 2006; Bacon et al., 2012). The Alexander terrane and Figure 1. Map showing major terranes and faults along the northern North American Cordillera margin. Wrangellia, together with the Peninsular terrane, Marine sedimentary basin deposits (dark green) record accretion of the Insular terranes (Alexander, are collectively referred to as the Insular compos- Wrangellia, and Peninsular terranes—gray) against older inboard Intermontane terranes (brown). This study focuses the Nutzotin basin. Red rectangles mark focus areas shown in Figure 3. Figure is modified ite terrane (Colpron et al., 2007), or the Wrangellia from Wilson et al. (2015). Inset map shows location of Figure 1 in North America (NA). Abbreviations: composite terrane (Plafker and Berg, 1994). AK—Alaska, USA; BC—British Columbia, Canada; YT—Yukon Territory, Canada; Pz—Paleozoic. The precise location of initial collision of the Insular terranes with the former continental margin is controversial (Cowan et al., 1997; Stamatakos et been referred to as the Alaska Range suture zone much as 100 km wide in the eastern Alaska Range, al., 2001), and the timing of initial collision may (Ridgway et al., 2002; Brennan et al., 2011) or mega– Nutzotin Mountains, and Wrangell Mountains (Rich- have been diachronous (Trop and Ridgway, 2007). suture zone (Jones et al., 1982). Geophysical data ter, 1976; Trop et

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