Research Paper GEOSPHERE Evolution of the Jura-Cretaceous North American Cordilleran margin: Insights from detrital-zircon U-Pb and Hf isotopes of GEOSPHERE; v. 13, no. 6 sedimentary units of the North Cascades Range, Washington doi:10.1130/GES01501.1 Kirsten B. Sauer1, Stacia M. Gordon1, Robert B. Miller2, Jeffrey D. Vervoort3, and Christopher M. Fisher3 12 figures; 3 tables; 1 supplemental file 1Department of Geological Sciences, University of Nevada, Reno, 1664 N. Virginia Street, Reno, Nevada 89557, USA 2Department of Geology, San Jose State University, One Washington Square, San Jose, California 95192-0102, USA 3School of the Environment, Washington State University, P.O. Box 642812, Pullman, Washington 99164-2812, USA CORRESPONDENCE: kirsten .b .sauer@gmail .com CITATION: Sauer, K.B., Gordon, S.M., Miller, R.B., ABSTRACT sedimentary basins (e.g., Saleeby and Busby-Spera, 1992; Dickinson, 2004). Vervoort, J.D., and Fisher, C.M., 2017, Evolution of the Jura-Cretaceous North American Cordilleran The U-Pb age spectra of detrital zircons from western North American Cordi - margin: Insights from detrital-zircon U-Pb and Hf The U-Pb age and Hf-isotope composition of detrital zircons from Jurassic lleran sedimentary rocks have been used to help understand episodic high-flux isotopes of sedimentary units of the North Cas- to Upper Cretaceous sedimentary rocks adjacent to the southern North Cas- magmatism (Paterson and Ducea, 2015), the timing at which sediment sources cades Range, Washington: Geosphere, v. 13, no. 6, p. 2094–2118, doi:10.1130/GES01501.1. cades–Coast Plutonic Complex continental magmatic arc document shifting were uplifted and when basins subsided (e.g., DeGraaff-Surpless et al., 2003; provenance, the tectonic evolution of the arc system, and translation along Laskowski et al., 2013; Surpless et al., 2014), paleogeography, and terrane Received 20 January 2017 the continental margin. Systematic changes in the detrital-zircon data pro- mobility (e.g., Gehrels et al., 1995; Housen and Beck, 1999; Barbeau et al., Revision received 12 June 2017 vide insight that the western margin of North America evolved from: marginal 2005). Hafnium-isotope analyses of detrital zircons are used as an additional Accepted 25 July 2017 basins adjacent to continent-fringing oceanic arcs (ca. 160–140 Ma); forearc fingerprint of sedimentary provenance (e.g., Gehrels and Pecha, 2014; Surpless Published online 2 October 2017 basins adjacent to mid-Cretaceous (ca. 120–90 Ma) Andean-type continental et al., 2014; Holland et al., 2015) by comparing to zircon Hf-isotope compo- arcs; and addition of a cratonic source to forearc and accretionary wedge units sitions of potential source rocks (e.g., Goodge and Vervoort, 2006; Gaschnig to Cordilleran arc systems in the mid-Late Cretaceous (ca. 85 Ma). Jurassic et al., 2011; Lackey et al., 2012; Shaw et al., 2014). Methow terrane, Nooksack Formation, and western mélange belt units domi- Controversy surrounds the Late Cretaceous tectonic history of northwest- nantly contain detrital zircons derived from accreted oceanic terranes, whereas ern North America, with many studies suggesting significant terrane transla- Lower Cretaceous strata from the same units have age peaks that correspond tion for parts of the Insular and Intermontane superterranes and the plutonic to known pulses of magmatism in Cordilleran continental magmatic arc sys- rocks of the Coast Plutonic Complex–North Cascades range that separate the tems. The age peaks and Hf-isotope signature of the Jurassic and Lower Cre- two superterranes (e.g., Monger et al., 1982; Cowan et al., 1997) (Fig. 1). Early taceous strata are comparable to multiple sources exposed along the margin. paleomagnetic studies of the Cretaceous plutonic and sedimentary rocks In contrast, the Upper Cretaceous western mélange belt has distinct Precam- suggested that the Insular superterrane and Coast Plutonic Complex–North brian zircon populations and unradiogenic Late Cretaceous zircons that are Cascades formed ~2500–3000 km to the south relative to the North American more similar to southwestern than northwestern Laurentian sources. Statisti- craton and were translated to the north between ca. 90–55 Ma (the “Baja-BC” cal comparisons confirm provenance similarities between rocks of the North hypothesis; Beck et al., 1981; Umhoefer, 1987; Ague and Brandon, 1996; Enkin Cascades and those 700–2000 km to the south and, thus, support margin- et al., 2001). More recent paleomagnetic studies interpret moderate (~1600– parallel translation from as far as the latitude of southern California. 2000 km) translation of these same rocks from reconstructions based on a combination of corrections to the paleomagnetic data and known fault offsets (Kim and Kodama, 2004; Krijgsman and Tauxe, 2006; Umhoefer and Blakey, INTRODUCTION 2006; Rusmore et al., 2013). Conversely, evidence from measured lateral off- sets on faults as well as stratigraphic correlations between similar packages Sedimentary basins associated with ancient arc systems arguably yield a of rocks indicate significantly less (<1000 km) northward translation (Price and more detailed history of arc evolution compared to arc volcanic components, Carmichael, 1986; Monger, 1997; Wyld et al., 2006). In comparison, paleomag- which are typically not preserved, or the plutonic rocks, which are variably netic signatures of rocks in the Intermontane superterrane, located to the east eroded and exposed (Gehrels, 2014). Jurassic to Eocene convergence along the of the Coast Plutonic Complex–North Cascades arc, suggest they originated For permission to copy, contact Copyright western margin of the North American continent resulted in the accretion of ~1100 km to the south of their current position relative to the North American Permissions, GSA, or [email protected]. multiple oceanic-arc terranes, intrusion of arc plutons, and formation of large craton (Irving et al., 1995; Symons et al., 2005). © 2017 Geological Society of America GEOSPHERE | Volume 13 | Number 6 Sauer et al. | Evolution of the North American Cordilleran margin Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/13/6/2094/3990859/2094.pdf 2094 by University of Nevada Reno user on 11 February 2019 Research Paper Chugach- The North Cascades range is located at the southern end of the “Baja-BC” Prince William Terrane block and the Jurassic to Eocene Coast Plutonic Complex–North Cascades AK conti nental magmatic arc, which stretches from Alaska to Washington (Fig. 1). Accretionary The crystalline core of the North Cascades arc system is juxtaposed with co- Complexes eval sedimentary units and Paleozoic and Mesozoic tectonostratigraphic ter- Jurassic to Eocene forearc/backarc basins ranes by major dextral strike-slip structures, the Ross Lake fault zone to the Jurassic to Eocene east and the Straight Creek fault to the west (Misch, 1966; Monger, 1986; Miller YK magmatic arc North American and Bowring, 1990; Umhoefer and Miller, 1996; Gordon et al., 2010). The sedi- passive margin mentary units and terranes, from west to east, are grouped into: (1) the west- BC Inter Insular superterrane ern mélange belt (WMB), representative of accretionary-wedge material that montane Intermontane is outboard of the arc; (2) the northwest Cascades thrust system (NWCS) and Insula superterrane its footwall sedimentary rocks, presently in a forearc position to the arc; and Paleozoic-Jurassic arc r terranes (3) the Methow terrane, which was formed as a forearc basin but was jux- ST Cordilleran taposed with the eastern, inboard boundary of the North Cascades core by foreland the Late Cretaceous (Miller, 1994) (Fig. 2). These packages of rocks are fault- Sevier thrust belt bounded, and all include sediment that was deposited before and during the Coast Undifferentiated interval when proposed terrane translation was occurring (ca. 90–55 Ma) (e.g., Plutonic Pacific Complex Misch, 1966; Brandon et al., 1988; Hurlow, 1993; Tabor, 1994; Umhoefer, 2003; QU plate Brown and Gehrels, 2007; Brown, 2012). Thus, the sedimentary rocks surround- Figure 1. Generalized geologic map of western North America highlighting the ing the North Cascades core likely contain valuable information about their WR major tectonic elements of the Cordilleran provenance, which may provide insight into terrane-translation hypotheses. Nanaimo arc system and the sedimentary units ad­ NWCS Methow This study uses U-Pb and Hf-isotope analyses of detrital zircons from accre- jacent to the different arc belts (modified CANADA tionary-wedge and forearc-basin deposits inboard and outboard of the North from Yonkee and Weil, 2015). BM—Blue U.S.A. Mountains; FB—Foothills Belt; HB—Horn­ WMB Belt Cascades crystalline core to interpret the Jurassic–Late Cretaceous tectonic North brook Basin; KM—Klamath Mountains; Cascades Supergroup history surrounding the arc (Fig. 2). The new zircon analyses presented here QU—Quesnellia; NWCS—Northwest Cas­ Juan de WA Lehmhi are used to evaluate potential source terranes for these sediments and are cades thrust system; SAFZ—San Andreas Fuca plate subbasin fault zone; ST—Stikine terrane; WMB— Cenozoic compared to previous detrital-zircon and Hf-isotope studies of the western cover western mélange belt; WR—Wrangellia. MT BM Cordillera to evaluate terrane translation. Idaho Batholith HB KM OR ID GEOLOGIC SETTING CA NV WY The western margin of the North American continent experienced multi- UT North UST FB ple episodes of accretion of oceanic-arc terranes, batholith emplacement,