TECTONICS, VOL. 32, 1–22, doi:10.1002/tect.20065, 2013

Detrital zircon geochronology of Cordilleran retroarc foreland basin strata, western North America Andrew K. Laskowski,1 Peter G. DeCelles,1 and George E. Gehrels 1 Received 27 February 2013; revised 21 June 2013; accepted 11 July 2013.

[1] We present a compilation of 8717 U-Pb analyses from 95 detrital zircon samples of Jurassic-Eocene North American Cordillera foreland basin strata. Of these samples, 30 are new and previously unpublished. Variation in detrital zircon age spectra between samples records erosion or recycling of basement and cover rocks within the Cordilleran orogenic wedge. Each sample can be classified into one of six major provenance groups, whose age spectra suggest derivation from (1) Mesozoic eolianites of the western United States, (2) Paleozoic passive margin strata of the western United States, (3) Paleozoic passive margin strata of western Canada, (4) the Mogollon Highlands, (5) the Cordilleran magmatic arc, or (6) Yavapai-Mazatzal Province crystalline basement rocks. Referencing these provenance interpretations to their location and stratigraphic deposition age produces a detailed spatial and temporal record of sediment dispersal within the foreland basin system. Late Jurassic provenance is dominated by recycling of Mesozoic eolianites from sources in the Sevier thrust belt. Cretaceous-Eocene provenance is dominated by recycling of the passive margin, with increasing complexity upsection. We interpret that this provenance transition records a basin-wide unroofing sequence. A composite age-probability plot of 1539 young (<250 Ma) detrital zircons reveals at least four age-abundance peaks that we interpret to represent periodic high-flux magmatism in the Cordilleran arc. Citation: Laskowski, A. K., P. G. DeCelles, and G. E. Gehrels (2013), Detrital zircon geochronology of Cordilleran retroarc foreland basin strata, western North America, Tectonics, 32, doi:10.1002/tect.20065.

1. Introduction individual orogenic systems. Provenance analysis conducted in the North American Cordillera is particularly successful at [2] Siliciclastic strata deposited in continental basins con- linking synorogenic strata to specific orogenic wedge struc- tain detrital zircons with uranium-lead (U-Pb) age spectra tures [e.g., Dickinson and Gehrels, 2008; Fuentes et al., that in many cases vary systematically throughout geologic 2009; Lawton and Bradford, 2011; Lawton et al., 2010; time. Within sufficiently populated data sets, the relative Leier and Gehrels, 2011]. abundance of specific ages can be used to identify the timing fi [3] In this paper, we present a large detrital zircon data- of rst-order magmatic and accretionary processes [e.g., base (8717 U-Pb ages) that samples Jurassic-Eocene Condie and Aster, 2009]. This approach is particularly salient synorogenic strata deposited within the Cordilleran foreland in understanding ancient supercontinent cycles, as detrital basin system of North America (Figure 1). The objectives of zircons have higher preservation potential than prima facie this study are to (1) define a framework for interpreting detri- bedrock exposures. Detrital zircon geochronology is also tal zircon provenance in the foreland basin system, (2) utilize applicable at the continent scale. For example, numerous provenance interpretations and paleocurrent data to map studies show that variations in detrital zircon age spectra sediment dispersal pathways during Cordilleran orogenesis, track the long-term distribution of orogenic belts, Andean- and (3) track exhumation of specific tectonostratigraphic type magmatic arcs, and sediment dispersal systems [e.g., sequences in the Cordilleran orogenic wedge. All of the Dickinson and Gehrels, 2003, 2009a; LaMaskin, 2012; samples included in this study can be categorized into one Leier and Gehrels, 2011; Rainbird et al., 1992]. Moreover, of six provenance groupings, which are genetically tied to detrital zircons can resolve crustal recycling within recycling of sedimentary sequences or erosion of primary Laurentian igneous and metamorphic rocks. Whenever pos- Additional supporting information may be found in the online version of sible, provenance interpretations were guided by the use of this article. Kolmogorov-Smirnov (K-S) statistics, which test whether 1 Department of Geosciences, University of Arizona, Tucson, Arizona, age spectra could have been derived from the same parent USA. population. The 27 samples that could not be grouped using Corresponding author: A. K. Laskowski, Department of Geosciences, K-S statistics were qualitatively interpreted based on com- University of Arizona, Tucson, AZ 85721, USA. ([email protected]) parison of age peaks with published references. In general, ©2013. American Geophysical Union. All Rights Reserved. samples that could not be classified statistically displayed 0278-7407/13/10.1002/tect.20065 mixed provenance.

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Figure 1. Tectonic overview map of the North American Cordillera showing the location of foreland basin system samples, their interpreted provenance (coded by symbol), their stratigraphic age (coded by color), and aerial extent of major exposures of igneous and metamorphic rocks (references in Table S1; bed- rock geology from USGS National Map, http://www.nationalmap.gov). Chronostratigraphic relationships between samples from the four sampling regions (1, Four Corners; 2, Uinta; 3, Montana; 4, Canada) are discussed in the text and plotted in Figure 2. Overlapping sample icons of the same stratigraphic age and provenance interpretation were reduced to one symbol. Satellite imagery is from Esri EarthSat.

2. Samples each case, care was taken to avoid contamination during col- lection, transport, and storage processes. Contamination risk [4] Of the 95 detrital zircon samples considered in this study, is likely higher for cuttings samples, which were carried to 30 have not been reported previously and 65 were compiled the surface by drilling mud that may contain zircons. In addi- from literature [Dickinson and Gehrels, 2008; Lawton et al., tion, the inclusion of fragments of rock that cave from the 2010; Fuentes et al., 2011; Lawton and Bradford, 2011; hole above the stratigraphic level of interest is possible but Leier and Gehrels, 2011; Raines et al., 2013]. Here we summa- probably minimal. This process likely occurs only when the rize the sampled stratigraphy (Figure 2) at the regional scale, drilling head is nearby, minimizing the potential error. beginning with new samples from southwestern Montana. Detrital zircon sample metadata (Table S1), analytical data [5] Sixteen of the new samples were collected from fresh (Table S2), and representative cathodoluminescence images surfaces on roadcuts or outcrops, six were collected from drill (Figure S1) are available in the supporting information. core, and nine were collected from drill cuttings. Samples Stratigraphic depositional ages are described using the time consisted of ~10 kg of rock, core, or cuttings fragments. In scale of Walker and Geissman [2009].

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Figure 2. (a) Location of detrital zircon samples and boundaries of the four sampling regions charted in Figure 2b and discussed in the text. (b) Formation names and generalized stratigraphic relationships for detrital zircon samples. Where present, numbers in parentheses indicate the number of samples from individual units within a given sample region. New samples are highlighted in red. See Table S1 for depositional age references. Time scale simplified from Walker and Geissman [2009].

2.1. New Samples the range front to the north. Sample 10DM11 was collected [6] Seven Cretaceous and Paleogene foreland basin sam- from the Red Butte Conglomerate of the Beaverhead Group ples were collected in southwestern Montana. Sample in the Ashbough Canyon area, which is thought to be the only – 10DM25 was collected from a fluvial sandstone in the Paleocene (65.5 55.8 Ma) interval in the Group [Haley and Aptian (125–112 Ma) Kootenai Formation [DeCelles, 1986] Perry, 1991]. in a canyon ~9 km west of Dell, Montana, in the Tendoy [8] Eight detrital zircon samples were collected from the Mountains. The Kootenai Formation unconformably overlies foreland basin sequence in southwestern Wyoming and north- eastern Utah, in the region surrounding the Uinta Mountains the Upper Jurassic Morrison Formation. Sample 10DM17 “ ” was collected from a ledge of fluvial and littoral Frontier ( Uinta region, Figure 2). The only Jurassic sample in Formation sandstone located along a drainage on the north- the set was collected from the Upper Jurassic Salt Wash eastern flank of Mt. Cohen, in the Beartooth Range. Dyman Member of the Morrison Formation (sample 7.19.06.2), et al. [2008] reported palynological data indicating a located ~85 m above the base of the Morrison Formation in section 1RF of Currie [1998], near Redfleet reservoir, Utah. Coniacian (89.3–85.8 Ma) depositional age for the middle to Currie [1998] interpreted this interval as recording a sandy upper Frontier Formation in the nearby Centennial Range. braided river system. These data correlate well with existing geochronological and [9] The remainder of the Uinta region samples were palynological data from the Frontier Formation in the extreme deposited during the Cretaceous. Of these samples, three southwestern Lima Peaks region, which encompasses the bulk are fluvial sandstones and four are synorogenic conglomer- of the Montana samples. ates. Sample K2 was collected from the Lower Cretaceous [7] Five samples from various members of the synorogenic Kelvin Formation located 29 m stratigraphically above a Upper Cretaceous to Paleogene Beaverhead Group were col- 10 m thick massive gray calcrete zone that marks the contact lected from the Lima Peaks region. Depositional age ranges between the Kelvin Formation and the underlying Morrison for the Beaverhead Group samples presented here were Formation. Upward fining fluvial channel sandstones with determined using the nomenclature of Haley and Perry prominent chert pebble conglomerates in their lower parts [1991]. All Beaverhead Group samples were collected from are exposed in roadcuts along Utah State Highway 32, on fluvial sandstones and alluvial fan conglomerates [Haley the western shore of Rockport Reservoir. Sample EM6 and Perry, 1991]. In the McKnight Canyon area, located was collected from an outcrop of fluvial-deltaic channel sand- 10 km northwest of Dell, Montana, samples 10DM22 and stone of the Chimney Rock Member of the Rock Springs 10DM23 were collected from the Campanian (83.5–70.6 Ma) Formation along the eastern side of Wyoming State and lower Maastrichtian (70.6–65.5 Ma) intervals of the Highway 430. Sample EM4 was collected from distributary Beaverhead Group, respectively. These two samples are age mouth bar sandstone of the fluvial-deltaic basal Blair equivalent with samples of the lower limestone clast conglom- Formation. Devlin et al. [2009] reported likely Campanian de- erate (10DM09) and upper quartzite clast conglomerate positional ages for the Chimney Rock Member and the basal (10DM20) collected near Bannack, Montana ~50 km along Blair Formation of ~81 and ~82–83 Ma, respectively.

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[10] Detrital zircon samples collected from synorogenic [2011], and seven samples from Lawton et al. [2010]. When conglomerates in the Uinta region offer insight into prove- combined, these data provide good coverage of the Upper nance relationships within the Sevier belt during the Late Jurassic to Upper Cretaceous foreland basin throughout the Cretaceous. Sample ECH1 was collected from the upper part region. The initial stages of Cordilleran orogenesis are well of the lower member of the Echo Canyon Conglomerate. The resolved here, as 11 of the samples are from the Upper sampled interval is fluvial sandstone that is interbedded with Jurassic Morrison Formation. cobble to pebble conglomerates representing shallow braided [14] Samples from localities that trace the central Sevier belt streams on a stream-dominated alluvial fan. Nichols and in Utah, Colorado, Wyoming, and Idaho compose the Uinta re- Bryant [1990] and DeCelles [1994] reported palynological gion grouping. Of the 24 Uinta samples (Figure 2), only one data for these strata that indicate a Coniacian-Santonian was compiled from literature—the Campanian Kaiparowits (89.3–83.5 Ma) depositional age. Sample CR7 was collected Formation [Lawton and Bradford, 2011]. Therefore, our new from the type locality of the Canyon Range Conglomerate, in data are critical in bridging the gap in published data between Wildhorse Canyon in the northern Canyon Mountains of cen- the Four Corners region and Montana. tral Utah. This coarse-grained sandstone was interbedded [15] The Montana region data consist of a combination of with cobble to boulder conglomerate beds and has a poorly seven new and 11 compiled samples. New samples, along constrained Cenomanian-Turonian (99.6–89.3 Ma) deposi- with two samples from Leier and Gehrels [2011], are located tional age [DeCelles et al., 1995; DeCelles and Coogan, along the frontal Cordilleran thrust belt, south of the Helena 2006; Lawton et al., 2007]. Sample HF2 was collected from Thrust Salient [Schmidt and O’Neill, 1982]. Samples north an outcrop of coarse-grained sandstone of the Campanian- of the Salient include an additional sample from Leier and Maastrichtian Hams Fork Conglomerate member of the Gehrels [2011] and eight samples from Fuentes et al. [2011]. Evanston Formation [DeCelles, 1994; DeCelles and Cavazza, [16] Most samples from Canada are distributed along the 1999]. Samples EM2 and LM73 were collected from a frontal Cordilleran thrust belt in southwest Alberta and cen- coarse-grained upper shoreface sandstone in the upper tral British Columbia. An additional group of samples are part of the Little Muddy Creek Conglomerate. The Little from the distal foreland basin in central Alberta. These sam- Muddy Creek Conglomerate was likely deposited during ples consist of seven samples from Leier and Gehrels [2011] the Santonian [Pivnik, 1990]. and seven samples from Raines et al. [2013]. [11] Collaboration with ExxonMobil drilling projects in the La Barge and Piceance basins of southwestern Wyoming and northwestern Colorado yielded 15 core and cutting samples 3. Methods from the Cordilleran retroarc foreland basin system. Samples from the Piceance basin were collected at a drill site located 3.1. Detrital Zircon Uranium-Lead Geochronology ~50 km northwest of the town of Rifle, Colorado, on the west- [17] All detrital zircon samples included in this study— ern slope of the Rocky Mountains. These samples include the whether newly generated or compiled from the literature— Upper Cretaceous Mancos (T67-14419) and Corcoran were prepared and analyzed using consistent protocols at (PCU12120) formations, the Upper Cretaceous to Paleocene the Arizona Laserchron Center (http://www.laserchron.org) Williams Fork Formation (T67-7420, T67-8024, PCU7620, [Gehrels et al., 2008]. PCU7980, and PCU-9470), and the Paleocene to Eocene [18] Zircon grains were extracted from samples in the tra- Ohio Creek (T67-7084), Wasatch (T26-2673 and PCU4020), ditional crushing and grinding manner. Additional separation and Uinta formations (09CA01). Samples from the La Barge was accomplished using a Wilfley table, heavy liquids, and a basin were collected at a drill site located ~20 km northwest Frantz magnetic separator. A large aliquot (~1000–2000) of of La Barge, Wyoming, along State Highway 235. These in- zircon grains was mounted alongside fragments of the Sri clude the Adaville Formation (LBRG-3500) and the Almond Lanka standard on a 1 inch round epoxy “puck.” Prior to iso- Formation of the Mesaverde Group (LBRG-2700 and topic analysis, samples were sanded to a depth of ~20 μm, LBRG2900). All of the La Barge samples were deposited polished, and cleaned. during the Campanian (~84–71 Ma). [19] U-Pb analyses were conducted using laser ablation multicollector inductively coupled plasma mass spectrome- 2.2. Published Samples try (ICPMS) [Gehrels et al., 2006, 2008]. Zircons were [12] Sixty-five samples were compiled from literature ablated using a Photon Machines Analyte G2 excimer laser for analysis alongside the new data. These samples are with a 30 μm beam diameter. The net effect of the ablation distributed along the frontal Sevier belt in southern Canada process produces pits on the zircon crystals that are ~15 μm and the United States and span a >1500 km segment of deep. The ablated material is transported in helium to the Cordilleran orogenic system (Figure 1). Although strati- the plasma source of the Nu HR ICPMS, which measures graphic range and sample density vary along strike (Figure 2), U, Th, and Pb isotopes simultaneously. Measurements were most regions are sufficiently populated throughout the conducted in static mode using Faraday detectors with Late Jurassic-Paleocene phase of Cordilleran orogenesis. 3×1011 ohm resistors for 238U, 232Th, 208Pb-206Pb, and dis- The following is a summary of the compiled data, organized crete dynode ion counters for 204(Pb + Hg) and 202Hg. Each by region and author. analysis consists of one 15 s integration on peaks with the [13] Samples from the southwestern United States cluster laser off, 15 one-second integrations with the laser firing, around the shared border between the states of Colorado, and a 30 s delay to purge for the next analysis. The ablation Utah, Arizona, and New Mexico. These data from the Four process produces ion yields of ~0.8 mV per ppm. Corners region (Figure 2) include 21 samples from Dickinson [20] Individual analyses carry analytical uncertainties of and Gehrels [2008], 11 samples from Lawton and Bradford ~1–2% (at the 2-sigma level) for 206Pb/238U ages that result

4 LASKOWSKI ET AL.: CORDILLERAN FORELAND DZ GEOCHRONOLOGY from uncertainty in determining 206Pb/238Uand206Pb/204Pb. on published data sets (see detrital zircon signatures in section Errors in measurement of 206Pb/207Pb and 206Pb/204Pb pro- 5, below). The 27 samples that could not be grouped statistically duce similar ~1–2% (at the 2-sigma level) uncertainties for (distinguishable from >50% of grouped samples) were qualita- > 1.0 Ga 206Pb/207Pb ages. However, analytical error in deter- tively interpreted within the context of published data sets (see 206 207 mining Pb/ Pb ages substantially increases for zircon section 5) and Laurentian basement age domains (Figure 3). grains with ages <1.0 Ga. The cutoff for reporting These groupings include all samples that were interpreted to 206 238 206 207 Pb/ Uversus Pb/ Pb ages averages ~1.0 Ga but is document first-cycle erosion of primary igneous and meta- adjusted for each sample to avoid dividing clusters of morphic sources as well as mixed provenance signals. ~1.0 Ga analyses. Possible explanations for why qualitatively grouped samples [21] Inter-element fractionation of Pb/U (~5%) and Pb failed the statistical test are discussed in the provenance results < isotopes ( 0.2%) was corrected using in-run analyses of sections below (sections 6.1.1–6.1.7). fragments of the Sri Lanka zircon standard. This large zircon crystal has an age of 563.5 ± 3.2 Ma at 2-sigma uncertainty [Gehrels et al., 2008]. Concentrations of U and Th were also determined relative to known quantities in the Sri Lanka 4. Tectonic Setting zircon, which are ~518 ppm of U and 68 ppm of Th. 204Hg [24] The North American Cordilleran thrust belt and retroarc interference with 204Pb was accounted for by measuring foreland basin system (Figure 1) was initiated in Late Jurassic 202Hg during laser ablation and subtracting 204Hg according time in response to North Atlantic spreading and coeval to the natural 202Hg/204Hg of 4.35. Hg-corrected 204Pb and subduction of oceanic plates along the western margin of an assumed initial Pb composition [Stacey and Kramers, Laurentia [DeCelles, 2004]. At this time, the Cordilleran 1975] were used to correct for common Pb. Uncertainties fore-arc region transformed from a zone of fringing arcs of 1.5 for 206Pb/204Pb and 0.3 for 207Pb/204Pb were applied and interarc oceanic basins to a coherent, east dipping arc- to the compositional values based on observed variation in trench system [Harper and Wright, 1984; Wright and Pb isotopic composition in modern crustal rocks. Fahan, 1988; Saleeby and Busby-Spera, 1992; Dickinson [22] U-Pb analytical data are reported in Table S2. et al., 1996]. In the retroarc region, Late Jurassic topographic Uncertainties are at the 1-sigma level and include only mea- highs and magmatic centers formed and began to shed surement errors. U-Pb analyses in excess of 20% discordance volcanoclastic and siliciclastic sediments into marginal marine (determined by comparison of 206Pb/238U and 206Pb/207Pb basins of the western United States—marking the initiation of ages) or >5% reverse discordance were not considered. The a composite orogenic wedge [Jordan, 1985; Meyers and 20% discordance filter was applied to prevent biasing of Schwartz, 1994]. Sedimentation in the foreland basin system the age distribution due to preferential exclusion of older remained intimately linked with Cordilleran shortening in grains. Interpreted U-Pb ages based on the above corrections the retroarc thrust belt for the next >100 Ma. are plotted in Figures 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h using the [25] The modern expression of Mesozoic oceanic subduc- routines of Isoplot [Ludwig, 2008], which are available from tion along the western margin of North America is the the Berkeley Geochronology Center (http://www.bgc.org/ Cordilleran magmatic arc, a >5000 km long belt of Late isoplot_etc/isoplot.html). In this procedure, the distribution Triassic to Late Cretaceous calc-alkaline granitoid batholiths of ages and their measurement uncertainties are normalized and related volcanic rocks [Saleeby and Busby-Spera, 1992]. into single curves to create age-probability diagrams. These rocks crop out in a nearly continuous belt from the Coast Mountains batholith in southeastern Alaska and western 3.2. K-S Provenance Analysis Canada to the Peninsular Ranges batholith in Baja California [23] To simplify the process of statistical provenance analy- (Figure 1). The orogen-scale history of magmatism in the sis, samples were initially sorted into qualitative provenance Cordilleran arc is complex, as locations and magmatic groupings based on visual examination of their probability addition rates vary through time for individual arc segments distribution functions (PDFs), which display the presence and [Gaschnig et al., 2010; Paterson et al., 2011]. Of these relative abundance of age peaks (e.g., Figure 4). Qualitative segments, the Sierra Nevada batholith of central and southern groups were then tested for internal consistency, which is a California is perhaps the best understood. Radiometric ages of measure of the percentage of statistically indistinguishable spec- plutonic rocks in the Sierra Nevada reveal major pulses in tra in a given grouping, using the K-S statistical analysis [Press magmatic activity between 160–150 and 100–85 Ma et al., 1986] routine available at http://www.laserchron.org. The [Barton, 1990; Ducea, 2001]. K-S test compares detrital zircon age spectra to evaluate the null [26] Nearly orthogonal convergence between the rapidly fi hypothesis that the two distributions are the same. Speci cally, westward moving North American plate and the oceanic the K-S test compares the maximum probability difference Farallon plate drove shortening in the Cordilleran retroarc between two cumulative distribution function (CDF) represen- thrust belt [Engebretson, 1984]. This complex zone of tations of the age spectra. Dependence on the CDF, which sums eastward verging faulting and folding can be divided into probabilities with increasing age, results in heightened sensitiv- five tectonostratigraphic zones. From west to east, these ity to the relative abundance of age peaks rather than their zones include the Luning-Fencemaker thrust belt, the central presence or absence. This characteristic caused samples with Nevada thrust belt, a high-elevation plateau referred to as the fewer grains or skewed peak abundances to be rejected. Nevadaplano, the Sevier fold-thrust belt, and the Laramide Nevertheless, 69 samples were deemed statistically indistin- intraforeland basement uplifts [DeCelles,2004].Eachofthese guishable from >50% of other samples in one of the six tectonomorphic zones experienced shortening, crustal thicken- qualitative provenance groupings, which were defined based ing, metamorphism, and/or magmatic activity during the Late

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work has shown that significant slices of Precambrian metamor- phic basement rocks were incorporated into some thrusts [e.g., Burchfiel and Davis, 1972; Royse et al., 1975; Skipp, 1987; Schirmer, 1988; Yonkee, 1992; DeCelles, 1994]. Low-angle thrust faults of the Sevier belt merge with ductile shear zones at depth in eastern Nevada and western Utah [Camilleri et al., 1997; DeCelles and Coogan, 2006]. Therefore, the Sevier thrust belt spans a north-south distance of >1500 km and restores to ~200 km in maximum width following restoration for Cenozoic extension [Gans and Miller, 1983; Long, 2012]. Along-strike variations in structural style, lithofacies, and paleo- geography in the Sevier belt can be invoked to explain differing detrital zircon affinities in the Cordilleran retroarc foreland basin system.

5. Detrital Zircon Signatures

[28] Successful application of detrital zircon provenance analysis hinges upon sufficient understanding of the distribu- tion of primary igneous sources for the grains as well as the signature of potentially recycled sediments. Fortunately, the igneous history of North American basement and the detrital zircon characteristics of overlying sedimentary rocks are relatively well understood. Here we present relevant geo- chronological data that enable provenance interpretation using detrital zircon geochronology in the Cordilleran retroarc foreland basin system. Detrital zircon age spectra of potentially recycled tectonostratigraphic sequences are plotted in Figure 4. Also plotted on this figure, and mapped on Figure 3, are characteristic age ranges for major North American crustal provinces.

5.1. Laurentian Basement Rocks [29] The Laurentian craton, which is dominantly composed of reworked Archean (>1.8 Ga) continents and continental fragments, came together during the Paleoproterozoic (2.0–1.8 Ga) Trans-Hudson orogeny [Hoffman, 1988]. Today, these rocks are exposed in basement uplifts of the northern United States and in the Canadian Shield region Figure 3. Location of North American crustal provinces of central Canada and Greenland. During the Proterozoic, that may have supplied detrital zircons to the Cordilleran multiple collisional events (1.71–1.30 Ga) accreted juvenile retroarc foreland basin system. Age domains are color coded terranes to the cratonal core [Whitmeyer and Karlstrom, to match those of the age-probability diagrams in Figures 4 2007]. Yavapai (1.8–1.7 Ga), Mazatzal (1.7–1.65 Ga), and and 6a–6e. Adapted from Gehrels et al. [2011] and refer- Grenville (1.2–1.0 Ga) rocks compose the bulk of this more ences therein. Distribution of mesozoic eolianites from juvenile crust. Following their accretion, the Yavapai and Leier and Gehrels [2011]. Mazatzal provinces were intruded by plutons associated with an A-type magmatic event (1.48–1.34 Ga) [Van Jurassic to Eocene and are generally considered to be the Schmus et al., 1996]. The net effect of these processes was product of a coherent orogenic wedge with an eastward migrat- to create a stable Laurentian craton and platform composed ing thrust front and foreland basin system. The easternmost of distinct crustal provinces (Figure 3) whose age signatures expression of thin-skinned thrust faulting and related folding recur throughout North America’s sedimentary record. in the Cordilleran retroarc region is referred to by a variety of [30] In Montana, southern Alberta, and southern British terms, including the Sevier belt in Utah, Wyoming, and Columbia, Laurentian embayments provided the accommoda- Idaho; the Montana disturbed belt; and the Canadian Rocky tion space for a thick accumulation of Mesoproterozoic- Mountains thrust belt [Allmendinger, 1992]. Frontal thrusts in Neoproterozoic siliciclastic strata. These strata, which have this belt locally override the Cordilleran foreland basin system since been metamorphosed up to middle greenschist grade, that developed within North America’s >5,000,000 km2 contain detrital zircon ages that plot within the North Western Interior Basin. American Magmatic Gap—a time period for which no known [27] The Sevier thrust belt is dominated by low-angle thrust Laurentian sources are preserved. The presence of these zircons faults that transported Neoproterozoic-upper Mesozoic sedi- requires an exotic terrane outboard of western Laurentia. mentary rocks in their hanging walls. Although Armstrong Stewart et al. [2010] argued on the basis of crustal ages and [1968] defined the Sevier belt as exclusively thin skinned, later Hf isotopic signatures that these zircons were likely derived

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Figure 4. Composite normalized probability curves for potentially recycled tectonostratigraphic sequences of the western United States and Canada. Shaded age domains are color coded to match corre- sponding Laurentian crustal provinces that are mapped in Figure 3. Normalized probability curves for Ordovician passive margin samples (gray and unfilled) are plotted atop the rest of G. E. Gehrels and M. T. Pecha’s (U-Pb and Hf Detrital Zircon Reference for Paleozoic and Triassic Miogeoclinal Strata of Western North America, submitted to Geosphere, 2012) data to illustrate their pronounced differences. These curves are reflected horizontally in Figures 6c and 6e to facilitate visual comparison of the interpreted provenance matches. from eastern Antarctica and Australia when they were zircon provenance analysis between Sonora, Mexico, and connected to southwestern Laurentia within a proto-Rodinian southeastern Alaska. Their data set was updated by Gehrels supercontinent. Alternatively, these zircons may have been and Pecha (submitted manuscript, 2012), who present high- eroded from an undocumented 1.6–1.5 Ga African source age-density detrital zircon data from the same stratigraphy that was exposed during the Grenvillian orogeny. Whatever (n ~ 200). Their results, which reveal a dominance of local the case, sediments that filled these basins came to dominate Laurentian sources, enable K-S test fingerprinting of north- thrust sheets in the interior of the Montana disturbed belt and erly or southerly provenance for Cordilleran retroarc foreland the Canadian Rocky Mountains thrust belt (Figure 1) [Price, basin strata. The authors identified three major trends rele- 1981; Fuentes et al., 2012]. vant to this objective: (1) Ordovician strata are dominated by Trans-Hudson (1.8–2.0 Ga) and Wopmay (2.0–2.3) ages 5.2. North American Passive Margin along the entirety of the Laurentian margin; (2) non- [31] Thrust sheets of the Sevier belt are principally Ordovician strata generally mimic the age spectra of nearby constructed from an elongated prism of thick sediments that Laurentian basement provinces; and (3) Grenville-aged were deposited on the passive western margin of Laurentia (1.2–1.0 Ga) grains are ubiquitous throughout. following the breakup of Rodinia. Basal, Neoproterozoic strata of this sequence accumulated in embayments west of 5.3. Mesozoic Eolianites the Wasatch hinge line, which demarcates the eastern extent [33] Vast ergs (sand seas) developed in southwest of significant rifting of Laurentian crystalline basement rocks Laurentia during the Permian-Jurassic. Today, these ergs [Hintze, 1988]. These strata are dominated by siliciclastic are preserved in the form of eolianites in the Four Corners re- rocks that reached maximum thicknesses of >10 km [Link gion of the southwestern United States. Provenance analysis et al., 1993]. During the early Paleozoic, passive margin sed- of zircons from these sandstones reveals a dominance of imentation overlapped Precambrian crystalline basement Grenvillian (1315–1000 Ma), Pan-African (750–500 Ma), rocks east of the hinge line, reaching maximum thicknesses and Paleozoic (500–310 Ma) grains throughout the section of ~12 km in western Utah. [Dickinson and Gehrels, 2003]. In addition, each sample con- [32] Gehrels et al. [1995] systematically sampled five tran- tains zircons whose ages overlap with those of Paleozoic sects of the North American passive margin for detrital Appalachian plutons that trace the Laurentian-Gondwana

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Figure 5a. Individual normalized probability curves for detrital zircon samples of the Cordilleran mag- matic arc provenance interpretation group. Samples are plotted atop a graph of major crustal age domains that correspond to those mapped in Figure 3. Normalized probability curves are arranged so that the north- ernmost samples are at the top of the figure. Maximum depositional ages were calculated for each sample by averaging the youngest group of three zircons with overlapping ages [Dickinson and Gehrels, 2009b]. suture. These populations are interpreted to record a trans- system (Figure 1). Today, a discontinuous belt of deeply continental drainage system with headwaters in eastern exhumed granitic batholiths characterizes this zone. These Laurentia [Dickinson and Gehrels, 2003, 2009a]. During exposures have been studied in detail to reconstruct changing Cordilleran contractional deformation, leading thrusts of magmatic addition rates and paleogeography of the North the Sevier belt deformed these strata. Therefore, it is likely American margin [Tobisch et al., 1986; Busby-Spera, 1988; that Appalachian-derived sediments experienced second- Barth et al., 1997; Dunne et al., 1998; Ducea, 2001; cycle deposition within the Cordilleran retroarc foreland Paterson et al., 2004, Saleeby et al., 2008; Gehrels et al., basin system. 2009; Miller et al., 2009]. [35] Detrital zircon provenance analysis of retroarc region 5.4. Cordilleran Magmatic Arc strata indicates that the magmatic arc and retroarc thrust belt [34] Arc magmatism in western North America dates back formed a topographically integrated, Andean-type margin by to the initiation of subduction along the western margin of Late Jurassic-Early Cretaceous time [Fuentes et al., 2009]. Laurentia during the Permian [Dickinson and Lawton, These results are supported by geological investigation of 2001]. The oldest arc rocks are preserved in the Permian- Early to Middle Jurassic, intra-arc grabens that contain Triassic (284–232 Ma) magmatic arc of eastern Mexico, marine sediments [Saleeby and Busby-Spera, 1992] followed which intruded Gondwanan crust above a subduction zone by accumulation of substantial Late Jurassic arc-derived de- located in present-day central Mexico. This segment was tritus in the retroarc region, indicating significant elevation bound to the north by a transform fault, which truncated the gain [Christiansen et al., 1994]. This evidence suggests that continental margin prior to the breakup of Pangea. The oldest (1) detrital zircons of retroarc foreland basin strata record de facto Cordilleran magmatism initiated with subduction the magmatic history of the post-Late Jurassic arc and that beneath this truncated margin during mid-Early Triassic time (2) the Cordilleran magmatic arc formed a drainage divide [Dickinson, 2000]. Most Cordilleran magmatism intruded an beginning by Late Jurassic time that blocked eastward trans- elongate zone located 100–250 km inboard of the arc-trench port of Cordilleran terrane-derived sediments.

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Figure 5b. Composite normalized probability curve for the Yavapai-Mazatzal provenance interpretation group. Data are plotted against the age ranges of the Laurentian basement rocks mapped in Figure 3. Highlighted crustal age domain columns correspond to the age of the dominant probability peak that defines the interpretation group. Internal consistency of the grouped samples was quantified using K-S statistical analysis of all grains older than 250 Ma so as to avoid sampling bias. Detrital zircon ages not included in the comparisons are symbolized as a hollow curve. The chart at right displays P values for each K-S comparison. P values >0.05 indicate that two detrital zircon populations are statistically indistinguish- able and are highlighted in yellow.

6. Results interpreted to represent recycling of Mesozoic eolianites or the Laurentian passive margin. This type of interpretation, [36] Comparison of foreland basin age spectra (Figures 5a, which favors secondary sedimentary sources over primary 5b, 5c, 5d, 5e, 5f, 5g, 5h) to those of potential provenance igneous sources, is appropriate in this setting because the candidates (Figure 4) through K-S and qualitative prove- sedimentary rocks of interest dominate the North American nance analysis produced six major provenance groupings Cordilleran thrust belt. This interpretation is also consistent and two mixed provenance subgroupings that describe varia- with abundant conventional light-mineral sedimentary tions in age spectra within the Cordilleran retroarc foreland petrological data from Cretaceous and lower Cenozoic sand- basin system. In this section, we describe the individual stones from throughout the Cordilleran foreland basin, which groupings, quantify their internal consistency using K-S test- indicate predominantly recycled orogenic provenance [e.g., ing, then use stratigraphic depositional ages (see references, Suttner et al., 1981; Dickinson et al., 1986; DeCelles, 1986; Table S1) to reconstruct sediment dispersal pathways in the DeCelles and Burden, 1992; Goldstrand, 1992; Currie, foreland basin system during the Late Jurassic, Cretaceous, 1997; Lawton et al., 1993]. and early Paleogene (Figures 6a, 6b, 6c, 6d, 6e). 6.1.1. Cordilleran Magmatic Arc [38] A relatively small proportion of foreland basin sam- 6.1. Comparison With Potential Source Regions ples display a dominance of Cordilleran magmatic arc- [37] All samples included in this study can be categorized derived (<250 Ma) detrital zircons. Where present, this into one of six provenance interpretation groups that are signature overwhelmed all other age-probability peaks. genetically linked to tectonostratigraphic sequences that The eight samples whose PDFs are plotted in Figure 5a were exhumed during Cordilleran orogenesis. Samples with each contain at least 50% arc-derived detrital zircons. unimodal age distributions were generally interpreted to The group as a whole averages 75% arc-derived zircons. represent deposition of grains derived from primary igneous Despite these unimodal provenance characteristics, none or metamorphic sources. The remaining samples, which of the samples pass the K-S test for internal consistency. We are characterized by multiple age-probability peaks, were attribute this finding to the tendency of young age-probability

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Figure 5c. Composite normalized probability curve for the Mesozoic eolianite provenance interpretation group. Data are plotted against the age ranges of the Laurentian basement rocks mapped in Figure 3 and a reflected composite normalized probability curve of the interpreted source tectonostratigraphy. Highlighted crustal age domain columns correspond to the age of the dominant probability peak that defines the interpretation group. Internal consistency of the grouped samples was quantified using K-S statistical analysis of all grains older than 250 Ma so as to avoid sampling bias. Detrital zircon ages not included in the comparisons are symbolized as a hollow curve. The chart above displays P values for each K-S comparison. P values >0.05 indicate that two detrital zircon populations are statistically indistinguishable and are highlighted in yellow. peaks to cluster near the stratigraphic depositional age of each 2010; Paterson et al., 2011]. This transition is likely related sample, which ranges in age from the Early Cretaceous to the to propagation of the Laramide flat slab under the southwest- Eocene (125–48 Ma; Table S1). Maximum depositional ern United States, which displaced the melting zone of the ages (Figure 5a)—which were determined by averaging the Sierra Nevada arc [Coney and Reynolds, 1977; Dickinson age of the youngest coherent group of three detrital zircons and Snyder, 1978]. The remainder of the arc-dominated —fall within the stratigraphic depositional age brackets of all samples contain peak ages that are younger than ~90 Ma. arc-derived samples. Unfortunately, stratigraphic depositional Therefore, they were likely derived from some combination ages for some of the samples are relatively poorly constrained of sources that excludes the Sierra Nevada arc. (±12 Ma maximum). Therefore, we did not calculate detrital 6.1.2. Yavapai-Mazatzal zircon lag times. [40] Samples characterized by a unimodal, 1800–1600 Ma [39] Peak ages can be compared to magmatic flux curves relative abundance peak and <50% arc-derived detrital for segments of the Cordilleran magmatic arc (Figure 7) to zircons compose the Yavapai-Mazatzal provenance group guide provenance interpretations. The Sierra Nevada and (Figure 5b). We interpret that these 11 samples record first- Coast Mountains segments of the arc (Figure 1) were domi- cycle deposition of zircons eroded from the Yavapai- nant between ~180 and 90 Ma [Paterson et al., 2011]. In Mazatzal basement province in the western United States, addition, the Idaho batholith preserves plutons as old as as there are no known sedimentary sequences that can ~125 Ma, although abundant magmatism likely did not begin contribute Paleoproterozoic ages in such high abundance. until ~100 Ma [Gaschnig et al., 2010]. The Blackleaf and Initially, grains younger than ~250 Ma were included in Kootenai formations in northern Montana (ISR80 and K-S statistical comparison of grouped samples. However, 1FG70), which contain peak ages of ~97 and ~109 Ma, were the tendency of young age probability peaks to correlate likely derived from some combination of these sources. The with stratigraphic deposition age introduced cumulative Coast Mountains, Cascades, and Idaho-Montana segments relative abundance curve (CDF) variation powerful enough became the most productive after ~90 Ma [Gaschnig et al., to prevent consistent statistical matching. This is the same

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Figure 5d. Individual normalized probability curves for detrital zircon samples of the Mogollon Highlands provenance interpretation group. Samples are plotted atop a graph of major crustal age domains that correspond those mapped in Figure 3. Shaded domains correspond to the age-probability peak ranges that define this qualitative provenance classification. Normalized probability curves are arranged so that the northernmost samples are at the top of the figure.

phenomenon that prevented statistical grouping of the 6.1.4. Mogollon Highlands Cordilleran magmatic arc samples described above. A sec- [42] Nine samples of Upper Cretaceous foreland basin ond K-S test, this time excluding arc-derived (<250 Ma) system strata of the Four Corners region (Figure 2) are grains, was far more successful. The test revealed 98% characterized by Laurentian age-probability peaks centered internal consistency within this grouping, meaning that around 1700, 1450, and 1100 Ma (Figure 5d). In addition, each sample was deemed statistically indistinguishable these samples contain abundant arc-derived detrital zir- from other samples in the group 98% of the time. cons. K-S testing of these data against samples from the 6.1.3. Mesozoic Eolianite other provenance groups yielded no statistically indistin- [41] Samples that display similarities to a composite PDF guishable results. It is likely that the high variability of representation of 10 samples from Jurassic eolian and associ- peak relative abundance within this sample set precluded ated marine and fluvial sandstones [Dickinson and Gehrels, the possibility of quantitative provenance analysis using 2003; 2009a] of the southwestern United States (Figure 3) K-S statistics. Despite their mathematical dissimilarity, all were included in the Mesozoic eolianite provenance group of the samples were deposited within a relatively restricted (Figure 5c). Twenty-three samples match our criteria, which zone of the foreland basin system, in close proximity to include mirroring of the presence and relative abundance of the Mogollon Highlands of the southwestern United age-probability peaks at 420, 615, 1055, and 1160 Ma States (Figure 1). This ancient rift shoulder is a reasonable (Figure 5c). We interpret that these samples were recycled provenance candidate, as it exposed all of the required from Mesozoic eolianites in the western United States rather tectonostratigraphic elements—including Yavapai-Mazatzal than from a combination of primary Appalachian and basement, Paleozoic cover, and Cordilleran magmatic Grenville sources in eastern North America (Figure 3) so as arc rocks—during Jurassic-Cretaceous time [Dickinson to favor the simplest possible sediment dispersal system that and Gehrels, 2008]. Our interpretation of these samples is consistent with regional paleocurrent data. K-S testing of is consistent with those of the Dickinson and Gehrels the grouped samples reveals 92% internal consistency when [2008] and Lawton and Bradford [2011], from whom arc-derived detrital zircons are excluded. thesedatawerecompiled.

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Figure 5e. Composite normalized probability curve for the United States passive margin provenance inter- pretation group. Data are plotted against the age ranges of the Laurentian basement rocks mapped in Figure 3 and a reflected composite normalized probability curve of the interpreted source tectonostratigraphy. Highlighted crustal age domain columns correspond to the age of the dominant probability peak that defines the interpretation group. Internal consistency of the grouped samples was quantified using K-S statistical analysis of all grains older than 250 Ma so as to avoid sampling bias. Detrital zircon ages not included in the comparisons are symbolized as a hollow curve. The chart above displays P values for each K-S compar- ison. P values >0.05 indicate that two detrital zircon populations are statistically indistinguishable and are highlighted in yellow.

6.1.5. Laurentian Passive Margin 78% internally consistent. The Canada passive margin [43] One third of the foreland basin samples presented in group (Figure 5f) contains 10 samples with a dominant this study contain detrital zircon age-probability peaks age-probability peak centered at 1900 Ma and three sub- that match the distribution of local Laurentian cratonal and ordinate age-probability peaks at 2700, 2100, and 1100 Ma. platformal tectonostratigraphic elements. Rather than attrib- These samples mirror British Columbia passive margin age uting their detrital zircon spectra to a combination of primary spectra and are 64% internally consistent. Two of the samples sources, we infer that these samples were recycled from in the Canada passive margin group, BTC and SKR, were Laurentian passive margin strata that dominate the poor statistical matches. The fact that they are statistically Cordilleran thrust belts in the western United States and distinguishable from >50% of the other samples would Canada. Gehrels and Pecha’s (submitted manuscript, 2012) normally warrant rejection under our statistical provenance detrital zircon data from passive margin strata exposed in analysis criteria (see section 3.2). However, Leier and the Cordilleran thrust belt in the western United States Gehrels [2011] interpret these samples to have been recycled (Utah, Nevada) and southern Canada (British Columbia) from the Canada passive margin, alongside five other sam- form the basis for two provenance groupings that encompass ples (ODR, SHC, CDM, EBK, and GCH) from the Cadomin 34 foreland basin samples. Formation. These samples, which were also independently [44] The United States passive margin group (Figure 5e) categorized into this group, are much better statistical matches. contains 24 samples that display three dominant age-probability Therefore, we chose to retain samples BTC and SKR. peaks of equal relative probability centered at 1700, 1450, and 6.1.6. Mixed Passive Margin and Laurentian Basement 1100 Ma. The samples in this group mirror age-probability [45] Archean, Proterozoic, Paleozoic, and Mesozoic age- peaks from the Utah-Nevada passive margin and are probability peaks of similar magnitudes characterize four

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Figure 5f. Composite normalized probability curve for the Canada passive margin provenance interpre- tation group. Data are plotted against the age ranges of the Laurentian basement rocks mapped in Figure 3 and a reflected composite normalized probability curve of the interpreted source tectonostratigraphy. Highlighted crustal age domain columns correspond to the age of the dominant probability peak that defines the interpretation group. Internal consistency of the grouped samples was quantified using K-S statistical analysis of all grains older than 250 Ma so as to avoid sampling bias. Detrital zircon ages not included in the comparisons are symbolized as a hollow curve. The chart above displays P values for each K-S comparison. P values >0.05 indicate that two detrital zircon populations are statistically indistinguish- able and are highlighted in yellow. samples from southwest Montana (Figure 5g). The 05distrib- One sample resembles the Mesozoic eolianite group uted nature of the peaks, as well as our inability to correlate (UT06-8B) but is a poor statistical match. The sole character- all of the peaks to one source, implies that these strata were istic that these samples share is the presence of a well-defined derived from at least two distinct tectonostratigraphic to poorly defined, two-tiered age-probability peak that sequences. We infer that the Yavapai-Mazatzal (1800– straddles the age boundary between the Trans-Hudson 1600 Ma), Laurentian anorogenic plutonic (1480–1340 Ma), (2000–1800 Ma) and Wopmay (2300–2000 Ma) provinces Grenville (1200–1000 Ma), and Appalachian (750–300 Ma) (Figure 5h). Gehrels and Pecha (submitted manuscript, 2012), peaks reflect recycling of United States passive margin identified a similar age-probability peak in Ordovician passive detrital zircons (Figure 5e) into the southwestern Montana margin strata of the western United States and Canada foreland. However, the presence of an additional, Archean (Figure 4). Therefore, we propose that these anomalous (~2750) age-probability peak in these strata requires at least samples record mixing of passive margin or Mesozoic one additional source, which is likely the Archean basement eolianite strata with anomalously abundant Ordovician of the north central United States (Figure 3). K-S testing of passive margin strata. It is plausible that this signature is the four samples confirms that they were all derived from sta- indicative of erosion and recycling of passive margin and tistically indistinguishable parent populations, i.e., this group Mesozoic eolianite strata in an Ordovician-dominated thrust is 100% internally consistent. system, such as the Roberts Mountain allochthon in central 6.1.7. Mixed Passive Margin and Ordovician Nevada [e.g., Gehrels et al., 2000]. In this model, the tendency Passive Margin of samples to qualitatively represent United States, Canadian [46] The remaining nine samples are difficult to group passive margin, or Mesozoic eolianite strata likely depends using K-S or qualitative provenance analysis due to the high on the location of the thrust sheet along the Cordilleran variability in age-probability peak relative abundance. Some orogenic front. of these samples qualitatively resemble United States passive margin group spectra (GCMONTEITH, MB1007, and SKR), 6.2. Depositional Age-Referenced Provenance while others appear more similar to the Canada passive mar- [47] Detrital zircon samples were mapped on one of five gin group (BTC, 1SFSR1, 1GR100, UT0715, and UT06-4). paleogeographic reconstructions (R. Blakey, unpublished

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Figure 5g. Composite normalized probability curve for the mixed United States passive margin and Yavapai-Mazatzal provenance interpretation group. Data are plotted against the age ranges of the Laurentian basement rocks mapped in Figure 3. Highlighted crustal age domain columns correspond to the age of the dominant probability peak that defines the interpretation group. Internal consistency of the grouped samples was quantified using K-S statistical analysis of all grains older than 250 Ma, so as to avoid sampling bias. Detrital zircon ages not included in the comparisons are symbolized as a hollow curve. The chart above displays P values for each K-S comparison. P values >0.05 indicate that two detrital zircon populations are statistically indistinguishable and are highlighted in yellow. report, 2012, “Paleogeography and Geologic Evolution of the Westwater Canyon Member (CP21 and CP13) display North America”) and symbolized according to their prove- Mogollon Highlands provenance. The close spatial associa- nance interpretation group (coded by symbol shape and color). tion of samples from both groups (Figure 6a) implies that Paleogeographic reconstructions and a list of data sources are samples in this region were derived from a combination of available at http://cpgeosystems.com/nam.html. Knowledge thrust belt and Mogollon Highlands sources. Although a of the extent of interpreted sediment sources (Figure 3) and compilation of sediment dispersal directions [DeCelles, age-appropriate generalized paleocurrent directions [DeCelles, 2004] indicates a dominance of east directed transport, we 2004] was used to map likely sediment dispersal pathways propose that a northeast directed fluvial system may have within the foreland basin system (Figures 6a, 6b, 6c, 6d, 6e). also existed (Figure 6a) in the southern Four Corners region. Timing of the emergence of provenance groups was used to Our interpretation of Morrison Formation samples is consis- construct a record of Late Jurassic to Eocene tent with that of Dickinson and Gehrels [2008], from whom exhumation within the Cordilleran orogenic wedge. these data were compiled. 6.2.1. Late Jurassic Provenance [49] One new sample was collected from the Morrison [48] Most Late Jurassic detrital zircon samples are from (719062) formation in the Uinta region. This sample matches the Morrison Formation, which formed a 50–200 m thick the criteria of the Mesozoic eolianite interpretation group, blanket of fluvial deposits that covered ~150,000 km2 of the suggesting either that Mesozoic eolianites were exposed Cordilleran foreland between the Sevier thrust front and the in the Sevier belt to the west or that they were recycled Rio Grande rift [Furer, 1970; Currie, 1998; DeCelles and northward from the flanks of the Mogollon Highlands. Burden, 1992; Turner and Peterson, 2004]. Morrison Sedimentological data do not preclude either interpretation, Formation provenance in the Four Corners region is domi- as both northeast and southeast directed dispersals were nated by recycling of Mesozoic eolianites. This interpretation documented in the region (Figure 6a). However, petro- is consistent with DeCelles and Burden’s [1992] inference graphic data from the Morrison Formation in Wyoming that K-feldspar in the Morrison Formation is indicative of records an unroofing sequence, which is consistent with the Mesozoic eolianite recycling from the thrust belt to the west. bulk of Upper Jurassic strata in this region being recycled Samples that show this correlation are from the Jackpile from westerly, thrust belt sources [DeCelles and Burden, (CP53), Recapture (CP25), Salt Wash (CP49, CP36, CP35, 1992; Currie, 1998]. CP29, and CP19), Fiftymile (CP52), and Tidwell (CP41) [50] Two additional Morrison Formation samples were Members. However, two contemporaneous samples from collected in northern Montana (1GRX and 1GRZ). These

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Figure 5h. Individual normalized probability curves for detrital zircon samples of the mixed passive mar- gin and Ordovician passive margin provenance interpretation group. Samples are plotted atop a graph of major crustal age domains that correspond to those mapped in Figure 3. Shaded domains correspond to the age-probability peak ranges that define this qualitative provenance classification. Normalized probabil- ity curves are arranged so that the northernmost samples are at the top of the figure. samples have indistinguishable age spectra from Mesozoic previous arguments for the presence of a drainage divide north eolianite group samples of the southwestern United States. of the Omenica Belt, near the international border [Mack and The two samples are accompanied by one Kootenai Jerzykiewicz, 1989; Ross et al., 2005, Leier and Gehrels, Formation sample (TFI) that displays United States passive 2011] that prevented northward transport of Intermontane margin provenance in southwest Montana. Therefore, we in- Belt sediments. This inference is also valid for our provenance terpret that these samples were recycled from exposures of model, which links the late Mesozoic-Triassic grains to Mesozoic eolianites in the Sevier belt (Figure 6a). Fuentes Mesozoic eolianites rather than the Intermontane Belt. All of et al. [2009] propose an alternative, two-source provenance the Late Jurassic samples from Canada presented in this study model. In addition to recycling of Mesozoic eolianites, these were derived from passive margin strata, which were likely ex- authors inferred that Paleozoic and Triassic detrital zircons posed in thrust sheets of the Sevier and the Canadian Rocky (~330–180 Ma) in these samples (1GRX and 1GRZ) were Mountains thrust belts. Kootenay (BASALKOOTENAY), derived from igneous rocks in the eastern part of the Nikanassin (PROSPECTCREEK), and Monach Formation Intermontane Belt. However, both requisite age populations (GCMONACH) samples were predominately derived are present in Dickinson and Gehrels’ [2009a] Mesozoic from the passive margin of the United States, while eolianite data. Therefore, we prefer the interpretation that the three northernmost samples were derived from the Morrison Formation throughout the United States was de- local thrust belt. These interpretations imply northward rived mostly from Mesozoic eolianites rather than from mul- transport of United States passive margin strata, perhaps tiple sources that span a broad geographic range. via longshore transport along the western shoreline of [51] Upper Jurassic strata of the northern foreland basin sys- the interior seaway represented in the 145 Ma paleogeo- tem in Canada do not contain abundant Late Mesozoic- graphic reconstruction (Figure 6a) or along an axial Triassic detrital zircons. This observation is consistent with river system.

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fed arc-derived detritus into the foreland. Detrital zircons in these samples could have been derived from four segments of the magmatic arc that preserve age-appropriate igneous rocks. These include the Sierra Nevada arc, the Coast Mountains arc, the Cascades arc, and the Suture Zone Suite in the Idaho-Montana arc [Gaschnig et al., 2010] (Figures 1 and 6a, 6b, 6c, 6d, 6e). Our provenance model favors deriva- tion from the Idaho-Montana arc, as it is the most proximal (Figure 6b). 6.2.3. Cenomanian-Santonian Provenance [54] Cenomanian-Santoniandetritalzirconsamples(Figure6c) record complex, mixed provenance in the western United States. Nevertheless, a simple provenance model involving east directed dispersal in the Montana and Uinta regions and continued northeast directed dispersal in the Four Corners region can explain all of the samples. Generalized sediment dispersal data [DeCelles, 2004] from this period, which indi- cate east directed dispersal in the Montana region and a mix of east and north directed dispersal in the Uinta and Four Corners regions, are consistent with this interpretation. [55] Mancos (CP33 and CP23) and Toreva (CP9) formation samples record the reemergence of Mogollon Highlands prov- enance in the Uinta and Four Corners regions. These strata, which are of comparable fluviodeltaic facies [Dickinson and Gehrels, 2008], were deposited outboard of the United States

Figure 6a. Upper Jurassic detrital zircon sample locations, sample names, and interpreted provenance plotted on a late Late Jurassic (145 Ma) paleogeographic reconstruction (R. Blakey, unpublished report, 2012, http://cpgeosystems.com/ nam.html). Black arrows indicate generalized sediment dispersal directions after DeCelles [2004]. Dashed arrows indicate interpreted sediment dispersal pathways based on provenance.

6.2.2. Early Cretaceous Provenance [52] During the Early Cretaceous, the Cordilleran foreland shifted from a Mesozoic eolianite to Passive Margin-dominated provenance regime. Eighteen of the 27 samples from this period display either Canada passive margin or United States passive margin provenance (Figure 6b). However, the architecture of sediment dispersal systems remained largely the same. For example, we interpret that chert-rich, Monteith Formation (UPPERMONTEITH) in Canada was recycled from passive margin strata exposed in the Sevier belt. This interpretation re- quires northward transport, perhaps along the same pathway that we inferred for Upper Jurassic samples (Figures 6a and 6b). In addition, two samples (CP14 and CP27) of Burro Canyon Formation and one sample (UT06-8B) of Buckhorn Formation evidence continued northeast directed recycling of Mesozoic eolianites in the Four Corners region. Mesozoic eolianite provenance was also determined for the Kelvin (K2) and Kootenai (10DM25) formations in the Uinta and Montana regions. Figure 6b. Lower Cretaceous detrital zircon sample loca- [53] Kootenai and Blackleaf Formation samples (1FG70 tions, sample names, and interpreted provenance plotted on a and ISR80) in northern Montana are the earliest record of late Early Cretaceous (100 Ma) paleogeographic reconstruc- Cordilleran magmatic arc-dominated provenance in the fore- tion (R. Blakey, unpublished report, 2012 http:// land basin system. These samples imply that there was not a cpgeosystems.com/nam.html). Black arrows indicate general- regional topographic barrier between the magmatic arc and ized sediment dispersal directions after DeCelles [2004]. foreland basin system during the Early Cretaceous. An alter- Dashed arrows indicate interpreted sediment dispersal path- nate possibility is that an antecedent mega-drainage system ways based on provenance.

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requires local Yavapai-Mazatzal dominance in the Morrison Formation, which was not evidenced by any of the 14 Morrison Formation samples included in this study. [57] Detrital zircons from the Frontier Formation (10DM17) reveal continued erosion of Cordilleran magmatic arc rocks during the Coniacian (~89–86 Ma) in the Montana region. However, very few arc-derived detrital zircons were identified in the synorogenic, lower member of the Beaverhead Group (10DM09) in nearby southwest Montana, suggesting the existence of a local drainage divide. Instead, Beaverhead Group detrital zircon age spectra are dominated by Archean, Proterozoic, and Paleozoic ages that indicate mixed passive margin and Archean basement provenance. These characteristics suggest that basement-involved thrust sheets of the Cabin Culmination had been exhumed by Santonian time (~86–84 Ma). A study of paleovalleys in southwest Montana [Janecke et al., 2000] confirms that Beaverhead Group deposits were located along drainages whose headwa- ters tapped exposures of Archean Wyoming Province basement rocks. 6.2.4. Campanian-Paleocene Provenance [58] Thirty-one Campanian-Maastrichtian (~84–66 Ma) detrital zircon samples indicate complex, mixed provenance for foreland basin strata of the United States (Figure 6d). During this time, Idaho-Montana arc provenance continued

Figure 6c. Santonian-Cenomanian (~100–84 Ma) detrital zircon sample locations, sample names, and interpreted provenance plotted on a Santonian (85 Ma) paleogeo- graphic reconstruction (R. Blakey, unpublished report, 2012, http://cpgeosystems.com/nam.html). Black arrows indi- cate generalized Cenomanian sediment dispersal directions after DeCelles [2004]. Dashed arrows indicate interpreted sediment dispersal pathways based on provenance. passive margin-derived Canyon Range and Sanpete formation samples (CR7 and UT06-3). This relationship suggests that proximal samples were derived from local sources to the west, whereas distal samples were transported axi- ally. This pattern is consistent with the Santonian paleo- geographic reconstruction, which places the Cretaceous Interior Seaway shoreline precisely at the divide between the two provenance groupings. Therefore, this boundary might demarcate the transition between fluvial and longshore transport regimes. [56] Two new samples from the Mancos (T67-14419) and Blair (EM4) formations in the Uinta region signal the emer- gence of Yavapai-Mazatzal provenance in the retroarc region. These samples are difficult to interpret, as there is no petrographic or structural evidence for exhumation of Yavapai-Mazatzal basement thrust sheets in the Sevier belt or Laramide intraforeland province during this period. These samples might have been derived from basement Figure 6d. Campanian-Maastrichtian (~84–66 Ma) detrital exposures on the flanks of the Mogollon Highlands. This zircon sample locations, sample names, and interpreted interpretation requires ~1700 km of northeast directed axial provenance plotted on a latest Maastrichtian (65 Ma) paleo- transport, presumably via longshore transport along the shore- geographic reconstruction (R. Blakey, unpublished report, line of the Cretaceous Interior Seaway. Alternatively, these zir- 2012, http://cpgeosystems.com/nam.html). Black arrows cons may have been recycled from the Morrison Formation, indicate generalized Maastrichtian sediment dispersal direc- which contains clasts derived from the Ancestral Rocky tions after DeCelles [2004]. Dashed arrows indicate interpreted Mountains [Turner and Peterson, 2004]. This scenario sediment dispersal pathways based on provenance.

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Mesozoic eolianite sediments that were eroded from older fore- land basin strata such as the Morrison Formation. However, clast count data from coeval Campanian-Maastrichtian con- glomerates in the proximal foreland basin indicate widespread exposure of Mesozoic eolianites in the frontal thrust belt at this time [DeCelles, 1994; Lawton et al., 2007]. [60] The mixed provenance character of the Cordilleran retroarc foreland basin system continued into the Paleocene- Eocene in the Uinta region (Figure 6e). Seven samples of this age indicate United States passive margin, Yavapai-Mazatzal, and Cordilleran magmatic arc provenance. The youngest sam- ple from the Beaverhead Group in southwest Montana (10DM11) displays United States passive margin provenance, implying that significant quantities of Idaho-Montana arc- derived sediments remained isolated from Beaverhead Conglomerate drainages until at least ~65 Ma. However, sample 09CA01 from the Uinta Formation records mag- matic arc provenance with a dominant age peak at ~46 Ma (Figures 5a and 6e). These data suggest that the Idaho- Montana arc was shedding sediment into the foreland basin despite the absence of characteristic ages in the most proximal samples.

Figure 6e. Paleocene-Eocene (~66–47 Ma) detrital zircon sample locations, sample names, and interpreted provenance Arc-Derived Detrital Zircons (a) plotted on an Eocene (50 Ma) paleogeographic reconstruction Cordilleran Retroarc Region (R. Blakey, unpublished report, 2012, http://cpgeosystems. com/nam.html). Dashed arrows indicate interpreted sediment lower limit of dispersal pathways based on provenance. sampling Relative Probablity n=1535 to dominate in northern Montana, as shown by samples of the 150 Age of Farallon (my) (b) St. Mary’s River (1BB44) and Two Medicine (2SR240) forma- Age 150 tions. In southern Montana, arc-derived grains remained 100 subordinate, as three more samples from the Beaverhead 100 Group (10DM20, 10DM22, and 10DM23) indicate mixed 50 United States passive margin, Archean basement, and 50 Yavapai-Mazatzal basement provenance. The Yavapai- Speed (km/my) Mazatzal group sample (10DM20) was deposited north of Idaho Batholith (c) the northernmost extent of Yavapai-Mazatzal basement Montana Batholiths

(Figure 3). Therefore, we interpret that these ages were 1000 Sierra Nevada Batholith recycled from Paleoproterozoic Belt Supergroup strata, Coast Mountains which are exposed in trailing thrust sheets of the northern- 500 Batholith most Sevier belt [DeCelles, 2004]. Further support for this hypothesis is provided by abundant quartzite clasts in Apparent Intrusive Flux sample 10DM20, which is described as a quartzite con- 0 50 100 150 200 glomerate by Haley and Perry [1991]. Ma [59] Late Cretaceous Uinta and Four Corners region sam- ples indicate mixed United States passive margin, Mogollon Figure 7. (a) Probability distribution function of arc- Highlands, Cordilleran magmatic arc, and Yavapai-Mazatzal derived detrital zircons in the foreland basin system (this provenance (Figure 6d). We infer that all of these study). (b) Farallon plate velocity and age at the subduction tectonostratigraphic successions were exposed locally in the interface from Engebretson [1984]. (c) Relative flux curves Sevier belt and newly formed (~85 Ma) Laramide intraforeland interpreted from exposures of igneous rocks along three seg- province [DeCelles, 2004; Fuentes et al., 2012]. Mesozoic ments of the Cordilleran magmatic arc (Coast Mountains eolianite affinity also reappeared at this time, in the Wahweap Batholith after Gehrels et al. [2009], Cascades and Sierra (CP39) and Almond (LBRG-2700) formations. These data Nevada Batholith after Paterson et al. [2011], and references indicate that either Mesozoic eolianites continued to be ex- therein). No flux data are available for the Idaho and posed in the Sevier belt or that younger foreland basin strata Montana batholiths. To facilitate comparison, we plot age that inherited the Mesozoic eolianite signature began to be ex- ranges of major igneous suites in this region [Gaschnig humed. The latter model requires third-cycle deposition of et al., 2010].

18 LASKOWSKI ET AL.: CORDILLERAN FORELAND DZ GEOCHRONOLOGY

7. Discussion periods of high relative abundance between 160 and 40 Ma. Age-frequency peaks recur over a predictable, if not [61] Comparison of detrital zircon age spectra to those of constant, interval during this time. We interpret that these potential provenance candidates revealed six major prove- age-frequency peaks represent high magmatic flux events nance groupings in the Cordilleran retroarc foreland basin fi (HFEs) in the Cordilleran magmatic arc. Therefore, detrital system. Each of the groupings corresponds to a speci c suite zircon relative abundance in the foreland basin system pro- of igneous, metamorphic, or sedimentary rocks that were de- vide evidence for cyclical HFEs. Similar observations formed in or exposed near the Cordilleran orogenic wedge. inspired DeCelles et al. [2009] to develop the Cordilleran Referencing provenance interpretations to stratigraphic de- orogenic cyclicity model, which invokes interaction between positional ages revealed the chronology of exhumation and coupled upper-plate and subduction zone processes to predict transport within the retroarc region. the behavior of Cordilleran orogenic systems. Interpretation [62] In the United States, Late Jurassic foreland basin of our data within the framework of this model expands their sedimentation was dominated by recycling of Mesozoic relevance at the orogen scale. eolianites (Figure 6a). Paleocurrent measurements from these [65] In Cordilleran orogenic systems, convergence is strata indicate westerly to southwesterly provenance [Suttner accommodated by subduction of an oceanic plate and short- et al., 1981; DeCelles and Burden, 1992; Currie, 1998], ening of a continental plate. Typically, upper continental which is consistent with the requirements of our detrital crust shortens across a retroarc thrust belt, while the lower- zircon provenance analysis. These observations lead us to most continental crust is shoved beneath the arc—fueling conclude that most recycled Mesozoic eolianite sediment episodic high-flux magmatism [Ducea and Barton, 2007; was derived from the Sevier belt (Figure 1), implying that fl Mesozoic eolianites dominated leading thrust sheets during DeCelles et al., 2009]. The recurrence interval of high- ux this time. However, some Late Jurassic strata of the Four magmatism should therefore vary according to changes in Corners region may have been recycled from the flanks of the convergence rate. In the North American Cordillera, the the Mogollon Highlands. In contrast, provenance analysis Farallon and North America plates converged relatively of Upper Jurassic foreland basin strata in Canada reveals a slowly between ~160 and 100 Ma (Figure 7). This behavior dominance of Canada passive margin recycling. Yet some resulted in either a ~60 Ma recurrence interval between samples are more similar to the United States passive margin, two prominent HFEs at ~160 and ~100 Ma or diminished which implies that sediments may have experienced axial, magmatic flux during an intermediary HFE at ~125 Ma. northward transport along the shoreline of the Late Jurassic Convergence rates increased after ~100 Ma, as indicated by interior seaway or a parallel pathway (Figure 6a). an increase in Farallon plate velocity of ~100 km/Ma [63] Sedimentation above the basal Cretaceous unconfor- [Engebretson, 1984]. This increase coincided with either a mity was dominated by complex, mixed provenance in the reduction in HFE recurrence interval from ~60 to ~25 Ma foreland basin system. Variations during this period can be or an increase in overall magmatic flux, dependent upon the explained by the changing tectonostratigraphic composition existence of a subdued HFE at ~125 Ma. Periods of fast con- of the Cordilleran orogenic wedge as it propagated and vergence therefore correlate with increased productivity in progressively shortened over a period of ~100 Ma. In gen- the Cordilleran magmatic arc and ultimately with detrital zir- eral, Cretaceous samples evidence the waning influence of con relative abundance in the retroarc region. Mesozoic eolianite recycling on the foreland basin system. This trend may reflect unroofing of progressively older strata within the Cordilleran orogenic wedge, which was docu- 8. Conclusions mented at the regional scale in the western United States by [66] Upper Jurassic to Paleogene foreland basin strata in DeCelles and Burden [1992] and Currie [1998]. Mixed pas- the Cordilleran retroarc region contain age spectra with sive margin and Laurentian basement provenance group varying proportions of (1) 2.5 Ga cratonic, (2) 2.3–1.6 Ga samples from the western United States reveal that base- Wopmay, Trans-Hudson, and Yavapai-Mazatzal, (3) 1.48– ment-involved structural culminations were exposed by 1.34 Ga intracratonic magmatic, (4) 1.2–1.0 Ga Grenville, Campanian to Maastrichtian time (~86–66 Ma). In addition, (5) 750–250 Ma Appalachian, and (6) <250 Ma Cordilleran Mogollon Highlands group samples from the Four Corners magmatic arc detrital zircons. Variations in the presence, region reveal that basement, cover, and arc rocks were absence, and relative abundance of age peaks within these exposed on the Mogollon flanks during the Late Jurassic ranges defined eight provenance groupings that describe and Late Cretaceous. variations within the foreland basin system. Recycled sam- [64] Arc-derived detrital zircons, which were extracted ples compose the Mesozoic eolianite group, which is charac- from the composite spectrum of foreland basin detrital terized by Appalachian and Grenville ages; the Canada zircons, were used to construct a basin-averaged proxy for passive margin group, which is characterized by Wopmay, Cordilleran arc flux. This proxy depends upon the assump- Trans-Hudson, and Grenville ages; the United States passive tion that the various segments of the Cordilleran arc were margin group, which is characterized by Yavapai-Mazatzal, equally zircon fertile. All grains younger than 200 Ma were intracratonic magmatic, and Grenville ages; and the mixed plotted as a composite PDF in Figure 7 for comparison with passive margin and Ordovician passive margin group, which (1) velocity and age data for the Farallon plate [Engebretson, contains Laurentian and anomalously abundant Trans- 1984], (2) periods of arc magmatism in the Idaho-Montana Hudson and Wopmay ages. Samples whose age spectra arc [Gaschnig et al., 2010], and (3) relative flux curves for suggest a component of first-cycle sedimentation compose other segments of the Cordilleran arc [Paterson et al., the Yavapai-Mazatzal group, the Cordilleran magmatic arc 2011]. Visual inspection of this curve reveals at least four group, the mixed passive margin and Yavapai-Mazatzal

19 LASKOWSKI ET AL.: CORDILLERAN FORELAND DZ GEOCHRONOLOGY group, and the Mogollon Highlands group, which is character- Nevada, Southern Idaho and Central Mexico, vol. 42, edited by P. K. Link and B. J. Kowallis, pp. 297–309, BYU, Provo, UT. ized by Yavapai-Mazatzal, intracratonic magmatic, Grenville, Christiansen, E. H., B. J. Kowallis, and M. D. Barton (1994), Temporal and and Cordilleran magmatic arc ages. spatial distribution of volcanic ash in Mesozoic sedimentary rocks of the western [67] Late Jurassic provenance was dominated by recycling interior: An alternative record of Mesozoic magmatism, in Mesozoic Systems of the Rocky Mountain Region, USA,editedbyM.V.Caputo, of Mesozoic eolianites in the United States and passive mar- J. A. Peterson and K. J. Franczyk, pp. 73–94, SEPM Special Publication, gin strata in Canada. Most recycling can be explained by Denver, Colo. exhumation of progressively older strata within the Condie, K. C., and R. C. Aster (2009), Zircon age episodicity and growth of Cordilleran thrust belt. However, some samples from this pe- continental crust, Eos, 90(41), 364–364, doi:10.1029/2009EO410003. Coney, P. J., and S. J. Reynolds (1977), Cordilleran Benioff zones, Nature, riod suggest a component of axial transport, especially in the 270(5636), 403–406, doi:10.1038/270403a0. Four Corners region and in southern Canada (Figures 1 and Currie, B. S. (1997), Sequence stratigraphy of nonmarine Jurassic– 6a). Foreland basin provenance became increasingly com- Cretaceous rocks, central Cordilleran foreland-basin system, Geol. Soc. Am. Bull., 109(9), 1206–1222, doi:10.1130/0016-7606(1997)109<1206: plex during the Cretaceous-Eocene. Progressive shortening SSONJC>2.3.CO;2. and propagation in the Cordilleran orogenic wedge during Currie, B. S. (1998), Upper Jurassic-Lower Cretaceous Morrison and Cedar this period exhumed all of the crustal elements required to Mountain Formation, NE Utah-NW Colorado: Relationships between nonmarine deposition and early Cordilleran foreland-basin development, explain the provenance interpretation groups. Emergence of J. Sediment. Res., 68(4), 632–652, doi:10.2110/jsr.68.632. Yavapai-Mazatzal provenance in the Uinta and Montana DeCelles, P. G. (1986), Sedimentation in a tectonically partitioned, regions during the Campanian-Maastrichtian signaled the nonmarine foreland basin: The Lower Cretaceous Kootenai Formation, exhumation of basement-involved thrust sheets between southwestern Montana, Geol. Soc. Am. Bull., 97(8), 911–931, doi:10.1130/ 0016-7606(1986)97<911:SIATPN>2.0.CO;2. ~86 and 66 Ma. DeCelles, P. G. (1994), Late Cretaceous-Paleocene synorogenic sedimenta- [68] The detrital record of arc magmatism from the tion and kinematic history of the Sevier thrust belt, Northeast Utah and Cordilleran foreland basin system reveals a correlation Southwest Wyoming, Geol. Soc. Am. Bull., 106(1), 32–56, doi:10.1130/ < > between increasing convergence rates and a decrease in 0016-7606(1994)106 0032:LCPSSA 2.3.CO;2. DeCelles, P. G. (2004), Late Jurassic to Eocene evolution of the Cordilleran high-flux event recurrence interval at ~100 Ma. These data thrust belt and foreland basin system, western USA, Am. J. Sci., 304(2), corroborate predictions of the Cordilleran orogenic cyclic- 105–168, doi:10.2475/ajs.304.2.105. ity model of DeCelles et al. [2009], which links coupled DeCelles, P. G., and E. T. Burden (1992), Sedimentology and sedimentary petrology of Jurassic-Cretaceous Morrison and Cloverly Formations in upper-plate processes to subduction zone processes. The the overfilled part of the Cordilleran foreland basin, Basin Res., 4, apparent utility of detrital zircon data as a proxy for arc 291–314. magmatism in this study suggests that it is a useful tool DeCelles, P. G., and W. Cavazza (1999), A comparison of fluvial megafans for evaluating arc magmatism at the continent scale in in the Cordilleran (Upper Cretaceous) and modern Himalayan foreland ba- sin systems, Geol. Soc. Am. Bull., 111(9), 1315–1334, doi:10.1130/0016- retroarc settings. 7606(1999)111<1315:ACOFMI>2.3.CO;2. DeCelles, P. G., and J. C. Coogan (2006), Regional structure and kinematic history of the Sevier fold-and-thrust belt, central Utah, Geol. Soc. Am. Bull., 118(7–8), 841–864, doi:10.1130/B25759.1. [ ] DeCelles, P. G., T. F. Lawton, and G. Mitra (1995), Thrust timing, growth of 69 Acknowledgments. We thank the many tireless researchers at the structural culminations, and synorogenic sedimentation in the type Sevier — Arizona Laserchron center especially Mark Pecha, Gayland Simpson, and orogenic belt, western United States, Geology, 23(8), 699–702, — Nicky Geisler for training and support, Paul Kapp for insightful conversa- doi:10.1130/0091-7613(1995)023<0699:TTGOSC>2.3.CO;2. fi tions on Cordilleran tectonics, and Neil Laskowski for help in the eld. DeCelles, P. G., M. N. Ducea, P. Kapp, and G. Zandt (2009), Cyclicity in Funding for this research was provided by the ExxonMobil COSA Cordilleran orogenic systems, Nat. Geosci., 2,251–257, doi:10.1038/ngeo469. (Convergent Orogenic Systems Analysis) project at the University of Devlin, W. J., K. W. Rudolph, C. A. Shaw, and K. D. Ehman (2009), The Arizona. 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