Detrital Zircon Geochronology of Cordilleran Retroarc Foreland Basin Strata,
western North America
Andrew K. Laskowski, Department of Geosciences, University of Arizona, Tucson,
Arizona, USA.
1
Abstract
We present a compilation of 8,702 U-Pb analyses from 96 detrital zircon samples
of Jurassic-Eocene North American Cordillera foreland basin system strata. Of these
samples, 31 are new and unpublished.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, predominately from sources in the Sevier thrust belt. Cretaceous-Eocene
provenance is dominated by recycling of the passive margin, with increasing complexity
upsection. A composite age-probability plot of 1,539 arc-derived detrital zircons reveals
a decrease in high flux event recurrence interval that is correlated with an increase in
convergence rate. We interpret this relationship as evidence that corroborates some
predictions of the Cordilleran orogenic cyclicity model of DeCelles et al., [2009].
Section 1: Introduction
Siliciclastic strata deposited in continental basins contain detrital zircons with
U-Pb age spectra that vary systematically throughout geologic time. Within sufficiently
2
populated datasets, the relative abundance of specific ages can be used to identify the
timing of first-order magmatic and accretionary processes [e.g., Condie and Aster, 2009].
This approach is particularly salient in understanding ancient supercontinent cycles, as
detrital zircons have higher preservation potential than prima facie bedrock exposures.
Detrital zircon geochronology is also applicable at the continent scale. For example,
numerous studies show that variations in detrital zircon age spectra track the long-term
distribution of orogenic belts, Andean-type magmatic arcs, and sediment dispersal
systems [e.g. Dickinson and Gehrels, 2003; 2009; LaMaskin, 2012; Leier and Gehrels,
2011; Rainbird, et al., 1992]. Moreover, detrital zircons can resolve crustal recycling
within individual orogenic systems. Provenance analysis conducted in the North
American Cordillera is particularly successful at linking synorogenic strata to specific
orogenic wedge structures [e.g. Dickinson and Gehrels, 2008; Fuentes et al., 2009;
Lawton and Bradford, 2011; Lawton et al., 2010; Leier and Gehrels, 2011].
In this paper, we present a large detrital zircon database (8,702 U-Pb ages) that
samples Jurassic-Eocene synorogenic strata deposited within the Cordilleran foreland
basin system of North America (Figure 1). The objectives of this study are to 1) define a
framework for interpreting detrital zircon provenance in the foreland basin system, 2)
utilize provenance interpretations and paleocurent data to map sediment dispersal
pathways during Cordilleran orogenesis, and 3) track exhumation of specific
tectonostratigraphic sequences in the Cordilleran orogenic wedge. All of the samples
included in this study can be categorized into one of six provenance groupings, which are
genetically tied to recycling of sedimentary sequences or erosion of primary Laurentian
igneous and metamorphic rocks. Whenever possible, provenance interpretations were
3
guided by the use of Kolmogorov–Smirnov (K-S) statistics, which test whether age
spectra could have been derived from the same parent population. The 27 samples that
could not be grouped using K-S statistics were qualitatively interpreted based on
comparison of age peaks with published references. In general, samples that could not be
classified statistically displayed mixed provenance.
Section 2: Samples
Of the 96 detrital zircon samples considered in this study, 31 have not been
reported previously. Here we summarize the sampled stratigraphy (Figure 2) at the
regional scale, beginning with new samples from southwestern Montana. All of the new
samples were collected from fresh surfaces on roadcuts or outcrops. Samples consisted
of ~10 kg of rock fragments. In each case, care was taken to avoid contamination during
collection, transport, and storage processes. Detrital zircon sample metadata (Table
DR1), analytical data (Table DR2), and representative cathodoluminescence (CL) images
(Figure DR1) are available in the data repository.
Section 2.1: New Samples
Seven Cretaceous and Paleogene foreland basin samples were collected in
southwestern Montana. Sample 10DM25 was collected from a fluvial sandstone in the
Aptian (125-112 Ma) Kootenai Formation [DeCelles, 1986] in a canyon ~9 km west of
Dell, Montana, in the Tendoy Mountains. The Kootenai Formation unconformably
overlies the Upper Jurassic Morrison Formation. Sample 10DM17 was collected from a
ledge of fluvial and littoral Frontier Formation sandstone located along a drainage on the
northeastern flank of Mt. Cohen, in the Beartooth Range. Dyman et al. [2008] reported
palynological data indicating a Coniacian (89.3-85.8 Ma) depositional age for the middle
4
to upper Frontier Formation in the nearby Centennial Range. These data correlate well
with existing geochronological and palynological data from the Frontier Formation in the
extreme southwestern Lima Peaks region, which encompasses the bulk of the Montana
samples.
Five samples from various members of the synorogenic, Upper Cretaceous to
Paleogene Beaverhead Group were collected from the Lima Peaks region. Depositional
age ranges for the Beaverhead Group samples presented here were determined using the
nomenclature of Haley and Perry (1981). All Beaverhead Group samples were collected
from fluvial sandstones and alluvial fan conglomerates (Haley and Perry, 1981). In the
McKnight Canyon area, located 10 km northwest of Dell, Montana, samples 10DM22
and 10DM23 were collected from the Campanian (83.5-70.6 Ma) and lower
Maastrichtian (70.6-65.5 Ma) intervals of the Beaverhead Group, respectively. These
two samples are age equivalent with samples of the lower limestone conglomerate
(10DM09) and upper quartzite conglomerate (10DM20) collected near Bannack,
Montana ~50 km along the range front to the north. Sample 10DM11 was collected from
the Red Butte Conglomerate of the Beaverhead Group in the Ashbough Canyon area,
which is thought to be the only Paleocene (65.5-55.8 Ma) interval in the Group.
Eight detrital zircon samples were collected from the foreland basin sequence in
southwestern Wyoming and northeastern Utah, in the region surrounding the Uinta
Mountains (“Uinta” region, Figure 2). The only Jurassic sample in the set was collected
from the Upper Jurassic Salt Wash Member of the Morrison Formation (sample
7.19.06.2), located ~85 m above the base of the Morrison Formation in section 1RF of
Currie [1998], near Redfleet reservoir, Utah. Currie [1998] interpreted this interval as
5
recording a sandy braided river system.
The remainder of the Uinta region samples were deposited during the Cretaceous.
Of these samples, three are fluvial sandstones and four are synorogenic conglomerates.
Sample K2 was collected from the Lower Cretaceous Kelvin Formation located 29 m
stratigraphically above a 10 m thick massive gray calcrete zone in the lower part of the
formation. This calcrete marks the contact between the Kelvin Formation and the
underlying Morrison Formation. Upward-fining fluvial channel sandstones with
prominent chert pebble conglomerates in their lower parts are exposed in roadcuts along
Utah State Highway 32, on the western shore of Rockport Reservoir. Sample EM6 was
collected from an outcrop of fluvial-deltaic channel sandstone of the Chimney Rock
Member of the Rock Springs Formation along the eastern side of Wyoming State
Highway 430. Sample EM4 was collected from distributary mouth bar sandstone of the
fluvial-deltaic basal Blair Formation, located just east of County Road 48, ~830 m north
of its junction with Wyoming State Highway 430. Devlin et al. [1993] reported likely
Campanian depositional ages for the Chimney Rock Member and the basal Blair
Formation of ~81 Ma and ~82-83 Ma, respectively.
Detrital zircon samples collected from synorogenic conglomerates in the Uinta
region offer insight into provenance relationships within the Sevier belt during the Late
Cretaceous. Sample ECH1 was collected from the upper part of the lower member of the
Echo Canyon Conglomerate, ~860 m northeast of the Echo Junction exit on Interstate
Highway 80. The sampled interval is fluvial sandstone that is interbedded with cobble to
pebble conglomerates representing shallow braided streams on a stream-dominated
alluvial fan. Nichols and Bryant [1990] and DeCelles [1994] reported palynological data
6
for these strata that indicate a Coniacian-Santonian (89.3-83.5 Ma) depositional age.
Sample CR7 was collected from the type locality of the Canyon Range Conglomerate, in
Wildhorse Canyon in the northern Canyon Mountains of central Utah. This coarsegrained sandstone was interbedded with cobble to boulder conglomerate beds, and has a
poorly constrained Cenomanian-Turonian (99.6-89.3 Ma) depositional age [DeCelles et
al., 1995; DeCelles and Coogan, 2006; Lawton et al., 2007]. Sample HF2 of the
Campanian-Maastrichtian Hams Fork Conglomerate member of the Evanston Formation
[DeCelles, 1994; DeCelles and Cavazza, 1999] was collected from coarse-grained
sandstone exposed in outcrop along the north side of the frontage road, ~4.3 km
southwest from the Emory exit on Interstate Highway 80. This locality is in the upper
reaches of Echo Canyon, where a natural bridge is present in the sandstone just below the
sample site. Samples EM2 and LM73 were collected from a coarse-grained upper
shoreface sandstone in the upper part of the Little Muddy Creek Conglomerate, in a
canyon ~8 km west of the intersection of Interstate Highway 189 and Utah State
Highway 412. The Little Muddy Creek Conglomerate was likely deposited during the
Santonian [Pivnik, 1990].
Collaboration with ExxonMobil drilling projects in the La Barge and Piceance
basins of southwestern Wyoming and northwestern Colorado yielded 15 core and cutting
samples from the Cordilleran retroarc foreland basin system. Samples from the Piceance
basin were collected at a drill site located ~50 km northwest of the town of Rifle,
Colorado, on the western slope of the Rocky Mountains. These samples include the
Upper Jurassic Entrada Formation (T52X-17935), the Upper Cretaceous Mancos (T6714419) and Corcoran (PCU12120) Formations, the Upper Cretaceous to Paleocene
7
Williams Fork Formation (T67-7420, T67-8024, PCU7620, PCU7980, PCU-9470) and
the Paleocene to Eocene Ohio Creek (T67-7084), Wasatch (T26-2673, PCU4020), and
Uinta Formations (09CA01). Samples from the La Barge basin were collected at a drill
site located ~20 km northwest of La Barge, Wyoming along State Highway 235. These
include the Adaville Formation (LBRG-3500) and the Almond Formation of the
Mesaverde Group (LBRG-2700, LBRG2900). All of the La Barge samples were
deposited during the Campanian (~84-71 Ma).
Section 2.2: Published Samples
65 samples were compiled from literature for analysis alongside the new data
presented here. These samples are distributed along the frontal Sevier belt in southern
Canada and the United States and span a >1500 km segment of the Cordilleran orogenic
system (Figure 1). Although stratigraphic range and sample density vary along strike
(Figure 2), most regions are sufficiently populated throughout the Late JurassicPaleocene phase of Cordilleran orogenesis. The following is a summary of the compiled
data, organized by region and author.
Samples from the southwestern United States cluster around the shared border
between the states of Colorado, Utah, Arizona, and New Mexico. These data from the
Four Corners region (Figure 2) include 21 samples from Dickinson and Gehrels [2008],
11 samples from Lawton & Bradford [2011], and seven samples from Lawton et al.
[2010]. When combined, these data provide good coverage of the Upper Jurassic to
Upper Cretaceous foreland basin throughout the region. The initial stages of Cordilleran
orogenesis are well resolved here, as 11 of the samples are from the Upper Jurassic
Morrison Formation.
8
Samples from localities that trace the central Sevier belt in Utah, Colorado,
Wyoming, and Idaho compose the Uinta region grouping. Of the 24 Uinta samples
(Figure 2), only one was compiled from literature—the Campanian Kaiparowits
Formation [Lawton & Bradford, 2011]. Therefore, our new data are critical in bridging
the gap in published data between the Four Corners region and Montana.
The Montana region data consist of a combination of seven new and 11 compiled
samples. New samples, along with two samples from Leier and Gehrels [2011] are
located along the frontal Cordilleran thrust belt, south of the Helena Thrust Salient
[Schmidt and O'Neill, 1982]. Samples north of the Salient include an additional sample
from Leier and Gehrels [2011] and eight samples from Fuentes et al. [2011].
Most samples from Canada are distributed along the frontal Cordilleran thrust belt
in southwest Alberta and central British Columbia. An additional group of samples are
from the distal foreland basin in central Alberta. These samples consist of seven samples
from Leier and Gehrels [2011] and seven samples from Raines et al. [submitted].
Section 3: Methods
Section 3.1: Detrital Zircon Uranium-Lead Geochronology
All detrital zircon samples included in this study—whether newly generated or
compiled from the literature—were prepared and analyzed using consistent protocols at
the Arizona Laserchron Center (http://www.laserchron.org).
Zircon grains were extracted from samples in the traditional crushing and
grinding manner. Additional separation was accomplished using a Wilfley table, heavy
liquids, and a Frantz magnetic separator. A large aliquot (~1000-2000) of zircon grains
was mounted alongside fragments of the Sri Lanka standard on a 1-inch round epoxy
9
“puck”. Prior to isotopic analysis, samples were sanded to a depth of ~20 microns,
polished, and cleaned.
U-Pb analyses were conducted using laser ablation multicollector inductively
coupled plasma mass spectrometry (LA-MC-ICPMS) [Gehrels et al., 2006, 2008].
Zircons were ablated using a Photon Machines Analyte G2 excimer laser with a 30micron beam diameter. The net effect of the ablation process produces pits on the zircon
crystals that are ~15 microns deep. The ablated material is transported in helium to the
plasma source of the Nu HR ICPMS, which measures U, Th, and Pb isotopes
simultaneously. Measurements were conducted in static mode using Faraday detectors
with 3x1011 ohm resistors for 238U, 232Th, 208Pb-206Pb, and discrete dynode ion counters for
204
(Pb+Hg) and 202Hg. Each analysis consists of one 15 second integration on peaks with
the laser off, 15 one second integrations with the laser firing, and a 30 second delay to
purge for the next analysis. The ablation process produces ion yields of ~0.8 mv per
ppm.
Individual analyses carry analytical uncertainties of ~1-2% (at the 2-sigma level)
for 206Pb/238U ages that result from uncertainty in determining 206Pb/238U and 206Pb/204Pb.
Errors in measurement of 206Pb/207Pb and 206Pb/204Pb produce similar ~1-2% (at the 2sigma level) uncertainties for > 1.0 Ga 206Pb/207Pb ages. However, analytical error in
determining 206Pb/207Pb ages substantially increases for zircon grains with ages <1.0 Ga.
The cutoff for reporting 206Pb/238U versus 206Pb/207Pb ages averages ~1.0 Ga, but is
adjusted for each sample to avoid dividing clusters of ~1.0 Ga analyses.
Inter-element fractionation of Pb/U (~5%) and Pb isotopes (<0.2%) was corrected
using in-run analyses of fragments of the Sri Lanka zircon standard. This large zircon
10
crystal has an age of 563.5 ± 3.2 Ma at 2-sigma uncertainty. Concentrations of U and Th
were also determined relative to known quantities in the Sri Lanka zircon, which are
~518 ppm of U and 68 ppm of Th.
204
Hg interference with 204Pb was accounted for by
measuring 202Hg during laser ablation and subtracting 204Hg according to the natural
202
Hg/204Hg of 4.35. Hg-corrected 204Pb and an assumed initial Pb composition [Stacey
and Kramers, 1975] were used to correct for common Pb. Uncertainties of 1.5% for
206
Pb/204Pb and 0.3% for 207Pb/204Pb were applied to the compositional values based on
observed variation in Pb isotopic composition in modern crustal rocks.
U-Pb analytical data are reported in Table DR2. Uncertainties are at the 1-sigma
level and include only measurement errors. U-Pb analyses in excess of 20% discordance
(determined by comparison of 206Pb/238U and 206Pb/207Pb ages) or >5% reverse discordance
were not considered. Interpreted U-Pb ages based on the above corrections are plotted in
Figure 5a-h using the routines of Isoplot [Ludwig, 2008]. In this procedure, the
distribution of ages and their measurement uncertainties are normalized into single curves
to create age-probability diagrams.
Section 3.2: K-S Provenance Analysis
To simplify the process of statistical provenance analysis, samples were initially
sorted into qualitiative provenance groupings based on visual examination of their
probability distribution functions (PDFs), which display the presence and relative
abundance of age peaks (e.g. Figure 4). Qualitiative groups were then tested for internal
consistency, which is a measure of the percentage of statistically indistinguishable spectra
in a given grouping, using an in-house K-S statistical program developed at the Arizona
Laserchron Center (available at http://www.laserchron.org). The K-S test compares
11
detrital zircon age spectra to evaluate the null hypothesis that the two distributions are the
same. Specifically, the K-S test compares the maximum probability difference between
two cumulative distribution function (CDF) representations of the age spectra.
Dependence on the CDF, which sums probabilities with increasing age, results in
heightened sensitivity to the relative abundance of age peaks rather than their presence or
absence. This characteristic caused samples with fewer grains or skewed peak
abundances to be rejected. Nevertheless, 69 samples were deemed statistically
indistinguishable from >50% of other samples in one of the six qualitative provenance
groupings, which were defined based on published datasets (see detrital zircon signatures
in Section 5, below). The 27 samples that could not be grouped statistically
(distinguishable from >50% of grouped samples) were qualitatively interpreted within the
context of published datasets (see Section 5) and Laurentian basement age domains
(Figure 3). These groupings include all samples that were interpreted to document firstcycle erosion of primary igneous and metamorphic sources, as well as mixed provenance
signals. Possible explanations for why qualitatively grouped samples failed the statistical
test are discussed in the provenance results sections, below (6.1.1-6.1.7).
Section 4: Tectonic Setting
The North American Cordilleran thrust belt and retroarc foreland basin system
(Figure 1) initiated in Late Jurassic time in response to North Atlantic spreading and
coeval subduction of oceanic plates along the western margin of Laurentia [DeCelles,
2004]. At this time, the Cordilleran forearc region transformed from a zone of fringing
arcs and interarc oceanic basins to a coherent, east dipping arc-trench system [Harper and
Wright, 1984; Wright and Fahan, 1988; Saleeby et al., 1992; Dickinson et al., 1996]. In
12
the retroarc region, Late Jurassic topographic highs and magmatic centers formed and
began to shed volcanoclastic and siliciclastic sediments into marginal marine basins of
the western United States—marking the initiation of a composite orogenic wedge
[Jordan, 1985; Meyers and Schwartz, 1994]. Sedimentation in the foreland basin system
remained intimately linked with Cordilleran shortening in the retroarc thrust belt for the
next >100 My.
The modern expression of Mesozoic oceanic subduction along the western margin
of North America is the Cordilleran magmatic arc, a >5000 km long belt of Late Triassic
to Late Cretaceous calc-alkaline granitoid batholiths and related volcanic rocks [Saleeby
et al., 1992]. These rocks crop out in a nearly continuous belt from the Coast Ranges
Batholith in southeastern Alaska and western Canada to the Peninsular Ranges batholith
in Baja California (Figure 1). The orogen-scale history of magmatism in the Cordilleran
arc is complex, as locations and magmatic addition rates vary through time for individual
arc segments [Gaschnig et al., 2010; Paterson et al., 2011]. Of these segments, the Sierra
Nevada batholith of central and southern California is perhaps the best understood.
Radiometric ages of plutonic rocks in the Sierra Nevada reveal major pulses in magmatic
activity between 160-150 Ma and 100-85 Ma [Barton, 1990; Ducea, 2001].
Nearly orthogonal convergence between the rapidly westward moving North
American plate and the oceanic Farallon plate drove shortening in the Cordilleran
retroarc thrust belt [Engebretson, 1984]. This complex zone of eastward verging faulting
and folding can be divided into five tectonostratigraphic zones. From west to east, these
zones include the Luning-Fencemaker thrust belt; the central Nevada thrust belt; a highelevation plateau referred to as the Nevadaplano; the Sevier fold-thrust belt; and the
13
Laramide intraforeland basement uplifts [DeCelles, 2004]. Each of these tectonomorphic
zones experienced shortening, crustal thickening, metamorphism, and/or magmatic
activity during the Late Jurassic to Eocene and are generally considered to be the product
of a coherent orogenic wedge with an eastward-migrating thrust front and foreland basin
system. The easternmost expression of thin-skinned thrust faulting and related folding in
the Cordilleran retroarc region is referred to by a variety of terms, including the Sevier
belt in Utah, Wyoming and Idaho; the Montana disturbed belt; and the Canadian Rocky
Mountains thrust belt [Allmendinger, 1992]. Frontal thrusts in this belt locally override
the Cordilleran foreland basin system that developed within North America’s >5,000,000
km2 Western Interior Basin.
The Sevier thrust belt is dominated by low angle thrust faults that transported
Neoproterozoic-upper Mesozoic sedimentary rocks in their hanging walls. Although
Armstrong [1968] defined the Sevier belt as exclusively thin-skinned, later work has
shown that significant slices of Precambrian metamorphic 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 paleogeography in the Sevier
belt can be invoked to explain differing detrital zircon affinities in the Cordilleran
retroarc foreland basin system.
14
Section 5: Detrital Zircon Signatures
Successful application of detrital zircon provenance analysis hinges upon sufficient
understanding of the distribution 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 geochronological 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.
Section 5.1: Laurentian Basement Rocks
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, 1989]. Today, these rocks are exposed in
basement uplifts of the northern United States and in the Canadian Shield region of
central Canada and Greenland. During the Proterozoic, multiple collisional events (1.711.30 Ga) accreted juvenile terranes to the cratonal core [Whitmeyer and Karlstrom,
2007]. Yavapai (1.8-1.7 Ga), Mazatzal (1.7-1.65 Ga), and Grenville (1.2-1.0 Ga) rocks
compose the bulk of this more juvenile crust. Following their accretion, the Yavapai and
Mazatzal provinces were intruded by plutons associated with an A-type magmatic event
(1.48-1.34 Ga) [Van Schmus et al., 1996]. The net effect of these processes was to
create a stable Laurentian craton and platform composed of distinct crustal provinces
15
(Figure 3) whose age signatures recur throughout North America’s sedimentary record.
In Montana, southern Alberta, and southern British Columbia, Laurentian
embayments provided the accommodation space for a thick accumulation of
Mesoproterozoic-Neoproterozoic siliciclastic strata. These strata, which have since been
metamorphosed up to middle greenschist grade, contain detrital zircon ages that plot
within the North American Magmatic Gap (NAMG)—a time period for which no known
Laurentian sources are preserved. The presence of these zircons requires an exotic
terrane outboard of western Laurentia. Stewart et al. [2010] argued on the basis of crustal
ages and Hf isotopic signatures that these zircons were likely derived from eastern
Antarctica and Australia when they were connected to southwestern Laurentia within a
proto-Rodinian supercontinent. Alternatively, these zircons may have been eroded from
an undocumented 1.6-1.5 Ga African source that was exposed during the Grenvillian
orogeny. Whatever the case, sediments that filled these basins came to dominate trailing
thrust sheets of the Montana disturbed belt and the Canadian Rocky Mountains thrust belt
(Figure 1) [Price, 1981; Fuentes et al., 2012].
Section 5.2: North American Passive Margin
Thrust sheets of the Sevier belt are principally constructed from an elongated
prism of thick sediments that were deposited on the passive western margin of Laurentia
following the breakup of Rodinia. Basal, Neoproterozoic strata of this sequence
accumulated in embayments west of the Wasatch hinge line, which demarcates the
eastern extent of significant rifting of Laurentian crystalline basement rocks [Hintze,
1988]. These strata are dominated by siliciclastic rocks that reached maximum
thicknesses of >10 km [Link et al., 1993]. During the early Paleozoic, passive margin
16
sedimentation overlapped Precambrian crystalline basement rocks east of the hinge line,
reaching maximum thicknesses of ~12 km in western Utah.
Gehrels et al., [1995] systematically sampled five transects of the North American
passive margin for detrital zircon provenance analysis between Sonora, Mexico and
southeastern Alaska. Their dataset was updated by Gehrels and Pecha [in prep], who
present high-age-density detrital zircon data from the same stratigraphy (n~200). Their
results, which reveal a dominance of local Laurentian sources, enable K-S test
fingerprinting of northerly or southerly provenance for Cordilleran retroarc foreland basin
strata. The authors identified three major trends relevant to this objective: 1) Ordovician
strata are dominated by Trans-Hudson (1.8-2.0 Ga) and Wopmay (2.0-2.3) ages along the
entirety of the Laurentian margin; 2) non-Ordovician strata generally mimic the age
spectra of nearby Laurentian basement provinces; and 3) Grenville-aged (1.2-1.0 Ga)
grains are ubiquitous throughout.
Section 5.3: Mesozoic Eolianites
Vast ergs (sand seas) developed in southwest Laurentia during the PermianJurassic. Today, these ergs are preserved in the form of eolianites in the Four Corners
region of the southwestern United States. Provenance analysis of zircons from these
sandstones reveals a dominance of Grenvillian (1315-1000 Ma), Pan-African (750-500
Ma), and Paleozoic (500-310 Ma) grains throughout the section [Dickinson & Gehrels,
2003]. In addition, each sample contains younger zircons whose ages overlap with those
of Appalachian plutons that trace the Laurentian-Gondwana suture. These populations
are interpreted to record a transcontinental drainage system with headwaters in eastern
Laurentia [Dickinson & Gehrels, 2003, 2009]. During Cordilleran contractional
17
deformation, leading thrusts of the Sevier belt deformed these strata. Therefore, it is
likely that Appalachian-derived sediments experienced second-cycle deposition within
the Cordilleran retroarc foreland basin system.
Section 5.4: Cordilleran Magmatic Arc
Arc magmatism in western North America dates back to the initiation of
subduction along the western margin of Laurentia during the Permian [Dickinson and
Lawton, 2001]. The oldest arc rocks are preserved in the Permian-Triassic (284-232 Ma)
magmatic arc of eastern Mexico, which intruded Gondwanan crust above a subduction
zone located in present-day central Mexico. This segment was bound to the north by a
transform fault, which truncated the continental margin prior to the breakup of Pangea.
The oldest de facto Cordilleran magmatism initiated with subduction beneath this
truncated margin during mid-Early Triassic time [Dickinson, 2000]. Most Cordilleran
magmatism intruded an elongate zone located 100-250 km inboard of the arc-trench
system (Figure 1). Today, a discontinuous belt of deeply exhumed granitic batholiths
characterizes this zone. These exposures have been studied in detail to reconstruct
changing magmatic addition rates and paleogeography of the North American margin
[Tobisch et al., 1986; Busby-Spera, 1988; Barth et al., 1997; Dunne et al., 1998; Ducea,
2001; Paterson et al., 2004, Saleeby et al., 2008; Gehrels et al., 2009; Miller et al., 2009].
Detrital zircon provenance analysis of retroarc region strata indicates that the
magmatic arc and retroarc thrust belt formed a topographically-integrated, Andean-type
margin by Late Jurassic-Early Cretaceous time [Fuentes et al., 2009]. These results are
supported by geological investigation of Early to Middle Jurassic, intra-arc grabens that
contain marine sediments [Saleeby and Busby-Spera, 1992] followed by accumulation of
18
substantial Late Jurassic arc-derived detritus in the retroarc region, indicating significant
elevation gain [Christiansen et al., 1994]. This evidence suggests that 1) detrital zircons
of retroarc foreland basin strata record the magmatic history of the post-Late Jurassic arc
and 2) that the Cordilleran magmatic arc formed a drainage divide beginning by Late
Jurassic time that blocked eastward transport of Cordilleran terrane-derived sediments.
Section 6: Results
Comparison of foreland basin age spectra (Figures 5a-h) to those of potential
provenance candidates (Figure 4) through K-S and qualitative provenance analysis
produced six major provenance groupings and two mixed provenance subgroupings that
describe variations in age spectra within the Cordilleran retroarc foreland basin system.
In this section, we describe the individual groupings, quantify their internal consistency
using K-S testing, then use stratigraphic depositional ages (see references, table DR1) to
reconstruct sediment dispersal pathways in the foreland basin system during the Late
Jurassic, Cretaceous, and early Paleogene (Figures 6a-e).
Section 6.1: Comparison with Potential Source Regions
All samples included in this study can be categorized into one of six provenance
interpretation groups that are genetically linked to tectonostratigraphic sequences that
were exhumed during Cordilleran orogenesis. Samples with unimodal age distributions
were generally interpreted to represent deposition of grains derived from primary igneous
or metamorphic sources. The remaining samples, which are characterized by multiple
age-probability peaks, were interpreted to represent recycling of Mesozoic eolianites or
the Laurentian passive margin. This type of interpretation, which favors secondary
sedimentary sources over primary igneous sources, is appropriate in this setting because
19
the sedimentary rocks of interest dominate the North American Cordilleran thrust belt.
This interpretation is also consistent with abundant conventional light-mineral
sedimentary petrological data from Cretaceous and lower Cenozoic sandstones from
throughout the Cordilleran foreland basin, which indicate predominantly recycled
orogenic provenance [e.g., Suttner et al., 1981; Dickinson et al., 1986; DeCelles, 1986;
DeCelles and Burden, 1992; Goldstrand, 1992; Currie, 1997; Lawton et al., 2003].
Section 6.1.1: Cordilleran Magmatic Arc
A relatively small proportion of foreland basin samples display a dominance of
Cordilleran magmatic arc-derived (<250 Ma) detrital zircons. Where present, however,
this signature overwhelmed all other age-probability peaks. The eight samples whose
PDF’s are plotted in Figure 5a each contain at least 50% arc-derived detrital zircons. The
group as a whole averages 75% arc-derived zircons. Despite these unimodal provenance
characteristics, none of the samples pass the K-S test for internal consistency. We
attribute this finding to the tendency of young age-probability peaks to cluster near the
stratigraphic depositional age of each sample, which ranges in age from the Early
Cretaceous to the Eocene (125-48 Ma; Table DR1). Maximum depositional ages (Figure
5a)—which were determined by averaging the age of the youngest coherent group of
three detrital zircons—fall within the stratigraphic depositional age brackets of all arcderived samples. Unfortunately, stratigraphic depositional ages for some of the samples
are relatively poorly constrained (+/- 12 My maximum). Therefore, we did not calculate
detrital zircon lag times.
Peak ages can be compared to magmatic flux curves for segments of the
Cordilleran magmatic arc (Figure 7) to guide provenance interpretations. The Sierra
20
Nevada and Coast Mountains segments of the arc (Figure 1) were dominant between
~180-90 Ma [Paterson et al., 2011]. In addition, the Idaho batholith preserves plutons as
old as ~125 Ma, although abundant magmatism likely did not begin until ~100 Ma
[Gaschnig et al., 2010]. The Blackleaf and Kootenai Formations in northern Montana
(ISR80, 1FG70), which contain peak ages of ~97 and ~109 Ma, were likely derived from
some combination of these sources. The Coast Mountains, Cascades, and Idaho-Montana
segments became the most productive after ~90 Ma [Gaschnig et al., 2010; Paterson et
al., 2011]. This transition is likely related to propagation of the Laramide flat slab under
the southwestern United States, which displaced the melting zone of the Sierra Nevada
arc [Coney and Reynolds, 1977; Dickinson and Snyder, 1978]. The remainder of the arcdominated samples contain peak ages that are younger than ~90 Ma. Therefore, they
were likely derived from some combination of sources that excludes the Sierra Nevada
arc.
Arc-derived detrital zircons in all samples can be examined to reveal a basinaveraged, relative magmatic flux curve. All grains younger than 200 Ma were plotted as
a composite PDF in Figure 7 for comparison with 1) velocity and age data for the
Farallon plate [Engebretson, 1984], 2) periods of arc magmatism in the Idaho-Montana
arc [Gaschnig et al., 2010], and 3) relative flux curves for other segments of the
Cordilleran arc [Paterson et al., 2011]. This analysis reveals a apparent increase in the
frequency of high relative flux events after ~100 Ma, from a recurrence interval of ~50
My to ~25 My. Possible explanations for what drove this increase are discussed in
section 7, below. The apparent similarity between the igneous and basin-averaged
detrital proxies suggests that detrital zircon geochronology is a valid tool for studying arc
21
magmatism.
Section 6.1.2: Yavapai-Mazatzal
Samples characterized by a unimodal, 1800-1600 Ma relative abundance peak and
<50% arc-derived detrital zircons compose the Yavapai-Mazatzal provenance group
(Figure 5b). We interpret that these 11 samples record first cycle deposition of zircons
eroded from the Yavapai-Mazatzal basement province in the western United States, as
there are no known sedimentary sequences that correlate can contribute Paleoproterozoic
ages in such high abundance. Initially, grains younger than ~250 My were included in KS statistical comparison of grouped samples. However, the tendency of young age
probability peaks to correlate with stratigraphic deposition age introduced cumulative
relative abundance curve (CDF) variation powerful enough to prevent consistent
statistical matching. This is the same phenomenon that prevented statistical grouping of
the Cordilleran Magmatic Arc samples, described above. A second K-S test, this time
excluding arc-derived (<250 Ma) grains, was far more successful. The test revealed 98%
internal consistency within this grouping, meaning that each sample was deemed
statistically indistinguishable from other samples in the group 98% of the time.
Section 6.1.3: Mesozoic Eolianite
Samples that display similarities to a composite PDF representation of 10 samples
from Jurassic eolian and associated marine and fluvial sandstones [Dickinson & Gehrels,
2003; 2009] of the southwestern United States (Figure 3) were included in the Mesozoic
Eolianite provenance group (Figure 5c). Twenty three samples match our criteria, which
include mirroring of the presence and relative abundance of age-probability peaks at 420
Ma, 615 Ma, 1055 Ma, and 1160 Ma (Figure 5c). We interpret that these samples were
22
recycled from Mesozoic eolianites in the western United States rather than from a
combination of primary Appalachian and Grenville sources in eastern North America
(Figure 3) so as to favor the simplest possible sediment dispersal system that is consistent
with regional paleocurrent data. K-S testing of the grouped samples reveals 92.5%
internal consistency when arc-derived detrital zircons are excluded.
Section 6.1.4: Mogollon Highlands
Nine samples of Upper Cretaceous foreland basin system strata of the Four
Corners region (Figure 2) are characterized by Laurentian age-probability peaks centered
around 1700 Ma, 1450 Ma, and 1100 Ma (Figure 5d). In addition, these samples contain
abundant arc-derived detrital zircons. K-S testing of these data against samples from the
other provenance groups yielded no statistically indistinguishable results. It is likely that
the high variability of peak relative abundance within this sample set precluded the
possibility of quantitative provenance analysis using K-S statistics. Despite their
mathematical dissimilarity, all of the samples were deposited within a relatively restricted
zone of the foreland basin system, in close proximity to the Mogollon Highlands of the
southwestern United States (Figure 1). This ancient rift shoulder is a reasonable
provenance candidate, as it exposed all of the required tectonostratigraphic elements—
including Yavapai-Mazatzal basement, Paleozoic cover, and Cordilleran magmatic arc
rocks—during Jurassic-Cretaceous time [Dickinson and Gehrels, 2008]. Our
interpretation of these samples is consistent with those of the Dickinson and Gehrels,
[2008] and Lawton & Bradford [2011], from whom these data were compiled.
Section 6.1.5: Laurentian Passive Margin
One third of the foreland basin samples presented in this study contain detrital
23
zircon age-probability peaks that match the distribution of local Laurentian cratonal and
platformal tectonostratigraphic elements. Rather than attributing their detrital zircon
spectra to a combination of primary sources, we infer that these samples were recycled
from Laurentian passive margin strata that dominate the Cordilleran thrust belts in the
western United States and Canada. Gehrels and Pecha’s [in prep] detrital zircon data
from passive margin strata exposed in the Cordilleran thrust belt in the western United
States (Utah, Nevada) and southern Canada (British Columbia) form the basis for two
provenance groupings that encompass 34 foreland basin samples.
The United States passive margin group (Figure 5e) contains 24 samples that
display three dominant age-probability peaks of equal relative probability centered at
1700 Ma, 1450 Ma, and 1100 Ma. The samples in this group mirror age-probability
peaks from the Utah-Nevada passive margin and are 78% internally consistent. The
Canada passive margin group (Figure 5f) contains 10 samples with a dominant ageprobability peak centered at 1900 Ma and three subordinate age-probability peaks at 2700
Ma, 2100 Ma, and 1100 Ma. These samples mirror British Columbia passive margin age
spectra and are 64% internally consistent. Two of the samples in the Canada passive
margin group, BTC and SKR, were poor statistical matches. The fact that they are
statistically distinguishable from >50% of the other samples would normally warrant
rejection under our statistical provenance analysis criteria (see Section 3.2). However,
Leier and Gehrels [2011] interpret these samples to have been recycled from the Canada
passive margin, alongside five other samples (ODR, SHC, CDM, EBK, and GCH) from
the Cadomin Formation. These samples, which were also independently categorized into
this group, are much better statistical matches. Therefore, we chose to retain samples
24
BTC and SKR.
Section 6.1.6: Mixed Passive Margin and Laurentian Basement
Archean, Proterozoic, Paleozoic, and Mesozoic age-probability peaks of similar
magnitudes characterize four samples from southwest Montana. The distributed nature of
the peaks, as well as our inability to correlate all of the peaks to one source, implies that
these strata were derived from at least two distinct tectonostratigraphic sequences. We
infer that the Yavapai-Mazatzal (1800-1600 Ma), Laurentian anorogenic plutonic (14801340 Ma), Grenville (1200-1000 Ma), and Peri-Laurentian (750-300 Ma) peaks reflect
recycling of United States passive margin detrital zircons (Figure 5e) into the
southwestern Montana foreland. However, the presence of an additional, Archean
(~2750) age-probability peak in these strata requires at least one additional source, which
is likely the Archean basement of the north-central United States (Figure 3). K-S testing
of the four samples confirms that they were all derived from statistically indistinguishable
parent populations, i.e., this group is 100% internally consistent.
Section 6.1.7: Ordovician Passive Margin
The remaining nine samples are difficult to group using K-S or qualitative
provenance analysis due to the high variability in age-probability peak relative
abundance. Some of these samples qualitatively resemble United States passive margin
group spectra (GCMONTEITH, UT06-8B, MB1007, and SKR), while others appear
more similar to the Canada passive margin group (BTC, 1SFSR1, 1GR100, UT0715,
AND UT06-4). The sole characteristic that these samples share is the presence of a well
to poorly defined, two-tiered age-probability peak that straddles the age boundary
between the Trans-Hudson (2000-1800 Ma) and Wopmay (2300-2000 Ma) provinces.
25
Gehrels and Pecha (in prep) identified a similar age-probability peak in Ordovician
passive margin strata of the western United States and Canada (Figure 4). Therefore, we
propose that these anomalous samples record mixing of passive margin strata with
anomalously abundant Ordovician passive margin strata. It is plausible that this signature
is indicative of erosion and recycling of passive margin strata in an Ordoviciandominated thrust system, such as the Roberts Mountain allochthon in central Nevada [e.g.
Gehrels et al., 2000]. In this model, the tendency of samples to qualitatively represent
United States or Canadian passive margin strata likely depends on the location of the
thrust sheet along the Cordilleran orogenic front.
Section 6.2: Depositional Age-Referenced Provenance
Detrital zircon samples were mapped on one of five paleogeographic
reconstructions (R. Blakey, “Paleogeography and Geologic Evolution of North
America”) and symbolized according to their provenance interpretation group (coded by
symbol shape and color). Paleogeographic reconstructions and a list of data sources are
available at http://cpgeosystems.com/nam.html. Knowledge of the extent of interpreted
sediment sources (Figure 3) and age-appropriate generalized paleocurrent directions
[DeCelles, 2004] was used to map likely sediment dispersal pathways within the foreland
basin system (Figures 6a-e). Timing of the emergence of provenance groups was used to
construct a record of Late Jurassic to Eocene exhumation within the Cordilleran orogenic
wedge.
Section 6.2.1: Late Jurassic Provenance
PLACEHOLDER FOR Figure 6A
Most Late Jurassic detrital zircon samples are from the Morrison Formation,
26
which formed a 50-200 m thick blanket of fluvial deposits that covered ~150,000 km2 of
the Cordilleran foreland between the Sevier thrust front and the Rio Grande rift [Furer,
1970; Currie, 1998; DeCelles and Burden, 1992; Turner and Peterson, 2004]. Morrison
Formation provenance in the Four Corners region is dominated by recycling of Mesozoic
eolianites. This interpretation is consistent with DeCelles and Burden’s [1992] inference
that K-feldspar in the Morrison Formation is indicative of Mesozoic eolianite recycling
from the thrust belt to the west. Samples that show this correlation are from the Jackpile
(CP53), Recapture (CP25), Salt Wash (CP49, CP36, CP35, CP29, CP19), Fiftymile
(CP52), and Tidwell (CP41) Members. However, two contemporaneous samples from
the Westwater Canyon Member (CP21, CP13) display Mogollon Highlands provenance.
The close spatial association of samples from both groups (Figure 6a) implies that
samples in this region were derived from a combination of thrust belt and Mogollon
Highlands sources. Although a compilation of sediment dispersal directions [DeCelles,
2004] indicates a dominance of east-directed transport, we propose that a northeastdirected fluvial system may have also existed (Figure 6a) in the southern Four Corners
region. Our interpretation of Morrison Formation samples is consistent with that of
Dickinson and Gehrels [2008], from whom these data were compiled.
Two new samples were collected from the Upper Jurassic Entrada (T52X-17935)
and Morrison (719062) Formations in the Uinta region. These samples match the criteria
of the Mesozoic Eolianite interpretation group, suggesting either that Mesozoic eolianites
were exposed in the Sevier belt to the west, or that they were recycled northwards from
the flanks of the Mogollon Highlands. Sedimentological data does not preclude either
interpretation, as both northeast and southeast-directed dispersal was documented in the
27
region (Figure 6a). However, petrographic data from the Morrison Formations in
Wyoming records an unroofing sequence, which is consistent with the bulk of Upper
Jurassic strata in this region being recycled from westerly, thrust belt sources [DeCelles
and Burden, 1992; Currie, 1998].
Two additional Morrison Formation samples were collected in northern Montana
(1GRX, 1GRZ). These samples have indistinguishable age spectra from Mesozoic
Eolianite group samples of the southwestern United States. The two samples are
accompanied by one Kootenai Formation sample (TFI) that displays United States
Passive Margin provenance in southwest Montana. Therefore, we interpret that these
samples were recycled from exposures of Mesozoic eolianites in the Sevier belt (Figure
6a). Fuentes et al. [2009] interpreted that Late Paleozoic and Triassic detrital zircons
(~330-180 Ma) in these samples (1GRX, 1GRZ) were derived from igneous rocks in the
eastern part of the Intermontane Belt. In addition, those authors concluded that Late
Proterozoic to Cambrian detrital zircons in these samples must have originated in uplifted
Mesozoic eolianite strata of the Sevier belt. However, both of these age populations are
present in Dickinson and Gehrels’ [2009] Mesozoic Eolianite data. Therefore, we prefer
the interpretation that Morrison Formation throughout the United States was derived
mostly from Mesozoic Eolianites, rather than from multiple sources that span a broad
geographic range.
Upper Jurassic strata of the northern foreland basin system in Canada do not
contain abundant Late Mesozoic-Triassic detrital zircons. This observation was
previously used to argue for the presence of a drainage divide north of the Omenica Belt,
near the international border [Mack and Jerzykiewicz, 1989; Ross et al., 2005, Leier &
28
Gehrels, 2011] that prevented northward transport of Intermontane Belt sediments. This
inference is also valid for our provenance model, which links the Late Mesozoic-Triassic
grains to Mesozoic eolianites rather than the Intermontane Belt. All of the Late Jurassic
samples from Canada presented in this study were derived from passive margin strata,
which were likely exposed in thrust sheets of the Sevier and the Canadian Rocky
Mountains thrust belts. Kootenay (BASALKOOTENAY), Nikanassin
(PROSPECTCREEK), and Monach Formation (GCMONACH) samples were
predominately derived from the passive margin of the United States while the three
northernmost samples were derived from the local thrust belt. These interpretations
imply northward transport of United States passive margin strata, perhaps via longshore
transport along the western shoreline of the interior seaway represented in the 145 Ma
paleogeographic reconstruction (Figure 6a).
Section 6.2.2: Early Cretaceous Provenance
PLACEHOLDER FOR Figure 6B
During the Early Cretaceous, the Cordilleran foreland transitioned 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 requires northwards transport, perhaps
along the same pathway that we inferred for Upper Jurassic samples (Figures 6a, 6b). In
addition, two samples (CP14, CP27) of Burro Canyon Formation and one sample (UT06-
29
8B) of Buckhorn Formation evidence continued northeast-directed recycling of Mesozoic
eolianites in the Four Corner’s region. Mesozoic Eolianite provenance was also
determined for the Kelvin (K2) and Kootenai (10DM25) Formations in the Uinta and
Montana regions.
Kootenai and Blackleaf Formation samples (1FG70, ISR80) in northern Montana
are the earliest record of Cordilleran magmatic arc dominated provenance in the foreland
basin system. These samples imply that there was not a regional topographic barrier
between the magmatic arc and foreland basin system during the Early Cretaceous.
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, 6a-e). Our provenance model
favors derivation from the Idaho-Montana arc, as it is the most proximal (Figure 6b).
Section 6.2.3: Cenomanian–Santonian Provenance
PLACEHODER FOR Figure 6C
Cenomanian-Santonian detrital zircon samples (Figure 6c) 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 indicate
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.
Samples of the Mancos (CP33, CP23) and Toreva (CP9) Formations record the
30
reemergence of Mogollon Highlands provenance in the Uinta and Four Corners regions.
These samples were deposited outboard of contemporaneous samples from the Canyon
Range and Sanpete Formations (CR7 and UT06-3), which record recycling of the United
States passive margin. These interpretations suggest that proximal samples were derived
from local sources to the west, whereas distal samples were transported axially. This
pattern is consistent with the Santonian paleogeographic reconstruction, which places the
Cretaceous Interior Seaway shoreline precisely at the divide between the two provenance
groupings. This boundary might demarcate the transition between fluvial and longshore
transport regimes.
Two new samples from the Mancos (T67-14419) and Blair (EM4) Formations in
the Uinta region signal the emergence 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 exposures on the flanks of the Mogollon Highlands. This
interpretation requires ~1700 km of northeast-directed axial transport, presumably via
longshore transport along the shoreline of the Cretaceous Interior Seaway.
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
31
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 headwaters tapped exposures of Archean Wyoming Province
basement rocks.
Section 6.2.4: Campanian-Paleocene Provenance
PLACEHOLDER FOR Figure 6D
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 to dominate in northern
Montana, as shown by samples of the St. Mary’s River (1BB44) and Two Medicine
(2SR240) Formations. In southern Montana, arc-derived grains remained subordinate, as
three more samples from the Beaverhead Group (10DM20, 10DM22, 10DM23) indicate
mixed United States passive margin, Archean basement, and Yavapai-Mazatzal basement
provenance. The Yavapai-Mazatzal group sample (10DM20) was deposited north of the
northernmost extent of Yavapai-Mazatzal basement (Figure 3). Therefore, we interpret
that these ages were recycled from Paleoproterozoic Belt Supergroup strata, which are
exposed in trailing thrust sheets of the northernmost Sevier belt [DeCelles, 2004].
Further support for this hypothesis is provided by abundant quartzite clasts in sample
10DM20, which is described as a quartzite conglomerate by Haley and Perry [1991].
Late Cretaceous Uinta and Four Corners region samples indicate mixed United
States passive margin, Mogollon Highlands, Cordilleran magmatic arc, and Yavapai-
32
Mazatzal provenance (Figure 6d). We infer that all of these tectonostratigraphic
sequences were exposed locally in the Sevier belt and newly formed (~85 Ma) Laramide
intraforeland province [DeCelles, 2004; Fuentes et al., 2012]. Mesozoic Eolianite
affinity also reappeared at this time, in the Wahweap (CP39) and Almond (LBRG-2700)
Formations. These data indicate that either Mesozoic eolianites continued to be exposed
in the Sevier belt, or that younger foreland basin strata that inherited the Mesozoic
eolianite signature began to be exhumed. The latter model requires third-cycle deposition
of Mesozoic eolianite sediments that were eroded from older foreland basin strata such as
the Morrison Formation. However, clast count data from coeval CampanianMaastrichtian conglomerates 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].
PLACEHOLDER FOR Figure 6E
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 sample 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 magmatic arc provenance with a
dominant age peak at ~46 Ma (Figures 5a, 6e. These data suggest that the IdahoMontana arc was shedding sediment into the foreland basin, despite the absence of
33
characteristic ages in the most proximal samples.
Section 7: Discussion
Comparison of detrital zircon age spectra to those of potential provenance
candidates revealed six major provenance groupings in the Cordilleran retroarc foreland
basin system. Each of the groupings corresponds to a specific sequence of igneous,
metamorphic, or sedimentary rocks that were defomed in or exposed near the Cordilleran
orogenic wedge. Referencing provenance interpretations to stratigraphic depositional
ages revealed the chronology of exhumation and transport within the retroarc region.
Arc-derived detrital zircons, which were extracted from the composite spectrum of
foreland basin detrital zircons, were used to construct a basin-averaged proxy for
Cordilleran arc flux. Integration of these datasets affirms the utility of detrital zircon
geochronology in studying orogenic systems on continents.
In the United States, Late Jurassic foreland basin sedimentation was dominated by
recycling of Mesozoic eolianites (Figure 6a). Paleocurrent measurements from these
strata indicate westerly to southwesterly provenance [Suttner et al., 1981; DeCelles and
Burden, 1992; Currie, 1998], which is consistent with the requirements of our detrital
zircon provenance analysis. These observations led us to conclude that most recycled
Mesozoic eolianite sediment was derived from the Sevier belt (Figure 1), implying that
Mesozoic eolianites dominated leading thrust sheets during this time. However, some
Late Jurassic strata of the Four Corners region may have been recycled from the flanks of
the Mogollon Highlands. In contrast, provenance analysis of Upper Jurassic foreland
basin strata in Canada reveals a dominance of Canada passive margin recycling. Yet
some samples are more similar to the United States passive margin, which implies that
34
sediments may have experienced axial, northward transport along the shoreline of the
Late Jurassic interior seaway (Figure 6a).
Sedimentation above the basal Cretaceous unconformity was dominated by
complex, mixed provenance in the foreland basin system. Variations during this period
can be explained by the changing tectonostratigraphic composition of the Cordilleran
orogenic wedge as it propagated and progressively shortened over a period of ~100 My.
The first appearance of particular provenance groups was used to determine the timing of
source exhumation. Deposition of mixed passive margin and Laurentian basement
provenance foreland basin strata in the western United States reveals that basementinvolved structural culminations were exposed by Campanian to Maastrichtian time (~8666 Ma). In addition, deposition of Mogollon Highlands group sediments in the Four
Corners region reveals that basement, cover, and arc rocks were exposed on the
Mogollon flanks during the Late Jurassic and Late Cretaceous.
Arc-derived detrital zircons with ages younger than 200 Ma were combined to
create a basin-averaged proxy for Cordilleran magmatic arc flux (Figure 7). Visual
inspection of this curve reveals high flux events (HFEs) at ~160 Ma, ~100 Ma, ~75 Ma,
and ~45 Ma. Before ~100 Ma, the interval between HFEs appears to have been ~60 My.
After ~100 Ma, this interval decreased to ~25 My. The cyclical nature of these HFEs
suggests that coupled upper-plate processes were likely interacting with subduction zone
processes to control the evolution of the North American Cordillera. Interpretation of the
detrital record of magmatic arc flux within the framework of the Cordilleran orogenic
cyclicity model of DeCelles [2009] explains the increase in high flux event frequency at
~100 Ma.
35
In Cordilleran orogenic systems, convergence is accommodated by subduction of
an oceanic plate and shortening of a continental plate. Typically, upper continental crust
shortens across a retroarc thrust belt while the lowermost continental crust is shoved
beneath the arc—fueling episodic high flux magmatism [Ducea and Barton, 2007;
DeCelles et al., 2009]. The recurrence interval of high flux magmatism should therefore
vary according to changes in the convergence rate. In the North American Cordillera,
relatively slow convergence between the Farallon and North America plates produced
two HFEs with a recurrence interval of ~60 My between 160-100 Ma (Figure 7).
Convergence rates increased after ~100 Ma, as indicated by an increase in Farallon plate
velocity of ~100 km/my [Engebretson, 1984]. This increase coincided with a >50%
reduction in HFE recurrence interval between ~100 Ma and 50 Ma, from ~60 My to ~25
My. We propose that the increase in plate convergence velocity caused the decrease in
HFE recurrence interval.
Detrital zircon geochronology is commonly used to investigate first-order
magmatic and accretionary processes. In addition, many workers have used detrital
zircon geochronology to resolve recycling and erosion of tectonostratigraphic sequences
within orogenic systems. This technique has proven particularly effective in North
American Cordillera. However, detrital zircons from the retroarc region of Cordilleran
orogenic systems should also be used to examine orogen-scale arc magmatic processes.
For instance, the detrital record of Cordilleran arc magmatism is much less difficult to
interpret at the orogen scale than the compilation of igneous flux curves presented in
Figure 7. These curves, despite their detail, do not reveal any clear trends in recurrence
interval of HFEs or relative flux between HFEs. The clarity of the detrital zircon curve is
36
undoubtedly related to the averaging that is characteristic of detrital proxies. However,
this characteristic should not be considered a limitation, especially when examining
orogen-scale tectonic processes.
Section 8: Conclusions
Foreland basin strata in the Cordilleran retroarc region contain age spectra with
varying proportions of 1) 2.5 Ga cratonic, 2) 2.3–1.6 Ga Wopmay, Trans-Hudson, and
Yavapai-Mazatzal, 3) 1.48-1.34 Ga intracratonic magmatic, 4) 1.2-1.0 Ga Grenville, 5)
750-250 Ma peri-Laurentian, and 6) <250 Ma Cordilleran magmatic arc detrital zircons.
Variations in the presence, absence, and relative abundance of age peaks within these
ranges defined six provenance groupings that describe variations within the foreland
basin system. Recycled groups include samples that display Mesozoic Eolianite, Canada
passive margin, and United States passive margin provenance. Groups whose age spectra
suggest a component of first-cycle erosion include the Yavapai-Mazatzal, Cordilleran
Magmatic Arc, Mogollon Highlands, Mixed Passive Margin and Ordovician Passive
Margin, and mixed Passive Margin + Yavapai-Mazatzal interpretation groups.
Characteristic age spectra for each grouping were defined in Section 6. Whenever
possible, K-S statistics were used to quanify the internal consistency of provenance
groups. These tests successfully categorized 69 of the 96 total samples.
Late Jurassic provenance was dominated by recycling of Mesozoic eolianites in the
United States and passive margin strata in Canada. Most recycling was linked to
exhumation Cordilleran thrust belt. However, some samples from this period suggest a
component of axial transport, especially in the Four Corners region and in southern
Canada (Figure 1, 6a). Foreland basin provenance became increasingly complex during
37
the Cretaceous-Eocene. Progressive shortening and propagation in the Cordilleran
orogenic wedge during this period exhumed all of the crustal elements required to explain
the provenance interpretation groups. Emergence of Yavapai-Mazatzal provenance in the
Uinta and Montana regions during the Campanian-Maastrichtian signaled the exhumation
of basement-involved thrust sheets between ~86-66 Ma.
The detrital record of arc magmatism from the Cordilleran foreland basin system
reveals a correlation between increasing convergence rates and a decrease in high flux
event recurrence interval at ~100 Ma. These data corroborate predictions of the
Cordilleran orogenic cyclicity model of DeCelles et al. [2009], which links coupled
upper-plate processes to subduction zone processes. The apparent utility of detrital
zircon data as a proxy for arc magmatism in this study suggests that it is a useful tool for
evaluating arc magmatism at the continent scale in retroarc settings.
38
References:
Allmendinger, R. (1992), Fold and thrust tectonics of the western United States exclusive
of the accreted terranes, in The Cordilleran Orogen: Conterminous U.S., vol. G-3,
edited by B. C. Burchfiel, 583–607, Boulder, CO.
Armstrong, R. L. (1968), Sevier Orogenic Belt in Nevada and Utah, GSA Bulletin, 79(4),
429, doi:10.1130/0016-7606.
Barth, A. P., R. M. Tosdal, J. L. Wooden, and K. A. Howard (1997), Triassic plutonism
in southern California: Southward younging of arc initiation along a truncated
continental margin, Tectonics, 16, 290–304, doi:10.1029/96TC03596.
Barton, M. D. (1990), Cretaceous magmatism, metamorphism, and metallogeny in the
east-central Great Basin, in The Nature and Origin of Cordilleran Magmatism:
Geological Society of America Memoir 174, edited by J. L. Anderson, 283–302.
Burchfiel, B. C., and G. A. Davis (1972), Structural framework and evolution of the
southern part of the Cordilleran orogen, western United States, American Journal of
Science, 272(2), 97–118, doi:10.2475/ajs.272.2.97.
Busby-Spera, C. J. (1988), Speculative tectonic model for the early Mesozoic arc of the
southwest Cordilleran United States, Geology, 16, 1121–1125.
Camilleri, P., W. A. Yonkee, J. C. Coogan, P. G. DeCelles, A. McGrew, and M. Wells
(1997), Hinterland to foreland transect through the Sevier orogen, NE Nevada to SW
Wyoming: structural style, metamorphism, and kinematic history of a large
contractional orogenic wedge, in Proterozoic to Recent Stratigraphy, Tectonics, and
Volcanology, Utah, Nevada, Southern Idaho and Central Mexico, vol. 42, edited by
P. K. Link and B. J. Kowallis, 297–309, Brigham Young University Geology
Studies.
Christiansen, E. H., B. J. Kowallis, and M. D. Barton (1994), Temporal and spatial
distribution of volcanic ash in Mesozoic sedimentary rocks of the western interior: an
alternative record of Mesozoic magmatism, edited by M. V. Caputo, J. A. Peterson,
and K. J. Franczyk, Mesozoic systems of the Rocky Mountain region, USA, 73–94.
Condie, K. C., and R. C. Aster (2009), Zircon Age Episodicity and Growth of
Continental Crust, Eos, 90(41), 364, doi:10.1029/2009EO410003.
Coney, P. J., and S. J. Reynolds (1977), Cordilleran Benioff zones, Nature, 270(5636),
403–406, doi:10.1038/270403a0.
Currie, B. S. (1997), Sequence stratigraphy of nonmarine Jurassic−Cretaceous rocks,
central Cordilleran foreland-basin system, Geological Society of America Bulletin,
109, 1206–1222.
Currie, B. S. (1998), Upper Jurassic-Lower Cretaceous Morrison and Cedar Mountain
Formation, NE Utah-NW Colorado: Relationships between nonmarine deposition
and early Cordilleran foreland-basin development, Journal of Sedimentary Research,
68, 632–352.
DeCelles, P. G. (1986), Sedimentation in a tectonically partitioned, nonmarine foreland
basin: The Lower Cretaceous Kootenai Formation, southwestern Montana,
Geological Society of America Bulletin, 97, 911–931.
DeCelles, P. G. (1994), Late Cretaceous-Paleocene Synorogenic Sedimentation and
Kinematic History of the Sevier Thrust Belt, Northeast Utah and Southwest
Wyoming, Geological Society of America Bulletin, 106(1), 32–56.
DeCelles, P. G. (2004), Late Jurassic to Eocene evolution of the Cordilleran thrust belt
and foreland basin system, western USA, American Journal of Science, 304(2), 105.
DeCelles, P. G., and E. T. Burden (1992), Sedimentology and sedimentary petrology of
Jurassic-Cretaceous Morrison and Cloverly Formations in the overfilled part of the
Cordilleran foreland basin, Basin Research, 4, 291–314.
DeCelles, P. G., and J. C. Coogan (2006), Regional structure and kinematic history of the
Sevier fold-and-thrust belt, central Utah, Geological Society of America Bulletin,
118, 841–864, doi:10.1130/B25759.1.
DeCelles, P. G., and W. Cavazza (1999), A comparison of fluvial megafans in the
Cordilleran (Upper Cretaceous) and modern Himalayan foreland basin systems,
Geological Society of America Bulletin, 111, 1315–1334, doi:10.1130/0016-7606.
DeCelles, P. G., M. N. Ducea, P. Kapp, and G. Zandt (2009), Cyclicity in Cordilleran
orogenic systems, Nature Geosciences, 2(4), 251–257, doi:10.1038/ngeo469.
DeCelles, P. G., T. F. Lawton, and G. Mitra (1995), Thrust timing, growth of structural
culminations, and synorogenic sedimentation in the type Sevier orogenic belt,
western United States, Geology, 23, 699–702, doi:10.1130/0091-7613.
Devlin, W. J., K. W. Rudolph, C. A. Shaw, and K. D. Ehman (1993), The effect of
tectonic and eustatic cycles on accommodation and sequence stratigraphic framework
in the Upper Cretaceous foreland basin of southwestern Wyoming, International
Association of Sedimentologists Special Publication, 18, 501–520.
Dickinson, W. R. (2000), Geodynamic interpretation of Paleozoic tectonic trends oriented
oblique to the Mesozoic Klamath-Sierran continental margin in California,
Geological Society of America Special Paper 347, 209–245.
Dickinson, W. R., and G. E. Gehrels (2003), U-Pb ages of detrital zircons from Permian
and Jurassic eolian sandstones of the Colorado Plateau, USA: Paleogeographic
implications, Sedimentary Geology, 163(1-2), 29–66.
Dickinson, W. R., and G. E. Gehrels (2008), Sediment Delivery to the Cordilleran
Foreland Basin: Insights from U-Pb Ages of Detrital Zircons in Upper Jurassic and
Cretaceous Strata of the Colorado Plateau, American Journal of Science, 308(1), 1–
48, doi:10.2475/01.2008.01.
Dickinson, W. R., and G. E. Gehrels (2009), U-Pb ages of detrital zircons in Jurassic
eolian and associated sandstones of the Colorado Plateau: Evidence for
transcontinental dispersal and intraregional recycling of sediment, Geological Society
of America Bulletin, 121(3-4), 408–433, doi:10.1130/B26406.1.
Dickinson, W. R., and T. F. Lawton (2001), Tectonic setting and sandstone petrofacies of
the Bisbee basin (USA-Mexico), Journal of South American Earth Sciences, 14,
475–504.
Dickinson, W. R., C. A. Hopson, and J. B. Saleeby (1996), Alternate origins of the Coast
Range Ophiolite (California): introduction and implications, GSA Today, 6, 1–10.
Dickinson, W. R., T. F. Lawton, and K. F. Inman (1986), Sandstone Detrital Modes,
Central Utah Foreland Region: Stratigraphic Record of Cretaceous-Paleogene
Tectonic Evolution, Journal of Sedimentary Petrology, 56, 276–293.
Dickinson, W. R., and W. S. Snyder (1978), Plate tectonics of the Laramide orogeny, in
Laramide folding associated with basement block faulting in the western United
States: Geological Society of America Memoir 151, edited by V. Matthews, pp. 355–
366.
Ducea, M. (2001), The California Arc: Thick Granitic Batholiths, Eclogitic Residues,
Lithospheric-Scale Thrusting, and Magmatic Flare-Ups, GSA Today, 11, 4–10.
Ducea, M. N., and M. D. Barton (2007), Igniting flare-up events in Cordilleran arcs,
Geology, 35(11), 1047–1050.
Dunne, G. C., T. P. Garvey, M. Oborne, D. Schneidereit, A. E. Fritsche, and J. D. Walker
(1998), Geology of the Inyo Mountains Volcanic Complex: Implications for Jurassic
paleogeography of the Sierran magmatic arc in eastern California, Geological Society
of America Bulletin, 110, 1376–1397, doi:10.1130/0016-7606.
Dyman, T. S., R. G. Tysdal, W. J. J. Perry, D. J. Nichols, and J. D. Obradovich (2008),
Stratigraphy and structural setting of Upper Cretaceous Frontier Formation, western
Centennial Mountains, southwestern Montana and southeastern Idaho, Cretaceous
Research, 29, 237–248, doi:10.1016/j.cretres.2007.05.001.
Engebretson, D. C. (1984), Correlation of Plate Motions with Continental Tectonics:
Laramide to Basin-Range, Tectonics, 3, 115–119.
Fuentes, F., P. G. Decelles, and K. N. Constenius (2012), Regional structure and
kinematic history of the Cordilleran fold-thrust belt in northwestern Montana, USA,
Geosphere, 8(5), 1104–1128, doi:10.1130/GES00773.1.
Fuentes, F., P. G. DeCelles, and G. E. Gehrels (2009), Jurassic onset of foreland basin
deposition in northwestern Montana, USA: Implications for along-strike
synchroneity of Cordilleran orogenic activity, Geology, 37(4), 379–382,
doi:10.1130/G25557A.1.
Fuentes, F., P. G. DeCelles, K. N. Constenius, and G. E. Gehrels (2011), Evolution of the
Cordilleran foreland basin system in northwestern Montana, U.S.A, Geological
Society of America Bulletin, 123(3-4), 507–533, doi:10.1130/B30204.1.
Furer, L. C. (1970), Nonmarine upper Jurassic and lower Cretaceous rocks of western
Wyoming and southeastern Idaho, American Association of Petroleum Geologists
Bulletin, 54, 2282–2304.
Gans, P. B., and E. L. Miller (1983), Style of mid-Tertiary extension in east-central
Nevada, in Geologic excursions in the overthrust belt and metamorphic core
complexes of the intermountain region: Geological Society of America Rocky
Mountain and Cordilleran Sections meeting, Salt Lake City, Utah, Utah Geological
and Mineral Survey Special Studies 59, Guidebook Part I, edited by K. D. Gurgel,
107–139.
Gaschnig, R. M., J. D. Vervoort, R. S. Lewis, and W. C. Mcclelland (2010), Migrating
magmatism in the northern US Cordillera: in situ U–Pb geochronology of the Idaho
batholith, Contributions to Mineralogy and Petrology, 159(6), 863–883,
doi:10.1007/s00410-009-0459-5.
Gehrels, G. E., R. Blakey, K. E. Karlstrom, J. M. Timmons, B. Dickinson, and M. Pecha
(2011), Detrital zircon U-Pb geochronology of Paleozoic strata in the Grand Canyon,
Arizona, Lithosphere, 3(3), 183–200, doi:10.1130/L121.1.
Gehrels, G. E., W. R. Dickinson, B. C. D. Riley, S. Finney, and M. T. Smith (2000),
Detrital zircon geochronology of the Roberts Mountains allochthon, Nevada, in
Paleozoic and Triassic paleogeography and tectonics of western Nevada and
northern California: Geological Society of America Special Paper 347, pp. 19–42,
Boulder, Colorado.
Gehrels, G. E., W. R. Dickinson, G. M. Ross, J. H. Stewart, and D. G. Howell (1995),
Detrital zircon reference for Cambrian to Triassic miogeoclinal strata of western
North America, Geology, 23, 831–834, doi:10.1130/00917613(1995)023<0831:DZRFCT>2.3.CO;2.
Gehrels, G. E., V. Valencia, and A. Pullen (2006), Detrital zircon geochronology by
Laser-Ablation Multicollector ICPMS at the Arizona LaserChron Center, in
Geochronology: Emerging Opportunities, Paleontology Society Short Course:
Paleontology Society Papers, vol. 11, p. 10.
Gehrels, G. E., V. Valencia, and J. Ruiz (2008), Enhanced precision, accuracy,
efficiency, and spatial resolution of U-Pb ages by laser ablation–multicollector–
inductively coupled plasma–mass spectrometry, Geochemistry Geophysics
Geosystems, 9, 13 pp., doi:10.1029/2007GC001805.
Gehrels, G. et al. (2009), U-Th-Pb geochronology of the Coast Mountains batholith in
north-coastal British Columbia: Constraints on age and tectonic evolution,
Geological Society of America Bulletin, 121(9-10), 1341–1361,
doi:10.1130/B26404.1.
Goldstrand, P. M. (1992), Evolution of Late Cretaceous and Early Tertiary Basins of
Southwest Utah Based on Clastic Petrology, Journal of Sedimentary Petrology, 62,
495–507.
Haley, J. C., and W. J. Perry (1991), The Red Butte Conglomerate: A thrust-belt-derived
conglomerate of the Beaverhead Group, southwestern Montana, U.S. G.P.O.,
Washington.
Harper, G. D., and J. E. Wright (1984), Middle to Late Jurassic tectonic evolution of the
Klamath Mountains, California-Oregon, Tectonics, 3(7), 759–772,
doi:10.1029/TC003i007p00759.
Hintze, L. F. (1988), Geologic history of Utah, in Brigham Young University Geology
Studies Special Publication 7, 202 pp.
Hoffman, P. F. (1988), United plates of America, the birth of a craton; early Proterozoic
assembly and growth of Laurentia, Annual Review of Earth and Planetary Sciences,
16, 543–603.
Janecke, S. U., C. J. VanDenburg, J. J. Blankenau, and J. W. M'gonigle (2000), Longdistance longitudinal transport of gravel across the Cordilleran thrust belt of Montana
and Idaho, Geology, 28(5), 439–442.
Jordan, T. E. (1985), Tectonic setting and petrography of Jurassic foreland basin
sandstones, Idaho-Wyoming-Utah, Utah Geological Society Publication 14, 201–
213.
LaMaskin, T. A. (2012), Detrital zircon facies of Cordilleran terranes in western North
America, GSA Today, 22(3), doi:10.1130/GSATG142A.1.
Lawton, T. F., and B. A. Bradford (2011), Correlation and Provenance of Upper
Cretaceous (Campanian) Fluvial Strata, Utah, U.S.A., from Zircon U-Pb
Geochronology and Petrography, Journal of Sedimentary Research, 81(7), 495–512,
doi:10.2110/jsr.2011.45.
Lawton, T. F., G. J. Hunt, and G. E. Gehrels (2010), Detrital zircon record of thrust belt
unroofing in Lower Cretaceous synorogenic conglomerates, central Utah, Geology,
38(5), 463–466, doi:10.1130/G30684.1.
Lawton, T. F., D. A. Sprinkel, and G. L. Waanders (2007), The Cretaceous Canyon
Range Conglomerate, Central Utah–Stratigraphy, Structure, and Significance, in
Central Utah: Diverse Geology of a Dynamic Landscape, edited by G. C. Willis, M.
D. Hylland, D. L. Clark, and T. C. Chidsey Jr, pp. 101–122, Utah Geological
Association.
Lawton, T. F., P. J. Talling, R. S. Hobbs, J. H. J. Trexler, M. P. Weiss, D. W. Burbank,
and D. W (1993), Structure and stratigraphy of Upper Cretaceous and Paleogene
strata (North Horn Formation), eastern San Pitch Mountains, Utah—Sedimentation at
the front of the Sevier orogenic belt, US Geological Survey Bulletin 1787, II1–II33.
Leier, A. L., and G. E. Gehrels (2011), Continental-scale detrital zircon provenance
signatures in Lower Cretaceous strata, western North America, Geology, 39(4), 399–
402, doi:10.1130/G31762.1.
Link, P. K. et al. (1993), Middle and Late Proterozoic stratified rocks of the western US
Cordillera, Colorado Plateau, and Basin and Range province, in Precambrian:
Conterminous U.S., edited by J. C. Reed Jr., M. E. Bickford, R. S. Houston, P. K.
Link, D. W. Ranking, P. K. Sims, and W. R. Van Schmus, Geological Society of
America, The Geology of North America, Boulder, Colorado.
Long, S. P. (2012), Magnitudes and spatial patterns of erosional exhumation in the Sevier
hinterland, eastern Nevada and western Utah, USA: Insights from a Paleogene
paleogeologic map, Geosphere, 8, 881–901, doi:10.1130/GES00783.1.
Ludwig, K. R. (2008), Isoplot 3.60.
Mack, G. H., and T. Jerzykiewicz (1989), Provenance of post-Wapiabi sandstones and its
implications for Campanian to Paleocene tectonic history of the southern Canadian
Cordillera, Canadian Journal of Earth Sciences, 26(4), 665–676, doi:10.1139/e89057.
Meyers, J. H., and R. K. Schwartz (1994), Summary of depositional environments,
paleogeography, and structural control on sedimentation in the late Jurassic
(Oxfordian) Sundance foreland basin, western Montana, in Mesozoic systems of the
Rocky Mountain region, USA, edited by M. V. Caputo, J. A. Peterson, and K. J.
Franczyk, 331–350, Denver, Colorado.
Miller, R. B., S. R. Paterson, J. P. Matzel, and J. P (2009), Plutonism at different crustal
levels: Insights from the ~5–40 km (paleodepth) North Cascades crustal section,
Washington, in Crustal cross sections from the western North American Cordillera
and elsewhere: Implications for tectonic and petrologic processes:, edited by R. B.
Miller and A. W. Snoke, 125–149, Geological Society of America Special Paper 456.
Nichols, D. J., and B. Bryant (1990), Palynologic data from Cretaceous and lower
Tertiary rocks in the Salt Lake City 30“ x 60” Quadrangle, in Geologic map of the
Salt Lake City 30“ x 60” Quadrangle, north-central Utah, and Uinta County,
Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map I-1994,
edited by B. Bryant.
Paterson, S. R., D. Okaya, V. Memeti, R. Economos, and R. B. Miller (2011), Magma
addition and flux calculations of incrementally constructed magma chambers in
continental margin arcs: Combined field, geochronologic, and thermal modeling
studies, Geosphere, 7(6), 1439–1468, doi:10.1130/GES00696.1.
Paterson, S. R., R. B. Miller, H. Alsleben, D. L. Whitney, P. M. Valley, H. Hurlow, and
H (2004), Driving mechanisms for >40 km of exhumation during contraction and
extension in a continental arc, Cascades core, Washington, Tectonics, 23, TC3005,
doi:10.1029/2002TC001440.
Pivnik, D. A. (1990), Thrust-Generated Fan-Delta Deposition: Little Muddy Creek
Conglomerate, SW Wyoming, Journal of Sedimentary Research, 60, 489–503.
Price, R. A. (1981), The Cordilleran foreland thrust and fold belt in the southern
Canadian Rocky Mountains, in Thrust and nappe tectonics: Geological Society of
London Special Publication 9, edited by K. J. McClay and N. J. Price, pp. 427–448.
Rainbird, R. H., L. M. Hearnan, and G. Young (1992), Sampling Laurentia: Detrital
zircon geochronology offers evidence for an extensive Neoproterozoic river system
originating from the Grenville orogen, Geology, 20(4), 351–354.
Rogers, J. J. W., and M. Santosh (2003), Supercontinents in Earth History, Gondwana
Research, 6(3), 357–368, doi:10.1016/S1342-937X(05)70993-X.
Ross, G. M., P. J. Patchett, M. Hamilton, L. Heaman, P. G. DeCelles, E. Rosenberg, and
M. K. Giovanni (2005), Evolution of the Cordilleran orogen (southwestern Alberta,
Canada) inferred from detrital mineral geochronology, geochemistry, and Nd
isotopes in the foreland basin, Geological Society of America Bulletin, 117(5), 747,
doi:10.1130/B25564.1.
Royse, F., Jr, and M. A. Warner (1975), Thrust belt structural geometry and related
stratigraphic problems Wyoming-Idaho-northern Utah, in Deep drilling frontiers of
the central Rocky Mountains, edited by D. W. Bolvard, pp. 41–54, Denver.
Saleeby, J. B., and C. Busby-Spera (1992), Early Mesozoic tectonic evolution of the
western U.S. Cordillera, in Precambrian: Conterminous U.S., edited by J. C. Reed
Jr., M. E. Bickford, R. S. Houston, P. K. Link, D. W. Ranking, P. K. Sims, and W. R.
Van Schmus, Geological Society of America, The Geology of North America,
Boulder, Colorado.
Saleeby, J. B., M. N. Ducea, C. J. Busby, E. S. Nadin, and P. H. Wetmore (2008),
Chronology of pluton eplacement and regional deformation in the southern Sierra
Nevada batholith, California, in Ophiolites, Arcs, and Batholiths: A Tribute to Cliff
Hopson, edited by C. A. Hopson, J. E. Wright, and J. W. Shervais, 397–427,
Geological Society of America Special Paper 438.
Schirmer, T. W. (1988), Structural analysis using thrust-fault hanging-wall sequence
diagrams: Ogden duplex, Wasatch Range, Utah, American Association of Petroleum
Geologists Bulletin, 72, 573–585.
Schmidt, C. J., and J. M. O'Neill (1982), Structural Evolution of the southwest Montana
transverse zone, in Geologic studies of the Cordilleran thrust belt, 193–218, Denver,
Colorado.
Skipp, B. (1987), Basement Thrust Sheets in the Clearwater Orogenic Zone, Central
Idaho and Western Montana, Geology, 15(3), 220–224.
Stacey, J. S., and J. D. Kramers (1975), Approximation of terrestrial lead isotope
evolution by a two‑stage model, Earth and Planetary Science Letters, 26, 207–221.
Stewart, E. D., P. K. Link, C. M. Fanning, C. D. Frost, and M. McCurry (2010),
Paleogeographic implications of non-North American sediment in the
Mesoproterozoic upper Belt Supergroup and Lemhi Group, Idaho and Montana,
USA, Geology, 38(10), 927–930, doi:10.1130/G31194.1.
Suttner, L. J., A. Basu, and G. H. Mack (1981), Climate and the Origin of Quartz
Arenites, Journal of Sedimentary Research, 51(4), 1235–1246.
Tobisch, O. T., J. B. Saleeby, and R. S. Fiske (1986), Structural history of continental
volcanic arc rocks, eastern Sierra Nevada, California: A case for extensional
tectonics, Tectonics, 5(1), 65-94, doi:10.1029/TC005i001p00065.
Turner, C. E., and F. Peterson (2004), Reconstruction of the Upper Jurassic Morrison
Formation extinct ecosystem—a synthesis, Sedimentary Geology, 167(3-4), 309–355,
doi:10.1016/j.sedgeo.2004.01.009.
Van Schmus, W. R., M. E. Bickford, and E. Turek (1996), Proterozoic geology of the
east-central mid-continent basement, in Basement and basins of eastern North America: Geological Society of America Special Paper 308, edited by B. A. Van der
Pluijm and P. A. Catacosinos, pp. 7–32.
Walker, J. D., and J. Geissman (2009), 2009 Geologic Time Scale, Geological Society of
America.
Whitmeyer, S. J., and K. E. Karlstrom (2007), Tectonic model for the Proterozoic growth
of North America, Geosphere, 3(4), 220-259, doi:10.1130/GES00055.1.
Wright, J. E., and M. R. Fahan (1988), An expanded view of Jurassic orogenesis in the
western United States Cordillera: Middle Jurassic (pre-Nevadan) regional
metamorphism and thrust faulting within an active arc environment, Klamath
Mountains, California, GSA Bulletin, 100(6), 859–876, doi:10.1130/0016-7606.
Yonkee, W. A. (1992), Basement-cover relations, Sevier orogenic belt, northern Utah,
Geological Society of America Bulletin, 104, 280–302.
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CA
500
Late Cretaceous-Eocene
Early Cretaceous
Arc Magmatism
#
th
oli
#
#
#
WA
OR
###
*
ath
sB
50°N
Sample Stratigraphic Age
#
#
n
tai
BC
1
AZ
%
%
%
X CO
%
X%
W
X
W
X
%
%
NM
Mogo
llon Highlands
110°W
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 DR1; bedrock geology
from USGS National Map, http://www.nationalmap.gov). Chronostratigraphic
relationships between samples from the four sampling regions (1- Four Corners 2Uinta 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.
120° W
B
110° W
4
#
*
SK
56
#
*
3
66
ID
#
*
WY
2
#
*
"
)
%
,
,
%
40° N
#
*
%
,
,
%
"
)
!
(
,
%
#
*
CA
W
X
Cordilleran thrust front
100
CO
,X
%
(
!
W W
X
,
%%
,
"
) %
,
%
(
!
,
W
X
,
%
%
,
,
,%
%
W
X
,
%
XX
W
,
W%
1
,
%
{
Ohio Creek
Williams Fork (5)
Hams Fork
Kaiparowits
Wahweap (2)
Almond (2)
Tuscher (2)
Corcoran
Kaiparowits (4)
Adaville
Farrer (2)
Rock Springs
Neslen (2)
Echo Canyon
Mesaverde Grp. (3)
Little Muddy Ck.(2)
Mancos (2)
Mancos
Sanpete
Blair
Canyon Range
{
San Pitch
Cedar Mtn. (3)
Burro Canyon (2)
Buckhorn (3)
Kelvin
Two Medicine
St. Mary’s River
Beaverhead Grp. (5)
Frontier
Blackleaf
Kootenai (4)
Pryor
NM
,
%
146
AZ
J
Southern/eastern boundary,
retroarc foreland basin.
#
*
UT
NE
,
%
#
*
#
*#
*
*#
*
#
*#
#
**
#
NV
!
(
Late
SD
Cretaceous
#
*
*
##
*
#
*
,
%
ND
Ma
"
)
(
!
MT
Wasatch (3)
#
*
#
*
#
*
"
)
"
)
%
,
"
)
WA
OR
4. Canada
Eocene
AB
#
*
#
*
#
*
Paleocene
#
*
#
*
BC
Paleogene
#
*
#
#
*
*
50° N
3. Montana
Uinta
Early
#
*
2. Uinta
1. Four Corners
#
*
*
##
*
40
161
Late
A
Morrison (11)
Entrada
Morrison
Kootenay (2)
Morrison (2)
Cadomin (7)
Monach
Monteith (4)
Nikassin
Kootenay
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. See table DR1 for depositional age references. Time
scale simplified from Walker and Geissman [2009].
Cale
d
an
ni
i
l
nk
Fra
1000 km
onia
n
60º N
? ?
Co
rdi
lleran
60º N
40º N
Ap
pa
lachia
n
40º N
?
?
20º N
20º N
120º W
Mesozoic eolianites
Cordilleran miogeocline
Peri-Laurentian Terranes
Amarillo-Wichita Province (~530 Ma)
Suwanee Terrane (720-400 Ma)
Grenville orogen (1.2-1.0 Ga)
1.48-1.34 Ga Magmatic Province
Mazatzal (1.7-1.6 Ga)
Yavapai (1.8-1.7 Ga)
Archean with 2.3-1.8 Ga reworking
Archean (>2.5 Ga)
North
80º W
Figure 3 - Location of North American crustal
provinces that may have supplied detrital
zircons to the Cordilleran retroarc foreland
basin system. Age domains are color-coded to
match those of the age-probability diagrams in
Figures 4 and 6a-h. Adapted from Gehrels et al.
(2011) and references therein.
Source Signatures: Spectra-based
Mesozoic Eolianites
(Dickinson & Gehrels, 2009) n=942
10 Samples
Central North American Passive Margin
(Gehrels & Pecha, in prep) n=1237
12 Samples
Northern North American Passive Margin
(Gehrels & Pecha, in prep) n=1783
11 Samples
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
Ordovician strata of North American Passive Margin
(Gehrels & Pecha, in prep) n=1096
7 Samples
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
0
200
400
600
800
1000
1200 1400
1600 1800 2000
Detrital zircon age (Ma)
2200
2400
2600 2800
3000 3200
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 corresponding 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
Gehrels & Pecha’s [in prep] data to illustrate their pronounced differences. These curves are reflected horizontally in Figures 6c, 6e,
and 6f to facilitate visual comparison of the interpreted provenance matches.
Max depo: ~86 Ma
2SR240 (Two Medicine) n=19
Max depo: ~97 Ma
ISR80 (Blackleaf) n=95
Max depo: ~109 Ma
1FG70 (Kootenai) n=99
Max depo: ~68 Ma
IBB44 (St. Mary River) n=95
Max depo: ~97 Ma
10DM17 (Frontier) n=91
Max depo: ~46 Ma
09CA01 (Uinta) n=90
Max depo: ~75 Ma
KK0607 (Kaiparowits) n=98
Max depo: ~73 Ma
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
KK0207 (Kaiparowits) n=96
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
0
200
400
600
800
1000
1200 1400
1600 1800 2000
Detrital zircon age (Ma)
2200
2400
2600 2800
3000 3200
Figure 5a - Individual normalized probability curves for detrital zircon samples of the Cordilleran Magmatic 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 northernmost 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.
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
Yavapai Mazatzal n=1011
11 Samples
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
1.000
0.705
0.991
0.204
0.868
0.110
0.464
0.061
0.390
0.239
0.974
0.884
0.518
0.087
0.165
0.056
0.790
0.537
0.741
0.765
0.999
0.296
0.174
0.955
3000 3200
EXXONMOBIL6
2600 2800
MT0907
0.199
0.708
0.243
0.189
0.117
0.655
2400
MT0107
0.872 0.794 0.116 0.561 0.024
0.872
0.794 0.753 0.692 0.546
0.794 0.794
0.415 0.482 0.306
0.116 0.753 0.415
0.940 0.528
0.561 0.692 0.482 0.940
0.473
0.024 0.546 0.306 0.528 0.473
0.199 0.708 0.243 0.189 0.117 0.655
1.000 0.705 0.991 0.204 0.868 0.110
0.061 0.390 0.239 0.974 0.884 0.518
0.056 0.790 0.537 0.741 0.765 0.999
0.486 0.592 0.529 0.299 0.145 0.372
K-S P-values using error in the CDF
2200
EM4
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
statistcally indistinguishable, and are highlighted
in yellow.
1600 1800 2000
Detrital zircon age (Ma)
KK0507
1200 1400
T67-8024
1000
PCU4020
800
PCU-9470
600
10DM20
400
T67-7084
200
T67-14419
0
0.486
0.592
0.529
0.299
0.145
0.372
0.755
0.674
0.371
0.483
0.464
0.087 0.165
0.296 0.174 0.955
0.755 0.674 0.371 0.483
Internal Consistency: 98%
T67-14419
T67-7084
10DM20
PCU-9470
PCU4020
T67-8024
KK0507
EM4
MT0107
MT0907
EXXONMOBIL6
Mesozoic Eolianite Interpretation Group n=2091
23 Samples
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
Mesozoic Eolianites (Dickinson & Gehrels, 2009) n=942
10 Samples
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
K-S P-values using error in the CDF
0.253
0.854
0.203
0.801
0.362
0.962
0.858
0.538
0.455
0.516
0.329
0.532
0.174
0.679
0.786
0.518
0.006
0.071
0.006
0.318
0.641
0.861
0.400
0.069
0.605
0.435
0.012
0.793
0.119
0.307
0.802
0.274
0.828
1.000
0.810
0.703
0.357
0.981
0.999
0.405
0.995
0.956
0.497
0.974
0.077
0.095
0.008
0.021
0.840
0.105
0.169
0.678
0.105
0.764
0.190
0.771
0.238
0.070
0.196
0.743
0.011
0.538
0.861
0.810
0.008
0.271
0.021
0.827
0.946
0.335
0.123
0.114
0.040
0.720
0.759
0.031
0.455
0.400
0.703
0.021
0.642
0.011
0.952
0.797
0.607
0.948
0.044
0.810
0.324
0.415
0.651
0.377
0.516
0.069
0.357
0.840
0.922
0.749
0.469
0.408
0.122
0.351
0.266
0.794
0.619
0.271
0.642
0.922
0.395
0.677
0.920
0.462
0.997
0.103
0.150
0.021
0.011
0.749
0.210
0.152
0.546
0.085
0.608
0.834
0.827
0.952
0.469
0.398
0.790
0.162
0.574
0.673
0.946
0.797
0.408
0.777
0.942
0.132
0.993
0.728
0.607
0.122
0.988
0.575
0.034
0.988
0.169
0.351
0.228
0.543
0.115
0.529
0.371
0.120
0.385
0.828
0.261
0.869
0.397
0.551
0.738
0.454
0.066
0.400
0.118
0.329
0.605
0.981
0.105
0.395
0.210
0.398
0.777
0.988
0.228
0.120
0.998
0.138
0.996
0.481
0.716
0.302
0.288
0.340
0.181
0.804
0.392
0.532
0.435
0.999
0.169
0.677
0.152
0.790
0.942
0.575
0.543
0.385
0.998
0.951
0.022
0.306
0.156
0.278
0.242
0.484
0.174
0.012
0.405
0.678
0.920
0.546
0.162
0.132
0.034
0.115
0.828
0.138
0.341
0.341
0.913 0.077
0.453 0.893
0.349
0.870
0.416
0.185
0.191
0.435
0.120
0.679
0.793
0.995
0.105
0.462
0.085
0.574
0.993
0.988
0.529
0.261
0.996
0.913
0.077
0.572
3000 3200
T52X-17935
0.422
0.344
0.645
0.349
0.431
0.840
0.108
0.858
0.641
1.000
0.095
0.619
0.150
0.834
LBRG-2900
0.406
0.126
0.469
0.247
0.883
0.999
0.091
0.962
0.318
0.828
0.077
0.794
0.103
2600 2800
K2
0.977
0.047
0.533
0.267
0.328
0.447
0.514
0.362
0.006
0.274
0.974
0.266
EXXONMOBIL-2
0.921
0.134
0.760
0.426
0.853
0.920
0.597
0.801
0.071
0.802
0.497
2400
ECH1
719062
0.211
0.008
0.339
0.721
0.597
0.514
0.091
0.108
0.011
0.031
0.377
0.118
0.392
0.484
0.120
0.856
UT-8A
0.974
0.023
0.645
0.401
0.127
0.317
0.721
0.203
0.006
0.307
CP53
0.632
0.570
0.757
0.526
0.306
0.842
0.339
0.854
0.518
CP40
0.145
0.749
0.066
0.021
0.113
0.441
0.008
0.253
CP52
0.435
0.116
0.982
0.472
0.536
0.986
0.211
2200
CP49
0.996
0.027
0.756
0.460
0.270
0.322
1600 1800 2000
Detrital zircon age (Ma)
CP41
CP36
1200 1400
CP35
0.604 0.531 0.506
0.107 0.031 0.118
0.973 0.242 0.817
0.158 0.740
0.158
0.916
0.740 0.916
0.460 0.270 0.322
0.472 0.536 0.986
0.021 0.113 0.441
0.526 0.306 0.842
0.401 0.127 0.317
0.426 0.853 0.920
0.267 0.328 0.447
0.247 0.883 0.999
0.349 0.431 0.840
0.070 0.196 0.743
0.040 0.720 0.759
0.324 0.415 0.651
0.454 0.066 0.400
0.340 0.181 0.804
0.156 0.278 0.242
0.185 0.191 0.435
0.707 0.423 0.903
1000
CP27
800
CP25
CP19
600
CP14
0.172 0.669
0.274
0.274
0.107 0.973
0.031 0.242
0.118 0.817
0.027 0.756
0.116 0.982
0.749 0.066
0.570 0.757
0.023 0.645
0.134 0.760
0.047 0.533
0.126 0.469
0.344 0.645
0.771 0.238
0.123 0.114
0.044 0.810
0.551 0.738
0.302 0.288
0.022 0.306
0.870 0.416
0.197 0.971
1GRX
1GRZ
400
CP29
0.172
0.669
0.604
0.531
0.506
0.996
0.435
0.145
0.632
0.974
0.921
0.977
0.406
0.422
0.190
0.335
0.948
0.397
0.716
0.951
0.349
0.959
10DM25
200
LM73
0
0.959
0.197
0.971
0.707
0.423
0.903
0.856
0.786
0.119
0.956
0.764
0.997
0.608
0.673
0.728
0.169
0.371
0.869
0.481
0.453
0.893
0.572
LM73
10DM25
1GRZ
1GRX
CP19
CP25
CP29
CP14
CP27
CP35
CP36
CP41
CP49
CP52
CP40
CP53
UT-8A
719062
ECH1
EXXONMOBIL-2
K2
LBRG-2900
T52X-17935
Internal Consistency: 93%
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 statistcally indistinguishable, and are highlighted in yellow.
MK0407 (Farrer) n=92
MF0607 (Farrer) n=100
CP33 (Ferron Mbr. of Mancos) n=99
KK0107 (Kaiparowits) n=97
CP13 (Westwater Canyon Mbr. of Morrison) n=94
CP21 (Westwater Canyon Mbr. of Morrison) n=80
CP9 (Toreva) n=86
CP22 (Menefee) n=119
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
CP23 (Gallup Mbr. of Mancos) n=87
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
0
200
400
600
800
1000
1200 1400
1600 1800 2000
Detrital zircon age (Ma)
2200
2400
2600 2800
3000 3200
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 corresponed 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.
US Passive Margin Interpretation Group n=2201
24 Samples
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
UT-NV Passive Margin (Gehrels & Pecha, in prep) n=1237
12 Samples
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
K-S P-values using error in the CDF
0.005
0.013
0.200
0.306
0.460
0.686
0.033
0.163
0.177
0.067
0.210
0.227
0.001
0.035
0.000
0.002
0.000
0.232
0.948
0.006
0.137
0.000
0.249
0.107
0.057
0.052
0.302
0.000
0.201
0.082
0.073
0.993
0.180
0.004
0.021
0.506
0.457
0.636
0.999
0.147
0.061
0.671
0.337
0.988
0.487
0.991
0.812
0.523
0.809
0.686
0.091
0.035
0.137
0.302
0.993
0.007
0.040
0.111
0.019
0.003
0.057
0.017
0.044
0.001
0.103
0.069
0.030
0.119
0.033
0.000
0.000
0.000
0.000
0.180
0.374
0.374
0.099 0.001
0.056 0.001
0.669 0.071
0.875
0.006
0.089
0.042
0.091
0.080
0.367
0.036
0.098
0.019
0.180
0.584
0.247
0.163
0.000
0.002
0.249
0.201
0.004
0.099
0.001
0.822
0.001
0.021
0.017
0.027
0.021
0.162
0.003
0.017
0.003
0.079
0.245
0.113
0.177
0.000
0.000
0.107
0.082
0.021
0.056
0.001
0.940
0.940
0.005
0.000
3000 3200
LBRG3500
0.096
0.253
0.790
0.026
0.004
0.132
0.023
0.863
0.069
0.806
0.151
0.062
0.175
0.460
0.002
0.001
0.006
0.052
GRF
0.975
0.001
0.429
0.351
0.159
0.491
0.667
0.355
0.907
0.105
0.310
0.285
0.118
0.306
0.067
0.227
0.948
KK0407
UT-3
0.209
0.064
0.067
0.002
0.091
0.000
0.000
0.000
0.247
0.991
0.003
0.244
0.711
0.356
0.238
0.947
0.137
0.821
0.184
0.320
0.319
0.193
0.200
0.064
0.210
2600 2800
UPPERMONTEITH
0.747
0.097
0.105
0.193
0.118
0.175
0.809
0.119
0.247
0.113
0.276
0.060
0.001
0.098
0.042
0.051
0.109
0.389
0.038
0.598
0.074
0.151
0.082
0.105
0.013
0.209
2400
BASALKOOTENAY
1.000
0.437
0.031
0.082
0.319
0.285
0.062
0.523
0.030
0.584
0.245
0.080
0.015
0.001
0.110
0.034
0.024
0.111
0.174
0.054
0.249
0.083
0.082
0.031
0.097
0.005
BRM
0.830
0.994
0.208
0.082
0.151
0.320
0.310
0.151
0.812
0.069
0.180
0.079
0.068
0.718
0.073
0.357
0.098
0.129
0.103
0.409
0.180
0.228
0.168
0.208
0.437
0.747
2200
CR7
0.543
0.156
0.520
0.168
0.083
0.074
0.184
0.105
0.806
0.991
0.103
0.019
0.003
0.766
0.517
0.228
0.948
0.558
0.494
0.843
0.777
0.522
0.457
0.520
0.994
1.000
UT0714
0.461
0.838
0.797
0.457
0.228
0.249
0.598
0.821
0.907
0.069
0.487
0.001
0.098
0.017
0.475
0.856
0.085
0.748
0.433
0.543
0.540
0.980
0.272
0.797
0.156
0.830
UT0711
0.663
0.994
0.553
0.272
0.522
0.180
0.054
0.038
0.137
0.355
0.863
0.988
0.044
0.036
0.003
0.848
0.896
0.080
0.989
0.503
0.263
0.994
0.896
0.553
0.838
0.543
TFI
0.138
0.349
0.921
0.055
0.013
0.386
0.181
0.994
0.461
1600 1800 2000
Detrital zircon age (Ma)
PROSPECTCREEK
0.422
0.015
0.853
0.268
0.166
0.700
0.868
0.663
MN0807
0.157
0.084
0.810
0.064
0.013
0.390
0.144
MN0707
1200 1400
CP39
0.454 0.479 0.548 0.951
0.019 0.004 0.110 0.071
0.244 0.077 0.867 0.369
1.000 0.894 0.928
1.000
0.497 0.977
0.894 0.497
0.907
0.928 0.977 0.907
0.064 0.013 0.390 0.144
0.268 0.166 0.700 0.868
0.055 0.013 0.386 0.181
0.503 0.263 0.994 0.896
0.433 0.543 0.540 0.980
0.558 0.494 0.843 0.777
0.098 0.129 0.103 0.409
0.034 0.024 0.111 0.174
0.042 0.051 0.109 0.389
0.711 0.356 0.238 0.947
0.351 0.159 0.491 0.667
0.026 0.004 0.132 0.023
0.147 0.061 0.671 0.337
0.019 0.003 0.057 0.017
0.042 0.091 0.080 0.367
0.017 0.027 0.021 0.162
0.024 0.053 0.065 0.269
1000
CP34
800
T67-7420
T26-2673
600
PCU7980
PCU7620
PCU12120
0.035 0.569
0.126
0.126
0.019 0.244
0.004 0.077
0.110 0.867
0.071 0.369
0.084 0.810
0.015 0.853
0.349 0.921
0.080 0.989
0.085 0.748
0.228 0.948
0.073 0.357
0.001 0.110
0.001 0.098
0.003 0.244
0.001 0.429
0.253 0.790
0.636 0.999
0.040 0.111
0.006 0.089
0.001 0.021
0.323 0.162
400
CP32
0.035
0.569
0.454
0.479
0.548
0.951
0.157
0.422
0.138
0.896
0.856
0.517
0.718
0.015
0.060
0.991
0.975
0.096
0.457
0.007
0.875
0.822
0.019
LBRG-2700
200
HF2
0
0.019
0.323
0.162
0.024
0.053
0.065
0.269
0.848
0.475
0.766
0.068
0.080
0.276
0.067
0.247
0.232
0.057
0.073
0.506
0.669
0.071
0.005
0.000
HF2
LBRG-2700
PCU12120
PCU7620
PCU7980
T26-2673
T67-7420
CP32
CP34
CP39
MN0707
MN0807
PROSPECTCREEK
TFI
UT-3
UT0711
UT0714
CR7
BRM
KK0407
GRF
BASALKOOTENAY
UPPERMONTEITH
LBRG3500
Internal Consistency: 78%
Figure 5e - Composite normalized probability curve for the United States Passive Margin 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 statistcally indistinguishable, and are highlighted in yellow.
Canada Passive Margin Interpretation Group n=949
10 Samples
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
British Columbia Passive Margin (Gehrels & Pecha, in prep) n=1783
11 Samples
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
BTC
SKR
1600 1800 2000
Detrital zircon age (Ma)
GCH
0.940 0.649 0.577 0.693 0.473
0.940
0.355 0.341 0.357 0.238
0.649 0.355
0.182 0.538 0.031
0.577 0.341 0.182
0.976 0.862
0.693 0.357 0.538 0.976
0.726
0.473 0.238 0.031 0.862 0.726
0.738 0.401 0.903 0.209 0.634 0.052
0.587 0.754 0.901 0.720 0.952 0.311
0.002 0.002 0.009 0.060 0.012 0.019
0.000 0.000 0.000 0.000 0.000 0.000
K-S P-values using error in the CDF
1200 1400
EBK
1000
CDM
800
CARBONCREEKRD
600
MIDDLEMONTEITH
GCMONACH
400
SHC
200
ODR
0
0.738
0.401
0.903
0.209
0.634
0.052
0.587
0.754
0.901
0.720
0.952
0.311
0.906
0.002
0.002
0.009
0.060
0.012
0.019
0.032
0.006
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.082
0.906
0.032 0.006
0.000 0.000 0.082
Internal Consistency: 64%
2200
2400
2600 2800
3000 3200
ODR
SHC
GCMONACH
MIDDLEMONTEITH
CARBONCREEKRD
CDM
EBK
GCH
BTC
SKR
Figure 5f - Composite normalized probability curve for the Canada Passive Margin 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 statistcally indistinguishable, and are highlighted in yellow.
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
US Passive Margin + Yavapai Mazatzal n=357
4 Samples
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
600
800
1000
10DM11
400
10DM09
10DM22
200
10DM23
0
0.884 0.888 0.185 10DM23
0.884
0.991 0.329 10DM22
0.888 0.991
0.731 10DM09
0.185 0.329 0.731
10DM11
K-S P-values using error in the CDF
Internal Consistency: 100%
1200 1400
1600 1800 2000
Detrital zircon age (Ma)
2200
2400
2600 2800
3000 3200
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 statistcally
indistinguishable, and are highlighted in yellow.
GCMONTEITH (Monteith) n=88
1SFSR1(Kootenai) n=97
1GR100 (Kootenai) n=99
UT06-8B (Buckhorn) n=93
MB1007 (Bluecastle Mbr. of Castlegate) n=95
UT0715 (Cedar Mountain) n=139
Cordilleran Margin Magmatic Arcs
Appalachian orogen
Amarillo-Wichita uplift
Wopmay
TransHudson
Yavapai
Mazatzal
NAMG
Taconic
Acadian
Alleghenian
J-K Volcanism
UT06-4 (Cedar Mountain) n=97
Suwanee terrane
Grenville orogen
1.34-1.48 anorogenic magmatism
1.6-1.8 terrane
1.8-2.3 Orogens
Wyoming/Hearne/Rae Craton
0
200
400
600
800
1000
1200 1400
1600 1800 2000
Detrital zircon age (Ma)
2200
2400
2600 2800
3000 3200
Figure 5h - Individual normalized probability curves for detrital zircon samples of the mixed passive margin and Ordovician passive
margin provenance interpretation group. Samples are plotted atop a graph of major crustal age domains that corresponed 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.
Late Jurassic Detrital Zircon Provenance
145 Ma Paleogeography
tM
as
Co
# MIDDLEMONTEITH
GCMONTEITH
nta
c
Ar
#
ins
BASALKOOTENAY
n Thrust Belt
llera
rdi
Co
%1GRX
,
1GRZ
#
ou
#
#
#GCMONACH
PROSPECTCREEK
TFI
719062
%
Sie
N
rra
ad
ev
CP41
#
rc
# Canada Passive Margin
United States Passive Margin
% Mesozoic Eolianite
X Mogollon
CP35
%% %CP19
%% X3% CP29
1 % CP49
CP
CP21X
%CP25
%CP53
CP36
CP52
aA
Provenance Interpretation
T52X-17935
%
Mo
g o ll
o n Highlands
500 Kilometers
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,
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.
Early Cretaceous (~130-100 Ma)
Detrital Zircon Provenance
CARBONCREEKRD 100 Ma Paleogeography
#
#
UPPERMONTEITH
GCH
e
ne B
B
ust
Thr
ran
lle
#BTC
EBK
#
# SHC
#ODR
lt
#
elt
1GR100
1SFSR1
#
nta
rmo
Inte
Co #
r #CDM
c
di
s Ar
tain
oun
tM
s
Coa
#SKR
GRF
#
1FG70
ISR80
%
BRM
10DM25
K2
%
%
UT0CP32
714,
UT07
15
CP14
##
#
*
##
UT0711
UT06-4
rra
Sie
%
#
rc
Magmatic Arc
%CP27
aA
# Canada Passive Margin
United States Passive Margin
% Mesozoic Eolianite
d
va
Ne
Provenance Interpretation
B
-8 8A
06 06T
U UT
500 Kilometers
Figure 6b: Lower Cretaceous detrital zircon sample locations,
sample names, and interpreted provenance plotted on a late Early
Cretaceous (100 Ma) paleogeographic reconstruction (R. Blakey,
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.
!"#$%&'()%(*#$+,$-.*"#%($)#!./!%0$1/.*+(2$/($2%340#2
$+,$!"#$5#%6#."#%)$7+(80+3#.%!#
Cenomanian-Santonian (~100-84 Ma)
Detrital Zircon Provenance
85 Ma Paleogeography
A
ns
rc
lt
o -M
rc
Idah
sA
de
sca
Ca
ont
#
i
nta
ou
st B e
Thru
ran
ille
rd
Co
tM
as
Co
"
10DM17
a na
10DM09
Arc
EM4
LM73
% !
T67-14419
!
##
CR7
UT06-3
#
CP9
X X CP23
da A
eva
rc
Cordilleran Magmatic Arc
! Yavapai-Mazatzal
ra N
# Canada Passive Margin
United States Passive Margin
% Mesozoic Eolianite
X Mogollon
Sier
Provenance Interpretation
X CP33
500 Kilometers
Figure 6c: Santonian-Cenomanian (~100-84 Ma) detrital zircon
sample locations, sample names, and interpreted provenance
plotted on a Santonian (85 Ma) paleogeographic reconstruction (R.
Blakey, http://cpgeosystems.com/nam.html). Black arrows
indicate generalized Cenomanian sediment dispersal directions
after DeCelles (2004). Dashed arrows indicate interpreted
sediment dispersal pathways based on provenance.
M ou
a
ller
rdi
Co
st
Coa
Campanian-Maastrichtian (~84-66 Ma)
Detrital Zircon Provenance
65 Ma Paleogeography
nT
ns
ntai
s
hru
Arc
lt
t Be
##
a na
KK0407
#
#
##
X{
{
#
{
{
X
%
Sie
{
rra
XCP22
aA
vad
Ne
#
%
%
%
ifts
Upl
LBRG-2700
LBRG2900 " LBRG-3500
EXXONMOBIL-2
! EXXONMOBIL6
ECH1
PCU-9470
MT010
MT090 7
! PCU7620
PCU7980
7
MK
! MN0 PCU12120
MF0064007
MB1 807
7
007 MN0
KK0107
707
CP34
CP39
CP40
KK0507 ! KK0607
" KK0207
Arc
rc
# Canada Passive Margin
United States Passive Margin
% Mesozoic Eolianite
X Mogollon
La
r
10DM20!
10DM22
10DM23
nd
rela
afo
Intr
ide
am
ont
Provenance Interpretation
1BB44
#
o -M
Arc
Idah
es
cad
Cas
2SR240 "
Cordilleran Magmatic Arc
! Yavapai-Mazatzal
500 Kilometers
Figure 6d: Campanian-Maastrichtian (~84-66 Ma) detrital zircon
sample locations, sample names, and interpreted provenance
plotted on a latest Maastrichtian (65 Ma) paleogeographic
reconstruction (R. Blakey, http://cpgeosystems.com/nam.html).
Black arrows indicate generalized Maastrichtian sediment dispersal directions after DeCelles (2004). Dashed arrows indicate
interpreted sediment dispersal pathways based on provenance.
Paleocene-Eocene (~66-47 Ma)
Detrital Zircon Provenance
50 Ma Paleogeography
st
Coa
ns
ntai
a
ller
rdi
Co
Mou
nT
Arc
s
hru
U 02
76 0
20
09
C
###PPCUA01
C 4
rc
nd
rela
afo
Intr
ide
am
aA
tan
on
#
lt
t Be
Arc
-M
ho
Ida
es
cad
Cas
La
r
10DM11
aA
#
d
va
rc
Cordilleran Magmatic Arc
! Yavapai-Mazatzal
Ne
# Canada Passive Margin
United States Passive Margin
% Mesozoic Eolianite
X Mogollon
rra
Sie
Provenance Interpretation
ifts
Upl
"
! T26-2673
!T T67
T6!
7-8 67- -74
02 708 20
4 4
500 Kilometers
Figure 6e: Paleocene-Eocene (~66-47 Ma) detrital zircon sample
locations, sample names, and interpreted provenance plotted on
an Eocene (50 Ma) paleogeographic reconstruction (R, Blakey,
http://cpgeosystems.com/nam.html). Dashed arrows indicate
interpreted sediment dispersal pathways based on provenance.
Relative Probablity
Arc-derived Detrital Zircons
Cordilleran Retroarc Region
A
lower limit of
sampling
n=1539
50
Speed (km/my)
100
Age
Age of Farallon (my)
150
150
B
100
50
Idaho Batholith
C
Relative Flux
Montana Batholiths
Sierra Nevada Batholith
Coast Mountains Batholith
Cascades
0
50
100
150
200
Ma
Figure 7: a. Probability distribution function of arc-derived detrital
zircons in the foreland basin system [this study]. b. Farallon plate velocity
and age at the subduction interface from Engebretson [1984]. c. Relative
flux curves interpreted from exposures of igneous rocks along three
segments of the Cordilleran magmatic arc after Paterson et al. [2011],
and references therein. No flux data are available for the Idaho and
Montana batholiths. To facilitate comparison, we plot age ranges of
major igneous suites in this region [Gaschnig et al., 2010] above the
relative flux curves.