The Early Mesozoic Cordilleran Arc and Late Triassic Paleotopography: the Detrital Record in Upper Triassic Sedimentary Successions on and Off the Colorado Plateau

Home , Palen Mountains, Vampire Formation, Waterman Mountains

The Early Mesozoic Cordilleran arc and Late Triassic paleotopography: The detrital record in Upper Triassic sedimentary successions on and off the Colorado Plateau

N.R. Riggs1, S.J. Reynolds2, P.J. Lindner1,*, E.R. Howell1,†, A.P. Barth3, W.G. Parker4, and J.D. Walker5 1School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA 2School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA 3Department of Earth Sciences, Indiana University–Purdue University Indianapolis, Indianapolis, Indiana 46202, USA 4Division of Resource Management, Petriﬁ ed Forest National Park, Petriﬁ ed Forest, Arizona 86028, USA 5Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA

ABSTRACT eroding into the stream systems that depos- of the record of magmatism is in backarc sedi- ited the three units. Streams diverged from mentary successions. Upper Triassic sandstones in diverse loca- a common source that maintained a rela- Unmetamorphosed Paleozoic sections tions in eastern California, southern Arizona, tively uniform magma composition over are exposed on the Colorado Plateau and in and on the Colorado Plateau (USA) yield time, as indicated by a narrow range of southern Arizona, and equivalent strata have detrital zircons that are remarkably similar in Th/U values, as well as tapping a somewhat long been recognized in deformed sections in age and geochemistry, leading to the hypoth- different source evidenced by a grouping eastern California and western Arizona, where esis that they are temporally related and in which Th/U ratios are lower. Once the they are overlain by strata of the Buckskin and were derived from similar sources. Volcani- streams left the highlands of the arc and the Vampire Formations; these two units are con- clastic sandstone from the lowest Vampire depocenter of the lowest Vampire Forma- sidered to be correlatives of the Triassic Moen- Formation in eastern California, the Sonsela tion, they diverged, such that one fl owed to kopi and Chinle Formations and parts of the Member of the Chinle Formation at Petrifi ed the area of the Colorado Plateau while the Jurassic Glen Canyon Group (Reynolds and Forest National Park, northeastern Arizona, second fl owed toward southern Arizona. At Spencer, 1989). The position of these Meso- and the herein-named Waterman formation the same time, a stream system originating zoic rocks close to remnants of the Cordilleran in southern Arizona yield zircons that range in the older, Sonoran part of the arc fl owed magmatic arc suggests that the more proximal in age from ca. 205 to ca. 235 Ma. Together from the south into southern Arizona. setting would be refl ected in more arc-derived with the similar range of ages, these zircons detritus. Similarly, Paleozoic passive-margin uniformly have Th/U ratios between ~0.2 INTRODUCTION sedimentary strata in southern Arizona locally and 2. In addition, the Waterman formation underlie a sedimentary succession that is contains zircon grains with an age range from Much of the understanding of the inception in turn overlain by Jurassic volcanic rocks. ca. 225 to 250 Ma, but with markedly lower and development of the late Paleozoic–early These post-Paleozoic strata off the Colorado Th/U ratios of 0.1–0.2, and a distinctively Mesozoic Cordilleran magmatic arc along Plateau complement the understanding of the older group with ages to ca. 280 Ma. In a southwestern North America is based on plu- timing of arc magmatism afforded by Triassic general sense, variations in Hf concentrations tonic rocks in the Mojave Desert (Miller et al., units on the Plateau, and add to the expanding and Yb/Gd ratios support the discrimination 1995; Barth and Wooden, 2006) and northwest- knowledge of the drainage systems that fl owed of grains based on age and Th/U. ern Sonora (Riggs et al., 2009, 2010; Arvizu from the arc. We use age and geochemical data from et al., 2009) and on backarc sedimentary strata We present the results of U-Pb geochronol- the zircons to infer that these units cap- deposited on the continent (Fig. 1). The nature ogy and geochemistry of zircons from the low- ture a slice of time during development of of deposition as recorded by sedimentary est Vampire Formation in eastern California and the early Mesozoic Cordilleran magmatic strata in southwestern Laurentia changed dra- from fl uvial sedimentary strata from southern arc along western North America. Plutonic matically in late Paleozoic time from carbonate Arizona that we name the Waterman formation rocks that record magmatism in the arc are platform rocks (Kaibab and Rain Valley Forma- (Fig. 1). Our results show that both units off the Permian–Triassic in age, and match zircon tions: Blakey and Knepp, 1989) to dominantly Colorado Plateau are temporally correlated with ages in the detrital grains, thus providing a fl uvial and terrestrial environments (Lower the Chinle Formation, and that each unit pro- view of which parts of the arc were actively Triassic Moenkopi Formation, Upper Trias- vides a distinct and critical clue about Triassic sic Chinle Formation; Stewart et al., 1972a, paleogeography of southwestern Laurentia as *Present address: Pioneer Resources, 5205 N. 1972b). In the absence of volcanic sections in well as the growth and erosion of the Cordi lleran O’Connor Blvd., Suite 200, Irving, Texas 75039, USA †Present address: Noble Energy, 1625 Broadway, many parts of the early Cordilleran arc, much magmatic arc. Suite 2200, Denver, Colorado 80202, USA

Geosphere; June 2013; v. 9; no. 3; p. 602–613; doi:10.1130/GES00860.1; 11 ﬁ gures; 1 supplemental ﬁ le; 1 supplemental table. Received 11 August 2012 ♦ Revision received 1 February 2013 ♦ Accepted 13 March 2013 ♦ Published online 7 May 2013

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117o 113o 109o records transport from highlands to the east; S I E R R A N E V A D A overall, the depositional setting is attributed to 215–230 Ma a ﬂ exural foreland basin developed behind the NEVADA CALIFORNIA UTAH COLO Permian–Triassic Sonoma orogen (Dickinson ARIZONA NMX and Gehrels, 2008). The Moenkopi Formation

Las N C O L O R A D O C

Vegas O comprises an array of facies, from ﬂ uvial to

L o O CHINLE 36 R the east to intercalation with marine limestone Palen A D P L A T E A U

Mountains 0 10 km O FORMATION farther west; paleocurrents indicate ﬂ ow from

R N I

240–260 Ma V

E the south and southeast (Stewart et al., 1972b; PERMO-TRIASSICM O J A V E10 Blythe R 0 10 km Barstow Holbrook 40 Blakey, 1989; Blakey et al., 1993; Dubiel, D E S E R T Holbrook National Park 1994). Detrital zircons from one sample of BUCKSKIN 240–250 Ma LLongong LoLogsgs fl uvio-deltaic facies in the Moenkopi Formation o FORMATION * 34 San JJimim* CCampamp WWashash suggest a maximum depositional age of 235 Ma, Bernardino 210–225 MaCORDI Blythe and Dickinson and Gehrels (2008) inferred that WATERMAN most or all detrital zircons in the Moenkopi For- N LLE FORMATION mation were derived from the southeast, includ- CALIFORNIA RAN MAG CA Tucson ing early Mesozoic zircons from the poorly BAJA 10 N o understood East Mexico arc. 32 ARIZ Waterman ONA TUCSON 0 20 km The Upper Triassic Chinle Formation was MATICSONOR Mountains 260–270 Ma A0 20 km Tucson deposited in a back-bulge basin (Lawton, ARC Mountains 1994) or one resulting from dynamic backarc Caborca 10 subsidence as Pacifi c oceanic lithosphere was subducted (Dickinson and Gehrels, 2008). The Sierrita 0 200 km ? 19 Chinle Formation comprises fl uvial facies that 113o ? Mountains109o Mustang overall record transport from south and south- Mountains east toward coastal to shallow-marine environ- Figure 1. Map showing approximate location of the early Mesozoic Cordilleran mag- ments in Nevada (Stewart et al., 1972a; Blakey matic arc and outcrops of Upper Triassic units. Pink areas are Triassic plutons (Barth and Gubitosa, 1983; Lupe and Silberling, 1985; and Wooden, 2006 in California; Campbell and Anderson, 2003, and Arvizu et al., 2009, Lucas and Marzolf, 1993; Riggs et al., 1996), in Sonora). Enlarged boxes show sample areas of three units discussed herein. Movement but that locally were derived from the grow- along the San Andreas fault restored. ing magmatic arc to the west (e.g., Howell and Blakey, 2013). The southern and southwestern edges of Chinle Formation outcrops are erosional; to the east and southeast the Chinle For- TECTONIC AND MAGMATIC fornia, and where dates of 232–218 Ma (Barth mation correlates with the Dockum Group in SETTING OF THE EARLY et al., 2011) were obtained on volcanic rocks New Mexico (e.g., Lucas, 1991). MESOZOIC CORDILLERA interpreted to be outfl ow from that caldera complex. Depositional features of these volcanic Shinarump Member The Mesozoic Cordilleran arc formed along rocks, including angular fragmentation and fi ne the truncated western coast of Laurentia. Along ash-rich laminations, suggest that they were The basal Shinarump Member of the Chinle the southwestern margin, northeast-southwest– erupted subaqueously (Douglas et al., 2011). In Formation (Fig. 2) consists of fl uvial conglomer- trending Paleozoic passive-margin facies were the Mineral King pendant, a tuff dated as 220 Ma ate and sandstone (Stewart et al., 1972b; Blakey faulted in Pennsylvanian–Permian time by a (N. Riggs and C. Busby, 2012, personal observ.) and Gubitosa, 1984). Volcanic clasts are rare, strike-slip system that accompanied the initia- is interstratifi ed with marine sedimentary rocks and throughout the Chinle Formation decrease tion of subduction of the Pacifi c oceanic litho- (Busby-Spera, 1984, 1986). These observations in size and abundance from south to north sphere under North America (Walker, 1988; suggest that at least the northern part of the arc, (Stewart et al., 1972b), suggesting deposition Stone and Stevens, 1988; Bateman, 1992; Miller in Late Triassic time, was marine. To the south on a broad alluvial plain linked to highlands to et al., 1992; Saleeby et al., 1992; Dickinson and of the Sierra Nevada, however, early Mesozoic the south termed the Mogollon Slope (Bilodeau, Lawton, 2001). Plutonic rocks that record sub- volcanic rocks are rare and poorly dated where 1986). Triassic igneous sources in these high- duction are exposed in eastern California and present. lands, however, have not been documented, and northern Sonora and range in age from ca. 270 central Arizona, where they would have been, to ca. 215 Ma (Fig. 1; Miller et al., 1995; Barth TRIASSIC SEDIMENTATION TO THE now consists of uplifted Proterozoic basement. et al., 1997, 2011; Barth and Wooden, 2006; EAST OF THE CORDILLERAN ARC Paleocurrents in the Shinarump Member indi- Riggs et al., 2009; Arvizu et al., 2009). cate fl ow from the south and southeast (Stewart Preserved sections with volcanic rocks Truncation of the Neoproterozoic–Paleo- et al., 1972b; Blakey and Gubitosa, 1983). recording Permo-Triassic igneous activity are zoic margin brought about the end of marine Dickinson and Gehrels (2008, 2009) sug- rare in most parts of the arc. The notable excep- passive-margin sedimentation and coincided gested that deposition of the basal Shinarump tion is in the east-central Sierra Nevada, where with a major change in the nature of continen- Member began ca. 230 Ma, well after magma- Schweickert and Lahren (1993, 1999) docu- tal sedimentation (e.g., Lawton, 1994). The tism began in the Mojave Desert and Sonora, mented a caldera complex at Tioga Pass, Cali- Lower–Middle Triassic Moenkopi Formation Mexico. Volcanic clasts in the Shinarump

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Member range in age from ca. 220 to 230 Ma Stage approximate (Oberling et al., 2010; our data). Although the Owl scale Rock source of the clasts is uncertain, they correlate in 50 m RHAE- TIAN Member age, and broadly in chemistry, with Triassic plutons in the Mojave Desert (Oberling et al., 2010). Black Forest Bed

0 Blue Mesa, Sonsela, and Petriﬁ ed Petrified Forest Forest Members Member

The middle and upper Chinle Formation is dominantly mudstone (Fig. 3), with sandstone Martha’s Butte beds interbeds throughout and conglomerate horizons Figure 2. Generalized strati- that are mostly conﬁ ned to the Sonsela Member Jim Camp Wash beds graphic log of the Chinle For- (Fig. 2). Depositional environments are domi- Long Logs ss mation on the Colorado Plateau, nantly ﬂ uvial and paludal (Stewart et al., 1972a; Sonsela

N O R I A showing stratigraphic level of Member Jasper Forest bed Blakey and Gubitosa, 1983; Dubiel, 1987, 1989; two samples (050508–1, Long

Dubiel et al., 1991). Paleocurrents are variable CHINLE FORMATION Lot’s Wife beds Logs); ss—sandstone. but most commonly indicate transport from the south and southwest in the more southern expo- Camp Butte beds sures in Petrifi ed Forest National Park (Howell, Blue Mesa 2010; Howell and Blakey, 2013), where our EXPLANATION Member sandstone, locally samples were collected. The local stratigraphy tuffaceous for the Chinle Formation in Petrifi ed Forest Mesa mudrock, locally National Park follows Woody (2006) and Martz Redondo Mbr tuffaceous Shinarump and Parker (2010). Exposed strata are assigned limestone, gypsum Mbr pebbly sandstone, to fi ve members; from oldest to youngest, these CARN- IAN ? ~235 Ma conglomerate Moenkopi Fm are the Mesa Redondo, Blue Mesa, Sonsela, sample 050508-1 Petrifi ed Forest (previously the upper Petrifi ed Long Logs sample Forest), and Owl Rock Members. Igneous detritus is present throughout much of the Blue Mesa, Sonsela, and Petrifi ed Forest Members. Volcanic and rare plutonic detritus ranges from fi ne, altered ash and pyrogenic crystals throughout the three members to granules, pebbles, and cobbles in the Sonsela Member . Ramezani et al. (2011) established maximum ages of deposition of ca. 225 to ca. 208 Ma for these three units based on high-precision CA-TIMS (chemical abrasion-thermal ioniza- tion mass spectrometry) dating of detrital zircons. Volcanic clasts range in age from 235 Ma to ca. 217 Ma (Riggs et al., 2012).

TRIASSIC(?) STRATA OFF THE COLORADO PLATEAU

Buckskin and Vampire Formations

The Buckskin Formation (Reynolds and Spencer, 1989) was named to describe green- schist-grade metamorphosed (Stone and Kelly, 1989) sandstone, siltstone, and conglomerate that disconformably overlie the Permian Kai- bab Formation in the Mojave Desert of western Arizona and eastern California (Fig. 1). The Buckskin Formation consists of four infor- mal members (Reynolds and Spencer, 1989; Hargrave, 1999) that are correlated with the Figure 3. Tuffaceous mudstone to sandstone characteristic of the ﬁ ne-grained facies of the Moenkopi Formation (Reynolds and Spencer, Sonsela and Blue Mesa Members of the Chinle Formation. Sample site of Jim Camp Wash 1989) or the Moenkopi and Chinle Formations bed (050508–1).

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(Hargrave and Reynolds, 1999) on the Colorado Plateau based on lithology and stratigraphic position overlying the Permian Kaibab Forma- tion. The contact between the Buckskin and Vampire Formations is marked by conglomerate (Fig. 4) that is locally interbedded with volcaniclastic sandstone (Volcanic sandstone unit of Stone and Kelly, 1989). Thick quartzite that overlies the conglomerate is well sorted, ﬁ ne grained to gritty, and in some exposures has large-scale cross-bedding. The basal conglomerate of the Vampire Formation records an early Mesozoic uplift (Reynolds et al., 1989), and has been correlated with the Chinle Forma- tion (Hargrave, 1999; Hargrave and Reynolds, 1999); the formation as a whole is broadly within the Chinle Formation–Glen Canyon Group (i.e., Late Triassic–Middle Jurassic) interval. Although depositional environments of the Vampire Formation are incompletely documented, the unit is inferred to be subaerial based on the presence of cross-bedded (i.e., eolian) sandstone, interbedded conglomerate and sandstone lenses, and its stratigraphic position overlying a regional unconformity. Figure 4. Lowest Vampire Formation conglomerate; clasts are quartzite and granite and/ or granodiorite. Waterman Formation

Sedimentary rocks that overlie Permian carbonate and underlie Mesozoic volcanic rocks tact (Hall, 1985). Clasts are as much as 20 cm in and Raup, 1968) on an irregular contact with a in the Waterman Mountains (Fig. 1) were fi rst diameter, with an average diameter of 4–5 cm, few meters relief. Facies are very similar to those described by Hall (1985). Similar rocks consid- and comprise quartzite, chert, and carbon- in the Waterman Mountains. Clasts are angular ered to be equivalent are also exposed in the Sier- ate commonly armored by chert; the clasts are in places (Fig. 5D), and in general smaller than rita, Tucson, and Mustang Mountains (Fig. 1). In derived from the underlying Paleozoic section. clasts in the type section; clast types are similar, the Mustang Mountains, Hayes and Raup (1968) Dark orange to red, very dense quartzite clasts although white chert is more common than in fi rst mapped “Volcanic and sedimentary rocks are likely Cambrian Bolsa Quartzite, which is the Waterman Mountains section. Overall the of Mustang Mountains,” which they assigned a far more durable than locally derived Permian average clast size is 2 cm; outsize clasts have Triassic and Jurassic age. In general the rocks sandstone (Scherrer Formation). Very rare clasts a maximum diameter of 12 cm, and average are poorly exposed and facies are discontinu- of conglomerate are present (possibly the Jelly ~6 cm. Red, fi ne-grained sandstone intervals are ous from outcrop to outcrop. Exposures in the Bean conglomerate of Armin, 1987, which is 5–8 cm thick; the lateral extent is masked by the Waterman Mountains are the most complete, exposed in the underlying Paleozoic section), poor exposures. In both sections, the relatively and this area is considered the type locality for but no igneous clasts of any kind were found in poor exposure and structural disruption pre- these strata, which we call the Waterman forma- this study or reported by Hall (1985). Channel- clude gathering any paleocurrent data. tion. Strata in the Sierrita Mountains are strongly form coarse sandstone is interbedded locally Hall (1985) interpreted the depositional sheared and altered, in part due to proximity to a within the conglomerate (Fig. 5C) in discontinu- environment of the succession in the Water- Cretaceous intrusion and its mineralizing fl uids. ous lenses and stringers as much as 20 cm thick. man Mountains as braided stream or alluvial The outcrop in the Tucson Mountains is part of Thin sections reveal rounded-quartz-dominated fan; a similar environment is reasonable for the a slide block in the Cretaceous Tucson Mountain sand grains with as much as 100% monocrys- Mustang Mountains. The angularity of clasts in caldera. These exposures do not provide useful talline and polycrystalline quartz and pseudo some places indicates relatively short distance of stratigraphic information, but lithologic similari- matrix; other constituents are 2%–13% feldspar travel and the nearby topography; the dominant ties among scattered outcrops suggest that the and very rare altered volcanic and metamor- clast types in both sections refl ect the immedi- formation was originally widespread across phic grains. Conglomerate is overlain in places ately underlying rock. Very well-rounded clasts the backarc region. by structureless red sandstone and siltstone as suggest a well-developed fl uvial system and In the Waterman Mountains, the Waterman much as 2 m thick that has identical composi- long transport distances. formation is as much as 20 m thick. Basal con- tion to the sandstone lenses and matrix within The Waterman formation exposures in the glomerate (Figs. 5A, 5B) that is 2–10 m thick the conglomerate. Mustang and Waterman Mountains are con- overlies Permian Concha Limestone, a Middle– The Waterman formation in the Mustang sidered to be stratigraphically equivalent and Late Permian formation equivalent to the Kai- Mountains (Figs. 1 and 5A) is poorly exposed, the same unit based on composition and strati- bab Formation on the Colorado Plateau (Blakey and, although faulted, ~10 m thick. The forma- graphic position. Both units comprise conglom- and Knepp, 1989), on an irregular eroded con- tion overlies Permian Concha Limestone (Hayes erate and sandstone with some fi ne-grained

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Figure 5. Waterman formation. (A) Sche- A MMiddle(?)iddle(?) JurassicJurassic matic stratigraphic section showing ero- vvolcanicolcanic aandnd sional contact of Waterman formation with vvolcaniclasticolcaniclastic rrockock underlying Paleozoic rocks, and overlying MMiddleiddle JurassicJurassic ppyroclasticyroclastic rocksrocks Jurassic volcanic rocks. (B) Conglomerate in the Waterman Mountains; note ubiquitous RRainain ValleyValley FmFm rounded clasts, dominantly of limestone. WATERMAN PPermianermian ConchaConcha FORMATION CConchaoncha LLimestoneimestone (C) Sandstone interbedded in conglomerate LLimestoneimestone SchererScherer FFmm (sampled horizon). Clasts are limestone and lesser chert and quartzite. (D) Sandstone C D and conglomerate in the Mustang Moun- tains; clasts are in general smaller and more angular compared to Waterman Mountains outcrop and most commonly consist of chert.

mudstone-siltstone lenses, although some differ- ples of the Waterman formation, one each from and Pb isotopes and for trace element concen- ences exist within conglomerates in each area. the Waterman and Mustang Mountains (Fig. 1; trations at the University of California, Santa Both sections overlie Middle–Upper Permian 111308–1, 111408–2, Supplemental Table [see Barbara, Laser Ablation Split-Stream labora- limestone, and in the Mustang Mountains footnote 1]). Two samples of the Sonsela Mem- tory using a Nu Plasma HR MC-ICP-MS (high this erosional surface is part of a deep canyon ber of the Chinle Formation are included here, resolution multi-collector-inductively coupled fi lled by younger pyroclastic units. The upper- both from Petrifi ed Forest National Park (Figs. plasma–mass spectrometer), a Nu AttoM sin- most sandstone in the Waterman Mountains is 1 and 2; Jim Camp Wash bed sample 050508–1, gle collector ICP-MS (Nu Instruments Ltd., overlain by a volcaniclastic unit (Fig. 5A) that and Long Logs sandstone, Supplemental Table Wrexham, UK), and an Analyte 193 excimer contains andesitic to dacitic clasts, and by lava [see footnote 1]). Although the detrital zircon ArF laser-ablation system equipped with a fl ows, one of which yielded a multigrain, three- signature of the Sonsela Member in Petrifi ed HeLex sample cell (Photon Machines, San fraction, TIMS U-Pb zircon age of 176 Ma (our Forest National Park is almost certainly not Diego, USA) using a 24 μm beam. Analytical data). In the Mustang Mountains, conglomerate representative of the unit across the entire Colo- and procedural details and all analytical data and sandstone are overlain by ignimbrite (Fig. rado Plateau, the detrital zircon signatures of the are provided in the table in the Supplemen- 5A), from which Lawton et al. (2012) obtained lowermost Vampire Formation and the Water- tal File2; all age errors reported are 2σ, unless a single-crystal SHRIMP (sensitive high-resolu- man formation, as discussed in the following explicitly stated otherwise. Data were reduced tion ion microprobe) U-Pb age of 176 ± 2 Ma. section, indicate that these units reasonably using Iolite 2.10 and 2.21 in Igor Pro 6.2 (www correlate with the Sonsela or Petrifi ed Forest .wavemetrics.com). Analyses were evaluated for METHODS Members. The provenance and signifi cance of discordance based on a comparison of 235U/207Pb the Sonsela Member in Petrifi ed Forest National and 238U/206Pb for Permian and Triassic grains, We collected one sample of the lowermost Park was described in Howell (2010) and How- and 207Pb/206Pb and 238U/206Pb for Proterozoic Vampire Formation in the “Volcanic Sand- ell and Blakey (2013). grains. Grains that were >10% normally dis- stone (Triassic or Jurassic)” unit of Stone and Samples were crushed and zircons separated cordant (i.e., 235U/207Pb age or 207Pb/206Pb age Kelly (1989) in the Palen Mountains (Fig. 1; according to standard techniques of density sepa- >10% older than 238U/206Pb age) or 5% reversely 030509–3, Supplemental Table1) and two sam- ration (e.g., Gehrels, 2000) and only minimal (0.1–0.3a) magnetic separation was done. All 2Supplemental File. PDF fi le containing a table 1Supplemental Table. Laser-ablation inductively samples except Long Logs were then annealed of instrumental parameters of laser-ablation split- coupled mass spectrometer results for sandstone at 875 °C for 48 h, followed by 12 h in an 80 °C stream ICP-MS (inductively coupled plasma–mass spectrometry), information on the University of samples from Petrifi ed Forest National Park (Jim Camp oven in a 10:1 HF-HNO mixture. Zircons were Wash bed and Long Logs sandstone), Lowest Vam- 3 California Santa Barbara LASS (laser ablation split pire Formation, and Waterman formation (Waterman washed in warm HNO3 and ultrapure H2O, then stream) procedure, and a comparison of LA-ICP-MS Mountains, Mustang Mountains). Waterman Moun- mounted and polished. Cathodoluminescence and SHRIMP (sensitive high-resolution ion micro- tains sample divided into group 1 and group 2; see imaging was done at Northern Arizona Uni- probe) methods for zircon geochemistry. If you are text for discussion. If you are viewing the PDF of this viewing the PDF of this paper or reading it offl ine, versity using a JSM-6480LV scanning electron please visit http://dx.doi.org/10.1130/GES00860.S2 paper or reading it offl ine, please visit http://dx.doi microscope to identify grain shapes, zoning pat- .org/10.1130/GES00860.S1 or the full-text article on or the full-text article on www.gsapubs.org to view www.gsapubs.org to view the Supplemental Table. terns, and cores. Samples were analyzed for U the Supplemental File.

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discordant (i.e., 238U/206Pb age >5% older than 235U/207Pb age) were not used in interpretations; A 240 these are indicated by “discordant” in the Sup- plemental Table (see footnote 1). Zircon grain shapes in the lowest Vampire 220

detrital age 20 Formation sample are quite different from those 80 in the Sonsela Member of the Chinle Forma- n=75 200 15 tion and Waterman formation. Zircons in the 60 Vampire Formation sample are euhedral for the 10 most part, and cathodoluminescence images, 40 Number although generally poor in quality, show chemi- Number 5 cal zones parallel to grain boundaries, indicating 20 little modiﬁ cation of grain shape. In the Water- 0 0 man formation, grains range in shape from euhe- 200 600 1000 1400 1800 2200 2600 200 220 240 260 280 300 320 dral to subrounded, and zoning within grains is AGE, Ma AGE, Ma 050508-1 Jim Camp Wash bed commonly truncated by the grain boundaries. Sonsela Mbr, Chinle Fm Grain shapes and zoning-band truncations in the Jim Camp Wash bed zircons (Sonsela Member) are similar to those in the Waterman formation, although a greater percentage of grains are B euhedral. Images are not available for the Long 240 Logs sandstone sample. These observations suggest that, as would be expected for a volcanic sandstone, zircons in the lowest Vampire 220

60 detrital age 20 Formation sample underwent little transport 50 n=54 prior to deposition. This contrasts with samples 200 15 from the other two units, in which subrounded 40 grains indicate a degree of transport. Common 30 10

euhedral grains in the Jim Camp Wash bed sug- Number Number 20 gest original transport by ash clouds. 5 10 RESULTS 0 0 200 600 1000 1400 1800 2200 2600 200 220 240 260 280 300 320 AGE, Ma AGE, Ma Density probability plots (Fig. 6) show very Long Logs bed distinct similarities and differences between Sonsela Mbr, Chinle Fm repre sentative samples of the three units. In addition to the density probability plots, an average- age plot shows the range of ages in each sample. Sonsela Member samples from Petriﬁ ed Forest National Park (Figs. 6A, 6B) are dominated by C Triassic grains nearly to the exclusion of all 240 other ages. Of 83 Phanerozoic grains in the Jim Camp Wash bed, 86% have ages in a continuous 60 range from 202 to 223 Ma (Fig. 6A) and only 6 220 10 50 detrital age are Proterozoic (7%). Similar to the Jim Camp 8 n=47 Wash bed zircons, 77% of grains in the Long 40 200 Logs sandstone have Phanerozoic ages between 6 30 209 and 232 Ma (Fig. 6B). In both units, the Number Number 4 Proterozoic grains are spread from ca. 1000 to 20 1700 Ma, but clusters have too few grains to be 10 2 statistically signiﬁ cant. 0 0 The lowest Vampire Formation (Fig. 6C) 200 600 1000 1400 1800 2200 2600 200 220 240 260 280 300 320 grain distribution is nearly identical to that of AGE, Ma AGE, Ma the Long Logs sandstone, including minimum 030509-3 Vampire Fm, Palen Mtns and maximum ages and the small number (6%) of Proterozoic grains. Phanerozoic grains are all Figure 6 (on this and following page). Age-probability plots for all samples. Left box in all Triassic and range in age smoothly from 215 to is the full spectrum; right box is Phanerozoic grains only. Small inset box shows range of 235 Ma. The Waterman formation shows the Phanerozoic ages; note that scale changes for D and E. (A) Chinle Formation, Jim Camp greatest internal diversity. The grains from Wash bed (050508–1). (B) Chinle Formation, Long Logs bed. (C) Lowest Vampire Forma- the Waterman Mountains sample (Fig. 6D) tion (030509–3); note strong similarity with Chinle samples.

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the age range of ca. 210–235 Ma and Th/U values of 0.3–2; the Sonsela Member from 280 D Petriﬁ ed Forest National Park and the lowest Vampire Formation samples overlap strongly. 240 The Waterman formation, in contrast, shows a

detrital age tripartite division of ages and Th/U values. A major part of the 210–235 Ma grains plot in the 70 200 25 60 fi eld encompassed by the Sonsela Member and 20 Vampire Formation samples; the fi eld is referred 50 n=82 to as Waterman Mountains group 1. Another 40 15 distinct fi eld comprises grains from the Mus- 30 tang Mountains sample that range in age from Number 10 20 Number ca. 245 to 280 Ma and have variable Th/U ratios. 5 10 A few grains from the Mustang Mountains are in a third fi eld that consists of Waterman Moun- 0 0 tains grains that range in age from ca. 225 to 200 600 1000 1400 1800 2200 2600 200 220 240 260 280 300 320 AGE, Ma AGE, Ma 250 Ma, thus overlapping in age with the Son- 111308-2 Waterman Fm, sela Member and Vampire Formation fi eld, but Waterman Mtns having distinctively lower Th/U ratios that range from 0.1 to ~0.3 (called group 2). A plot of Yb/Gd versus Hf ppm (Fig. 8) sup- 295 ports the similarity of the Waterman Mountains E group 1 grains to Sonsela Member and Vampire 275 Formation grains and the differences between the Waterman formation groups. The dashed- 10

detrital age 255 B outline box in Figure 8 demonstrates that the 9 area of overlap between the Waterman Moun- 40 8 235 n=34 tains group 1 grains, the lowest Vampire Forma- 30 6 tion sample, and the Sonsela Member sample is relatively noncoincident with group 2 grains, 20 4 although the data overlap more than would be Number

Number inferred by the comparison of Th/U ratios. 10 2 DISCUSSION 0 0 200 600 1000 1400 1800 2200 2600 200 220 240 260 280 300 320 AGE, Ma AGE, Ma U-Pb ages, Th/U ratios, and rare earth geo- 111408-1 Waterman Fm, chemistry highlight similarities and differ- Mustang Mtns ences between the three Upper Triassic units. The units are remarkably similar in terms of Figure 6 (continued). (D) Waterman formation, Waterman Mountains (111308–2). the age and composition of sources, although (E) Waterman formation, Mustang Mountains (111408–1). zircon geochemistry allows distinctions to be made about magmatic provinces within the arc. In addition, these data allow us to make infer- range in age from ca. 210 to 250 Ma; Protero- solution in zircon that accompanies decreasing ences about the timing of magmatism, topogra- zoic grains (16%) are ca. 1400 Ma and 1600 Ma temperature is matched by a decrease in Th/U phy, and evolution of continental landscape to populations. The Mustang Mountains sample and relative enrichment in heavy rare earth the east of the arc. Geochemistry of zircons has (Fig. 6E), in contrast, is dominated by ca. elements (Claiborne et al., 2006, 2010; Fohey- been used successfully to demonstrate cogene- 1400 Ma grains. Phanerozoic grains range from Breting et al., 2010; Barth et al., 2011, 2012). sis of plutonic and volcanic facies (Barth et al., ca. 240 to 280 Ma, although few grains are older This observation has been successfully used 2012); we suggest here that this geochemistry than ca. 260 Ma, and very few grains overlap to correlate intrusive and extrusive phases of can also be used to infer cogenesis of suites of in age with the Waterman Mountains sample. the early Mesozoic California Cordilleran arc detrital zircons, as well as to highlight potential The Mustang Mountains sample thus bears little (Barth et al., 2012) and to make provenance differences in source. resemblance to the other Triassic units. inferences about the igneous sources of detrital The Cordilleran arc in Late Triassic time is The differences and similarities between zircons (Riggs et al., 2012). In this case, we generally envisioned as marine to the north and the units are additionally highlighted by Th/U propose that zircons carry distinctive signatures subaerial to the south, at least in California. The ratios and trace elements such as Hf, Yb, and Gd that can be used to isolate groups of cogenetic observations that the Chinle Formation con- (Figs. 7 and 8). Use of these trace elements is grains within a detrital sample and enhance the tains volcanic detritus as old as 235 Ma and that based on the assumption that changes in magma correlation of disparate groups of rocks. deposition began ca. 230 Ma (Dickinson and chemistry during cooling are reﬂ ected in zircon Figure 7 compares Th/U with age and shows Gehrels, 2008, 2009) indicate that by middle chemistry. In general, the increase in Hf solid that all three units have grains that plot within Carnian time, the portion of the arc now exposed

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Waterman Fm Gd/Yb and Hf ppm (Fig. 8) supports a similar Mustang Mtns chemistry for the sources of group 1 grains and Figure 7. Th/U compared to 10 Waterman Mtns those from the Sonsela Member and the Buck- Phanerozoic ages of zircons Group 1 Group 2 skin Formation. It remains equally likely, how- from three samples. Waterman Chinle Fm. ever, that the range of values describes a variety formation is divided into three of sources, but the drainage systems between arc groups: those from the Mus- lowest Vampire Fm 1 and backarc were relatively few and entrenched, tang Mountains, those from Th/U perhaps analogous to the relatively few major the Waterman Mountains that rivers that drain the eastern Cascade Range strongly overlap the other two and the wide dispersal area of these rivers. One units, and those with very low 0.1 indication of this possibility is exemplifi ed by a Th/U values. 200 220 240 260 280 300 comparison of detrital grain chemistry to that of Age (Ma) the plutonic remnants of the Cordilleran arc in the Mojave Desert. Permo-Triassic plutons in the Mojave Desert in Southern California was a subaerial, eroding as Lower Triassic (Riggs et al., 2010; Lindner are characterized by low Th/U ratios (Barth and feature that shed detritus eastward. Stratigraphic et al., 2012), indicating that this southern part of Wooden, 2006); these low ratios are not gener- evidence for this is in the Black Mountain the arc was actively eroding long before areas to ally refl ected in Chinle Formation zircons from region to the north of San Bernardino (Fig. 1), the north. By Late Triassic time, both volcanic volcanic clasts in the Sonsela Member (Riggs where a ca. 244 Ma pluton is nonconformably and plutonic parts of the arc at least as far north et al., 2012). The Th/U ratios of the sandstones overlain by Lower Jurassic strata (Miller, 1981; as the central Mojave Desert were eroding and discussed herein are more variable, but in part Stone, 2006), indicating that post–Early Trias- shedding material to the north-northeast. are within the low Th/U fi elds of Mojave Desert sic, pre–Early Jurassic uplift brought magmatic plutons (Fig. 9). (See the Supplemental File [see arc rocks to the surface. Similarly aged uplift is Discriminating Source Areas Based on footnote 2] for a discussion regarding compari- documented in western Arizona (Reynolds et al., Detrital Zircon Chemistry son of data derived from LA-ICP-MS [data in 1989), although in western Arizona the uncon- this paper] and those derived by reverse geom- formity does not involve magmatic arc rocks. The pronounced similarity in age and Th/U etry–SHRIMP [Mojave Desert Triassic plutons; Knowing the precise location of volcanoes that ratio between zircons from group 1 of the Barth and Wooden, 2006].) This suggests that the fed Late Triassic streams into the backarc region Waterman formation, the Sonsela Member of Mojave Desert plutons were a source of detritus, is diffi cult (Riggs et al., 2012), but it is easiest to the Chinle Formation, and the lowest Vampire and that another, as-yet undiscovered source area infer that the closest present-day exposures of Formation strongly suggests that sources were was also present. Based on the differences in zir- the arc were the closest sources. similar in time and space. Grains vary in age con chemistry between volcanic clasts from the Deciphering paleotopography and uplift his- over 30 m.y., and volcanic arcs change in chem- Chinle Formation and Triassic plutons, Riggs tory in northern Sonora is also important for istry and character over such time spans, but et al. (2012) speculated that such a source lay understanding the distribution of grains derived the general nature of the underlying continen- near the present Colorado River, where Reynolds from the southern sources. The presence of tal crust should remain relatively constant, and et al. (1989) documented uplift and erosion of Permian plutons (Arvizu et al., 2009; Riggs all currently known remnants of the arc were pre-Triassic strata. Although it is also possible et al., 2009, 2010) indicates that the arc is older emplaced into Mojave crust (Barth and Wooden, that the differences in Th/U seen between these in Sonora, and detritus from this part of the arc 2006). The value of using Th/U ratios to assess clasts and plutons can be attributed to chemical is represented by zircon grains in the Water- magmatic provinces within the arc is supported stratifi cation with a magma chamber, Barth et al. man formation. The Permian–Jurassic Antimo- by the presence of ~15 grains from the Water- (2012) have used a strong similarity in whole nio Group in northwest Sonora records forearc man formation within group 2 that have ages rock and zircon chemistry, including Th/U, to shallow-marine and fluvial sedimentation similar to group 1 grains, but much lower Th/U show that Triassic plutons and ignimbrites in the (González-León, 1997; González-León et al., values than group 1 grains (Fig. 7); we infer that Sierra Nevada are cogenetic. 2005; Lindner et al., 2012); these strata con- these were derived from a very different source The detrital zircon signature of the Chinle tain Permian cobbles (280 Ma) in strata as old from group 1 grains. Likewise, a comparison of Formation varies depending on depositional sites. For example, the Sonsela Member detrital zircon spectrum from a sample northeast of 100 Petrifi ed Forest National Park (Dickinson and 90 Gehrels, 2008) includes Paleozoic and Neo- 80 Waterman Mtns 70 Figure 8. Yb/Gd compared to proterozoic zircon populations not found in the Waterman Fm gp 2 60 Hf. All units and groups over- Petrifi ed Forest National Park samples. Regard- 50 lap to a certain extent; dot- less, we fi nd it signifi cant that (as observed by lowest 40 dash box outlines area in which Howell, 2010) the Sonsela Member within Petri- Vampire Fm Yb / Gd Yb 30 very few Waterman Mountains fi ed Forest National Park carries a distinctive 20 group (gp) 2 grains (shaded) detrital zircon signature that refl ects a dominant Waterman Mtns 10 contribution from the Cordilleran arc and that Sonsela Mbr Waterman Fm gp 1 are present. 0 this signature closely parallels that of the lowest 1000 10,000 100,000 Vampire Formation sample, which had a very Hf (ppm) proximal depocenter with respect to the arc.

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10 tetravalent-cation diffusion rates are even slower (e.g., Cherniak and Watson, 2003; Cherniak, 2010). Thus, we assume that ratios of trivalent and tetravalent cations are no more affected by Waterman Fm 1 postcrystallization diffusional fractionation than is U/Pb, and that these cation ratios yield insight lowest Vampire Fm into magmatic processes at the time of closure

Th/U Chinle Fm of the U/Pb system in these zircons. 0.1 Mojave Desert plutonic Late Triassic Dispersal System

Sonsela Mbr cobbles The age equivalence of three geographically disparate units and the correlation of these units 0.01 based on zircon geochemistry provide the basis 200 220 240 for improved understanding of the topography Age of southwestern North America during a slice Figure 9. Th/U for Triassic grains from this study compared to of Late Triassic time (Fig. 11). By Late Trias- Mojave Desert plutons (data from Barth and Wooden, 2006). Also sic time, a continental magmatic arc, which may shown are Th/U values from volcanic clasts from a conglomerate previously have been offshore and thus unavail- bed in the Sonsela Member that is stratigraphically ~40 m above the able to contribute detritus to the continental inte- Jim Camp Wash and Long Logs beds. Note that Sonsela clasts show rior, constituted a subaerial series of volcanoes poor overlap with the Mojave Desert plutons, whereas a distinct along the western coast from the central Mojave population of the Chinle sandstones, the lowest Vampire Formation, Desert in California to Sonora, Mexico. In Fig- and the Waterman formation group 1 grains show good overlap. ure 11, the shoreline is inferred to cross the arc in the southern Sierra Nevada based on marine facies in volcanic and sedimentary rocks in the The differences between the two Waterman ratios. If this were the case, then measured central and northern Sierra Nevada (Busby- formation samples require explanation. The trace element ratios in zircon would represent Spera, 1984, 1986; Douglas et al., 2011). majority of grains in the Mustang Mountains an integrated signal of igneous and sedimen- Interpretation of the pathways taken by rivers sample range in age from ca. 245 to 265 Ma; tary processes, and their ages and compositions that drained the arc is constrained by the three those from the Waterman Mountains are ca. would be more diffi cult to interpret in terms of major observations and inferences regarding the 207–245 Ma. The formation is everywhere the range of source areas and the fl uvial path- detrital zircons. (1) The ages, Th/U ratios, and underlain by Permian sedimentary rocks and ways described here. We consider this explana- trace element compositions of zircons from the overlain by Jurassic volcanic rocks and thus tion unlikely, however, because experimental volcanic sandstone in the lowest Vampire For- occupies the same stratigraphic level across data show that Pb diffusion rates are very slow, mation are the best possible approximation of southern Arizona. Despite the difference in similar to those of smaller trivalent cations, and the composition of the magmatic arc in that area; age implied by the zircons in the two samples, in addition, the ubiquitous euhedral shape of we infer that, similar to the Chinle Formation, grains indicates that for the most part, pre depo- this broadly coeval and correlative formation sitional transport of these grains was minimal. 10 Waterman Fm Mustang exposed over a wide area had variable source Mtns (2) The similarity in ages, Th/U ratios, and trace areas over time. Plutons in the Mojave Desert are Sonoran arc pluton and element compositions of zircons from the lowest as old as ca. 250 Ma (Barth and Wooden, 2006), volcanic clasts Vampire Formation, from the two Chinle For- and igneous rocks in northwestern Sonora are as 1 mation samples, and from group 1 of the Water- old as ca. 280 Ma (Riggs et al., 2010; Lindner man formation suggests that the grains were et al., 2012); although Th/U data are relatively derived from petrologically similar sources, Th/U sparse, ratios in these igneous rocks are between possibly in a relatively small geographic area, ~0.06 and 0.8. A Th/U versus age plot (Fig. 0.1 although these areas exposed rocks that ranged 10) shows some overlap between the Mustang in age as much as 30 m.y. (3) The Chinle Forma- Mountains and Sonoran arc igneous rocks from tion samples in Petrifi ed Forest National Park do the Los Tanques pluton and volcanic clasts; it is not contain a record of the Sonoran portion of 0.01 therefore reasonable to infer that grains in the 240 260 280 300 the magmatic arc. In addition, any interpretation Waterman formation were derived both from Age (Ma) needs to accommodate paleocurrent studies that the Mojave Desert and from the arc in Sonora, indicated paleofl ow to the northeast in Petrifi ed or that Triassic igneous rocks in Sonora are as Figure 10. Th/U for oldest Mustang Moun- Forest National Park (Howell, 2010; Howell and young as 240 Ma, although ages this young are tains grains compared to Sonoran arc plu- Blakey, 2013). as yet undocumented. ton and volcanic clast (Riggs et al., 2009, A few plausible scenarios accommodate An alternative explanation for the compo- and our data). The Sonoran fi eld represents these observations, and Figure 11 presents our sitional range in these zircons is that selective few data points, but the overlap supports preferred interpretation. In all cases, groups diffusion of trace elements took place during derivation of the Mustang grains from that 1 and 2 in the Waterman formation must have transport , yielding a distorted range of Th/U part of the arc. been deposited by different strands, considering

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117o 113o 109o The lowest Vampire Formation sample was likely derived from proximal sources. Low o Late Triassic Th/U grains match values of Mojave Desert plu- 38 S I E R R A N E V A D A shoreline tons (Barth and Wooden, 2006), but many grains have Th/U > 1. We surmise that the mountains of CALIFORNIANEVADA UTAH COLO the arc contained volcanic and plutonic deposits ARIZONA NMX of varying ages but relatively similar composi- Las C O L O R A D O Vegas tions that were tapped by a river. This river then 36o CHINLE fl owed east and north from the Vampire area to P L A T E A U FORMATION deposit grains in the Chinle Formation samples, an interpretation consistent with paleocurrents M O J A V E in the Sonsela Member of the Chinle Formation. Barstow The Chinle Formation grains, which range in D E S E R T age over ~30 m.y. and in Th/U between 0.4 and 2, must have had multiple sources. For example, o 34 euhedral grains suggest that ash clouds played San Bernardino VVAMPIREAMPIRE a role in carrying zircons from source to depo- FFORMATIONORMATION Waterman sitional site, and it is unlikely that these grains Mtns were from the same volcano as zircons carried N WATERMAN ARIZONA Tucson by the stream system. SONORA FORMATION Proterozoic grains are very common in the o 32 Mustang Mustang Mountains sample of the Waterman Mtns formation; the majority of these are 1.4–1.46 Ga, BAJA with a smaller set of 1.6–1.65 Ga grains. Protero- CA exposed Paleozoic and Proterozoic zoic and Paleozoic rocks are not exposed Caborca bedrock between southern Arizona and Caborca, Sonora (Papago terrane of Haxel et al., 1988, 2005; 0 200 km ? 30o Stewart and Poole, 2002; Fig. 11), so the source 113o ? 109o of the Proterozoic grains is uncertain. Protero- zoic plutonic rocks are common in southwestern Figure 11. Proposed fl uvial pathways from the arc to the continental backarc. Double lines North America outside of the Papago terrane, represent projected Late Triassic shoreline. Note divergence of streams carrying detritus and zircons from them are known or likely in to northern and southern Arizona. Strong contribution of Proterozoic grains in Mustang overlying Paleozoic strata (Stewart and Poole, Mountains sample suggests Proterozoic bedrock exposed between Sonoran portion of the 2002; González-León et al., 2005; Soreghan arc and the depocenter; the stream from western Arizona may have traversed limestone-rich et al., 2007; Dickinson and Gehrels, 2008, 2009). terranes from which far fewer zircons were eroded. Light shaded line in southern Arizona An interesting result of the proposed dispersal marks northern boundary of the Papago domain, a region of southern Arizona and northern system is the requirement that two rivers with Sonora in which no rocks older than Jurassic are exposed (Haxel et al., 1988, 2005). origins in the same part of the magmatic arc diverged, apparently immediately after leaving the highlands. This topographic setting is analo- the differences in grain ages. The similarity Arizona, but it is diffi cult to envision how ca. gous to present-day rivers that head within a few between Waterman formation group 1 grains 225–245 Ma, low Th/U zircons, which are not tens of kilometers of each other in the Boliv- and those in the Chinle Formation suggests present in the Chinle Formation samples, would ian Andes, with the northern stream eventually a connection between these two units. In this have been selectively winnowed out of the sys- joining the Amazon to reach the Atlantic Ocean case, we envision that the Mustang Mountains tem between southern and northern Arizona. in northern Brazil, and the southern stream a section was deposited by a stream system that Our preferred interpretation (Fig. 11) is that tributary of the Rio de la Plata, which fl ows into originated in the Sonoran portion of the arc, the Waterman formation grains were depos- the Atlantic 4000 km to the south. The fate of to account for the numerous Permian grains. ited by two strands, one of which came east- the paleorivers that joined in southern Arizona As the Permo-Triassic arc grew in Sonora (cf. ward from the Mojave Desert, and the other remains uncertain. Arvizu et al., 2009), younger (Triassic) grains derived from sources in the Sonoran arc. The were incorporated into the stream system and pathways shown in Figure 11 are speculative, CONCLUSIONS the older sources were to the southwest of a but allow the Mojave Desert strand to deposit divide that kept their detritus moving to the grains only as old as ca. 250 Ma, whereas the Detrital zircons from three Upper Triassic south and west. This younger stream system Sonoran strand carried older grains. The depo- sedimentary sections separated by several hun- was the source of group 2 in the Waterman center topography, as indicated by deposition in dred kilometers are very similar in age, Th/U Mountains and would have also tapped a source paleochannels in Paleozoic rocks and conglom- ratio, Hf content, and Yb/Gd ratio, leading to that was younger and with different chemistry, erate that contains clasts as old as Cambrian, the hypothesis that the zircons were derived providing the ca. 205–225 Ma higher Th/U zir- refl ects the immediate area, but clast composi- from magmas similar in time, space, and com- cons of group 1. This scenario provides a short tions suggest substantial relief at least locally position. Samples of the Chinle Formation on and direct link between southern and northern between source and depocenter. the Colorado Plateau are strongly dominated

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by grains ca. 205–230 Ma and Th/U ratios of ety of America Bulletin, v. 99, p. 42–65, doi:10.1130 Cherniak, D.J., and Watson, E.B., 2003, Diffusion in zir- 0.3–2. This pattern is mirrored in the lowest /0016-7606(1987)99<42:SATSOW>2.0.CO;2. con: Reviews in Mineralogy and Geochemistry, v. 53, Arvizu, H.E., Iriondo, A., Izaguirre, A., Chávez-Cabello, G., p. 113–143. Vampire Formation sample in eastern Califor- Kamenov, G.D., Solís-Pichardo, G., Foster, D.A., and Claiborne, L.L., Miller, C.F., Walker, B.A., Wooden, J.L., nia, although the youngest grains are older in Lozano-Santa Cruz, R., 2009, Rocas graníticas pérmi- Mazdab, F.K., and Bea, F., 2006, Tracking magmatic cas en la Sierra Pinta, NW de Sonora, México: Magma- processes through Zr/Hf ratios in rocks and Hf and Ti this sample (ca. 215 Ma). The similarity of these tismo de subducción asociado al inicio del margen zoning in zircons: An example from the Spirit Moun- grains in age and, in part, in Th/U to Triassic continental activo del SW de Norteamérica: Revista tain batholith, Nevada: Mineralogical Magazine, v. 70, plutonic rocks in the Mojave Desert supports the Mexicana de Ciencias Geológicas, v. 26, p. 709–728. p. 517–543, doi:10.1180/0026461067050348. Barth, A.P., and Wooden, J.L., 2006, Timing of magmatism Claiborne, L.L., Miller, C.F., and Wooden, J.L., 2010, Trace interpretation that these rocks, or cogenetic vol- following initial convergence at a passive margin, element composition of igneous zircon: A thermal canoes, were the source of some backarc mate- southwestern U.S. Cordillera, and ages of lower crustal and compositional record of the accumulation and rial. More signifi cantly, these patterns verify the magma sources: Journal of Geology, v. 114, p. 231– evolution of a large silicic batholith, Spirit Mountain, 245, doi:10.1086/499573. Nevada: Contributions to Mineralogy and Petrology, correlation between the three units. Barth, A.P., Tosdal, R.M., Wooden, J.L., and Howard, v. 160, p. 511–531, doi:10.1007/s00410-010-0491-5. The Waterman formation, in contrast, has K.A., 1997, Triassic plutonism in southern California; Dickinson, W.R., and Gehrels, G.E., 2008, U-Pb ages of southward younging of arc initiation along a truncated detrital zircons in relation to paleogeography: Triassic a tripartite division of grains. Group 1 is very continental margin: Tectonics, v. 16, p. 290–304, doi: paleodrainage networks and sediment dispersal across similar to the other two samples, implying a 10.1029/96TC03596. southwest Laurentia: Journal of Sedimentary Research, cogenesis of the source rocks. Group 2 com- Barth, A.P., Walker, J.D., Wooden, J.L., Riggs, N.R., and v. 78, p. 745–764, doi:10.2110/jsr.2008.088. Schweickert, R.A., 2011, Birth of the Sierra Nevada Dickinson, W.R., and Gehrels, G.E., 2009, Use of U-Pb ages prises several grains that are age equivalent to magmatic arc: Early Mesozoic plutonism and vol- of detrital zircons to infer maximum depositional the Chinle and Vampire grains, but that have canism in the east-central Sierra Nevada of California: ages of strata: A test against a Colorado Plateau Meso- very different Th/U ratios, suggesting deriva- Geosphere, v. 7, p. 877–897, doi:10.1130/GES00661.1. zoic database: Earth and Planetary Science Letters, Barth, A.P., Feilen, A.D.G., Yager, S.L., Douglas, S.R., v. 288, p. 115–125, doi:10.1016/j.epsl.2009.09.013. tion from a different source. The third group Wooden, J.L., Riggs, N.R., and Walker, J.D., 2012, Dickinson, W.R., and Lawton, T.F., 2001, Carbonifer- consists of grains that are substantially older Petrogenetic connections between ash-fl ow tuffs and ous to Cretaceous assembly and fragmentation of a granodioritic to granitic intrusive suite in the Sierra Mexico: Geological Society of America Bulletin, (245–280 Ma) than any grains in the other sam- Nevada arc, California: Geosphere, v. 8, p. 250–264, v. 113, p. 1142–1160, doi:10.1130/0016-7606(2001)113 ples. These oldest grains are inferred to have doi:10.1130/GES00737.1. <1142:CTCAAF>2.0.CO;2. derived from the early Mesozoic arc in Sonora, Bateman, P.C., 1992, Plutonism in the central part of the Douglas, S., Riggs, N., Barth, A.P., and Economos, R.C., Sierra Nevada Batholith, California: U.S. Geological 2011, The breccia of Frog Lakes: Record of mafi c arc where plutonic remnants are older than those Survey Professional Paper 1483, 186 p. magmatism in the Mesozoic Sierra Nevada, Califor- in the Mojave Desert. These data suggest that Bilodeau, W.L., 1986, The Mesozoic Mogollon Highlands, nia: American Geophysical Union, Fall Meeting 2011, three major streams were sourced in the mag- Arizona: An Early Cretaceous rift shoulder: Journal of abs. V21C–2506. Geology, v. 94, p. 724–735, doi:10.1086/629077. Dubiel, R.F., 1987, Sedimentology of the Upper Triassic matic arc (Fig. 11): one fl owed from plutonic Blakey, R.C., 1989, Triassic and Jurassic geology of the south- Chinle Formation, southeastern Utah: Paleoclimate sources through the Vampire depocenter and on ern Colorado Plateau, in Jenney, J.P., and Reynolds , S.J., implications, in Morales, M., and Elliot, D.K., eds., eds., Geologic evolution of Arizona: Arizona Geologi- Triassic continental deposits of the American South- to the present-day Colorado Plateau; one fl owed cal Society Digest 17, p. 369–396. west: Journal of the Arizona-Nevada Academy of Sci- from a source near the fi rst, but southeastward to Blakey, R.C., and Gubitosa, R., 1983, Late Triassic paleo- ence, v. 22, no. 1, p. 35–45. the Waterman depocenter; and the third fl owed geography and depositional history of the Chinle Dubiel, R.F., 1989, Depositional and climatic setting of the Formation, southern Utah and northern Arizona, in Upper Triassic Chinle Formation, Colorado Plateau, in northeastward from the Sonoran arc. The added Reynolds, M.W., and Dolly, E.D., eds., Mesozoic Lucas, S.G., and Hunt, A.P., eds., Dawn of the Age of layer of distinguishing subgroups of Th/U ratios paleogeography of the west-central United States: Dinosaurs in the American Southwest: Albuquerque, within the main sediment group, and comparing Rocky Mountain Section, Society of Economic Paleon- New Mexico Museum of Natural History, p. 171–187. tologists and Mineralogists, Rocky Mountain Paleo- Dubiel, R.F., 1994, Triassic deposystems, paleogeography, these subgroups to potential sources, suggests geography Symposium 2, p. 57–76. and paleoclimate of the western interior, in Caputo, that multiple volcano-plutonic complexes were Blakey, R.C., and Gubitosa, R., 1984, Controls of sand- M.V., et al., eds., Mesozoic systems of the Rocky stone body geometry and architecture in the Chinle Mountain region, USA: Rocky Mountain Section, eroded and tapped by streams within the arc. Formation (Upper Triassic), Colorado Plateau: Sedi- SEPM (Society for Sedimentary Geology), p. 133–168. Thus the added geochemical fi lter can provide mentary Geology, v. 38, p. 51–86, doi:10.1016/0037 Dubiel, R.F., Parrish, J.T., Parrish, J.M., and Good, S.C., important information to refi ne geologic inter- -0738(84)90074-5. 1991, The Pangaean megamonsoon: Evidence from the Blakey, R.C., and Knepp, R., 1989, Pennsylvanian and Upper Triassic Chinle Formation, Colorado Plateau: pretations. Permian geology of Arizona, in Jenney, J.P., and Palaios, v. 6, p. 347–370, doi:10.2307/3514963. Reynolds, S.J., eds., Geologic evolution of Arizona: Fohey-Breting, N.K., Barth, A.P., Wooden, J.L., Mazdab, ACKNOWLEDGMENTS Arizona Geological Society Digest 17, p. 313–347. F.K., Carter, C.A., and Schermer, E.R., 2010, Rela- Blakey, R.C., Basham, E.L., and Cook, M.J., 1993, Early tionship of voluminous ignimbrites to continental arc Funding for this study was provided by the National and Middle Triassic paleogeography of the Colorado plutons: Petrology of Jurassic ignimbrites and contem- Science Foundation through grants EAR 0711541 to Plateau and vicinity, in Morales, M., ed., Aspects of poraneous plutons in southern California: Journal of Riggs and EAR 0711115 and EAR 0711119 to Barth. Mesozoic geology and paleontology of the Colorado Volcanology and Geothermal Research, v. 189, p. 1–11, We are very grateful to Andrew Kylander-Clark, Plateau: Museum of Northern Arizona Bulletin 59, doi:10.1016/j.jvolgeores.2009.07.010. p. 13–26. Gehrels, G.E., 2000, Introduction to detrital zircon studies UCSB, for guidance through the LASS system and Busby-Spera, C.J., 1984, Large-volume rhyolite ash fl ow of Paleozoic and Triassic strata in western Nevada and interpretation and presentation of results. Excellent eruptions and submarine caldera collapse in the lower northern California, in Soreghan, M.J., and Gehrels, reviews by Tim Lawton, Brendan Murphy, and Paul Mesozoic Sierra Nevada, California: Journal of Geo- G.E., eds., Paleozoic and Triassic paleogeography and Stone helped us clarify our ideas and were extremely physical Research, v. 89, p. 8417–8427, doi:10.1029 tectonics of western Nevada and northern California: helpful. Ongoing and fruitful conversations with Ron /JB089iB10p08417. Geological Society of America Special Paper 347, Blakey and Zach Oberling are appreciated. Carmen Busby-Spera, C.J., 1986, Depositional features of rhyolitic p. 1–17, doi:10.1130/0-8137-2347-7.1. Winn and Courtney Pulido did the mineral separa- and andesitic volcaniclastic rocks of the Mineral King González-León, C., 1997, Sequence stratigraphy and paleo- tions, and the warm hospitality of the Tiffney-Gowen submarine caldera complex, Sierra Nevada, California: geographic setting of the Antimonio Formation (Late Journal of Volcanology and Geothermal Research, Permian–Early Jurassic), Sonora, Mexico: Revista family is much appreciated. Bill Dickinson fi rst gave v. 27, p. 43–76, doi:10.1016/0377-0273(86)90080-6. Mexicana de Ciencias Geológicas, v. 14, p. 136–148. Riggs the invaluable advice to look at the Waterman Campbell, P.A., and Anderson, T.H., 2003, Structure and González-León, C.M., Stanley, G.D., Jr., Gehrels, G.E., Mountains rocks. kinematics along a segment of the Mojave-Sonora and Centeno-García, E., 2005, New data on the megashear: A strike-slip fault that truncates the Juras- lithostratigraphy, detrital zircon and Nd isotope prov- REFERENCES CITED sic continental magmatic arc of southwestern North enance, and paleogeographic setting of the El Anti- America: Tectonics, v. 22, no. 6, p. 16-1–16-21, doi: monio Group, Sonora, Mexico, in Anderson, T.H., Armin, R., 1987, Sedimentology and tectonic signifi cance 10.1029/2002TC001367. et al., eds., The Mojave-Sonora megashear hypothesis: of Wolfcampian (Lower Permian) conglomerates in the Cherniak, D.J., 2010, Diffusion in accessory minerals: Zircon, Development, assessment, and alternatives: Geologi- Pedregosa basin: Southeastern Arizona, southwestern titanite, apatitie, monzanite, and xenotime: Reviews in cal Society of America Special Paper 393, p. 259–282, New Mexico, and northern Mexico: Geological Soci- Mineralogy and Geochemistry, v. 72, p. 827–869. doi:10.1130/2005.2393(09).

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