The Early Mesozoic Cordilleran Arc and Late Triassic Paleotopography: the Detrital Record in Upper Triassic Sedimentary Successions on and Off the Colorado Plateau
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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 602 For permission to copy, contact [email protected] © 2013 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/9/3/602/3344967/602.pdf by guest on 28 September 2021 Correlation of Upper Triassic strata on and off the Colorado Plateau 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 sub sidence 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 ero- sional; 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 com- plex. Depositional features of these vol canic 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).