Early Cretaceous Construction of a Structural Culmination, Eureka, Nevada, U.S.A.: Implications for Out-Of- Sequence Deformation in the Sevier Hinterland
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Early Cretaceous construction of a structural culmination, Eureka, Nevada, U.S.A.: Implications for out-of- sequence deformation in the Sevier hinterland Sean P. Long1,*, Christopher D. Henry1, John L. Muntean1, Gary P. Edmondo2, and Elizabeth J. Cassel3 1Nevada Bureau of Mines and Geology, Mail Stop 178, University of Nevada, Reno, Nevada 89557, USA 2Timberline Resources Corporation, 101 East Lakeside, Coeur D’Alene, Idaho 83814, USA 3Department of Geological Sciences, University of Idaho, P.O. Box 443022, Moscow, Idaho 83844, USA ABSTRACT can be traced for ~100 km north-south on the 1968; Burchfi el and Davis, 1975; Oldow et al., basis of Paleogene erosion levels. The culmi- 1989; Allmendinger, 1992; Burchfi el et al., Assessing temporal relationships between nation is interpreted as a fault-bend fold that 1992; DeCelles, 2004; Dickinson, 2004). In foreland and hinterland deformation in fold- formed from ~9 km of eastward displace- the western interior United States, major com- thrust belts is critical to understanding the ment of the Ratto Canyon thrust sheet over a ponents of the Cordillera include the Sierra dynamics of orogenic systems. In the western buried footwall ramp. Nevada magmatic arc in California, and a broad U.S. Cordillera, the central Nevada thrust belt The type exposure of the Early Cretaceous retroarc region across Nevada and western Utah (CNTB) has been interpreted as a hinterland (Aptian) Newark Canyon Formation (NCF) in which most crustal shortening was accom- component of the Sevier fold-thrust belt in is preserved on top of Mississippian, Penn- modated (Fig. 1). The retroarc region has been Utah. However, imprecise timing constraints sylvanian, and Permian rocks on the eastern divided into distinct tectonic zones, including on CNTB deformation have hindered evalu- limb of the Eureka culmination. We propose the Jurassic Luning-Fencemaker thrust belt in ation of space-time patterns of strain par- that the NCF was deposited in a piggy back western Nevada (e.g., Oldow, 1983, 1984; Wyld, titioning between these two thrust systems. basin on the eastern limb of the culmina- 2002) and the Cretaceous frontal Sevier thrust To address this problem, new 1:24,000-scale tion as it grew, which is consistent with belt in Utah (e.g., Armstrong, 1968; Burchfi el geologic mapping and balanced cross sec- published east-directed paleocurrents and and Davis, 1975; Royse et al., 1975; Villien tions are presented through the CNTB near provenance data suggesting derivation from and Kligfi eld, 1986; DeCelles and Coogan, Eureka, Nevada, in conjunction with industry proximal late Paleozoic subcrop units. Syn- 2006). Between these two loci of Cordilleran drill-hole data, conodont age determinations, contractional deposition of the NCF is used crustal shortening is a broad hinterland region and 40Ar/39Ar and U-Pb ages from volcanic, to defi ne the probable Aptian construction of that underwent distinct Jurassic and Cretaceous intrusive, and sedimentary rocks. the Eureka culmination and associated slip magmatic, metamorphic, and shortening events, Our mapping redefi nes the fi rst-order on the Ratto Canyon thrust at depth. After although the timing and relative magnitude of structures and deformation geometry of the deposition, the NCF continued to be folded Jurassic versus Cretaceous deformation within CNTB at the latitude of Eureka. Contrac- during late-stage growth of the culmination. this region are debated (e.g., Armstrong, 1972; tional structures include two north-striking, Aptian deformation in the CNTB at Allmendinger and Jordan, 1981; Gans and east-vergent thrust faults, the Prospect Moun- Eureka postdated migration of the Sevier Miller, 1983; Miller et al., 1988; Speed et al., tain thrust and Moritz-Nager thrust, which thrust front into Utah by at least ~10 m.y. and 1988; Thorman et al., 1991, 1992; Bjerrum are connected as the same fault in cross sec- possibly as much as ~30 m.y., and therefore and Dorsey, 1995; Miller and Hoisch, 1995; tion, several north-striking map-scale folds, represents out-of-sequence hinterland defor- Camilleri and Chamberlain, 1997; Taylor et al., and a Cambrian over Silurian relationship mation. CNTB deformation was coeval with 2000; Wyld et al., 2001; Martin et al., 2010; observed in multiple drill holes, correspond- emplacement of the Canyon Range thrust Greene, 2014). ing to repetition of ~2–2.5 km of stratigraphy, sheet in the type-Sevier thrust belt in western One debate centers on the timing of deforma- that defi nes the blind Ratto Canyon thrust. Utah, and may represent internal shortening tion in the central Nevada thrust belt (CNTB), Two distinct sets of normal faults cut the con- of this orogen-scale thrust sheet that acted to defi ned by Taylor et al. (1993) as a series of tractional structures, and are overlapped by a promote further eastward translation. dominantly east-vergent thrust faults and folds regional late Eocene (ca. 37 Ma) subvolcanic exposed between the towns of Alamo and unconformity. Retrodeformation of both sets INTRODUCTION Eureka, Nevada (Fig. 1). Thrust systems in the of normal faults reveals the existence of the southern part of the CNTB connect southward Eureka culmination, a 20-km-wide, 4.5-km- The Jurassic–Paleogene North American with thrust faults of the Sevier belt in southern tall anticline with limb dips of 25°–35°, that Cordillera is the type example of an ancient Nevada (Bartley and Gleason, 1990; Armstrong orogen that formed between converging con- and Bartley, 1993; Taylor et al., 1993, 2000; *Corresponding author: splong@ unr .edu tinental and oceanic plates (e.g., Armstrong, Long, 2012), implying an overlap in deforma- Geosphere; June 2014; v. 10; no. 3; p. 564–584; doi:10.1130/GES00997.1; 13 fi gures; 1 table; 3 plates; 1 supplemental fi le. Received 24 October 2013 ♦ Revision received 25 February 2014 ♦ Accepted 8 April 2014 ♦ Published online 25 April 2014 564 For permission to copy, contact [email protected] © 2014 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/3/564/3333888/564.pdf by guest on 02 October 2021 Construction of a structural culmination, Eureka, Nevada Idaho age determinations, and U-Pb and 40Ar/39Ar 120° Nevada 117° 114° 111° geochronology of volcanic, intrusive, and sedi- mentary rocks. These data facilitate redefi nition RMT Salt of the fi rst-order structures that compose the GT Lake Wyoming Elko City 41° CNTB, and reconstruction of the regional pre- Utah extensional deformation geometry. In addition, a Area of structural model is presented that relates deposi- Fig. 2 tion in the type-NCF basin to CNTB deforma- Reno Sevier fold- tion, including growth of a regional-scale anti- LFTB Eureka thrust belt cline and associated motion on a thrust fault at Austin Ely depth, thereby placing the CNTB and NCF into Sevier region 39° the broader spatiotemporal framework of Sevier hinterland deformation and synorogenic deposition. This cross-section line work is aided by recent U-Pb geochronology in Sierra Nevada magmatic arc CNTB of DeCelles and the NCF type section (Druschke et al., 2011) and Tonopah Coogan (2006) a recent synthesis of the timing and magnitude of crustal shortening accommodated in the type- Alamo Cedar Sevier thrust belt at the latitude of our study area City (DeCelles and Coogan, 2006), both of which 37° facilitate assessment of temporal relationships Arizona between foreland and hinterland shortening. Las Vegas Implications of this work for the dynamics of the Cordilleran orogenic wedge are then explored. 050100 150 200 N GEOLOGIC SETTING AND ESTB STRATIGRAPHY California scale (km) Eastern Nevada has occupied a diverse range Figure 1. Map showing Paleozoic and Mesozoic thrust systems of Nevada, Utah, and south- of tectonic settings that have evolved through east California (modifi ed from Long, 2012). Approximate deformation fronts of Paleozoic the Phanerozoic (e.g., Dickinson, 2006). In the and Mesozoic thrust systems are shown in brown and blue, respectively, and spatial extents study area this tectonic development is pre- are shaded. Location of Sierra Nevada magmatic arc is from Van Buer et al. (2009) and served in a rock record that spans the Paleozoic, DeCelles (2004). Abbreviations: GT—Golconda thrust; RMT—Roberts Mountains thrust; Mesozoic, and Tertiary (Plate 1; Fig. 3). LFTB—Luning-Fencemaker thrust belt; CNTB—central Nevada thrust belt; ESTB—East- ern Sierra thrust belt. Paleozoic tion timing between these two thrust systems. (Nolan et al., 1971, 1974; Hose, 1983; Vander- From the late Neoproterozoic to the Devo- However, on the basis of crosscutting relation- voort and Schmitt, 1990) (Fig. 2). Contractional nian, the Cordilleran passive margin sequence, a ships, southern CNTB thrust faults can only be deformation in the Eureka region has been pro- westward-thickening section of clastic and car- broadly bracketed between the Pennsylvanian posed to be bracketed between the Permian and bonate rocks, was deposited on the rifted North and the Late Cretaceous (Taylor et al., 2000), Early Cretaceous (Nolan, 1962; Taylor et al., American continental shelf in what is now east- hindering evaluation of space-time patterns of 1993; Lisenbee et al., 1995), to be dominantly ern Nevada and western Utah (e.g., Stewart and strain partitioning between the CNTB and the Early Cretaceous, coeval with deposition of the Poole, 1974). Eureka was situated near the dis- Sevier thrust belt. NCF (Vandervoort and Schmitt, 1990; Carpen- tal, western margin of the shelf (Cook and Cor- This problem is compounded in the north- ter et al., 1993; Ransom and Hansen, 1993), boy, 2004). In the study area the exposed part ern part of the CNTB, near the town of Eureka and possibly to be as young as Late Creta- of the passive margin sequence is 4.7 km thick, (Fig. 1), an area that has been interpreted as ceous (Vandervoort and Schmitt, 1990; Taylor and consists of lower Cambrian clastic rocks, occupying a zone of thrust faults and folds in et al., 1993).