Paleomagnetic results from the eastern Caliente- Enterprise zone, southwestern Utah: Implications for initiation of a major Miocene transfer zone Michael S. Petronis1,*, Daniel K. Holm2, John W. Geissman3, David B. Hacker2, and Billie J. Arnold2 1Environmental Geology, Natural Resource Management Department, New Mexico Highlands University, Las Vegas, New Mexico 87701, USA 2Department of Geology, Kent State University, Kent, Ohio 44242, USA 3Department of Geosciences, University of Texas at Dallas, ROC 21, 800 West Campbell Road, Richardson, Texas 75080-3021, USA ABSTRACT large and statistically signifi cant. For exam- defi ne the CEZ after Axen (1998) as the region ple, site P-18 from the Bauers Tuff yields an encompassing all transverse structures whether The Miocene Caliente-Enterprise zone R = –61.1° ± 5.3° and F = –0.6° ± 5.0°. Rela- or not they include evidence for counterclock- (CEZ) in southwestern Utah (USA) is a tive to the expected Miocene direction, in situ wise vertical axis rotation. Displacement trans- 20–50-km-wide east-northeast–trending left- paleomagnetic data from the Iron Axis lac- fer systems, or accommodation zones, are often lateral transfer zone that displaces north- coliths, specifi cally the Three Peaks laccolith, subvertical fault systems that transfer displace- south–trending crustal blocks of the eastern yield a mean that is discordant in declination, ment from one region of the crust to another Basin and Range Province to the west. Pre- with estimated R = –22.2° and F = –8.8° val- (Moustafa, 1976; Bosworth, 1985, 1986; Lister vious paleomagnetic results from the central ues. These rotation and fl attening estimates, et al., 1986; Rosendahl, 1987; Chapin, 1989; and western CEZ show signifi cant counter- although consistent with the overall data set Faulds et al., 1990; Faulds and Varga, 1998). clockwise vertical axis rotations of strike- from volcanic rocks, must be considered of Transfer zones accommodate or partition strain slip–bounded fault blocks, and these rotation lesser quality, as we are unable to accurately into areas of heterogeneous extension, and often estimates vary in magnitude both across and correct these data for possible effects of local are not simple strike-slip or oblique-slip fault along the strike of the zone. Results of recent tilting. If the rotation estimate is viable, then systems, but tend to be associated with diffuse detailed geologic mapping and new geo- we suggest that this component of deforma- belts of magmatism and, at times, signifi cant chrono logic data in the area east of previous tion involves much of the upper crust, and vertical axis rotation of fault-bound structural studies allow us to extend paleomagnetic stud- we furthermore propose that the boundary blocks (Faulds and Varga, 1998; Hudson et al., ies into the easternmost CEZ. New paleomag- of the eastern CEZ extends farther east than 1998; Petronis et al., 2002, 2007, 2009). The netic results include data from 4 regionally previously envisioned, to within a few kilome- CEZ is a sinistral transfer zone that has under- extensive latest Oligocene to early Miocene ters of the breakaway with the Colorado Pla- gone vertical axis rotation of spatially vari- (ca. 24–22 Ma) ignimbrite sheets and from 3 teau. The transitional zone between the east- able, yet systematic magnitudes (Hudson et al., ca. 22–20 Ma Iron Axis laccoliths. These data ern CEZ and Colorado Plateau is therefore 1998). Emplaced within the CEZ are numerous reveal signifi cant magnitudes and similar spa- abrupt and occurs within a narrow zone near 22–20 Ma laccoliths of the Iron Axis magmatic tially variable components of counterclock- Cedar City, Utah. province, a northeast-trending igneous feature wise vertical axis rotation. Rotation estimates in southwestern Utah characterized by several from the ignimbrites are assessed relative to INTRODUCTION early Miocene laccolithic intrusions, including what we interpret to be a nonrotated to only the Pine Valley megalaccolith and extensive minimally rotated reference section just north Since the middle Cenozoic, continental litho- latest Oligocene to earliest Miocene regional of the Colorado Plateau (Grass Valley) and spheric extension in the southwestern United ignimbrites (Hacker et al., 1996, 1999; Axen, from several low-extension areas in southeast States has resulted in the relative westward 1998). Previous paleomagnetic studies in the Nevada. Accepted tilt-corrected paleomag- transport of crustal material away from unex- CEZ concentrated on rocks from the central netic data from sites away from the reference tended stable crust of the Colorado Plateau and western part of its extent, predominantly areas are discordant in declination from the (Fig. 1). In general, the transition zone separat- because those areas were already mapped (Hud- expected individual ash-fl ow tuff directions, ing the extended and unextended regions trends son et al., 1998). This study focuses on the more with rotation (R) and fl attening (F) estimates north-south; however, in southwestern Utah the recently mapped areas to the east and southeast that range from R = –2° to –84° and F = +15° transition zone swings nearly 90° and trends (Hurlow, 2002; Rowley et al., 2006; Biek et al., to –14°. Many of the rotation estimates are roughly east-west, forming a major displace- 2009). We report paleomagnetic data from late ment transfer system known as the Caliente- Oligocene and Miocene volcanic and intrusive *Corresponding author e-mail: mspetro@ nmhu Enterprise zone (CEZ) (Anderson and Mehnert, rocks from the eastern CEZ, which is the area .edu. 1979; Hudson et al., 1998; Fig. 2A). Here we thought to record the earliest phase of deforma- Geosphere; June 2014; v. 10; no. 3; p. 534–563; doi:10.1130/GES00834.1; 14 fi gures; 5 tables. Received 11 June 2012 ♦ Revision received 26 August 2013 ♦ Accepted 2 April 2014 ♦ Published online 25 April 2014 534 For permission to copy, contact [email protected] © 2014 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/3/534/3333171/534.pdf by guest on 01 October 2021 Paleomagnetic results from the eastern Caliente-Enterprise zone, SW Utah active during vertical axis rotation, resulting in 118W 114W as much as 45°–85° of counterclockwise rota- tion, as evidenced by paleomagnetic data from Northern Basin the volcanic rocks in the area (Hudson et al., and Range Provence 1998). The central section of the CEZ overlaps the Caliente caldera complex, the eruption his- 40N tory of which lasted from ca. 23 to 12 Ma. The Caliente caldera is centered in eastern Nevada; UTAH the eastern edge of the caldera extends to within CALIFORNIA NEVADA 25 km of Enterprise, Utah. Early eruptions appear to have occurred before major exten- Sierra Nevada sion to the north or south during the Miocene, whereas the latter part of the caldera’s activ- CEZ ity occurred coincident with large-magnitude San Andreas Fault extension and detachment faulting to the north and south (Axen, 1998). The western section Central Basin of the CEZ is defi ned by the Pahranagat fault and Range Provence Colorado Plateau 36N zone (Tschanz and Pampeyan, 1970), which is composed of three northeast-striking sinistral ARIZONA faults and includes the area north of the fault. Southern Basin Pacific Ocean These faults have been interpreted to accommo- and Range Provence date varying degrees of extension that was trans- ferred from the Dry Lake Valley–Delamar Val- ley area to the Desert Valley west of the Sheep Range, where discrete faults of the system end Figure 1. Simplifi ed map of the central part of the western United (Liggett and Ehrenspeck, 1974; Wernicke et al., States showing the major tectonic provinces in the northern Basin 1984; Hudson et al., 1998). Areas north of the and Range Province. The trace of the San Andreas fault (dashed Pahranagat fault zone were also shown by Hud- line) is after Stewart (1988). CEZ—Caliente-Enterprise zone. Star son et al. (1995, 1998) to have rotated >15° represents the approximate location of the southern Delamar– counterclockwise. Meadow Valley Mountains and Condor Canyon reference areas. This area provides reference locations to base vertical axis rotation STRATIGRAPHY, LACCOLITHS, estimates for the Harmony Hills and Bauers Tuffs. AND GEOCHRONOLOGY Ignimbrite Stratigraphy tion within the zone (Hacker, 1998). New paleo- the early Miocene. This has been interpreted magnetic data from the eastern part of the CEZ to refl ect increased crustal ductility beneath the Cenozoic volcanic rocks, dominated by allow us to assess the amount and variation of zone as the result of the ca. 23–12 Ma magma- Oligo cene to Miocene ash-fl ow tuffs and lava vertical axis rotation where the CEZ interacts tism within the Caliente caldera complex (Hud- fl ows, as well as intrusive rocks, are abundant with the Iron Axis laccolith province along the son et al., 1998), in addition to the extension that and well exposed in southeastern Nevada and western margin of the Colorado Plateau and to occurred to the north of the adjacent Colorado southwestern Utah. The volcanic stratigraphy better defi ne the eastern extent of the zone. Plateau during the middle Miocene to Holocene of the eastern segment of the CEZ is, in part, (Axen, 1998). Two episodes of major Miocene the result of Iron Axis magmatic activity that GEOLOGIC SETTING to Holocene extension probably occurred north produced an assortment of ash-fl ow tuffs, lava of the CEZ and led to the current arrangement fl ows, and allochthonous gravity slide masses The CEZ trends east-northeast across the of basins and ranges. To the south, the Mio- related to the rapid emplacement and subsequent approximately north-south structural grain of the cene to Holocene extensional history was high- eruption of some of the Iron Axis laccoliths eastern Basin and Range Province for ~220 km lighted by a single, large-magnitude extensional (Hacker, 1998; Hacker et al., 2002).