Závada et al. Devils Tower (Wyoming, USA): A lava coulée emplaced into a maar-diatreme volcano? P. Závada1,*,†, P. Dědeček1,†, J. Lexa2,†, and G.R. Keller3,† 1Institute of Geophysics of the Czech Academy of Sciences, v.v.i., Boční II/1401, 141 31, Praha 4, Czech Republic 2Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, P.O. Box 106, 840 05, Bratislava 45, Slovak Republic 3School of Geology and Geophysics, University of Oklahoma, 100 E. Boyd Street, Sarkeys Energy Center, Suite 710, Norman, Oklahoma 73019, USA ABSTRACT intrusive body in the form of a magmatic stock primarily on the basis of spatial distribution of (Russell, 1896; Robinson, 1956), a laccolith magmatic fabrics and their kinematics (Cloos We have investigated the mode of emplace- (Pirsson, 1894; Jaggar, 1901), or a volcanic con- and Cloos, 1927; Varet, 1971; Jančušková et al., ment of iconic Devils Tower, which is a phono- duit (Carpenter, 1888; Halvorson, 1980); the lat- 1992; Arbaret et al., 1993; Závada et al., 2009a). lite porphyry monolith in the state of Wyo- ter interpretation is presented in many Earth sci- One of these well-exposed phonolite buttes ming in the western United States. Our fi eld ence textbooks. Although conclusive evidence (Bořeň phonolite body, Czech Republic) was survey of this structure and its geological set- is lacking, it is generally accepted that it repre- recently investigated and interpreted as a rem- ting, its radiometric dating, and the tectono- sents an intrusion of phonolite magma that was nant of a lava dome extrusion into the crater of magmatic evolution of the region suggest a exposed after erosion of the surrounding weakly a maar-diatreme volcano by combined methods new genetic interpretation of the vol cani clastic consolidated Mesozoic and Cenozoic sedi- of magmatic fabrics and cooling fracture pat- rocks in the area and provide a basis for a new mentary layers (e.g., Robinson and Davis, 1995; terns (Závada et al., 2011). hypothetical emplacement scenario for Devils Sigurdsson, 2000). Corry (1988) claimed that The fact that Devils Tower is also associated Tower. This interpretation was inspired by an Devils Tower is a volcanic neck that may have with phreatomagmatic pyroclastic rocks simi- analogy of the tower with a similar phono lite formed from solidifi ed magma that extruded lar in composition to those associated with dia- butte in the Cenozoic vol canic region of the along a failure zone in the extended roof of a tremes elsewhere in the Black Hills (Effi nger, Czech Republic and analogue modeling using Christmas-tree laccolith. Lisenbee and Roggen- 1934; Lisenbee and Roggenthen, 1990; Kirch- plaster of paris combined with fi nite element then (1990) and Rakovan (2006) suggested ner, 1996) and exhibits remarkable similari- thermal numerical modeling. Our results that the emplacement of phonolite magma was ties with the Bořeň body (e.g., size, phonolitic indicate that Devils Tower is a remnant of a somehow associated with diatremes or phreato- composition, inverted fan pattern of columnar coulée or low lava dome that was emplaced magmatic volcanoes; however, they did not jointing) motivated us to undertake a new sur- into a broad phreatomagmatic crater at the address the mode of Devils Tower emplace- vey and analysis in Devils Tower area to con- top of a maar-diatreme volcano. ment. In contrast to all intrusive scenarios, Kiver sider alternative models for its emplacement. and Harris (1999) argued that the tower could We propose a new emplacement scenario that represent a remnant of a surfi cial lava body is supported by a conceptual analogue model INTRODUCTION or welded pyroclastic material emplaced into using plaster of paris as an analogue of magma the phreatomagmatic maar crater. Spry (1962) that shows the internal fl ow pattern from mag- Devils Tower is a dominant landmark of the explained the inverted fan columnar jointing netic fabrics of dispersed magnetic particles northern Great Plains (Wyoming, USA). It rep- pattern on Devils Tower by cooling of an extru- and serves as a template for numerical model resents the world’s fi nest example of columnar sive lava sheet above the conduit based on the of cooling that is matched with the Devils jointing in phonolite and possibly the longest mathematical model of Jaeger (1961). Tower columnar jointing pattern. Owing to the columns developed in a volcanic rock (Fig. 1). Understanding the emplacement mode for National Monument administrative limitations The Cenozoic phonolite porphyry monolith Devils Tower requires additional study using we could not carry out direct structural mea- forming Devils Tower is located in the western modern techniques of structural analysis of surements or collect samples for a systematic Black Hills in northeastern Wyoming (Fig. 2). magmatic fabrics and fracture systems that anisotropy of magnetic susceptibility (AMS) The scientifi c debate on the origin of Devils develop during cooling of magmatic bodies. study as intended. Tower has lasted for more than 100 years. Additional insight can be gained by studies of The majority of previous studies of Devils similar features around the world, such as those CENOZOIC IGNEOUS AND Tower have concluded that it is a remnant of an found in the Cenozoic volcanic provinces of VOLCANIC ACTIVITY IN THE western and central Europe. These features are BLACK HILLS UPLIFT located in the foreland of the Alpine belt (Cajz *Corresponding author. †Emails: Závada: zavada@ ig .cas .cz; Dědeček: et al., 1999; Ziegler, 1994), and the emplace- The Devils Tower phonolite monolith (Figs. pd@ ig .cas .cz; Lexa: geoljalx@ savba .sk; Keller: ment mode of phonolite or trachyte bodies that 1A, 1C–1E) and Missouri Buttes, a group of grkeller@ ou .edu. are similar to Devils Tower has been interpreted fi ve bodies of similar composition located 5 km Geosphere; April 2015; v. 11; no. 2; p. 354–375; doi:10.1130/GES01166.1; 17 fi gures; 3 tables; 1 supplemental fi le. Received 5 August 2014 ♦ Revision received 18 November 2014 ♦ Accepted 13 January 2015 ♦ Published online 17 February 2015 354 For permissionGeosphere, to copy, contact April [email protected] 2015 © 2015 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/354/3335355/354.pdf by guest on 03 October 2021 Devils Tower as a lava coulée? A B B WNW ESE C D UCUC LCLC S B SE NW NE SW E F DT MB WEE W Figure 1. Field photographs of Devils Tower and Missouri Buttes with orientation indicated. (A) Southwestern side of the tower shows vertical and horizontal joints of the base and curved columns plunging to the west. (B) Detail of the southwestern wall shows apparent compositional layering as dark horizontal streaks across the columns (stippled black line), and a suture between the upper and lower colonnades indicated by columns of the upper colonnade that split to two or three narrower columns of the lower colonnade (indicated by arrows). Dashed white lines indicate broad suture between both colonnades. (C) The asymmetrical shape of Devils Tower, with straight columns plunging at ~65° on the southeast and curved columns on the northwest, is seen best from the northeast. (D) In contrast, view from the northwest shows symmetrical shape of subvertical columns on both sides with slight bend to shallower plunge angles on their lower ends. B—base, S—shoulder, LC—lower colonnade, UC—upper colonnade. (E) Missouri Buttes, located ~5 km northwest from Devils Tower, represented by 5 separate phonolite bodies distributed along a periphery of a north-south elongated ellipse of short and long axes of 1 and 2 km, respectively. (F) Two northern buttes of Missouri Buttes in a view from the north. Geosphere, April 2015 355 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/354/3335355/354.pdf by guest on 03 October 2021 Závada et al. 103.3°W Black Hills uplift VOLCANICLASTIC DEPOSITS AND 44.9°N STRUCTURAL DEFORMATION N Tertiary igneous rocks OF THE AREA MMBB 50 km Cretaceous DDTT Jurassic(Fm.) Sundance M The distribution of Mesozoic and Tertiary S Triassic and Permian (sFm.)Spearfi h marine and terrestrial sediments surrounding Fig. 3 T MMCC Paleozoic limestones the Devils Tower and Missouri Buttes bodies Precambrian basement (Fig. 3) and the approximate average thick- River PowderBasin Rapid nesses from borehole data (Robinson et al., City Location of diatremes 1964; DeWitt et al., 1989; Sutherland, 2008) in the Black Hills are presented in Table 1. The youngest exposed MB - Missouri Buttes deposits are represented by volcaniclastic 43.5°N DT - Devils Tower material that is found in four areas (DT-2, S - Sugarloaf MB-C, MB-N, MB-D; Figs. 3 and 4). Photo- Wyoming M - Maitland South T - Tomahawk graphs of some of the samples we collected 104.9°W Dakota 103.3°W MC - Meadow creek are shown in Figure 5: (1) DT-2, found ~230 m west-southwest of Devils Tower is representa- Figure 2. Schematic map of the Black Hills, which represent a tive of rounded clasts of granite, limestone, and lithospheric-scale uplift exposing Precambrian basement in its core limestone conglomerate not found in the sur- and the entire section of the Phanerozoic sedimentary cover. Cenozoic rounding sedimentary units (Fig. 3); (2) MB-C, igneous centers associated by domes in the host rocks are aligned in found in outcrops or blocks in the central area west-northwest–east-southeast direction across the uplift. Stars show between the buttes (Figs. 4B, 5A, and 5B); locations of the six diatremes in the Black Hills (after Lisenbee and (3) MB-N, found between the two northern Roggenthen, 1990). buttes (Fig. 3C) that also contains an erratic granite boulder 1 m in diameter (Fig.