Geosphere, Published Online on 13 September 2013 As Doi:10.1130/GES00862.1
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Geosphere, published online on 13 September 2013 as doi:10.1130/GES00862.1 Geosphere Synvolcanic crustal extension during the mid-Cenozoic ignimbrite flare-up in the northern Sierra Madre Occidental, Mexico: Evidence from the Guazapares Mining District region, western Chihuahua Bryan P. Murray, Cathy J. Busby, Luca Ferrari and Luigi A. Solari Geosphere published online 13 September 2013; doi: 10.1130/GES00862.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geosphere Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. 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Solari2 1Department of Earth Science, University of California, Santa Barbara, Webb Hall, Santa Barbara, California 93106-9630, USA 2Centro de Geociencias, Universidad Nacional Autónoma de México, Boulevard Juriquilla 3001, Querétaro, 76230, México ABSTRACT basaltic andesite province that were intermit- INTRODUCTION tently erupted across all of the northern Sierra The timing and spatial extent of mid-Ceno- Madre Occidental toward the end of and fol- Silicic large igneous provinces are signifi - zoic ignimbrite fl are-up volcanism of the Sierra lowing the Early Oligocene ignimbrite pulse; cant in the geologic record due to their unusu- Madre Occidental silicic large igneous prov- and (3) the initiation of explosive and effusive ally extensive areal coverage (>100,000 km2), ince of Mexico in relation to crustal extension silicic fi ssure magmatism in the study area large volumes (>250,000 km3), and potential to is relatively unknown. Extension in the Sierra during the Early Miocene pulse of the mid- induce environmental change (e.g., Bryan, 2007; Madre Occidental has been variably inter- Cenozoic ignimbrite fl are-up. Cather et al., 2009; Jicha et al., 2009; Bryan and preted to have preceded, postdated, or begun The main geologic structures identifi ed Ferrari, 2013). Compositions within silicic large during Early Oligocene fl are-up vol canism of in the Guazapares Mining District region igneous provinces range from basalt to high- the silicic large igneous province. New geologic are NNW–trending normal faults, with an silica rhyolite, but are volumetrically dominated mapping, zircon U-Pb laser ablation–induc- estimated minimum of 20% total horizontal (>80%) by dacite-rhyolite compositions, with tively coupled plasma–mass spectrometry extension. Normal faults were active during >75% of the total magmatic volume emplaced dating, modal analysis, and geochemical data deposition of all three formations (Parajes, during short duration (~1–5 Myr) pulses over a from the Guazapares Mining District region Témoris, and Sierra Guazapares), and bound maximum province lifespan of ~50 Myr (Bryan, along the western edge of the northern Sierra half-graben basins that show evidence of syn- 2007; Bryan and Ernst, 2008). Previous studies Madre Occidental silicic large igneous prov- volcanic extension (e.g., growth strata) dur- suggest that silicic large igneous provinces may ince have identifi ed three informal syn exten- ing deposition. Normal faulting began by ca. be characteristic of continental regions undergo- sional formations. The ca. 27.5 Ma Parajes 27.5 Ma during deposition of the youngest ing broad lithospheric extension and typically formation is an ~1-km-thick succession com- ignimbrites of the Parajes formation, concur- initiate as prerifting magmatic events (Bryan posed primarily of welded to nonwelded rent with the end of the Early Oligocene silicic et al., 2002; Bryan, 2007; Best et al., 2013; silicic outfl ow ignimbrite sheets erupted from ignimbrite pulse to the east and before mag- Bryan and Ferrari, 2013). Therefore, determin- distant sources. The 27–24.5 Ma Témoris for- matism began in the study area. In addition, ing the timing of extensional deformation in mation is interpreted as an ande sitic volcanic preexisting normal faults localized andesitic relation to magmatism is an important consider- center composed of locally erupted mafi c to volcanic vents of the Témoris formation and ation toward understanding silicic large igneous intermediate composition lavas and associated silicic vents of the Sierra Guazapares forma- province processes, as crustal extension is sug- intrusions, with interbedded andesite-clast tion, and some faults were reactivated during, gested as one mechanism that favors the genera- fl uvial and debris fl ow deposits, and an upper as well as after, deposition of these formations. tion of large silicic magma volumes (Hildreth , section of thin distal silicic outfl ow ignim- We interpret extensional faulting and mag- 1981; Wark, 1991; Hanson and Glazner, 1995) brites. The 24.5–23 Ma Sierra Guaza pares matism in the Guazapares Mining District as well as very large magnitude explosive formation is composed of silicic vent facies region to be part of a regional-scale Middle silicic eruptions (Aguirre-Díaz and Labarthe- ignimbrites to proximal ignimbrites, lavas, Eocene to Early Miocene southwestward Hernández , 2003; Costa et al., 2011). plugs, dome-collapse deposits, and fl uvially migration of active volcanism and crustal The Sierra Madre Occidental of western or debris fl ow–reworked equivalents. These extension in the northern Sierra Madre Occi- Mexico is the third largest silicic large igneous three formations record (1) the accumula- dental. We show that extension accompanied province of the Phanerozoic and is the largest tion of outfl ow ignimbrite sheets, presumably silicic volcanism in the Guazapares region, and best-preserved of the Cenozoic (Fig. 1; erupted from cal deras mapped ~50–100 km and overlapped with the peak of mid-Ceno- Bryan, 2007; Ferrari et al., 2007). It extends east of the study area that were active during zoic ignimbrite fl are-up in the Sierra Madre for ~1200 km south from the U.S.-Mexico bor- the Early Oligocene pulse of the mid-Cenozoic Occidental; this supports the interpretation der to the Trans-Mexican Volcanic Belt, form- ignimbrite fl are-up; (2) development of an that there is a relationship between litho- ing a high plateau with an average elevation andesitic volcanic fi eld in the study area, likely spheric extension and silicic large igneous >2000 m, consisting primarily of Oligocene related to rocks of the Southern Cordillera province magmatism. to Early Miocene ignimbrites that cover an Geosphere; October 2013; v. 9; no. 5; p. 1–35; doi:10.1130/GES00862.1; 15 fi gures; 3 tables; 5 supplemental fi les. Received 21 August 2012 ♦ Revision received 19 June 2013 ♦ Accepted 14 August 2013 ♦ Published online 12 September 2013 For permission to copy, contact [email protected] 1 © 2013 Geological Society of America Geosphere, published online on 13 September 2013 as doi:10.1130/GES00862.1 Murray et al. 1991; McDowell and Mauger, 1994; Albrecht Tuscon main highway El Paso railroad and Goldstein, 2000; Swanson et al., 2006; McDowell , 2007; McDowell and McIntosh, SMO 2012) (Fig. 1). As a result, the age relation- TMVB ships between ignimbrite fl are-up volcanism 30°N and crustal extension remain unclear. Previous studies have suggested that signifi cant crustal U.S.A. Hermosillo extension in the region did not occur until after Mexico the peak of large volume ignimbrite fl are-up Gulf of California Tomóchic Chihuahua volcanism, which was inferred to have occurred between ca. 32 and 28 Ma (Early Oligocene; Basaseachic San Juanito e.g., McDowell and Clabaugh , 1979; Wark et al., Fig. 2 Creel Divisadero unextended 1990; McDowell and Mauger, 1994; Gans, 1997; core of the SMO Grijalva-Noriega and Roldán-Quintana, 1998). However, other studies have inferred that initial regional extension is recorded by the onset of Los Mochis large volume Early Oligocene ignimbrite fl are- up volcanism (e.g., Aguirre-Díaz and McDowell , La Paz 1993), or that extensional deformation began Durango before the fl are-up (e.g., Dreier, 1984; Ferrari et al., 2007). Uncertainty regarding the timing of extension relative to ignimbrite fl are-up vol- Mazatlán canism is also a problem in the Basin and Range of the western U.S., where previous studies have 0 Mesa Central 400 km inferred that extension preceded, postdated, or began during ignimbrite fl are-up volcanism (e.g., 0 200 mi Gans et al., 1989; Best and Christiansen, 1991; Guadalajara N TMVB Axen et al., 1993; Best et al., 2013).