Major Ignimbrites and Volcanic Centers of the Copper Canyon Area: a View Into the Core of Mexico’S Sierra Madre Occidental
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Major ignimbrites and volcanic centers of the Copper Canyon area: A view into the core of Mexico’s Sierra Madre Occidental Eric R. Swanson* Department of Earth and Environmental Science, The University of Texas at San Antonio, San Antonio, Texas 78249, USA Kirt A. Kempter 2623 Via Caballero del Norte, Santa Fe, New Mexico 87505, USA Fred W. McDowell Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA William C. McIntosh New Mexico Geochronology Research Laboratory, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA ABSTRACT ing picture is one of a dramatically thickened (see Nieto-Samaniego et al., 1999; Ferrari et and stratigraphically complex volcanic sec- al., 2002), the Durango-Mazatlán highway in Reconnaissance mapping along Copper tion related to numerous overlapping caldera the central part of the range (see McDowell and Canyon highway has established ignimbrite complexes, much like that documented for Clabaugh, 1979), and the El Paso–Chihuahua stratigraphic relationships over a relatively the core of the San Juan Mountains volcanic and Chihuahua-Hermosillo highways of the large area in the central part of the Sierra fi eld, Colorado. northern Sierra Madre Occidental (see McDow- Madre Occidental volcanic fi eld in western ell and Mauger, 1994; Swanson and McDowell, Chihuahua, Mexico. The oldest ignimbrites Keywords: calderas, ignimbrite, Sierra 1985; Cochemé and Demant, 1991; McDowell are found in the central part of the area, and Madre Occidental, volcanism, Mexico. et al., 1997). they include units previously mapped from These studies, and others, have shown that north of the study area, in and around the INTRODUCTION the Sierra Madre Occidental volcanic fi eld con- Tomóchic volcanic complex. Copper Canyon, sists of a relatively unfaulted central core of at the southern end of the study area, exposes The Sierra Madre Occidental Volcanic Field Tertiary volcanic rock, framed by NNW-trend- younger units, including the intracaldera tuff ing normal faults that enter Mexico from the of the Copper Canyon caldera and fi ve over- The Sierra Madre Occidental volcanic fi eld Basin and Range Province of the southwest- lying ignimbrites. Well-exposed calderas are (Fig. 1), from the United States–Mexico border ern United States, diverge around the core of found near San Juanito, in the central part to its intersection with the younger Mexican the Sierra Madre Occidental, and recombine at of the map area, and at Sierra Manzanita, to volcanic belt, covers at least 296,000 km2 of the southern end of the mountain range (Henry the far north. Stratigraphic evidence for yet western Mexico and is composed of lava and and Aranda-Gómez, 1992; Ferrari et al., 2002). another caldera in the northern part of the ignimbrite related to an estimated 350 major Several periods of faulting have been identi- area is found in the Sierra El Comanche. The calderas (Swanson and McDowell, 1984). If fi ed (Nieto-Samaniego et al., 1999; Henry and stratigraphic and limited available isotopic exposures of equivalent age in southern Mex- Aranda-Gómez, 2000; Ferrari et al., 2002). age data suggest that volcanism was particu- ico are considered, the volcanic cover grows Studies, mostly from the west side of the larly active ~30 m.y. ago. This reconnaissance to ~393,000 km2 (Aguirre-Díaz and Labarthe- Sierra Madre Occidental, reveal that western survey also documented lava-fl ow litholo- Hernández, 2003). Although the general aerial Mexico has experienced a lengthy, subduction- gies consistent with previous observations extent and dominantly silicic composition of the related magmatic history (see Roldán-Quintana from Tomóchic that intermediate lavas have Sierra Madre Occidental volcanic fi eld has been et al., 2003; Ferrari et al., 2005). This includes erupted throughout that area’s volcanic his- known for more than a century (Ordóñez, 1896), the emplacement of Cretaceous to early Tertiary tory and that basaltic andesite became par- detailed geologic maps showing ignimbrite cool- batholithic rocks and the widespread eruption ticularly abundant as felsic volcanism waned. ing units and calderas did not appear until the of the coeval, but relatively unstudied, andesite The combined Copper Canyon–Tomóchic 1970s (Swanson et al., 1978). Since that time, and rhyolite informally known as the lower vol- area gives the fi rst view into the core of the a series of “discovery-phase” mapping projects canic complex (McDowell and Keizer, 1977). giant Sierra Madre Occidental volcanic fi eld, have progressed, mainly along the major access Subduction-related volcanism culminated with expanding that offered by earlier reports, routes crossing and fl anking the area. Notably, massive outpourings of mid-Tertiary volcanic mostly from peripheral regions. The emerg- these are the Guadalajara-Zacatecas and Gua- rocks, mostly ignimbrite (informally the upper dalajara-Fresnillo highways and connecting volcanic supergroup of McDowell and Keizer, *E-mail: [email protected]. roads in the southern Sierra Madre Occidental 1977), which were emplaced toward the end Geosphere; May 2006; v. 2; no. 3; p. 125–141; doi: 10.1130/GES00042.1; 8 fi gures, 2 tables, Data Repository 2006119. For permission to copy, contact [email protected] 125 © 2006 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/2/3/125/3335324/i1553-040X-2-3-125.pdf by guest on 23 September 2021 E.R. SWANSON et al. W 110° W 100° CA AZ NM TX El Paso N 30° Hermosillo Figure 1. Major exposures of Chihuahua Tertiary volcanic rocks of the Tomóchic Sierra Madre Occidental volca- Study nic fi eld and of adjacent regions Creel Area in Baja California, Arizona, New Mexico, Texas, and in Sierra Madre Occidental southwestern Colorado (inset volcanic field Hidalgo at the same scale). Outcrop Los del Parral pattern is adapted from Swan- Mochis son and McDowell (1984), and modifi ed by information from Durango Ferrari et al. (2002). CO Zacatecas San Juan Mazatlan UT volcanic field km Guadalajara N 20° NM 0 400 of Farallon–North America plate convergence. exposure of the overriding plate to hotter asthe- Western Chihuahua Ignimbrite volcanism in the core of the volca- nospheric mantle (Ferrari et al., 2002). nic fi eld began as early as 38 Ma (Wark et al., All current tectonic and petrogenetic interpre- Mexican national highway 16 (here called the 1990), and volcanism appears to have become tations rely on the “discovery-phase” mapping Chihuahua-Hermosillo highway) has previously extremely voluminous just prior to abruptly ter- begun in the 1970s. While much progress has served as the locus for a series of mapping proj- minating over most the Sierra Madre Occidental been made toward understanding the origin of ects across the northern part of the Sierra Madre volcanic fi eld at 28 Ma. Younger ignimbrites rocks of the Sierra Madre Occidental, we esti- Occidental volcanic fi eld. These include the (ca. 24–21 Ma), however, are found in a belt mate that more than 90% of this great volcanic Tomóchic area (Fig. 2) in the core of the range, along the western fl ank of the volcanic fi eld that fi eld remains unmapped and that fewer than 10% where two overlapping calderas and six major expands southward to cover much of the south- of its calderas have been identifi ed. Mapped ignimbrite formations with K-Ar ages ranging ern Sierra Madre Occidental (see Ferrari et al., areas in the central Sierra Madre Occidental are in age from 38 to 29 Ma are found (Swanson 2002; Roldán-Quintana et al., 2003). Basaltic particularly sparse, and for over 1000 km along and McDowell, 1985; Kempter, 1986; Wark et andesite lava fl ows, the Southern Cordilleran the length of the fi eld, except for very narrow al., 1990). Wark (1991) also studied the pet- Basaltic Andesite, or SCORBA, of Cameron et transects along the Durango-Mazatlán highway, rogenesis of Tomóchic volcanic center rocks, al. (1989), appear to be widespread throughout the Chihuahua-Hermosillo highway, and along emphasizing a genetic relationship between the range and are commonly found intercalated highways north of Guadalajara, the core of the the large-volume rhyolite ignimbrites and more with, or overlying, each area’s youngest ignim- Sierra Madre Occidental volcanic fi eld is virtu- mafi c lithologies, the dominate role played by brites. Mechanisms explaining the timing, pet- ally unknown. This paper presents new infor- crystal fractionation, and the temporal relation- rogenesis, and extreme volume of the Sierra mation on ignimbrites and their source calderas ship between rhyolite volcanism and the waning Madre Occidental volcanic fi eld have focused for a large area in the heart of the Sierra Madre stages of Farallon plate subduction. A study of on a change in stress regime from compression Occidental, giving a view into the geologic core the isotopic composition of Tomóchic volcanic to one of extension (Wark et al., 1990) and on of this great volcanic fi eld and providing infor- rocks (McDowell et al., 1999) indicated that a transient thermal event possibly triggered by mation needed for more detailed studies of all Laurentian basement, like that in the south- foundering of the Farallon slab with resulting descriptions. western United States, does not extend under 126 Geosphere, May 2006 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/2/3/125/3335324/i1553-040X-2-3-125.pdf by guest on 23 September 2021 IGNIMBRITES AND CALDERAS OF THE COPPER CANYON AREA W108°00’ W107°45’ W107°30’ 2 16 Tomóchic Rio Papigochic 127 1 Pachera Sierra N28°15’ Gasachic Rio Terrero 3 Rio Sierra Tomóchic El Comanche Sierra Manzanita La Canoa Rancho Pescaditos Cueva Blanco del Toro 4 Road to El Piloncillo Basaseachic Alamito River Cordon Cumbre Alta Unpaved road Rio Terrero Figure 2. Location map for the Paved highway N28°00’ Copper Canyon and Tomóchic Train tracks 5 San Juanito areas with numbers (1–6) marking the names and loca- Study Areas tions of the various calderas Northern Section listed in the legend.