The Early Mesozoic Volcanic Arc of Western North America in Northeastern Mexico

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Journal of South American Earth Sciences 25 (2008) 49–63 www.elsevier.com/locate/jsames

The Early Mesozoic volcanic arc of western North America in northeastern Mexico

Jose´ Rafael Barboza-Gudinõ a,*, Marıá Teresa Orozco-Esquivel b, MartıńGo´mez-Anguiano c, Aurora Zavala-Monsivaís d

a Instituto de Geologıá, Universidad Autońoma de San Luis Potosı´, Manuel Nava No. 5. Zona Universitaria, 78240 San Luis Potosı´, S.L.P., Mexico b Centro de Geociencias, Universidad Nacional Autońoma de Me´xico, Campus Juriquilla, 76230 Quere´taro, Qro., Mexico c Universidad Tecnolo´gica de La Mixteca, Carretera a Acatuma Km. 2.5, 69000 Huajuapan de Leoń, Oaxaca, Mexico d Posgrado en Geologıá Aplicada, Universidad Autońoma de San Luis Potosı´, Manuel Nava No. 5, Zona Universitaria, 78240 San Luis Potosı´, S.L.P., Mexico

Abstract

Volcanic successions underlying clastic and carbonate marine rocks of the Oxfordian–Kimmeridgian Zuloaga Group in northeastern Mexico have been attributed to magmatic arcs of Permo–Triassic and Early Jurassic ages. This work provides stratigraphic, petrographic geochronological, and geochemical data to characterize pre-Oxfordian volcanic rocks outcropping in seven localities in northeastern Mexico. Field observations show that the volcanic units overlie Paleozoic metamorphic rocks (Granjeno schist) or Triassic marine strata (Zacatecas Formation) and intrude Triassic redbeds or are partly interbedded with Lower Jurassic redbeds (Huizachal Group). The volcanic rocks include rhyolitic and rhyodacitic domes and dikes, basaltic to andesitic lava flows and breccias, and andesitic to rhyolitic pyroclastic rocks, including breccias, lapilli, and ashflow tuffs that range from welded to unwelded. Lower–Middle Jurassic ages (U/ Pb in zircon) have been reported from only two studied localities (Huizachal Valley, Sierra de Catorce), and other reported ages (Ar/ Ar and K–Ar in whole-rock or feldspar) are often reset. This work reports a new U/Pb age in zircon that confirms a Lower Jurassic (193 Ma) age for volcanic rocks exposed in the Aramberri area. The major and trace element contents of samples from the seven localities are typical of calc-alkaline, subduction-related rocks. The new geochronological and geochemical data, coupled with the lithological features and stratigraphic positions, indicate volcanic rocks are part of a continental arc, similar to that represented by the Lower–Middle Jurassic Nazas Formation of Durango and northern Zacatecas. On that basis, the studied volcanic sequences are assigned to the Early Jurassic volcanic arc of western North America. Ó 2007 Elsevier Ltd. All rights reserved.

Keywords: Stratigraphy; Volcanic rocks; Arc; Jurassic; Mexico

1. Introduction lini et al., 2003; Barboza-Gudinõ et al., 1998, 1999, 2004) reveal diverse lithologies and stratigraphic position below Volcanic successions underlie clastic and carbonate mar- Oxfordian limestones. In northern Durango and Zacate- ine sequences of the Oxfordian–Kimmeridgian Zuloaga cas, the volcanic pre-Oxfordian rocks have been assigned Group in northeastern Mexico. Studies of the successions to the Jurassic continental volcanic arc, related to the (e.g., Pantoja-Alor, 1972; Blickwede, 2001; Lo´pez-Infan- active continental margin of southwestern North America zoń, 1986; Jones et al., 1990, 1995; Bartolini, 1998; Barto- (Grajales-Nishimura et al., 1992; Jones et al., 1995; Barto- lini, 1998; Bartolini et al., 2003), whereas in areas of San Luis Potosı´, Nuevo Leoń, and Tamaulipas, they have been * Corresponding author. Fax: +52 444 8111741. considered products of a Permo–Triassic volcanic arc (Mei- E-mail address: [email protected] (J.R. Barboza-Gudinõ). burg et al., 1987; Bartolini et al., 1999).

However, the assignments are uncertain because reli- 2. The exposed sequences able isotopic data are lacking, and petrographic and geochemical information is scarce. In this article, we Localities described in this section are shown in Fig. 1. report new geochemical, petrographic, and stratigraphic Some outcrop aspects and textural or microstructural data for pre-Oxfordian rocks exposed in northeastern details of the pre-Oxfordian volcanic rocks studied in local- Mexico in the Sierra de Salinas, Sierra de Charcas, ities from northeastern Mexico are illustrated in Fig. 2. and Sierra de Catorce in San Luis Potosı´; the Aramb- In northern Durango, intermediate to felsic volcanic erri and San Marcos areas in Nuevo Leoń; and the rocks are exposed in the Villa Jua´rez area. Pantoja-Alor Huizachal Valley in Tamaulipas (Fig. 1). The main pur- (1972) defines this unit as the Nazas Formation, with its pose of the geochemical analyses is to characterize the type locality at Cerritos Colorados and a reported Pb-a rocks with regard to the tectonic setting in which they age of 230 ± 20 Ma from a rhyolitic flow. In the Villa could have originated, rather than providing informa- Jua´rez area, Bartolini and Spell (1997) obtain a 40Ar/39Ar tion leading to a detailed evolutionary model of the age of 195 ± 55 Ma from plagioclase in rhyolitic rocks, magmas. The new data, supported by information from probably comparable to those dated by Pantoja-Alor the literature, help establish the tectonic setting and the (1972). The Nazas Formation is the oldest exposed unit correlations among pre-Oxfordian volcanic rocks in in the Villa Jua´rez region, but 200 km northwest of this northeastern Mexico. locality, in Santa Marıá del Oro, northern Durango, the

Fig. 1. Geologic map of northeastern Mexico, showing outcrops of pre-Oxfordian volcanic and sedimentary rocks and location of samples. J.R. Barboza-Gudin˜o et al. / Journal of South American Earth Sciences 25 (2008) 49–63 51

Fig. 2. Details of the textures and microstructures observed in outcrops, hand samples, and thin sections of the volcanic rocks. (a) Volcanic breccia in the pyroclastic deposits of the Aramberri area, Nuevo Leoń. Knife is 11 cm long. (b) General aspect of a rhyolitic dike (R) in the Sierra de Catorce; Juj, Upper Jurassic La Joya Formation; volc., intermediate pre-Oxfordian volcanic rocks. Note person for scale. (c) Lithophyse contained in pyroclastic deposits outcropping west of Charcas, San Luis Potosı´ (long edge = 10 cm). (d) Fiamme structures in ignimbrites from Aramberri, Nuevo Leoń; hand-lens diameter is 2.5 cm. (e) Fragments of partially collapsed pumice in an ignimbrite of Charcas, San Luis Potosı´. (f) Trachytic or pylotaxitic texture in a basaltic andesite of La Ballena, Zacatecas, San Luis Potosı´. unit overlies Paleozoic metamorphic rocks (Bartolini, 1998) a K–Ar age of 183 Ma determined in hornblende from and unconformably underlies Upper Jurassic sandy lime- the so-called Rodeo Formation (Lo´pez-Infanzoń, 1986) stone of La Gloria Formation (Imlay, 1936). and an apparent U–Pb age of 158 ± 4 Ma in zircon grains In northern Zacatecas, lava flows, airfall and ashflow from the Caopas schist (Jones et al., 1995). In the Sierra de tuffs, and lahars correlated with the Nazas Formation have Teyra, the Nazas Formation overlies the marine siliciclastic been described in the Caopas–Rodeo area, including Sierra Taray Formation (Co´rdoba-Meńdez, 1964) of Triassic age de Teyra to the west and Sierra de San Juliań to the east (Silva-Romo et al., 2000) and underlies Upper Jurassic (Blickwede, 1981, 2001). Some units (Caopas schist and continental deposits of La Joya Formation (Mixon et al., Rodeo Formation) initially were considered pre-Jurassic 1959) and shallow marine limestones of the Zuloaga For- because of their very deformed and metamorphosed mation (Imlay, 1938). aspects (de Cserna, 1956; Co´rdoba-Meńdez, 1964). Subse- In western San Luis Potosı´, volcanic sequences compa- quent studies indicated that the deformed units are coeval rable to those of Durango and Zacatecas rest on Triassic with the Nazas Formation and belong to the same Jurassic thin-bedded strata interpreted as part of a turbiditic continental volcanic arc sequence (Lo´pez-Infanzoń, 1986; sequence known as the Zacatecas Formation (Martıńez- Jones et al., 1990, 1995). This hypothesis is supported by Pe´rez, 1972) or the La Ballena Formation (Silva-Romo, 52 J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63

1993; Centeno-Garcı´a and Silva-Romo, 1997). The volca-

nic units are unconformably overlain by Upper Jurassic Corr. coef. redbeds of La Joya Formation and shallow marine limestones of the Zuloaga Formation. The volcanic sequences crop out in the Sierra de Salinas, at the state border Pb age between Zacatecas and San Luis Potosı´ (Silva-Romo, 206 Pb/ (Ma) 1993; Barboza-Gudinõ et al., 1998, 1999; Zavala-Monsi- 207 vaís, 2000; Go´mez-Anguiano, 2001), in the Sierra de Charcas, and in the region of Tepozan in western San Luis Potosı´ state (Tristań-Gonza´lez and Torres-Hernańdez, U age 235 1992, 1994; Tristań-Gonza´lez et al., 1995; Zavala-Monsi- Pb/ (Ma) vaís, 2000), as well as in the Sierra de Catorce (Lo´pez- 207 Infanzoń, 1986; Barboza-Gudinõ et al., 1998, 1999; Zav- ala-Monsivaís, 2000; Hoppe, 2000; Go´mez-Anguiano, 2001). Barboza-Gudinõ et al. (2004) report U–Pb isotopic U age 238 analyses of zircon for rhyolite of the Sierra de Catorce. Pb/ (Ma) The fraction recording the least inheritance yields an age 206 of 174.7 ± 1.3 Ma, a maximum age of the rock. In Nuevo Leoń state, volcanic rocks comparable in their lithology and stratigraphic position with those Pb described previously have been observed in a sequence 206 Pb/

exposed in Aramberri (Jones et al., 1995). The sequence 207 consists predominantly of ignimbrites, volcanic breccias, and tuﬀs of intermediate to felsic composition, which overlie Paleozoic schist and unconformably underlie the U transgressive Upper Jurassic strata. Some authors con- 235 sider these volcanic units related to a Permo–Triassic vol- Pb/ 207 canic arc (Meiburg et al., 1987; Bartolini et al., 1999). We analyze three single zircon grains from a rhyodacitic

ignimbrite at the Mezquital section, north of Aramberri. U

One grain yields essentially concordant Pb/U ratios that 238 indicate an age of 193.1 ± 0.3 Ma for the rock (Table 1); Pb/ 206 an upper intercept at 193.3 ± 1.5 Ma is also shown in a Rad. %Err Rad. %Err Rad. %Err discordia plot (Fig. 3). In the redbed sequence exposed near San Marcos,

south of Galeana, Nuevo Leo´n, the volume of volcanic Pb (corr.) 206

and subvolcanic rocks is small, and the stratigraphic rela- / tions are uncertain. At this locality, some dikes and sills of 208 trachytic composition intrude Upper Triassic redbeds of the Lower Huizachal Group and are truncated by the unconformity beneath Upper Jurassic breccias of La Joya Pb (corr.)

Formation and Oxfordian–Kimmeridgian evaporites of 204 / Corrected atomic ratios the Minas Viejas Formation (Go´mez-Anguiano, 2001). 206 Pre-Oxfordian volcanic rocks are also present in the State of Tamaulipas, at Huizachal Valley (Jones et al., 1995; Fastowsky et al., 2005), the Miquihuana area (Bart- olini et al., 2003), and La Boca Canyon (Fig. 1). Meta- Com. Pb (pg) rhyolite exposed in the nearby Caballeros Canyon are apparently older and possibly of Paleozoic age (Gursky Pb (ppm) and Ramı´rez-Ramı´rez, 1986; Stewart et al., 1999). The best exposures of pre-Oxfordian volcanic and subvolcanic U (ppm) rocks in Tamaulipas are found in the Huizachal Valley, where they represent the basal part of the exposed Meso- g) l

zoic sequence, underlying and partially intruding Lower ( Jurassic redbeds; no older units crop out in this area. Vol- canic rocks in this locality consist of ignimbrite, fine- Table 1 U–Pb data for single zircon crystalsSample from a rhyodacitic Weight ashflow tuff, Aramberri area (sample MZQTG1) grained tuff, breccia, and lava of intermediate to felsic Z1Z2Z3 1.7 4.4 3.5 402 142 12.4 211 4.4 0.6 6.3 0.6 0.6 2276.1 2019.8 2234.7 0.133 0.155 0.169 0.030397 0.11 0.030071 0.20943 0.12 0.028584 0.16 0.11 0.20720 0.04997 0.22 0.19744 0.11 0.17 0.04997 193.0 0.18 0.05010 0.12 191.0 181.7 193.1 191.2 183.0 193.6 193.7 199.4 0.717 0.592 0.690 J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63 53

Data-point error ellipses are 2s 196 0.0308

0.0304 192

0.0300

206 Pb 0.0296 188 238 U 0.0292 184 0.0288 Intercepts at: 0.0284 -106±67 & 193.3±1.5 [±3.2] Ma MSWD = 0.13 0.0280 0.194 0.198 0.202 0.206 0.210 0.214 207Pb / 235U

Fig. 3. Concordia diagram for U–Pb isotope ratios of zircons from a rhyodacitic ashflow tuff in the Aramberri area (see Table 1). Error ellipses of individual spots are 2r. composition. In the Huizachal Valley, zircon grains from a Isotopic ages reported to date for pre-Oxfordian volca- pyroclastic flow are dated by U–Pb at 189 ± 0.2 Ma nic rocks in northeastern Mexico are summarized in Table (Fastowsky et al., 2005). At this locality, Fastowsky et al. 2. Three Lower–Middle Jurassic ages were obtained by the (2005) recognize an older volcanic sequence beneath an U–Pb method in zircons, whereas other included K–Ar and angular unconformity that underlies the dated pyroclastic Ar/Ar ages (whole-rock or feldspar) indicate Cretaceous– flow at the base of the Lower Jurassic redbed sequence of Paleogene ages and probably reflect age resetting during La Boca Formation. All features described by Fastowsky the Laramide event. et al. (2005) and those we observe in the same outcrops of the ‘‘older’’ sequence are typical textures and structures 3. Petrography of rhyolitic domes: spherulitic structures, steeply dipping flow-like bands, lithophysae, peripheral lava flows or lobes, The petrography and petrology of the Lower Jurassic and associated ash flow tuffs. In addition, we observe intru- volcanic rocks in the Nazas Formation and comparable sive relationships to Lower Jurassic redbeds of La Boca rocks from northeastern Mexico have been described from Formation. We interpret the steeply dipping features in this different localities by various authors. Blickwede (1981, sequence as subvertical flow bands resulting from magma 2001) provides petrographic and petrologic data on rocks injection into a volcanic dome, whose emplacement age is from Sierra de San Juliań; Lo´pez-Infanzoń (1986) offers not necessary much older than the dated Lower Jurassic data on rocks from the Caopas–Rodeo and Sierra de Teyra pyroclastic flow, and thus, we consider plausible the inclu- areas and compares them with rocks of the Sierra de Cator- sion of this lower sequence as part of the same Lower ce; Jones et al. (1995) describe volcanic rocks of the Cao- Jurassic volcanic arc. pas–Pico de Teyra region and compare them with rocks

Table 2 Summary of isotopic ages of pre-Oxfordian volcanic rocks from northeastern Mexico, including several Ar/Ar and K–Ar ages determined in whole-rock or feldspar that are considered reset ages Location name State Rock type Method Material dated Age (Ma) Error (Ma) Source Huizachal Valley Tamaulipas Pyroclastic flow U–Pb Zircon 189.0 0.2 Fastowsky et al. (2005) Sierra de Salinas S. Luis Potosı´ Basalt 40Ar/39Ar Whole rock 82.9 0.6 Bartolini (1998) Aramberri Nuevo Leoń Rhyolite K–Ar Whole rock 70.7 1.8 Fastowsky et al. (2005) Huizachal Valley Tamaulipas Rhyolite K–Ar Whole rock 52.1 1.4 Bartolini (1998) Miquihuana Tamaulipas Rhyolite K–Ar Whole rock 57.8 1.5 Bartolini (1998) San Marcos Nuevo Leoń Andesitic dike K–Ar Whole rock 104 3 Bartolini (1998) Sierra de Salinas S. Luis Potosı´ Andesitic basalt K–Ar Whole rock 81.9 4.1 Barboza-Gudinõ et al. (1999) Sierra de Catorce S. Luis Potosı´ Rhyolite K–Ar Feldspar 110.0 1.9 This work Sierra de Catorce S. Luis Potosı´ Rhyolite U–Pb Zircon 174.7 1.3 Barboza-Gudinõ et al. (2004) Aramberri Nuevo Leoń Pyroclastic rock U–Pb Zircon 193.1 0.3 This work 54 J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63 from Torreoń, Sierra de Catorce, Charcas, Aramberri, indicators. The textures are diverse, including breccia, lap- Miquihuana, and Huizachal Valley; and finally, Zavala- illi tuff, and fine volcanic ash. Some deposits display weld- Monsivaís (2000) describes the petrography of pre-Oxfor- ing and devitrification, whereas others appear to be dian volcanic rocks included in this study from western unwelded rocks, compacted by deformational processes, San Luis Potosı´ State at Sierra de Salinas, Charcas, that record intense foliation and jointing. Tepozań, and Sierra de Catorce. We compile relevant In the Sierra de San Juliań, Blickwede (1981, 2001) petrographic data and add new petrographic descriptions describes a 1000 m thick volcanic sequence consisting of of the main lithologic features, which we summarize in 65% pyroclastic rocks, 25% sedimentary and volcaniclastic Table 3. rocks, and only 10% lavas. Volcanic breccias or tuff-breccias are the predominant rocks in the various small out- 3.1. Rhyolite crops exposed in the Arroyo El Tepozań, northern Sierra de Charcas. A volcanic breccia that crops out in Aramb- Porphyritic rhyolite with quartz and sanidine pheno- erri, Nuevo Leoń(Fig. 1), consists of angular fragments crysts is abundant in the ‘‘Caopas schist,’’ exposed near of rhyodacitic to rhyolitic welded tuffs in a sandy matrix the town of same name, and in the Nazas Formation out- (Fig. 2a). These deposits are directly overlain by shallow crops of Villa Jua´rez and Sierra de San Juliań. In the Sierra marine sandstone with calcareous cement of La Joya For- de Catorce, a rhyolitic dike (Fig. 2b) exhibits porphyritic mation that represents the base of the Late Jurassic marine texture, with phenocrysts of hypidiomorphic quartz in a transgression (Mixon et al., 1959). groundmass of feldspar and quartz. The rhyolitic dike is Typical ignimbrites with notable development of fiamme strongly altered, as shown by totally kaolinitized feldspar structures are identified in outcrops at Charcas, Aramberri, phenocrysts and subsequent silicification of the rock. and Huizachal Valley (Fig. 2d and e). In La Boca Canyon, Locally, foliation with lepidoblastic texture results from the pyroclastic deposits are represented by fine-grained the presence of oriented sericite associated with dynamic tuffs that partly contain deformed accretionary lapilli. metamorphism. In the Huizachal Valley, rhyolitic domes are characterized by steeply dipping flow bands and the 4. Geochemistry development of abundant spherulites, ranging from one to several centimeters in diameter. Ten samples were collected for geochemical analysis from six exposures of pre-Oxfordian volcanic units in the 3.2. Basalts and basaltic andesites states of San Luis Potosı´, Nuevo Leoń, and Tamaulipas (Fig. 1). Sampling of the diverse lithologies in the studied In the Caopas–Rodeo area, Jones et al. (1995) describe areas was strongly restricted by the availability of accept- sparse basaltic lavas in the Nazas Formation, whereas ably fresh samples. Major and trace-element analysis of andesitic lava flows are more common in the unit known whole-rock samples was performed by ICP-MS at the Cen- as the Rodeo Formation. In the Sierra de Salinas, north tre des Recherches Pe´trographiques et Geoćhimiques of the town La Ballena, basaltic–andesitic lava is the dom- (CNRS) of Nancy, France (samples: PBLG1 from Sierra inant rock type; some lavas display fluidal porphyritic tex- de Salinas, CHRG1 from Sierra de Charcas, RCG1 from ture with highly altered, probable hornblende phenocrysts, Sierra de Catorce; MZQTG1 collected in the Mezquital scarce pyroxene, olivine, and plagioclase in a fine ground- area, north of Aramberri; SM1 from the San Marcos area mass composed of acicular plagioclase, ferromagnesian, south of Galeana, Nuevo Leoń; HZCHG1 and HZCHG2 and opaque grains. At the base of the sequence, the lavas from Huizachal Valley in Tamaulipas), and Activation are brecciated. Similar basaltic–andesitic lavas crop out Laboratories Ltd. (samples: TPZ1 from Tepozań outcrops, at Sierra de Catorce and Charcas. In the latter area, andes- northern Sierra de Charcas; RCG3 from north of Real de itic lava flows contain a brecciated zone that, given the Catorce, Sierra de Catorce; SM3 from San Marcos area presence of autoclasts arranged in a ‘‘puzzle structure,’’ is in Nuevo Leoń). The composition of analyzed samples is interpreted as an autoclastic breccia and probable peperite, summarized in Table 4. associated with a flow front or basal breccia that was The analyzed volcanic rocks are classified as intermedi- apparently engulfed by igneous material of the same com- ate to felsic after the silica content limits proposed by Pec- position, and in part mixing with wet sediment. Finally, cerillo and Taylor (1976). Following the total alkalis vs. volcanic products in the Huizachal Valley include layers silica (TAS) classification of Le Bas et al. (1986), the sam- of cinders, scoreaceous material, and andesitic lava. These ples are classified as trachyandesite, andesite, dacite, and rocks are dark to reddish brown due to oxidation and have rhyolite. The use of the TAS diagram to classify volcanic a very compact, deformed aspect, with vestiges of vesicles. rocks is restricted to fresh rocks because of the high mobil- ity of alkaline elements during secondary processes. The 3.3. Pyroclastic deposits analyzed samples have high volatile contents (LOI) and show evidence of oxidation, which basically makes them The most common rocks are andesitic to dacitic unsuitable for TAS classification. Nevertheless, the and rhyolitic pyroclastic products that show clear flow obtained chemical classification is supported by its agree- Table 3 Petrographic features observed in the studied pre-Oxfordian volcanic rocks of northeastern Mexico Rock Feature La Ballena Charcas Sierra de Catorce Aramberri Huizachal Valley La Boca Canyon

Rhyolite- Macrostructure Lava dome, dikes, flow Lava dome, lava flow Barboza-Gudin J.R. Rhyodacite banding flow banding Texture Porphyritic Glassy Components Quartz, feldspar Quartz, feldspar Alteration Kaolinite, sericite Kaolinite, opaque minerals opaque minerals minerals (oxide) ˜

Basalt– Macrostructure Lava flow, basal Lava flow, basal flow breccia Lava flow, basal flow Lava flow basal flow 49–63 (2008) 25 Sciences Earth American South of Journal / al. et o Andesite flow breccia breccia breccia Texture Airfall deposits, Porphyritic, trachytic, Porphyritic, trachytic, Vesicular laminated ash, pilotaxitic pilotaxitic porphyritic, trachytic, pilotaxitic Components Plagioclase, olivine, Plagioclase, olivine, Plagioclase, olivine, Plagioclase pyroxene, Pyroxene, pyroxene, biotite, hornblende hornblende Alteration Chlorite, epidote, Chlorite, epidote, oxide Chlorite, sericite, Opaque minerals (oxide) minerals oxide epidote, oxide Pyroclastic Macrostructure Airfall deposits, Ash flow tuff (ignimbrites), Airfall deposits, Ash flow tuff (ignimbrites), Ash flow tuff Airfall deposits, rocks laminated ash airfall deposits, welded basal laminated ash airfall deposits, laminated (ignimbrites), airfall laminated ash vitrophyre, spherulites ash, massive welded zone, deposits, spherulites vapour zone, massive welded eutaxitic structure, fiammen, vapor zone, massive zone, eutaxitic structure, volcaniclastic breccia welded zone, eutaxitic fiammen, volcaniclastic structure, fiammen, breccia rheomorphic folding, ash flows, flow banding Texture Unwelded Porphyritic, glassy, welded, Unwelded Porphyritic, glassy, welded, Glassy welded, unwelded Unwelded unwelded unwelded Components Quartz, lithic Quartz, lithic fragments, Quartz, lithic fragments, Quartz, lithic fragments, Quartz, lithic fragments, Quartz plagioclase, fragments, pumice pumice fragments pumice fragments pumice fragments pumice fragments lithic fragments, fragments pumice fragments, distorted lapillus Alteration Kaolinite, epidote, Kaolinite, sericite, epidote, Sericite, opaque minerals Kaolinite, opaque minerals Kaolinite, opaque Kaolinite,opaque minerals opaque minerals opaque minerals (oxide) (oxide) (oxide) minerals (oxide) minerals (oxide) (oxide) 55 56 J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63

Table 4 Major- and trace-element composition of pre-Oxfordian volcanic rocks, northeastern Mexico Sample PBLG1a CHRG1a TPZ1b RCG1a RCG3b MZQTG1a SM1a SM3 b HZCHG1a HZCHG2a Locality SS SCH SCH SC SC A SM SM HV HV Type Trachyandesite Dacite Andesite Dacite Rhyolite Rhyolite Trachyandesite Trachyandesite Rhyolite Rhyolite Major elements (wt%)

SiO2 53.16 65.07 54.50 62.19 78.75 71.97 52.53 54.68 77.34 76.89 TiO2 1.25 0.48 0.954 2.11 0.235 0.15 0.78 0.638 0.24 0.27 Al2O3 18.79 15.23 16.19 11.85 14.10 13.25 18.34 18.0 12.51 14.24 Fe2O3 4.54 5.6 6.37 11.97 0.69 2.06 2.94 6.33 3.16 0.57 FeO 1.92 0.79 1.12 0.66 0.13 0.55 4.59 1.12 0.06 0.22 MgO 5.21 1.53 6.06 0.75 0.09 1.09 2.23 1.86 0.26 0.36 MnO 0.11 Traces 0.081 Traces 0.005 0.02 0.12 0.098 Traces Traces CaO 2.81 0.67 5.38 2.19 Traces 1.74 4.58 4.03 0.31 0.11

Na2O 6.2 2.21 3.83 0.08 0.24 0.53 5.52 5.52 0.25 0.21 K2O 1.82 3.72 0.76 4.24 3.57 4.59 1.64 2.07 3.17 3.88 P2O5 0.32 0.16 0.19 1.34 0.05 0.04 0.3 0.32 Traces 0.06 LOI 3.55 3.02 4.17 2.35 2.19 3.83 6.42 4.78 2.49 2.74 Total 99.68 98.48 99.60 99.73 100.05 99.82 99.99 99.44 99.79 99.51 Trace elements (ppm) Rb 57.82 154.0 14 139.3 90 166.6 51.09 54 94.91 94.21 Sr 387 156 480 107 56 30 320 251 29.1 30.5 Y 28.6 36.1 18.8 32.9 14.4 16.9 20.7 27.9 31.4 23.7 Zr 212 338 129 804 113 142 126 120 230 219 Nb 12.93 17.51 5.7 27.74 8.9 7.27 5.78 4.2 9.87 11.01 Cs 5.1 12.96 6.6 10.65 8.4 7.38 2.16 4.0 2.99 3.22 Ba 538 1987 501 1069 318 709 455 227 799 607 La 20.41 38.73 15.1 128.8 34.8 25.55 38.68 39.0 27.81 41.55 Ce 47.53 81.14 33.3 331.3 68.3 46.74 76.64 79.9 60.28 82.97 Pr 5.93 9.85 4.10 35.48 7.43 4.92 8.82 8.94 7.05 9.43 Nd 23.5 38.77 17.9 129.4 27.8 16.9 34.83 35.5 27.8 35.11 Sm 5.12 7.92 4.20 20.68 5.58 3.17 6.93 7.0 5.69 5.9 Eu 1.57 2.12 1.33 8.04 1.59 0.72 2.18 1.65 1.08 0.95 Gd 5.16 6.75 4.04 13.27 4.65 2.71 5.25 5.83 4.52 4.02 Tb 0.76 1.04 0.65 1.51 0.62 0.41 0.76 0.88 0.77 0.65 Dy 4.52 6.18 3.78 6.95 2.94 2.48 3.99 4.91 4.86 4.29 Ho 1.02 1.25 0.77 1.06 0.54 0.542 0.66 1.03 1.01 0.82 Er 2.56 3.46 2.26 2.73 1.63 1.54 1.97 3.18 3.04 2.51 Tm 0.4 0.53 0.331 0.34 0.245 0.249 0.29 0.475 0.51 0.4 Yb 2.42 3.42 2.03 2.09 1.62 1.66 1.98 3.06 3.3 2.5 Lu 0.4 0.54 0.325 0.29 0.253 0.27 0.3 0.502 0.52 0.43 Hf 4.96 8.62 3.2 20.4 3.4 3.94 3.32 3.0 5.93 6.02 Ta 0.943 1.33 0.35 1.5 1.42 0.749 0.424 0.18 0.872 0.974 Th 4.58 10.07 2.10 28.55 8.44 12.54 9.25 13.8 10.44 11.56 U 1.26 1.82 0.63 5.05 1.15 2.97 2.28 3.69 1.91 3.75 CIPW normative minerals (wt.%) qz – 35.9 11.8 43.2 65.0 48.3 1.4 3.6 64.3 62.5 c 2.4 7.1 – 6.6 10.1 4.5 – 0.1 8.3 10.0 hy 9.9 6.7 16.3 6.5 0.1 3.0 8.9 8.1 1.5 0.6 ol 2.3 – – – – – – – – – Notes: SS, Sierra de Salinas; SCH, Sierra de Charcas; SC, Sierra de Catorce; A, Aramberri; SM, San Marcos; HV, Huizachal Valley. For sample locations, see Fig. 1. a Analyses performed by ICP-MS at Centre des Recherches Pe´trographiques et Geoćhimiques (CNRS) of Nancy, France. b Analysis performed by ICP-MS at Activation Laboratories, Ltd., Ancaster, Ontario, Canada. ment with the petrographic classification based on the min- sample collected in the northern Sierra de Charcas eralogical composition of the samples. (TPZ1) is a silica saturated andesite with 11.8% qz and Sample PBLG1 from Sierra de Salinas is a silica under- 16.3% hy. Samples classified as dacites were collected at saturated trachyandesite with 2.3% normative olivine and Sierra de Charcas (CHRG1) and Sierra de Catorce 9.9% normative hypersthene (hy). Samples SM1 and SM3 (RCG1); they have qz contents of 35.9% and 43.2% and from the San Marcos area in Nuevo Leoń are slightly over- hy contents of 6.7% and 6.5%, respectively. Samples RC3 saturated trachyandesite with low normative quartz (qz) (Sierra de Catorce), MZQTG1 (Aramberri area), content (1.4 and 3.6%, respectively) and 8.1–8.9% hy.A HZCHG1 and HZCHG2 (Huizachal Valley) are rhyolite, J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63 57 with variable qz contents between 48.3% and 65.0% and hy samples have different trace-element enrichments, their pat- contents of 0.1–3.0%; these rocks are peraluminous with terns are similar and show common features. The most rel- normative corundum contents varying from 4.5% to 10.1%. evant feature observed in this diagram is a well-developed The analyzed samples trend toward lower contents of negative anomaly in the elements Nb and Ta, considered most oxides (e.g., CaO, Al2O3, MgO, NaO, TiO2, and one of the most distinctive characteristics of rocks gener- P2O5) as silica increases, whereas K2O tends to be enriched ated by subduction processes (e.g., Hawkesworth et al., as silica increases and then diminish at higher silica con- 1993), and generally related to the enrichment of large- tents, as is characteristic of calc-alkaline magmas evolving ion lithophile elements (e.g., Rb, Ba, K) and light rare through the fractional crystallization of plagioclase and earth elements (e.g., La, Ce) in fluids and melts released ferromagnesian minerals. The late potassium depletion from the subducting plate to the overlying mantle. The neg- could indicate K-feldspar crystallization in the most ative anomalies in Sr, P, and Ti are most likely controlled evolved rocks. The samples represent a broad region, so by the fractionation of individual minerals, in that they they cannot be treated as comagmatic, though the observed become more pronounced in the most differentiated rocks. tendencies prompt us to interpret them as originating in a Because Sr is a fluid-mobile element, the Sr anomalies common tectonic setting. could result partly from element mobilization during alter- Trace-element abundances are shown in a multi-element ation, though the development of similar anomalies for diagram (Fig. 4), normalized against the primordial mantle relatively immobile elements such as P and Ti as differenti- composition of Sun and McDonough (1989). Although the ation proceeds indicate that mineral fractionation is the

1000 Sierra de Salinas PBLG1 (TA) Sierra de Charcas CHRG1 (D) 100 TPZ1 (A) Sierra de Catorce RCG1 (D) RCG3 (R)

Sample/Primitive mantle 1

0.1 Rb Ba Th UK Nb Ta La Ce Pr Sr Nd P Zr Hf Sm Eu Ti Gd Tb Dy Ho Er Yb Y Lu

1000 Aramberri area MZQTG1 (R) San Marcos area SM1 (TA) 100 SM3 (TA) Huizachal valley HZCHG1 (R) HZCHG2 (R)

Sample/Primitive mantle 1

0.1 Rb Ba Th UK Nb Ta La Ce Pr Sr Nd P Zr Hf Sm Eu Ti Gd Tb Dy Ho Er Yb Y Lu

Fig. 4. Normalized multielement diagrams for samples collected from six different outcrops of pre-Oxfordian volcanic rocks in northeastern Mexico (for sample location, see Fig. 1). Sample elemental abundances are normalized to the primitive mantle values of Sun and McDonough (1989). A, andesite; TA, trachyandesite; D, dacite; R, rhyolite. 58 J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63 dominant process of depletion. In the analyzed samples, Hf/3 concentrations of P could have been controlled by apatite fractionation; Sr by plagioclase, and Ti by ilmenite, rutile, or sphene (Rollinson, 1993). The patterns in this diagram do not show significant deviations caused by element mobilization, despite of the Island-arc tholeiites N-MORB observed alteration in the rocks. The trace-element patterns in the normalized multi-element diagram are strong basalts evidence of an origin of pre-Oxfordian rocks in a continen- E-MORB & tal arc setting. ic-arc within-plate Calk-alkaline tholeiites

Rare earth element (REE) abundances normalized basalts Volcan against chondrite values from Anders and Grevesse Alkaline (1989) are shown in Fig. 5. The REE can be used reliably within-plate in this type of rock because they are considered to remain basalts immobile during alteration. All samples are enriched in light REE relative to heavy REE. With the exception of sample RCG1 from Sierra de Catorce, all samples have a Th Ta relatively steep slopes for the LREE (La-Eu) and a flat pat- 10000 tern for the HREE (Gd-Lu). The most evolved samples (northeast area: MZQTG1, HZCHG1, and HZCHG2) show weak negative Eu-anomalies, indicating plagioclase Syn-cillisional 1000 fractionation. The REE pattern of sample RCG1 is charac- granites terized by a stronger enrichment in LREE relative to Within-plate granites HREE and a continuous decrease of element abundances 100 between La and Lu. Rb The REE diagrams show that the pre-Oxfordian volcanic rocks from broadly distributed localities have similar 10 compositions and probably originated in similar condi- Volcanic-arc Oceanic-ridge tions. The differences observed in sample RCG1 could be granites granites attributed to differences in source composition or melting 1 process, but the available data do not allow a more defin- 1 10 100 1000 10000 itive interpretation. Y+Nb Discrimination among tectonic settings on the basis of geochemical data has been proposed in several works Fig. 6. Tectonomagmatic discrimination diagrams showing the composition of analyzed samples. (a) Th–Ta–Hf/3 ternary diagram of Wood (1980). (e.g., Pearce and Cann, 1971, 1973; Wood, 1980; Pearce, (b) Rb vs. Y + Nb diagram after Pearce et al. (1984). Symbols as in Fig. 5.

1000 Sierra de Salinas PBLG1 (TA) Sierra de Charcas CHRG1 (D) TPZ1 (A) Sierra de Catorce 100 RCG1 (D) RCG3 (R)

Aramberri area 10 MZQTG1 (R) Sample/Chondrite San Marcos area SM1 (TA) SM3 (TA) Huizachal valley HZCHG1 (R) HZCHG2 (R) 1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Fig. 5. Rare earth element diagrams of the pre-Oxfordian volcanic units from northeastern Mexico, normalized to chondrites values of Anders and Grevesse (1989). A, andesite; TA, trachyandesite; D, dacite; R, rhyolite. J.R. Barboza-Gudin˜o et al. / Journal of South American Earth Sciences 25 (2008) 49–63 59

1982; Shervais, 1982; Meschede, 1986). The diagram Hf/3– 1. Pyroclastic volcanic products, in the form of ashflows Th–Ta of Wood (1980) is particularly useful for discrimi- and ignimbrites, airfall tuffs, breccias, and probable lah- nating altered and metamorphosed rocks because of the ars and avalanches predominate at all localities, whereas relative immobility of these elements during secondary pro- lava flows, rhyolitic domes, and dikes are present in les- cesses. This diagram was originally proposed for basic ser proportion. rocks but can be satisfactorily applied to rocks of interme- 2. The observed volcanism is of eminently subaerial char- diate to felsic composition (Wood, 1980). The pre-Oxfor- acter. The existence of large volcanoes is suggested by dian volcanic rocks analyzed in this work plot within the the presence of lahars and possible avalanche deposists. field of calc-alkaline continental volcanic arcs (Fig. 6A). Furthermore, there is evidence of separate volcanic cen- To confirm the tectonomagmatic discrimination, the data ters or volcanic fields in the region. were plotted in the Rb vs. Y + Nb diagram (Fig. 6B) pro- 3. The rocks in this study have intermediate to felsic composed by Pearce et al. (1984), which applies to rocks of gra- positions and calc-alkaline characters, as found in volca- nitic composition and is thus more indicative for the nic arcs worldwide. The abundance of silica-rich evolved rocks. Again, all pre-Oxfordian volcanic rocks plot magmas, partly K-rich, is also typical for continental in the field of volcanic arc granites (VAG), independently arcs. Moreover, the patterns observed in normalized of their composition. It is noteworthy that the samples plot multi-element diagrams are characteristic of subduc- in the same field in both diagrams, though Rb is considered tion-related rocks. a mobile element during secondary processes. 4. Two different discrimination diagrams that show the The general features of the exposed volcanic sequences, behavior of some trace elements for different rock com- the petrography of the diverse materials, and the geochemi- positions support an origin of these rocks in a continen- cal data support the conclusion that all the studied pre- tal volcanic arc. Oxfordian volcanic rocks originated in a continental arc. Our analyses provide a general idea of the compositional 5. Correlation variations among the sequences or localities, which, however, are common in volcanic arcs composed of different vol- The stratigraphic correlation of pre-Oxfordian units in canic centers. These variations also document the changes in northeastern Mexico is shown in Fig. 7. In most outcrops composition of all volcanic products during magmatic evo- of Zacatecas and San Luis Potosı´ (southwestern part of lution in space and time. The following observations suggest the studied region), the volcanic rock sequences overlie an origin of these rocks in a continental volcanic arc: Upper Triassic siliciclastic marine sequences of the Zacate-

Sierra de Caopas San Period La Ballena Charcas Miquihuana Aramberri Novillo Huizachal V. La Boca C. Alamar C. Age Ma Catorce S. Teyra Marcos Tithonian La Casita Formation 150 La Caja Formation Kimmeridgian Zuloaga Formation Zuloaga Formation 156 Zuloaga Formation Minas Viejas Formation Zuloaga Group Oxfordian Novillo Formation Minas Viejas Formation 163 Callovian La Joya Formation 169 Bathonian 175 Bajocian 181 Huizachal Group Aaleniano

Jurassic 188 Toarcian La Boca Formation 194 Nazas Formation Pliensbachian 200 Sinemurian 206 Hettangian 213 Rhaetian 219 Norian Continental Continental red beds 225 Taray Carnian Zacatecas Formation red beds (“lower Huizachal 231 Fm. Group”) Ladinian 238 Triassic Anisian 243 Scythian 248 Guacamaya Formation

Granjeno Schist Paleozoic 590 Precambrian Novillo Gneiss

Fig. 7. Stratigraphic correlation of the pre-Oxfordian units of northeastern Mexico. The studied volcanic sequences belong to the Nazas Formation, which overlies Triassic units of marine origin in central Mexico and sequences of continental origin in northeastern Mexico, and underlies or is partly interlayered with the basal parts of the Middle–Upper Jurassic redbed sequences (La Boca Formation). 60 J.R. Barboza-Gudin˜o et al. / Journal of South American Earth Sciences 25 (2008) 49–63

Fig. 8. Tectonic setting of pre-Oxfordian volcanic rocks in a model of continental volcanic arc associated with the development of the active continental margin of southwestern North America during Late Triassic–Middle Jurassic time. J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63 61 cas and Taray formations (Cantu´-Chapa, 1969; Gallo- Group and La Joya Formation, followed by the eastward Padilla et al., 1993; Go´mez-Luna et al., 1998), whereas in displacement of Mexico along the Mojave–Sonora mega- the northeastern part of the region, the underlying rocks shear (Silver and Anderson, 1974; Anderson and Silver, are continental redbed sequences of Late Triassic age 2005) and/or other Late Jurassic sinistral strike-slip faults. (Weber, 1997; Silva-Pineda and Buitroń-Sańchez, 1999). Roughly coeval to sinistral transcurrent faulting, eastward Triassic rocks are absent in localities where the volcanic subduction of a North American segment of oceanic litho- rocks directly overlie older sedimentary or metamorphic sphere took place under the Pacific plate (Barboza-Gudinõ rocks. In turn, the volcanic rocks underlie or are interbed- et al., 1998; Dickinson and Lawton, 2001), resulting in the ded in the basal part of redbeds of either La Boca Forma- development of an intraoceanic volcanic arc complex tion (Mixon et al., 1959) – dated as Sinemurian by Rueda- (Guerrero Terrane). Since Late Jurassic time, the evolution Gaxiola et al. (1993) and as Early–Middle Jurassic by of northeastern Mexico has been associated with the evolu- Fastowsky et al. (2005) – or the Upper Jurassic La Joya tion of the Gulf of Mexico Basin, and the ‘‘Cordilleran Formation (Mixon et al., 1959). Both Jurassic redbed terranes’’ in this region were covered by the Upper Juras- sequences frequently contain clasts of pre-Oxfordian volca- sic–Cretaceous Gulf sequences (e.g., Wilson and Ward, nic rocks and, in some localities, are almost solely consti- 1993). tuted by these rocks. La Joya Formation, in turn, is The stratigraphic position and existing absolute ages of overlain by the transgressive carbonate sequences of the the studied volcanic sequences indicate they belong to a Oxfordian–Kimmeridgian Zuloaga Group. Jurassic arc, related to the active Pacific continental margin The lithological similarities, stratigraphic position, and of southwestern North America, rather than to the Permo– available absolute ages of the localities studied in this work Triassic arc. This older arc has been inferred from isolated lead us to conclude that all the volcanic sequences localities east and north of the studied area under the Gulf described here are part of a Jurassic volcanic arc, related of Mexico coastal plain in Tamaulipas and near Coahuila to the active margin of southwestern North America. The and Chihuahua (Bartolini et al., 1999; Torres et al., 1999). available ages (Tables 1 and 2) indicate that the volcanic The assignment of the studied volcanic sequences to the arc was probably active for a period of 40 Ma during the Jurassic arc provides an excellent guide for discriminating Jurassic. The volcanic rocks of the described localities cor- between Triassic and Jurassic redbeds, which commonly relate with the Nazas Formation of northern Durango and have been considered a single unit (La Boca Formation Zacatecas and therefore represent a key unit for the strati- [Mixon et al., 1959]; Huizachal Formation [Carrillo-Bravo, graphic subdivision, as well as paleogeographic and paleo- 1961]; or Los San Pedros Alogroup [Rueda-Gaxiola et al., tectonic interpretations of north and northeastern Mexico. 1993), which blurs stratigraphic details and leads to a mis- understanding of the tectonic evolution and main processes 6. Conclusions acting in these periods.

The evidence presented herein indicates that the pre- Acknowledgments Oxfordian volcanic rocks of Tamaulipas and Nuevo Leoń are similar in composition, age, and tectonic setting to We acknowledge support from SEP/CONACYT (pro- those of Durango and Zacatecas and that these sequences ject 485100-5-25400T and 2002-CO2-41239) and FAI/ continue toward the western part of San Luis Potosı´. The UASLP (project C02-FAI-11-27.88) and thank J. Blickw- tectonic setting, defined on the basis of petrographic and ede and C. Bartolini for their revisions and suggestions. geochemical studies of the volcanic rocks, is a continental Detailed reviews by the JSAES-designed reviewers, T.H. arc. Fig. 8 summarizes the tectonic evolution of pre-Oxfor- Anderson and T.F. Lawton, greatly helped improve this dian units from northeastern Mexico according to their work. stratigraphic positions, geochemical–petrological charac- ter, and available paleontological and isotopic age References determinations. The Upper Triassic and Lower Jurassic rocks from Anders, E., Grevesse, N., 1989. Abundances of the elements: meteoritic northeastern Me´xico may be interpreted as related to the and solar. Geochimica et Cosmochimica Acta 53, 197–214. evolution of the Cordilleran system (Jones et al., 1995; Anderson, T.H., Silver, L.T., 2005. The Mojave-Sonora Megashear – field Bartolini et al., 2003). During the Middle–Late Triassic, and analytical studies leading to the conception and evolution of the hypothesis. In: Anderson, T.H., Nourse, J.A., McKee, J.W., Steiner, turbiditic sequences (Zacatecas Formation) related to sub- M.B. (Eds.), The Mojave-Sonora Megashear Hypothesis: Develop- marine fans formed at the western margin of North Amer- ment, Assessment and Alternatives. Geological Society of America ica; subsequent eastward subduction of the Kula plate Special Paper, vol. 393, pp. 1–50. caused the first deformation of the turbiditic sequences. Barboza-Gudinõ, J.R., Tristań-Gonza´lez, M., Torres-Hernańdez, J.R., In the Early Jurassic, the development of a continental vol- 1998. The Late Triassic–Early Jurassic active continental margin of western North America in northeastern Me´xico. Geofı´sica Internac- canic arc (recorded by the Nazas Formation) began as part ional 37 (4), 283–292. of the Cordilleran magmatic arc. Finally, the volcanic arc Barboza-Gudinõ, J.R., Tristań-Gonza´lez, M., Torres-Hernańdez, J.R., was eroded and buried beneath the Upper Huizachal 1999. Tectonic setting of pre-Oxfordian units from central and 62 J.R. Barboza-Gudinõ et al. / Journal of South American Earth Sciences 25 (2008) 49–63

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