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The Geological Society of America Field Guide 25 2012

Sierra de Catorce: Remnants of the ancient western equatorial margin of Pangea in central Mexico

José Rafael Barboza-Gudiño* Instituto de Geología, Universidad Autónoma de San Luis Potosí, Manuel Nava 5, Zona Universitaria C.P. 78240 San Luis Potosí, S.L.P, México

Roberto S. Molina-Garza Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro

Timothy F. Lawton Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA

ABSTRACT

The Sierra de Catorce in northern San Luis Potosí, Mexico, represents an uplifted block with exposures of the oldest rocks of the region which include Upper Trias- sic turbidites interpreted as deposits of a submarine fan system (“Potosí Fan”) and overlying Lower Jurassic volcanic and volcaniclastic strata interpreted as a record of the Early-Middle Jurassic volcanic arc (“Nazas Arc”) of western North America. These lower Mesozoic units, recognized in several exposures in the region, are inter- preted as remnants of the ancient western margin of Pangea prior to accretion of Late Jurassic–Early Cretaceous magmatic arc complexes and associated marginal basins that constitute the Guerrero composite terrane in western Mexico and that resulted in construction of a new Pacifi c margin. A fi eld trip in the Sierra de Catorce and sur- rounding exposures of the Upper Triassic–Lower Jurassic succession allows observa- tion and discussion of key features that demonstrate the sedimentary and tectonic history of the western equatorial margin of Pangea.

INTRODUCTION faults, which are cut also by west-northwest–striking normal faults. The Sierra de Catorce is reached by an ~200 km freeway The Sierra de Catorce, located at the eastern edge of the from San Luis Potosí to and then to Cedral, along the Mesa Central Province, directly west of the Sierra Madre Orien- northern side of the Sierra. The village of , in the tal, in northern San Luis Potosí, Mexico, represents an uplifted internal part of the sierra is reached by a 14 km long road, and block with an internal folded structure and exposures of the old- the ~2.7 km long “Tunel de Ogarrio,” constructed in 1800 as the est rocks of the region. The current horst structure of the sierra access to the old mining district located at an altitude of 2700 m is delimited by “basin and range” north-south–striking normal (Fig. 1).

*[email protected]

Barboza-Gudiño, J.R., Molina-Garza, R.S., and Lawton, T.F., 2012, Sierra de Catorce: Remnants of the ancient western equatorial margin of Pangea in central Mexico, in Aranda-Gómez, J.J., and Tolson, G., eds., [[space for volume title space for volume title space for volume title space for volume title space for volume title]]: Geological Society of America Field Guide 25, p. 1–18, doi:10.1130/2012.0025(01). For permission to copy, contact [email protected]. ©2012 The Geological Society of America. All rights reserved.

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2 Barboza-Gudiño et al.

Discovered before 1773, Real de Catorce was an important Triassic to Lower Jurassic lithostratigraphic units exposed mining district during the nineteenth and part of the twentieth cen- in the Sierra de Catorce, as well as in several places in the Mesa turies. The district attracted the attention of Mexican and foreign Central, such as Charcas, Presa de Santa Gertrudis, La Ballena, miners, as well as geoscientists. For geologists, the district offers Zacatecas, and Sierra de Teyra, are closely related to the ancient an interesting stratigraphic section which records the complex tec- western equatorial margin of Pangea. After collision and suturing tonic evolution described in several published works (del Castillo of Laurentia and Gondwana during the Late Paleozoic, the region and Aguilera-Serrano, 1895; Baker, 1922; Erben, 1956; Mixon, of what today is central Mexico occupied a remnant basin at the 1963; Bacon, 1978; Cuevas-Pérez, 1985; Zarate del Valle, 1982; westernmost culmination of the Ouachita-Marathon belt, at the López-Infanzón, 1986; Barboza-Gudiño, 1989; Barboza-Gudiño west equatorial margin of Pangea. The earliest deposits in this et al., 1999, 2004; Franco-Rubio, 1999; Hoppe, 2000). paleo-pacifi c sub-basin were Middle to Upper Triassic turbidites

28To Laredo 33To Monterrey 38 Estación CCedraledral

Í N S S A O C T

E O T P 263 A RealReal C S I La A N U Estación dede CatorceCatorce Z L Paz N Catorce A S Matehuala

Santa RRefugioefugio ddee Rita SAN LUIS POTOSÍ CoronadosCoronados S a Guadalupe nL N uev

del Carnicero ui

s o

P León otos VVillailla dede GuadalupGuadalupe í 258 258 SSanan FFranciscorancisco

CCharcasharcas Estación San Charcas Rafael

Entronque Venadoenado El Huizache

63 253 253 To Cd. del

MMoctezumoctezuma 57

16 Maíz Arista Guadalcázar

49 La illa Hidalgo slp Ballena Viillalla HidalgoHidalgo slpslp La AhualulcoAhualulco

To Zacatecas To Pendencia 248 248 Villa Hidalgo Pinos MMexquiticexquitic zac.

SANSAN LLUISUIS PPOTOSÍOTOSÍ

s

To Ríoverde To

70

Zacateca San Luis Potosí Key areas 80 57 JALJ 243 AL km 243 ISCOIS CO

OOjuelosjuelos 01020 50 GGUANAJUATOGUANAJUAUANAJUATOTO 23 28 To Queretaro 33 38

Figure 1. Locality map and access to the selected areas. fl d025-01 1st pgs page 3

Sierra de Catorce 3 known as the Zacatecas Formation and interpreted as deposits of In our interpretation, the Potosí Fan was formed in a basinal a submarine fan named the Potosí Fan (Silva-Romo et al., 2000). setting at the western margin of Pangea. As a consequence of Deposition of the fan was followed by deposition of volcanic latest Triassic–Early Jurassic subduction along this continental and volcaniclastic strata of the Lower Jurassic Nazas Formation, margin, the Potosí Fan was deformed and uplifted, so that the fi rst interpreted as remnants of the Early Jurassic continental volcanic volcanic deposits of the Nazas Formation are subaerial and rest arc, known also as “Nazas Arc.” Overlying the Nazas succession, unconformably on the Triassic Zacatecas Formation. The Nazas the La Joya Formation, consisting of Middle to Upper Jurassic Formation is unaffected by the intense folding and thrusting alluvial to lagoonal and shallow marine deposits, represents a registered in the Triassic rocks. Deposits of La Joya Formation basal transgressive succession in the region (Michalzik, 1988). represent development of an erosional unconformity following This unit grades upsection to the Upper Jurassic–Cretaceous the main period of volcanic activity and erosion of the arc in an carbonate and evaporitic successions of the Gulf Series which extensional setting. are widely distributed from north-central to northeastern Mexico The main goal of this excursion is to visit some of the Lower

(Figs. 2 and 3). Mesozoic stratigraphic units (Upper Triassic–Middle Jurassic) 101°

Monterrey G.G. PPalacioalacio COAHUILA N Villa Torreónoorreónrreón JJuarezuarez Saltillo SierraS de Jimulco ie r NUEVO ra d e LEÓN J im S u i lc e o r

S r a SierraS de S.S i ie r . San ra S e d a GaleanaGaleana e Rodeo n RamirezR JJulián S.MARCOSS.MARCOS r CaopasCaopas DURANGO a u m li i S. de Teyra á r r n M ez a a

d La Boca

Canyon

M r

e 24°24° a AramberriAramberri -

s d E o . L r n eL oC MiquihuanaMiquihuana l

Al y r S e a n Mesa Central B c b aO r aA e RC Canyon o CCaballeros t a

O HuizachalHuizachal C

e MatehualaMatehuala VValleyalleyalley dde Catorce

O r a

r

r

e i c i

SierraS e

c n i . de TAMAULIPASTAMAULIPAS ZACATECAS S 23° d t Charcas CharcasCharcas

e a 50 km n l t SAN LUIS POTOSÍ a Zacatecas l s a n i linasl a S

LaLa BBallenaallena e Sa d

. SanSan LuisLuis PotosíPotosí S.S d Jurassic-Cretaceous volcano- Cenozoic (Neogene) cover sedimentary sequence

Cenozoic volcanics Pre-Mesozoic rocks and UpperTriassic- Lower Jurassic marine-continental red beds and volcanics Upper Jurassic-Cretaceous Thrust Normal fault sedimentary cover fault

Fig ure 2. Synthesis of regional geology. fl d025-01 1st pgs page 4

4 Barboza-Gudiño et al.

SERIES

Ma System

E R A E R STAGE

HOLOCENE 0.01 Alluvium

QUATER. PLEISTOCENE 1.68 Conglomerate PLIOCENE 5.1 MIOCENE 23.7 Basalt OLIGOCENE 37 EOCENE

TERTIARY 55 Quartzmonzonit C E N O Z I PALEOCENE 53 Ma

PALEOGENE NEOGENE 67 MAASTRICHTIAN 71.5 CAMPANIAN 83 Mudstone - Sandstone SANTONIAN 86 (Caracol Formation)

SENONIAN CONIACIAN 89 Limestone - Mudstone TURONIAN (Indidura Formation) 91 Limestone CENOMANIAN (Cuesta del Cura Formation) 97.5

ALBIAN 108 Limestone - Marl (Formación Tamaulipas Superior Formation) APTIAN Marl -mudstone (La Peña Formation)

CRETAEOUS 114

BARREMIAN Limestone

N A

I (Tamaulipas Inferior Formation)

LOWERHAUTERIVIAN UPPER

M

O C

O VALANGINIAN

E Marl - Mudstone N (Taraises Formation) BERRIASIAN 140 Siltstone - Marl TITHONIAN (La Caja Formation)

UPPER KIMMERIDGIAN Limestone (Zuloaga Formation ) OXFORDIAN 160 CALLOVIAN Siltstone-Sandstone BATHONIAN

M E S O Z I C Polimictic Conglomerate- La Joya Formation BAJOCIAN breccia

M IDDLE Rhyolitic Porphyr AALENIAN (174.7 ± 1.3) JURASSIC 184 Dacit TOARCIAN

PLIENSBACHIAN Volcanic succession (Nazas Formation) Andesit SINEMURIAN LOWER andesític- HETANGIAN basaltic dike 210 Sandstone-mudstone Cerro El Mazo beds UPPER 230 siliciclastic succession

MIDDLE (”Fm. Zacatecas”) 243

TRIASSIC LOWER 250 PERMIAN 290 PENNSYLVANIAN No deposits

A L E O Z I C L A MISSISSIPPIAN P 360 CARBON.

Figure 3. Stratigraphic column of the Sierra de Catorce. fl d025-01 1st pgs page 5

Sierra de Catorce 5 which crop out in several places of the Mesa Central province, mation of the Potosí Fan is not well understood, but accretion- and whose tectonic setting is interpreted as linked to the evolution ary prism and subduction complex settings have been proposed of the ancient margin of Pangea, prior to opening of the Gulf of (Centeno-García, 2005; Anderson et al., 2005). Although this Mexico. These units are particularly well preserved in the Sierra interpretation is somewhat speculative, it is clear that shortening de Charcas, and nicely exposed in Cañón General of the Sierra and thrust faulting registered in the Triassic succession, predated de Catorce. In Cañón General, exposures of the complete strati- less deformed Jurassic arc volcanic rocks. graphic column of the region allow unambiguous reconstruction of tectonic setting and, therefore, they are of great interest for DAY 1 understanding the western Pangea and Cordilleran evolution. We will show that the Potosí Fan is a quartz-rich turbidite Stop 1.1. Charcas: 200 m Trip along the Arroyo San Rafael succession composed of detritus eroded from the East Mexico (274188 2553577) Arc (Dickinson and Lawton, 2001), as well as from Grenville and Pan African basement sources. This suggests that basement The Arroyo San Rafael is placed few kilometers west of Char- uplifts associated with Triassic rifting existed at that time. Defor- cas, San Luis Potosí (Fig. 4) and drains a large range located in

23°°10′ 23°°10′

′

0

1

°

1°

B 10 Cenozoic cover

A r r o y o

L a s

P a l m a s Late Jurassic- Cretaceous limestone LA TRINIDAD A rr MORELOS oy o C ha rca s V ie jas SAN ANTONIO DE LAS HUERTAS Lower to Middle Jurassic redbeds Figure 4. Geological map of the La 23°°05′ Trinidad Anticlinorium, west of Char- cas showing the location of Arroyo San Rafael and Arroyo San Antonio. EL PERDIDO Lower Jurassic SAN RAFAEL EL LLANO POTRERO volcanic rocks EL LLANO

Triassic marine succession

N Sierra de Catorce C Matehuala B Sierra de Charcas Zacatecas A Sierra de Salinas San LuisPotosí Rioverde Valles 0 5 500 1 10000 200200 kmkm Normal fault

1 2

3 San Luis Potosí

′

5

1 2 km

°

101° 23°°00′ fl d025-01 1st pgs page 6

6 Barboza-Gudiño et al.

an uplifted area known as La Trinidad Anticlinorium. It contains source are as follows: 290–220 Ma (Permo-Triassic east Mexico the best preserved exposures of Upper Triassic strata (Zacatecas magmatic arc); 440–400 Ma (peri-Gondwanan magmatic assem- Formation, after Martínez-Pérez, 1972, or La Ballena Formation, blages); 700–500 Ma (Pan-African-Brasiliano basement); and following Centeno-García and Silva-Romo, 1997), consisting of 1300–900 Ma (Grenvillian basement). massive thick-bedded sandstone, conglomeratic sandstone, and The Triassic turbiditic succession exposed west of Char- turbidites with partially developed Bouma sequences and inter- cas is interpreted as part of the “Potosí Fan” (Silva-Romo et al., bedded subordinate shales. Some beds contain common graded 2000; Centeno-García, 2005), a submarine fan deposited in a bedding. Other sedimentary structures include load and groove basinal setting during Middle to Late Triassic at the paleo-margin casts –which constitute the most common sole marks and slump of Pangea or in a remnant basin at the westernmost culmination structures. The clastic components of the sandstone are quartz, of the Ouachita-Marathon belt. feldspar, detrital mica, and shale intraclasts in a matrix of detrital and diagenetic quartz, muscovite+illite, and chlorite (Hoppe et Stop 1.2. Charcas: 300 m Trip along the Arroyo al., 2002). The resulting lithofacies assemblage corresponds to San Antonio “facies A,” “facies B,” and “facies C” of Mutti and Ricci Lucchi (276995 2555811) (1972), interpreted as channel and channel margin environments (Fig. 5). Subordinate facies “D,” “E,” “F,” and “G” (suprafan West of Charcas, in the Arroyo San Antonio, at the eastern lobe, levee, and inter-channel fl ats), corresponding to a midfan or extreme of La Trinidad Anticlinorium, there are exposures of a suprafan zone, are especially well exposed at Arroyo San Rafael. volcanic succession of Early to Middle Jurassic age. Although the Also interesting are excellent exposures of a wild fl ysch, consist- volcanic rocks in Arroyo San Antonio are in tectonic contact with ing of decimeter-sized to several meter–sized intraformational the Triassic Zacatecas Formation, in other sections measured in sandstone blocks, embedded in a sandstone-siltstone and mud- the region, the volcanic succession rests unconformably on the stone matrix, which correspond to facies “F” of Mutti and Ricci Triassic rocks. The volcanic rocks, exposed in several isolated Lucchi (1972). outcrops from west to east along the Arroyo San Antonio, con- A Late Triassic age for this succession is well established sist of rhyodacitic ash fl ow tuff (ignimbrites), welded basal vit- through uncommon ammonites (Early Carnian Juvavites sp. rophyre, distorted spherulites and vapor zones, massive welded reported by Cantú-Chapa, 1969, as well as Carnian Anatomites zones, volcaniclastic breccias and epiclastic strata (Fig. 7). The aff. herbichi and Aulacoceras sp., reported by Gallo-Padilla et al., most common structures observed in the fi eld are eutaxitic struc- 1993), conodonts (Carnian Neogondolella polygnatiformis and tures, fi amme, the already described spherulites, lithophysae, and Epigondolella primitia, reported by Cuevas-Pérez, 1985), and collapsed pumice. Petrographic and reconnaissance geochemical results of detrital zircon geochronology (Barboza-Gudiño et al., studies in several localities of comparable rocks in the region, 2010) that yielded an Early Triassic maximal depositional age of included rocks of Charcas (Barboza-Gudiño et al., 2008) indicate ca. 230 Ma for a sample of medium-grained sandstone collected a continental volcanic arc setting. from the Arroyo San Rafael. The main clusters of individual To the west along the arroyo, basaltic-andesitic lava fl ows zircon ages reported for this sample (Fig. 6) and their possible are well exposed; commonly they occur as brecciated lava fl ows, which contain angular fragments with common puzzle-structure consisting of tightly packed angular clasts. Petrographic exami- nation reveals porphyritic, trachytic, and pilotaxitic textures. Sev- eral lithic fragments that occur in the previously described rhyo- dacitic fl ows are trachytic andesites, suggesting that the andesitic lava fl ows are older than the rhyodacitic pyroclastic fl ows and were incorporated in the rising magmas that erupted to form the pyroclastic succession. The andesitic lava fl ows unconformably underlie clastic deposits of the Callovian-Oxfordian La Joya For- mation. This clastic sequence grades upwards into limestones of the Oxfordian Zuloaga Formation. La Joya consists of sandstone, conglomerate, and mudstones. Conglomerate clasts are domi- nated by volcanic rocks, which we infer were derived from the Nazas Formation. The age of the volcanic succession is well established by a U-Pb date for a rhyodacitic ignimbrite, 29 concordant zircon ages from the rock yielded a mean age of 176.8 +4.9/–1.7 Ma, a rather Toarcian/Aalenian boundary age (Zavala-Monsiváis et Figure 5. General features of the Triassic turbiditic sequence exposed al., 2012). An Early to Middle Jurassic age for the succession along the Arroyo San Rafael, west of Charcas. is likewise supported by its stratigraphic relations, in which the fl d025-01 1st pgs page 7

Sierra de Catorce 7

116666 MMaa Middle Jurassic La Joya Formation Miquihuana 210210 MMaa Lower Jurassic C. El Mazo beds Los Catorce 222525 MMaa Upper Triassic Charcas 223838

Upper Triassic Los Catorce Figure 6. Plots of Paleozoic to Juras- sic published detrital zircon data from northeastern Mexico. The plots are 219219 Upper Triassic San Marcos probability curves, showing maximal deposition age of the sediments. 215215 MMaa Upper Triassic La Boca

530530 MMaa PaleozoicPaleozoic Aramberri

458458 MMaa PaleozoicPaleozoic CCaballerosaballeros

0 1.0Age (Ga) 2.0 3.0

volcanic succession overlies the Late Triassic Zacatecas Forma- San Luis Potosí State (Table 1). These volcanic rocks are thus tion and unconformably underlies the Callovian–early Oxfordian considered part of the Early Jurassic continental volcanic arc, La Joya Formation. located along the paleo-margin of Pangea, possibly extending The Nazas volcanic succession has been correlated by litho- from California, through Sonora (Mauel et al., 2011), and into logical similarity and stratigraphic position with volcanic succes- eastern Mexico. sions exposed in Durango, Zacatecas, and Coahuila (Nazas For- mation), and with volcanic-volcaniclastic successions exposed in DAY 2 southern Nuevo León, Tamaulipas, and other localities in western Stop 2.1. Real de Catorce (“Mirador”) (310202 2622353)

The point known as “Mirador,” at the entrance to the Ogar- rio tunnel, offers a good regional overview of the region’s rocks and style of deformation of the Jurassic-Cretaceous succession of the Sierra de Catorce uplift. Cretaceous limestones are well exposed along the road to Real de Catorce, and at this point Upper Jurassic medium-bedded limestone of the upper Oxford- ian Zuloaga Formation (Reyeros de Castillo, 1978) and marls of the Kimmeridgian-Berriasian La Caja Formation (Olóriz, et al., 1999) are well exposed. They are intensely deformed by folding and thrusting as a result of Laramide shortening, which also pro- duced uplift of the sierra and detachment of its mostly calcare- ous cover. The detachment zone is at the contact between shale of the top of La Joya Formation and limestone of the Zuloaga Formation. This weak zone allowed independent deformation of Figure 7. Outcrops of the Nazas Formation. Arroyo San Antonio, west of Charcas. (A) Pyroclastic fl ow; (B) vitrophyre at the base of a young- the cover into north-northwest–trending asymmetrical and over- er welded ash fl ow tuff or ignimbrite; (C) spherulitic horizon of the turned fold structures. The general asymmetry of these folds is same ash fl ow tuff; and (D) ignimbrite. to the east-northeast. The age of folding is constrained between fl d025-01 1st pgs page 8

8 Barboza-Gudiño et al.

TABLE 1. REPRESENTATIVE ISOTOPIC AGES OF LOWER TO MIDDLE JURASSIC VOLCANIC ROCKS FROM THE NAZAS FORMATION IN NORTH-CENTRAL TO NORTHEASTERN MEXICO

Locality State Rock type Method Material dated Age Source (Ma) Caopas Zacatecas Meta-rhyolitic sub-volcanic Rb-Sr Whole rock 195 ± 20 Fries and Rincón-Orta (1965) Caopas Zacatecas Meta-rhyolitic sub-volcanic Rb-Sr Whole rock 156 ± 40 Fries and Rincón-Orta (1965) Caopas Zacatecas Meta-andesite (rodeo formation) K-Ar Hornblende 183 ± 8 López-Infanzón (1986) Caopas Zacatecas Meta-rhyolitic sub-volcanic U-Pb Zircon 158 ± 4 Jones et al. (1995) Villa Juárez Durango Rhyolite 40Ar/39Ar Plagioclase 195.3 ± 5.5 Bartolini and Spell, (1997) Catorce San Luis Potosí Rhyolite U-Pb Zircon 174.7 ± 1.3 Barboza-Gudiño et al. (2004) Charcas San Luis Potosí Rhyolitic ignimbrite U-Pb Zircon 176.8 +4.9/–1.7 Zavala-Monsiváis et al. (2012) Coherent grains Huizachal Tamaulipas Rhyolitic ash flow U-Pb Zircon 189.0 ± 0.2 Fastovsky et al. (2005) Aramberri Nuevo León Rhyolitic ignimbrite U-Pb Zircon 193.1 ± 0.3 Barboza-Gudiño et al. (2008) Huizachal Tamaulipas Rhyolite U-Pb Zircon 194.1 +4.1/–4.5 Zavala-Monsiváis et al. (2009) Aramberri Nuevo León Rhyolitic ignimbrite U-Pb Zircon 189.5 ± 3.8 Zavala-Monsiváis et al. (2009) Note: See Figure 2 for location of the areas. the Campanian-Maastrichtian folded successions and the old- The different facies of La Joya Formation record several est unfolded rocks or structures in the area. Specifi cally, for the depositional environments, interpreted by Michalzik (1988) as Sierra de Catorce, unfolded rocks are middle Eocene quartz- follows: fanglomerates, channels and distal alluvial fan con- monzonitie dikes. These dikes also crop out in the “Mirador” glomerates, shallow-marine carbonates and caliche concretions point as a porphyritic rock consisting of idiomorphic centimeter- and crusts, fi ne-grained alluvial plain deposits, and lagoonal to sized white feldspar and plagioclase crystals and minor quartz in sabkha evaporites. a microcrystalline, gelb to gray and green matrix. The age of the La Joya Formation is known only from its stratigraphic position, overlying Lower Jurassic volcanic rocks, Stop 2.2. Real de Catorce (“Puerta del Sol”) and underlying Oxfordian limestone of the Zuloaga Formation. (306924 2621952) Detrital zircon geochronology results yielded a maximal depo- sitional age of ca. 170 Ma, a rather Bajocian age (Table 2; Fig. View of the Cañón General (General Canyon of Sierra de 9), in agreement with its stratigraphic position and the Early to Catorce): Polymictic conglomerate and conglomeratic red sand- Middle Jurassic age of volcanic rocks exposed northwest of Real stones of La Joya Formation (Callovian-Oxfordian) form a prom- de Catorce and contained as clastic fragments in a basal brec- inent cliff west of Real de Catorce, and offer a panoramic view cia of La Joya Formation. Rubio-Cisneros and Lawton (2011) of the stratigraphic units exposed in the Cañón General (Fig. 8). reported a single younger grain age of 163.6 ± 2.6 Ma, a rather The units include from base to top, marine beds of the Upper Callovian age from La Joya Formation in the Huizachal Valley. Triassic Zacatecas Formation, Lower Jurassic marine marginal facies, and interlayered greenstone informally named “Cerro El Stop 2.3. Cañada Ojo de Agua (El Salto) Mazo beds,” rhyolitic, dacitic, and andesitic volcanic rocks of (306272 2625008) the Lower to Middle Jurassic Nazas Formation, continental to shallow marine conglomerate and red sandstone of La Joya For- About 5 km north-northwest of Real de Catorce, at Cañada mation, and limestone of the Zuloaga Formation. The basal part Ojo de Agua or El Salto, a conspicuous rhyolitie dike exhibiting of the Zuloaga Formation constitutes an intensely sheared zone, steeply dipping banding underlies La Joya Formation. At the same which resulted from Laramide detachment faulting. locality, La Joya Formation is composed of conglomerates with a The La Joya Formation was defi ned by Mixon et al. (1959) variety of volcanic rocks as angular to subrounded pebbles and cob- as a Middle to Late Jurassic conglomeratic redbed sequence bles up to several cm in diameter. These include rhyolitic fragments exposed in the Huizachal-Peregrina Anticlinorium. They pro- identical to the rhyolite of the dike. The rhyolite has a porphyritic posed a type locality at Rancho La Joya Verde in the Huizachal texture, with hypidiomorphic quartz phenocrysts in a groundmass Valley, Tamaulipas, ~200 km east of Real de Catorce. La Joya of totally kaolinitized feldspar. The rhyolitic dike is strongly altered Formation consists of an upward fi ning megasequence composed and affected by subsequent silicifi cation of the rock. Locally, folia- of a basal polymictic breccia and conglomerate-fanglomerate tion with lepidoblastic texture results from the occurrence of ori- facies overlain by red sandstone, siltstone, and mudstone. The ented sericite associated with a dynamic metamorphism. clastic components of La Joya basal breccia in Real de Catorce The analysis of three zircon grains from a sample of a rhy- are volcanic, sedimentary, and light-colored metamorphic rocks, olite collected at this point yielded an age of 174 Ma, a rather as well as white hydrothermal quartz. In the Huizachal area, early Aalenian age on the basis of a single concordant zircon, and the main detrital components are gneiss, schist or phyllite, and quartz. La Joya Formation varies locally in its thickness, ranging from a few meters to as much as 200–300 m, and is absent in some localities in northeastern Mexico. Figure 8. Geological map of the northwestern Sierra de Catorce. fl d025-01 1st pgs page 9

′ Sierra de Catorce 9

100°5 Kt Cz-Lu

T-Q al N T-Q al

Kace Cz 2200

Kapa Cz-Mg Kap Mg-Lu Alluvium (silt, sand, gravel) T-Q al Neogene-Quaternary Jco Lm-Ar

70 Tmi Ba Basalt, Miocene

Limestone-shale 71 Kt Cz-Lu Upper Cretaceous 23°45′ 23 45 (Turonian/Indidura Formation ) 73 Jbac Thin bedded limestone with black chert Khba Cz Kace Cz

Cgp C. LA CUEVA DEL SOL bands (Albian-Cenomanian, 2800 A. El Jamoncillo Cuesta del Cura Formation) T-Q al e Tmi Ba Padr 43 Limestone-marl (Upper Aptian-Albian, Cañada Ojo de Agua C. LA CAMPANA Kapa Cz-Mg C. EL PAISANO Tamaulipas Superior Formation) POBLAZON 13 C. LA CALABAZA C. EL AGUILA Marl-Shale (Aptian, Kap Mg-Lu La Peña Formation )

89 0 Kace Cz JmRi 280 Kapa Cz-Mg Thick bedded limestone, EL SALTO Khba Cz chert nodules (Hauterivian- 2200 TR Lu-Ar Barremian, Tamaulipas Inferior Formation) Jok Cz KbevMg-Lu 8 A. El Tunalillo KbevMg-Lu Marl-shale (Berriasian-Valanginian, Taraises Formation) Jkt Lm-Mg A. El Coyote 85 Siltstone, marl (Kimmeridgian-Tithonian, Jkt Lm-Mg Tmi Ba C. EL INDIO C. PUERTO La Caja Formaction) DEL AIRE

00

30 Limestone (Oxfordian-Kimmeridgian, Kapa Jok Cz Zuloaga Formation) Cz-Mg LA BUFA 89 C. LA DESCUBRIDORA Red siltstone-sandstone (Callovian- 65 52 20 Jkt Lm-Mg Jco Lm-Ar Oxfordian, Upper part of La Joya TR Lu-Gr Formation) Khba Cz 88 2800 Ji Ar-Lu 65 Polygmictic Conglomerate-breccia Tmi Ba A′ JbacCgp A ELMAZO LOS CATORCE (Bathoniano-Calloviano, Lower part of La TO Ge Joya Formation) EDUC neral 83 SOCAVON DE C. EL ZANJON ACU d e CatorPURISIMA SANTA CRUZ Tmi Ba JmRi Rhyolite (Nazas Formation) DE CARRETAS Jok Cz ce 29 43 Volcanics dacitic-andesitic (Lower Jurassic) REAL DE CA T ORCE JimA 7 C. EL RUCIO (Nazas Formation) Jok Cz Sandstone and shale A. El Pino 85 30 Ji Ar-Lu PUERTO DE PALILLO (Lower Jurassic, Cerro El Mazo beds) JbacCgp ALAMITOS 2 800 C. LA Siliciclastic turbiditic succession DEL PALILLO 55 MISIÓN TR Lu-Gr Upper Triassic 18 2800 (Zacatecas Formation) C. EL QUEMADO Dykes, cuarzo-monzonite (Eocene)

A. El Tecolote 50 70 00

2800 30 detachment 23°40′ BORREGO C, GRANDE 25 CAÑON EL 80 23°40′ Jco Lm-Ar

C. EL ARCO 35 Normal fault Khba Cz 04 Jco Lm-Ar Inferred normal fault 2000 62

anticline T-Q al JimA JbacCgp syncline 23 65 Kapa Cz-Mg SAN JUAN DE nima 0 topography A 0 El 3

A. 2 2400 MATANZAS 12 A 18 A. Matanzas . S LAS ADJUNTAS an Ign bedding 25

′ a Kt Cz-Lu Jok Cz cio cleavage (S1)

100°5 frequently subparallel to bedding 75 (S0) A A′ cleavage (S ) 2800 38 2 2600 A A′ 2400 section 2200 2000

1 km fl d025-01 1st pgs page 10

10 Barboza-Gudiño et al. TABLE 2. DETRITAL ZIRCON AGES FOR A SAMPLE FROM LA JOYA FORMATION, REAL DE CATORCE AREA

Apparent ages Isotope ratios U 206Pb/ 206Pb*/ ± ± Error (Ma) Best age ± U/Th ppm 204Pb 207Pb* % 207Pb*/ ± 206Pb*/ (%) corr. 206Pb*/ ± 207Pb*/ ± 206Pb*/ ± (Ma) Ma 235U* % 238U 238U* (Ma) 235U (Ma) 207Pb* (Ma) 1 357 15512 1.5 20.4754 3.3 0.1759 3.5 0.0261 1.1 0.32 166.2 1.9 164.5 5.4 140.1 78.6 166.2 1.9 2 194 5229 1.8 19.5030 11.7 0.1929 11.9 0.0273 2.4 0.20 173.5 4.1 179.1 19.6 253.2 269.3 173.5 4.1 3 258 10826 2.1 20.5031 3.5 0.1901 4.0 0.0283 1.9 0.48 179.7 3.4 176.7 6.5 136.9 82.2 179.7 3.4 4 132 3724 1.0 17.2239 12.8 0.2267 13.2 0.0283 3.0 0.23 180.0 5.4 207.5 24.7 532.0 281.7 180.0 5.4 5 507 12947 1.8 19.3236 3.7 0.2197 3.8 0.0308 1.0 0.26 195.5 1.9 201.6 7.0 274.4 84.2 195.5 1.9 6 181 10374 2.0 19.9201 3.4 0.2357 3.5 0.0341 1.0 0.29 215.9 2.1 214.9 6.8 204.3 78.3 215.9 2.1 7 254 7721 1.3 18.3306 2.9 0.2877 3.7 0.0383 2.4 0.63 242.0 5.6 256.8 8.4 393.9 64.6 242.0 5.6 8 684 25725 1.1 19.0884 1.8 0.2779 3.7 0.0385 3.3 0.88 243.4 7.8 249.0 8.2 302.4 40.7 243.4 7.8 9 253 4403 0.5 14.9900 18.6 0.3642 18.9 0.0396 2.9 0.16 250.3 7.2 315.3 51.2 828.7 392.0 250.3 7.2 10 207 10826 1.4 19.7918 5.8 0.2761 5.9 0.0396 1.3 0.21 250.5 3.1 247.5 12.9 219.2 133.3 250.5 3.1 11 80 4508 1.5 22.4680 8.3 0.2442 8.4 0.0398 1.4 0.16 251.6 3.4 221.9 16.7 -82.5 202.6 251.6 3.4 12 273 18603 2.0 19.9656 3.6 0.2752 4.1 0.0399 2.1 0.50 251.9 5.1 246.9 9.1 199.0 83.0 251.9 5.1 13 477 26838 1.9 19.3655 3.8 0.2844 4.0 0.0399 1.3 0.32 252.5 3.2 254.1 9.0 269.4 87.3 252.5 3.2 14 166 7756 1.2 19.8495 9.6 0.2783 9.7 0.0401 1.8 0.19 253.2 4.6 249.3 21.5 212.5 222.1 253.2 4.6 15 298 19761 1.1 19.9041 2.5 0.2788 3.5 0.0402 2.4 0.69 254.4 6.0 249.7 7.7 206.1 58.7 254.4 6.0 16 172 9125 0.9 18.9678 13.0 0.2930 14.8 0.0403 7.1 0.48 254.7 17.7 260.9 34.1 316.8 296.6 254.7 17.7 17 403 26992 1.6 19.6869 1.9 0.2826 3.1 0.0403 2.4 0.79 255.0 6.1 252.7 6.9 231.5 43.9 255.0 6.1 18 282 17070 1.0 19.4055 5.3 0.2869 5.4 0.0404 1.3 0.24 255.1 3.3 256.1 12.3 264.7 120.9 255.1 3.3 19 679 16618 0.7 18.7672 1.9 0.3007 2.4 0.0409 1.4 0.57 258.5 3.4 266.9 5.5 340.9 43.6 258.5 3.4 20 174 9559 1.5 19.8414 4.7 0.2886 5.4 0.0415 2.6 0.48 262.3 6.7 257.4 12.3 213.4 110.0 262.3 6.7 21 151 6395 1.1 17.8541 7.6 0.3212 7.7 0.0416 1.2 0.15 262.7 3.0 282.8 19.1 452.7 169.7 262.7 3.0 22 320 15386 1.4 19.4941 6.1 0.2974 6.3 0.0420 1.5 0.24 265.5 3.9 264.3 14.7 254.2 141.3 265.5 3.9 23 336 8666 1.5 18.8629 4.6 0.3083 4.9 0.0422 1.6 0.32 266.3 4.1 272.9 11.7 329.4 105.1 266.3 4.1 24 603 30580 1.3 19.1531 2.0 0.3048 2.2 0.0423 1.0 0.45 267.3 2.6 270.2 5.3 294.6 45.9 267.3 2.6 25 82 5121 1.6 19.4898 10.0 0.3061 10.1 0.0433 1.0 0.10 273.1 2.7 271.2 23.9 254.7 230.6 273.1 2.7 26 484 30114 1.2 18.8660 1.5 0.3215 1.8 0.0440 1.0 0.55 277.5 2.7 283.0 4.5 329.0 34.4 277.5 2.7 27 83 3455 1.4 17.9821 9.5 0.3466 9.9 0.0452 2.7 0.28 285.0 7.6 302.2 25.8 436.8 211.8 285.0 7.6 28 337 21476 4.7 19.7858 3.9 0.3165 4.5 0.0454 2.1 0.48 286.4 6.0 279.2 10.9 219.9 91.3 286.4 6.0 29 954 28868 1.3 19.3410 2.4 0.3243 4.1 0.0455 3.3 0.81 286.8 9.3 285.2 10.2 272.3 54.8 286.8 9.3 30 96 7014 2.3 19.3639 10.3 0.3307 10.4 0.0464 1.5 0.14 292.6 4.3 290.1 26.3 269.6 236.6 292.6 4.3 31 237 16048 1.7 18.2202 6.6 0.3556 6.7 0.0470 1.1 0.16 296.0 3.2 308.9 17.8 407.5 147.8 296.0 3.2 32 137 7032 2.6 18.3147 5.8 0.3628 5.9 0.0482 1.2 0.21 303.4 3.6 314.3 16.0 395.9 130.3 303.4 3.6 33 38 3563 1.7 17.8392 17.2 0.4110 17.2 0.0532 1.0 0.06 334.0 3.3 349.6 51.0 454.6 384.5 334.0 3.3 34 349 57897 3.7 17.1415 2.8 0.6897 3.0 0.0857 1.2 0.40 530.3 6.2 532.6 12.5 542.5 60.2 530.3 6.2 35 625 57313 11.2 17.2178 1.8 0.6920 3.3 0.0864 2.7 0.83 534.3 13.8 534.0 13.5 532.7 39.9 534.3 13.8 36 329 51643 3.7 16.2093 1.8 0.8907 2.1 0.1047 1.0 0.48 642.0 6.1 646.8 10.0 663.5 39.3 642.0 6.1 37 80 10052 1.9 15.6931 2.1 0.9799 2.5 0.1115 1.4 0.55 681.6 9.0 693.5 12.6 732.4 44.3 681.6 9.0 38 148 15071 2.4 13.8840 2.3 1.1450 4.6 0.1153 4.0 0.86 703.4 26.5 774.9 25.0 986.6 47.6 703.4 26.5 39 474 24035 2.9 15.5665 2.7 1.0426 4.2 0.1177 3.3 0.77 717.3 22.1 725.2 21.8 749.5 56.2 717.3 22.1 40 529 76013 7.2 14.5866 2.7 1.2233 5.3 0.1294 4.6 0.86 784.5 34.0 811.3 29.8 885.4 55.4 784.5 34.0 41 369 73931 1.4 14.4126 2.5 1.3920 2.8 0.1455 1.1 0.41 875.7 9.3 885.6 16.3 910.2 51.9 875.7 9.3 42 262 52129 6.6 14.1546 2.5 1.4983 3.7 0.1538 2.7 0.73 922.3 23.5 929.7 22.7 947.2 52.0 922.3 23.5 43 109 33943 1.5 14.2724 2.6 1.5118 3.1 0.1565 1.8 0.56 937.3 15.3 935.2 19.1 930.2 53.1 937.3 15.3 44 41 10409 1.4 14.1585 3.7 1.5547 3.9 0.1597 1.2 0.31 954.8 10.5 952.4 23.9 946.7 75.4 954.8 10.5 45 61 17546 1.2 14.0023 2.9 1.6260 5.3 0.1651 4.5 0.83 985.2 40.7 980.3 33.6 969.3 60.1 969.3 60.1 46 616 154448 4.4 13.9353 1.2 1.6231 1.8 0.1640 1.4 0.75 979.2 12.5 979.2 11.5 979.1 24.5 979.1 24.5 47 692 155309 28.6 13.9340 2.8 1.6200 3.2 0.1637 1.6 0.50 977.4 14.4 978.0 20.2 979.3 56.8 979.3 56.8 (continued) fl d025-01 1st pgs page 11

Sierra de Catorce 11 TABLE 2. DETRITAL ZIRCON AGES FOR A SAMPLE FROM LA JOYA FORMATION, REAL DE CATORCE AREA (continued)

Apparent ages Isotope ratios U 206Pb/ 206Pb*/ ± ± Error (Ma) Best age ± U/Th ppm 204Pb 207Pb* % 207Pb*/ ± 206Pb*/ (%) corr. 206Pb*/ ± 207Pb*/ ± 206Pb*/ ± (Ma) Ma 235U* % 238U 238U* (Ma) 235U (Ma) 207Pb* (Ma) 49 186 34213 1.6 13.7837 2.2 1.6766 2.6 0.1676 1.4 0.54 998.9 12.9 999.7 16.4 1001.4 43.9 1001.4 43.9 50 302 79408 2.5 13.7106 1.9 1.6899 2.2 0.1680 1.1 0.50 1001.3 10.2 1004.7 14.2 1012.2 39.1 1012.2 39.1 51 229 54282 1.9 13.6443 1.0 1.7970 1.4 0.1778 1.0 0.71 1055.1 9.7 1044.4 9.2 1022.0 20.3 1022.0 20.3 52 166 47282 8.7 13.5813 2.1 1.8322 3.2 0.1805 2.4 0.76 1069.6 24.0 1057.1 21.1 1031.3 42.1 1031.3 42.1 53 92 25092 2.7 13.5206 3.0 1.8002 3.3 0.1765 1.3 0.40 1048.0 12.8 1045.5 21.7 1040.4 61.5 1040.4 61.5 54 153 19016 1.3 13.4709 2.3 1.6292 6.0 0.1592 5.5 0.92 952.2 48.7 981.6 37.5 1047.8 46.2 1047.8 46.2 55 101 19600 2.7 13.4700 1.5 1.7517 1.9 0.1711 1.2 0.62 1018.3 11.0 1027.8 12.1 1048.0 29.5 1048.0 29.5 56 114 20850 7.8 13.4465 3.1 1.6288 4.2 0.1588 2.9 0.69 950.4 25.6 981.4 26.6 1051.5 62.1 1051.5 62.1 57 290 43337 2.9 13.4290 2.5 1.7898 2.8 0.1743 1.2 0.42 1035.9 11.3 1041.7 18.2 1054.1 51.2 1054.1 51.2 58 129 41059 4.7 13.3029 1.3 1.8636 1.8 0.1798 1.2 0.68 1065.9 11.8 1068.3 11.7 1073.1 26.3 1073.1 26.3 59 198 21725 1.1 13.2460 1.6 1.9416 1.9 0.1865 1.0 0.52 1102.6 10.1 1095.6 12.8 1081.7 32.7 1081.7 32.7 60 256 31147 1.8 13.1684 2.6 1.9299 2.8 0.1843 1.0 0.37 1090.5 10.4 1091.5 18.6 1093.4 51.7 1093.4 51.7 61 860 182539 3.1 13.1266 2.3 1.8945 2.9 0.1804 1.9 0.64 1069.0 18.3 1079.2 19.5 1099.8 45.2 1099.8 45.2 62 356 80693 3.3 13.1198 4.1 1.7857 4.2 0.1699 1.0 0.24 1011.6 9.4 1040.3 27.4 1100.9 81.8 1100.9 81.8 63 30 9716 4.9 13.0294 3.4 1.7347 3.9 0.1639 2.0 0.51 978.6 17.9 1021.5 25.1 1114.7 67.1 1114.7 67.1 64 196 60876 4.8 13.0247 2.1 1.8489 2.6 0.1747 1.5 0.58 1037.7 14.4 1063.0 17.0 1115.4 41.9 1115.4 41.9 65 41 12922 1.4 13.0224 5.2 2.0218 5.9 0.1910 2.8 0.47 1126.6 28.5 1122.9 40.0 1115.7 103.7 1115.7 103.7 66 756 147217 6.1 12.9750 4.4 1.6605 8.6 0.1563 7.5 0.86 936.0 65.0 993.6 54.8 1123.0 87.2 1123.0 87.2 67 312 83167 2.0 12.9050 1.4 1.9861 2.9 0.1859 2.5 0.87 1099.0 25.2 1110.8 19.4 1133.8 28.3 1133.8 28.3 68 415 135513 5.3 12.7241 1.8 2.1584 2.3 0.1992 1.5 0.64 1171.0 15.7 1167.8 16.0 1161.8 35.3 1161.8 35.3 69 180 59269 2.7 12.6976 1.1 2.1804 1.5 0.2008 1.0 0.69 1179.6 10.8 1174.8 10.1 1166.0 20.8 1166.0 20.8 70 145 55307 3.3 12.6870 2.0 2.1627 2.2 0.1990 1.0 0.45 1170.0 10.7 1169.1 15.5 1167.6 39.4 1167.6 39.4 71 95 21378 2.6 12.6815 2.8 2.0719 3.0 0.1906 1.1 0.37 1124.4 11.7 1139.6 20.7 1168.5 55.5 1168.5 55.5 72 433 84991 3.3 12.6709 1.0 2.0006 3.4 0.1839 3.2 0.96 1088.0 32.4 1115.7 23.0 1170.1 19.8 1170.1 19.8 73 65 14067 5.1 12.6044 5.3 2.0460 6.0 0.1870 2.7 0.44 1105.3 26.9 1130.9 40.7 1180.5 105.6 1180.5 105.6 74 116 42693 3.5 12.5895 2.4 2.0647 4.4 0.1885 3.7 0.84 1113.4 37.6 1137.2 30.0 1182.9 47.1 1182.9 47.1 75 221 28805 2.3 12.5892 4.1 1.9521 5.9 0.1782 4.2 0.72 1057.4 41.2 1099.2 39.6 1182.9 81.3 1182.9 81.3 76 534 138404 5.5 12.5053 3.2 1.8247 5.0 0.1655 3.9 0.78 987.3 36.0 1054.4 33.0 1196.1 62.1 1196.1 62.1 77 121 34297 2.7 12.4711 1.3 2.1364 2.3 0.1932 1.9 0.83 1138.9 19.7 1160.7 15.8 1201.5 25.3 1201.5 25.3 78 103 21756 2.8 12.4551 1.8 2.2532 2.3 0.2035 1.4 0.60 1194.3 14.9 1197.8 16.1 1204.1 36.1 1204.1 36.1 79 58 17696 2.3 12.4447 3.9 2.2456 5.1 0.2027 3.3 0.64 1189.7 35.9 1195.4 36.0 1205.7 77.3 1205.7 77.3 80 556 52070 19.3 12.4038 2.6 2.1088 3.2 0.1897 1.9 0.58 1119.8 19.1 1151.7 22.0 1212.2 51.0 1212.2 51.0 81 147 72678 3.6 12.2902 1.1 2.3837 1.5 0.2125 1.0 0.67 1242.0 11.3 1237.7 10.7 1230.3 21.8 1230.3 21.8 82 333 89404 3.3 12.2889 2.3 2.3293 2.8 0.2076 1.6 0.58 1216.0 18.1 1221.3 20.1 1230.5 45.3 1230.5 45.3 83 282 84172 2.7 12.2385 1.7 2.4600 2.7 0.2184 2.1 0.77 1273.2 23.8 1260.4 19.3 1238.6 33.3 1238.6 33.3 84 171 37611 2.1 12.1875 1.1 2.4278 2.6 0.2146 2.3 0.90 1253.3 26.3 1250.9 18.5 1246.7 22.1 1246.7 22.1 85 381 99414 2.6 12.1005 2.2 2.4812 3.6 0.2178 2.9 0.80 1270.0 32.9 1266.6 25.9 1260.7 42.4 1260.7 42.4 86 81 3742 2.5 11.8179 2.4 2.0238 2.9 0.1735 1.6 0.56 1031.2 15.3 1123.5 19.5 1306.8 46.1 1306.8 46.1 87 198 65898 1.3 11.7905 1.9 2.6382 2.3 0.2256 1.2 0.55 1311.4 14.7 1311.4 16.7 1311.3 36.9 1311.3 36.9 88 145 55787 1.8 11.7181 2.1 2.7817 2.4 0.2364 1.2 0.51 1368.0 15.0 1350.6 17.8 1323.2 39.7 1323.2 39.7 89 246 85358 2.6 11.6508 1.3 2.7740 1.8 0.2344 1.3 0.69 1357.5 15.4 1348.6 13.6 1334.4 25.3 1334.4 25.3 90 590 139706 3.0 11.5709 1.6 2.7869 2.1 0.2339 1.3 0.63 1354.8 15.9 1352.0 15.3 1347.7 30.7 1347.7 30.7 91 54 16300 5.4 11.4981 2.8 2.6194 3.2 0.2184 1.5 0.48 1273.6 17.6 1306.1 23.2 1359.8 53.4 1359.8 53.4 92 151 59990 2.6 10.6641 2.3 3.3796 2.6 0.2614 1.2 0.45 1496.9 15.9 1499.7 20.5 1503.5 44.0 1503.5 44.0 93 197 75012 1.9 9.7939 2.1 3.8152 2.6 0.2710 1.6 0.60 1545.9 21.4 1596.0 20.8 1662.7 38.1 1662.7 38.1 94 431 131079 2.3 9.7750 1.0 4.0892 2.5 0.2899 2.3 0.92 1641.0 33.3 1652.2 20.5 1666.3 18.5 1666.3 18.5 95 225 54436 2.4 7.5945 1.5 4.9690 9.6 0.2737 9.4 0.99 1559.5 130.6 1814.1 80.9 2120.4 26.8 2120.4 26.8 Note: Analysis performed in the LaserChron Center, Arizona, following procedures of Gehrels et al. (2006). Coordinates: 306190 2625120. fl d025-01 1st pgs page 12

12 Barboza-Gudiño et al.

16

255 Ma 14

12

10

8

6 1056 Ma 166 Ma 1186 Ma 4

2

0 0 400 800 1200 1600 2000 2400 2800 Ma

data-point error ellipses are 68.3% conf ζ 0.4

1800 0.3

1400 Pb

0.2 206

U/ 1000 238

0.1 600

0.0 02468 207Pb/235U

Figure 9. Detrital zircon plots as relative probability curve and histogram (A) and U/Pb concordia- diagrams for the analyzed sample (2σ error ellipses) (B), obtained from a sample from La Joya Forma- tion, collected in the Sierra de Catorce (see data and coordinates in Table 2). fl d025-01 1st pgs page 13

Sierra de Catorce 13

176 Ma a rather late Toarcian age on the basis of a lower concor- with interbedded thin shale horizons of the Taraises Formation dia intercept (Barboza-Gudiño et al., 2004). (Berriasian-Valanginian), thick-bedded micritic limestone with brown-gray chert nodules of the Tamaulipas Inferior Formation Stop 2.4. Transect along the “Upper” Cañón General (Barremian), and thin-bedded limestone and marls of La Peña (“La Purisima-Real de Catorce”) Formation (Aptian). Figure 3 shows the complete stratigraphic (306838 2621719) column of Sierra Catorce and a brief lithologic description of the units exposed (after Barboza-Gudiño and Torres-Hernández, At the point known as La Purisima, on the road from 1999, and Barboza-Gudiño et al., 2004). For comparison, Fig- Estación Catorce to Real de Catorce, the base of a sequence ure 10 shows a general correlation table of the Sierra de Catorce of pyroclastic rocks of rhyolitic composition rests on red sand- stratigraphy with the Mesozoic stratigraphy of other localities in stones to mudstones, greenstones and quarzites of the Lower northern Mexico and southeastern United States. Jurassic marine marginal facies known as “Cerro El Mazo beds” (Barboza-Gudiño et al., 2004; Venegas-Rodríguez et al., 2009). Stop 3.2. Cerro El Mazo Maher et al. (1991), Bartolini et al. (1999), and McKee et al. (304502 2622356) (1999) reported plant fossils from this unit that suggests an Early Jurassic age. The pyroclastic rocks consist of airfall deposits or Two km west of the town of Los Catorce, along the road laminated ash, unwelded tuff with volcanic breccia horizons and from this town to Carretas, the Upper Jurassic is represented by marked pseudostratifi cation at the base, grading upsection into marls, shaly limestone, and uncommon interlayered sandstone massive deposits, showing several intensely sheared zones con- of the La Caja Formation (Kimmeridgian-Berriasian) overlying taining sericite as a result of dynamic metamorphism and associ- thick-bedded limestone of the Zuloaga Formation (Oxfordian). ated hydrothermal alteration. The Zuloaga Formation gradationally overlies redbeds of the La Basaltic-andesitic lava also occurs in the volcanic succes- Joya Formation, which constitute an upward-fi ning succession sion exposed in the Sierra de Catorce. The lava contains fl uidal of more than 250 m that includes breccias and conglomerates at porphyritic texture with highly altered, probable hornblende the base, grading upward into red sandstone, with a dominantly phenocrysts, scarce pyroxene, olivine, and plagioclase in a fi ne fi ne sequence of siltstone and claystone at the top. The transition groundmass composed of acicular plagioclase, ferromagnesian between mudstones of La Joya into limestone of the Zuloaga For- minerals, and opaque grains. Some lavas are brecciated. Similar mation is characterized by thin evaporite interbeds and progres- basaltic-andesitic lavas crop out at Sierra de Salinas and Sierra sively more abundant limestone. However, this interval contains de Charcas. The volcanic units are unconformably overlain by numerous detachment surfaces where the limestone of the basal Middle to Upper Jurassic redbeds of La Joya Formation. The Zuloaga Formation is commonly mylonitized. This is expressed exposed succession along this trip forms part of the eastern fl ank as a foliated white fault rock with a very fi ne SC fabric, which is of an uplifted structure known as the “Los Catorce Antiform.” visible only in thin section. In the west fl ank of the Los Catorce Antiform, the volcanic DAY 3 succession of the Nazas Formation is markedly diminished to a few meters of red-purple, possibly epiclastic deposits, which are Stop 3.1. Trip along the “Lower” Cañón General similar to interlayered horizons within the volcanic succession (Los Catorce) that occur in the eastern fl ank of the same structure. The Lower (303145 2621843) Jurassic succession here includes the “Cerro El Mazo beds” unit, consisting of quartzite and litharenite and interlayered red and The fi eld trip follows the road from Real de Catorce to Cedral yellow mudstone (Fig. 11), and containing remains of plants for 14 km and then the highway to Vanegas, where it crosses the (probably Cycadeoids) as well as basaltic-andesitic greenstones Mexico-Laredo railroad; from there, a paved road parallel to the both as dikes or sills and lava fl ows, the products of synsedimen- tracks leads to Estacion Catorce, and to the east a dirt road leads tary volcanic activity. The Cerro El Mazo beds are interpreted into the lower part of Cañon General of Sierra de Catorce. Along as shallow marine and marginal facies. This unit of the Sierra de this part of the canyon the western fl ank of the Los Catorce Anti- Catorce is comparable in age with Lower Jurassic strata cropping form is exposed, in the northwestern Sierra de Catorce uplift. out near El Alamito, west of Rioverde, 200 km SE of Catorce, and Along the road to Los Catorce from the small town of Carre- with strata of the Huayacocotla Formation in Hidalgo and Vera- tas, there are excellent exposures of the mid-Cretaceous (Albian- cruz. Cerro El Mazo beds may be also correlative with Lower Cenomanian) Cuesta del Cura and Tamaulipas Superior forma- Jurassic strata of the Santa Rosa Formation of Sonora (González tions. These units are characterized by medium- to thin-bedded León et al., 2009). limestone with black chert bands and nodules. They were depos- An initial report of the probable existence of Lower Juras- ited in the Mexican Sea, west of the Valles–San Luis platform. sic strata in the Sierra de Catorce, based on the presence of the To the west along the same road, the Lower Cretaceous units are ammonites Vermiceras sp. and Arnioceras cf. Abjectum Fucini n. also exposed; these occur as thin- to medium-bedded limestone subsp., has remained in doubt since 1956 because of uncertainty fl d025-01 1st pgs page 14

14 Barboza-Gudiño et al. regarding the precise location of the outcrop and a lack of sub- the Permo-Triassic magmatic arc (ca. 245–280 Ma). The inter- sequent reports of fossils. However, detrital zircon geochronol- layered mafi c rocks likely record the onset of Jurassic volcanic ogy on coarse-grained litharenites from the Cerro El Mazo beds arc activity, but it is also possible that this earliest Jurassic mafi c (Venegas-Rodríguez et al., 2009) yielded a Late Triassic–Early magmatism is not related to the Nazas arc. This is because there Jurassic maximum depositional age on the basis of the youngest are several differences in the geochemistry of these rocks. The zircon grains in the sample (age of youngest zircons here), as well chemistry of Cerro El Mazo volcanic rocks is typical of poorly as three possible basement sources of zircons that include Gren- evolved magmatic rocks, and their petrographic features are more villian (ca. 900–1200 Ma), Pan-African (ca. 500–700 Ma) and characteristic of spilitic rocks. However, these rocks are indicative

Sierra de CatorceGaleana, N.L. La Boca canyon Texas Maastrichtian Navarro Caracol/Mendez Mendez Mendez Campanian Taylor Santonian Indidura Coniacian San Felipe San Felipe Austin Turonian Agua Nueva Agua Nueva Eagle Ford Cenomanian Cuesta del Cura Cuesta del Cura Cuesta del Cura Woodbine-Buda Tamaulipas sup. Tamaulipas sup. Tamaulipas sup. Fredericksburg Albian Trinity Aptian La Peña (Otates) La Peña (Otates) La Peña (Otates) Pearsall Barremian Hauterivian Tamaulipas inf. Tamaulipas inf. Tamaulipas inf. Sligo Valanginian Cretaceous Taraises Hosston Berriasian Taraises Taraises Sycamore Tithonian La Caja La Casita La Casita Cotton Valley Kimmeridgian Zuloaga Zuloaga Olvido Buckner Oxfordian Olvido Smackover Minas Viejas Caliza Novillo Callovian Louann- La Joya La Joya La Joya Werner Bathonian Bajocian Aalenian

Jurassic Toarcian Nazas La Boca Pliensbachian

Sinemurian Hettangian

Rhaetian

Norian Carnian Zacatecas El Alamar El Alamar Ladinian

Triassic Anisian Scythian

Figure 10. Correlation chart for northeastern Mexico and southeastern Texas. fl d025-01 1st pgs page 15

Sierra de Catorce 15

Figure 11. Aspect of the Lower Jurassic Cerro El Mazo beds, near Los Catorce, Sierra de Catorce. This succession con- sists of sandstones or litharenites (Sst.) and quarzites (Qz.), red purple to yellow-green siltstone and shale (Sh.), alternat- ing with several basaltic-andesitic lava fl ows (greenstones, Gst.); sills and dikes also are present in the area. of subduction volcanism (Rodríguez-Hernández, 2009). On the Triassic age of deposition for this succession. The facies associa- basis of our observations, we conclude that marginal marine tions in Triassic strata in Real de Catorce are comparable with strata of Cerro El Mazo in the Sierra de Catorce (post-Norian to those of the Charcas exposures visited in Day 1, but fi ner grained pre-Bajocian?) were probably deposited along the paleo-Pacifi c rocks dominate the section at Real de Catorce. These are inter- margin of Mexico during the Early Jurassic in a forearc setting. preted as inter-channel deposits (lithofaces “D,” “E,” and “G”), and subordinate suprafan, levee, and channel deposits (Fig. 12). Stop 3.3. Los Catorce: Late Triassic Turbidite Succession (305484 2622469) DISCUSSION AND CONCLUSIONS

The Zacatecas Formation in Sierra de Catorce consists of One of the most relevant aspects of the Mesozoic evolution fi nely laminated shale and intercalated thin siltstone and sand- of the Mexican subcontinent is a continuous stratigraphic record stone layers. The exposures at Cañón General, around the village of plate convergence along its Pacifi c margin (e.g., Dickinson of Los Catorce represent the most extensive exposures of Trias- and Lawton, 2001; Sedlock et al., 1993). Convergence has been sic rocks in the Sierra de Catorce. In addition, there are outcrops related to subduction of the Farallon plate. Stratigraphic units in of comparable strata in Cañon Ojo de Agua or “El Salto” to the several uplifted structural complexes in north-central and north- north and the southern Sierra de Catorce in El Astillero canyon. eastern Mexico indicate repeated tectonic-magmatism cycles A Late Triassic age for the succession is inferred from lithologic from Permian to Cretaceous, corresponding to sedimentation, similarities with fossil-bearing strata at other localities and their magmatism and deformation in subduction settings (Fig. 13). stratigraphic position; there are no reports of Triassic fossils in The geologic record of subduction in Mexico during that time this locality. An older age has been suggested by a possible late is complex, but in general there is a westward younging trend Paleozoic fl ora (Franco-Rubio, 1999) and late Paleozoic spores in the locus of magmatism. Each cycle of sedimentation, mag- (Bacon, 1978), but recently published detrital zircon geochronol- matism, and deformation is displaced progressively more than ogy (Fig. 6; Barboza-Gudiño et al., 2010) and geochronologi- 500 km westward from the Permian paleo-Pacifi c margin of Pan- cal data obtained from Jurassic volcanic rocks in the Sierra de gea, whose remnants are located today in eastern Mexico up to Catorce (Barboza-Gudiño et al., 2004) are consistent with a Late the present Pacifi c margin. fl d025-01 1st pgs page 16

16 Barboza-Gudiño et al.

Figure 12. Triassic turbiditic sequence exposed by Los Catorce, Cañon general, Sierra de Catorce.

Nascent Guerrero Terrane

subduction Late Jurassic-Cretaceous

Nazas Arc

Early to Middle Jurassic

Low stress subduction

Deformation of the Potosi Fan Late Triassic El Alamar Formation

Latest Triassic-Early Jurassic high stress subduction Figure 13. Model of the tectonic evo- lution of the ancient western margin of Pangea, during the Late Paleozoic– Potosi Fan Early Mesozoic.

Late Triassic

Permian-Triassic Permo-Triassic Arc Low stress subduction WSW ENE metamorphism of Granjeno shist Oaxaquia

Carboniferous-Permian high stress subduction fl d025-01 1st pgs page 17

Sierra de Catorce 17

At several localities of the Mesa Central province, Upper Pacifi c margin of western Pangea during early Mesozoic times. Triassic strata of the Zacatecas Formation and its correlatives, West of this ancient margin, parts of the sedimentary pile of the which form the record of the “Potosí submarine Fan,” are strongly voluminous Potosí Fan were likely deposited on the continental deformed and locally exhibit low-grade metamorphism. Lithofa- slope and the adjacent oceanic crust and carried eastward into cies assemblages have locally been interpreted as the record of the active trench. During the Late Jurassic and Early Cretaceous, a subduction complex (Anderson et al., 2005; Dávila- Alcocer the intraoceanic volcanic activity of the Guerrero terrane was ini- et al., 2008), suggesting that a subduction zone was active in tiated, followed in the Late Cretaceous by the consolidation of a high-stress stage during the latest Triassic time, producing most of the actual Mexican subcontinent. deformation and uplift of Zacatecas Formation strata. Whereas Centeno-García (2005) suggested that the fan was formerly ACKNOWLEDGMENTS located to the northwest and was displaced to its present position by the hypothetical Mojave-Sonora megashear, the detrital zircon We acknowledge constructive reviews and suggestions by Ana geochronology of this unit is consistent with an autochthonous or Bertha Villaseñor and Federico Olóriz. para-autochthonous setting. Widespread arc-volcanism occurred during a subsequent REFERENCES CITED low-stress stage of subduction. 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