Jurassic Volcanic and Sedimentary Rocks of the La Silla and Todos

Jurassic volcanic and sedimentary rocks of the La Silla and Todos Santos Formations, Chiapas: Record of Nazas arc magmatism and rift-basin formation prior to opening of the Gulf of Mexico Antonio Godínez-Urban1, Timothy F. Lawton2, Roberto S. Molina Garza3, Alexander Iriondo3, Bodo Weber4, and Margarita López-Martínez4 1Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico 2Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico, USA 3Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico 4División de Ciencias de la Tierra, CICESE (Centro de Investigación Científi ca y de Educación Superior de Ensenada), Ensenada, Baja California, Mexico ABSTRACT depositional age. Volcanic activity continued by continental rifting, sea-fl oor spreading, and into the upper part of the El Diamante Mem- associated counterclockwise rotation of the Stratigraphic relationships, detrital zir- ber, but with a more mafi c character. We also Maya (or Yucatan) block in the Late Jurassic con provenance, U-Pb and 40Ar/39Ar geo- recognize an upper member, which we term (Pindell and Dewey, 1982; Ross and Scotese, chronology, and trace element geochemistry the Jericó Member. This member is charac- 1988; Dickinson and Lawton, 2001; Bird et al., in volcanic and sedimentary rocks of the terized by thickly bedded, coarse-grained 2005). These models are based on geometric Sierra homocline of central Chiapas near La pebbly arkose intercalated with several thick and plate kinematic constraints such as the Angostura reservoir in Mexico document an intervals (tens of meters) of conglomerate reconstruction of western equatorial Pangea extensive pulse of Early–Middle Jurassic arc and pebbly sandstone. Sandstone petrology and the drift history of South America (Pin- magmatism in rocks that overlie and intrude indicates a source in the granitic rocks of dell and Dewey, 1982; Pindell et al., 1988), the the Permian–Triassic Chiapas massif. Upper the Chiapas massif, with a tendency to show Jurassic stratigraphy of the gulf and northeast- Jurassic rift-basin strata unconformably deep-seated sources and a diverse zircon ern Mexico (e.g., Winker and Buffl er, 1988; overlie the volcanic rocks and the massif. A population in the upper part of the section. Salvador, 1987; Goldhammer, 1999), the tec- Pliensbachian U-Pb (zircon) SHRIMP (sen- The upper Todos Santos Formation in the tonic fabric of the deep gulf (Scott and Peel, sitive high-resolution ion microprobe) age study area is gradational into the overlying 2001), and paleomagnetic data (Molina-Garza from porphyritic andesite (191.0 ± 3.0 Ma), San Ricardo Formation ( Kimmeridgian– et al., 1992; Guerrero et al., 1990). Early to Middle Jurassic 40Ar/39Ar dates Tithonian ). The La Silla Formation was Other details of the reconstruction of the from andesitic dikes, U-Pb grain ages of deposited in volcanic-complex environments, Maya block in the northern Gulf of Mexico detrital zircons in overlying strata (196– with a clear lack of differentiated vol canic region are less well constrained. For example, 161 Ma), and previously reported K-Ar dates rocks. Fluvial strata of the El Diamante the Chiapas massif can be reconstructed in indicate that subduction-related magmatism Member were deposited in a mud-rich sinu- the Río Grande embayment or in the Burgos occurred in the western portion of the Maya ous river system. The Jericó Member was Basin prior to opening of the Gulf of Mexico. block from Early to latest Middle Jurassic deposited in large, sand-rich fl uvial systems, Similarly, the orientation of the continental time. We assign the volcanic rocks to the La which probably represent deposits of rift- rift basins that preceded opening of the gulf is Silla Formation, which correlates with the axis trunk streams; conglomerate facies were uncertain and somewhat controversial (Salva- informal Pueblo Viejo andesite of the Cinta- deposited in adjacent and interfi ngering allu- dor, 1987; Pindell et al., 2006; Exxon, 1985). lapa and Uzpanapa regions to the northwest. vial fan systems. We suggest that the strati- The rotation of the Maya block assumes an La Silla magmatism predates opening of the graphic record of the western Maya block Euler pole in the general region between the Gulf of Mexico Basin. The Todos Santos For- records a transition from volcanic arc to Florida peninsula and southern Cuba (e.g., Hall mation, which overlies La Silla Formation, intra-arc basin and subsequently to rift basin and Najmuddin, 1994; Marton and Buffl er , was deposited in extensional basins during during Pliensbachian to Oxfordian time. 1994). Estimates of the amount of rotation the early stages of gulf opening. We recognize range between ~30° and 60°. Rotation was a lower El Diamante Member of the Todos INTRODUCTION accommodated by the Tamaulipas-Chiapas Santos, consisting of red fl uvial sandstone, transform, along the gulf coast region of the mudstone, and minor conglomerate contain- The Gulf of Mexico is best interpreted as states of Tamaulipas and Veracruz. ing primarily volcanic-lithic detritus; this a subsidiary basin to the Atlantic Ocean (Pin- The role of arc magmatism in northern member is characterized by a nearly uni- dell et al., 2006). Most models suggest that the Mexico, represented by the Nazas Formation, modal Jurassic detrital zircon age popula- Gulf of Mexico Basin formed after the central in the geodynamic context of opening of the tion that indicates a Callovian or younger Atlantic, and invoke origin of the gulf basin Gulf of Mexico has seldom been explored in Geosphere; February 2011; v. 7; no. 1; p. 121–144; doi: 10.1130/GES00599.1; 10 fi gures; 5 tables. For permission to copy, contact [email protected] 121 © 2011 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/1/121/3339291/121.pdf by guest on 28 September 2021 Godínez-Urban et al. the literature despite the fact that arc volcanic Todos Santos Formation The Todos Santos Formation in Chiapas rocks are spatially associated with rift succes- consists of polymictic conglomerate, sand- sions (Fastovsky et al., 2005; Barboza-Gudiño, Prior to this study, the nonmarine Todos San- stone, mudstone, volcanic rocks, and volcani- 2008). The Gulf of Mexico was recently inter- tos Formation was the oldest Mesozoic unit clastic deposits. These rocks were deposited preted as a backarc basin as a result of inferred recognized in the Maya block. It was deposited in alluvial fans, fl uvial systems, and lacus- association with Jurassic Nazas magmatism in extensional basins during the early stages of trine environments, forming vertically stacked (Stern and Dickinson, 2009, 2010). continental rifting in the Gulf of Mexico region cyclic mega sequences hundreds of meters in In order to better constrain the tectonic setting (Fig. 1). Elsewhere in Mexico, similar litholo- thickness; Blair (1987) reported a thickness of of the Maya block prior to opening of the Gulf gies have been assigned to the Huizachal For- 250–1350 m for this unit. The formation uncon- of Mexico, we integrate geochronologic, strati- mation (Mixon et al., 1959). Some confusion formably overlies rocks of the Chiapas massif graphic, and detrital zircon provenance data for exists in the literature because the name Todos and upper Paleozoic strata in the Chicomuselo the Todos Santos Formation and underlying Santos has been applied to continental redbeds uplift (Anderson et al., 1973; Castro-Mora volcanic rocks (La Silla Formation) in central and other terrigenous sequences across southern et al., 1975; López-Ramos, 1981), suggesting Chiapas. Reconstruction of the Chiapas massif Mexico (Chiapas and Oaxaca), Guatemala, and deposition on irregular topography formed by offshore of Tamaulipas in Early Jurassic time Honduras; the name thus applies to Jurassic and extensional tectonics (Meneses-Rocha, 1985; indicates that the Nazas and La Silla Forma- Cretaceous strata in different tectonic settings Blair, 1987). There are excellent exposures of tions are part of the same arc system, and that and in different basins (e.g., Burkart et al., 1973; Todos Santos strata in the Sierra homocline the overlying Todos Santos Formation records Blair, 1987; Rueda-Gaxiola, 1998; Gose and province of west-central Chiapas (Fig. 3). The rift-basin extension immediately following ces- Finch, 1992). following section summarizes our observations sation of arc magmatism. These data, together Clemons et al. (1974) assigned a Late Jurassic– and mapping, the basis for proposing a new with reappraisal of the relevant circum-gulf Early Cretaceous age to Todos Santos strata stratigraphic scheme for this region. Jurassic geology, leads us to the conclusion in Guatemala, at the type locality in the Altos that the Middle–Late Jurassic rift basins of the Cuchumatanes. However, in rocks overlying METHODS Gulf of Mexico region evolved as successors of the Chiapas massif, Jurassic K-Ar ages (from intra-arc extensional basins of the central Mexico 196 ± 3 to 148 ± 6 Ma) have been reported This work is based in photointerpretation Nazas arc. near Cintalapa for intermediate volcanic rocks, and fi eld mapping at a scale 1:25,000 of an which were interpreted as part of the Todos area ~700 km2 in the Sierra homocline of west- REGIONAL SETTING Santos succession (Castro-Mora et al., 1975; central Chiapas, centered near the village of Herrera-Soto and Estavillo-González, 1991). If Independencia (Fig. 4). This work is supple- Basement Todos Santos strata in Chiapas were indeed Late mented by reconnaissance description of key Jurassic–Early Cretaceous in age, as is the case stratigraphic columns, petrography (from which Basement of the Maya block includes the in Guatemala, these rocks could not be related we obtained modal compositions), and sam- Permian–Triassic metamorphic and plutonic to the early stages of continental rifting in the pling for U-Pb geochronology, trace element complex of the Chiapas massif (Weber et al., gulf.

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