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Oaxaca Mexico
Pollen morphology of columnar cacti from Tehuacán-Cuicatlán Valley, Mexico
Late Cambrian Pywackia is a cnidarian, not a bryozoan: Insights from skeletal microstructure
New rhynchonellid and spire-bearing brachiopods from the Carboniferous of Mexico. Paleogeographical significance of the Oaxacan brachiopod fauna through the Serpukhovian–Moscovian
A Test of the Earthquake Gap Hypothesis in Mexico: The Case of the Guerrero Gap
The Mechanisms of Tsunami Amplification and the Earthquake Source of the 2021 M 7 Acapulco, Mexico, Earthquake
Integrated Analysis of the 2020 M w 7.4 La Crucecita, Oaxaca, Mexico, Earthquake from Joint Inversion of Geodetic and Seismic Observations
The “Nazas Arc” is a continental rift province: Implications for Mesozoic tectonic reconstructions of the southwest Cordillera, U.S. and Mexico
ABSTRACT Jurassic northward migration of Mexico, which lay on the southern part of the North America plate, resulted in temporal evolution of climate-sensitive depositional environments. Lower–Middle Jurassic rocks in central Mexico contain a record of warm-humid conditions, indicated by coal, plant fossils, and compositionally mature sandstone deposited in continental environments. Paleomagnetic data for central Oaxaca and other regions of central and eastern Mexico indicate that Lower and Middle Jurassic rocks were deposited at near-equatorial paleolatitudes. In the Late Jurassic, the Gulf of Mexico formed as a subsidiary basin of the Atlantic Ocean when the Pangea supercontinent ruptured. Upper Jurassic strata across Mexico, including eolianite and widespread evaporite deposits, indicate dry-arid conditions. Available paleomagnetic data (compaction-corrected) from southern and northeast Mexico for Upper Jurassic strata indicate deposition at ~15°N–20°N. As North America moved northward during Jurassic opening of the Atlantic Ocean, different latitudinal regions experienced coeval Middle–Late Jurassic climatic shifts. Climate transitions have been widely recognized in the Colorado Plateau region. The plateau left the horse latitudes in the late Middle Jurassic to reach temperate humid climates at ~40°N in the latest Jurassic. Affected by the same northward drift, the southern end of the North America plate represented by central Mexico gradually reached the arid horse latitudes in the late Middle Jurassic as the Colorado Plateau was leaving them. As a result, Late Jurassic epeiric platforms developed in the circum–Gulf of Mexico region after a long period of margin extension and were surrounded by arid land masses. We propose that hydrocarbon source-rock deposition was facilitated by arid conditions and wind-induced coastal upwelling.
ABSTRACT The Oaxacan Complex represents the largest outcrop of Grenvillian basement in Mexico. Broadly, it consists of pelitic gneisses, quartzofeldspathic gneisses, metasomatic calc-silicates, orthoamphibolites, and marbles, all intruded by anorthosites, orthocharnockites, and orthogneisses. The entire assemblage underwent granulite-facies metamorphism ca. 1 Ga. We studied for the first time the ultramafic rocks of the Oaxacan Complex, represented by six different samples, all corresponding to ultramafic granulites. Their igneous equivalents are orthopyroxenites, websterites, and clinopyroxenites, and they occur as metric-scale lenses or centimetric layers in paragneisses, or in mingling textures with anatectic marbles. We studied their petrography, geochemistry, geochronology, and geothermobarometry to elucidate their genesis and tectonic implications. Our samples have enriched mid-ocean-ridge basalt and oceanic-island-arc affinities, both tholeiitic and calc-alkaline. Rare earth element patterns normalized to chondritic uniform reservoir from whole rock or single minerals define two or three main groups related to their origin and metamorphic history. Based on their protoliths, these rocks can be divided into: (1) ortho-derived pyroxenites (pre–Grenvillian orogeny), the origin of which was a magmatic cumulate or mafic melt or a mantle rock that had undergone metasomatism; and (2) para-derived pyroxenites (syn- or post-Grenvillian orogeny), the origin of which was a calc-silicate rock undergoing pervasive anatectic and metasomatic processes. The geothermobarometry revealed different stages in the syn- and post-Grenvillian granulitic metamorphic history of the Oaxacan Complex. The high temperature calculated from one sample (~945 °C), in the ultrahigh-temperature metamorphic field, is probably closer to the granulitic metamorphism peak than those obtained in previous studies, although a relict igneous temperature cannot be ruled out with the present data.
ABSTRACT The Gulf of Mexico is best understood as a subsidiary basin to the Atlantic, resulting from breakup of Pangea. The rifting process and stratigraphy preceding opening of the gulf are, however, not fully understood. We present new stratigraphic, sedimentologic, and provenance data for the Todos Santos Formation (now Todos Santos Group) in southern Mexico. The new data support a two-stage model for rifting in the Gulf of Mexico. Field and analytical evidence demonstrate that strata assigned to the Todos Santos Group in Mexico belong to two unrelated successions that were juxtaposed after rotation of the Yucatán block. An Upper Triassic fluvial siliciclastic succession in the western Veracruz basin is intruded by the San Juan del Río pluton (194 Ma, U-Pb) along the Valle Nacional fault. We refer to this succession as the Valle Nacional formation (informal) of the Todos Santos Group, and correlate it with El Alamar Formation of northeast Mexico and the Eagle Mills Formation of the northern Gulf of Mexico. Triassic red beds register an early rifting phase in western equatorial Pangea. Sandstone composition indicates that the Valle Nacional formation is mostly arkoses derived from multiple sources. Paleocurrent indicators in fluvial strata of the Valle Nacional formation are S-SW directed, but restoration of paleomagnetically determined counterclockwise rotation indicates a W-SW–flowing fluvial system. Triassic rifting in the Valle Nacional formation and the Central Cordillera of Colombia Triassic extensional event, the record of which is preserved in mid-crustal levels, may represent conjugate margins. The Early–Middle Jurassic Nazas continental volcanic arc predated the Jurassic rifting phase that led to opening of the gulf. A record of arc magmatism is present in eastern Mexico underlying Middle Jurassic synrift successions, and it is present in La Boca and Cahuasas formations in the Sierra Madre Oriental and La Silla Formation north of the Chiapas Massif. These units have a similar age range between ca. 195 and 170 Ma. Arc magmatism in eastern Mexico is correlated with the Jurassic Cordilleran arc of Sonora, California, and Arizona, as well as the Jurassic arc of the Central Cordillera of Colombia. La Boca and La Silla units record intra-arc extension driven by slab rollback. The Jurassic rifting phase is recorded in the Jiquipilas formation of the Todos Santos Group and is younger than ca. 170 Ma, based on young zircon ages at multiple locations. The informal El Diamante member of the Jiquipilas formation records the maximum displacement rift stage (rift climax). Coarse-grained, pebbly, arkosic sandstones with thin siltstone intercalations and thick conglomerate packages of the Jericó member of the Jiquipilas formation are interpreted as deposits of a high-gradient, axial rift fluvial system fed by transverse alluvial fans. These rivers flowed north to northeast (restored for ~35° rotation of Yucatán). The Concordia member of the Jiquipilas formation records the postrift stage. Thick synrift successions are preserved in the subsurface in the Tampico-Misantla basin, but they cannot be easily assigned to the Triassic or the Jurassic rifting stages because of insufficient study. The Todos Santos Group at its type locality in Guatemala marks the base of the Lower Cretaceous transgression. Overall, three regional extensional events are recognized in the western Gulf of Mexico Mesozoic margin. These include Upper Triassic early rifting, an extensional continental arc, and Middle Jurassic main rifting events that culminated with rotation of Yucatán and formation of oceanic crust in the gulf.