ABSTRACT We generated low-temperature thermochronological data on crystalline rocks from the Chiapas Massif in southern Mexico to constrain the complex relationship among tectonics, exhumation, and sedimentation in the region. Our data show that the first recorded cooling event occurred at ca. 40–25 Ma due to denudation of the sedimentary cover of the Chiapas Massif at slow rates of ~0.1 km/m.y. This was followed by a period of tectonic quiescence from ca. 25 to 14 Ma. Between ca. 14 and 7 Ma, cooling implying exhumation of the massif at rates of up to ~0.7 km/m.y. was renewed, and this was associated with, and possibly responsible for, the Miocene “Chiapanecan” deformational event observed in the Chiapas fold-and-thrust belt to the northeast of the massif. This younger uplift was also accompanied by the onset of arc-related magmatism beneath the massif, between ca. 13 and 9 Ma, along the Tonalá shear zone at the Pacific coast. Since ca. 7 Ma, additional but slower cooling and exhumation are indicated along the length of the Chiapas Massif, and arc magmatism has jumped north by ~125 km from the Tonalá shear zone into the Chiapas fold-and-thrust belt. Concurrently, subsidence and sedimentation have persisted along the offshore Tehuantepec Shelf to the south, suggesting that the Tonalá shear zone has been recently active (despite no magnitude 4 or larger earthquakes), with up-to-the-north vertical displacement. We interpret the exhumation at ca. 40–25 Ma to pertain to displacement of the Chortis block along the paleo–Motagua fault zone, either as a northward propagation of a basement thrust beneath the massif within a regional transpressional setting, or as a deep, ductile crustal thickening and attendant isostatic uplift of the southern flank of the massif during the transpressional passage of the Chortis block. The ensuing quiescence (25–14 Ma) coincided, we believe, with the passage of the “western tail” of Chortis, which is internally deformed and perhaps transferred compressive stress less effectively than had the central, continental core of the Chortis block earlier. Renewed uplift and exhumation of the region began by ca. 14–10 Ma. An onset at ca. 10 Ma is probably the best estimate for the beginning of exhumation of the northwestern and central portions of the Chiapas Massif, whereas the present-day southeastern tip of the massif (potentially an allochthonous sliver belonging to the Chortis block) started to exhume earlier, at ca. 14 Ma. By ca. 13 Ma, arc magmatism had moved into the western Tehuantepec area, marking the onset of subduction of the Cocos plate beneath the Chiapas Massif. Hence, we interpret the main period of uplift of the Chiapas Massif and primary shortening of the Chiapas fold-and-thrust belt (ca. 14–7 Ma) as being driven by the establishment of Cocos subduction beneath the area.

Abstract The structural evolution of southern Mexico is described in the context of its plate tectonic evolution and illustrated by two restored crustal scale cross-sections through Cuicateco and the Veracruz Basin and a third across Chiapas. We interpret the Late Jurassic–Early Cretaceous opening of an oblique hyper-stretched intra-arc basin between the Cuicateco Belt and Oaxaca Block of southern Mexico where Lower Cretaceous deep-water sediments accumulated. These rocks, together with the hyper-stretched basement beneath them and the Oaxaca Block originally west of them, were thrust onto the Cretaceous platform of the Cuicateco region during a Late Cretaceous–Eocene orogenic event. The mylonitic complex of the Sierra de Juárez represents this hyper-stretched basement, perhaps itself an extensional allochthon. The Chiapas fold-and-thrust belt is mainly Neogene in age. Shallowing of the subduction angle of the Cocos Plate in the wake of the Chortis Block, suggested by seismicity and migrating arc volcanism, is thought to play an important role in the development of the Chiapas fold-and-thrust belt itself, helping to explain the structural dilemma of a vertical transcurrent plate boundary fault (the Tonalá Fault) at the back of an essentially dip-slip fold-and-thrust belt.

Abstract Of all the countries in the world considered to be oil rich, Mexico is the only one that consistently has been losing production and reserves in the last ten years. Even though Mexico has five major producing provinces: two for oil (the Southeast and the Tampico–Misantla basins) and three for gas (the Sabinas, Burgos and Veracruz basins), and has seven more with potential, (California, Gulf of Cortès, Chihuahua, Sierra Madre Oriental, Sierra de Chiapas, Progreso shelf, and the deep Gulf of Mèxico), its output and reserves have declined consistently. Many reasons can be attributed for these results, and as this note proves, least of them is the country’s endowment of oil and gas resources. The problem is that Mexico, since 1938, has had only one oil company responsible for all of its upstream activities and even though Pemex’s performance is comparable with that of most of the majors’ (it is world’s third largest in terms of production), it is impossible that all the remaining potential of the entire country can be found and produced with only one company, no matter how large, wealthy, efficient, technologically advanced, and successful it can be. The good news is that once the country opens up for third-party participation in exploration, which will eventually take place, results are going to be spectacular. So far there has only been a timid opening for development and exploitation opportunities.

This paper integrates, analyzes, and interprets the existing geological and geophysical information related to the opening of the Gulf of Mexico. The analysis of this information has the objective to consider the opening of the Gulf of Mexico as a result of global tectonic processes. Without doubt, the opening of the Gulf of Mexico has its origin in the interaction of two important tectonic events that generated the separation of Pangea: the Farallon Plate subduction in the Pacific and on the opening of the Central Atlantic, whose start is marked by the presence of the Central Atlantic magmatic province. A proposal of this work is that as much oceanic crust was generated in the Oxfordian, as part of the stage in the Central Atlantic Jurassic opening. This Oxfordian period is characterized by a large positive geomagnetic chron, which explains the absence of polarity changes in the magnetic response for the Gulf of Mexico. Another proposal is that the Sierra de Chiapas is the transpressional front that represents the final stage in the gulf opening and is associated with the edge effect of gravity anomaly that can be observed in the overall gravimetric maps. The proposed model assumes that the magmatic arc causes continental rifting, creating basins containing red beds deposits that are located parallel to the orientation of the arc; these rifting areas evolve to form the subbasins of Chihuahua, Sabinas, and Burgos in the northeast of Mexico and Tampico Misantla, Veracruz, and Southeastern basins in eastern Mexico.

Abstract The Yucatan Block is a rifted continental microplate covering 450,000 sq km in southern Mexico, northern Guatemala, and Belize. The crystalline basement is mantled by a Late Jurassic through Holocene carbonate/evaporite platform up to six-km thick. While the northern and western edges of the Yucatán Block have been passive margins since the Mesozoic, its southern margin was affected by Late Cretaceous suturing to the Chortis microplate, followed by Miocene to Holocene strike-slip faulting. Its eastern margin was modified by Paleogene strike slip against the Cuban Arc Terrane. The Yucatán Block has received very little terrigenous sedimentation since being isolated from nearby landmasses by the Jurassic separation of North and South America. Major hydrocarbon production exists in Mexico from the area immediately west of the Yucatán Block in the Reforma Trend, Campeche Sound, and the Macuspana Basin. Oil has also been found west and south of the block in the Sierra de Chiapas of Guatemala and Mexico. Only one commercial oil accumulation has been found to date on the stable block itself (Xan field in Guatemala), and mineral exploration without commercial success has been limited to the small area of exposed crystalline basement in the Maya Mountains of Belize. Based on current knowledge, it is the author’s opinion that the economic potential of the Yucatán Block should not be discounted.Hydrocarbon and mineral exploration has been sporadic and generally low-tech, and there is a clear need for high-quality regional seismic data to reveal structural configuration and sedimentary architecture. Among the many geological factors to be understood are: 1) geometry of Triassic-Jurassic rift structures (horsts and grabens); 2) location and geometries of possible Jurassic and Cretaceous intraplatform hydrocarbon source basins, carbonate buildups, and structural traps in the evaporite/carbonate section; 3) paleoheatflow as it affected organic maturation; 4) effects within the block of tectonics along its margins (tilting, mass wasting, and foreland bulging); and 5) possible role of the Chicxulub K/T astrobleme in hydrocarbon and mineral occurrence.

Abstract The Yucatan block is a rifted continental microplate covering 450,000 sq km in southern Mexico, northern Guatemala, and Belize. The crystalline basement is mantled by a Late Jurassic through Recent carbonate/evaporite platform up to six km thick. The southern margin of the block was affected by Late Cretaceous suturing to the Chortis microplate followed by Miocene to Recent strike slip faulting. Its eastern margin was modified by Paleogene strike-slip against the Cuban Arc Terrane. The Yucatan Block has received very little terrigenous sedimentation since it was isolated from nearby landmasses by the Jurassic separation of North and South America. There is major hydrocarbon production in Mexico from the area immediately west of the Yucatan block in the Reforma trend, Campeche Sound, and the Macuspana basin. Oil has also been found in the Sierra de Chiapas west and south of the block in Guatemala and Mexico. Only one commercial oil accumulation has been found to date on the stable block itself, i.e. , Xan Field in Guatemala, while unsuccessful mineral exploration has been limited to the small area of exposed crystalline basement in the Maya Mountains of Belize. Based on current knowledge, it is the author’s opinion that the economic potential of the Yucatan block should not be discounted. Hydrocarbon exploration has been sporadic and generally low-tech, and there is a clear need for high quality regional seismic data to reveal the structural configuration and sedimentary architecture. Among the many geological factors to be understood are: The geometry of Triassic-Jurassic rift structures (horsts and grabens) The location and geometries of possible Jurassic and Cretaceous intraplatform hydrocarbon source basins, potential carbonate buildups, and structural traps within the evaporite/carbonate section Paleo-heatflow as it affected organic maturation The effects within the block of tectonics along its margins (tilting, mass wasting and foreland bulging.) The effects of the Chicxulub K/T astrobleme.

Abstract The Ixtapa graben is located in the center of the Strike-slip Fault province of the Sierra de Chiapas, Mexico. In this graben, rocks of middle Cretaceous (Albian-Cenomanian) to Pleistocene age represent a section in which successively younger beds lie to the south-east. This section is 15,365 m thick and represents marine, transitional, and continental environments with numerous vertical and lateral facies changes through the whole section and unconformities in the uppermost part. Along the flanks of the graben, beds are upturned and form positive flower structures.