Southern and Central Mexico: Basement Framework, Tectonic Evolution, and Provenance of Mesozoic–Cenozoic Basins

Central and southern Mexico represents a strategic place to understand the dynamics of Pangaea break-up and its influences on the evolution of the Pacific margin of North America. Lower–Middle Jurassic volcano-sedimentary successions, and scarce magmatic rocks, crop out discontinuously across this region and have been interpreted either as a vestige of a continental arc or as several deposits of syn-rift magmatism. At present, their origin is controversial. Available geochemical data on these igneous rocks suggest that they represent almost pure crustal melts produced in a rift environment rather than in an arc. In fact, the studied rocks exhibit the high silica contents and moderate to strong peraluminous character typical of sediment melts. The enriched isotopic composition (high86Sr/87Sr and low143Nd/144Nd) and the age distributions of inherited zircon grains readily identify the widespread Upper Triassic metasedimentary sequences presently exposed in southwestern and central Mexico as the most likely crustal source of these Jurassic igneous rocks. Accordingly, we argue that these Early–Middle Jurassic magmas originated in a syn-rift igneous province associated with extensional-driven crustal attenuation in the context of Pangaea fragmentation. Our findings also constrain post-Pangaea subduction initiation to be younger than Middle Jurassic time in central and southern Mexico.

Properties of the subduction system in Mexico

Distribution of hydrous minerals in the subduction system beneath Mexico

Biomass burning from grassland, forests, and agricultural waste results in large amounts of gases and particles emitted to the atmosphere, which affect air quality, population health, crop development, and natural vegetation. Regional atmospheric circulations can transport those plumes of pollutants over hundreds of kilometers, affecting vulnerable environments such as those considered protected natural areas (PNAs). This study evaluates the spatiotemporal distribution of active fires detected, and associated emissions, in central and southern Mexico from satellite data between March and June 2017, to assess the impact of the smoke plumes on protected ecosystems. The arrival of smoke plumes to selected PNAs (both near large urban centers and in remote areas) is assessed using airmass forward trajectories from selected emission sources. The spatial distribution of the remotely derived aerosol optical depth confirms the regional impact of particle emissions from the observed fires on PNAs, particularly in central Mexico. The identified areas of high fire density are also associated with large coarse particle concentrations at the surface. Moreover, there is a significant contribution of organic carbon to the total coarse particle mass, 60% on average. Finally, while most of the impact in ambient pollution is observed in PNAs located close to the regions with active fires in southern Mexico and Central America, the long-range transport of smoke plumes reaching the USA was also confirmed.

A major provenance change in sandstones from the Tezoatlán basin, southern Mexico, controlled by Jurassic, sinistral normal motion along the Salado River fault: Implications for the reconstruction of Pangea

Cretaceous Formations of Central America and Mexico

In Mexico, ultramafic complexes are present in different regions from the northwest (Baja California Norte) to the southeast (Chiapas). In this paper, we present the results of the exploration of three ultramafic (serpentine) habitats in central and southern Mexico: Cuicatlán–Concepción Pápalo (Oaxaca), Tehuitzingo–Tecomatlán (Puebla), and San Juan de Otates (Guanajuato). Previous geology studies showed that these complexes are mainly made up of serpentinized peridotites. Soil analyses demonstrated typical ultramafic characteristics such as high content of Mg in relation to Ca, and high concentrations of Fe, Cr, Co, and Ni. Soil samples from Oaxaca and Puebla had similar Ni contents around 2300 mg kg−1, while samples of Guanajuato showed the lowest Ni levels with an average of 200 mg kg−1 as well as for other metals such as Co, Cr, Mn, and Zn. During this study, 83 plant specimens were collected, of which 52 were identified at genus level and 40 at species level. The collected plants belong to 19 different families such as Anacardiaceae, Fabaceae, Acanthaceae, Asteraceae, Sterculiaceae, and Verbenaceae which are also widely present in other ultramafic areas in Iran, Brazil, Sri Lanka, and Costa Rica. Only two Mexican endemic species are included in the collection. Ni hyperaccumulators were not detected at any of the studied sites. Therefore, hyperaccumulation, as a tolerance mechanism of the flora in response to ultramafic geochemical stress, does not seem to be developed in Central Mexico, as observed in the close Costa Rican site of Santa Elena.

Ipomoea purpurea (common morning glory) is an annual vine native to Mexico that is well known for its large, showy flowers. Humans have spread morning glories worldwide, owing to the horticultural appeal of morning glory flowers. Ipomoea purpurea is an opportunistic colonizer of disturbed habitats including roadside and agricultural settings, and it is now regarded as a noxious weed in the Southeastern US. Naturalized populations in the Southeastern United States are highly polymorphic for a number of flower color morphs, unlike native Mexican populations that are typically monomorphic for the purple color morph. Although I. purpurea was introduced into the United States from Mexico, little is known about the specific geographic origins of US populations relative to the Mexican source. We use resequencing data from 11 loci and 30 I. purpurea accessions collected from the native range of the species in Central and Southern Mexico and 8 accessions from the Southeastern United States to infer likely geographic origins in Mexico. Based on genetic assignment analysis, haplotype composition, and the degree of shared polymorphism, I. purpurea samples from the Southeastern United States are genetically most similar to samples from the Valley of Mexico and Veracruz State. This supports earlier speculation that I. purpurea in the Southeastern United States was likely to have been introduced by European colonists from sources in Central Mexico.

The Euphorbia adiantoides complex is here considered to consist of four species. This group is readily distinguished from other New World Euphorbia by the combination of two unusual features: entire styles with capitate stigmas and dichasial bracts with relatively long, filiform stipules. Euphorbia sonorae is reduced to a synonym of Euphorbia adiantoides, a taxon disjunctly distributed between Mexico and western South America. The other species of the complex are all restricted to Mexico. Two of these are described as new: E. zamudioi, an endemic to the Sierra Madre Oriental, and E. breedlovei, which is widespread in central and southern Mexico. A key to distinguish the species is provided, as too are data concerning their morphology, distribution, habitat, phenology, common names, and uses. Phylogenetic analyses were conducted using the nuclear ITS and the chloroplast psbA-trnH regions and including multiple samples of each species. The phylogenetic results are not always congruent with morphology, and of the four species herein recognized, only Euphorbia zamudioi is suggested to form an exclusive, well-supported lineage. This species is nested within E. breedlovei, and two collections of E. breedlovei from central Mexico are more closely related to E. zamudioi than they are to other E. breedlovei from southern Mexico. We hypothesize that E. zamudioi arose through peripatric speciation, in which a northern population of E. breedlovei became reproductively isolated and morphologically differentiated from the remainder of the populations of E. breedlovei.

The 3DVp,Vp/Vs, P‐ and S‐wave attenuation structure of the Cocos subduction zone in Mexico is imaged using earthquakes recorded by two temporary seismic arrays and local stations. Direct P wave arrivals on vertical components and direct S wave arrivals on transverse components from local earthquakes are used for velocity imaging. Relative delay times for P and PKP phases from teleseismic events are also used to obtain a deeper velocity structure beneath the southern seismic array. Using a spectral‐decay method, we calculate a path attenuation operatort* for each P and S waveform from local events, and then invert for 3D spatial variations in attenuation (Qp−1andQs−1). Inversion results reveal a low‐attenuation and high‐velocity Cocos slab. The slab dip angle increases from almost flat in central Mexico near Mexico City to about 30° in southern Mexico near the Isthmus of Tehuantepec. High attenuation and low velocity in the crust beneath the Trans‐Mexico Volcanic Belt correlate with low resistivity, and are probably related to dehydration of the slab and melting processes. The most pronounced high‐attenuation, low‐Vpand high‐Vp/Vsanomaly is found in the crust beneath the Veracruz Basin. A high‐velocity structure dipping into the mantle from the side of Gulf of Mexico coincides with a discontinuity from a receiver functions study, and provides an evidence for the collision between the Yucatán Block and Mexico in the Miocene.

Red dendrocronológica del pino de altura (Pinus hartwegii Lindl.) para estudios dendroclimáticos en el noreste y centro de México

This chapter provides a glimpse of the native experience in central Mexico since independence. Before independence, many legal and historical documents relating to central Mexico were still written in Nahuatl, and native litigants could present their cases in their own languages. Between independence and the present, most native peoples were culturally absorbed into a more Europeanized, Spanish-speaking nation. At the time of independence, many native people in both central and southern Mexico were members of former Indian republics or native pueblos, with their own land base and separate administrative structures. The social structure of native pueblos, throughout Mesoamerica, is usually depicted as a closed corporate community. Going back even before Mexican independence, the struggle of native peoples for land has been intrinsically related to legal battles in the courts, ideological debates, and armed rebellion. The logic of native political participation takes on a different form during times of relative political stability on the national level.

Seed and endocarp traits as markers of the biodiversity of regional sources of germplasm of tejocote ( Crataegus spp.) from Central and Southern Mexico

The Paleozoic Acatlan complex and Grenville-age Oaxaca terrane of southern Mexico have been suggested to be the southern continuation of North American orogenic systems. The Oaxaca terrane yields interpreted ages of ∼1.0 Ga and has many of the characteristics typical of Grenville belt rocks. The Paleozoic Acatlan complex consists of multiply deformed metasedimentary rocks, schists, granitoids, and eclogites that have been compared to rocks of the Appalachian belt. The northward extension of both the Oaxaca terrane and Acatlan complex, how-ever, are obscured by younger rock cover as they enter central Mexico. Furthermore, the configuration of these orogenic systems in southern Mexico is the reverse of that of the rest of North America, with the Grenville Oaxaca terrane to the east of the Paleozoic Acatlan complex. Isotopic studies show that the Acatlan complex records three tectonothermal events. The Sm-Nd whole-rock/mineral isochrons from schists as well as eclogites yield metamorphic ages of 410-380 Ma. This age of metamorphism is supported by U-Pb zircon data from a granitoid which yields an age of 370 ± 34 Ma. A later intrusion of a large stock in the Late Pennsylvanian (287 ± 2 Ma) was probably closely followed by a less significant deformational event. Small granitic intrusions and migmatites were later emplaced at 205-170 Ma (Rb-Sr and Sm-Nd mineral/ whole rock). The metasedimentary rocks and Paleozoic granitoids of the Acatlan complex have present-day e Nd of -9 to -11, with crustal residence ages (T DM ) of 1.3-1.6 Ga. These rocks must have been derived at least in part from a Proterozoic source area, and it is significant that crustal residence ages are identical to those of the Oaxaca terrane. The Oaxaca terrane, along with some South American Precambrian complexes, of which the Oaxaca terrane was probably once a part, may be considered the most likely source areas for the Acatlan complex. The less extensive eclogite, trondjhemite, and amphibolite bodies in the Acatlan complex yield model ages that show them to be juvenile additions to the crust. Neodymium model ages of the Acatlan complex are unlike those of some accreted crustal blocks of the Pacific margin, such as the Alexander, Stikine, and Wrangellia terranes, which have little signs of crustal recycling. Similarities between the Acatlan complex and the Acadian belt, as well as current Paleozoic paleogeographic and paleomagnetic reconstructions, suggest that the Devonian metamorphic event that affected these two areas was the result of a Laurentia-Gondwana collision. A later collision in late Carboniferous time caused deformation in the Acatlan complex, plutonic activity in southern Mexico, and deformation in the Ouachita, Marathon, and Appalachian belts. Both the Acatlan and Oaxaca terranes would have been continuous with South America until the break-up of Pangea in the Mesozoic era.

Mesozoic tectono-magmatic evolution of Mexico: An overview