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Simplified geologic map in Oaxaca State. Inset shows major faults in Mexico with probable Jurassic displacements: 1, Mojave- Sonora megashear (Silver and Anderson, 1974). 2, Trans-Mexican volcanic belt lineament (Gastil and Jensky, 1973). 3, Acapulco-Guatemala megashear (Anderson and Schmidt, 1983). 4, Tamaulipas–Golden Lane–Chiapas fault zone (Pindell, 1985). 5, Tamaulipas-Oaxaca fault (Padilla y Sá nchez, 1986). Black rectangle is enlarged area, black diamond shows location of geochronologic samples. Equal-area lowerhemisphere projections with poles of foliations. Note that although there is considerable scatter in foliation trends, stretching lineation (net labeled L) is very consistent with north-south strike and very shallow dip of <25°.
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One of the least-known aspects of the evolution of the Gulf of Mexico is the nature and location of shear zones along which the relevant continental fragments were displaced. The Sierra de Juárez mylonitic complex, located in southern Mexico, is a polyorogenic north-northwest trending structure. Here we report U-Pb mylonitization dates of 165 ± 20...
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The Triassic and Jurassic geology of northern Sonora encompasses important events that are linked to the late Paleozoic history of the region. The fossiliferous El Antimonio Group in the Sierra del álamo includes the upper Permian-Triassic Antimonio, and Río Asunción formations and the Hettangian-Sinemurian Sierra de Santa Rosa Formation. These for...
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... 120 km long, NNW-SSE trending composite metamorphic belt delimited by Cenozoic faults (Oaxaca and Siempre Viva faults) between the Zapoteco and Cuicateco terranes in southern Mexico (Figs. 1 and 2). The lithologies and structure of the SJC were pervasively modified by extensive Middle Jurassic and Lower Cretaceous strike-slip shearing events, likely related to the opening of the Gulf of Mexico and the evolution of Mexico peninsular Alaniz-Álvarez et al., 1996;Martini and Ortega-Gutiérrez, 2016;Pindell et al., 2021;Espejo-Bautista et al., 2022). Mylonitic foliation dips 50-30 • to the west, and the stretching lineation usually exhibits a sub-horizontal ~ N-S orientation. ...
... Ductile deformation was accommodated by 10-m scale anastomosed shearing bands wrapping regional low-strain sectors. The relict non-mylonitic zones preserve gneisses and schists with prograde amphibolite-facies assemblages and variable degrees of folding, reflecting pre-mylonitic deep-crustal tectonic events (Sedlock et al., 1993;Alaniz-Álvarez et al., 1996;Espejo-Bautista et al., 2021). The overprinting Mesozoic mylonitization has two critical tectonic implications: (1) the SJC represents an extinct transform along the current eastern border of the Oaxacan Complex, and (2) the SJC is allochthonous relative to the Oaxacan Complex. ...
The eastern and southern Precambrian basement of Mexico is composed of crustal blocks linked to northern Amazonia before and during the assembly of the Rodinia supercontinent. In this paper, we examine an extensive basement block known as the Sierra de Juárez Complex (SJC) in southern Mexico by integrating fieldwork, in-situ zircon U–Pb geochronology by LA-ICPMS and whole-rock geochemistry by X-ray fluorescence. The results provide evidence for a continuous low-to high-grade metamorphic succession here re-defined as the Pochotepec suite (PS), which comprises an upper lithodeme with volcanosedimentary precursors and a lower lithodeme that includes mafic to intermediate orthogneisses and migmatites. The analytical results suggest that the PS protoliths originated in a continental-arc tectonic setting ca. 1080-1050 Ma along the northern edge of Amazonia before the consolidation of Rodinia. In addition, xenocrystic zircon U–Pb analyses indicate the presence of a recycled older crust of ca. 1200–1300 Ma. Finally, U–Pb data of recrystallized zircon rims and younger metamorphic zircon grains recorded the timing of metamorphism and anatexis of the PS during the early Tonian (954-933 Ma). The crystallization ages of two trondhjemitic leucosomes of 954 and 933 Ma strongly support the migmatization age. The Tonian metamorphic/anatectic episode of the PS differs in grade and age from the typical metamorphism related to the amalgamation of Rodinia reported in Mexico and Colombia (granulite-facies at ca. 990 Ma). Therefore, we interpret this event as produced by either post-orogenic crustal collapse or contractive tectonics.
... Despite undergoing intense Mesozoic re-working related to the breaking up of Pangaea (e.g. Alaniz-Álvarez et al. 1996;Martini and Ortega-Gutiérrez 2016;Pindell et al. 2021), the SJC has been proved to encompass an intricate multitectonothermal record developed over more than 1100 Ma from the Stenian Period (Espejo-Bautista et al. 2023) to the Cenozoic (e.g. Graham et al. 2021). ...
... km long and c. 15 km wide that constitutes the basement of the western Cuicateco Terrane (Sedlock et al. 1993). It is bounded to the west by the Cenozoic normal-type Oaxaca Fault that cuts a former thrust contact with the Oaxacan Complex (Alaniz-Álvarez et al. 1996;Ortega-Gutiérrez et al. 2018;Graham et al. 2021). During the Upper Cretaceous-Eocene, the SJC was thrust eastwards over Lower Cretaceous successions (Chivillas and Jaltepetongo formations) along the Siempre Viva Fault, which forms its eastern border (Figs 1 & 2;Ángeles-Moreno et al. 2012;Graham et al. 2021). ...
... Different tectonic interpretations have been provided for the mylonitic event. Alaniz-Álvarez et al. (1996) suggested that it reflects the development of a right-lateral c. north-south transform system along eastern peninsular Mexico in response to the opening of the Gulf of Mexico during the Middle Jurassic. Alternatively, Pindell et al. (2021) suggested that it records a west-dipping sinistral shear zone related to the southeastward translation of the 'Oaxaca Block' during the Middle-Upper Jurassic. ...
The Sierra de Juárez Complex (SJC) of southern Mexico contains an extensive geological record from Precambrian to Cenozoic, involving Rodinia, NW-Gondwana, western equatorial Pangea, and eastern peninsular Mexico. It is thus critical for palinspastic reconstructions and lithotectonic correlations, mainly between the Mexican and NW South America terranes. In this contribution, we investigate the tectonic evolution of the northern SJC from Silurian to the Lower Cretaceous on the basis of fieldwork, petrography, and zircon U-Pb geochronology by LA-ICPMS. Our results allow us to constrain five main geologic events. (1) Middle Paleozoic sedimentation along NW-Gondwana during transtensional tectonics. (2) Volcanosedimentary activity between 292-281 Ma in NW-Gondwana during Rheic Ocean closure. (3) Early Permian metamorphism related to flat-slab subduction postdating Pangea assembly. (4) Early-Middle Jurassic anatexis and magmatism coeval with regional shearing at ca. 175 Ma influenced by transtensional tectonics along eastern peninsular Mexico during Pangea tenure. (5) Intermediate to acid magmatism between ca. 136-129 Ma, correlated with the Zongolica continental arc in southern Mexico, followed by deep-crustal shearing related to either the formation of the extensional Chivillas basin or the Upper Cretaceous-Cenozoic contractional episode documented in the Cuicateco Terrane.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6282721
... During the Late Jurassic, changes in the subduction angle of the Farallon plate underneath the Guerrero plate evolved into a high-angle oblique subduction zone that also developed an extensional and transtensional continental arc (s.s., Busby, 2012). The arc was associated with normal and lateral faults that favored exhumation and erosion of the Early to Middle Jurassic volcano-sedimentary successions of the Nazas arc (Bassett and Busby, 2005 Gulf of México led to left-lateral strike-slip faults, pull-apart and strike-slip basins in México and southern USA (e.g., the Chihuahua and Monterrey troughs; Rosaz, 1989;Goldhammer, 1999;Haenggi, 2002;Bassett and Busby, 2005;Ocampo-Díaz, 2011) continued deposition of continental evaporites in the same area (Marton, 1995;Alaníz-Alvarez et al., 1996;Pindell and Kennan, 2009). Due to the Gulf opening, the Tethys Ocean flooded the continent from the east. ...
The Monterrey Metropolitan Area (MMA), in the state of Nuevo León, México, has had a significant increase in its population and associated urban footprint for decades. From a population standpoint, it represents the second largest urban area in México. Its growth has required increasing infrastructure for the necessary services including public access to potable water, which will continue to increase over time. The supply of water resources for the metropolis comes mainly from groundwater sources. These sources are subject to certain conditions influenced by their geographical location, physiographical characteristics, and the geological environment, having a direct impact on the water recharge system of the regional aquifers. The government of the State of Nuevo León has developed an investment master plan for a water resource, outlined to be completed in 2050, which includes the construction of new dams and the setting up of additional shallow and deep production wells. With a constant annual population growth from one to five percent, additional stresses and vulnerability to this valuable resource will occur. Based on the changing demographics and additional stresses to water resources, it is essential to understand the localized natural groundwater regime extending from the precipitation recharge zones to the individual aquifers that serve the needs of the population. The following study evaluates specific aspects of the water regime (recharge zones and springs), in an area approximately 25 km south of central Monterrey, in the Santiago area of the MMA which is expected to have significant urban expansion in the future. The central portion of the Sierra del Cerro de la Silla, which constitutes the study area is a catchment and infiltration zone for meteoric water. Within the study area, five springs were identified and sampled during the dry season, and the collected spring water samples were submitted for geochemical analyses. Field surveys, data collection and interpretation have contributed to the understanding of the water origin and associated physical-chemical characteristics during infiltration through the geological succession and ultimate incorporation into the aquifer. The characterization of the regime through a series of field surveys and the spring water characterization has determined the presence of a low enthalpy geothermal system at the depth, that has the potential to impact shallow freshwater regimes. In addition to contributing to the knowledge of the local hydrogeological system, this study can support the understanding of the vulnerability of the natural resource due to human activity and back up concepts of optimal use and protection.
... The trans-Mexican volcanic belt formed in early Miocene time, about 19 Ma (Ferrari et al. 2012). This magmatic activity occurred over an earlier strike slip fault between western and eastern Mexico -the Trans-Mexican volcanic belt lineament, a sinistral strike slip fault in the Jurassic and displacing southern Mexico to the southeast (Alaniz-Alvarez et al. 1996). It is possible that all three tectonic and geological processes affected differentiation of Phassus and Schausiana, but much more extensive geographic sampling and systematic resolution of both genera will be essential to address these possibilities. ...
A new species of Phassus Walker, Phassus zapalinamensis sp. n., is described from northeastern Mexico based on a single male and female from the Parque Ecoturístico El Chorro (Coahuila) and the Área Natural Protegida Estatal "Cerro La Mota"(Nuevo León), with supplementary geographic records from photos posted at inaturalist.org. Conspecificity of the specimens is supported by a 100% bootstrap in the COI gene. Adults, male and female genitalia and external appearance are illustrated. The forewing pattern is most similar to P. huebneri (Geyer, [1838]), a species known only from illustration of the female moth which probably represents several cryptic species in Mexico and Central America. A syntype female specimen of Phassus marcius Druce, 1892 and a syntype female of Phassus argentiferus Walker, 1856 are designated here as respective lectotypes. The new species extends the previously documented range of Phassus between Central America and the trans-Mexican Volcanic belt, to almost the Mexico-United States border. This is currently the northernmost limit known for any genus of Hepialidae with Central or South American affinities. We discuss the potential evolutionary significance of the distributional boundary with respect to the possible role of the Jurassic-Cretaceous Mojave-Sonora Megashear fault system and earlier magmatic arcs in northern Mexico.
... The Siempre Viva Fault is a major thrust that puts the Sierra de Juárez Complex above the Cuicateco Belt (Fig. 1). The Sierra de Juárez Complex forms a ~ 170 km long and ~ 10-15 km wide migmatitic-mylonitic belt previously interpreted as a thrust zone reactivated by possibly dextral shearing during the opening of the Gulf of Mexico (Delgado-Argote, 1988;Alaniz-Álvarez et al., 1996). This complex includes a series of ortho-and para-gneisses that show evidence of partial migmatization and mylonitization. ...
An extensive dataset of existing and new geo/thermochronological data from several areas in Southern Mexico constrains the tectonic history of the region, as well as various source-to-sink relationships and local burial histories. Our interpretation acknowledges that not all cooling/heating observed in the source areas is due to erosional exhumation/burial but, in some cases, due to advective heat transfer from magmatic sources, which potentially overprinted earlier events. In this work, we identified several areas that have been exhumed since the Early Cretaceous and potentially provided clastic material to the southern Gulf of Mexico area.
We help to document how the Mexican (Laramide) Orogeny propagated eastwards and southwards from the Late Cretaceous through the early Oligocene. The first sediments reaching the Tampico–Misantla and Veracruz basins derived mostly from eroded Cretaceous carbonate material that covered the Sierra Madre Oriental, the Sierra de Juárez Complex and the Cuicateco belts, as well as foredeep/intra-orogenic basin deposits formerly covering them. Possibly by the end of the Mexican Orogeny, the clastic Jurassic and older crystalline basement rocks became exposed and became the main sources of quartz-rich clastic material to the most easterly foreland basins and Gulf of Mexico. Exposure was probably assisted by higher angle basement thrusts such as the Vista Hermosa/Valle Nacional faults. The Mixtequita and Guichicovi blocks have also provided an important source of quartz-rich and metamorphic lithic-rich material to the southern Veracruz Basin possibly since the Eocene.
For most of the Cenozoic, the Chiapas and the Sureste basins were sourced from areas south of the Chiapas Massif, i.e., the North America–Caribbean plate boundary zone along today's Chiapas coastal plain. This plate boundary zone accommodated relative displacement between Mexico and the Chortis Block of the Caribbean Plate. Paleocene–middle Miocene sediments within the Chiapas Basin were at least partially sourced from i) metamorphic complexes in the northern Chortis Block; ii) the parautochthonous Chontal Complex, an oceanic-like basin sandwiched between Chortis and southern Mexico; iii) the elongating volcanic arc along southern Mexico and western Chortis; and iv) the Cretaceous and Jurassic sedimentary cover of the southern flank of the Chiapas Massif,
The westward telescoping of southern Mexico onto the Cocos Plate in the wake of Chortis has produced flat slab subduction geometry and eastwardly-younging uplift of the Xolapa Belt (Oligo–Miocene) and the Chiapas Massif (late Miocene). It also caused reorganization of the drainage systems providing material to the Chiapas and Sureste basins.
Our results highlight the importance of understanding relative block and plate boundary displacements in a dynamic hinterland and consider the role of major faults when interpreting source-to-sink relationships in the area. We describe the latter relationships for several geologic time intervals in which reservoir-prone sediments were delivered to the southern Gulf of Mexico. Finally, we integrate the source-to-sink history to provide an assessment of reservoir quality and hydrocarbon prospectivity in the region.
... The crystalline basement rocks forming the Yucat an platform belong to the Maya block ( Fig. 1), which is generally described as encompassing the Yucat an peninsula, the northeast of Mexico, the coastal plains of the western and northern Gulf of Mexico, and the Chiapas massif complex (Keppie et al. 2011;Weber et al. 2012Weber et al. , 2018, with its north and northeastern boundaries bordered by continental shelves and oceanic lithosphere (Alaniz- Alvarez et al. 1996;Keppie et al. 2011). The Maya block was thought to be bordered in the northwest by the Oaxaquia block (Grenvillian-aged); in the southwest by the Cuicateco complex; and in the south by the Polochic, Motagua, and Jocotl an-Chamale on fault systems (Fig. 1), making the separation with the Caribbean plate (Dengo 1969;Donnelly et al. 1990;Weber et al. 2012Weber et al. , 2018. ...
The IODP-ICDP Expedition 364 drilling recovered a 829 m core from Hole M0077A, sampling ˜600 m of near continuous crystalline basement within the peak ring of the Chicxulub impact structure. The bulk of the basement consists of pervasively deformed, fractured, and shocked granite. Detailed geochemical investigations of 41 granitoid samples, that is, major and trace element contents, and Sr–Nd isotopic ratios are presented here, providing a broad overview of the composition of the granitic crystalline basement. Mainly granite but also granite clasts (in impact melt rock), granite breccias, and aplite were analyzed, yielding relatively homogeneous compositions between all samples. The granite is part of the high-K, calc-alkaline metaluminous series. Additionally, they are characterized by high Sr/Y and (La/Yb)N ratios, and low Y and Yb contents, which are typical for adakitic rocks. However, other criteria (such as Al2O3 and MgO contents, Mg#, K2O/Na2O ratio, Ni concentrations, etc.) do not match the adakite definition. Rubidium–Sr errorchron and initial ⁸⁷Sr/⁸⁶Srt=326Ma suggest that a hydrothermal fluid metasomatic event occurred shortly after the granite formation, in addition to the postimpact alteration, which mainly affected samples crosscut by shear fractures or in contact with aplite, where the fluid circulation was enhanced, and would have preferentially affected fluid-mobile element concentrations. The initial (ɛNd)t=326Ma values range from −4.0 to 3.2 and indicate that a minor Grenville basement component may have been involved in the granite genesis. Our results are consistent with previous studies, further supporting that the cored granite unit intruded the Maya block during the Carboniferous, in an arc setting with crustal melting related to the closure of the Rheic Ocean associated with the assembly of Pangea. The granite was likely affected by two distinct hydrothermal alteration events, both influencing the granite chemistry: (1) a hydrothermal metasomatic event, possibly related to the first stages of Pangea breakup, which occurred approximately 50 Myr after the granite crystallization, and (2) the postimpact hydrothermal alteration linked to a long-lived hydrothermal system within the Chicxulub structure. Importantly, the granites sampled in Hole M0077A are unique in composition when compared to granite or gneiss clasts from other drill cores recovered from the Chicxulub impact structure. This marks them as valuable lithologies that provide new insights into the Yucatán basement.
... This indicates that the Salado River-Axutla and Caltepec faults took part in the process of continental attenuation related to Pangea breakup. The Caltepec fault has a NNW trend that is similar to the trend of other major normal faults (e.g., Oaxaca, Texcalapa, and El Sabino faults; Alaniz-Álvarez et al., 1996;Campos-Madrigal et al., 2013;Fig. 1) that developed between eastern Mexico and the Yucatán block during Early-Middle Jurassic time (Fig. 14A). ...
During Pangea breakup, several Jurassic extensional to transtensional basins were developed all around the world. The boundaries of these basins are major structures that accommodated continental extension during Jurassic time. Therefore, reconstructing the geometry of Jurassic basins is a key factor in identifying the major faults that produced continental attenuation during Pangea breakup. We reconstruct the tectono-sedimentary evolution of the Jurassic Tlaxiaco Basin in southern Mexico using sedimentologic, petrographic, and U-Pb geochronologic data. We show that the northern boundary of the Tlaxiaco Basin was an area of high relief composed of the Paleozoic Acatlán Complex, which was drained to the south by a set of alluvial fans. The WNW-trending Salado River–Axutla fault is exposed directly to the north of the northernmost fan exposures, and it is interpreted as the Jurassic structure that controlled the tectono-sedimentary evolution of the Tlaxiaco Basin at its northern boundary. The eastern boundary is represented by a topographic high composed of the Proterozoic Oaxacan Complex, which was exhumed along the NNW-trending Caltepec fault and was drained to the west by a major meandering river called the Tlaxiaco River. Data presented in this work suggest that
continental extension during Pangea breakup was accommodated in Mexico not only by NNW-trending faults associated with the development of the Tamaulipas–Chiapas transform and the opening of the Gulf of Mexico, but also by WNW-trending structures. Our work offers a new perspective for future studies that aim to reconstruct the breakup evolution of western equatorial Pangea.
... Despite this, the age of the Pangea breakup onset remains inconclusive in southern Mexico. Most authors suggested that the rupture of Pangea started during Early Jurassic time (Ross and Scotese, 1988;Pindell and Kennan, 2009), forming rift basins bounded by normal faults (Alaniz-Alvarez et al., 1996;Martini and Ortega-Gutiérrez, 2018). ...
Southern Mexico is a key area for unraveling the tectonic evolution of North America because it contains the stratigraphic and structural record of the major tectonic events that shaped this continental mass, such as the breakup of Pangea and the growth of the North America Cordilleran Orogeny. However, multiple reactivations of faults and erosion of the stratigraphic record do not permit to adequately assess the timing of these tectonic events. Although most authors suggested that lithospheric extension and exhumation of continental blocks during Pangea breakup started in Mexico by Early Jurassic time, works published in the last decade provide an increasing number of thermo-tectonic evidence of an earlier phase of continental thinning. In this work, we present detrital apatite thermochronological and geochemical data (trace elements including rare earth elements) from fluvial deposits of the Tianguistengo formation, which is the oldest stratigraphic unit of the Otlaltepec Basin, a major basin in southern Mexico that has been linked to Pangea breakup. Our data show that at least a part of the Tianguistengo formation was derived from the adjacent Pennsylvanian–Cisuralian Totoltepec pluton. Apatite fission-track-based time–temperature modelling for unreset apatite populations suggests that the main exhumation of the Totoltepec pluton, which prompted the deposition of a part of the Tianguistengo formation, took place during Late Triassic time. Thus, our results suggest that Pangea breakup in southern Mexico started at least by Middle–Late Triassic time (240–230 Ma), as it is recorded in the Otlaltepec Basin.
... Here, the crystalline basement is part of the Maya block, the southeasternmost Mexican geological terrane ( Fig. 1; Keppie et al., 2011;Weber et al., 2012Weber et al., , 2018. The Maya block has traditionally been inferred to encompass the Yucatán Peninsula in the north, including the coastal plains of the western and northern Gulf of Mexico (Weber et al., 2012) to the Chiapas Massif complex in the south ( Fig. 1B; Keppie et al., 2011;Weber et al., 2012Weber et al., , 2018, with the northern and northeastern boundaries bordered by continental shelves and oceanic lithosphere (Alaniz-Álvarez et al., 1996;Keppie et al., 2011). ...
This study presents petrographic and geochemical characterization of 46 pre-impact rocks and 32 impactites containing and/or representing impact melt rock from the peak ring of the Chicxulub impact structure (Yucatán, Mexico). The aims were both to investigate the components that potentially contributed to the impact melt (i.e., the pre-impact lithologies) and to better elucidate impact melt rock emplacement at Chicxulub. The impactites presented here are subdivided into two sample groups: the lower impact melt rock−bearing unit, which intrudes the peak ring at different intervals, and the upper impact melt rock unit, which overlies the peak ring. The geochemical characterization of five identified pre-impact lithologies (i.e., granitoid, dolerite, dacite, felsite, and limestone) was able to constrain the bulk geochemical composition of both impactite units. These pre-impact lithologies thus likely represent the main constituent lithologies that were involved in the formation of impact melt rock. In general, the composition of both impactite units can be explained by mixing of the primarily felsic and mafic lithologies, but with varying degrees of carbonate dilution. It is assumed that the two units were initially part of the same impact-produced melt, but discrete processes separated them during crater formation. The lower impact melt rock−bearing unit is interpreted to represent impact melt rock injected into the crystalline basement during the compression/excavation stage of cratering. These impact melt rock layers acted as delamination surfaces within the crystalline basement, accommodating its displacement during peak ring formation. This movement strongly comminuted the impact melt rock layers present in the peak ring structure. The composition of the upper impact melt rock unit was contingent on the entrainment of carbonate components and is interpreted to have stayed at the surface during crater development. Its formation was not finalized until the modification stage, when carbonate material would have reentered the crater.
... Villagómez (2014) postulated hyper-extension on a detachment fault in the region to explain rapid cooling and associated retrograde mylonitization between 134 and 130 Ma in the Sierra de Juárez, but other studies emphasized the strike-slip displacement along the Sierra Juárez mylonitic belt (e.g. Alaniz-Álvarez et al. 1996). In Neogene times, westward drift of southern Mexican lithosphere over the Cocos slab, recorded by the northeastward arc migration from near the Oaxacan coast to its current location in the coastal plain of the Veracruz Basin (Las Tuxtlas volcanic centre), is thought to have significantly elevated the surface topography of the Cuicateco Belt (Pindell and Miranda 2011). ...
... The traverses were chosen partly because of access considerations and partly because the northern one crosses the Córdoba-Orizaba Platform while, thanks to erosion, the southern one traverses the Cuicateco basement beneath it (Fig. 2). The sections cross the northern and southern extremities of the mylonitic terrain of the Sierra de Juárez in the western part of Cuicateco (Alaniz-Álvarez et al. 1994(Alaniz-Álvarez et al. , 1996. Another shorter (15 km) section across the mylonitic belt was made east of the town of San Juan Bautista Cuicatlán, some 80 km north of Oaxaca City. ...
... They Integrated plate tectonics and structural geology in Mexico 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 are summarized in Figure 9, and described in detail by Dávalos-Alvarez et al. (2007). In the footwall of the fault and throughout the crystalline basement of the western outcrop of crystalline basement of Cuicateco (the 'Aloapan Complex' of the SGM geological maps, the 'Sierra de Juárez mylonitic belt' of Alaniz-Álvarez et al. 1994Alaniz-Álvarez et al. , 1996, and here), strong, mylonitic tectonic fabrics are developed (Fig. 10). The general dip is around 30°west or SW, and the dominant linear component (stretching direction) is north-south or NE-SW (Fig. 10d). ...
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.
