An upper limit for slow-earthquake zones: self-oscillatory behavior through the Hopf bifurcation mechanism from a spring-block model under lubricated surfaces

"The complex oscillatory behavior of a spring-block model is analyzed via the Hopf bifurcation mechanism. The mathematical spring-block model includes Dieterich Ruina's friction law and Stribeck's effect. The existence of self-sustained oscillations in the transition zone where slow earthquakes are generated within the frictionally unstable region is determined. An upper limit for this region is proposed as a function of seismic parameters and frictional coefficients which are concerned with presence of fluids in the system. The importance of the characteristic length scale L, the implications of fluids, and the effects of external perturbations in the complex dynamic oscillatory behavior, as well as in the stationary solution, are take into consideration.

Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

Abstract: The Granjeno Schist is a meta-volcanosedimentary upper Paleozoic complex in northeastern Mexico. We suggest different tectonic settings for metamorphism of its serpentinite and talc-bearing rocks based on petrographic and geochemical compositions. According to the REE ratios (LaN/YbN = 0.51–20.0 and LaN/SmN = 0.72–9.1) and the enrichment in the highly incompatible elements Cs (0.1 ppm), U (2.8 ppm), and Zr (60 ppm) as well as depletion in Ba (1 – 15 ppm), Sr (1–184ppm),Pb(0.1–14ppm),andCe(0.1–1.9ppm)the rocks have mid-ocean ridge and subduction zones characteristics.TheserpentinitecontainsAl-chromite,ferrian chromiteandmagnetite.TheAl-chromiteischaracterized byCr#of0.48to0.55suggestingaMORBorigin,andCr#of 0.93 to 1.00 for the ferrian chromite indicates a prograde metamorphism.Weproposeatleasttwoserpentinization stagesoflithosphericmantlefortheultramaficrockofthe GranjenoSchist,(1)afirstinanocean-floorenvironment atsub-greenschisttogreenschistfaciesconditionsand(2) later a serpentinization phase related to the progressive replacement of spinel by ferrian chromite and magnetite atgreenschisttolowamphibolitefaciesconditionsduring regional metamorphism. The second serpentinization phase took place in an active continental margin during the Pennsylvanian. We propose that the origin of the ultramaficrocksisrelated toanobductionandaccretional eventatthewesternmarginofPangea. Keywords: ultramafic rocks; serpentinite; Granjeno Schist;northeasternMexico,Gondwana,Pange

Grafito en el complejo metamórfico paleozoico esquisto granjeno

El Complejo Metamórfico Paleozoico Esquisto Granjeno se compone por rocas con eductos sedimentarios e ígneos. El énfasis de este trabajo radica en la una unidad grafítica, de la cual no se ha entendido completamente su origen y evolución. Durante el metamorfismo las condiciones de grafitización corresponden a un proceso irreversible. Por lo cual el proceso de grafitización se considera un indicador confiable para estimar las condiciones térmicas máximas durante el metamorfismo. Se realizaron análisis geoquímicos en roca total y mineral con la finalidad de estimar las condiciones de grafitización y la mineralogía formada durante este proceso. Se estima que el proceso de grafitización ocurrió en dos rangos de temperatura de 318–339°C y 426–432°C. Por lo tanto, los sedimentos ricos en materia orgánica depositados en una cuenca oceánica localizada en la periferia del NW Gondwana fueron afectados por alto grado de metamorfismo regional durante el cierre de Pangea

Geositios y potencial turístico: acercamiento a la Huasteca Potosina, San Luis Potosí, México

El presente trabajo es la primera contribución en su tipo al conocimiento de la riqueza geológica y natural en 9 de los 20 municipios constituyentes de la Huasteca Potosina del estado de San Luis Potosí, México. En dicho espacio geográfico, está contenida una geodiversidad notable con lugares de interés geológico diverso, múltiples recursos paisajísticos que pueden promoverse como georecursos y que representan un potencial para fomentar actividades turísticas, educativas, culturales y/o científicas en el ámbito de la actividad del geoturismo. Mediante trabajo de campo y gabinete, con la utilización de fichas de evaluación para geositios, fue posible la identificación de 56 espacios. El geoturismo puede contribuir al mejoramiento de la calidad de vida de los habitantes del área de estudio.This paper is the first contribution to the knowledge of the geological and natural wealth of nine of the twenty municipalities comprising the Huasteca Potosina, located in San Luis Potosi State, Mexico. Its great geodiversity is refleted in the different geological attractions and multiple landscape resources that can be promoted as georesources and that represent a potential to explote tourism, educational, cultural, and scientific activities in the field of geotourism. Fifty six spaces were identified by means of field and office work, using geosite evaluation sheets. Geotourism can contribute to improve the quality of life of the inhabitants of this study area.Fil: Suárez Rodríguez, Irma B. Universidad Autónoma de San Luis Potosí. Unidad Académica Multidisciplinaria Zona Huasteca; México.Fil: Gaitán Morán, Javier. Universidad Autónoma de Baja California Sur. Departamento Académico de Ciencias de la Tierra; México.Fil: Hart Robertson, Margaret J. Universidad de Las Palmas de Gran Canaria. Departamento de Turismo; España.Fil: Barboza Gudiño, José Rafael. Universidad Autónoma de San Luis Potosí. Instituto de Geología; México.Fil: Gutiérrez Hernández, Alejandro. Universidad Autónoma de San Luis Potosí. Unidad Académica Multidisciplinaria Zona Huasteca; México.Fil: Márquez González, Antonio Romualdo. Universidad Autónoma de Nayarit. Unidad Académica de Economía; México

Análisis sedimentológico-facial de clastos formadores de brechas calcáreas cretácicas de una zona transicional plataforma�cuenca en el centro de México

A sedimentological facies analysis of the carbonate breccias deposited in a transitional platform to basin setting was conducted in the central part of San Luis Potosí, Mexico. The goal was to determine the origin and provenance of breccia components, mechanisms of deposition and the final depositional environment in order to better understand the depositional development of the Valles � San Luis Potosí Platform and western slope to the Central Mexico Mesozoic Basin during the mid-Cretaceous. The sedimentological characteristics of these breccias include planar basal contacts with evidence of erosion, transitional upper contacts, thicknesses from 0.5 to 14 m, lenticular to massive bedding with local normal grading, polymictic and clast sizes up to blocks of 1 m to 2 m. Clast morphology includes tabular clasts ranging from angular to subrounded with low sphericity to rounded with high sphericity. Sorting is poor to moderate. Clast orientation is random with local imbrication indicating W-NW transport. Matrix is micritic or sparitic and locally argillaceous. Textures of these carbonate breccias range from floatstone to rudstone with deep water clasts, bioclasts and resedimented shallow water clasts. Two types of breccias record different sedimentation processes. The first type is represented by breccias with tabular, angular clasts, which range from spiculite wackestone to mudstone or wackestone with pelagic fauna and millimeter lamination. These indicate pelagic sedimentation in deep water, in a basin, deep shelf and even toe-of- slope. The second is represented by subrounded clasts of resedimented material, transported by gravitational and suspension processes from the margin of the platform and back-reef zones. Noteworthy components are bioclasts, algae, sponges, corals, rudists, brachiopods and foraminifers (orbitolinids and miliolids). Resedimented clasts include. packstone with coated grains, bioclasts and pellets, ooid grainstones and grainstone or packstone with abundant benthic foraminifers. The lithologic, morphologic and textural characteristics of the breccias indicate that the transitional zone between the Valles-San Luis Potosí Platform and the Central Mexico Mesozoic Basin was an abrupt margin. This is suggested by the coexistence of deep-water and platform components. The breccias contain reef and back-reef material transported through channels or collapse of the unstable margin of the platform, generating debris flows and turbidity currents. Microfacies analysis indicates that the breccias with less developed textural maturity (tabular, angular and poorly sorted clasts) show more transport, than breccias with rounded and moderately sorted clasts. Important variations in the presence of rudist bioclasts suggest a discontinuous reefal rim along the western margin of the platform.A sedimentological facies analysis of the carbonate breccias deposited in a transitional platform to basin setting was conducted in the central part of San Luis Potosí, Mexico. The goal was to determine the origin and provenance of breccia components, mechanisms of deposition and the final depositional environment in order to better understand the depositional development of the Valles � San Luis Potosí Platform and western slope to the Central Mexico Mesozoic Basin during the mid-Cretaceous. The sedimentological characteristics of these breccias include planar basal contacts with evidence of erosion, transitional upper contacts, thicknesses from 0.5 to 14 m, lenticular to massive bedding with local normal grading, polymictic and clast sizes up to blocks of 1 m to 2 m. Clast morphology includes tabular clasts ranging from angular to subrounded with low sphericity to rounded with high sphericity. Sorting is poor to moderate. Clast orientation is random with local imbrication indicating W-NW transport. Matrix is micritic or sparitic and locally argillaceous. Textures of these carbonate breccias range from floatstone to rudstone with deep water clasts, bioclasts and resedimented shallow water clasts. Two types of breccias record different sedimentation processes. The first type is represented by breccias with tabular, angular clasts, which range from spiculite wackestone to mudstone or wackestone with pelagic fauna and millimeter lamination. These indicate pelagic sedimentation in deep water, in a basin, deep shelf and even toe-of- slope. The second is represented by subrounded clasts of resedimented material, transported by gravitational and suspension processes from the margin of the platform and back-reef zones. Noteworthy components are bioclasts, algae, sponges, corals, rudists, brachiopods and foraminifers (orbitolinids and miliolids). Resedimented clasts include. packstone with coated grains, bioclasts and pellets, ooid grainstones and grainstone or packstone with abundant benthic foraminifers. The lithologic, morphologic and textural characteristics of the breccias indicate that the transitional zone between the Valles-San Luis Potosí Platform and the Central Mexico Mesozoic Basin was an abrupt margin. This is suggested by the coexistence of deep-water and platform components. The breccias contain reef and back-reef material transported through channels or collapse of the unstable margin of the platform, generating debris flows and turbidity currents. Microfacies analysis indicates that the breccias with less developed textural maturity (tabular, angular and poorly sorted clasts) show more transport, than breccias with rounded and moderately sorted clasts. Important variations in the presence of rudist bioclasts suggest a discontinuous reefal rim along the western margin of the platform.En la porción central del Estado de San Luis Potosí se realizó un estudio sedimentológico-facial de los clastos formadores de brechas calcáreas depositadas en una zona de transición plataforma-cuenca, de la plataforma, originando depósitos de flujos de escombros y corrientes turbidíticas. Comparando los resultados morfológicos y texturales con el análisis microfacial destaca que las brechas, con una pobre madurez textural (clastos tabulares, angulosos y mal clasificados), muestran un mayor transporte que las brechas con clastos redondeados y moderadamente clasificados. Variaciones importantes en la presencia de bioclastos de rudistas sugiere la existencia de bordes arrecifales discontinuos a lo largo del margen occidental de la Plataforma. para determinar el origen y proveniencia de sus componentes, sus mecanismos de depósito, así como su ambiente final de depósito y de este modo contribuir al mejor conocimiento sobre el desarrollo de los procesos de depósito entre la Cuenca Mesozoica del Centro de México y la Plataforma Valles-San Luis Potosí, en su margen occidental, durante el Cretácico. Las características sedimentológicas que presentan estas brechas son contactos inferiores planos con evidencias de erosión, contactos superiores transicionales, espesores desde 0.5 hasta 14 m; afloran lenticularmente, masivas y localmente presentan gradación normal en la cima, polilitológicas, componentes con bloques de 1 m a 2 m, de forma tabular, angulosos a subredondeados, con baja esfericidad o redondeados con alta esfericidad, clasificación pobre a moderada, de arreglo caótico con una ligera imbricación con inclinaciones que muestran un transporte al W-NW, en una matriz micrítica, microesparítica y localmente arcillosa. El estudio microfacial muestra que estas brechas calcáreas tienen texturas que varían de floatstonerudstone de clastos de aguas profundas, bioclastos y clastos de aguas someras resedimentados, dentro de las cuales se diferencian dos tipos de sedimentación, el primero está representado por clastos tabulares angulosos que varían desde wackestone con espículas a mudstone-wackestone con fauna pelágica y laminación milimétrica, indicando una sedimentación pelágica en ambientes de aguas profundas característica de zonas de facies de cuenca, plataforma de mar abierto e incluso pie de talud, y el segundo está representado por clastos subredondeados de material resedimentado, transportados por procesos gravitacionales y de suspensión desde el margen de la plataforma y zonas postarrecifales, sobresaliendo los bioclastos (algas, esponjas, corales, rudistas y braquiópodos), foraminíferos (orbitolínidos y miliólidos) y clastos resedimentados (p.ej., packstone de granos cubiertos, bioclastos y pellets, grainstone de ooides, grainstone-packstone con abundantes foraminíferos bentónicos). Las características litológicas, morfológicas y texturales de las brechas indican que en la zona de transición entre la Plataforma Valles-San Luis Potosí y la Cuenca Mesozoica del Centro de México prevaleció un margen abrupto, evidenciado por la coexistencia de componentes de aguas profundas y de plataforma indicando que la formación y origen de las brechas estudiadas se debió al aporte de material desde zonas arrecifales y postarrecifales a través de canales o colapsos de zonas inestables del marge