Papers by Francisco M. Alonso-Chaves
Ensenanza De Las Ciencias De La Tierra, 2013
Resumen En este trabajo se presentan algunas ideas que pueden aplicarse en clase para que los est... more Resumen En este trabajo se presentan algunas ideas que pueden aplicarse en clase para que los estudiantes aprendan las técnicas y principios del mapa geológico. Los estudiantes tendrán la oportunidad de conocer el arte de hacer un mapa geológico. Cualquier profesor puede seguir las explicaciones detalladas del texto y con ello hacer pensar a los estudiantes sobre: i) las curvas de nivel en los mapas topográficos, ii) patrones de afloramiento de los contactos geológicos y las reglas de la "V", iii) espesor real y aparente de los niveles geológicos (estratos / unidades). Las láminas que hemos elaborado, a modo de modelos geológicos 2-D y 3-D dibujados en papel, ayudan a entender mejor el concepto mismo del mapa geológico. Este trabajo presenta un caso práctico que analiza la elaboración del mapa geológico de la ciudad de Huelva y un modelo geológico tridimensional donde se observan estratos subhorizontales.
This paper shows the preliminary results of a laboratory geotechnical test for the identification... more This paper shows the preliminary results of a laboratory geotechnical test for the identification and determination of consolidation properties of the soils of Huelva. The fine-grained soils (Arcillas de Gibraleón, Arenas de Huelva and Arenas de Bonares units) have a high consistency. These are over-consolidated soils which have few compressibilities. The Arcillas de Gibraleón Unit presents expansive clay minerals.
Geogaceta, 2011
RESUMEN Este trabajo describe la terminación oriental de la Zona de Fractura Azores-Gibraltar y s... more RESUMEN Este trabajo describe la terminación oriental de la Zona de Fractura Azores-Gibraltar y se propone, basándonos de datos sísmicos, la existencia de una zona de restraining bend formada por fallas inversas de dirección NESO y fallas EO de ...
Ensenanza De Las Ciencias De La Tierra Revista De La Asociacion Espanola Para La Ensenanza De Las Ciencias De La Tierra, 2013
Resumen Este artículo contiene una revisión de la historia y contenido actual de un concepto, el ... more Resumen Este artículo contiene una revisión de la historia y contenido actual de un concepto, el de astenosfera, clave en las modernas Ciencias de la Tierra. Definido por Barrell en 1914, cuando Wegener diseñaba su primer ataque a la Tierra inmóvil, fue rescatado por los geofísicos revolucionarios de la década de 1960 sólo para ser secuestrado a continuación por algunos sismólogos y, por último, devuelto al centro del escenario en la versión actual de la tectónica de placas. Con los mejores datos geofísicos, la astenosfera se define hoy como todo el manto superior no litosférico. Los autores aprovechan esta revisión para actualizar otros conceptos recientes sobre el interior de la Tierra, como son el motor de las placas litosféricas o las avalanchas en el manto. Y destacan también las áreas más inciertas, como son los procesos en la interfase manto superior-manto inferior y las fuentes del calor interno de nuestro planeta.
Geogaceta, 2012
Within Alpujarride units cropping out in La Axarquia region, recumbent folds with different orien... more Within Alpujarride units cropping out in La Axarquia region, recumbent folds with different orientations are observed. In some units, as in the Tejeda and Benthomiz ones, kilometer-size overturned limbs belonging to individual regional antiforms, are described. The axial surfaces of these folds are now folded as a result of the superposition of deformation that occurred during the late Miocene. Simultaneously to recumbent folding (F 3) ductile shear zones, as observed in the core of the Benthomiz Unit antiform which crops out in the Torrox area, formed. A top-to-the E-NE transport direction for the hanging wall of the ductile extensional detachments, can be proposed.
The Puebla de Guzman Anticline (PGA) is one of the main structural features of the Spanish sector... more The Puebla de Guzman Anticline (PGA) is one of the main structural features of the Spanish sector of the Iberian Pyrite Belt (IPB), along with the Valverde del Camino Antiform (VCA). Two main tectonic deformation phases have been recognized in the PGA, the antiform being essentially a second phase structure with some previous deformation inherited from the first phase. Seismic and field data support the interpretation of its internal architecture as an antiform with its southern limb affected by a south-vergent imbricate thrust system (Simancas et al., 2004; Mantero et al., 2006). Actually, the antiform is a thrust propagation fold linked to the development of the southern-limb thrust system. Its geometry is characterized by the presence of a frontal ramp (N100oE) ahead of its southern limb and a lateral ramp with approximately NNE-SSW strike, located at the eastern closure. The tectonic movement is distributed along a high number of thrust faults related to multiple detachment leve...
The Science of the total environment, Jan 15, 2019
This paper is focused on the hydrogeochemical characterization of the Negro River along its cours... more This paper is focused on the hydrogeochemical characterization of the Negro River along its course, as well as in the proposal of a functioning model for the contamination processes in order to establish potential cause-effect relationships between water quality, geology (ARD), mining activities (AMD) and the tectonic framework as transmission vector of acidity, metals and sulphates. The scenario shows a heavily-contaminated river compared to the unaffected regional background. By graphical and statistical treatments of physico-chemical data of Negro River and the unaffected values of regional background and other AMD/ARD representative rivers' it is possible to conclude that Antamina Mine, is not the cause of the Negro River contamination, without the need of isotopic tracers, but just through the inexistent concentrations of Cu, Bi and Mo found in the waters. In the proposed contamination model, climatic factors (glacial retreat) activate geological (ARD) processes. The tecton...
es la más meridional de las diversas zonas geológicas que se han diferenciado en el Macizo Ibéric... more es la más meridional de las diversas zonas geológicas que se han diferenciado en el Macizo Ibérico. Se extiende desde el suroeste de Portugal hasta la Sierra Norte de Sevilla (Fig.1). De los sectores geológicos diferenciados en este libro es el que ocupa la mayor extensión en la provincia de Huelva, puesto que comprende las rocas aflorantes en el Andévalo y parte de la Sierra de Huelva.
Tectonophysics, 2015
The post-Paleozoic tectonothermal evolution of the SW Iberian Variscides is poorly known mainly d... more The post-Paleozoic tectonothermal evolution of the SW Iberian Variscides is poorly known mainly due to the scarce low-temperature geochronological data available. We have obtained new apatite fission-tracks and apatite (U-Th)/He ages to constrain the Mesozoic and Cenozoic tectonic evolution of this portion of the Iberian Massif located just north of the Betic-Rif Alpine orogen. We have obtained nine apatite fission-track ages on samples from Variscan and pre-Variscan granitoids. These ages range from 174.4 (± 10.8) to 54.1 (± 4.9) Ma, with mean track lengths between 10.3 and 13.9 μm. We have also performed 5 (U-Th)/He datings on some of the same samples, obtaining ages between 74.6 (±1.6) and 18.5 (±1.4) Ma. Time-temperature path modeling of these low-temperature geochronological data leads us to envisage four post-Paleozoic tectonically controlled exhumation episodes in the SW Iberian Variscides. Three of these episodes occurred in Mesozoic times (Middle Triassic to Early Jurassic, Early Cretaceous, and Late Cretaceous) at rates of ≈1.1 to 2.5°C Ma −1 , separated by periods with almost no cooling. We relate these Mesozoic cooling events to the formation of important marginal reliefs during the rifting and opening of the central and northern Atlantic realm. The fourth exhumation episode occurred in Cenozoic times at rates of ≈3.2 to 3.6°C Ma −1 , being only recorded in samples next to faults with topographic escarpments. These samples cooled below 80°C at ≈20 Ma at rates of 3-13°C Ma −1 due to roughly N-S oriented compressional stresses affecting the whole Iberian plate, which, in the particular case of SW Iberia, reactivated some of the previous Late Paleozoic thrusts.
The Puebla de Guzmán and Valverde del Camino Anticlines consist of fault-propagation folds linked... more The Puebla de Guzmán and Valverde del Camino Anticlines consist of fault-propagation folds linked to a frontal thrust system striking N110ºE. In the Puebla de Guzmán Anticline, the thrust system has a fan imbricated geometry and represents a ~40 km-long and 4-5 km-wide frontal ramp; its internal structure results from the tectonic stacking of thrust sheets with normal stratigraphic polarities. Some thrusts show relay geometries, as for example the Valdecascajos and the Sierra de la Estrella Thrusts. An antiform-sinform system is developed in the intervening thrust sheet. Fault-propagation folds are very conspicuous in the hanging wall of most internal thrusts, where a rather continuous reverse limb is present. Both thrust system and fault-propagation folds, as well as a locally developed crenulation cleavage, were generated in a second tectonic phase.
Three major tectonic domains have been established in the South Portuguese Zone on the basis of c... more Three major tectonic domains have been established in the South Portuguese Zone on the basis of cartographic, stratigraphic, lithologic, structural and metamorphic criteria. They are from north to south and from the upper to lowest tectonic position: Northern Domain, Central Domain or Iberian Pyrite Belt and Southern Domain.
Geological Society, London, Special Publications, 2011
In the South Portuguese Zone (Iberian Massif), thin-skinned tectonics linked to the collision wit... more In the South Portuguese Zone (Iberian Massif), thin-skinned tectonics linked to the collision with the Ossa-Morena Zone produced the inversion of previous extensional basins in Carboniferous times. Its central domain, namely the Iberian Pyrite Belt, underwent two deformation phases at mostly low-grade metamorphic conditions linked to a progressive deformation migrating upwards from a basal detachment and from north to south. The Puebla de Guzmán Antiform is one of the most outstanding cartographic structures in the Iberian Pyrite Belt, representing a imbricate fan thrust system developed during the second regional deformation phase. In the Puebla de Guzmán Antiform, the first deformation phase gave rise to a penetrative slaty cleavage (S1), which is also recognized in the whole Iberian Pyrite Belt and constitutes the main foliation all over the region. Its genesis is possibly linked to the coetaneous development of thrusts at deeper crustal levels and SSW-vergent folds at all levels...
This work deals with the analysis of the seismicity and tectonic evolution of the eastern end of ... more This work deals with the analysis of the seismicity and tectonic evolution of the eastern end of the Azores-Gibraltar Fracture Zone. The location of the main seismogenetic areas in this region is related to the complex geometry of the boundary between the Iberian and African lithospheric plates. To the west of the San Vicente Cape the seismicity can be related to a local compression at the Gorringe Bank. A detailed seismotectonic analysis allows the geological interpretation of the position of the hypocenter for the 12th February 2007 earthquake. It had Mw 6.0 and was placed on a fault having a NNE-SSW strike and a high dip to NW. The fault shows an oblique displacement (sinistral) and locates in the margin of the Horseshoe abyssal basin. Displacement along this fault is here tentatively related to complex deformation in the outer swell of an incipient downgoing plate. This can be the first indication of the beginning of subduction of the northern part of the African plate under the continental margin of Iberia. On the other hand, an analysis of the location of earthquakes having Mw >6.0 generated to the SW of the San Vicente Cape and the estimated isoseismal map has been made. It can be noted the importance of the uppermost crustal materials on the seismic intensity measurement. Sea waves resulting from these earthquakes and measured in the littoral of the Huelva province have an average velocity of propagation of approximately 600 km/h.
Geologica Acta, 2017
The existence in the Alpujarride Complex (Betic Cordillera, southern Spain) of a relatively conti... more The existence in the Alpujarride Complex (Betic Cordillera, southern Spain) of a relatively continuous extensional event (following crustal thickening) is based on detailed structural studies and is consistent with the P-T paths and geochronological data established for the Alpujarride rocks. According to our research, the Alpujarride Complex contains two large-scale shear zones accommodating early Miocene extension. The shear zones contain km-scale recumbent folds, some with sheath fold geometry, and megaboudinage structures, and are closely associated with detachment faults. Large-scale folds and boudins cause dome-like undulations in the detachments, which are inferred to overlap in time with the deformation in the shear zones. One shear zone in the eastern part of the orogen is top-N; the other, in the western part, is top-E. The change in the shear direction may represent a temporal evolution in the direction of shear, possibly related to a change in the subduction direction in...
Bulletin of the Geological Society of Greece, 2004
The Betic (Southern Spain) and the Rif (Morocco) mountain chains, connected through the Gibraltar... more The Betic (Southern Spain) and the Rif (Morocco) mountain chains, connected through the Gibraltar Strait, shapes a W-E elongated and arcuate Alpine orogenic belt. The Alborân Sea, in continuity to the east with the South Balearic Basin, is located in the inner part of this alpine belt. The Iberian and African continental forelands bound the region as a whole to the north and south, respectively, and to the east it is connected to the oceanic Sardine-Balearic Basin. The peculiarities of these westernmost Mediterranean chains result from: (1) its position between two large convergent plates -Africa and Europe- that have had variable directions of relative motion since the late Cretaceous; and (2) the Neogene westward migration of the orogenic hinterland and its simultaneous "back-arc"-like extension, generating the Alborén Sea basin. The complexes and large paleogeographic terrains traditionally recognized in the Betic and Rif chains belong to four pre-Neogene crustal domain...
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Papers by Francisco M. Alonso-Chaves