Resumen: En algunos sectores de las zonas Cantábrica y Asturoccidental-leonesa se ha desarrollado... more Resumen: En algunos sectores de las zonas Cantábrica y Asturoccidental-leonesa se ha desarrollado un clivaje incongruente con posterioridad a los principales pliegues variscos. Para su análisis se han considerado los siguientes mecanismos: anti-flexural flow, anti-deformación longitudinal tangencial inversa, deformación homogénea y deformación en las capas incompetentes por traslación de las competentes. Los tres primeros corresponden a mecanismos de plegamiento operando en sentido inverso. En la Zona Cantábrica, el mecanismo esencial de formación del clivaje incongruente es la deformación homogénea con máximo acortamiento subvertical. Cuando el clivaje tiene distinta orientación en los dos flancos, esta es probablemente debida a un plegamiento posterior, como lo indica la presencia frecuente de clivaje de crenulación. En el caso de la Zona Asturoccidental-leonesa, el clivaje incongruente tiene siempre distinta orientación en ambos flancos y su formación ha sido interpretada como de...
Geological Society, London, Special Publications, 2005
A Geographical Information System (GIS) has been applied to shape-fabric analysis and strain meas... more A Geographical Information System (GIS) has been applied to shape-fabric analysis and strain measurement. It works in either raster or vectorial format, allows determination of many geometrical features of grains and stores additional descriptive information linked to all these graphic elements. Some new applications for shape characterization and strain measurement have been developed, e.g. the shape parameter S, the Fry method installed as a variant that uses only contiguous grains (TFry method) and a new method (ASPAS method), based on the intersection lengths of the lines of a radial network with the grain boundaries. A compilation of finite-strain estimates on a tectonite sample has been used to compare the results obtained by the new methods. As the shape fabric does not register the full strain history, the strain ratios obtained from the shape-fabric analysis are lower in most cases than those obtained using pretectonic markers.
The Courel recumbent syncline is one of the best examples of a regional scale recumbent fold outc... more The Courel recumbent syncline is one of the best examples of a regional scale recumbent fold outcropping in the NW Iberian massif. A strain, microfabric and minor fold analysis of this structure has been integrated in an evolutionary model that begins with an episode of layer shortening, buckling and body rotation associated with deformation dominated by simple shear. Subsequently, the fold was flattened by dominant irrotational strain with maximum shortening perpendicular to the axial surface and maximum stretching parallel to the fold axis. This occurred during the first phase of the Variscan deformation, and gave rise to a fold with an axial surface dipping moderately towards the hinterland (SSW). The recumbent character of the fold was increased during the third phase of the Variscan deformation, which produced a large-scale open structure with a subhorizontal limb.
EI anolisis de la evolucion estructural de 18 Cuenca Carbonifera Central (Zona Cantabrica, NO de ... more EI anolisis de la evolucion estructural de 18 Cuenca Carbonifera Central (Zona Cantabrica, NO de Es pana), ha permitido diferenciar una franja en su borde sur, Jimitada por la Falla de Leon, entre el valie del do Huerna y el del Curueno, donde con posterioridad a las dos fases principales de pJegamiento se desarrolla una esquistosidad no genel'alizada, que suele (Usponerse SU8vemente inclinada al norte.
En los tiltimos an05. el conocimiento sobre la estructura del area del Manto de Mondoiiedo se ha ... more En los tiltimos an05. el conocimiento sobre la estructura del area del Manto de Mondoiiedo se ha incrementado notablemente merced a las aportaciones de varios autores , BASTtDA y PULGAR 1978, MARTINEZ-CATALAN 1981 BASTIDA, MARTfNEZ-CATAL. .{N y PULGAR en prensa). A la luz de estos nuevos datos (ver ), resulta interesante buscar alguna' interpretacion, Que desde un punlo de vista geologico resulte coherente, de la anomaJia magnetica regional exislente en este sector, para la que hasta esle momento no se habi'a sugerido una explicacion de ningun tipo. En esle trabajo se realizara, en primer lugar, una descripci6n de las caracteristicas de esla anomalia con base en lod05 los datos disponibles. A continuaci6n, se discutinin las diversas causas que pueden buscarse para ella, a fin de escoger la que presenta una mayor coherencia con los datos geol6gicos existentes en la actualidad. Partiendo de esta estructura geol6gicamente mas probable, se hara, para terminar, un ensayo de interpretacion cuantitativa de Ia anomalia en su parte Norte, a partir de un modele geofisico coherente con la interpretacion geolOgica propuesta.
In the Cantabrian Zone (C.Z., Hercynian Cordillera, NW Spain), where cleavage and metamorphism se... more In the Cantabrian Zone (C.Z., Hercynian Cordillera, NW Spain), where cleavage and metamorphism seldom occur, a gradual increase in metamorphic conditions can be locally observed, usually accompanied by cleavage development. This happens at the western and southern boundaries of the C.Z., in the transition to the Westasturian-Leonese Zone, in which cleavage and metamorphism are generally developed, and also in some sectors within the C.Z. related to thermal events later than the general structural evolution of the C.Z. or to gradients inside some allochthonous units. Three basic cleavage types have been distinguished in low grade metamorphic areas: rough cleavage. rough slaty cleavage and slaty cleavage. The cleavage front is located in different metamorphic zones (from diagenesis to epizone) in different areas, and this has been related to the amount of strain. Nevertheless, in all the cases studied. the development of the different cleavage types requires an increase 01 pressure and temperatures into a metamorphic range. Rough slaty cleavage has been observed exclusively from the anchizone-epizone boundary and slaty cleavage exclusively within the epizone.
Interpretacion en 2 1/2D de la anomaHa magnetica del Pais Vasco: implicaciones geodinamicas A 2 1... more Interpretacion en 2 1/2D de la anomaHa magnetica del Pais Vasco: implicaciones geodinamicas A 2 1/2D interpretation of the Basque magnetic anomaly: geodynamical implications ALLER, J.; ZEYEN, H. J.
Una primera observacion del mapa geologico de Asturias per mite recotlocer la existencia de dos c... more Una primera observacion del mapa geologico de Asturias per mite recotlocer la existencia de dos conjunros de rocas que se diferencian por su edad y modo de afforamienw, EI conjuoto m.1s antiguo esra constituido por rocas precam bricas y, sobre todo, palcozoicas pre-permicas, y ocupa la mayor
The Olio de Sapo antiform is located in the hinterland of the Hercynian Iberian belt in NW Spain.... more The Olio de Sapo antiform is located in the hinterland of the Hercynian Iberian belt in NW Spain. It consists mainly of Lower Paleozoic siliciclastic rocks with important lateral facies changes in the Lower Ordovician. These rocks underwent three main deformation phases during the Hercynian orogeny. D] gave rise to close east-facing folds with an associated foliation (S1)' D 2 is responsible for the thrust emplacement of the Cabo Ortegal Complex on the rocks of the Olio de Sapo antiform. D J resulted in the development of a major synform-antiform pair. The competent and massive character of the rocks of the Cabo Ortegal Complex conditioned the geometry of the D structures and resulted J in an increase in the tightening of D, folds towards the south and the development of a fan of folds in the southern part of the zone. D, microstructures include crenulation, crenulation cleavage, differentiated cleavage and schistosity. A peraluminous leucogranite with K-feldspar megacrysts (Forgoselo granite) intruded in the final stages of D J in a hinge dilation space of the major D J synform and constitutes an example of folding related intrusion in a crustal shortening regime. This type of structural control for granite emplacement is tentatively proposed for some other granites outcropping in the adjoining West-Asturian Leonese zone. which belong to the same compositional group as the Forgoselo granite.
This paper analyses a major shear zone from the Iberian Hercynian belt which forms the basal thru... more This paper analyses a major shear zone from the Iberian Hercynian belt which forms the basal thrust of the Mondoiiedo Nappe. The shear zone developed by ductile deformation under amphibolite facies metamor phic conditions and later by brittle-ductile deformation ·in greenschists facies. Folds in the shear zone are asymmetric, very tight, Ie or similar class and frequently developing sheath geometries. The sheath folds originated by non-coaxial flow superimposed on earlier irregularities. The fabric of quartzitic rocks in the shear zone changes from bottom to top from ultramylonites through blastomylonitic rocks to non-mylonitic tectonites. c-axis fabrics vary across the shear zone, but show a dominant monoclinic symmetry. The blastomylonitic rocks include the fabrics representing the highest temperatures. The main foliation ofthe schists results from flattening of an earlier foliation, recording occasional microfolds. The use of different kinematic criteria has allowed an analysis of their validity as well as an assessment of movement direction towards the foreland of the orogen. 1406 J. ALLER and F. BASTIDA 43' 30'
Resumen: En algunos sectores de las zonas Cantábrica y Asturoccidental-leonesa se ha desarrollado... more Resumen: En algunos sectores de las zonas Cantábrica y Asturoccidental-leonesa se ha desarrollado un clivaje incongruente con posterioridad a los principales pliegues variscos. Para su análisis se han considerado los siguientes mecanismos: anti-flexural flow, anti-deformación longitudinal tangencial inversa, deformación homogénea y deformación en las capas incompetentes por traslación de las competentes. Los tres primeros corresponden a mecanismos de plegamiento operando en sentido inverso. En la Zona Cantábrica, el mecanismo esencial de formación del clivaje incongruente es la deformación homogénea con máximo acortamiento subvertical. Cuando el clivaje tiene distinta orientación en los dos flancos, esta es probablemente debida a un plegamiento posterior, como lo indica la presencia frecuente de clivaje de crenulación. En el caso de la Zona Asturoccidental-leonesa, el clivaje incongruente tiene siempre distinta orientación en ambos flancos y su formación ha sido interpretada como de...
Geological Society, London, Special Publications, 2005
A Geographical Information System (GIS) has been applied to shape-fabric analysis and strain meas... more A Geographical Information System (GIS) has been applied to shape-fabric analysis and strain measurement. It works in either raster or vectorial format, allows determination of many geometrical features of grains and stores additional descriptive information linked to all these graphic elements. Some new applications for shape characterization and strain measurement have been developed, e.g. the shape parameter S, the Fry method installed as a variant that uses only contiguous grains (TFry method) and a new method (ASPAS method), based on the intersection lengths of the lines of a radial network with the grain boundaries. A compilation of finite-strain estimates on a tectonite sample has been used to compare the results obtained by the new methods. As the shape fabric does not register the full strain history, the strain ratios obtained from the shape-fabric analysis are lower in most cases than those obtained using pretectonic markers.
The Courel recumbent syncline is one of the best examples of a regional scale recumbent fold outc... more The Courel recumbent syncline is one of the best examples of a regional scale recumbent fold outcropping in the NW Iberian massif. A strain, microfabric and minor fold analysis of this structure has been integrated in an evolutionary model that begins with an episode of layer shortening, buckling and body rotation associated with deformation dominated by simple shear. Subsequently, the fold was flattened by dominant irrotational strain with maximum shortening perpendicular to the axial surface and maximum stretching parallel to the fold axis. This occurred during the first phase of the Variscan deformation, and gave rise to a fold with an axial surface dipping moderately towards the hinterland (SSW). The recumbent character of the fold was increased during the third phase of the Variscan deformation, which produced a large-scale open structure with a subhorizontal limb.
EI anolisis de la evolucion estructural de 18 Cuenca Carbonifera Central (Zona Cantabrica, NO de ... more EI anolisis de la evolucion estructural de 18 Cuenca Carbonifera Central (Zona Cantabrica, NO de Es pana), ha permitido diferenciar una franja en su borde sur, Jimitada por la Falla de Leon, entre el valie del do Huerna y el del Curueno, donde con posterioridad a las dos fases principales de pJegamiento se desarrolla una esquistosidad no genel'alizada, que suele (Usponerse SU8vemente inclinada al norte.
En los tiltimos an05. el conocimiento sobre la estructura del area del Manto de Mondoiiedo se ha ... more En los tiltimos an05. el conocimiento sobre la estructura del area del Manto de Mondoiiedo se ha incrementado notablemente merced a las aportaciones de varios autores , BASTtDA y PULGAR 1978, MARTINEZ-CATALAN 1981 BASTIDA, MARTfNEZ-CATAL. .{N y PULGAR en prensa). A la luz de estos nuevos datos (ver ), resulta interesante buscar alguna' interpretacion, Que desde un punlo de vista geologico resulte coherente, de la anomaJia magnetica regional exislente en este sector, para la que hasta esle momento no se habi'a sugerido una explicacion de ningun tipo. En esle trabajo se realizara, en primer lugar, una descripci6n de las caracteristicas de esla anomalia con base en lod05 los datos disponibles. A continuaci6n, se discutinin las diversas causas que pueden buscarse para ella, a fin de escoger la que presenta una mayor coherencia con los datos geol6gicos existentes en la actualidad. Partiendo de esta estructura geol6gicamente mas probable, se hara, para terminar, un ensayo de interpretacion cuantitativa de Ia anomalia en su parte Norte, a partir de un modele geofisico coherente con la interpretacion geolOgica propuesta.
In the Cantabrian Zone (C.Z., Hercynian Cordillera, NW Spain), where cleavage and metamorphism se... more In the Cantabrian Zone (C.Z., Hercynian Cordillera, NW Spain), where cleavage and metamorphism seldom occur, a gradual increase in metamorphic conditions can be locally observed, usually accompanied by cleavage development. This happens at the western and southern boundaries of the C.Z., in the transition to the Westasturian-Leonese Zone, in which cleavage and metamorphism are generally developed, and also in some sectors within the C.Z. related to thermal events later than the general structural evolution of the C.Z. or to gradients inside some allochthonous units. Three basic cleavage types have been distinguished in low grade metamorphic areas: rough cleavage. rough slaty cleavage and slaty cleavage. The cleavage front is located in different metamorphic zones (from diagenesis to epizone) in different areas, and this has been related to the amount of strain. Nevertheless, in all the cases studied. the development of the different cleavage types requires an increase 01 pressure and temperatures into a metamorphic range. Rough slaty cleavage has been observed exclusively from the anchizone-epizone boundary and slaty cleavage exclusively within the epizone.
Interpretacion en 2 1/2D de la anomaHa magnetica del Pais Vasco: implicaciones geodinamicas A 2 1... more Interpretacion en 2 1/2D de la anomaHa magnetica del Pais Vasco: implicaciones geodinamicas A 2 1/2D interpretation of the Basque magnetic anomaly: geodynamical implications ALLER, J.; ZEYEN, H. J.
Una primera observacion del mapa geologico de Asturias per mite recotlocer la existencia de dos c... more Una primera observacion del mapa geologico de Asturias per mite recotlocer la existencia de dos conjunros de rocas que se diferencian por su edad y modo de afforamienw, EI conjuoto m.1s antiguo esra constituido por rocas precam bricas y, sobre todo, palcozoicas pre-permicas, y ocupa la mayor
The Olio de Sapo antiform is located in the hinterland of the Hercynian Iberian belt in NW Spain.... more The Olio de Sapo antiform is located in the hinterland of the Hercynian Iberian belt in NW Spain. It consists mainly of Lower Paleozoic siliciclastic rocks with important lateral facies changes in the Lower Ordovician. These rocks underwent three main deformation phases during the Hercynian orogeny. D] gave rise to close east-facing folds with an associated foliation (S1)' D 2 is responsible for the thrust emplacement of the Cabo Ortegal Complex on the rocks of the Olio de Sapo antiform. D J resulted in the development of a major synform-antiform pair. The competent and massive character of the rocks of the Cabo Ortegal Complex conditioned the geometry of the D structures and resulted J in an increase in the tightening of D, folds towards the south and the development of a fan of folds in the southern part of the zone. D, microstructures include crenulation, crenulation cleavage, differentiated cleavage and schistosity. A peraluminous leucogranite with K-feldspar megacrysts (Forgoselo granite) intruded in the final stages of D J in a hinge dilation space of the major D J synform and constitutes an example of folding related intrusion in a crustal shortening regime. This type of structural control for granite emplacement is tentatively proposed for some other granites outcropping in the adjoining West-Asturian Leonese zone. which belong to the same compositional group as the Forgoselo granite.
This paper analyses a major shear zone from the Iberian Hercynian belt which forms the basal thru... more This paper analyses a major shear zone from the Iberian Hercynian belt which forms the basal thrust of the Mondoiiedo Nappe. The shear zone developed by ductile deformation under amphibolite facies metamor phic conditions and later by brittle-ductile deformation ·in greenschists facies. Folds in the shear zone are asymmetric, very tight, Ie or similar class and frequently developing sheath geometries. The sheath folds originated by non-coaxial flow superimposed on earlier irregularities. The fabric of quartzitic rocks in the shear zone changes from bottom to top from ultramylonites through blastomylonitic rocks to non-mylonitic tectonites. c-axis fabrics vary across the shear zone, but show a dominant monoclinic symmetry. The blastomylonitic rocks include the fabrics representing the highest temperatures. The main foliation ofthe schists results from flattening of an earlier foliation, recording occasional microfolds. The use of different kinematic criteria has allowed an analysis of their validity as well as an assessment of movement direction towards the foreland of the orogen. 1406 J. ALLER and F. BASTIDA 43' 30'
Uploads
Papers by Jesus Aller