Please use this identifier to cite or link to this item: http://hdl.handle.net/2445/107485
Title: Geoelectrical characterisation of Alpine orogenic belts in the Iberian Peninsula using the magnetotelluric method
Author: Seillé, Hoël
Director: Pous, Jaume
Keywords: Tectònica de plaques
Serralada Cantàbrica
Serralada Ibèrica
Plate tectonics
Cantabrian Mountains
Iberian Mountains
Issue Date: 26-Jul-2016
Publisher: Universitat de Barcelona
Abstract: [eng] The Iberian Peninsula is considered as a “micro-continent”, located between the Eurasian and the African plates. Several ranges formed during the Alpine orogeny, in the borders of the plate or intraplate. As part of this thesis the first magnetotelluric (MT) data was collected across the intraplate Iberian fold and thrust belt and the first long-period magnetotelluric was collected across the Cantabrian Mountains, located in the northern boundary of the Iberian plate. This MT data was used to image the electrical conductivity distribution of the crust beneath these two orogens. The analysis of the MT data revealed the presence of three-dimensional structures in both studied areas and therefore 3-D inversion algorithms were used to obtain the final resistivity models. In the Cantabrian Mountains the correlation between the geoelectric image, the existing geophysical models and the surface geology provided a deeper understanding of the lithospherical processes. The final model shows excellent correlation with the superficial geology, depicting the main faults and lithologies at depth. The Duero Basin sediments are well delineated. A thickness of 2.5 to 3.5 km was deduced, and is in agreement with the seismic studies and well log data. Conductive zones in the Palaeozoic basement are related to enhanced permeability along the main Alpine faults. These conductive zones detected in the model do not reach more than 10 km in the southern part of the Cantabrian Mountains and 15 km in the northern part, and are therefore concentrated in the upper crust. The hydration/serpentinization of the upper mantle within the mantle wedge and beneath the Moho of the Cantabrian Margin is imaged as a zone of low resistivities. In the Iberian Chain the 3-D inversion model indicates that several Alpine thrusts are imaged as dipping conductors, which are limited to the upper crust. Two of them are the North Iberian Thrust and the Serranía de Cuenca Thrust, which bound to the north and to the south respectively the basement involved areas of the Iberian Chain. Both faults do not reach more than 15 km depth, suggesting that they are linked to the thrust system detachment at 10–15 km depth. This indicates that the Cenozoic thrust system causing the crustal thickening of the Iberian Chain is concentrated in the upper crust, which confirms the previous geological hypothesis proposed by Guimerà and Alvaro (1990). The 3-D inversion model is consistent with the collocated seismic image. A statistical analysis of the correlation between seismic velocity and electrical resistivity along a NE-SW profile is carried out for the upper crust and shows a clear correlation between both parameters. An increase in both seismic velocity and electrical resistivity is observed and is related to the depth at which the geological formations are located.
[spa] La Península Ibérica es un micro continente situado entre las Placas Euroasiática y Africana. Existen varios orógenos alpinos situados en el borde de placa y en su interior. En esta tesis se han realizado perfiles de magnetotelúrica a través de dos de estos orógenos: la Cordillera Cantábrica y la Cadena Ibérica. A partir de los datos de magnetotelúrica se han obtenido las imágenes de resistividad eléctrica a escala litosférica en la Cordillera Cantábrica y a escala cortical en la Cadena Ibérica. En ambos casos el análisis de la dimensionalidad de la estructura geoléctrica ha puesto de relieve un comportamiento 3-D. Por tanto se han realizado en cada caso inversiones 3-D conjuntas de las cuatro componentes del tensor de impedancias y de la función de transferencia geomagnética. En la Cordillera Cantábrica, la correlación de la distribución de resistividad eléctrica con otros modelos geofísicos y la geología de superficie ha conducido a una mejor comprensión de los procesos litosféricos de formación de la cordillera. El modelo de resistividades obtenido da una imagen de las principales fallas y estructuras en profundidad. La Cuenca del Duero está formada por sedimentos con un espesor variable, entre 2.5 a 3.5 km. El basamento paleozoico resistivo presenta zonas de conductividad elevada relacionadas con las fallas alpinas que no superan los 10 km de profundidad en la parte más meridional de la Cordillera y los 15 km en la parte septentrional de la misma, lo que indica que se sitúan en la corteza superior. La hidratación /serpentinización en la cuña del manto del margen cantábrico aparece reflejada por una zona de elevada conductividad eléctrica. En la Cadena Ibérica el modelo de inversión 3D obtenido revela la geometría de los cabalgamientos alpinos mediante zonas de elevada conductividad. Los dos principales son el Cabalgamiento Frontal Noribérico y el de la Serranía de Cuenca que limitan, al Norte y al Sur respectivamente, el basamento de la Cadena Ibérica. Ambas fallas no superan los 15 km de profundidad, indicando que el sistema de cabalgamientos cenozoico causante del engrosamiento de la cadena se concentra en la corteza superior. Se ha realizado un análisis estadístico de la correlación entre el modelo de resistividades obtenido y un modelo de velocidades sísmicas existente. El resultado indica una coincidencia entre un aumento de velocidades sísmicas y un aumento de resistividad eléctrica relacionado con la localización de las formaciones geológicas a distintas profundidades.
URI: http://hdl.handle.net/2445/107485
Appears in Collections:Tesis Doctorals - Departament - Dinàmica de la Terra i de l'Oceà

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