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El basamento ígneo-metamórfico pre-mesozoico de la Cordillera Nordpatagónica se asigna al Complejo Colohuincul. El mismo incluye rocas metamórficas de medio-alto grado ubicadas en el área de San Martín de los Andes, rocas metamórficas de bajo grado ubicadas en Cuesta de Rahue y rocas ígneas intrusivas devónicas (ca. 400 Ma). Estas rocas fueron deformadas por eventos orogénicos distintos, uno pre-Wenlock (rocas metamórficas de alto grado) y otro Carbonífero superior-Pérmico inferior (rocas metamórficas de bajo grado e intrusivos). Investigaciones previas sobre circones detríticos en las metamorfitas de la Cuesta de Rahue han arrojado edades máximas de sedimentación de 364 Ma (Devónico Superior). Nuevos trabajos de campo en la zona de San Martín de los Andes indican que las rocas metamórficas de alto grado serían roof pendants y encajantes de los cuerpos ígneos intrusivos del Devónico Inferior, por lo cual estas metamorfitas tendrían una edad anterior a ca. 400 Ma. En este trabajo presentamos nuevos datos de circones detríticos obtenidos en las metamorfitas de alto grado que permiten interpretar una edad máxima de sedimentación de 506 Ma. Esta nueva edad señala que en la zona de San Martín de los Andes se encuentra el basamento más antiguo conocido de los Andes Norpatagónicos., Instituto de Investigación en Paleobiología y Geología, Universidad Nacional de Río Negro, Argentina, Instituto Geológico y Minero de España, España, Escuela Superior de Ciencias Experimentales y Tecnología, Universidad Rey Juan Carlos, España, Departamento de Geología, Universidad de Oviedo, España

The illite crystallinity index of Kubler (1C) has been studied to establish the conditions of the last deformation stages in the Santa María de la Alameda shear zone. For this study, it has been used mainly the fine grained fraction of the samples (less than 2 mm) which is concentrated along small brittle fractures and zones of protocataclasitic material. The studied rocks give "illite crystallinity index" values between 0.35 D°2q and 0.25 D°2q, pointing to deformation conditions at temperatures which denotes a retrograde metamorphismo zone belonging to the epizone and anquizone. These results indicate a a rétrogradation condition for the late brittle deformation stage of the Santa Maria de alameda fault, in temperatures range between 255 and 200° C

Principles of fractal geometry have been applied to the description of quartz grain borders and to the assessment of deformation temperature in milonitic rocks at the Santa Maria de la Alameda Ductile Shear Zone (Central System). This shear zone have evolved during late variscan tectonic period in a large temperature range, which goes from regional metamorphic pick conditions (Amphibolite facies) to temperatures lower than for Greenschists facies. Using fractal dimension analysis techniques and the temperature calibration performed by Kruhl y Nega (1996), have been established a temperature sequence, diminishing from around 490°C to 325°C during the simultaneous processes of milonitization and retrogressive metamorphism. These results are in agreement with temperatures obtained from deformation mechanisms in quartz and potassium feldspar showming the validity of fractal geometry method to deformation temperature assessment

Principles of fractal geometry have been applied to the description of quartz grain borders and to the assessment of deformation temperature in milonitic rocks at the Santa Maria de la Alameda Ductile Shear Zone (Central System). This shear zone have evolved during late variscan tectonic period in a large temperature range, which goes from regional metamorphic pick conditions (Amphibolite facies) to temperatures lower than for Greenschists facies. Using fractal dimension analysis techniques and the temperature calibration performed by Kruhl y Nega (1996), have been established a temperature sequence, diminishing from around 490°C to 325°C during the simultaneous processes of milonitization and retrogressive metamorphism. These results are in agreement with temperatures obtained from deformation mechanisms in quartz and potassium feldspar showming the validity of fractal geometry method to deformation temperature assessment

In this work is shown how an active fold (the Sierra de Cartama fault) is marked by the drainage pattern and topography, besides of structural data. The Sierra de Cartama fold is an asymmetric fold with double plunge and determines the shape of an elongated saw in the Western Betic Chains (South of Spain). Watching the drainage patterns, it can be noticed how streams and creeks round the saw. The uplift of the saw raise the valleys steeply, even leaving a hanging valley ("wind gap ") at the western part of the structure. Regarding to these observations, the lateral propagation of the fold seems to be toward the west. The proposed structure implies the existence of a compressive neotectonic activity in the zone. The compressive horizontal direction is N10e-30eW, perpendicular to the fold axis. In this tectonic environment it could be possible to interpret a reverse fault in deep associated with the fold growth

The Santa Maria de Alameda (Madrid) Ductile Shear Zone is a complex mylonitic belt trending east -West and dipping 30°-60° southward. The hanging wall block sinks towards the South-Southeast. Its kinematics is in relation to an extensional tectonic regime with North-south stretching direction. This large structure belongs to the early stages of the Malagon tectonic period, where important faulting and dike emplacement were produced. The shearing process was developed in retrograde metamorphic conditions in a wide range of temperature, which goes from 400° C to 150° C. The age of this deformation is constrained by the variscan regional metamorphic peak and the intrusion of late variscan granitoids (Las Navas del Marques adamellites), being therefore, between early Namurian and Stephanian

The Santa Maria de Alameda (Madrid) Ductile Shear Zone is a complex mylonitic belt trending east -West and dipping 30°-60° southward. The hanging wall block sinks towards the South-Southeast. Its kinematics is in relation to an extensional tectonic regime with North-south stretching direction. This large structure belongs to the early stages of the Malagon tectonic period, where important faulting and dike emplacement were produced. The shearing process was developed in retrograde metamorphic conditions in a wide range of temperature, which goes from 400° C to 150° C. The age of this deformation is constrained by the variscan regional metamorphic peak and the intrusion of late variscan granitoids (Las Navas del Marques adamellites), being therefore, between early Namurian and Stephanian