Tensorial analisis of the superposed deformation in the easthern border of the Madrid basin

An analysis of Neogene brittle deformation using fault populatíon analysis methods has been carried out between the SW border of the Iberian Range and Altomira Range. Two main paleostress fields have been established: 1) N70E - N120E compression (Altomira paleostress field) ofLate Oligocene - Early Miocene age that induced the formation of the SW border of Iberian Range and Altomira - Pareja thrust belts with reverse and strike-slip faults. 2) N140-N160E compression (Guadarrama paleostress field) of Middle Aragonian - early Pleistocene age that reactivated previous faults with strikeslip movement along the Iberian Range. A superposition of two regional stress fields (Iberian and Guadarrama) is proposed to explain E-W compression that formed Altomira Range. Stress tensorial additions have been realized to check this hypothesis

Strain quantification related to the Berzosa/fault (Spanish Central System)

[Resumen] En relación con la zona de cizalla dúctil de Berzosa Honrubia que actúa durante la segunda fase de deformación Hercínica, se han calculado los elipsoides de deformación finita asociados a la misma. Para el cálculo se usan los métodos de Ramsay (1967), Dunnet (1969), y Fry (1979). Los resultados muestran una variación en el tipo de elipsoide a lo largo de la traza de la zona de cizalla. En los extremos tienen valores K>t, y en la parte central de Kl en la región donde son paralelos.[Abstract] In the ductil shear zone of Berzosa Honrubia, active during the Hercynic second phase, finite strain ellipsoids have been calculated. Methods of Ramsay, Dunnet, and Fry have been used for this calculation. The results show a variation in the strain elipsoid shape through the shear zone trace. The central part h(!s strain ellipsoids with K1. Interpretation of those values is based on the variation in the orientation of the fault cartographic trace and tectonic transport direction. Ellipsoids with K1 are located where the trace and tectonic transport direction are parallel

Population analysis of the late hercynian faulting in the Spanish Central System

[Resumen] En la región comprendida entre Cercedilla, El Espinar y Robleao de Chavela (Sistema Central), se han observado una serie de zonas de cizalla ductiles que cortan a las estructuras Hercínicas anteriores; son de dirección N80-NIIOE y poseen movimientos de tipo normal. Este tipo de régimen distensivo concuerda con tipos deformacionales descritos por otros autores en el Sistema Central Español. En la misma zona están también presentes una serie de diques y fallas frágiles que corresponden a un régimen deformacional inicialmente de tipo distensión uniaxial, según NS-NIOE. Las principales direcciones de fraturación se concretan en dos familias muy próximas (N80E y NIOOE), o en una única familia según N90E. A favor de esta última dirección, yen régimen de tipo extensión uniaxial se emplazan una serie de porfidos graníticos, muy característicos del área estudiada. Debido al temprano emplazamiento de estos diques ya los planos de movimiento deducibles para unos y otros tipos de fallas, pensamos que ambos eventos han de tener una cierta relación temporal. La distensión uniaxial pasa en el tiempo, mediante aumento de las compresiones de dirección N9S-NIOO E, a tectónica de tipo de desgarre. A toda esta evolución deformacional se le denomina «Etapa Malagon». Estos desgarres afectan de una manera dúctil, si bien sin recristalizaciones posteriores, a los diques de porfido granítico, que aun se están emplazando. Posteriormente, y ya dentro de la tectónica netamente de tipo frágil, se produce un régimen deformacional de tipo desgarre, con dirección de compresión NSOE que termina en distensión radial, que hemos denominado «Etapa Hiendelaencina ». En esta fase se emplazan diques de cuarzo y baritina de direcciones N20E' y N80E.[Abstract] In the region between Cercedilla, El Espinar and Robledo de Chavela (Middle Occidental Sector of the Central System) a series of ductile shear zones have been observed that cut to the former Hercynian structures with Nao-NIOO trends and having normal movement. This extensive regime agrees with other previous works. There are, in the same area, a series of dykes and brittle faults that correspond .to a deformational regime with uniaxial extension (initially from N5 to NIO). The main fault trends are Nao and NIOO (or only one with N90 trend). Following this last direction a series of granitic dykes are emplaced. This dyke emplacement and the movement scheme make us think in a certain temporal relation between them. The uniaxial extension changes, with an increase of the compresive axis (N95-NIOO), to a strike-slip fault tectonics. We will call this deformational evolution, «Malagon Phase». Subsequently, and in a clear brittle tectonics, it is produced a deformational regime of strike slip type with a direction of compression of N50E, ending in a radial extension named «Hiendelaencina Phase», with emplacement of quartz and baryte dykes with N20 and Nao trends

Neoteetonics of the eastern border of the Madrid basin

[Abstract] An analysis ofthe neotectonic activity and the current stress state of the eastern border of Madrid Basin has been carried ont using structural-methods (fault population analysis), as well as seismological methods. Two stress tensors have been established: - Tensor 1: with a N1500E shortening trend, characterized mainly by strikeslip faults. This tensor corresponds to the «Guadarrama» stress field (Capote et al., 1990), wihch causes the Central System structure; dated middle Aragonian -lower Pleistocene in the eastern border ofMadrid Basin (Muñoz Martín, 1993). - Tensor 2: dated post-Iower Pleistocene, with a N150° E extension trend, characterized basically by normal faults. Actual stress tensor deduced focal mechanisms by the seismological method is compatible with the paleostress field deduced for the middle-Iower Pleistocene (tensor 2)

Kinematic and dynamic array of the alpine deformations in alto Tajo area (Guadalajara)

The geological macrostructure of Alto Tajo is defined by several N1500E dextral strike-slip faults with related secundary structures. The former set of faults together with others N-S sinistral strike-slip faults delimited areas in transtension and transpession. Four tectonic phases have been detected by means of microstructural analysis: N600E compression; N1500E compression (the main deformation phase). N-S compression, without important structures asociated and a last episode of radial extension.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasFALSEpu

Alpine structure and evolution of central Spain

Dirección General de Investigación Científica y Técnica; PB91-039

Integrated gravity and topography analysis in analog models: Intraplate deformation in Iberia

Trends in the topography of the Iberian Peninsula show a pronounced contrast. In the western part of the Iberian microplate the main topographic highs trend E-W to NE-SW and are periodically spaced with wavelengths of 250 km. Conversely, in the northeastern part, the region of the Iberian Chain, topography is more irregular and strike directions vary from NW-SE to E-W and NE-SW. We relate this phenomenon to shortening of a continental lithosphere, which contains two different, well-defined domains of lithospheric strength. Our hypothesis is supported by physical analog models. A new processing method has been developed to assist the interpretation of the model results. It utilizes spectral analysis of gravity and topography data derived from the experiments. Folding of the crust and mantle lithosphere yields periodic gravity fluctuations, while thickening processes lead to localized gravity lows. In this way gravity data can be used to distinguish between the two forms of lithosphere deformation and to correlate areas that underwent the same type of deformation. Gravity modeling has been performed under full in-depth control of the experimental lithosphere structure. As such, gravity signals from the models may be compared to field gravity data for better understanding the underlying deformation mechanism.Peer reviewe

Exceptional river gorge formation from unexceptional floods

An understanding of rates and mechanisms of incision and knickpoint retreat in bedrock rivers is fundamental to perceptions of landscape response to external drivers, yet only sparse field data are available. Here we present eye witness accounts and quantitative surveys of rapid, amphitheatre-headed gorge formation in unweathered granite from the overtopping of a rock-cut dam spillway by small-moderate floods (~100–1,500 m3 s−1). The amount of erosion demonstrates no relationship with flood magnitude or bedload availability. Instead, structural pattern of the bedrock through faults and joints appears to be the primary control on landscape change. These discontinuities facilitate rapid erosion (\u3e270 m headward retreat; ~100 m incision; and ~160 m widening over 6 years) principally through fluvial plucking and block topple. The example demonstrates the potential for extremely rapid transient bedrock erosion even when rocks are mechanically strong and flood discharges are moderate. These observations are relevant to perceived models of gorge formation and knickpoint retreat

Receptores homodinos a 300 GHz basados en tecnología CMOS

Using CMOS transistors for terahertz detection is currently a disruptive technology that offers the direct integration of a terahertz detector with video preamplifiers. The detectors are based on the resistive mixer concept and its performance mainly depends on the following parameters: type of antenna, electrical parameters (gate to drain capacitor and channel length of the CMOS device) and foundry. Two different 300 GHz detectors are discussed: a single transistor detector with a broadband antenna and a differential pair driven by a resonant patch antenna

Cenozoic deformation of Iberia: a model for intraplate mountain building and basin development based on analogue modelling

Inferences from analogue models support lithospheric folding as the primary response to large-scale shortening manifested in the present day topography of Iberia. This process was active from the late Oligocene-early Miocene during the Alpine orogeny and was probably enhanced by reactivation of inherited Variscan faults. The modeling results confirm the dependence of fold wavelength on convergence rate and hence the strength of the layers of the lithosphere such that fold wavelength is longest for fast convergence rates favoring whole lithosphere folding. Folding is associated with the formation of dominantly pop-up type mountain ranges in the brittle crust and thickening of the ductile layers in the synforms of the buckle folds by flow. The mountain ranges are represented by upper crustal pop-ups forming the main topographic relief. The wavelengths of the topographic uplifts, both, in model and nature suggest mechanical decoupling between crust and mantle. Moreover, our modeling results suggest that buckling in Iberia took place under rheological conditions where the lithospheric mantle is stronger than the lower crust. The presence of an indenter, inducing oblique shortening in response to the opening of the King's Trough in the north western corner of the Atlantic Iberian margin controls the spacing and obliquity of structures. This leads to the transfer of the deformation from the moving walls towards the inner part of the model, creating oblique structures in both brittle and ductile layers. The effect of the indenter, together with an increase on the convergence rate produced more complex brittle structures. These results show close similarities to observations on the general shape and distribution of mountain ranges and basins in Iberia, including the Spanish Central System and Toledo Mountains.Peer reviewe