Stratígraphy and structure of the Preordovician series in the Coria region (Province of Caceres)

[Resumen] El estudio de los materiales preordovícicos que afloran al Norte del Sinclinal de Cañaveral, en las proximidades de Coria (Cáceres), permite separar dos grandes conjuntos litoestratigráficos: Uno inferior, de litología arenoso-pelítica con tramos conglomeráticos intercalados, y otro superior con claro predominio limo-pelítico, ambos de edad Precámbrico Superior. El conjunto arenoso-pelítico tiene un carácter turbidítico, siendo correlacionable con la Formación «Areniscas y Pizarras del Estomiza», mientras que el conjunto limo- pelítico podría tener afinidades con las «Limolitas del Cubilar» (ambas Formaciones definidas en el Anticlinal de Valdelacasa). Se discuten otras divisiones y correlaciones litológicas propuestas por autores anteriores. El estudio estructural detallado muestra la presencia de pliegues de eje vertical, pliegues cortados por la esquistosidad y otros criterios estructurales indicativos de que las series están afectadas por al menos tres etapas de deformaci6n, de importancia variable. Por comparación con zonas próximas, las deformaciones corresponderían a la Precámbrica (Vendiense Superior), una posible Sárdica, y Hercínica, que es la más importante; dan lugar a una superposición de estructuras, principalmente pliegues.[Abstract] Precambrian outcrops in the North of the Cañaveral Syncline, Coria village (Caceres, Spain), allows us to separate two lithostratigraphical units. The Lower one consist of lutitic sandstones with conglomerate intercalations; it has a turbiditic character and can be correlated with «Areniscas y Pizarras del Estomiza» Formation. In the Upper one, silty claystones dominate and it shows certain affinites with «Limolitas del Cubilar» Formation. These two formations were defined at «Valdelacasa» Anticline. Previous lithostratigraphical divisions and lithologic correlations are discussed. Detail structural analysis shows the presence of vertical axis folds and cleavage- crossed folds which indicate that the Precambrian units are affected, at least, by three different deformation stages, which here caused a structural superposition, folds mainly. By comparison with adyacent areas , Precambrian (Upper Vendian), Sardic and, the most important, Hercynian phases can be dated

La cuarta fase de deformación hercínica en la zona centroibérica del Macizo Hespérico

[Resumen] Se define una cuarta fase de denominación hercínica de alcance regional aunque i- rregularmente desarroll ada, en vari os sectores de 1a zona Centroibérica a partir de un estudio de diversos elementos estructurales que presentan características semejantes. - En base a una correlación de los acontecimientos principales de la Orogenía Hercínica, situamos esta fase de deformación con posterioridad al desarrollo de las tres fases tectogenética principales reconocidas y con anterioridad al emplazamiento de los granitoides tardihercínicos y a otros fenómenos significativos ligados al ciclo hercínico. Esta cuarta fase genera estructuras a nivel macroscópico (pliegues hectométricos y cambios locales de la orientación regional de las direcciones estructura1es anteri ores) y mesoscópicos (p1iegues suaves de escala métrica y pl iegues angulosos de escala centimétrica); localmente produce esqulstosidad de fractura y de "strain-sli p". - La orientación principal de esta fase es N10E-N30E, si bien varía progresivamente en el sector oriental del Sistema Central hasta alcanzar direcciones de N90E-N100E. Esta variación es de la misma magnitud que las experimentadas por 1as direcciones estructural es de 1as fases hercín i cas anteriores, por lo que podría estar originada por el movimiento y rotación de bloques ligado a la fracturación tardihercínica.[Abstract] The study of structural elements in several areas of the Centrolberian zone support the existence of a forth deformation(F4) regionally developed. According with a correlation based on the main events during the Hercini an orogeny, these F4 may be chrono1og i ca 11 y P1aced after the three main deformation phases usually recognized and before 1ate-hercinyan gran it i crocks emplacement and also before other signifiicative hercinyan events. The F4 gives rise to macroscopic structures (hectometric fol ds and orientation changes of older structures) and mesoscopic structures(open metric folds and centrimetric chevron folds); locally produces fractura and strain-slip schistosity. The orientation of F4 structures is nearing N10E-N30E, altough changes progressively on the oriental zone of the Sistema Central until N90E-N100E. This change is similar to the variation of older structures; there before could be arised by the movement and rotation of blocks by late-hercinyan fractures

Cenozoic thick-skinned deformation and topography evolution of the Spanish Central System

The Spanish Central System is a Cenozoic pop-up with an E-W to NE-SW orientation that affects all the crust (thick-skinned tectonics). It shows antiform geometry in the upper crust with thickening in the lower crust. Together with the Iberian Chain it constitutes the most prominent mountainous structure of the Pyrenean foreland. The evolutionary patterns concerning the paleotopography of the interior of the Peninsula can be established by an analysis of the following data: gravimetric, topographical, macro and micro tectonic, sedimentological (infilling of the sedimentary basins of the relative foreland), P-T-t path from apatite fission tracks, paleoseismic and instrumental seismicity. Deformation is clearly asymmetric in the Central System as evidenced by the existence of an unique, large (crustal-scale) thrust at its southern border, while in the northern one there is a normal sequence of north verging thrusts, towards the Duero Basin, whose activity ended during the Lower Miocene. This deformation was accomplished under triaxial compression, Oligocene- Lower Miocene in age, marked by NW-SE to NNW-SSE shortening. Locally orientations of paleostresses deviate from that of the regional tensor, following a period of relative tectonic quiescence. During the Upper Miocene-Pliocene, a reactivation of constrictive stress occurred and some structures underwent rejuvenation as a consequence of the action of tectonic stresses similar to those of today (uniaxial extension to strike-slip with NW-SE shortening direction). However, the westernmost areas show continuous activity throughout the whole of the Tertiary, with no apparent pulses. At the present time there is a moderate seismic activity in the Central System related to faults that were active during the Cenozoic, with the same kinematic characteristics