Geogaceta -- Nº 20-4, (1996)

Permanent URI for this collectionhttps://hdl.handle.net/10272/12411

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Zonación tectónica, primer estadio de la zonación sismotectónica del NE de la península Ibérica (Catalunya)
(Sociedad Geológica de España, 1996) Fleta, J.; Escuer, J.; Goula, Xavier; Olivera Serrano, César; Combes, Ph.; Grellet, B.; Granier, Th.
In areas characterized by a moderate seismicity, it is necessary to regionalize the seismic hazard, introducing concepts such as seismotectonic domains more than active faults. A first step of seismotectonic zonation is tectonic zonation. Various themes have been chosen for their ability to describe the present state and the different tectonic stages of structuration of the crust. The consideration of homogeneous zones with similar characteristics allows us to propose a tectonic zonation of the NE of Iberian Peninsula
Velocidades de transmisión de ondas P y S en rocas máficas y ultramáficas. Datos obtenidos experimental mente y calculados. Macizo de Sierra Alpujata. (Cordilleras Béticas)
(Sociedad Geológica de España, 1996) García San Millán, R. S.; Kern, H.; Tubía, José María; Mainprice, D.
The seismic properties of upper mantle representative samples from the Ronda ultramafic body (Betic Cordillera, Spain) have been determined using laboratory direct measurements and calculations based on the lattice preferred orientations (LPOs) of major minerals. Samples of selected mafic and ultramafic rocks collect the main petrological facies and microstructures present in the Sierra Alpujata Massif. This allows to analyse the lithological and microestructural Influence in the P-and S-waves velocities and seismic anisotropy and the strong control produced by the serpentization degree. Reflection coefficients between lithological interfases have been calculated from laboratory measurements allowing the characterization of potential seismic reflectors in the subcontinental upper mantle
Un modelo Gravimetrico 3-D para la corteza del NE de la península Ibérica
(Sociedad Geológica de España, 1996) Suriñach, Emma; Chávez, R.
Attention is focused on a three-dimensional model for the crustal structure of Catalonia (NE of the Iberian Peninsula). We combine different methodologies normally used separately in exploration geophysics to obtain the topographies of the Moho discontinuity and a crustal interface by separating their effects in the Bouguer anomaly map. The separation and isolation of the different components included in the Bouguer anomaly map were performed in the wavenumber domain by using the Spectral Factorization Method (SFM) (Spector and Grant, 1970). The three-dimensional model producing the different components o f the gravity anomaly map was estimated by separately inverting the corresponding domains of the power spectrum. The inversion method applied permitted us to obtain the three-dimensional Moho discontinuity and the three-dimensional top of the lower crust, which are consistent with the two-dimensional models for the area. The SFM seems to be a good tool for differentiating the different parts of the crust. There is a good correlation between the SFM depths and the upper and lower boundaries of the reflective area (layered lower crust) observed along the reflection seismic lines in the area
Tectónica extensional en el borde occidental de la Cuenca VascoCantábrica (Cordillera Cantábrica, NO de España)
(Sociedad Geológica de España, 1996) Espina, R. G.
A geological cross-section in the western border of the Vasco-Cantabrian Basin show extensional faults active during Permo-Mesozoic sedimentation , as well as the tectonic inversion of these faults during Alpine deformation. The hercynian basement of the Cantabrian Zone was deformed together with the Meso-Cenozoic cover during the extension and subsequent compression, without the existence of detachments betwen them. Cross-section restauration allow to reconstruct the sedimentary basins from Permian to Upper Cretaceus times. The calculated extension during this time is of about 7.5 Km and the alpine shortening of 20 Km.
Tectónica de cabalgamientos en la Faja Pirítica Ibérica (Zona Sur Portuguesa): el Antiforme de la Puebla de Guzmán, y la lámina de cabalgamiento de Sanlúcar de Guadiana
(Sociedad Geológica de España, 1996) Soriano Clemente, C.
The Sanlucar de Guadiana thrust sheet and the Puebla de Guzmán Antiform in the central Iberian Pyrite Belt are interpreted as alloctonous units displaced to the south, forming part of an imbricated thrust system dipping to the north . Shortening calculations account for the part of bulk shortening involved in macroscopic fault related folds and in fault displacements
Subduction and syn-collisional exhumation of a Paleozoic continental margin: an integrated study based on structures and P-T paths of the Basal Units in the Ordenes Complex (Galicia, Spain)
(Sociedad Geológica de España, 1996) Martínez Catalán, José R.; Arenas, R.; Díaz García, F.; Rubio Pascual, F. J.; Abati, Jacobo; Marquínez, J.
According to their metamorphic evolution, the Basal Units of the Galician Allochthonous Complexes are thought to represent a part of the margin of the Paleozoic Gondwana, subducted at the onset of the Variscan Orogeny. Variations in the P-T conditions of the first HP metamorphic event along the units suggest an important westward component for the direction of sucduction. Subsequent underthrusting of more continental material blocked the subduction and triggered the ascent and exhumation of the Basal Units whereas the convergence continued. Compressional and extensional structures were synchronous or alternated in time and, together, induced the thinning and tapering of the orogenic wedge. The unroofing took place locally under an inverted temperature gradient, caused by a detachment which carried a part of the hot mantle wedge, above the subduction zone, over the subducted units.
Sobre el origen de la falla de Viveiro y su evolución respecto al macizo hercinico (Prov. De Lugo)
(Sociedad Geológica de España, 1996) Fernández García, J.
The Viveiro fault is a ductile normal fault of Hercynian age which separates two distinct lithological units metamorphic evolution and tectonic styles. The foot wall in the east forms the Lugo dome, made with diferent Cambrian and pre-Cambrian metasediments with dominant flat-lying foliation and E-W trending stretching lineation. The hanging-wall in the west consist of a domain of tight upright folds with associated west dipping dominant foliation. An upright synform with a core of Silurian rocks is pinched between the Viveiro fault and the westerly located complex Olio de Sapo antiform
Sismicidad en el antepaís de las cordilleras Béticas orientales: determinación del tensor de esfuerzos actual
(Sociedad Geológica de España, 1996) Rincón Calero, P. J.; Giner Robles, J. L.; Vegas, Ramón; Vicente, Gerardo de
The seismicity in the Castilian foreland of the Betic Cordilleras is in accordance with an intraplate compressive stress-field that is characterized by the coexistence of two stress tensors: SHmax N140°-160°E (regional tensor) and SHmax N60°-70°E (secondary tensor). The subsequent intraplate deformation is accommodated by means of dextral strike-slip faults and crustal flexures. The seismic activity seems to be concentrated in some N130°-150°E fault zones in the front of the Alcaraz Arc
Red GPS para medidas geodinámicas en el Pirineo (ResPyr)
(Sociedad Geológica de España, 1996) Fleta, J.; Soro, M.; Giménez, J.; Suriñach, Emma
A second geodynamical network has been set up in the Central and Eastern Pyrenees to quantify tectonic horizontal movements. The network is localized on the two sides of the Pyrenees and is composed by 20 points in the Spanish side and 27 on the French one. There are three types of bench marks; 1 fiducial station, 4 pillars and 15 nails. The first campaign was carried out in July 1995 during seven days
Preliminary results on 3He/4He isotopic ratios in terrestrial fluids from Iberian peninsula: seismoctectonic and neotectonic implications
(Sociedad Geológica de España, 1996) Pérez, N. M.; Nakai, S.; Wakita, H.; Albert Bertrán, J. F.; Redondo, R.
La sistemática de isotópos de helio está siendo aplicada en la península Ibérica con el fin de obtener información adiccional sobre las características neotectónicas y sismotectónicas del área de estudio. Resultados preliminares sobre la distribución geográfica de las relaciones isotópicas 'H e/4He en fluidos terrestres reflejan variaciones de los niveles de emisión de helio-3 significativas, y estas están intrínsecamente ligadas a las características sismotectónicas y neotectonicas d e la península Ibérica
Períodos de recurrencia de paleoterremotos en sedimentos varvados lacustres del Mioceno superior. Cuenca de Híjar (Albacete)
(Sociedad Geológica de España, 1996) Rodríguez Pascua, Miguel Ángel; Vicente, Gerardo de; Ramírez Rayo, M. S.; Martín Velázquez, Silvia; Calvo, J. Pedro
Paleoseismic imprimt in lacustrine varved sediments (Upper Miocene) has been made in the Hijar Basin (External Prebetic, Albacete). Mixed layers related to seismic activity have been observed in the varved sediments. These deformational structures are associated with earthquake's magnitude 3 5.5. Each varve may be considered as annual laminae and used to date the time among deformation structures. The average recurrence interval for these study section is 119 years (± 33 years of standard desviation) for 1189 recorded years.
Origen de las brechas de la base del Jurásico en Morata de Jalón (Zaragoza)
(Sociedad Geológica de España, 1996) Campos, S.; Aurell, Marc; Casas Sainz, Antonio
A sedimentary breccia is found in the lower Liassic (Hettangian?) in wide areas of the Iberian Chain (NE Spain). This breccia was originated during a tectonic extension at the onset of the Jurassic by a number of procceses, including: (1) the erosion of the underlying Triassic units; (2) the tectonic breakage of a shallow carbonate platform developed coevally to the tectonic extension. The main contribution of this paper is the finding and description of a lower Liassic carbonate platform, which is preserved on its original position
Neotectónica en el antepaís castellano de las cordilleras Béticas orientales
(Sociedad Geológica de España, 1996) Rincón Calero, P. J.; Vegas, Ramón
The major morphotectonic features in the foreland of the Eastern Betics can be explained within the frame of the weak compressive stress field originated in the Prebetic fold and thrust belt. This NW directed compression is partitioned by N130°-150° dextral strike-slip corridors and orthogonal crustal flexures. The Neogene-Quaternary volcanism and the distribution of seismicity can be also considered within this compressive neotectonic regimen
Modelos tectono-sedimentarios de cuencas extensivas: serhigraben, graben de compensación y sinclinal sobre rampa (margen pasivo del Golfo de León, SE de Francia)
(Sociedad Geológica de España, 1996) Benedicto, A.
Three tectono-sedimentary models are proposed for extensiona/basins in the Guif of Lion passive margin: (1) haif-graben associated to a listric fault, (2) compensation graben associated to a two-segments planar fault and (3) hangingwall ramp syndine associated to a ramp-flat listric fault. In the Vistrenque graben, along-strike changes in the geometry of the Nimes fault induced along-strike changes of the geometry of the basin: in the south, a half-graben resulted from a listric fault profile at depth; in the north, a compensation graben results from a two-segments planar fault profile. The Les Matelles basin is a hangingwall syncline which results from a ramp-flat listric fault geometry. Erosion of the hangingwall during extension controlled the architecture of the syn-rift sedimentation, resulting in a rapid migration of the depocentres towards the fault.
Modelos gravimétrico y estructural del Sistema Central
(Sociedad Geológica de España, 1996) Tejero López, Rosa; Perucha Atienza, María Ángeles; Rivas Rivas, Ana María; Bergamín, J. F.
A gravity modelling of the Spanish Central System Crust has been carried out along two profiles. In order to constrain gravity modelling results Profile I runs along the Toledo-Salamanca seismic profile. Profile II trends perpendicular to the range trend. The seismic crustal model reproduced the Bouguer anomaly in a suitable way. The crust is thickening and the crust-mantle boundary descends between the Duero Basin southern zone and the central part of the Madrid Basin, from 32 to 35 km. Thickening occurs mainly in the middle crust, whose upper and lower boundaries exhibit a different geometry. The upper boundary appears upheaved, as well as the upper crust beneath the Spanish Central System. Two reverse faults limit this uplifted block. The lower boundary Is deflected 3 km, like Moho surface. This crustal structure suggests that the Spanish Central System represents a crustal pop-up, related to a deep detachment, south-dipping, located between a depth of 12 to 20 km. Terctiary compression results of crustal shortening in the Iberian Plate interior.
Modelos analógicos de la formación de lacolitos
(Sociedad Geológica de España, 1996) Román Berdiel, Teresa; Gapais, D.; Brun, J. P.
Dynamically scaled analogue models oflaccolithiç intrusions have been made. Experiments consisted of the injection of a Newtonian fluid (low-viscosity silicone putty) into a sandpack, with or without an interbedded ductile layer of silicone putty acting as a potential décollement level. Boundary conditions were chosen to analyze the influence of the thickness of the brittle cover and of the décollement layer on the pattern of intrusion. Further experiments were made to examine the effects of an extensional regime during intrusion
Modelos de elementos finitos sobre los campos de paleoesfuerzos terciarios en el borde oriental de la cuenca del Tajo (España central)
(Sociedad Geológica de España, 1996) Muñoz Martín, Alfonso; Cloetingh, Sierd; Vicente, Gerardo de
Two groups of finite element models have been carried out over Tertiary paleostress fields deduced from fault-slip data in the eastern part of the Tajo Basin. The first group corresponds to cover paleostress modelling, and the second one to basement paleostress modelling. Three different paleostress fields have been made for each group. Obtained results from two regional stress fields models show that maximum horizontal stresses (SHMAX) are controlled by two factors: limits geometry and boundary co nd itio ns applied on these lim its. A local stress field ( "A lto m ira ") appears by means of an addition of the two major paleostress fields ("Iberico" and "Guadarrama"). Different paleostress fields due to reological contrasts between different basement blocks have been investigated. Results on this kind of models show that a decouple between the cover and the basement paleostress fields could have been possible, specially for the "Altomira" paleostress field. Finally, model results are discussed related to Altomira Range origin
Modelización numérica de la evolución geodinámica del surco de Valencia
(Sociedad Geológica de España, 1996) Negredo, A. M.; Fernández, M.; Torné, M.
A numerical kinematic model of extension has been used to study the geodynamic evolution of the Valencia Trough. The model allows for depth-dependent lithospheric extension and lateral accommodation of extension. The best fitting model of the geophysical observations is obtained by assuming a phase of synrift evolution lasting 15 Ma, with maximum lithospheric thinning in the trough duringd the Early Miocene (25-15 Ma) and reduced extension during the Serravallian (15-10 Ma). The lower crust and lithospheric mantle would be stretched by a higher amount than the upper crust The evolution of the Balearic Promontory would be characterised by a first stage o f crustal thickening during the Lower Miocene and a second stage of thinning related to the opening of the Algerian Basin during the Serravallian
Modelización de la estructura litosférica del margen Sur Chileno a partir de datos gravimétricos y sísmicos
(Sociedad Geológica de España, 1996) Rubio, E.; Torné, M.; Vera, E.
The Chilean convergent margin south of the strait of Magellan represents an excellent opportunity to study a style of subduction where most of the parameters controlling this process remain approximately constant except one: obliquity. Modelling of Free Air anomaly data constrained with seismic data along a track perpendicular to the margin shows a well developed bathymetric terrace (Fuegian terrace) with a pronounced negative gravity anomaly, a common feature of active trenches, and a gently dipping (8U) slab subducting beneath the Scotia plate
Modelización gravimétrica en el SW de la Península Ibérica
(Sociedad Geológica de España, 1996) Sánchez Jiménez, N.; Bergamín, J. F.; Fernández Rodríguez, Carlos; Castro Dorado, Antonio
A gravity research has been carried out in the southwestern part of the Iberian Massif to study the contact between the Ossa-Morena (OMZ) and Southportuguese zones (SPZ). The Bouguer anomaly map shows a relative gravity high over the Aracena metamorphic belt (AMB), and a strong gradient from this high to the N N E as the most conspicuous features. A21/2D gravity modelling has been carried out to explain the Bouguer anomalies in the area. Three different interpretations of the same profile have been elaborated. The first model shows a continuous continental crust and the second one a mantle inflexion. None of them provide a good adjust to the data. In the third model presented the gravity high related to the AMB has been fitted in the model with a north-dipping wedge of lithospheric mantle and metabasites (with tholeiitic oceanic affinity) separating two different continental crust appearing to the north (OMZ) and south (SPZ) of this wedge, which was the suture between these two continents. The results of the gravity modelling process demonstrate that this hipothesis does satisfy the observed gravity data

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