Topography of the Moho undulations in Central Spain from gravity data

El análisis espectral de datos gravimétricos ha sido utilizado para investigar la geometría de las principales discontinuidades gravimétricas corticales del centro peninsular. El área estudiada presenta una anomalía de Bouguer negativa en la que se superponen los efectos superficiales del relleno de las cuencas sedimentarias terciarias, cuencas del Duero y del Tajo, y los efectos de fuentes más profundas como el descenso de la discontinuidad del Moho bajo el Sistema Central puesto de manifiesto por estudios sísmicos. Para discriminar los efectos de las fuentes superficiales y profundas de similar longitud de onda se ha optado por calcular el efecto gravimétrico de los sedimentos terciarios y restarlo del mapa gravimétrico observado. El espectro de potencia del mapa gravimétrico obtenido frente a la frecuencia, muestra que la fuente regional está situada a una profundidad media de 29.9 ± 4.6 km. El mapa de anomalía regional, asociada a esta fuente, muestra un mínimo relativo NE-SO en el Sistema Central y otro mínimo relativo NO-SE en la zona oriental y central de la Cordillera Ibérica. De acuerdo con los datos sísmicos esta profundidad corresponde a la posición de la principal discontinuidad de densidad de la corteza, es decir del Moho. Mediante la inversión de los datos gravimétricos se ha calculado la geometría del Moho. Esta geometría indica la existencia de dos dominios bien diferenciados: un dominio norte y nororiental caracterizado por alineaciones NO-SE a E-O y un dominio suroccidental caracterizado por alineaciones NNE-SSO a E-O. El mayor descenso del Moho se produce bajo el Sistema Central y la Cordillera Ibérica, alcanzando el espesor de la corteza más de 34 km. La relación entre la geometría obtenida y las grandes estructuras alpinas del centro peninsular sugiere el importante papel que la deformación a escala cortical ha tenido en las etapas de deformación alpinas.Spectral analysis of gravity data has been used to investigate the geometry of the main gravity discontinuities in Central Spain. The area shows a negative Bouguer Anomaly in which the gravity effect of both tertiary basins (Duero and Tajo river basins) and the deeper crustal sources, as it is shown in Central Spain seismic data, are superimposed. In order to isolate the gravity effect due to regional and residual sources, which provide the same wavelength, the gravity effect due to the tertiary basins has been calculated and subtracted from the observed gravity map. Calculating the gravity power spectrum for the new Bouguer anomaly map previously obtained, and representing its natural logarithm versus the frequency, a regional source located at a mean depth of 29.9 ± 4.6 km is obtained. Regional anomaly gravity map shows two relative minimum trending NE-SW, corresponding to the Spanish Central System and NW-SE, in the Iberian Chain. Regarding the seismic data in Central Spain, this depth corresponds to the main discontinuity in the crust, so is the Moho. The inversion of gravity data has provided the geometry of the Moho. The Moho geometry shows the occurrence of two remarkable domains: the North and Northeast domain with NW-SE and E-W trending and the Southwest domain with NNE-SSW and E-W trending. The Moho deepens under the Spanish Central System and the Iberian Chain, providing a crust thickness of more than 34 km. The connection between the obtained Moho geometry and the main Alpine structures in Central Spain suggest the important role that the cortical scale deformation has had in the Alpine tectonic deformation.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEEspaña. Ministerio de Ciencia y Tecnología. Dirección General de Investigación. Secretaría de Política Científica y Tecnológicapu

Late Variscan, Permo-Carboniferous, Al-K plutonism in the South Portuguese Zone : El Crispinejo cordierite-bearing granite

The El Crispinejo granite forms part of a small, but distinctive late intrusive suite of cordierite-bearing peraluminous granites in the South Portuguese Zone (SPZ). This granite has the best outcrop relationships of the suite. It cross-cuts different members of the Sierra Norte Batholith of the SPZ and the Carboniferous Volcano-Sedimentary Complex of the Iberian Pyrite Belt, producing contact metamorphism. This late pluton has a high K content which results in a contrasting geophysical response (K-Th-U) with respect to the surrounding trondhjemitic granitoids of the TTG suite of the Sierra Norte Batholith. A concordant monazite-zircon U-Pb ID-TIMS age of 300.5 +0.5/-1.5Ma demonstrates Permo-Carboniferous age for this late Variscan magmatic event. The granite is associated with a series of ore showings (F-Pb-Zn and Sn-W) which are completely different from the nearby, massive sulphide and manganese ore deposits of the Iberian Pyrite Belt, indicating the unique character of this intrusion

Study of the eastern margin of the Antarctic Peninsula based on gravimetric and magnetic data

La península Antártica, constituida fundamentalmente por rocas ígneas y metamórficas, forma parte del cinturón orogénico andino de edad mesozoico-cenozoica, y fue separada de Sudamérica tras la apertura del paso de Drake desde el Oligoceno. La península está formada por procesos relacionados con la subducción de la corteza oceánica del Pacífico en su margen occidental, que aún hoy es activa al NE de la zona de fractura Hero, dando lugar a la formación de la cuenca de trasarco de Bransfield. El margen oriental es el menos conocido por su inaccesibilidad, es de tipo pasivo y se caracteriza por una plataforma continental extensa con un tránsito gradual hacia el dominio oceánico del mar de Weddell. La modelización de 2 perfiles magnéticos y gravimétricos indica [1] que la estructura cortical presenta un adelgazamiento progresivo de la corteza hacia el SE, [2] una gran variación del espesor de sedimentos y [3] la existencia de una zona de diques basálticos asociada al borde occidental del mar de WeddellThe Antarctic Peninsula, mainly composed of igneous and metamorphic rocks, was separated from South America during the opening of the Drake Passage from the Oligocene, as part of the Mesozoic-Cenozoic Andean orogenic belt. It was formed by processes related to the subduction of Pacific Ocean floor at its western margin, still active northwards of the Hero fracture zone, where the Bransfield backarc basin was developed. The eastern margin is less known due to its inaccessibility and is described as a continental passive margin gradually in transition to the Weddell Sea ocean floor. The modelling of 2 magnetic and gravimetric profiles shows [1] that the eastern margin of the Antarctic Peninsula depicts a progressively thinning of the upper crust towards the SE, [2] a remarkable sediment thickness changes, and [3] basaltic dikes related to the western edge of the Weddell Se

Campaña gravimétrica en el extremo meridional de la zona volcánica de Taupo. (Nueva Zelanda)

The gravity survey which we report here forms one part of a multidisciplinary study whose goals are understanding the kinematics, structure, and geodynamic controls, o f the abrupt termination of the Taupo Volcanic Zone (TVZ) in central North Island, New Zealand. The TVZ is the volcanic arc and backarc basin associated with the Hikurangi Subduction Margin (the southern extension o f the Tonga-Kermadec subduction system) along eastern North Island and northeast South Island, New Zealand. The TVZ is characterised by active normal faults, high heat flow (>700mW/m2), andesite, dacite and rhyolite volcanic centres, and many shallow earthquakes defining an 8 km thick seismogenic crust. Whereas the subduction zone continues into northern South Island, the TVZ terminates in a series o f east-east faults immediately to the south of Mount Ruapehu, the southernmost andesite volcano. Preliminary interpretation o f the gravity are consistent with the mapped pattern of active faults and structural geology

Estudio morfoestructural de la red de drenaje en la cuenca de Almazán

Almazan Basin, localised in the northeastern part of the Iberian Plate, shows a characteristic drainage network formed by the Duero river, E-W trend in the main part of it trajectory, shifting suddenly into a N-S trend by the Almazan town. The morphological study based on a map subenvelopes and some asymmetry index suggest a relation with the N20a-30aE Spanish Central System tectonic trend. Moreover, the study of the morphologic surfaces, longitudinal profiles and the main faults, reveal a major river incision in the south slope, while the north slope tributaries fit into a more tectonically stable area. These two remarkable areas would be divided by a major uneveness, E-W trend, located underneath the Duero river. Present fluvial network is controlled by NW-SE and E-W to WNW-ESE fault systems

Basement-Cover Relationships and Their Along-Strike Changes in the Linking Zone (Iberian Range, Spain): A Combined Structural and Gravimetric Study

Contractional deformation in the transition between the Iberian and Catalan Coastal Ranges (Linking Zone) generated both thin-skinned structures detached in low-strength Triassic units and basement-involved structures. To evaluate their extent and relative contribution to the overall structure, we carried out a study combining structural geology and gravimetry. New gravity data (938 stations) and density determinations (827 samples) were acquired and combined with previous existing databases to obtain Bouguer anomaly and residual Bouguer anomaly maps of the study area. Seven serial and balanced cross sections were built, their depth geometries being constrained through the 2.5-D gravity modeling and the 3-D gravity inversion that we accomplished. The residual Bouguer anomaly map shows a good correlation between basement antiforms and gravity highs whereas negative anomalies mostly correspond to (i) Meso-Cenozoic synclines and (ii) Neogene-Quaternary basins. Cross sections depict a southern, thick-skinned domain where extensional, basement faults inherited from Late Jurassic-Early Cretaceous times were inverted during the Cenozoic. To the north, we interpret the existence of both Triassic-detached and basement-involved deformation domains. The two deformation styles are vertically overlapped in the southernmost part of the Catalan Coastal Ranges but relay both across and along strike in the Eastern Iberian Range. These basement and cover relationships and their along-strike variations are analyzed in terms of the interplay between structural inheritance, its obliquity to the shortening direction, and the continuity and effectiveness of Triassic décollements in the study area

Nuevos datos gravimétricos en los Pirineos Centrales (NE de España)

El proyecto GeoPiri3D tiene como objetivo caracterizar la geo-metría y la cinemática de los batolitos permo-carboníferos del Piri-neo Central por medio de una combinación de campos potenciales y de datos estructurales. Durante 2018 se han adquirido 824 nuevas estaciones de gravedad y 186 muestras de roca. Los datos de gra-vedad se han procesado e integrado en la base de datos del IGME y se ha calculado un nuevo mapa de anomalías de Bouguer. Los dos cuerpos graníticos principales (La Maladeta y Andorra-Mount Louis) proporcionan diferentes respuestas gravimétricas. La anomalía sobre el afloramiento de granito de La Maladeta presenta pequeñas variaciones en su amplitud que se asocian con cambios de facies. Los datos petrofísicos proporcionan una densidad media de ca. 2, 6 g/cm3 que son consistentes con su composición, predominantemente granodiorítica. El afloramiento del plutón de Mount Louis-Andorra se caracteriza por un mínimo relativo, lo que sugiere una composición predominantemente granítica (aún no se tienen resultados de las me-didas de densidad). Además, el mínimo se extiende en dirección NE, lo que sugiere que parte del plutón está enterrado. El mínimo relativo al SO del granito de La Maladeta probablemente está relacionado con las acumulaciones de evaporitas triásicas. The GeoPiri3D project aims to characterize the geometry and kinematics of the Permo-Carboniferous batholiths of the Central Pyrenees through a combination of potential fields and structural data. During 2018 we have acquired 824 new gravity stations and 186 rock samples. The gravity data were processed and integrated into the IGME database and a new Bouguer anomaly was calculated. The two main granite bodies (La Maladeta and Andorra-Mount Louis) provide different gravimetric responses. The anomaly on the La Maladeta granite outcrop presents a zonation with small variations in its amplitude. The petrophysical data provide an average density of ca. 2.6 g/cm3, which is consistent with its granodioritic composition. The outcrop of the Andorra-Mount Louis pluton is characterized by a relative minimum, suggesting a dominant granitic composition. In addition, the minimum extends in an oblique NE direction indicating that part of the pluton is buried. The relative minimum to the SW of La Maladeta is probably linked to accumulations of Triassic evaporites

Petrophysical properties in the Iberian Range and surrounding areas (NE Spain): 1-density

We introduce the first map of density data in Northeastern Spain which can help in the interpretation of gravimetric surveying. The background map is a simplified version of the Geode continuous geological cartography (scale 1:200.000) of the Iberian Range and Ebro basin. These maps are synthetic and homogeneous maps based on previous 1:50, 000 scale geological maps (MAGNA). The map uses the ETRS89 datum and UTM coordinates (30T northern zone) and covers an area of 140, 000 sq km. The compiled data shown in the map come from previous papers of the region (˜ 700 points) as well as from more than 800 additional points developed in the course of an exploratory project focused on the underground characterization of a potential CO2 reservoir in the so-called ‘Linking Zone''. The new data accomplish some basic criteria; they are accurately georeferenced and lithology, stratigraphic age and other technical details about the measurements (e.g. means and error) and methods are fully displayed

Nuevos datos gravimétricos en los Pirineos Centrales (NE de España).

The GeoPiri3D project aims to characterize the geometry and kinematics of the Permo-Carboniferous batholiths of the Central Pyrenees through a combination of potential fields and structural data. During 2018 we have acquired 824 new gravity stations and 186 rock samples. The gravity data were proces- sed and integrated into the IGME database and a new Bouguer anomaly was calculated. The two main granite bodies (La Mala- deta and Andorra-Mount Louis) provide different gravimetric responses. The anomaly on the La Maladeta granite outcrop presents a zonation with small variations in its amplitude. The petrophysical data provide an average density of ca. 2.6 g/cm3, which is consistent with its granodioritic composition. The out- crop of the Andorra-Mount Louis pluton is characterized by a relative minimum, suggesting a dominant granitic composition. In addition, the minimum extends in an oblique NE direction in- dicating that part of the pluton is buried. The relative minimum to the SW of La Maladeta is probably linked to accumulations of Triassic evaporites. El proyecto GeoPiri3D tiene como objetivo caracterizar la geo- metría y la cinemática de los batolitos permo-carboníferos del Piri- neo Central por medio de una combinación de campos potenciales y de datos estructurales. Durante 2018 se han adquirido 824 nuevas estaciones de gravedad y 186 muestras de roca. Los datos de gra- vedad se han procesado e integrado en la base de datos del IGME y se ha calculado un nuevo mapa de anomalías de Bouguer. Los dos cuerpos graníticos principales (La Maladeta y Andorra-Mount Louis) proporcionan diferentes respuestas gravimétricas. La anomalía sobre el afloramiento de granito de La Maladeta presenta pequeñas variaciones en su amplitud que se asocian con cambios de facies. Los datos petrofísicos proporcionan una densidad media de ca. 2,6 g/ cm3 que son consistentes con su composición, predominantemente granodiorítica. El afloramiento del plutón de Mount Louis-Andorra se caracteriza por un mínimo relativo, lo que sugiere una composición predominantemente granítica (aún no se tienen resultados de las me- didas de densidad). Además, el mínimo se extiende en dirección NE, lo que sugiere que parte del plutón está enterrado. El mínimo relativo al SO del granito de La Maladeta probablemente está relacionado con las acumulaciones de evaporitas triásicas