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A combined structural and AMS analysis is made in Upper Cretaceous rocks from the periclinal closure of the Biscay Synclinorium (Basque-Cantabrian basin). Fieldwork has led to the recognition of a broad band with a pervasive foliation along the NE limb. The magnetic fabrics are grouped into two zones: 1) the samples from the core record magnetic lineations coincident with the SO/S 1 intersection lineation that are parallel to the synclinorium axis, and 2) the magnetic lineations from the NE limb are orthogonal to the synclinorium axis and concentrate around the down-dip direction of S 1. This partitioning of magnetic fabrics suggests in creasing deformation from the core, characterised by mixed (sedimentary and tectonic) magnetic fabrics, to the northeastern limb, where tectonic fabrics prevail. Field data and magnetic fabrics are consistent with an unusually high deformation in the NE limb of the synclinorium, which could be associated with a hitherto unknown shear zone at regional scale. A top to the NE movement of the shear zone would explain the trend of the magnetic lineation in the northeastern limb of the Biscay Synclinorium Se ha realizado un estudio estructural de las rocas del Cretácico Superior del cierre del Sinclinorio de Bizkaia (Cuenca Vasco-Cantábrica) combinado con un estudio de la fábrica magnética. A partir del trabajo de campo se ha establecido la presencia de una banda continua en el flanco NE donde la foliación aflora de manera penetrativa. Los resultados obtenidos con el estudio de la fábrica magnética se pueden agrupar en dos zonas: 1) Las estaciones localizadas en el núcleo registran lineaciones magnéticas situadas en la intersección entre SO y SI y son paralelas al eje del sinclinorio. 2 ) Las lineaciones magnéticas de las muestras del flanco NE son perpendiculares aleje del sinclinorio y se concentran sobre la línea de máxima pendiente de S1. Esta distribución indica un aumento de la deformación de núcleo a flanco, con fábricas magnéticas mixtas (sedimentarias y tectónicas) en el núcleo y tectónicas en el flanco. Los datos de campo y las fábricas magnéticas señalan una acumulación anómala de la deformación en el flanco NE del sinclinorio, que puede explicarse por la localización de una zona de cizalla de escala regional. El movimiento hacia el NE asociado a la zona de cizalla explicaría la disposición de la lineación magnética en dicho flanco

A combined structural and AMS analysis is made in Upper Cretaceous rocks from the periclinal closure of the Biscay Synclinorium (Basque-Cantabrian basin). Fieldwork has led to the recognition of a broad band with a pervasive foliation along the NE limb. The magnetic fabrics are grouped into two zones: 1) the samples from the core record magnetic lineations coincident with the SO/S 1 intersection lineation that are parallel to the synclinorium axis, and 2) the magnetic lineations from the NE limb are orthogonal to the synclinorium axis and concentrate around the down-dip direction of S 1. This partitioning of magnetic fabrics suggests in creasing deformation from the core, characterised by mixed (sedimentary and tectonic) magnetic fabrics, to the northeastern limb, where tectonic fabrics prevail. Field data and magnetic fabrics are consistent with an unusually high deformation in the NE limb of the synclinorium, which could be associated with a hitherto unknown shear zone at regional scale. A top to the NE movement of the shear zone would explain the trend of the magnetic lineation in the northeastern limb of the Biscay Synclinorium, Se ha realizado un estudio estructural de las rocas del Cretácico Superior del cierre del Sinclinorio de Bizkaia (Cuenca Vasco-Cantábrica) combinado con un estudio de la fábrica magnética. A partir del trabajo de campo se ha establecido la presencia de una banda continua en el flanco NE donde la foliación aflora de manera penetrativa. Los resultados obtenidos con el estudio de la fábrica magnética se pueden agrupar en dos zonas: 1) Las estaciones localizadas en el núcleo registran lineaciones magnéticas situadas en la intersección entre SO y SI y son paralelas al eje del sinclinorio. 2 ) Las lineaciones magnéticas de las muestras del flanco NE son perpendiculares aleje del sinclinorio y se concentran sobre la línea de máxima pendiente de S1. Esta distribución indica un aumento de la deformación de núcleo a flanco, con fábricas magnéticas mixtas (sedimentarias y tectónicas) en el núcleo y tectónicas en el flanco. Los datos de campo y las fábricas magnéticas señalan una acumulación anómala de la deformación en el flanco NE del sinclinorio, que puede explicarse por la localización de una zona de cizalla de escala regional. El movimiento hacia el NE asociado a la zona de cizalla explicaría la disposición de la lineación magnética en dicho flanco

El granito de La Paya se localiza en la Sierra de Cachi (Salta,Argentina),que pertenece a la Cordillera Oriental de Los Andes. Los nuevos datos estructurales y cartográficos disponibles, combinados con el estudio de lafábrica magnética del granito, ponen de manifiesto que: 1) El plutón es uncuerpo laminar, de unos 400 metros de espesor, que dibuja un pliegue antiforme,2) su techo corresponde a una zona de cizalla dúctil plegada. Las observacionesde campo y microestructurales indican un emplazamiento sincinemáticodel plutón, asociado al funcionamiento de una zona de cizalla extensionalque se plegó durante un episodio posterior compresivo. The La Paya granite is located in the Sierra de Cachi (Salta, Argentina) and belongs to the Eastern Cordillera of the Andean belt. New structural and cartographic data combined with the study of the magnetic fabric of the granite indicate that: 1) the pluton is a sheeted body, about 400 metres thick, that outlines an antiformal fold, 2) its roof is coincident with a folded ductile shear zone. Moreover, field and microstructural observations point to a syn-kinematic emplacement of the pluton linked to an extensional shear zone that was folded by a subsequent compressional event Fil: Vegas, Néstor. Universidad del Pais Vasco; España Fil: Hongn, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Bio y Geociencias del Noroeste Argentino; Argentina Fil: Aranguren, Aitor. Universidad del Pais Vasco; España Fil: Tubía, José María. Universidad del Pais Vasco; España

Por primera vez en las Cordilleras Béticas describimos, en este trabajo, la existencia y las principales características mineralógicas y petrológicas de birbiritas que son el resultado de un intenso metasomatismo de serpentinitas. Con los datos que se aportan se puede deducir que las birbiritas se han formado por la infiltración de fluidos hidrotermales de baja temperatura (< 200 ºC), bajo pH y enriquecidos en SiO2 /CO2 . La canalización de estos fluidos por planos de discontinuidad ha conducido a la silicificación generalizada de peridotitas que ya estaban serpentinizadas, In this work we describe, by first time in the Betic Cordilleras, the occurrence and the main petrological and mineralogical features of birbirites, as result of intense metasomatism of serpentinites. According to presented data the birbirites had been formed by the infiltration of SiO2 /CO2 enriched and low pH and low temperature (< 200 ºC) hydrothermal fluids channelized through discontinuities planes that lead to the pervasive silicification of already serpentinized peridotites

Se presentan dos nuevas dataciones de granitoides Variscos de la región de Sanabria (Zona Centro-Ibérica, Macizo Ibérico), con las que se establecen los límites de los pulsos magmáticos registrados en este sector. Por una parte, una edad concordia U-Pb de 318 ± 1 Ma que data el magmatismo Varisco precoz, mediante zircones y esfenas (titanitas) de tonalitas/ cuarzodioritas del plutón de Ribadelago. Este pulso magmático fue coetáneo con la acción de zonas de cizalla dextras transpresivas y con un proceso de migmatización regional. Por otra parte, una edad plateau 40Ar/39Ar de 287 ± 1 Ma obtenida en moscovitas del leucogranito de Pradorramisquedo, que data el último pulso magmatico, postectónico, en la región. Esta última edad coincide con una datación previa de la cercana granodiorita de Veiga, cuya intrusión fue coetánea con el funcionamiento de la falla normal de Chandoiro New ages are presented for two Variscan granitoids in the Sanabria region (Central Iberian Zone, Iberian Massif), which set time limits for the different magmatic pulses in the study area. A U-Pb Concordia age of 318 ± 1 Ma obtained for combined zircon and sphene (titanite) in tonalite/quartzdiorite from the Ribadelago pluton dates the first Variscan magmatism in the region. This magmatic pulse was coeval with dextral transpressive shear zones and with regional migmatisation. A 40Ar/39Ar plateau age of 287 ± 1 Ma obtained for white mica from the Pradorramisquedo leucogranite dates the post-tectonic, last magmatic pulse in the region. This age coincides with previous geochronological data for the adjacent Veiga granodiorite, which is affected by the coeval Chandoiro normal fault

Se presentan dos nuevas dataciones de granitoides Variscos de la región de Sanabria (Zona Centro-Ibérica, Macizo Ibérico), con las que se establecen los límites de los pulsos magmáticos registrados en este sector. Por una parte, una edad concordia U-Pb de 318 ± 1 Ma que data el magmatismo Varisco precoz, mediante zircones y esfenas (titanitas) de tonalitas/ cuarzodioritas del plutón de Ribadelago. Este pulso magmático fue coetáneo con la acción de zonas de cizalla dextras transpresivas y con un proceso de migmatización regional. Por otra parte, una edad plateau 40Ar/39Ar de 287 ± 1 Ma obtenida en moscovitas del leucogranito de Pradorramisquedo, que data el último pulso magmatico, postectónico, en la región. Esta última edad coincide con una datación previa de la cercana granodiorita de Veiga, cuya intrusión fue coetánea con el funcionamiento de la falla normal de Chandoiro, New ages are presented for two Variscan granitoids in the Sanabria region (Central Iberian Zone, Iberian Massif), which set time limits for the different magmatic pulses in the study area. A U-Pb Concordia age of 318 ± 1 Ma obtained for combined zircon and sphene (titanite) in tonalite/quartzdiorite from the Ribadelago pluton dates the first Variscan magmatism in the region. This magmatic pulse was coeval with dextral transpressive shear zones and with regional migmatisation. A 40Ar/39Ar plateau age of 287 ± 1 Ma obtained for white mica from the Pradorramisquedo leucogranite dates the post-tectonic, last magmatic pulse in the region. This age coincides with previous geochronological data for the adjacent Veiga granodiorite, which is affected by the coeval Chandoiro normal fault

This preliminary work illustrates the chemical composition of sphene from Variscan tonalites with sphene-centered ocellar texture (Ribadelago pluton, NW Iberian Massif). The ocellar texture is linked with the percolation of a tardimagmatic melt, with trondhjemitic affinities, through an hyperdense crystal mush. Chemical zoning in sphene, revealed by BSE imaging, shows a heterogeneous distribution of heavy trace elements (Nb, Y, Ce and Zr) that depicts concentric, oscillatory, sector and patchy patterns. Application of the Zr-in-sphene thermometer yields a temperature range of 746 to 778 ºC for the crystallization of sphene in the tardimagmatic melt. It also constitutes a minimum temperature estimation for biotite partial destabilization in this lithology

We report the presence of large aggregates (diameter > 1 cm) of diaspore related to the serpentinization of the Sierra Alpujata massif of the Ronda peridotites (Betic Cordilleras, southern Spain). The diaspore is found in two different but related settings: in narrow metasomatic rims pervading the peridotites from steeply dipping tension joints and in the blackwall zone developed along the normal fault that separates the peridotites from the overlying metamorphic cover. The systematic association of diaspore with chlorite points to very low temperature conditions (T < 100 ºC) for diaspore formation

We report the presence of large aggregates (diameter > 1 cm) of diaspore related to the serpentinization of the Sierra Alpujata massif of the Ronda peridotites (Betic Cordilleras, southern Spain). The diaspore is found in two different but related settings: in narrow metasomatic rims pervading the peridotites from steeply dipping tension joints and in the blackwall zone developed along the normal fault that separates the peridotites from the overlying metamorphic cover. The systematic association of diaspore with chlorite points to very low temperature conditions (T < 100 ºC) for diaspore formation

This preliminary work illustrates the chemical composition of sphene from Variscan tonalites with sphene-centered ocellar texture (Ribadelago pluton, NW Iberian Massif). The ocellar texture is linked with the percolation of a tardimagmatic melt, with trondhjemitic affinities, through an hyperdense crystal mush. Chemical zoning in sphene, revealed by BSE imaging, shows a heterogeneous distribution of heavy trace elements (Nb, Y, Ce and Zr) that depicts concentric, oscillatory, sector and patchy patterns. Application of the Zr-in-sphene thermometer yields a temperature range of 746 to 778 ºC for the crystallization of sphene in the tardimagmatic melt. It also constitutes a minimum temperature estimation for biotite partial destabilization in this lithology

This work deals with the structure and emplacement of the alkaline complex of the Sierra de Rangel, a Cretaceous stock intruding in Ordovician metamorphic rocks of the Puna region at Salta, northwest Argentina. Field structures and magnetic fabrics reveal a complex structure composed by multiple sheets and feeding chanels. Both, the ascent and the lateral spreading of magma exploited old fractures in the country rocks

This work analyzes the structural features of the Sopelana Fault, developed in extensional conditions during Cretaceous and Tertiary times, and inverted during the Alpine orogeny. The study area is located on the NE limb of the Biscay Synclinorium, a major structure in the Basque Arc. The Sopelana Fault bounds the northern outcrops of the Cenozoic materials in the Biscay Synclinorium. The structural analysis indicates that the inversion process related to the Alpine shortening generates folds verging towards the North and reverse faults, sometimes with a minor strike-slip component of movement. Kinematic criteria along the Sopelana Fault indicate a top to the NE shear sense, consistent with the regional compression direction, approximately NE-SW in the western area of the Basque Arc. The normal component of the Sopelana Fault was not fully recovered after the tectonic inversion that preserves younger materials of Upper Cretaceous and Tertiary times in the hanging-wall block, marked by evaporitic rocks

This work analyzes the structural features of the Sopelana Fault, developed in extensional conditions during Cretaceous and Tertiary times, and inverted during the Alpine orogeny. The study area is located on the NE limb of the Biscay Synclinorium, a major structure in the Basque Arc. The Sopelana Fault bounds the northern outcrops of the Cenozoic materials in the Biscay Synclinorium. The structural analysis indicates that the inversion process related to the Alpine shortening generates folds verging towards the North and reverse faults, sometimes with a minor strike-slip component of movement. Kinematic criteria along the Sopelana Fault indicate a top to the NE shear sense, consistent with the regional compression direction, approximately NE-SW in the western area of the Basque Arc. The normal component of the Sopelana Fault was not fully recovered after the tectonic inversion that preserves younger materials of Upper Cretaceous and Tertiary times in the hanging-wall block, marked by evaporitic rocks

A paleointensity study has been carried out on samples from 13 volcanic sites belonging to four different types of volcanism of late Miocene to Pliocene age from south-eastern Spain. Rock-magnetic experiments including measurement of thermomagnetic curves and hysteresis parameters as well as ore microscopy showed that the main carriers of remanence were low-Ti titanomagnetite and titanohematite. A PSD domain structure was observed in most samples. 43 of 90 samples from only 7 sites provided successful paleointensity determinations. 4 sites yield very low paleointensity values, but only in sites M4 and G15 anomalous paleomagnetic directions confirm an intermediate polarity. Lamproitic and calc-alkaline volcanics proved to be more suitable for paleointensity determinations in this area

The Sanabria Lake plutons, located in the Central Iberian Zone of the Iberian Massif, intruded in a dextral strike-slip fault bridge under transpressive conditions. The deformed zone underwent a strain partitioning process, so that large folded domains and narrow shear zones were developed coevally. The microstructural study of the granitoids shows that the shear zones concentrate a variable degree of solid state deformation at high and medium temperatures, whereas the folded areas preserve microstructural evidences of magmatic and submagmatic flow at high temperatures, too. The most common fabric in these folded areas is defined by two sets of conjugate planes, composed by aligned crystals of plagioclase and biotite, which are bisected by the flow foliation. These conjugate bands represent an incipient phase of the strain localization process that involves strain weakening, migration of the late-magmatic melts and enhancement of the shear zones

A paleointensity study has been carried out on samples from 13 volcanic sites belonging to four different types of volcanism of late Miocene to Pliocene age from south-eastern Spain. Rock-magnetic experiments including measurement of thermomagnetic curves and hysteresis parameters as well as ore microscopy showed that the main carriers of remanence were low-Ti titanomagnetite and titanohematite. A PSD domain structure was observed in most samples. 43 of 90 samples from only 7 sites provided successful paleointensity determinations. 4 sites yield very low paleointensity values, but only in sites M4 and G15 anomalous paleomagnetic directions confirm an intermediate polarity. Lamproitic and calc-alkaline volcanics proved to be more suitable for paleointensity determinations in this area

This work deals with the structure of the Lower Cambrian batholith of Tastil (Salta, NW Argentina) and its influence on the development of younger Andean structures. Anisotropy of magnetic susceptibility data reveal a laccolithic intrusion spreading laterally from a central root zone. The N-S elongation of the batholith reflects the westward propagation of Andean thrusts through the sheeted domains of the intrusion, the root zone acting as a buttress that restricted the propagation of the Andean structures

This work deals with the magnetic fabrics of the doleritic dykes intruded in the Panticosa pluton. The dykes are grouped in two main families: one with N-S direction and another one E-W, the most common. The measured magnetic susceptibility values range from 390 10-6SI to 1464 10-6SI, being representative of paramagnetic rocks with a minor ferromagnetic component. The recorded magnetic foliations and lineations show a strong structural homogeneity all over the sampling transects. The obliquity between the magnetic foliations and lineations, and the walls of the dykes, implies that the magma was intruded taken advantage of an extensional process, oblique to the strike of the dykes. This process could be related with the regional stress field invoked to explain the intrusion of the Panticosa pluton

This work deals with the magnetic fabrics of the doleritic dykes intruded in the Panticosa pluton. The dykes are grouped in two main families: one with N-S direction and another one E-W, the most common. The measured magnetic susceptibility values range from 390 10-6SI to 1464 10-6SI, being representative of paramagnetic rocks with a minor ferromagnetic component. The recorded magnetic foliations and lineations show a strong structural homogeneity all over the sampling transects. The obliquity between the magnetic foliations and lineations, and the walls of the dykes, implies that the magma was intruded taken advantage of an extensional process, oblique to the strike of the dykes. This process could be related with the regional stress field invoked to explain the intrusion of the Panticosa pluton

From structural and magnetic fabric patterns, this work reports a complex folded structure in the La Fronda pluton, a small trondhjemite massif located in the Sierras de Córdoba which form the eastern part of the Sierras Pampeanas in Argentina. Isoclinal folds with no thickening at the hinge zones deform the compositional banding of these igneous rocks. Both the orientation of axial surfaces and fold axes vary from place to place and do not concur with the orientation of folds from the metamorphic country rocks. Microstructural data point to a fabric formed by grain-supported flow in a crystal-rich magma during the imprint of a vanishing regional stress field

Magnetic fabric and rock magnetism studies were performed in 14 samples of the Ribadelago and Sotillo plutons (Iberian Variscan belt, NW Spain). These heterogeneous granitoids are composed by granodiorites, tonalités, quarz-diorites and diorites, mainly organized into dikes and sills. The magnetic fabric, revealed by the anisotropy of low-field magnetic susceptibility (AMS), is dominantly carried by paramagnetic iron-bearing silicates (biotite and amphibole), as infered from the thermomagnetic curves. However, a small contribution of magnetite, titanomagnetite, and perhaps pyrrhotite can be evidenced. In some cases, the magnetite seems to be restricted to the feldspar fraction. Remanent coercitivity spectra, determined from implementation of anhysteretic remanent magnetization during alternating field (AF) tumbling reveal that two magnetite families with different coercitivity distributions are present: A main one within 13-35 mT and a minor fraction within 35-60 mT. The anisotropy of anhisteretic remanence has been studied within these two coercivity windows (pAAR 13-35 mT and pAAR 35-60 mT). Comparison between the pAAR fabrics and the AMS fabric, helps to distinguish between primary (magmatic) and secondary fabrics (post-magmatic) of the ferromagnetic phases

The Ribadelago and Sotillo plutons are located in the Central Iberian Zone, a tectonic domain of the Iberian Variscan belt (NW Spain). These synkinematic granitoids are composed by swarms of sheeted intrusions parallel to the overall elongation, 130°E, of both plutons. Most of these igneous sheets show pronounced planar fabrics and provide high values of magnetic anisotropy (P%>5%), related to submagmatic and solid state deformations evolving from high to low temperature conditions. These igneous sheets are emplaced in the releasing bridge defined by two 130°E-Trending and south-dipping dextral shear zones that form a linked fault system

The Ribadelago and Sotillo plutons are located in the Central Iberian Zone, a tectonic domain of the Iberian Variscan belt (NW Spain). These synkinematic granitoids are composed by swarms of sheeted intrusions parallel to the overall elongation, 130°E, of both plutons. Most of these igneous sheets show pronounced planar fabrics and provide high values of magnetic anisotropy (P%>5%), related to submagmatic and solid state deformations evolving from high to low temperature conditions. These igneous sheets are emplaced in the releasing bridge defined by two 130°E-Trending and south-dipping dextral shear zones that form a linked fault system