Space and time in the tectonic evolution of the northwestern Iberian Massif: Implications for the Variscan belt.

Recent advances in geochemical studies of igneous rocks, isotopic age data for magmatism and metamorphism, quantitative pressure-temperature (P-T) estimates of metamorphic evolution, and structural geology in the northwestern Iberian Massif are integrated into a synthesis of the tectonic evolution that places the autochthonous and allochthonous terranes in the framework of Paleozoic plate tectonics. Because northwestern Iberia is free from strike-slip faults of continental scale, it is retrodeformable and preserves valuable information about the orthogonal component of convergence of Gondwana with Laurentia and/or Baltica, and the opening and closure of the Rheic Ocean. The evolution deduced for northwest Iberia is extended to the rest of the Variscan belt in an attempt to develop a three-dimensional interpretation that assigns great importance to the transcurrent components of convergence. Dominant Carboniferous dextral transpression following large Devonian and Early Carboniferous thrusting and recumbent folding is invoked to explain the complexity of the belt without requiring a large number of peri-Gondwanan terranes, and its ophiolites and highpressure allochthonous units are related to a single oceanic closure. Palinspastic reconstruction of the Variscan massifs and zones cannot be achieved without restoration of terrane transport along the colliding plate margins. A schematic reconstruction is proposed that involves postcollisional strike-slip displacement of ~3000 km between Laurussia and Gondwana during the Carboniferous

Las Hoyas de la dehesa de Cañal (Salamanca, España): una labor minera antigua de oro secundario

El paraje conocido como Las Hoyas, en el término municipal de Pelayos (Salamanca), corresponde a una labor minera a cielo abierto de gran antigüedad, en la que se beneficiaba oro sedimentario. Su tipología concuerda con la tradicional en la minería romana, aunque las ruinas existentes en el lugar corresponden a un poblado visigodo. La existencia de varios asentamientos y obras de ingeniería romanas en la comarca, junto con ruinas aún no estudiadas con topónimos de posible origen romano, permiten argumentar que esta explotación minera estuvo activa en el Alto Imperio. Los materiales portadores del oro son continentales de edad cenozoica (Oligocéno) y ocupan una depresión tectónica de origen alpino limitada por fallas de direcciones SO-NE, las principales, y NO-SE, las secundarias. Sus aportes provienen de los cercanos relieves situados al SE, que constituyen las primeras elevaciones del Sistema Central Español.Facultad de Ciencias, Universidad de Vigo, Campus OurenseDepartamento de Geología, Universidad de SalamancaInstituto Geológico y Minero de España, Unidad de Salamanc

The Cambrian-Ordovician boundary in the Peña de Francia syncline: lithological, sedimentological and geochemical evidences

Several levels of conglomerate cropping out in the Peña de Francia syncline were previously included in the Ordovician basal unit. However, a Lower Cambrian conglomerate can be identified inside, even in the areas where the basal Ordovician unconformity is not exposed. The Cambrian conglomerate witness the filling of deep water channels by mass flow; whereas the Basal Ordovician conglomerate indicates the starting of the Ordovician transgression in a coastal environment under tides and waves regime. Sedimentary and lithological data from the conglomerates and geochemical data from interlayered slates support this interpretatio

Furongian-Lower Ordovician metavolcanites from the Toledo Mountains (Spain) and its relationship with the Toledanian phase

Ordovician geodynamics: The Sardic Phase in the Pyrenees, Mouthoumet and Montagne Noire massifs International Meeting (2017. Figueras, España)In the Toledo Mountains of the Central-Iberian Zone (CIZ), some scattered outcrops with volcanic and metavolcanic rocks occur interbedded across Cambro-Ordovician strata (Martínez Escorza, 1976; Ramírez-Merino et al., 2000). The authors differentiated two volcanic suites: (i) some volcanic rocks underlying the Cambrian Cortijos Sandstone Formation (VR1), and (ii) a volcanosedimentary complex (VSC) sandwiched between the Valdehierro and the Purple Series. Thirteen samples of both volcanic suites were selected for geochemical analysis. According to geochemical characteristics, VSC can be subdivided into two sets: (i) VSC1 displays similar geochemical characters than suite VR1 and is composed of andesite to subalcaline basaltic andesites in the Pearce (1996) diagram; whereas (ii) VSC2 exhibits a dacitic to rhyolitic composition (Fig. 1). Because of their stratigraphic position and age, VR1 and VSC are associated with the volcanic events of the Toledanian Phase, a widespread Furongian Lower Ordovician tectono-magmatic episode related to generalize tilting, uplift and subaerial erosion in the Central-Iberian Zone.Instituto Geológico y Minero de España, EspañaUnidad de Salamanca, Instituto Geológico y Minero de España, EspañaInstituto de Geociencias, Consejo Superior de Investigaciones Científicas, EspañaInstituto de Geociencias, Universidad Complutense de Madrid, EspañaPeer reviewe

Aportaciones estructurales al conocimiento del sinclinal de Tamames: dominio del Esquisto Grauváquico de la Zona Centro Ibérica (Macizo Ibérico)

Un estudio estructural del sector oriental del sinclinal de Tamames, en la Zona Centro Ibérica (ZCI) del Macizo Ibérico, evidencia que la foliación tectónica asociada a los pliegues mayores es una crenulación que, por su relación temporal con el metamorfismo térmico del granito de Los Santos (309-307 Ma), corresponde a una convergencia tardi Varisca. Estos pliegues, al afectar a los materiales por encima y debajo de la discordancia Toledánica, presentan un salto de sus planos axiales, creando la falsa apariencia de una fase de plegamiento pre-ordovícica no esquistosa. Una extensión tardía genera pliegues abiertos subhorizontales con crenulación asociada, como los encontrados en otros sectores de la ZCI. La evidencia de una edad tardi-Varisca para la el acortamiento que generó el sinclinal de Tamames es coherente con el modelo del Arco Centro Ibérico del Macizo Ibérico.Unidad de Salamanca, Instituto Geológico y Minero de España, EspañaDepartamento de Geología, Universidad de Salamanca, Españ

Detrital Zircon U/Pb ages in synorogenic deposits of the Internal Zones of the Iberian Variscan Massif and their significance in the orogenic evolution

The Variscan synorogenic rocks present extensive exposures in the external parts of the Iberian Variscan massif, namely the Cantabrian and South Portuguese Zones. Nevertheless, in the internal part of the chain this type of sedimentary bodies was preserved exclusively in the nucleus of the main synformal structures. A total of 13 samples were gathered for study of the U-Pb ages in sedimentary zircons belonging to the internal part of the Iberian Variscan Massif: 7 samples collected and analyzed in this research are considered together to previous 6 samples analysis results which are now reinterpretedUnidad de Salamanca, Instituto Geológico y Minero de España, EspañaDepartamento de Geología, Universidad de Salamanca, EspañaLaborátorio Nacional de Energia e Geologia, PortugalARC National Key Centre for Geochemical Evolution and Metallogeny of Continents, Macquarie University, Australi

Structural contributions on the Tamames syncline: Schist and Greywacke Domain of the Central Iberian Zone (Iberian Massif)

Un estudio estructural del sector oriental del sinclinal de Tamames, en la Zona Centro Ibérica (ZCI) del Macizo Ibérico, evidencia que la foliación tectónica asociada a los pliegues mayores es una crenulación que, por su relación temporal con el metamorfismo térmico del granito de Los Santos (309-307 Ma), corresponde a una convergencia tardi-Varisca. Estos pliegues, al afectar a los materiales por encima y debajo de la discordancia Toledánica, presentan un salto de sus planos axiales, creando la falsa apariencia de una fase de plegamiento pre-ordovícica no esquistosa. Una extensión tardía genera pliegues abiertos subhorizontales con crenulación asociada, como los encontrados en otros sectores de la ZCI. La evidencia de una edad tardi-Varisca para la el acortamiento que generó el sinclinal de Tamames es coherente con el modelo del Arco Centro Ibérico del Macizo IbéricoA structural study on the eastern part of the Tamames syncline, in the Central Iberian Zone (CIZ) of the Variscan Massif, discloses that the tectonic foliation related to the major folds is a late-Variscan crenulation. This foliation is roughly coeval to the thermal metamorphism generated by Los Santos granite (309-307 Ma). The axial planes of these folds are displaced when they cross cut the Toledanic unconformity creating the illusion of a non-schistose pre-Ordovician folding event. Later on, open sub-horizontal folds with associated crenulation cleavage are generated by a late-Variscan extensional event, as recognized in other areas of the CIZ. The evidence of a late-Variscan age for the shortening phase that generated the Tamames syncline is consistent with the existence of the Central Iberian Arc in the Iberian Massi

U/Pb age of a large dacitic block locked in an Early Carboniferous synorogenic mélange in the Parautochthon of NW Iberia: New insights on the structure/sedimentation Variscan interplay

At the NW of the Iberian Variscan Massif the Parautochthon is envisaged as an intervening structural unit located between the far-traveled allochthonous stacked units and the autochthon. It has been recently divided in two structural slices; the Upper constitutes a repetition of the upper Cambrian to Silurian sequence of the Central Iberian Zone autochthon, while the Lower has been proposed as a thick Variscan synorogenic deposit. A large volcanic block embedded in the uppermost Devonian–lower Carboniferous Lower Parautochthon yields an U/Pb age of 497 ± 2 Ma (upper Cambrian). This age, joined to the petrographic features and the chemical composition, supports the provenance area for the large glided block in the Upper Parautochthon, where a magmatic event of similar age and characteristics has been identified. This source area for the slid block reinforces the idea of a mélange developed in the synorogenic trough at the front of a main thrust structure, which over thrusts the Upper Parautochthon on top of the Lower Parautochthon.Unidad de Salamanca, Instituto Geológico y Minero de España, EspañaDepartamento de Geología, Universidad de Salamanca, EspañaInstituto Dom Luiz, Universidade de Lisboa, PortugalGeology and Geography Department, Tomsk State University, Rusi

An overview on the Ordovician volcanic rocks and unconformities in the Central Iberian and Galicia-Trás-os-Montes Zones of the Iberian Variscan Massif

Ordovician geodynamics: The Sardic Phase in the Pyrenees, Mouthoumet and Montagne Noire massifs International Meeting (2017. Figueras, España)New detailed continuous digitalized maps (1:50.000 scale Geode program of the Spanish Geological Survey: IGME) facilitate an innovative regional approach to the Ordovician unconformities and volcanic rocks interbedded in the sequence (Clariana García et al., online; Villar Alonso et al., online). For this work, these maps have been actualized by up to date references from Spain and Portugal. At the selected areas of the Variscan Massif, two main Ordovician unconformities are generally described: (known ad the Toledanic and Sardic) but the regional approach unveils different stratigraphic positions at the diverse sectors. Besides, a new picture on the vulcanite abundance and variety arises. The general advances in geochronology and geochemistry of the interbedded volcanic bodies have been very useful to correlate the effusive events all over the vast area covered by this review (Coke et al., 2011; Dias da Silva et al., 2014, 2015; Díez Montes, 2007; Talavera et al., 2013).Unidad de Salamanca, Instituto Geológico y Minero de España, EspañaInstituto Dom Luis, Universidade de Lisboa, PortugalInstituto Geológico y Minero de España, EspañaPeer reviewe