Person: Díez Fernández, Rubén
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 65
PublicationThe metahyaloclastitic matrix of a unique metavolcanic block reveals subduction in the Somozas Mélange (Cabo Ortegal Complex, NW Iberia): tectonic implications for the assembly of Pangea(Wiley Online Library, 2016) Novo Fernández, Irene; Garcia Casco, Antonio; Arenas Martín, Ricardo; Díez Fernández, RubénThe allochthonous Cabo Ortegal Complex (NW Iberian Massif) contains a ~ 500 m thick serpentinite-matrix mélange located in the lowest structural position, the Sómozas Mélange. The mélange occurs at the leading edge of a thick nappe pile constituted by a variety of terranes transported to the East (present-day coordinates; NW Iberian allochthonous complexes), with continental and oceanic affinities, and represents a Variscan suture. Among other types of metaigneous (calc-alkaline suite dated at 527-499 Ma) and metasedimentary blocks, it contains close-packed pillow lavas and broken pillow-breccias with a metahyaloclastitic matrix formed by muscovite – paragonite – margarite – garnet – chlorite – kyanite – hematite – epidote – quartz - rutile. Pseudosection modelling in the MnCNTKFMASHO system indicates metamorphic peak conditions of ~ 17.5-18 kbar and ~ 550 °C followed by near-isothermal decompression. This P-T evolution indicates subduction/accretion of an arc-derived section of peri-Gondwanan transitional crust. Subduction below the Variscan orogenic wedge evolved to continental collision with important dextral component. Closure of the remaining oceanic peri-Gondwanan domain and associated release of fluid led to hydration of the overlying mantle wedge and the formation of a low-viscosity subduction channel, where return flow formed the mélange. The submarine metavolcanic rocks were deformed and detached from the subducting transitional crust and eventually incorporated into the subduction channel, where they experienced fast exhumation. Due to the cryptic nature of the high-P metamorphism preserved in its tectonic blocks, the significance of the Somozas Mélange had remained elusive, but it is made clear here for the first time as an important tectonic boundary within the Variscan Orogen formed during the late stages of the continental convergence leading to the assembly of Pangea.convergence leading to the assembly of Pangea. PublicationGeochemistry and Sm–Nd isotopic sources of Late Ediacaran siliciclastic series in the Ossa–Morena Complex: Iberian–Bohemian correlations(Springer, 2021) Rojo-Pérez, Esther; Fuenlabrada Pérez, José Manuel; Linnemann, Ulf; Arenas Martín, Ricardo; Sánchez Martínez, Sonia; Díez Fernández, Rubén; Martín Parra, Luis Miguel; Matas, Jerónimo; Andonaegui Moreno, Pilar; Fernández Suárez, JavierThe Cadomian basement in central and southern Europe is composed by Ediacaran–Early Cambrian sequences that appear dismembered along the Variscan Orogen. These ancient series contain geochemical and isotopic keys related to their deposition in different basins located along the paleo margin of Gondwana. The southwest of Iberian Massif (Ossa–Morena Complex) contains an excellent representation of Cadomian basement. The oldest sedimentary succession of this region, the Serie Negra Group (c. 600–541 Ma), is composed by the Montemolín Formation which consists of metapelites, metagreywackes and abundant amphibolites; and the Tentudía Formation which consists of metagreywackes, black quartzites and metapelites. The whole-rock and Nd isotopic geochemistry of the Montemolín and Tentudía formations, are consistent with a deposition in a back-arc or fore-arc setting. Their Nd isotopic composition shows highly negative εNd(t) values in a range between − 6.9 and − 11.5, resulting in old Paleoproterozoic Nd model ages between 1.9 and 1.7 Ga. The Nd isotopic signatures obtained for the Cadomian basement in the Iberian Massif are almost identical to those obtained for equivalent sedimentary series in the Saxo-Thuringian Zone (Bohemian Massif), where Nd model ages range between 2 and 1.6 Ga. The limited variability of these Nd-TDM ages suggests that the southwestern Iberian and North Bohemian series shared a common source during Ediacaran times, which would be located close to the periphery of the West African Craton. The Nd isotopic data considered herein provide solid evidence about the peri-Gondwanan location and correlation between the Cadomian basement of southwestern Iberia and North Bohemia. PublicationPaleogeografía geoquímica de las series metasedimentarias del Macizo Ibérico(Sociedad Geológica de España., 2016) Fuenlabrada Pérez, José Manuel; Arenas Martín, Ricardo; Sánchez Martínez, Sonia; Díez Fernández, Rubén; Pieren Pidal, Agustín PedroLas características geoquímicas e isotópicas de las series turbidíticas del Macizo Ibérico reflejan distintos escenarios tectónicos en la periferia de Gondwana. Estos cambios se observan en el registro sedimentario de la transición Ediacarense-Cámbrico, que tuvo lugar en el contexto general de un margen continental activo. TDM jóvenes y ɛNd menos negativos resultan característicos de cuencas sedimentarias más exteriores, con una importante contribución de material juvenil derivado del sector más activo del arco volcánico (metagrauvacas culminantes de las Unidades Superiores del Complejo de Órdenes). Las cuencas sedimentarias más próximas al continente se caracterizan por mayores aportes desde dominios alejados del arco activo que dan lugar a valores de TDM más antiguos y ɛNd muy negativos (metagrauvacas de las Unidades Basales del Complejo de Malpica-Tui). Una evolución desde contextos activos hasta otros más propios de márgenes pasivos se detecta con claridad en la transición Ediacarense-Cámbrico, y debe relacionarse con una disminución de la actividad del arco volcánico y la transición hacia un margen pasivo. El diagrama de fSm/Nd vs ɛNd confirma esta variación de los escenarios tectónicos asociados al margen de Gondwana, perfectamente registrados en los metasedimentos de diferentes sectores y unidades del Macizo Ibérico. PublicationEvolución tectónica del Macizo Ibérico durante la orogenia Varisca: colisión Gondwana - Laurrusia(Sociedad Geológica de España., 2016) Díez Fernández, Rubén; Arenas Martín, Ricardo; Pereira, M. Francisco; Sánchez Martínez, Sonia; Albert Roper, Richard; Martín Parra, Luis Miguel; Rubio Pascual, Francisco J.; Matas, J.La revisión de la evolución tectonometamórfica y magmática del Macizo Ibérico revela periodos de extensión y convergencia alternantes dentro de un proceso global de convergencia entre Gondwana y Laurrusia durante la formación de Pangea en el Paleozoico Superior. Fases dominadas por compresión a escala litosférica se caracterizan por el desarrollo de subducción oceánica y continental, generación de arcos magmáticos, cabalgamientos y procesos de acreción de litosfera continental y plegamiento. Eventualmente, la convergencia Varisca durante el Carbonífero produjo la transferencia de un conjunto de terrenos alóctonos peri-Gondwánicos, el denominado Alóctono Ibérico, sobre Gondwana. El Alóctono Ibérico muestra una impronta tectonometamórfica previa a ese proceso de transferencia fruto de la yuxtaposición temprana de Gondwana y Laurrusia tras el cierre del océano Reico en el Devónico Inferior. Las fases dominadas por fenómenos extensionales están representadas por la apertura de dos cuencas oceánicas efímeras a expensas de la corteza orogénica formada hasta el momento, primero en el Devónico Inferior-Medio, tras el cierre del Reico, y luego durante el Carbonífero Inferior, tras el emplazamiento del alóctono peri-Gondwánico. Seguidamente, un evento de extensión intra-orogénica durante el Carbonífero Inferior-Medio desmembró al Alóctono Ibérico en apilamientos individuales de unidades exóticas separados por fallas extensionales y domos. La tectónica transcurrente jugó un papel fundamental durante toda la orogenia Varisca, especialmente durante la creación de nuevos bloques tectónicos separados por zonas de cizalla transcurrentes intra-continentales en las últimas etapas de convergencia continental. PublicationA complex accretionary assembly of Pangea developed in the range c. 400–340 Ma: the four successive events of high-P/ultra-high-P metamorphism of the Variscan Orogen(Taylor & Francis, 2022-10-09) Novo Fernández, Irene; Arenas Martín, Ricardo; Díez Fernández, Rubén; Garcia Casco, AntonioIn the most internal zone of the Variscan Orogen, a stack of ophiolites and (ultra)high-P belts hold evidence for c. 60 Myr (c. 400–340 Ma) of almost continuous metamorphism and accretion onto the continental margin of Gondwana. Subduction of the peri-Gondwanan lithosphere led to three successive (ultra)high-P metamorphic episodes prior to the continental collision between Gondwana and Laurussia that shaped Pangea. A first high-P, high-T metamorphic belt developed during subduction of a peri-Gondwanan magmatic arc in the Early Devonian. Related to this event is the ensuing opening of intra-Gondwana Middle Devonian oceanic basins, which rapidly closed leading to ophiolite accretion. The second high-P metamorphic episode is related to the formation of a serpentinitic mélange after the sequential subduction of oceanic and transitional crust during Middle Devonian time. Tectonic blocks of subducted crustal material recording high-P, low-T metamorphism were detached from the slab and incorporated into a low-viscosity channel developed between the downgoing slab and the mantle wedge. As convergence progressed, a Late Devonian high-P, low- to intermediate-T metamorphic belt developed due to subduction of the most external margin of Gondwana. Subsequently, the scenario switched to continental collision. In this context, Early Carboniferous intracontinental subduction of the Gondwanan foreland below the accretionary wedge triggered ultra-high-P metamorphism and ensuing exhumation via trans-lithospheric diapirism and doming up to the base of the accretionary wedge. PublicationTectonic evolution of a continental subduction‐exhumation channel: Variscan structure of the basal allochthonous units in NW Spain(European Geoscience Union, 2011) Díez Fernández, Rubén; Martínez Catalán, José Ramón; Arenas Martín, Ricardo; Abati Gómez, JacoboA regional study starting from detailed geological mapping has been carried out in the Malpica‐Tui Complex of Galicia in NW Spain. The complex is formed by two units representing pieces of the external edge of Gondwana, subducted and exhumed during the Variscan collision. The study shows that synsubduction and early synexhumation structures in continental subduction channels tends to be obscured and even erased once exhumation is complete. Detailed structural analysis, matched with the knowledge of the history, and available data for other Galician basal units have elucidated the major structures developed during the subduction‐exhumation process. The results include evidence of the plate convergence causing early Variscan continental subduction of the Gondwana margin. Subduction was followed by exhumation driven by ductile thrusting within the subduction channel, which, in turn, provoked crustal duplication in the subducted slab and modified the initial tectonometamorphic architecture of the subduction wedge. The next step was accretion to the adjacent continental domains, placing the subduction wedge on top of unsubducted parts of the Gondwana margin via ductile thrusting. Thrusting was preceded by progressive propagation of a train of recumbent folds toward the foreland that affected the previous structural stack. Subsequent transference of oceanic (Rheic) and peri‐Gondwanan terranes to the Gondwana margin took place by out‐of‐sequence thrusting followed by crustal extensional collapse and strike‐slip tectonics PublicationMagmatism and early-Variscan continental subduction in the northern Gondwana margin recorded in zircons from the basal units of Galicia, NW Spain(Geological Society of America, 2010) Abati Gómez, Jacobo; Fernández Suárez, Javier; Arenas Martín, Ricardo; Whitehouse, Martín J.; Díez Fernández, RubénIn situ uranium-lead dating (LA-SF-ICPMS and SIMS) and Lu-Hf isotope analyses (LA-MC-ICP-MS) of zircon from eclogite facies rocks from the basal units of the Variscan Belt in Galicia constrain their magmatic and metamorphic evolution and give some clues about the nature and origin of the involved basement. The samples studied are two felsic gneisses, two eclogites, and one eclogitic gneiss of intermediate composition (metatonalite). Oscillatory-zoned zircon cores from the felsic samples gave a main clustering of U-Pb ages at 493 ± 2 and 494 ± 2 Ma, and some older ages that represent inherited cores. Zircon grains from the intermediate and one of the mafic rocks show no inherited cores and yielded ages of 494 ± 3 and 498 ± 6 Ma, respectively, interpreted as time of protolith crystallization. Variably developed homogeneous zircon rims in one felsic gneiss yielded an age of 372 ± 3 Ma, and very tiny zircons of one eclogite gave 350 ± 2 Ma, both of which we interpret as metamorphic ages. The new age data demonstrate that the calc-alkaline magmatic suite described in the basal unit is ca. 20 Ma older than the alkaline to peralkaline plutonic suite of the same unit (dated at 472 ± 2 Ma; Rodríguez et al., 2007), and thus probably represents a distinct geologic event. Overgrowth rims are interpreted as metamorphic on the basis of their Lu/Hf and Th/U ratios. The 372 ± 3 age is considered as dating the high-pressure (high-P) metamorphism, and is essentially in agreement with previous Ar-Ar and Rb-Sr data. This high-P metamorphism marks the initial early-Variscan subduction of the Gondwana margin. The inherited zircon ages and Hf isotopic composition of zircons point to a considerable input of crustal material with West African Craton provenance to the felsic magma. PublicationThe Galicia–Ossa-Morena Zone: Proposal for a new zone of the IberianMassif. Variscan implications(Elsevier, 2016-06) Arenas Martín, Ricardo; Díez Fernández, Rubén; Rubio Pascual, Francisco J.; Sánchez Martínez, Sonia; Martín Parra, Luis Miguel; Matas, Jerónimo; González del Tánago y del Río, José; Jiménez Díaz, Alberto; Fuenlabrada, José M.; Andonaegui Moreno, Pilar; Garcia Casco, AntonioCorrelation of a group of allochthonous terranes (referred to as basal, ophiolitic and upper units) exposed in theNW and SW of the Iberian Massif, is used to propose a new geotectonic zone in the southern branch of theVariscan Orogen: the Galicia–Ossa-Morena Zone. Recent advances in SW Iberia identify most of the formerOssa-Morena Zone as another allochthonous complex of the Iberian Massif, the Ossa-Morena Complex, equiva-lent to the Cabo Ortegal, Órdenes, Malpica-Tui, Bragança and Morais complexes described in NW Iberia. Thenew geotectonic zone and its counterparts along the rest of the Variscan Orogen constitute an Internal VariscanZone with ophiolites and units affected by high-P metamorphism. The Galicia–Ossa-Morena Zone includes aVariscan suture and pieces of continental crust bearing the imprint of Ediacaran–Cambrian events related tothe activity of peri-Gondwanan magmatic arcs (Cadomian orogenesis). In the Iberian Massif, the general struc-ture of this geotectonic zone represents a duplication of the Gondwanan platform, the outboard sections beingjuxtaposed on top of domains located closer to the mainland before amalgamation. This interpretation offersan explanation that overcomes some issues regarding the differences between the stratigraphic and paleontolog-ical record of the central and southern sections of the Iberian Massif. Also, equivalent structural relationships be-tween other major geotectonic domains of the rest of the Variscan Orogen are consistent with our interpretationand allow suspecting similar configurations along strike of the orogen. A number of issues may be put forward inthis respect that potentially open new lines of thinking about the architecture of the Variscan Orogen. PublicationGeochemistry of the Ediacaran–Early Cambrian transition in Central Iberia: Tectonic setting and isotopic sources(Elsevier, 2016-06) Fuenlabrada Pérez, José Manuel; Pieren Pidal, Agustín Pedro; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Arenas Martín, RicardoA complete Ediacaran–Early Cambrian stratigraphic transition can be observed in the southern part of the Central Iberian Zone (Iberian Massif). Two different stratigraphic units, underlying Ordovician series, display geochemical and Sm–Nd isotopic features in agreement with an evolving geodynamic setting. Pusa Shales (Early Cambrian) rest unconformably on greywackes of the Lower Alcudian Formation (Late Ediacaran). Both sequences present minor compositional variations for major and trace element contents and similar REE patterns, close to those of PAAS (Post Archean Australian Shale). Trace element contents and element ratios suggest mixed sources, with intermediate to felsic igneous contributions for both units. Tectonic setting discrimination diagrams for the Ediacaran greywackes indicate that these turbiditic series were deposited in a sedimentary basin associated with a mature active margin (volcanic arc). However, the compositions of the Cambrian shales fit better with a more stable context, a back-arc or retro-arc setting. εNd(T) and TDM ages are compatible with dominance of a similar cratonic source for both sequences, probably the West Africa Craton. εNd565 values for the Ediacaran greywackes (−3.0 to −1.4) along with TDM ages (1256–1334 Ma) imply a significant contribution of juvenile material, probably derived from the erosion of the volcanic arc. However, εNd530 values in the Cambrian shales (−5.2 to −4.0) together with older TDM ages (1444–1657 Ma), suggest a higher contribution of cratonic isotopic sources, probably derived from erosion of the adjacent mainland. Coeval with the progressive cessation of arc volcanism along the peri-Gondwanan realm during the Cambrian, there was a period of more tectonic stability and increasing arrival of sediments from cratonic areas. The geochemistry of the Ediacaran–Cambrian transition in Central Iberia documents a tectonic switch in the periphery of Gondwana, from an active margin to a more stable context related to the onset of a passive margin. PublicationThe onset of the assembly of Pangaea in NW Iberia: Constraints on the kinematics of continental subduction(Elsevier Science B. V., Amsterdam, 2012) Díez Fernández, Rubén; Martínez Catalán, José Ramón; Arenas Martín, Ricardo; Abati Gómez, JacoboExcellent exposures of high-pressure rocks developed in a Variscan continental subduction system outcrop in NW Iberia. The kinematic criteria provided by the high-pressure metamorphic fabrics can be used to infer tectonic flow within the deep sections of this system. The dominant trend of the ductile flow is oblique to that of the orogenic belt, indicating oblique continental subduction. Its azimuth, a few tens of degrees clockwise relative to the orogenic trend, suggests dextral transpression between Gondwana and Laurussia during continental subduction that took place at the Upper Devonian, and provides a consistent kinematic reference for the earliest assembly of Pangaea in NW Iberia.