Person:
Díez Fernández, Rubén

First Name

Rubén

Last Name

Díez Fernández

URI

https://hdl.handle.net/20.500.14352/81248

Affiliation

Universidad Complutense de Madrid

Area

Geodinámica Interna

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Now showing 1 - 10 of 67

Two-stage collision: Exploring the birth of Pangea in the Variscan terranes.
(Gondwana research, 2014) Arenas Martín, Ricardo; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Gerdes, Axel; Fernández Suárez, Javier; Albert Roper, Richard
The Variscan suture exposed in NW Iberia contains a stack of terranes including two allochthonous units with continental affinity and Gondwanan provenance (Upper and Basal Units), separated by an ophiolite belt where the most common units show protolith ages at c. 395 Ma. Recent Lu–Hf zircon data obtained from these ophiolites indicate interaction between the gabbroic magmas and old continental crust. Hence, the ophiolites could not have originated in a deep ocean basin associated with a mature mid-ocean-ridge or intraoceanic subduction. The tectonothermal evolution of the continental terranes bounding the suture zone records two consecutive events of deep subduction. The Upper Units record an initial high-P/ultra-high-P metamorphic event that occurred before 400–390 Ma, while the Basal Units were affected by a second high-P/low-to-intermediate-T metamorphic event dated at c. 370 Ma. Continental subduction affected the most external margin of Gondwana and developed in a setting of dextral convergencewith Laurussia. Development of the two high-P events alternated with the opening of an ephemeral oceanic basin, probably of pull-apart type, in Early Devonian times. This ephemeral oceanic domain is suggested as the setting for the protoliths of the most common ophiolites involved in the Variscan suture. Current ideas for the assembly of Pangea advocate a single collisional event between Gondwana and Laurussia in the Carboniferous. However, the new evidence from the allochthonous terranes of the Variscan belt suggests a more complex scenario for the assembly of the supercontinent, with an interaction between the colliding continental margins that started earlier and lasted longer than previously considered. Based onmodern analogs of continental interaction, the development of complex collisions, as here suggested for Gondwana and Laurussia during the assembly of Pangea, could have been the norm rather than the exception throughout Earth history.
A two-stage collision at the origin of Pangea: the allochthonous Variscan terranes
(Geotemas, 2016) Arenas Martín, Ricardo; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Gerdes, Axel; Fernández Suárez, Javier; Albert, R.; Fuenlabrada Pérez, José Manuel
The Variscan suture exposed in NW Iberia contains two allochthonous terranes with Gondwanan provenance (upper and basal units), separated by ophiolites with protolith ages at c. 395 Ma. The tectonothermal evolution of the continental terranes records two consecutive events of deep subduction. The upper units record an initial high-P/ultrahigh-P metamorphic event that occurred before 400-390 Ma, while the basal units were affected by a second high-P/low-to-intermediate-T metamorphic event at c. 370 Ma. Repeated continental subduction affecting the most external margin of Gondwana occurred in a setting of dextral convergence with Laurussia. The two high-P events alternated with the opening of an ephemeral oceanic basin, probably of pull-apart type, in Early Devonian times. This ephemeral oceanic domain is suggested as the setting for the protoliths of the most common ophiolites involved in the Variscan Orogen. Current ideas for the assembly of Pangea advocate a single collisional event in Carboniferous times. However, the new evidence from the allochthonous terranes of the Variscan Orogen suggest a more complex scenario for the assembly of the supercontinent, with an interaction between the colliding continental margins that started earlier and lasted longer than previously considered.
Magmatism 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 Bulletin, 2010) Abati Gómez, Jacobo; Gerdes, Axel; Fernández Suárez, Javier; Arenas Martín, Ricardo; Whitehouse, Martín J.; Díez Fernández, Rubén
In 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.
2-D thermal modeling of HT–LP metamorphism in NW and Central Iberia: Implications for Variscan magmatism, rheology of the lithosphere and orogenic evolution
(Tectonophysics, 2015) Alcock, James E; Martínez Catalán, José R.; Rubio Pascual, Francisco J.; Díez Montes, Alejandro; Díez Fernández, Rubén; Gómez Barreiro, Juan; Arenas Martín, Ricardo; Dias da Silva, Ícaro; González Clavijo, Emilio
A model for the P–T–t evolution of NW and Central Iberia is presented to better understand its metamorphic evolution from initial Barrovian stage through HT–LP conditions. The model is constrained by the well-known succession of structural events and geochronology of the Variscan deformation, standard physical parameters, and conservative values for the surface heat flow and radiogenic heat production. The goals are to test an orogenic model derived from observations against a physical reality constrained by the thermal properties of the lithosphere, and to explore the implications for Variscan orogenic evolution. A600 km section, parallel to the axial surface of the Central Iberian arc is modeled to the scale of the continental lithosphere. The model outcomes are presented as sections showing the evolution of isotherms over 65 Ma, as the variation of the lithospheric geotherm and as P–T–t paths for significant parts of the model section and for points originating at different depths. Profiles of lithosphere strength have been constructed combining the maximum shear stress for brittle fracture with published flow–stress–depth profiles of characteristic rocks and temperatures obtained for the different depths in the model. Quantitative constraints from 2-D thermal models suggest that the metamorphic and magmatic evolution can be explained by the succession of three orogenic stages, namely crustal thickening, a period of thermal relaxation, and subsequent extensional collapse, providing that the first stage doubles the thickness of the continental crust. Thrusting of a thick nappe stack, well preserved in NW Iberia, seems to be the likely cause of the high temperatures reached later during the HT–LP event that occurred during late orogenic extension. The late addition of heat from asthenospheric upwelling remains a possibility, but the model results suggest that it is not necessary to explain the Variscan P–T–t paths.
Large-scale flat-lying isoclinal folding in extending lithosphere: Santa María de la Alameda dome (Central Iberian Massif, Spain)
(Lithosphere, 2013) Arango, César; Díez Fernández, Rubén; Arenas Martín, Ricardo
The exhumation mechanisms of deep-seated continental crust can be constrained by analyzing the structural and metamorphic imprints left in lithological ensembles. The Santa María de la Alameda dome formed during the collision of Gondwana and Laurussia in late Paleozoic time and is located in the Central Iberian Zone of the Iberian Massif (Spain). Rocks of the dome are part of the autochthonous Gondwanan sections of the Variscan belt, and they occur in the Variscan hinterland. The lithostratigraphy of the dome consists of metasedimentary rocks alternating with orthogneiss massifs showing irregular and sinuous structure. The metamorphic record indicates peak pressures indicative of lower-crust depths followed by isothermal decompression to middle-upper-crust levels. Exhumation resulted in the exposure of different crustal levels (represented by subsolidus vs. supersolidus mineral assemblages). The exhumation was accompanied by initial layer-parallel stretching and subsequent large-scale isoclinal folding developed in a heterogeneous, flat-lying shear zone with top-to-the-SE kinematics. SE-directed shearing and lateral extensional flow occurred in response to thermomechanical disequilibrium of previously thickened orogenic crust, probably assisted by coeval accretion of tectonic slices and lithospheric bending about a vertical axis. Positive feedback among partial melting, exhumation, and crustal attenuation resulted in the formation of a NE-SW–trending, migmatite-cored dome, and in refolding of early isoclinal folds and an associated axial surface regional foliation. The dome formed beneath a set of extensional detachments and was reshaped by WNW-ESE upright folds during later convergent deformation. The latter event brought in further instabilities throughout the belt, triggering in this region the development of a late extensional detachment under low-grade metamorphic conditions (top-to-the-S kinematics). The development of a regional train of flat-lying isoclinal folds is presented here as the macrostructural expression of the combination of vertical and lateral extensional flow, both of which are particularly common in orogens worldwide.
Opening and closure of Cadomian peri-Gondwanan oceans: age and evolution of the Mérida Ophiolite (SW Iberia)
(International geology review, 2022) Arenas Martín, Ricardo; Rojo-Pérez, Esther; Díez Fernández, Rubén; Albert, R.; Novo Fernández, Irene; Sánchez Martínez, Sonia; Andonaegui Moreno, María Del Pilar; Moreno Martín, Diana; Gerdes, Axel; Garcia Casco, Antonio
In the SW Iberian Massif, the Ossa-Morena Complex contains a stack of units of different origin and tectonothermal evolution. Individual terranes of the complex record a Cadomian history, traditionally interpreted in relation to the dynamics of a peri-Gondwanan volcanic arc. The interpretation of the Cadomian terranes is a key issue in the reconstruction of the Ediacaran margin of Gondwana in NW Africa. In the Mérida Massif, a mafic – ultramafic unit stacked between two units of continental or arc affinity is interpreted as a Cadomian ophiolite, the Mérida Ophiolite. Within it, mafic lithologies dated at c. 596 Ma (U-Pb in zircon) have calc-alkaline or tholeiitic affinity, indicating generation in a supra-subduction zone setting. The ophiolite shows a main event of Cadomian metamorphism (c. 590 Ma, U-Pb garnet dating) with a prograde P-T path and peak conditions at c. 700°C and 8 kbar. The mafic rocks show Nd isotopic compositions clearly different from those characteristics of the mafic rocks formed in the axial zone of the volcanic arc. Hence, the Mérida Ophiolite probably represents oceanic lithosphere of a back-arc basin, opened between the volcanic arc and the outer margin of Gondwana. Closure of the back-arc occurred during collision of the volcanic arc with the margin of Gondwana (starting at c. 590 Ma), which caused rapid accretion of the back-arc oceanic lithosphere beneath the arc and prograde metamorphism typical of subduction inception. The Mérida Ophiolite was finally obducted above the continental margin of Gondwana, presently preserved in gneissic unit piled beneath the ophiolite. Cadomian evolution of this peri-Gondwanan arc section continued with new tectonothermal events dated in the range 560–540 Ma that alternated with episodes of intense magmatic activity and preceded the collapse of the magmatic arc and its erosive levelling, followed by the generation of a new episode of intense magmatic activity in the arc and the unconformable deposition of the Ediacaran-Cambrian Malcocinado Formation.
Isotopic and geochemical record of the active to passive margin transition in NW Iberia during the Cambrian-Ordovician: vestiges of a waning continental arc
(Journal of Iberian Geology, 2021) Andonaegui Moreno, María Del Pilar; Díez Fernández, Rubén; Abati Gómez, Jacobo
Time-resolved geochemical data from the orthogneisses of the basal units of the Allochthonous complexes of NW Iberian Massif allow us to track the changes in composition of the magmas generated in a subduction-related setting that affects a continental margin, which evolves from the building of a volcanic arc to its dismantlement during a rifting episode. The basal units are interpreted as a peripheral section of the North African margin of Gondwana and record Neoproterozoic to Cambrian arc-related magmatism, followed by an episode of Cambro-Ordovician rifting. The intrusive rocks of the basal units, preserved as orthogneisses, can be grouped into two magmatic suites: calc-alkaline (c. 493–475 Ma) and alkaline to per-alkaline (c. 475–470 Ma). The calc-alkaline association has a chemical composition ranging from magnesian calcic metaluminous types to ferroan calc-alkalic and alkali-calcic peraluminous types. The moderately alkaline association and per-alkaline metagranites have ferroan alkalic and per-alkaline to metaluminous composition. The chemical characteristics of the metaigneous rocks from the basal units indicate that the older members of the calc-alkaline suite (tonalites and granodiorites) were generated in a continental arc environment, while the alkaline and per-alkaline rocks were formed in an intraplate extensional setting. The negative values in εNd (− 7.8 to − 1.5) of the calc-alkaline suite suggest a crustal influence in its generation. The εNd values in the alkaline orthogneisses range between − 2.0 and 2.2, and are positive in the per-alkaline group, suggesting a greater participation of a mantle component. The transition from the calc-alkaline suite to the alkaline suite is represented by alkali-granites, which are coeval with the intrusion of basic magmas, and likely derived from a mantle magma underplating that triggered the rifting episode after the cessation of continental arc magmatism during the Ordovician.
A rootless suture and the loss of the roots of a mountain chain: The Variscan belt of NW Iberia
(Comptes rendus. Géoscience, 2009) Martínez Catalán, José R.; Arenas Martín, Ricardo; Abati Gómez, Jacobo; Sánchez Martínez, Sonia; Díaz García, Florentino; Fernández Suárez, Javier; González Cuadra, Pablo; Castiñeiras García, Pedro; Gómez Barreiro, Juan; Díez Montes, Alejandro; González Clavijo, Emilio; Rubio Pascual, Francisco J.; Andonaegui Moreno, María Del Pilar; Jeffries, Teresa E.; Alcock, James E.; Díez Fernández, Rubén; López Carmona, Alicia
Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins, whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots. [RÉSUMÉ] Une suture sans racines et la perte des racines d’une chaîne montagneuse : la chaîne varisque du Nord-Ouest de l’Ibérie. Des ophiolites d’âges différents affleurent dans le Nord-Ouest de l’Ibérie dans une suture sans racines, témoin de l’océan Rhéïque. Les terrains allochtones sur et sous la suture dérivent de ses deux marges, tandis que l’autochtone relatif appartient à la marge passive du Nord de Gondwana. On peut déduire l’évolution des plaques dans cette partie de la région circum-Atlantique à partir des données stratigraphiques, pétrologiques, structurales, métamorphiques et géochronologiques. Cette évolution inclut le développement d’un rift continental et l’ouverture de l’océan Rhéïque pendant le Cambro-Ordovicien ainsi que sa fermeture au Dévonien moyen à supérieur. On décrit aussi l’évolution de la convergence et collision varisque entre Laurussia et Gondwana, du début jusqu’aux derniers stades d’un effondrement associé à la perte des racines orogéniques.
The Late Devonian Variscan suture of the Iberian Massif: A correlation of high-pressure belts in NW and SW Iberia
(Tectonophysics, 2015) Díez Fernández, Rubén; Arenas Martín, Ricardo
Correlation of three high-P and low to intermediate-T belts from NW and SW Iberia allows recognition of a single terrane affected by Late Devonian continental subduction during the Variscan orogeny. This terrane is located in the lower part of the allochthonous complexes of NW Iberia, and in a lower position in most of the Ossa Morena Zone that, therefore, emerges as another allochthonous complex of Iberia. The Ossa Morena Complex together with the allochthonous complexes of NW Iberia form a huge rootless nappe that was transported towards the Variscan foreland during final assembly of Pangea.
Extensional Flow during Gravitational Collapse: A Tool for Setting Plate Convergence (Padrón Migmatitic Dome, Variscan Belt, NW Iberia)
(The Journal of geology, 2012) Díez Fernández, Rubén; Martínez Catalán, José Ramón; Gómez Barreiro, Juan; Arenas Martín, Ricardo
Plate convergence analysis in collisional orogens is usually based on the study of major contractional structures and strike-slip shear zones. Here we show how the structural analysis of extensional structures may report the regional or far stress field during relatively local, gravity-driven extensional collapse of a thickened continental crust and how this information may be used to constrain the broad vectors of plate convergence at that time. The Padro´n migmatitic dome is a synconvergent extensional system developed in the axial zone of the Variscan belt exposed in the NW part of the Iberian Massif of Spain. This system affected the allochthonous and autochthonous sequences involved in Pangaea’s assembly in Southern Europe. It includes three major extensional shear zones, which have been analyzed in detail to provide a wide ground data set for the discussion of the proposed model. The tectonic flow in the Padrón migmatitic dome and in other coeval structures is characterized by vectors ranging from parallel to oblique, in the latter case with a counterclockwise azimuth in relation to the trend of the orogenic belt. Our model suggests that the extensional collapse of the Variscan belt inNWIberia would have developed if the convergence between Gondwana and Laurussia had not stopped and that it would have included a dextral component.