Person:
Díez Fernández, Rubén

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First Name
Rubén
Last Name
Díez Fernández
URI
https://hdl.handle.net/20.500.14352/81248
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Universidad Complutense de Madrid
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Geodinámica Interna
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2016 - 20174
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    Geochemistry of the Ediacaran–Early Cambrian transition in Central Iberia: Tectonic setting and isotopic sources
    (Tectonophysics, 2016) Fuenlabrada Pérez, José Manuel; Pieren Pidal, Agustín Pedro; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Arenas Martín, Ricardo
    A 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.
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    Los metagranitos de las Unidades Basales de los complejos alóctonos de Galicia (NO del Macizo Ibérico): Evolución geoquímica y contexto geodinámico
    (Geotemas, 2016) Andonaegui Moreno, María Del Pilar; Díez Fernández, Rubén; Abati Gómez, Jacobo
    Las Unidades Basales de los complejos alóctonos de Galicia incluyen rocas metamórficas paraderivadas que alternan con abundantes rocas ortoderivadas con edades comprendidas entre 500 y 470 Ma. Por su composición, tanto mineralógica como química de roca total, las rocas ortoderivadas se dividen en dos grandes grupos: uno de gneises graníticos s.l. (tonalíticos, granodioríticos y graníticos), con una composición química que transita de tipos magnesianos-cálcicos meta-aluminosos, hasta tipos férricos calcoalcalinos y alcalino-cálcicos peralumínicos; y otro segundo grupo de gneises alcalinos y peralcalinos con una composición férrico alcalina que varía de términos peralcalinos a meta-aluminosos, llegando a tener un carácter per-alumínico los tipos más diferenciados. Los gneises graníticos s.l. presentan anomalías negativas en Nb y Ta, sugiriendo su relación con un margen continental activo, mientras que las rocas alcalinas y peralcalinas están enriquecidas en elementos traza incompatibles y presentan altos contenidos en Th, Ga y Nb, característicos de magmas asociados a un régimen extensional. Esta evolución geoquímica probablemente refleja el tránsito desde un régimen geodinámico convergente caracterizado por un sistema de arcos magmáticos hacia un rifting intracontinental.
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    Isotopic and igneous record of the Avalonian-Cadomian arc in NW Iberia
    (Geotemas, 2016) Arenas Martín, Ricardo; Andonaegui Moreno, María Del Pilar; Albert Roper, Richard; Sánchez Martínez, Sonia; Díez Fernández, Rubén
    The upper allochthonous units of NW Iberian Massif montain an extensive Cambrian magmatism (c. 500 Ma), that generated large massifs of granitic rocks and gabbros with calc-alkaline and tholeiitic compositions, respectively. Petrological and geochemical features of these massifs are characteristic of volcanic arcs. The plutons intruded siliciclastic series deposited in the periphery of the West Africa Craton. U-Pb/Hf isotopic compositions of detrital zircon in the siliciclastic series, indicate arc activity between c. 750 Ma and c. 500 Ma. It was characterized by a large variety of isotopic sources, including from very old continental input, even Archean, to the addition of a significant amount of juvenile mafic material. These isotopic sources experienced an extensive mixing that explains the composition and isotopic features of the represented Cambrian plutons. The Cambrian igneous rocks of the upper units of NW Iberia can be related to the latest activity of the Avalonian-Cadomian arc. From Middle Cambrian times, arc activity in the periphery of Gondwana was replaced by pronounced extension associated with continental rifting, which finally led to separation of the microcontinent Avalonia. Subsequent drifting of Avalonia to the North caused progressive opening of one of the main Paleozoic ocean, the Rheic Ocean.
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    Late Cambrian magmatic arc activity in peri-Gondwana: geochemical evidence from metagranitoid rocks of the Basal Allochthonous Units of NW Iberia
    (Geologica Acta, 2017) Andonaegui Moreno, María Del Pilar; Abati Gómez, Jacobo; Díez Fernández, Rubén
    The North African section of the Gondwana margin was the site of voluminous, arc-related magmatism during the Late Neoproterozoic (Avalonian–Cadomian orogen). The lower (and older) metasedimentary sequence that constitutes the Basal Units of the Allochthonous Complexes of NW Iberia was deposited in that setting. In these units, sedimentation was followed by the intrusion of tonalites and granodiorites in the late Cambrian (ca. 493–489Ma). In the Late Paleozoic, the collision of Gondwana and Laurussia (Variscan orogeny) deformed and metamorphosed the whole ensemble. New whole rock geochemical analysis performed in seven samples of metatonalites and fourteen samples of metagranodiorites are characterized by: i) slight enrichment in incompatible elements (Rb, Ba, Th, U), ii) negative anomalies in Nb, Ta, P, and Ti, and iii) negative anomalies in Eu. These chemical features are in agreement with a subduction-related setting for the genesis of both types of magma, which is also supported by chemical discrimination using tectonic setting diagrams. Positive anomalies of Pb suggest a crustal component. The new geochemical data reveal that the convergent orogen that ruled the paleogeography of the Gondwana periphery during the Neoproterozoic (Cadomian orogen) remained active beyond the Neoproterozoic-Cambrian transition, up to at least late Cambrian times.