Person:
Novo Fernández, Irene

First Name

Irene

Last Name

Novo Fernández

URI

https://hdl.handle.net/20.500.14352/81525

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Geológicas

Department

Mineralogía y Petrología

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Now showing 1 - 10 of 17

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.
On the Rootless Nature of a Devonian Suture in SW Iberia (Ossa-Morena Complex, Variscan Orogen): Geometry and Kinematics of the Azuaga Fault
(Tectonics, 2021) Díez Fernández, Rubén; Fernández Rodríguez, Carlos; Arenas Martín, Ricardo; Novo Fernández, Irene
Suture zones are key to understand collisional orogens, but not all the remains of subduction leading to collision occur in the root of the suture. The Azuaga Fault bounds a Devonian suture zone known as Central Unit. This fault is a steeply NE-dipping, Variscan strike-slip fault with left-lateral and reverse oblique slip components formed during sinistral transpression in the Pennsylvanian. Motion along this fault was coeval with folding and fabric development in both its hanging wall and footwall, and also with the Matachel Fault. Tectonic flow associated with the Azuaga Fault shows high-vorticity, explaining the exhumation of a flat-lying Devonian suture zone via WNW-plunging extrusion from the upper-middle crust under inclined triclinic transpression during ENE-WSW convergence. The exposed basal contact of the Central Unit is not the root zone of a Variscan suture zone, but instead is a NE-dipping breaching fault that cuts across the suture zone that is contiguous to the SW under the upper section of the footwall. The peri-Gondwanan terrane between the Central Unit and the South-Portuguese Zone of the Iberian Massif (most of the Ossa-Morena Zone) is underlain by a Devonian suture, implying it is a continental allochthon. Variscan suture zones in Europe are affected by strike-slip faults. In our case, this pattern implies the location of suture zone exposures and location of its root are different. Suture zones and strike-slip faults are common in orogens and analysis of their relationships may lead to relocation of suture zone roots and re-thinking of upper and lower plates.
Single subduction zone for the generation of Devonian ophiolites and high‐P metamorphic belts of the Variscan Orogen (NW Iberia)
(Terra Nova, 2021) Díez Fernández, Rubén; Arenas Martín, Ricardo; Sánchez Martínez, Sonia; Novo Fernández, Irene; Albert Roper, Richard
Within the Variscan Orogen, Early Devonian and Late Devonian high‐P belts separated by mid‐Devonian ophiolites can be interpreted as having formed in a single subduction zone. Early Devonian convergence nucleated a Laurussia‐dipping subduction zone from an inherited lithospheric neck (peri‐Gondwanan Cambrian back‐arc). Slab‐retreat induced upper plate extension, mantle incursion and lower plate thermal softening, favouring slab‐detachment within the lower plate and diapiric exhumation of deep‐seated rocks through the overlying mantle up to relaminate the upper plate. Upper plate extension produced mid‐Devonian suprasubduction ocean floor spreading (Devonian ophiolites), while further convergence resulted in plate coupling and intraoceanic ophiolite imbrication. Accretion of the remaining Cambrian ocean heralded Late Devonian subduction of inner sections of Gondwana across the same subduction zone and the underthrusting of mainland Gondwana (culmination of NW Iberian allochthonous pile). Oblique convergence favoured lateral plate sliding, and explained the different lateral positions along Gondwana of terranes separated by Palaeozoic ophiolites.
Exhumation of high-pressure rocks: role of late faulting (Eastern Ossa–Morena Complex, Iberian Massif)
(Geological Society Special Publications, 2024) Díez Fernández, Rubén; Novo Fernández, Irene; Moreno Martín, Diana; Arenas Martín, Ricardo; Rojo Pérez, Esther; Martín Parra, Luis Miguel; Matas, Jerónimo
Tracking the Late Devonian high-P metamorphic belt in the Variscan Orogen: New constraints on the PT evolution of eclogites from the Cubito-Moura Unit (SW Iberian Massif)
(Lithos (Oslo. Print), 2021) Novo Fernández, Irene; Arenas Martín, Ricardo; Capitani, Christian de; Pereira, M. Francisco; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Garcia Casco, Antonio
The Cubito-Moura Unit is a high-P metamorphic succession that occurs in the southern part of the Ossa-Morena Complex (SW Iberian Massif). It includes a series of metasedimentary, metafelsic and metamafic rocks affected by a high-P, low to intermediate-T metamorphic event during Late Devonian times. Geochemistry of the metabasic rocks reveals that the generation of the protoliths occurred in a supra-subduction zone setting during Late Ediacaran to Early Ordovician times, either in a back-arc or fore-arc context. The eclogites contain atoll-like garnets, omphacite, amphibole, phengite (up to Si = 3.38 apfu), paragonite, rutile and quartz. Thermodynamic modelling in the MnNCKFMASTH system indicates a high-P metamorphic event at ~24 kbar and ~ 585 °C followed by a thermal peak at ~19 kbar and ~ 630 °C, and a subsequent exhumation to ~15 kbar. This P-T path indicates deep subduction at c. 370 Ma of this arc-related section. The lithostratigraphy and tectonothermal evolution of the Cubito-Moura Unit are equivalent to that of a number of units along the Iberian, Armorican and Bohemian massifs that can be correlated as a part of the same Basal Allochthonous Terrane. These units define a single Late Devonian high-P, low- to intermediate-T metamorphic belt developed during the first stages of the Variscan Orogeny.
Application of X-ray mapping to the interpretation of silicate mineral assemblages
(Macla, 2023) Novo Fernández, Irene; Arenas Martín, Ricardo; Garcia Casco, Antonio
Metamorphism, magmatism and the formation of ore deposits imply the often sequential (re)crystallization of mineral phases. Hence, an intensive study of the textural-mineralogical development of the rocks greatly increases the understanding of the processes involved in their formation, such as growth and dissolution. The invention of the electron probe microanalyzer (EPMA) in 1951 by Raymond Castaing entailed a significant contribution to the chemical characterization of the mineral phases. One of the EPMA applications that should be not underestimated is the X-ray intensity mapping of areas of interest in thin sections. This technique allows obtaining two-dimensional spatial distribution maps of several measured elements in their textural context that, together with the development of appropriate software, allows deciphering the processes involved in their formation and evolution. In this contribution we show X-ray maps applied to silicate mineral assemblages. To do so, we study different lithologies and illustrate the importance of this technique in the textural-chemical analysis of minerals.
Estudio mineralógico y termodinámico de las meta-hialoclastitas de Espasante (Complejo de Cabo Ortegal)
(Macla, 2016) Novo Fernández, Irene; Arenas Martín, Ricardo; Garcia Casco, Antonio; Díez Fernández, Rubén
A 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
(International geology review, 2022) Novo Fernández, Irene; Arenas Martín, Ricardo; Díez Fernández, Rubén; Garcia Casco, Antonio
In 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.
The 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
(Journal of metamorphic Geology, 2016) Novo Fernández, Irene; Garcia Casco, Antonio; Arenas Martín, Ricardo; Díez Fernández, Rubén
The 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.
Lower Cambrian magmatism in the SW Iberian sector of the African–Gondwana margin: geochemical and isotopic keys to incipient tectonic switching
(Supercontinents, Orogenesis and Magmatism, 2024) Rojo Pérez, Esther; Arenas Martín, Ricardo; Fuenlabrada Pérez, José Manuel; Novo Fernández, Irene; Sánchez Martínez, Sonia; Moreno Martín, Diana; Díez Fernández, Rubén; Nance, R. Damian; Strachan, Robin A.; Quesada Ochoa, Cecilio; Lin, S.
Aspects of the evolution of the Pan-African–Cadomian arc have been recognized in several European massifs. The Ossa–Morena Complex (SW Iberian Massif) is one of the best-preserved sections of this palaeo-Gondwana margin. In this domain, recent studies suggest that arc magmatism followed a cyclical pattern during the Upper Ediacaran and Lower Cambrian. However, its initial and more mature stages remain unclear. Upper Ediacaran magmatism (c. 602 Ma) appears to be uninterrupted and driven by slab–mantle wedge–upper plate interactions. The early Paleozoic was a period of significant change along the Gondwana margin. In the Ossa–Morena Complex, the beginning of the Cambrian (c. 541 Ma) is marked by a strong unconformity over the Ediacaran basement, which is linked to destabilization of the arc. However, subduction-related magmatism continued with increasing mantle input, driving the geochemistry to more alkaline compositions. This paper summarizes the geochemical and isotopic evolution of the peri-Gondwana arc preserved in SW Iberia during this period. These results highlight shifts in geochemistry related to a higher slab angle during each magmatic episode, suggesting a tectonic switch toward an extensional regime in this section of the Gondwana margin.