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 11

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.
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.
Reconstruction of the prograde PT history of high‐P migmatitic paragneisses via melt‐reintegration approach and thermodynamic modelling (Allochthonous Complexes, NW Iberian Massif)
(Journal of Metamorphic Geology, 2020) Novo Fernández, Irene; Albert Roper, Richard; Arenas Martín, Ricardo; Garcia Casco, Antonio; Díez Fernández, Rubén; Sánchez Martínez, Sonia
The Upper Units of the allochthonous complexes of the NW Iberian Massif constitute a terrane with continental affinity. They represent the vestiges of a Cambrian magmatic arc developed in the periphery of Gondwana (West African Craton) which was involved in the Devonian Variscan collision, undergoing high‐P, high‐T metamorphism. This includes ultramafic rocks, high‐P mafic rocks (eclogites and granulites) and high‐P migmatitic paragneisses. The latter rocks show an extensive migmatization with the leucosomes oriented parallel to the regional foliation. The migmatitic paragneisses are composed of garnet, kyanite, biotite, quartz, plagioclase, K‐feldspar, rutile and Ti‐hematite. Thermodynamic modelling using the measured bulk composition in the NCKFMASTHO system indicates metamorphic peak conditions of ~15 kbar and ~800 to 835°C, followed by a significant cooling. The prograde evolution is assessed by means of a melt‐reintegration approach, using the composition of the garnet and its inclusions. An appropriate composition of liquid is added to the measured bulk composition to emulate the pre‐melting bulk composition. Modelling of this melt‐reintegrated composition allows to identify a colder high‐P episode below ~500°C. Zircon crystals extracted from the leucosomes show overgrowths crystallized from the partial melt at c. 389 Ma (U–Pb system). The P–T–t path proposed reveals a subduction of the peri‐Gondwanan arc‐derived section down to mantle depths. An isobaric heating stage occurred as a result of residence at great depths and/or inception of a transient oceanic basin at c. 395 Ma. The ensuing near‐isothermal exhumation occurred due to the extension related to the inception of the basin, reaching the thermal peak shortly before c. 389 Ma. Subsequent cooling is related to the underthrusting of colder oceanic and transitional crust below the HP‐HT Upper Units.
Metamorfismo de alta-P en las rocas volcánicas submarinas de Espasante (Complejo de Cabo Ortegal) I: Petrografía y mineralogía
(Geotemas, 2016) Novo Fernández, Irene; Arenas Martín, Ricardo; Garcia Casco, Antonio; Díez Fernández, Rubén
En la base del Complejo de Cabo Ortegal, en una posición estructural inferior, aparece una mélange serpentinítica, la Mélange de Somozas. Próximo a la localidad de Espasante se encuentra un bloque tectónico de metavulcanitas constituido por rocas volcánicas submarinas masivas, brechas de pillow lavas fragmentadas, pillow-lavas empaquetadas y una matriz hialoclastítica. El estudio detallado de la petrografía y mineralogía de las hialoclastitas revela unas rocas que se caracterizan por una gran complejidad textural y mineralógica. La asociación mineral del pico metamórfico está constituida por moscovita+paragonita+cuarzo+hematites+distena+granate+clorita+epidota, con rutilo, apatito y turmalina como minerales accesorios. La margarita se presenta como mineral retrógrado reemplazando a la distena desde los bordes hacia el interior. La composición de todas estas fases minerales junto con su posición textural sugiere condiciones de metamorfismo de alta-P para el pico metamórfico.
Metamorfismo de alta-P en las rocas volcánicas submarinas de Espasante (II): Condiciones P-T y evolución reaccional
(Geotemas, 2016) Novo Fernández, Irene; Garcia Casco, Antonio; Arenas Martín, Ricardo; Díez Fernández, Rubén
El bloque tectónico de metavulcanitas de la Mélange de Somozas se caracteriza por registrar un evento de alta-P ocurrido durante su subducción. Este evento se refleja únicamente en la matriz hialoclastítica, que desarrolló una mineralogía compleja favorecida por la alteración hidrotermal de fondo oceánico previa que modificó su composición primaria y favoreció el desarrollo de fases minerales de alta-P durante la subducción. La modelización termodinámica de las metahialoclastitas ha permitido determinar las condiciones P-T de la asociación mineral del pico metamórfico, constituida por moscovita+paragonita+granate+clorita+distena+hematites+epidota+ cuarzo+rutilo. Las pseudosecciones, calculadas en el sistema KNCFMnMASHTO, indican unas condiciones para el pico metamórfico de aproximadamente 17.5-18 kbar de presión y 550ºC de temperatura. La margarita aparece como mineral retrógrado en las muestras, y se forma por debajo de los 11 kbar de presión. La trayectoria P-T propuesta para estas rocas indica una drástica descompresión y un rápido ascenso del bloque de metavulcanitas a través del canal de baja viscosidad en el cual se desarrolló la mélange en sí.
A unique blueschist facies metapelite with Mg-rich chloritoid from the Badajoz-Córdoba Unit (SW Iberian Massif): correlation of Late Devonian high-pressure belts along the Variscan Orogen
(International Geology Review, 2021) Arenas Martín, Ricardo; Novo Fernández, Irene; Garcia Casco, Antonio; Díez Fernández, Rubén; Fuenlabrada Pérez, José Manuel; Pereira, Manuel Francisco; Abati Gómez, Jacobo; Sánchez Martínez, Sonia; Rubio Pascual, Francisco J.
The Badajoz-Córdoba Unit (BCU, SW Iberian Massif) is a Variscan high-P unit mainly constituted by metapelites, metagreywackes, orthogneisses, Grt-amphibolites, and retrogressed eclogites (high-P metamorphism at c. 377 Ma). Discovery of rare metapelites with well-preserved high-P mineral assemblages, including large garnets up to 1 cm in diameter with abundant inclusions, chloritoid (up to XMg = 0.32), kyanite, staurolite, chlorite, phengite (up to Si = 3.16 apfu), paragonite, margarite, and rutile, allows detailed determination of the tectonothermal evolution of the unit. Pseudosection modelling of representative samples indicates that this mineral assemblage formed in blueschist facies (near eclogite facies transition) at P conditions higher than 20 kbar at c. 525°C and that it underwent a subsequent severe exhumation and moderate heating. The lithological composition of the BCU, the age of high-P metamorphism and the characteristics of the high-P mineral assemblages are similar to those found in other high-P and low to intermediate-T units of the Variscan Orogen. All these units form part of a single blueschist-eclogite facies metamorphic belt formed during Late Devonian subduction of the external margin of Gondwana.