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 18

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.
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.
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.
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.
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.
Thermodynamic modelling of high-P mineral assemblages from the Iberian Massif
(2022) Novo Fernández, Irene; Arenas Martín, Ricardo; García Casco, Antonio; Díez Fernánde, Rubén
The Variscan Orogen formed as a consequence of the collision of two large landmasses, Gondwana to the South and Laurussia to the North, during the final assembly of Pangea that took place in Late Paleozoic times. Nowadays this orogen can be tracked from the Bohemian Massif to the East, through the French Massif Central and the Armorican Massif, to the westernmost Iberian Massif. The most internal zone of the orogen crops out in several allochthonous complexes and it is characterized by several suture zones, featured by high-P metamorphic units and ophiolites. In the Iberian Massif, units that belong to four high-P metamorphic belts are identified, three of which formed during the initial stages of the collision. This PhD Thesis presents the results obtained for the three oldest high-P belts. To the top of the allochthonous complexes, the base of the Upper Allochthon (or Upper Units) is part of a first high-P, high-T metamorphic belt formed during Early Devonian times (c. 400-390 Ma). At the base of the complexes, the Basal Allochthon (or Basal Units) represents a section of another high-P metamorphic belt, in this case characterized by low- to intermediate-T, dated at Late Devonian (c. 377-370 Ma). Finally, the Middle Allochthon contains ophiolitic units of different nature and age. The lower and easternmost section of the ophiolites contains the Somozas Mélange, a serpentinite-matrix mélange formed in a subduction channel that includes abundant tectonic blocks of diverse nature and size. One of the blocks is composed by submarine metavolcanites that underwent high-P metamorphism. The age of the high-P metamorphism is uncertain, although an intermediate age between the high-P metamorphism of the Upper and Basal Allochthons is the most likely...
Reply to Comment by Azor et al. on “On the Rootless Nature of a Devonian Suture in SW Iberia (Ossa-Morena Complex, Variscan Orogen): Geometry and Kinematics of the Azuaga Fault”
(Tectonics, 2022) Díez Fernández, Rubén; Fernández Rodríguez, Carlos; Arenas Martín, Ricardo; Novo Fernández, Irene
Geological mapping, structural data, and analytical modeling by Díez Fernández et al. (2021), https://doi.org/10.1029/2021tc006791 supported that the Central Unit belonged to a rootless Devonian suture zone contiguous to the SW of its exposure and under the upper section of the footwall to the Azuaga Fault. Late exhumation of the Central Unit was via extrusion from the upper-middle crust under inclined triclinic sinistral transpression, which favored upright folding of the suture zone. Azor and coworkers argue that the upright folds that affect the Central Unit are local, despite geological maps and structural data demonstrate they are km-scale and occur all across the Central Unit. Besides ignoring structural data regarding the kinematics of the Azuaga Fault, Azor et al. (2022), https://doi.org/10.1029/2021TC006982 fail to recognize the net upthrown movement of the NE side of the Azuaga Fault, as the Central Unit in that side is juxtaposed against syn-orogenic strata that rest unconformably onto other metamorphic units in the SW side of the fault. Seismic data that image the Central Unit as a NE-dipping rock package is used as an argument against the proposal by Díez Fernández et al. (2021), https://doi.org/10.1029/2021tc006791. However, the section of the Central Unit those data account for, are from a different part of the Central Unit, the real dip of some structures in the seismic image is not properly interpreted, and the model by Díez Fernández et al. (2021), https://doi.org/10.1029/2021tc006791 is compatible with a Central Unit that also dips to the NE. Overall, the model proposed by Díez Fernández et al. (2021), https://doi.org/10.1029/2021tc006791 remains valid.
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.