Person:
López Carmona, Alicia

First Name

Alicia

Last Name

López Carmona

URI

https://hdl.handle.net/20.500.14352/75237

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Geológicas

Department

Mineralogía y Petrología

Area

Petrología y Geoquímica

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Now showing 1 - 10 of 21

Sm–Nd isotope geochemistry and tectonic setting of the metasedimentary rocks from the basal allochthonous units of NW Iberia (Variscan suture, Galicia)
(Lithos (Oslo. Print), 2012) Fuenlabrada Pérez, José Manuel; Arenas Martín, Ricardo; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Abati Gómez, Jacobo; López Carmona, Alicia
The basal units of the allochthonous complexes of NW Iberia are formed by thick metasedimentary rock sequences intruded by granitoids, ranging in composition from calc-alkaline (c. 493 Ma) to minor alkaline– peralkaline massifs (c. 475–470 Ma), and mafic rocks. The granitoids were transformed into variably deformed othogneisses and the associated mafic rocks were transformed into amphibolites, blueschists and eclogites during eo-Variscan high-P metamorphism dated at c. 370 Ma. Two different superimposed metasedimentary rock sequences can be distinguished. The lower sequence (maximum depositional age at c. 560 Ma) is mainly composed of metagreywackes, while the upper sequence (maximum depositional age at c. 500 Ma) consists of mica schists and other minor types. Major and trace element geochemistry of the metagreywackes of the lower sequence suggests that they were generated in relation to a peri-Gondwanan arc system built on the thinned continental margin, although some chemical transition to passive margin greywackes is also observed. This sedimentary sequence was probably deposited in an Ediacaran–Early Cambrian back-arc setting or retro-arc setting, closer to the thinned platform of the continental margin. The geochemical features of the sedimentary rocks of the upper sequence suggest some affinity with passive margin sediments; they were probably deposited closer to the continental domain and to certain distance from the most active zones of the magmatic arc. The Nd model ages of 23 analysed samples are Paleoproterozoic and range between 1782 Ma and 2223 Ma (average value 1919 Ma). The Nd model ages are slightly younger in the upper sequence than in the lower sequence, but altogether they define a single population, and therefore the two metasedimentary rock sequences can be clearly related. Sedimentation probably took place within the same basin located in the continental platform of Gondwana, the main source areas of these sedimentary rocks did not change during the Late Neoproterozoic and Cambrian times. The Nd model ages are very old and they seem to be compatible with Paleoproterozoic or Archean source areas, with only minor participation of younger sources probably represented by intrusive Cadomian–Pan-African granitoids.
Blueschist-facies metapelites from the Malpica–Tui Unit (NW Iberian Massif): phase equilibria modelling and H2O and Fe2O3 influence in high-pressure assemblages
(Journal of metamprphic geology, 2013) López Carmona, Alicia; Pitra, Pavel; Abati Gómez, Jacobo
The Malpica–Tui Unit (Galicia, NW Spain) records eclogite- and blueschist-facies metamorphism during the onset of the Variscan orogeny in Europe. Petrological analysis involving pseudosections calculated using THERMOCALC shows that the Upper Sheet of this unit, the Ceán Schists, recorded a threestage metamorphic evolution involving (i) Early subduction-related medium-pressure ⁄ low-temperature metamorphism (M1) constrained at ~º350–380 ºC, 12–14 kbar, which is only recorded in the basal part (lower metapelites, LM) of the Cea´n Schists. (ii) Subduction-related blueschist facies prograde metamorphism (M2) going from 19 kbar, 420 ºC to 21 kbar, 460 ºC in the LM, and from 16 kbar 430 ºC to 21–22 kbar, 520 ºC in the structurally upper metapelites (UM). (iii) Exhumation-related metamorphism (M3) is characterized by a decompression to 8–10 kbar, 470–490 ºC in the LM. This decompression is also recorded in the UM, but it was not possible to estimate precise P–T conditions. The calculations indicate that (i) the prograde evolution in subduction zones may occur in fluidundersaturated conditions due to the crystallization of lawsonite, even in metapelitic rocks. This significantly influences phase equilibria and hence the P–T estimates. (ii) The proportion of ferric iron also has a strong influence on phase equilibria, even in metapelites. However, the analysed values of Fe2O3 may not reflect the oxidation state during the main metamorphic evolution and are probably easily modified by superficial alteration even in apparently fresh samples. The use of P–T–X(Fe2O3) pseudosections together with petrographic observations is then necessary to estimate the real oxidation state of the rocks and correctly evaluate the P–T conditions.
Petrologic and thermobarometric study of the Riás schists (NW Iberian Massif)
(Boletín geológico y minero, 2019) Solís Alulima, Byron Ernesto; López Carmona, Alicia; Gutiérrez Alonso, Gabriel; Álvarez Valero, Antonio M.
The Riás Schists crop out in the so-called Iberian Variscan parautochthon, surrounding the Malpica-Tui Complex (NW Iberian Massif), as part of the westernmost internal areas of the European Variscan belt. Three Variscan metamorphic events have been identified in the Riás Schists (M1, M2 and post-M2). M1 comprise unoriented microinclusions that have only been identified in garnet porphyroblast cores and inside staurolite crystals. M2, comprises the matrix foliation (S2) and the assemblage garnetRIM + staurolite + muscovite + biotite + chlorite + rutile/ilmenite + magnetite + quartz and the development of syntectonic andalusite. Finally, postM2 (post-S2) includes andalusite and plagioclase together with secondary muscovite, biotite and chlorite and accessory tourmaline, Fe/Ti oxides, apatite and carbonate. Results of multi-equilibrium thermobarometry (pressure-temperature pseudosections), for M2 indicates a medium-pressure Barrovian metamorphic event (0.5-0.6 GPa; 580-570 o C; ca. 20 km deep), followed by moderate cooling during decompression, together with the extensional collapse of the Variscan orogenic pile (post-M2; 0.3 GPa; 540 o C; ca. 10 km deep). Inferred P T conditions in the Riás Schists, and their spatial relationship with the overlying allochthonous high-pressure pelitic schists (i.e. Ceán Schists), suggest that both lithologies were part of the same continental margin during the beginning of the Variscan orogeny. However, they experienced very different tectonothermal evolutions due to their putative locations in the orogenic wedge.
Exhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?
(Lithosphere, 2018) Gutiérrez-Alonso, Gabriel; Fernández Suárez, Javier; López Carmona, Alicia; Gärtner, Andreas
In this study we report laser ablation–inductively coupled plasma–mass spectrometer U-Pb ages of granitoids from the so-called early granodiorites of the northwest Iberian Variscan belt. The U-Pb results attest to significant magmatic activity in Visean time (ca. 347–337 Ma) that generated a hitherto poorly constrained granitoid suite in the northwest Iberian tract of the western European Variscan belt realm. This early Carboniferous suite (ECS) is mainly composed of peraluminous cold and hot crustal granodiorites and monzogranites with minor associated mafic rocks that attest to minor involvement of mantle melting. Based on the geochronological and geochemical data, we compare the Visean granitoids with younger Variscan granitoids in northwest Iberia and, in view of the tectonothermal scenarios of the Variscan collision in northwest Iberia, propose a model for the genesis of the ECS in northwest Iberia that involves rapid melting upon fast exhumation of the thickened Gondwanan crust in the course of the protracted Variscan collision.
An extensive K-bentonite as an indicator of a super-eruption in northern Iberia 477 My ago
(IOP Conference Series: Earth and Environmental Science, 2019) Gutiérrez-Alonso, Gabriel; Gutiérrez Marco, Juan Carlos; Fernández Suárez, Javier; Bernárdez Rodríguez, Enrique; Corfu, F.; López Carmona, Alicia
Zircon and monazite ID-TIMS U-Pb dating of four Lower Ordovician altered ash-fall tuff beds (K-Bentonites) in NW Iberia provided coetaneous ages of 477.5±1, 477±1.3 Ma, 477.2±1.1 Ma and 477.3±1 Ma, with a pooled concordia age of 477.2±0.74 Ma. A conservative estimation of the volume and mass of the studied K-bentonite beds (using data from the Cantabrian Zone) returns a minimum volume for the preserved deposits of ca. 37.5 km3 (Volcanic Explosivity Index - VEI = 6, Colossal). When considering other putative equivalent beds in other parts of Iberia and neighbouring realms the volume of ejecta associated to this event would make it reach the Supervolcanic-Apocalyptic status (VEI=8, >1000 km3). Contrary to most cases of this kind of gargantuan eruption events, the studied magmatic event took place in relation to continental margin extension and thinning and not to plate convergence. We speculate that a geochronologically coincident large caldera event observed in the geological record of NW Iberia could be ground zero of this super-eruption.
Geochronology and detrital zircons sources from the Sierra Albarrana Domain (SW Iberian Massif)
(Geogaceta, 2023) Solís Alulima, Byron Ernesto; Abati Gómez, Jacobo; López Carmona, Alicia; Gutiérrez Alonso, Gabriel; Fernández Suárez, Javier
This study compiles the U-Pb and 40Ar/39Ar geochronology of the metasedimentary, migmatitic and granitic rocks of the Sierra Alba-rrana Domain, based on data recently published by the authors to-gether with other bibliographic sources. Maximum depositional ages (MDA) and magmatic and metamorphic events ages are discussed.MDAs suggest that this domain was deposited during the midd-le Cambrian (ca. 511) and U-Pb ages of zoned magmatic and me-tamorphic zircon grains indicate that the main tectono-magmatic event is late Cambrian (granite emplacement; 481 ± 2 Ma) to early Ordovician (migmatization; 478 ± 2 Ma). The 40Ar-39Ar ages eviden-ce a Cambro-Ordovician metamorphic event (ca. 482 Ma) and ano-ther related to the Variscan Orogeny (ca. 337-392 Ma). The most important detrital source corresponds to a Cambrian magmatic event (535-515 Ma), probably developed during the initial episodes of the early Paleozoic rifting affecting the N margin of Gond-wana. The remaining Mesoproterozoic, Paleoproterozoic and Archean zircon grains would have been contributed by Paleoproterozoic base-ment and/or older continental crust recycled in the western sections of the Gondwana margin. We suggest that this domain is probably part of the autochthonous section of the Central Iberian Zone (CIZ) and derived from the Saharan Metacraton and/or Tuareg Shield.
Petrologic modeling of chloritoid–glaucophane schists from the NW Iberian Massif
(Gondwana research, 2010) López Carmona, Alicia; Abati Gómez, Jacobo; Reche i Estrada, Juan
Two P–T pseudosections computed with Thermocalc and Perplex software for high-pressure pelitic Ceán Schists from the NWIberian Massif show that the paragenesis chloritoid+glaucophane, preserved as relict micro-inclusions in garnet porphyroblasts, is stable above 17–18 kbar, indicating a first stage of subduction with 65–70 km of burial. The subsequent growth of biotite and albite porphyroblasts, according to their stability fields in a MnNCKFMASH P–T phase diagram, indicates strong decompression accompanied by slight heating to reach a metamorphic peak at ∼500 °C. This mineral association, described in many subduction-related terranes around the world as one of the high-pressure indicators for metapelites, has not been reported previously in the NW Iberian Massif. The schists contains an initial high-pressure assemblage formed by chloritoid+garnet (Alm0.58 Prp00.03 Grs0.38 Sps0.09)±glaucophane+phengite (3.5–3.4Sip.f.u.)+paragonite+chlorite+epidote+rutile+ilmenite+quartz, preserved as micro-inclusions in garnet, chloritoid and albite porphyroblasts defining an S1 internal fabric. The matrix foliation (S2) additionally contains a high-pressure association formed by garnet (Alm0.68 Prp0.04 Grs0.25 Sps0.03)+ phengite (3.4–3.3Si p.f.u.)+paragonite+winchite+barroisite+hornblende+chloritoid+chlorite+ epidote+rutile+ilmenite+albite+quartz±biotite. An initial pseudosection calculated in the KFMASH system with Thermocalc 3.26 gives pressure estimates through Si-content in phengite barometry that are in agreement with conventional thermobarometry and Thermocalc average P–T calculations, but is unable to describe the full complexity of the mineral assemblages of the schists. For this reason, a more complete P–T pseudosection in the model system MnNCKFMASH was calculated with Perplex 07. This provides a reliable succession of mineral assemblages that are consistent with the petrographic observations and allows a mineralogical sequence to be set for each metamorphic event in the P–T evolution of the high-P pelitic Ceán Schists.
P–T and structural constraints of lawsonite and epidote blueschists from Liberty Creek and Seldovia: Tectonic implications for early stages of subduction along the southern Alaska convergent margin
(Lithos (Oslo. Print), 2011) López Carmona, Alicia; Kusky, Timothy M.; Santosh, M.; Abati Gómez, Jacobo
The southern Alaska convergent margin contains several small belts of sedimentary and volcanic rocks metamorphosed to blueschist facies, located along the Border Ranges fault on the contact between theWrangellia and Chugach terranes. These belts are significant in that they are the most inboard, and thus probably contain the oldest record of Triassic–Jurassic northward-directed subduction beneath Wrangellia. The Liberty Creek HP-LT schist belt is the oldest and the innermost section of the Chugach terrane.Within this belt lawsonite blueschists contains an initial high-pressure assemblage formed by lawsonite+phengite+chlorite+sphene+albite± apatite±carbonates and quartz. Epidote blueschists are composed of sodic, sodic–calcic and calcic amphiboles+ epidote+phengite+chlorite+albite+sphene±carbonates and quartz. P–T pseudosections computed from four representative samples constrain maximumpressures at 16 kbar and 250–280 °C for the Lawsonite-bearing blueschists, and 15 kbar and 400–500 °C for the epidote-bearing blueschists, suggesting a initial subduction stage of 50–55 km depth. The growth of late albite porphyroblasts in all samples suggests a dramatic decompression fromca. 9 kbar to 5 kbar. The Liberty Creek schists can be correlated with the Seldovia blueschist belt on the Kenai Peninsula.Metamorphismin both terranes took place in the Early Jurassic (191–192 Ma), recording an early stage of subduction beneathWrangellia. In the nearby terranes of the same margin, the age ofmetamorphismrecords an early stage of subduction at 230 Ma. Based on this difference in age, a maximum of 40Ma were necessary to subduct the protoliths of the Seldovia and Liberty Creek blueschists to depths of circa 50–55 km, suggesting a minimum vertical component of subduction of 1.2–1.5 cm/year.
U-Pb geochronolgy of the deformed Juzbado Granite (Salamanca, NW Spain)
(Geogaceta, 2018) Gutiérrez Alonso, Gabriel; López Carmona, Alicia; Fernández Suárez, Javier; Jablonski, Jerónimo; Hofmann, Mandy; Gärtner, Andreas
Este trabajo se centra en el estudio de la edad de cristalización del granito deformado de Juzbado mediante geocronología U-Pb a través de ablación láser. Se dataron 7 granos de circón, obteniéndose edades comprendidas entre 340 y 2500 Ma. Los datos obtenidos proporcionan una edad máxima de cristalización de 340 Ma y aportan datos sobre la naturaleza de los potenciales materiales fuente. Las edades de circones heredados existentes en el granito son coincidentes con las encontradas en las posibles rocas fuente. Dado que esta intrusión está deformada intensamente por la fábrica relacionada con la Zona de Cizalla de Juzbado-Penalva do Castelo, la edad mínima de este cuerpo es de 308 Ma. La comparación de las características petrológicas de este granito con las de otros en los alrededores (en el Domo del Tormes) permite asignarle una edad en torno a 320 Ma.
Rocas en facies de esquistos azules del complejo de Malpica-Tuy (NO del Macizo Ibérico)
(2014) López Carmona, Alicia; Abati Gómez, Jacono; Pitra, Pavel