Person: López Carmona, Alicia
Universidad Complutense de Madrid
Faculty / Institute
Mineralogía y Petrología
Petrología y Geoquímica
Now showing 1 - 10 of 18
- PublicationAllochthonous terranes involved in the Variscan suture of NW Iberia: A review of their origin and tectonothermal evolution(Elsevier, 2016-10) Arenas Martín, Ricardo; Sánchez Martínez, Sonia; Díez Fernández, Rubén; Gerdes, Axel; Abati Gómez, Jacobo; Fernández Suárez, Javier; Andonaegui Moreno, Pilar; González Cuadra, Pablo; López Carmona, Alicia; Albert Roper, Richard; Fuenlabrada Pérez, José Manuel; Rubio Pascual, Francisco J.NW Iberia includes a rather complete section of a Variscan suture, where different terranes with continental or oceanic affinities appear with clear structural relationships. Three groups of terranes, namely Upper, Ophiolitic and Basal units and a frontal tectonic mélange appear in Galicia, in Cabo Ortegal, Órdenes and Malpica-Tui complexes. They constitute a huge allochthonous pile thrust over the Iberian parautochthonous and autochthonous domains, which represent the section of the Gondwanan margin that escaped continental subduction during the Variscan cycle. Considering the allochthonous character of the nappe pile and the strong deformation associated to the Variscan collision, there are problems to identify the original tectonic setting of the terranes and thence, it is difficult to reconstruct the paleogeographic context during the Variscan and pre-Variscan times in detail. Key features to perform any model for the Variscan convergence should consider the existence of two different high-P metamorphic events (dated at c. 400 and 370 Ma, respectively), separated in time for the generation of mafic-ultramafic sequences at c. 395 Ma which constitute the most common ophiolites described in the Variscan suture. Some dynamic models developed in NW Iberia have important problems to explain the observed tectonothermal evolution, especially the older high-P metamorphic event and the exhumation of deeply subducted transitional-type sections. On the other hand, the recently discovered participation of an older continental crust in the generation of different protoliths of the Middle Devonian ophiolites, makes difficult the interpretation of these ophiolites in relation to open wide oceanic domains. This paper describes the distribution, structure, lithologies, geochronology and chemical composition of the terranes involved in the Variscan suture of NW Spain. The scope of this description ranges from detailed regional aspects to the discussion of the development of the Variscan Orogen in the context of the assembly of Pangea. A two-stage collisional model affecting a wide Gondwanan platform may explain most of the evidences in NW Iberia. The generation of a long pull-apart basin probably occurred after the first collision, where the Devonian ophiolites were formed. These ophiolites have been in general described in the context of the Rheic Ocean, but according to the new existing data they do not seem related to this ocean, but rather they were formed after its closure.
- PublicationRocas en facies de esquistos azules del complejo de Malpica-Tuy (NO del Macizo Ibérico)(Universidad Complutense de Madrid, 2014-03-11) López Carmona, Alicia; Abati Gómez, Jacono; Pitra, Pavel
- PublicationPetrologic modeling of chloritoid–glaucophane schists from the NW Iberian Massif(Elsevier Science B. V., Amsterdam, 2010) López Carmona, Alicia; Abati Gómez, Jacobo; Reche i Estrada, JuanTwo 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.
- PublicationExhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?(Geological Society of America, 2018-02-09) Gutiérrez-Alonso, Gabriel; Fernández Suárez, Javier; López Carmona, Alicia; Gärtner, AndreasIn 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.
- PublicationU-Pb geochronolgy of the deformed Juzbado Granite (Salamanca, NW Spain)(Sociedad Geológica de España, 2018) Gutiérrez Alonso, Gabriel; López Carmona, Alicia; Fernández Suárez, Javier; Jablonski, Jerónimo; Hofmann, Mandy; Gärtner, AndreasEste 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.
- PublicationP–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(Elsevier Science B.V., Amsterdam, 2011) López Carmona, Alicia; Kusky, Timothy M.; Santosh, M.; Abati Gómez, JacoboThe 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.
- PublicationSm–Nd isotope geochemistry and tectonic setting of the metasedimentary rocks from the basal allochthonous units of NW Iberia (Variscan suture, Galicia)(Elsevier Science B.V., Amsterdam, 2012) Fuenlabrada Pérez, José Manuel; Arenas Martín, Ricardo; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Abati Gómez, Jacobo; López Carmona, AliciaThe 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.
- PublicationBlueschist-facies metapelites from the Malpica–Tui Unit (NW Iberian Massif): phase equilibria modelling and H2O and Fe2O3 influence in high-pressure assemblages(Blackwell Publishing Ltd, 2013) López Carmona, Alicia; Pitra, Pavel; Abati Gómez, JacoboThe 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.
- PublicationDetrital zircon ages and provenance of a Cambrian succession in the Sierra Albarrana Domain (SW Iberian Massif)(Elsevier, 2022-01) Solís Alulima, B.E.; Abati Gómez, Jacobo; López Carmona, Alicia; Gutiérrez Alonso, Gabriel; Fernández Suárez, Javier; Stockli, Daniel F.This study presents the first U-Pb geochronological data on detrital zircon grains from the metasedimentary successions of the Sierra Albarrana Domain (SW Iberian Massif) obtained by SHRIMP and LA-ICP-MS. We provide new information on the Maximum Depositional Ages (MDA) during the middle Cambrian through a systematic study, together with age comparisons of the successions, using Kernel Density Estimates (KDE) diagrams, Cumulative Age Distributions (CADs) and the Kolmogorov–Smirnov (K-S) test. On the other hand, the U-Pb zircon data presented in this study have been compared with all the existing data from detrital zircon grains in Neoproterozoic and Cambrian rocks of the Iberian Massif (20 samples, 2706 U–Pb zircon ages). For the comparison, in addition to the KDEs, CADs and K-S test, we apply 3D multidimensional scaling techniques (3D-MDS). The results, together with the geochemical and isotopic characterisation from previous studies, suggest that this domain is likely to be part of the autochthonous section of the Central Iberian Zone (CIZ). Zircon age patterns indicate a probable sedimentary provenance from the Saharan Metacraton with, or without, minor input from the Tuareg Shield. The most important local detrital source corresponds to Cadomian magmatism developed during a magmatic event (535–515 Ma) followed by back-arc extension and early Paleozoic rifting (535–460 Ma). The remaining Mesoproterozoic, Paleoproterozoic and Archean zircon grains would have been provided by the Paleoproterozoic basement and/or the older continental crust recycled in the western sections of the Gondwana margin.
- PublicationPolycyclic metamorphic evolution of the Sierra Albarrana Schists (SW Iberian Massif): From low-pressure Ordovician rifting to medium-pressure Variscan overprint(Elsevier Science B.V., Amsterdam, 2023-05) Solís Alulima, B.E.; López Carmona, Alicia; Abati Gómez, Jacobo; Rojas Agramonte, Yamirka; Bousquet, Romain; González del Tánago y del Río, JoséThis study presents new information on the polycyclic metamorphic evolution of the Sierra Albarrana Domain (SW Iberian Massif) obtained through a comprehensive assessment of mineral assemblages and petrological modelling (P–T–X pseudosection approach). The pelitic schists in this domain depict the uncommon paragenesis St-Grt-And together with And-Grt-Sil-bearing schists. The first assemblage has been accurately reproduced by pseudosection modelling using the whole rock composition directly analysed by XRF. In contrast, early attempts to model And-Grt-Sil-bearing schists were not as successful. Fe3+ can be a critical element influencing the phase relations in pelites. For this reason, we investigated the influence of the effective amounts of Fe3+ to estimate the oxidation estate during the metamorphism by computing a series of P/T–X pseudosections to explore whether somewhere in P–T–X space the matrix association can be reproduced. The Sierra Albarrana Domain recorded a regional low-pressure metamorphic event accompanied by a complex structural evolution, probably related with the Middle Cambrian-Lower Ordovician rifting developed in the NW Gondwanan margin. This episode has been constrained at ∼4 kbar and 580 °C in the St-Grt-And pelitic schists. Related granitic magma pulses contributed to a local thermal increase of the extending crust (preserved in the And-Grt-Sil-bearing schists), where temperature reaches up to 595 °C. This area shows the syntaxial replacement of coarse-grained andalusite porphyroblasts by sillimanite. This was followed by exhumation, characterised by decompression at ∼2 kbar and 510 °C. After the main pre-Variscan Buchan-type regional metamorphism, a localised medium-pressure metamorphic event, limited to granitic pegmatites and concordant ky-bearing quartz segregation veins was recorded, possibly due to the tectonic thickening corresponding to the Variscan cycle.