Person:
Abati Gómez, Jacobo

First Name

Jacobo

Last Name

Abati Gómez

URI

https://hdl.handle.net/20.500.14352/75247

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 23

Magmatism and early-Variscan continental subduction in the northern Gondwana margin recorded in zircons from the basal units of Galicia, NW Spain
(Geological Society of America Bulletin, 2010) Abati Gómez, Jacobo; Gerdes, Axel; Fernández Suárez, Javier; Arenas Martín, Ricardo; Whitehouse, Martín J.; Díez Fernández, Rubén
In situ uranium-lead dating (LA-SF-ICPMS and SIMS) and Lu-Hf isotope analyses (LA-MC-ICP-MS) of zircon from eclogite facies rocks from the basal units of the Variscan Belt in Galicia constrain their magmatic and metamorphic evolution and give some clues about the nature and origin of the involved basement. The samples studied are two felsic gneisses, two eclogites, and one eclogitic gneiss of intermediate composition (metatonalite). Oscillatory-zoned zircon cores from the felsic samples gave a main clustering of U-Pb ages at 493 ± 2 and 494 ± 2 Ma, and some older ages that represent inherited cores. Zircon grains from the intermediate and one of the mafic rocks show no inherited cores and yielded ages of 494 ± 3 and 498 ± 6 Ma, respectively, interpreted as time of protolith crystallization. Variably developed homogeneous zircon rims in one felsic gneiss yielded an age of 372 ± 3 Ma, and very tiny zircons of one eclogite gave 350 ± 2 Ma, both of which we interpret as metamorphic ages. The new age data demonstrate that the calc-alkaline magmatic suite described in the basal unit is ca. 20 Ma older than the alkaline to peralkaline plutonic suite of the same unit (dated at 472 ± 2 Ma; Rodríguez et al., 2007), and thus probably represents a distinct geologic event. Overgrowth rims are interpreted as metamorphic on the basis of their Lu/Hf and Th/U ratios. The 372 ± 3 age is considered as dating the high-pressure (high-P) metamorphism, and is essentially in agreement with previous Ar-Ar and Rb-Sr data. This high-P metamorphism marks the initial early-Variscan subduction of the Gondwana margin. The inherited zircon ages and Hf isotopic composition of zircons point to a considerable input of crustal material with West African Craton provenance to the felsic magma.
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.
Detrital zircon ages of Neoproterozoic sequences of the Moroccan Anti-Atlas belt
(Precambrian research, 2010) Abati Gómez, Jacobo; Aghzer, Abdel Mouhsine; Gerdex, Axel; Ennih, Nasser
Detrital zircon dating from Neoproterozoic successions in the Sirwa inlier of the Anti-Atlas belt in Morocco confirms that the maximum depositional age of the main stratigraphic groups is significantly younger than has been previously proposed in lithostratigraphic correlations. This can probably be extended to the whole Anti-Atlas according to other recent data from the Saghro inlier. Although the relative stratigraphic position of the different units remains valid as published previously, a crucial implication of the new ages is that the sequences believed to be contemporaneous with oceanic crust and island arc formation during the rifting and break-up of the northern margin of the West African Craton (WAC), and believed to be involved in the first phases of the Pan-African orogeny, are actually late to postorogenic. The age of the main deformation associated with the collision of the oceanic- and arc-derived terranes to the WAC, allegedly affecting the sediments of the Saghro Group, has been estimated at around 663–640 Ma. However, the youngest zircon populations of sediments of the Saghro and Bou Salda Groups, obtained in this study, cluster around 620–610 Ma, constraining the maximum age of deposition. This age of sedimentation is indistinguishable from the age of intrusive high-K calc-alkaline plutons of the Assarag Suite, suggesting a very rapid cycle of magmatism, relief formation, erosion and sedimentation in an active geodynamic scenario. Moreover, the proportion of the 610Ma detrital zircons becomes less with respect to the Paleoproterozoic zircons at higher stratigraphic levels, suggesting that the source of young zircons was progressively eroded and more extensive cratonic areas, that probably underlie the Neoproterozoic rocks, were exposed. We interpret these data in terms of the development of a ca. 610Ma magmatic arc, built upon WAC basement, and its progressive dismantling. This arc can be correlated with the voluminous late Neoproterozoic (ca. 640–570 Ma) arc magmatism characteristic of the north Gondwana margin and the peri-Gondwanan terranes. The diamictite beds that appear in the Imghi Formation of the Saghro Group have been correlated with the Sturtian glacial period ca. 700 Ma. However, zircons from one sample of these diamictites indicate that this correlation cannot be longer maintained, and instead they should be correlated with the Marinoan glacial period ca. 630–610 Ma, with a widespread distribution of glaciogenic deposits in West Africa. In addition, around 375 U–Pb concordant analyses obtained from Paleoproterozoic zircons from six samples represent a statistically significant population of this area of theWACbasement, which can be a useful database for comparison with the detrital zircon populations of the peri-Gondwanan terranes of Europe and North America, as the WAC margins were one of the major sediment suppliers for these terranes.
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.
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.
The Bazar Ophiolite of NW Iberia: a relic of the Iapetus–Tornquist Ocean in the Variscan suture
(Terra nova, 2012) Sánchez Martínez, Sonia; Gerdex, Axel; Arenas Martín, Ricardo; Abati Gómez, Jacobo
The Bazar Ophiolite, one of the ophiolitic units involved in the Variscan suture of NW Iberia, is mainly formed by metagabbroic high T amphibolites with N-MORB affinity. The ophiolite appears accreted under an arc-derived upper terrane affected by intermediate-P granulite facies metamorphism dated at 496– 484 Ma. U-Th-Pb geochronology and Lu-Yb-Hf isotope geochemistry of zircons allow recognizing two growth stages. The first occurred during crystallization of the gabbroic protolith and has been dated at 495 ± 2 Ma, whereas the second one, interpreted as dating the high T metamorphism, yielded an age of 475 ± 2 Ma. The chronology of the Bazar Ophiolite and its accretionary history suggest that this unit is a relic of the Cambrian ocean located to the North of Gondwana, the Iapetus–Tornquist Ocean, accreted to a dissected arc during or before the early stages in the opening of the Rheic Ocean.
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.
A Peri-Gondwanan arc active in Cambrian-Ordovician times: the evidence of the uppermost terrane of NW Iberia
(2011) Arenas Martín, Ricardo; Abati Gómez, Jacobo; Sánchez Martínez, Sonia; Andonaegui Moreno, María Del Pilar; Fuenlabrada Pérez, José Manuel; Fernández Suárez, Javier; González Cuadra, P.; Gutiérrez-Marco, Juan Carlos; Rábano, Isabel; García-Bellido, Diego
Insights on the crustal evolution of the West African Craton from Hf isotopes in detrital zircons from the Anti-Atlas belt
(Precambrian research, 2012) Abati Gómez, Jacobo; Aghzer, Abdel Mouhsine; Gerdes, Axel; Ennih, Nasser
The Lu-Hf isotopic composition of detrital zircons has been used to investigate the crustal evolution of the northern part of the West African Craton (WAC). The zircons were separated from six samples of siliciclastic sedimentary rocks from the main Neoproterozic stratigraphic units of the Anti-Atlas belt, from the Sirwa and Zenaga inliers. The data suggest that the north part of the WAC formed during three cycles of juvenile crust formation with variable amount of reworking of older crust. The younger group of zircons, with a main population clustering around 610 Ma, has a predominant juvenile character and evidences of moderate mixing with Paleoproterozoic and Neoarchean crust, which supports that most igneous and metamorphic rocks where zircons originally crystallized were formed in an ensialic magmatic arc environment. The group of zircons in the age range 1.79–2.3 Ga corresponds to the major crust forming event in the WAC: the Eburnian orogeny. The isotopic data indicate that the provenance area should represent a crustal domain that was separated from a mantle reservoir at ∼2050–2300 Ma, and further evolved with a time-integrated 176Lu/177Hf of ∼0.01, characteristic of continental crust. The evolution of the Eburnian orogeny is, consequently, compatible with new crust formation in an island arc environment, the transition to a continental arc setting and a final continent–continent collision. The Lower Paleoproterozoic and Neoarchean evolution (2.3–2.75 Ga) includes a group of detrital zircon ages that has not been identified up to now in the igneous or metamorphic rocks of the north WAC basement. Their Hf isotopic signature points to reworking of mainly juvenile Neoarchean crust with some Meso- to Palaearchean contributions. The significance of these ages is uncertain: they can represent a tectonothermal event not discovered yet in the Reguibat Shield or the zircons can be far traveled from an unknown source.
Project number: 74
Material audiovisual para el aprendizaje de métodos y conceptos básicos en Geología
(2017) Orejana García, David; Abati Gómez, Jacobo; Andonaegui Moreno, María Del Pilar; Calvo Sorando, José Pedro; De Ignacio San José, Cristina; Galindo Francisco, María Del Carmen; Varas Muriel, María Josefa
El proyecto se centra en la elaboración de vídeos en los que se resuelven problemas prácticos relacionados con conceptos básicos de Geología General, principalmente relacionados con mapas topográficos y mapas geológicos. El objetivo es que estos vídeo-tutoriales sirvan de apoyo a los alumnos de los primeros cursos de las titulaciones de Grado en Geología y Grado en Ingeniería Geológica, para el estudio de los contenidos y ejercicios prácticos.