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 32

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.
Metamorphic evolution of anthophyllite/cummingtonite-cordierite rocks from the upper unit of the Ordenes Complex (Galicia, NW Spain)
(European Journal of Mineralogy, 2005) Abati Gómez, Jacobo; Arenas Martín, Ricardo
Two types of low-Ca amphibolites are described for the first time in the Ordenes Complex (Galicia, NW Spain). The first type exhibits an initial mineral assemblage containing sillimanite, staurolite and anthophyllite, which are found as microinclusions in cordierite crystals. This association indicates medium pressure and temperatures above 600ºC, and is replaced in the matrix by a medium to low-pressure assemblage of anthophyllite, cordierite and garnet. The second type is represented by lowpressure amphibolitic gneisses formed mainly of cummingtonite, cordierite, andalusite and garnet. The first type of amphibolite would appear to give rise to the second type as a result of metamorphic evolution to lower pressures . A fragment of the decompressive P-T path was obtained by a detailed study of the mineral assemblage succession and the textural relationships of these rocks. The P-T path begins with an almost isothermal decompression from ca. 6-7 kbar and 650ºC. This kind of P-T path (isothermal) is usually interpreted, according to thermal models, as originating during exhumation favoured by some tectonic process. Hence, the exhumation of the uppermost unit of the Ordenes Complex, in which the anthophyllite-cummingtonite rocks are located, appears to have been facilitated by some kind of extensional tectonic process.
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.
U–Pb evidence for a polyorogenic evolution of the HP–HT units of the NW Iberian Massif
(Contributions to mineralogy and petrology, 2002) Fernández Suárez, Javier; Corfu, Fernando; Arenas Martín, Ricardo; Marcos Vallaure, Alberto; Martínez Catalán, José Ramón; Díaz García, Florentino; Abati Gómez, Jacobo; Fernández Rodríguez, Francisco José
A isotope dilution thermal ionisation mass spectrometry U–Pb geochronological study was carried out on the high-pressure and high-temperature units (HP–HT units) overlyingthe oceanic suture in the Allochthonous Complexes of the NW Iberian Variscan Belt. The rocks investigated are seven granulite- to eclogitefacies paragneisses and one leucosome within mafic highpressure granulites in the Ordenes and Cabo Ortegal Complexes of NW Spain. U–Pb datingof zircon, monazite, titanite and rutile reveal the presence of a pervasive Early Ordovician metamorphic event at ca. 500–480Ma and a later Early Devonian event at ca. 400–380 Ma. The U–Pb ages, in conjunction with petrological and structural data, indicate that the high-pressure event recorded by these rocks is Early Ordovician in age. Monazite ages in the paragneisses suggest that peak metamorphic conditions were reached at ca. 500–485Ma. Subsequently, the rock ensemble underwent exhumation accompanied by partial meltingan d zircon growth at ca. 485–470Ma. Meltingof mafic granulites was coeval with this latter episode as indicated by zircon crystallisation age in the leucosomes dated at ca. 486 Ma. Based on these data and on the general features of magmatism and metamorphic evolution, it is proposed that this process took place at a convergent plate boundary within a peri-Gondwanan oceanic domain. Monazite, titanite and rutile data in some of the samples studied show evidence of a second metamorphic episode that took place between ca. 400 and 380 Ma (with a peak at ca. 390–385Ma). This Early Devonian event, at variance with the previous one, was not pervasive, but, rather, was localised in areas of intense Variscan tectonothermal reworking. It is claimed that this later metamorphic event was recorded by the U–Pb system in areas where monazite and titanite growth was enhanced by fluid circulation in highly strained rocks (Variscan shear zones). Accordingto previous structural studies and Ar–Ar datingof fabrics, this Early Devonian episode took place as the HP–HT units were deformed and thrusted upon the ophiolitic units in the early stages of the Variscan collision.
Thrust and detachment systems in the Ordenes Complex (northwestern Spain): Implications for the Variscan-Appalachian geodynamics.
(Special paper - Geological Society of America, Variscan-Appalachian dynamics: The building of the late Paleozoic basement, 2002) Martínez Catalán, José Ramón; Díaz García, Florentino; Arenas Martín, Ricardo; Abati Gómez, Jacobo; Castiñeiras García, Pedro; González Cuadra, Pablo; Gómez Barreiro, Juan; Rubio Pascual, Francisco J.; Martínez Catalán, José Ramón; Hatcher, Robert D.; Arenas Martín, Ricardo; Díaz García, Florentino
The allochthonous complexes of northwestern Iberia consist of a pile of units of Gondwanan and peri-Gondwanan provenance, and include oceanic lithosphere. The units are classiµed into upper, intermediate (ophiolitic), and basal. We present a dettailed geological map and sections across the Ordenes Complex, together with a brief description of its units and a discussion of its structures. In the upper units, two complete cycles of burial and exhumation have been identiµed. The first cycle, of Early Ordovician age, records a convergent plate margin, possibly in a peri-Gondwanan domain. The second is Variscan, and the structural evollution of the three groups of allochthonous units re×ects progressive accretion to an acctive orogenic wedge. Continuous understacking of continental and oceanic fragments toward the west began with the upper units and ended with the basal units. The latter represent the outermost margin of Gondwana, and their subduction marked the closure of the intervening ocean, and the change from subduction to a collisional regime. Terrane accretion took place in the Devonian and, during the Late Devonian and the Carboniferous, the deformation progressed inboard of the Gondwana margin. Variscan emplacement of the allochthonous units occurred in two successive thrusting episodes. The µrst placed the basal units over the sedimentary cover of the Gondwana margin in what seems to follow a normal sequence of thrusting. The second carried the upper and ophiolitic units on top of the previous nappe pile and has an out-of-sequence character. A possible correlation of the Early Ordovician convergence, early Variscan accretion, subsequent oceanic closure, continent-continent collision, and renewed thrust activity during the late Carboniferous in northwestern Iberia is established with the Taconian, Acadian, and Alleghanian orogenies in the Appalachians.
Tectonic evolution of the upper allochthon of the Órdenes complex (northwestern Iberian Massif): Structural constraints to a polyorogenic peri-Gondwanan terrane
(The Evolution of the Rheic Ocean: From Avalonian-Cadomian Active Margin to Alleghenian-Variscan Collision, 2007) Gómez Barreiro, Juan; Martínez Catalán, José Ramón; Arenas Martín, Ricardo; Castiñeiras García, Pedro; Abati Gómez, Jacobo; Díaz García, Florentino; Wijbrans, Jan R.; Linnemann, Ulf; Nance, R. Damian; Kraft, Petr; Zulaud, Gernold
The upper allochthon of northwest Iberia represents the most exotic terrane of this part of the European Variscan belt. Recent advances in the metamorphic petrology, structural geology, and geochronology of the upper allochthon in the Órdenes complex are integrated into a synthesis of its tectonic evolution, constraining the main tectonothermal events. Important aspects of this synthesis are (1) the interpretation of Cambro-Ordovician magmatism and earliest metamorphic event, as the result of drifting of a peri-Gondwanan terrane; (2) the subsequent shortening and crustal thickening of the terrane related to its subduction and accretion to Laurussia; (3) a younger cycle of shortening and extension resulting from convergence between Laurussia and Gondwana; and (4) the emplacement of this exotic terrane as the upper allochthon, together with underlying ophiolitic and basal allochthons, during the Laurussia-Gondwana collision. Implications derived from the well-established tectonothermal sequence are discussed in the context of Paleozoic paleogeography and geodynamics. The evolution of this part of the belt is related first to the closure of the Tornquist Ocean, and later to that of the eastern branch of the Rheic Ocean. Furthermore, the relative paleopositions of the upper allochthon and the Iberian autochthon in northern Gondwana are discussed.
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
U-Pb chronometry of polymetamorphic high-pressure granulites: An example from the allochthonous terranes of the NW Iberian Variscan belt
(4-D Framework of Continental Crust, 2007) Fernández Suárez, Javier; Arenas Martín, Ricardo; Abati Gómez, Jacobo; Martínez Catalán, José Ramón; Whitehouse, Martín J.; Jeffries, Teresa E.; Hatcher, Robert D.; Carlson, Marvin P.; McBride, John H.; Martínez Catalán, José Ramón
Secondary ion mass spectrometry (SIMS) U-Pb geochronology of zircons from high-pressure granulite units within the allochthonous complexes of the northwestern Iberian Variscan belt illustrates the complexity of dating high-pressure events using the U-Pb chronometer. Zircons from four rocks belonging to the high-pressure (P), high-temperature (T) units were dated by SIMS. A gabbro body with preserved igneous texture within the Órdenes Complex high-P granulites yielded a crystallization age of ca. 515 Ma. A high-P mafic granulite within the same unit contained zircons that had U-Pb ages clustered around 387 Ma, and it preserved no record of events between the crystallization of precursor gabbros and the granulite event (sensu lato). A mafic high-P granulite from an equivalent structural unit in the Cabo Ortegal Complex contained abundant zircons that recorded crystallization of igneous protolith at 490–520 Ma and crystallization of new zircon from a melt phase starting at ca. 404 Ma, and zircons with 206Pb/238U ages between ca. 480 and 430 Ma that are interpreted to reflect partial Pb loss during the granulite-facies event. Bright luminescent cores in zircons from a leucosome pod within the outcrop area of the latter granulite yielded a mean age of 397 Ma, whereas dark U-rich rims in zircons from this leuco-some yielded a mean age of 390 Ma. These data, in conjunction with previous isotope dilution–thermal ionization mass spectrometry (ID-TIMS; zircon, monazite, titanite) U-Pb ages and 40Ar/39Ar dating of fabrics from rocks within the same units, point to a Silurian age for the high-P metamorphism. Timing of the peak pressure cannot be further constrained with available data because, in this case, we infer that the U-Pb system in zircon recorded only a segment of the retrograde path. We suggest that the high-P metamorphic event is related to the accretion and understacking of these units to the margin of Baltica or Laurentia following the closure of the Iapetus or Tornquist Oceans and concomitant opening of the Rheic Ocean.
Variscan accretionary complex of northwest Iberia: Terrane correlation and succession of tectonothermal events
(Geology (Boulder Colo.), 1997) Martínez Catalán, José Ramón; Arenas Martín, Ricardo; Díaz García, Florentino; Abati Gómez, Jacobo
The allochthonous terranes of northwest Iberia can be correlated with specific paleogeographic realms of the continental masses and intervening oceans involved in the Variscan collision. Assuming that the existing ophiolites represent the suture formed by the closure of the Rheic ocean, the units in the footwall to the suture correspond to the outer edge of the Gondwana continental margin, and the units in the hanging wall are interpreted as fragments of the conjugate margin, represented by the Meguma terrane. This correlation establishes a precise link between circum-Atlantic terranes, and makes it possible to draw a relatively simple scenario of the successive tectonothermal events recorded. Following the amalgamation of Avalon to Laurentia, the remaining outboard terranes underwent a progressive accretion to this continent that ended with the collision between Laurentia and Gondwana.
Constraints on the provenance of the uppermost allochthonous terrane of the NW Iberian Massif: inferences from detrital zircon U–Pb ages
(Terra nova, 2003) Fernández Suárez, Javier; Díaz García, Florentino; Jeffries, Teresa E.; Arenas Martín, Ricardo; Abati Gómez, Jacobo
Insight into the origin and pre-orogenic palaeogeographical links of terranes involved in the assembly of collisional mountain belts is fundamental to the understanding of orogenic processes. Here we address the provenance and possible tectonic settings of the uppermost allochthonous terrane of the NW Iberian Variscan Belt through a 213-nm Laser Ablation ICP-MS study of U–Pb ages of detrital zircons. The age groups of zircons from greywackes in this terrane (c. 480–610, 1900–2100, 2400–2500 Ma) and the lack of Mesoproterozoic zircons suggest an origin in a Neoproterozoic – Early Palaeozoic peri- Gondwanan realm along the periphery of the west African craton. It is further inferred that the greywackes were deposited in the periphery of a crustal unit that had been detached from the Gondwanan margin in relation to the opening of the Rheic ocean in Cambro-Ordovician times. This terrane was thrusted back upon the Gondwanan margin during the course of the Variscan collision and closure of the intervening ocean.