Person: Abati Gómez, Jacobo
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First Name
Jacobo
Last Name
Abati Gómez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Petrología y Geoquímica
Identifiers
15 results
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Item 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, RicardoTwo 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.Item 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 JoséA 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.Item 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, FlorentinoThe 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.Item 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, GernoldThe 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.Item 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 RamónSecondary 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.Item 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, JacoboInsight 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.Item Using SHRIMP zircon dating to unravel tectonothermal events in arc environments. The early Palaeozoic arc of NW Iberia revisited(Terra nova, 2007) Abati Gómez, Jacobo; Castiñeiras García, Pedro; Arenas Martín, Ricardo; Fernández Suárez, Javier; Gómez Barreiro, Juan; Wooden, Joseph L.Dating of zircon cores and rims from granulites developed in a shear zone provides insights into the complex relationship between magmatism and metamorphism in the deep roots of arc environments. The granulites belong to the uppermost allochthonous terrane of the NW Iberian Massif, which forms part of a Cambro-Ordovician magmatic arc developed in the peri-Gondwanan realm. The obtained zircon ages confirm that voluminous calc-alkaline magmatism peaked around 500 Ma and was shortly followed by granulite facies metamorphism accompanied by deformation at c. 480 Ma, giving a time framework for crustal heating, regional metamorphism, deformation and partial melting, the main processes that control the tectonothermal evolution of arc systems. Traces of this arc can be discontinuously followed in different massifs throughout the European Variscan Belt, and we propose that the uppermost allochthonous units of the NW Iberian Massif, together with the related terranes in Europe, constitute an independent and coherent terrane that drifted away from northern Gondwana prior to the Variscan collisional orogenesis.Item Petrología metamórfica y geocronología de la unidad culminante del complejo de Órdenes en la región de Carballo (Galicia, NW del Macizo Ibérico)(2003) Abati Gómez, Jacobo; Arenas Martín, Ricardo; Martínez Catalán, José Ramón; Díaz García, FlorentinoEn esta Tesis Doctoral se presenta el resultado de un estudio integrado de petrología metamórfica y geocronología(método U-Pb) realizado en el sector occidental de la unidad culminante del Complejo de Ordenes. Este complejo es la más extensa de las estructuras alóctonas que afloran en el NW del Macizo Ibérico, caracterizadas por la presencia de varias láminas de origen oceánico que marcan una de las principales suturas del Orógeno Varisco Europeo. La datación de los principales tipos de rocas ígneas y de fábricas metamórficas, en conjunto con el estudio de su evolución P-T, ha permitido el descubrimiento de un ciclo orogénico pre-varisco en la unidad culminante, manifestándose por tanto como un terreno poliorogénico. Las dataciones U-Pb de circones del gabro de Monte Castelo(499+-2Ma) y de un granitoide (500+-2 Ma) indican la existencia de un evento magmático bimodal próximo al límite Cámbrico-Ordovicico. Las edades de monacitas obtenidas en una granulita metapelítica y en dos muestras de paragneises de la zona de la sillimanita de la Serie de Ordenes(493-498 Ma) indican que el metamorfismo regional fue prácticamente sincrónico con el magmatismo. También se analizaron rutilos de la misma muestra de granulitas, que proporcionan una edad entre 380 y 390 Ma que se interpreta como el momento de la incorporación de la unidad culminante a la cuña orogénica varisca. El cálculo de condiciones P-T mediante termobarometria convencional y multiequilibrio(método TWQ) muestra una trayectoria caracterizada por fuerte presurización a altas temperaturas que alcanza unos 10 kbar y más de 800 º C. La trayectoria P-T deducida para las granulitas indica un engrosamiento cortical considerable que se produce a altas temperaturas. De acuerdo con los modelos térmicos existentes, este tipo de trayectoria sólo es competible con una región calentada por un intenso magmatismo de forma previa y/o durante un engrosamiento cortical, lo que resulta característico de arcos magmáticos. Como consecuencia de todo lo anterior,la unidad culminante se considera originada en un arco magmático, probablemente en un arco de islas, desarrollado durante el Ordovícico Inferior. Fragmentos de este arco fueron posteriormente incorporados al margen de Gondwana durante la colisión varisca, produciéndose entonces la superposición de un metamorfismo en facies de los esquistos verdes al metamorfismo previo de mayor grado.Item 40Ar/39Ar laserprobe dating of mylonitic fabrics in a polyorogenic terrane of NW Iberia(Journal of the Geological Society, 2006) Gómez Barreiro, Juan; Wijbrans, Jan R.; Castiñeiras García, Pedro; Martínez Catalán, José R.; Arenas Martín, Ricardo; Díaz García, Florentino; Abati Gómez, JacoboThe tectonothermal evolution of a polyorogenic terrane in the Variscan belt of NW Spain has been constrained by 40Ar/39Ar laserprobe incremental heating experiments on mylonitic fabrics developed in major structures. Transitional levels between HP–HT and IP upper units in the O´ rdenes Complex where metamorphic and structural records demonstrate two cycles of burial and exhumation were selected for dating. Two groups of ages have been defined: (1) Silurian–Early Devonian, obtained from mylonites of the Forna´s extensional detachment, here considered as the minimum age for the start of tectonic exhumation of the HP– HT units and an upper age-limit for the HP–HT event itself; (2) Early to Mid-Devonian, from structures related to the Variscan convergence in the area, which include top-to-the-east thrusts and extensional detachments. A single, younger Carboniferous age obtained from the uppermost allochthonous sequences possibly reflects the final stages of emplacement of the allochthonous complexes. Our data indicate a polyorogenic character for a part of the Iberian allochthonous complexes, including Variscan (sensu stricto) and Early Variscan convergence, as well as an older, Early Palaeozoic cycle.Item Supporting info item, In: "Using SHRIMP zircon dating to unravel tectonothermal events in arc environments. The early Palaeozoic arc of NW Iberia revisited"(Terra nova, 2007) Abati Gómez, Jacobo; Castiñeiras García, Pedro; Arenas Martín, Ricardo; Fernández Suárez, Javier; Gómez Barreiro, Juan; Wooden, Joseph L.