Caracterización cinemática del contacto inferior de la Unidad de Fornás (Complejo de Ordenes, NW del Macizo Ibérico)
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La reactivacion de contactos tectonicos es un fenomeno frecuente en los orogenos, ya que son zonas de debilidad relativa en la litosfera. Es necesario realizar analisis precisos de la cinematica y de los procesos asociados a la deformacion en el interior de la falla/zona de cizalla, para desentranar evoluciones complejas. La superposicion de varios episodios de deformacion en una zona de cizalla puede dar lugar a un aspecto final enrevesado, con rocas que presentan una evolucion cinematica y termica opuesta. El empleo de criterios cinematicos independientes y el estudio de las rocas de falla, nos daran la clave para comprender este tipo de contactos. El Contacto Inferior de la Unidad de Fornas (CIUF) forma parte del sistema tectonico de escala regional en el Complejo de Ordenes. El CIUF esta formado por los despegues de Bembibre, Santiago y Pico Sacro. Los criterios cinematicos y metamorficos muestran dos grupos de resultados: en primer lugar, los relacionados con un movimiento del bloque de techo hacia el E, relacionado con cabalgamientos, seguido de un ...Cite
Analysis of the Careón Unit in the Ordenes Complex (northwest Iberian Massif) has supplied relevant data concerning the existence of a Paleozoic oceanic lithosphere, probably related to the Rheic realm, and the early subduction-related events that were obscured along much of the Variscan belt by subsequent collision tectonics. The ophiolite consists of serpentinized harzburgite and dunite in the lower section and a crustal section made up of coarse-grained and pegmatitic gabbros. An Early Devonian zircon age (395+/-2 Ma, U-Pb) was obtained in a leucocratic gabbro. The whole section was intruded by numerous diabasic gabbro dikes. Convergence processes took place shortly afterward, giving rise to a mantle-rooted synthetic thrust system, with some coeval igneous activity. Garnet amphibolite, developed in metamorphic soles, was found discontinuously attached to the thrust fault. The soles graded downward to epidote-amphibolite facies metabasite and were partially retrogressed to greenschist facies conditions. Thermobarometric estimations carried out at a metamorphic sole (T approximately 650 degrees C; P approximately 11.5 kbar) suggested that imbrications developed in a subduction setting, and regional geology places this subduction in the context of an early Variscan accretionary wedge. Subduction and imbrication of oceanic lithosphere was followed by underthrusting of the Gondwana continental margin.
Obduction
Greenschist
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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.
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