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EVOLUCIÓN GEODINÁMICA Y PROCESOS MANTÉLICOS EN EL MACIZO DE HERBEIRA, COMPLEJO DE CABO ORTEGAL (NO DE LA PENÍNSULA IBÉRICA)
... The new set of field, petrographic, thermobarometric, microstructural, geochemical and crystallographic data collected for the Limo peridotite massif (Cabo Ortegal Complex, NW Spain) reveals high-temperature deformation, percolation of melts/fluids coming from a subducting slab in a suprasubduction mantle wedge, and deformations in a subduction channel before the final exhumation. Thus, although the Limo massif has been described so far as a homogeneous (Ben Jamaa 1988;Girardeau and Gil Ibarguchi 1991;García Izquierdo 2005) and structurally simple harzburgitic body (e.g., Girardeau and Gil Ibarguchi 1991;Á balos et al. 2003), the data presented in this paper highlight the great relevance of this massif as an exceptional study case to gain insight into the dynamics of the mantle wedge in a suprasubduction context. ...
... Major and trace element bulk rock and mineral compositions of harzburgite have residual characteristics comparable to those of peridotites from arc settings. A fractionation trend from dunite to pyroxenite suggests that the latter crystallized from primitive arc-related magmas but with components that attest to isotopic disequilibrium and contamination (Van Calsteren et al. 1979;Peucat et al. 1990;Gravestock 1992;Laribi-Halimi 1992;Santos Zalduegui et al. 2002;García Izquierdo 2005). In this line, the authors cited as well as Moreno et al. (2001) have proposed a suprasubduction arc-root setting for the peridotite-pyroxenite ensemble, variably modified by fluid/melt infiltration derived from subducted oceanic lithosphere. ...
... The recrystallization conditions suggested by the microstructural and petrofabric data obtained for the Herbeira massif (Ben Jamaa 1988;García Izquierdo 2005) attest to a high-temperature stage ([1,000°C) followed by a complex tectonothermal history involving a late, synkinematic development of garnet after spinel in pyroxenites at 800°C, 1.65 GPa (Girardeau and Gil Ibarguchi 1991). Precise U-Pb ages of ca. ...
The Limo harzburgites constitute a hm-thick tectonic stack where extremely elongated meter-scale sheath folds occur, bearing axes parallel to the macroscopic lineation recognized across the whole complex. They can be identified as close to L-type tectonites, with a weak foliation, a well-developed stretching, and a mineral lineation defined by the mineral assemblage in equilibrium. The linear fabric is recognizable at every scale, from aerial photos to the crystallographic orientation of the harzburgite-forming minerals measured by means of the electron back-scatter diffraction technique. These rocks registered initial deformation under high-temperature and low water fugacity conditions at low stress levels in an anhydrous mantle wedge context, as it is inferred from the activity of the [100](010) slip system in olivine. Then, the ongoing eo-Variscan subduction incorporated fluid/melts from the subducting plate into the suprasubduction mantle wedge zone. The variation in the ambient physicochemical conditions led to the operation of the [001](010) slip system in olivine, indicative of lower temperature and higher water fugacity and stress levels. These changes are recorded, too, by synkinematic recrystallization of oriented chlorite. The L-type fabric of clinopyroxene points to constriction conditions during deformation. The active deformational processes continued along the subduction conduit with the thrust of the peridotites onto the high-pressure granulites of the Bacariza Formation. Posteriorly, the whole ensemble would have shared a common deformational history related to exhumation and initial amphibolitization. Subsequent deformation processes under greenschist facies conditions took place until effective continental collision during the Early Carboniferous gave rise to the Variscan orogen.
... Estos dos sectores, petrológica y geoquímicamente diferentes (Garcia Izquierdo, 2005;García Izquierdo et al., 2011) se ponen en contacto por medio de una zona de cizalla, la Falla de Trans Herbeira (FTH), la cual fue interpretada por Moreno (1999) como una falla subvertical, de componente normal, con un salto moderado, de tal manera que el sector occidental representa el bloque hundido con respecto al sector oriental. Sin embargo trabajos posteriores (García Izquierdo, 2005) ...
The Herbeira ultramafic massif is located in the structural upper portions of the Cabo Orte-gal Variscan Complex, NW Galicia, which form part of a thrust sheet that shows a complex deformational evolution. An important strike-slip fault, the Trans Herbeira Fault, divides the massif into two different zones. The eastern one is composed of amphibole bearing harzburgites, whilst the western one has a more complete lithological succession: basal harzburgite, lower dunite, medium pyroxenite and upper dunite. Equigranular and porphyroclastic microfabrics are observed in these rocks under optical microscope and SEM, providing evidence of a succession of several tectonic stages. The analysis of olivine CPO was carried out through electron backscattering diffraction techniques (EBSD). As a result the operating slip systems may be inferred. During de high temperature deformation stage D A the active slip systems were (010)[100] and {0kl}[100]. The activation of [001] axis along the slip direction occurred at lower temperatures (D 1 tectonic stage). The estimation of tectonic stress and strain rate was performed by palaeopiezometry of olivine. During D A deformation the temperature reached more than 1000ºC, the tectonic stress level was very low (3-6 MPa) and the strain rate oscillated between 10-9 s-1 and 10-15 s-1 , in accordance to the expected values at the mantle. Finally, the D 1 deformation was developed at lower temperature (less than 1000ºC), moderately high tectonic stress level (8-35 MPa), and low strain rates (10-12 s-1 to 10-19 s-1), more coherent with the lower crust or uppermost mantle. Resumen: En el Macizo de Herbeira, situado en el Complejo varisco de Cabo Ortegal (NO del Macizo Ibérico), forma parte de una lámina de cabalgamiento constituida por rocas ultramáficas que han sufrido una compleja historia de deformación. La falla de Trans Herbeira (FTH), divide el macizo en dos sec-tores diferentes. El sector oriental está formado mayoritariamente por harzburgitas ricas en anfíbol, mientras que el sector occidental es litológicamente más variado, con una sucesión de harzburgita basal, dunita inferior, piroxenita media y dunita superior. Se han observado mediante microscopio óptico y SEM, microfábricas equigranulares y porfiroclásticas que evidencian la sucesión de diferentes fases de deformación. Con el análisis de la orientación cristalográfica preferente (OCP) del olivino mediante técnicas de difracción de electrones retrodispersados (EBSD), se han observado sistemas de desliza-miento (010)[100] y {0kl}[100], los cuales se activan en condiciones de altas temperaturas (>1000 ºC), por lo que estas fábricas se desarrollaron durante una fase de deformación de alta temperatura D A. La activación de sistemas de deslizamiento en la dirección cristalográfica [001], así como la observación patrones axiales (010), indican un descenso de la temperatura durante la deformación, por lo que estos patrones han sido atribuidos a una fase de deformación posterior D 1. Las temperaturas y las tasas de de-formación, de las diferentes fases de deformación observadas, se han estimado mediante paleopiezo-metría del olivino. Durante la deformación D A las temperaturas alcanzaron más de 1.000ºC, el esfuerzo diferencial fue muy bajo (3-6 MPa) y las tasas de deformación oscilaron entre 10-9 y 10-15 s-1 , condi-135
This paper presents the discovery of Ni-Cu-Co-Bi mineralization in Valea Muntelui ultramafic bodies from the Southern Carpathians. Core samples from two exploration drill holes in the ultramafic body were studied using optical microscopy and SEM/EDS measurements. All of the described ore minerals were discovered in highly serpentinized ultramafic rocks, with the mineral association consisting of ferromagnesian and calcic amphiboles, chlorite, talc, and dolomite, as well as chromiferous spinel grains partially transformed into magnetite. Pentlandite, pyrrhotite, cubanite, cobaltite, chalcopyrite, nickeline, maucherite, parkerite, native Bi, native Pb and natural CuZn alloys were identified. The mineralization process appears to be linked to metasomatic fluids and the redox process leading to the development of a reducing character of the fluids. This research is the first description of Ni-CuCo-Bi mineralization in the region, and the first mention of
parkerite in Romania and the Balkan Region.
En este trabajo se estudian los macizos situados en el Anticlinorio de Olivenza-Monesterio, prestando especial atención al macizo Cerro Cabrera. Este cuerpo contiene mineralizaciones de Cr, Ni, Cu y Elementos del Grupo del Platino de características similares a las existentes en otras partes de Ossa Morena. En la actualidad, estas mineralizaciones son objeto de especial interés para la prospección de yacimientos de interés económico. El objetivo principal de este trabajo es conocer las características de la deformación dúctil y la estructura del macizo peridotítico Cerro Cabrera y de sus rocas encajantes. Para alcanzar este objetivo principal ha sido necesario afrontar una serie de objetivos parciales a lo largo de la investigación: en primer lugar, el estudio de la macroestructura en el área de Calzadilla de los Barros, y en segundo lugar, el estudio de la deformación dúctil asociada a la Zona de Cizalla de los Llanos.
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