Chemical characterization of igneous sphene and application of the Zr-in-sphene thermometer to tardimagmatic processes

This preliminary work illustrates the chemical composition of sphene from Variscan tonalites with sphene-centered ocellar texture (Ribadelago pluton, NW Iberian Massif). The ocellar texture is linked with the percolation of a tardimagmatic melt, with trondhjemitic affinities, through an hyperdense crystal mush. Chemical zoning in sphene, revealed by BSE imaging, shows a heterogeneous distribution of heavy trace elements (Nb, Y, Ce and Zr) that depicts concentric, oscillatory, sector and patchy patterns. Application of the Zr-in-sphene thermometer yields a temperature range of 746 to 778 ºC for the crystallization of sphene in the tardimagmatic melt. It also constitutes a minimum temperature estimation for biotite partial destabilization in this litholog

Structure of the Rangel alkaline complex (Salta, Argentina)

This work deals with the structure and emplacement of the alkaline complex of the Sierra de Rangel, a Cretaceous stock intruding in Ordovician metamorphic rocks of the Puna region at Salta, northwest Argentina. Field structures and magnetic fabrics reveal a complex structure composed by multiple sheets and feeding chanels. Both, the ascent and the lateral spreading of magma exploited old fractures in the country rock

Strain partition in synkinematic granitoids intruded in a transpressive setting (Sanabria, Central Iberian-Zone, Iberian Massif)

The Sanabria Lake plutons, located in the Central Iberian Zone of the Iberian Massif, intruded in a dextral strike-slip fault bridge under transpressive conditions. The deformed zone underwent a strain partitioning process, so that large folded domains and narrow shear zones were developed coevally. The microstructural study of the granitoids shows that the shear zones concentrate a variable degree of solid state deformation at high and medium temperatures, whereas the folded areas preserve microstructural evidences of magmatic and submagmatic flow at high temperatures, too. The most common fabric in these folded areas is defined by two sets of conjugate planes, composed by aligned crystals of plagioclase and biotite, which are bisected by the flow foliation. These conjugate bands represent an incipient phase of the strain localization process that involves strain weakening, migration of the late-magmatic melts and enhancement of the shear zone

Petrographical and mineralogical characteristics of birbirites from the Ronda peridotites (Betic Cordilleras)

Por primera vez en las Cordilleras Béticas describimos, en este trabajo, la existencia y las principales características mineralógicas y petrológicas de birbiritas que son el resultado de un intenso metasomatismo de serpentinitas. Con los datos que se aportan se puede deducir que las birbiritas se han formado por la infiltración de fluidos hidrotermales de baja temperatura (< 200 ºC), bajo pH y enriquecidos en SiO2 /CO2 . La canalización de estos fluidos por planos de discontinuidad ha conducido a la silicificación generalizada de peridotitas que ya estaban serpentinizadasIn this work we describe, by first time in the Betic Cordilleras, the occurrence and the main petrological and mineralogical features of birbirites, as result of intense metasomatism of serpentinites. According to presented data the birbirites had been formed by the infiltration of SiO2 /CO2 enriched and low pH and low temperature (< 200 ºC) hydrothermal fluids channelized through discontinuities planes that lead to the pervasive silicification of already serpentinized peridotite

Structural control of the Tastil batholith (Salta, Argentina) on the development of Andean thrusts

This work deals with the structure of the Lower Cambrian batholith of Tastil (Salta, NW Argentina) and its influence on the development of younger Andean structures. Anisotropy of magnetic susceptibility data reveal a laccolithic intrusion spreading laterally from a central root zone. The N-S elongation of the batholith reflects the westward propagation of Andean thrusts through the sheeted domains of the intrusion, the root zone acting as a buttress that restricted the propagation of the Andean structure

Magmatic folds in the La Fronda trondhjemite pluton, Sierras Pampeanas at Córdoba, Argentina

From structural and magnetic fabric patterns, this work reports a complex folded structure in the La Fronda pluton, a small trondhjemite massif located in the Sierras de Córdoba which form the eastern part of the Sierras Pampeanas in Argentina. Isoclinal folds with no thickening at the hinge zones deform the compositional banding of these igneous rocks. Both the orientation of axial surfaces and fold axes vary from place to place and do not concur with the orientation of folds from the metamorphic country rocks. Microstructural data point to a fabric formed by grain-supported flow in a crystal-rich magma during the imprint of a vanishing regional stress fiel

New ages in granitoids from Sanabria region: relationships between tectonics and magmatism

Se presentan dos nuevas dataciones de granitoides Variscos de la región de Sanabria (Zona Centro-Ibérica, Macizo Ibérico), con las que se establecen los límites de los pulsos magmáticos registrados en este sector. Por una parte, una edad concordia U-Pb de 318 ± 1 Ma que data el magmatismo Varisco precoz, mediante zircones y esfenas (titanitas) de tonalitas/ cuarzodioritas del plutón de Ribadelago. Este pulso magmático fue coetáneo con la acción de zonas de cizalla dextras transpresivas y con un proceso de migmatización regional. Por otra parte, una edad plateau 40Ar/39Ar de 287 ± 1 Ma obtenida en moscovitas del leucogranito de Pradorramisquedo, que data el último pulso magmatico, postectónico, en la región. Esta última edad coincide con una datación previa de la cercana granodiorita de Veiga, cuya intrusión fue coetánea con el funcionamiento de la falla normal de ChandoiroNew ages are presented for two Variscan granitoids in the Sanabria region (Central Iberian Zone, Iberian Massif), which set time limits for the different magmatic pulses in the study area. A U-Pb Concordia age of 318 ± 1 Ma obtained for combined zircon and sphene (titanite) in tonalite/quartzdiorite from the Ribadelago pluton dates the first Variscan magmatism in the region. This magmatic pulse was coeval with dextral transpressive shear zones and with regional migmatisation. A 40Ar/39Ar plateau age of 287 ± 1 Ma obtained for white mica from the Pradorramisquedo leucogranite dates the post-tectonic, last magmatic pulse in the region. This age coincides with previous geochronological data for the adjacent Veiga granodiorite, which is affected by the coeval Chandoiro normal faul

Granite emplacement by crustal boudinage: example of the Calmayo and El Hongo plutons (Córdoba, Argentina)

This study deals with the structure and emplacement of the Calmayo and El Hongo trondhjemite plutons (Famatinian belt of Córdoba, Argentina). It provides structural data from the granites and the country rocks and a study of the magnetic fabric in the plutons. New U/Pb geochronological data yield intrusion ages of 512.1 ± 3.4 Ma and 500.6 ± 4.5 Ma for the Calmayo and El Hongo plutons respectively. The El Hongo massif and the southern part of the Calmayo trondhjemite preserve magmatic structures, whereas the northern domain of Calmayo shows the imprint of solid-state deformation. The main foliation in the country rocks outlines a boudin-like pattern at the map scale and the granites are located along boudin necks, suggesting that the emplacement of these trondhjemite plutons was linked to large-scale boudinage of the country rocks.Fil: D'eramo, Fernando Javier. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tubía, José M.. Universidad del País Vasco; EspañaFil: Pinotti, Lucio Pedro. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vegas, Néstor. Universidad del País Vasco; EspañaFil: Coniglio, Jorge Enrique. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Demartis, Manuel. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aranguren, Aitor. Universidad del País Vasco; EspañaFil: Basei, Miguel. Universidade de Sao Paulo; Brasi

The Ribadelago and Sotillo plutons, examples of sheet-like intrusions in the releasing stepover of a transpressional dextral shear zone

The Ribadelago and Sotillo plutons are located in the Central Iberian Zone, a tectonic domain of the Iberian Variscan belt (NW Spain). These synkinematic granitoids are composed by swarms of sheeted intrusions parallel to the overall elongation, 130°E, of both plutons. Most of these igneous sheets show pronounced planar fabrics and provide high values of magnetic anisotropy (P%>5%), related to submagmatic and solid state deformations evolving from high to low temperature conditions. These igneous sheets are emplaced in the releasing bridge defined by two 130°E-Trending and south-dipping dextral shear zones that form a linked fault syste

Estructura del Complejo Alcalino de Rangel (Salta, Argentina)

This work deals with the structure and emplacement of the alkaline complex of the Sierra de Rangel, a Cretaceous stock intruding in Ordovician metamorphic rocks of the Puna region at Salta, northwest Argentina. Field structures and magnetic fabrics reveal a complex structure composed by multiple sheets and feeding chanels. Both, the ascent and the lateral spreading of magma exploited old fractures in the country rocks.Fil: Vegas, Néstor. Universidad del País Vasco; EspañaFil: Hongn, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Tubía, José María. Universidad del País Vasco; EspañaFil: Menegatti, Nilda. Universidad Nacional de Salta; Argentin