Person: Sánchez Martínez, Sonia
Loading...
First Name
Sonia
Last Name
Sánchez Martínez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Petrología y Geoquímica
Identifiers
4 results
Search Results
Now showing 1 - 4 of 4
Item A peri-Gondwanan arc in NW Iberia. II: Assessment of the intra-arc tectonothermal evolution through U–Pb SHRIMP dating of mafic dykes(Gondwana research, 2009) Díaz García, Florentino; Sánchez Martínez, Sonia; Castiñeiras García, Pedro; Fuenlabrada Pérez, José Manuel; Arenas Martín, RicardoThe arc-derived upper units of the Órdenes Complex, NW Iberia, are emplaced above the Variscan suture and contain a low-grade metasedimentary uppermost section, with a maximum depositional age of 510–530 Ma, intruded by a number of mafic dykes. Three deformational events affect the metasedimentary section. The youngest deformation event (D3) is of undifferentiated Variscan age and consists of metre- to decametre-scale, close upright folds with axes plunging gently towards N20°E. The most important D2 structure is a regional S2 foliation axial planar of minor foldswith dextral asymmetry. The presence of a stretching lineation parallel to the D2 fold axes is related to a top-to-the-north sense of shearing in a context of regional extension. The oldestmeterscale D1 folds are developed in suitable greywacke–pelite alternations and consist of tight folds with chevron and similarmorphologies, axes plunging gently toward N20°E, and a continuous S1 axial planar foliation. The essential characteristic of the D1 deformation event is depicted by a set of west-vergent folds with reverse limbs less than 2 kmin wavelength, that are affected in their lower part by the generalised presence of the regional S2 foliation. The age of D2 and D1 structures is notwell constrained. The diabase dykes intruding the low-grade turbidites cut the D1 folds and their field relationships suggest that they were emplaced at the end of the D2 shearing event and prior to the upright D3 Variscan folds. Zircon grains obtained from one of the diabase dykes were analysed for U–Pb at the SHRIMP-RG facility at Stanford University. An age of c. 510 Ma, based on the analysis of 31 individual zircon grains, is interpreted to date the crystallization of the Ares dyke. The tectonic and magmatic evolution of the top turbiditic series of the Órdenes Complex is tentatively related to the dynamics of a peri- Gondwanan arc developed during active subduction beneath Gondwana and suggests: (1) accretion beneath the arc during west-vergent (present coordinates) nappe development (D1); (2) extension of the arc during top-tothe- north shearing (D2); and (3) final intrusion of the diabasic dykes into an intra-arc turbiditic series. This evolution spans the end of volcanic arc activity and the onset of the opening of the Rheic Ocean.Item The basal tectonic mélange of the Cabo Ortegal Complex (NW Iberian Massif): a key unit in the suture of Pangea(Journal of iberian geology, 2009) Arenas Martín, Ricardo; Sánchez Martínez, Sonia; Castiñeiras García, Pedro; Jeffries, Teresa E.; Díez Fernández, Rubén; Andonaegui Moreno, María Del PilarRecent field work and mapping in the lower units of the Cabo Ortegal Complex provided new data about the tectonic mélange that appears in the lowest structural position: the Somozas Mélange. This mélange unit with average thickness of 1800 m is restricted to the eastern part of the complex, and is located at the advancing front of the allochthonous complexes of NW Iberia. Three rock units are involved in the mélange: 1) an ophiolitic mélange consisting of igneous rocks mixed with serpentinites; 2) a metasedimentary unit with phyllites and phyllonites, with scarce conglomerates, marbles and quartzites; 3) high-T metamorphic rocks with varied types of amphibolites and orthogneisses. Two granitic rocks within the ophiolitic mélange were dated using U-Pb zircon geochronology at 527 ± 2 Ma and 499 ± 1 Ma. Two different series of igneous rocks can be distinguished in this mélange. The first series consists of gabbros, diorites, granitoids and basalts-basaltic andesites with calc-alkaline affinities. The second series contains common basaltic rocks, diabasic dikes and gabbros with chemical compositions typical of island-arc tholeiites. Both igneous series shared a common geographic setting, but the island-arc tholeiites are younger than the calc-alkaline igneous rocks. The two igneous series were probably generated in a mature volcanic arc located along the periphery of Gondwana. In the metasedimentary unit, a conglomerate from a large tectonic block included in serpentinites yielded age populations of detrital zircons suggesting that the sediments were deposited along the periphery of the West-African Craton. This conglomerate contains a large number of zircons (n = 24) with ages ranging 630-464 Ma, probably representing the chronology of the Pan-African event, including the magmatic activity in the volcanic arc where the igneous lithologies involved in the mélange were generated. The maximum age of sedimentation for this conglomerate is estimated as latest Cambrian – earliest Ordovician, and constraints the end of the magmatic activity in the volcanic-arc. Within the unit of high-T rocks, an orthogneiss yields a U-Pb protolith age of 485 ± 6 Ma, which is similar to other ages of igneous rocks in the basal allochthonous terrane in NW Iberia. The three rock assemblages forming part of the Somozas Mélange may be linked to the evolution of a mature peri-Gondwanan volcanic arc. This volcanic arc was affected by pronounced extension which caused the opening of intra-arc basins, culminating the rifting and subsequent drift of the external parts of the arc during the opening of the Rheic Ocean. This opening started during a time interval constrained by the peak activity in a mature volcanic arc (c. 527-499 Ma) and the generation of intraarc basins around the Cambrian-Ordovician boundary. Tectonic mélanges including high-P rocks have been classically related to subduction zone environments. Regional relationships in NW Iberia and the nature of the rock units involved in the Somozas Mélange, suggest that two different subduction zones generated during oblique convergence and collision between Gondwana and Laurussia were active during the final stages of the assembly of Pangea. The first related to the underthrusting beneath Laurussia of the most external Gondwana margin (c. 370 Ma). The second subduction zone was a new one which accreted later remnants of a peri-Gondwanan arc and sediments of the continental margin below a layer of exhumed high pressure rocks. This oblique collision finished the closure of the Rheic Ocean and contributes to define the new oceanic domain located to the East of Pangea, the Palaeotethys. [RESUMEN] Nuevos datos de campo y cartográficos en las unidades inferiores del Complejo de Cabo Ortegal, han proporcionado información relevante sobre la mélange tectónica situada en la posición estructural inferior: la Mélange de Somozas. Esta unidad de mélange tiene una potencia media de unos 1800 m y su aparición está restringida a la parte oriental del complejo; representa por tanto una gran unidad de mezcla localizada en el frente de avance de los complejos alóctonos del NW de Iberia. Tres conjuntos litológicos diferentes se distinguen en la mélange: 1) un conjunto formado por rocas ígneas mezcladas con serpentinitas, formando una mélange ofiolítica típica; 2) un conjunto metasedimentario con filitas y filonitas, con escasos conglomerados, mármoles y cuarcitas; 3) rocas metamórficas de alta-T con tipos variados de anfibolitas y ortogneises. Dos rocas graníticas incluidas en la mélange ofiolítica han sido datadas mediante geocronología U-Pb en 527 ± 2 Ma y 499 ± 1 Ma. La mélange ofiolítica contiene dos series diferentes de rocas ígneas. Una primera serie está formada por gabros, dioritas, granitoides y basaltos-andesitas basálticas con afinidades calcoalcalinas. La segunda serie contiene diques diabásicos, gabros y rocas basálticas comunes con composiciones químicas típicas de toleitas de arco-isla. Ambas series compartieron un marco geográfico común, pero las toleitas de arco-isla son más jóvenes que las rocas ígneas calcoalcalinas, y fueron generadas en un arco volcánico maduro situado en la periferia de Gondwana. Dentro del conjunto de rocas metasedimentarias, un conglomerado procedente de un gran bloque tectónico incluido en serpentinitas ha proporcionado poblaciones de edades de circones detríticos que indican que su sedimentación se produjo en la periferia del Cratón del Oeste de África. Este conglomerado contiene una población principal de circones (24 cristales) con edades que oscilan entre 630-464 Ma, que reflejan la cronología del evento Pan-Africano y también la actividad magmática en el arco volcánico donde se generaron las dos series ígneas existentes en la mélange ofiolítica. La edad máxima de sedimentación de este conglomerado se sitúa en el límite Cámbrico-Ordovícico, y puede considerarse también una edad de referencia para la terminación de la actividad magmática principal en el arco volcánico. Dentro del conjunto de rocas de alta-T, un ortogneis ha proporcionado una edad U-Pb del protolito de 485 ± 6 Ma. Esta edad es similar a otras edades de rocas ígneas pertenecientes al terreno alóctono basal del NW de Iberia. Los tres conjuntos de rocas que forman parte de la Mélange de Somozas pueden relacionarse con la evolución de un arco volcánico peri-Gondwánico maduro. Este arco volcánico acabó siendo afectado por una extensión pronunciada que favoreció la apertura de cuencas de intra-arco, y finalmente la separación y posterior deriva de las partes externas del arco durante la apertura del Océano Rheico. En concreto, el comienzo de la apertura se produjo en algún momento situado entre el episodio de actividad magmática principal en el arco volcánico maduro (c. 527-499 Ma), y la generación de cuencas de intra-arco hacia el límite Cámbrico-Ordovícico. Las mélanges tectónicas que incluyen rocas de alta-P se han relacionado clásicamente con contextos de subducción. Las relaciones regionales en el NW de Iberia y la naturaleza de las litologías que aparecen en la Mélange de Somozas, sugieren que dos zonas de subducción diferentes, generadas durante la convergencia y colisión oblicuas entre Gondwana y Laurussia, fueron activas durante los estadios finales del ensamblado de Pangea. La primera relacionada con el enterramiento bajo Laurussia del margen más externo de Gondwana (c. 370 Ma). La segunda zona de subducción fue diferente y responsable de la acreción poco después de los restos de un arco peri-Gondwánico y sedimentos del margen continental, bajo una lámina de rocas de alta presión exhumadas. Esta colisión oblicua culminó el cierre del Océano Rheico, contribuyendo a definir el nuevo dominio oceánico situado al Este de Pangea, el Paleotethys.Item The Corredoiras orthogneiss (NW Iberian Massif): Geochemistry and geochronology of the Paleozoic magmatic suite developed in a peri-Gondwanan arc(Lithos, 2012) Andonaegui Moreno, María Del Pilar; Castiñeiras García, Pedro; González Cuadra, Pablo; Arenas Martín, Ricardo; Sánchez Martínez, Sonia; Abati Gómez, Jacobo; Díaz García, Florentino; Martínez Catalán, José RamónThe Corredoiras orthogneiss belongs to the intermediate pressure upper units of the Órdenes Complex (Variscan belt, NW Spain), mainly composed by granodioritic orthogneisses, with small bodies of tonalitic orthogneisses, amphibole-rich orthogneisses and metagabbronorites. In this work we study their chemical and isotopic composition, to gain insight into the linkage between plate tectonics and magmatism and to improve the knowledge of the paleogeographic evolution of the European Variscan Belt. Granodioritic and tonalitic orthogneisses range from intermediate to felsic rocks, with K2O/Na2O ratios≈1, typical of calc-alkaline rocks, and high Na2O content, characteristic of I-type granites. Metagabbronorites are basic rocks, but some of them are contaminated by interaction with the felsic magmas, showing enrichment in SiO2, Na2O and K2O. All Corredoiras metaigneous rocks are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE), resulting in a high LILE/HFSE ratio. These geochemical features are the most characteristic of magmas related to subduction zones; furthermore all orthogneisses display significant negative anomalies in Ta, Nb and Zr, which together with their low contents in Y and Yb match up with granitoids generated in volcanic arcs or subduction zones. SHRIMP U–Pb zircon dating provides a concordia age of 492±3 Ma. Granodioritic orthogneiss has negative εNd(492 Ma) values (−2.2 to −3.6) and high (87Sr/86Sr)i ratios (0.707 to 0.708), on the other hand tonalitic orthogneisses and metagabbronorites have positive εNd(492 Ma) (1.0 to 2.4) and low (87Sr/86Sr)i (0.703 to 0.705), suggesting that granodioritic orthogneisses have a clear crustal influence in their generation, whereas tonalitic orthogneisses and metagabbros can be related to basic magmas extracted from the mantle or from a basic lower continental crust. The Corredoiras chemical characteristics permit us to interpret that this rocks were probably generated in an ensialic island arc and may represent a peri-Gondwanan fragment drifted away to open the Rheic Ocean.Item Geoquímica de rocas máficas en un arco magmático Cámbrico peri-Gondwánico (Complejo de Órdenes, NO del Macizo Ibérico)(Geotemas, 2016) Andonaegui Moreno, María Del Pilar; Sánchez Martínez, Sonia; Castiñeiras García, Pedro; Abati Gómez, Jacobo; Arenas Martín, RicardoLas Unidades Superiores de los Complejos alóctonos del NO del Macizo Ibérico, han sido interpretadas como parte de un arco magmático peri-Gondwánico, activo desde el Cámbrico medio hasta el Ordovícico inferior. Los principales cuerpos plutónicos, con una edad de ca. 500 Ma., son las gabronoritas de Monte Castelo, y los ortogneises de Corredoiras, que incluyen pequeños cuerpos de metagabronoritas. Estas rocas máficas presentan en efecto características geoquímicas compatibles con su generación en un arco magmático, pero ocupando distinta posición dentro del mismo. Las metagabronoritas de Monte Castelo tienen afinidad toleítica, anomalía negativa de Nb, altas relaciones 143Nd/144Nd (0.5143119–0.513019), bajas de 87Sr/86Srinicial (0.702562–0.703174) y valores positivos de εNdi (+7.8 a +5.4). Sin embargo, las rocas máficas de Corredoiras son de afinidad calco-alcalina, con anomalía negativa de Nb, pero con valores bajos en la relación 143Nd/144Nd (0.512575–0.512436), altos en 87Sr/86Srinicial (0.705082–0.706684) y valores de εNdi entre -0.65 y +1.83. Estas características geoquímicas permiten interpretar estas rocas máficas como generadas en distintas posiciones del arco magmático, localizándose las de Monte Castelo más próximas a la trinchera y las de Corredoiras en una posición más distal.