46 research outputs found
El magmatismo (Ortoneises y volcanismo del OrdovĂcico Superior) del Paleozoico de los Catalánides.
En el presente trabajo se caracterizan petrolĂłgica y geoquĂmicamente las rocas metavolcánicas del OrdovĂcico Superior de los Catalánides (Gavarres y Guilleries) y los ortoneises de las Guilleries. Estos Ăşltimos se encuentran en disposiciĂłn estratiforme en materiales metasedimentarios cuya edad supuesta es Proterozoico Superior o Cámbrico Inferior. Las rocas metavolcánicas están constituidas por metarriolitas masivas y tobas dacĂtico-riolĂticas con abundante mezcla de material fragmentario. Corresponden a un volcanismo explosivo subaĂ©reo y de carácter freatomagmático. Sus caracteres geoquĂmicos lo definen como los tĂ©rminos ácidos de una secuencia calcoalcalina de procedencia cortical emplazada postcolisionalmente dentro de un contexto extensivo. El modelo de REE indica que se trata de fundidos poco fraccionados procedentes de la fusiĂłn de una corteza reciclada. Los "Ortoneises de las Guilleries" corresponden a leuconeises biotĂticos con granate. Sus caracteres geoquĂmicos los caracterizan como metagranilos alumĂnicos de procedencia cortical. Sus espectros geoquĂmicos (elementos incompatibles y REE) presentan pautas análogas a los de las rocas metavolcánicas e indican que se trata de fundidos de procedencia cortical de baja alcalinidad emplazados en un contexto anorogĂ©nico. La ausencia de correlaciĂłn geoquĂmica y de pautas de fraccionaciĂłn entre metavolcanitas y ortoneises descarta la idea de una fuente comĂşn para ambos
Early Ordovician Magmatism in the northern Central Iberian Zone (Iberian Massif): New U-Pb (SHRIMP) ages and isotopic Sr-Nd data
Depto. de MineralogĂa y PetrologĂaFac. de Ciencias GeolĂłgicasTRUEpu
Variscan metamorphism in the eastern Pyrenees and its relation to Late-Variscan magmatism revealed by U-Pb zircon dating: implications for the configuration of the Variscan Belt in the NE Iberian Peninsula
Variscan migmatites cropping out in the eastern Pyrenees were dated together with Late Variscan plutonic rocks. Upper Proterozoic–Lower Cambrian series were migmatized during a thermal episode that occurred in the interval 320–315 Ma coeval with the main Variscan deformation event (D1). The calc-alkaline Sant Llorenç–La Jonquera pluton and the gabbro–diorite Ceret stock were emplaced during a later thermal episode synchronous with the D2 deformation event. A tonalite located at the base of La Jonquera suite intruded into the upper crustal levels between 314 and 311 Ma. The gabbro–diorite stock was emplaced in the middle levels of the series in two magmatic pulses at 312 and 307 Ma. The thermal evolution recorded in the eastern Pyrenees can be correlated with that of neighbouring areas of NE Iberia (Pyrenees–Catalan Coastal Ranges) and SE France (Montagne Noire). The correlation suggests a NW–SE-trending zonation where the northeasternmost areas (Montagne Noire and eastern Pyrenees) would occupy relatively more internal zones of the orogen than the southwesternmost ones
ComparaciĂłn entre poblaciones de circones detrĂticos de rocas ordovĂcicas del Pirineo y de otros terrenos perigondwánicos: implicaciones paleogeográficas
The first LA-ICP-MS U-Pb detrital zircon ages from quartzites located in the Ordovician rocks from the Central Pyrenees (the Rabassa Dome, Andorra) were investigated. The four studied samples present very similar U-Pb age patterns. The main age populations correspond to Neoproterozoic (Ediacarian–Cryogenian, ca. 550–750 Ma), Grenvillian (Tonian–Stenian, ca. 850–1100 Ma), Paleoproterozoic (Orosirian, ca. 1900–2100 Ma) and Neoarchean (ca. 2500–2650 Ma). The results presented here enable us to discuss the lower Paleozoic paleoposition of the Pyrenean basement rocks. We have compared our samples with that from other Perigondwanan terrains such as Sardinia, Sicily and the Iberian Massif. The similarity with the Sardinian age distribution suggests that these two terranes could share the same source area and that they were paleogeographically close in Ordovician times in front of the Arabian-Nubian Shield. Comparisons with previous proposed reconstructions allow us to obtain a more complete view of the paleogeography of the Northern Gondwana margin during the Cambro-Ordovician.Se han estudiado los primeros datos de edades de LA-ICP-MS U-Pb en circones detrĂticos correspondientes
a rocas ordovĂcicas del Pirineo central (Domo de la Rabassa, Andorra). Las cuatro muestras estudiadas presentan
unos patrones de edades U-Pb muy similares. Las principales poblaciones corresponden al Neoproterozoico
(Ediacárico – Criogénico, ca. 550-750 Ma), Grenvilliense (Tónico – Esténico, ca. 580-1100 Ma), Paleoproterozoico
(OrosĂrico, ca. 1900-2100 Ma) y Neoarcaico (ca. 2500-2650 Ma). Los resultados presentados nos permiten discutir
sobre la paleoposiciĂłn de las rocas del basamento pirenaico durante el Paleozoico inferior. Se han comparado
nuestras muestras con las de otros terrenos perigondwánicos tales como Cerdeña, Sicilia y el Macizo Ibérico. Las
similitudes con la distribuciĂłn de edades de las muestras de Cerdeña sugieren que estos dos terrenos podrĂan
compartir las mismas áreas fuente y que se podrĂan encontrar en posiciones cercanas durante el OrdovĂcico, en frente
del escudo de Arabia y Nubia. Las comparaciones con algunas reconstrucciones propuestas previamente nos han
permitido obtener una visiĂłn más completa de la paleogeografĂa del margen norte de Gondwana durante el Cambro-
OrdovĂcico.Depto. de MineralogĂa y PetrologĂaFac. de Ciencias GeolĂłgicasTRUEMinisterio de EconomĂa y Competitividad (MINECO)Consolider-Ingenio 2010pu
CorrelaciĂłn de las series neoproterozoicas del Pirineo oriental a partir de datos U-Pb (SHRIMP) en zircones
New geochronological data from pre-Variscan igneous rocks of the Eastern Pyrenees (CanigĂł, Roc de Frausa and Cap de Creus massifs) confirm the presence of Neoproterozoic series in the Pyrenees, as the Balaig micaschists in the CanigĂł massif and the Lower Series in the Roc de Frausa and Cap de Creus massifs. That is, most of the pre-Upper Ordovician sequence in these massifs has to be Late Neoproteozoic in age. These geochronological data allow the correlation of the series along the Eastern Pyrenean massifs. The data also show two different ages (Late Neoproterozoic and Early Ordovician) and significance for the large bodies of granitic orthogneisses intruded at different levels in the series.Se han obtenido nuevos datos geocronolĂłgicos en rocas Ăgneas pre-variscas del Pirineo
oriental (macizos del CanigĂł, Roc de Frausa y Cap de Creus). Se han datado metavulcanitas ácidas interestratificadas en la serie y gneises que derivan de granitos prevariscos. Las rocas metavolcánicas confirman la edad neoproterozoica de los esquistos de Balaig en el macizo del CanigĂł y de las series inferiores de los macizos del Roc de Frausa y del Cap de Creus. Estos datos implican que la mayor parte de la serie pre-ordoviciana superior tiene edad neoproterozoica y permiten correlacionar las series de los tres macizos. Las dataciones en los gneises evidencian dos edades distintas (neoproterozoica y ordovĂcica inferior) para los protolitos intruidos en niveles distintos de la serie.Depto. de MineralogĂa y PetrologĂaFac. de Ciencias GeolĂłgicasTRUEMinisterio de Ciencia e InnovaciĂłn (MICINN)Consolider-Ingenio 2010pu
Évolution pression–température des amphibolites de la zone axiale au cours du métamorphisme hercynien des Pyrénées orientales
Nous avons Ă©tudiĂ© des amphibolites provenant des massifs du Canigou, des Albères et du cap de Creus dans le but d’établir leur Ă©volution pression–tempĂ©rature au cours du temps (chemins P–T –t ). Les valeurs de P et T ont Ă©tĂ© calculĂ©es Ă l’aide du thermobaromètre amphibole–plagioclase–quartz Ă l’équilibre. Si on connaĂ®t Si, Al, Mg et Fe Ă partir d’analyses ponctuelles Ă la microsonde Ă©lectronique du coeur Ă la pĂ©riphĂ©rie d’amphiboles zonĂ©es, l’évolution P–T –t complète peut ĂŞtre Ă©tablie en reliant les analyses obtenues Ă partir de chaque cristal. Dans le massif du Canigou, les amphibolites ont enregistrĂ© des chemins P–T –t anti-horaires autour d’un pic du mĂ©tamorphisme qui se situerait Ă environ 650 â—¦C et 6,1 kbar. Dans le massif des Albères, les chemins P–T –t des amphibolites proches des paragneiss sont seulement rĂ©trogrades, de 600 â—¦C–5 kbar Ă 450 â—¦C–2,5 kbar. Une amphibolite Ă cummingtonite a enregistrĂ© une Ă©volution anti-horaire autour de 650 â—¦C–4,5 kbar. Dans le massif du cap de Creus, l’évolution est rĂ©trograde entre 650 â—¦C–6 kbar et 400 â—¦C–1 kbar.Depto. de MineralogĂa y PetrologĂaFac. de Ciencias GeolĂłgicasTRUEpu
Detrital zircons from the pre-Silurian rocks of the Pyrenees: Geochronological constraints and provenance
The first LA-ICP-MS U-Pb detrital zircon ages from quartzites located below (three samples) and above (one sample) the Upper Ordovician unconformity in the Central Pyrenees (the Rabassa Dome, Andorra) were investigated. The maximum depositional age for the JĂşjols Group, below the unconformity, based on the youngest detrital zircon population, is around 475 Ma (Early Ordovician), whereas for the Bar Quartzite Fm., above the unconformity, the presence of only two zircons of 442 and 443 Ma precludes obtaining a precise maximum sedimentation age. A time gap of ~ 20 million years for the Upper Ordovician unconformity in the Pyrenees can be proposed, similar to that of the Sardic unconformity in Sardinia. The similar age patterns obtained on both sides of the Upper Ordovician unconformity suggest that there was no change in the source area of these series, while the absence of a Middle Ordovician age population may be due to a lack of sedimentation at that time. The four study samples present very similar U-Pb age patterns: the main age populations correspond to Neoproterozoic (Ediacarian-Cryogenian, ca. 550-750 Ma); Grenvillian (Tonian-Stenian, ca. 850-1100 Ma); Paleoproterozoic (Orosirian, ca.1900-2100 Ma) and Neoarchean (ca. 2500-2650 Ma). The similarity with the Sardinian age distribution suggests that these two terranes could share the same source area and that they were paleogeographically close in Ordovician times in front of the Arabian-Nubian Shield