Métodos de aprendizaje colaborativos, creativos e interdisciplinarios en petrología

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasFALSEsubmitte

Aprender ciencia investigando, colaborando y mentorizando, en un entorno interdisciplinar

Depto. de Física de la Tierra y AstrofísicaDepto. de Mineralogía y PetrologíaFac. de Ciencias FísicasFac. de Ciencias GeológicasFALSEsubmitte

Página web para el aprendizaje autónomo de Petrología Ïgnea: Atlas de Rocas Ígneas

El documento expone brevemente los objetivos, metodología y resultados de un proyecto de innovación docente dedicado a continuar con el desarrollo de una página web para el aprendizaje de aspectos prácticos de petrología ígnea. Este proyecto es la continuación de otro desarrollado durante la convocatoria 2013. La página web creada, denominada ATLAS DE ROCAS ÍGNEAS (http://petroignea.wordpress.com), incluye fotografías de muestras de mano, imágenes de microscopio y de afloramiento de rocas ígneas, así como breves explicaciones de las características principales que se aprecian en dichas imágenes. También se introducen conceptos sobre la clasificación de las rocas ígneas. El proyecto de la convocatoria de 2014 se ha centrado más específicamente en desarrollar aspectos meso y macroscópicos relacionados con la manera en la que se disponen las rocas ígneas en la naturaleza en forma de depósitos más o menos grandes. Para ello, además de fotografías de campo, se han incluido esquemas, diagramas, mapas geológicos o imágenes de satélite. Esta página es de libre acceso y cuenta ya con una notable afluencia de visitantes

Alkaline Silicate Metasomatism Recorded through Fe-Ti-Rich Mantle Xenoliths from the Calatrava Volcanic Field (Spain)

Much of the lithospheric subcontinental mantle (SCLM) sampled in the Calatrava Volcanic Field (CVF) shows refertilization by alkaline metasomatic agents. The Cerro Pelado and El Palo ultramafic xenolith suites record the best evidence of this type of metasomatism in this volcanic field. Several groups of peridotite (lherzolite, wehrlite, and dunite) and pyroxenite (clinopyroxenite and websterite) xenoliths have been distinguished. Despite having scarce phlogopites and amphiboles as modal metasomatic phases, all studied xenoliths present a variable cryptic metasomatism, highlighted by the strong Fe-Ti enrichment and fractionated REE patterns in the most evolved wehrlite and pyroxenite varieties. They show a common trend of an Fe-Ti-Ca increase, whereas the pyroxenites are more depleted in Fe compared to the lherzolites and wehrlites. Trace-element (REE and multi-trace) patterns are roughly similar among them, suggesting different interactions and refertilization degrees by alkaline silicate melts. The same Sr–Nd isotopic EAR composition, combined with trace-element chemistry of metasomatic xenolith phases and phenocrysts from the Calatrava volcanics, highlights the main role of this magmatism in percolation processes beneath Central Iberia. These mantle xenoliths also show variable amounts of interstitial glass that originated by in situ partial melting, favored by the enriched chemical nature of cryptically metasomatized clinopyroxene during their volcanic transport. This alkaline-refertilized mantle type represents the main domain within the SCLM beneath Central Iberia, as was also recorded in other Western European Cenozoic volcanic fields.Ministerio de Ciencia e InnovaciónDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

U–Pb isotopic ages and Hf isotope composition of zircons in Variscan gabbros from central Spain: evidence of variable crustal contamination

Received: 1 July 2010 / Accepted: 9 December 2010 / Published online: 31 December 2010 © Springer-Verlag 2010 e-mail C. Villaseca: [email protected] microprobe U–Pb analyses of zircons from three gabbroic intrusions from the Spanish Central System (SCS) (Talavera, La Solanilla and Navahermosa) yield Variscan ages (300 to 305 Ma) in agreement with recent studies. Only two zircon crystals from La Solanilla massif gave slightly discordant Paleoproterozoic ages (1,848 and 2,010 Ma). Hf isotope data show a relatively large variation with the juvenile end-members showing ɛHfi values as high as +3.6 to +6.9 and +1.5 to +2.9 in the Navahermosa and Talavera gabbros, respectively. These positive ɛHfi values up to +6.9 might represent the composition of the subcontinental mantle which generates these SCS gabbros. This ɛHfi range is clearly below depleted mantle values suggesting the involvement of enriched mantle components on the origin of these Variscan gabbros, and is consistent with previous whole-rock studies. The presence of zircons with negative ɛHfi values suggest variable, but significant, crustal contamination of the gabbros, mainly by mixing with coeval granite magmas. Inherited Paleoproterozoic zircons of La Solanilla gabbros have similar trace element composition (e.g. Th/U ratios), but more evolved Hf-isotope signatures than associated Variscan zircons. Similar inherited ages have been recorded in zircons from coeval Variscan granitoids from the Central Iberian Zone. Granitic rocks have Nd model ages (TDM) predominantly in the range of 1.4 to 1.6 Ga, suggesting a juvenile addition during the Proterozoic. However, Hf crustal model ages of xenocrystic Proterozoic zircons in La Solanilla gabbro indicate the presence of reworked Archean protoliths (TDM2 model ages of 3.0 to 3.2 Ga) incorporated into the hybridized mafic magma.Ministerio de Ciencia y Tecnología (España)Universidad Complutense de MadridDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Felsic magmatism and hydrothermal activity of the Central Igneous Complex of Boa Vista (Cape Verde islands): Insights from zircon, titanite and apatite geochronology

Studies focused on the U-Pb geochronology and oxygen isotope composition of magmatic zircon formed in intraplate oceanic islands are very scarce. The Boa Vista Island (Cape Verde archipelago) displays one of the few felsic igneous complexes (alkaline volcanic and plutonic rocks) in an oceanic setting and provides the opportunity to date and characterise magmatic-hydrothermal events based on the isotopic records of zircon. Due to the scarcity of this mineral in these igneous rocks, we have separated detrital zircon from sediments of dry riverbeds of the Central Igneous Complex of the island of Boa Vista, which is dominantly felsic in composition. Zircon has been analysed to determine the U–Pb–O isotopic composition and trace element contents. All zircon grains display complex CL textures indicative of a strong transformation due to interaction with a hydrothermal agent. This reactive event led to a strong disturbance of the U-Pb system, enrichment of trace elements (Ti, Nb, Ta, Th, U, Pb, Y and REE) and decrease of δ18O values (down to −6 ‰). These features suggest that the magmatic U–Th-rich zircon crystallised from highly evolved melts and experienced partial metamictization prior to its transformation. High-T hydrothermal fluids were likely mixed with groundwater (imprinting such low oxygen isotope composition) and reacted with and transformed zircon crystals from the main felsic igneous formations. The geochronological results obtained by SHRIMP on zircon have been complemented with U-Pb ages obtained by laser ablation SF–ICP–MS on titanite and apatite of syenitic intrusions. Overall, the geochronological results fall within a restricted range of ages from 13.3 to 15 Ma. These results, together with literature data, imply that most of the felsic volcanic and plutonic rocks from Boa Vista were formed in the range ∼ 12–15 Ma (episodes 1 and 2 of the second stage of magmatism). The hydrothermal process observed in the studied detrital zircon likely occurred during the last felsic magmatic events (∼10–12 Ma).Ministerio de Ciencia e InnovaciónDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

The old central igneous complexes of Sal, Boa Vista and Maio islands: Implications for 17 Ma of isotopic evolution of the Cape Verde archipelago

The central igneous complexes of the easternmost islands (Sal, Boa Vista and Maio) preserve some of the most ancient outcropping rocks of the Cape Verde (CV) archipelago. These Early to Middle Miocene (about 25 to 12 Ma) complexes show marked isotopic differences between mafic rocks from the northern (Sal and Boa Vista) and the southern Maio Island, the latter showing lower 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and higher 87Sr/86Sr ratios. The main mantle plume composition beneath Cape Verde is here considered to be dominated by the FOZO component. Our data supports previous models suggesting the incorporation to plume components of minor DMM mantle sources in the northern CV island alignment, whereas mixing with the EM1 pole is prevalent on the southern CV islands. These isotopic differences are evident since the early stages of Cape Verde magmatism. The Late Miocene to Holocene time period (7 to 1.7 Ma) is characterized by the irruption of silica-undersaturated and carbonatite magmas with a relatively homogeneous isotopic composition and highly radiogenic Pb signatures (206Pb/204Pb up to 20.6 in carbonatitic rocks and 20.2 in silicate rocks) throughout most of the Cape Verde archipelago. During this transitional stage, the input of this new HIMU mantle component overprinted the previous mixing of the main FOZO plume component with shallow mantle members (DMM, EM1) of minor contribution.Ministerio de Ciencia e InnovaciónFundação para a Ciência e Tecnologia (Portugal)Banco SantanderUniversidad Complutense de MadridDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu