Search

La mayor parte de los islotes que constituyen las islas Columbretes son de composición fonolítica y constituyen una sucesión de pequeños volcanes que se alinean según una dirección N170ºE. De norte a sur se suceden los volcanes fonolíticos de Ferrera, Piedra Joaquín, La Horadada y El Bergantín. Los restos de otros volcanes, hoy sumergidos, al norte y sur, completan esta alineación de más de 12 kilómetros de longitud, Most of the islets that constitute the Columbretes Islands are phonolitic in composition and constitute a succession of small volcanoes that line up in a N170ºE direction. From north to south, the phonolitic volcanoes of Ferrera, Piedra Joaquín, La Horadada and El Bergantín follow one another. The remains of other volcanoes, now submerged, to the north and south, complete this alignment of more than 12 kilometers in length

Se ha datado radiométricamente (K/Ar) el volcán de Bienvenida, uno de los volcanes de melilititas olivínicas más representativo de la región volcánica de Campos de Calatrava. Se ha analizado la roca y las principales fases minerales, lo que ha permitido obtener información sobre las condiciones de formación, Bienvenida volcano, one of the more representative olivine melilitite volcanoes of the volcanic region of Campos de Calatrava, has been radiometrically dated (K/Ar). The rock and main mineral phases have been analysed, which has allowed us to obtain information about the conditions of formation

En el sur de la isla de Tenerife, en el Edificio Roque del Conde, se encuentran estructuras en forma de domo denominadas “Roques", formadas por rocas intrusivas sálicas de composiciones ácidas e intermedias, fuertemente y moderadamente alcalinas: traquiandesitas, fonolitas y traquitas. Algunos de los roques son homogéneos composicionalmente, mientras que otros varían de composición de unas zonas a otras. Las traquiandesitas siguen pautas composicionales lineales con las rocas más básicas del edificio Roque del Conde y parecen haberse formado por un proceso de cristalización fraccionada relativamente sencillo y continuo. Las traquitas y las fonolitas siguen pautas composicionales diferentes a las anteriores. Están también esencialmente controladas por procesos de cristalización fraccionada, en los que las plagioclasas y los feldespatos potásicos, en diferentes proporciones según los casos, son las fases principales extraídas. Las fases accesorias, como la titanomagnetita, la esfena y el apatito, y el anfíbol han tenido también un papel importante en estos procesos, In Roque del Conde Old Edifice at the south of Tenerife Island there are domatic structures called “roques " that are formed by intrusive salic rocks of acidic and intermediate compositions, and alkaline and strongly alkaline: trachyandesites, phonolites and trachytes. Some of the roques are compositionally homogeneous whereas others have a compositional variation in different zones. Trachyandesites follow a lineal pattern with the most basic rocks of Roque del Conde edifice and have been formed by a process of fractional crystallization. Trachytes and phonolites follow different patterns from the former. They are essentially controlled by fractional crystallization processes, where plagioclase and K-feldspars are the main removed phases. Accessory phases like Ti-magnetite, sphene and apatite, or amphibole have also an important role in these processes

En el Edificio mioceno de Roque del Conde, en el sur de la isla de Tenerife, aparecen varias estructuras abovedadas que dan lugar a singulares morfologías de “roques". Se trata de traquiandesitas, traquitasy fonolitas constituidas por fenocristales de feldespatos y clinopiroxenos y, ocasionalmente también de anfíboles y feldespatoides, en una matriz de similar composición. Los feldespatos son esencialmente anortoclasas y sanidinas ricas en sodio, estando las plagioclasas restringidas a las rocas traquiandesíticas. Los clinopiroxenos son muy variados composicionalmente, observándose un enriquecimiento en el contenido en FeO de los mismos a medida que la roca es más evolucionada. En general, se trata de diópsidosyaugitas, siendo hedenbergitas en las rocas traquíticas. En algunos de los roques los piroxenos son egirínicos. Los anfíboles están frecuentemente transfomados a minerales anhidros y son bastante variados: magnesio-hastingsitas, pargasitas, ferropargasitas y kaersutitas. Los feldespatoides aparecen sólo en las fonolitas y son nefelinas y sodalitas Se han determinado las condiciones de formación de los minerales máficos, obteniéndose temperaturas de unos 1000°C para los anfíboles y 870°C para los piroxenos y presiones similares para ambos (unos 3kbar) lo que indicaría que estas rocas se habrían formado en los niveles inferiores de la corteza de la isla, At the south of Tenerife island on the Miocene Roque del Conde Old Edifice emerge various domed structures that form singular morphologies of " roques". They are trachyandesites, trachytes and phonolites composed by phenocrysts of feld sparsanddino pyroxenes, occasion ally with amphiboles and feldspathoids in a groundmass of similar composition. Feldspars are essentially sodium-rich sanidine and anorthoclase. Plagioclase is restricted to trachyandesitic rocks. Clinopyroxenes have a strong variation in their composition and can be observed an enrichment in the FeO content with the moste volved rocks. Generally, clinopyroxenes are diopside and augite, whereas hedenbergites appear in trachytic rocks. In some of the roques clinopyroxenes are egirinic. Amphiboles are frequently transformed to anhydrous minerals and have a broad compositional range: magnesiumhastingsites, pargasites, ferropargasites and kaersutites. Feldspathoids are restricted to phonolites and are nephelines and sodalites. It has been determ in ed th e form atio n c o n d itio n s o f m a fic m in erals: tem pe ra tu res a ro u n d 1000°C for amphiboles and 870°C for clinopyroxenes with similar pressure for both (around 3kbar), which indicate that these rocks could have been for medin low deep crust levels of the island

Santa Luzia island is essentially formed by erosional remnants of, at least, one volcanic edifice: the Old Edifice. The remains of this edifice are now a NW-SE trending mountain range. It is a fisural edifice that follows this trend and is formed by hundreds of meters of aa-type lava flows crosscut by dikes. Lithologic compositions are basic and ultrabasic (picrobasalts, basanites, basalts and trachybasalts), intermediate (trachyandesites) and felsic (trachytes and phonolites). The main process generating these compositional differences is fractional crystallization, La isla de Santa Luzia está formada esencialmente por los restos erosivos de, al menos, un edificio volcánico: el Edificio Antiguo. Los restos de este edificio forman en la actualidad una alineación montañosa de dirección NWSE. Se trata de un edificio fisural alineado en la mencionada dirección formado por centenares de metros de coladas de lava de tipo aa y por diques que lo atraviesan. Las rocas que lo forman son básicas y ultrabásicas (basaltos picríticos, basanitas, basaltos y traquibasaltos), intermedias (traquiandesitas) y félsicas (traquitas y fonolitas). El principal proceso generador de estas diferencias composicionales es la cristalización fraccionada

27 páginas, 14 figuras, 5 tablas., Spinel lherzolite xenoliths from the Cenozoic Calatrava volcanic field provide a sampling of the lithospheric mantle of central Spain. The xenoliths are estimated to originate from depths of 35–50 km. Trace element content of clinopyroxene and Cr-number in spinel indicate low degrees of partial melting (≤ 5%) of the xenoliths. Although a major element whole-rock model suggests wider degrees of melting, the Calatrava peridotite chemistry indicates a moderately fertile mantle beneath central Spain. Calatrava peridotite xenoliths bear evidence for interaction with two different metasomatic agents. The enrichment in LREE(light rare earth element), Th, U and Pb, and the negative anomalies in Nb–Ta in clinopyroxene and amphibole from xenoliths of El Aprisco, indicate that the metasomatic agent was probably a subduction-related melt, whereas the enrichment in MREE in clinopyroxene from xenoliths of the Cerro Pelado centre suggests an alkaline melt similar to the host undersaturated magmas. These metasomatic agents are also consistent with the chemistry of interstitial glasses found in xenoliths of the two volcanic centres. Differences in metasomatism but also in mantle composition is supported by Sr–Nd whole-rock data which show a more radiogenic nature for Sr isotopes of samples from the El Aprisco centre (87Sr/86Sr ratios of 0.7035–0.7044 instead of 0.7032–0.7037 for samples from Cerro Pelado). The timing of the subduction-related metasomatic stage is unconstrained, although the Calatrava intraplate volcanism intrudes an old Variscan lithospheric section reworked during the converging plate system affecting SE Iberia in the Tertiary. The presence of wehrlite types within the Calatrava peridotite xenoliths is here interpreted as a reaction of host lherzolites with silica-undersaturated silicate melts that could be related to the Calatrava alkaline magmatism. The Sr–Nd isotopic composition of Calatrava peridotites plot within the European athenospheric reservoir(EAR) mantle, these values represent more enriched signatures than those found in the other Spanish Cenozoic alkaline province of Olot., This work was supported by grants CGL-2006-03414 and CGL-2008-05952 of the Ministerio de Educacio´n y Ciencia of Spain. This research also received support from the SYNTHESYS project GB-TAF-2768 funded by the European Community Research Infrastructure Action under the FP6 ‘Structuring the European Research Area’ Programme.

This essay shows some new dating of the Basal Complex of La Gomera Island and among them, the first ones obtained using the 40Ar-39Ar methodology. Two of them are rocks of the Submarine Edifice. In the first one we obtain an age of 11,49 ± 0,66 Ma by the 40Ar-39Ar method, and in the second one 11,4 ± 1,6 Ma by the K-Ar method. These ages reveal that the volcanic activity of the NW outcroping Submarine Edifice is approximately 11,5 Ma in age, close to the beginning of the Lower Old Edifice activity. The third sample dated also by the 40Ar-39Ar method, is from the only syenitic rocks outcrop of La Gomera (Tamargada syenite); its age, 7,59 ± 0,81 Ma, confirms that these rocks represent the roots of one of the Old Edifice felsic episodes and that they do not belong to a felsic stage contemporary with the submarine growth of the island.

A more than 1000m thick pile of basaltic lava flows and pyroclasts dipping seawards rises on the western sector of San Vicente. Several systems of dikes cut across the succession that is composed of two different sequences. The lower sequence (Lazareto Formation), about 400 m thick, is formed mainly by pahoe-hoe, frequently ankaramitic, basalt lavas and some breccias intercalated. This sequence is exposed in small hills and low rounded ridges of gentle slopes. The upper sequence (Monte Cara Formation), some 700 m thick, consisting in individually thicker basaltic lava flows with typical scoria levels is well exposed in high scarps. Numerous subvertical dikes cross the entire succession. The dikes vary increasingly their strike from south to north. Frequent sills (one every 3-5 m) also intrude the lower sequence. The distribution of the lava flow dip strikes as well as the dike strikes suggests that the succession as a whole was part of a central volcanic edifice, of which the eruptive centre was once located south of the city of Mindelo. This giant volcanic edifice, 16-20 km in diameter and 1600-2000m high, would have extended off the present coast. According to the radiometric ages obtained the volcano built up between 6,1Ma and 4,6 Ma with maximum activity concentrated between 5,5 and 5 Ma

The first data about the composition of lava flows from Branco Island (Cabo Verde) are presented in this work. Most lava flows in the sequence are alkali basalts (Fo84-76 olivine, En44-36 diopside, An83-31 plagioclase) showing geochemical affinity of typical ocean island basalts. The scarce most evolved members are mugearites (olivine absent, En41-31 clinopyroxene, An51-26 plagioclase, and kaersutite). The compositional variations between both the types are explained by crystal fractionation and extraction of pyroxene (up to 29%) and lesser proportions of olivine and Fe and Ti oxides (Cpx: 75; Ol: 21; OxFeTi: 4). The transition to mugearites from the most evolved basalts would mainly be due to extraction of pyroxene (24%) and Fe and Ti oxides (Cpx: 68; Ol: 3; Plag: 5; OxFeTi: 30)

The Submarine Edifice rocks are the oldest rocks in La Gomera. This edifice is made up of submarine lava and breccias, with marine sediments associated, all of which is transverse by a very dense network of diques. This essay shows the first geochemical and mineralogical submarine volcanic rocks data. These rocks are intensely altered and have an alkaline chemical affinity. Compositions vary between alkaline basalts and trachyandesites, and all of them show typical Within Plate and Ocean Island basalts immobile elements contents. The latter Subaerial Edifice volcanic rocks are similar in composition, although they are slightly less alkaline and they have less evolved types

The morphological, structural and volcanological aspects of Branco, an island of the Cape Verde Archipelago, are described and interpreted in this work. The isle consists of a 700 m thick pile of basalt lava flows and scarce pyroclastics crossed by several families of dikes. The structure of the island could correspond to the remaining fragment of a primitive large shield volcano. The main hypothetical emission centre could once be situated between the present islands of Santa Luzia and Branco

The new radiometric data from felsic domes on La Comerá allow to separate two different felsic both intrusive and extrusive episodes on the island. The early one, upper Miocene in age, includes the domes on the eastern sector of the island as well as the radial and the conical dikes cropping out on the north. Within this early episode of felsic magmatism, the domes on the eastern sector and the so called eastern radial dike-swarm seem to be contemporaneous and slightly older (8.6-7.9 Ma) than the western radial-dike swarm and the cone-sheet complex, a structure which also includes some related domes (7.5-6.4 Ma). A later felsic episode, lower Pliocene in age (4.5-3.9 Ma),includes all the rest of existent domes on La Gomera which are less alkaline and peralkaline than the older ones

The "Horizontal Basalts" in the Agulo area are made up of a more than 600m thick succession of basaltic flows that filled a SW-NE trending paleo-valley. Compositions vary between picrite and trachybasalt. The lithologic and geochemical variability of these rocks indicates that they were generated mainly by fractional crystallization. The recognition of several evolution cycles suggests the involvement of other processes that modify the general fractional crystallization trend

The magnetostratigraphic sequence of the volcanosedimentary materials near to Poblete (Ciudad Real) has allowed dating the most recent eruption of the volcanism of the Campo de Calatrava. The chronology of the magnetostratigraphic sequence has based on the radiometric dating of one lava flow that was previous to the explosive episodes. A great variety of volcanic materials and several sedimentary levels and soils compose the sequence

Pliocene-Quaternary nephelinitic and alkali basaltic lavas and pyroclastic deposits from Cofrentes and Tallante and Miocene lamproitic lavas from Aljorra host xenoliths and megacrysts of lithospheric mantle origin. The xenolith suite consists of spinel Iherzolites and harzburgites and with protogranular, porphyroclastic and equigranular or transitional (protogranular to porphyroclastic) textures. The textural features provide evidence of ductile-brittle deformation of Tallante xenoliths, whose mineralogy and mineral chemistry data (presence of kaersutite and phlogopite) also bear evidence of fluid-induced metasomatism of the lithospheric mantle. P-T estimates suggests that mostly protogranular xenoliths are reliable to define a palaeogeotherm, which is from 950-1185°C at 2,5-3.0 CPa, 794-805°C and 1,7-7,3 CPa for Cofrentes to 936-958°C, at 1,1 -1,2 CPa for Tallantes. The Aljorra peridotite suggests a temperature of ~880°C and a pressure of ~1,8 GPa. The picture of equilibrium P-T conditions indicates that the differences in the mantle lithosphere composition is related to (1) its deformation state and (2) metasomatic events, but also to (3) the location of entrapment during magma ascent in the lithosphere generated by diapiric uprising of asthenospheric mantle. The location of the entrainment is either close to the magma generation area or is situated at the mantle-crust boundary

During fifty five years professor José María Fúster Casas (1 923-2000) works in (Central) Complutense University of Madrid in Igneous and Metamorphic Petrology. He collaborates actively in introducing new petrological techniques as optical microscopy and developping new geochemical laboratories. After his Ph D in Spanish Guinea he works mainly in two geological areas: the Hercynian Iberian Belt and the Cenozoic volcanism of Spain. From 1960 (when he became Professor) to 1990 (retiring) he developed a great number of projects summarized in many publications (articles, geological sheets, books) organizing international meetings (Canary 68, W Peninsular 81) and leading douzaines of Ph D projects, creating a vast school of geologists. Last years he concentrated his efforts in Canarian Volcanism

Several trachytic and phanalitic, radial and canical dyke-swarms crap out an the La Gomera narthern regian. The first age data abtained situate the intrusian episades coinciding in time with the extrusian af the Old Basalts. The earlier dykes shaw a radial pattern, centred in Tamargada. They have been dated in 8.0 Ma and 7.9 Ma. The canical swarm centred farther west, in Vallehermasa, has a slightly more recent age, between 7.5 Ma and 6.4 Ma. A third dyke-swarm is spatially assaciated with the canical structure and has likely a similar age.

During the evolution of the Las Cañadas volcanic edifice, debris avalanches were very significant destructive events. The Roques de Garcia unit was generated by such an event. 39Ar/40Ar dating has been carried out on different rock types related to this deposit. 1.70-1.40 Ma ages were measured on volcanic matérial involved in the avalanche deposit, 0.43 Ma on a phonolitic dyke cutting this formation. These results bracket the age of the debris avalanche emplacement which could mark either the transition between Cañadas ll-Cañadas III (1.4-1.1 Ma) or Cañadas Illa-Cañadas lllb (0.6-0.7 Ma) volcanic phases

During the evolution of the Las Cañadas volcanic edifice, debris avalanches were very significant destructive events. The Roques de Garcia unit was generated by such an event. 39Ar/40Ar dating has been carried out on different rock types related to this deposit. 1.70-1.40 Ma ages were measured on volcanic matérial involved in the avalanche deposit, 0.43 Ma on a phonolitic dyke cutting this formation. These results bracket the age of the debris avalanche emplacement which could mark either the transition between Cañadas ll-Cañadas III (1.4-1.1 Ma) or Cañadas Illa-Cañadas lllb (0.6-0.7 Ma) volcanic phases

A mainly phonolitic, 10 km in diameter, cone-sheet complex crops out on the northern area of La Comera. The swarm intrudes into the Basal Complex, The Old Basalts and other rocks of the Trachytic-phonolitic Complex to which they belong. The cone-sheet complex center lies south of Vallehermoso. Most of the dykes in the core of the structure are "conic dome-sheets" which start to be evidenced 400m far from the center and dip over 50°. In the surrounding area the dome-sheets are less frequent while simple cone-sheets are more abundant and dip more gently towards the periphery. From the analysis of their dips and distribution a single conic structure is deduced. The cone-sheets were originally connected to a hypothetical dome-shaped magmatic body whose uppermost part is at present located 1350m under sea level

Nevado del Huila Volcano (VNH), the highest volcano of the Colombian Andes (5360m) has been relatively inactive for a long time, may be since prehistoric times because there is no historical record of volcanic activity. This continental margin volcano zone belongs to the volcanic ridge associated to the subduction of the Nazca Plate beneath the South American Plate. VNH has been generally classified as stratovolcano with predominant effusive activity. However the recent discovery of new pyrodastic deposits identified by the authors, suggest that VNH had more than one explosive episode in past time. The lavas of VNH are typical andesites of active continental margin, belonging to calcoalcaline series. Only a few of the these lavas are slightly tholeitic, all of them have a clear subalcaline tendency (Na20 + K20 < 8%) with a high to medium K20 contents varying between 7,5 - 3%

The distributidn of felsic dykes on La Comera northern area corresponds to several swarms. The first radial dyke swarm is centered on the Tamargada area. The second radial dyke swarm center, located farther west, south of Vallehermoso is associated with a cone sheet complex