Els isòtops radiogènics(Sr i Nd) en diferents contextes geodinàmics: Illes Canaries i Vesuvi. Preparació i anàlisi de mostres mitjançant la tècnica analítica TIMS

Projecte de recerca elaborat a partir d’una estada l’ Osservatorio Vesuviano (Nàpols, Italia) entre novembre del 2006 i març del 2007. Un dels objectius principals de l’estada ha estat conèixer la tècnica analítica Thermal Ionisation Mass Spectrometry (TIMS ) per l’anàlisi d’isòtops radiogènics (Sr i Nd). Aquesta estada ha permès aprendre tant la part de preparació de les mostres, com la part d’utilització i programació de l’instrument. Inicialment en el projecte es va programar l’anàlisi dels isòtops radiogènics en laves i xenòlits de l’illa de Gran Canaria (Illes Canàries) amb l’objectiu de modelar geoquímicament el mantell terrestre sota les illes Canàries. Finalment, i a part de les mostres inicials de Gran Canaria, es van incloure mostres del volcà Vesuvi per tal de concloure un projecte iniciat el 2003 amb el Professor Giovanni Orsi i la Professora Lucia Civetta. L’estudi dels isòtops radiogènics en contextes geodinàmics tant diferents ha permès comparar la variació dels isòtops radiogènics de Sr i Nd que existeix entre volcanisme d’ intraplaca (Illes Canàries) i volcanisme en zones convergents (Vesuvi).

El vulcanisme bàsic del Carbonífer inferior de la Serra de Miramar

El Carbonífer Inferior de la Serra de Miramar conté manifestacions de roques volcàniques. Llur caracterització petrogràfica permet la seva classificació com a laves i diabases subvolcàniques; l'estudi geoquímic palesa la seva afinitat alcalina.

The Hercynian ore deposits from the Catalonian Coastal Ranges

Many mineralizations, showings and geochemical anomalies have been found in the Hercynian of the Catalonian Coastal Ranges during the last ten years. Many of them are enclosed in the Paleozoic sediments and volcanics and display pre-metamorphic syngenetic characteristics. The lower carboniferous manganese and base meta1 deposits appear to be formed from hydrothermal fluids springing up in the sea floor through active fractures controlling the filling of the basins in a extensional geotectonic setting. Although less evidence and more controversy is available, similar ore forming processes could have taken place in older Paleozoic times. The deformation and metamorphism have not played an important remobilization role, and most epigenetic deposits of Hercynian age are related to the hydrothermal cells induced by the post-metamorphic granitic intrusives.

El Complejo Turbidítico del Carbonífero del Priorat (Tarragona)

Relaciones entre las asociaciones de facies de las tres unidades litoestratigráficas del complejo turbidítico y su asimilación a unidades deposicionales dentro de modelos de sedimentación submarina.

Volcanic stratigraphy of Hannah Point, Livingston Island, South Shetland Islands, Antarctica

The Upper Cretaceous volcanic succession of Hannah Point is the best exposure of the Antarctic Peninsula Volcanic Group on L ivingston Island. The aim of the present paper is to contribute to the characterisation of the stratigr a p hy and petrogr a p hy of this little studied succession, and briefly discuss some aspects of the eru p t ive style of its volcanism. The succession is about 470 m thick and is here subdivided into five lithostratigraphic units (A to E from base to top). Unit A, approximately 120 m thick, is mainly composed of polymict clast-supported volcaniclastic breccias and also includes a dacitic lava laye r. Interstratified in the breccias of this unit, there is a thin laminated devitrified layer which shows some degree of welding. Unit B, approx imately 70 m thick, is almost entirely composed of volcaniclastic breccias, and includes a volcaniclastic conglomerate laye r. Breccias in this unit can be subdivided into two distinct types; polymict clast-supported breccias, and monomict matrix-supported breccias rich in juvenile components and displaying incipient welding. Unit C, about 65 m thick, is mainly composed of basaltic lavas, which are interlayered with minor vo lcaniclastic breccias. Unit D, approximately 65 m thick, is lithologically similar to unit B, composed of an alternation of polymict clasts upported breccias and matrix-supported breccias, and includes a volcaniclastic conglomerate laye r. Unit E, about 150 m thick, is mainly formed of thick andesitic lava layers. Minor basaltic dykes and a few normal faults cut the succession, and the contact betwe e n units A and B can be interpreted both as an unconformity or a fault. The matrix-supported breccias included in the succession of Hannah Point have high contents of juvenile components and incipient welding, which suggest that part of the succession is the result of pyroclastic fragmentation and emplacement from pyroclastic flows. In contrast, the polymict clast-supported breccias suggest reworking of previous deposits and deposition from cool mass flows. The lavas indicate eff u s ive volcanic eruptions, and the absence of features indicative of subaqueous volcanism suggests that at least these portions of the succession were emplaced in a subaerial environment .

Paleozoic stratigraphy of the Central and Northern part of the Catalonian Coastal Ranges (NE Spain)

The Paleozoic stratigraphic succession in the Catalonian Coastal Ranges spans the interval from Cambrian(?) to Carboniferous, with only one break, separating the pre-Carboniferous part of the sequence from the Carboniferous. The oldest rocks exposed form a sequence of schists, fine grained sandstones, gneisses (laminar pre-Hercynian intrusions), marbles, orto- and para-amphibolites and calcsilicate rocks. comparison with other localities iuggests an Early Cambrian age (or perhaps in part older). Upwards the sequence becomes more monotonous andconsists only of schists (or slates where themetamorphic grade is lower) and thin fine-grained sandstone layers (Cambrian-Ordovician). Still higher in the sequence, an altemation of greywackes and slates is found, with interlayered mud-supported conglomerates at its lower part and acid volcanic rocks which occur throughout the whole sequence. This part of the sequence has provided the oldest faunas known in the Catalonian Coastal Ranges, which indicate the Caradoc. Finally, in its uppermost part, the Ordovician sequence contains some thin limestone layers that contain Ashgill faunas. The Silurian, from Llandovery to Lower Ludlow, consists of black graptolitic shales with dolerite sills, whilst the upper Ludlow, Pridolian and Devonian consist of nodular limestones and marls withpelagic and hemipelagic faunas. The youngest Devonian faunas found correspond in general to the Emsian. The existence of a gap at this point of the sequence suggests the possibility that part of the Devonian could have been eroded. The Carboniferous is characterized by a thick culm sequence (Visean to Westphalian?), resting on thin chert and limestone layers (Tournaisian and Visean). A comparison with neighbouring areas shows a similarity regarding succession and facies with other Paleozoic massifs around the Western Mediterranean.

The Hercynian structure of the Catalonian Coastal Ranges (NE Spain)

In the Catalonian Coastal Ranges, Paleozoic sedimentary and meta-sedimentary rocks crop out in severa1 areas, intruded by late tectonic Hercynian granitoids and separated by Mesozoic and Tertiary cover sediments. Large structures are often difficult to recognize, although a general east-west trend can be observed on the geological map. Deformation was accompanied by the development of cleavages and regional metamorphism. Green-schist facies rocks are prominent throughout the Ranges, while amphibolite facies are restricted to small areas. In low-grade areas, the main deformation phase generated south-facing folds with an axial plane cleavage (slaty cleavage in metapelitic rocks). The intersection lineation (Ss/Sl) and the axes of minor folds trend cast-west, as do all mapable structures. Late deformations generated coarse crenulations, small chevrons and kink-bands, all intersecting the slaty cleavage at high angles. In medium- to high-grade areas no major folds have been observed. In these areas, the main foliation is a schistosity and is often folded, giving centimetric to decimetric, nearly isoclinal intrafolial folds. In schists, these folds aremuchmore common than inother lithologies, and can be associated with a crenulation cleavage. All these planar structures in high-grade rocks are roughly parallel. The late Hercynian deformational events, which gave rise to the crenulations and small chevrons, also produced large (often kilometric) open folds which fold the slaty cleavage and schistosity. As aconsequence, alternating belts with opposite dip (north and south) of the main foliation were formed. With respect to the Hercynian orogenic belt, the Paleozoic outcrops of the Catalonian Coastal Ranges are located within the northern branch of the Ibero-Armorican arc, and have a relatively frontal position within the belt. The Carboniferous of the Priorat-Prades area, together with other outcrops in the Castellón Province, the Montalbán massif (Iberian Chain) and the Cantabrian zone (specially the Pisuerga-Carrión Province) probably form part of a wide area of foreland Carboniferous deposition placed at the core of the arc.

El volcanismo jurásico del sector valenciano de la Cordillera Ibérica. Distribución y trama estructural

En el sector valenciano de la Cordillera Iberica se desarrolla durante el Jurásico un volcanismo fundamentalmente piroclastico, con emisiones basalticas y traquibasalticas en el Pliensbachiense, Toarciense y Bajociense. La cartografia de los afloramientos permite definir dos alineaciones NW-SE (franja de Caudiel, alineación piroclástica de Alcublas), asi como un rea ms amplia de traza general NE-SW en las sierras de Javalambre y Camarena. Tal disposicion regional sugiere que las manifesiaciones volcaiiicas ocurren segun dosdirecciones principales de fracturacion tardihercinica~(NW-SEy NK-SW) y an posiblemente a favor de los puntos de interseccin de ambos sistemas estructurales. La direccin NW-SE ejerce el maximo control de la actividad volcnica jursica, al igual que previamente durante el Triasico superior (linea ofitica de Altura).

The Hercynian intrusive rocks of the Catalonian Coastal Ranges (NE Spain).

The hercynian outcrops of the Catalonian Coastal Ranges (NE Spain) consist mainly of Lower Permian-Upper Carboniferous, post-tectonic, epizona1 granitoid intrusions which form a typical applutonic calc-alkaline suite ranging from mafic hornblende gabbros and ultramafic olivine homblendites throught on alites and granodioritcs to leucogranites. This suite displays major andtrace-element characteristics and Sr isotope ratios similar to volcanic arc and post-collision magmatism oceanic lithosphere and to have been modified by contamination and is therefore believed to have formed above subducted with melts from the crust

El volcanismo neógeno-cuaternario de Catalunya: caracteres estructurales, petrológicos y geodinámicos

El volcanismo neógenocuaternario de Catalunya está asociado al sistema de fracturas escalonadas, de orientación preferente SW-NE y NW-SE, que condiciona también las depresiones tectónicas o fosas neógenas. Las dataciones radiométricas ponen de manifiesto una actividad volcánica entre 10 y 0.1 m.a., localizándose las erupciones más antiguas en la fosa del Empordà, mientras que el volcanismo cuaternario se concentra en las proximidades de Olot (La Garrotxa). El magmatismo es de carácter alcalino, con términos exclusivamente básicos (basanitas), salvo un afloramiento traquítico. Son frecuentes los xenolitos de rocas sedimentarias y plutónicas básicas y ácidas, presentando estos últimos el mayor grado de transformación. Los caracteres estructurales, geoquímicos y mineralógicos, junto a las relaciones isotópicas Sr8YlSr86 apoyan un origen profundo, subcrustal, del magma, y definen un volcanismo intraplaca como el que corresponde a un modelo de rift embrionario sin atenuación litosférica y con escasas manifestacion

Procesos de incorporación y preservación de bioclastos en flujos piroclásticos subacuáticos: dos ejemplos y un modelo genético

Se ofrecen dos ejemplos de incorporación de bioclastos por parte de coladas piroclásticas en ambiente subacuático. Estos ejemplos proceden del Ordovicico Superior-Silrico inferior del Sarrabus (Sureste de Cerdeña, Italia) y el Mioceno del Arcuentu (Suroeste de Cerdeña, Italia). Los bioclastos aparecen en ambos casos en el frente de coladas piroclásticas, y se han preservdo en forma de moldes. Tras una exposición detallada de los materiales se propone un modelo genético común para ambos ejemplos, en el que tras la asimilación de los bioclastos en el frente de la colada estos sufren disolución y se preservan en los raros casos en los que la colada piroclástica se enfria rápidamente.

Estimating 750 years of temperature variations and uncertainties in the Pyrenees by tree-ring reconstructions and climate simulations.

Past temperature variations are usually inferred from proxy data or estimated using general circulation models. Comparisons between climate estimations derived from proxy records and from model simulations help to better understand mechanisms driving climate variations, and also offer the possibility to identify deficiencies in both approaches. This paper presents regional temperature reconstructions based on tree-ring maximum density series in the Pyrenees, and compares them with the output of global simulations for this region and with regional climate model simulations conducted for the target region. An ensemble of 24 reconstructions of May-to-September regional mean temperature was derived from 22 maximum density tree-ring site chronologies distributed over the larger Pyrenees area. Four different tree-ring series standardization procedures were applied, combining two detrending methods: 300-yr spline and the regional curve standardization (RCS). Additionally, different methodological variants for the regional chronology were generated by using three different aggregation methods. Calibration verification trials were performed in split periods and using two methods: regression and a simple variance matching. The resulting set of temperature reconstructions was compared with climate simulations performed with global (ECHO-G) and regional (MM5) climate models. The 24 variants of May-to-September temperature reconstructions reveal a generally coherent pattern of inter-annual to multi-centennial temperature variations in the Pyrenees region for the last 750 yr. However, some reconstructions display a marked positive trend for the entire length of the reconstruction, pointing out that the application of the RCS method to a suboptimal set of samples may lead to unreliable results. Climate model simulations agree with the tree-ring based reconstructions at multi-decadal time scales, suggesting solar variability and volcanism as the main factors controlling preindustrial mean temperature variations in the Pyrenees. Nevertheless, the comparison also highlights differences with the reconstructions, mainly in the amplitude of past temperature variations and in the 20th century trends. Neither proxy-based reconstructions nor model simulations are able to perfectly track the temperature variations of the instrumental record, suggesting that both approximations still need further improvements.

Geología y composición de materias primas magmáticas neógenas de Catalunya

El volcanismo neógeno catalán se divide en 3 áreas: Cordillera Transversal o área de La Garrotxa, El Emporda y La Selva. Se han realizado análisis químicos de los materiales de los afloramientos principales, así como un estudio mineralógico mediante difractometria de rayos X y estudio de láminas delgadas al microscopio óptico. Se ha visto que son lavas relativamente homogéneas pertenecientes al grupo de los basaltos y basanitas. El empleo de la microscopía de calefacción permitió conocer la variación de la viscosidad de estos materiales con el aumento de la temperatura, viendo que funden a temperaturas relativamente bajas.