Elements traça en esfalerites i galenes del dipòsit de Cierco (Pb-Zn), Alta Ribagorça, Pirineu Central

El diposit consisteix en dos filons E-W, tallats per un altre N-S. El rebliment filonia és zonat amb esfalerita- galena-calcita als nivells profunds i galena-baritina als superiors. Els elements traca en esfalerites i galenes, plenament separades, han estat analitzats mitjancant fluoresckncia de raigs X. Els resultats mostren que l'esfalerita concentra la majoria d'elements traca, preferentment Fe, Co, Cd, Sn, Sb, Ga, Cu, Ge i Ag, amb una bona correlació entre els sis primers. La galena concentra únicament Sb, Ag i As, amb bona correlació entre els dos primers. Els continguts en elements traca estan homogkniament distribuits en tot el diposit

Elements traça en esfalerites i galenes del dipòsit de Cierco (Pb-Zn). Alta Ribagorça, Pirineu Central

El diposit consisteix en dos filons E-W, tallats per un altre N-S. El rebliment filonia ès zonat amb esfalerita- galena-calcita als nivells profunds i galena-baritina als superiors. Els elements traça en esfalerites i galenes, plenament separades, han estat analitzats mitjancant fluorescència de raigs X. Els resultats mostren que l'esfalerita concentra la majoria d'elements traça, preferentment Fe, Co, Cd, Sn, Sb, Ga, Cu, Ge i Ag, amb una bona correlació entre els sis primers. La galena concentra únicament Sb, Ag i As, amb bona correlació entre els dos primers. Els continguts en elements traça estan homogèniament distribuits en tot el diposit

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

Variscan and Alpine structure of the hills of Barcelona: geology in an urban area

Line 9 of the underground railway is currently being constructed in Barcelona. This undertaking necessitates tunnelling through a number of hills that are mainly made up of Paleozoic rocks, which exhibit a complex structure due to the superposition of Variscan, Mesozoic, Paleogene, and Neogene structures. We present a geological map of the hills of Barcelona originally compiled at 1:5000 scale. Unpublished field notes from surveys carried out in the 1940s and in the early 1970s were crucial for drawing up this detailed map, which together with subsurface data from public works and our study of the few remaining outcrops, enabled us to provide fresh insights into the structure of this area. We also discuss the age of the structures on the basis of cross-cutting relationships and regional considerations. Our conclusions highlight the ongoing need for a geological survey of cities given that our understanding of their geology depends on impermanent outcrops and on the recovery of lost subsurface data. These considerations call for a suitable management of the geological information in urban areas with a complex geology for planning and developing safe infrastructures

Correlación 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 (Canigó, Roc de Frausa and Cap de Creus massifs) confirm the presence of Neoproterozoic series in the Pyrenees, as the Balaig micaschists in the Canigó 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 geocronológicos en rocas ígneas pre-variscas del Pirineo oriental (macizos del Canigó, 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 Canigó 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 ordovícica inferior) para los protolitos intruidos en niveles distintos de la serie.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEMinisterio de Ciencia e Innovación (MICINN)Consolider-Ingenio 2010pu

Comparative geochemical study on Furongian-earliest Ordovician (Toledanian) and Ordovician (Sardic) felsic magmatic events in south-western Europe: underplating of hot mafic magmas linked to the opening of the Rheic Ocean

A geochemical comparison of early Palaeozoic felsic magmatic episodes throughout the south-western European margin of Gondwana is made and includes (i) Furongian-Early Ordovician (Toledanian) activities recorded in the Central Iberian and Galicia-Trás-os-Montes zones of the Iberian Massif, and (ii) Early-Late Ordovician (Sardic) activities in the Eastern Pyrenees, Occitan Domain (Albigeois, Montagne Noire and Mouthoumet massifs) and Sardinia. Both phases are related to uplift and denudation of an inherited palaeorelief, and stratigraphically preserved as distinct angular discordances and paraconformities involving gaps of up to 22 million years. The geochemical features of the predominantly felsic Toledanian and Sardic activities point to a predominance of magmatic byproducts derived from the melting of metasedimentary rocks, rich in SiO2 and K2O and with a peraluminous character. Zr ∕ TiO2, Zr ∕ Nb, Nb ∕ Y and Zr vs. Ga ∕ Al ratios, and rare-earth element (REE) and εNd(t) values suggest the contemporaneity, for both phases, of two geochemical scenarios characterized by arc and extensional features evolving to distinct extensional and rifting conditions associated with the final outpouring of mafic tholeiite-dominant lava flows. The Toledanian and Sardic magmatic phases are linked to neither metamorphism nor penetrative deformation; on the contrary, their unconformities are associated with foliation-free open folds subsequently affected by the Variscan deformation. The geochemical and structural framework precludes subduction-generated melts reaching the crust in a magmatic arc-to-back-arc setting and favours partial melting of sediments and/or granitoids in the lower continental crust triggered by the underplating of hot mafic magmas related to the opening of the Rheic Ocean

New geoelectrical characterization of a continental collision zone in the Central - Eastern Pyrenees: Constraints from 3-D joint inversion of electromagnetic data

Continent-continent collisions are responsible for the formation of large mountain ranges like the Himalayas and the Alps and play a primary role in the development of the continents. The continental collision between the Iberian and European plates during the Alpine Orogeny resulted in the formation of the Pyrenees. In this study new electromagnetic data from the Eastern Pyrenees were complemented with older data from the Central Pyrenees, constraining the physical and geological processes at the eastern end of the Pyrenean mountain range. The electrical resistivity distribution beneath the Central-Eastern Pyrenees was characterized by means of three-dimensional (3-D) joint inversion of three electromagnetic datasets: (1) the MT impedance tensor (Z), (2) the geomagnetic transfer function (T), and (3) the inter-station horizontal magnetic transfer function (H). The main finding was the non-continuity to the east of the major conductive anomaly observed previously beneath the Central and West-Central Pyrenees related to partial melting of the Iberian subducted lower crust. Lower amounts of water (related to the presence of muscovite and biotite) in the subducted lower crust beneath the Eastern Pyrenees were suggested to explain the lack of partial melting in this part of the mountain range. The electrical resistivity model also revealed higher electrical resistivity values for the lithospheric mantle beneath the Eastern Pyrenees than beneath the Central Pyrenees, thus supporting the hypothesis of an heterogeneous Iberian plate inherited from the Variscan Orogeny. A less clear signature was the lateral variation along the strike direction of the lithosphere-asthenosphere boundary beneath the Eastern Pyrenees (relatively flat, between 110 km and 140 km depth) and the Central Pyrenees (north dipping, between 80 km and 120 km depth beneath the Iberian Plate and between 110 km and 160 km depth beneath the European plate), supporting the hypothesis of a missing lithospheric root beneath the Eastern Pyrenees

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 Jújols 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

Cadomian metabasites of the Eastern Pyrenees revisited

This study presents a new geochemical, petrological, and geochronological U-Pb dataset from Ediacaran metabasites of the Canigó and Cap de Creus massifs, Eastern Pyrenees. The rocks are composed of calcic amphibole + plagioclase + chlorite + epidote ± quartz plus titanite + apatite + ilmenite ± biotite ± rutile as accessory phases and show relict igneous textures. Peak pressure-temperature determinations share common conditions, ranging 452-482ºC and 5.2-7.7kbar. These intermediate P-T conditions suggest Barrovian-type metamorphism, most likely related to a collisional setting. The metabasites correspond to evolved basaltic rocks (Mg#<0.55) with moderate TiO2 content (up to 2.08wt.%) and relatively low Cr (43-416ppm). The rocks are moderately enriched in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) (average (La/Lu)n of 2.7) and the N-MORB normalized multi-element patterns show negative slopes, with prominent negative Nb anomalies ((Nb/La)NMORB=0.33-0.78). These variations are akin to island arc tholeiites generated in back-arc basins and to other metabasites described in the Eastern Pyrenees with a putative Ediacaran age, and they differ from the Ordovician tholeiitic metabasites from the Canigó massif, which derived from a contaminated E-MORB source. The positive ƐNd(T) values (0.82-3.05) of the studied metabasites preclude a notable contribution from an older continental crust. U-Pb dating (LA-ICP-MS) of one chlorite-rich schist sample in contact with the metabasites from the Canigó massif yielded a main peak at ca. 632Ma. We argue that the Cadomian metabasites from the Pyrenees formed during back-arc extension in the continental margin of Gondwana and were later affected by (probably early Variscan) medium-P metamorphism before the HT-LP metamorphism classically described in the Pyrenees