Evolución de la deformación y los fluidos durante el tránsito dúctil-frágil del basamento cristalino Paleozoico de la Cadena Litoral Catalana.

El Turó de les Forques es un horst aislado de la Cadena Litoral Catalana, formado principalmente por filitas ordovícicas, caracterizado por una intensa fracturación que abarca desde el Hercínico al Neógeno. La deformación Hercínica está representada por una foliación muy penetrativa y por venas de quarzo-clorita sinesquistosas y tardiesquistosas de carácter dúctil. La extensión Mesozoica está definida por venas y brechas cementadas por las asociaciones albita-cuarzo-clorita±titanita-rutilo y dolomita-clorita-cuarzo y marca el cambio hacia condiciones de deformación frágiles. La compresión Paleógena genera cabalgamientos y fracturas cementadas por calcita-barita. Finalmente la extensión Neógena está representada por fallas normales que generan harinas de falla y fracturas cementadas por calcita. Tanto la deformación Hercínica como la Mesozoica están relacionadas con un flujo de fluidos local ligados al metamorfismo de bajo grado. En cambio, durante las dos siguientes fases deformativas, el flujo de fluidos se da a nivel de cuenca. La localización de este bloque a lo largo de la evolución de la Cadena Costero Catalana tuvo que jugar un control principal en la formación de las fracturas y paragénesis exclusivas del Turó de les Forques

Influence of basement rocks on fluid evolution during multiphase deformation: the example of the Estamariu thrust in the Pyrenean Axial Zone

Calcite veins precipitated in the Estamariu thrust during two tectonic events decipher the temporal and spatial relationships between deformation and fluid migration in a long-lived thrust and determine the influence of basement rocks on the fluid chemistry during deformation. Structural and petrological observations constrain the timing of fluid migration and vein formation, whilst geochemical analyses (δ13C, δ18O, 87Sr/86Sr, clumped isotope thermometry and elemental composition) 15 of the related calcite cements and host rocks indicate the fluid origin, pathways and extent of fluid-rock interaction. The first tectonic event, recorded by calcite cements Cc1a and Cc2, is related to the Alpine reactivation of the Estamariu thrust, and is characterized by the migration of meteoric fluids, heated at depth (temperatures between 56 and 98 ºC) and interacted with crystalline basement rocks before upflowing through the thrust zone. During the Neogene extension, the Estamariu thrust was reactivated and normal faults and shear fractures with calcite cements Cc3, Cc4 and Cc5 developed. Cc3 and Cc4 precipitated 20 from hydrothermal fluids (temperatures between 127 and 208 ºC and between 102 and 167 ºC, respectively) derived from crystalline basement rocks and expelled through fault zones during deformation. Cc5 precipitated from low temperature meteoric waters percolating from the surface through small shear fractures. The comparison between our results and already published data in other structures from the Pyrenees suggests that regardless of the origin of the fluids and the tectonic context, basement rocks have a significant influence on the fluid chemistry, particularly on the 87Sr/86Sr ratio. Accordingly, the cements 25 precipitated from fluids interacted with crystalline basement rocks have significantly higher 87Sr/86Sr ratios (> 0.710) with respect to those precipitated from fluids that have interacted with the sedimentary cover (< 0.710)

Fluid composition changes in crystalline basement rocks from ductile to brittle regimes

The relationships between deformation and fluid flow have been investigated in the Paleozoic basement of an isolated horst of the Catalan Coastal Ranges. A structural, petrological and geochemical study has been performed in a complex fracture network that resulted from a long-lived tectonic history (from Carboniferous to Miocene). Nine fracture types, developed from a ductile regime in the greenschist facies to a shallow brittle regime, have been characterized in order to establish P, T and fluid compositions during the evolution of the horst. Syncleavage and late-cleavage quartz veins (qtz1-chl1 ± mu and late qtz2-chl2-dol1) formed during the Hercynian ductile deformation. These minerals precipitated from metamorphic fluids, possibly evolved from seawater, at temperatures between 240 and 340 °C. En-echelon albite vein arrays (ab-qtz3-chl3 ± ti-an) and NE-SW normal faults generating breccias mark the change from ductile to brittle, from compression to extension and from a closed to an open hydrologic regime. This paragenesis precipitated from the mixing of metamorphic and magmatic fluids at temperatures between 180 and 290 °C during the early Permian extension. Dolomite veins (dol2-chl4-qtz4), precipitated at 210-280 °C from the mixing of previous fluids with hypersaline oxidizing external brines, possibly during the late stage of the early Permian extension. Reverse faults and calcite veins (Cc1-ba) formed either during the Paleogene compression or during the Langhian to early Serravallian minor compression. Calcite and barite precipitated from meteoric or marine waters in an open hydrological system at temperatures below 50 °C. The Miocene extension is represented by NE-SW normal faults with fault gouges and NNW-SSE normal faults cemented by calcite 2 that precipitated at temperatures below 50 °C from meteoric fluids in an open basin-scale hydrological system. The studied horst was part of a relay zone between two segments of the NNW-SE Llobregat fault during the early Permian, explaining the high fracture density and the fast upflowing of hydrothermal fluids at that time, thus controlling the development of albite veins exclusively in this area

Integració dels sistemes de classificació de les roques: eina d'aprenentatge transversal per al foment d'equips docents en l'àmbit de la Geologia.

As a response to the need to implement a comprehensive tool for the classification of rocks, an interdisciplinary and interuniversity teaching team formed by teachers and students has been constituted. The team develops teaching actions to improve the university learning on petrology and mineralogy. Such actions will have positive repercussions to undergraduates and postgraduates students as well as to secondary and baccalaureate teachers, and to other professional not directly related to teaching. Moreover, with the implementation of such tool will clearly promote the self-learning of students by means of a uniform and common system of classification of rocks aimed to all types of public

Barcelona Rocks, A mobile App to learn Geology in your city.

Barcelona Rocks is an application for personal mobile devices suitable for secondary and high school students as well as the general public without a solid background in Earth Sciences

BCN Rocks: aprendiendo geología urbana a través de una aplicación App interactiva.

Barcelona Rocks (BCN Rocks) es una aplicación (App) para dispositivos móviles personales (con versiones para Android y iOS) apta para ser utilizada por estudiantes de Enseñanza Secundaria Obligatoria (ESO) y Bachillerato, y para el público en general, con el objetivo de aprender geología a partir de recursos didácticos proporcionados por las rocas de las fachadas y pavimentos de dos zonas emblemáticas y céntricas de la ciudad de Barcelona como son el Passeig de Gràcia y el Barri Gòtic. La aplicación presenta tres grandes apartados "ELEMENTOS", "EXPLORA" y "LABORATORIO" que pretenden satisfacer diversas facetas del usuario. En el apartado Elementos, el usuario encontrará el conjunto de edificios que contiene la aplicación, toda la información sobre las rocas que los forman, así como una breve explicación sobre la historia y arquitectura de cada uno de ellos. Con el apartado Explora, se pretende despertar la curiosidad o la parte más expedicionaria del usuario. Para ello se proponen una serie de rutas que pueden realizarse siguiendo, bien el criterio de posición geográfica de los edificios incluidos en la App, bien teniendo en cuenta la antigüedad de las construcciones (desde la Barcino romana hasta la Barcelona actual). Finalmente, el partado Laboratorio, permite al usuario investigar distintos aspectos geológicos mediante experimentos interactivos

Evolución metamórfica de las kinzigitas en facies granulita del macizo del Aglí

In the Agly massif outcrops one of the deepest parts of the Hercynian crust. Its basement is constituted by a monotonous pile of paragneisses and anatectic migmatites which presents numerous intercalations of kinzigites, marbles, calcsilicates and basic rocks. This work describes the main structural and metamorphic features of the kinzigites in order to define the P-T evolution of a granulite facies crustal segment. The main mineral metamorphic association is in equilibrium at the univariant prograde reaction biotite + sillimanite + quartz = cordierite + garnet + K-feldspar + H2O and it is formed synchronously with the development of the regional foliation (S2). Following this association and close to the climax, there is a slight pressure drop recorded in the formation of cordierite coronas around garnet porphyroblasts; finally there is a retrograde stage linked to a high grade extensional event (D3). Petrographic observations in conjunction with Schreinemakers analysis and thermobarometric calculations have enable the construction of a nearlyisobaric P-T path and determine that the metamorphic peak is reached at 790 ºC and 5,5 kbar by the deepest rocks. Assuming a linear gradient it is concluded that the climax is achieved at different times and at different crustal levels and that, af ter the climax, there is an important shor tening of the lithological column consistent with an extensional unroofing

Polyphasic hydrothermal and meteoric fluid regimes during the growth of a segmented fault involving crystalline and carbonate rocks (Barcelona Plain, NE Spain)

A polyphasic tectonic‐fluid system of a fault that involves crystalline and carbonate rocks (Hospital fault, Barcelona Plain) has been inferred from regional to thin section scale observations combined with geochemical analyses. Cathodoluminescence, microprobe analyses and stable isotopy in fracture‐related cements record the circulation of successive alternations of hydrothermal and low‐temperature meteoric fluids linked with three main regional tectonic events. The first event corresponds to the Mesozoic extension, which had two rifting stages, and it is characterized by the independent tectonic activity of two fault segments, namely southern and northern Hospital fault segments. During the Late Permian‐Middle Jurassic rifting, these segments controlled the thickness and distribution of the Triassic sediments. Also, dolomitization was produced in an early stage by Triassic seawater at shallow conditions. During increasing burial, formation of fractures and their dolomite‐related cements took place. Fault activity during the Middle Jurassic-Late Cretaceous rifting was localized in the southern segment, and it was characterized by hydrothermal brines, with temperatures over 180°C, which ascended through this fault segment precipitating quartz, chlorite, and calcite. The second event corresponds to the Paleogene compression (Chattian), which produced exhumation, folding and erosion, favouring the percolation of low‐temperature meteoric fluids which produced the calcitization of the dolostones and of the dolomite cements. The third event is linked with the Neogene extension, where three stages have been identified. During the syn‐rift stage, the southern segment of the Hospital fault grew by tip propagation. In the relay zone, hydrothermal brines with temperature around 140°C upflowed. During the late postrift, the Hospital fault acted as a unique segment and deformation occurred at shallow conditions and under a low‐temperature meteoric regime. Finally, and possibly during the Messinian compression, NW‐SE strike‐slip faults offset the Hospital fault to its current configuration

Identifying metamorphic rocks with the help of the petrographic microscope

El metamorfismo es un proceso que tiene lugar en el interior de la corteza y el manto superior, generalmente asociado a los límites de placas tectónicas, y que da lugar a la formación de rocas metamórficas. Este proceso se caracteriza por un conjunto de cambios en la textura y la mineralogía, en el estado sólido, que experimenta cualquier roca sometida a condiciones de presión y temperatura diferentes a las de su formación, excluyendo los procesos diagenéticos propios de rocas sedimentarias. La clasificación de las rocas metamórficas resulta bastante compleja ya que están constituidas por una gran variedad de minerales y de texturas que a menudo requieren ser identificados con la ayuda del microscopio petrográfico. En las aulas de Secundaria y Bachillerato siempre es un reto para el profesorado la enseñanza de estas rocas. Por ello, en este trabajo se describen los aspectos más relevantes a cerca del metamorfismo y se propone una actividad didáctica la cual incluye fichas de apoyo a la identificación del tipo de metamorfismo y los grupos composicionales y 13 descripciones de rocas metamórficas en lámina delgada

The importance of structural complexity in the localization of geothermalsystems: A case study along the Vallès-Penedès Fault in the Catalan CoastalRanges (NE Spain)

The Vallès-Penedès Fault is a Neogene normal fault marked by the presence of two established geothermalsystems at La Garriga-Samalús and Caldes de Montbuí, within the Catalan Coastal Ranges (NE Spain). Theanalysis and collation of existing and new geological and geophysical datasets provide the basis for the developmentof an improved conceptual model that explains the presence and localization of hot geothermal fluidsystems at relatively shallow depths (e.g., 60 ◦C at surface and 90 ◦C at 1 km). Geothermal flow is concentratedwithin Paleozoic granodiorites of the immediate footwall of the V-P fault, host rocks that are susceptible to faultrelatedfracturing, and the generation of both extension and hybrid fracture systems in association with activefault displacements. Flow localization is enhanced further by the presence of fault-related structural complexities,with both systems marked by 300 m wide steps in the main fault trace. These are attributed to relaydevelopment and breaching characterizing host rocks by high fracture intensities and fault rock development ona fault that locally has a vertical displacement of over 1.5 km. Accentuated fracturing and deformation areconsistent with strain localization predicted by existing models for the development of fault zones along normalfaults. The plumbing of the geothermal systems is attributed to up-fault flow in combination with lateral flowcontrolled by the intersection of the V-P fault with a low-angled Paleogene thrust defining the base of the hostrockgranodiorites, with the geothermal systems localized at the distal end of the thrust. Sustained geothermalflow is attributed to groundwater flow circulation associated with seismic pumping and valving of warmer anddeeper fluids, and the ingress of groundwater along faults and within fractured basement rocks