Person: Gómez Barreiro, Juan
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First Name
Juan
Last Name
Gómez Barreiro
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
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Item Modelo petrogenético de las mineralizaciones de Sn-W asociadas al domo de Martinamor (Salamanca): planteamiento del problema(Macla, 2022) Ortega Menor, Lorena; Bermejo López, Daniel; Castiñeiras García, Pedro; Crespo Feo, María Elena; Barrios Sánchez, Santos; Gómez Barreiro, JuanItem Unraveling the origins and P-T-t evolution of the allochthonous Sobrado unit (Órdenes Complex, NW Spain) using combined U–Pb titanite, monazite and zircon geochronology and rare-earth element (REE) geochemistry(Solid Earth and Discussions, 2020) Benítez Pérez, José Manuel; Castiñeiras García, Pedro; Gómez Barreiro, Juan; Martínez Catalán, José Ramón; Kylander-Clark, Andrew; Holdsworth, RobertThe Sobrado unit, within the upper part of the Órdenes Complex (NW Spain) represents an allochthonous tectonic slice of exhumed high-grade metamorphic rocks formed during a complex sequence of orogenic processes in the middle to lower crust. In order to constrain those processes, U–Pb geochronology and rare-earth element (REE) analyses of accessory minerals in migmatitic paragneiss (monazite, zircon) and mylonitic amphibolites (titanite) were conducted using laser ablation split stream inductively coupled plasma mass spectrometry (LASS-ICP-MS). The youngest metamorphic zircon age obtained coincides with a Middle Devonian concordia monazite age (∼380 Ma) and is interpreted to represent the minimum age of the Sobrado high-P granulite facies metamorphism that occurred during the early stages of the Variscan orogeny. Metamorphic titanite from the mylonitic amphibolites yield a Late Devonian age (∼365 Ma) and track the progressive exhumation of the Sobrado unit. In zircon, cathodoluminescence images and REE analyses allow two aliquots with different origins in the paragneiss to be distinguished. An Early Ordovician age (∼490 Ma) was obtained for metamorphic zircons, although with a large dispersion, related to the evolution of the rock. This age is considered to mark the onset of granulite facies metamorphism in the Sobrado unit under intermediate-P conditions, and related to intrusive magmatism and coeval burial in a magmatic arc setting. A maximum depositional age for the Sobrado unit is established in the late Cambrian (∼511 Ma). The zircon dataset also record several inherited populations. The youngest cogenetic set of zircons yields crystallization ages of 546 and 526 Ma which are thought to be related to the peri-Gondwanan magmatic arc. The additional presence of inherited zircons older than 1000 Ma is interpreted as suggesting a West African Craton provenance.Item Orogenic reworking and reactivation in Central Iberia: A record of Variscan, Permian and Alpine tectonics(Tectonophysics, 2022) Moreno Martín, Diana; Díez Fernández, Rubén; Vicente Muñoz, Gerardo de; Fernández Rodríguez, Carlos; Gómez Barreiro, JuanInterference between orogenic systems and deformation phases within them may lead to reworking and reactivation of previous structures. The eastern sector of the Spanish-Portuguese Central System holds evidence of two orogenic systems, Variscan and Alpine, plus a stage of Permian extension. We perform an integrated structural analysis to identify reworking and reactivation processes throughout the geological record. The Variscan record starts with crustal thickening (D1; E-verging overturned folds). A second phase features the intra-orogenic collapse of an overthickened crust (D2; top-to-the-SE ductile extensional shear zone), which produced intense structural reworking at the core of the shear zone and moderate reworking at its hanging wall. During subsequent strike-slip tectonics, crustal thickening parted transpressional deformation into a dextral shear zone and upright folds (D3). Variscan deformation did not reactivate previous structures, but exploited a weak rheological boundary defined by contrasted lithologies (sedimentary versus igneous rocks) to accommodate D2 shearing. Reactivation played a role afterwards: Variscan strike-slip shear zone acted as a transfer fault to accommodate Permian extension (post-orogenic collapse), and then Alpine contraction. The Permian extension record is blurred by Alpine inversion, although the trend of Alpine structures in Central Iberia, and the Spanish-Portuguese Central System, may result from Permian structural inheritance.Item Morphological and compositional analysis of alluvial gold: The Fresnedoso gold placer (Spain)(Ore Geology Reviews, 2020) Dos Santos Alves, Kelvin; Barrios Sánchez, Santos; Gómez Barreiro, Juan; Merinero Palomares, Raúl; Compaña Prieto, José ManuelThe Fresnedoso creek gold placer (FGP) in the Moraleja Basin (W Iberian Massif) has been investigated in terms of morphological, textural and compositional evolution of gold particles. A mixture of two populations has been identified being coherent with primary sources located at a proximal (2.5–10 km), and distal (20–50 km) range. Shape and compositional evidences suggest recycling of paleoplacers (tertiary) has to be considered to some extend. Primary laminar morphologies point to lode deposits in small-flat veins hosted in the metasediments of the Schist Greywacke Complex. All these features suggest the Fresnedoso creek gold placer is a deposit constituted by with mono- and polycyclic particles. Transport distance – Flattening indexes (CFI, Shilo) models have been tested and result in useful information for exploration of undiscovered deposits, even with a limited dataset. Compositional analysis of gold particle morphotypes has revealed that the Fresnedoso gold is a AuAg bimetallic alloy. Textural and compositional groups include: type 1 (Au1 = Au88-94Ag12-6), type 2 (Au2 = Au99 Ag1) and type 3 (Au3 ~ Au99Ag1). Variations in composition of type 1 (Particle's cores) could reflect differences in primary composition, spatial dispersion of sources or secondary processes, but fit within the compositional range of orogenic gold deposits. Secondary processes have been explored to explain compositional heterogeneity in the particles. Gold type 2 (rim) and 3 (micro-aggregates) represents two different de-alloying stages, from initial Ag-leaching at the rim and/or through grain-boundaries and microfractures (Au2), to complete resetting of primary chemical imprint, pervasive porous texture and Au re-precipitation with Fe-OOH and clays (Au3). A model is proposed which combines: Ag de-alloying enhanced in a Cl-Fe rich environment (lateritic) and the deformation/recrystallization processes related to mechanical cold-work in the river load-bed during transport.Item Epitactic growth of celestite on anhydrite: substrate induced twinning and morphological evolution of aggregates(CrystEngComm, 2020) Forjanes Pérez, Pablo Cayetano; Gómez Barreiro, Juan; Morales, Juan; Astilleros García-Monge, José Manuel; Fernández Díaz, María LourdesEpitactic crystal growth plays a main role in the development of mineral processes and in the synthesis of advanced materials. Celestite (SrSO4) forms epitactic overgrowths on anhydrite (CaSO4) (100), (010) and (001) surfaces upon interacting with Sr-bearing aqueous solutions. Two populations of differently oriented celestite crystals related by symmetry operators of substrate are identified on (001)Anh and (100)Anh anhydrite substrates by SEM observations and synchrotron X-ray diffraction analysis. Substrate-induced twins arise after the coalescence of individuals belonging to these populations. Progressing growth results in a marked morphological evolution of epitactic celestite, whose crystals undergo sustained branching and loss of co-orientation that result in the formation of sheaf-like aggregates, on (100)Anh, and swan-like aggregates, on (001)Anh. We relate this evolution to celestite growth in a Ca-rich environment due to continued anhydrite dissolution and incorporation of small amounts of Ca into celestite structure. This incorporation would induce lattice strain which would be released through the formation of dislocations. The regular arrangement of these dislocations in small-angle boundaries would result in progressive splitting, driving the evolution from celestite single crystals to aggregates. Sharp compositional gradients in the boundary layer could explain the anisotropic development that leads to the formation of the swan-like celestites.