Tectonic evolution of Variscan Iberia: Gondwana–Laurussia

An integrated interpretation of the late Paleozoic structural and geochronological record of the Iberian Massif is presented and discussed under the perspective of a Gondwana-Laurussia collision giving way to the Variscan orogen. Compressional and extensional structures developed during the building of the Variscan orogenic crust of Iberia are linked together into major tectonic events operating at lithosphere scale. A review of the tectonometamorphic and magmatic evolution of the IberianMassif reveals backs and forths in the overall conver- gence between Gondwana and Laurussia during theamalgamation of Pangea in late Paleozoic times. Stages dom- inated by lithosphere compression are characterized by subduction, both oceanic and continental, development of magmatic arcs, (over- and under-) thrusting of continental lithosphere, and folding. Variscan convergence re- sulted in the eventual transference of a large allochthonous set of peri-Gondwanan terranes, the Iberian Allochthon, onto the Gondwana mainland. The Iberian Allochthon bears the imprint of previous interaction be- tween Gondwana and Laurussia, including their juxtaposition after the closure of the Rheic Ocean in Lower De- vonian times. Stages governed by lithosphere extension are featured by the opening of two short-lived oceanic basins that dissected previous Variscan orogenic crust, first in the Lower-Middle Devonian, following the closure of the Rheic Ocean, and then in the early Carboniferous, following the emplacement of the peri-Gondwanan allochthon. An additional, major intra-orogenic extensional event in the early-middle Carboniferous dismem- bered the Iberian Allochthon into individual thrust stacks separated by extensional faults and domes. Lateral tec- tonics played an important role through the Variscan orogenesis, especially during the creation of new tectonic blocks separated by intracontinental strike-slip shear zones in the late stages of continental convergence

Variscan metamorphism and hydrothermalism recorded in lower Cambrian carbonates (Toledo Mountains, Central Iberian Zone, Spain)

Las rocas carbonáticas del Cámbrico inferior de la Zona Centroibérica (Formación Calizas de Los Navalucillos) presentan en la localidad de Urda (Toledo) asociaciones minerales que pueden estar producidas por procesos metamórficos variscos. La textura y mineralogía observadas consisten en dominios siliciclásticos de cuarzo + sericita ± micrita en contacto con nódulos carbonáticos con bioclastos de arqueociatos. Los bordes de estos nódulos contienen biotita magnesiana ± clorita-clinocloro ± óxidos y sulfuros de hierro ± feldespato potásico. Fuera de los bordes y en la matriz siliciclástica suelen aparecer biotita magnesiana ± moscovita ± feldespato potásico ± clorita-clinocloro ± titanita ± plagioclasa cálcica y sulfuros de hierro. La modelización P-T-XCO2 indica condiciones de baja presión, temperaturas de 310-355 oC y composición del fluido de 0.05-0.55 XCO2 para producir las paragénesis minerales observadas. En base a estos datos se consideran dos hipótesis: 1) Un metamorfismo regional varisco que afectó a rocas compuestas por cuarzo + sericita + calcita/dolomita. 2) Un metamorfismo de contacto asociado al emplazamiento tardivarisco de un plutón granítico, que generó de forma puntual calor y fluidos hidrotermales de H2O ± CO2. Estos fluidos serían en parte magmáticos-graníticos (>H2O) y en parte metamórficos (>CO2) procedentes de los metasedimentos de contacto.The early Cambrian carbonate rocks of the Central Iberian Zone (Navalucillos Limestone Formation) show in Urda location (Toledo) a mineral paragenesis probably linked to Variscan metamorphic processes. The textures consist in quartz + sericite ± micrite domains that include calcite nodules with archaeocyathan bioclasts and silicate rims of Mg-biotite ± clinochlore ± iron-oxides and sulfides ± K-feldspar. Outside the rims, the silicate phases are Mg-biotite ± muscovite ± K-feldspar ± chlorite-clinochlore ± titanite ± calcic-plagioclase, and iron sulfides. P-T-XCO2 modeling indicates low pressure conditions of metamorphism, low to moderate XCO2 fluid (≈ 0.1-0.5) and a T range of ≈ 300-355 ºC. Two hypothesis are considered: 1) Regional metamorphism of a quartz + sericite + calcite/dolomite assemblage. 2) Infiltration of the carbonate rocks by H2O ± CO2 external fluids, magmatic/metamorphic derived. This consists in hydrothermal inputs from a local source (granite intrusions) and from dehydration of contact sediments. The high variability of the isotopic δ18O values in the carbonates supports this hypothesis.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)pu

Half-sandwich isocyanide, phosphine, methyl and phosphanido pentamethylcyclopentadienylniobium(V) complexes

[NbCp★Cl4] Cp★ = ν5-C5Me5) reacts with one molar equivalent of isocyanides and phosphines to give pseudo-octahedral adducts [NbCp★Cl4·L], (Full-size image (<1 K), 4) and the dinuclear complex [∗[NbCp★Cl4∗]2(μ-dmpe)], 5. Reactions of [NbCp★Cl4] with appropriate amounts of MgClMe yield the correspodning dimethyl [NbCp★Cl2Me2], 6, and tetramethyl [NbCp★Me4], 7 derivatives. Similarly, when [∗[NbCp★Cl3∗2(μ-O)] an and 3 are treated with the alkylating magnesium reagent, [∗[NbCp★Me3∗]2(μ-O)], 8, and [NbCp★Cl3Me(PMe2Ph)], 9, are obtained in high yields. A new phosphanido-niobium(V) complex [NbCp★Cl3(PPh2)] 10, is formed in the reaction of the starting tetrachloro complex with one equivalent of LiPPh2. All the complexes were characterized by IR and NMR spectroscopy, and most of them were studied by mass spectrometry

Subduction and syn-collisional exhumation of a Paleozoic continental margin: an integrated study based on structures and P-T paths of the Basal Units in the Ordenes Complex (Galicia, Spain)

According to their metamorphic evolution, the Basal Units of the Galician Allochthonous Complexes are thought to represent a part of the margin of the Paleozoic Gondwana, subducted at the onset of the Variscan Orogeny. Variations in the P-T conditions of the first HP metamorphic event along the units suggest an important westward component for the direction of sucduction. Subsequent underthrusting of more continental material blocked the subduction and triggered the ascent and exhumation of the Basal Units whereas the convergence continued. Compressional and extensional structures were synchronous or alternated in time and, together, induced the thinning and tapering of the orogenic wedge. The unroofing took place locally under an inverted temperature gradient, caused by a detachment which carried a part of the hot mantle wedge, above the subduction zone, over the subducted units

Variscan exhumation of a subducted Paleozoic continental margin: The basal units of the Ordenes Complex, Galicia, NW Spain

A structural and metamorphic study was carried out in the basal units of the Ordenes Complex in Spain, thought to represent a subducted part of the Paleozoic margin of Gondwana. According to their metamorphic evolution, this part of the margin was subducted at the onset of the Variscan Orogeny, becoming part of an accretionary complex developed below a colliding element built previously. Variations in the PT conditions of the first high-pressure metamorphic event along the units indicate a polarity of the subduction to the west. Subsequent underthrusting of more continental material blocked the subduction and triggered the ascent and exhumation of the basal units, whereas the convergence continued. Recumbent folds and thrusts de ve loped along with successive normal detachments. Compressional and extensional structures were synchronous or alternated in time and together induced the thinning and tapering of the orogenic wedge and its lateral spreading. The unroofing took place locally under an inverted temperature gradient caused by a detachment which carried a part of the hot mantle wedge above the subduction zone over the subducted units

Level of blood pressure control in a hypertensive population when measurements are performed outside the clinical setting

Background: To determine whether the number of optimally controlled hypertensive patients is higher using self-measurement of blood pressure at home and ambulatory monitoring, compared to using conventional blood pressure measurements at the doctor&#8217;s office. Method: An observational, cross-sectional, multicentre, descriptive study of a random sample of 237 primary health care patients, known to be hypertensive, from Badajoz (Spain). Blood pressure was measured at the doctor&#8217;s office and by self-measurement at home. Those patients showing good control by self-measurement were subjected to 24-hour ambulatory monitoring. Optimal control was understood as blood pressure < 140/90 mm Hg when measured at the doctor&#8217;s office, and < 135/85 mm Hg when self-measured at home and by daytime ambulatory monitoring. Results: Mean systolic/diastolic measurements at the doctor&#8217;s office and by self-measurement were 145.6/83.9 and 134.0/78.7 mm Hg, respectively (p < 0.000). In the population optimally controlled by self-measurement and who subsequently received ambulatory monitoring, the mean blood pressure was 121.8/73.4 and 125.6/76.2 mm Hg, respectively (p = 0.002; p < 0.000). When measured at the doctor&#8217;s office blood pressure was controlled in about 29.5% (95% CI 23.7-35.3%) of patients, in 38% when self-measured (95% CI 31.4-44.2%; p < 0.000), and in 24.5% when it was confirmed through ambulatory monitoring (95% CI 15.4-33.6%). Sensitivity and positive predictive values of the office measurements for the detection of patients who were well-controlled by self-measurement were 50% and 64.3%, respectively, and 53.4% and 73.8% as regards ambulatory monitoring. Conclusions: A higher level of control is achieved with self-measurement at home not confirmed by ambulatory monitoring. Therefore, the white coat effect does not seem to influence the percentage of well-controlled patients detected at the doctor&#8217;s office. Office blood pressure does not appear to be useful in distinguishing which individual patients are optimally controlled

Mapa Geológico de España E 1:200000, hoja 69, Pozoblanco

Peer reviewe

Space and time in the tectonic evolution of the northwestern Iberian Massif: Implications for the Variscan belt.

Recent advances in geochemical studies of igneous rocks, isotopic age data for magmatism and metamorphism, quantitative pressure-temperature (P-T) estimates of metamorphic evolution, and structural geology in the northwestern Iberian Massif are integrated into a synthesis of the tectonic evolution that places the autochthonous and allochthonous terranes in the framework of Paleozoic plate tectonics. Because northwestern Iberia is free from strike-slip faults of continental scale, it is retrodeformable and preserves valuable information about the orthogonal component of convergence of Gondwana with Laurentia and/or Baltica, and the opening and closure of the Rheic Ocean. The evolution deduced for northwest Iberia is extended to the rest of the Variscan belt in an attempt to develop a three-dimensional interpretation that assigns great importance to the transcurrent components of convergence. Dominant Carboniferous dextral transpression following large Devonian and Early Carboniferous thrusting and recumbent folding is invoked to explain the complexity of the belt without requiring a large number of peri-Gondwanan terranes, and its ophiolites and highpressure allochthonous units are related to a single oceanic closure. Palinspastic reconstruction of the Variscan massifs and zones cannot be achieved without restoration of terrane transport along the colliding plate margins. A schematic reconstruction is proposed that involves postcollisional strike-slip displacement of ~3000 km between Laurussia and Gondwana during the Carboniferous