Ultrapotassic volcanic centres as potential paleogeographic indicators : the Mediterranean Tortonian 'salinity crisis', southern Spain

Dated peperites associated with ultrapotassic volcanic centres of the Neogene Volcanic Province of southeast Spain are of particular interest within the complex tectonomagmatic context of the Western Mediterranean because they show clear volcano-sedimentary interactions making them a valuable tool for correlating between Miocene sedimentary basins in the region. Detailed field mapping of two coeval, but geographically separate, ultrapotassic volcanic centres (Zeneta and La Aljorra), and comparison of sedimentary facies and radiometric ages with another at Fortuna, suggest that these centres apparently formed at approximately the same time, late Tortonian, by the same tectonomagmatic process, strike-slip, and in the same, shallow marine, paleogeographical context. Stratigraphic indicators in the Miocene basins suggest that basin-closure initiated in the region during the late Tortonian, prior to the main Mediterranean Messinian salinity crisis. Notably, many of the ultrapotassic volcanic centres are situated close to, and elongated along, the basin margins faults. We suggest, therefore, that movement of basin margin faults that closed the Miocene sedimentary basins causing drying out also facilitated the contemporaneous ascent of ultrapotassic magma. So, volcano-sedimentary interactions may be used to make inferences about both the tectonomagmatic and paleogeographic evolution of a region. In southeast Spain peperites provide evidence that the Tortonian 'salinity crisis' was geographically more widespread, extending to the southeast, than previously recognized

Fluid flow in the subduction channel: Tremolite veins and associated blackwalls in antigoritite (Villa Clara serpentinite mélange, Cuba)

Exotic blocks of massive antigorite-serpentinite (antigoritite) document a deep-seated subduction channel in the Villa Clara serpentinite-matrix mélange, central Cuba. The petrological and geochemical characteristics of antigoritite allow distinguishing two types of rock: i) antigoritite and ii) dolomite-bearing antigoritite. Both types are intimately related in field exposures and represent deep peridotite infiltrated by H2O-CO2 fluid mixtures that triggered antigoritization and local carbonation. Fluid infiltration continued after antigoritization forming a vein network as a potential response to hydrofracturing that precipitated tremolitite in the veins and triggered fluid-antigoritite reaction forming blackwalls. The mineralogical and chemical zoning in the blackwalls (Atg + Chl + Tr adjacent to antigoritite and Chl + Tr adjacent to the tremolitite vein) attest for multi-step metasomatic processes during fluid-rock interaction characterized by advection of infiltrating fluid towards the blackwall and, possibly, by diffusion out of the blackwall towards the fluid-filled vein. Tentative thermodynamic modeling of the blackwall domain Atg + Chl + Tr points vein network formation at 400–500 °C and 5–10 kbar during exhumation in the subduction channel, suggesting the infiltration of deep-seated pressurized fluid that triggered hydrofracturing. The chemical compositions of antigoritites, veins and blackwalls indicate a LILE- and LREE-enriched fluid evolved from the subducting plate, while Srsingle bondNd isotope systematics are compatible with an external fluid composed of a mixture of fluids evolved from sediments and, probably to a lesser extent, altered oceanic crust.This research was funded by projects MICINN PID2019-105625RB-C21 (co-funded by Fondo Europeo de Desarrollo Regional, FEDER), Junta de Andalucía P20_00550, Catalonian project SGR 2014-1661 and the University of Granada. LD acknowledges PhD grant BES-2013-063205 of the Spanish Ministry of Economy and Competitiveness and scholarship of Fundació Universitària Agustí Pedro i Pons. Funding for open access charge: Universidad de Granada / CBUA

Petrología y geoquímica de la ofiolita neoproterozoica de Bou Azzer (Marruecos)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Data for: Constraints of mantle and crustal sources and interaction during orogenesis: a zircon SHRIMP U-Th-Pb and O isotope study of the 'calc-alkaline' Brovales pluton, Ossa-Morena Zone, Iberian Variscan Belt

Supplementary material from: Constraints of mantle and crustal sources and interaction during orogenesis: a zircon SHRIMP U-Th-Pb and O isotope study of the 'calc-alkaline' Brovales pluton, Ossa-Morena Zone, Iberian Variscan Belt. Cambeses et al

Data for: Constraints of mantle and crustal sources and interaction during orogenesis: a zircon SHRIMP U-Th-Pb and O isotope study of the 'calc-alkaline' Brovales pluton, Ossa-Morena Zone, Iberian Variscan Belt

Supplementary material from: Constraints of mantle and crustal sources and interaction during orogenesis: a zircon SHRIMP U-Th-Pb and O isotope study of the 'calc-alkaline' Brovales pluton, Ossa-Morena Zone, Iberian Variscan Belt. Cambeses et al.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Lu-Hf ratios of crustal rocks and their bearing on zircon Hf isotope model ages: The effects of accessories

All other factors being equal, the calculation of zircon Hf two stage model ages (T DM Hf) depends on the particular Lu/Hf value assumed for the magmatic source, the effect being more pronounced as the age difference between zircon and magmatic source increases. It is generally considered that the Lu/Hf measured in the zircon-hosting rock does not represent the composition of the source because of potential garnet or zircon fractionation. Accordingly, most authors either assume a single fixed value for Lu/Hf source , often Lu/Hf≈0.079 to 0.108, or use two alternative models, one for felsic sources, often Lu/Hf≈0.09, and the other for mafic sources, often Lu/Hf≈0.165. In contrast with these opinions, however, here we show that partial melting of peraluminous sources causes little decoupling of Lu from Hf because of similar solubilities of zircon and monazite. Furthermore, the effects of residual garnet are largely compensated by the numerous zircon inclusions that garnet and other residual minerals almost always contain. Partial melting of metaluminous sources may significantly decouple Lu from Hf if allanite and/or titanite are not present in the source, but the effect decreases as the melt fraction increases. Similarly, fractional crystallization of metaluminous magmas may decouple Lu from Hf if amphibole or clinopyroxene begin to crystallize before zircon saturation. The Lu/Hf distribution in 4784 rocks from different regions and ages is lognomal rather than normal, and the calculated medians, i.e. the maximum of the probability density function for the logarithmically transformed Lu/Hf, are Lu/Hf mafic rocks ≈0.08, Lu/Hf felsic rocks ≈0.05, i.e. notably lower than the above-mentioned felsic and mafic magmatic source averages. Magmatic sources may be remarkably heterogeneous with respect to Lu/Hf. Our calculations show that fixed Lu/Hf source values translate the Lu/Hf heterogeneity of the source to the T DM Hf thus producing an artificial distribution of model ages that may be erroneously interpreted as different episodes of crustal growth. Therefore, we propose that the best strategy to calculate two stage Hf model ages of zircon is to use the analytically determined whole-rock Lu/Hf ratio as a proxy of the source. In the case of detrital or inherited zircons, for which no whole-rock information is available, it is advisable first to determine whether they come from a mafic or felsic rock by interpreting cathodoluminescence images, Th/U ratios and other chemical parameters, and then venture an estimate of the Lu/Hf source from the SiO2 average.Fil: Bea, F.. Universidad de Granada; EspañaFil: Montero, P.. Universidad de Granada; EspañaFil: Molina, J.F.. Universidad de Granada; EspañaFil: Scarrow, J.H.. Universidad de Granada; EspañaFil: Cambeses, A.. Universidad de Granada; EspañaFil: Moreno Moreno, Juan Antonio. Universidad de Granada; Españ

Palaeogeography and crustal evolution of the Ossa–Morena Zone, southwest Iberia, and the North Gondwana margin during the Cambro-Ordovician: a review of isotopic evidence

<p>Cambro-Ordovician palaeogeography and fragmentation of the North Gondwana margin is still not very well understood. Here we address this question using isotopic data to consider the crustal evolution and palaeogeographic position of the, North Gondwana, Iberian Massif Ossa–Morena Zone (OMZ). The OMZ preserves a complex tectonomagmatic history: late Neoproterozoic Cadomian orogenesis (ca. 650–550 Ma); Cambro-Ordovician rifting (ca. 540–450 Ma); and Variscan orogenesis (ca. 390–305 Ma). We place this evolution in the context of recent North Gondwana Cambro-Ordovician palaeogeographic reconstructions that suggest more easterly positions, adjacent to the Sahara Metacraton, for other Iberian Massif zones. To do this we compiled an extensive new database of published late Proterozoic–Palaeozoic Nd model ages and detrital and magmatic zircon age data for (i) the Iberian Massif and (ii) North Gondwana Anti-Atlas West African Craton, Tuareg Shield, and Sahara Metacraton. The Nd model ages of OMZ Cambro-Ordovician crustal-derived magmatism and Ediacaran-Ordovician sedimentary rocks range from ca. 1.9 to 1.6 Ga, with a mode ca. 1.7 Ga. They show the greatest affinity with the Tuareg Shield, with limited contribution of more juvenile material from the Anti-Atlas West African Craton. This association is supported by detrital zircons that have Archaean, Palaeoproterozic, and Neoproterozoic radiometric ages similar to the aforementioned Iberian Massif zones. However, an OMZ Mesoproterozoic gap, with no ca. 1.0 Ga cluster, is different from other zones but, once more, similar to the westerly Tuareg Shield distribution. This places the OMZ in a more easterly position than previously thought but still further west than other Iberian zones. It has been proposed that in the Cambro-Ordovician the North Gondwana margin rifted as the Rheic Ocean opened diachronously from west to east. Thus, the more extensive rift-related magmatism in the westerly OMZ than in other, more easterly, Iberian Massif zones fits our new proposed palaeogeographic reconstruction.</p

Insights into the temporal evolution of magma plumbing systems from compositional zoning in clinopyroxene crystals from the Agnano-Monte Spina Plinian eruption (Campi Flegrei, Italy)

The complex sequential compositional zoning of clinopyroxene crystals erupted &lt;5 ka during the Agnano-Monte Spina (A-MS) eruption, which is considered to be the reference event for a future large-scale explosive eruption at Campi Flegrei caldera (Italy), has been characterized in detail. Concentration profiles (20–800 lm long, spacing 2.5–10 lm) of major (Si, Ti, Al, Fe, Mg and Ca) and minor (Mn, Na, Ni and Cr) elements were measured along different directions in the clinopyroxene crystals. The zoning patterns of Fe–Mg and selected elements (e.g., Al, Ti) often consist of two or more compositional plateaus with both sharp and/or slightly diffuse boundaries between the plateaus. Each compositional population results from a growth stage in a distinct Magmatic Environment (ME), which is identified as a defined set of intensive thermodynamic variables (pressure, temperature, bulk composition and fugacity of fluids including oxygen). The large range of chemical compositions of clinopyroxenes reveals the existence of at least four MEs that are characterized by different compositional populations; two of these are dominant. The variation in zoning pattern from one plateau composition to another fingerprints the transfer of the crystal from one ME to another. In combination with Sr isotopic data and thermobarometric estimates, our systematic characterization of clinopyroxene zoning patterns suggests recharge by deep mafic magmas (ME0: Mg# = 85–92) of an evolved shallow reservoir (ME2: Mg# = 70–78). Such a process also led to the formation of a compositionally intermediate environment (ME1: Mg# = 84–80), that is detected in the clinopyroxene zoning pattern. A new method has been developed in this work to evaluate the effective diffusive modifications that affect the concentration profiles of zoned crystals. The application of different diffusion modeling methods indicates that deep and shallow reservoirs beneath the Campi Flegrei caldera were connected to each other over several tens of years until the amount of mafic recharge increased during the last 10–15 years before the A-MS eruption. This study highlights the complex relationships between events of magma recharge and the onset of eruption. Our results provide a contribution to the knowledge of timescales of magmatic processes that have recently occurred beneath the Campi Flegrei caldera, which is useful for risk assessment