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Borisova A.Y.,French National Center for Scientific Research | Borisova A.Y.,Moscow State University | Toutain J.-P.,French National Center for Scientific Research | Toutain J.-P.,Institute Of Recherche Pour Developpement | And 3 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2012

To constrain the temporal evolution of the fluid-magma system responsible for the 2010 Eyjafjallajkull eruption (20 March to 20 May, 2010, Southern Iceland), we investigated the volatile, major, trace element, and Sr-Nd-Pb isotopic compositions of bulk lapilli and ash samples representing different stages of the eruption. In addition, we analyzed ash leachates and volcanic plume-derived aerosols sampled over Southern Europe in early May 2010. Available remote-sensing data for the total mass of SO2 liberated in the 2010 eruption, together with data obtained in this study, suggest that the high explosivity of the 2010 sub-plinian Eyjafjallajkull eruption was caused by saturation of the pre-eruptive hybrid trachyandesitic magma with aqueous fluid. We hypothesize that the bulk of the aqueous fluid had been dissolved in the trachydacitic melt at least since the eruption of 1821-1823. The trachydacitic melt was enriched in volatiles, large-ion lithophile elements, and high field strength elements, a composition similar to that of oceanic sediments. The Sr-Nd-Pb isotopic data obtained in this study, combined with existing O isotopic data on bulk 2010 Eyjafjallajkull lapilli and ashes, demonstrate that this melt enrichment was due to its primary source being hydrous oceanic lithosphere entrained in a deep mantle plume rather than shallow hydrothermally altered crust. The hypothesized strong crystal fractionation of plume-derived mafic melts (crystallized fraction >90%) from an enriched mantle source can explain the observed high explosivity of silicic and hybrid Icelandic magmas, especially those of the southeastern volcanic zone (Eyjafjallajkull, Katla, and Hekla). Copyright 2012 by the American Geophysical Union. Source


Borisova A.Y.,Geosciences Environnement Toulouse | Borisova A.Y.,Moscow State University | Toutain J.-P.,Geosciences Environnement Toulouse | Toutain J.-P.,Institute Of Recherche Pour Developpement | And 4 more authors.
Bulletin of Volcanology | Year: 2014

The factors that trigger explosive eruptions often remain elusive because of the lack of direct data from representative samples. Here, we report the first micro-Raman spectroscopy measurements of fluid and multiphase inclusions trapped in quartz xenocrysts and microlites from andesitic lavas and basaltic enclaves of the 1991 Mount Pinatubo eruption. Our analyses reveal two-phase H2O-CO2-S inclusions containing a CO2-dominated phase and an aqueous sulfate-bearing liquid phase and, less commonly, anhydrite (CaSO4(solid)). The two fluid phases are low-temperature products of a supercritical H2O-CO2-S fluid which was associated with a hydrous silicate melt prior to eruption. The average density of the CO2 phase is 0.4 ± 0.2 g/cm3 at room temperature, corresponding to a supercritical fluid density of 0.6 ± 0.1 g/cm3 at the conditions of entrapment at 760-1000 °C and up to ∼260 MPa. For the first time, a dense CO2-bearing fluid is reported in Mount Pinatubo volcanic samples. We suggest that this hybrid H2O-CO2-S fluid originated from mixing between sulfur-rich basaltic and hydrous dacitic magmas, as the former was intruded into and interacted with the pre-eruptive Mount Pinatubo dacite magma reservoir, at depths of at least 10 km. Thermodynamic modeling demonstrates that part of the SO2 liberated from the intruded basaltic magma was consumed via interaction with the aqueous fluid-saturated dacitic magma according to the reaction 4SO2 basalt + 4H2Odacite = 3HSO4 - + H2S + 3H+, yielding early Cu-rich sulfides, late abundant anhydrite, and SO4-rich apatites, which are commonly found in the Mount Pinatubo dacites. We suggest that this hybrid H2O-CO2-S fluid played an important role in triggering the 1991 climactic eruption. © 2014 Springer-Verlag Berlin Heidelberg. Source


Cordeiro R.C.,Federal University of Fluminense | Cordeiro R.C.,Institute Of Recherche Pour Developpement | Cordeiro R.C.,University of Antofagasta | Turcq B.,Federal University of Fluminense | And 24 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

We present a geochemical record of a 113.6-cm sediment core (LPT V) from Lagoa da Pata, which is located in the forested upper Rio Negro basin. The record reveals significant changes in the environmental history of Amazonia during the late Quaternary. The results of biogeochemical analyses revealed three hydrological and climatic regimes from 50,000 to 10,000calyr BP. The first phase, between 50,000 and 26,300calyr BP, was characterized by a relatively wet climate as suggested by relatively high total organic carbon (TOC) and chlorophyll derivate concentrations, indicating high productivity linked to a high lake level. A decrease of the TOC and chlorophyll derivate accumulation rates between 43,100calyr BP and 26,300calyr BP marks a decrease in the productivity linked to a reduced lake level, indicating a decrease in moisture at the end of this phase. The second phase, between 26,300 and 15,300calyr BP, was characterized by a decrease in productivity, reaching a minimum at 21,950calyr BP, as indicated by a minima in sedimentary chlorophyll and TOC accumulation rates. Values of δ13C increased by 5‰ in relation to the preceding phase, indicating an influence of the C4 organic matter. High iron concentrations and accumulation rates, related to intense erosion of the lateritic crust in the watershed, were observed. All of the observations indicate a dry phase during this period. A third phase, from approximately 15,300 to 10,000calyr BP, was characterized by an increase in lacustrine productivity, as shown by an increased in TOC and chlorophyll derivate concentrations and accumulation rates. These increases likely correspond to a lake level rise due to a wetter climate. © 2010. Source

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