Descripción geoquímica y geocronológica de secuencias volcánicas neógenas de Trasarco, en el extremo oriental de la Cadena Volcánica Transversal del Quevar (Noroeste de Argentina)

New geochronological data (34) and 39 new geochemical analyses have been made in the Neogene backarc volcanic sequences in the “El Quevar Transversal Volcanic Chain” defined by Viramonte et al (1984a). This chain starts at the present N-S arc with WNW-ESE trend. New volcanic centres have been recognised and analysed at the eastern end of this chain. The different pulses from each volcanic centre (Aguas Calientes, Acay, El Morro - Organullo and Tocomar) are petrographically and geochemically homogeneous. This suggests that the magma chambers related in each volcano, were geochemically homogeneous and did not have crystal enriched sectors. The Acay eruptive centre is an exception of this assumption; a compositionally differentiated magmatic chamber could be inferred. The isotopic composition of the Aguas Calientes emission centre has a crust signature in its origin, related with melts generated by crustal fussion. The geochronological determinations show volcanic pulses at 17-19 Ma, 13-12 Ma, 10 Ma, 7-6 Ma, 1-0.5 Ma in this region of the Central Andes

Potential renewable energy resources of the Lerma Valley, Salta, Argentina for its strategic territorial planning

Renewable energy sources are considered as strategic opportunities to improve the population's quality of life, to promote the development of more efficient and equitable economic systems, and to favor environmental sustainability in the territorial planning of Lerma Valley (Salta, Argentina). The mapping in raster format (each pixel having a reference value) of the potential renewable energy sources (solar, wind, biomass, hydraulic, mixed) is essential to define ideal locations for different types of renewable applications, and to plan suitable strategies for its implementation. It is necessary considering environmental diversity and site conditions (topographic, natural resource, infrastructure and service availability, social and economical) of the intervention area. Different methodologies are used for mapping of potential energy resources. Solar radiation is spatialized through the application of statistical regressions between altitude, latitude, precise incident solar radiation records, and radiation data estimated with the Geosol V.2.0.(TM) software. The Argentina Map program is used for the wind potential resource modeling. It requires as inputs: a Digital Elevation Model, a land use and cover map (to determine roughness), and measured and/or estimated wind speed and frequency data. The hydroelectric potential for microturbine applications is calculated from the topographic drop and the annual mean flow in cumulative models, through the application of the Idrisi Kilimanjaro(TM)'s runoff tool; while the power densities are compared at the watershed. Biomass potential (at this exploratory stage), is interpreted from the available biomass type (land use and cover map), its energy application availability, and some quantitative indicators associated with the biomass types identified as priority. In conclusion, the renewable energy potential in Lerma Valley is very high and diverse, and its close connection with social-environmental conditions is basic for the creation of energy resource-related territorial plans.Renewable energy Territorial planning Potential energy resources GIS

Long-range volcanic ash transport and fallout during the 2008 eruption of Chaitén volcano, Chile

The May 2008 eruption of Chaitén volcano, Chile, provided a rare opportunity to measure the long-range transport of volcanic emissions and characteristics of a widely-dispersed terrestrial ash deposit. Airborne ash mass, quantified using thermal infrared satellite remote sensing, ranged between 0.2 and 0.4 Tg during the period 3–7 May 2008. A high level of spatiotemporal correspondence was observed between cloud trajectories and changes in surface reflectivity, which was inferred to indicate ash deposition. The evolution of the deposit was mapped for the first time using satellite-based observations of surface reflectivity.The distal (>80 km) ash deposit was poorly sorted and fine grained, and mean particle size varied very little beyond a distance >300 km. There were three particle size subpopulations in fallout at distances >300 km which mirror those identified in fallout from the 18 May 1980 eruption of Mount St. Helens, known to have a high propensity for aggregation. Discrete temporal sampling and characterisation of fallout demonstrated contributions from specific eruptive phases. Samples collected at the time of deposition were compared to bulk samples collected months after deposition and provided some evidence for winnowing.Experimentally-derived ash leachates had near-neutral pH values and charge balance which indicates minimal quantities of adsorbed acids. X-ray Photoelectron Spectroscopy (XPS) analyses revealed surface enrichments in Ca, Na and Fe and the presence of coatings of mixed Ca-, Na- and Fe-rich salts on ash particles prior to deposition. Low S:Cl ratios in leachates indicate that the eruption had a low S content, and high Cl:F ratios imply gas–ash interaction within a Cl-rich environment. We estimate that ash fallout had potential to scavenge ~42% of total S released into the atmosphere prior to deposition. XPS analyses also revealed ash particle surfaces were strongly enriched in Fe (in contrast to the results from bulk leachate analyses), which suggests that Chaitén ash fallout over oceans had potential to influence productivity in high-nutrient, low-chlorophyl regions of the oceans. Therefore ash particle surface geochemical analysis should be applied to quantify Fe-modulated biologically-forced CO2 draw-down potential of volcanic ash fallout over oceans

New contraints on ages of glasses proposed as Reference Materials for Fission-Track Dating

New analyses have been performed in order to enhance the data-set on the independent ages of four glasses that have been proposed as reference materials for fission-track dating. The results are as follows. Moldavite - repeated 40Ar/39Ar age determinations on samples from deposits from Bohemia and Moravia yielded an average of 14.34 ± 0.08 Ma. This datum agrees with other recent determinations and is significantly younger than the 40Ar/39Ar age of 15.21 ± 0.15 Ma determined in the early 1980s. Macusanite (Peru) - four K-Ar ages ranging from 5.44 ± 0.06 to 5.72±0.12 Ma have been published previously. New 40Ar/39Ar ages gave an average of 5.12 ± 0.04 Ma. Plateau fission-track ages determined using the IRMM-540 certified glass and U and Th thin films for neutron fluence measurements agree better with these new 40Ar/39Ar ages than the previously published ages. Roccastrada glass (Italy) - a new 40Ar/39Ar age, 2.45 ± 0.04 Ma, is consistent with previous determinations. The Quiron obsidian (Argentina) is a recently discovered glass that has been proposed as an additional reference material for its high spontaneous track density (around 100 000 cm-2). Defects that might producem “spurious” tracks are virtually absent. An independent 40Ar/39Ar age of 8.77 ± 0.09 Mamwas determined and is recommended for this glass. We believe that these materials, which will be distributed upon request to fission-track groups, will be very useful for testing system calibrations and experimental procedures