1,721,026 research outputs found
Non-methane Volatile Organic Compounds (VOCs) at El Chichón volcano (Chiapas, México):Geochemical features, origin and behavior
Full text linkSe presenta un estudio de las características geoquímicas de la fracción orgánica en las fumarolas del volcán Chichón (Estado de Chiapas, México) para obtener información sobre el origen de los compuestos orgánicos volátiles exceptuando el metano (VOCs) y los procesos que rigen su comportamiento. Los VOCs en fumarolas y pozas burbujeantes consisten principalmente de alcanos (C2-C5) cuya abundancia total tiene un orden de magnitud menor que el metano, y concentraciones altas de aromáticos (benceno y tolueno) y C2-C3 alquenos (principalmente propano e iso-butano). Se encontraron también concentraciones significativas de compuestos de azufre substituidos que en su mayoría pertenecen al grupo de los heterocíclicos. Esta composición, similar a la de las emisiones gaseosas relacionadas a sistemas geotérmicos, sugiere que la producción de gases orgánicos en el volcán El Chichón es principalmente debida a procesos termogénicos. La abundancia total de VOCs es relativamente baja en comparación con la composición típica de fluidos hidrotermales, lo que podría estar relacionado a una contribución importante de fluidos de origen magmático al reservorio que alimenta las emisiones termales del cráter. Sin embargo, la ausencia de compuestos de O-substituidos parece indicar que la composición de los fluidos hidrotermales no es afectada por el aporte de especies orgánicas producidas en profundidades someras por la descomposición de material vegetal reciente, como aquél sepultado por los productos de la erupción de 1982.
doi: https://doi.org/10.22201/igeof.00167169p.2009.48.1.10
Light hydrocarbons as redox and temperature indicators in the geothermal field of El Tatio (northern Chile)
No full textEl Tatio (northern Chile), one of the largest geothermal fields of South America, is presently undergoing a new program
of geothermal exploration, after the failure of the first exploration phase in the early 1970s. The geochemical features of the
fluid discharges characterizing this system mainly consist of boiling pools and fumaroles, and represent the result of a complex
mixing process involving 3 main components: (i) hydrothermal; (ii) atmospheric; (iii) magmatic. Chemical reactions
involving light hydrocarbons equilibrate at higher temperature than those directly measured in the geothermal wells and
calculated on the basis of the composition of the inorganic gas species. This suggests that in the deeper parts of the hydrothermal
system temperatures higher than 300 C may be achieved. Such results can have a strong impact for the evaluation
of the potential resources of this geothermal system. Moreover, the chemical characteristics of the organic gas fraction
allow the assessment of the chemical–physical conditions governing the geochemical processes acting on geothermal fluids
at depth
Aquifer-type behaviour of Marnoso-Arenacea formation in Northern Apennines: evidences from hydrogeological monitoring and hydrochemical data
No full textOptimization of an analytical protocol for the determination of trace metals in fumarolic condensates: the case of “La Fossa” crater, Volcano Island, Italy
No full textEvolution of δ11B on tourmaline during prograde contact metamorphism in the thermal aureole of the Adamello batholith (Southern Alps, Italy)
No full textThe Permian continental deposits of the Verrucano Lombardo formation (Southern Alps, Italy) are conglomeratic to pelitic redbeds deriving from the disgregation of vulcanites and of the Variscan basement. In the Forcel Rosso area, this formation underwent high-grade metamorphism and partial melting caused by the emplacement of the Adamello batholith during the Eocene. Tourmaline is ubiquitous in the pelitic and metapelitic layers up to migmatitic conditions and this allowed the investigation of the δ11B evolution during the prograde metamorphic history. Tourmalines δ11B values in the unmetamorphosed pelites show a wide difference between the extremely negative cores, and the positive rims. We interpret the cores to be detrital, while the rims were crystallized at low temperature in equilibrium with high δ11B diagenetic or hydrothermal fluids. This δ11B core-rim variation persists up to the greenschist facies while, from lower amphibolitic facies, tourmaline grains recrystallize and become more homogeneous with δ11B values intermediate between cores and rims. Above the solidus, two types of metatexites were recognized based on the tourmaline δ11B signatures. Type-I metatexites are characterized by euhedral tourmalines showing a very narrow range of positive δ11B values. In Type-II metatexites euhedral tourmalines show slightly negative δ11B composition. In the Forcel Rosso area, Type-I metatexites were formed in an isochemical closed system while Type-II metatexites required the influx of external fluids. Preliminar calculations suggest that the δ11B signature of such external fluids was negative. Based on melt-fluid fractionation factors, if these fluids had been exsolved from a magmatic source, the coexisting melt would have had negative δ11B signature outside the range of I-type granitoids. This advocates for a metamorphic source while excluding the influx of magmatic fluids from the nearby I-type Adamello pluton
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Physical-chemical characteristics of CO2 altered rocks
No full textCarbon capture and storage (CCS) is considered a valid option to reduce the CO2 concentration in atmosphere. The gas is collected from industrial plants, then injected and stored underground in geological reservoirs. A very wide range of information about chemical-physical characteristics of the sequestration site is therefore needed and, among them, data on porosity microstructure are crucial. Part of the processes which affect micro-porosity and act during and after the rock formation can be reconstructed by studying micro-porosity features. In this work, different experimental approaches have been combined to reconstruct the mineral association, bulk chemistry and microporous structure of rocks from a natural CO2 reservoir (which represents a natural analogue of a CCS site). The fluid reservoir, i.e. Caprese Reservoir, was discovered while drilling PSS1 borehole in San Cassiano Basin (Eastern Tuscany, Central Italy) and consists of sedimentary rocks (Burano Fm.) interbedded with altered volcanic rocks, its depth being about 3,300 m with respect to the land surface. At 3,700 m depth fluid pressure and temperature are 700 bars and 120 °C respectively, with a calculated density for CO2 of 860 Kg·m-3. The study was conducted on the volcanic rocks altered by CO2 from the PSS1 wellbore drill cores and on some volcanic rocks unaffected by the presence of CO2. Lastly, rocks from the Burano Formation, unavailable from PSS1, have been sampled on outcrop. Drill core samples corresponding to the depth 3,864-3,871 m with respect to PSS1 log, have been investigated with SEM-EDS, XRD, EMP, ICP-MS and LOI and for the mineralogical and chemical characterization. The SANS/VSANS experiments at LLB (Saclay, France) served for microporous structure investigation of PSS1 rocks, volcanic rocks from Eastern Alps (IG1) and the Albani Hills (IG2 and IG3) unaffected by CO2 and Burano Formation
The hydrothermal-volcanic system of Rincon de la Vieja volcano (Costa Rica): A combined (inorganic and organic) geochemical approach to understanding the origin of the fluid discharges and its possible application to volcanic surveillance
No full textIn the period 1998–2002 thermal spring discharges of Rincon de la Vieja volcano (NW Costa Rica) have been sampled and
analyzed for major, trace and isotopic (18O/16O and D/H in waters and 3He/4He and 13C/12C in CO2 in gases) composition. The
boiling pools hosted inside the summit crater (Active Crater) are characterized by high contents of magmatic-related compounds
(SO2, HCl and HF) that strongly affect the chemistry of the crater lake. These chemical features are not shown by the thermal
discharges seeping out in the surrounding area of the volcano. Here, the shallow aquifer apparently masks any possible clues
related to the magmatic system. This suggests that the fluid vents located inside the Active Crater are likely to represent the
most appropriate sampling sites for geochemical surveillance purposes, although the high gas discharge rate from the lake may
occasionally prevent any fluid sampling. Alternatively, as already suggested by recent studies on the behavior of light
hydrocarbons in different volcanic environments, the compositional features of the organic gas fraction in the more accessible
outer flank thermal discharges could usefully be utilized, at least, to assess the thermodynamic conditions of the volcanichydrothermal
system, since these compounds are affected by secondary processes only at limited extent
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