Search results for "chemistry [Water]"
showing 10 items of 2369 documents
Geochronology of the Hout River Shear Zone and the metamorphism in the Southern Marginal Zone of the Limpopo Belt, Southern Africa
2001
Abstract In this paper monazite U–Pb and zircon evaporation dates, stepleaching Pb/Pb results on garnet, staurolite and kyanite, and hornblende Ar/Ar data are presented which constrain the timing of granulite facies metamorphism in the Southern Marginal Zone of the Limpopo Belt and its thrusting onto the Kaapvaal Craton. The Southern Marginal Zone of the Limpopo Belt is considered to be a lower crustal equivalent of the northern Kaapvaal Craton. Granulite exhumation is associated with southward thrusting along the Hout River Shear Zone which is a set of thrust and strike slip shear zones. Zircon ages for the Matok Intrusive Complex which was emplaced within the zone during this thrusting (c…
Magmatic degassing of multicomponent vapors and assessment of magma depth: application to Vulcano Island (Italy)
2001
Degassing of magmatic H2O, CO2 and rare gases plays a major role in understanding large-scale Earth processes and in the assessment of volcanic activity. Here we describe a quantitative model for magmatic degassing of H2O–CO2–noble gas–N2 mixtures. Our modeling takes into account non-ideal behaviors by adopting recently developed approaches for the solubility of H2O–CO2 mixtures in silicate liquids and for noble gas partitioning in H2O–CO2 bearing magmas. This new approach allows quantitative treatment of inert gas fractionation throughout the degassing of any H2O–CO2 bearing natural magma in a wide range of thermo-baric conditions. Magma degassing simulations performed by our model have cl…
Zircon ages defining deposition of the Palaeoproterozoic Soutpansberg Group and further evidence for Eoarchaean crust in South Africa
2014
Abstract The precise age of the volcano-sedimentary Soutpansberg Group, which was deposited upon the Palala shear belt separating the Kaapvaal Craton from the Central Zone of the Limpopo Belt, has long been debated. The Soutpansberg Group is subdivided into a lower and upper succession, which are separated from each other by a prominent regional unconformity. Zircon grains from silicic pyroclastic rocks of both successions were investigated in order to constrain the timing of deposition of the Soutpansberg Group rocks. The zircon grains of the investigated samples from both successions yield a wide range of ages, spanning from 1831 to 3937 Ma. Most of the zircon grains have rounded shapes, …
Major and trace element geochemistry of neutral and acidic thermal springs at El Chichón volcano, Mexico
2008
Abstract Four groups of thermal springs with temperatures from 50 to 80 °C are located on the S–SW–W slopes of El Chichon volcano, a composite dome-tephra edifice, which exploded in 1982 with a 1 km wide, 160 m deep crater left. Very dynamic thermal activity inside the crater (variations in chemistry and migration of pools and fumaroles, drastic changes in the crater lake volume and chemistry) contrasts with the stable behavior of the flank hot springs during the time of observations (1974–2005). All known groups of hot springs are located on the contact of the basement and volcanic edifice, and only on the W–SW–S slopes of the volcano at almost same elevations 600–650 m asl and less than 3…
The aquatic geochemistry of arsenic in volcanic groundwaters from southern Italy
2003
Abstract This paper discusses the abundance, speciation and mobility of As in groundwater systems from active volcanic areas in Italy. Using literature data and new additional determinations, the main geochemical processes controlling the fate of As during gas–water–rock interaction in these systems are examined. Arsenic concentrations in the fluids range from 0.1 to 6940 μg/l, with wide differences observed among the different volcanoes and within each area. The dependence of As content on water temperature, pH, redox potential and major ions is investigated. Results demonstrate that As concentrations are highest where active hydrothermal circulation takes place at shallow levels, i.e. at …
Aspects of the kinematic history and mechanisms of superposition of the proterozoic mobile belts of eastern Central Africa (northern Malawi and south…
1993
Abstract Commonly the Proterozoic tectonic evolution of the Central African basement is subdivided into three major events: (1) the Ubendian (∼2300−1800 Ma), (2) the Irumide (∼1350−950 Ma), and (3) the Pan-African (∼900−450 Ma) orogenic cycles. Relics of the Ubendian event are granite intrusions and, possibly, an amphibolite- to granulite-facies metamorphism. The Ubendian orogeny was followed by deposition of clastic sediments (Muva supergroup). In northern Malawi these sediments and the underlying basement were then thrust to the east-southeast/southeast during the Irumide orogeny. Horizontal shearing along subvertical zones (i.e. the Ubendian belt) was associated with subhorizontal crusta…
Generation of early Archaean grey gneisses through melting of older crust in the eastern Kaapvaal craton, southern Africa
2014
Abstract We report zircon ages, Hf-in-zircon isotopes as well as whole-rock geochemistry and Hf–Nd isotopic systematics for Palaeoarchaean grey gneisses of the Ancient Gneiss Complex of Swaziland, the oldest components of the Kaapvaal craton, southern Africa. The Hf-in-zircon isotopic compositions in these compositionally heterogeneous, multicomponent, migmatitic gneisses are highly variable, even in the oldest zircons dating back to 3.66 Ga, suggesting growth of zircon from melts representing a mix of juvenile and anatectic material derived from differentiated continental crust of Eoarchean to late Hadean age. In contrast, the initial Nd and Hf whole-rock isotopic compositions are frequent…
H2S fluxes from Mt. Etna, Stromboli, and Vulcano (Italy) and implications for the sulfur budget at volcanoes
2005
Abstract We present here new measurements of sulfur dioxide and hydrogen sulfide emissions from Vulcano, Etna, and Stromboli (Italy), made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes. Measurements at the F0 and FA fumaroles on Vulcano yielded SO 2 /H 2 S molar ratios of ≈0.38 and ≈1.4, respectively, from which we estimate an H 2 S flux of 6 to 9 t · d −1 for the summit crater. For Mt. Etna and Stromboli, we found SO 2 /H 2 S molar ratios of ≈20 and ≈15, respectively, which combined with SO 2 flux measurements, suggest H 2 S emission rates of 50 to 113 t · d −1 and 4 to 8 t · d −1 , respectively. We observe that “source” and plume SO 2 /H 2 …
Continuous monitoring of hydrogen and carbon dioxide at Mt Etna
2013
article i nfo This study assessed the use of an H2 fuel cell as an H2-selective sensor for volcano monitoring. The resolution, repeatability, and cross-sensitivity of the sensor were investigated and evaluated under known laboratory conditions. A tailor-made device was developed and used for continuously monitoring H2 and CO2 at Mt Etna throughout 2009 and 2010. The temporal variations of both parameters were strongly correlated with the evolution of the volcanic activity during the monitoring period. In particular, the CO2 flux exhibited long-term variations, while H2 exhibited pulses immediately before the explosive activity that occurred at Mt Etna during 2010.
Tunable diode laser measurements of hydrothermal/volcanic CO<sub>2</sub> and implications for the global CO<sub&am…
2014
Abstract. Quantifying the CO2 flux sustained by low-temperature fumarolic fields in hydrothermal/volcanic environments has remained a challenge, to date. Here, we explored the potential of a commercial infrared tunable laser unit for quantifying such fumarolic volcanic/hydrothermal CO2 fluxes. Our field tests were conducted between April 2013 and March 2014 at Nea Kameni (Santorini, Greece), Hekla and Krýsuvík (Iceland) and Vulcano (Aeolian Islands, Italy). At these sites, the tunable laser was used to measure the path-integrated CO2 mixing ratios along cross sections of the fumaroles' atmospheric plumes. By using a tomographic post-processing routine, we then obtained, for each manifestati…