Search results for "Geochemistry"
showing 10 items of 2967 documents
Magmatic gas percolation through the old lava dome of El Misti volcano
2017
International audience; The proximity of the major city of Arequipa to El Misti has focused attention on the hazards posed by the active volcano. Since its last major eruption in the fifteenth century, El Misti has experienced a series of modest phreatic eruptions and fluctuating fumarolic activity. Here, we present the first measurements of the compositions of gas emitted from the lava dome in the summit crater. The gas composition is found to be fairly dry with a H2O/SO2 molar ratio of 32 ± 3, a CO2/SO2 molar ratio of 2.7 ± 0.2, a H2S/SO2 molar ratio of 0.23 ± 0.02 and a H2/SO2 molar ratio of 0.012 ± 0.002. This magmatic gas signature with minimal evidence of hydrothermal or wall rock int…
Rapid laccolith intrusion driven by explosive volcanic eruption
2016
Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordón Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ∼0.8 km3. Deformation and conduit flow models indicate laccolith depths of only ∼20–200 m and ov…
Helium and CO2 soil gas emission from Santorini (Greece)
1994
Soil gas investigation is a useful tool to detect active faults. The sudden appearance of soil gas anomalies in zones of deep-reaching faults represents a promising potential precursor of earthquakes and volcanic eruptions. In volcanic areas the development of soil gas monitoring techniques is particularly important, as they can represent, together with remote sensing techniques, the only geochemical methods that can be safely applied during volcanic unrest, when it becomes impossible or too dangerous to sample crater fumaroles. A soil gas survey was carried out in June 1993 at the main island of Thera, in the Santorini volcanic complex. CO2 flux and CO2 and helium concentrations were measu…
Monticchio Lakes
2020
The crater lakes are a natural hazard for the population living near them because they can generate liminic explosions, like as the disaster of Nyos lake (Cameroon 1986), in which 1476 people and thousands of animals died. Crater lakes are able to store magmatic and hydrothermal gases and solubilising them into the water. An overpressure of the dissolved gases can generate a limnic eruption. Italy is characterised by an intense volcanic and seismic activity. Evidences of this past volcanism are the numerous crater lakes in Lazio and Campania. The most famous are Bolsena lakes, Vico, Bracciano, Monticchio lakes, Mezzano, Martignano, Albano, Nemi, Averno. The Monticchio lakes (Piccolo Lake (L…
Water alteration of rocks and soils on Mars at the Spirit rover site in Gusev crater
2005
The cover shows part of the Larry's Lookout panorama, seen from the Mars Exploration Rover (MER) Spirit during its drive up Husband Hill: the summit is about 200 metres from the rover. Six papers this week report in detail on the MER mission. An Analysis compares predictions used to select a landing site with the conditions actually encountered. This ‘ground truth’ will be invaluable for interpreting future remote-sensing data. Surface chemistry suggests that the upper layer of soil may contain 1% meteoritic material. MER provides a unique glimpse of solar transits of the moons Phobos and Deimos. Rover Opportunity examined wind-related processes, and spectroscopy indicates a dry origin for …
Archaean Granitoid–Greenstone Geology of the Southeastern Part of the Kaapvaal Craton
2019
The southeastern Kaapvaal Craton is a Palaeoarchaean granitoid–greenstone terrain. Supracrustal rocks are dominated by metamorphosed mafic–ultramafic volcanic rocks intercalated with minor felsic volcanic and chemical sedimentary rocks, including carbonaceous chert and minor iron formation. Siliciclastic sedimentary rocks are rare. The greenstones occur in the Schapenburg and Dwalile fragments close to the Barberton greenstone belt, the Assegaai, De Kraalen, Witrivier and Commondale fragments in the vicinity of Piet Retief, and the Nondweni and Ilangwe greenstone belts together with several smaller fragments in the southern part of the craton. The greenstones are locally in tectonic contact…
Single zircon ages for two Archean banded migmatitic gneisses from central Zimbabwe
2004
We report new single zircon ages for two Archean banded gneisses from the Shangani Batholith in central Zimbabwe. The ages of ~2.77 and ~2.84 Ga do not support previous views that the area west of the current exposure of the Tokwe Segment was part of an early- to mid-Archean (>2.95 Ga) domain (Sebakwe Proto-craton). The data correspond to ~2.9 to 2.8 Ga dates for TTG granitoids of the Chingezi Suite. Members of this suite occur as intrusions within the south-central part of the Zimbabwe Craton and are associated with contemporaneous felsic volcanic rocks. On the basis of their age distribution, isotopic characteristics and outcrop pattern with respect to the Tokwe Segment, the formation of …
SHRIMP zircon ages for post-Usagaran granitoid and rhyolitic rocks from the Palaeoproterozoic terrain of southwestern Tanzania
2005
We report SHRIMP zircon U-Pb ages for post-Usagaran granitic- to granodioritic intrusives and a rhyolitic agglomerate from the Palaeoproterozoic terrain of southwestern Tanzania. This terrain consists of strongly deformed and metamorphosed rocks ascribed to the ca. 2 Ga Usagaran mobile belt, voluminous post-Usagaran granitoids, and minor supracrustal successions. The southeastern part of this terrain is characterized by the occurrence of little deformed and virtually unmetamorphosed rhyolithic, dacitic and andesitic volcanic rocks which overlie the older Usagaran basement. These rocks extruded between 1820 and 1921 Ma, as documented by SHRIMP zircon ages, which are in good agreement with pr…
Palaeomagnetic investigations of the tertiary and quaternary igneous rocks: IV The tertiary volcanic rocks of the Tokaji mountains, Hungary
1971
Measurements are reported from samples collected at twenty three sites in the Tokaj mountains of north-eastern Hungary. The simplest interpretation of the results is in terms of geomagnetic field reversals, for there is no petrological or magnetic evidence of self reversal or of correlation of oxidation state and magnetic sign. Four magnetic zones satisfy the minimum stratigraphic requirements, speculative use of these zones against theHeirtzler et al. magnetic time scale as a control suggests locating the Miocene-Pliocene boundary at 11.75 my. However it seems probable that much of the lower Sarmatian is not represented in the Tokaj samples, although the scatter of individual readings sugg…
The Permocarboniferous Basin and Range Province of Europe. An Application op Plate Tectonics
1976
Distribution and development of European late Hercynian intermontane troughs and associated volcanicity are related to an upper mantle diapir which formed above two subduction zones during the Hercynian cycle of orogenesis. Lateral spreading of the diapir caused regional extension of the previously folded crust and enabled tholeiitic magmas from the upper mantle and rhyolitic magmas from the lower crust to reach the surface.