Search results for "Rhyolite"
showing 10 items of 27 documents
The role of melt-fracture degassing in defusing explosive rhyolite eruptions at volcán Chaitén
2012
Explosive volcanic eruptions of silicic magma often evolve towards non-explosive emissions of lava. The mechanisms underlying this transition remain unclear, however, a widely cited idea holds that shear-induced magma fragmentation plays a critical role by fostering volatile loss from fragmentary magma and through ash-filled cracks termed tuffisite. We test this hypothesis by measuring H2O concentrations within glassy tuffisite from the 2008–2011 rhyolitic eruption at volcan Chaiten, Chile. We show that while H2O concentrations decrease next to tuffisite veins and at the margins of obsidian fragments, the depletions cannot account for the disparity in H2O between explosively and effusively …
Halogen (Cl, F) release during explosive, effusive, and intrusive phases of the 2011 rhyolitic eruption at Cordón Caulle volcano (Chile)
2019
We investigate sulphur, chlorine and fluorine release during explosive, effusive and intrusive phases of the 2011 Cordon Caulle eruption, with a focus on halogen devolatilization. Petrological analysis shows halogen release to have been promoted by isobaric crystallization in slowly-cooled magma that was emplaced in a lava flow and sub-vent intrusion. Fluorine in particular mobilized only after extensive groundmass crystallization and incipient devitrification. By 2017, the gas emitted from vent-proximal fumaroles had hydrothermal compositions, with HCl/HF ratios decreasing with decreasing temperature. We estimate that the eruption could eventually emit up to 0.84 Mt of SO2, 6.3 Mt of HCl, …
Volatiles and trace elements content in melt inclusions from the zoned Green Tuff ignimbrite (Pantelleria, Sicily): petrological inferences
2018
International audience; The island of Pantelleria is one of the best known localities of bimodal mafic-felsic magmatism (alkali basalt and trachyte-pantellerite). Among the felsic rocks, the coexistence in a single eruption of products of both trachyte and pantellerite compositions is limited to few occurrences, the Green Tuff (GT) ignimbrite being one of these. The GT is compositionally zoned from pantellerite (70.1 wt% SiO2, mol Na+K/Al = 1.86, 1871 ppm Zr) at the base to crystal-rich (>30 vol%) comenditic trachyte (63.4 wt% SiO2, mol Na+K/Al = 1.10, 265 ppm Zr) at the top, although the pantellertic compositions dominate the erupted volume. We present here new data on melt inclusions (MIs…
Pliocene tourmaline rhyolite dykes from Ikaria Island in the Aegean back-arc region: geodynamic implications
2009
Very rare rhyolite dykes cross-cutting a Miocene I-type biotite-granite were discovered on Ikaria Island in the Aegean back-arc region. Their intrusion postdates exhumation of the granite to brittle crust at about 6.0-3.6 Ma; hence a Pliocene age is inferred. Petrological, geochemical and isotopic arguments indicate an origin through melting of crustal lithologies (tourmaline greywackes/semipelites) with no detectable contribution from asthenospheric sources. Strontium isotope ratios are relatively low unlike values for sediments entering the Hellenic trench but similar to those for certain Miocene Cycladic I-type granites and low-Rb Permo-Carboniferous Cycladic basement acid orthogneisses.…
�ber den ?Hygrophyllit? im Rotliegenden des Saar-Nahe-Gebietes, ein Beitrag zur Diagenese pyroklastischer Gesteine
1971
In certain areas rhyolitic tuffs of the Upper Rotliegend include a greenish, talc-like substance, called “Hygrophyllit”. It has been found too at the base of the Rotliegend in the Saarland. It is shown, that Hygrophyllit corresponds to decomposed pumice, related to the acid permian volcanism. X-ray, DTA and chemical investigations yielded, that Hygrophyllit consists essentially of a mixed layer mica-Ca-montmorillonite with random interstratification and previously about 33 % expandable layers. In consequence there are in the Rotliegend of the Saar-Nahe-Basin three different diagenetic developments of acid pyroclastic rocks: The formation of Kaolinite in the Lower Rotliegend, of devitrificat…
Evolution of Pan-African island arc assemblages in the southern Red Sea Hills, Sudan, and in southwestern Arabia as exemplified by geochemistry and g…
1991
Kr6ner, A., Linnebacher, P., Stern, R.J., Reischmann, T., Manton, W. and Hussein, I.M., 1991. Evolution of Pan-African island arc assemblages in the southern Red Sea Hills, Sudan, and in southwestern Arabia as exemplified by geochemistry and geochronology. In: R.J. Stern and W.R. van Schmus (Editors), Proterozoic Crustal Evolution in the Late Proterozoic. Precambrian Res., 53:99-117. We report Rb-Sr whole-rock and zircon ages for metavolcanic and plutonic associations in the southeastern part of the Red Sea Hills, Sudan, and show that these rocks constitute one of the earliest Pan-African arc assemblages within the Arabian-Nubian shield. The remarkable similarity in geochemistry and age bet…
Hydrothermal synthesis of zeolites from rhyolitic pumice of different geological origins
1983
Abstract Twelve samples of rhyolitic pumice from widely different origins were subjected to zeolitization in standard hydrothermal conditions (solid/liquid ratio, 1 5 ; T , 95°C; reaction time, 5 h; alkaline solution 5 N NaOH). The Si Al ratio of the starting material was of special importance in that zeolites formed with Si Al ratios similar to or smaller than that of the parent material. Pumice with low SiO 2 Al 2 O 3 , and high Fe content, preferentially gave rise to zeolites with lower SiO 2 Al 2 O 3 ratio than in the case of lower Fe and higher SiO 2 Al 2 O 3 ratio.
Collapse structures in the Permian of the Saar-Nahe area, Southwest Germany
1971
Volcanic breccias near an intrusive rhyolite dome in the Permian Saar-Nahe trough of southwest Germany have been identified as complex pipe-like subsidence-structures occupying the site and immediate neighbourhood of “explosive” volcanoes.
Geochronology and palaeomagnetism of a late Proterozoic island arc terrane from the Red Sea Hills, northeast Sudan
1992
Abstract Size fractions and single grains of zircon, hornblende and biotite have been dated to define the formation age and thermal history of the northern Haya Terrane (NHT), a late Proterozoic island arc terrane of the Red Sea Hills (RSH), northeast Sudan. U Pb and 207 Pb/ 206 Pb zircon data for acidic volcanics and granitoid rocks bracket the time of formation of the NHT between 887 ± 20 and 854 ± 9 Ma. 40 Ar/ 39 Ar hornblende and biotite ages of a gabbro near Suakin suggest passage through the argon closing temperature for hornblende at about 841 ± 4 Ma and 782 ± 6 Ma for biotite. The hornblende age is considered to be representative of the age of magnetic blocking and, hence, the age o…
VolcDeGas: A program for modelling hydrogen isotope fractionation during degassing of rhyolitic melts
2020
Magma degassing mechanisms are key determinants of explosive and effusive eruption styles. Paired measurements of H2O content and hydrogen isotopic ratios (e.g., dD) in pyroclastic and effusive products can elucidate end-member degassing mechanisms (e.g. closed and open system) during eruption. Here we present VolcDeGas, a MatLab program that models dD-H2O degassing trajectories of rhyolitic magma. Operating within an intuitive GUI, VolcDeGas calculates degassing paths based on: initial dD (in ‰), the H2O content of the melt (wt.%), degassing step size, and temperature. VolcDeGas also calculates hydrous speciation based on either empirical models or analytical data, and incorporates this…