Search results for "Continent"
showing 10 items of 598 documents
Microbiology and atmospheric processes: biological, physical and chemical characterization of aerosol particles
2008
Abstract. The interest in bioaerosols has traditionally been linked to health hazards for humans, animals and plants. However, several components of bioaerosols exhibit physical properties of great significance for cloud processes, such as ice nucleation and cloud condensation. To gain a better understanding of their influence on climate, it is therefore important to determine the composition, concentration, seasonal fluctuation, regional diversity and evolution of bioaerosols. In this paper, we will review briefly the existing techniques for detection, quantification, physical and chemical analysis of biological particles, attempting to bridge physical, chemical and biological methods for …
Pre- and syn-eruptive geochemistry of volcanic gases from Soufriere Hills of Montserrat, West Indies
1998
International audience; Soufriere Hills fumaroles contained magmaderived volatiles before and during the eruption initiated in 1995 but also preserved a typical and quite steady hydrothermal coinposition. Chemical changes due to increased boiling and a greater input of oxidizing magmatic gas occurred only at Galway's Soufriere, the most active fumarolic field. Hydrothermal buffering of the fumaroles has been favoured by their remote location (!-2 km) froin the eruptive vents and by a preferential degassing of the uprising magma through intrusive conduits under the crater. High temperature (720øC) gas collected froin the extruding lava dome in Feb. 1996 was chemically and isotopically repres…
Igneous petrology, zircon geochronology and geochemistry of multiply emplaced granitoid bodies from the Palaeoproterozoic Usagaran domain in central …
2019
Abstract This study reports igneous petrology, zircon ages and geochemistry for Palaeoproterozoic I-type granitic, granodioritic, Qtz-monzonitic, Qtz-monzodioritic and monzodioritic rocks from the Usagaran domain of southwestern Tanzania. These rocks can be subdivided into three groups according to their age, T-t evolution and geochemistry. The oldest group is made up of amphibolite-facies calcic-alkalic gneisses, ranging in age between ∼1984 and ∼1910 Ma, which have been divided into two subgroups regarding their T-t evolution. The first subgroup shows a constant increase in T, and the second subgroup first shows a decrease in T, followed by an increase in T. The second group consists of a…
Trace elements in the thermal groundwaters of Vulcano Island (Sicily)
2000
The chemical concentrations of many trace elements that have never before been examined in Vulcano Island groundwaters are reported. Chemical data indicate that rock composition is not the only factor determining the metal content in the aqueous system. The observed concentrations depend mainly on: (1) the chemical composition of the host rocks; (2) the chemical–physical conditions of the weathering solution (temperature, acidity, redox conditions); (3) input of magmatic gases; (4) adsorption of metal ions on oxide particles, formation of soluble complexes and/or precipitation of solid phases. Chloride complexes in solution are of minimal significance for all elements with the exception of …
Tectono-metamorphic evolution of the internal zone of the Pan-African Lufilian orogenic belt (Zambia): Implications for crustal reworking and syn-oro…
2016
Abstract The internal zone of the Pan-African Lufilian orogenic belt (Zambia) hosts a dozen uranium occurrences mostly located within kyanite micaschists in a shear zone marking the contact between metasedimentary rocks attributed to the Katanga Neoproterozoic sedimentary sequence and migmatites coring domes developed dominantly at the expense of the pre-Neoproterozoic basement. The P–T–t–d paths reconstructed for these rocks combining field observations, microstructural analysis, metamorphic petrology and thermobarometry and geochronology indicate that they have recorded burial and exhumation during the Pan-African orogeny. Both units of the Katanga metasedimentary sequence and pre-Katanga…
A space-time rainfall generator for highly convective Mediterranean rainstorms
2003
Distributed hydrological models require fine resolution rainfall inputs, enhancing the practical interest of space-time rainfall models, capable of generating through numerical simulation realistic space-time rainfall intensity fields. Among different mathematical approaches, those based on point processes and built upon a convenient analytical description of the raincell as the fundamental unit, have shown to be particularly suitable and well adapted when extreme rainfall events of convective nature are considered. Starting from previous formulations, some analytical refinements have been considered, allowing practical generation of space-time rainfall intensity fields for that type of rai…
Carboniferous granites on the northern margin of Gondwana, Anatolide-Tauride Block, Turkey - Evidence for southward subduction of Paleotethys
2016
Carboniferous metagranites with U-Pb zircon crystallization ages of 331-315 Ma crop out in the Afyon zone in the northern margin of the Anatolide-Tauride Block, which is commonly regarded as part of Gondwana during the Late Palaeozoic. They are peraluminous, calc-alkaline and are characterized by increase in Rb and Ba, decrease in Nb-Ta, and enrichment in Sr and high LILE/HFSE ratios compatible with a continental arc setting. The metagranites intrude a metasedimentary sequence of phyllite, metaquartzite and marble; both the Carboniferous metagranites and metasedimentary rocks are overlain unconformably by Lower Triassic metaconglomerates, metavolcanics and Upper Triassic to Cretaceous recry…
Active tectonics along the south east offshore margin of Mt. Etna: New insights from high-resolution seismic profiles
2018
The offshore margin of Mt. Etna has been shaped by Middle Pleistocene to Holocene shortening and extension and, more recently, by gravity-related sliding of the volcanic edifice. These processes have acted contemporaneously although the gravitational component largely prevails over the tectonic one. In order to investigate this issue, we focused on the main role of active tectonics along the south-eastern offshore of Mt. Etna by means of marine high-resolution seismic data. Seismic profiles revealed post-220 ka sedimentary deposits unconformably overlaying the Lower-Middle Pleistocene Etnean clayey substratum and volcanics of the Basal Tholeiitic phase and the Timpe phase. Offshore Aci Trez…
Mountain building in NW Sicily from the superimposition of subsequent thrusting and folding events during Neogene: structural setting and tectonic ev…
2017
We present a 1:25.000 scale geological map of the Kumeta-Pizzuta ridge in north-western Sicily (Italy), achieved by integrating stratigraphic, structural and geophysical data. In this area, the tectonic edifice results from the piling-up of deep-water-, carbonate platform- and pelagic platform-derived tectonic units (Imerese and Sicilide, Panormide and Trapanese domains, respectively) resulting from deformations of the former southern Tethyan continental margin. The structural setting shows interference of tectonic events, different types of structural styles and different scales of deformational patterns. Early overthrust of the Imerese on the Trapanese units (since the late Serravallian) …
How Offshore Groundwater Shapes the Seafloor
2018
The MARCAN project, launched last January, is working to fill a gap in our knowledge of how freshwater flowing underground shapes and alters the continental margins.