Search results for "FEA"
showing 10 items of 4862 documents
Metamorphic and structural evolution of the Maures-Tanneron massif (SE Variscan chain): evidence of doming along a transpressional margin
2009
AbstractThe Variscan metamorphic and structural evolution of the Maures-Tanneron massif is divided in two main post-collisional phases: (1) a MP-MT regional gradient is developed during nappe-piling process between 350 and 320 Ma, followed by (2) LP-HT regional gradient coeval with doming between 320 and 300 Ma. During this late phase, the tectonic context was dominated by E-W shortening, which produced crustal-scale upright folds and major strike-slip displacement along trans-crustal faults. Symmetric extensional fabrics are observed on the limbs of crustal-scale anticlines, and are ascribed to local accommodation of lower crust exhumation. Heat and magma transfer are allowed by these larg…
A Damara orogen perspective on the assembly of southwestern Gondwana
2008
The Pan-African Damara orogenic system records Gondwana amalgamation involving serial suturing of the Congo-Sao Francisco and Ro ´o de la Plata cratons (North Gondwana) from 580 to 550 Ma, before amalgamation with the Kalahari - Antarctic cratons (South Gondwana) as part of the 530 Ma Kuunga-Damara orogeny. Closure of the Adamastor Ocean was diachronous from the Aracuao ´ Belt southwards, with peak sinistral transpressional deformation followed by craton overthrusting and foreland basin development at 580- 550 Ma in the Kaoko Belt and at 545-530 Ma in the Gariep Belt. Peak deformation/metamorphism in the Damara Belt was at 530-500 Ma, with thrusting onto the Kalahari Craton from 495 Ma thro…
Environment in Megacities: Tehran Waterscapes
2021
Defining contemporary urban paradigms is the challenge of this time, especially when the urban dynamics are so fluid they spread uncontrollably in overextended and overpopulated territories. This is the case for megacities, metropolitan areas with more than 10 million inhabitants, which place the emphasis on how to manage energy consumption in such filled places. In this frame, the city of Tehran, the capital of the Islamic Republic of Iran, scene of political and cultural disputes, administrative and economic headquarter of the country, with its nearly 15 million residents and a daily traffic of more than 20 million people, is currently one of the most populous cities in the world and repr…
Ozone depletion in tropospheric volcanic plumes
2010
Ground based remote sensing techniques are used to measure volcanic SO2 fluxes in efforts to characterise volcanic activity. As these measurements are made several km from source there is the potential for in-plume chemical transformation of SO2 to sulphate aerosol (conversion rates are dependent on meteorological conditions), complicating interpretation of observed SO2 flux trends. In contrast to anthropogenic plumes, SO2 lifetimes are poorly constrained for tropospheric volcanic plumes, where the few previous loss rate estimates vary widely (from 99% per hour). We report experiments conducted on the boundary layer plume of Masaya volcano, Nicaragua during the dry season. We found that SO2…
Towards a representation of halogen chemistry within volcanic plumes in a chemistry transport model
2014
Volcanoes are a known source of halogens to the atmosphere. HBr volcanic emissions lead rapidly to the formation of BrO within volcanic plumes as shown by recent work based on observations and models. BrO, having a longer residence time in the atmosphere than HBr, is expected to have a significant impact on tropospheric chemistry, at least at the local and regional scales. The objective of this paper is to prepare a framework that will allow 3-D modelling of volcanic halogen emissions in order to determine their fate within the volcanic plume and then in the atmosphere at the regional and global scales. This work is based on a 1-D configuration of the chemistry transport model MOCAGE whose …
Intercomparison of SO2 camera systems for imaging volcanic gas plumes
2015
Abstract SO 2 camera systems are increasingly being used to image volcanic gas plumes. The ability to derive SO 2 emission rates directly from the acquired imagery at high time resolution allows volcanic process studies that incorporate other high time-resolution datasets. Though the general principles behind the SO 2 camera have remained the same for a number of years, recent advances in CCD technology and an improved understanding of the physics behind the measurements have driven a continuous evolution of the camera systems. Here we present an intercomparison of seven different SO 2 cameras. In the first part of the experiment, the various technical designs are compared and the advantage…
Laminar Micrite Crusts and Associated Foreslope Processes, Red Sea
1991
ABSTRACT Forereef slopes in the Red Sea of Sudan exhibit a uniform biozonation that is independent from the topography of the slopes. Below - 120 m, ledges protrude horizontally from sleep cliffs of barrier reefs and atolls as well as from patches of in situ lithified slope sediment on inclined fringing reef slopes. Free surfaces and cavities within these ledges are partly covered by laminar micrite crusts of 7-20 mm thickness. The ledges are formed by an organic framework of living azooxanthellate corals, bryozoans, serpulids and fossil red algae. They are affected by repeated episodes of boring, infilling, and cementation which obliterate much of the original fabric. Concomitant cementati…
Using calculated chemical potential relationships to account for coronas around kyanite: an example from the Bohemian Massif
2010
Corona textures around kyanite, involving for example zoned plagioclase separating kyanite from the matrix, reflect the instability of kyanite with the matrix on changing P-T conditions, commonly related to decompression. The chemical potential gradients set up between the kyanite and the matrix as a consequence of slow Al diffusion drive corona development, with the zoning of the plagioclase reflecting the gradients. Calculated mineral equilibria are used to account for corona textures involving plagioclase ± garnet around kyanite, and replacement of kyanite by plagioclase + spinel symplectite, in quartz + plagioclase + K-feldspar + garnet + kyanite granulite facies gneiss from the Blanský…
Trace metal modeling of groundwater–gas–rock interactions in a volcanic aquifer: Mount Vesuvius, Southern Italy
2005
We report a detailed study of trace metals in groundwaters from the Somma-Vesuvius volcanic complex and present a model of the chemical processes that control the fate of these components during gas–water–rock interactions. Trace metal concentrations in Vesuvian groundwaters range from 0.01 to 0.1 Ag/l for ultra-trace elements (Sb, Cs, Co, Cd, and Pb) up to 0.1–10 mg/l for minor elements (Fe and Sr), leading to water–rock ratios from ~0.5 to 10 � 9 when normalized to trace element concentrations in the host rocks. Our results indicate non-isochemical dissolution of local volcanic rocks by groundwaters, during which mobile trace elements (As, Se, Mo, V, Li) are enriched and elements such as …
The viscous-brittle transition of crystal-bearing slilic melt: direct observation of magma rupture and healing
2012
Magmas may fl ow or break depending on their deformation rate. The transition between such viscous and brittle behavior controls the style of volcanic eruptions. While the brittle failure of silicate melts is reasonably well characterized, the effect of crystals on the viscous-brittle transition has not yet been constrained. Here we examine the effect of suspended crystals on the mechanical failure of magmas using torsion experiments performed at temperatures (600‐ 900 °C), strain rates (10 ‐4 ‐10 ‐1 s ‐1 ), and confi ning pressures (200‐300 MPa) relevant for volcanic systems. We present a relationship that predicts the critical stress and associated strain rate at which magmas fail as a fu…