Search results for "Magma"
showing 10 items of 262 documents
Structural architecture and active deformation pattern in the northern sector of the Aeolian-Tindari-Letojanni fault system (SE Tyrrhenian Sea-NE Sic…
2017
Framed in the current geodynamics of the central Mediterranean, the Aeolian-Tindari-Letojanni fault system is part of a wider NW-SE oriented right-lateral wrench zone which accommodates diverging motion between regional-scale blocks located at the southern edge of the Calabrian Arc. In order to investigate the structural architecture and the active deformation pattern of the northern sector of this tectonic feature, structural observations on-land, high and very-high resolution seismic reflection data, swath bathymetry data and seismological and geodetic data were merged from the Lipari-Vulcano volcanic complex (central sector of the Aeolian Islands) to the Peloritani Mountains across the G…
Petrology of some amphibole-bearing volcanics of the pre-Ellittico period (102-80 ka), Mt. Etna
2006
We present here petrological and geochemical data on volcanics cropping out in southern and northeastern walls of the Valle del Bove (Mt. Etna), belonging to the Rocche, Serra Giannicola Grande and Canalone della Montagnola Units. These units constitute the remnants of several volcanoes that were active in the time span 102-80 ka, i.e. before the growth of the Ellittico-Mongibello strato-volcano. Their products, range in composition from hawaiites to benmoreites. Amphibole (kaersutite) is present as phenocryst in all the studied rocks, and commonly shows breakdown coronas of rhönite ± clinopyroxene and plagioclase formed during magma ascent. Nevertheless, in mafic rocks, amphibole occurs as…
Geology and petrochemistry of recent (25 ka) silicic volcanism at Pantelleria Island
2007
built a complex sequence of interfingered deposits emitted by closely spaced eruptive vents which are frequently associated with dome-building phases and pantelleritic lavas flows. Field relationships allowed us to recognize eight eruptive units, all lying above the Montagna Grande trachytes. As a whole, petrochemical characteristics of the erupted products indicate an evolutionary trend in which Na-clinopyroxene was the liquidus phase, followed by alkali feldspar. Amphibole and quartz are late-crystallizing, whereas aenigmatite is both early- and late-crystallizing as well. Aenigmatite and Na-clinopyroxene crystallization buffers efficiently the increase of agpaicity, induced by feldspar c…
Steam and gas emission rate from La Soufriere volcano, Guadeloupe (Lesser Antilles): implications for the magmatic and hydrothermal fluid supply duri…
2014
Since its last magmatic eruption in 1530 AD, La Soufrière andesitic volcano in Guadeloupe has displayed intense hydrothermal activity and six phreatic eruptive crises. Here we report on the first direct quantification of gas plume emissions from its summit vents,which gradually intensified during the past 20 years. Gas fluxes were determined in March 2006 and March 2012 by measuring the horizontal and vertical distributions of volcanic gas concentrations in the air-diluted plume and scaling to the speed of plume transport. Fluxes in 2006 combine realtime measurements of volcanic H2S concentrations and plume parameters with the composition of the hot (108.5 °C) fumarolic fluid at exit. Fluxe…
Changes in fluid geochemistry and physico-chemical conditions of geothermal systems caused by magmatic input: The recent abrupt outgassing off the is…
2005
Abstract Hydrothermal systems and related vents can exhibit dramatic changes in their physico-chemical conditions over time as a response to varying activity in the feeding magmatic systems. Massive steam condensation and gas scrubbing processes of thermal fluids during their ascent and cooling cause further compositional changes that mask information regarding the conditions evolving at depth in the hydrothermal system. Here we propose a new stability diagram based on the CO2-CH4-CO-H2 concentrations in vapor, which aims at calculating the temperatures and pressures in hydrothermal reservoirs. To filter gas scrubbing effects, we have also developed a model for selective dissolution of CO2-…
On thrusting, regional unconformities and exhumation of high-grade greenstones in Neoarchean orogens. The case of the Waroonga Shear Zone, Yilgarn Cr…
2017
Abstract During the Neoarchean, the dominant tectonic style progressively changed from an episodic-overturn/stagnant-lid regime to modern-style plate tectonics. The Neoarchean strengthening of continental lithosphere changed the style of deformation of orogenic belts. The case study presented here provides insights into how such transition in tectonic style occurred, a matter that is generally controversial. We present structural and metamorphic data from the c. 2660 Ma Waroonga Shear Zone (WSZ) in the Neoarchean Yilgarn orogen (Western Australia). The WSZ contains a syntectonic pluton and older, high-grade greenstones. The tectonic fabric in the pluton developed during melt-present thrusti…
Geochemistry, PbPb single zircon ages and NdSr isotope composition of Precambrian rocks from southern and eastern Ethiopia: implications for crusta…
1998
Abstract Geochemical and isotope data for granitoid rocks from southern and eastern Ethiopia delineate the presumed margin of the Pan-African juvenile terrain of the Arabian-Nubian Shield against an older crustal segment of unknown origin extending from eastern Ethiopia to northern Somalia. Granitoids from southern Ethiopia have higher Na2O and Na 2 0 K 2 O and lower Cr and Ni than granitoids with comparable SiO2 values from eastern Ethiopia. In southern Ethiopia three periods of magmatism are identified on the basis on single zircon 207 Pb 206 Pb evaporation ages, namely at ∼850, ∼750-700 and ∼650-550 Ma, and these correlate well with events documented from other parts of Ethiopia and the …
Regional variations in the chemical and helium–carbon isotope composition of geothermal fluids across Tunisia
2011
Abstract Tunisia has numerous thermo-mineral springs. Previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology. However little work has been done so far to study the isotopic composition of volatiles associated with these geothermal manifestations. Here, we report on the results of an extensive survey of both natural hot springs and production wells across Tunisia, aimed at investigating the spatial distribution of thermal fluids' geochemical characteristics and He–C isotopic composition. The chemistry of the analyzed samples highlights the heterogeneity of the water mineralization processes in Tunisia, as a consequence of th…
Magmatism Along Lateral Slab Edges: Insights From the Diamante-Enotrio-Ovidio Volcanic-Intrusive Complex (Southern Tyrrhenian Sea)
2019
Volcanic‐intrusive complexes often formed along lateral slab edges as a consequence of subduction‐induced mantle flow. We investigate this process in the southern Tyrrhenian Sea by integrating multibeam bathymetry, seismic‐reflection data, regional magnetic anomalies data, and seismological data. The interpretation of the data highlights the presence of magmatic intrusions that locally reach the seafloor forming volcanic edifices. Chimneys, lava flows, and laccoliths are observed beneath and surrounding the volcanoes. The emplacement and cooling of the magma occurred during the Brunhes Chron. The volcanoes are not active even if the hydrothermal activity occurs. The volcanic‐intrusive compl…
Tethyan vs. Cordilleran ophiolites: a reappraisal of distintctive tectono-magmatic features of supra-subduction complexes in relation to the subducti…
2004
Abstract Supra-subduction zone (SSZ) ophiolites deserve special attention because they represent fundamental markers of intraoceanic convergence and generation of new lithosphere above subduction zones. Moreover, owing to their structural characteristics and location in the overriding plate, these complexes are far better represented and preserved than Mid-Ocean-Ridge-Basalt (MORB) ophiolites in orogenic belts. In terms of their structure, tectonics, and magmatic features, SSZ ophiolites may be classified in two main types: (1) “Tethyan complexes” (such as those of the Albanide-Hellenide belt), which mostly consist of complete and extensive volcanic, dyke, plutonic, and mantle sections with…