Search results for "Volcanic Arc"

Estimation of the geogenic carbon degassing of Greece

2019

Abstract Greece belongs to the most geodynamically active regions of the world and as such it has to be considered an area of intense geogenic degassing. Here we review all the papers already published in the scientific literature on both the geochemistry of gas manifestations and the CO2 and CH4 release, in an attempt to obtain the first nationwide inventory of the natural output of these carbon gases in Greece. The best studied and most exhaling area is the South Aegean Active Volcanic Arc (SAAVA), which releases more than 1.3 × 105 tons of CO2 per year. Continental Greece, on the contrary, is much less studied but may release CO2 in the same order of magnitude in its eastern-central and …

Trench-parallel spreading ridge subduction and its consequences for the geological evolution of the overriding plate: Insights from analogue models a…

2018

A series of 3-D asthenospheric-scale analogue models have been conducted in the laboratory in order to simulate the arrival of a spreading ridge at the trench and understand its effect on plate kinematics, slab geometry, and on the deformation of the overriding plate. These models are made of a two-layered linearly viscous system simulating the lithosphere and asthenosphere. We reproduce the progressive decrease in thickness of the oceanic lithosphere at the trench. We measure plate kinematics, slab geometry and upper plate deformation. Our experiments reveal that the subduction of a thinning plate beneath a freely moving overriding continent favors a decrease of the subduction velocity and…

Volatile contents of mafic-to-intermediate magmas at San Cristóbal volcano in Nicaragua

2017

San Cristóbal volcano in northwest Nicaragua is one of the most active basaltic–andesitic stratovolcanoes of the Central American Volcanic Arc (CAVA). Here we provide novel constraints on the volcano's magmatic plumbing system, by presenting the first direct measurements of major volatile contents in mafic-to-intermediate glass inclusions from Holocene and historic-present volcanic activity. Olivine-hosted (forsterite [Fo] < 80; Fo< 80) glass inclusions from Holocene tephra layers contain moderate amounts of H2O (0.1–3.3 wt%) and S and Cl up to 2500 μg/g, and define the mafic (basaltic) endmember component. Historic-present scoriae and tephra layers exhibit more-evolved olivines (Fo69…

Multistage geochronological evolution of the Velká Fatra Mountains—a combined TIMS and ion-microprobe study on zircons

2005

Abstract New isotopic and geochronological data from the Velka Fatra Mountains (Tatric Unit of the Central Western Carpathians) are presented and discussed with a focus on the Variscan orogeny and events during Permian and Early Triassic times. The investigated samples are meta- to per-aluminous granitoids and their trace element patterns indicate a volcanic arc origin. This study presents U–Pb single zircon data, measured on TIMS as well as on an ion-microprobe (SIMS). The zircon age determinations were additionally constrained by cathodoluminescence (CL). Most of the investigated granitoids yield Variscan emplacement ages of about 310 Ma. However, for the Lubochna leucogranite a Triassic …

The fate of subducted oceanic slabs in the shallow mantle: Insights from boron isotopes and light element composition of metasomatized blueschists fr…

2012

Abstract Serpentine muds from South Chamorro Seamount (SCS), drilled during ODP Leg 195 at Site 1200 contain metamafic clasts that experienced blueschist-facies metamorphism (including the critical mineral assemblage pumpellyite – Na-amphibole – epidote). These schists represent fragments from the actual slab–mantle interface at ~ 27 km depth. Their heterogeneous lithology with a metasomatic character indicates significant mobility of major elements in the Mariana forearc, a region of melange formation as it can also be observed in onland exposures such as the Catalina Schist. As the Mariana forearc blueschists show no late stage alteration they permit the direct study of material transfer …

Chemical characterisation of the gases released at Gyali Island, Dodecanese, Greece and preliminary estimation of the CO2 output

2021

Greece belongs to the most geodynamically active regions of the world and as such, it has to be considered an area of intense geogenic degassing. In terms of carbon, the territory is characterized by the high hydrothermal and volcanic activity of the South Aegean Active Volcanic Arc (SAAVA), and by widespread geological seeps of buried carbon dioxide and methane. In the present work, we investigate the island of Gyali located in the volcanic system Kos-Gyali-Nisyros. Nine gas samples have been collected on the island of Gyali in areas found both on land, in a small lake (∼2000 m2) along its beach, and in the sea close to the shore at shallow depths (<20 m). Results show that CO2 is the p…

Shallow submarine gas manifestations in the Aegean Sea: preliminary catalogue and geochemical characterization

2017

The Aegean area, like other regions of intense geodynamic activity, is characterised by extensive geogenic degassing. Gas manifestations widespread on land are also very frequent underwater. The present study aims at producing a first catalogue of these manifestations together with the geochemical characterization of the emitted gases. Sixty-one samples at 21 different sites have been collected by diving up to 15 m depth, mainly along the south Aegean active volcanic arc (SAAVA). The sites displayed very different gas fluxes. Most of them showed a very sluggish gas bubbling while a few had spatially large and strong bubbling. The most intense manifestation has been found at Kos Island along…

THE NATURE AND SOURCE OF MAJOR MAGMATIC VOLATILES: OPEN-VENT DEGASSING VOLCANOES IN THE CENTRAL AMERICAN VOLCANIC ARC

Major volatiles play an important role in subduction zone magmatism, from magma generation in the mantle, to crustal ascent and evolution, until its dramatic expression during a volcanic eruption. In the attempt to add a piece of information on source and behavior of major volatiles in arc volcanism, I here report on the geochemistry of H2O, CO2, S and Cl in two volcanic systems in NW Nicaragua (Central America), San Cristóbal and Telica. The observational approach is based upon combination of some of the most recent techniques in volcanic gas monitoring and petrology. I here explore quiescent and eruptive degassing processes by combining both volcanic gas and melt inclusion approaches. Fie…

Palaeozoic pre- and post-collision calc-alkaline magmatism in the Qinling orogenic belt, central China, as documented by zircon ages on granitoid roc…

1996

Based on large-scale reconnaissance mapping, we identified two calc-alkaline plutonic assemblages from the northern Qinling orogenic belt. central China. The older assemblage of intrusions. closely associated and deformed coevally with their host volcanic arc sequences, seems to represent the fractionation product of basaltic arc magma. It therefore predates the collision of the North China Block with the Central Qinling island-arc system that developed in a SW Pacific-type oceanic domain south of the North China Block. Single-zircon 207Pb/206Pb evaporation dating yielded early to middle Ordovician ages for this assemblage. with a relatively small range from 487.2 ± 1.1 to 470.2 ± 1.3 Ma. I…

Cold plumes trigger contamination of oceanic mantle wedges with continental crust-derived sediments: Evidence from chromitite zircon grains of easter…

2018

The origin of zircon grains, and other exotic minerals of typical crustal origin, in mantle-hosted ophiolitic chromitites are hotly debated.We report a population of zircon grains with ages ranging from Cretaceous (99 Ma) to Neoarchean (2750 Ma), separated from massive chromitite bodies hosted in the mantle section of the supra-subduction (SSZ)-type Mayarí-Baracoa Ophiolitic Belt in eastern Cuba. Most analyzed zircon grains (n = 20, 287 +/- 3 Ma to 2750 +/- 60 Ma) are older than the early Cretaceous age of the ophiolite body, show negative εHf(t) (+/-26 to +/-0.6) and occasional inclusions of quartz, K-feldspar, biotite, and apatite that indicate derivation from a granitic continental crust…