Search results for "Geophysic"
showing 10 items of 2684 documents
On the Rifting Dynamics of Plate Divergence and Magma Accumulation at Oceanic Ridge Axes
1995
Rifting dynamics at spreading axes is governed by two processes: the large-scale plate divergence and the local magma accumulation in the crust-mantle transition layer. Both evolve simultaneously. A model is developed particularly for the situation in Iceland where a well studied rifting episode occurred in the Krafla volcanic system 1975–1984. Both the divergence and the buoyant rise of magma create tensile deviatoric stress in the axial region, but while divergence generates an altogether extensional stress field, uprising of buoyant melt produces tension only near the axis but compression of the sides. The buoyant rise is driven by the differential pressure gradient in rock and melt. The…
Tectonics and seismicity of the Tindari Fault System, southern Italy: Crustal deformations at the transition between ongoing contractional and extens…
2006
[1] The Tindari Fault System (southern Tyrrhenian Sea, Italy) is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab. Onshore structural data, an offshore seismic reflection profile, and earthquake data are analyzed to constrain the present geometry of the Tindari Fault System and its tectonic evolution since Neogene, including the present seismicity. Results show that this zone of deformation consists of a broad NNW trending system of faults including sets of right-lateral, left-lateral, and extensional faults as well as early strike-slip faults rewor…
The Pan-African continental margin in northeastern Africa: evidence from a geochronological study of granulites at Sabaloka, Sudan
1987
Ion microprobe zircon ages, a Nd model age and RbSr whole-rock dates are reported from the high-grade gneiss terrain at Sabaloka on the River Nile north of Khartoum, formally considered to be part of the Archaean/early Proterozoic Nile craton. The granulites, which are of both sedimentary and igneous derivation, occur as remnants in migmatites. Detrital zircon ages range from ≈ 1000 to ≈ 2650 Ma and prove the existence of Archaean to late Proterozoic continental crust in the sedimentary source region. The Nd model age for one sedimentary granulite is between 1.26 (TCHUR) and 1.70 (TDM) Ga and provides a mean crustal residence age for the sedimentary precursor. Igneous zircons in enderbitic …
Fluid escape structures in the north Sicily continental margin
2014
Abstract High resolution and multichannel seismic profiles coupled with multibeam echosounder (seafloor relief) data, acquired along the northern Sicily continental margin (southern Tyrrhenian Sea), document the occurrence of mound and pockmark features, revealing fluid escape processes. Along this margin, morphology of the high-gradient continental slope is irregular due to the presence of structural highs, slope failures and canyons, and is interrupted by flat areas at a mean depth of 1500 m. Seismostratigraphic analysis tools and methods were used to identify fluid escape structures and to work out a classification on the basis of their morpho-acoustic characteristics. The detailed 3D ba…
Crustal structure of the Reykjanes Ridge near 62°N, on the basis of seismic refraction and gravity data
2007
Explosion deep seismic sounding data sections of high quality had been obtained with RV Meteor in the Reykjanes Iceland Seismic Project (RRISP77 [Angenheister, G., Gebrande, H., Miller, H., Goldflam, P., Weigel, W., Jacoby, W.R., Palmason, G., Bjornsson, S., Einarsson, P., Pavlenkova, N.I., Zverev, S., Litvinenko, I.V., Loncarecic, B., Solomon, S., 1980. Reykjanes Ridge Iceland Seismic Experiment (RRISP 77). J. Geophys. 47, 228–238]) which close an information gap near 62°N. Preliminary results were presented by Weigel [Weigel, W., 1980. Aufbau des Reykjanes Ruckens nach refraktionsseismischen Messungen. In: Weigel, W. (Ed.), Reykjanes Rucken, Island, Norwegischer Kontinentalrand. Abschluss…
230Th/U dating of Last Interglacial brain corals from Bonaire (southern Caribbean) using bulk and theca wall material
2016
Abstract We compared the suitability of two skeletal materials of the Atlantic brain coral Diploria strigosa for 230Th/U-dating: the commonly used bulk material comprising all skeletal elements and the denser theca wall material. Eight fossil corals of presumably Last Interglacial age from Bonaire, southern Caribbean Sea, were investigated, and several sub-samples were dated from each coral. For four corals, both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty. Three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232Th content and (230Th/238U) ratios. The bulk mat…
First volatile inventory for Gorely volcano, Kamchatka
2012
[1] We report here the very first assessment of volatile flux emissions from Gorely, an actively degassing volcano in Kamchatka. Using a variety of in situ and remote sensing techniques, we determined the bulk plume concentrations of major volatiles (H2O ∼93.5%, CO2, ∼2.6%, SO2 ∼2.2%, HCl 1.1%, HF 0.3%, H20.2%) and trace-halogens (Br, I), therefore estimating a total gas release of ∼11,000 tons·day−1during September 2011, at which time the target was non-eruptively degassing at ∼900°C. Gorely is a typical arc emitter, contributing 0.3% and 1.6% of the total global fluxes from arc volcanism for CO2 and HCl, respectively. We show that Gorely's volcanic gas (H2O/SO2 ∼43, CO2/SO2 ∼1.2, HCl/SO2∼…
Focused and diffuse effluxes of CO2 from mud volcanoes and mofettes south of Mt. Etna (Italy).
2007
Abstract Several sites with anomalous emissions of carbon dioxide were investigated in the region south of Mt. Etna volcano in order to assess the types of emission (focused and/or diffuse), their surface extension and the total output of CO 2 . Most of the studied emissions are located on the southwest boundary of Mt. Etna, near the town of Paterno. They consist of three mud volcanoes (known as Salinelle), one spring with bubbling gas (Acqua Grassa) and one area of diffuse degassing (Pescheria). Another site (Naftia Lake) with remarkable gas emissions (bubbling gas into a lake as well as adjacent areas of diffuse soil degassing) is located further southwest of Mt. Etna in an area of extinc…
AGU Centennial Grand Challenge: Volcanoes and Deep Carbon Global CO 2 Emissions From Subaerial Volcanism—Recent Progress and Future Challenges
2020
Quantifying the global volcanic CO2 output from subaerial volcanism is key for a better understanding of rates and mechanisms of carbon cycling in and out of our planet and their consequences for the long-term evolution of Earth's climate over geological timescales. Although having been the focus of intense research since the early 1990s, and in spite of recent progress, the global volcanic CO2 output remains inaccurately known. Here we review past developments and recent progress and examine limits and caveats of our current understanding and challenges for future research. We show that CO2 flux measurements are today only available for ~100 volcanoes (cumulative measured flux, 44 Tg CO2/y…
Rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere
1998
An important and novel mechanism for ductile failure of the lithosphere is identified here, which is intrinsic to the thermal-mechanical feedback in a temperature dependent plastic body with coupled elastic fields. Both a temperature-dependent power-law visco-elasto-plastic rheology and a temperature-dependent elasto-plastic rheology are employed to study in a self-consistent fashion the deformation of the lithosphere subject to extension by means of a two-dimensional, finite-element code. A structural perturbation initially localizes elasto-plastic deformation only in its immediate vicinity. However, after 800,000 years have elapsed the localized zone of deformation takes off in a ‘crack-l…