Search results for "mantle"

The effect of energy feedbacks on continental strength

2005

The classical strength profile of continents is derived from a quasi-static view of their rheological response to stress--one that does not consider dynamic interactions between brittle and ductile layers. Such interactions result in complexities of failure in the brittle-ductile transition and the need to couple energy to understand strain localization. Here we investigate continental deformation by solving the fully coupled energy, momentum and continuum equations. We show that this approach produces unexpected feedback processes, leading to a significantly weaker dynamic strength evolution. In our model, stress localization focused on the brittle-ductile transition leads to the spontaneo…

Generation of Earth's early continents from a relatively cool Archean mantle

2019

This research has been supported by DFG grant, SPP 1833 Building a Habitable Earth and MAGMA Consolidator Grant (ERC project #71143). Several lines of evidence suggest that the Archean (4.0 2.5 Ga) mantle was hotter than today's potential temperature (TP) of  1350 ° C. However, the magnitude of such difference is poorly constrained, with TP estimation spanning from 1500 ° C to 1600 ° C during the Meso‐Archean (3.2‐2.8 Ga). Such differences have major implications for the interpreted mechanisms of continental crust generation on the early Earth, as their efficacy is highly sensitive to the TP. Here, we integrate petrological modeling with thermomechanical simulations to understand the dynami…

Active geodynamics of the central Mediterranean Sea: Tensional tectonic evidences in western Sicily from mantle-derived helium

2005

[1] We report results on the measured high 3He/4He isotope ratio in western Sicily, interpreted together with the heat data. The study of this sector of the Europe-Africa interaction is crucial to a better understanding of the tectonics and the geodynamical evolution of the central Mediterranean area. The estimated mantle-derived helium fluxes in the investigated areas are up to 2–3 orders of magnitude greater than those of a stable continental area. The highest flux, found in the southernmost area near the Sicily Channel, where recent eruptions of the Ferdinandea Island occurred 20 miles out to sea off Sciacca, has been associated with a clear excess of heat flow. Our results indicate that…

Analysis of thermally induced flows in the laboratory by geoelectrical 3-D tomography

2010

[1] Many natural bodies as well as materials inside industrial installations, such as the Earth's mantle and the glass inside melting furnaces, exchange matter through convection. These processes result from differences in temperature, density, and chemical concentration. In this analysis, we focus on the visualization of thermally driven flows in the laboratory. In nature and in industrial installations, it is difficult to measure the temperature inside the object of interest directly. We benchmark a new DC-geoelectrical 3-D tomography method for temperature measurements that allows obtaining temperature values without influencing the flow pattern. For verification of the method, we use di…

Geoid effects in a convecting system with lateral viscosity variations

1992

The geoid signal and the flow patterns of two-dimensional steady state convection models with exponential temperature- and depth dependent viscosity are compared with results for an equivalent stratified viscosity structure. In analogy to Richards and Hager [1989], the latter are computed by a “dynamic response” approach. The flow fields obtained with this approach are quite different from the full solution; the geoid signals are similar but the amplitudes differ significantly. The differences are analysed in the horizontal wavenumber domain and in the spatial domain. They may lead to an overestimation of the viscosity contrast of the earth's mantle derived by modeling the earth's geoid wit…

A self-consistent 2-D model for the dip angle ofmantle downflow beneath an overriding continent

1999

Abstract We demonstrate how the inclination of descending mantle flow is affected by thepresence of a continent overriding the downwelling zone. The mantle is modelled by a fluidhaving a temperature- and pressure-dependent viscosity which describes a low viscosityasthenosphere and a higher viscosity lower mantle. The fluid occupies a square x:y=10:1 boxheated from below. In the absence of overlying continents thermal convection sets in with colddownwellings being nearly vertical. A continent is placed on the convecting mantle and starts todrift. The continent is assumed to be a thick rigid plate. We consider models of two types. Model1 involves a free-floating continent. The continent is pu…

Forearc carbon sink reduces long-term volatile recycling into the mantle

2019

Carbon and other volatiles in the form of gases, fluids or mineral phases are transported from Earth's surface into the mantle at convergent margins, where the oceanic crust subducts beneath the continental crust. The efficiency of this transfer has profound implications for the nature and scale of geochemical heterogeneities in Earth's deep mantle and shallow crustal reservoirs, as well as Earth's oxidation state. However, the proportions of volatiles released from the forearc and backarc are not well constrained compared to fluxes from the volcanic arc front. Here we use helium and carbon isotope data from deeply sourced springs along two cross-arc transects to show that about 91 per cent…

Crust Formation and Plate Motion in the Early Archean

1992

Mounting evidence for voluminous continental crust formation in the early Archean involving intracrustal melting and selective preservation of granitoid rocks suggests that initial crust formation crust formation and growth were predominantly by magmatic underplating in plumegenerated Iceland-type settings. Collision of these early islands to give rise to larger blocks is suggested by extensive horizontal shortening in both supracrustal and granitoid assemblages. Preservation of early Archean high-grade gneisses that were once at depths of 20 to 30 kilometers implies that these blocks developed thick, subcrustal roots despite high mantle heat flow. Rigid continental plates must have existed…

Goldschmidt Abstracts 2010 – R

2010

Helium isotope systematics of volcanic gases and thermal waters of Guadeloupe Island, Lesser Antilles

2014

Abstract The island of Guadeloupe is located in the middle of the 850 km long Lesser Antilles island arc. Present-day volcanic and geothermal activity is concentrated in two systems both located in the southwestern part of the island (Basse Terre): the La Soufriere volcanic complex and the Bouillante hydrothermal system, some 20 km to the northwest of the volcano. We report here the largest isotopic data set for helium isotopes in hydrothermal gases and waters from both systems, acquired between 1980 and 2012. 3 He/ 4 He ratios in the fumarolic gases of La Soufriere volcano have been quite homogeneous and stable over the last thirty years. The average ratio of 8.2 ± 0.2 R a confirms that th…