CNRS Institute of Earth Sciences

Grenoble, France

CNRS Institute of Earth Sciences

Grenoble, France
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Weiss J.,CNRS Institute of Earth Sciences | Dansereau V.,CNRS Laboratory for Glaciology and Environmental Geophysics
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2017

Mechanics plays a key role in the evolution of the sea ice cover through its control on drift, on momentum and thermal energy exchanges between the polar oceans and the atmosphere along cracks and faults, and on ice thickness distribution through opening and ridging processes. At the local scale, a significant variability of the mechanical strength is associated with the microstructural heterogeneity of saline ice, however characterized by a small correlation length, below the ice thickness scale. Conversely, the sea ice mechanical fields (velocity, strain and stress) are characterized by long-ranged (more than 1000 km) and long-lasting (approx. few months) correlations. The associated space and time scaling laws are the signature of the brittle character of sea ice mechanics, with deformation resulting from a multiscale accumulation of episodic fracturing and faulting events. To translate the short-range-correlated disorder on strength into long-range-correlated mechanical fields, several key ingredients are identified: long-ranged elastic interactions, slow driving conditions, a slow viscous-like relaxation of elastic stresses and a restoring/healing mechanism. These ingredients constrained the development of a new continuum mechanics modelling framework for the sea ice cover, called Maxwell-elastobrittle. Idealized simulations without advection demonstrate that this rheological framework reproduces the main characteristics of sea ice mechanics, including anisotropy, spatial localization and intermittency, as well as the associated scaling laws. © 2016 The Author(s) Published by the Royal Society. All rights reserved.

Capitanio F.A.,Monash University | Replumaz A.,CNRS Institute of Earth Sciences
Geochemistry, Geophysics, Geosystems | Year: 2013

We test the link between large-scale Asian continent deformations and Indian slab subduction and breakoff during convergence by means of three-dimensional numerical models of the subducting-upper plates system. We find that the subduction of the buoyant continent results in the reduction of convergence velocity comparable to that observed in the Indian motions, yet the upper plate deformation remains accommodated in a narrow belt along a straight margin. Comparable rates are measured when the subducting slab breakoff is modeled, although the convergent margin deforms and curves markedly, with large underplating contiguous to ongoing subduction, similar to what observed along the Himalayan range. The models support the interpretation of the Himalayan Western Syntaxis evolution, the progressive curvature of the Indian margin and the underthrusting as a consequence of the Indian slab breakoff. The modeled slab detachment is followed by short-lived large stresses in the upper plate interiors, propagating at large distance from the margin with a trend similar to several major Asian lithospheric faults. Such localized stress has likely provided the conditions for the formation of the Central Asian intracontinental faulting, the Bangong-Red River and the Altyn Tagh faults, that followed successive Indian slab breakoff episodes. Continent subduction and breakoff during India-Asia convergence offer an explanation for the different deformation mechanisms as the long-lived understhrusting and the episodic lithospheric faulting in the Asian continent and their link to deep processes. © 2013. American Geophysical Union. All Rights Reserved.

Braun J.,CNRS Institute of Earth Sciences | Willett S.D.,ETH Zurich
Geomorphology | Year: 2013

We present a new algorithm to solve the basic stream power equation, which governs channel incision and landscape evolution in many geomorphic settings. The algorithm is highly efficient because computation time increases linearly with the number of points used to discretize the landscape and is ideally suited to parallelization. It is also unconditionally stable because it uses an implicit scheme for the time integration of the landscape evolution equation, which means that large time steps can be used without sacrificing accuracy. In this paper we describe the algorithm and present results that demonstrate its efficiency and accuracy. © 2012 Elsevier B.V.

Hirth G.,Brown University | Guillot S.,CNRS Institute of Earth Sciences
Elements | Year: 2013

Serpentinites occur in many active geologic settings and control the rheology of the lithosphere where aqueous fluids interact with ultra-mafic rocks. The crystal structure of serpentine-group minerals results in diagnostic physical properties that are important for interpreting a wide range of geophysical data and impart unique rheological behaviors. Serpentinites play an important role during continental rifting and oceanic spreading, in strain localization along lithospheric strike-slip faults, and in subduction zone processes. The rheology of serpentine is key for understanding the nucleation and propagation of earthquakes, and the relative weakness of serpentinite can significantly affect geodynamic processes at tectonic plate boundaries.

Snieder R.,Colorado School of Mines | Larose E.,CNRS Institute of Earth Sciences
Annual Review of Earth and Planetary Sciences | Year: 2013

Recent research has shown that noise can be turned from a nuisance into a useful seismic source. In seismology and other fields in science and engineering, the estimation of the system response from noise measurements has proven to be a powerful technique. To convey the essence of the method, we first treat the simplest case of a homogeneous medium to show how noise measurements can be used to estimate waves that propagate between sensors. We provide an overview of physics research-dating back more than 100 years-showing that random field fluctuations contain information about the system response. This principle has found extensive use in surface-wave seismology but can also be applied to the estimation of body waves. Because noise provides continuous illumination of the subsurface, the extracted response is ideally suited for time-lapse monitoring. We present examples of time-lapse monitoring as applied to the softening of soil after the 2011 Tohoku-oki earthquake, the detection of a precursor to a landslide, and temporal changes in the lunar soil. © Copyright ©2013 by Annual Reviews. All rights reserved.

Ponty Y.,University of Nice Sophia Antipolis | Plunian F.,CNRS Institute of Earth Sciences
Physical Review Letters | Year: 2011

The dynamo equations are solved numerically with a helical forcing corresponding to the Roberts flow. In the fully turbulent regime the flow behaves as a Roberts flow on long time scales, plus turbulent fluctuations at short time scales. The dynamo onset is controlled by the long time scales of the flow, in agreement with the former Karlsruhe experimental results. The dynamo mechanism is governed by a generalized α effect, which includes both the usual α effect and turbulent diffusion, plus all higher order effects. Beyond the onset we find that this generalized α effect scales as O(Rm-1), suggesting the takeover of small-scale dynamo action. This is confirmed by simulations in which dynamo occurs even if the large-scale field is artificially suppressed. © 2011 American Physical Society.

Zuddas P.,CNRS Institute of Earth Sciences
Elements | Year: 2010

The chemical composition of groundwater results from the reaction of mineral dissolution and precipitation. We can use the thermodynamic approach to predict water composition under conditions where water and newly formed minerals are in equilibrium. Although some minerals exist in a state of equilibrium with water, other minerals are always unstable. In the latter case, we can evaluate the extent of the overall irreversible mass transfer between minerals and water to quantify the mineral surface area participating in the water-rock interaction. This parameter is fundamental to basic and applied research in areas such as the geological sequestration of CO2 and the safe geological storage of waste.

Based on a review of published literature and on the report of a few case studies, this paper summarizes the state of the art on paleostress determinations by fault slip data inversions, with the aim at discussing whether these techniques actually yield a quantity that has a " paleostress meaning" (i.e., ancient stress) and whether there is an adequate basis for a reliable comparison of such " paleostresses" with contemporary stresses in terms of orientations and patterns at different scales of time and space in the Earth's crust. © 2012 Académie des sciences.

Mouthereau F.,CNRS Institute of Earth Sciences
Geological Magazine | Year: 2011

The motion of Arabia was stable with respect to Eurasia over the past 22 Ma. Deformation and exhumation in the Zagros is seen to initiate at the same time as argued by new detrital thermochronologic constraints and increasing accumulation rates in synorogenic sediments. A recent magnetostratigraphic dating of the Bakhtyari conglomerates in the northern Fars region of the Zagros further suggests that shortening and uplift in the Zagros Folded Belt accelerated after 12.4 Ma. Available temporal constraints from surrounding collision belts indicate that shortening and uplift focused in regions bordering the Iranian plateau to the south between 15 and 5 Ma. As boundary velocity was kept constant this requires concomitant decreasing strain rates in the Iranian plateau. Slab detachment has been proposed to explain the observed changes as well as mantle delamination, but the insignificant change in the Arabian slab motion and lack of unambiguous constraints make both hypotheses difficult to account for. It is proposed based on a review of shortening estimates provided throughout the Arabia-Eurasia collision that the total 440 km of convergence predicted by geodesy and plate reconstruction over the past 22 Ma can be accounted for by distributed shortening. I suggest that the topography and expansion of the Iranian plateau over Late Miocene-Pliocene time can be reproduced by the progressive thickening of the originally thin Iranian continental lithosphere presumably thermally weakened during the Eocene extensional and magmatic event. © 2011 Cambridge University Press.

Charvet J.,CNRS Institute of Earth Sciences
Journal of Asian Earth Sciences | Year: 2013

This paper gives a brief review of what I consider as the state of the art regarding the largely accepted data and ideas concerning the Proterozoic to Early Paleozoic tectonic evolution of South China. The South China craton was built by the welding of the Yangtze and Cathaysia blocks, with a different previous history giving a different pre-Neoproterozoic basement composition, due to the Jiangnan (Jinning, Sibao) orogeny. This Jiangnan orogeny was a collisional event, induced by the consumption of an intervening oceanic domain by subduction beneath the Yangzte plate. The evolution involved a volcanic arc on the Yangtze active margin, active from ca. 980. Ma to ca. 850. Ma, the subsequent collision beginning at around 870-860. Ma and responsible for the emplacement of thrust sheets of ophiolitic mélange (dated around 1000-900. Ma) and blueschists (900-870. Ma), followed by late- to post-collisional granitic plutonism (840-800. Ma). The newly amalgamated South China craton suffered from rifting, starting around 850. Ma, marked by mafic-ultramafic magmatism until ca. 750. Ma. The Nanhua rift basin evolved with a thick sedimentation in its middle part until the Ordovician. South China was affected by the Early Paleozoic orogeny (mainly Silurian), characterized by a strong quasi-symmetrical intracontinental shortening, involving the sedimentary cover of the rift and its margins as well as the basement, leading to crustal thickening. This crustal thickening induced an important anatexis and emplacement of peraluminous granites during the Silurian. Unlike the Jiangnan orogeny, which was of collisional type, the Early Paleozoic one was a bit similar to a Pyrenean intracontinental type.Some pending problems need further research for clarification, for example: the location and timing of integration of South China within Rodinia, the triggering factor of the Early Paleozoic orogeny, the mapping of the contacts bounding the Lower Paleozoic thrust sheets responsible for the crustal thickening. © 2013 Elsevier Ltd.

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