Subduction processes by Vincent Strak
Earth and Planetary Science Letters, 2014
Available online xxxx Editor: J. Brodholt Keywords: subduction mantle flow slab edges analogue mo... more Available online xxxx Editor: J. Brodholt Keywords: subduction mantle flow slab edges analogue models stereoscopic PIV
Editor: J. Brodholt Keywords: subduction geodynamic analogue modelling subduction-induced mantle ... more Editor: J. Brodholt Keywords: subduction geodynamic analogue modelling subduction-induced mantle flow backarc extension velocity gradient shear traction
The impact of slab width W (i.e., trench-parallel extent) on subduction-induced upper mantle flow... more The impact of slab width W (i.e., trench-parallel extent) on subduction-induced upper mantle flow remains uncertain. We present a series of free subduction analog models where W was systematically varied to upscaled values of 250-3600 km to investigate its effect on subducting plate kinematics and upper mantle return flow around the lateral slab edges. We particularly focused on the upwelling component of mantle flow, which might promote decompression melting and could thereby produce intraplate volcanism. The models show that W has a strong control on trench curvature and on the trench retreat, subducting plate, and subduction velocities, generally in good agreement with previous modeling studies. Upper mantle flow velocity maps produced by means of a stereoscopic particle image velocimetry technique indicate that the magnitude of the subduction-induced mantle flow around the lateral slab edges correlates positively with the product of W and trench retreat velocity. For all models an important upwelling component is always produced close to the lateral slab edges, with higher magnitudes for wider slabs. The trench-parallel lateral extent of this upwelling component is the same irrespective of W, but its maximum magnitude gets located closer to the subducting plate in the trench-normal direction and it is more focused when W increases. For W ≤ 2000 km the upwelling occurs laterally (in the trench-parallel direction) next to the subslab domain and the mantle wedge domain, while for W ≥ 2000 km it is located only next to the subslab domain and focuses closer to the trench tip, because of stronger poloidal flow in the mantle wedge extending laterally. STRAK AND SCHELLART SUBDUCTION AND MANTLE FLOW MODELING 4641 PUBLICATIONS
Morphotectonics by Vincent Strak
Tectonically controlled landforms develop morphologic features that provide useful markers to inv... more Tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics. In this paper, we present results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes (erosion, transport, and sedimentation), coupled with accurate model monitoring techniques. This approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end-member geological settings: compression, extension, and strike–slip.
Experimental results outline first that experimental morphologies evolve significantly at a short time scale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth, and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp, and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike–slip setting, the complex morphology of the wrench zone, composed of several interacting fault segments, enhances the interactions with the drainage network. Because of the widening of the main fault zone toward the surface, a significant amount of distributed deformation is observed along the wrench zone. Locally, where two terminations of fault segments interact, less than a quarter of the far field displacement can remain measurable using fault offsets, leading to a systematic underestimation of the real fault slip rate.
These different experimental examples illustrate the great potential of the approach coupling deformation mechanisms and erosion–transport–sedimentation processes to investigate qualitatively and quantitatively the morphotectonic evolution of tectonically controlled landscapes.
Tectonophysics, 2011
The growth of relief in active tectonic areas is mainly controlled by the interactions between te... more The growth of relief in active tectonic areas is mainly controlled by the interactions between tectonics and surface processes (erosion and sedimentation). The study of long-lived morphologic markers formed by these interactions can help in quantifying the competing effects of tectonics, erosion and sedimentation. In regions experiencing active extension, river-long profiles and faceted spurs (triangular facets) can help in understanding the development of mountainous topography along normal fault scarps. In this study, we developed analogue experiments that simulate the morphologic evolution of a mountain range bounded by a normal fault. This paper focuses on the effect of the fault slip rate on the morphologic evolution of the footwall by performing three analogue experiments with different fault slip rates under a constant rainfall rate. A morphometric analysis of the modelled catchments allows comparing with a natural case (Tunka halfgraben, Siberia). After a certain amount of fault slip, the modelled footwall topographies of our models reaches a dynamic equilibrium (i.e., erosion balances tectonic uplift relative to the base level) close to the fault, whereas the topography farther from the fault is still being dissected due to regressive erosion. We show that the rates of vertical erosion in the area where dynamic equilibrium is reached and the rate of regressive erosion are linearly correlated with the fault throw rate. Facet morphology seems to depend on the fault slip rate except for the fastest experiment where faceted spurs are degraded due to mass wasting. A stream-power law is computed for the area wherein rivers reach a topographic equilibrium. We show that the erosional capacity of the system depends on the fault slip rate. Finally, our results demonstrate the possibility of preserving convex river-long profiles on the long-term under steady external (tectonic uplift and rainfall) conditions.
We present new results on the long-term throw rates of active normal faults in the North Baikal R... more We present new results on the long-term throw rates of active normal faults in the North Baikal Rift (NBR), eastern Siberia, based on a statistical analysis of triangular faceted scarps. Faceted spurs or triangular facets are morphologic features frequently observed along normal fault scarps, and result from the progressive denudation and incision of the footwall during fault activity. Fault-bounded ridges
Ce manuscrit est l'aboutissement de 4 années de doctorat au sein de l'Institut des Sciences de la... more Ce manuscrit est l'aboutissement de 4 années de doctorat au sein de l'Institut des Sciences de la Terre de Paris (ISTeP). Ces années ont été pour moi une expérience très enrichissante, tant sur le plan professionnel que personnel. Je tenais à remercier ici toutes les personnes qui ont contribué, de près ou de loin, à cet enrichissement. Tout d'abord, je souhaite remercier mes directeurs de thèse, Carole Petit et Bertrand Meyer. Merci pour votre soutien, votre implication, votre patience, et pour m'avoir transmis une part de votre savoir et de votre « savoir faire ». Quatre années à vos côtés ça n'est pas rien et une part de vous restera gravée en moi. Je tiens à remercier les membres du jury : Stéphane Bonnet, Peter Van Der Beek, Michel Sébrier, Sébastien Castelltort et Bernard Delcaillau qui ont accepté de donner leur avis sur ce travail de thèse et de partager leur réflexion. Je souhaite ensuite remercier Stéphane Dominguez, qui a grandement collaboré à ce travail de thèse. Merci de m'avoir fait découvrir le monde de la recherche depuis mon master à Montpellier et, en particulier, le monde de la modélisation analogique. Tu l'as toujours fait avec passion et avec une grande curiosité scientifique, ce qui m'a motivé pour poursuivre en thèse. Un grand merci pour ton investissement, pour ton soutien et pour m'avoir mis le pied à l'étrier. Merci également à Fabien Graveleau pour tous les échanges enrichissants que l'on a eu sur l'aspect modélisation analogique. J'en profite pour remercier Christian Romano pour m'avoir transmis de bonnes astuces côté bricolage (Stéphane aussi d'ailleurs !). Encore un grand merci à tous les trois. J'ai espoir que l'on se retrouve tous autour d'une table (à déformation ou pas !) un jour… Un merci particulier à Nicolas Loget et Michel Sébrier pour l'intérêt que vous avez porté à mon travail de thèse et pour les discussions enrichissantes que j'ai eues avec vous.
Special Issue "200 years of geodynamic modelling" by Vincent Strak
We present a review of the analogue modelling method, which has been used for 200 years, and cont... more We present a review of the analogue modelling method, which has been used for 200 years, and continues to be used, to investigate geological phenomena and geodynamic processes. We particularly focus on the following four components: (1) the different fundamental modelling approaches that exist in analogue modelling; (2) the scaling theory and scaling of topography; (3) the different materials and rheologies that are used to simulate the complex behaviour of rocks; and (4) a range of recording techniques that are used for qualitative and quantitative analyses and interpretations of analogue models. Furthermore, we apply these four components to laboratory-based subduction models and describe some of the issues at hand with modelling such systems. Over the last 200 years, a wide variety of analogue materials have been used with different rheologies, including viscous materials (e.g. syrups, silicones, water), brittle materials (e.g. granular materials such as sand, microspheres and sugar), plastic materials (e.g. plasticine), viscoplastic materials (e.g. paraffin, waxes, petrolatum) and visco-elasto-plastic materials (e.g. hydrocarbon compounds and gelatins). These materials have been used in many different set-ups to study processes from the microscale, such as porphyroclast rotation, to the mantle scale, such as subduction and mantle convection. Despite the wide variety of modelling materials and great diversity in model set-ups and processes investigated, all laboratory experiments can be classified into one of three different categories based on three fundamental modelling approaches that have been used in analogue modelling: (1) The external approach, (2) the combined (external + internal) approach, and (3) the internal approach. In the external approach and combined approach, energy is added to the experimental system through the external application of a velocity, temperature gradient or a material influx (or a combination thereof), and so the system is open. In the external approach, all deformation in the system is driven by the externally imposed condition, while in the combined approach, part of the deformation is driven by buoyancy forces internal to the system. In the internal approach, all deformation is driven by buoyancy forces internal to the system and so the system is closed and no energy is added during an experimental run. In the combined approach, the externally imposed force or added energy is generally not quantified nor compared to the internal buoyancy force or potential energy of the system, and so it is not known if these experiments are properly scaled with respect to nature. The scaling theory requires that analogue models are geometrically, kinematically and dynamically similar to the natural prototype. Direct scaling of topography in laboratory models indicates that it is often significantly exaggerated. This can be ascribed to (1) The lack of isostatic compensation, which causes topography to be too high.
Introduction to the special issue celebrating 200 years of geodynamic modelling a b s t r a c t S... more Introduction to the special issue celebrating 200 years of geodynamic modelling a b s t r a c t Since the first published laboratory models from Sir James Hall in 1815, analogue and numerical geodynamic modelling have become widely used as they provide qualitative and quantitative insights into a broad range of geological processes. To celebrate the 200th anniversary of geodynamic modelling, this special issue gathers review works and recent studies on analogue and numerical modelling of tectonic and geodynamic processes, as an opportunity to present some of the milestones and recent breakthroughs in this field, to discuss potential issues and to highlight possible future developments.
Earthquakes in the laboratory by Vincent Strak
Tectonics, 2015
Nowadays, technological advances in satellite imagery measurements as well as the development of ... more Nowadays, technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle. However, the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years. To overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters, we have developed a new experimental approach allowing for the simulation of strike-slip fault earthquakes and analyze in detail hundreds of successive seismic cycle. Model rheology is made of multilayered visco-elasto-plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle/ductile coupling, postseismic deformation phase and far-field stress transfers. The kinematic evolution of the model surface is monitored using an optical system, based on subpixel spectral correlation of high-resolution digital images. First, results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory. These results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth, along the fault plane. Our analog modeling approach appears, then, as an efficient complementary approach to investigate earthquake dynamics.
Uploads
Subduction processes by Vincent Strak
Morphotectonics by Vincent Strak
Experimental results outline first that experimental morphologies evolve significantly at a short time scale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth, and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp, and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike–slip setting, the complex morphology of the wrench zone, composed of several interacting fault segments, enhances the interactions with the drainage network. Because of the widening of the main fault zone toward the surface, a significant amount of distributed deformation is observed along the wrench zone. Locally, where two terminations of fault segments interact, less than a quarter of the far field displacement can remain measurable using fault offsets, leading to a systematic underestimation of the real fault slip rate.
These different experimental examples illustrate the great potential of the approach coupling deformation mechanisms and erosion–transport–sedimentation processes to investigate qualitatively and quantitatively the morphotectonic evolution of tectonically controlled landscapes.
Special Issue "200 years of geodynamic modelling" by Vincent Strak
Earthquakes in the laboratory by Vincent Strak