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Etude géodynamique de la Zone de subduction Tonga-Kermadec par une approche couplée de modélisation numérique 3D et de sismotectonique

Abstract : The Tonga-Kermadec subduction zone is the consequence of a complex geodynamical evolution. The interaction between the back-arc opening mechanisms, the subduction of the oblique aseismic Louisville Seamount Chain, the tearing of the Pacific Plate and the increasing obliquity of convergence from North to South results in the present-day morphotectonic segmentation of the convergent system. Using both 3-D numerical modelling and seismotectonics, we attempt to determine the state of stress inferred in a convergent system (1) from a convergence accommodated along a curved margin and (2) from the subduction of an oceanic aseismic ridge. For that purpose, a finite element thermo-mechanical code was developped in 3-D by R. Hassani and then validated within the framework of this study. The results highlight a significant effect of the along-strike variations in a convergent system on the style of lithospheric deformation. (1) A convexity or concavity of the margin towards the ocean enhances respectively a compressive or extensive regime within the upper plate, whatever are the density contrast between the lithosphere and the asthenosphere or the value of the friction coefficient. (2) The results from both the numerical simulations and the seismotectonics study highlight a significant role of an oceanic ridge subduction on the state of stress within the overriding plate. A compressive regime as well as the uplift of the margin are induced in front of the subducted ridge. The numerical simulations indicate that the stress distribution within the upper plate is controlled by the obliquity of the subducted ridge. A tectono-kinematics segmentation of the arc and back-arc domains in the Tonga-Kermadec subduction zone, is revealed through the stress tensor resolution deduced from the CMTS. Since this segmentation is likely correlated to the numerical results, we confirm the influence of the Louisville Seamount Chain on the present-day structure of the Lau back-arc basin. (3) The study of the shallow seismicity distribution and of the CMTS indicate also the influence of the Louisville ridge on the deep slab behaviour. A subduction jump correlated with the initiation of the Louisville Ridge subduction is identified to the North of the Peggy Ridge. A detachment of the deep slab, which is underlined by a major seismic gap below the Lau Basin, accommodated this subduction jump. From a precise study of the shallow seismicity distribution, new tectonic features are identified in the Northern part of the Lau Basin : the Futuna-Niua Fo ou alignement interpreted as a fossil plate boundary and the intra-arc Niuatoputapu structure. They are both involved in the global reorganisation of the subduction zone.
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Contributor : Marie-Aude Bonnardot Connect in order to contact the contributor
Submitted on : Tuesday, January 15, 2008 - 5:14:18 PM
Last modification on : Tuesday, November 16, 2021 - 4:05:30 AM
Long-term archiving on: : Thursday, September 27, 2012 - 2:40:12 PM


  • HAL Id : tel-00204905, version 1


Marie-Aude Bonnardot. Etude géodynamique de la Zone de subduction Tonga-Kermadec par une approche couplée de modélisation numérique 3D et de sismotectonique. Géologie appliquée. Université Nice Sophia Antipolis, 2006. Français. ⟨tel-00204905⟩



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