Les dorsales ultra-lentes, une réponseau jeu de la tectonique des plaques et de laconvection mantellique

• Main Authors: Husson , Laurent, Yamato, Philippe, Bezos, Antoine
• Other Authors: Institut des Sciences de la Terre (ISTerre), Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement IRD : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Systèmes Tectoniques, Géosciences Rennes (GR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Planétologie et Géodynamique UMR 6112 (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2014
• Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Arctic; Indian
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-01080752

International audience Ultra-slow spreading ridges such as the South West Indian ridge orthe Arctic ridge system are oddities amongst oceanic ridges. Indeed,conversely to faster oceanic ridges, petrographic and seafloor studieshave shown that they characterized by low melt supply and present lowcrustal thicknesses and heat flow; these features are interpreted as anevidence for a cooler sublithospheric mantle. In cartoonish sketches ofplate tectonics, ridges open above upwellings, subduction zones occurover downwellings, and plates are riding over the mantle convectioncells. In this study, we designed a simple yet dynamically consistentthermal convection model to test the impact of far-field forces on spreadingridges and show that this pattern is disrupted by plate tectonics. Inparticular, continental collisions modulate the spreading rates becauseresisting forces build up at plate boundaries. As a consequence, thismodifies the surface boundary conditions and therefore the underlyingmantle flow. We show that the ideal convection cell pattern quicklybreaks down when plate motion is impeded by continental collisions inthe far field. Not only the decreasing spreading rates are diagnostic, butin the same time, (i) the heat flow is decreasing at the ridge, (ii) the thermalstructure of the cooling lithosphere no longer matches the coolinghalf-space model, and (iii) the mantle temperature beneath the ridgedrops by more than 100 degrees. We compare our model predictions toavailable observables and show that this simple mechanism explains theatypical thermo-mechanical evolution of the South West Indian ridgeand Arctic ridge system. Last, the recent S wave seismic tomographymodel of Debayle and Ricard (2012) reveals that only away from thosetwo ridges does lithospheric thickening departs from the half-space coolingmodel, in accord with our model predictions.