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Does unsteady overriding plate kinematics explain variability of slab dip and upper plate deformation?

Abstract : Plates reorganization associated with mantle convection leads to changes in absolute plate velocities which may in turn impact the geometry of slabs and the upper plate regime of deformation. Analogue experiments suggest a very good correlation between overriding plate absolute motion and, slab dip and upper plate deformation: steep slab and extension are associated with overriding plate moving away from the trench while shallow slab and shortening occur when the upper plate goes the other way. However, these correlations are established on models in which the motion of the overriding plate is constant and the subduction steady-state which may not correspond to the general case: How does the subduction adapt to the changes of overriding plate absolute velocity? What is the impact on slab dip and upper plate deformation? Could it explain why correlations in Nature between overriding plate absolute motion and slab dip are poorer than expected? We herein present a study coupling 3D analogue models of subduction and observations of present-day subduction parameters. The models show that instantaneous changes in the overriding plate absolute velocity produce a transient stage during which both upper plate deformation and slab dip adjust, followed by a period of stabilization. Specifically, deformation velocity adjusts rapidly while slab dip requires a larger time. For deep slab dip this time delay is on average 17 ± 4 Myr and is independent of both the absolute velocity and changes in absolute velocity. There is a systematic trend toward lower than expected slab dip when upper plate slowdowns and higher when it accelerates. In Nature, there is the same general trends but correlations are poorer than in laboratory models. The distribution of slab dip as a function of overriding plate accelerations or decelerations above specific periods of time supports the idea of a global adjustment time of 10 Ma, close to what found in analogue models. Over this time period, deep slab dips tend to be lower than expected when the overriding plate constantly decelerated and higher when it accelerated. The same analysis for upper plate deformation gives a best result for an adjustment time of 5 Ma. Thus, there is a delay in the response of the system to the changes of overriding plate absolute velocity. The poor correlation in Nature between presentday subduction kinematics, slab dip and upper plate deformation may explain because the present-day velocities correspond to a snapshot in the evolving history of subduction
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Submitted on : Wednesday, October 26, 2016 - 3:43:11 PM
Last modification on : Thursday, June 2, 2022 - 2:48:13 PM


  • HAL Id : insu-01388163, version 1


Solenn Hertgen, Benjamin Guillaume, Joseph Martinod. Does unsteady overriding plate kinematics explain variability of slab dip and upper plate deformation?. 25 ème Réunion des sciences de la Terre (RST 2016), Société Géologique de France, Oct 2016, Caen, France. pp.159. ⟨insu-01388163⟩



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