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Title:
Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements
Authors:
Doubre, Cécile; Déprez, Aline; Masson, Frédéric; Socquet, Anne; Lewi, Elias; Grandin, Raphaël; Nercessian, Alexandre; Ulrich, Patrice; De Chabalier, Jean-Bernard; Saad, Ibrahim; Abayazid, Ahmadine; Peltzer, Gilles; Delorme, Arthur; Calais, Eric; Wright, Tim
Affiliation:
AA(Université de Strasbourg, CNRS, IPGS-UMR 7516, F-67000 Strasbourg, France. ), AB(Université de Strasbourg, CNRS, IPGS-UMR 7516, F-67000 Strasbourg, France), AC(Université de Strasbourg, CNRS, IPGS-UMR 7516, F-67000 Strasbourg, France), AD(Univ. Grenoble Alpes, CNRS, ISTerre, Grenoble, France), AE(Addis Ababa University Arat Kilo Campus, Institute of Geophysics, Space Science and Astronomy, Addis Ababa, Ethiopia), AF(Institut de Physique du Globe de Paris; UMR 7154, Paris, France), AG(Institut de Physique du Globe de Paris; UMR 7154, Paris, France), AH(Université de Strasbourg, CNRS, IPGS-UMR 7516, F-67000 Strasbourg, France), AI(Institut de Physique du Globe de Paris; UMR 7154, Paris, France), AJ(Observatoire Géophysique d'Arta - Centre d'Etudes et de Recherche de Djibouti, Djibouti), AK(Observatoire Géophysique d'Arta - Centre d'Etudes et de Recherche de Djibouti, Djibouti), AL(Earth and Space Science Department, University of California Los Angeles, CA, USA. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA), AM(Institut de Physique du Globe de Paris; UMR 7154, Paris, France), AN(Ecole Normale Supérieure, Dpt of Geosciences, UMR CNRS 8538, Paris, France), AO(COMET, School of Earth and Environment, University of Leeds, United Kingdom)
Publication:
Geophysical Journal International, Volume 208, Issue 2, p.936-953 (OUP Homepage)
Publication Date:
02/2017
Origin:
OUP
Keywords:
Transient deformation, Mid-ocean ridge processes, Continental tectonics: extensional, Kinematics of crustal and mantle deformation, Africa
Abstract Copyright:
The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society.
DOI:
10.1093/gji/ggw434
Bibliographic Code:
2017GeoJI.208..936D

Abstract

Kinematics of divergent boundaries and Rift-Rift-Rift junctions are classically studied using long-term geodetic observations. Since significant magma-related displacements are expected, short-term deformation provides important constraints on the crustal mechanisms involved both in active rifting and in transfer of extensional deformation between spreading axes. Using InSAR and GPS data, we analyse the surface deformation in the whole Central Afar region in detail, focusing on both the extensional deformation across the Quaternary magmato-tectonic rift segments, and on the zones of deformation transfer between active segments and spreading axes. The largest deformation occurs across the two recently activated Asal-Ghoubbet (AG) and Manda Hararo-Dabbahu (MH-D) magmato-tectonic segments with very high strain rates, whereas the other Quaternary active segments do not concentrate any large strain, suggesting that these rifts are either sealed during interdyking periods or not mature enough to remain a plate boundary. Outside of these segments, the GPS horizontal velocity field shows a regular gradient following a clockwise rotation of the displacements from the Southeast to the East of Afar, with respect to Nubia. Very few shallow creeping structures can be identified as well in the InSAR data. However, using these data together with the strain rate tensor and the rotations rates deduced from GPS baselines, the present-day strain field over Central Afar is consistent with the main tectonic structures, and therefore with the long-term deformation. We investigate the current kinematics of the triple junction included in our GPS data set by building simple block models. The deformation in Central Afar can be described by adding a central microblock evolving separately from the three surrounding plates. In this model, the northern block boundary corresponds to a deep EW-trending trans-tensional dislocation, locked from the surface to 10-13 km and joining at depth the active spreading axes of the Red Sea and the Aden Ridge, from AG to MH-D rift segments. Over the long-term, this plate configuration could explain the presence of the en-échelon magmatic basins and subrifts. However, the transient behaviour of the spreading axes implies that the deformation in Central Afar evolves depending on the availability of magma supply within the well-established segments.
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