Sallarès Valenti auteur aut IRD Charvis Philippe auteur aut IRD Flueh E.R. auteur aut IRD Bialas J. auteur aut IRD text journalArticle eng text/pdf reformatted digital access The Cocos and Malpelo Volcanic Ridges are blocks of thickened oceanic crust thought to be the result of the interaction between the Galapagos hot spot and the Cocos Nazca Spreading Center during the last 20 m.y. In this work we investigate the seismic structure of these two aseismic ridges along three wide angle transects acquired during the Panama basin and Galapagos plume New Investigations of Intraplate magmatism (PAGANINI) 1999 experiment. A two dimensional velocity field with the Moho geometry is obtained using joint refraction/reflection travel time tomography, and the uncertainty and robustness of the results are estimated by performing a Monte Carlo type analysis. Our results show that the maximum crustal thickness along these profiles ranges from 16.5 km (southern Cocos) to 19 km (northern Cocos and Malpelo). Oceanic layer 2 thickness is quite uniform regardless of total crustal thickness variations; crustal thickening is mainly accommodated by layer 3. These observations are shown to be consistent with gravity data. The variation of layer 3 velocities is similar along all profiles, being lower where crust is thicker. This leads to an overall anticorrelation between crustal thickness and bulk lower crustal velocity. Since this anticorrelation is contrary to crustal thickening resulting from passive upwelling of abnormally hot mantle, it is necessary to consider active upwelling components and/or some compositional heterogeneities in the mantle source. The NW limit of the Malpelo Ridge shows a dramatic crustal thinning and displays high lower crustal velocities and a poorly defined crust mantle boundary, suggesting that differential motion along the Coiba transform fault probably separated Regina and Malpelo Ridges. specialized VOLCANISME POINT CHAUD TOMOGRAPHIE SISMOTECTONIQUE CROUTE OCEANIQUE GEODYNAMIQUE COLON ARCHIPIELAGO 066GPHMAR 108 B12 5-1-5-21 2003 0148-0227 https://www.documentation.ird.fr/hor/fdi:010032982 10.1029/2003JB002431 0148-0227 [F B010032982] https://www.documentation.ird.fr/hor/fdi:010032982 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-10/010032982.pdf IRD - Base Horizon / Pleins textes 2004-03-23 2021-02-12 fdi:010032982 fre