%0 Journal Article %T Geological context and vents morphology of the ultramafic-hosted Ashadze hydrothermal areas (Mid-Atlantic Ridge 13°N) %+ Géosciences Marines (GM) %+ Institut de Physique du Globe de Paris (IPGP) %A Ondréas, Hélène %A Cannat, Mathilde %A Fouquet, Yves %A Normand, Alain %< avec comité de lecture %@ 1525-2027 %J Geochemistry, Geophysics, Geosystems %I AGU and the Geochemical Society %V 13 %N 11 %8 2012 %D 2012 %R 10.1029/2012GC004433 %K Ashadze %K Mid-Atlantic Ridge %K hydrothermal activity %K hydrothermal explosion crater %K ultramafic rocks %Z Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] %Z Sciences of the Universe [physics]/Earth Sciences/OceanographyJournal articles %X Recent ROV dives and high-resolution bathymetric data acquired over the Ashadze fields on the Mid-Atlantic Ridge (13 N) allow us to derive constraints on the regional and local geological setting of ultramafic-hosted hydrothermal fields. The active vent fields of Ashadze hydrothermal fields are located in the western axial valley wall, downslope from the termination of a prominent corrugated surface and in a transitional domain with respect to ridge segmentation. The study of the shipboard and ROV bathymetry shows that decameter (100 m by 60 m) to kilometer-scaled rockslides shape the axial valley wall slopes in this region. The Ashadze 1 vent field occurs on a coherent granular landslide rock mass that is elongated in an E-W direction. The Ashadze 1 vent field comprises hundreds of active and inactive sulfide chimneys. The Ashadze 2 vent field is located in a NNE-trending linear depression which separates outcrops of gabbros and serpentinized peridotites. Active black smokers in the Ashadze 2 field are located on ultramafic substratum in a 40-m diameter crater, 5-m deep. This crater recalls similar structures described at some vents of the Logatchev hydrothermal field (Mid-Atlantic Ridge 15 N). We discuss the mode of formation for these craters, as well as that for a breadcrust-like array of radial fissures identified at Ashadze 1. We propose that hydrothermalism at Ashadze can be an explosive phenomena associated with geyser-like explosions. Our study also constrains the geological and geophysical context of the ultramafic-hosted Ashadze hydrothermal system that may use the oceanic detachment fault as a preferred permeability conduit. %G English %2 https://insu.hal.science/insu-01819614/document %2 https://insu.hal.science/insu-01819614/file/Ondr-as_et_al-2012-Geochemistry%252C_Geophysics%252C_Geosystems.pdf %L insu-01819614 %U https://insu.hal.science/insu-01819614 %~ INSU %~ UNIV-PARIS7 %~ AFRIQ %~ CNRS %~ IPGP %~ IFREMER %~ GIP-BE %~ UNIV-PARIS