Open AccessGeological context and vents morphology of the ultramafic‐hosted Ashadze hydrothermal areas (Mid‐Atlantic Ridge 13°N)
Author(s) -
Ondréas Hélène,
Cannat Mathilde,
Fouquet Yves,
Normand Alain
Publication year - 2012
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2012gc004433
Subject(s) - geology , ultramafic rock , hydrothermal circulation , ridge , mid atlantic ridge , bathymetry , context (archaeology) , impact crater , seafloor spreading , hydrothermal vent , outcrop , geochemistry , geomorphology , seismology , petrology , paleontology , oceanography , astrobiology , physics
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.