[1] Multiple-and single-beam bathymetric data are compiled over the Azores plateau to produce a 1 km  1 km grid between latitudes 32°N and 49°N and longitudes 22°W and 43°W. Mantle Bouguer anomalies are then calculated from this grid and the satellite-derived gravity. These grids provide new insights on the temporal and spatial variations of melt supply to the ridge axis. The elevated seafloor of the Azores plateau is interpreted as resulting from the interaction of a mantle plume with the Mid-Atlantic Ridge (MAR). The presence of a large region of elevated seafloor associated with a thick crust between the Great Meteor Seamounts and the Azores platform on the Africa plate, and less developed conjugate structures on the North America plate, favors genetic relations between these hot spot-derived structures. This suggests that a ridge-hot spot interaction has occurred in this region since 85 Ma. This interaction migrated northward along the ridge axis as a result of the SSE absolute motion of the Africa plate, following a direction grossly parallel to the orientation of the MAR. Kinematic reconstructions from chron 13 ($35 Ma) to the present allow a proposal that the formation of the Azores plateau began around 20 Ma and ended around 7 Ma. A sharp bathymetric step is associated with the beginning of important melt supply around 20 Ma. The excess of melt production is controlled by the interaction of the ridge and hot spot melting zones. The geometry and distribution of the smaller-scale features on the plateau record episodic variations of the hot spot melt production. The periodicity of these variations is about 3-5 Myr. Following the rapid decrease of widespread volcanism, the plateau was subsequently rifted from north to south by the Mid-Atlantic Ridge since 7 Ma. This rifting begins when the MAR melting zone is progressively shifted away from the 200-km plume thermal anomaly. These results bear important consequences on the motion of the Africa plate relative to the Azores hot spot. They also provide an explanation to the asymmetric geochemical signature of the Azores hot spot along the MidAtlantic Ridge.Components: 12,255 words, 10 figures, 1 table.Keywords: mid-ocean ridges; plume; plume-ridge interaction; geodynamics; north Atlantic Ocean; Azores.

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Between 1999 and 2009, autonomous hydrophones were deployed to monitor seismic activity from 16° N to 50° N along the Mid-Atlantic Ridge. These data were examined for airgun sounds produced during offshore surveys for oil and gas deposits, as well as the 20 Hz pulse sounds from fin whales, which may be masked by airgun noise. An automatic detection algorithm was used to identify airgun sound patterns, and fin whale calling levels were summarized via long-term spectral analysis. Both airgun and fin whale sounds were recorded at all sites. Fin whale calling rates were higher at sites north of 32° N, increased during the late summer and fall months at all sites, and peaked during the winter months, a time when airgun noise was often prevalent. Seismic survey vessels were acoustically located off the coasts of three major areas: Newfoundland, northeast Brazil, and Senegal and Mauritania in West Africa. In some cases, airgun sounds were recorded almost 4000 km from the survey vessel in areas that are likely occupied by fin whales, and at some locations airgun sounds were recorded more than 80% days/month for more than 12 consecutive months.

International audienceAutonomous hydrophones arrays are an excellent tool for monitoring mid-ocean ridge seismic activity. The major advantage of using arrays of autonomous hydrophones for recording deep-ocean ridge earthquakes is its low magnitude detection thresholds achievable using hydroacoustic techniques. Regional analysis of the detection thresholds of the different autonomous hydrophones arrays deployed along the Mid-Atlantic Ridge reveals the strong influence of the detection threshold in the number of recorded events and it must be taken into account in any further analysis. In this study, the analysis of both autonomous hydrophones and teleseismically detected Mid-Atlantic Ridge seismicity reveals that the background seismicity from the relatively short recording periods of the autonomous hydrophones mimic the results of the much longer teleseismic recording. It also reveals that seismicity generally cluster at both the segment scale and on Mantle Bouguer Anomaly maxima. The big majority of these clusters seem to be related to dyke intrusions and propagation along the Mid-Atlantic Ridge. These dyke intrusions interact with the mainshock-aftershock sequences. The seismic sequences mainshock-aftershock analysis reveals that the strength of the faults is highly influenced by the mode, or style, of faulting. Detachment faults, which are ubiquitous along the Mid-Atlantic Ridge, can produce more prolific shorter duration seismic sequences revealing faster and reduced strain releases in comparison to higher angle normal faults. This reduced strain release is most likely to occur due to the presence of higher levels of serpentinization on detachment faults. Higher levels of serpentenisation can also promote an aseismic transient slip on the mainshock-aftershock sequences