Interaction between the Mid‐Atlantic Ridge and the Azores hot spot during the last 85 Myr: Emplacement and rifting of the hot spot‐derived plateaus

Abstract

[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.

Constraints on the structure of the crust and lithosphere beneath the Azores Islands from teleseismic receiver functions

“…3), that is, the depth of the interface is generally shallower beneath the islands closer to the MAR (35-55 km, 5-6.5 s delay time) and deepens with increasing distance to the MAR (∼85 km, ∼9 s delay time). Our results also agree with previous geophysical and geochemical studies which estimated the LAB depth to deepen from ∼35-40 km under the Western and Central Islands to ∼70-80 km under São Miguel and Santa Maria (Gente et al 2003;Silveira et al 2010;Genske et al 2012). There are, however, some ambiguous results at the islands of Terceira and Santa Maria that warrant closer inspection.…”

“…Schilling 1975;Gente et al 2003). The development of the plateau is inferred to have occurred mainly between 20 and 7 Ma, and was followed by significant post-volcanic tectonic rifting (Gente et al 2003;Luis & Miranda 2008). Whilst being stretched along the MAR, the plateau has been split into a smaller western and larger eastern sector.…”

“…This area of elevated seafloor corresponds to a massive volcanic plateau, interpreted as the result of the interaction of a mantle plume with the MAR (e.g. Schilling 1975;Gente et al 2003). The development of the plateau is inferred to have occurred mainly between 20 and 7 Ma, and was followed by significant post-volcanic tectonic rifting (Gente et al 2003;Luis & Miranda 2008).…”

“…The Azores Islands rest on a wide triangular-shaped bathymetric anomaly-the Azores Plateau-roughly outlined by the −2000 m isobath (Searle 1980;Lourenço et al 1998;Gente et al 2003). This area of elevated seafloor corresponds to a massive volcanic plateau, interpreted as the result of the interaction of a mantle plume with the MAR (e.g.…”

Formation and evolution of Shatsky Rise oceanic plateau: Insights from IODP Expedition 324 and recent geophysical cruises

“…Plate reconstructions indicate that the largest known oceanic LIP, the Ontong Java-Hikurangi-Manihiki LIP also formed at a triple junction (Taylor, 2006;Chandler et al, 2012;Hochmuth et al, 2015). The same can be said of the next largest oceanic LIP, the Indian Ocean's Kerguelen Plateau (Royer et al, 1991), and the Azores Plateau (Gente et al, 2003) in the Atlantic. In addition, it has been noted that many oceanic hotspots have erupted at spreading ridges (Whittaker et al, 2015).…”