Progressive changes in magma transport at the active Serreta Ridge, Azores

Volcanism in the Eastern Azores Plateau occurs at large central volcanoes and along subaerial and submarine fissure zones, resulting from a mantle melting anomaly combined with transtensional stresses. Volcanic structures are aligned WNW-ESE and NW-SE, reflecting two tectonic stress fields that control the direction of lateral melt transport. Terceira Island is influenced by both stress fields, dividing the island into an eastern and western part. Several submarine volcanic ridges with variable orientations are located west of Santa Barbara, the youngest central volcano on Terceira. Major, trace element and Sr-Nd-Pb-Hf isotope compositions from submarine lavas and glasses, in part associated with the 1998-2001 Serreta Ridge eruption, vary between different lava suites, suggesting a formation from different mantle sources. Submarine lavas are more primitive than those from Santa Barbara volcano, indicating that they are not laterally connected with the shallow magma reservoir located in 2- to 5-km depth beneath the central volcano. Mineral thermobarometric data suggest that the older Serreta magmas were laterally transported at depths >5 km from Santa Barbara predominantly in WNW direction. We propose that lithospheric extension controls magma transport from the central volcano to Serreta Ridge. The youngest Serreta lavas differ from Santa Barbara and other submarine ridges in having less radiogenic Pb and higher Hf isotope ratios representing a new magma pulse ascending from the mantle. We conclude that lateral magma transport and the morphology of volcanic ridges are controlled by tectonic stresses in the lithosphere, whereas vertical melt transport is initiated by processes in the mantle.Peer reviewe

Cruise Report - METEOR-Berichte Azores Plateau Cruise No. M128 02.07.2016 – 27.07.2016, Ponta Delgada (Azores, Portugal) – Ponta Delgada (Azores, Portugal)

The research program of cruise M128 Azores Plateau mainly aimed at improving our understanding of the igneous and tectonic processes that occur during the initial emplacement of large igneous plateaus and the subsequent interaction between intraplate volcanism and ultraslow rifting. The sampling program targeted the oldest and youngest igneous volcanic edifices in the Azores to better constrain the age of the submarine Plateau and the processes that led to changes in the magmatic activity. We obtained a total of more than 330 rock samples and more than 435 biological specimens during 70 TV grab stations (63 containing samples) and 19 successful ROV dives. The combination of bathymetric maps (1980 km hydroacoustic profile length) and petrological samples allows us to better constrain the evolution of rift systems in this tectonically and magmatically active region. A major sampling focus were the volcanic rift systems west of the islands along the Terceira Rift axis and west of São Jorge and Faial. In addition, six stratigraphic dive profiles will yield important constraints on the early magmatic evolution of the Azores Plateau. The samples and geochemical, petrological, volcanological and biological data will provide a unique and detailed picture of how and when the Azores submarine Plateau formed and the extent to which the local tectonic processes influenced the formation and ascent of melts. The macrofauna samples will yield detailed information on the function of the Azores Plateau as a bathymetric swell in the Central Atlantic Ocean