Mid-Atlantic Ridge-Azores hotspot interactions:: along-axis migration of a hotspot-derived event of enhanced magmatism 10 to 3 Ma ago

A recent survey of the Mid-Atlantic Ridge over the southern edge of the Azores Platform shows that two anomalously shallow regions located off-axis on both sides of the ridge are the two flanks of a single rifted volcanic plateau. Crustal thickness over this plateau is up to twice that of surrounding oceanic areas, and original axial depths were near sealevel. The lack of a coherent magnetic anomaly pattern, and the near absence of fault scarps over the plateau suggest that its formation involved outpouring of lava over large distances off-axis. This volcanic plateau formed in Miocene times during an episode of greatly enhanced ridge magmatism caused, as proposed by P.R. Vogt [Geology 7 (1979) 93-98], by the southward propagation of a melting anomaly originated within the Azores hotspot, This melting anomaly could reflect excess temperatures of similar to 70 degrees C in the mantle beneath the ridge. It propagated at rates of similar to 60 mm/yr and lasted no more than a few million years at any given location along the ridge. Enhanced magmatism due to this melting anomaly played a significant role, some 10 Ma ago, in the construction of the Azores Platform. (C) 1999 Elsevier Science B.V. All rights reserved.