There has been much recent interest in the volcanic and tectonic structure of ultra-slow spreading ridges such as the Southwest Indian Ridge and Gakkel Ridge in the Arctic, because the extreme spreading rate may potentially shed light on melting processes in the underlying mantle and delivery of melt through the lithosphere to form the oceanic crust (Mapping and Sampling the Arctic Ridges: A Project Plan, InterRidge, pp. 25, Dec. 1998). Spreading at ~3 mm/yr [Searle, 1980], the Azores region is an ultra-slow spreading plate boundary, much slower than the Gakkel Ridge (6-15 mm/yr [deMetts et al., 1990]). Volcanism is distributed sporadically across the plate boundary, creating the individual islands and interspersed submarine edifices, a result of a broad underlying melting anomaly [Bonatti, 1990]. The volcanic centres illustrated by the topography (Figure 2) show that volcanism is localized in a way that is comparable to that of Gakkel Ridge [Edwards et al., 2001].
|
Figure 2. Topography of the central Azores islands (contours every 200 m with bold contours annotated every 1 km). The structure forming Faial-Pico and the island of S‹o Jorge are elongated volcanic ridges, and further volcanic ridges exist among the islands. An eruption on the ridge immediately west of Terceira in particular was the subject of a previous article by Freire Luis et al. [InterRidge News, 8(1), 13-14, 1999].
|