Terceira Rift

The Terceira Rift is 550 km long, and represents the world's slowest spreading center, with plate divergence of 2–4 mm/year. It developed from a transform fault and now operates as a hyper-slow spreading center, as recognized by the relative movement between the African and Eurasian plates. There is a strong resemblance between the Terceira Rift and other ultra- or super- slow spreading ridges, such as the Gakkel Rift and the Southwest Indian Ridge. In particular, high obliquity values of 40°–65°, and a magmatic segmentation wavelength of 100 km, are similar to other very slow rifts. Furthermore, the majority of inter-plate deformation is focused on the Terceira Rift, although a clear deformation pattern has not yet been recognized. ==Pre-rift influences==

The structures present along the Terceira Rift have directions likely associated with pre-rift geometry, as they do not correspond to the current direction of spreading motion, which is approximately N70°. ==The Azores Hotspot and the resulting Azores Plateau==

The Azores Plateau began to form around 10 Ma, and is characterized by isotopic and elemental variations indicative of large heterogeneities in the mantle beneath it. There is also evidence of only one magmatic source, and no interaction with other volcanic systems. Additionally, the presence of thick crust and complex volcano-tectonic fabric implies the plateau developed through the migration of the Terceira Rift towards the NE, causing a constant position over a fixed hotspot. Lines of evidence for the plume-shaped structure in this area include mantle seismic anomalies, bathymetry and gravity anomalies, and plume noble gas signatures associated with the hotspot. However, there is also a possibility the increased magmatic activity on the Terceira Rift is a partial result of the involvement with the rift–rift–rift triple junction between the Eurasian, African, and North American plates. ==References==