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Terceira Rift
The Terceira Rift is a geological rift located amidst the Azores islands in the Atlantic Ocean. It runs between the Azores Triple Junction to the west and the Azores–Gibraltar Transform Fault to the southeast. It separates the Eurasian Plate to the north from the African Plate to the south. The Terceira Rift is named for Terceira Island through which it passes.
==Geological information==
The Terceira Rift is 550 km long, and represents the world’s slowest spreading center, with plate divergence of 2-4 mm/year.〔Vogt, P. R., & Jung, W. Y. (2004). The Terceira Rift as hyper-slow, hotspot-dominated oblique spreading axis: A comparison with other slow-spreading plate boundaries. Earth and Planetary Science Letters, 218(1), 77-90.〕 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.〔Beier, C., Haase, K. M., Abouchami, W., Krienitz, M. S., Hauff, F. (2008). Magma genesis by rifting of oceanic lithosphere above anomalous mantle: Terceira Rift, Azores. Geochemistry Geophysics Geosystems (G3), 9, Q12013.〕 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 ridges. In particular, high obliquity values of 40°-65°, and a magmatic segmentation wavelength of 100 km, are similar to other very slow rifts.〔 Rift valleys present along the rift are 1000-2200 m deep, and 30-60 km wide, similar to the Mid-Atlantic Ridge median valley. However, the amplitude of the Terceira Rift along-strike topography is 2000-4000 m, which is much larger than expected for ultraslow spreading ridges.〔 This irregularity is thought to be due to the association of the rift with the Azores hotspot, in combination with slow spreading rates. Slow spreading results in a strong and thick axial elastic plate, and slower volcanic extrusions from the rift zone, resulting in high topography when merged with plume-related volcanism.〔 The large volume of volcanism associated with the hotspot is mainly controlled by regional extension between Africa and Eurasia, as indicated by strikes of extension fractures.〔Navarro, A., Lourenço, N., Chorowicz, J., Miranda, J. M., & Catalão, J. (2009). Analysis of geometry of volcanoes and faults in Terceira Island (Azores): Evidence for reactivation tectonics at the EUR/AFR plate boundary in the Azores triple junction. Tectonophysics, 465(1), 98-113.〕 Furthermore, the majority of inter-plate deformation is focused on the Terceira Rift, although a clear deformation pattern has not yet been recognized.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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