King’s Trough: An Ancient Analogue of the Terceira Rift (North Atlantic)

The paper compares the young structures of the Terceira Rift and the ancient ones of King’s Trough. It has been shown that despite the significant difference in the time of their formation, they have much in common. They are placed obliquely relative to all the structures that formed within the Mid-Atlantic Ridge, have a similar extent, and combine parameters typical of both continental (superslow rate of extension, thickness of the lithosphere, and alkaline volcanism) and oceanic rifts (segmentation and magmatism localized in a narrow area). The structures went through similar stages being formed on the already existing oceanic crust. The initial stage in both cases is associated with diffuse plume tholeiitic magmatism, distributed over a somewhat extended area of extension with the formation of large linear rises. The second stage was characterized by almost complete cessation of magmatism and localization of extension in one narrow area. Alkaline magmatism of the central type was typical for the final stage. Both of these structures are part of triple junctions, being fragments of lithospheric plates boundaries. The marked similarities point to the recurrent kinematics of North Atlantic lithospheric plates movement with the formation of structures at the plate boundaries that are different in age but similar in their geological history and mechanisms of formation.