The Eastern Branch of Icelandic Rifts: Morphology and Tectonics

The eastern branch of Icelandic rifts includes the Northern and the Eastern Rift Zones whose morphologies are rather different; this is determined by different period of their formation, as well as by the structural and kinematic position relative to the Reykjanes and Kolbeinsey spreading ridges, the rift zones of the western branch, and the center of the Icelandic plume. The Northern Rift Zone includes both mature central volcanoes containing long fissure swarms, and embryonic edifices within the latter ones. The Eastern Rift Zone contains large conic and shield edifices of central volcanoes and comparatively young fissure swarms. We sought to reveal the present-day tectonic structure and geodynamic processes by morphometric analysis that included examination of variation for five parameters of fault scarps along the striking of the rift zones. The present-day propagation of the Northern Rift Zone is northward; the propagation does not occur throughout the entire length of volcanic systems, but focuses on individual fault groups. The present-day structural rearrangement of the Northern Rift Zone implies a gradual simplification of its tectonics, resulting in the formation of an en-echelon structure that includes several short segments of volcanic systems. At the same time, tectono-magmatic activity gradually concentrates in the western part of the rift zone. The Eastern Rift Zone divides into two separate branches having similar parameters of tectono-magmatic activity, with no signs of an ongoing structural rearrangement being observed at present, even though the western branch is recedes southwards. In addition, a relationship has been identified between the parameters of the fault scarps and the rheologic properties of the crust: in the conditions of higher magmatism and a shallower magma chamber, it is observed shorter and high-density fault groups of small amplitude, and frequent seismic activity.