Horizontal and vertical crustal movements in Iceland

Abstract

Based mainly on geodetic and geological investigations, an attempt is made to demonstrate the kinematic bearing of the Icelandic crust while drifting apart from its birthplace in the axial rift zone to the 12 m.y. old east coast of the island. The 40 km wide rift ‘val-ley’ floor is subjected to horizontal and vertical crustal movements that are in a ratio of 1. The ground deformation within the rift zone is predominantly confined to scattered narrow grabens whose width does not exceed 5 km. It is suggested that the layer 2/3-boundary plays a similar role for oceanic rifting as the Moho does for continental grabens. A maximum subsidence of superficially deposited flood basalt to a depth of more than 10 km within the limits of the axial rift zone can be expected. Outside the axial rift zone, a continuous uplift of the crust attains 1300 m along a 100 km distant culmination axis, as shown by the distribution of zeolite zones which have been secondarily formed within deeply buried, reheated flood basalts within the axial rift zone. The state of crustal stress changes from mainly tensional within the rift ‘valley’ to predominantly compressive along the rift flanks. A change from normal to reverse faulting when going across the margins of the axial rift zone can be expected. The discrepancy of the topography of Iceland with a submarine part of the Mid-Atlantic Ridge is probably due to more lava production within its ‘median valley’ and also due to an erosional degradation of its ‘rift mountains’.