Spatial relationship between recent compressional structures and older high-velocity crustal structures; examples from the Vøring Margin, NE Atlantic, and Northern Honshu, Japan

Abstract

The geological evolution of the volcanic passive margin off mid-Norway, NE Atlantic, and the active volcanic arc in northern Honshu, related to the subduction of the Pacific plate beneath Japan, are similar in the sense that long periods of extensional deformation has shifted to recent compression with formation of domal structures. Seismic wide-angle data have been acquired across six contractional domes in the Vøring Basin, mid-Norwegian Margin, and over the Ou Backbone Range ‘pop-up’ structure, northern Honshu. The models derived from the seismic data reveal that the location of all investigated structures in the Vøring Basin is between, or in the vicinity of pre-Eocene high-velocity structures, which may act as rigid blocks during compression. It is proposed that the existence and trend of these structures, subject to mild NW–SE compression, is the most important factor controlling the formation, spatial distribution and trend of the domes. Structures in the high-velocity lower crust may be the single most important element in controling the domal formation; all modelled highs in the lower crustal early Tertiary intrusive layer seem to be related to the formation of domes in the NW–SE direction. The Ou Backbone Range pop-up structure is localised at a low rigidity zone mapped as low upper crustal seismic velocities. The structure coincides with the present day volcanic front, which may be interpreted as the main reason for the existence of low velocities and the main factor controling the localization of compressional deformation. The Ou Backbone Range is squeezed between a high velocity upper crustal block to the east and a high velocity lower crustal block to the west, and it is speculated that the corresponding lateral and vertical variations in crustal rigidity may have contributed to the actual localization of the present day volcanic front.