Continent-ocean transition and voluminous magmatic underplating derived fromP-wave velocity modelling of the East Greenland continental margin

Abstract

SUMMARY Deep seismic refraction data were gathered across the entire East Greenland rifted margin north of the Jan Mayen Fracture Zone between 72°N and 75°N in 2003. Investigations of the deep crustal structure of this continental margin provide constraints on the formation of the margin and its structural evolution during and after late Cretaceous–early Tertiary rifting and continental break-up. We present here the results along two profiles located in the prolongation of the Godthab Gulf and the Kejser Franz Joseph Fjord. Regional P-wave velocity models were derived from forward traveltime modelling of land stations and ocean bottom hydrophone (OBH) recordings. For the first time, long deep seismic sounding transects off East Greenland provide a full insight into the crustal architecture of the transition from continental to oceanic crust. A mean result is the identification of voluminous magmatic underplating, which is wider and thicker than previously thought. P-wave velocities of the underplated material range between 7.1 and 7.4 km s−1 and the horizontal extents on the profiles are 225 and 190 km. The maximum thickness of the underplated material is 15–16 km. Furthermore, the P-wave velocity models reveal a 120–130 km wide continent–ocean transition zone (COT), based on an interpretation of the extent of Cretaceous syn-rift sediments mixed with basaltic intrusions and the lateral increase of velocities in the crustal layers. Excess magmatism must have been present during a long-term rifting process, accompanying the extension of the continental crust and giving rise to the voluminous magmatic underplating. A consequence of our interpretation of the seismic refraction data is a likely rift propagation in the Greenland Sea from north to south. Additionally, a comparison of P-wave velocity models of the East Greenland Margin and Voring Margin reveals significantly asymmetric crustal architectures. The voluminous magmatic underplating and asymmetrical conjugate margins formations are considered as a mirror of complex pre- and syn-rift processes.