Jurassic failed rift system below the Filchner-Ronne-Shelf, Antarctica: New evidence from geophysical data

- A crustal model is presented for the Weddell Sea embayment showing for the central part velocity-depth functions similar to oceanic crust
- The continental margins of the Antarctic Peninsula and East Antarctica are interpreted in the research area as conjugate rifted margins.
- The crustal fabric excludes any large scale displacement of the Ellsworth Whitmore Mountains passing the research area

During the austral summer of 1994/95, reasonable ice conditions in the Weddell Sea allowed the acquisition of new high quality seismic refraction data parallel to the Filchner-Ronne Ice Shelf (FRS), Antarctica. Although pack ice conditions resulted in some data gaps, the final velocity-depth/2D-density models cover the entire FRS in E-W direction using all available deep seismic data/picks from this remote area. The velocity-depth model shows a sedimentary basin with a thickness up to 12 km and a large velocity inversion in the lowermost sedimentary unit. The crustal thickness reaches a maximum of 40 km along the basin's margins in the Antarctic Peninsula and East Antarctica. In the central shelf area, numerous interfering seismic phases occur from the crust-mantle boundary at decreasing distances indicating a thinning of the crust. Here, the modelled velocities and densities reveal a thickness of 20 km for the igneous crust. This corridor of overthickened oceanic or close to oceanic crust is 160 km wide. The corridor is characterized by weak, but in general continuous magnetic anomalies, which we interpret as isochrons developed during the rifting or the initial formation of oceanic crust. If the crustal composition represents an old stripe of oceanic crust, a minimum estimate for the early formation of the oceanic crust is 145/148 Ma (Late Jurassic). However, based on the velocity of rift propagation during the initial opening of the adjacent Weddell Sea the oceanic crust is likely to have formed around 160 Ma. The onset of rifting and development of a thick igneous crust can be related to stresses developed between the interior and the southwestern paleo-Pacific subduction margin of the fragmenting Gondwana supercontinent in combination with additional melt supply from a deeper mantle source that arrived and spread in the period 183-155 Ma.