Rift systems give important insights into the processes that control the beginning extension and subsequent break-up of continents. Quantifying the amount of crustal stretching and the position of the continent-ocean boundary helps refining plate-kinematic reconstructions, as this will overcome problems in previous models which were based on rigid plate assumptions. The submarine continental plateaux off southeastern New Zealand (NZ), Chatham Rise (CR) and Campbell Plateau (CP), were adjacent to Marie Byrd Land (MBL) of Antarctica until extension and subsequent seafloor spreading formed the Southern Ocean in the Late Cretaceous. While the timing of the BT opening between CR and CP is indirectly derived from plate-tectonic evidence, the processes of extension of the Bounty Trough (BT) and the development of the fragments forming CR and CP are not yet understood. Models suggest either a rift system of the Southern Pacifics early opening or a subsequent opening of an already existing back-arc basin, a proto-BT.To investigate the evolutionary processes of these submarine plateaux, a geophysical and geological survey was conducted across CP and BT in early 2003 with the German R/V SONNE during cruise SO-169 (project CAMP). The survey carried out two deep crustal seismic transects and a series of multichannel seismic reflection lines across GSB and across BT.Velocity-depth and gravity models infer an extremely thinned crust beneath the Bounty Trough and the Great South Basin (GSB). The thickness of the crystalline crust is reduced from 20-23 km under the CR and the CP to some 12 km under the BT. Beneath the GSB, the crystalline crust thins to some 14 km from about 26 km towards CP and the South Island of NZ. P- and S-velocities are significantly increased directly beneath the Bounty Channel. We interpret a high-velocity, high-density body in the BT as a magmatic intrusion into thinned continental crust. Crustal thinning ceased shortly prior to the onset of seafloor spreading. The modelled magnitude and style of rifting along BT and GSB places constraints on reconstructing the Cretaceous break-up process between NZ and MBL.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > MAR2-Palaeo Climate Mechanisms and Variability