Magnetic data on the Northeastern Margin of the Kerguelen Plateau: Constraints for the Australia-Antarctica Separation

Three recent oceanographic surveys on the R/V Marion Dufresne II, were conducted around the Kerguelen Archipelago, in the context of Extraplac, the french program aimed at preparing submissions for extension of the continental shelf according to UNCLOS article 76. Different kinds of data were acquired: bathymetry, gravity, magnetism, seismic, dredges. Some of these data concern the not much explored Northeastern margin of the Kerguelen Plateau, from 77E30 up to the St Paul fracture zone, where the South East Indian Ridge (SEIR) shows a large offset toward the Kerguelen Plateau. The opening between Kerguelen Plateau and Broken Ridge has preserved morphologically homologous margins on each side of the SEIR. While East of 74E, the magnetic anomalies are regular, parallel to the SEIR and also to the morphological boundary of the plateau, interpretation of the margin of the Northern Kerguelen Plateau is less obvious, because volcanic masses overly discordantly the oceanic crust. Moreover, debate on the kinematic models in this part of the Indian Ocean is still open, and the differences in the fit in recent reconstruction models between Kerguelen Plateau and Broken Ridge are as large as 200 km. Using both the published opening models and conjugate Northern anomalies, interpretation of the set of old and new magnetic data allows us to identify with more confidence the oldest anomalies at the plateau margin. From these interpretations, we discuss both the fit between Kerguelen and Broken Ridge and the implication for the opening between Australia and Antarctica as well as the possible junctions along the St Paul fracture zone with the Crozet basin where the spreading rate was much faster before A18.