A Late Miocene plate boundary reorganization along the westernmost Pacific-Antarctic ridge

Magnetic and bathymetric measurements carried out in the southwest Pacific between New Zealand and Antarctica south of 60°S, combined with the satellite-derived gravity map, add new information on the structural fabric and tectonic development of the westernmost portion of the Pacific-Antarctic plate boundary. The plate boundary includes in its northern part a series of short spreading centres offset by NNW-SSE-trending fracture zones. Towards the south, it becomes structurally more complicated and appears to be formed by extension along an ancient strike-slip lineation, as a consequence of a change in the Pacific-Antarctic relative motions that resulted in a geometric readjustment of the plate boundary. The identification of marine magnetic lineations crossing this portion of the boundary testifies that this readjustment is relatively recent; the newly created crust is not older than Late Miocene and is presently surrounded by oceanic regions where the magnetic anomalies range from 19 to 24 (∼41-53 Ma) northeastward, and from 7 to 9 (∼24.5-28 Ma) southwestward. This segment of the plate boundary formed along an older fracture zone that was pulled-apart by the new plate motions, and the segmented ridge-transform system then evolved.