Cenozoic motion between East and West Antarctica

The West Antarctic rift system is the result of late Mesozoic and Cenozoic extension between East and West Antarctica, and represents one of the large st active continental rift systems on Earth. But the timing and magnitude o f the plate motions leading to Be development of this rift system remain po orly known, because of a lack of magnetic anomaly and fracture zone constra ints on seafloor spreading. Here we report on magnetic data, gravity data a nd swath bathymetry collected in several areas of the south Tasman Sea and northern Boss Sea. These results enable us to calculate mid-Cenozoic rotati on parameters for East and West Antarctica. These rotations show that there was roughly 180 km of separation in the western Ross Sea embayment in Eoce ne and Oligocene time. This episode of extension provides a tectonic settin g for several significant Genozoic tectonic events in the Ross Sea embaymen t including the uplift of the Transantarctic Mountains and the deposition o f large thicknesses of Oligocene sediments. Inclusion of this East-West Ant arctic motion in the plate circuit linking the Australia, Antarctic and Pac ific plates removes a puzzling gap between the Lord Howe rise and Campbell plateau found in previous early Tertiary reconstructions of the New Zealand region. Determination of this East-West Antarctic motion also resolves a l ong standing controversy regarding the contribution of deformation in this region to the global plate circuit linking the Pacific to the rest of the w orld.