The data collected during cruises TACT 2012 and TACT 2016 proved to be crucial to constrain the relative motion of the Australian and East Antarctic plates since 20 million years. The very good quality of these data results of the proximity of the South geomagnetic pole off Adélie Land and the GPS navigation, by comparaison to the poorly navigated older data . Combined to data acquired by the Korean icebreaker Araon East of the Balleny Fracture Zone and TransformFault, they constrain the existence of an independent Macquarie Plate in the southeastern part of the Australian Plate senso largo since 3 million years and to constrain the motion of this plate with respect to the Australian Plate (Choi et al., EPSL, 2017). Combined to older American data, they allow us todefine the extension and duration of the West Antarctica - East Antarctica plate boundary, which extend along the Balleny Island Ridge until about 11 million years (Granot & Dyment, Nat. Comm., 2018). Former studies dated the demise of this plate boundary at  28 Ma and llimited its northward extension to the Adare Basin. The Balleny Island Riddge would represent the fossil remnant of an ultra-slow spreading center.