The peculiarities of the formation of the structure of the Earth's crust in the Australian-Antarctic basin during the early break-up between Australia and Antarctica are considered. The study period encompasses long-lasting rifting (similar to 160-80 Ma), ultraslow spreading (similar to 80-45 Ma) with the formation of the proto-oceanic mainly ultrabasic crust, spreading (similar to 45-40 Ma), and stationary sea-floor spreading with intermediate velocities (after 40 Ma). The various stages of the oceanic opening clearly manifest themselves by the change in the basement morphology (the top of the second oceanic layer) on the seismic profiles. Physical modeling has made it possible to reveal the peculiarities of the surface morphology of the oceanic (magmatic) crust which developed in the conditions of the transition from ultraslow to slow and intermediate spreading. Our experiments established that (1) the presence of a stronger block in the pre-breakup model lithosphere in the pathway of the propagating rift faults can significantly affect the geometry of the spreading axis in its vicinity and lead to the development of transverse structures and a highly rugged relief; (2) under the conditions of ultraslow spreading, numerous ridge jumps occur; (3) the temporary cessation of the sea-floor spreading leads to the development of linear high-amplitude rises which in the natural conditions correspond to amagmatic ridges.