Structure formation peculiarities at early stage of Antarctic–Australia separation based on physical modeling

Abstract

The paper addresses crustal formation in the Australian–Antarctic basin at the early period of separation of Australia and Antarctica. The study covers long rifting (~160–80 Ma), ultraslow spreading (~80–45 Ma) with the formation of proto-oceanic, mainly ultrabasic crust, spreading (~45-40 Ma), and stationary spreading at medium velocities (after 40 Ma). The different stages of oceanic opening are clearly expressed in the changes of basement morphology (the top of the second oceanic layer) on seismic profiles. Physical modeling is used to reveal the peculiarities in the surface morphology of the oceanic (magmatic) crust which developed in the transitional conditions from ultraslow to slow and medium 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 transversal structures and a highly rugged relief; (2) under the conditions of ultraslow ocean accretion, numerous jumps of the spreading axes occur; (3) the temporary cessation of spreading leads to the development of linear high-amplitude uplifts corresponding to amagmatic ridges in the natural conditions.