Abstract The Australian continent records c. 1860–1800 Ma orogenesis associated with rapid accretion of several ribbon micro-continents along the southern and eastern margins of the proto-North Australian Craton during Nuna assembly. The boundaries of these accreted micro-continents are imaged in crustal-scale seismic reflection data, and regional gravity and aeromagnetic datasets. Continental growth ( c. 1860–1850 Ma) along the southern margin of the proto-North Australian Craton is recorded by the accretion of a micro-continent that included the Aileron Terrane (northern Arunta Inlier) and the Gawler Craton. Eastward growth of the North Australian Craton occurred during the accretion of the Numil Terrane and the Abingdon Seismic Province, which forms part of a broader zone of collision between the northwestern margins of Laurentia and the proto-North Australian Craton. The Tickalara Arc initially accreted with the Kimberley Craton at c. 1850 Ma and together these collided with the proto-North Australian Craton at c. 1820 Ma. Collision between the West Australian Craton and the proto-North Australian Craton at c. 1790–1760 Ma terminated the rapid growth of the Australian continent.

Abstract A simple geometrical explanation is provided for the distribution of the well-known architectural zonation across fully developed magma-poor margins (e.g. , limited crustal stretching, extreme crustal thinning, exhumed mantle, ultraslow or normal “Penrose” oceanic crust). This zonation is observed along the lengths of many margins on the super-regional scale. Diachronous development of the oceanic crust, younging towards the rift tip, indicates that at the plate tectonic scale break-up occurred on these margins by rift propagation. At the local to regional scale propagation occurs by progressive opening of segments. Because the relative motion of crust adjacent to a rift segment can be described by an Euler pole, the local linear plate separation rate can be interpreted as a function of distance to that pole. In turn, plate separation rates influence the architectural zonation and ultimately the degree of melt generation. Within each rift segment, the rift tip propagates by “unzipping” the hyperextended continental crust. A stepwise migration of Euler poles must occur in order for a large continent to break up, leading in turn to faster linear rates and attendant melt generation/oce-anization at margin segments that have become more distal. Although this conceptual rifting model primarily explains magma-poor rift architecture, it may also apply to magma-rich margins. The latter may form when continents break apart at a high extension rate following rapid propagation (e.g. , a long-distance pole jump). Both rifted margin types can be viewed as end members of the same process, firmly rooted in geometric requirements of plate tectonics.

Abstract Seismic reflection and refraction profiles, and potential field data, complemented by crustal-scale gravity modelling, plate reconstructions and well cross-sections are used to study the evolution of the South Segment of the South Atlantic conjugate margins. Distinct along-margin structural and magmatic changes that are spatially related to a number of conjugate transfer systems are revealed. The northern province, between the Rio Grande Fracture Zone and the Salado Transfer Zone, is characterized by symmetrical seawards-dipping reflections (SDRs) and symmetrical continent–ocean transitional domain. The central province, between the Salado Transfer Zone and the conjugate Colorado–Hope transfer system, is characterized by along-strike tectonomagmatic asymmetry. The Tristan da Cunha plume, located on the central province of the South Segment, may have influenced the volume of magmatism but did not necessarily alter the process of rifted margin formation. Thus implying that, apart from voluminous magmatism, the extensional evolution of the central province of the South Segment may have much in common with ‘magma-poor’ margins.