Structural inheritance at extensional continental margins: Implications for the tectonic evolution of the Northern Carnarvon Basin, Western Australia

Abstract

Rifted continental margins are economically important regions of Earth. Many of these margins are a product of multiple phases of rifting, where structural inheritance plays a role in subsequent deformation. The Northern Carnarvon Basin of Australia’s North-West Shelf is an example of a polyphase margin that has undergone several episodes of extension in the Palaeozoic to Early Cretaceous. This thesis presents original regional scale interpretations of publicly available seismic data from the inboard margin of the Northern Carnarvon Basin. This work shows two distinct orientations of Palaeozoic structures providing evidence for a polyphase Palaeozoic rift history of the basin. These structural trends influence the subsequent fault patterns associated with Mesozoic rifting. Two-dimensional, isothermal mechanical numerical experiments are used to test seismic observations by forward modelling lithospheric extension at a polyphase continental margin. These experiments document different modes of deformation including “narrow rifts” and “wide rifts” and a dual mode of extension with coeval narrow and wide rift attributes. These experiments potentially shed light on the crustal structure of the Northern Carnarvon Basin, revealing that the dual mode of extension observed could be the result of the removal of the lower crust adjacent to the Pilbara craton and subdued extensional strain rate in the Exmouth Plateau. Three-dimensional ‘numerical sandbox’ experiments where inherited structures are at varying degrees of obliquity to the imposed extension direction are also presented. These experiments generate complex time-dependent deformation patterns. Learnings from this work demonstrates that the Mesozoic deformation patterns of the Northern Carnarvon Basin can be explained by just one extension vector associated with the rifting of Greater India and that the rifting of the Argo block potentially had little effect on the first order deformation patterns of the basin.