Volcanic margin formation and Mesozoic rift propagators in the Cuvier Abyssal Plain off Western Australia

Abstract

The western margin of Australia is characterized by synrift and postrift magmatism which is not well understood. A joint interpretation of magnetic anomaly, satellite gravity anomaly and seismic data from the Cuvier Abyssal Plain and margin shows that the breakup between India and Australia started circa 136 Ma (M14) and was followed by two rift propagation events which transferred portions of the Indian Plate to the Australian Plate. Post breakup magmatism continued with the emplacement of the Wallaby and Zenith plateaus (∼17–18 km thick at their centers) along a transform margin. Two narrow magmatic edifices adjacent to the Wallaby Plateau (Sonne and Sonja ridges) represent an extinct ridge and a pseudofault, respectively. They formed by excess volcanism, probably by lateral migration of buoyant melt along upside‐down crustal drainage channels from the melt source underneath the Wallaby Plateau. In a mantle plume scenario a small plume (∼400 km diameter) located underneath the rift could have locally uplifted the Bernier Platform and Exmouth Sub‐basin in the Early Cretaceous and left a track consistent with the azimuth of the Wallaby and Zenith plateaus. In this case, ridge‐plume interaction would have caused two consecutive ridge propagation events towards the plume while the ridge moved away from the hotspot. The abrupt end of the hotspot track west of the Zenith Plateau would be a consequence of the accelerating south‐eastward motion of the spreading ridge relative to the mantle after 120 Ma, leaving the mantle plume underneath the Indian Plate. An alternative nonmantle‐plume scenario is based on the observation that between breakup and chron M0 (∼120 Ma) the ocean crust in the southern Cuvier Abyssal Plain was formed while the spreading ridge abutted Indian continental crust. Small‐scale convection may have been initiated during rifting in the Early Cretaceous and maintained until the Wallaby‐Zenith ridge‐transform intersection passed by the eastern edge of Indian continental crust at chron M0.