Development of William’s Ridge, Kerguelen Plateau: tectonics, hotspot magmatism, microcontinents, and Australia’s Extended Continental Shelf

The complex evolution of the Indian Ocean, which began forming more than 150 million years ago, has featured isolation of numerous continental fragments by jumps of seafloor spreading ridges, formation of multiple oceanic plateaus by hotspot/mantle plume magmatism, and many changes in tectonic plate configurations. Between ~120 and ~95 million years ago magmatic processes formed the massive, then- contiguous Kerguelen Plateau and Broken Ridge, which incorporated some continental fragments. Initiation of seafloor spreading along the Southeast Indian Ridge ~45 million years ago separated the enormous original feature into the Kerguelen Plateau and Broken Ridge. Extending southeast from the Central Kerguelen Plateau, William’s Ridge is a prominent 500-km-long spur that probably nearly completely separated from the Kerguelen Plateau during the initial stages of rifting. Through acquisition, analysis, and interpretation of new geophysical data and geological samples from William’s Ridge, as well as the portion of Broken Ridge that once abutted William’s Ridge, we aim to determine the origin and evolution of William’s Ridge. The data will reveal the nature of the crust (continental, hotspot-related, oceanic, or hybrid), and the tectonic evolution of the region in relation to voluminous magmatism associated with hotspot/mantle plume activity and changing tectonic plate configurations. These results will, in turn, help elucidate the underlying geodynamic processes responsible for hotspots/mantle plumes and changes in plate configuration, and the formation of microcontinents. Additionally, testing current hypotheses for formation of William’s Ridge through partial separation from the Kerguelen Plateau in Cretaceous time due to a complex breakup history provides the required framework for successful formulation of a renewed submission to the United Nations Commission on the Limits of the Continental Shelf (CLCS) for inclusion of William’s Ridge into Australia’s Extended Continental Shelf (ECS). Success of the submission will result in Australia gaining the significant territory of William’s Ridge and surrounding areas.