The Motion and Boundary Between the Capricorn and Australian Plates

The motions between the Somalian, Antarctic, and Australian plates—the three plates believed to meet at the Rodrigues triple junction in the Indian Ocean—are inconsistent with the assumption that all three plates are rigid. The discrepancy is best explained if the Australian plate contains two component plates. Thus, the traditionally defined Indo-Australian plate consists of three component plates and multiple diffuse plate boundaries. The pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone, which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction.