THE ORIGINS OF THE INTRAPLATE STRESS-FIELD IN CONTINENTAL AUSTRALIA

The ridge push force acting on the Indo-Australian plate exerts a significant torque (8.5 X 10(25)N m) about a pole at 30.3 degrees N, 34.5 degrees E. The angular difference between this torque pole and the observed pole of rotation for the plate (19.2 degrees N, 35.6 degrees E) is less than 12 degrees and suggests that the ridge push force plays an important role in the dynamics of the Indo-Australian plate. We have used an elastic finite-element analysis to study the predicted intraplate stress field in continental Australia for four models which employ different boundary conditions to balance the ridge push torque acting on the plate. The modeling indicates that a number of important features of the observed stress field within the Australian continent can be explained in terms of balancing the ridge push torque with resistance imposed along the Himalaya, Papua New Guinea, and New Zealand collisional boundaries segments. These features include N-S-to NE-SW-oriented compression in the northern Australia and E-W-oriented compression in southern Australia. Our analysis also shows that subduction processes along the northern and eastern boundaries provide only second-order controls on the intraplate stress field in continental Australia.