The ridge push force acting on the Indo--Australian plate exerts a significant torque (8.5 x 10**25N m) about a pole at 30.3N, 34.5E. The angular difference between this torque pole and the observed pole of rotation for the plate (19.2N, 35.6E) 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.
Predicted stresses for continental Australia. Solid bars indicate deviatoric compression; open arrows indicate deviatoric tension. Also shown are the average SHmax orientations within 3 x 3 degree bins from Figure 4. Force parameters applied for each model are listed in Tables 1 and 4. (a) Model 1: Ridge push torques acting on the plate are balanced by fixing the entire northern and eastern plate boundaries. Predicted stresses throughout continental Australia are compressional (approaching 18 MPa) with SHmax oriented nearly uniformly NE--SW. (b) Model 2: Ridge push torques are balanced by fixing the collisional boundary segments along the Himalayan, Papua New Guinea, and New Zealand collisional boundary segments. The predicted stress field is dominated by NE--SW compression (approaching 80 MPa) due to focusing of ridge push torque along the Papua New Guinea boundary segment. (c) Model 3: Basal drag is used to balance torque acting on plate from ridge push and collisional boundary forces. Other boundary segments were left free. The predicted stress field is compressional throughout continental Australia (approaching 20 MPa in most regions), with SHmax varying from NW--SE to E--W in western and southeastern Australia to N--S in the north--central continental regions. (d) Model 4: Basal drag is used to balance torque acting on the plate from ridge push and boundary forces. The predicted stress field is very similar to that of Model 3, suggesting that the primary control on the stress field in continental Australia is exerted by the collisional boundary forces acting along the Papua New Guinea boundary segment.