A first-order study of the tectonic stress field within the South American plate in response to various plate boundary forces and intraplate stress sources was carried out using an elastic finite element analysis. The finite element mesh consisted of 3100 nodes in a network of 5993 equal-area triangular elements which provided a spatial resolution of about 1 degree at the equator. This study builds on previous modeling studies in two important respects. First, we have explicitly included forces due to lateral density variations within the lithosphere such as those associated with elevated continental topography and continental margins. Second, we evaluate the tectonics stresses predicted by models which balance the total torque acting on the plate with both driving and resistive basal drag forces. Predicted stresses were constrained by 213 stress indicators extracted from the World Stress Map Project which provide information about the orientation of the observed maximum horizontal compressive stress, SHmax and provide a five-fold increase in the the number of stress indicators used in previous modeling studies. The predicted stress field for a number of models of the tectonic forces acting on the plate are evaluated in order to determine which of the forces exert the greatest first--order control on the intraplate stress field. The analysis demonstrates that the first--order stress field in the plate is characterized by nearly uniform E--W compression throughout most regions of the plate with stress magnitudes in the range of 20-40 MPa averaged over a 100--km thick lithosphere. Significant perturbation of this regional stress field occurs in the western part of the plate in response to forces associated with the high topography of the Andes. The modeling results demonstrate that the first--order features of the observed stress field in the plate can be explained with simple tectonic models which balance the torque acting on the plate either with a fixed western margin or drag forces applied along the base of the plate. While the magnitude of the collisional boundary forces acting along the western margin remain poorly constrained, the results presented demonstrate that a force of 5.0x10**12 N/m acting along the Peru--Chile Trench is an upper limit on the magnitude and a force of about 2.5x10**12 N/m per unit length produces a predicted stress field which is consistent with the observed South American intraplate stress field.
Predicted stresses for Model 4 [see Table 2]. Solid bars indicate deviatoric compression; open arrows indicate deviatoric tension. The dashed--line designates the profile discussed in Figure 7. Collisional boundary forces applied in this model produce predicted stresses in the mid--plate continental regions and the Andes which are consistent with previous modeling studies. See Figure 7 for detail about the predicted stresses along the profile.