Topography, boundary forces, and the Indo‐Australian intraplate stress field

Abstract

The relative contribution of topographic (e.g., ridge push, continental margins, and elevated continental crust) and plate boundary (e.g., subduction and collisional) forces to the intraplate stress field in the Indo‐Australian plate (IAP) is evaluated through a finite element analysis. Two important aspects of the IAP intraplate stress field are highlighted in the present study: (1) if substantial focusing of the ridge push torque occurs along the collisional boundaries (i.e., Himalaya, New Guinea, and New Zealand), many of the first‐order features of the observed stress field can be explained without appealing to either subduction or basal drag forces; and (2) it is possible to fit the observed SHmax, (maximum horizontal stress orientation) and stress regime information with a set of boundary conditions that results in low tectonic stress magnitudes (e.g., tens of megapascals, averaged over the thickness of the lithosphere) throughout the plate. This study therefore presents a plausible alternative to previous studies of the IAP intraplate stress field, which predicted very large tectonic stress magnitudes (hundreds of megapascals) in some parts of the plate. In addition, topographic forces due to continental margins and elevated continental material were found to play an important role in the predicted stress fields of continental India and Australia, and the inclusion of these forces in the modeling produced a significant improvement in the fit of the predicted intraplate stresses to the available observed stress information in these continental regions. A central focus of this study is the relative importance of the boundary conditions used to represent forces acting along the northern plate margin. We note that a wide range of boundary conditions can be configured to match the large portion of the observed intraplate stress field, and this nonuniqueness continues to make modeling the IAP stress field problematic. While our study is an important step forward in understanding the sources of the IAP intraplate stress field, a more complete understanding awaits a better understanding of the relative magnitude of the boundary forces acting along the northern plate margin.