EFFECT OF THICKNESS VERSUS STRENGTH ON STRESS DISTRIBUTION IN EXTENSIONAL SETTINGS

Continental rifting results in massive variations in thickness and strength across an area of regional extension. While rifting models vary, all continental rifts have areas of thick and thinned crust and areas of crustal weakness. Crustal weakness is usually produced via heating thinned crust, hydrothermal circulation, and volcanism. Both strength and weakness have been shown to affect how stress is distributed and, therefore, how further deformation will occur. The elastic finite element software LISA was used to construct 2D models of rift basins to determine how changes in strength and thickness affect stress distribution. Specifically, the model consisted of two rift basins in a line with a small transfer zone between them while a displacement that resulted in regional extension was applied to the margins of the plate. The thickness of the rift basins relative to the surrounding plate was modified in increments and the effect of sudden changes in plate thickness versus gradual changes were also investigated. Thinning rift basins resulted in a concentration of extensional stress in the rift basins suggesting that deformation would be concentrated. However, changing the strength of the rift basins to simulate magmatic intrusions resulted in changes in stress distribution both within and adjacent to the rift basin, including possible areas of compression due to warping of the plate. These results suggest that changing the thickness of the rift basins relative to the surrounding plate would not significantly affect the plate adjacent to the rift basins, however, changing the strength of the rift basins may result in significant deformation outside of the rift basins. Further studies, including 3-D models need to be created to properly investigate this phenomenon. But, even these basic models can be used to make predictions about deformation patterns associated with poorly exposed rifting, as in the Triassic basins of South Carolina.