Investigating the Role of Extensional Deformation at Convergent Margins Using a Combined Analog and Numerical Approach.

Understanding why extensional stress occurs and how it is accommodated at convergent margins remains fundamental to understanding the structural and mechanical evolution of wide array of contractional orogens. We investigate the parameters that control the occurrence of extension coeval with contraction, specifically, variations in rheology (laterally and with depth) and initial plate geometries, (i.e., plate motion obliquity). Understanding the specific contribution of these parameters to the development of contractional orogens is fundamental to a better understanding of the tectonics and seismic hazards of many convergent margins. To this end, we have used a multifaceted modeling approach that employs 3-dimensional analog modeling with quantitative analysis in conjunction with 2 and 3-dimensional finite element numerical modeling. We find that a relatively small amount of extensional stress will play an important role in the long-term structural evolution of convergent systems. However, the manner in which this stress will be translated to deformation (localized on discrete accommodation structures), and in particular how the style of strain (extension or contraction) will evolve, is a strong function of rheology at depth and the initial geometry of the margin.