The structural evolution of convergent margins in response to strain partitioning

In this study I examine the evolution of deformation at model convergent margins in response to changes in plate geometry, primarily related to the orientation of relative plate motion in conjunction with detachment rheology and the presence of migrating terranes. It is frequently unclear what relative plate motion has been responsible for the evolution of a margin's structures based on the current orientation of structures at an ancient fold-and-thrust belts, This is true, at active and ancient margins alike, particularly when the relative plate motion is oblique to the strike of the margin and where the partitioning of strain may have occurred. Using our understanding of active convergent margin mechanics I investigate the role factors, including plate motion obliquity and terrane migration, have on strain partitioning. I employ finite element calculations and utilize a newly developed analogue modeling technique that allows for detailed quantitative measurements of displacement and strain. This enhanced analogue modeling technique enables the investigation of a variety of 3-dimensional model geometries typical of convergent settings. In addition to a series of experiments that investigate individual parameters of convergence (e.g., obliquity or terrane migration) I present a detailed model for the development of the active Pakistani margin, which allows for a comparison to be made to the strain fields of numerical models and empirical data sets (e.g. earthquake moment tensors and GPS data). As part of the work presented here I also examine the ambiguities involved in determining solutions for strain and other aspects of distributed strain often observed in convergent settings.