Dip analysis as a tool for estimating regional kinematics in extensional terranes

In basin analyses that rely almost solely on seismic reflection data to configure the underlying structure, it has become common practice to use extensional fault geometries to infer kinematic histories. This procedure relies on the existence of fault geometries predicted by ideal orthogonal extension and assumes the structure is well constrained. In areas where data are sparse or of equivocal quality this often leads to circular analysis. That is, ideal orthogonal extension is assumed to have been operative, then under-constrained fault geometries are mapped according to model predictions. Fault geometries so derived are subsequently used as evidence that orthogonal extension was operative and that the direction of extension is determinable. We develop an alternative tool for inferring kinematics which is independent of fault geometries. The method relies on the empirical evidence that the dip of the hangingwall(s) is systematic and predictable in extensional systems, even when fault geometries are non-ideal. Although not without significant limitations, dip analysis can provide additional constraints for structural and kinematic interpretations, especially where seismic reflection data are the main source of information and dip domains define discrete crustal blocks.