Exploring the interactions between rift propagation and inherited crustal fabrics through experimental modelling

Continental rifting is a geodynamic process that involves the breakup of the crust, and may eventually evolve to sea floor spreading. Although it is often assumed to be a product of orthogonal divergence, continental rifting may result from oblique extension, and in several cases it is related to the rotation of plates or crustal blocks about a vertical axis. This implies the occurrence of rifts with straight but not parallel margins and rift axis-parallel gradients in extension velocity and amount of strain. The effects of rift propagation through the continental crust has only recently started to be addressed, and even less investigated is the interaction between rift propagation and inherited crustal fabrics. We have studied this issue by carrying out a series of analogue laboratory experiments. Modelling results suggest that inherited linear discontinuities in the model brittle upper crust that are oriented above a threshold angle (>=45°) from the orthogonal to the rift axis, have the ability to interact with rift-related structures. Depending on their orientation, such inherited discontinuities are reactivated as either transfer zones or rift-bounding faults. We compare our models with four natural prototypes in which rift propagation is likely to have occurred (the Trans Mexican Volcanic belt, the Gofa Province, the Gulf of Suez and the Kenya rift). For each case study, we show how the kinematics of propagating rifts is comparable to our model results, and we provide insights into how rift-related deformation may interact with inherited crustal fabrics.