Enhanced-gravity Analog Modelling of the Influence of Pre-existing Brittle Fabrics on Continental Rifting

Along with other parameters (e.g., plate kinematics), the presence of pre-existing structures at all lithospheric scales has been proven to be of primary importance in controlling the evolution and characteristics of continental rifts. Indeed, observations from many natural examples show that even in conditions of orthogonal rifting (when extension should result in simple fault patterns dominated by normal faults orthogonal to the extension vector) the presence of inherited fabrics may result in complex arrangements of differently-oriented extension-related structures.

Here, we explored the influence of pre-existing fabrics on the evolution and pattern of rift-related structures by conducting a series of analogue models deformed in an enhanced gravity field produced by a centrifuge apparatus. The crustal models reproduced a brittle-ductile system and considered the presence of pre-existing discrete fabrics in the upper, brittle crust under conditions of orthogonal narrow rifting. These fabrics were reproduced by cutting the brittle layer at different orientations with respect to the extension direction.

Modelling results show that pre-existing fabrics have a significant influence on the rift-related fault pattern. These fabrics cause curvature of extension-related faults, resulting in S-shaped faults and -in some cases- en-echelon arrangement of oblique fault segments. In addition, the presence of these heterogeneities influences the rift floor subsidence by inducing significant segmentation and development of isolated depocenters. These effects are more visible during initial rifting and less pronounced for more advanced rifting stages. Similarly, increased syn-rift sedimentation tends to decrease the impact of pre-existing structures. Model results show many significant similarities with the fault pattern in many rift basins worldwide, and these findings have important insights into the development of continental rift systems in nature.