Influence of Inherited Brittle Fabrics on Continental Rifting: Insights From Centrifuge Experimental Modeling and Application to the East African Rift System

Abstract

The presence of pre-existing fabrics at all lithospheric scales has been proven to be of primary importance in controlling the evolution of continental rifts. Indeed, observations from natural examples show that even in conditions of orthogonal rifting, when extension should result in simple fault patterns dominated by normal faults orthogonal to extension vectors, inherited fabrics induce complex arrangements of differently-oriented extension-related structures. This paper explored the influence of inherited fabrics on rift-related structures by using a series of analog models deformed in a centrifuge. The models reproduced a brittle-ductile crustal system and considered the presence of pre-existing discrete fabrics in the brittle crust in conditions of orthogonal narrow rifting. These fabrics were reproduced by cutting the brittle layer at different orientations with respect to the extension direction. Modeling shows pre-existing fabrics have a significant influence on rift-related faults, provided that the angle between inherited fabrics and the rift trend is less than 45°. In these conditions, fabrics cause prominent segmentation of rift-related faults and induce the development of isolated depocenters. Pre-existing fabrics strongly influence the geometry of extension-related structures, resulting in curved fault patterns and en-echelon arrangement of oblique faults. These findings provide insights into the development of continental rift systems in nature: our modeling shows indeed significant similarities (i.e., peculiar fault architecture and geometries) with the faults in different sectors of the East African Rift System (e.g., the Magadi and Bogoria basin, Kenya Rift), testifying that reactivation of inherited fabrics is a paramount process in shaping continental rifts.