THE ROLE OF PRE-EXISTING STRUCTURES IN RIFT EVOLUTION: INSIGHTS FROM GRAVITY AND MAGNETIC DATA

Understanding how rift systems develop is essential to elucidate the active tectonic processes during the continental breakup and the transition to seafloor spreading. This abstract explores the vital role of pre-existing structures in the evolution of rifts, focusing on insights obtained from gravity and magnetic data. We examine the spatial relation between the Precambrian and Miocene-Recent structures in rift strain localization, strain transfer, propagation, segmentation, and rift termination.

Magnetic data has contributed to understanding rift-related magmatic processes and identifying volcanic features associated with pre-existing structures. For example, in the Ethiopian rift, magnetic anomalies delineate variations in crustal magnetization, aiding in mapping volcanic centers, dike swarms, and intrusive bodies. Precambrian structures are suggested to control strain localization in initiating the Albertine and Rhino grabens in the Western branch of the East African Rifts system. These studies demonstrate the ability to identify structural trends, infer lithospheric thickness variations, and map volcanic features critical to the overall rift architecture. The along-strike border fault propagation curved into parallelism with basement structural grain in the Albertine, showing that the NE trending Precambrian structures are responsible for strain transfer from Albertine to Rhino grabens.

Studies using magnetic and seismic data in the Rukwa Rift, Malawi, Norway, and the Albertine Rift have suggested that lithospheric fabrics control sediment accumulation. Additionally, intra-rifts within the Albertine contributed to strain localization and strain transfer from the Albertine facilitated by the NE series of rift relay ramps, hence contributing to fault propagation from the Albertine to the Rhino through soft linkages. Magnetic data from the EARS branches has shown how the rift follows the preferred orientation of basement structural grain that facilitated rift segmentation through the border fault polarity switch and change from a symmetrical rift in the Albertine to the asymmetrical rift in the Rhino. Finally, magnetic data has shown how the Albertine rift and Rhino grabens terminated against the NW trending lithospheric Precambrian Aswa shear Zone.