HOW DO CONTINENTAL RIFTS GROW? (Invited Presentation)

Models of narrow rifting show that continental rifts grow by the interaction, linkage, and coalescence of initially isolated rift segments. However, there is limited understanding of the systematic and progressive transformation of isolated rift segments into continuous chains of coalesced basins. This knowledge gap limits the complete understanding of the processes governing continental extension leading to break-up. In my talk, I present results on a global compilation of rift lengths and widths spanning various rift settings (e.g., active, failed, early-, and late-stage rifts, and rifted margins), and show a distinction in their statistical trends from those of active early-stage rift settings. In the areas of active early-stage continental extension, a plot of rift segment length vs average width shows an exponential trend, and reveals distinct systematic groupings of <250 km rift lengths (dubbed "short narrow rifts"), 250 - 425 km rift lengths ("moderately-long narrow rifts"), and >500 km rift lengths ("very long narrow rifts"). I argue that this distribution likely indicates a temporal evolution of rift growth from isolated rift segments (short and moderately-long narrow rifts) to composite rift basins (very long narrow rifts), and that the evolution is facilitated by the progressive interaction, linkage, and coalescence of initially 'short' isolated rift segments.

Further, I present results from detailed observations across the zones of rift segment interaction (RIZ) along the Western Branch of the East African Rift System, demonstrating that: 1.) the interaction and linkage of active rift segments can be assessed by the large-scale patterns of structural deformation and topographic morphology of their intervening RIZs; 2.) irrespective of geometry, the RIZs are at different stages of their evolution, associated with the degree of the rift linkage; and 3.) the stages of evolution include unbreached, partially-breached, recently-breached, and breached RIZs. These findings offer a broader insight into the processes that modulate the spatiotemporal propagation and growth of rift systems in areas of active continental extension.