Abstract
AbstractTransform faults are a fundamental tenet of plate tectonics, connecting offset extensional segments of mid‐ocean ridges in ocean basins worldwide. The current consensus is that oceanic transform faults initiate after the onset of seafloor spreading. However, this inference has been difficult to test given the lack of direct observations of transform fault formation. Here we integrate evidence from surface faults, geodetic measurements, local seismicity, and numerical modeling of the subaerial Afar continental rift and show that a proto‐transform fault is initiating during the final stages of continental breakup. This is the first direct observation of proto‐transform fault initiation in a continental rift and sheds unprecedented light on their formation mechanisms. We demonstrate that they can initiate during late‐stage continental rifting, earlier in the rifting cycle than previously thought. Future studies of volcanic rifted margins cannot assume that oceanic transform faults initiated after the onset of seafloor spreading.
Highlights
Transform faults have long been known to play a key role in seafloor spreading (Macdonald et al, 1988)
We integrate evidence from surface faults, geodetic measurements, local seismicity, and numerical modeling of the subaerial Afar continental rift and show that a proto-transform fault is initiating during the final stages of continental breakup. This is the first direct observation of proto-transform fault initiation in a continental rift and sheds unprecedented light on their formation mechanisms. We demonstrate that they can initiate during late-stage continental rifting, earlier in the rifting cycle than previously thought
While we must consider the possibility that not all of these surface faults are tectonic in origin (e.g., Eusden et al, 2005), we interpret the increased variability in fault orientations in the Giulietti Plain as being due to interaction between the Erta-Ale and Tat-Ale magmatic segments
Summary
Transform faults have long been known to play a key role in seafloor spreading (Macdonald et al, 1988) They link and accommodate strike-slip motion between laterally offset mid-ocean ridge segments and occur in ocean basins worldwide. Previous numerical modeling of continental rifting has suggested that oceanic style transform faults do not form in early-stage rifts (Allken et al, 2012), so it is generally assumed that transform faults originate during seafloor spreading (Eagles et al, 2015; Nguyen et al, 2016) It is not known whether transform faults can initiate in mature continental rift systems
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