Abstract
The kinematics of rift segment linkage in magmatic rifts remain debated. Strain patterns from Afar provide tests of current models of how segmented rifts grow in areas of incipient oceanic spreading. Here, we present a combined analysis of seismicity, interferometric synthetic aperture radar (InSAR), and GPS–derived strain rate maps to reveal that the plate-boundary linkage between the Red Sea and Gulf of Aden rifts of Afar is accommodated primarily by distributed extensional faulting. Large rotations about vertical axes predicted by bookshelf faulting models are not detected. Additionally, models of stress changes and seismicity induced by recent dikes provide poor fits to the observed time-space patterns of strike-slip earthquakes. Instead, we explain these features as resulting from rift-perpendicular shearing at the tips of spreading rifts where extension terminates against less stretched lithosphere. Our results demonstrate that distributed extension drives rift-perpendicular shearing, achieving plate-boundary linkage during incipient seafloor spreading.
Highlights
Continental rifts are three-dimensional structures with complex fault kinematics ranging from extensional to strike-slip (i.e., Kebede et al, 1989; Sigmundsson, 1992)
During the initial continental extension, rifts show along-axis segmentation by large-offset faults but, as plate stretching and heating progresses to rupture, magma intrusion may accommodate a large percentage of the plate boundary deformation, and along-axis segmentation is in part controlled by the distribution of magma chambers (Ebinger and Casey, 2001; Keir et al, 2009)
Extension along the southern Red Sea was initially accommodated on large border faults but during the past ~4 Ma strain localized to axial magmatic segments, which mark the active plate boundary from latitude ~15° to 12°N in the Red Sea rift, and south of 11°N in the Main Ethiopian rifts (MER) (Fig. 1) (Hayward and Ebinger, 1996; Manighetti et al, 1998)
Summary
Continental rifts are three-dimensional structures with complex fault kinematics ranging from extensional to strike-slip (i.e., Kebede et al, 1989; Sigmundsson, 1992). We present a combined analysis of seismicity, InSAR and GPS derived strain rate maps to reveal that the plate boundary linkage between the Red Sea and Gulf of Aden rifts of Afar is accommodated primarily by distributed extensional faulting.
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