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Strain Localization and Migration During the Pulsed Lateral Propagation of the Shire Rift Zone, East Africa
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  • Folarin Kolawole,
  • Travis Vick,
  • Estella A Atekwana,
  • Daniel A Laó-Dávila,
  • Aristides Costa,
  • Brett M Carpenter
Folarin Kolawole
BP Exploration, BP Exploration

Corresponding Author:[email protected]

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Travis Vick
University of Oklahoma, University of Oklahoma
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Estella A Atekwana
University of California, Davies, University of California, Davies
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Daniel A Laó-Dávila
Oklahoma State University, Oklahoma State University
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Aristides Costa
University of Oklahoma, University of Oklahoma
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Brett M Carpenter
University of Oklahoma, University of Oklahoma
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We investigate the spatiotemporal patterns of strain accommodation during multiphase rift evolution in the Shire Rift Zone (SRZ), East Africa. The NW-trending SRZ records a transition from magma-rich rifting phases (Permian-Early Jurassic: Rift-Phase 1 (RP1), and Late Jurassic-Cretaceous: Rift-Phase 2 (RP2)) to a magma-poor phase in the Cenozoic (ongoing: Rift-Phase 3 (RP3)). Our observations show that although the rift border faults largely mimic the pre-rift basement metamorphic fabrics, the rift termination zones occur near crustal-scale rift-orthogonal basement shear zones (Sanangoe (SSZ) and the Lurio shear zones) during RP1-RP2. In RP3, the RP1-RP2 sub-basins were largely abandoned, and the rift axes migrated northeastward (rift-orthogonally) into the RP1-RP2 basin margin, and northwestward (strike-parallel) ahead of the RP2 rift-tip. The northwestern RP3 rift-axis side-steps across the SSZ, with a rotation of border faults across the shear zone and terminates further northwest at another regional-scale shear zone. We suggest that over the multiple pulses of tectonic extension and strain migration in the SRZ, pre-rift basement fabrics acted as: 1) zones of mechanical strength contrast that localized the large rift faults, and 2) mechanical ‘barriers’ that refracted and possibly, temporarily halted the propagation of the rift zone. Further, the cooled RP1-RP2 mafic dikes facilitated later-phase deformation in the form of border fault hard-linking transverse faults that exploited mechanical anisotropies within the dike clusters and served as mechanically-strong zones that arrested some of the RP3 fault-tips. Overall, we argue that during pulsed rift propagation, inherited strength anisotropies can serve as both strain-localizing, refracting, and transient strain-inhibiting tectonic structures.
Sep 2022Published in Tectonophysics volume 839 on pages 229499. 10.1016/j.tecto.2022.229499