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 period. 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 farther 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) favorably-oriented zones of mechanical strength contrast that localized the large rift faults, and 2) mechanical ‘barriers’ that refracted and possibly, temporarily halted the lateral propagation of the rift zone. Further, the cooled RP1-RP2 mafic dikes localized later-phase deformation in the form of border fault hard-linking transverse faults that exploited strength contrasts 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 crustal strength anisotropies may serve as both strain-localizing, refracting, and ‘strain barrier’ tectonic structures.

我们研究了东非夏尔裂谷带 (SRZ) 多期裂谷演化过程中应变调节的时空模式。NW向的SRZ记录了从富含岩浆的裂谷阶段（二叠纪-早侏罗世：裂谷期1（RP1）和晚侏罗世-白垩纪：裂谷期2（RP2））到岩浆贫乏阶段的转变。新生代（进行中：裂谷第三阶段（RP3））。我们的观察表明，尽管裂谷边界断层在很大程度上模拟裂谷前的基底变质组织，但裂谷终止带出现在 RP1-RP2 时期地壳尺度裂谷正交基底剪切带（Sanangoe (SSZ) 和 Lurio 剪切带）附近. 在 RP3，RP1-RP2 次盆地大部分被废弃，裂谷轴向东北（裂谷正交）迁移到 RP1-RP2 盆地边缘，并在 RP2 裂谷尖端之前向西北（走向平行）迁移。西北 RP3 裂谷轴侧步穿过 SSZ，边界断层旋转穿过剪切带，并在更远的西北处终止于另一个区域尺度的剪切带。我们认为，在 SRZ 的构造伸展和应变迁移的多个脉冲中，裂谷前的基底组织充当：1) 定位大裂谷断层的机械强度对比有利定向的区域，以及 2) 机械“障碍”，折射并可能暂时停止裂谷带的横向扩展。此外，冷却的 RP1-RP2 镁铁质岩脉以边界断层硬连接横向断层的形式局部化后期变形，利用了岩脉簇内的强度对比，并充当了阻止一些 RP3 断层尖端的机械强区。全面的，