Low-temperature thermochronology studies record Miocene rift initiation of the Northern Malawi Rift. However, no such studies are available that constrain the onset time of rifting of the Southern Malawi Rift, and Cenozoic reactivation of the older Carboniferous-Jurassic Shire Rift. Here we present thermal history models derived from new apatite fission-track and (U-Th-Sm)/He data from the footwalls of major border faults of the Southern Malawi Rift and Shire Rift. Results reveal three distinct cooling episodes: fast cooling in the Cretaceous, slow cooling from the Late Cretaceous until the Miocene, and fast cooling starting in the Late Miocene–Pliocene. The latter phase of cooling indicates that strain along the border faults of the Southern Malawi Rift was initiated at the same time as the Northern Malawi Rift. The timing and rate of extension were further constrained using remote sensing to map the fault networks of the Southern Malawi and Shire rifts and estimate fault displacement and geometry. These results, when combined with our thermal history modeling, yield inferred deformation strain rates that support the linkage between the modern Malawi Rift and the reactivation of border faults of the older Shire Rift since the Miocene. These results support the coeval onset of extension along the full length of the Malawi Rift, with an overall southward decrease in total extension instead driven by a southward decrease in plate-scale cumulative strain rates along the Western Branch of the East African Rift System.

中文翻译：

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马拉维南部裂谷的新近纪-第四纪起始及其与重新激活的石炭纪-侏罗纪夏尔裂谷的联系

低温热年代学研究记录了马拉维北部裂谷的中新世裂谷起始。然而，目前还没有此类研究来限制马拉维南部裂谷的裂谷开始时间以及较早的石炭纪-侏罗纪夏尔裂谷的新生代重新激活。在这里，我们提出了从新的磷灰石裂变径迹和来自马拉维南部裂谷和夏尔裂谷主要边界断层下盘的 (U-Th-Sm)/He 数据得出的热历史模型。结果揭示了三个不同的冷却阶段：白垩纪的快速冷却、从白垩纪晚期到中新世的缓慢冷却以及中新世晚期至上新世开始的快速冷却。冷却的后一阶段表明，沿马拉维南部裂谷边界断层的应变与马拉维北部裂谷同时开始。使用遥感技术绘制马拉维南部和夏尔裂谷的断层网络图并估计断层位移和几何形状，进一步限制了延伸的时间和速度。这些结果与我们的热历史模型相结合，得出推断的变形应变率，支持现代马拉维裂谷和自中新世以来旧夏尔裂谷边界断层重新活动之间的联系。这些结果支持沿马拉维裂谷全长同时开始延伸，总延伸总体向南减少，而不是由东非裂谷系统西支沿板块尺度累积应变率向南减少驱动。