Long-term reactivation and morphotectonic history of the Zambezi Belt, northern Zimbabwe, revealed by multi-method thermochronometry
Résumé
Neoproterozoic-early Paleozoic Pan-African mobile belts that formed during the amalgamation of Gondwana, such as the Zambezi Belt, are inherently weak zones that are susceptible to reactivation by later tectonism. With the exception of Karoo rifting, however, the post-Pan-African morphotectonic history of the Zambezi Belt is poorly constrained. Here, we use multiple low-temperature thermochronometers on samples collected across major structures in northern Zimbabwe to reveal the temporal and spatial pattern of tectonism and denudation in this portion of the Zambezi Belt. Thermal history modelling suggests that a large crustal block encompassing part of the Zambezi Belt and northern margin of the Zimbabwe Craton experienced differential denudation during three main Phanerozoic episodes. This denudation of the Archean-Proterozoic basement was associated with reactivation of the Zambezi Escarpment Fault, which demarcates the southern margin of the Karoo Cabora Bassa Basin. In contrast, other major structures within the region remained relatively stable. The results highlight the value of using a multi-thermochronometer approach, where essentially zircon (U-Th)/He data preserve evidence of late Carboniferous Karoo rifting, apatite fission track data record the thermal effects of Jurassic tectonism associated with Gondwana breakup, and the apatite (U-Th-Sm)/He data reveal Paleogene reactivation of the basin-bounding fault. Thermal history modelling also suggests that the Cabora Bassa Basin experienced Gondwana breakup-related denudation, potentially associated with a proposed concurrent major regional drainage reversal. Since the Cretaceous, the basin has experienced limited sedimentation and erosion.
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