303-7 Normal Fault Growth and its Influence on Basin Morphology during the Earliest Phases of Continental Rifting, Okavango-Makgadikgadi Rift Zone, Botswana

Session: Honoring the Late Professor Mohamed Abdelsalam: Outstanding Researcher, Generous Colleague, Legendary Mentor, and Ambassador for the Geosciences In Africa (Posters)

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Abstract:

In the incipient Okavango-Makgadikgadi Rift Zone, Northern Botswana, previous studies show anomalous fault length-to-maximum displacement patterns that suggest that the normal faults are under-displaced, raising questions on the mechanisms of lateral fault propagation and lengthening relative to vertical displacement accrual. The subsiding hangingwall of the incipient rift zone hosts the Okavango Delta which represents the largest endorheic delta on African continent, which along with isolated depocenter wetlands along the border fault system, provide a rare opportunity to investigate how fault growth modulates basin morphology and its depositional environments in the early phases of rift formation. Here, we manually quantify the along-fault surface displacements on the faults using 12.5 m resolution topography data (TanDEM-X) at 1 km intervals, analyse fault segmentation, and integrate with quantitative morphology of the active rift lakes and distributary clusters of the Okavango Delta along the border-fault hangingwalls. Displacement-distance (D-D) plots of the largest faults in the rift zone reveal 60 - 90-km long super-segments that host 20 - 50-km long composite segments and 5 - 9-km long distinct ‘atomic’ segments. Along the Kunyere border fault of the southern Okavango Rift, we find that the largest deltaic distributary clusters occur at/near the maximum of the composite segments, and the smaller distributary clusters at the maximum of the ‘atomic’ segments. The distributary outlets on the border fault footwall are in several cases occur at displacement minima between the ‘atomic’ segments, but in a few cases are co-located with their displacement maxima. The modern Lake Ngami, which marks a significant terminal lake fed by the delta, is confined to one of two major composite segments on the southernmost section of the border fault system, but in which the other composite segment exhibits a larger displacement (11 m) than the segment bounding the lake (6 m), reflecting a temporal along-fault migration of strain on this super-segment. Additionally, the fault segment bounding the lake extends across a major relay zone between two super-segments of the Kunyere border fault, indicating possible acceleration of slip post fault linkage. These results suggest that border fault segmentation and displacement distribution exert multiple orders of control on the basin-wide morphology of intra-rift drainage systems during the early phases of rift evolution.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9768

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