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Abstract The oldest structures in a rift basin define incipient rift architecture, and commonly modulate the patterns of landscape evolution, sedimentation, and associated hazards in subsequent phases of rift development. However, due to deep burial beneath younger, thick syn‐rift sequences, and limited resolution of seismic imaging, critical early‐rift processes remain poorly understood. In the Tanganyika Rift, East Africa, we augment existing 2‐dimensional (2‐D) seismic reflection data with newly acquired aeromagnetic and Full‐Tensor Gradiometry data to assess the deep basin and underlying basement structure. Aeromagnetic and gravity grids show a dominance of NW‐trending long‐wavelength (>5 km) structural fabrics corresponding to the deeper basement, and dominant NW‐trending with a secondary NNE‐trending shorter‐wavelength (<3 km) fabric representing shallower, intra‐basin structures. Seismically‐constrained 2‐D forward modeling of the aeromagnetic and gravity data reveals: (a) an anomalously high‐density (2.35–2.45 g/cc) deep‐seated, fault‐bounded wedge‐shaped sedimentary unit that directly overlies the pre‐rift basement, likely of Mesozoic (Karoo) origin; (b) ∼4 km‐wide sub‐vertical low‐density (2.71 g/cc) structures within the 3.2 g/cc basement, interpreted to be inherited basement shear zones, (c) early‐rift intra‐basin faults co‐located with the modeled shear zone margins, in some places defining a persistent structurally‐controlled intra‐basin “high,” and (d) a shallow intra‐sedimentary V‐shaped zone of comparatively dense material (∼2.2 g/cc), interpreted to be a younger axial channel complex confined between the intra‐basin “high” and border fault. These results provide new insight into the earliest basin architecture of the Tanganyika Rift, controlled by inherited basement structure, and provide evidence of their persistent influence on the subsequent basin evolution.
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Heterogeneous Strain Distribution in the Malawi (Nyasa) Rift, East Africa: Implications for Rifting in Magma‐Poor, Multi‐Segment Rift Systems
Abstract Half‐graben basins bounded by border faults typify early‐stage continental rifts. Deciphering the role that intra‐rift faults play in rift basin development is challenging as patterns of early‐stage faulting are commonly overprinted by subsequent deformation; yet the characterization of these faults is crucial to understand the fundamental controls on their evolution, their contribution to rift opening, and to assess their seismic hazard. By integrating multiple offshore seismic reflection data sets with age‐dated drill core, late‐Quaternary and cumulative faulting patterns are characterized in the Central and South Basins of the Malawi (Nyasa) Rift, an active, early‐stage rift system. Almost all intra‐rift faults offset a late‐Quaternary lake lowstand surface, suggesting they are active and should be considered in hazard assessments. Fault throw profiles reveal sawtooth patterns indicating segmented slip histories. Observed extension on intra‐rift faults is approximately twice that predicted from hanging wall flexure of the border fault, suggesting that intra‐rift faults accommodate a proportion of the regional extension. Cumulative and late‐Quaternary throws on intra‐rift faults are correlated with throw measured on the border fault in the Central Basin, whereas an anticorrelation is observed in the South Basin. Viewed in a regional context, these differences do not relate solely to the proposed southward younging of the rift. Instead, it is inferred that the distribution of extension is also influenced by variations in lithospheric structure and crustal heterogeneities that are documented along the rift axis.
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- Award ID(s):
- 2116017
- PAR ID:
- 10468083
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Tectonics
- Volume:
- 42
- Issue:
- 9
- ISSN:
- 0278-7407
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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