The Influence of Inherited Structures on Segmentation and Linkage of Subparallel Faults in the Southern Malawi Rift
Daniel Lao-Davila, Boone Pickens School of Geology, Oklahoma State University, Stillwater, Oklahoma, USA
Steven Johnson, Boone Pickens School of Geology, Oklahoma State University, Stillwater, Oklahoma, USA
Estella Atekwana, University of Delaware, Department of Geological Sciences, Newark, DE, 19716, USA
Mohamed Abdelsalam, Boone Pickens School of Geology, Oklahoma State University, Stillwater, Oklahoma, USA
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Inherited structures have been recognized to affect the propagation, segmentation, and location of continental rifts. At the lithospheric scale, lithospheric heterogeneity has played a major role in facilitating the segmentation of the young and magma-poor Malawi Rift. Furthermore, in the northern Malawi Rift, the orientation of Precambrian shear zones influence strain accommodation and have important implications for seismic hazards. Still, the role that inherited structures play in the growth and linkage of 100 km-long and potentially seismically hazardous border faults remains poorly understood. We have explored the spatial relationship of inherited structures on the growth and evolution of the subparallel Bilila-Mtakataka Fault (BMF) and Chirobwe-Ntcheu Fault (CNF) in the southern Malawi Rift. We used Shuttle Radar Topography Mission Digital Elevation Model (SRTM-DEM) and aeromagnetic data to characterize the orientations and locations of both inherited structures and faults, to examine their spatial relationships. We also used fault throws extracted from the SRTM-DEM as a proxy of fault displacement to identify fault segments and linkage zones for both faults. Our observations indicate that the two normal faults occur in areas with a diversely oriented Precambrian foliation and regional joints. The BMF is composed of 5 segments with an average throw of 187 m and a maximum throw of 627 m. The CNF is composed of 3 segments with an average throw of 430 m and a maximum throw of 1137 m. The apparent throw profiles and location of segments are supported by source parameter imaging of the magnetic data. The BMF at the southern segments is subparallel to the Precambrian foliation that forms resistant ridges. The linkage for segments BM 2-3 occurs at the intersection of differently striking foliation and joints. The BMF cuts oblique to the foliation at its northernmost segment where the regional joints produce a zig-zag pattern of the fault scarp. The CNF follows the foliation in the southern segment as well. Linkage zones occur where the well-defined foliation is intersected by obliquely oriented foliation. In the northernmost segment, the CNF orientation is controlled by the presence of folded fabric and a late Jurassic to Cretaceous syeno-granitic pluton. Fault displacements and a greater number of segments suggest that the BMF is younger than the CNF. Orientation and location of Precambrian foliation, regional joints, and pluton suggest that segmentation and linkage of both faults were, in part, controlled by the inherited structures.