Hierarchical segmentation of the Malawi Rift: The influence of inherited lithospheric heterogeneity and kinematics in the evolution of continental rifts

Abstract

We used detailed analysis of Shuttle Radar Topography Mission-digital elevation model and observations from aeromagnetic data to examine the influence of inherited lithospheric heterogeneity and kinematics in the segmentation of largely amagmatic continental rifts. We focused on the Cenozoic Malawi Rift, which represents the southern extension of the Western Branch of the East African Rift System. This north trending rift traverses Precambrian and Paleozoic-Mesozoic structures of different orientations. We found that the rift can be hierarchically divided into first-order and second-order segments. In the first-order segmentation, we divided the rift into Northern, Central, and Southern sections. In its Northern Section, the rift follows Paleoproterozoic and Neoproterozoic terrains with structural grain that favored the localization of extension within well-developed border faults. The Central Section occurs within Mesoproterozoic-Neoproterozoic terrain with regional structures oblique to the rift extent. We propose that the lack of inherited lithospheric heterogeneity favoring extension localization resulted in the development of the rift in this section as a shallow graben with undeveloped border faults. In the Southern Section, Mesoproterozoic-Neoproterozoic rocks were reactivated and developed the border faults. In the second-order segmentation, only observed in the Northern Section, we divided the section into five segments that approximate four half-grabens/ asymmetrical grabens with alternating polarities. The change of polarity coincides with flip-over full-grabens occurring within overlap zones associated with~150 km long alternating border faults segments. The inherited lithospheric heterogeneity played the major role in facilitating the segmentation of the Malawi Rift during its opening resulting from extension. Key Points:• Segmentation of the Malawi Rift is studied using SRTM DEM and magnetic data • The rift is hierarchically divided into first-order and second-order segments • Lithospheric heterogeneity controls firstand second-order segmentation

Controls of Basement Fabric on the Linkage of Rift Segments

“…Our morphological assessments focus on the variation in the scarp heights (relief above the surface) of exposed normal faults along the RMNRS. This provides the minimum estimate of the relative vertical displacements of the faults at the point of assessment, hence the term “exposed minimum vertical displacement” (Lao‐Davila et al, ).…”

“…Similar to the Rukwa Rift, second‐order rift bifurcations are common along the East African Rift System. Examples include the Southern Malawi Rift bifurcation around the Shire Horst (Lao‐Davila et al, ), the Shire Graben bifurcation around the Namalambo Horst (Castaing, ), and the Albertine Graben bifurcation around the Rwenzori Block (Koehn et al, ; Xue et al, ).…”

Control of Pre‐rift Lithospheric Structure on the Architecture and Evolution of Continental Rifts: Insights From the Main Ethiopian Rift, East Africa

“…In these profiles, the subsurface geology and the resulting basin architecture are derived from published cross sections, extrapolation of surface geology, or available subsurface data (see list of references in the caption of Figure ). Faults are differentiated based on their exposed minimum vertical displacement (e.g., Laó‐Dávila et al, ), a value that underestimates the actual fault motion since other processes (e.g., erosion and deposition) likely altered the topography of the plateaus and the rift floor (see below). Henceforth, we use the term “rift symmetry” when the cumulative exposed minimum vertical displacement on major boundary faults is similar on both rift margins, and the term “rift asymmetry” when this value is significantly lower on one margin with respect to the other (e.g., Laó‐Dávila et al, ).…”

Lithospheric Structure of the Malawi Rift: Implications for Magma‐Poor Rifting Processes

“…The 2009 M w 6.0 Karonga earthquake in the NMR is related to migration of tectonic activity from the Livingstone border fault onto the hanging wall faults (Biggs et al, ; Fagereng, ; Gaherty et al, ) where the earthquake reactivated prerift Precambrian basement structures along the hanging wall hinge zone (Kolawole et al, ). The ~200‐km long Usisya fault system dominates the central MR (henceforth CMR; Figure a; Contreras et al, ; Laó‐Dávila et al, ), whereas the ~125‐km long Bilila‐Mtakataka fault dominates the southern segment of the MR (henceforth SMR; Figure a; Jackson & Blenkinsop, ). The SMR terminates against the NW trending Shire Graben bounded by the Mwanza fault (Figure 2a; Castaing, ).…”

“…(b) Tectonic map showing the exposures of the Precambrian and Paleozoic‐Mesozoic units around the Malawi Rift. Modified after Westerhof et al (), Fritz et al (), and Laó‐Dávila et al (). SZ = Shear Zone, Zimb.…”