Tectonic model of the Malaŵi rift, Africa

Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers

“…If the 3 per cent reduction in velocity in the Central Basin relative to the North Basin is due to syn-rift sediment, then this would require an increase in the thickness of basin sediments, and thus could imply an increase in total extension, from north to south. Alternatively, the Central Basin is also thought to contain several kilometres of Karoo super-group sediments (Ebinger et al 1987;Mortimer et al 2016), which are exposed onshore in the Ruhuhu basin (Kreuser et al 1990) and could contribute significantly to the strong short-period velocity anomaly. Several lines of evidence point to the presence of Karoo sediments in the Central Basin including a transition in the character of seismic reflectors between the North and Central basins (Ebinger et al 1987) and the location/orientation of horsts within the Central Basin which are thought to be controlled by pre-existing structures associated with Karoo rifting (Mortimer et al 2016).…”

“…Alternatively, the Central Basin is also thought to contain several kilometres of Karoo super-group sediments (Ebinger et al 1987;Mortimer et al 2016), which are exposed onshore in the Ruhuhu basin (Kreuser et al 1990) and could contribute significantly to the strong short-period velocity anomaly. Several lines of evidence point to the presence of Karoo sediments in the Central Basin including a transition in the character of seismic reflectors between the North and Central basins (Ebinger et al 1987) and the location/orientation of horsts within the Central Basin which are thought to be controlled by pre-existing structures associated with Karoo rifting (Mortimer et al 2016). Additionally, preliminary observations from the SEGMeNT activesource refraction study report a significant increase in the crossover distance between sedimentary and crustal refractions in the Central Basin (Accardo et al 2016), and preliminary P-wave velocity models contain a several kilometres thick layer with P-wave velocities between 3 and 5 km s −1 , which may be consistent with older, more indurated Karoo sediments (Shillington et al 2015).…”

Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)

“…The Nkhata basin is one of the three deep basins of the Malawi rift that accommodate >4 km sediment, and are connected across transfer, or accommodation, zones (Ebinger, 1987;Versfelt and Rosendahl, 1989;Ebinger et al, 1993). Existing structures of significance are the Ubendian Proterozoic mobile belt, known to have exerted strong influence on the location and orientation of the northern (Karonga) basin of the Malawi Rift (Rosendahl, 1987;King, 1994), and later Permian Karoo extensional basins onto which many basin separating accommodation zones are juxtaposed (e.g., Versfelt and Rosendahl, 1989) .…”

“…Following the margins of the Tanzanian craton, the East African Rift System (EARS; Figure 1) is divided into two structurally distinct west and east branches (e.g., Ebinger, 1987). Past tectonic activity since the Proterozoic is responsible for inducing structural weakness in the lithosphere, which strongly influences the location and orientation of late-Cenozoic structures in both branches (Rosendahl, 1987;Versfelt and Rosendahl, 1989;.…”

“…However, in this study we focus on the basin-scale Cenozoic structural evolution of the c.150 km-long, 40 km-wide central or 'Nkhata' (Ebinger et al, 1987) basin of the Malawi rift which is in part superimposed onto a SW-NE trending Karoo basin preserved onshore and inferred to continue into the region currently occupied by Lake Nyasa (Figure 1). It is bounded to the west by a steep, east-dipping, 120 km border fault system (Mlowe-Nkhata fault) and to the east by a shorter,~30 km-long, border fault (Mbamba fault; Figure 2a).…”