The Rukwa and North Malawi Rift Segments (RNMRS) both define a major rift‐oblique segment of the East African Rift System and are often regarded as discrete rifts due to the presence of the uplifted Mbozi block between them. Here we investigate the influence of basement fabrics on the coupling and linkage of border faults across an interrift transfer zone between discrete juvenile rift segments. We utilized satellite digital elevation model to investigate the morphological architecture of the rift domains and aeromagnetic data to assess the relationships (plan view) between the rift structures and the prerift basement fabrics. Our results show that the present‐day morphology of the RNMRS is characterized by along‐rift alternation of rift shoulder polarity, characteristic of coupled rift segments. Interpretation of filtered aeromagnetic maps along the boundaries of the RNMRS reveals striking alignment of the rift‐bounding faults with colinear NW‐SE trending preexisting basement fabrics. We find that rift coupling along the NE boundary of the Mbozi transfer zone is accommodated by fault‐assisted magma plumbing, whereas coupling along the SW boundary is accommodated by strike‐slip and oblique‐normal faulting that reactivated the Proterozoic Mughese shear zone, within the collisional boundary between the Tanzania craton and the Bangweulu cratonic block. Further, we show how the configuration of the basement fabrics may influence the formation of rift bifurcation across inter‐rift transfer zones. We suggest that the structural connectivity of the boundary faults along the RNMRS and their alignment with colinear basement fabrics demonstrate the influence of structural inheritance on the amalgamation of approaching rift segments.

The Rukwa Rift and North Malawi Rift Segments (RNMRS) both define a major rift-oblique segment of the East African Rift System (EARS), and although the two young rifts show colinear approaching geometries, they are often regarded as discrete rifts due to the presence of the intervening Mbozi Block uplift located in-between. This problem has been complicated by the dominance of the Rungwe volcanic features along the northeastern boundary of the Mbozi Block and lack of distinct normal faults along the southwestern boundary of the block. Here, we investigate the coupling of discrete rift segments during the onset of continental rifting, modulated by the control of pre-existing basement fabrics on the development of the border fault geometries and linkage across the intra-rift transfer zone. We utilized the Shuttle Radar Topography Mission Digital Elevation Models (SRTM-DEM) to investigate the morphological architecture of the rift domains; and aeromagnetic data and SRTM-DEM to assess the relationships between the rift structures and the pre-existing basement fabric (in plan-view). Our results show that the present-day morphology of the RNMRS is characterized by along-rift alternation of rift shoulder polarity, characteristic of coupled rift segments. Careful interpretation of filtered aeromagnetic maps along the northeastern and southwestern boundaries of the RNMRS reveal striking alignment of the rift-bounding faults with colinear NW-SE-trending pre-existing basement fabrics. We find that rift coupling along the northeastern boundary of the Mbozi Block transfer zone is accommodated by magmatism utilizing pre-existing fault systems, whereas, coupling along the southwestern boundary is accommodated by a new-found dextral strike-slip fault. Additionally, we show how the configuration of the pre-existing basement fabrics may influence the development of rectilinear or curvilinear normal fault geometries (plan-view) along the rifts, and the formation of basin-scale rift bifurcation around basement inter-rift transfer zones. In summary, we suggest that the structural continuation of the boundary faults along the RNMRS, and their alignment with colinear basement fabrics demonstrate the influence of structural inheritance on the coupling and amalgamation of approaching rift segments.

Ross Island is located in the southern Victoria Land Basin along the western margin of the West Antarctic Rift System. Episodic volcanism since ca. 4.6 Ma produced a discontinuous sedimentary moat around the island, coeval with regional extension. The moat is a composite of four smaller sub‐basins created during distinct episodes of volcanism. Subsidence within each sub‐basin is modeled as bending of a continuous elastic plate, first considering subsidence that occurred only during the time in which the associated volcano was active, and then considering cumulative subsidence since the onset of volcanism on Ross Island. Models based on strata deposited in each sub‐basin during the time interval in which the respective volcano was active yield flexural rigidities ranging from 6–36 × 1018 N‐m, with the lowest values associated with the youngest volcanoes on the south and southwest sides of the island. Models based on the entire stratigraphic interval deposited since the onset of volcanism yield flexural rigidities up to 20 times greater than models that consider only strata deposited within each sub‐basin when the associated volcano was active. Models of the composite basin overestimate the strength of the lithosphere due to inclusion of strata deposited during periods in which regional extension rather than local flexure dominated subsidence. The models indicate that Ross Island is in near flexural isostatic equilibrium with moderately low‐density (3,260 kg m−3) upper mantle, although an additional buoyant load equivalent to a mantle temperature anomaly of up to 200°C is permissible.

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