Seismological Constraints on Subduction and Suture Zone Architecture in the Central African Copperbelt

Summary Central Africa marks a major collisional zone of the Pan-African Orogeny, involving convergence of the Congo and Kalahari plates during Gondwana assembly (~600–500 Ma). This collision formed the Lufilian Belt and one of the world’s most significant metallogenic provinces—the Central African Copperbelt. However, the deep lithospheric architecture underpinning this mineral-rich region remains poorly understood. Fundamental questions persist regarding the role of subduction, convergence polarity, and suture-zone geometry. We address this using broadband seismic data collected across Zambia’s Pan-African orogenic belts to construct a lithospheric shear-wave velocity model via joint inversion of receiver functions and surface-waves. Common conversion point stacking of P-to-S receiver functions further enhances imaging of subsurface discontinuities. Our results reveal pronounced crustal deformation below the central Lufilian Belt, where the Moho is deepest (~48 km) and most gradational, marking the suture zone during continent-continent collision. Elsewhere, Moho architecture is shallower and uniform despite protracted convergence, suggesting lower-crustal flow accompanying orogenesis smoothed crustal thickness contrasts. At mantle depths, thick (160–180 km), homogeneously fast wavespeed (4.5–4.74 km/s) lithosphere delineates the unmodified Congo Craton margin. Further south, thinner lithosphere (140–150 km) contains a pervasive mid-lithospheric low-velocity zone (4.3–4.4 km/s) at 50–80 km depth, interpreted as metasomatically-modified Proterozoic lithosphere rich in easily-fusible phases emplaced during Pan-African subduction. This contrast in mantle wavespeeds, together with southward-dipping Moho geometry and intra-crustal structure, indicates underthrusting of the Congo beneath the Kalahari plate. The spatial coincidence of mantle metasomes and zones of crustal reworking with critical mineral occurrences across the Copperbelt highlights their role in creating favourable conditions for mineralisation in overlying sedimentary basins.