Crustal structure beneath the Kivu Rift and Virunga Volcanic Province, Western Rift, Africa

Magmatism can substantially modify continental crust during rifting, yet the distribution of melt and intrusive additions to the crust is often difficult to resolve, particularly in rift sectors where volcanism is spatially localised. Unlike the Ethiopian and Eastern rift sectors of East Africa, volcanism in the Western Rift is concentrated in a few spatially isolated volcanic provinces, raising questions about where magma is stored and how it interacts with fault-controlled extension during the early stages of rifting. We use teleseismic Ps receiver functions (RFs) from the Kivu Rift sector (networks 7G, YA, and KV) to constrain crustal thickness, bulk P-to-S wave velocity ratio (κ), and the character of intracrustal and Moho impedance contrasts across the Kivu Rift that includes the Virunga and South Kivu volcanic provinces. We combine H–κ stacking, 1-D receiver function waveform inversion, and forward modelling to map lateral variations in crustal structure. Crustal thickness varies systematically with tectonic setting: the thinnest crust occurs at stations within the rift (∼28–34 km), whereas thicker crust (mid-30s to low-40s km) characterises the flanks and the broader province. Elevated κ values and increased waveform complexity are concentrated around the Virunga Volcanic Province, consistent with mid- to lower-crustal modification by mafic intrusions and/or melt–fluid effects. We also assess whether topographic variations are isostatically compensated after accounting for the dynamically-supported broad plateau uplift. The thinner crust within the fault-bounded basin confirms extension by a mean stretching factor of ~1.23, locally reaching ~1.32 where crust thins to ~28 km, but the basin–flank elevation contrast is smaller than expected from crustal thinning alone, suggesting that lower crust and/or sub-crustal density variations are important. Together, these observations indicate that the crust beneath the Kivu Rift sector is felsic in composition, has magmatic modification localised to the Virunga Volcanic Province, and crustal stretching is comparable to other Western Rift sectors with deeper basins.