Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola

Abstract

The origin of intraplate carbonatitic to alkaline volcanism in Africa is controversial. A tectonic control, i.e., decompression melting associated far-field stress, is suggested by correlation with lithospheric sutures, repeated magmatic cycles in the same areas over several Myr, synchronicity across the plate, and lack of clear age progression patterns. Conversely, a dominant role for mantle convection is supported by the coincidence of Cenozoic volcanism with regions of lithospheric uplift, positive free-air gravity anomalies and slow seismic velocities. To improve constraints on the genesis of African volcanism, here we report the first radiometric and isotopic results for the Catanda complex, which hosts the only extrusive carbonatites in Angola. Apatite (U-Th-Sm)/He and phlogopite 40Ar/39Ar ages of Catanda aillikite lavas indicate eruption at ~500-800 ka, >100 Ma after emplacement of abundant kimberlites and carbonatites in this region. The lavas share similar HIMU-like Sr-Nd-Pb-Hf isotope compositions with other young mantle-derived volcanics from Africa (e.g., Northern Kenya Rift; Cameroon Line). The position of the Catanda complex in the Lucapa corridor, a long-lived extensional structure, suggests a possible tectonic control for the volcanism. The complex is also located on the Bié Dome, a broad region of fast Pleistocene uplift attributed to mantle upwelling. Seismic tomography models indicate convection of deep hot material beneath regions of active volcanism in Africa including a large area encompassing Angola and northern Namibia. This is strong evidence that intraplate late-Cenozoic volcanism, including the Catanda complex, resulted from the interplay between mantle convection and pre-existing lithospheric heterogeneities. only notable exceptions are Late Cretaceous and Paleogene alkaline volcanic centers in southern Namibia, possibly related to the passage of hot spots currently in the South Atlantic (Reid et al., 1990). Regions of active and recent volcanism coincide with some of the several swells (i.e., topographic highs) that characterize the surface morphology of the African continent (e.g., Burke, 1996). These zones are characterized by positive free-air gravity anomalies (e.g., Burke, 1996; Al-Hajri et al., 2009) and slow seismic velocities in the mantle (e.g., Forte et al., 2010; French and Romanowicz, 2015), suggesting that sublithospheric convection plays a significant role in sustaining the high topography of the swells and triggering intraplate volcanism (Fishwick and Bastow, 2011). With evidence for tectonic, lithospheric and convective controls, the ultimate trigger(s) of mantle-derived Cenozoic intraplate volcanism in Africa remains unresolved. To contribute to this discussion, we report the first geochronological and radiogenic isotope results for aillikite (i.e., carbonate-rich ultramafic lamprophyre) lavas from the Catanda volcanic complex in central Angola (Fig. 1 and Fig. DR1 inSupplementary Material). This complex also includes the only extrusive carbonatites documented in Ango...

A tale of two domes: Neogene to recent volcanism and dynamic uplift of northeast Brazil and southwest Africa

“…In both cases, volcanism is concentrated in the vicinity of the peak amplitudes of free-air gravity anomalies, topographic swells, and of low shear wave velocity anomalies. Eruptions are more abundant in northeast Brazil, and extend over a longer time period (Giuliani et al, 2017;Guimarães et al, 2020). This activity has previously been attributed either to a plume located beneath Fernando de Noronha, to edge-driven convection, or to re-activation of lithospheric-scale fault zones (e.g.…”

Scales of Similarity and Disparity Between Drainage Networks

“…I focus on the Bie dome, which intersects West Africa's passive margin and has a wavelength of a few hundred kilometers (e.g., Burke, 1996;Burke & Gunnell, 2008). The domal shape of this swell, the colocation of mafic magmatism, slow asthenospheric shear wave velocity anomalies, positive long wavelength free-air gravity anomalies, and a smoothly varying suite of residual ocean age-depth measurements indicate that most of its topography was generated and is maintained by regional subplate processes (e.g., Fishwick, 2010;Giuliani et al, 2017;Hoggard et al, 2016;Jones et al, 2012;Schaeffer & Lebedev, 2013). A drainage network across the swell and its surroundings was extracted from the 3 arc sec (∼90 × 90 m) Shuttle Radar Topographic Mission (SRTM) digital elevation model using standard Esri flow routing techniques (e.g., Tarboton, 1997).…”

Thermochemical structure and evolution of cratonic lithosphere in central and southern Africa

“…Figs. [22][23][24][25] for examples of data fits). Since the datasets used in this study have different units, uncertainties, data coverage and sensitivities to different aspects of the problem, the simultaneous inversion of these data requires an adequate weighting of each dataset.…”

“…3) likely contributing to the weakening and thinning of the lithospheric mantle. Carbonate-rich ultramafic lavas < 1 Ma old in Angola's Catanda volcanic complex 22 have been interpreted to originate from local mantle upwelling beneath thinned lithosphere 22 , but the nature and size of the upwelling and the LAB depth were poorly constrained. Our results confirm significant thinning of the lithosphere beneath this region (Fig.…”