African cratonic lithosphere carved by mantle plumes

Abstract

How cratons, the ancient cores of continents, evolved since their formation over 2.5 Ga ago is debated. Seismic tomography can map the thick lithosphere of cratons, but its resolution is low in sparsely sampled continents. Here we show, using waveform tomography with a large, newly available dataset, that cratonic lithosphere beneath Africa is more complex and fragmented than seen previously. Most known diamondiferous kimberlites, indicative of thick lithosphere at the time of eruption, are where the lithosphere is thin today, implying surprisingly widespread lithospheric erosion over the last 200 Ma. Large igneous provinces, attributed to deep-mantle plumes, were emplaced near all lithosphere-loss locations, concurrently with or preceding the loss. This suggests that the cratonic roots foundered once modified by mantle plumes. Our results imply that the total volume of cratonic lithosphere has decreased since its Archean formation, with the fate of each craton depending on its movements relative to plumes.

Igneous Rock Associations 26. Lamproites, Exotic Potassic Alkaline Rocks: A Review of their Nomenclature, Characterization and Origins

“…Most earlier studies of the Kaapvaal craton suggested the presence of a thick craton with a "smooth" keel (see Mitchell 1986;Haggerty 1989) and the location of subducted material at the lithosphere-asthenosphere boundary. In contrast, recent geophysical studies (Celli et al 2020) have shown this simple picture does not describe the current configuration of most African cratons, and that much of the of original Kaapvaal craton, including any subducted components, has been removed by sub-lithospheric erosion. The 180 Ma Karroo large igneous province, the 150-110 Ma lamproites, and the 9 0 Ma kimberlites, are all now situated over an eroded thinned part of the craton.…”

“…Hence, the depths and temperatures of lamproite magma generation in the lithospheric mantle that have been estimated by the geothermobarometry of entrained eclogite and ultrabasic xenoliths refer to the paleo-configuration of the craton and not its current state (Shaikh et al 2019). These observations, and the work of Celli et al (2020), have implications for the genesis and preservation of lithospheric metasomes and highlight the need for detailed studies of the current and past structure of cratons. Many of the existing models for incorporation of diamond xenocrysts in lamproites and kimberlites (e.g.…”

“…3) explanations are required for the apparent paucity of cratonic lamproites in some cratons (Slave, Rae, Superior, Tanzanian, Yilgarn, Amazon), and of orogenic lamproites in the South America Cordillera. High resolution studies of the structure of cratons, their delamination and erosion following the methods of Celli et al (2020) are essential. 4) modern methods of in situ analytical geochemistry, such as LA-ICP-MS, should be applied to individual minerals and glasses in lamproites to determine how particular elements are distributed for general petrogenetic purposes.…”

Global distribution of sediment-hosted metals controlled by craton edge stability

“…For comparison, we include LAB maps derived from three additional upper mantle seismic tomography datasets with global coverage in Extended Data Figure 1. These include the 3D2015-07Sv model of , the CAM2016 model of Ho et al (2016) and Priestley et al (2018), and a version of SL2013sv into which we have blended the regional updates SL2013NA in North America (Schaeffer & Lebedev, 2014), AF2019 in Africa (Celli et al, 2020a), and SA2019 in South America and the South Atlantic Ocean (Celli et al, 2020b) to produce a combined model SLNAAFSA. For the continental analyses in Australia, we also consider regional model AuSREM of Kennett et al (2013) and Y14 of .…”

Weak orogenic lithosphere guides the pattern of plume-triggered supercontinent break-up

“…Conventionally, orogens are considered "weaker" than cratons due to anisotropy anomalies and/or major lithospheric shear zones, high crustal fluids, or thinner lithosphere. The latter is either intrinsic to the location or due to convective or gravitational removal of mantle lithospheric roots [29][30][31][32][33][34] . Orogens are therefore likely locations for subsequent continental rifting.…”