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Extended Data Fig. 6 | Structure of the lithospheric keels beneath South
Africa. a, The Limpopo Belt area^5. The section shows an ultradepleted layer
from 140–180 km depth, overlain by a more fertile layer with high XMgOliv
(refs.^5 ,^29 ,^30 ). The deeper part is moderately melt-metasomatized with the
introduction of Al and Fe, corresponding to sheared lherzolites, but chromite
is most abundant at 170–190 km depth, and the depleted root may originally
have extended to depth of about 210 km. Van der Meer et al.^83 have verified the
structure with xenolith studies and suggest that the two layers have distinct
provenances. b, The northern Lesotho area. Harzburgites are mostly confined
to the more fertile layer (high Al 2 O 3 ) above 120 km, but the section is dominated
by depleted lherzolites from 140–180 km depth, and the base is marked by a
dominance of lherzolites produced by intense melt-related metasomatism.
c, The northern Botswana area. A relatively depleted (but mainly lherzolitic)
section from 120–190 km depth is overlain by more fertile (higher-Al 2 O 3 ) rocks,
but with similarly high XMgOliv more characteristic of depleted rocks. This
suggests that the upper layer in this case represents the refertilization of a
depleted section, rather than a separate unit.