The isotopic data stored in detrital and magmatic zircons are crucial for assessing magma
sources, terrane correlation, paleogeography and plate reconstructions. In many cases the
comparison of the zircon age and isotope signature of a terrane of unknown provenance with
the signature of possible sources, generally old cratonic areas, can resolve questions of origin
and paleoposition. Obviously, a precise knowledge of the zircon characteristics of these old
areas is essential for reliable comparisons.
One of the major sources of sediments of the peri-Gondwanan terranes and of the European
Variscan Belt is the West African craton. The northern boundary of this craton is the Pan-
African Anti-Atlas belt, which is therefore an ideal place to better constrain the zircon isotopic
features of sediments sourced from it. With that aim, we obtained LA-ICM-MS U-Pb and Hf
isotopic data of more than 600 zircons separated from six samples of siliciclastic sedimentary
rocks from the main Neoproterozoic stratigraphic units of the Anti-Atlas belt, from the Sirwa
and Zenaga inliers.
The data suggest that the north part of the West African craton formed during three cycles of
juvenile crust formation, with variable amount of reworking of older crust. The youngest group
of zircons, with a main population clustering around 610 Ma, has a predominantly juvenile
character and evidence of moderate mixing with Paleoproterozoic crust, suggesting that the
igneous and metamorphic rocks in which the zircons originally crystallized were formed in
an ensialic magmatic arc environment. A group of zircons with ages in the range 1.79–2.3
Ga corresponds to the major crust forming event in the West African craton: the Eburnian-
Birimian orogeny. The isotopic data indicate that the provenance area should represent a crustal
domain that separated from a mantle reservoir at ∼2050–2300 Ma, and further evolved with
a time-integrated 176Lu/177Hf of ∼0.013, characteristic of continental crust. The evolution
of the Eburnian orogeny is apparently dominated by new crust formation in a magmatic arc
environment. The Lower Paleoproterozoic and Neoarchean evolution (2.3–2.75 Ga) involves a
group of detrital zircon ages that has not been identified up to now in the igneous or metamorphic
rocks of the north West African craton basement. Their Hf isotopic signature points to reworking
of juvenile crust mixed with moderate amounts of Archean crust. The significance of these ages
is uncertain: they could represent a tectonothermal event not discovered yet in the Reguibat
Shield or the zircons can be far-travelled from an unknown source.Peer Reviewe
