A large number of studies have demonstrated that the combination of in-situ U-Pb and Lu-Hf isotope analyses carried out on single zircon grains provides a powerful tool, to further understand crust formation and reworking processes through time (e.g. Eglinger et al., 2017). When combined with lithogeochemical data, such analysis may help to fingerprint the different magma sources at play through the crust formation processes and provide an insight into the Precambrian lithospheric architecture (Mole et al., 2014). To further the understanding of the southern West African Craton (SWAC) that include Paleoproterozoic and Archean domains, zircon grains from felsic intrusions were analysed for Hf-isotopes over the SWAC. The results of the study point toward: 1) the presence of ancient meso- to paleo- Archean lithosphere in Guinea, Liberia and Sierra Leone that appears to have been significantly reworked during the Paleoproterozoic (Eglinger et al., 2017) and 2) the presence of broadly juvenile Proterozoic domains with localised evidence of Archean crustal reworking (Parra-Avilla et al., 2017). Temporally-constrained Lu-Hf analyses enable to image the SWAC magmatic evolution in space and time highlighting a two-step magmatic evolution. From c. 2300 Ma to 2100 Ma the plutonic activity is associated with input of juvenile material following a north-south corridor running from Burkina Faso to Ghana as well as further west in the KKI. Elsewhere in the SWAC the magmatic signature suggest the reworking of older crustal material like in west Cote D’Ivoire, west Mali but also in the East (Ghana and Burkina Faso) (Petersson et al., 2016). The period from c. 2110 to 2080 Ma which mark the peak of the Eburnean orogeny is associated with a decrease of juvenile input and progressive reworking of the Eoeburnean. This second period is also associated with a remarkable shift of magmatism towards the western part of the SWAC that significantly rework older Archean crustal domains located in southern Guinea (Eglinger et al., 2017). Collectively the data acquired offer a new perspective on the Archean crustal evolution and associated crustal architecture that punctuated the geodynamic evolution of the SWAC.

Reference(s)

Eglinger A, Thébaud N, Zeh A, Davis J, Miller J, Parra-Avila LA, Loucks R, McCuiag C, Belousova E (2017) New insights into the crustal growth of the Paleoproterozoic margin of the Archean Kénéma-Man domain, West African craton (Guinea): Implications for gold mineral system. Precambrian Research 292:258-289.

Parra-Avila LA, Belousov E, Fiorentini M, Eglinger A, Blocke S, Miller J (2017) Zircon Hf and O-isotope constraints on the evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton Precambrian Research 306 (2018) 174–188.

Petersson, A., Scherstén, A., Kemp, A.I.S., Kristinsdóttir, B., Kalvig, P., Anum, S., (2016). Zircon U–Pb–Hf evidence for subduction related crustal growth and reworking of Archaean crust within the Palaeoproterozoic Birimian terrane, West African Craton, SE Ghana. Precambrian Research, 275, 286–309. 

Mole DR, Fiorentini ML, Cassidy KF, Kirkland CL, Thébaud N, McCuaig TC, Doublier MP, Duuring P, Romano SS, Maas R, Belousova EA, Barnes SJ and Miller J (2013) Crustal evolution, intra-cratonic architecture and the metallogeny of an Archaean craton, Geological Society, London, Special Publications, 393.