TY - JOUR
T1 - Petrological and geochemical study of Birimian ultramafic rocks within the West African Craton
T2 - Insights from Mako (Senegal) and Loraboué (Burkina Faso) lherzolite/harzburgite/wehrlite associations
AU - Labou, Ibrahima
AU - Benoit, Mathieu
AU - Baratoux, Lenka
AU - Grégoire, Michel
AU - Ndiaye, Papa Moussa
AU - Thebaud, Nicolas
AU - Béziat, Didier
AU - Debat, Pierre
PY - 2020/2
Y1 - 2020/2
N2 - In Archean and Paleoproterozoic greenstone belts, ultramafic (UM) rock occurrences are commonly found in close association within basic and differentiated magmatic series. In the Kedougou-Kenieba Inlier (West African Craton), UM rocks are interbedded within the Birimian (2.1 Ga) Mako tholeiitic series (basalts, gabbros). UMs are typically lherzolite, harzburgite and wehrlite, characterized by their cumulative textures and relative proportions of chromite, olivine, clinopyroxene, amphibole ± orthopyroxene. Geochemical study (Major, REE and trace elements in whole rocks and mineral (mainly clinopyroxene and amphibole) and Sr/Nd isotopic records suggest the existence of different types of complexes. The first one consists of lherzolite + harzburgite assemblages whereas the second one consists of isolated wehrlite massifs. Both complexes highlight two different geodynamic environments, the first association being significantly more juvenile or mantle-related than isolated wehrlites which show more evolved geochemical signatures. UM rocks (dunite + wehrlite) of Loraboué (greenstone belt of Boromo, Burkina Faso) associated with calc-alkaline series display the same mineralogical composition as the Mako UM rocks but exhibit a different whole rock composition characteristic of mature island-arc magmas and showing U-shaped REE pattern for both clinopyroxene and host rock, and a clear negative Nb anomaly. The Mako UMs suggest that this portion of the Birimian crust was built in an oceanic context evolving from a MORB-like domain to an increasingly mature volcanic arc domain.
AB - In Archean and Paleoproterozoic greenstone belts, ultramafic (UM) rock occurrences are commonly found in close association within basic and differentiated magmatic series. In the Kedougou-Kenieba Inlier (West African Craton), UM rocks are interbedded within the Birimian (2.1 Ga) Mako tholeiitic series (basalts, gabbros). UMs are typically lherzolite, harzburgite and wehrlite, characterized by their cumulative textures and relative proportions of chromite, olivine, clinopyroxene, amphibole ± orthopyroxene. Geochemical study (Major, REE and trace elements in whole rocks and mineral (mainly clinopyroxene and amphibole) and Sr/Nd isotopic records suggest the existence of different types of complexes. The first one consists of lherzolite + harzburgite assemblages whereas the second one consists of isolated wehrlite massifs. Both complexes highlight two different geodynamic environments, the first association being significantly more juvenile or mantle-related than isolated wehrlites which show more evolved geochemical signatures. UM rocks (dunite + wehrlite) of Loraboué (greenstone belt of Boromo, Burkina Faso) associated with calc-alkaline series display the same mineralogical composition as the Mako UM rocks but exhibit a different whole rock composition characteristic of mature island-arc magmas and showing U-shaped REE pattern for both clinopyroxene and host rock, and a clear negative Nb anomaly. The Mako UMs suggest that this portion of the Birimian crust was built in an oceanic context evolving from a MORB-like domain to an increasingly mature volcanic arc domain.
KW - Birimian
KW - Geochemistry
KW - Paleotectonic setting
KW - Sr–Nd isotopes
KW - Ultramafic rocks
KW - West African Craton
UR - http://www.scopus.com/inward/record.url?scp=85074515366&partnerID=8YFLogxK
U2 - 10.1016/j.jafrearsci.2019.103677
DO - 10.1016/j.jafrearsci.2019.103677
M3 - Review article
AN - SCOPUS:85074515366
SN - 1464-343X
VL - 162
JO - Journal of African Earth Science
JF - Journal of African Earth Science
M1 - 103677
ER -