Sub-continental lithospheric mantle beneath the Adamawa volcanic area (Cameroon Volcanic Line): inference from lavas and hosted mantle xenoliths from Bini Warack, NE-Ngaoundéré, Cameroon (Central Africa)

Sub-continental lithospheric mantle beneath the Adamawa volcanic area (Cameroon Volcanic Line): inference from lavas and hosted mantle xenoliths from Bini Warack, NE-Ngaoundéré, Cameroon (Central Africa) · UY1 Research Hub

Résumé

The sub-continental lithospheric mantle (SCLM) beneath the Cameroon Volcanic Line (CVL) is vertically and laterally heterogeneous, consisting of a complex mixing of DMM, HIMU, and EM1, affected by modal or cryptic metasomatism, depending on the area. The petrography, whole-rock geochemical data, and minerals’ chemical composition of lavas and mantle xenoliths from the Bini Warack area, combined with Sr isotope compositions, provide constraints on the origin and thermochemical evolution of the SCLM beneath this sector of the CVL. The host lavas are basanite, basalt, and latite with OIB affinity, characterized by moderate to high silica and alkali contents (SiO 2 = 42.35–56.56 wt%, K 2 O+Na 2 O = 2.34–7.07 wt%), a high Ba/Rb ranging from 12.2 to 26.1, a low Rb/Sr from 0.03 to 0.08, strong enrichment in LREE relative to HREE (La N /Yb N : 9.3–30), and moderate enrichment in radiogenic isotopes ( e.g. , 0.702987 < 87 Sr/ 86 Sr initial < 0.703206; 0.512854 < 143 Nd/ 144 Nd initial < 0.512918) with positive εNd initial (+4.84 to +6.09). These features are consistent with an origin of the lavas by a low degree of partial melting (<2%) of a lherzolitic mantle source containing 2% to 6% garnet. These lavas have then evolved by fractional crystallization without any evidence of crustal contamination. The studied mantle xenoliths are spinel-bearing lherzolites, characterized by U/Th ratios typically lower than 1, a slight enrichment in LILE relative to HFSE, and mainly consist of minerals with fertile composition (Fo 84-91 ; spinel Cr#: 0.1–0.22; Al-rich pyroxenes). They are consistent with refractory mantle peridotite that evidences low partial-melting degrees. Trace element concentrations of host lavas (high Ba/Rb: 12.2–26.1 and low Rb/Sr: 0.03–0.08), together with olivine’s crystals chemical features (high Ca/Fe and 100*Mn/Fe ratios; low 100*Ni/Mg ratios) and low Ca/Al ratios (<5) of clinopyroxenes in spinel-bearing lherzolite xenoliths suggest that the SCLM beneath the Bini Warack area is likely a juvenile lithospheric mantle which that undergone a carbonate-rich metasomatism.

Sub-continental lithospheric mantle beneath the Adamawa volcanic area (Cameroon Volcanic Line): inference from lavas and hosted mantle xenoliths from Bini Warack, NE-Ngaoundéré, Cameroon (Central Africa) (ouvre dans un nouvel onglet)

Auteurs

Université de Yaoundé I

Institut de Recherches Géologiques et Minières

Centre National de la Recherche Scientifique

University of Douala

Résumé

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