2012/07/15 by G.I.B. Mbowou, Claudial Amane Lagmet, Sébastien Nomade +3 · 1 citation
Earth and Planetary Sciences · #Geological and Geochemical Analysis #Geological and Geophysical Studies Worldwide #Geological formations and processes #Geology #Cretaceous #Peralkaline rock #Archaeology #Humanities #Paleontology #Geography #Art
paper · pdf · doi:10.3190/jgeosci.118
openalex publication_date 2012/07/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
Late Cretaceous peralkaline rhyolites (69.4 0.4 Ma -2 analytical, 1.9 Ma full external uncertainty, 40 Ar/ 39 Ar sanidine single crystal laser dating) from Lake Chad are the oldest lavas of the "Cameroon Hot Line". These lavas (pantellerite and comendite), consisting of quartz alkali feldspar fluoro-arfvedsonite augite-hedenbergite aegirine fayalite (Fa 97-99 ) and ilmenite, are characterized by a progressive increase in the total REE contents and the magnitude of the negative Eu anomaly owing to the alkali feldspar-dominated fractionation. Two groups of peralkaline rhyolites have been distinguished according to mineralogical and geochemical data. Both, group-1 (La N /Yb N : 8.4-9.0; Zr/Nb: ~ 8) and group-2 (La N /Yb N : 10.7-12.6; Zr/Nb: ~ 6) are genetically related. The peralkaline rhyolites from Lake Chad could not be solely the product of fractional crystallization from a basaltic parental magma. The influx of F-rich fluids could have greatly modified the composition of rhyolitic magmas as attested by the presence of fluoro-arfvedsonite.