New petrological and geochronological data on Neogene to Recent alkaline volcanism of the western part of Noun Plain (Cameroun Line)

Three types of volcanic rocks are described in the western part of Noun Plain: picrite, alkali basalt, hawaiite. They contain: olivine, clinopyromme, plagioclase and Fe-Ti oxides as phenocrysts and microlites, and sometimes nepheline as microlites (in picrites). Fassaite and Al-Cr spinel occur in picrites. Lavas form an alkaline series slightly evolving according to a fractional crystallization (DI increasing from 18 to 40). Rare earth spectrum is rather similar to those of OIB. Picrites could result of a mantle partial melting of about 5%. Three new datations give ages of 10.43 +/- 0.28, 4.59 +/- 0.12 and 0.20 +/- 0.20 Ma. Old effusive episodes (11 +/- 4 Ma) on the board of Noun Plain have been followed by an explosive one (0.4 +/- 0 Ma) in the central part of the plain.