Spinel-lherzolite xenoliths trapped within the alkali basalts flow in the Liri region (Kapsiki Plateau) have a protogranular texture and consist of olivine, orthopyroxene, clinopyroxene and spinel crystals. These xenoliths are residues of partial melting of the primitive mantle, with the low titanium content in clinopyroxene crystals (TiO2 < 0.5 wt.%). The clinopyroxene of the spinel-lherzolite xenoliths from Liri, are divided into two distinct groups according to their trace element characteristics. The variations in the rare earths elements make it possible to classify the different clynopyroxenes in two groups: the first group consisting of the samples of Liri (Liri 1, Liri 02, Liri 3, Liri 05 and Liri 5) rich in light rare earths elements (LREEs), with ratios (Ce/Yb)N normalized which vary between 3.00 and 7.78. It is probably a cryptic metasomatism due to the absence of hydrated minerals (such as amphibole) which caused these enrichments. The second group comprises samples of Liri (Liri 01, Liri 2, Liri 04, Liri 4) depleted in light rare earths elements, with the ratio in (Ce/Yb) N < 1.2. This depletion in rare earths elements results from the extraction of the melting liquid.
Peridotite xenoliths, raised to the surface by alkaline basalts or kimberlites,provide us direct information on the processes and composition of the upper mantle. They are the major source of information on the state of stress,pressure and temperature in the deep mantle. They are thus a source of petrological and geochemical information that is generally not available on the Earth’s surface. Fresh spinel-lherzolite xenoliths exhibit a protogranular components of the Tello volcano. The Tello is the continental sector of the Cameroon Line, located in the South East of the town of Ngaoundéré at 75 km approximately between (N7° 13’, N7° 14’) and (E13° 40’ and E13° 60’). Minerals’ composition of the xenoliths is ~64% olivine, ~24% orthopyroxene, ~11% clinopyroxene and ~1% spinel. Significant variation in (Cr/Cr + Al) of the system shows the reciprocal nature of the spinel solution.The Tello spinel lherzolites show internal chemical homogeneity and represent a normal upper mantle. Their mineral chemistries suggest equilibrium condition of 830° - 925° and 1.4 GPa-2.3 GPa. These data suggest that there is good correlation bracket between increasing activity of Al2O3 and decreasing of practionning of TiO2 into spinel. The AlIV and AlVI contents vary by 0.05-0.2 and 0.03-0.2 respectively. The majority of samples caracterise the lithospheric mantle.
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