FeO*-Al 2 O 3 -TiO 2 -rich rocks are found associated with transitional tholeiitic lava fl ows in the Tertiary Bana plutono-volcanic complex in the continental sector of the Cameroon Line. These peculiar rocks consist principally of iron-titanium oxides, aluminosilicates and phosphates, and occur as layers 1 -3 m thick occupying the upper part of lava fl ows on the southwest (site 1) and northwest (site 2) sites of the complex. Mineral constituents of the rocks include magnetite, ilmenite, hematite, rutile, corundum, andalusite, sillimanite, cordierite, quartz, plagioclase, alkali feldspar, apatite, Fe-Mn phosphate, Al phosphate, micas and fi ne mixtures of sericite and silica. Texturally and compositionally, the rocks can be subdivided into globular type, banded type, and Al-rich fi ne-gained massive type. The fi rst two types consist of dark globule or band enriched in Fe-Ti oxides and apatite and lighter colored groundmass or bands enriched in aluminosilicates and quartz, respectively. The occurrence of andalusite and sillimanite and the compositional relations of magnetite and ilmenite in the FeO*-Al 2 O 3 -TiO 2 -rich rocks suggest temperatures of crystallization in a range of 690 -830°C at low pressures. The Bana FeO*-Al 2 O 3 -TiO 2 -rich rocks are characterized by low concentrations of SiO 2 (25 -54.2 wt%), Na 2 O + K 2 O (0 -1%), CaO (0 -2%) and MgO (0 -0.5%), and high concentrations of FeO* (total iron as FeO, 20 -42%), Al 2 O 3 (20 -42%), TiO 2 (3 -9.2%), and P 2 O 5 (0.26 -1.30%). TiO 2 is positively correlated with Al 2 O 3 and inversely correlated with FeO*. The bulk rock compositions cannot be derived from the associated basaltic magma by crystal fractionation or by partial melting of the mantle or lower crustal materials. In ternary diagrams of (Al 2 O 3 )−(CaO + Na 2 O + K 2 O)−(FeO* + MnO + MgO) and (SiO 2 )−(FeO*)−(Al 2 O 3 ), the compositional fi eld of the rocks is close to that of laterite and is distinct from the common volcanic rocks, suggesting that the rocks are derived from lateritic materials by recrystallization when the materials are heated by the basaltic magmas. A hydrothermal origin is discounted because the rocks contain high-temperature mineral assemblages and lack sulfi de minerals. It is proposed that the FeO*-Al 2 O 3 -TiO 2 -rich rocks of the Bana complex were formed by pyrometamorphism of laterite by the heat of basaltic magmas.
