PETROLOGICAL DIFFERENTIATION PATTERNS AND GEOMORPHIC DISTRIBUTION OF FERRICRETES IN CENTRAL-AFRICA

Geomorphic distribution and petrological differentiation patterns of f erricretes widespread on landsurfaces were studied in the Dembia-Zemio area, southeastern Central African Republic. Four types of ferricrete s are distributed on high plateaux, hillslopes and low plateaux. The m ain contrast corresponds to the differentiation between ferricretes of high plateaux rich in poorly hydrated minerals, hematite and kaolinit e, and those covering hillslopes and low plateaux richer in hydrated m inerals, goethite and gibbsite, A Principal Component Analysis of geoc hemical and mineralogical data was used to characterize the main diffe rentiation patterns of ferricretes in relation with their petrographic facies and the geomorphic features of the landscape. The distribution of secondary minerals and their relationships to trace elements withi n and between the ferricrete types reflects differences in weathering and erosion processes. Our results document that the petrological patt erns and the distribution of ferricretes are related to geomorphic fea tures depending on hydroclimatic variations that govern the landscape evolution of many tropical shields.