『Abstract
This study analyses the behaviour and mobility of major and some
trace elements during the physical and chemical development of
landslide-prone soil profiles in Limbe, SW Cameroon. The soils
result from in situ weathering of Tertiary basaltic and picrobasaltic
rocks. Textural and chemical characterizations, together with
two mass balance models are applied to understand the mobility
and redistribution of elements during the weathering of pyroclastic
cones and lava flows. Weathering indices are used to estimate
the extent of weathering. The chemical composition of the samples
is evaluated by Inductively Coupled Plasma-Optical Emission Spectroscopy
(ICP-OES) and their mineralogical composition by X-ray Diffraction
(XRD) analyses。It is observed that intensive weathering results
in thick meta-stable soils in which significant loss of Ca, K,
Mg, Na and Sr has taken place. There is a noticeable relative
enrichment in all analysed trace elements (Ba, Zr, Y, Sc, V, Ni,
and Co). Ti,Fe, Al, Mn, P and Ce tend to be leached in some horizons
and concentrated in others. Zr, Ti, and Ce concentrations are
greater in the soils than in the bedrock but show slight fluctuations
in the soil and saprolites hence cannot be used as immobile elements
for mass balance evaluations. Y increases progressively with advanced
weathering. Major secondary mineral phases developed through weathering
are a mixture of expanding (smectites) and non-expanding clays
(kaolinite, halloysite and mica). The profiles show the presence
of textural heterogeneities that can be exploited as slip surfaces.
Data plotted in Si-Al-Fe diagram point out that the most advanced
stage of weathering noted in these profiles is the kaolinitisation
stage.
Keywords: Weathering; Volcanic soil; Mineralogy; Textural heterogeneities;
Basalts; Cameroon』
1. Introduction
2. Geologic and physiographic characteristics of the study area
3. Sampling and experimental procedures
4. Results
4.1. Profile description
4.1.1. Profile 1
4.1.2. Profile 2
4.1.3. Profile 3
4.2. Whole rock (WR) geochemistry
4.3. Variation in physical characteristics between parent rock
and soils and correlation with chemical elements
4.4. Relative element mobility and absolute mass change during
weathering
4.4.1. Weathering indices
5. Discussion
6. Conclusions
Acknowledgement
References