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International Journal of Research and Innovation in Applied Science (IJRIAS) |Volume VII, Issue X, October 2022|ISSN 2454-6194

Dispersion of Trace Elements as Consequence of in-situ Weathering in granite-derived Tropical Soils in Southwestern Nigeria

Oluwatoyin, O. Akinola, and Olusola, A. OlaOlorun*
Department of Geology, Faculty of Science, Ekiti State University, Ado-Ekiti, Nigeria
Correspondence author

IJRISS Call for paper

Abstract: Trace elements composition of granite and tropical soils formed by in-situ weathering over the basement complex of Ikere-Ekiti, Ado-Ekiti and Igbrara-Odo areas of SW Nigeria is evaluated and reported. The granitoids exhibit chemical features such as is common to other granite bodies across the basement areas. The soil profiles typically have four different horizons with contrasting physical characteristics. Analytical result from ICP-MS technique revealed compositional variation along vertical direction within depth of the profiles. Trace element as average for the granite reveals low Tm (0.5 ppm), Eu (2.1 ppm), Co (5.1 ppm), Sc (7.2 ppm), Hf (7.6 ppm), Sm (12.6 ppm), and Th (30.5 ppm) values, while La (110 ppm), Ce (216 ppm), Cr (235.5 ppm), and Ba (963 ppm) show enrichments. All the soils have Sm, Eu, Th, Hf and Co contents below 10 ppm; Sc, La and Ce values fall between 10-100 ppm, while Cr and Ba contents fall between 200-1500 ppm. Variation between trace contents in granite and the derived soils as revealed along depths of the profile indicates greater mobility of Th, Sc and Ba during chemical weathering while Eu and Tm are least mobile. Pronounced compositional variation occur at relatively shallow (0-1m) depth in near surface area all the profiles.

Keywords: In-situ weathering, tropical soils, Nigeria, mobility, soil profile, trace elements

I. INTRODUCTION

More than 70% of elements in the periodic table occur naturally in rocks, these elements ultimately become incorporated into soils through weathering. Hence, through mobilization and dispersion of elements, soils have chemistries that are much different from the parent rocks (Nesbitt, 1979; Nesbitt et al. 1980; Topp et al., 1984; Subramanian et al., 1980). However, the abundances of these elements vary significantly from one place to another as their distribution is influenced by cosmic abundances, geochemical behaviour, and environmental factors. Trace elements content of rocks are expressed in parts per million (ppm) or parts per billion (ppb) because they have abundances less than can be expressed in percentages (1% equals 10,000 ppm), as they are present only in minute amounts in any geological sample or environment. Trace element composition of tropical soils could vary in arid, semi arid and tropical domains, while average chemical composition of such soils are dependent on combination of factors ranging from parent materials, degree of weathering and climatic conditions. On the other hand, the chemistry of granite is mostly dictated by its tectonic setting, evolution and the