Ge-Ga-Cs in agricultural and grazing land soils at European continental scale
Résumé
Germanium-silicon and gallium-aluminum are two geochemically-related pairs of elements which follow each other during weathering. The coherence of the behavior between these pairs of elements is due to the similarity in ionic radius, valence and ionization potential. Aluminum plays an important role in weathering/reverse weathering processes and silicon is one of the tracers of silicate weathering of felsic (granite) and mafic lithologies (basalt). Thus, Ge and Ga can be used as possible analogues of the two major ions Si and Al. Furthermore, Ge and Ga are elements interacting with clays similarly as Cs. Caesium has similar chemical properties to potassium, both playing important role in weathering processes and clay formation. Therefore, all three trace elements can be used in investigations of clay distribution at the continental scale Agricultural soil (Ap-horizon, 0–20 cm) and grazing land soil (Gr-horizon, 0–10 cm) samples were collected from a large part of Europe (33 countries, 5.6 million km2) as part of the recent GEMAS (GEochemical Mapping of Agricultural and grazing land Soil) soil mapping project. These data have been used to provide a general view of element mobility and source rocks at the continental scale, either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes. The survey area includes a diverse group of soil parent materials with varying geological history, a wide range of climate zones, and landscapes. The concentrations of Ge, Ga, and Cs in European soil were determined by ICP-MS after a hot aqua regia extraction, and their spatial distribution patterns generated by means of a GIS software.
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