Abstract
In the Plateau of Lages, intrusions of alkaline and ultrabasic rocks occur, rocks of rare occurrence in Brazil, whose soils derived from them are practically unknown. The study aimed to evaluate the chemical composition, mineralogy, genesis, and classification of the soils developed from the rocks Nepheline Sienite (P1), Volcanic Breccia (P2), Kimberlitic Breccia (P3), Phonolitic Tephrite (P4), and Phonolite (P5). After the morphological description (field) and the collection of soil samples, chemical analyses of the soils, mineralogical of the clay fraction and the total elements of the soils and the corresponding rocks that gave rise to them were carried out. Three Humudepts (Cambissolos), a Hapludolls (Chernossolo), and a Kandiudox (Nitossolo) were identified. Except for the P3 profile, the others are acidic soils, with high levels of exchangeable aluminum, poor in basic cations, with low sum and base saturation, showing a high degree of weathering and strong leaching. In the clay fraction, the presence of 2:1 clay minerals predominated with kaolinite with interlayered hydroxy-Al polymers. The P3 profile showed a slightly acidic reaction, high sum and base saturation, and practically zero exchangeable aluminum, a situation compatible with mineralogy, where trioctahedral vermiculite predominated, revealing that it was a young, slightly weathered soil.
Highlights
In the region of Plateau of Lages, SC, lies the Lages Alkaline Complex (Complexo Alcalino de Lages) (CPRM, 2014), a formation composed of intrusions of alkaline and ultrabasic rocks
Almeida et al (2019) mainly identified Cambissolos Húmicos e Háplicos derived from Gondwana sedimentary rocks, all with strongly acidic reaction and low natural fertility, which presented clay mineralogy dominated by kaolinite, but with variable and expressive proportions of 2:1 clay minerals with hydroxy-Al interlayer polymers, (2:1HE) interstratified, and illites
For soils derived from the lava flow rocks of the Serra Geral Formation, the mineralogy is generally similar to soils derived from sedimentary rocks, but with lower crystallinity of kaolinites, lower exchangeable Al contents (1.01 to 2.65 cmolc kg-1) and with slightly higher sum (0.13 a 1.02 cmolc kg-1) and base saturation (3 to 13%) values (Teske et al 2013; Ferreira, 2013; Almeida et al, 2019)
Summary
In the region of Plateau of Lages, SC, lies the Lages Alkaline Complex (Complexo Alcalino de Lages) (CPRM, 2014), a formation composed of intrusions of alkaline and ultrabasic rocks They occupy a small geographic extension, the rocks in the complex are described by Scheibe (1986) as peculiar, with great lithological diversity, where phonolites, nepheline syenites, olivine-melilithites, lamprophyres, in addition to carbonatites, kimberlites, and breccia pipe stand out (Machado et al, 2012). For soils derived from the lava flow rocks of the Serra Geral Formation (basalt and rhyodacites), the mineralogy is generally similar to soils derived from sedimentary rocks, but with lower crystallinity of kaolinites, lower exchangeable Al contents (1.01 to 2.65 cmolc kg-1) and with slightly higher sum (0.13 a 1.02 cmolc kg-1) and base saturation (3 to 13%) values (Teske et al 2013; Ferreira, 2013; Almeida et al, 2019)
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