GEOCHEMISTRY OF A WEATHERING PROFILE DEVELOPED IN GRANITIC ROCKS FROM PARQUE ESTADUAL DE ITAPUÃ, RS, BRAZIL
DOI:
https://doi.org/10.22456/1807-9806.135777Keywords:
granites, tropical weathering, rare earth elements, geochemical mobility of elementsAbstract
In order to provide interpretations concerning the geochemistry mobility of major and trace elements in supergenic environment, a series of petrographic, pedologic, and geochemistry data were acquired in a weathering profile developed in granitic rocks from Parque Estadual de Itapuã, RS. This profile is represented at the bottom by the unaltered rock (granite), followed by the saprolite (S1 and S2) and the pedogenetic horizons (Cr and A). Detailed pedologic analyses help to classify this weathering profile as a litholic dystrophic neosoil. Main minerals in this profile are quartz, K-feldspars, plagioclase, biotite, and oxides, while X-ray diffraction identified kaolinite and micas as clay minerals present in the < 2mm fraction at pedogentic horizons. Geochemistry of major elements suggest the leaching of SiO2, CaO, Na2O e K2O and the relative concentration of Al2O3, TiO2 e Fe2O3(T). Trace elements are dominantly leached, with a few exceptions, represented by Cu, Co, Ni, Cr and V, which are relatively enriched when compared to granitic rock. Also, earth-rare elements are leached in the weathering profile, presenting Eu anomaly in all profiles, and positive Ce anomaly only in the A horizon. Thus, integrating analyses performed in this weathering profile, the geochemistry observed supports that the mobility of elements is related to natural intemperic processes, such as hydrolysis, lessivage, and dessilification, in response to the new pressure and temperature conditions of the granitic rock in a supergenic environment.
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