Abstract The geochemical behavior of the major, minor, trace and rare earths elements (REEs) in soil profiles from ultramafic volcanoclastic rocks of the Vulcão do Paredão and Morro Vermelho Formation from Trindade Island (TI) was analyzed in this study. Losses and gains of chemical elements were calculated through the mass balance for two profiles along the slope: one located at higher altitude (460 m) and the other at lower altitude (258 m). In all profiles, Al, Fe and Ti accumulate due to their low mobility, whereas Ca, Na, K and Mg are the most intensely leached. Soils located at lower altitude show higher K and Mg values in the surface due to the contribution of saline sprays. Leaching of the REEs from higher to the lower slope led to the enrichment of these elements, especially the light REEs, in the soil at the lowest altitude (258 m). The high altitude profile showed Ce positive anomaly due to longer exposure to weathering. The geochemical balance shows a relative enrichment of Ti, Mn, Fe, Co, Cr, Ni, V, Zr, S related to the loss of mobile elements during the soil formation process, despite the youthful nature of these volcanic rocks.

ABSTRACT The pedological studies carried out so far in Trindade Island (TI) have obtained patchy evidences of allophane, without detailed mineralogical and micromorphological studies to confirm the occurrence of Andosols in TI. Therefore, in this study, the mineralogical, micromorphological, physical and chemical characterization of four soil profiles from Vulcão do Paredão (P1) and Morro Vermelho formations (P2, P3, and P4) were carried on the latest volcanic events in Brazil from Trindade Island (TI) with the aim of to evaluate the presence of Andosols in this oceanic island. Profiles P1 and P2 are developed on pyroclastic bombs, and show, respectively, A-Bi- C and decapitated A-C horizons, whereas P3 and P4 are developed on lapillitic and bomb pyroclasts, show A-C horizons. The soil profiles have a reddish and brownish clayey matrix, are highly friable and show a plastic consistency. Their microstructures are granular, single grain and intergrain microaggregate, in which aggregates display an undifferentiated b-fabric. The mineralogical constituents of the bulk fraction are biotite, hematite, magnetite, ilmenite, pyroxene, olivine, halloysite, goethite, anatase, and rutile. The clay fraction is marked by the presence of halloysite, ferrihydrite, and little amounts of allophane. All soils presented andic properties and can be classified as non-allophanic Andosols. In addition, micromorphological features closely resemble those reported in Andosols from other volcanic islands from elsewhere. The predominance of halloysite in the clay fraction formed by alteration of sideromelane, suggests that allophane would be an intermediate phase of this rapid transformation favored by the wet climate conditions of the highest parts of TI.

ABSTRACT Pedological studies using X-ray diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, and scanning electron microscopy (SEM-EDS) showed a Xanthic Ferralsol formed from the degradation of bauxite on a slope in the Caparaó region, in southeastern Brazil. We found a decrease in the number and size of bauxite fragments toward the top of the profiles, bauxite fragments that were more degraded at the top of the profiles, transformation of gibbsite into kaolinite, and absolute enrichment in silicon in the mass balance. These indicators suggest that resilication could be the major process responsible for formation of the soil; detailed studies are needed to verify the origin of the silica. The reintroduction of silica into the system occurs by the biogeochemical cycling of vegetation and, in some cases, water table fluctuations, highlighting the role of resilication as a soil-forming process in bauxite-derived soils.