Mineralogical and geochemical studies of hardened subsurface layers in soils of the Azufres and Atecuaro volcanic calderas, southwestern Mexico

Abstract

Ostrooumov, M., Monroy, V. H. G. and Servenay, A. 2005. Mineralogical and geochemical studies of hardened subsurface layers in soils of the Azufres and Atecuaro volcanic calderas, southwestern Mexico. Can. J. Soil Sci. 85: 611-624. Free silica and halloysite-bearing hardened subsurface layers in the ash fall deposits of the Azufres and Atecuaro volcanic calderas (Michoacan State, southwestern Mexico), known as "tepetates", have been characterized by chemical analysis, X-ray diffraction (XRD), Raman and Infrared spectrometry, optical (OM) and scanning (SEM) microscopy with energy dispersive X-ray analysis (EDXRA). Chemical analysis of these weathered and hardened formations shows the oxidation of Fe 2+ , enrichment of Al, Fe 3+ and Ti, loss of Si, Na, Ca, K, Mg, and formation of minerals with hydroxyls groups. Tepetates are characterized by elevated SiO 2 /Al 2 O 3 molar ratios (4. 86-8.82) that show part of the SiO 2 has crystallized in free siliceous phases. X-ray analysis reveals hydrated (1.0 nm) and dehydrated halloysite (0.7 nm), sanidine, plagioclases, cristobalite, and tridymite. Raman and infrared spectra confirm the presence of these mineral phases and show that the structural transformations occur in opal neoformations. SEM shows a compact matrix with a skeleton of different phenocrysts (aluminosilicates, ferromagnesian minerals and various crystalline silica phases) and the presence of non-crystalline silica (volcanic glass and opal with different degrees of crystallinity). The tepetates form by interaction of two processes: volcanic ash fall then subsequent weathering under variable climatic conditions. These indurated horizons are partly or totally cemented by the diagenetic secondary minerals: non-crystalline silica with variable crystal chemical characteristics and clay minerals. . Ils ont pour cela recouru à l'analyse chimique, à la diffraction par rayons X, à la spectrométrie Raman et à infrarouge, à la microscopie photonique et par balayage (MB) ainsi qu'à l'analyse radiologique par dispersion d'énergie. L'analyse chimique de ces formations durcies et altérées révèle l'oxydation du Fe 2+ , un apport d'Al, de Fe 3+ et de Ti, la perte de Si, Na, Ca, K et Mg, et la formation de minéraux à groupes hydroxyles. Les tepetates se caractérisent par un ratio molaire élevé de SiO 2 /Al 2 O 3 (4,86 à 8,82), signe qu'une partie du SiO 2 s'est cristallisée dans la silice libre. L'analyse radiologique révèle de l'halloysite hydratée (1,0 nm) et déshydratée (0,7 nm), de la sanidine, des plagioclases, de la cristobalite et de la tridymite. L'analyse par spectrométrie Raman et infrarouge confirme la présence de ces phases minérales et montre que les transformations structurales surviennent dans les néoformations d'opales. La MB montre une matrice compacte ayant pour squelette différents phénocristaux (aluminosilicates, minéraux ferro-magnésiens et diverses phases de silice cristalline) ainsi que la présence de silice non cristalline (verre volcanique et opales à cristallinité variable). Les tepetates naissent ...

Distribution and partitioning of iron, zinc, and arsenic in surface sediments in the Grande River mouth to Cuitzeo Lake, Mexico

“…4), are higher in sites located in Grande River (RG3 and RG4) or at its vicinity (RG1 and RG2) and lower total iron concentrations are present in sediments inside the lake located far from the outfall of the river, particularly in site HDA ( Fig. 4), suggesting that iron concentrations in sediments could be attributed to the iron-rich soil of Cuitzeo area, due to Fe enrichment and oxidation of hardened subsurface layers in the zone (Ostrooumov et al 2005), and they are influenced also by anthropogenic inputs. The Grande River has been reported to contain a high concentration of iron on the water column which could be introducing significant quantities of this metal to the lake.…”

“…The basin is part of the upper Lerma River, whose watershed is one of the most polluted in Mexico. Cuitzeo Lake presents serious problems of contamination, drying up, and refilling by sediments, as well as weathering of ash fall deposits into hardened volcanic soils, which causes Fe enrichment (Servenay and Prat 2003;Ostrooumov et al 2005). The origin of potential pollution at Cuitzeo Lake comes from the increase in industrial, urban, and agricultural activities during the last decades in the region.…”

Copper Speciation in Soil: Time Evolution and Effect of Clay Amendment

“…Figure 4 shows the IR spectra, from bottom to top: the pristine soil; pure SB; soil at day 3 with Cu (200 mg kg −1 ); the same with SB added at experiment start; the soil with Cu at day 160; the same with SB added at day 1; and the soil with Cu, with SB added at day 90. The general features are typical of soil mainly composed of aluminosilicate minerals (Lerot 1976;Malhotra and Ogloza 1989;Bukka et al 1992;Ostrooumov et al 2005;Fonseca et al 2009;Sdiri et al 2011;Musso et al 2014):…”