Modelling the chemical weathering fluxes at the watershed scale in the Tropics (Mule Hole, South India): Relative contribution of the smectite/kaolinite assemblage versus primary minerals

We investigate the chemical weathering processes and fluxes in a small experimental watershed (SEW) through a modelling approach. The study site is the Mule Hole SEW developed on a gneissic basement located in the climatic gradient of the Western Ghats, South India. The model couples a lumped hydrological model simulating the water budget at the watershed scale to the WITCH model estimating the dissolution/precipitation rates of minerals using laboratory kinetic laws. Forcing functions and parameters of the simulation are defined by the field data. The coupled model is calibrated with stream and groundwater compositions through the testing of a large range of smectite solubility and abundance in the soil horizons. We found that, despite the low abundance of smectite in the dominant soil type of the watershed (4 vol.%), their net dissolution provides 75% of the export of dissolved silica, while primary silicate mineral dissolution releases only 15% of this flux. Overall, smectites (modelled as montmorillonites) are not stable under the present day climatic conditions. Furthermore, the dissolution of trace carbonates in the saprolitic horizon provides 50% of the calcium export at the watershed scale. Modelling results show the contrasted behavior of the two main soil types of the watershed: red soils (88% of the surface) are provider of calcium, while black soils (smectite-rich and characterized by a lower drainage) consumes calcium through overall carbonate precipitation. Our model results stress the key role played by minor/accessory minerals and by the thermodynamic properties of smectite minerals, and by the drainage of the weathering profiles on the weathering budget of a tropical watershed. (C) 2010 Elsevier B.V. All rights reserved.

Thermoluminescence, infrared reflectivity and electron paramagnetic resonance properties of hemimorphite

Silicate mineral hemimorphite has been investigated concerning its TL, IR and EPR properties. A broad TL peak around 180 degrees C and a weaker and narrower peak around 360 degrees C were found in a sample annealed at 600 degrees C for I h and then irradiated. The deconvolution using the CGCD method revealed peaks around 132, 169, 222 and 367 degrees C. The reflectivity measurements showed several bands in the NIR region due to H(2)O, OH and Al-OH complexes. No band was observed in the visible region. The thermal treatments were carried out from similar to 110 to 940 degrees C and dehydration was observed, first causing a diminishing optical absorption in general and the disappearance of water and hydroxyl absorption bands. The EPR spectrum of natural hemimorphite, presented Cu(2+) signals at g = 2.4 and g = 2.1 plus E(1)` signal superposed to Fe(3+) signal around g = 2.0. (C) 2008 Elsevier Ltd. All rights reserved.

Thermoluminescence, electron paramagnetic resonance and optical absorption in natural and synthetic rhodonite crystals

Thermoluminescence, electron paramagnetic resonance and optical absorption properties of rhodonite, a natural silicate mineral, have been investigated and compared to those of synthetic crystal, pure and doped. The TL peaks grow linearly for radiation dose up to 4 kGy, and then saturate. In all the synthetic samples, 140 and 340 degrees C TL peaks are observed; the difference occurs in their relative intensities, but only 340 degrees C peak grows strongly for high doses. Al(2)O(3) and Al(2)O(3) + CaO-doped synthetic samples presented several decades intenser TL compared to that of synthetic samples doped with other impurities. A heating rate of 4 degrees C/s has been used in all the TL readings. The EPR spectrum of natural rhodonite mineral has only one huge signal around g = 2.0 with width extending from 1,000 to 6,000 G. This is due to Mn dipolar interaction, a fact proved by numerical calculation based on Van Vleck dipolar broadening expression. The optical absorption spectrum is rich in absorption bands in near-UV, visible and near-IR intervals. Several bands in the region from 540 to 340 nm are interpreted as being due to Mn(3+) in distorted octahedral environment. A broad and intense band around 1,040 nm is due to Fe(2+). It decays under heating up to 900 degrees C. At this temperature it is reduced by 80% of its original intensity. The pink, natural rhodonite, heated in air starts becoming black at approximately 600 degrees C.

Thermo luminescence of natural and synthetic diopside

Diopside, a natural silicate mineral of formula CaMgSi2O6, has been investigated concerning its thermoluminescence (TL) and electron paramagnetic resonance (EPR) properties. Glow curves and TL vs. gamma-dose were obtained irradiating natural samples to additional dose varying from 50 to 10,000Gy. Except for a 410 degrees C peak found in the Al-doped artificial diopside, all the other peaks grow linearly with radiation dose, but saturate beyond -1 kGy. To investigate high-temperature effect before irradiation, measurements of TL intensity in samples annealed at 500-900 degrees C and then irradiated to I kGy gamma-dose were carried out. Also the TL emission spectrum has been obtained. To compare with natural diopside, a synthetic pure polycrystal was produced and further those doped with iron, aluminum and manganese were also produced. (c) 2007 Elsevier B.V. All rights reserved.

Filossilicatos: efeitos no crescimento e na nutrição de plantas de milho e no teor de silício do solo

Importance of silicon fertilization is related to the benefits that silicon is able to promote tolerance to heavy metals, reduce the incidence of pests and diseases, increased productivity, drought tolerance, among others. The objective of this study was to evaluate the phyllosilicates effect on biomass formation, nutrients and silicon on the early stages of corn plants compared to wollastonite. Experiment was installed and conducted in a greenhouse located at the Universidade Estadual Paulista, UNESP, in Registro, SP. Consisting of 10 treatments established in a randomized block design in scheme factorial (2 x 5), with five replications. First factor corresponds to the two types of soil (Oxisol and Ultisol) and the second factor, five treatments (control, 0 kg ha-1 Si; wollastonite W13, 13 kg ha-1 Si; wollastonite W26, 26 kg ha-1 Si; phyllosilicates F13, 13 kg ha-1 Si; phyllosilicates F26, 26 kg ha-1 Si). In Ultisol, phyllosilicates increased production of fresh, dry biomass and silicon content in shoots of corn compared to treatment with wollastonite and control. Highest Si content compared to control (6.2 g kg-1) was obtained with 13 kg ha-1 Si of phyllosilicates (9.8 g kg-1). The greatest accumulation mass and Si in plants by applying phyllosilicates were observed in Ultisol, although this display Si content higher than Oxisol.

Resposta dos tecidos periodontais aos cimentos de silicato tricálcico associado ao óxido de zircônio ou óxido de nióbio usados no selamento de perfurações de furca em molares de ratos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Resposta dos tecidos periodontais aos cimentos de silicato tricálcico associado ao óxido de zircônio ou óxido de nióbio usados no selamento de perfurações de furca em molares de ratos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Geology of a Kyanite Deposit Near Ennis, Montana

A deposit of kyanite, an aluminum silicate mineral used in the ceramic industry, occurs in the low foothills of the Gravelly range about 10 miles south of Ennis, Montana. This study deals primarily with the character and origin of the deposit, and its relationship to the surrounding rocks.

Mineralogy and geochemistry of ODP Hole 176-735B minerals

We present a synthesis of some 20,504 mineral analyses of ~500 Hole 735B gabbros, including 10,236 new analyses conducted for this paper. These are used to construct a mineral stratigraphy for 1.5-km-deep Hole 735B, the only long section of the lower crust drilled in situ in the oceans. At long wavelengths, generally >200 m, there is a good chemical correlation among the principal silicate phases, consistent with the in situ crystallization of three or four distinct olivine gabbro bodies, representing at least two major cycles of intrusion. Initial cooling and crystallization of these bodies must have been fairly rapid to form a crystal mush, followed by subsequent compaction and migration of late iron-titanium-rich liquids into shear zones and fractures through which they were emplaced to higher levels in the lower crust where they crystallized and reacted with the olivine gabbro host rock to form a wide variety of ferrogabbros. At the wave lengths of the individual intrusions, as represented by the several olivine gabbro sequences, there is a general upward trend of iron and sodium enrichment but a poor correlation between the compositions of the major silicate phases. This, together with a wide range in minor incompatible and compatible element concentrations in olivine and pyroxene at a given Mg#, is consistent with widespread permeable flow of late melt through these intrusions, in contrast to what has been documented for a 600-m section of reputedly fast-spreading ocean crust in the Oman Ophiolite. This unexpected finding could be related to enhanced compaction and deformation-controlled late-stage melt migration at the scale of intrusion at a slow-spreading ocean ridge, compared to the relatively static environment in the lower crust at fast-spreading ridges.

Concentrations of rare earth elements in pore waters of IODP Holes 323-U1345A and 323-U1345B

We studied the diagenetic behavior of rare earth elements (REEs) in a highly productive passive margin setting of the Bering Sea Slope. Site U1345 was drilled during the Integrated Ocean Drilling Program Expedition 323 at a water depth of 1008 m currently in the center of an oxygen minimum zone. Pore water concentrations of fourteen REEs were determined down to ~ 140 meters below the seafloor (mbsf). The REE concentrations were higher in the pore water than the deep seawater, indicating that there was significant liberation from the sediments during diagenesis. There was a major peak at ~ 10 mbsf that was more pronounced for the heavy REE (HREE); this peak occurred below the sulfate-methane transition zone (6.3 mbsf) and coincided with high concentrations of dissolved iron and manganese. At ~ 2 mbsf, there was a minor peak in REE and Mn contents. Below ~ 40 mbsf, the REE concentration profiles remained constant. The Ce anomaly was insignificant and relatively constant (PAAS-normalized Ce/Ce = 1.1 ± 0.2) throughout the depth profile, showing that the Ce depleted in seawater was restored in the pore water. HREE-enrichment was observed over the entire 140 m except for the upper ~ 1 m, where a middle REE (MREE)-bulge was apparent. REE release in shallow depths (2-4 mbsf) is attributed to the release of light REEs (LREEs) and MREEs during the organoclastic reduction of Mn oxides in anoxic sediments. The high HREE concentrations observed at ~ 10 mbsf can be attributed to the reduction of Fe and Mn minerals tied to anaerobic oxidation of methane or, less significantly, to ferromagnesian silicate mineral weathering. The upward diffusion flux across the sediment-water interface was between 3 (for Tm) and 290 (for Ce) pmol/m**2/y.