Polyphase metamorphism in the eastern Carnic Alps (N Italy–S Austria): clay minerals and conodont Colour Alteration Index evidence

Thermal evolution of the Palaeozoic–Triassic sequences of the Carnic Alps has been characterized by b cell dimension and Kübler Index (illite “crystallinity”) of K-white micas (KI), árkai Index (AI) of chlorites, clay mineral assemblages and conodont Colour Alteration Index (CAI). Data indicate at least two metamorphic events, Variscan and Alpine. In the older event high anchizonal conditions predominated although epizonal conditions were reached over wide areas. It was characterized by low-intermediate pressure facies. The thermal peak was mainly due to an extensional regime during the Bashkirian. A younger thermal overprint generated by Alpine orogeny was of lower grade, reaching high diagenetic–anchizonal conditions characterized by high-pressure facies. Inverted metamorphic patterns are associated with middle to late Miocene thrusting. Hydrothermal alteration in the northern part of the region can be linked with emplacement of Oligocene plutons and high heat flow along the Periadratic lineament. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

远震数据显示贝加尔裂谷带北穆伊斯克(Severomuysk)段地壳和上地幔的精细结构

通过贝加尔裂谷系统北穆伊斯克(Severomuysk)段的密集地震台站线性网络获得的远距离强震记录,并利用P波接收函数技术,揭示了地壳和上地幔顶部的复杂分层块状结构。横波速度的分布表明构成北穆伊斯克地壳的地块具有不同性质。这些地块的西部聚散和地壳下部的分层证实了该地区隆起的堆积-碰撞起源。位于西伯利亚克拉通变薄的倾斜边缘上的北穆伊斯克段解释了该地区地壳碰撞效应的强度。2015年地震的震中深度与Muyakan 凹陷地壳上部的明显速度差异存在令人信服的相关性。     

Integrated modelling for water quality management in a eutrophic reservoir in south-eastern Portugal

The Enxoé Reservoir was built in 1998. Since 2000, it has exhibited frequent high chlorophyll-a concentrations, reaching a geometric mean three times higher than the national limit for eutrophication, presenting the reservoir with the highest eutrophic state in Portugal. Toxic algal blooms have also often been observed, which pose serious challenges to water managers, as the reservoir is used for potable water production (25,000 inhabitants). The objective of this study was to implement a reservoir model (CE-QUAL-W2), with inputs from a watershed model (SWAT), in order to represent the actual reservoir state and to test management measures to reduce its trophic level and algal bloom concentration peaks. The integrated model was used to depict the origin of its trophic status. Simulations were also compared to measured data at the reservoir surface (water level, nitrate, orthophosphate, suspended solids, and oxygen) and in water profiles (temperature, oxygen). The model was able to represent stratification and thermocline depths, as well as the actual chlorophyll-a and dissolved oxygen concentrations. The model results showed that internal phosphorus load from deposited sediments was an important factor in fuelling the algal blooms. This process occurs predominantly in summer, when stratification takes place and aeration is reduced, promoting anoxic conditions in the bottom waters. Since the reservoir is relatively shallow (average 5 m), released phosphorus is then easily able to reach the photic zone in most parts of the reservoir, where it is consumed. Different management scenarios were tested, suggesting that a mesotrophic level could barely be reached and maintained simply by reducing the nutrient loads (both external and internal). It is suggested that only an increase in the reservoir dam height could produce a mesotrophic level, averting anoxia by blocking the release of phosphorus from sediments to the photic zone. Future work should focus on a cost–benefit analysis to test the feasibility of each of the proposed scenarios, taking advantage of the integration strategy to assess where in the watershed load reductions would be most effective.     

Effects on runoff caused by changes in land cover in a Brazilian southeast basin: evaluation by HEC-HMS and HEC-GEOHMS

The Southeast Region of Brazil has undergone major changes in land cover, especially after the eighteenth century. It is currently the most populous region of the country, highly urbanized, with a high degree of industrial and agricultural development. Extensive areas of native vegetation have been replaced by pastures, crops and urban areas, which have increased runoff, causing environmental, economic and social problems related to flooding. The objective of this study was to analyze effects of land cover changes in a basin with rural and urban characteristics on the flow of its main river. Hydrological data, orbital images, soils and topographical maps were used for this purpose. Based on the land cover maps for the years of 1989, 2001 and 2015, and on the hydrological modeling performed using the Hec-HMS 4.1 software, scenarios were simulated and showed that the land cover changes in this basin significantly affect the flow behavior of the main river. The simulated runoff was calibrated using the data observed in the field during 2001, and validation was performed using data from 1989. After the calibration and validation processes, a scenario was simulated where the rainiest month of the whole series measured by the rainfall station (during December 1989) acted on the land cover of 2015. There was an increase in pasture areas and impermeable spaces in the basin, which caused a decrease in infiltration and an increase in surface runoff, and also an increase in the flow peaks and a reduction in the time of concentration. The hydrological modeling was satisfactory, since the uncertainties related to the simulation were low.     

Model biomimetic studies of templated growth and assembly of nanocrystalline FeOOH

We studied biomimetic mineralization of self-assembling polymer matrices in order to develop a model for biomineralization of iron oxides in nature. High-resolution transmission electron microscopy (HRTEM), rheology, and fluorescence probe analyses show self-assembly of acidic polysaccharide alginic acid (Alg) to form fibrils in dilute solutions. The resulting Alg fibrils are subsequently mineralized by FeOOH in a biomimetically controlled process. Experiments were conducted in pH 9.2 solutions containing millimolar concentrations of iron at 38°C. The unperturbed state of the hybrid mineral-organic structures was studied by characterization of samples of interfacial films collected from an inorganic-organic interface. Progress of mineralization over a 4-week period was followed by HRTEM, energy-dispersive X-ray analysis, and selected area electron diffraction. Morphologies of hybrid structures determined by HRTEM, X-ray powder diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, and selected area electron diffraction suggest formation of iron (III) oxyhydroxide phases and their assembly through a variety of mechanisms, possibly occurring simultaneously. An initial step involves precipitation of nanometer-scale amorphous particles and two-line ferrihydrite in bulk solution. Some nanoparticles assemble into chains that recrystallize to form akaganeite (β-FeOOH), presumably via a solid-state transformation pathway. Small organic molecules may mediate this process by stabilizing the akaganeite structure and controlling particle assembly. Ferrihydrite particles also bind to acidic polysaccharide fibrils and are transformed to ordered arrays of akaganeite. The parallel orientation of adjacent akaganeite nanocrystals may be inherited from the orientation of precursor ferrihydrite, possibly conferred during attachment of ferrihydrite to the polyacid fibrils. Alternatively, particle-particle interactions may induce orientation, leading to recrystallization. Subsequently, akaganeite is transformed to goethite that is characterized by nanoscale porosity and fine-scale twinning on {021}. Dislocation, twin, and nanopore microstructures are consistent with coarsening by nanoparticle assembly, possibly templated by the substrate. Nanoparticle assembly to generate biomimetic hybrid materials may be relevant to formation of complex natural biominerals in natural systems where mineral nanoparticles, small organic molecules, and more complex polymers coexist.     

Electron microprobe dating of monazite from high-T shear zones in the São José de Campestre Massif, NE Brazil

The easternmost domain of the Borborema Province, northeastern Brazil, presents widespread, extensional-related high-temperature metamorphism during the Brasiliano (=Pan-African) orogeny. This event reached the upper amphibolite to granulite facies and provoked generalized migmatization of Proterozoic metapelitic rocks of the Seridó Group and tonalitic to granodioritic orthogneisses of the Archean to Paleoproterozoic basement. We report new geochronological data based on electron microprobe dating of monazite from metapelitic migmatite and leuconorite within the high-T shear zones that make up the eastern continuation of the huge E–W Patos shear belt. These data were also constrained by using the Sm–Nd isotopic systematic on garnet from a syntectonic alkaline granite and two garnet-bearing leucosomes. The results suggest an age of about 578 to 574 Ma for the peak of the widespread high-T metamorphism. This event is best recorded by Sm–Nd garnet-whole rock ages. The U–Th–Pb isotopes on monazite of the metapelitic migmatite show a younger thermal event at 553 ± 10 Ma. When compared to the Sm–Nd garnet-whole rock ages, the U–Th–Pb electron probe monazite ages seem to record an event of slightly lower temperatures after the peak of the high-T metamorphism. This may reflect the difference in the isotopic behavior of the geochronological methods employed. Otherwise, the U–Th–Pb ages on monazites could indicate an event not yet very well defined. In anyway, this paper reveals the partial or even complete re-opening and resetting of the U–Th–Pb isotopic system produced by the action of low-T Ca-rich fluid.     

High-temperature single-crystal neutron diffraction study of natural chondrodite

The H-atom environment in a Tilly Foster chondrodite was analyzed using single-crystal neutron-diffraction data collected at 500, 700 and 900 K and previously published low temperature data collected at 10, 100 and 300 K on the same crystal (Mg_4.64Fe_0.28Mn_0.014Ti_0.023(Si_1.01O₄)₂F_1.16(OH)_0.84; Friedrich et al. in Am Mineral 86:981–989, 2001). The full mean square displacement matrix Σ of the O–H pair was determined from the temperature dependence of the anisotropic displacement parameters, enabling a proper correction of the O–H bond for thermal vibration without assumptions about the correlation of O and H movements. The results show that the perpendicular O–H motions in chondrodite are intermediate between the riding and the independent motion models. The corrected O–H bond lengths do not change with temperature whereas the corrected H···F distances show an increase of ~0.02 Å with temperature, as do the Mg–O distances. This result shows that spectroscopic observations on the strength of the covalent O–H bond cannot be interpreted unambiguously in terms of a corresponding behaviour of the associated H···O/F hydrogen bond.     

Arsenic incorporation into FeS2 pyrite and its influence on dissolution: A DFT study

FeS₂ pyrite can incorporate large amounts of arsenic (up to ca. 10 wt%) and hence has a strong impact on the mobility of this toxic metalloid. Focussing on the lowest arsenic concentrations for which the incorporation occurs in solid solution, the substitution mechanisms involved have been investigated by assuming simple incorporation reactions in both oxidising and reducing conditions. The solution energies were calculated by Density Functional Theory (DFT) calculations and we predict that the formation of AsS dianion groups is the most energetically favourable mechanism. The results also suggest that the presence of arsenic will accelerate the dissolution and thus the generation of acid drainage, when the crystal dissolves in oxidising conditions.     

Assessment of future trends on groundwater quality in a nitrate vulnerable zone (Esposende–Vila do Conde sector,NW Portugal): towards a combined conceptual and mass transport modelling

Hydrogeology Journal - Nitrate contamination of groundwater is an important public health issue worldwide. For environmental and public health reasons, water should not contain more than...