A re-examination of the role of hydrogen in Al−Si interdiffusion in feldspars

Recent experimental studies have shown that the rates of Al–Si order-disorder and interdiffusion in alkali feldspars at high pressures under dry conditions increase dramatically in the approximate pressure range 7–14 kb, depending on temperature and feldspar composition (Goldsmith 1987, 1988). Enhancement of Al–Si interdiffusion rates is ascribed to the involvement of hydrogen, but the species of hydrogen involved is undetermined.A simple kinetic analysis of the data of Goldsmith (1987) on disordering of dry albite at 800°–950° C and 6–24 kb in the solid media press is consistent with the NaCl pressure cell acting as a proton donor by enhancing dissociation of water in the pressure medium, generating a high in the experimental environment. The rate constant for disordering of albite is found to increase linearly with the estimated experimental and with the density of aqueous salt solution, implicating H⁺ as the rate-enhancing species.Further experimental studies confirm the importance of . At 16 kb and 850° C, dry albite in sealed Pt capsules in a NaCl cell containing tantalum powder (which reduces H₂O to H₂) remains highly ordered over the same time that complete disordering would occur in the absence of Ta. H₂ cannot therefore be the rate-enhancing species. At 1 kb and 850° C, the extent of Al–Si disorder in albite in direct contact with various NaCl–H₂O solutions increases from partially disordered for pure H₂O to completely disordered for saturated aqueous NaCl solution, giving strong support to the proton model. SIMS scanning ion imaging of albite run products demonstrates conclusively that solution-reprecipitation is not responsible for enhanced disordering rates.Results of disordering experiments in the solid media apparatus cannot be duplicated in Ar gas media internally-heated pressure vessels, even with the same experimental configuration around the albite-bearing capsules, due to the different proton-buffering capacities of the solid and gas media apparatus.     

The role of acidity–basicity in evaporating refractory inclusions in chondrites

When melts of Ca–Al inclusions in chondrites, which are dominated by the oxides SiO₂, MgO, CaO, and Al₂O₃, evaporate at high temperatures, the SiO₂ and MgO fugacities are inverted: SiO₂, which is more volatile than MgO, becomes less volatile when melts rich in refractory CaO and Al₂O₃ evaporate. This fugacity inversion can be realistically explained within the framework of D.S. Korzhinskii’s theory of acid–base interaction between components in silicate melts. According to this theory, an increase in CaO concentration in the melt increases its basicity, and this, in turn, increases the activity (and hence, also fugacity) of MgO and decreases those of SiO₂. In the real compositions of the Ca–Al inclusions in chondrites, the MgO/SiO₂ ratio systematically decreases with an increase in the CaO concentration under the effect of acid–base interaction.     

The place of ecological–geophysical studies in the system of urban ecology

According to the forecasts of the World Health Organization, 70% of the world’s population will have lived in large and small cities by 2050. This means that more than two-thirds of the planet’s population will become a part of new natural-technical formation, that is, geobiotechnoecosystems. Such ecosystems are characterized by profound changes in natural properties during active human impacts and by acquiring new qualities. The changes manifest themselves in all ecological functions of the terrestrial spheres: the atmosphere, the hydrosphere, and the lithosphere, including a change in the geophysical (energetic) potential as well. The presented material can be considered as a basis for the formation of Geophysical Urban Ecology, which is a new scientific and practical field.     

The March–April 2014 sequence of earthquakes in North Chile

During March–April 2014 a series of earthquakes occurred around the Iquique city located in the northern Chile region. The two largest events of this sequence are the Mw8.2, April 1, 2014 and Mw7.7, April 4, 2014 quakes. Here we computed the nodal planes of eight of the large and well teleseismically recorded events of this series based on grid search, teleseismic moment tensors inversion, empirical Green's function deconvolution and its stack to average the deconvolutions for the Mw = 8.2, April 1, 2014, synthetic Green's function deconvolution and its stack to average the deconvolutions for the same event and 3D static deformation analysis of the above mentioned events based on the AK135 model. Grid search nodal planes and moment tensors suggest the dominance of reverse faulting. Almost all of the calculated teleseismic moment tensors represent a considerable amount of DC (usually more than 90%) and lower amount of CLVD for this sequence of events. Empirical and synthetic Green's function deconvolution showing down dip rupture propagation and 3D static deformation representing higher amount of vertical deformation in comparison with horizontal deformation components plus the existence of uplift and subsidence. According to the aftershocks distribution there is a bilateral distribution of the aftershocks around the first large event of this sequence that occurred March 16, 2014 (Mw6.7) so that they are approximately limited between the Mw8.2 (at north) and Mw7.7 (at south) quakes. Moreover there exist two bands of regional seismicity during early-mid 2014: a shallow off-shore band between the trench and coast and a deeper inland band under the active volcanic chain (both nearly parallel to the trench).     

Ca–Mg diffusion in diopside: tracer and chemical inter-diffusion coefficients

We have experimentally determined the tracer diffusion coefficients (D*) of ⁴⁴Ca and ²⁶Mg in a natural diopside (~Di₉₆) as function of crystallographic direction and temperature in the range of 950–1,150 °C at 1 bar and f(O₂) corresponding to those of the WI buffer. The experimental data parallel to the a*, b, and c crystallographic directions show significant diffusion anisotropy in the a–c and b–c planes, with the fastest diffusion being parallel to the c axis. With the exception of logD*(²⁶Mg) parallel to the a* axis, the experimental data conform to the empirical diffusion “compensation relation”, converging to logD ~ −19.3 m²/s and T ~ 1,155 °C. Our data do not show any change of diffusion mechanism within the temperature range of the experiments. Assuming that D* varies roughly linearly as a function of angle with respect to the c axis in the a–c plane, at least within a limited domain of ~20° from the c-axis, our data do not suggest any significant difference between D*(//c) and D*(⊥(001)), the latter being the diffusion data required to model compositional zoning in the (001) augite exsolution lamellae in natural clinopyroxenes. Since the thermodynamic mixing property of Ca and Mg is highly nonideal, calculation of chemical diffusion coefficient of Ca and Mg must take into account the effect of thermodynamic factor (TF) on diffusion coefficient. We calculate the dependence of the TF and the chemical interdiffusion coefficient, D(Ca–Mg), on composition in the diopside–clinoenstatite mixture, using the available data on mixing property in this binary system. Our D*(Ca) values parallel to the c axis are about 1–1.5 log units larger than those Dimanov et al. (1996). Incorporating the effect of TF, the D(Ca–Mg) values calculated from our data at 1,100–1,200 °C is ~0.6–0.7 log unit greater than the experimental quasibinary D((Ca–Mg + Fe)) data of Fujino et al. (1990) at 1 bar, and ~0.6 log unit smaller than that of Brady and McCallister (1983) at 25 kb, 1,150 °C, if our data are normalized to 25 kb using activation volume (~4 and ~6 cm³/mol for Mg and Ca diffusion, respectively) calculated from theoretical considerations.     

Fe–Mg interdiffusion rates in clinopyroxene: experimental data and implications for Fe–Mg exchange geothermometers

Chemical interdiffusion of Fe–Mg along the c-axis [001] in natural diopside crystals (X _Di = 0.93) was experimentally studied at ambient pressure, at temperatures ranging from 800 to 1,200 °C and oxygen fugacities from 10^?11 to 10^?17 bar. Diffusion couples were prepared by ablating an olivine (X _Fo = 0.3) target to deposit a thin film (20–100 nm) onto a polished surface of a natural, oriented diopside crystal using the pulsed laser deposition technique. After diffusion anneals, compositional depth profiles at the near surface region (~400 nm) were measured using Rutherford backscattering spectroscopy. In the experimental temperature and compositional range, no strong dependence of D ^Fe–Mg on composition of clinopyroxene (Fe/Mg ratio between Di₉₃–Di₆₅) or oxygen fugacity could be detected within the resolution of the study. The lack of fO₂-dependence may be related to the relatively high Al content of the crystals used in this study. Diffusion coefficients, D ^Fe–Mg, can be described by a single Arrhenius relation with $$D^{{{\text{Fe}} - {\text{Mg}}}} = 2. 7 7\pm 4. 2 7\times 10^{ - 7} {\text{exp(}}-3 20. 7\pm 1 6.0{\text{ kJ}}/{\text{mol}}/{\text{RT)m}}^{ 2} /{\text{s}}.$$ D ^Fe–Mg in clinopyroxene appears to be faster than diffusion involving Ca-species (e.g., D ^Ca–Mg) while it is slower than D ^Fe–Mg in other common mafic minerals (spinel, olivine, garnet, and orthopyroxene). As a consequence, diffusion in clinopyroxene may be the rate-limiting process for the freezing of many geothermometers, and compositional zoning in clinopyroxene may preserve records of a higher (compared to that preserved in other coexisting mafic minerals) temperature segment of the thermal history of a rock. In the absence of pervasive recrystallization, clinopyroxene grains will retain compositions from peak temperatures at their cores in most geological and planetary settings where peak temperatures did not exceed ~1,100 °C (e.g., resetting may be expected in slowly cooled mantle rocks, many plutonic mafic rocks, or ultra-high temperature metamorphic rocks).     

The Role of Hydrocarbons in the Formation of Epithermal Gold–Silver Deposits in Kamchatka,Russia

Doklady Earth Sciences - Data on the mineralogical and geochemical features of three epithermal gold deposits in Kamchatka, as well as on the compositions and physicochemical parameters of...     

The Sr–Nd–Pb–Hf Isotopic Composition of Late Paleozoic Granitoids in Central Chukotka

Doklady Earth Sciences - The results of Sr–Nd–Pb–Hf isotope analysis of Late Paleozoic granitoids of Central Chukotka, which are exemplified by the Kibera and Kuekvun plutons, are...     

The role of water resources in the evolution of the Israeli–Lebanese border

The current location of the border between Lebanon and Palestine, today's Israel, is a product of various competing forces. The Zionist Organization aspired to include the entire Galilee region up to the lower reaches of the Litani River (also known as the Kassimiyah River) within Palestine. The river itself was the desired northern border of the country. The Zionists supported their position by employing instrumental arguments that were largely related to the availability of water resources. On the other hand, residents of the upper Galilee, today's southern Lebanon, demanded that they be included with Lebanon. They used their trade links with Beirut, and cultural and familial ties with other parts of Lebanon to support their position. These instrumental and expressive arguments appear to have assisted in the demarcation of the border between Lebanon and Palestine. Currently, access to the water resources, not necessarily control over them, is likely to influence negotiations between Israel and Lebanon over the future of the Israeli-occupied security zone in southern Lebanon.     

Dualistic distribution coefficients of trace elements in the system mineral–hydrothermal solution. IV. Platinum and silver in pyrite

The FeS₂–Ag–Pt–As system was studied using hydrothermal thermogradient synthesis (with internal sampling) of pyrite crystals at a temperature of 500°C and pressure of 1 kbar in ammonium chloridebased solutions. The modes of occurrence of precious metals (PM) were determined using atomic absorption spectrometry (AAS) in its version of statistical selections of analytical data on single crystals (SSADSC), electron microprobe analysis (EMPA), scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The concentration of Pt in its structural mode in pyrite is as high as 10–11 ppm and is practically not correlated with the As concentration. The dualistic distribution coefficient of Pt between pyrite and hydrothermal solution is 21 ± 7 for the structural mode and 210 ± 80 for the surface-related mode of this element. No inclusions of either any Pt-bearing minerals or Pt itself was detected. Platinum is an element highly compatible with hydrothermal pyrite and is different in this sense from gold, and pyrite is underestimated as a potential concentrator of platinumgroup elements (PGE). The distribution of Ag in pyrite is highly heterogeneous. The likely reason for this is that the Ag solid solution cannot be quenched, and hence, the Ag concentrations broadly vary and are very unsystematically distributed in natural pyrite crystals. Assuming this hypothesis, the limit for Ag accommodation in FeS₂ can be estimated using SSADSC at 0.09 ± 0.06 wt % under the experimental parameters, and the distribution coefficient of the structural Ag mode is thereby evaluated at 1400 ± 700. When crystallizing together with FeS₂ proustite (Ag₃AsS₃) near its melting point, forms mixtures with dervillite (Ag₂AsS₂), in which Ag deficit is counterbalanced by excess divalent As. The limit of As incorporation into pyrite under these conditions is ≤0.1 wt %. SEM-EDS and XPS data indicate that the surface phases are of three types. In the course of crystal growth, practically two-dimensional nonautonomous phases (NP) are aggregated into submicroscopic and micrometer-sized crystalline bodies (mesocrystals) that largely inherit their unusual minor-element composition from NP and are enriched in Ag, Pt, As, and other minor elements. NP and mesocrystals are enriched in Al, which was transferred into them from the Al-bearing Ti alloy of the reaction containers. Silver occur in the volume of the crystals and on their surface as monovalent silver sulfide. Arsenic was detected mostly in the form of di- and trivalent arsenic sulfides. Pentavalent arsenic oxide was identified only on the surface of the crystals and can be easily eliminated by ion milling.     

The results of measurements of heavy metals in atmospheric aerosols in the open areas of the Arctic Seas in 2009–2010

By experimental data on the concentration of toxic microelements (Pb, Cd, Cu, Zn, Ni, Co, and Cr) in atmospheric aerosols over the White and Norwegian Seas in winter-spring period of 2009–2010, the contamination of air environment over two sea basins, significantly different by geographical conditions but being heavily impacted by North-European industrial centres, including the impact of the largest in the European Arctic Kola industrial centre, has been analyzed. It has been indicated and described that the air basin over the White Sea water area, when compared to the Norwegian Sea, is under a significantly greater impact of the emission sources of heavy metals, located on the Kola Peninsula.     

Lattice strain across Na–K interdiffusion fronts in alkali feldspar: an electron back-scatter diffraction study

Cation exchange experiments between gem quality sanidine \((X_\mathrm{Or} = 0.85)\) and KCl melt produced chemical alteration of alkali feldspar starting at the grain surface and propagating inwards by highly anisotropic Na–K interdiffusion on the alkali sublattice. Diffusion fronts developing in b-direction are very sharp, while diffusion fronts within the a–c-plane are comparatively broad. Due to the composition dependence of the lattice parameters of alkali feldspar, the diffusion induced compositional heterogeneity induces coherency stress and elastic strain. Electron back-scatter diffraction combined with the cross-correlation technique was employed to determine the lattice strain distribution across the Na–K interdiffusion fronts in partially exchanged single crystals of alkali feldspar. The strain changes gradually across the broad fronts within the a–c-plane, with a successive extension primarily in a-direction conferring to the composition strain in unstressed alkali feldspar. In contrast, lattice strain characterised by pronounced extension in b-direction is localised at the sharp diffusion fronts parallel to b, followed by a slight expansion in a-direction in the orthoclase-rich rim. This strain pattern does not confer with the composition induced lattice strain in a stress-free alkali feldspar. It may rather be explained by the mechanical coupling of the exchanged surface layer and the mechanically strong substratum. The lattice distortion localised at the sharp diffusion front may have an influence on the diffusion process and appears to produce a self-sharpening feedback, leading to a local reduction of component mobilities.     

The political ecology of territoriality: territorialities in farmer–herder relationships in Northern Ghana

Fulani herder and farmer relationships in West Africa have always been troublesome as a result of farmers’ fundamental rejection of the herders’ inroads into their areas and also because of increased competition for available resources. In countries such as Ghana, local and even national campaigns have been launched to expel the herders but they persist. This case-study which utilised interviews and group discussions involving farmers and herders, sought to understand the dynamics and subtleties of herders’ resilience in an environment where natural resource access and use rights are tied to common property principles and where herders have no enshrined land and resource rights. Using territoriality as the analytical capsule, we found that the herders’ persistence is related to mainly non-territoriality where the goal is to influence relationships and resource access but not control area. Categorising their non-territorial expression into persuasive and aggressive forms, we provide a new platform for deconstructing farmer-herder relationships in the West African sub-region.     

The effect of Ca–Fe–As coatings on microbial leaching of metals in arsenic bearing mine waste

Globally arsenic (As) is a ubiquitous trace element derived from the natural weathering of As-bearing rock. With the onset of reducing conditions, the prevalence of aqueous As(III) may be intensified through biotic and abiotic processes. Here we evaluate the stability of arsenic bearing Ca–Fe hydroxide phases collected from exposed tailings at Ketza River mine, Yukon, Canada, during the reductive dissolution of both acid treated and untreated samples by Shewanella putrefaciens 200R and Shewanella sp. ANA-3. Samples were acid treated in order to remove Ca–Fe oxide coatings and evaluate the influence of these coatings on the rates of microbial Fe(III) and As(V) reduction. Environmental scanning electron microscope (ESEM) micrographs of the solid phase show significant differences in the chemistry and physical morphology of the material by the bacteria over time and are especially evident in the acid treated samples. Moreover, while solution chemistry showed similar As(III) respiration rates of the inoculated acid treated samples for both ANA3 and 200R at ~ 1.1 × 10⁻⁶ μM·s^− 1·m^− 2, the Fe(II) respiration rates differed at 1.4 × 10^− 7 and 9.5 × 10^− 8 μM·s^− 1·m⁻² respectively, thus suggesting strain specific metal reduction metabolic pathways Additionally, the enhanced metal reduction observed in the acid treated inoculated samples suggests that the presence of the Ca–Fe hydroxide phase in the untreated samples acted as a barrier, inhibiting the bacteria from accessing the metals. This has implications for increased mobilization of metals by metal reducing bacteria within areas of increased acidity, such as acid mine drainage sites and industrial tailings ponds that can come into contact with surface and ground water sources.     

The First Finding of Sapphirine in Granulites of the Angara–Kan Block: Evidence of Ultra-High–Temperature Metamorphism in the SW Siberian Craton

This work reports the first discovery of sapphirine-bearing mineral parageneses in granulites of the Angara–Kan block, information on the mineral assemblage of rocks, and the mineral composition. Based on mineral geothermometers utilizing alumina content in orthopyroxene, reconstruction of the composition of ternary feldspar, and the titanium content in zircon, it was revealed that the peak temperatures of metamorphism reached 1100°C, after which the rocks underwent cooling under sub-isobaric conditions. It is assumed that the pulse of ultra-high-temperature metamorphism correlates with processes of extension and intraplate magmatism during the age interval of 1.78–1.75 Ga.     

Mg–Fe interdiffusion rates in wadsleyite and the diffusivity jump at the 410-km discontinuity

Mg–Fe interdiffusion rates have been measured in wadsleyite aggregates at 16.0–17.0 GPa and 1230–1530 °C by the diffusion couple method. Oxygen fugacity was controlled using the NNO buffer, and water contents of wadsleyite were measured by infrared spectroscopy. Measured asymmetric diffusion profiles, analyzed using the Boltzmann–Matano equation, indicate that the diffusion rate increases with increasing iron concentration and decreasing grain size. In the case of wadsleyite containing 50–90 weight ppm H₂O, the Mg–Fe interdiffusion coefficients at compositions of Mg/(Mg + Fe)=0.95 in the coarse-grained region (about 60 m) and 0.90 in the fine-grained region (about 6 m) were determined to be a D_Xmg = 0.95 (m² s^–1)=1.24 × 10^–9 exp[–172 (kJ mol^–1)/RT] and D_Xmg = 0.90 (m² s^–1)=1.77 × 10^–9 exp[–143 (kJ mol^–1)/RT], respectively. Grain-boundary diffusion rates were estimated to be about 4 orders of magnitude faster than the volume diffusion rate. Grain-boundary diffusion dominates when the grain size is less than a few tens of microns. Results for the nominally dry diffusion couple in the present study are roughly consistent with previous studies, taking into account differences in pressure and grain size, although water contents of samples were not clear in previous studies. We observed that the diffusivity is enhanced by about 1 order of magnitude in wadsleyite containing 300–2100 wt. ppm H₂O at 1230 °C, which is almost identical to the enhancement associated with a 300 °C increase in temperature. It is still not conclusive that a jump in diffusivity exists between olivine and wadsleyite because water contents of olivine in previous diffusion studies and effects of water on the olivine diffusivity are uncertain.     

The microstructure and internal architecture of shear bands in sand–clay sequences

The microstructures of cm-scale displacement faults offsetting unlithified sequences of finely interbedded sands, silts and clays from outcrops in Denmark have been examined. A variety of shear band types are recognised based on their grain-scale deformation mechanism and internal structure. Shear bands in a Jurassic sequence exposed along the coastline of Bornholm are characterised by intense cataclasis of both sand and clay layers. This deformation mechanism is accompanied by extensive grain scale mixing along discrete shear bands to give a fault rock composition that reflects the relative amount of sand and clay within the faulted sequence. In contrast, shear bands at Nr. Lyngby and Jensgaard, both on the Jutland coast, are characterised by granular flow within the sand units. Grain scale mixing is subdued at these locations so that layers maintain their integrity across the shear band to form a layered internal structure of sand, silt and clay smears. In some instances, particularly at Nr. Lyngby, clays have deformed in a brittle manner so that they do not contribute material to the shear band, which is then comprised exclusively of coarser-grained components. The different deformation mechanisms and internal structures of shear bands are thought to be controlled by burial depth at the time of faulting.     

The force function of two rigid celestial bodies in Delaunay–Andoyer variables

Two new expansions of the force function of two rigid celestial bodies of finite size and arbitrary shape are obtained in Delaunay–Andoyer variables with any degree of accuracy, in the form of a partial sum of an eight dimensional Fourier series. These expansions of the force function contain products of expressions for the momenta and Stokes constants in terms of sines and cosines, whose arguments are linear combinations of the Delaunay and Andoyer angular variables. These representations of the force function are compact and convenient for applications in various problems in celestial mechanics and astrodynamics.     

The enhanced element enrichment in the supercritical states of granite–pegmatite systems

In this paper, we show that supercritical fluids have a greater significance in the generation of pegmatites, and for ore-forming processes related to granites than is usually assumed. We show that the supercritical melt or fluid is a silicate phase in which volatiles; principally H₂O are completely miscible in all proportions at magmatic temperatures and pressures. This phase evolves from felsic melts and changes into hydrothermal fluids, and its unique properties are particularly important in sequestering and concentrating low abundance elements, such as metals. In our past research, we have focused on processes observed at upper crustal levels, however extensive work by us and other researchers have demonstrated that supercritical melt/fluids should be abundant in melting zones at deep-crustal levels too. We propose that these fluids may provide a connecting link between lower and upper crustal magmas, and a highly efficient transport mechanism for usually melt incompatible elements. In this paper, we explore the unique features of this fluid which allow the partitioning of various elements and compounds, potentially up to extreme levels, and may explain various features both of mineralization and the magmas that produced them.