Ab initio calculations on (OH)4 defects in α-quartz

Ab initio total energy calculations based on a new optimized oxygen psuedopotential have been used to study the structures and relative energies of α-quartz, a partly (OH)₄ substituted version of the α-quartz structure, and interstitial water molecules in α-quartz. Hydrogen bonds formed from two hydroxyl groups of the (OH)₄ defects in the substituted α-quartz structure promote a stable structure for the defect α-quartz at low temperature. Comparable ab initio calculation of the energy of the interstitial water molecule in the quartz structure indicates that, energetically, the (OH)₄ defect is likely to be strongly favoured as a mode for the incorporation of water. Ab initio stress calculations confirm that the (OH)₄ defect in quartz has a large associated stress field which is likely to lead to segregation of these defects on supersaturation in wet quartz. The calculations indicate that segregation should occur in the plane (10 0) of the α-quartz structure.     

Five new E′ centers and their 29Si hyperfine structures in electron-irradiated α-quartz

Single-crystal electron paramagnetic resonance (EPR) spectra of fast-electron-irradiated quartz, after annealing at 120 and 200°C, reveal five new E′ type centers, herein labeled E ₅^￠ , E ₆^￠ , E ₇^￠ , E ₈^￠ , \textand E ₉^￠ E_{ 5}^{\prime } ,\,E_{ 6}^{\prime } ,\,E_{ 7}^{\prime } ,\,E_{ 8}^{\prime } ,\,{\text{and}}\,E_{ 9}^{\prime } . Centers E ₅^￠ , E ₇^￠ , \textand E ₉^￠ E_{ 5}^{\prime } ,\,E_{ 7}^{\prime } ,\,{\text{and}}\,E_{ 9}^{\prime } are characterized by the orientations of the unique principal g and A(²⁹Si) axes close to a short Si–O bond direction, hence representing new variants of the well-established E ₁^￠ E_{ 1}^{\prime } center. Centers E ₆^￠ E_{ 6}^{\prime } and E ₈^￠ E_{ 8}^{\prime } have the orientations of the unique principal g and A(²⁹Si) axes approximately along a long Si–O bond direction, similar to the E ₂^￠ E_{ 2}^{\prime } centers. Therefore, these new E′ type centers apparently arise from the removal of different oxygen atoms and represent variable local distortions around the oxygen vacancies.     

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.     

Theoretical reaction pathways for the formation of [Si(OH)5]1− and the deprotonation of orthosilicic acid in basic solution

Ab initio, molecular orbital calculations at the 6-31G¹ level including second-order Møller-Plesset electron correlation predict that the species [Si(OH)₅]¹⁻ is dynamically stable in a distorted trigonal bipyramid configuration. Reaction pathways for Si(OH)₄ + (OH)⁻ → [Si(OH)₅]¹⁻ → [(OH)₃SiO]¹⁻—H₂O are also calculated. The first reaction represents the formation of pentacoordinate Si from orthosilicic acid and hydroxide. The activation energy for adding a fifth Si-(OH)⁻ bond to the Si(OH)₄ molecule is ≈0.1 eV /molec (≈10kJ/mol). The second reaction is the deprotonation of the Si(OH)₄ which forms as a hydroxyl group leaves the [Si(OH)₅]¹⁻ molecule. Removal of a bond from this complex requires 0.9 eV/molecule (≈85 kJ/mol). Lengthening the Si—OH₂ distance results in the isolated molecules [(OH)₃SiO]¹⁻ + H₂O. This represents dehydration of the deprotonated orthosilicic acid.[Si(OH)₅]¹⁻ and [(OH)₃SiO]¹⁻- H₂O have the same energetic stability within the accuracy of these calculations. The potential energies of the isolated molecular systems [(OH)₃SiO]¹⁻+ H₂O and Si(OH)₄ + (OH)⁻ are considerably higher. These results suggest that [Si(OH)₅]¹⁻ may be a stable species or reaction intermediate in dissolution of silicate minerals in basic aqueous solutions.     

The Ural–Herirud transcontinental postcollisional strike-slip fault and its role in the formation of the Earth’s crust

The paper considers the morphology, deep structure, and geodynamic features of the Ural–Herirud postorogenic strike-slip fault (UH fault), along which the Moho (the “M”) shifts along the entire axial zone of the Ural Orogen, then further to the south across the Scythian–Turan Plate to the Herirud sublatitudinal fault in Afghanistan. The postcollisional character of dextral displacements along the Ural–Herirud fault and its Triassic–Jurassic age are proven. We have estimated the scale of displacements and made an attempt to make a paleoreconstruction, illustrating the relationship between the Variscides of the Urals and the Tien Shan before tectonic displacements. The analysis of new data includes the latest generation of 1: 200000 geological maps and the regional seismic profiling data obtained in the most elevated part of the Urals (from the seismic profile of the Middle Urals in the north to the Uralseis seismic profile in the south), as well as within the sedimentary cover of the Turan Plate, from Mugodzhary to the southern boundaries of the former water area of the Aral Sea. General typomorphic signs of transcontinental strike-slip fault systems are considered and the structural model of the Ural–Herirud postcollisional strike-slip fault is presented.     

The nature of metals—sediment—water interactions in freshwater bodies,with emphasis on the role of organic matter

A review with 227 references of the title subject is presented. It is divided into two main sections, viz., nature and properties of humic matter, and water—metal—sediment interactions.The first section deals with the essential properties of organic matter which occurs naturally in drainage sediments and waters. Discussion of the basic molecular structure of humic and fulvic acids is followed by some details of the chemical nature of functional groups within these structures which are important in metal-ion adsorption and complexing reactions which these materials can undergo. Information is also presented for colloidal and polyelectrolyte properties, complexation properties, and finally a summary discussion of metal-ion—humic-acid, metal-ion—fulvic-acid stability constants for both single ligand and mixed ligand systems completes the section.The second section comprises discussions of some specific aspects of interactions between metals, sediments and waters, including metal and organic speciation studies; sorption interactions between organic matter, clays and humic acids; chemical reaction between humic acids, heavy-metal minerals, clays and other silicate minerals; metal-ion adsorption—desorption studies, oxidation—reduction reactions between metal ions and humic acids; effects of sulphide ion on some of the above interactions and finally a summary of some relevant field geochemical dispersion studies.This second section describes both laboratory and field studies for each aspect.     

Granitoid massif of the Dal’negorsk borosilicate deposit in the Primorye region of Russia: The role of the intrusion in the formation of the boron mineralization

The granitoids of the Dal’negorsk borosilicate deposit are ascribed mainly to the high-K metaluminous rocks of the calcic and alkali-calcic series. The thermo-baro-geo-chemical studies showed that they originated from melts with low contents of water (H₂O < 3.5% H₂O) and CO₂ at 800–850°C and 65–90 MPa. The data on the average contents of elements in the rock-forming minerals and the estimated initial water content in the magma point to the absence of a genetic relation between the intrusion and boron mineralization. The granitoid magma was responsible for the skarn formation and for the mobilization and remobilization of boron under a favorable environment. The K/Ar dating (51.0 ± 10 Ma), the geochemical typification (signatures of within-plate, subduction, and collisional granitoids), and the low water content in the parental melts of the granitoids, in accordance with the scheme of the geodynamic evolution of the region, indicate their formation in the lithospheric plate sliding environment.     

The solubility of calcite in water at 6–16 kbar and 500–800 °C

The solubility of calcite in H₂O was measured at 6–16 kbar, 500–800 °C, using a piston-cylinder apparatus. The solubility was determined by the weight loss of a single crystal and by direct analysis of the quench fluid. Calcite dissolves congruently in the pressure (P) and temperature (T) range of this study. At 10 kbar, calcite solubility increases with increasing temperature from 0.016±0.005 molal at 500 °C to 0.057±0.022 molal at 750 °C. The experiments reveal evidence for hydrous melting of calcite between 750 and 800 °C. Solubilities show only a slight increase with increasing P over the range investigated. Comparison with work at low P demonstrates that the P dependence of calcite solubility is large between 1 and 6 kbar, increasing at 500 °C from 1.8×10^–5 molal at 1 kbar to 6.4×10^–3 molal at 6 kbar. The experimental results are described by:

Diamonds in the products of the 2012–2013 Tolbachik eruption (Kamchatka) and mechanism of their formation

The origin of diamonds in the lava and ash of the recent Tolbachik eruption of 2012–2013 (Kamchatka) is enigmatic. The mineralogy of the host rocks provides no evidence for the existence of the high pressure that is necessary for diamond formation. The analysis of carbon isotope systematics showed a similarity between the diamonds and dispersed carbon from the Tolbachik lava, which could serve as a primary material for diamond synthesis. There are grounds to believe that the formation of Tolbachik diamonds was related to fluid dynamics. Based on the obtained results, it was suggested that Tolbachik microdiamonds were formed as a result of cavitation during the rapid movement of volcanic fluid. The possibility of cavitation-induced diamond formation was previously theoretically substantiated by us and confirmed experimentally. During cavitation, ultrahigh pressure is generated locally (in collapsing bubbles), while the external pressure is not critical for diamond synthesis. The conditions of the occurrence of cavitation are rather common in geologic processes. Therefore, microdiamonds of such an origin may be much more abundant in nature than was supposed previously.     

Assessment of changes in the area of the water conservation forest in the Qilian Mountains of China’s Gansu province, and the effects on water conservation

The Qilian Mountains water conservation forest in Gansu province is an important ecological barrier surrounding the oasis in China’s Hexi Corridor. The water they provide is the basis for the existence and sustainable socioeconomic development of those oases. As a result of unsustainable use of the water conservation forest until the 1980s, the oasis ecosystems of the Hexi region were seriously damaged, and the oasis areas experienced deterioration of their ecological environment. In this paper, Landsat images were used to monitor the temporal and spatial changes in area of water conservation in Qilian Mountains of China’s Gansu province and to assess the effect on water conservation by analyzed relationship between water conservation forest area, climatic data and hydrological data. The results showed that the forest covered 15.1% of the study area in 2007 and has followed different trends during the study period. From 1978 to 1990, the forest area decreased; however, from 1990 to 2007, the forest area increased, with a faster rate of increase from 1990 to 2000, and the rate of increase averaged 2,733.89 ha per year since 1990. The water conservation forest appears to play an important role in flood control, runoff regulation, the prevention of soil erosion, and water conservation; and these benefits increase with an increasing area of forest.     

The concentration and distribution of different mercury species in the water columns and sediment of Aha Lake

In order to find out whether Aha Lake was polluted by the acid mining waste water or not, the concentration and distribution of different mercuryspecies in the water columns and sediment profile collected from Aha Lake were investigated. It was found that discernible seasonal variation of different mercury species in water body were obtained in the Aha Reservoir. With regards to the whole sampling periods, the concentrations of HgP in the Aha Reservoir water body were evidently correlated to the concentrations of total mercury, showing that total mercury was mostly associated with particle mercury. The concentrations of methylmercury in water body were also evidently correlated to the concentrations of dissolved mercury. The dissolved mercury evidently affects the distribution and transportation of methylmercury. However, there is no correlation between methylmercury and total mercury. The dissolved mercury, reactive mercury, dissolved methylmercury levels in the water body of high flow period were much higher than those in low flow period. The distribution, speciation and levels of mercury within the Aha Reservoir water body were governed by several factors, such as the output of river, the release of sediment . Discernible seasonal variation of total mercury and methylmercury in porewater was described during the sampling periods, with the concentrations in high flow period generally higher than those in low flow period. The methylmercury in pore water column was evidently correlated to that of the sediment. The results indicated that highly elevated MeHgD concentrations in the porewater were produced at the depths from 2 to 5 cm in the sediment profile, and decreased sharply with depth. A positive correlation has been found between MeHgD formation and sulfate reducing bacterial activity. These highly elevated concentrations of MeHgD at the intersurface between waters and sediments suggest a favorable methylation condition. Moreover,     

The solubility of water in NaAlSi3O8 melts: a re-examination of Ab−H2O phase relationships and critical behaviour at high pressures

The solubility of water in melts in the NaAlSi₃O₈–H₂O system at high P and T was deduced from the appearance of quenched products and from water concentrations in the quenched glasses measured by ion probe, calibrated by hydrogen manometry. Starting materials were gels with sufficient water added to ensure saturation of the melts under the run conditions. Experiments were carried out for 10–30 h in an internally heated argon pressure vessel (eight at 1400° C and 0.2–0.73 GPa and three at 0.5 GPa and 900–1200° C) and for 1 h in a piston-cylinder apparatus (three at 1200° C, 1–1.3 GPa). No bubbles were observed in the glasses quenched at P<0.5 GPa or from T<1300° C at 0.5 GPa. Bubble concentration in glasses quenched from 1400° C was low at 0.5, moderate at 0.55 GPa and very high at 0.73 GPa and still higher in glasses quenched in the piston cylinder. Water concentration was measured in all glasses, except for the one at 0.55 GPa, for which it was only estimated, and for those at 0.73 GPa because bubble concentration was too high. Inferred water solubilities in the melt increase strongly with increasing P at 1400° C (from 6.0 wt% at 0.2 GPa to 15 at 0.55 GPa) and also with increasing T at 0.5 GPa (from 9.0 wt% at 900° C to 12.9 at 1400° C). The T variation of water solubility is fundamental for understanding the behaviour of melts on quenching. If the solubility decreases with T at constant P (retrograde solubility), bubbles cannot form by exsolution on isobaric quenching, whereas if the solubility is prograde they may do so if the cooling rate is not too fast. It is inferred from observed bubble concentrations and from our and previous solubility data that water solubility is retrograde at low P and prograde at and above 0.45 GPa; it probably changes with T from retrograde below to prograde above 900° C at 0.5 GPa. Moreover, the solubility is very large at higher pressures (possibly>30 wt% at 1.3 GPa and 1200° C) and critical behaviour is approached at 1.3 GPa and 1200° C. The critical curve rises to slightly higher P at lower T and intersects the three-phase or melting curve at a critical end point near 670° C and 1.5 GPa, above which albite coexists only with a supercritical fluid.     

Crystal structure of yegorovite Na4[Si4O8(OH)4] · 7H2O

Doklady Earth Sciences - Using X-ray analysis, the crystal structure of yegorovite Na4[Si4O8(OH)4] · 7H2O, a newly-discovered mineral from the Lovozero alkaline complex (Kola Peninsula,...     

Correlated δ18O and [Ti] in lunar zircons: a terrestrial perspective for magma temperatures and water content on the Moon

Zircon grains were separated from lunar regolith and rocks returned from four Apollo landing sites, and analyzed in situ by secondary ion mass spectrometry. Many regolith zircons preserve magmatic δ¹⁸O and trace element compositions and, although out of petrologic context, represent a relatively unexplored resource for study of the Moon and possibly other bodies in the solar system. The combination of oxygen isotope ratios and [Ti] provides a unique geochemical signature that identifies zircons from the Moon. The oxygen isotope ratios of lunar zircons are remarkably constant and unexpectedly higher in δ¹⁸O (5.61 ± 0.07 ‰ VSMOW) than zircons from Earth’s oceanic crust (5.20 ± 0.03 ‰) even though mare basalt whole-rock samples are nearly the same in δ¹⁸O as oceanic basalts on Earth (~5.6 ‰). Thus, the average fractionation of oxygen isotopes between primitive basalt and zircon is smaller on the Moon [Δ¹⁸O(WR-Zrc) = 0.08 ± 0.09 ‰] than on Earth (0.37 ± 0.04 ‰). The smaller fractionations on the Moon suggest higher temperatures of zircon crystallization in lunar magmas and are consistent with higher [Ti] in lunar zircons. Phase equilibria estimates also indicate high temperatures for lunar magmas, but not specifically for evolved zircon-forming melts. If the solidus temperature of a given magma is a function of its water content, then so is the crystallization temperature of any zircon forming in that melt. The systematic nature of O and Ti data for lunar zircons suggests a model based on the following observations. Many of the analyzed lunar zircons are likely from K, rare earth elements, P (KREEP)-Zr-rich magmas. Zircon does not saturate in normal mafic magmas; igneous zircons in mafic rocks are typically late and formed in the last most evolved portion of melts. Even if initial bulk water content is moderately low, the late zircon-forming melt can concentrate water locally. In general, water lowers crystallization temperatures, in which case late igneous zircon can form at significantly lower temperatures than the solidus inferred for a bulk-rock composition. Although lunar basalts could readily lose H₂ to space during eruption, lowering water fugacity; the morphology, large size, and presence in plutonic rocks suggest that many zircons crystallized at depths that retarded degassing. In this case, the crystallization temperatures of zircons are a sensitive monitor of the water content of the parental magma as well as the evolved zircon-forming melt. If the smaller Δ¹⁸O(zircon–mare basalt) values reported here are characteristic of the Moon, then that would suggest that even highly evolved zircon-forming magmas on the Moon crystallized at higher temperature than similar magmas on Earth and that magmas, though not necessarily water-free, were generally drier on the Moon.     

Application of IR and Raman spectroscopy for the determination of the role of oxygen fugacity in the formation of N–С–О–Н molecules and complexes in the iron-bearing silicate melts at high pressures

Large-scale melting of the Earth’s early mantle under the effect of global impact processes was accompanied by the generation of volatiles, which concentration was mainly controlled by the interaction of main N, C, O, and H gas-forming elements with silicate and metallic melts at low oxygen fugacity (fO₂), which predominated during metallic segregation and self-oxidation of magma ocean. The paper considers the application of Raman and IR (infrared) Fourier spectroscopy for revealing the mechanisms of simultaneous dissolution and relative contents of N, C, O, and H in glasses, which represent the quench products of reduced model FeO–Na₂O–Al₂O₃–SiO₂ melts after experiments at 4 GPa, 1550°C, and fO₂ 1.5–3 orders of magnitude below the oxygen fugacity of the iron—wustite buffer equilibrium (fO₂(IW)). Such fO₂ values correspond to those inferred for the origin and evolution of magma ocean. It was established that the silicate melt contains complexes with N–H bonds (NH₃, NH ₂ ⁺ , NH ₂ ^- ), N₂, H₂, and CH₄ molecules, as well as oxidized hydrogen species (OH^– hydroxyl and molecular water H₂O). Spectral characteristics of the glasses indicate significant influence of fO₂ on the N–C–O–H proportion in the melt. They are expressed in a sharp decrease of NH ₂ ⁺ , NH ₂ ^- (O–NH₂), OH^–, H₂O, and CH₄ and simultaneous increase of NH ₂ ^- (≡Si–NH₂) and NH₃ with decreasing fO₂. As a result, NH₃ molecules become the dominant nitrogen compounds among N–C–H components in the melt at fO₂ two orders of magnitude below fO₂(IW), whereas molecular СН₄ prevails at higher fO₂. The noteworthy feature of the redox reactions in the melt is stability of the ОН^– groups and molecular water, in spite of the sufficiently low fO₂. Our study shows that the composition of reduced magmatic gases transferred to the planet surface has been significantly modified under conditions of self-oxidation of mantle and magma ocean.     

The role of precursory structures on Tertiary deformation in the Black Forest—Hegau region

International Journal of Earth Sciences - Structural inheritance of preexisting crustal discontinuities is widely accepted to have played a crucial role during the Cenozoic tectonic evolution of...     

The Anna's Rust Sheet and related gabbroic intrusions in the Vredefort Dome-Kibaran magmatic event on the Kaapvaal Craton and beyond?

The Anna's Rust Sheet (ARS) and a suite of mineralogically and chemically related intrusions in the core and collar of the Vredefort Dome (in particular, the Vredefort Mafic Complex: VMC) represent a newly recognised type of high Ti gabbro in this central part of the Kaapvaal Craton. This lithology, referred to as the Vredefort Type IV mafic intrusion, is distinguished from chemically similar Type V intrusions (the Karoo dolerites) by the presence of glomeroporphyritic plagioclase and higher Th content and from Type III intrusions (≈ 1600 Ma gabbro) by the lack of cross-cutting pseudotachylitic breccia veinlets. Petrographic features and both major and trace element compositions of all Type IV intrusions are very similar. Based on its Rb-Sr isotope age and character, a gabbroic intrusion from Majuba Colliery (Mpumalanga Province) is also thought to belong to the ARS (Type IV) suite of tholeiitic intrusions. Rb-Sr isotopic analysis resulted in a preferred age of 1052±11 Ma (2ω) for biotite and plagioclase data for ARS, VMC and Majuba samples. The Rb-Sr age for the ARS is further supported by ⁴⁰Ar-³⁹Ar stepheating ages for plagioclase and pyroxene separates from two ARS and VMC samples, which favour formation of this gabbroic intrusion at ca 1000 Ma ago. These results suggest that an ≈ 120 m thick sheet intrusion may be present throughout a major part of the Vredefort Dome. While Kibaran-age (ca 1–1.2 Ga) alkaline, both mafic and felsic, magmatism, as well as tectonic and hydrothermal activity at that time, have been known in the central Kaapvaal Craton, a widespread tholeiitic magmatic component has now been added to this record. There is a strong likelihood that this magmatic event occurred throughout the southern African subcontinent and perhaps into Antarctica.