An internal variable model for the creep of rocksalt

Summary The creep strain rate of rocksalt, like that of other ductile crystalline materials, can be described by a power law equation of the type ( ) ⁿ , where the active stress is the difference between the total deviatoric applied stress and an internal stress _i . In this paper, the origin and the nature of this internal stress, which develops during inelastic deformation of the material, are discussed. It is shown that this internal stress can serve as an internal (or state) variable in the constitutive model of rocksalt, which reflects the microstructure evolution of the material under the competitive action of hardening and recovery mechanisms.An analysis of experimental data, both our own and those taken from the literature, demonstrates that such a law is able to correctly reproduce rocksalt creep test results in the steady-state domain. The proposed model is in accordance with the macroscopic and microscopic behavior of salt, and with direct measurements of the internal stresses made by others on this material.     

Lithology of recent sandy sediments of Lake Baikal

Evidence from the Olkhon Island-Maloe More Strait area, one of the most representative areas of Lake Baikal, has revealed the following unique phenomenon. Under certain favorable conditions, the transport of sedimentary matter to water basin from land is supplemented with the abundant delivery of loose material in the form of sand flows over large areas (up to 3 km² ) to the adjacent coast. We have revealed a specific cycle of material (reversible lithoflow) accompanied by the differentiation of sediments. The pelitic and silty fractions are separated from the psephitic and psammitic fractions in the subaqueous setting. The eolian transport of the psammitic material from the beach zone into the island is predominated by the removal of the medium-grained sand (fraction 0.5–0.25 mm). The mineral composition of main sources of terrigenous material is given. Formation conditions of the areas of eolian sands and their mineral and grain-size compositions, which reflect the existence of reversible lithoflows on the Baikal coast, are described. The physicomechanical properties (strength and adherence) of sandy sediments are assessed.Translated from Litologiya i Poleznye Iskopaemye, No. 2, 2005, pp. 133–142.Original Russian Text Copyright © 2005 by Akulov, Agafonov, Lomonosova, Vologina.     

Vendian-Cambrian carbonate sequences in sedimentary cover of the Tuva-Mongol microcontinent

Lihological-geochemical investigations of Vendian-Cambrian carbonate rocks from sedimentary cover of the Tuva-Mongol microcontinent revealed that the Bokson Group (Oka structural-formational zone), as well as the Gorlyk and Ara-Oshei formations (Ilchir structural-formational zone), characterize a common carbonate platform. Together with the Bokson Group, the combined Gorlyk and Ara-Oshei formations, which correlate with the complete Bokson Group, make up the Vendian-Cambrian sedimentary cover of the Tuva-Mongol microcontinent. Carbonate sequences accumulated in a shallow-water basin with differentiated bottom topography. Vendian-Cambrian carbonate rocks are characterized by constant geochemical composition due to the stability of provenance (basic and subordinate ultrabasic rocks) and the lack of admixture of pyroclastic material and influence of submarine hydrothermal solutions. Lithological and geochemical features of carbonate sequences imply a gradual deepening of basin in the course of sedimentary cover formation.Translated from Litologiya i Poleznye Iskopaemye, No. 2, 2005, pp. 192–204.Original Russian Text Copyright © 2005 by Letnikova, Geletii.     

Lithology and geochemistry of Albian-Cenomanian sandy sequences of the Voronezh Anteclise and their paleogeographic implication

The paper proposes subdivision of Albian and Cenomanian monotonous sandy sequences of the Voronezh anteclise on the basis of textural-structural features and distribution of accessory minerals. Distribution of rare earth, trace, and major elements was studied in sandy rocks and early diagenetic formations (glauconites and phosphorites). Dependence of the distribution on tectonic factor is noted.Translated from Litologiya i Poleznye Iskopaemye, No. 2, 2005, pp. 159–171.Original Russian Text Copyright © 2005 by Sirotin, Shatrov, Koval, Bugelskii, Voitsekhovskii, Nikulshin.     

Geochemical Features of Carbonaceous Rocks on the Western Slope of the Southern Urals

Based on the study of rocks in fault zones on the western slope of the southern Urals, it is shown that carbonaceous rocks are confined to the most dislocated parts of the sections and spatially associated with magmatic rocks. They are characterized by specific geochemical features with anomalous contents of gold and platinum group elements (PGE) and native tin mineralization that is atypical of terrigenous rocks. Transformation of these rocks is mainly governed by reduced mantle fluids penetrating into upper levels of the Earths crust at early stages of tectonomagmatic activation. The subsequent inversion of the fluids in the Earths crust leads to the formation of carbonaceous rocks with atypical mineralization and high PGE content.__________Translated from Litologiya i Poleznye Iskopaemye, No. 3, 2005, pp. 281–291.Original Russian Text Copyright © 2005 by Kovalev, Michurin.     

Redox states of lithospheric and asthenospheric upper mantle

The oxidation state of lithospheric upper mantle is heterogeneous on a scale of at least four log units. Oxygen fugacities ( ) relative to the FMQ buffer using the olivine-orthopyroxene-spinel equilibrium range from about FMQ-3 to FMQ+1. Isolated samples from cratonic Archaean lithosphere may plot as low as FMQ-5. In shallow Proterozoic and Phanerozoic lithosphere, the relative is predominantly controlled by sliding Fe³⁺-Fe²⁺ equilibria. Spinel peridotite xenoliths in continental basalts follow a trend of increasing with increasing refractoriness, to a relative well above graphite stability. This suggests that any relative reduction in lithospheric upper mantle that may occur as a result of stripping lithosphere of its basaltic component is overprinted by later metasomatism and relative oxidation. With increasing pressure and depth in lithosphere, elemental carbon becomes progressively refractory and carbon-bearing equilibria more important for control. The solubility of carbon in H₂O-rich fluid (and presumably in H₂O-rich small-degree melts) under the P,T conditions of Archaean lithosphere is about an order of magnitude lower than in shallow modern lithosphere, indicating that high-pressure metasomatism may take place under carbon-saturated conditions. The maximum in deep Archaen lithosphere must be constrained by equilibria such as EMOG/D. If the marked chemical depletion and the orthopyroxene-rich nature of Archaean lithospheric xenoliths is caused by carbonatite (as opposed to komatiite) melt segregation, as suggested here, then a realistic lower limit may be given by the H₂O +C=CH₄+O₂ (C-H₂O) equilibrium. Below C –H₂O a fluid becomes CH₄ rather than CO₂-bearing and carbonatitic melt presumably unstable. The actual in deep Archaean lithosphere is then a function of the activities of CO₂ and MgCO₃. Basaltic melts are more oxidized than samples from lithospheric upper mantle. Mid-ocean ridge (MORB) and ocean-island basalts (OIB) range between FMQ-1 (N-MORB) and about FMQ +2 (OIB). The most oxidized basaltic melts are primitive island-arc basalts (IAB) that may fall above FMQ+3. If basalts are accurate probes of their mantle sources, then asthenospheric upper mantle is more oxidized than lithosphere. However, there is a wide range of processes that may alter melt relative to that of the mantle source. These include partial melting, melt segregation, shifts in Fe³⁺/Fe²⁺ melt ratios upon decompression, oxygen exchange with ambient mantle during ascent, and low-pressure volatile degassing. Degassing is not very effective in causing large-scale and uniform shifts, while the elimination of buffering equilibria during partial melting is. Upwelling graphite-bearing asthenosphere will decompress along -pressure paths approximately parallel to the graphite saturation surface, involving reduction relative to FMQ. The relative will be constrained to below the CCO equilibrium and will be a function of . Upwelling asthenosphere whose graphite content has been exhausted by partial melting, or melts that have segregated and chemically decoupled from a graphite-bearing residuum will decompress along -decompression paths controlled by continuous Fe³⁺-Fe²⁺ solid-melt equilibria. These equilibria will involve increases in relative to the graphite saturation surface and relative to FMQ. Melts that finally segregate from that source and erupt on the earth's surface may then be significantly more oxidized than their mantle sources at depth prior to partial melting. The extent of melt oxidation relative to the mantle source may be directly proportional to the depth of graphite exhaustion in the mantle source.     

Predicting phosphate saturation in silicate magmas: An experimental study of the effects of melt composition and temperature

A series of 1 atm experiments has been performed to test the influence of iron content and oxidation state on the saturation of phosphate minerals in magmatic systems. Four bulk compositions of different iron content have been studied. The experiments cover a range of temperature from 1030 to 1070 °C and oxygen fugacity from 1.5 log units below to 1.5 log units above the Fayalite-Magnetite-Quartz buffer. The results demonstrate that neither iron content of the liquid nor oxidation state play a significant role on phosphate saturation. On the other hand, SiO₂ and CaO contents of the liquid strongly influence the appearance of a crystalline phosphate. Our results are combined with data from the literature to define an equation which predicts the P₂O₅ content of silicate liquids saturated in either whitlockite or fluorapatite:

     

The pleochroism of a gem-quality enstatite in the region of the OH stretching frequency,with a stereochemical interpretation

Summary The pleochroic behaviour of a gem-quality enstatite from Tanzania was investigated in the region =2500 to 4000 cm^–1. Two sharp absorption bands at =3410 cm^–1 and =3510 cm^–1 are interpreted to be caused by OH stretching vibrations. As their absorption coefficients are considerably larger parallel to [001] (=direction of the silicate chains) than perpendicular to this direction, the OH dipoles have to be oriented approximately parallel to [001]. On this basis, a stereochemical interpretation of the incorporation of the OH groups into the structure is given.

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Der Pleochroismus eines Enstatits von Edelsteinqualität im Gebiet der OH-Streckfrequenz und seine kristallchemische Interpretation

Zusammenfassung Das pleochroitische Verhalten eines Enstatits von Edelsteinqualität aus Tansania wurde im Bereich =2500 bis 4000 cm^–1 untersucht. Von zwei scharfen Banden bei =3410 cm^–1 und 3510 cm^–1 wird angenommen, daß sie durch OH-Streckschwingungen herrühren. Da ihre Absorptionskoeffizienten parallel zu [001] (=Richtung der Silikatketten) beträchtlich größer sind als senkrecht dazu, müssen die OH-Dipole ungefähr parallel zu [001] liegen. Auf dieser Basis wird der Einbau der OH-Gruppen in die Struktur diskutiert.

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Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling

The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3 h) and low concentrations of phosphate (?50 μM). Sorption of phosphate on calcite was studied in 11 different calcite-equilibrated solutions that varied in pH, P_CO2, ionic strength and activity of Ca²⁺, and . Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2-3 h while desorption is complete in less than 0.5 h. The reversibility of the sorption process indicates that phosphate is not incorporated into the calcite crystal lattice under our experimental conditions. Precipitation of phosphate-containing phases does not seem to take place in systems with ?50 μM total phosphate, in spite of a high degree of super-saturation with respect to hydroxyapatite (SI_HAP ? 7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the activity decreases (at constant pH) and as pH increases (at constant activity). The primary effect of ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. The experimental results were modeled satisfactorily using the constant capacitance model with >CaPO₄Ca⁰ and either >CaHPO₄Ca⁺ or > as the adsorbed surface species. Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.     

Natural boehmite single crystals from Ceylon

Single crystals of boehmite, up to 0.1 mm in size, were found in open cavities inside a corundum crystal from the Ratnapura area gem gravels in Ceylon. The unit cell parameters are (X-ray powder pattern): a ₀=3.695 Å b ₀=12.212 Å, c ₀=2.867 Å. The crystallographic orientation is based on X-ray single-crystal precession photographs. The crystals show the faces (it010), (001), (101), and (221). Systematic extinctions agree with the space group Amam. Optical orientation: a, b, c. Refractive indices are given. The mineral is optically positive with a large optic axial angle.     

Specific Features of Lithological and Mineralogical Compositions of Moraines in the Don Region

Results of the detailed lithological-mineralogical study of moraines from the well-known key sections in the Don Basin are presented. Important debatable issues concerning the age of Early Pleistocene glacial sediments are considered. Together with biostratigraphic data, recent data on the mineral composition of key moraine units can be used for solving these issues. The layered moraine sequence of the Don Basin (hereafter, Don moraine) shows compositional similarity in a regional scale. However, it is characterized by a spatiotemporal variation in the mineral and petrographic associations governed by specific paleogeographic settings and stages of moraine formation. Specific features of temporal rearrangement of these associations indicate the general paleogeographic trend of glacial lithogenesis. Therefore, they make it possible to compare moraines from the Kuznetsovka and Volnaya Vershina sections that include a combination of the most stable (and, generally, local) minerals and rocks of early stages of glacial lithogenesis. The compositionally most exotic Novokhopersk and Moiseevo moraines are logically attributed to the later stage of moraine formation. This does not contradict specific features of teriofauna in the interglacial sediments underlying and overlying the moraines. It is shown the spatiotemporal variation in the mineral composition of moraines of the Don region can be used for their stratigraphic correlation.__________Translated from Litologiya i Poleznye Iskopaemye, No. 3, 2005, pp. 321–332.Original Russian Text Copyright © 2005 by Bylinskii, Ananeva, Sudakova.     

Estimating relative bed-load contributions by lithology counts

In gravel-bedded streams where bed material of a tributary differs distinctly in lithology from that of the main stream, rock-type percentages can be used to estimate bed-load contributions of the two streams. The rock type that shows the greatest difference in abundance between the two streams is selected as the indicator lithology. Percentages of this lithology are estimated in both the main stream and tributary stream above their junction, and also in the main stream at a distance sufficiently downstream from the junction to allow complete mixing. The fraction of bed load contributed by the main stream, p,is estimated by ,where is an estimate of the proportion of indicator rock fragments in the bed of the main stream above the junction, is an estimate of the proportion in the bed of the tributary above the junction, and is an estimate of the proportion in the bed of the main stream below the junction. The variance of is obtained as var ( )= [p₁q₁(p_r – p₂)²/n(p₁ – p₂)⁴] + [p₂q₂(p_r – p₁)²/n(p₁ – p₂)⁴] + [p_rq_r/n(p₁ – p₂)²].Although no estimate of actual quantity of bed load is provided, the indicator rock technique supplies data that can serve as a check on data obtained by means of empirical formulas or actual transport measurements.     

Oxygen isotope fractionation between oxygen of different sites in illite minerals: a potential single-mineral thermometer

The experimental results of Hamza and Epstein mark internal oxygen isotope fractionations of hydrosilicates as potential single-mineral thermometers. In this study methodical investigations were made to determine the oxygen isotope ratios of hydroxyl groups in silicate minerals. As a reference material a commercial kaolinite was examined by vacuum extraction and by use of a modified partial fluorination technique first deseribed by Hamza and Epstein. The concordance of the results argue against oxygen isotope fractionation during dehydroxylation. Consequently, vacuum extraction can be used to determine the internal fractionation of minerals, which contain no ferrous iron. For calibration of the internal oxygen isotope fractionation, hydrothermally formed illites from the Lone Gull uranium deposit in Canada and from the Leuggern exploration drill site in Switzerland were investigated. Formation temperatures of the hydrothermal mineralization were estimated by mineral paragenesis, illite crystallinity and by oxygen isotope fractionations on coexisting mineral phases. the oxygen isotope fractionation between oxygen of different sites in several selected illites from both regions has been analysed. The results indicate a linear correlation between the illite-OH oxygen isotope fractionation and temperature. The fractionation can be expressed by the following equation:

In situ and laboratory treatment tests for lowering of excess manganese and iron in drinking water sourced from river–groundwater interaction

Manganese and iron are essential nutrients at low doses. However, long-term exposure in high doses may be harmful. Human activities and natural sources are responsible for manganese and iron contamination in water. This study aimed to investigate the source of high manganese and iron contents in shallow groundwater, where the groundwater is used for drinking purpose, and to decrease the excess manganese and iron from shallow groundwater. Based on the on-site analytical results taken from the wells in the study area, iron contents in water samples varied between 30 and 200 μg/L, which were under the allowable limits of Turkish Drinking Water Standards (TDWS) (Water intended for human consumption, http://rega.basbakanlik.gov.tr/eskiler/2005/02/20050217-3.htm, 2005). However, manganese levels varied from 30 to 248 μg/L, which some of them are higher than the allowable limits of TDWS (Water intended for human consumption, http://rega.basbakanlik.gov.tr/eskiler/2005/02/20050217-3.htm, 2005) (50 μg/L), and EPA (http://water.epa.gov/drink/contaminants/index.cfm, 2006) (50 μg/L). The source of excess manganese is originated mainly from geogenic source besides Porsuk River interaction in shallow aquifer in the specific section of the study area. To decrease high manganese content from the well water and reservoir water, laboratory and in situ treatment tests were applied. Among these tests, chlorination, associated with filtration (by fine sand, active carbon and zeolite) and the use of different filtration procedures by cation exchange resin were determined as the most effective methods, which was not previously applied on-site as a combinative approaches to reduce the excess manganese in water.     

Synthesis and stability of bastnaesites in a part of the system (Ce,La)-F-H-C-O

Summary Bastnaesites of Ce and La and their OH-analogs were synthesized and their stability relations were determined atPf = 1 kbar andT = 400 to 900°C in a part of the system (Ce,La)-F-H-C-0. The initial fluid compositions were such that and HF/(HF + H₂O) ratios were 0 to 0.172. XRD and IR studies indicate that bastnaesites equilibrated in initial fluids low in HF are all F-enriched. The hydroxylbastnaesite-(La) is stable up to 810°C and the fluorbastnaesite-(La) is stable up to 860°C. Their condensed breakdown products are La₂O₂CO₃ and LaOF, respectively. The stability of Ce bastnaesites is slightly dependent. The hydroxylbastnaesite-(Ce) is stable up to 660°C at the defined by the IQF buffer and up to 640°C by the MH buffer. The fluorbastnaesite-(Ce) is stable up to 800°C at the defined by the IQF and up to 760°C by the MH buffer. The condensed breakdown product for the hydroxyl end-member is simply CeO₂ but for the fluorine one is a combination of CeO₂, CeF₃, and CeOF. Factors, such as OH vs F, , and bulk composition, that affect the stability of individual species are discussed. Petrogenic implications resulting from the present study include that bastnaesites can be stable from hydrothermal to magmatic conditions, that F-enriched species can form in an environment relatively low in F content, and that OH-species are rare and occur only in low-temperature environments essentially devoid of F.

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Synthese und Stabilität von Bastndsil in einem Teil des Systems (Ce,La)-F-H-C-O

Zusammenfassung Ce- und La-Bastnäsite, sowie deren OH-Analoga wurden synthetisiert und ihre Stabilitätsbeziehunger beiP _f = 1 kbar undT = 400 bis 900°C wurden im System (Ce,La)F-H-C-O bestimmt. Die anfänglichen Flüssigkeitszusammensetzungen waren so, daß und die HF/(HF + H₂O)-Verhältnisse 0–0.172 waren. Röntgenpulver- und Ultrarot-Untersuchungen zeigten, daß Bastnäsite, die mit anfänglich HF-armen Flüssigkeiten equilibriert wurden, alle an F angereichert sind. Hydroxilbastndsit-(La) ist bis 810°C und Fluorbastnäsit-(La) bis 860°C stabil. Ihre festen Zersetzungsprodukte sind La₂O₂O₃, bzw. LaOF. Die Stabilität der Ce-Bastnäsite hängt etwas von ab. Hydroxilbastnäsit-(Ce) ist bei des Eisen-Quarz-Fayalit-Puffers bis 660°C stabil und mit Magnetit-Hämatit-Puffer bis 640°C. Das feste Zerfallsprodukt ist für das Hydroxil-Glied nur CeO₂, für das Fluor-Glied eine Mischung aus CeO₂, CeF₃ und CeOF. Faktoren, welche die Stabilität der einzelnen Spezies beeinflussen, werden diskutiert, wie das Verhältnis OH zu F, und die Gesamtzusammensetzung. Petrogenetische Folgerungen aus der vorliegenden Studie schließen ein, daß Bastnäsite von hydrothermalen bis zu magmatischen Bedingungen stabil sein können, daß sich an F angereicherte Glieder in relativ F-armer Umgebung bilden können, und daß OH-Glieder selten sind und nur unter Bildungsbedingungen niedriger Temperatur und weitgehender Abwesenheit von F auftreten.

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Stochastic methods for the prediction of strata behaviour

Summary A two-dimensional finite difference computer program, with the facility to represent stratified material by means of a mesh of mass points with different material properties in each square of the mesh, is adapted to run on a mesh whose material properties are selected stochastically from a specified distribution. The program uses an iterative method to solve the equations of equilibrium, giving estimates of displacements and stresses.Lattices of normally distributed (zero mean, unit variance) random values are produced: lattices of statistically independent values and lattices whose values are spatially correlated, to give the effect of gradual variations resulting in regions of positive values and regions of negative values.These lattices are used to generate the material properties: Young's modulus, Poisson's ratio and density. Each property has a specified mean and standard deviation for each material in the model, and the precise values for each mass point are calculated from the relevant lattices.A simple model with a square opening is used to investigate the effect of this stochastic generation of material properties, by comparison of stresses and displacements near the opening for runs of the program with (1) deterministic and (2) stochastic properties.Similar lattices of random values are used to introduce a stochastic element in the criterion for failure of materials. This is applied to a more realistic simulation of a mining situation, where Mohr's Criterion is used, with a stochastic component, to determine whether failure has occurred at each point of the mesh.     

Probable Endogenic Origin of Conglomerate-type Rocks on the Southeastern Coast of the White Sea

The southeastern coast of the White Sea and Kii Island incorporates outcrops of conglomerate-type rocks similar to boulder dikes filling tensile fractures in the early Precambrian basement of the platform. They are related to the southwestern flank of the Onega Graben representing the southeastern segment of the Onega–Kandalaksha paleorift. Genesis of these conglomerate-type rocks, previously considered sedimentary ones, is problematic. Special study of the cement of these rocks revealed that it has probably an endogenic nature. It is dominated by carbonate material replacing ultramafic volcanic glass. Carbonatization and analcime mineralization took place at the regressive stage of cement formation within a temperature range of 450–550°C with active release of H₂O- and CO₂-saturated fluids. Data on the isotopic composition (¹³C and ¹⁸O) for carbonate material of cement from the brecciated rocks testify that the carbonatization was related to input of deep-seated carbon dioxide under subsurface environment. The studies carried out allow us to suppose that these rocks were formed as a result of consolidation of solid–gaseous suspensions inside fractures in the crystalline basement. Penetration of fluidized material along them produced dike-shaped bodies. Such rocks are recently called fluidizates. The sources of solid–gaseous suspension fluxes were basic magmas with a high content of volatiles. Discharge of gases from the magmas was caused by their decompression due to the appearance of tensile zones in lithosphere during rifting.