Перша конференція архівів слов’янських країн

7–10 жовтня 2010 р. у Словенії, у туристичному центрі Ліпіца, що на кордоні з Італією, в готелі “Маестозо” відбулася Перша конференція архівів слов’янських країн

Selective dissolution of magnetic iron oxides in the acid-ammonium oxalate/ferrous iron extraction method-I. Synthetic samples

In soil magnetism, the magnetic parameters alone are not always sufficient to distinguish the lithogenic from the pedogenic magnetic fractions. Sequential extraction techniques have therefore been incorporated into magnetic studies to constrain the environmental interpretation. Here we report on the dissolution behaviour of magnetite and maghemite in the acid-ammonium oxalate method to see whether the method is suitable for specific dissolution of magnetic minerals from soils and sediments. To prevent changes in the extraction mechanism during the experiments (see Appendix A), we used an adapted version of the acid-ammonium oxalate (AAO) method, in which Fe2+ is added to the extraction solution prior to the experiment [the AAO-Fe(II) method]. The procedure was divided into several 30 min extraction steps to check the dissolution progress. Synthetic samples containing a quartz matrix with 0.1 wt per cent of iron oxides were extracted with the AAO-Fe(II) method. The iron oxides consisted of either magnetite or maghemite with grain sizes of <0.5 mm (fine grained or SD/PSD) and <5 mm (coarse grained or MD/PSD), or a 1 : 1 mixture of both minerals. Because only magnetite and maghemite were studied, the changes in magnetic characteristics could be monitored after each extraction step by analysis of the bulk susceptibility and hysteresis parameters measured at room temperature. The AAO-Fe(II) method preferentially dissolved the smaller iron oxides from the samples. For samples containing iron oxides with coarse grain size there is a preference for dissolving maghemite rather than magnetite. Extractions of the samples containing mixtures of two different grain sizes or with different mineralogy show that the method preferentially dissolves the smaller grains before attacking the coarse grains in the sample

Discharge of hydrothermal fluids through sediment at the Escanaba Trough, Gorda Ridge (ODP Leg 169): assessing the effects on the rock magnetic signal

An integrated rock-magnetic and multivariate statistical analysis of a suite of sediment samples recovered from ODP Sites 1037 and 1038 (Leg 169, Escanaba Trough, Gorda Ridge spreading center, NE Pacific Ocean) has been carried out to assess the use of the sediment magnetic signal as a tracer of post-depositional alteration related to the discharge of hydrothermal fluids through these sediments. The uppermost (above 40 mbsf) section of three separate holes (Holes 1037 B, 1038 I and 1038 G) was sampled; previous sedimentological and geochemical studies indicated that these holes represent a transect from unaltered to strongly hydrothermally influenced sediments. Analysis of NRM, ARM, anisotropy of magnetic susceptibility (AMS), hysteresis parameters and low-temperature magnetic properties suggest increasing alteration of the magnetic minerals with increasing circulation of hydrothermal circulation of fluids. Fuzzy c-means clustering combined with non-linear mapping yields a more elaborate picture because similar alteration groupings at different holes can be compared. At Hole 1037 B, a sedimentary reference site drilled away from the area of high heat flow, the rock-magnetic signal is a sensitive record of changes in detrital inputs. Magnetite and some monoclinic pyrrhotite are detected. The detrital magnetic signal is still apparent at intermediate Hole 1038 I, but cluster analysis detects an increasing hydrothermal influence on the magnetomineralogy in the lower part of the hole. Strong hydrothermal alteration at Hole 1038 G results in a complete loss of the detrital/diagenetic magnetic signal, which is replaced by a much weaker `hydrothermal' signal composed of monoclinic pyrrhotite and pyrite. The alteration of the magnetic signal is not restricted to the uppermost few meters of the sediment column and the magnetic properties of the sediment can be used to trace even minor alterations of marine sediments related to the lateral and vertical advection of hydrothermal fluids which may easily be overlooked by more traditional methods

Quantication of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation

A new method of analysing isothermal remanent magnetisation (IRM) acquisition curves based on cumulative log Gaussian analysis [Robertson and France, Phys. Earth Planet. Inter. 82 (1994) 223-234] is proposed. It is based on the curve fitting of the IRM acquisition curve versus the logarithm of the applied field with: (i) the acquisition curve on a linear scale, (ii) the acquisition curve expressed as a gradient, and (iii) the acquisition curve on a probability scale. Even when a sample is not saturated, its magnetic properties can be defined, although with less certainty. The number of magnetic components required for an optimal fit to a measured IRM acquisition curve is evaluated statistically. The method discriminates on the basis of different mineral coercivity. Therefore, additional rock-magnetic tests are still required to separate minerals with similar coercivities

Magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern Mediterranean Sea

Magnetic properties (IRM, ARM, xin, S-ratio at 0.3 T, room temperature (RT) hysteresis and thermomagnetic curves) and geochemical data (Fe, S, Mn, Al, Ti, organic C) were studied in two eastern Mediterranean boxcores (ABC26 and BC19) at a resolution of 3-5 mm. The boxcores contain sapropel S1 (9-6 kyr BP) at a few decimetres below seafloor. The magnetic fraction consists predominantly of single-domain (SD) to pseudo-singledomain (PSD) magnetite in the entire cores. The original input of magnetic grains comes from two sources: aeolian dust (both cores) and volcanic ash from the Minoan eruption of Santorini (core BC19 only). Non-steady-state diagenesis has changed the magnetic mineralogy considerably in these alternating organic-rich/organic-poor sediments. During deposition of sapropel S1, reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities, coarser magnetic grain sizes and partial maghemitization. In thermomagnetic curves two types of pyrite can be identified: one oxidizes below 450 uC and the other above 450 uC. The higher oxidation temperature is predominantly found below the sapropel. This may be related to the microtexture of pyrite, which is euhedral below sapropels and mainly framboidal within sapropels. Since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half (c. 5 cm) of the sapropel. The oxidized part of the sapropel is enriched in diagenetically formed Fe oxides with relatively high coercivity and ARM. The maximum coercivity is found in a distinct layer between the present-day Mn- and Fe-redox boundaries at the top of the unoxidized sapropel. The freshly precipitated Fe oxides in this centimetre-thick layer contain a mixture of superparamagnetic (SP) grains and high-coercivity SD magnetite. Higher in the oxidized zone the freshly precipitated Fe oxides have aged into generally slightly lower-coercivity SD grains, with relatively high ARM. In addition to the diagenetic formation of Fe oxides at the top of the sapropel, formation of a ferrimagnetic Fe monosulphide may have occurred within the sapropel during later stages of diagenesis, which may have enhanced the ARM signal in the organic-rich interval in particular

Magnetic properties of hydrothermally synthesized greigite (Fe3S4)- II. High- and low-temperature characteristics

The magnetic behaviour of hydrothermally synthesized greigite was analysed in the temperature range from 4 K to 700 °C. Below room temperature, hysteresis parameters were determined as a function of temperature, with emphasis on the temperature range below 50 K. Saturation magnetization and initial susceptibility were studied above room temperature, along with X-ray diVraction analysis of material heated to various temperatures. The magnetic behaviour of synthetic greigite on heating is determined by chemical alteration rather than by magnetic unblocking. Heating in air yields more discriminative behaviour than heating in argon. When heated in air, the amount of oxygen available for reaction with greigite determines the products and magnetic behaviour. In systems open to contact with air, haematite is the final reaction product. When the contact with air is restricted, magnetite is the final reaction product. When air is excluded, pyrrhotite and magnetite are the final reaction products; the amount of magnetite formed is determined by the purity of the starting greigite and the degree of its surficial oxidation. The saturation magnetization of synthetic greigite is virtually independent of temperature from room temperature down to 4 K. The saturation remanent magnetization increases slowly by 20-30 per cent on cooling from room temperature to 4 K. A broad maximum is observed at ~10 K which may be diagnostic of greigite. The coercive and remanent coercive force both increase smoothly with decreasing temperature to 4 K. The coercive force increases from ~50 mT at room temperature to approximately 100-120 mT at 4 K, and the remanent coercive force increases from approximately 50-80 mT at room temperature to approximately 110-180 mT at 4 K

Low-temperature behaviour of haematite: susceptibility and magnetization increase on cycling through the Morin transition

It has been realized previously (e.g. Borradaile 1994) that cycling through the Morin transition (Tm, occurring in ideal a-Fe2O3 at -10 °C) may have implications for the NRM of some haematite-bearing rocks. We investigate the behaviour of the low-field susceptibility (xlf), several magnetizations (in fields of 5, 25, 100 and 1600 mT) and SIRM on cycling through Tm of several well-characterized haematite types of varying crystallinity and particle shape. Before low-temperature treatment, xlf of the haematites varied between ~40 and ~235*10^(-8) m^3 kg^(-1). Below Tm, where only haematite's defect moment resides, xlf was much more uniform at ~19 to ~28*10^(-8) m^3 kg^(-1). After return to room temperature, increases in xlf of up to ~50 per cent were observed (when cycling in the Earth's magnetic field as well as in a field-free space), inferred to be a function of the domain state of the haematite. This was shown for one of the haematites (LH2 which occurs as small platelets and is particularly well crystalline) where a relation y=(8.60±1.01) ln(x)-2.98 was obtained, where x is the grain size (mm) and y is the percentage susceptibility increase.We suggest that transdomain changes induce the change in xlf. The nucleation of (additional) domain walls in metastable single-domain (SD) to pseudo-single-domain (PSD) grains is made possible by the low anisotropy at the Morin transition. In view of this mechanism, small stable SD haematite particles would not be affected and the grain size corresponding to y=0 (~1.5 mm for LH2) would represent the real SD threshold size. Thermal cycling to over the Curie temperature (680 °C) is needed to return to the original domain state before the LT treatment, as expressed by a return to the original xlf values. Measuring xlf between alternating field (AF) demagnetization steps shows that AF demagnetization gradually removes the xlf increase, which appears to be soft; 30 mT is sufficient to erase 90 per cent. Thermal cycling in a 5 mT field between temperatures above Tm showed that irreversible changes in domain structure are noticeable before the isotropic point is passed. After cycling, magnetization is added to PSD and multidomain (MD) grains that intriguingly appears to be remanence, probably induced by the broadening and subsequent irreversible displacement of loosely pinned domain walls. Complete cycling through the isotropic point considerably enhances the new remanence component in metastable SD to MD particles by an increase in the number of domains. If this behaviour can be extrapolated to the intensity of the Earths magnetic field, this would imply that large metastable SD to MD specularite crystals with a well-developed Morin transition are susceptible to acquiring geologically irrelevant remanence components when subjected to low ambient temperatures. Fine-grained haematite pigment, on the other hand, would not be affected. Thermal demagnetization alone would not be able to separate these two remanences as the new domain structure persists up to close to the Curie temperature. Our findings indicate that a cleaning procedure consisting of an initial AF step followed by stepwise thermal demagnetization is preferable in order to isolate the original remanence component properly in haematite-bearing rocks

Rock-magnetic properties of TRM carrying baked and molten rocks straddling burnt coal seams

The subsurface spontaneous combustion of coal seams in Xinjiang (NW China) during Pleistocene to recent times produced large areas of thermally altered sedimentary rocks with large magnetic moments. The natural remanent magnetization (NRM) and thermoremanent magnetization (TRM) intensities and low-field susceptibilities of such combustion-metamorphic rocks range from 0.1 to 10 A/m and 100 × 10^(-4) to 1000 × 10^(-4) SI, respectively, which is two to three orders of magnitude higher than values typical of their sedimentary protoliths. The dominant magnetic carriers in the burnt rocks appear to include relatively pure forms of magnetite, maghemite and hematite as well as more complex spinel phases. These magnetic phases mainly occur as fine pseudo-single-domain (PSD) particles. Conspicuous is the presence of pure metallic iron (aFe) in some samples. This highly magnetic phase is inferred to appear as more or less elongated super paramagnetic and single-domain (SD) inclusions in host silicate phases, which prevent them from oxidizing. The SD aFe particles can carry a highly stable remanence, having remanent coercivities ranging 70-140mT. The ARM and IRM stability of all burnt rock samples to alternating fields is shown to be relatively high; median destructive fields, B(1/2)A and B(1/2)I, respectively, range of 25-46 and ~20-30mT for dominant spinel-bearing samples, 34-36 and 47-53mT for maghemite-hematite-bearing samples, and 48-89 and 64-84mT for metallic iron-bearing samples. Consequently, burnt rocks are high-quality geomagnetic field recorders. Their very nature makes them useful for paleointensity determinations, although age determination is a limiting factor. Furthermore, remanence intensities and susceptibilities of these magnetically enhanced rocks are sufficient to produce observable magnetic anomalies. This property illustrates the potential to delineate the areal extent and depth of (extinct) coal fires with magnetic exploration. Such information is necessary to refine estimates of hazardous CO2 emission and furthers our understanding of natural coal fires

Комунікативно-маніпулятивні чинники політичної мотивації

Аналізуються основні комунікативно-маніпулятивні чинники політичної мотивації, які визначили формування відповідних електоральних теорій. Зокрема, увагу приділено метафоричним моделям, політико-комунікативній теорії, теорії мотивованого політичного мислення, технологічним (маркетинговим) теоріям та ін.Анализируются основные коммуникативно-манипулятивные факторы политичес­кой мотивации, которые определили формирование соответствующих электоральных теорий. В частности, внимание уделено метафорическим моделям, политико-коммуникативной теории, теории мотивированного политического мышления, технологиче­ским (маркетинговым) теориям и др.The article analyzes the basic communicative, manipulative political motivation factors that have determined the formation of the electoral theories. In particular, attention is given to metaphorical models, political and communication theory, the theory of reasoned political thought, technological (marketing) theories, etc

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