Magnetic structure of polluted soil profiles from Eastern Ukraine

Our study concerned magnetic properties of soil profiles taken from polluted regions of Eastern Ukraine around the industrial centres Krivyj Rig, Mariupol and Komsomolsk. Soils represent chernozem and podzoluvisol. The low-field magnetic susceptibility shows enhancement in the topsoil caused by contamination by coarse-grain magnetite connected with industrial pollution. Magnetic mineralogy was determined by means of thermal demagnetisation of SIRM, monitoring of susceptibility changes during warming from ?196°C to room temperature and heating to 700°C, and Mössbauer analysis. Granulometry of magnetic particles was investigated by determination of hysteresis parameters, susceptibility, M _s , SIRM and ARM ratios and frequency dependence of susceptibility. The chemical parameters, namely pH, organic carbon and iron content in different pedogenic and lithogenic minerals, measured for particular horizons determined pedogenic characteristic of soil profiles. Our study showed that differences in magnetic parameters of non-polluted and polluted soil profiles are not limited to the topsoil, but reach deep layers of the parent material. Industrial pollution promotes formation of the so-called “pedogenic” SP and SD particles in these layers.     

Seasonality and anomalies of sea surface temperature off the coast of Nayarit, Mexico

Sea surface temperature (SST) harmonic and empirical orthogonal function (EOF) analyses covering 18 years were performed for the area located from 114° to 105° W and from 18° to 25° N. The results indicate that the influence of the annual signal predominates over the semi-annual signal, and the closer to the coast, the stronger the annual harmonic. Several interannual anomalies arose that are connected with the main global indexes, especially the Oceanic Niño Index. Pearson correlations between the first temporal mode of the SST and regional rainfalls in Nayarit indicate that maximum correlations (r?>?0.7) are observed when there is a +1-month lag between the series. However, this result indicates that SST is delayed with 1 month after rainfall occurrence, which shows that the dominant influence in this relationship is not the SST forcing.     

Precambrian microcontinents of the Ural-Mongolian Belt: New paleomagnetic and geochronological data

The knowledge on the early stages of evolution of the Ural-Mongolian Belt (UMB) (Late Neoproterozoic-Cambrian) is a key for understanding of its evolution in the Paleozoic. Unfortunately, this stage remains poorly studied. The tectonic reconstructions of the UMB for this time primarily depend on the views on the kinematics and tectonic evolution of numerous sialic massifs with Precambrian basement in the structure of the Tien Shan, Kazakhstan, Altai, and Mongolia. At present, the concept of the origin of these massifs is largely based on the lithostratigraphic similarity of the Neoproterozoic and Lower Paleozoic sections of the Tarim, South China, and Siberian platforms with coeval sections of Precambrian massifs within the UMB. New paleomagnetic and geochronological data can serve as additional sources of information on the origin and paleotectonic position of the microcontinents. In this paper, we present new isotopic datings and a new paleomagnetic determination for the Neoproterozoic volcanic rocks of the Zabhan Formation from the Baydrag microcontinent in central Mongolia. It is established that 805−770 Ma ago (U-Pb LA-MC-ICP-MS age of zircon) the Baydrag microcontinent was situated at a latitude of 47 ± 14° in the Northern or Southern hemisphere. These data provide new insights into the possible origin of the Precambrian micro-continents in the UMB. Analysis of paleomagnetic data and comparison of the age of the basement beneath various plates allow us to state rather confidently that ∼800 Ma ago the micro-continents of the UMB belonged to one of the North Rodinian plates: Indian, Tarim, or South China; their Australian origin is less probable.     

On the Stability of Planar Oscillations and Rotations of a Satellite in a Circular Orbit

We deal with the stability problem of planar periodic motions of a satellite about its center of mass. The satellite is regarded a dynamically symmetric rigid body whose center of mass moves in a circular orbit.By using the method of normal forms and KAM theory we study the orbital stability of planar oscillations and rotations of the satellite in detail. In two special cases we investigate the orbital stability analytically by introducing a small parameter. In the general case, numerical calculations of Hamiltonian normal form are necessary.     

Inclusions of Cr- and Cr–Nb-Rutile in pyropes from the Internatsionalnaya kimberlite pipe,Yakutia

The results of study of rutile inclusions in pyrope from the Internatsionalnaya kimberlite pipe are presented. Rutile is characterized by unusually high contents of impurities (up to 25 wt %). The presence of Cr₂O₃ (up to 9.75 wt %) and Nb₂O₅ (up to 15.57 wt %) are most typical. Rutile inclusions often occur in assemblage with Ti-rich oxides: picroilmenite and crichtonite group minerals. The Cr-pyropes with inclusions of rutile, picroilmenite, and crichtonite group minerals were formed in the lithospheric mantle beneath the Mirnyi field during their joint crystallization from melts enriched in Fe, Ti, and other incompatible elements as a result of metasomatic enrichment of the depleted lithospheric mantle.     

Inclusions of crichtonite group minerals in pyropes from the Internatsionalnaya kimberlite pipe,Yakutia

The results of study of crichtonite group minerals in pyropes from the Internatsionalnaya kimberlite pipe are reported. Most of the studied samples are characterized by high concentrations of Sr, Ca, Na, and LREEs in comparison with minerals of the LIMA series from kimberlites of South Africa, whereas the average concentrations of Ba and K are significantly lower. Crichtonite group minerals in pyropes are characterized by predomination of Na over K in most samples and by a high concentration of Al₂O₃ (up to 4.5 wt %). Findings of inclusions of crichtonite group minerals with high concentrations of incompatible elements provide evidence for the metasomatic origin of host chromium-rich pyropes.     

Evidence for Multistage and Polychronous Alkaline–Ultrabasic Mesozoic Magmatism in the Area of Diamondiferous Placers of the Ebelyakh River Basin (Eastern Slope of the Anabar Shield)

Doklady Earth Sciences - New mineralogical and isotope–geochemical data for zircon megacrysts (n = 48) from alluvium of Kholomolokh Creek (a tributary of the Ebelakh River) are reported....     

Magnetic and nuclear structure and thermal expansion of orthorhombic and monoclinic polymorphs of CoGeO3 pyroxene

CoGeO₃ was synthesized at 1,273 and 1,448 K using ceramic sintering techniques in the monoclinic and orthorhombic modification, respectively. The two compounds were analysed by magnetic susceptibility measurements and neutron diffraction in order to study magnetic ordering and spin structures at low temperature. The monoclinic form of CoGeO₃ has C2/c symmetry and orders magnetically below 36 K with a small negative paramagnetic Curie temperature θ _P = −4.6 (2) K. The magnetic structure can be described with k = (1, 0, 0) in the magnetic space group C2′/c′ having a ferromagnetic spin arrangement within the chains of M1 sites, but a dominating antiferromagnetic coupling between the chains. At the M1 sites the magnetic spins are aligned within the a–c plane forming an angle of 120° with the +a-axis and they are not parallel to the spins at M2. Here spins are also ferromagnetically coupled within, but antiferromagnetically coupled between the M1/M2 site bands. The orthorhombic phase of CoGeO₃ displays Pbca symmetry and transforms to an antiferromagnetically ordered state [θ _P = −18.6(2) K] below 33 K. The magnetic spin structure can be described with k = (0, 0, 0) in space group Pbca′ and it is similar to the one of the C2/c phase except that it is non-collinear in nature, i.e. there are components of the magnetic moment along all three crystallographic axes. Small magneto-elastic coupling is observed in the orthorhombic phase.     

A note on the effects of an individual large rainfall event on saline Lake Alchichica, Mexico

The present study reports on perturbations of the water column by large rainfall at Lake Alchichica, a saline lake in Central Mexico. Alchichica is located in the “Llanos de San Juan,” a high-altitude plateau with a minimum elevation of 2,300 m above sea level. The climate is arid with annual precipitation less than 400 mm and annual evaporation of 500–600 mm. A single day large rainfall event delivered 1,810,000 m³ of water to the basin, raising the lake’s water level by about 1 m. Temperature and salinity profiles showed an atypical temperature inversion up to 1°C in the upper layer accompanied by salinity decrease up to 0.5 g l⁻¹. Transparency and pH were slightly altered, but dissolved oxygen, nutrients and chlorophyll a concentrations were not changed. In spite of the heavy rainfall and associated wind, the effects of the event were limited to the upper half of the epilimnion. After 2 days, the lake water level returned to its original level. The rapid leakage of the runoff minimized any long-term effects of the large rainfall.