俄罗斯东北部提高寒冻土壤稳定性与肥力的工程措施

The rational usage of low productive cryogenic landscapes in the North-Eastern part of Russia is impossible without carrying out special engineering preparation [1]. The preventing from negative that often has destructive cryogenic processes in the area of ice-covered permafrost soils, provided by its thawing into the marginally necessary depth in the whole area. The simplest and the most effective engineering method of faulting as an age-old stock (reserve) of surplus moisture in the form of ice from the upper parts of permafrost soils is the creation of continuous furrows net on the whole surface. This method also raises the fertility of soils, reduces acidity, and raises microbiological activity and the degree of internal structure decaying. Thermophysical calculations and the results of the field study in the experimental firing grounds are the available evidences of this method which raises the thermal stability of cryogenic landscapes while mastering of global climate changes in different parts of cryolithozone.     

Terrane analysis and accretion in North-East Asia

Abstract A terrane map of North-East Asia at 1:5 000 000 scale has been compiled. The map shows terranes of different types and ages accreted to the North-Asian craton in the Mesozoic–Cenozoic, sub-and superterranes, together with post-amalgamation and post-accretion assemblages. The great Kolyma-Omolon superterrane adjoins the north-east craton margin. It is composed of large angular terranes of continental affinity: craton fragments and fragments of the passive continental margin of Siberia, and island arc, oceanic and turbidite terranes that are unconformably overlain by shallow marine Middle-Upper Jurassic deposits. The superterrane resulted from a long subduction of the Paleo-Pacific oceanic crust beneath the Alazeya arc. Its south-west boundary is defined by the Late Jurassic Uyandina-Yasachnaya marginal volcanic arc which was brought about by subduction of the oceanic crust that separated the superterrane from Siberia. According to paleomagnetic evidence the width of the basin is estimated to be 1500–2000 km. Accretion of the superterrane to Siberia is dated to the late Late Jurassic-Neocomian. The north-east superterrane boundary is defined by the Lyakhov-South Anyui suture which extends across southern Chukotka up to Alaska. Collision of the superterrane with the Chukotka shelf terrane is dated to the middle of the Cretaceous. The Okhotsk-Chukotka belt, composed of Albian-Late Cretaceous undeformed continental volcan-ites, defines the Cretaceous margin of North Asia. Terranes eastward of the belt are mainly of oceanic affinity: island arc upon oceanic crust, accretion wedge and turbidite terranes, as well as cratonic terranes and fragments of magmatic arcs on the continental crust and metamorphic terranes of unclear origin and age. The time of their accretion is constrained by post-accretionary volcanic belts that extend parallel to the Okhotsk-Chukotka belt but are displaced to the east: the Maastrichtian-Miocene Kamchatka-Koryak belt and the Eocene-Quaternary Central Kamchatka belt which mark active margins of the continent of corresponding ages.     

Collision of the Kronotskiy arc at the NE Eurasia margin and structural evolution of the Kamchatka–Aleutian junction

Structural evolution of the Kamchatka–Aleutian junction area in late Mesozoic and Tertiary was generally controlled by (1) the processes of subduction in Kronotskiy and Proto-Kamchatka subduction zones and (2) collision of the Kronotskiy arc against NE Eurasia margin. Two structural zones of the pre-Pliocene age and six structural assemblages are recognized in studied region. 1: Eastern ranges zone comprises SE-vergent thrust folded belt, which evolved in accretionary and collisional setting. Two structural assemblages (ER1 and ER2), developed there, document shortening in the NW–SE direction and in the N–S direction, respectively. 2: Eastern Peninsulas zone generally corresponds to Kronotskiy arc terrane. Four structural assemblages are recognized in this zone. They characterize (1) precollisional deformations in the accretionary wedge (EP1) and in the fore-arc basin and volcanic belt (EP2), and (2) syn-collisional deformation of the entire Kronotskiy terrane in plunging folds (EP3) and deformations in the foreland basin (EP4). Analysis of paleomagnetic declinations versus present day structural strike in the Kronotskiy arc terrane shows that originally the arc was trending from west to east. Relative position of the accretionary wedge, fore-arc basin and volcanic belt, as well as northward dipping thrusts in accretionary wedge indicate, that a northward dipping subduction zone was located south of the arc. The accretionary wedge developed from the Late Cretaceous through the Eocene, and it implies that the subduction zone maintained its direction and position during this time. It implies that Kronotskiy arc was neither a part of the Pacific nor Kula plates and was located on an individual smaller plate, which included the arc and Vetlovka back-arc basin. Motion of the Kronotskiy arc towards Eurasia was connected only with NW-directed subduction at Kamchatka margin since Middle Eocene (42–44 Ma). Emplacement of the Kronotskiy arc at the Kamchatka margin occurred between Late Eocene and Early Miocene. This is based on the age of syn-collisional plunging folds in Kronotskiy terrane, and provenance data for the Upper Eocene to Middle Miocene Tyushevka basin, which indicate in situ evolution of the basin with respect to Kamchatka. Collision was controlled by the common motion of the Kronotskiy arc with Pacific plate towards the northwest, and by the motion of the Eurasian margin towards the south. The latter motion was responsible for the southward deflection of the western part of the Kronotskiy arc (EP3 structures), and for oblique transpressional structures in the collisional belt (ER2 structures).     

From an ocean floor wrench zone origin to transpressional tectonic emplacement of the Sithonia ophiolite,eastern Vardar Suture Zone,northern Greece

International Journal of Earth Sciences - In the Hellenides of northern Greece, the Sithonia back-arc ophiolite constitute an element of the Vardar suture zone against the Chortiatis island arc...     

Contents Volume 89

Volume Contents

Contents Volume 89     

On the determination of the effect of horizontal ionospheric gradients on ranging errors in GNSS positioning

An alternative approach to the traditionally employed method is proposed for treating the ionospheric range errors in transionospheric propagation such as for GNSS positioning or satellite-borne SAR. It enables the effects due to horizontal gradients of electron density (as well as vertical gradients) in the ionosphere to be explicitly accounted for. By contrast with many previous treatments, where the expansion of the solution for the phase advance is represented as the series in the inverse frequency powers and the main term of the expansion corresponds to the true line-of-sight distance from the transmitter to the receiver, in the alternative technique the zero-order term is the rigorous solution for a spherically layered ionosphere with any given vertical electron density profile. The first-order term represents the effects due to the horizontal gradients of the electron density of the ionosphere, and the second-order correction appears to be negligibly small for any reasonable parameters of the path of propagation and its geometry for VHF/UHF frequencies. Additionally, an “effective” spherically symmetric model of the ionosphere has been introduced, which accounts for the major contribution of the horizontal gradients of the ionosphere and provides very high accuracy in calculations of the phase advance.     

Petrology, geochemistry and geodynamic implications of Jurassic island arc magmatism as revealed by mafic volcanic rocks in the Mesozoic low-grade sequence, eastern Rhodope, Bulgaria

In the eastern Bulgarian Rhodope, mafic extrusive rocks and underlying greenschists are found in the Mesozoic low-grade unit, which represents the northern extension of similar sequences including the Evros ophiolites in Thrace (Greece). Both rock types define a suite of low-Ti tholeiitic basalts to transitional boninitic basaltic andesites and andesites and associated metapyroclastites (greenschists), intruded at its base by diorite dikes of a boninitic affinity. Mafic lavas and greenschists display large ion lithophile element (LILE) enrichment relative to high-field strength elements (HFSE), flat REE patterns of a slight light REE depletion, a strong island arc tholeiite (IAT) and weak MORB-like signature. All these rocks are characterized by negative Nb anomalies ascribed to arc lavas. They have positive Nd_i values in the range of + 4.87 to + 6.09, approaching the lower limit of MORB-like source, and relatively high (²⁰⁷Pb/²⁰⁴Pb)_i (15.57–15.663) at low (²⁰⁶Pb/²⁰⁴Pb)_i (18.13–18.54) ratios. The Nd isotopic compositions coupled with trace element data imply a dominantly depleted MORB-like mantle source and a contribution of subduction modified LILE-enriched component derived from the mantle wedge. The diorite dike has a low Nd_i value of − 2.61 and is slightly more Pb radiogenic (²⁰⁷Pb/²⁰⁴Pb)_i (15.64) and (²⁰⁶Pb/²⁰⁴Pb)_i (18.56), respectively, reflecting crustal contamination. Petrologic and geochemical data indicate that the greenschists and mafic extrusive rocks represent a magmatic assemblage formed in an island arc setting. The magmatic suite is interpreted as representing an island arc–accretionary complex related to the southward subduction of the Meliata–Maliac ocean under the supra-subduction back-arc Vardar ocean/island arc system. Magmatic activity appears to have initiated in the north during the inception of the island arc system by the Early–Middle Jurassic time in the eastern Rhodope that most likely graded to back-arc spreading southwards as represented by the Late Jurassic MORB-type Samothraki Island ophiolites. This tectonic scenario is further constrained by paleotectonic reconstructions. The arc–trench system collided with the Rhodope in the Late Jurassic times.     

A GIS-based modeling of snow accumulation and melt processes in the Votkinsk reservoir basin

Coupled hydrological and atmospheric modeling is an efficient method for snowmelt runoff forecast in large basins. We use short-range precipitation forecasts of mesoscale atmospheric Weather Research and Forecasting (WRF) model combining them with ground-based and satellite observations for modeling snow accumulation and snowmelt processes in the Votkinsk reservoir basin (184,319 km²). The method is tested during three winter seasons (2012–2015). The MODIS-based vegetation map and leaf area index data are used to calculate the snowmelt intensity and snow evaporation in the studied basin. The GIS-based snow accumulation and snowmelt modeling provides a reliable and highly detailed spatial distribution for snow water equivalent (SWE) and snow-covered areas (SCA). The modelling results are validated by comparing actual and estimated SWE and SCA data. The actual SCA results are derived from MODIS satellite data. The algorithm for assessing the SCA by MODIS data (ATBD-MOD 10) has been adapted to a forest zone. In general, the proposed method provides satisfactory results for maximum SWE calculations. The calculation accuracy is slightly degraded during snowmelt periods. The SCA data is simulated with a higher reliability than the SWE data. The differences between the simulated and actual SWE may be explained by the overestimation of the WRF-simulated total precipitation and the unrepresentativeness of the SWE measurements (snow survey).     

Sedimentation patterns in the Selenga River delta under changing hydroclimatic conditions

The Selenga River delta (Russia) is a large (>600 km²) fluvially dominated fresh water system that transfers water and sediment from an undammed drainage basin into Lake Baikal, a United Nations Educational, Scientific, and Cultural Organization World Heritage Site. Through sedimentation processes, the delta and its wetlands provide important environmental services, such as storage of sediment‐bound pollutants (e.g., metals), thereby reducing their input to Lake Baikal. However, in the Selenga River delta and many other deltas of the world, there is a lack of knowledge regarding impacts of potential shifts in the flow regime (e.g., due to climate change and other anthropogenic impacts) on sedimentation processes, including sediment exchanges between deltaic channels and adjacent wetlands. This study uses field measurements of water velocities and sediment characteristics in the Selenga River delta, investigating conditions of moderate discharge, which have become more frequent over the past decades (at the expense of peak flows, Q > 1,350 m³ s^?1). The aims are to determine if the river system under moderate flow conditions is capable of supporting sediment export from the main distributary channels of the delta to the adjacent wetlands. The results show that most of the deposited sediment outside of the deltaic channels is characterized by a large proportion of silt and clay material (i.e., <63 μm). For example, floodplain lakes function as sinks of very fine sediment (e.g., 97% of sediment by weight < 63 μm). Additionally, bed material sediment is found to be transported outside of the channel margins during conditions of moderate and high water discharge conditions (Q ≥ 1,000 m³ s^?1). Submerged banks and marshlands located in the backwater zone of the delta accumulate sediment during such discharges, supporting wetland development. Thus, these regions likely sequester various metals bound to Selenga River sediment.     

Semiparametric regression models for spatial prediction and uncertainty quantification of soil attributes

In many studies, the distribution of soil attributes depends on both spatial location and environmental factors, and prediction and process identification are performed using existing methods such as kriging. However, it is often too restrictive to model soil attributes as dependent on a known, parametric function of environmental factors, which kriging typically assumes. This paper investigates a semiparametric approach for identifying and modeling the nonlinear relationships of spatially dependent soil constituent levels with environmental variables and obtaining point and interval predictions over a spatial region. Frequentist and Bayesian versions of the proposed method are applied to measured soil nitrogen levels throughout Florida, USA and are compared to competing models, including frequentist and Bayesian kriging, based an array of point and interval measures of out-of-sample forecast quality. The semiparametric models outperformed competing models in all cases. Bayesian semiparametric models yielded the best predictive results and provided empirical coverage probability nearly equal to nominal.