Geochemistry of ultrahigh-pressure anatexis: fractionation of elements in the Kokchetav gneisses during melting at diamond-facies conditions

The Kokchetav complex in Kazakhstan contains garnet-bearing gneisses that formed by partial melting of metasedimentary rocks at ultrahigh-pressure (UHP) conditions. Partial melting and melt extraction from these rocks is documented by a decrease in K₂O and an increase in FeO + MgO in the restites. The most characteristic trace element feature of the Kokchetav UHP restites is a strong depletion in light rare earth elements (LREE), Th and U. This is attributed to complete dissolution of monazite/allanite in the melt and variable degree of melt extraction. In contrast, Zr concentrations remain approximately constant in all gneisses. Using experimentally determined solubilities of LREE and Zr in high-pressure melts, these data constrain the temperature of melting to ~1,000 °C. Large ion lithophile elements (LILE) are only moderately depleted in the samples that have the lowest U, Th and LREE contents, indicating that phengite retains some LILE in the residue. Some restites display an increase in Nb/Ta with respect to the protolith. This further suggests the presence of phengite, which, in contrast to rutile, preferentially incorporates Nb over Ta. The trace element fractionation observed during UHP anatexis in the Kokchetav gneisses is significantly different from depletions reported in low-pressure restites, where generally no LREE and Th depletion occurs. Melting at UHP conditions resulted in an increase in the Sm/Nd ratio and a decoupling of the Sm–Nd and Lu–Hf systems in the restite. Further subduction of such restites and mixing with mantle rocks might thus lead to a distinct isotopic reservoir different from the bulk continental crust.     

Moderately compact helix antennas with cutoff patterns for millimeter RTK positioning

GPS Solutions - Helical antennas have been developed that feature a cutoff pattern and are suitable for practical positioning at millimeter level. The antennas are in the form of a tube with...     

Influence of frost weathering on the recession of surfaces of technogenic landforms in Yakutia

The article assesses the influence of permafrost weathering on the rate of destruction of technogenic land forms, as exhibited on as illustrated by the railway embankment of the Amur-Yakut mainline in the Sakha Republic(Yakutia). Studies were carried out on a railway section more than 375 km long. The subsidence rate of the embankment slopes and structural excavations was determined using laboratory methods that simulate various mechanisms of temperature(with a transition through 0 ℃) impact on rocks. For the first time, a quantitative assessment of the influence of cryogenic weathering on the stability of the railway in the region belonging to the northern building-climatic zone is given. For the territory under consideration, embankment rocks were experimentally determined to undergo more than 100 freezing and thawing cycles during a year. Under the existing climatic conditions, cryogenic weathering actively affects the embankment of the railway to a depth of 30 cm. Most of the embankment deformations detected during field observations are due to defects in the integrity of this particular layer. The size of the disintegrating layer of particular types of rock comprising the railway embankment has been established as reaching 10 cm per year. In 5 years following the formation of embankments comprising the upper structure of the railroad tracks, the physical and mechanical properties of rocks, which initially had a tensile strength for uniaxial compression in the range of 40-70 MPa, were reduced by more than 50%. According to the authors, the establishment of regional cryohypergenesis features is universal in nature and can be applied to solving a wide range of tasks related to the assessment and prediction of the degree of cryogenic transformation of rocks having different structural properties.     

基于冻融次数-物理时间比拟理论的冻土长期强度预测方法

冻融作用可以改变土的结构,引起其力学特征的变化,从而影响到冻土工程的稳定性。由于冻融周期的设定不尽相同,因此大量的试验结果不能有效地进行对比分析。另外,对于冻融作用下土体力学特征的预测也成为研究的难点。在冻土遗传蠕变理论的基础上,利用球型模板压入仪作为测试方法,提出了一种冻融次数-物理时间比拟的方法。把冻融周期(次数)转化成物理时间(min),将不同冻融周期土的长期强度曲线簇映射到同一坐标中,利用该归一化曲线进行长期抗剪强度的预测,并选取了两种土样进行了测试,分别得到了相关的长期抗剪强度的预测方程。该方法对冻融作用下土体力学行为的成果对比研究以及长期强度的预测有重要的理论意义,对寒区工程稳定性预测分析也具有工程实践价值。     

A two‐phase automatic static correction method

Statics are an effective approach to correct for complex velocity variations in the near surface, but so far, to a large extent, a general and robust automatic static correction method is still lacking. In this paper, we propose a novel two‐phase automatic static correction method, which is capable of handling both primary wave statics (PP statics) and converted‐wave statics (S‐wave statics). Our method is purely data driven, and it aims at maximizing stacking power in the target zone of the stack image. Low‐frequency components of the data are analysed first using an advanced genetic algorithm to estimate seed statics and the time structure for an event of interest, and then the original full‐band data are further aligned via the back‐and‐forth coordinate descent method using the seed statics as initial values and the time structure for event alignment guidance. We apply our new method to two field datasets, i.e., one for 2D PP static correction and the other for 3D S‐wave static correction.     

Modification of Two-Equation Models to Account for Plant Drag

A modification of the most popular two-equation (E–φ) models, taking into account the plant drag, is proposed. Here E is the turbulent kinetic energy (TKE) and φ is any of the following variables: El (product of E and the mixing length l), (dissipation rate of TKE), and ω (specific dissipation of TKE, ). The proposed modification is due to the fact that the model constants estimated experimentally for ‘free-air’ flow do not allow for adequate reconstruction of the ratio between the production and dissipation rates of TKE in the vegetation canopy and have to be adjusted. The modification is universal, i.e. of the same type for all E–φ models considered. The numerical experiments carried out for both homogeneous and heterogeneous plant canopies with E–φ models (and with the E–l model taken as a kind of reference) show that the modification performs well. They also suggest that E– and E–ω schemes are more promising than the E–El scheme for canopy flow simulation since they are not limited by the need to use a wall function.In addition, a new parameterization for enhanced dissipation within the plant canopy is derived. It minimizes the model sensitivity to C _μ, the key parameter for two-equation schemes, and whose estimates unfortunately vary considerably from experiment to experiment. The comparison of results of new modified E– and E –ω models with observations from both field and wind-tunnel experiments shows that the proposed parameterization is quite robust. However, because of uncertainties with the turbulence Prandtl and Schmidt numbers for the E– model within the canopy, the E–ω model is recommended for future implementation, with the suggested modifications.     

Nickel Isotope Variations in Terrestrial Silicate Rocks and Geological Reference Materials Measured by MC‐ICP‐MS

Although initial studies have demonstrated the applicability of Ni isotopes for cosmochemistry and as a potential biosignature, the Ni isotope composition of terrestrial igneous and sedimentary rocks, and ore deposits remains poorly known. Our contribution is fourfold: (a) to detail an analytical procedure for Ni isotope determination, (b) to determine the Ni isotope composition of various geological reference materials, (c) to assess the isotope composition of the Bulk Silicate Earth relative to the Ni isotope reference material NIST SRM 986 and (d) to report the range of mass‐dependent Ni isotope fractionations in magmatic rocks and ore deposits. After purification through a two‐stage chromatography procedure, Ni isotope ratios were measured by MC‐ICP‐MS and were corrected for instrumental mass bias using a double‐spike correction method. Measurement precision (two standard error of the mean) was between 0.02 and 0.04‰, and intermediate measurement precision for NIST SRM 986 was 0.05‰ (2s). Igneous‐ and mantle‐derived rocks displayed a restricted range of δ^60/58Ni values between ?0.13 and +0.16‰, suggesting an average BSE composition of +0.05‰. Manganese nodules (Nod A1; P1), shale (SDO‐1), coal (CLB‐1) and a metal‐contaminated soil (NIST SRM 2711) showed positive values ranging between +0.14 and +1.06‰, whereas komatiite‐hosted Ni‐rich sulfides varied from ?0.10 to ?1.03‰.     

Physical mechanisms of submesoscale eddies generation: evidences from laboratory modeling and satellite data in the Black Sea

Ocean Dynamics - The observed evidence of the implementation of three different mechanisms of the submesoscale eddies generation in the Black Sea previously studied by the field research and...     

Air–Sea/Land Interaction in the Coastal Zone

Atmospheric turbulence measurements made at the U.S. Army Corps of Engineers Field Research Facility (FRF) located on the Atlantic coast near the town of Duck, North Carolina during the CASPER-East Program (October–November 2015) are used to study air–sea/land coupling in the FRF coastal zone. Turbulence and mean meteorological data were collected at multiple levels (up to four) on three towers deployed at different landward distances from the shoreline, with a fourth tower located at the end of a 560-m-long FRF pier. The data enable comparison of turbulent fluxes and other statistics, as well as investigations of surface-layer scaling for different footprints, including relatively smooth sea-surface conditions and aerodynamically rough dry inland areas. Both stable and unstable stratifications were observed. The drag coefficient and diurnal variation of the sensible heat flux are found to be indicators for disparate surface footprints. The drag coefficient over the land footprint is significantly greater, by as much as an order of magnitude, compared with that over the smooth sea-surface footprint. For onshore flow, the internal boundary layer in the coastal zone was either stable or (mostly) unstable, and varied dramatically at the land-surface discontinuity. The offshore flow of generally warm air over the cooler sea surface produced a stable internal boundary layer over the ocean surface downstream from the coast. While the coastal inhomogeneities violate the assumptions underlying Monin–Obukhov similarity theory (MOST), any deviations from MOST are less profound for the scaled standard deviations and the dissipation rate over both water and land, as well as for stable and unstable conditions. Observations, however, show a poor correspondence with MOST for the flux-profile relationships. Suitably-averaged, non-dimensional profiles of wind speed and temperature vary significantly among the different flux towers and observation levels, with high data scatter. Overall, the statistical dependence of the vertical gradients of scaled wind speed and temperature on the Monin–Obukhov stability parameter in the coastal area is weak, if not non-existent.