Numerical viscoelastic modelling by the spectral Laguerre method

Seismic wave propagation in a viscoelastic media can be described by a system of integro-differential equations. The solution of such equations requires special methods when using finite-difference techniques in the time domain. In the frequency domain, the integral terms are represented by complex elastic parameters. This paper presents an efficient algorithm for viscoelastic modelling based on the integral Laguerre transform for the approximation of temporal derivatives and for the calculation of convolution integrals. For the calculation of spatial derivatives, it is possible to use various methods: finite-difference and finite-element techniques, spectral and pseudo-spectral methods. We then obtain a system of algebraic equations with a matrix independent of the parameter m , i.e. the degree of the Laguerre polynomials. In this case, only the right-hand side of the system has recurrent dependence on the parameter m , which is an analogue of the temporal frequency in the frequency domain. The obtained system with a large number of right-hand sides can be solved using fast methods, where the matrix is transformed only once, as opposed to the frequency-domain approach, when the matrix is transformed for each temporal frequency.     

The Mechanism of Disordered Graphite Formation in UHP Diamond-Bearing Complexes

Doklady Earth Sciences - Kyanite gneiss from the “New Barchinsky” locality (Kokchetav Massif) was studied in detail. This rock is characterized by zonal distribution of the C and SiO2...     

Sulfide Sulfur in Water Objects with Different Mineralization

Water Resources - Hydrogen sulfide, like other sulfides, is formed in aquatic environments due to sulphate reduction processes and putrefactive decomposition of organic matter of bottom sediments,...     

Influence of the Grain Size Composition of Bottom Sediments in Lake Baikal on the Distribution of Methane and Sulfide Sulfur

Lithology and Mineral Resources - Based on the study of separate areas of Lake Baikal (depth from 14 to 250 m), influence of the grain size composition of bottom sediments on the distribution of...     

Numerical modelling of propagation of elastic waves in anisotropic inhomogeneous media for the half-space and the sphere

Summary. A method based on a combination of partial separation of variables and finite-difference method is used for the calculation of complete theoretical seismograms for inhomogeneous anisotropic media. Examples of theoretical seismograms for several anisotropic models are presented.     

Silicate Inclusions in Metamorphic Diamonds from the Ultra-High Pressure Kokchetav Complex (Kazakhstan)

Doklady Earth Sciences - Mineral inclusions in cubic diamonds from garnet–clinopyroxene rock of the Kokchetav massif were studied. The coexistence of fluid and silicate inclusions in the...     

Methane in Water and Bottom Sediments of Lake Baikal

Water Resources - The distribution of methane concentration measured in 2014 and 2015 in different parts of Lake Baikal has been analyzed. In the period of expedition studies, methane concentration...     

New Data on Diamond–Graphite Relationships in the Gneisses of the Kokchetav Massif (Northern Kazakhstan)

The results of studying an aggregate of graphite-and-diamond crystal in tourmaline 5 μm of the Kokchetav massif by the method of transmission electron microscopy are presented. The detail studies of the interface between the crystals of graphite and diamond have revealed the absence of disordered graphite that is detail partially graphitized diamond. Intense deformation changes in the graphite crystal occurred after it was captured by tourmaline at the regression stage, which led to considerable kinking of the graphite crystal along the a-axis. Thus, the coexistence of graphite and diamond crystals cannot be unambiguously interpreted as a product of partial diamond graphitization. Graphite could have crystallized syngenetic with a diamond crystal or at the retrograde stage in the graphite stability field.

     

The first finding of graphite inclusion in diamond from mantle rocks: The result of the study of eclogite xenolith from Udachnaya pipe (Siberian craton)

A xenolith of eclogite from the kimberlite pipe Udachnaya–East, Yakutia Grt+Cpx+Ky + S + Coe/Qtz + Dia + Gr has been studied. Graphite inclusions in diamond have been studied in detail by Confocal Raman (CR) mapping. The graphite inclusion in diamond has a highly ordered structure and is characterized by a substantial shift in the band (about 1580 cm^–1) by 7 cm^–1, indicating a significant residual strain in the inclusion. According to the results of FTIR spectroscopic studies of diamond crystals, a high degree of nitrogen aggregation has been detected: it is present mainly in form A, which means an “ancient” age of the diamonds. In the xenolith studied, the diamond formation occurred about 1 Byr, long before their transport by the kimberlite melt, and the conditions of the final equilibrium were temperatures of 1020 ± 40°C at 4.7 GPa. Thus, these graphite inclusions found in a diamond are the first evidence of crystallization of metastable graphite in a diamond stability field. They were formed in rocks of the upper mantle significantly below (≥20 km) the graphite-diamond equilibrium line.     

Formation of Polycrystalline Graphite Aggregates in High-Pressure Metamorphic Rocks from the Kokchetav Massif,Northern Kazkhstan

Doklady Earth Sciences - An inclusion of graphite in zircon from the diamond- and tourmaline-bearing rocks of the Kokchetav massif (Northern Kazakhstan) has been studied. The inclusion, associated...