The posthumous tectonics and mechanism of exhumation of granitic plutons: The case of the Transbaikal region and the Tien Shan

The study of granitic plutons of the Baikal Highland and the Tien Shan has made it possible to establish new features of their posthumous (after incorporation into the consolidated Earth’s crust) structural reworking and to understand the implications of the cataclastic flow for the exhumation of the crystalline basement in the studied regions. It is shown that granitic plutons undergo appreciable structural transformation at the stages of tectonic reactivation that is significantly separated in time from the moment of formation of plutons as geological bodies. The 3D cataclastic deformation is the main mode of structural reworking of granitic plutons, while the cataclastic flow is the main form of their mobility. Newly recognized slice structures characterize the volumetric deformation of granites.     

Directional dependence of P- and S-wave propagation and polarization in foliated rocks from the Kola superdeep well: Evidence from laboratory measurements and calculations based on TOF neutron diffraction

We have measured P- and S-wave velocities on two amphibolite and two gneiss samples from the Kola superdeep borehole as a function of pressure (up to 600 MPa) and temperature (up to 600 °C). The velocity measurements include compressional (Vp) and shear wave velocities (Vs1, Vs2) propagating in three orthogonal directions which were in general not parallel to inherent rock symmetry axes or planes. The measurements are accompanied by 3D-velocities calculations based on lattice preferred orientation (LPO) obtained by TOF (Time Of Flight) neutron diffraction analysis which allows the investigation of bulk volumes up to several cubic centimetres due to the high penetration depth of neutrons. The LPO-based numerical velocity calculations give important information on the different contribution of the various rock-forming minerals to bulk elastic anisotropy and on the relations of seismic anisotropy, shear wave splitting, and shear wave polarization to the structural reference frame (foliation and lineation). Comparison with measured velocities obtained for the three propagation directions that were not in accordance with the structural frame of the rocks (foliation and lineation) demonstrate that for shear waves propagating through anisotropic rocks the vibration directions are as important as the propagation directions. The study demonstrates that proper measurement of shear wave splitting by means of two orthogonal polarized sending and receiving shear wave transducers is only possible when their propagation and polarization directions are parallel and normal to foliation and lineation, respectively.     

Structure,magmatism, and Paleozoic tectonic evolution of the Uakit Zone in the context of the formation of the Angara-Vitim batholith in the western Transbaikal region

The problem of the tectonic evolution of the Angara-Vitim batholith, the largest igneous complex of the western Transbaikal region, is discussed. This problem is still far from an unequivocal solution; however, it is evident that the Late Paleozoic stage was crucial in the evolution of the Angara-Vitim batholith, and precisely this stage has determined the main structural features of the western Transbaikal region. The geodynamics that controlled the batholith formation in the Late Paleozoic is exemplified in the Uakit Zone. New data are presented on the stratigraphy of country rocks and on the age and composition of the Vitimkan granitoid complex, the most abundant complex in the batholith. It has been shown that the main tectonic events in the Uakit Zone occurred from the Devonian to the Late Carboniferous. The ensialic orogeny in the form of a reduced Wilson cycle that developed under within-plate conditions was the main mechanism of structure formation. The effect of collision is a self-sufficient mechanism of superplume evolution provided by the origin and passing away of particular, relatively short lived streams of the superplume. The short-lived rifts (aulacogens) arose above the ascending streams during the most active development of superplume and then closed up under tangential compression caused by spatially conjugated younger plumages. The closure of rifts was controlled by pseudosubduction and particular collision. As a result, the mosaic block megastructure was created, being underlain by the hydrated mantle necessary for extensive granite formation. Such a mechanism probably was dominant during a “vague time” in the Riphean geological history of the Earth after the breakdown of Rodinia.     

Acoustic emission of quasi-isotropic rock samples initiated by temperature gradients

The influence of temperature gradients and heating rate on crack formation in quasi-isotropic samples of marble and sandstone is studied using acoustic emission records. The behavior of velocities and attenuation of elastic waves in the samples is also examined. The crystallographic textures of marble and sandstone are measured by the neutron diffraction method, and it is shown that temperature gradients of up to 52°C/cm do not lead to a change in the textures. It is established that the temperature dependence of acoustic activity in the sandstone samples strongly depends on the internal heating rate. The maximum acoustic activity of the sandstone samples was observed at maximum temperature gradients in the samples. The temperature dependence of acoustic activity in marble differs significantly from that in sandstone. Maximums of acoustic activity in the marble samples are observed at temperatures of 30–60 and higher than 200°C. A decrease in acoustic activity was recorded in the interval between these temperatures. Such behavior suggests a predominant role of the surface structure and the concentration of surface defects in the process of crack formation in marble. During cooling, all samples demonstrate similar behavior: maximum acoustic activity is observed at the switching-off of the heating element and the emission activities of different samples are comparable in intensity.     

Wave propagation in elastic media with stress-induced anisotropy

Summary. The effect of initial stress on the velocities of plane elastic waves is considered and corrections to the first order in terms of initial stress for P -and S -waves are obtained. The results are compared with those of Dahlen, who found that to the first order the initial stress had no effect on P -wave velocities: this conclusion is shown to be correct only when the unstressed material is isotropic.     

Three-dimensional numerical simulation of a nonstationary gravitating <Emphasis Type="Italic">N</Emphasis>-body system with gas

We developed a three-dimensional numerical model to investigate nonstationary processes in gravitating N-body systems with gas. We used efficient algorithms for solving the Vlasov and Poisson equations that included the evolutionary processes under consideration, which ensures rapid convergence at high accuracy. We give examples of the numerical solution of the problem on the growth of physical instability in the model of a flat rotating disk with a gaseous component and its three-dimensional dynamics under various initial conditions including a nonzero velocity dispersion along the rotation axis.     

Complex scientific and technical trends of Russian Federation Arctic offshore hydrocarbon resource development

Based on the analysis of geological, technical and hydrometeorological conditions of the coastal part of the Arctic offshore, a concept of its hydrocarbon resource development is submitted.     

A finite volume scheme with improved well modeling in subsurface flow simulation

We present the latest enhancement of the nonlinear monotone finite volume method for the near-well regions. The original nonlinear method is applicable for diffusion, advection-diffusion, and multiphase flow model equations with full anisotropic discontinuous permeability tensors on conformal polyhedral meshes. The approximation of the diffusive flux uses the nonlinear two-point stencil which reduces to the conventional two-point flux approximation (TPFA) on cubic meshes but has much better accuracy for the general case of non-orthogonal grids and anisotropic media. The latest modification of the nonlinear method takes into account the nonlinear (e.g., logarithmic) singularity of the pressure in the near-well region and introduces a correction to improve accuracy of the pressure and the flux calculation. In this paper, we consider a linear version of the nonlinear method waiving its monotonicity for sake of better accuracy. The new method is generalized for anisotropic media, polyhedral grids and nontrivial cases such as slanted, partially perforated wells or wells shifted from the cell center. Numerical experiments show noticeable reduction of numerical errors compared to the original monotone nonlinear FV scheme with the conventional Peaceman well model or with the given analytical well rate.     

Detailed geological-geophysical studies of active fault zones and the seismic hazard in the south Yakutia region

Active faults play the key role in the formation of the morphological structures and control the seismicity in the Olekma-Stanovoi seismic zone. The detailed geological-structural and morphotectonic studies of fault zones made it possible to estimate the kinematics of the active faults and their activity degree in the Holocene (the last 10 000 years). The latter include old faults such as, for example, the Stanovoi Suture of the Proterozoic age. Most of these faults are the Late Mesozoic and Cenozoic in age. The studies were aimed at reconstructing the past seismogeological processes and were accompanied by trenching across morphological structures that are presumably associated with zones of active tectonic fractures preliminarily studied by geophysical methods. The applied approach allowed us to substantially specify the available information on the seismotectonics and the potential seismic hazard in the region.