Vol 10, No 6 (2016)

The transverse current anomalies evident from magnetotelluric sounding (MTS) data in the transition zone from the Asian continent to the Pacific Ocean and a geoelectrical model suitable for explaining these effects are discussed. Using simulation results and new MTS data on Sakhalin and northern Vietnam, ultra-deep fluid–fault system (UDFFS) models are constructed, comprising steeply dipping low-resistivity and high-resistivity linear bodies which penetrate through the whole section of the lithosphere, continuing deep into the asthenosphere. The structure of these systems reflects the development of deep and ultra-deep fault zones, along which mantle-originated fluids may migrate through sediments to reach the surface. This allows the anisotropic–conductive fractured structures adjacent to these faults to be considered as being most favorable for hydrocarbon accumulations.

A module for simulation of seismic and geodeformation processes when fluid is injected into and extracted from the geomedium is developed. Calculation of the stress–strain state of the geomedium involves a modified Biot model that takes the rate of bulk strain in the Darcy equation into account. For software implementation of the module simulating the processes during fluid motion in terms of the Biot model, we applied the OpenFOAM 2.4.0 free package of C++ libraries. This package is a set of compiled modules and their source codes; the latter encapsulate all of the most commonly used objects and operations from computational continuum mechanics in accordance with the principles of object-oriented programming. Development of the stress calculation module is based on the standard solver for elastic deformation of an isotropic body from the OpenFOAM package. Its code was supplemented with the procedure of discretization and solution of the Darcy equation for pore pressure. Geodeformation effects are estimated by direct calculation of free surface displacements near the sources of fluid injection and extraction; these displacements can lead, in particular, to dangerous subsidence and induced seismicity. Triggering seismic effects are estimated by calculation of the accumulation rate for excessive tangential stresses in a fault zone at the depth of the seismogenic layer (5–15 km), with the ratios linking the historical seismicity and the tectonic stress accumulation rate in terms of the modified Dietrich’s model being taken into account. Seismological validation of the possible maximum magnitudes of technogenic earthquakes and their recurrence periods in the NE Sakhalin region of intensive oil and gas development is performed. The models of seismic process activation during technogenic impacts on the geomedium are specified.

Analysis of detailed bathymetric charts and records of phototelevision profiling over the surfaces of the guyots of the Magellan Seamounts reveals many cones and domes. Their diameters and heights vary from a few hundreds of meters to 10 km and from 30 to 350 m, respectively. The age generations of these mesomorphic structures correspond to the Campanian–Maastrichtian, Late Paleocene–Eocene, and Miocene. The formation of complicating volcanic edifices is most likely determined by late phases of volcanic activity related to differentiation of magmatic melts. At the same time, the tectonic factor responsible for their formation is also sufficiently well evident: volcanic edifices on plateau summits are associated spatially with linear morphostructures and lineaments.

This paper presents original data on the content and distribution of major and rare-earth elements in the modern hydrothermal systems of the Paratunka and Bol’shebannyi thermal water deposits. In spite of the similar geochemical type of the waters, the individual sites of the hydrothermal systems differ in the major component composition, which is caused by the time of water–rock interaction, temperature control, and the possible influence of seawater intrusions. The REE concentrations in the studied thermal waters are extremely low (a few tenths of ppb). A distinctive feature of these thermal waters is the presence of a positive Eu anomaly. The possible reasons for its appearance are discussed. Calculation of REE speciation shows that the main parameters controlling the formation of the REE complexes in the Paratunka and Bol’shebannyi hydrothermal systems are their individual chemical properties, as well as pH, Eh, and temperature of the aqueous solution.