Home – Home – Jornals – Russian Geology and Geophysics 2013 number 7

The specific chemical and mineral composition of discoid, cake-shaped, and platy ferromanganese nodules (FMNs) from the Chukchi Sea are considered. The main ore components of these FMNs are Fe, Mn, and P. The contents of trace elements (except for Ba and Sr) do not exceed hundredths of percent. Maximum concentrations of most of these elements are specific for the cake-shaped nodules. In general, Mn accumulates most intensely in FMNs. Next (in order of decrease) are Ag(?), Co, Pb; Sr, Fe, P, Y, Ca; and Ni, La, Zn, Cu. As for Ba, Cr, Mg, and K, they do not accumulate in the FMNs. «Dilution» is typical of Si, Al, Na, and Ti. The main ore phases are strengite and amorphous Mn hydroxides. It has been revealed for the first time for the Chukchi Sea that Cu, Zn, Sn, Ni, Pb, W, Bi, Cr, Fe, Ti, Ag, Au, Y, Zr, and La–Nd lanthanides form individual mineral microphases in FMNs: native elements, intermetallic compounds, oxides, and, much more seldom, tungstates, silicates, and phosphates. Accessory ore mineralization is the best pronounced and most diverse in the platy nodules. Though the FMNs from the Chukchi Sea are diagenetic, high-temperature fluids are, most likely, the source of microinclusions of various accessory ore minerals.

The first data on PGE contents in the volcanic rocks of the West Siberian Plate are presented. Analysis has shown that most of the studied rocks have clarke contents of these elements. Rocks from the central areas of paleorift valleys are enriched in ∑PGE (2.0–32.0 ppb), particularly in Pt (0.1–24.2 ppb) and Pd (0.3–8.0 ppb), which might be related to the action of plume. The magmatic PGE pattern confirms the earlier conclusions about the mantle genesis of the studied rocks.

We performed system studies of age parageneses and lateral conjugation of peat and gold accumulation areas, as well as the regularities of formation of noble- and rare-metal mineralization in Cenozoic coaliferous deposits in the south of the Russian Far East. The migration properties of noble metals (NMs) and their behavior in different media are considered. Based on literature data and results of experimental studies, we performed analysis and selection of the most optimal methods for the quantitative determination of NMs and trace and rare-earth elements. The experiments have confirmed the NM fugacity and have shown for the first time the scales of transportation of NMs as ultrafine particles during coal combustion. The obtained results significantly expand the notions of the migration properties of NMs and serve as the key to the solution of the problem of NM extraction in analytical and technological processes. Also, areas promising for noble- and rare-metal mineralization have been revealed in coal basins.

The history of the peneplain in East Sayan was studied using apatite fission-track analysis (AFTA). This method is suitable for determining the formation time of the erosional surface and estimating its denudation rate. The largest known relic of the peneplanation surface in this area is the Oka Plateau, separated from the Kropotkin Ridge by the Oka–Jombolok fault. The AFTA shows that the peneplain on the Oka Plateau formed in the Late Jurassic–Early Cretaceous. This peneplain is much younger than the erosional surfaces that persist today in the Tien Shan, Gobi Altai, and Mongolian Altay (Early Jurassic). However, it is older than that on the Chulyshman Plateau, Altai (Late Cretaceous), suggesting asynchronous formation of the ancient peneplain in Central Asia. The similar exhumation histories of samples from the Oka Plateau and Kropotkin Ridge indicate that these morphotectonic structures developed from Jurassic to late Miocene as a single block, which underwent continuous slow denudation at an average rate of 0.0175 mm/yr. Active tectonic processes in the Late Miocene caused the destruction of the peneplanation surface and its partial uplifting to different altitudes. The rate of Pliocene–Quaternary vertical movements along the Oka–Jombolok fault is roughly estimated at 0.046–0.080 mm/yr, which is several times higher than the denudation rate in this area. During the Pliocene–Quaternary, the Oka Plateau has not undergone any significant morphologic changes owing to its intermediate position between the summit plain and datum surface of East Sayan and to its partial shielding by basaltic lavas.

Seismic-tomography studies were conducted in the Kyrgyz Tien Shan using two different observation schemes. The first was based on the arrival times of P and S waves from regional earthquakes recorded with local seismological networks (local scheme). Nonlinear tomographic inversion with the LOTOS algorithm was used to construct the 3D distributions of P and S wave velocities in the crust beneath the Kyrgyz Tien Shan and to refine the earthquake locations. The second scheme was used to study the upper-mantle structure based on data from world earthquake catalogs (regional scheme). All the data on waves which at least partly travel within the volume studied were used here, including (1) those from regional earthquakes recorded at world seismic stations and (2) teleseisms recorded at the local stations. This approach was earlier applied to calculate the upper-mantle structure beneath Asia. We used a fragment of this structure beneath the Tien Shan and adjacent areas. A series of synthetic tests was performed to estimate the resolution provided by both schemes. The tomography shows traces of the delamination of the Tarim mantle lithosphere from south to north. Also, the local and regional schemes reveal evidence for cold-matter descent from north to south in the northern Tien Shan but on a much smaller scale. Low velocities in the upper mantle beneath the Tien Shan indicate lithospheric thinning. These data suggest that mantle lithosphere delamination is taking place underneath both the northern and the southern margins of the Tien Shan collision belt. Lack of the mantle lithosphere beneath the Tien Shan leads to lithospheric weakening and active deformation, thus causing intense orogeny.

The results of studying Ordovician ostracods from the southeastern Siberian Platform are presented. Ordovician sections are described in brief from outcrop and core studies. Four of the ostracod zones distinguished in the Ordovician strata of the Siberian Platform have been found in the Volgian, Kirensko-Kudrinoan, Chertovskaya, and Baksanian Horizons. Stratigraphic correlation takes into account the available data on the distribution of other groups (e.g., conodonts and cephalopods).

We discuss the results of study of the Holocene seismic activity in the zone of the Hustai Fault, Central Mongolia. Applying seismological methods (remote, trenching, geophysics), we have revealed signs and determined the quantitative parameters of the paleoearthquake that led to the fault dissection at 3.0–5.5 ka. The high seismic potential of the Tola zone and its proximity to Ulaanbaatar confirm earlier estimates of the seismicity of the capital of Mongolia, 8 points on the MSK-64 scale.

The aim of the study is to increase the reliability of estimation of the acoustic parameters of a layered permeable formation using a new software, based on two-velocity continuum equations for 2D numerical simulation of acoustic waves propagating in a borehole. The key method is the method of finite differences as applied to solving equations of the continuum filtration theory. The dissipative characteristics of Stoneley waves have been identified for the case of their propagation in a layered formation. These aspects should be taken into account when using Stoneley waves to estimate the permeability of geologic media.