Home – Home – Jornals – Russian Geology and Geophysics 2014 number 9

The paper summarizes data on the Pleistocene combustion metamorphic complexes of the Kuznetsk Coal Basin. Paralava and clinker samples are dated by ⁴⁰Ar/³⁹Ar incremental heating. The ⁴⁰Ar/³⁹Ar ages of the combustion metamorphic rocks permit reconstructions of the succession of renewed activity of ancient faults in the Salair zone and age estimates for the evolution of the present-day drainage network. Cross sections of burned rocks from the western margin and center of the Kuznetsk Basin are compared. The geologic factors of coal ignition risks are analyzed. On the western margin of the Kuznetsk Basin, paleofires occurred in steeply dipping thick seams with predominant crushed vitrain-clarain coal, which has a high oxygen and methane adsorption capacity. Highly denuded high-temperature combustion metamorphic complexes are most often localized in the arches of slightly broken anticlines. Oxygen was supplied to the coals during the Late Cenozoic renewed fault activity and the subsequent erosion of the sediments. The natural fires in the area were a result of external rather than spontaneous ignition. The paleofire depths (up to 200 m) indicate that they occurred in a warm and dry climate. In the center of the Kuznetsk Basin, dispersed fire foci appeared in seams of self-igniting coals with the erosion propagation of the current drainage network. The combustion metamorphic complexes here are partly eroded and consist mostly of clinkers with a low degree of alteration. The ⁴⁰Ar/³⁹Ar ages and geological data indicate that the earliest large-scale combustion events on the western periphery of the basin occurred in the Eopleistocene (1.3–0.9 Ma). The oldest ⁴⁰Ar/ ³⁹Ar age of a coal fire episode (1.7 ± 0.3 Ma) might be the upper age boundary of the altitude differentiation of topography, which corresponds to the renewed activity of the Tyrgan and Afonino-Kiselevsk faults. The later coeval combustion events on the western margin (0.2 ± 0.1 Ma) and in the center of the basin (0.13–0.02 Ma), most probably, occurred during the Kazantsevian interglacial, which gave rise to the present-day drainage network.

We present the first results of application of long-term tree-ring chronologies for dating seismically triggered rockfalls and determining the upper age of Holocene rockfalls in southeastern Altai. Based on the results of seismic dendrochronological analysis, dating of penetrating wood injuries is proposed and tested, and the criterion for the distinguishing of seismically triggered rockfalls among slope processes of climatic nature is formulated. An earlier unknown strong earthquake of 1532 has been recognized; its traces are dated by the radiocarbon method. Based on the new data and calibration of earlier radiocarbon dates, the recurrence period of strong earthquakes in the southeastern Altai is refined.

The problems of identification of A-type granitoids, igneous anhydrous alkaline aluminous rocks, are analyzed. These rocks occur in different geodynamic settings. Owing to their mantle nature, they show distinct REE specialization. These are felsic intrusive rocks, whose volcanic products are of crucial scientific and practical significance. However, neither the great number of proposed classification schemes and diagrams, including those based on expensive analytical data, nor hot scientific discussions of their identification and the ambiguity of the term A-granitoids helped to determine their classification features in full measure. A principally new discriminant diagram is proposed for the classification of igneous A-type rocks, based on the analysis of earlier obtained results and the petrochemical composition of these rocks. A comparative analysis of subdivision of granites and related felsic volcanic rocks (SiO₂ > 67 wt.%), based on the ternary (Na₂O + K₂O)–Fe₂O₃*×5–(CaO + MgO)×5 and other widely applied diagrams, has shown the advantage of the proposed discriminant diagram for the classification of A-type granitoids from different geodynamic settings.

The Bo Phloi gem field in Kanchanaburi Province, Western Thailand, is closely associated with Cenozoic basalts. Blue and yellow sapphire, black spinel, and minor zircon have been mined for over three decades. The mineral inclusions observed in sapphire samples are alkali feldspar, nepheline, hercynitic spinel, zircon, manganiferous ilmenite, silica-rich enstatite, almandine-pyrope garnet, monazite, calcite, sapphirine, biotite-phlogopite mica, and staurolite. Based on their geochemical affinity, these mineral inclusions can be categorized into two main groups: felsic alkaline and contact-metamorphic, which appear to have originated from different processes. These inclusions provide new evidence for proposing a bimodal genetic model. Felsic alkaline origin is evidenced by the occurrence of a felsic alkaline inclusion suite and the REE geochemistry of sapphire-associated zircon, which indicates that most of the sapphires crystallized from a high-alkali felsic melt (probably, in the lower crust). Contact-metamorphic origin is evidenced by the presence of a contact-metamorphic inclusion suite, suggesting that some of these sapphires might also have originated from metasomatized crustal rocks and a contaminated melt along the contact zone of a basaltic intrusion (probably, in the upper mantle or lower crust).

The state of Azad Kashmir is rich in three types of rocks, namely, sedimentary, metamorphic, and igneous rocks. These rocks contain extensive deposits of graphite, marble, limestone, quartzite, granite, dolerite, and sandstone, which are widely used for the construction of dwellings in Azad Kashmir and Pakistan. Therefore, knowledge about the presence of natural radioactivity in these materials is desirable to assess the radiological hazards associated with it. In this context, 30 rock samples were collected from different geologic formations of the Muzaffarabad Division, Azad Kashmir. After processing the samples, the specific activities of ²²⁶Ra, ²³²Th, and ⁴⁰K in them were measured using a P-type coaxial high-purity germanium detector. The observed highest dose rate values for sedimentary, metamorphic, and igneous rocks have been found to be 83.16 ± 1.08, 135.87 ± ± 1.18, and 115.98 ± 1 nGy · h^-1, respectively. The radium equivalent activity (Ra_eq ) varied from 23.76 ± 1.15 for dolerite sample (igneous rock) to 293.69 ± 2.60 Bq·kg^-1 for marble (metamorphic rock). The Ra _eq values of all rock samples are lower than the limit mentioned in the Organization for Economic Cooperation and Development (OECD, 1979) report (370 Bq·kg^-1, equivalent to γ-dose of 1.5 mSv · y^-1). The values of external (H_ex ) and internal (H_in ) hazard indices are less than unity. The mean outdoor and indoor annual effective dose equivalents are 0.073 mSv · y^-1 and 0.29 mSv · y^-1, respectively. The mean (over all types of rock samples) annual effective dose equivalent is reported as 0.36 mSv · y^-1.

This paper is concerned with study and comparison of Berriasian, Valanginian, and lower Hauterivian foraminifer associations in northeastern West Siberia. Micropaleontological analysis of the Lower Cretaceous deposits of the Ust’-Yenisei region has given an insight into the taxonomic composition of microfossils in the studied sections. Analysis of the stratigraphic occurrence of foraminifers has revealed four successive biostratons in zones and beds. Communities of Berriasian, Valanginian, and earliest Hauterivian microbenthos are reconstructed, the regularities of their evolution are established, and the sequence of bionomic zones is revealed.

Lake Baikal is the only fresh-water lake where natural gas hydrate accumulations were found in sediments. For the recent decade, Baikal has become a natural laboratory for investigation of the properties of gas hydrates, their indicators, and recovery of gas from subsurface (subbottom) gas hydrates. We present the main results of subsurface gas hydrate mapping and gas recovery test near the delta of the Goloustnaya River.

New results of the study of the distorting effect of paleoclimate on the formation of the thermal field of the Earth’s uppermost crust in the South Urals are presented. We discuss some consequences of taking into account the paleoclimate influence on estimates of deep heat flow and possible applications of these data. The dependence of the heat flow density on the studied depth of boreholes is considered, and deep heat loss and deep temperatures are estimated. A new method for deep-temperature estimation is proposed, which takes into account the paleoclimate influence on the heat flow. The method is tested on the available high-quality temperature data for deep boreholes. Deep temperatures to a depth of –10,000 m are estimated for the platform part of the Republic of Bashkortostan using the proposed method. Isotherm schemes are constructed for elevations of –5000 and –10,000 m below sea level. The necessity of using heat flow values corrected for the paleoclimate influence to estimate the Earth’s thermal state is justified. Some examples illustrate that underestimation of heat flow values measured in shallow boreholes might lead to underestimation of deep temperatures and global heat loss.

Global geomagnetic data are inverted for detecting a high–conductivity layer at depths of 1500–2000 km to test the hypothesis of a magnesiowüstite phase transition in the lower mantle. The results of processing of both synthetic and global data — average monthly values of the geomagnetic field from 1920 to 2009 — are presented. The inverted global data are consistent with the possible existence of a high-conductivity layer at great depths in the lower mantle.

It is proposed to consider data both on the deep density distribution (gravity instability) and the bulk modulus of elasticity on estimation of the stability of layered mountain ranges. It is shown that an increase in bulk elastic rigidity with depth is the stable state of layered media in terms of energy in the field of gravity stress. In the tectonosphere, in which the moduli of elasticity are inverted (decrease) with depth, excess energy of elastic strain of volume change is generated by body forces, and it will determine the instability of the geologic medium.