SEISMICITY of the ALTAI and SAYAN region in 2015

A review of seismicity of the Altai and Sayan region in 2015 is presented. The stationary network of seismic stations included 52 stations. Compared to 2014, four new seismic stations were added in the region. Additionally, two local temporary networks including 37 temporary seismic stations operated in the region. 6206 earthquakes were recorded with a total seismic energy of 5.97•1012 J. A brief description of the seismicity in the Chui-Kurai zone of the Altai Mountains is given.

Stress-strain state of the earth’s crust of the Central Asian mountain belt: distant effect of the tectonic impact of the Indo-Eurasian collision

In recent decades, extensive geological, geophysical and geochronological data have been obtained that characterize in detail the results of the distant tectonic impact of the Indo-Eurasian collision on the lithosphere of Central Asia, which led to the formation of the mountain systems of the Pamirs, Tien Shan, Altai-Sayan region and Transbaikalia from the Late Paleogene (about 25 million years ago). It has been established that the formation of the structure of Central Asia occurred as a result of the transmission of deformations from the Indo-Eurasian collision over long distances according to the “domino principle” through the rigid structures of Precambrian microcontinents located among the Paleozoic-Mesozoic folded belts. The study of peneplain surfaces deformed into simple folds on high-mountain plateaus surrounded by rugged mountain ranges made it possible to reveal the parameters of the deformations of the earth’s crust, the interrelationship of the formation of relief and sedimentary basins. Apatite track dating data, structural and stratigraphic analyses of Late Cenozoic sediments in the basins prove a period of intense tectonic activation the entire lithosphere of Central Asia from the Indian continent to the Siberian platform starting from the Pliocene (about 3.5 million years). As a result of reactivation of the heterogeneous basement of Central Asia, high seismicity was manifested, which is concentrated mainly along the border of the microcontinents (Central Tianshan, Junggar and Tuva-Mongolian) and the Siberian craton, as well as in the zones of articulation of regional faults.

Petrogenesis of the Despen Volcanic Rocks of the Middle–Late Ordovician Volcanoplutonic Association of the Tannu-Ola Terrane (Southwestern Tuva)

––We have studied the structure and composition of a volcanic unit in the valley of the Despen River, on the southern slope of the East Tannu-Ola Ridge. The unit was earlier assigned to the Lower Devonian Kendei Formation. The new geological and geochronological data show that it resulted from explosive volcanism at 460–450 Ma. The Despen volcanic rocks formed in association with granitoids of the Argolik complex at the end of the accretion–collision stage of evolution of the Altai–Sayan region, in particular, the Tannu-Ola terrane. These are predominantly felsic ferroan metaluminous and weakly peraluminous nappe volcanic rocks resulted from the differentiation of tholeiitic basalts. Their REE patterns, like those of the Argolik granitoids, are flat in the HREE, show a distinct Eu anomaly, and suggest magma generation at shallow depths in the upper crust. The magmatic source was of subduction origin, as evidenced by the negative Ta–Nb anomalies in the multielement patterns and by εNd(T) = +3.1 to +5.6, and has a Neoproterozoic model age, TNd(DM-2st) = 0.94–0.69 Ga.

TO STUDY THE POSSIBILITIES OF USING THE SEISMOLOGICAL NETWORK OF THE ALTAI-SAYAN REGION FOR REGIME VIBRO-SEISMIC OBSERVATIONS

The results of experiments on the study of the radiation characteristics of powerful vibrators and reception conditions at a number of seismic stations in the Altai-Sayan region in the range of distances of 50-450 kilometers in the problem of selecting points for active vibro-seismic monitoring are presented. It is shown that the real effective range of the CV-40 vibrator can be significantly increased by using multiple and semi-multiple harmonics. A method for assessing the applicability of stations for vibration monitoring using special programs for assessing the seismic background and seismic resonances within the boundaries of the location of seismic stations is proposed and tested.

TO STUDY THE POSSIBILITIES OF USING THE SEISMOLOGICAL NETWORK OF THE ALTAI-SAYAN REGION FOR REGIME VIBRO-SEISMIC OBSERVATIONS

The results of deep seismic studies based on P - and S-wave data on the East-Stanov fragment of the reference 700-kilometer geophysical profile 8-DV are presented. Deep seismic sections of the upper crust (up to a depth of 20 km) with the distribution of the velocities of longitudinal and transverse waves are constructed. The P - wave velocities in the upper part of the section vary from 4-5 km / s within the Upper Zeya and Amur-Zeya depressions to 5.5-6.0 km/s within mountain ranges and plateaus; at depths of 10-20 km, lenses of high-velocity rocks up to 6.7-7.0 km/s are distinguished in the profile alignment. According to the S - waves in the upper part of the section, the velocity values are generally 3.0-3.2 km/s; reduced velocity values of 2.5-2.6 km / s are observed in the Upper Zey depression. At depths of 5-20 km within the section, according to the transverse wave data, a number of sections with reduced and increased velocity values are distinguished, respectively, up to 3.4-3.5 km/s and 3.75-3.8 km/s. The correlation of the selected anomalies according to the data of P-and S-waves is carried out.

Mitochondrial genome diversity on the Central Siberian Plateau with particular reference to the prehistory of northernmost Eurasia

The Central Siberian Plateau was the last geographic area in Eurasia to become habitable by modern humans after the Last Glacial Maximum (LGM). Through a comprehensive dataset of mitochondrial DNA (mtDNA) genomes retained in the remnats of earlier (“Old”) Siberians, primarily the Ket, Tofalar, and Todzhi, we explored genetic links between the Yenisei-Sayan region and Northeast Eurasia (best represented by the Yukaghir) over the last 10,000 years. We generated 218 new complete mtDNA sequences and placed them into compound phylogenies with 7 newly obtained and 70 published ancient mitochondrial genomes. We have considerably extended the mtDNA sequence diversity (at the entire mtDNA genome level) of autochthonous Siberians, which remain poorly sampled, and these new data may have a broad impact on the study of human migration. We compared present-day mtDNA diversity in these groups with complete mitochondrial genomes from ancient samples from the region and placed the samples into combined genealogical trees. The resulting components were used to clarify the origins and expansion history of mtDNA lineages that evolved in the refugia of south-central Siberia and beyond, as well as multiple phases of connection between this region and distant parts of Eurasia.

Multistage Thrust and Nappe Tectonics in the Southeastern Part of East Sayan and Its Role in the Formation of Large Gold Deposits

––Comprehensive studies of structural geology and metallogeny, taking into account the authors’ previous works started as early as the last century, have shown that the southeastern part of East Sayan formed mainly in the Neoproterozoic–early Paleozoic in the settings of multistage thrust and nappe tectonics and tectonomagmatic restructuring of autochthonous and overthrust allochthonous oceanic (ophiolitic), island arc, and ocean-marginal terranes as well as amalgamation of accretion–collision and postcollisional igneous complexes that formed during the opening and subsequent closure of the Paleoasian Ocean marginal structures. In the middle and late Paleozoic, active intraplate volcanic and plutonic processes continued in the thrust/overthrust fault setting, which led to the formation of new dome-shaped nappe structures and the redistribution of ore matter (gold etc.) in large mineral deposits. The final structure of the East Sayan region formed during the late Cenozoic as a result of mountain uplifting and volcanic eruptions, including those in the valley of the Zhombolok River.

DEFECTS OF MAGMA FORMATION ANALYSIS

The formation analysis of igneous rocks is a great achievement of the Soviet science in terms of classifying natural communities of magmatic rocks for the purpose of forecasting and prospecting of associated deposits. But due to the complexity of the problem itself, the uncertainty of boundaries between formational types in the practice of geological works, there are numerous defects that were clearly observed during the regional and interregional correlation of magmatic complexes of the Altai-Sayan region and Yenisey Ridge. The reasons and consequences of these defects, ways of their correction are analyzed.

ALTAI and SAYAN

The review of the seismicity in Altai and Sayan region for 2014 is presented. The stationary network of seismic stations included 48 stations. Compared to 2013, seven new seismic stations were added in the region. Additionally 3 local temporary networks including 39 temporary seismic stations operated in the region. 8828 earthquakes were recorded with the total seismic energy of 4.6•1012 J. A brief description of the seismicity in the Chui-Kurai zone of the Altai Mountains is given.