Alexei Didenko | Pacific National University (original) (raw)

Papers by Alexei Didenko

Pure and Applied Geophysics, 2021

Analysis of the available Moho models for the Sikhote Alin region revealed significant discrepanc... more Analysis of the available Moho models for the Sikhote Alin region revealed significant discrepancies between them both in depth for individual sites and isolines over the entire area of the orogenic belt. In this study, results of the two-dimensional power spectrum analysis of the gravity field based on a digital model of the Bouguer gravity field were used to calculate the crustal thickness (Moho depth). The data from seven seismic profiles were employed to adjust the new model. The new model and its correlation with structural and geological data allowed the following conclusions to be made. (1) The span of Moho depth variations for the southern part of the continental Far East of Russia is just over 18 km, with extreme values of 42.4 and 24.0 km. The Moho is deepest (41–42 km) beneath mountain ranges and massifs: Sikhote Alin in the east and Yam Alin and Aesop in the north-west. The Moho is most shallow (27–30 km) beneath the sedimentary basins Khanka, Partizan-Sukhodol, Suifun in the south, Middle Amur and Lower Amur in the central part of the study area, and Upper Zeya and Uda in the north-west. (2) Correlation of the Moho estimates derived from the Airy model and the power spectrum of the Bouguer gravity field shows significant positive correlation. The Moho depths practically coincide over 11% of the area, with a difference of ± 5%. The Moho depth discrepancies are in the range of 5–15% over 48% of the study area, and over the rest of the study area (41%), discrepancies are in the range of 15–30%. (3) A comparison between the new gravity Moho model and the geological and structural data shows that the model is highly correlated with the development of Cretaceous–Early Eocene orogenic and post-orogenic granitoid massifs and Cretaceous–Pliocene extrusive igneous rocks. The former geographically coincide with two linear zones in the Moho relief with depths of more than 35 km, and the latter with the Mesozoic–Cenozoic sedimentary basins and the East Sikhote Alin volcano–plutonic belt.

Earth-Science Reviews, 2016

Recent ICDP drilling and deep basin volcanic exploration of 3000 m below the surface in the Songl... more Recent ICDP drilling and deep basin volcanic exploration of 3000 m below the surface in the Songliao Basin (SB) have highlighted the 3-D delineation of the basin. The integrated new data led us to reevaluate the basin tectonics, for which the basin type, basin evolution and a number of geodynamic aspects have been controversial topics. We outline the position of a main lithospheric scale detachment fault beneath the SB, based on apparent crustal scale displacements, Moho breaks, the thinning of the Moho transition zone beneath the SB and the changing mantle thickness. This fault interpretation is consistent with simple shear as the rift mechanism. Based on a comprehensive analysis of the tectonic setting, underlying crust, structural style, sequence stratigraphy, subsidence history and volcanism, we propose an active continental margin model for the SB which shows some similarities to aulacogens but also notable differences. Situated between two Late Mesozoic active continental margins, the northern/northwestern Mongol-Okhotsk and the eastern Sikhote-Alin orogenic belts, the Cretaceous basin evolved on a pre-Triassic structurally weak basement mosaic. Its development began with regional mega-rifting from 150 to 105 Ma, followed by significant sagging between 105 and 79.1 Ma and ended with regional uplift and basin inversion from 79.1 to 64 Ma. Three regional angular unconformities separate the basin fill into three respective tectono-stratigraphic sequences. (1) The syn-rift stage is characterized by widespread fault-bounded grabens and volcanogenic successions, corresponding upward to the Huoshiling, Shahezi and Yingcheng Formations. (2) The post-rift stage includes the Denglouku, Quantou, Qignshankou, Yaojia and Nenjiang Formations. It is a special feature that the subsidence rate is abnormally high (mean of 103 m/Ma), and that flood basalt erupted along an axial wrench fault zone, associated with several marine intervals from the mid-Turonian to early Campanian (K 2 qn to K 2 n), possibly (not certainly) indicating incipient sea floor spreading characterized by Moho breaks along the basin axis in the SB around 88 Ma. Stretching stopped abruptly at approximately 79.1 Ma and was followed by uplift and rapid erosion (−145 m/Ma). (3) Recorded by the Sifangtai and Mingshui Formations the structural inversion stage included a continuous depocenter migration to the northwest. The basin was shrinking to demise as a result of changing subduction parameters of the Pacific subduction zone. In addition to the three tectonic basin cycles, a cyclic basin fill pattern exists with three volcanic basin fill intervals of Huoshiling, Yingcheng, and upper Qingshankou Formations that alternate with sedimentary basin fill intervals of Shahezi, Dengloukou-Quantou, and Yaojia-Nenjiang Formations. When determining the subsidence rates, we observed not only anomalously fast subsidence but also found an intricate link between the subsidence rate and type of basin fill. After each volcanic interval, the subsidence rates increased in a cyclic fashion during the sedimentary intervals. Thus, there is a system of three different types of important, basin-wide geological cycles that controlled the evolution of the SB. The subsidence rate was especially high (up to 199 m/Ma) after the last volcanic episode at 88 Ma. In addition to thermal subsidence and loading by the basin fill as causative processes, we also consider magmatic processes related to asthenospheric upwelling beneath the SB. They involve the roof collapse of shallow, depleted magma chambers, the igneous accretion of initially hot, dense, basic rocks, and lithospheric delamination beneath the SB. The difference in the subsidence rates during the volcanic and sedimentary intervals may in part also have been due to heating-related uplift during the volcanic intervals. The particularly high subsidence during the Late Cretaceous sedimentary cycles was partly increased by transtension.

Tectonic Evolution of the Bering Shelf-Chukchi Sea-Artic Margin and Adjacent Landmasses, 2002

... Bondarenko Sergei D. Sokolov Igor R. Kravchenko-Berezhnoy Geological Institute, Russian Acade... more ... Bondarenko Sergei D. Sokolov Igor R. Kravchenko-Berezhnoy Geological Institute, Russian Academy of Sciences, Moscow ABSTRACT Geologic and paleomagnetic research in the western part of the Omolon massif and in the Sugoi folded zone, northeastern Russia, suggests ...

Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was... more Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was maximum opening. Thus paleomagnetic data contribute to the reconstruc- tion of the primary tectonic position of the blocks of the paleoocean crust and blocks, surrounded this ocean. Revelation of geodynamic formations, boarded the Urals pale- oocean to the east and theirs

This paper reports and discusses the petromagnetic (i.e., rock magnetic) properties and chemical ... more This paper reports and discusses the petromagnetic (i.e., rock magnetic) properties and chemical compositions of titanomag-netites occurring within a bimodal suite of late Pliocene volcanic rocks obtained from the Taitao Ridge, at Site 862 in the Chile Triple Junction region. The results indicate a marked contrast in magmatic sources, as well as in the cooling and alteration histories for the silicic and basaltic lavas. Basaltic units have petromagnetic and chemical characteristics generally consistent with a mid-ocean ridge basalt (MORB) affinity, and show systematic differences that correlate with the texturally-inferred cooling and alteration histories. Magnetic phases in the silicic lavas are similar to those reported from calc-alkaline circum-Pacific suites. The secondary alteration of the titanomagnetites within the silicic units is much less than that observed within the basaltic lavas, in which titanomagnetite has been altered to titanomaghemite. Given the elevated forearc g...

Russian Journal of Earth Sciences

Physics of the Earth and Planetary Interiors, 1992

This paper presents new paleomagnetic data from South Mongolia. Middle Paleozoic rocks were studi... more This paper presents new paleomagnetic data from South Mongolia. Middle Paleozoic rocks were studied from three different tectonic zones within the South Mongolian fold belt. From north to south these are the Gobi-Altai zone (in terms of paleotectonic position, the 'north' shelf of the paleobasin), the Trans-Altai zone (ophiolite complexes) and the South Gobia zone (the 'south' shelf). Several paleomagnetic field tests, including conglomerate, baked contact and fold tests, were carried out to determine magnetic stability. In addition, principal component analysis of the stepwise thermal demagnetization data was used. The ophiolites are characterized by three ancient components. One magnetic component is pre-folding and directed to the south with a very gentle inclination (declination (D) 180-210°, inclination (I) =-6~~+ 2°,K 120). Two post-folding magnetic components were observed also. The first post-folding magnetic component has D = 282.4°, I =-36.4°,k 30.3, and the second has D = 3 18.6°, I 33.0°,k = 60.5. The final magnetic component is very close to the Permian paleomagnetic direction expected from the North China platform. The first post-folding component of magnetization may have been acquired during the Variscan accretion in Early Carboniferous time when the basin was closed. The South Mongolian paleo-ocean was located in equatorial latitudes near the Tarim block, the South China platform and probably the North China platform in the Devonian.

International Journal of Geosciences, 2012

Based on digital elevation models SRTM03 and SRTM30_Plus (Shuttle Radar Topography Mission Survey... more Based on digital elevation models SRTM03 and SRTM30_Plus (Shuttle Radar Topography Mission Survey) the technique for detecting major structural elements and elucidating details of the geologic structure including discrimination of linear structures and texture features is elaborated. The computation of the modulus of the first derivative by the coordinate, i.e., the modulus of the topography gradient, characterizing the state of the surface by steepness and direction of slope (azimuth) is assumed as a basis. The technique was applied for the study of tectonics and metallogeny of the Uchur-Maya Meso-Neoproterozoic basin. The structural and lithological controlling factors of ore occurrences are established. It has been shown the efficacy of using the transformed digital elevation models for the geological and tectonic studies.

Russian Journal of Earth Sciences, 2003

This paper is based on the results of the work done during a long period of time in the framework... more This paper is based on the results of the work done during a long period of time in the framework of the International Project "Atlas of Lithopaleographic, Structural and Geoecological Maps of Central Eurasia". Having generalized the original and published data available for the geologic structure and paleomagnetism of the Altai-Sayan and Ural regions, the Siberian Craton, the East-European Platform, Mongolia, Kazakhstan, and Tien Shan, palinspastic maps have been compiled for the Vendian, Early Cambrian, and Early and Late Ordovician (600, 525, 500, and 450 Ma). The maps depict the composition of the rocks and the environments of their origin. The structure, evolution, and geological history of the Paleoasian Ocean is described as a system of marginal basins and island arcs belonging to the continental margin of the East Paleogondwana (a fragment of the Rodinia Supercontinent), including the early stages of the transformation of the Paleoasian Ocean into a fold-and-nappe structure. The maps are accompanied by numerous cross sections, palinspastic profiles, and maps of some areas, showing the details of individual structural features. This paper is based on the results of the long investigations done in the framework of the international project "At

Russian Journal of Earth Sciences

Presented in this paper are paleomagnetic data for the Vendian sedimentary rocks of the southwest... more Presented in this paper are paleomagnetic data for the Vendian sedimentary rocks of the southwestern region of the Siberian Platform, obtained during the study of the reference rock sequences of the Central and Biryusa areas of the Sayan region and of the Yenisei mountain range in the lower reaches of the Angara River and its tributaries. This study proved the wide development of metachronous pre-and synfolding magnetization components which originated after the accumulation of the sedimentary rock sequences, yet, obviously not later than the Early Cambrian. All of the study rocks of the Nemakit-Daldynian age show two clearly distinguished paleomagnetic trends which seem to have formed during or soon after the accumulation of the rocks. Earlier, we got similar results for the Late Vendian rocks of the Southwest Baikal and East Sayan regions and also for the transitional Vendian-Lower Cambrian rock sequences of the Siberian Platform. This allowed us to infer the anomalous behavior of the geomagnetic field at the end of the Vendian to the beginning of the Lower Cambrian. The results obtained in the study reported here prove the actual basis of this hypothesis. During our study of the older Ediacarian and Ediacarian-Nemakit-Daldynian rocks, we managed to distinguish stable high-temperature magnetization components, obviously reflecting the trend of the geomagnetic field that existed during the accumulation of these rocks. The paleomagnetic poles corresponding to these components allowed us to reconstruct the late Vendian trend of the apparent migration of the pole and evaluate the character of the Siberian Platform movements during that time, which allowed us to chose the polarity for the Riphean paleomagnetic trends of Siberia.

Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was... more Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was maximum opening. Thus paleomagnetic data contribute to the reconstruc- tion of the primary tectonic position of the blocks of the paleoocean crust and blocks, surrounded this ocean. Revelation of geodynamic formations, boarded the Urals pale- oocean to the east and theirs

Tectonophysics, 1993

ABSTRACT We have completed a paleomagnetic reconnaissance study of sedimentary and volcanic extru... more ABSTRACT We have completed a paleomagnetic reconnaissance study of sedimentary and volcanic extrusive rocks collected from two major tectonic zones in northeastern Russia. Paleomagnetic sites were sampled within the fault-bounded structural units of the Khatyrka and Maynitsky superterranes and an overlap sequence of the Khatyrka superterrane. These sampling localities were chosen to allow both within-site and between-site fold tests. Stepwise thermal demagnetization within the temperature range 200–640°C showed a characteristic linear demagnetization path between thermal demagnetization steps of 400°C and 530°C. For thermal steps above 550°C, the magnetic intensity of many samples began to increase rapidly with magnetic directions, which were random between heating steps, suggesting the formation of new magnetic phases in these samples. Paleomagnetic samples collected from basalts and sediments of the Khatyrka superterrane and basalts and gabbros of the Maynitsky superterrane pass fold tests and show significant poleward motion of these superterranes since the formation of their rocks. The observed paleomagnetic paleolatitudes between 24°N or S and 32°N or S can be compared with expected paleolatitudes of 57°N to 79°N. Paleomagnetic results from sites collected from overlapping Senonian rocks pass a fold test at the 99% confidence level and give a pole position not significantly different from that expected from the apparent polar wander path for the Eurasia or North America plates, suggesting that these sedimentary units overlapping the Khatyrka superterrane were deposited along the ancient northeast margin of the Eurasian plate. The declination, in stratigraphie coordinates, shows a maximum clockwise rotation of about 20° when compared with the Eurasian APWP.

Russian Geology and Geophysics, 2009

We report a new paleomagnetic determination of Paleoproterozoic rocks from the Siberian craton wh... more We report a new paleomagnetic determination of Paleoproterozoic rocks from the Siberian craton which showed a positive baked contact test and a stable age of the high-temperature NRM component. The mean paleomagnetic pole of Siberia for ∼1730 Ma located at 42.9° S, 109.6° E (α95 = 5.3°) is compatible with the pole positions obtained recently for the middle and late Early Proterozoic.

Geophysical Journal International, 2012

A significant margin-parallel translation of terranes is postulated by all models for tectonic ev... more A significant margin-parallel translation of terranes is postulated by all models for tectonic evolution of the East Asian continental margin, although the timing and magnitude of displacements of individual elements are poorly constrained as yet. The West Sakhalin Basin-a forearc basin associated with the Cretaceous volcanic arcs-is one of the displaced tectonic elements. Our palaeomagnetic study of the basin rocks provides the first quantitative constraints on its Cretaceous history. We identified a characteristic magnetization in the Berriasian-Valanginian basalt representing the oceanic basement of the basin and four characteristic magnetizations in a continuous sequence of the Albian to Maastrichtian siliciclastic fill of the basin. A combination of the positive fold, conglomerate and reversals tests supports the primary origin of the remanence in the sediments. Palaeomagnetic data indicate a gradual shift of the West Sakhalin Basin from subequatorial latitudes during the Early Cretaceous to about 40 o N by the Late Cretaceous. The main phase of the margin-parallel migration took place during the Early Cretaceous, and ended by the Cenomanian. The continuous sedimentary sequence records ∼50 degrees of progressive clockwise rotation during the Late Cretaceous.

New paleomagnetic data have been obtained for the Late Vendian sedimentary rocks of the East Saya... more New paleomagnetic data have been obtained for the Late Vendian sedimentary rocks of the East Sayan and Southwest Baikal regions in the southwest of the Siberian platform. Two substantially different paleomagnetic components are isolated within the investigated stratigraphic interval in all objects of study. The prefolding age of these components, as well as their difference from all of the known Phanerozoic paleomagnetic directions of the Siberian platform, indicate the almost simultaneous formation of the respective magnetization components during the earliest stages of the existence of these rocks. The angular distance between the paleomagnetic poles calculated for these components is about 45 •. The analysis of the World Paleomagnetic Database shows that the presence of the discordant paleomagnetic directions in the Vendian-Early Cambrian rocks is characteristic not only of the Siberian objects but is also manifested in other continents and, hence, can be considered as the phenomenon of the planetary scale. We reckon that this fact can be explained by the anomalous behavior of the magnetic field of the Earth around the Precambrian-Cambrian boundary. In this paper we suggest a model describing the "geometry" of the Earth magnetic field in the Late Vendian-Early Cambrian, which allows one to explain the observed pattern of the paleomagnetic record.

Doklady Earth Sciences

ABSTRACT

Russian Journal of Pacific Geology, 2010

Pure and Applied Geophysics, 2021

Analysis of the available Moho models for the Sikhote Alin region revealed significant discrepanc... more Analysis of the available Moho models for the Sikhote Alin region revealed significant discrepancies between them both in depth for individual sites and isolines over the entire area of the orogenic belt. In this study, results of the two-dimensional power spectrum analysis of the gravity field based on a digital model of the Bouguer gravity field were used to calculate the crustal thickness (Moho depth). The data from seven seismic profiles were employed to adjust the new model. The new model and its correlation with structural and geological data allowed the following conclusions to be made. (1) The span of Moho depth variations for the southern part of the continental Far East of Russia is just over 18 km, with extreme values of 42.4 and 24.0 km. The Moho is deepest (41–42 km) beneath mountain ranges and massifs: Sikhote Alin in the east and Yam Alin and Aesop in the north-west. The Moho is most shallow (27–30 km) beneath the sedimentary basins Khanka, Partizan-Sukhodol, Suifun in the south, Middle Amur and Lower Amur in the central part of the study area, and Upper Zeya and Uda in the north-west. (2) Correlation of the Moho estimates derived from the Airy model and the power spectrum of the Bouguer gravity field shows significant positive correlation. The Moho depths practically coincide over 11% of the area, with a difference of ± 5%. The Moho depth discrepancies are in the range of 5–15% over 48% of the study area, and over the rest of the study area (41%), discrepancies are in the range of 15–30%. (3) A comparison between the new gravity Moho model and the geological and structural data shows that the model is highly correlated with the development of Cretaceous–Early Eocene orogenic and post-orogenic granitoid massifs and Cretaceous–Pliocene extrusive igneous rocks. The former geographically coincide with two linear zones in the Moho relief with depths of more than 35 km, and the latter with the Mesozoic–Cenozoic sedimentary basins and the East Sikhote Alin volcano–plutonic belt.

Earth-Science Reviews, 2016

Recent ICDP drilling and deep basin volcanic exploration of 3000 m below the surface in the Songl... more Recent ICDP drilling and deep basin volcanic exploration of 3000 m below the surface in the Songliao Basin (SB) have highlighted the 3-D delineation of the basin. The integrated new data led us to reevaluate the basin tectonics, for which the basin type, basin evolution and a number of geodynamic aspects have been controversial topics. We outline the position of a main lithospheric scale detachment fault beneath the SB, based on apparent crustal scale displacements, Moho breaks, the thinning of the Moho transition zone beneath the SB and the changing mantle thickness. This fault interpretation is consistent with simple shear as the rift mechanism. Based on a comprehensive analysis of the tectonic setting, underlying crust, structural style, sequence stratigraphy, subsidence history and volcanism, we propose an active continental margin model for the SB which shows some similarities to aulacogens but also notable differences. Situated between two Late Mesozoic active continental margins, the northern/northwestern Mongol-Okhotsk and the eastern Sikhote-Alin orogenic belts, the Cretaceous basin evolved on a pre-Triassic structurally weak basement mosaic. Its development began with regional mega-rifting from 150 to 105 Ma, followed by significant sagging between 105 and 79.1 Ma and ended with regional uplift and basin inversion from 79.1 to 64 Ma. Three regional angular unconformities separate the basin fill into three respective tectono-stratigraphic sequences. (1) The syn-rift stage is characterized by widespread fault-bounded grabens and volcanogenic successions, corresponding upward to the Huoshiling, Shahezi and Yingcheng Formations. (2) The post-rift stage includes the Denglouku, Quantou, Qignshankou, Yaojia and Nenjiang Formations. It is a special feature that the subsidence rate is abnormally high (mean of 103 m/Ma), and that flood basalt erupted along an axial wrench fault zone, associated with several marine intervals from the mid-Turonian to early Campanian (K 2 qn to K 2 n), possibly (not certainly) indicating incipient sea floor spreading characterized by Moho breaks along the basin axis in the SB around 88 Ma. Stretching stopped abruptly at approximately 79.1 Ma and was followed by uplift and rapid erosion (−145 m/Ma). (3) Recorded by the Sifangtai and Mingshui Formations the structural inversion stage included a continuous depocenter migration to the northwest. The basin was shrinking to demise as a result of changing subduction parameters of the Pacific subduction zone. In addition to the three tectonic basin cycles, a cyclic basin fill pattern exists with three volcanic basin fill intervals of Huoshiling, Yingcheng, and upper Qingshankou Formations that alternate with sedimentary basin fill intervals of Shahezi, Dengloukou-Quantou, and Yaojia-Nenjiang Formations. When determining the subsidence rates, we observed not only anomalously fast subsidence but also found an intricate link between the subsidence rate and type of basin fill. After each volcanic interval, the subsidence rates increased in a cyclic fashion during the sedimentary intervals. Thus, there is a system of three different types of important, basin-wide geological cycles that controlled the evolution of the SB. The subsidence rate was especially high (up to 199 m/Ma) after the last volcanic episode at 88 Ma. In addition to thermal subsidence and loading by the basin fill as causative processes, we also consider magmatic processes related to asthenospheric upwelling beneath the SB. They involve the roof collapse of shallow, depleted magma chambers, the igneous accretion of initially hot, dense, basic rocks, and lithospheric delamination beneath the SB. The difference in the subsidence rates during the volcanic and sedimentary intervals may in part also have been due to heating-related uplift during the volcanic intervals. The particularly high subsidence during the Late Cretaceous sedimentary cycles was partly increased by transtension.

Tectonic Evolution of the Bering Shelf-Chukchi Sea-Artic Margin and Adjacent Landmasses, 2002

... Bondarenko Sergei D. Sokolov Igor R. Kravchenko-Berezhnoy Geological Institute, Russian Acade... more ... Bondarenko Sergei D. Sokolov Igor R. Kravchenko-Berezhnoy Geological Institute, Russian Academy of Sciences, Moscow ABSTRACT Geologic and paleomagnetic research in the western part of the Omolon massif and in the Sugoi folded zone, northeastern Russia, suggests ...

Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was... more Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was maximum opening. Thus paleomagnetic data contribute to the reconstruc- tion of the primary tectonic position of the blocks of the paleoocean crust and blocks, surrounded this ocean. Revelation of geodynamic formations, boarded the Urals pale- oocean to the east and theirs

This paper reports and discusses the petromagnetic (i.e., rock magnetic) properties and chemical ... more This paper reports and discusses the petromagnetic (i.e., rock magnetic) properties and chemical compositions of titanomag-netites occurring within a bimodal suite of late Pliocene volcanic rocks obtained from the Taitao Ridge, at Site 862 in the Chile Triple Junction region. The results indicate a marked contrast in magmatic sources, as well as in the cooling and alteration histories for the silicic and basaltic lavas. Basaltic units have petromagnetic and chemical characteristics generally consistent with a mid-ocean ridge basalt (MORB) affinity, and show systematic differences that correlate with the texturally-inferred cooling and alteration histories. Magnetic phases in the silicic lavas are similar to those reported from calc-alkaline circum-Pacific suites. The secondary alteration of the titanomagnetites within the silicic units is much less than that observed within the basaltic lavas, in which titanomagnetite has been altered to titanomaghemite. Given the elevated forearc g...

Russian Journal of Earth Sciences

Physics of the Earth and Planetary Interiors, 1992

This paper presents new paleomagnetic data from South Mongolia. Middle Paleozoic rocks were studi... more This paper presents new paleomagnetic data from South Mongolia. Middle Paleozoic rocks were studied from three different tectonic zones within the South Mongolian fold belt. From north to south these are the Gobi-Altai zone (in terms of paleotectonic position, the 'north' shelf of the paleobasin), the Trans-Altai zone (ophiolite complexes) and the South Gobia zone (the 'south' shelf). Several paleomagnetic field tests, including conglomerate, baked contact and fold tests, were carried out to determine magnetic stability. In addition, principal component analysis of the stepwise thermal demagnetization data was used. The ophiolites are characterized by three ancient components. One magnetic component is pre-folding and directed to the south with a very gentle inclination (declination (D) 180-210°, inclination (I) =-6~~+ 2°,K 120). Two post-folding magnetic components were observed also. The first post-folding magnetic component has D = 282.4°, I =-36.4°,k 30.3, and the second has D = 3 18.6°, I 33.0°,k = 60.5. The final magnetic component is very close to the Permian paleomagnetic direction expected from the North China platform. The first post-folding component of magnetization may have been acquired during the Variscan accretion in Early Carboniferous time when the basin was closed. The South Mongolian paleo-ocean was located in equatorial latitudes near the Tarim block, the South China platform and probably the North China platform in the Devonian.

International Journal of Geosciences, 2012

Based on digital elevation models SRTM03 and SRTM30_Plus (Shuttle Radar Topography Mission Survey... more Based on digital elevation models SRTM03 and SRTM30_Plus (Shuttle Radar Topography Mission Survey) the technique for detecting major structural elements and elucidating details of the geologic structure including discrimination of linear structures and texture features is elaborated. The computation of the modulus of the first derivative by the coordinate, i.e., the modulus of the topography gradient, characterizing the state of the surface by steepness and direction of slope (azimuth) is assumed as a basis. The technique was applied for the study of tectonics and metallogeny of the Uchur-Maya Meso-Neoproterozoic basin. The structural and lithological controlling factors of ore occurrences are established. It has been shown the efficacy of using the transformed digital elevation models for the geological and tectonic studies.

Russian Journal of Earth Sciences, 2003

This paper is based on the results of the work done during a long period of time in the framework... more This paper is based on the results of the work done during a long period of time in the framework of the International Project "Atlas of Lithopaleographic, Structural and Geoecological Maps of Central Eurasia". Having generalized the original and published data available for the geologic structure and paleomagnetism of the Altai-Sayan and Ural regions, the Siberian Craton, the East-European Platform, Mongolia, Kazakhstan, and Tien Shan, palinspastic maps have been compiled for the Vendian, Early Cambrian, and Early and Late Ordovician (600, 525, 500, and 450 Ma). The maps depict the composition of the rocks and the environments of their origin. The structure, evolution, and geological history of the Paleoasian Ocean is described as a system of marginal basins and island arcs belonging to the continental margin of the East Paleogondwana (a fragment of the Rodinia Supercontinent), including the early stages of the transformation of the Paleoasian Ocean into a fold-and-nappe structure. The maps are accompanied by numerous cross sections, palinspastic profiles, and maps of some areas, showing the details of individual structural features. This paper is based on the results of the long investigations done in the framework of the international project "At

Russian Journal of Earth Sciences

Presented in this paper are paleomagnetic data for the Vendian sedimentary rocks of the southwest... more Presented in this paper are paleomagnetic data for the Vendian sedimentary rocks of the southwestern region of the Siberian Platform, obtained during the study of the reference rock sequences of the Central and Biryusa areas of the Sayan region and of the Yenisei mountain range in the lower reaches of the Angara River and its tributaries. This study proved the wide development of metachronous pre-and synfolding magnetization components which originated after the accumulation of the sedimentary rock sequences, yet, obviously not later than the Early Cambrian. All of the study rocks of the Nemakit-Daldynian age show two clearly distinguished paleomagnetic trends which seem to have formed during or soon after the accumulation of the rocks. Earlier, we got similar results for the Late Vendian rocks of the Southwest Baikal and East Sayan regions and also for the transitional Vendian-Lower Cambrian rock sequences of the Siberian Platform. This allowed us to infer the anomalous behavior of the geomagnetic field at the end of the Vendian to the beginning of the Lower Cambrian. The results obtained in the study reported here prove the actual basis of this hypothesis. During our study of the older Ediacarian and Ediacarian-Nemakit-Daldynian rocks, we managed to distinguish stable high-temperature magnetization components, obviously reflecting the trend of the geomagnetic field that existed during the accumulation of these rocks. The paleomagnetic poles corresponding to these components allowed us to reconstruct the late Vendian trend of the apparent migration of the pole and evaluate the character of the Siberian Platform movements during that time, which allowed us to chose the polarity for the Riphean paleomagnetic trends of Siberia.

Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was... more Ordovician time - one of the key events at the Urals: during this time the Urals pale- oocean was maximum opening. Thus paleomagnetic data contribute to the reconstruc- tion of the primary tectonic position of the blocks of the paleoocean crust and blocks, surrounded this ocean. Revelation of geodynamic formations, boarded the Urals pale- oocean to the east and theirs

Tectonophysics, 1993

ABSTRACT We have completed a paleomagnetic reconnaissance study of sedimentary and volcanic extru... more ABSTRACT We have completed a paleomagnetic reconnaissance study of sedimentary and volcanic extrusive rocks collected from two major tectonic zones in northeastern Russia. Paleomagnetic sites were sampled within the fault-bounded structural units of the Khatyrka and Maynitsky superterranes and an overlap sequence of the Khatyrka superterrane. These sampling localities were chosen to allow both within-site and between-site fold tests. Stepwise thermal demagnetization within the temperature range 200–640°C showed a characteristic linear demagnetization path between thermal demagnetization steps of 400°C and 530°C. For thermal steps above 550°C, the magnetic intensity of many samples began to increase rapidly with magnetic directions, which were random between heating steps, suggesting the formation of new magnetic phases in these samples. Paleomagnetic samples collected from basalts and sediments of the Khatyrka superterrane and basalts and gabbros of the Maynitsky superterrane pass fold tests and show significant poleward motion of these superterranes since the formation of their rocks. The observed paleomagnetic paleolatitudes between 24°N or S and 32°N or S can be compared with expected paleolatitudes of 57°N to 79°N. Paleomagnetic results from sites collected from overlapping Senonian rocks pass a fold test at the 99% confidence level and give a pole position not significantly different from that expected from the apparent polar wander path for the Eurasia or North America plates, suggesting that these sedimentary units overlapping the Khatyrka superterrane were deposited along the ancient northeast margin of the Eurasian plate. The declination, in stratigraphie coordinates, shows a maximum clockwise rotation of about 20° when compared with the Eurasian APWP.

Russian Geology and Geophysics, 2009

We report a new paleomagnetic determination of Paleoproterozoic rocks from the Siberian craton wh... more We report a new paleomagnetic determination of Paleoproterozoic rocks from the Siberian craton which showed a positive baked contact test and a stable age of the high-temperature NRM component. The mean paleomagnetic pole of Siberia for ∼1730 Ma located at 42.9° S, 109.6° E (α95 = 5.3°) is compatible with the pole positions obtained recently for the middle and late Early Proterozoic.

Geophysical Journal International, 2012

A significant margin-parallel translation of terranes is postulated by all models for tectonic ev... more A significant margin-parallel translation of terranes is postulated by all models for tectonic evolution of the East Asian continental margin, although the timing and magnitude of displacements of individual elements are poorly constrained as yet. The West Sakhalin Basin-a forearc basin associated with the Cretaceous volcanic arcs-is one of the displaced tectonic elements. Our palaeomagnetic study of the basin rocks provides the first quantitative constraints on its Cretaceous history. We identified a characteristic magnetization in the Berriasian-Valanginian basalt representing the oceanic basement of the basin and four characteristic magnetizations in a continuous sequence of the Albian to Maastrichtian siliciclastic fill of the basin. A combination of the positive fold, conglomerate and reversals tests supports the primary origin of the remanence in the sediments. Palaeomagnetic data indicate a gradual shift of the West Sakhalin Basin from subequatorial latitudes during the Early Cretaceous to about 40 o N by the Late Cretaceous. The main phase of the margin-parallel migration took place during the Early Cretaceous, and ended by the Cenomanian. The continuous sedimentary sequence records ∼50 degrees of progressive clockwise rotation during the Late Cretaceous.

New paleomagnetic data have been obtained for the Late Vendian sedimentary rocks of the East Saya... more New paleomagnetic data have been obtained for the Late Vendian sedimentary rocks of the East Sayan and Southwest Baikal regions in the southwest of the Siberian platform. Two substantially different paleomagnetic components are isolated within the investigated stratigraphic interval in all objects of study. The prefolding age of these components, as well as their difference from all of the known Phanerozoic paleomagnetic directions of the Siberian platform, indicate the almost simultaneous formation of the respective magnetization components during the earliest stages of the existence of these rocks. The angular distance between the paleomagnetic poles calculated for these components is about 45 •. The analysis of the World Paleomagnetic Database shows that the presence of the discordant paleomagnetic directions in the Vendian-Early Cambrian rocks is characteristic not only of the Siberian objects but is also manifested in other continents and, hence, can be considered as the phenomenon of the planetary scale. We reckon that this fact can be explained by the anomalous behavior of the magnetic field of the Earth around the Precambrian-Cambrian boundary. In this paper we suggest a model describing the "geometry" of the Earth magnetic field in the Late Vendian-Early Cambrian, which allows one to explain the observed pattern of the paleomagnetic record.

Doklady Earth Sciences

ABSTRACT

Russian Journal of Pacific Geology, 2010