An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070371

The history of the crustal subsidence in the Mesozoic and Cenozoic in the West Siberian Basin – the largest sedimentary basin in the world is considered. Most researchers associate its formation with post-rift crustal subsidence, which followed an episode of strong lithospheric stretching about 250 Ma ago at the Permian–Triassic transition. A characteristic feature of post-rift subsidence is a decrease in its rate in time. During the Mesozoic–Cenozoic history, the crustal subsidence rate in Western Siberia should have decreased by an order of magnitude. However, the analysis of long (700–900 km) seismic profiles in the north of Western Siberia and in the Southern Kara Sea shows that, on average, there has been an acceleration of the crustal subsidence since the beginning of the Mesozoic in these regions. Under such conditions, lithospheric stretching in them could be responsible for only a small fraction of the total crustal subsidence by 6–7 km. In Western Siberia, the crust is close to the isostatic equilibrium. Due to this, in the absence of strong stretching, the accumulation of thick sedimentary sequences in the basin could only have been caused by rock contraction in the lower crust due to prograde metamorphic reactions. To obtain the above results, we used some simple methods for the first time to analyze the structure of the sedimentary sequences in the West Siberian Basin. Detailed seismic profiles for many other deep basins on all the continents have been published. The methods of their interpretation implemented in the present paper can be easily applied to determine the role of lithospheric stretching in the formation of deep sedimentary basins on the global scale.

Slow crustal subsidence nonuniform in time and space occurred in the sedimentary basin of the Moscow Syneclise during 20 Ma in the Late Devonian. On the cool Precambrian lithosphere of the East European Craton, subsidence of this kind could have occurred only due to rock contraction in the lower crust resulting from prograde metamorphism. Crustal subsidence in the Middle and Late Devonian occurred after a long period of stability. This required the influx of mantle fluids into the lithosphere and then into the crust, which catalyzed the metamorphic reaction. The distribution of crustal subsidence was very heterogeneous, and its pattern repeatedly and radically changed over time. This indicates that the influx of deep fluids into the lithosphere was also highly variable, both in time and in space. There is no evidence of any connection between large basement faults and the pattern of the Late Devonian crustal subsidence. Together with a high variability of the subsidence, this suggests that, over the course of several million years, fluids have penetrated into the crust through an undisturbed mantle lithosphere 150 km thick. This indicates that the fluids had specific properties: they were surface-active and wetted grains of crystalline rocks, spreading as thin films into the inter-grain space. Rapid and frequent changes in the influx of deep fluids into the lithosphere rules out their connection with slow large-scale convective currents in the mantle. The slow, but long-term, extended over tens of millions of years, influx of surface-active mantle fluids into the lithosphere is also quite different from the powerful short-term outbursts of fluids from large mantle plumes approaching the lithospheric layer. The occurrence of crustal subsidence and kimberlite magmatism in a number of cratonic areas remote from each other suggests a widespread influx of deep fluids into the lithospheric layer on the continents.

The sedimentary basin of the Moscow syneclise is located in the central part of the East European craton. It is characterized by detailed drilling coverage and an extremely high degree of geological knowledge. During the Devonian the basin was exposed to laterally non-uniform crustal subsidence after a long period of erosion. Considering the large thickness of the ancient lithosphere, this subsidence regime could only take place here in connection with rock contraction in the lower part of the crust as a result of prograde metamorphism catalyzed by the infiltration of mantle fluids. Their inflow into the lithosphere of the East European craton is evidenced by the wide occurrence of basite and kimberlite magmatism during the Devonian. The lateral distribution of subsidence throughout the syneclise changed significantly over periods of several million years. This indicates the corresponding changes in the rate of inflow of the deep fluids into the ancient lithosphere and their high surface activity. This property of the fluids enabled their rapid infiltration into the mantle lithosphere and inflow into the crust over the entire syneclise. The long-term inflow of the deep fluids into the continental lithosphere, which frequently changed in time and space, is a hitherto unknown phenomenon not related to large-scale convection in the mantle or to the rise of large plumes. It could have been the cause of the formation of many intraplate sedimentary basins on the continents.

A vast area of up to five million square kilometers is located in the Pacific Ocean to the east of Australia. The Earth’s crust up to 10–23 km thick is submerged here to a depth of 1–4 km. This contrasts with the surrounding Southwest Pacific where the crust is submerged up to 5–6 km and has a thickness of 7 km, which is more typical for oceans. As is known from dredging and deep-sea drilling, Zealandia is composed of the continental crust. For a long time, it was close to the sea level and then it subsided into the depths. The same thickness, water depths, and subsidence history are found for some domains in the Central Arctic, Lomonosov Ridge, Podvodnikov Basin, and Mendeleev Ridge. The continental nature of the crust has been proven here by drilling and is suggested by the results of study of the sea floor bedrock. Deep basins of the Central Arctic and Zealandia were formed without intense crustal stretching. Its origin can be explained by the increase in density of gabbroids in the lower crust due to prograde metamorphism.

The western part of the large Amerasia Basin in the Arctic Ocean comprises the smaller basins of Podvodnikov and Makarov. Judging by the sedimentary structure and the crustal subsidence history, both basins were developed on the continental crust despite their 3-4 km water depths. By the early Miocene, prior to the rapid formation of the basins, the crustal surface had been close to the sea level for a long time. Lithospheric stretching had a minor input to the subsidence, which was rather driven mainly by the prograde metamorphism of gabbro in the lower crust and its transformation into denser eclogite. The mechanism of subsidence associated with the metamorphic transformation from gabbro to eclogite implies that high-velocity eclogite belongs to the lower continental crust metamorphosed under the effect of mantle fluids. This idea undermines the seismic and gravity basin models that commonly attribute mafic eclogite to the sub-Moho lithospheric mantle on the basis of P-wave velocities similar to those in peridotite and interprets the crust beneath the Podvodnikov and Makarov basins as thin continental and oceanic crustal types, respectively.

КОНТИНЕНТАЛЬНАЯ КОРА В ЗАПАДНОЙ ЧАСТИ АМЕРАЗИЙСКОГО БАССЕЙНА. МЕХАНИЗМЫ ПОГРУЖЕНИЯАртюшков Е. В., Смирнов О

Rapid glacio-isostatic rebound in Fennoscandia and Canada that is nonuniform in time and space indicates that there is a layer with strongly decreased viscosity at shallow crustal depths. The upper boundary of the layer is near the depth of 15 km, which corresponds to the maximum depth of earthquake hypocenters in the Precambrian cratons of the Kola Peninsula and Karelia. The position of the lower boundary is less distinct; however, most likely it is located near the base of the crust. The formation of such a layer in the Pliocene–Quaternary occurred due to infiltration of a large volume of mantle fluids into the crust. In many regions, this has led to retrograde metamorphism with rock expansion and a strong decrease in rocks viscosity.

The deep-water basin on the Lomonosov Ridge in Central Arctic was rapidly formed on a shallow water shelf in the early Miocene. The continuity of the main seismic reflectors in the sedimentary cover of the ridge indicates no significant crustal stretching during the subsidence. The absence of large free-air gravity anomalies above the ridge precludes the dynamic topography in the mantle from being a cause of the formation of the basin. In the Miocene, the ridge was very far from the convergent boundaries therefore lithospheric flexing is unlikely to produce the subsidence. Under these conditions, crustal subsidence on the ridge was most probably associated with the increase in the crustal density due to metamorphic reactions catalyzed by fluid infiltration from the mantle.

Precambrian cratons cover about 70% of the total continental area. According to a large volume of geomorphological, geological, paleontological, and other data for the Pliocene and Pleistocene, these cratons have experienced a crustal uplift from 100-200 m to 1000-1500 m, commonly called the recent or Neotectonic uplift. Shortening of the Precambrian crust terminated half a billion years ago or earlier, and its uplift could not have been produced by this mechanism. According to the main models of dynamic topography in the mantle, the distribution of displacements at the surface is quite different from that of the Neotectonic movements. According to seismic data, there is no magmatic underplating beneath most of the Precambrian cratons. In most of cratonic areas, the mantle lithosphere is very thick, which makes its recent delamination unlikely. Asthenospheric replacement of the lower part of the mantle lithosphere beneath the Precambrian cratons might have produced only a minor part of their Neotectonic uplifts. Since the above mechanisms cannot explain this phenomenon, the rock expansion in the crustal layer is supposed to be the main cause of the recent uplift of Precambrian cratons. This is supported by the strong lateral nonuniformity of the uplift, which indicates that expansion of rocks took place at a shallow depth. Expansion might have occurred in crustal rocks that emerged from the lower crust into the middle crust with lower pressure and temperature after the denudation of a thick layer of surface rocks. In the dry state, these rocks can remain metastable for a long time. However, rapid metamorphism accompanied by expansion of rocks can be caused by infiltration of hydrous fluids from the mantle. Analysis of phase diagrams for common crustal rocks demonstrates that this mechanism can explain the recent crustal uplift of Precambrian cratons. (C) 2018, VS. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All right reserved.

Analysis of the morphology of the recent uplifts on Precambrian cratons and geological–geophysical data on the structure of the crust and mantle indicate that these structures were formed due to expansion of the crustal rocks as a result of retrograde metamorphism. This occurred due to the contribution of large volumes of deep fluids to the complexes of the Early Proterozoic rocks, which underwent high-grade metamorphism in the lower crust. Later, these complexes were moved to the shallower depths after denudation of thick overlap sequences from the craton’s surfaces. The calculation of the volumetric expansion effects using P – T diagrams for the main types of metamorphic rocks shows that this mechanism could have prompted the uplifts of the Precambrian crust in recent time with amplitudes from 100–200 to 1000–1500 m.

The notions of deformations in the juncture area of the Eastern Arctic Shelf and Lomonosov Ridge are highly contradictory. It has been suggested that these geostructures were divided by a large right-lateral wrench fault of the transform type, which is known as the Khatanga–Lomonosov Fault. Data obtained by interpretation of the A7 profile have been compared with seismic sections crossing large-sized wrench faults in other sedimentary basins. The investigations have shown that on the A7 profile there are no structures typical of large-sized wrench faults. The Eastern Arctic Shelf and Lomonosov Ridge, which are located on the same lithospheric plate, form an integrated structure where the ridge is a natural continuation of the shelf.

According to a popular scheme of orogenesis, superposition of thick nappe on continental crust results in concomitant mountain building. In many cases plate collision was not accompanied by mountain building which actually occurred 10-100 Myr later. Thus in East Carpathians 12 Ma ago thick nappe was superimposed on the western margin of the East European Craton. The nappe remained near to sea level and mountain building began only 3 myr ago. In the Middle Urals collision developed in a number of phases during 70 Myr since the Late Devonian and until the earliest Permian; however, this produced no high topography. The formation of orogenic granitoids took place at the main stage of collision 306-300 Ma ago. High mountains were formed in the earliest Permian 10 Myr after the end of collision. In the Northern Tien Shan collision with intrusion of large granitic plutons occurred in the Late Ordovician-Middle Devonian. In the Southern Tien Shan these phenomena refer to the Late Carboniferous and Late Jurassic. In both regions collision was not accompanied by mountain building. High mountains were formed in the Tien Shan quite recently.

Up to 70% of the area of continents is occupied by the Precambrian crust. Shortening of this crust finished 0.5 Ga ago or earlier, while Pliocene–Quaternary rises made up of 100–200 to 1000–1500 m. In order to support these uplifts in the absence of shortening, the density in the lithosphere layer had to be considerably decreased. This lower density can be attributed to the replacement of the lower part of the mantle lithosphere with asthenospheric material or to the expansion of the inner parts of the crust resulting from repeated metamorphism. As is shown by our calculations, a decrease in density at depths of 150–250 km beneath the Precambrian cratons can lead to uplifts only up to 100 m in amplitude. Hence, the neotectonic uplifts were caused by expansion at higher crustal levels. This situation required the supply of a large amount of mantle fluid into the crust, and the volume of this fluid should be comparable to that of the new-formed relief

Consolidated crust in the North Barents basin with sediments 16-18 km thick is attenuated approximately by two times. The normal faults in the basin basement ensure only 10-15% stretching, which caused the deposition of 2-3 km sediments during the early evolution of the basin. The overlying 16 km of sediments have accumulated since the Late Devonian. Judging by the undisturbed reflectors to a depth of 8 s, crustal subsidence was not accompanied by any significant stretching throughout that time. Dramatic subsidence under such conditions required considerable contraction of lithospheric rocks. The contraction was mainly due to high-grade metamorphism in mafic rocks in the lower crust. The metamorphism was favored by increasing pressure and temperature in the lower crust with the accumulation of a thick layer of sediments. According to gravity data, the Moho in the basin is underlain by large masses of high-velocity eclogites, which are denser than mantle peridotites. The same is typical of some other ultradeep basins: North Caspian, South Caspian, North Chukchi, and Gulf of Mexico basins. From Late Devonian to Late Jurassic, several episodes of rapid crustal subsidence took place in the North Barents basin, which is typical of large petroleum basins. The subsidence was due to metamorphism in the lower crust, when it was infiltrated by mantle-source fluids in several episodes. The metamorphic contraction in the lower crust gave rise to deep-water basins with sediments with a high content of unoxidized organic matter. Along with numerous structural and nonstructural traps in the cover of the North Barents basin, this is strong evidence that the North Barents basin is a large hydrocarbon basin.