V. E. Khain

Tectonics of the eastern Arctic region

The Vendian (Baikalian), Late Devonian (Ellesmerian), and Mid-Cretaceous (Brookian) orogenies were three cardinal events in the history of formation and transformation of the continental crust in the eastern Arctic region. The epi-Baikalian Hyperborean Craton was formed by the end of the Vendian (660–550 Ma), when the Archean-Proterozoic Hyperborean continental block was built up by the Baikalian orogenic belt and concomitant collision granitoids. As judged from the localization of deepwater facies, the Early Paleozoic ocean occupied the western part of the Canadian Arctic Archipelago, western Alaska, and the southern framework of the Canada and Podvodnikov basins and was connected with the Iapetus ocean. The closure of the Early Paleozoic Arctic basins is recorded in two surfaces of structural unconformities corresponding to the pre-Middle Devonian Scandian orogenic phase and the Late Devonian Ellesmerian Orogeny; each tectonic phase was accompanied by dislocations and metamorphism. The Ellesmerian collision was crucial in the Caledonian tectogenesis. The widespread Late Devonian-Mississippian rifting probably was a reflection of postorogenic relaxation. As a result, the vast epi-Caledonian continental plate named Euramerica, or Laurussia, was formed at the Devonian-Carboniferous boundary. The East Arctic segment of this plate is considered in this paper. In the Devonian, the Angayucham ocean, which was connected with the Paleoasian and Uralian oceans [62], separated this plate from the Siberian continent. The South Anyui Basin most likely was a part of this Paleozoic oceanic space. The shelf sedimentation on the epi-Caledonian plate in the Carboniferous and Permian was followed by subsidence and initial rifting in the Triassic and Jurassic, which further gave way to the late Neocomian-early Albian spreading in the Canada Basin that detached the Chukchi Peninsula-Alaska microplate from the continental plate [25]. The collision of this microplate with the Siberian continent led to the closure of the South Anyui-Angayucham ocean and the development of the Mid-Cretaceous New Siberian-Chukchi-Brooks Orogenic System that comprised the back Chukchi Zone as a hinterland and the frontal New Siberian-Wrangel-Herald-Lisburne-Brooks Thrust Zone as a foreland; the basins coeval with thrusting adjoined the foreland. Collision started in the Late Jurassic; however, the peak of the orogenic stage fell on the interval 125–112 Ma, when ophiolites had been obducted on the margin of the Chukchi Peninsula-Alaska microplate along with folding and thrusting accompanied by an increase in the crust’s thickness, amphibolite-facies metamorphism, and growth of granite-gneiss domes. The magmatic diapir of the De Long Arch that grew within the continental plate in the Mid-Cretaceous reflected a global pulse of the lower mantle upwelling that coincided with the maximum opening of the Canada Basin. The present-day appearance of the eastern Arctic region arose in the Late Mesozoic and Cenozoic owing to the opening of the Amerasia and Eurasia oceans. Sedimentary basins of various ages and origins—including the Late Devonian-Early Carboniferous grabens, the spatially coinciding Late Jurassic-Early Cretaceous rifts related to the opening of the Canada Basin, the syncollision basins in front of the growing orogen, and the Cretaceous-Cenozoic basins coeval with strike-slip faulting and rifting at the final stages of orogenic compression and during the opening of the Eurasia ocean were telescoped on sea shelves.

The Arctida Craton and Neoproterozoic-Mesozoic orogenic belts of the Circum-Polar region

An attempt is made to characterize an assembly of Arctic tectonic units formed before the opening of the Arctic Ocean. This assembly comprises the epi-Grenville Arctida Craton (a fragment of Rodinia) and the marginal parts of the Precambrian Laurentia, Baltica, and Siberian cratons. The cratons are amalgamated by orogenic belts (trails of formerly closed oceans). These are the Late Neoproterozoic belts (Baikalides), Middle Paleozoic belts (Caledonides), Permo-Triassic belts (Hercynides), and Early Cretaceous belts (Late Kimmerides). Arctida encompasses an area from the Svalbard Archipelago in the west to North Alaska in the east. The Svalbard, Barents, Kara, and other cratons are often considered independent Precambrian minicratons, but actually they are constituents of Arctida subsequently broken down into several blocks. The Neoproterozoic orogenic belt extends as a discontinuous tract from the Barents-Ural-Novaya Zemlya region via the Taimyr Peninsula and shelf of the East Siberian Sea to North Alaska as an arcuate framework of Arctida, which separates it from the Baltica and Siberian cratons. The Caledonian orogenic belt consisting of the Scandian and Ellesmerian segments frames Arctida on the opposite side, separating it from the Laurentian Craton. The opposite position of the Baikalian and Caledonian orogenic belts in the Arctida framework makes it possible to judge about the time when the boundaries of this craton formed as a result of its detachment from Rodinia. The Hercynian orogenic belt in the Arctic Region comprises the Novozemel’sky (Novaya Zemlya) and Taimyr segments, which initially were an ending of the Ural Hercynides subsequenly separated by a strike-slip fault. The Mid-Cretaceous (Late Kimmerian) orogenic belt as an offset of Pacific is divergent. It was formed under the effect of the opened Canada Basin and accretion and collision at the Pacific margins. The undertaken typification of pre-Late Mesozoic tectonic units, for the time being debatable in some aspects, allows reconstruction of the oceanic basins that predated the formation of the Arctic Ocean.

Geodynamic cycles and geodynamic systems of various ranks: Their relationships and evolution in the Earth’s history

The previously stated ideas of hierarchical geodynamic cyclicity [42] and geodynamics of hierarchically subordinate geospheres [13] are compared in detail. The convective geodynamic system of the first rank (GS-1) that functions throughout the mantle and crust beneath the entire surface of the Earth corresponds to the geodynamic cycle of the first rank (GC-1, or the Wilson cycle). The geodynamic system of the second rank (GS-2) that embraces the mantle and crust only beneath oceans corresponds to the geodynamic cycle of the second rank (GC-2, or the Bertrand cycle). The geodynamic system of the third rank (GS-3) functioning in the tectonosphere (asthenosphere + lithosphere) in zones of elevated heat flow (spreading, subduction, and collision zones) is brought into the line with the geodynamic cycle of the third rank (GC-3, or the Stille cycle). The geodynamic system of the fourth rank (GS-4) that embraces the sedimentary cover of mobile belts corresponds to the geodynamic cycle of the fourth rank (GC-4) (the phase cycle of increasing and decreasing intensity of folding and thrusting). This hierarchy controlled by internal endogenic factors, above all, by the heat flow from the Earth’s core and internal sources within the mantle, is supplemented by the geodynamic system of the zeroth rank (GS-0) that embraces the entire Earth and that is controlled by external rotational factors, primarily, the tidal effect of the Moon. The GS-0 is characterized by interference of the permanent westward and meridional (southward and northward, alternately) continental drift in frames of the zeroth geodynamic cycle (GC-0) twice as long as the Wilson cycle (GC-1). An attempt is made to connect cyclicity of various ranks with periodic excitation and waning of convection in a geosphere of the respective rank. The convective geospheres progressively grew downward in the course of geologic history. Only the GS-3 functioned in the Archean, embracing tectonosphere and creating greenstone belts around the gray-gneiss islands with gradual accretion of these belts and the formation of the granite-greenstone continent (Pangea-0). In the Paleoproterozoic, the process spread over the entire upper mantle with switching Rayleigh-Benard polygonal convection expressed in pure form as granulite belts along the polygon perimeters that bounded the protoplatform blocks. The contemporaneous limited convection in the lower mantle (GS-1) led to some divergence of these blocks and formation of minor oceans and their subsequent closure, resulting in the formation of Pangea-1. This tendency developed further in the Mesoproterozoic and completed with the formation of Pangea-2 (Rodinia). Afterward, in the Neogean, the cyclic-hierarchical geodynamics started to work in full as described above.

Structural units of the central arctic and their relations to the mesozoic arctic plume

The integration of information obtained from onshore and offshore geological and geophysical research undertaken in the context of the International Polar Year has led to the following results. The continental crust is widespread in the Arctic not only beneath the shelves of polar seas in the framework of the Amerasia Basin but also in the Chukchi-Northwind, Lomonosov, and Mendeleev ridges; a combination of continental and oceanic crusts is inferred in the Alpha Ridge. The Amerasia Basin is not an indivisible element of the Arctic Ocean either in genetic or structural terms but consists of variously oriented basins different in age. The first, Mesozoic “minor ocean” of the Arctic Ocean—the Canada Basin—arose as a result of impact of the Arctic plume on the high-latitude region of Pangea. This inference is supported by the vast Central Arctic igneous province that comprises the Jurassic-Mid-Cretaceous within-plate and ocean-island basaltic and associated rocks. The rotational mechanism of opening of this basin is explained by the slant path of the plume head motion, which resulted in breaking-off and displacement of a fragment of Pangea. The effect of the Arctic plume was expressed during all stages of the opening of the Canada Basin and exerted effects on the adjacent part of the Eurasian continent during the formation of the Verkhoyansk-Chukotka tectonic domain. The Canada Basin was an element of the segmented system of Atlantic spreading ridges, while the Arctic plume that initiated its evolution was genetically related to the episodically acting African-Atlantic superplume. In comparison with the Pacific superplume, the low productivity of African-Atlantic lower mantle upwelling became the cause of slow and ultraslow spreading in the Atlantic and Arctic oceans and determined the passive character of their margins, including the Canada Basin.

Development of the Verkhoyansk-Kolyma orogenic system as a result of interaction of adjacent continental and oceanic plates

The Mid-Cretaceous Verkhoyansk-Chukchi Tectonic Domain is characterized by fanlike diverging systems of tectonic sheets and imbricate thrusts verging to the two framing continents. The Verkhoyansk and New Siberian-Chukchi-Brooks Fold-Thrust systems of the deformed margins of the Siberian and Hyperborean-North American continents, respectively, adjoin the inner Verkhoyansk-Kolyma Collision System. The above fold-thrust systems include the Verkhoyansk and Colville foredeeps coeval with thrusting. The Verkhoyansk-Kolyma Fold-Nappe System is composed of Cambrian to Upper Jurassic oceanic, marginal-sea, and island-arc complexes and bounded by a collision suture consisting of the Kolyma Loop abutted on the South Anyui segment along a left-lateral strike-slip fault. The inner root zone and the outer zone of nappes overthrusting the adjacent continents are distinguished in the suture. Several levels of structural unconformities, olistostrome-molasse sequences, and zones of amphibolite-greenschist metamorphism coeval with thrusting correspond to particular stages in the evolution of the Verkhoyansk-Kolyma System. The Neoproterozoic and Early Paleozoic oceans closed during the Baikalian and Caledonian orogenies. The Alazeya-South Anyui-Angayucham ocean that evolved from the Devonian to the Late Jurassic was subject to gradual closure against the background of trilateral compression during convergence of the Siberian and Hyperborean-North American cratons and accretion and collision along the Pacific margin. The fold-nappe structure of the Verkhoyansk-Kolyma Orogen and the boundary collision suture were disturbed by left-lateral strike-slip faults during Mid-Cretaceous compression, and the South Anyui segment of the suture was displaced to the northwest along the strike-slip fault. The Mid-Cretaceous Orogeny at the Pacific margin gave rise to meridional compression of its back zone and latitudinal squashing of the Verkhoyansk-Kolyma Orogen with formation of the Kolyma and Kobuk looplike limitations.

Large and giant hydrocarbon accumulations in the transitional continent-ocean zone

The petroleum resource potential is considered for the Atlantic, West Pacific, and East Pacific types of deepwater continental margins. The most considerable energy resources are concentrated at the Atlantic-type passive margins in the zone transitional to the ocean. The less studied continental slope of backarc seas of the generally active margins of the West Pacific type is currently not so rich in discoveries as the Atlantic-type margin, but is not devoid of certain expectations. In some of their parameters, the margins bounded by continental slopes may be regarded as analogs of classical passive margins. At the margins of the East Pacific type, the petroleum potential is solely confined to transform segments. In the shelf-continental-slope basins of the rift and pull-apart nature, petroleum fields occur largely in the upper fan complex, and to a lesser extent in the lower graben (rift) complex. In light of world experience, the shelf-continental-slope basins of the Arctic and Pacific margins of Russia are evaluated as highly promising.

Structure and Evolution of Nappe-Fold Edifices of the Alpine-Himalayan Belt: A Comparison

The Alpine-Himalayan Mesozoic-Cenozoic belt extends for ∼10,000 km and comprises ∼20 separate nappe-fold mountain edifices. These edifices in their internal structure, lithologic composition, and evolution exhibit both important similarities and differences, the analysis of which represents the purpose of this paper. Similarities include the nature of the lithologic-structural elements constituting these edifices, mutual disposition, and the sequence of development stages. Differences concern the age of the pre-Alpine basement, the age and degree of extension creating the deep-water basins existing at earlier stages of evolution of the orogenic edifices, the age and degree of deformation that led to the formation of the nappe-fold structure, and the direction of vergence. The nature of the formation of cratonic forelands on both sides of the mobile belt, the configuration of its borders, and the presence of numerous microcontinents inside the belt also have played substantial roles in determination of the...