Okhotsk-Chukotka Volcanogenic Belt Research Articles

Depth to the bottom of lithospheric magnetic sources beneath north-eastern Eurasia: lithospheric thermal regime and relation to seismicity

For north-eastern Eurasia (60—70° N, 90—180° E), the bottom depth of the lithospheric magnetoactive layer is estimated using the centroid method based on two-dimensional spectral analysis of the lithospheric magnetic field. The lithospheric magnetic field within the study region is described by the EMAG2v3 global model. The obtained results show that maximum values ( 50 km) of the depth to the bottom of lithospheric magnetic sources are observed almost everywhere under the Siberian platform north of 65° N. Minimum depth values (30 km) are traced under the Koryak-Kamchatka fold belt and the Okhotsk-Chukotka volcanogenic belt. Under the Verkhoyansk-Kolyma fold belt, different maximums (up to 40 km) and minimums (up to 30 km) of the bottom depth are seen. Assuming that magnetite is a main magnetic mineral in the continental lithosphere, our distribution of the bottom depth evidences for the eastward lithospheric heating — from the Siberian platform to the Koryak-Kamchatka fold belt. The revealed tendency is confirmed by independent geophysical data. Comparison of the obtained results with a distribution of epicenters of regional earthquakes (M ≥ 4.0, 1962—2020) shows that most sources of strong earthquakes (M ≥ 6.0), registered during the instrumental period of observation, are confined to zones in which a sharp change in the depth to the bottom of lithospheric magnetic sources occurs.

The Ages and Isotope Compositions of the Gold–Silver Deposits and Occurrences of the Evensk Group (Okhotsk–Chukotka Volcanogenic Belt, Northeast Russia)

The Ages and Isotope Compositions of the Gold–Silver Deposits and Occurrences of the Evensk Group (Okhotsk–Chukotka Volcanogenic Belt, Northeast Russia)

Porphyry–Copper Mineralization of Talnikovoye Ore Field (Okhotsk Segment of the Okhotsk–Chukotka Volcanogenic Belt)

Porphyry–Copper Mineralization of Talnikovoye Ore Field (Okhotsk Segment of the Okhotsk–Chukotka Volcanogenic Belt)

Composition and Age of the Ayanka Flora (Late Cretaceous, Santonian–Campanian) of the Okhotsk–Chukotka Volcanogenic Belt: Response to the Criticism

Composition and Age of the Ayanka Flora (Late Cretaceous, Santonian–Campanian) of the Okhotsk–Chukotka Volcanogenic Belt: Response to the Criticism

Composition and Age of the Ayanka Flora (Late Cretaceous, Santonian-Campanian) of the Okhotsk-Chukotka Volcanogenic Belt: Response to the Criticism

The main critical remarks to the paper by M.G. Moiseeva, A.B. Herman, A.B. Sokolova entitled “On the Stratigraphic Setting and Composition of the Ayanka Flora from the Upper Cretaceous of Okhotsk-Chukotka Volcanogenic Belt, Northeastern Russia” (Stratigraphy and Geological Correlation, 2022, vol. 30, No. 4, pp. 76–99), stated by S.V. Shczepetov in his article “On the Ayanka flora from the Upper Cretaceous of Northeastern Russia” (Stratigraphy and Geological Correlation, 2022, vol. 30, No. 6, pp. 113–120), are considered. Additional arguments are given to confirm the conclusions we’ve made earlier: (1) all three taphofloras from the Obryvistaya River basin came from a single straton; it however was named differently on two separate sheets of the 1:200000 State Geological Map: the Auney Member on the northern sheet and the Makkoveyem Formation on the southern one; (2) according to the composition of the plants of these taphofloras, all of them are about of the same age and can be considered as a single Ayanka Flora; (3) the most probable age of the Ayanka Flora is Santonian-Campanian, since it is undoubtedly the most similar to the Santonian-Campanian floras of Northeastern Russia and Northern Alaska.

ВОЗРАСТ И ИЗОТОПНЫЙ СОСТАВ ЗОЛОТО-СЕРЕБРЯНЫХ МЕСТОРОЖДЕНИЙ И РУДОПРОЯВЛЕНИЙ ЭВЕНСКОЙ ГРУППЫ (ОХОТСКО-ЧУКОТСКИЙ ВУЛКАНОГЕННЫЙ ПОЯС, СЕВЕРО-ВОСТОК РОССИИ)

Existing and recently acquired data on the isotope age and composition of volcanogenic Au-Ag deposits and occurrences of the Evensk group (Okhotsk-Chukotka volcanogenic belt, Northeast Russia) are summarized. The K-Ar isotopic and Rb-Sr isochron ages of Au-Ag ores from the deposits and occurrences studied is 82.7 ± 3–77.5 ± 3 Ma and 84.1 ± 2–79.7 ± 5, respectively. Au-Ag mineralization formed during a 5 million-year time interval. Au-Ag mineralization, typical of productive ore stages and practically unaffected by later thermal processes, is characterized by low values of primary 87Sr/86Sr(0) = 0.7055–0.7059 ratios close to primary 87Sr/86Sr(0) ratios in wall-rock metasomatites (0.7033–0.7082) and unaltered host rocks (0.7045–0.7048) indicative of a pronounced predominance of mantle Sr in the ores. The composition points of ore Pb on the 207Pb/204Pb – 206Pb/204Pb evolution diagram are grouped in close proximity to the Pb isotope composition points in the exhausted (depleted) mantle with a trend towards the volcanic rocks formed in subduction zones typical of the continental margin. A close genetic relationship between ore and magmatic processes is confirmed. It is assumed that this relationship is due to the functioning of a single mantle basaltoid chamber, a source of metal-bearing fluids and, probably, the primary source of Au and Ag.

On the Stratigraphic Setting and Composition of the Ayanka Flora from the Upper Cretaceous of Okhotsk-Chukotka Volcanogenic Belt, Northeastern Russia

On the Stratigraphic Setting and Composition of the Ayanka Flora from the Upper Cretaceous of Okhotsk-Chukotka Volcanogenic Belt, Northeastern Russia

Флюоритоносность Северо-Востока России

One deposit and 217 occurrences of fluorite, grouped in the fluorite, the rare-metal-fluorite, and the polymetal-fluorite mineral formations, are known in RussiaТs North-East. Occurrences of fluorite formations are most widespread, while the stratiform occurrences in the Urultun-Taskan zone at the Omulevskoye uplift are especially rich in resources. Fluorite occurrences themselves are widespread within the Okhotsk-Chukotka volcanogenic belt. Fluorite-bearing belts, areas, and zones are distinguished. Fluorite minerogenic resources of RussiaТs North-East are estimated.

Erguveem Ore Region in the eastern Chukotka Peninsula: An effect of the tectonics of the ore-bearing volcano-structures on composition of the gold-silver mineralization

The geological and structural position of the Pepenveem and Korrida Au-Ag ore occurrences situated in the East-Chukotka segment of the Okhotsk-Chukotka Volcanogenic Belt (OCVB) was studied. The Pepenveem ore occurrence was characterized by one (volcanogenic) mineralization stage. It is localized within a graben-like monocline composed of Late Cretaceous volcanics. A relatively stable tectonic regime caused rather low temperature and pressure gradients during the ore formation and, consequently, simple mineral composition of the ores and absence of advanced argillic alteration. In contrast, the Korrida ore occurrence was characterized by two (volcanogenic and plutonogenic) mineralization stages. It is localized within a plutonogenic uplift complicated by a regional fault zone. Here, the basement of the volcano-structure, composed of island-arc volcano-sedimentary rocks, was uplifted to the surface by numerous high-angle faults. The here observed extensive development of zoned metasomatic haloes (including advanced argillic alterations), abundance of mineral species, and sharp temperature and pressure gradients could resulted from tectonic activity in a zone of interaction between the plutonic dome and deep-seated regional fault.

Glass fission-track ages, composition, and origin of tephra beds in the Upper Cretaceous Kanguk Formation, Banks Island, Arctic Canada

More than 50 conspicuous tephra beds occur in the Kanguk Formation on the southwestern coast of Banks Island. Their glass shards are remarkably well preserved and permit comprehensive characterization, offering the potential for reliable, precise correlation of Upper Cretaceous sedimentary rocks across the three major depocentres of the Arctic Archipelago and adjacent northern continental margin: Sverdrup, Banks, and the Beaufort–Mackenzie basins. Twenty-one tephra beds were analyzed; all have a high-K, peraluminous, rhyolitic composition, with quartz, plagioclase, ilmenite, biotite, and zircon as the dominant minerals. Trace-element concentrations, especially low Nb and Ta, show that the parental magmas formed in a continental-margin subduction environment. Glass fission-track ages range from 100 Ma to younger than 60 Ma, and indicate a very low sedimentation rate giving a very condensed sedimentary sequence on southwestern Banks Island — a sequence that may well contain the K–Pg transition. Source calderas are unknown but most likely are situated in east-central Alaska and the central and northern Kuskokwim volcanic belt, some 1000 to 1500 km distant from southwestern Banks Island. It is also possible that some of the very thin tephra beds come from the Okhotsk–Chukotka volcanogenic belt in northeastern Russia.

The First Data of U/Pb and 40Ar/39Ar Dating of the Pre-Dzhugdzhur Volcanics: New Evidence of Time Diversity in the Formation of Individual Sectors of the Okhotsk–Chukotka Volcanogenic Belt

The First Data of U/Pb and 40Ar/39Ar Dating of the Pre-Dzhugdzhur Volcanics: New Evidence of Time Diversity in the Formation of Individual Sectors of the Okhotsk–Chukotka Volcanogenic Belt

Tectonic stress in the structures of the Northern Priokhotie (Magadan region) according to geological data

Tectonic fracturing of the Mesozoic and Cenozoic structures was studied in the Northern Priokhotie (Magadan region). The cataclastic analysis method and the statistical method of fracture density analysis were used to reconstruct their state of stress. It is revealed that the folded structures of the Arman’-Viliga synclinorium are subjected to horizontal shearing; the axis of maximum compression is sublatitudinal (azimuth 67°, angle 12°); extension is submeridional (azimuth 161°, angle 19°). In the Uda-Murgal volcanic arc, horizontal extension with shear takes place; the compression axis is directed to NW (azimuth 259°, angle 29°), and the extension axis to NE (azimuth 152°, angle 26°). In the Okhotsk-Chukotka volcanogenic belt, volcanic structures are in the field of varying tectonic stresses, from predominant horizontal extension to horizontal shear. The Cenozoic intermontane depressions of the Miocene – Pliocene ages are subjected to horizontal shear; the compression axis is directed to NE (azimuth 214°, angle 29°), and the extension axis to NW (azimuth 121°, angle 4°). The results of the comparative analysis of the stress states in the above-mentioned areas reliably show that the diversity of the stress state types is statistically related to the structural positions of the studies sites. Such diversity cannot be explained by an influence of active faults, or by any consecutive superposition of deformations at different stages, despite the fact that the deformations have complicated the observed pattern of the stress states. We conclude that each subsequent geodynamic stage only introduced additional elements into the previous structure, but did not completely transform it.

К ВОПРОСУ О ЧАУНСКОЙ ПАЛЕОФЛОРЕ ИЗ НЕМОРСКОГО МЕЛА ЧУКОТКИ

The Cretaceous fossil floras from the formations of the Okhotsk-Chukotka volcanogenic belt differ significantly by its systematic composition from the same-age fossil floras from the coastal lowland sedimentations. The peculiarities of fossil floras from the volcanogenic disposals are the most obvious in Chaun Flora firstly found in the volcanogenic formations of Pegtymelski Arch in Central Chukotka. L.B. Golovneva presented the results of the long-term study of this flora in the monograph published in 2018. On the base of these data and using our own experience in the stratigraphy of the Okhotsk-Chukotka volcanogenic belt and the study of the vegetation cover dynamics in the areas of modern volcanism of Kamchatka we showed that most likely Chaun Flora formed on juvenile substrata in the central parts of the vast volcanic fields being isolated form the sources of diasporas. The Chaun Flora has not clear affinity in neither lateral nor stratigraphic localization, because the fossil remains of characteristic plant species occur in different-age formations on all extent of the volcanogenic belt. The species characteristic for Chaun Flora are indicators of the certain environmental conditions and reflect the peculiarities of the processes of fossilization in the areas of terrestrial volcanism from Turon until Campanian inclusive.

Chingandzha Paleoflora and Age of Cretaceous Volcanites of the Balygychan and Sugoy Interfluve and Adjoining Part of Okhotsk–Kolyma Watershed

Most of the Okhotsk–Chukotka volcanogenic belt fossil floras differ significantly in systematic composition from the floras of coastal lowlands of the adjoining Anadyr–Koryak subregion dated by faunistic remains. That is the reason why its comparison is so difficult and, accordingly, why it is complicated to establish the age of volcanic formations. The only exception in this situation is a Chingandzha flora that is reliably compared with coastal floras and is dated to the Turonian–Coniacian. New data on the Chingandzha flora systematic composition make it possible to clarify its age. This flora shows the most similarity to a Kaivayam flora of the Anadyr–Koryak subregion; thus, it has to be dated to the Coniacian. The stratigraphic setting of the locations of the Chingandzha flora fossils makes it possible to date three lower strata of volcanites in the external zone of the Okhotsk-Chukotka volcanogenic belt to the Coniacian. During medium-scale geological mapping, younger formations were erroneously assigned to them in some cases. The Chingandzha flora could have preserved its coastal appearance and penetrated far into the continent along a lowland that probably originated in a linear zone of tectonic disturbances.

On the Age of the Buor-Kemus Flora of Northeast Asia Based on the Data on the Nonmarine Cretaceous in Eastern Chukotka

On the basis of the analysis of literature and cartographic materials, our field observations, results of U–Pb isotope dating of zircons, and examination of paleobotanical collections, it was established that the “Mesophytic” Buor-Kemus fern–gymnosperm flora existed in Eastern Chukotka in the Late Cretaceous longer than in other regions. The volcanics of the Nyrvakinot sequence are partly facially replaced by the sedimentary deposits of the Olkhovaya Formation. Both units contain plant remains of the Buor-Kemus flora. The Amgen volcanogenic sequence lies conformably and without any hiatus on the Nyrvakinot sequence and contains “Cenophytic” plant assemblages with a significant amount of angiosperms, ascribed to the Turonian–Coniacian. These three units were previously considered as the three major constituents of the Etelkuyum Formation. The U–Pb isotope ages of zircons from volcanogenic and tuffaceous sedimentary rocks of the Nyrvakinot sequence show that they accumulated in the Late Сretaceous in the age range of 93–87 Ma (Turonian–Coniacian). Taking into account all data available, it is evident that the Buor-Kemus flora (at least within the Eastern Chukotka segment of the Okhotsk–Chukotka Volcanogenic Belt) existed in the Albian, Cenomanian, Turonian, and, probably, in the early Coniacian.

On the Problem of Nonmarine Cretaceous Strata Correlation in the Northeast Russia: The Conditions of Florogenesis in Volcanic Areas

The majority of fossil floras from Cretaceous volcanogenic rocks of Northeast Russia considerably differ in taxonomy from the coeval paleofloras of coastal lowlands. In order to explain the peculiarities of their formation, we used the data on the modern vegetation dynamics for volcanic plateaus of Central Kamchatka. It is shown that there was virtually no erosion where paleofloras of the Okhotsk-Chukotka volcanogenic belt, represented in the burials, existed; however, volcanogenic material, suitable for burials to form, was supplied in abundance. After massive eruptions, inner parts of the vast volcanic zone appeared to be isolated from sources of diaspores. Vegetation cover in these areas was restored mainly owing to the pool of local taxa; i.e., it was supported as a diasporic subclimax. The absence of concurrent angiosperms favored the long-term preservation of ancient taxa in these paleofloras and the appearance of new taxa on their basis.

New insights into the thermal regime and hydrodynamics of the early Late Cretaceous Arctic

AbstractThe Arctic is warming faster than anywhere else of comparable size on Earth, impacting global climate feedbacks and the Arctic biota. However, a warm Arctic is not novel. The Late Cretaceous fossil record of the region enables a detailed reconstruction of polar environmental conditions, and a thriving extinct ecosystem, during a previous 'hothouse’ global climate. Using leaf form (physiognomy) and tree ring characteristics we reconstruct Cenomanian to Coniacian polar thermal and hydrological regimes over an average annual cycle at eight locations in NE Russia and northern Alaska. A new high spatial resolution (∼1 km) WorldClim2 calibration of the Climate Leaf Analysis Multivariate Program (CLAMP) yields results similar to, but often slightly warmer than, previous analyses, but also provides more detailed insights into the hydrological regime through the return of annual and seasonal vapour pressure deficit (VPD), potential evapotranspiration (PET) estimates and soil moisture, as well as new thermal overviews through measures of thermicity and growing degree days. The new results confirm the overall warmth of the region, particularly close to the Arctic Ocean, but reveal strong local differences that may be related to palaeoelevation in the Okhotsk–Chukotka Volcanogenic Belt in NE Russia. While rainfall estimates have large uncertainties due to year-round wet soils in most locations, new measures of VPD and PET show persistent high humidity, but with notably drier summers at all the Arctic sites.

New data on the volcanism of the Central Chukotka segment of Okhotsk-Chukotka volcanogenic belt

The article presents new geochronological and geochemical data on the age and composition of the undifferentiated Cretaceous volcanics of the basin of the Palyavaam river Central Chukotka region. These data indicate the heterogeneity of the rocks of etchikun suites, which are divided into two groups. The andesites of the first group (actually etchikun suites ) are of early Cretaceous age and represent a magmatic phase preceding the formation of the Okhotsk-Chukotka volcanogenic belt (OCHVB). The andesites of the second group correlate well in age and composition to the volcanic rocks of OCHVB. They lie at the base section of Chaunskaya series of OCHVB and indicate gomodromos the evolution of volcanism in the Central-Chukchi sector OCHVB.

New Data on Volcanism of the Central Chukotka Segment of the Okhotsk–Chukotka Volcanogenic Belt

New geochronological and geochemical data on the age and composition of undifferentiated Cretaceous volcanics from the Palyavaam River basin, Central Chukotka region, are presented. These data indicate the heterogeneity of rocks of the Etchikun Fm., which are divided into two groups. Andesites of the first group (Etchikun Fm. proper) are of early Cretaceous age and represent a magmatic phase preceding the formation of the Okhotsk–Chukotka volcanogenic belt (OChVB). Andesites of the second group correlate well in age and composition to the OChVB volcanic rocks. They occur at the base of the Chauna Series of the OChVB and indicate the homodromous character of the evolution of volcanism in the Central Chukotka sector of the OChVB.

Geochemistry and Geochronology of Cretaceous Volcanism of the Chaun Area of Central Chukotka

This paper reports new geochronological and geochemical data on the Cretaceous volcanic rocks of the Palyavaam River basin (Central Chukotka, Chaun area). The first of the considered complexes is mainly represented by rhyolites, ignimbrites, and felsic tuffs of the Chaun Formation of the Okhotsk–Chukotka volcanogenic belt (OCVB). The second complex comprises volcanic rocks of the Early Cretaceous latite–shoshonite series, which are united into the Etchikun Formation. The geotectonic affinity of the Etchikun Formation is controversial. Some researchers consider the rocks of the formation as representing the magmatic stage preceding the OCVB formation. Other geologists include the Etchikun Formation in the Chaun Group of the OCVB. Obtained data indicate that the volcanic rocks of the Etchikun Formation have a heterogeneous nature and can be subdivided into two groups. Andesites of the first group (Etchikun Formation proper) are Early Cretaceous in age and predate the formation of the OCVB. Andesites of the second group in age and composition are correlated with volcanic rocks of the OCVB. They lie at the base of the Chaun Group and testify to the basic to acid volcanic evolution in the Central Chukotka sector of the OCVB.