First paleomagnetic data for the New Siberian Islands: Implications for Arctic paleogeography

In this paper we present new paleomagnetic and paleontological data from the Ordovician and Silurian carbonate rocks of Kotelny Island (the Anjou Archipelago), and from the Ordovician turbidities of Bennett Island (the De Long Archipelago). It is assumed that both archipelagos belong to the NSI (New Siberian Islands) terrane — a key tectonic element in the Arctic region. Ages of the studied rocks have been established by paleontological data and lithological correlations. Our new data on conodonts combined with those from previous studies of Ordovician and Silurian fauna indicate a biogeographic similarity between the shelves of the Siberian paleocontinent and the NSI in the Early Paleozoic. Three new paleomagnetic poles for the NSI (48.9°N, 13.8°E, A₉₅ = 18.1° for 475 Ma; 45.5°N, 31.9°E, A₉₅ = 11.0° for 465 Ma, and 33.7°N, 55.7°E, A₉₅ = 11.0° for 435 Ma) fall between the south-eastern part of Central Europe and the Zagros Mountains. The similarity of paleomagnetic directions from Kotelny and Bennet islands confirms that both the Anjou and De Long archipelagos belong to the same terrane. Calculated paleolatitudes indicate that in Ordovician–Silurian times this terrane has been located between 30° and 45°, possibly in the northern hemisphere. Based on this observation, we suggest a linkage between the NSI and the Kolyma–Omolon superterrane. Comparison of apparent polar wander paths (APWPs) of the NSI, Siberia and other cratons/terranes suggests that the NSI drifted independently. We demonstrate that the structural line between Svyatoy Nos Peninsula and Great Lyakhovsky Island is the continuation of the Kolyma Loop suture on the Arctic shelf, and expect that the continuation of the South Anyui suture is to be found east of the NSI.     

The first paleomagnetic data on dolerites from Jeannette Island (New Siberian Islands,Arctic)

The first paleomagnetic data on dolerite dikes from the volcanogenic–sedimentary section of Jeannette Island (De Long Archipelago, New Siberian Islands) are discussed. The petromagnetic data and results of the baked contact and fold tests are used to substantiate the nature of the characteristic magnetization component, which in combination with the ⁴⁰Ar/³⁹Ar dates implies its likely Late Precambrian–Early Paleozoic age. The calculated paleomagnetic pole makes it possible to extend the trajectory of the apparent polar movement for the New Siberian Islands block and confirms the assumption that this structural element of the Arctic shelf evolved as a terrane. Two variants of paleotectonic interpretation of the obtained data and their consistency with the available data on the geology and tectonics of the New Siberian Islands are considered.     

Early Paleozoic tectonics for the New Siberian Islands terrane (Eastern Arctic)

The New Siberian Islands archipelago is one of the few research objects accessible for direct study on the eastern Arctic shelf. There are several models that have different interpretations of the Paleozoic tectonic history and the structural affinity of the New Siberian Islands terrane. Some infer a direct relationship with the passive continental margin of the Siberian paleocontinent. Others connect it with the marginal basins of Baltica and Laurentia, or the Chukotka-Alaska microplate. Our paleomagnetic investigation led us to create an apparent polar wander path for the early Paleozoic interval of geological history. Based on it we can conclude that the New Siberian Islands terrane could not have been a part of these continental plates. This study considers the possible tectonic scenarios of the Paleozoic history of the Earth, presents and discusses the corresponding global reconstructions describing the paleogeography and probable mutual kinematics of the terranes of the Eastern Arctic.     

The De Long Islands: A missing link in unraveling the Paleozoic paleogeography of the Arctic

The vast Laptev and East Siberian shelves in the eastern Russian Arctic, largely covered by a shallow sea and buried beneath sea ice for 9 months of the year, remain one of the least studied parts of continental crust of the Earth and represent a big unknown when performing pre-Cenozoic reconstructions of the Arctic. The De Long Islands provide an important window into the geology of this area and are a key for understanding the Early Paleozoic history of the Amerasian Arctic. Four of them (Jeannette, Henrietta, Bennett and Zhokhov islands) were studied using structural data, petrographic and geochemical analyses and U–Pb zircon age dating to offer the following new constraints for the Early Paleozoic paleogeography of the Arctic realm. The basement beneath the De Long Islands is of Late Neoproterozoic to earliest Cambrian age, about 670–535 Ma. In the Early Paleozoic, the De Long Islands were located along the broad Timanian margin of Baltica, with a clastic sediment provenance from the Timanian, Grenville–Sveconorwegian, and Baltic Shield domains. The Cambro-Ordovician volcaniclastic successions on Jeannette and Henrietta islands formed part of a continental volcanic arc with a corresponding back-arc basin located to the south (in present co-ordinates). On the continent-ward side of the back-arc basin, shallow marine shelf clastic and carbonate rocks were deposited, which are exposed today on Bennett Island in the south-west of the archipelago (in modern coordinates). The De Long Islands together with other continental blocks, such as Severnaya Zemlya, Arctic Alaska–Chukotka, and the Alexander Terrane, formed the contiguous active continental margin of Baltica during the Early Paleozoic. Today however, these terranes are spread out over a distance of 5000 km across the Arctic and eastern Pacific margins due to the subsequent opening of a series of Late Paleozoic, Mesozoic and Cenozoic oceanic basins.     

Causes of Cretaceous Remagnetization on the Southwestern Periphery of the Archipelago of the New Siberian Islands

This study demonstrates rock-magnetic and paleomagnetic investigations of Devonian and Mesozoic deposits of Kotelny, Stolbovoy, and Great Lyakhovsky islands. The results indicate that local remagnetization took place on the southwestern periphery on the archipelago of the New Siberian Islands. A comparison of new data with the apparent polar wander path for Siberia shows that the remagnetization happened during collisional events between 140 and 80 Ma and affected only the marginal part of the terrane of the New Siberian Islands that was directly facing the deformation front. The consistent younging of the remagnetization age from the south to the north indicates dextral rotation of the terrane of the New Siberian Islands during its collision with Siberia.     

Concerning tectonics and the tectonic evolution of the Arctic

The particularities of the current tectonic structure of the Russian part of the Arctic region are discussed with the division into the Barents–Kara and Laptev–Chukchi continental margins. We demonstrate new geological data for the key structures of the Arctic, which are analyzed with consideration of new geophysical data (gravitational and magnetic), including first seismic tomography models for the Arctic. Special attention is given to the New Siberian Islands block, which includes the De Long Islands, where field work took place in 2011. Based on the analysis of the tectonic structure of key units, of new geological and geophysical information and our paleomagnetic data for these units, we considered a series of paleogeodynamic reconstructions for the arctic structures from Late Precambrian to Late Paleozoic. This paper develops the ideas of L.P. Zonenshain and L.M. Natapov on the Precambrian Arctida paleocontinent. We consider its evolution during the Late Precambrian and the entire Paleozoic and conclude that the blocks that parted in the Late Precambrian (Svalbard, Kara, New Siberian, etc.) formed a Late Paleozoic subcontinent, Arctida II, which again “sutured” the continental masses of Laurentia, Siberia, and Baltica, this time, within Pangea.     

Paleomagnetism of the Late Paleozoic granites of the Angara-Vitim batholith and the host rocks of the Baikal-Patom folded area: Tectonic implications

The paper presents the results of paleomagnetic and geochronological studies of the Late Paleozoic granites of the Angara-Vitim batholith as well as Vendian-Early Cambrian sedimentary rocks and Late Devonian subvolcanic rocks of the Patom margin of the Siberian Platform. Primary and metachronous magnetization in the rocks of the study region was used to calculate an Early Permian (~ 290 Ma) paleomagnetic pole, which is proposed as a reference pole for the Siberian Platform in paleomagnetic reconstructions, plotting of the apparent polar-wander path curve, and other magnetotectonic studies. The published and obtained paleomagnetic data and analysis of the geological data confirm the Late Paleozoic age of the final folding in the Baikal-Patom area. Possible causes of Late Paleozoic deformations and large-scale granite formation in the Baikal-Patom area and Transbaikalia in the Late Paleozoic are discussed.     

Precambrian microcontinents of the Ural-Mongolian Belt: New paleomagnetic and geochronological data

The knowledge on the early stages of evolution of the Ural-Mongolian Belt (UMB) (Late Neoproterozoic-Cambrian) is a key for understanding of its evolution in the Paleozoic. Unfortunately, this stage remains poorly studied. The tectonic reconstructions of the UMB for this time primarily depend on the views on the kinematics and tectonic evolution of numerous sialic massifs with Precambrian basement in the structure of the Tien Shan, Kazakhstan, Altai, and Mongolia. At present, the concept of the origin of these massifs is largely based on the lithostratigraphic similarity of the Neoproterozoic and Lower Paleozoic sections of the Tarim, South China, and Siberian platforms with coeval sections of Precambrian massifs within the UMB. New paleomagnetic and geochronological data can serve as additional sources of information on the origin and paleotectonic position of the microcontinents. In this paper, we present new isotopic datings and a new paleomagnetic determination for the Neoproterozoic volcanic rocks of the Zabhan Formation from the Baydrag microcontinent in central Mongolia. It is established that 805−770 Ma ago (U-Pb LA-MC-ICP-MS age of zircon) the Baydrag microcontinent was situated at a latitude of 47 ± 14° in the Northern or Southern hemisphere. These data provide new insights into the possible origin of the Precambrian micro-continents in the UMB. Analysis of paleomagnetic data and comparison of the age of the basement beneath various plates allow us to state rather confidently that ∼800 Ma ago the micro-continents of the UMB belonged to one of the North Rodinian plates: Indian, Tarim, or South China; their Australian origin is less probable.     

Paleozoic terranes of eastern Australia and the drift history of Gondwana

Critical assessment of Paleozoic paleomagnetic results from Australia shows that paleopoles from locations on the main craton and in the various terranes of the Tasman Fold Belt of eastern Australia follow the same path since 400 Ma for the Lachlan and Thomson superterranes, but not until 250 Ma or younger for the New England superterrane. Most of the paleopoles from the Tasman Fold Belt are derived from the Lolworth-Ravenswood terrane of the Thomson superterrane and the Molong-Monaro terrane of the Lachlan superterrane. Consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic Australia by the late Early Devonian. The Lolworth-Ravenswood terrane is interpreted to have undergone a 90° clockwise rotation between 425 and 380 Ma. Although the Tamworth terrane of the western New England superterrane is thought to have amalgamated with the Lachlan superterrane by the Late Carboniferous, geological syntheses suggest that movements between these regions may have persisted until the Middle Triassic. This view is supported by the available paleomagnetic data. With these constraints, an apparent polar wander path for Gondwana during the Paleozoic has been constructed after review of the Gondwana paleomagnetic data. The drift history of Gondwana with respect to Laurentia and Baltica during the Paleozoic is shown in a series of paleogeographic maps.     

Permian-Triassic trap magmatism in Bel'kov Island (New Siberian Islands)

The study was inspired by information on Paleozoic andesites, dacites, and diabases in Bel'kov Island in the 1974 geological survey reports used to reconstruct the tectonic evolution of the continental block comprising the New Siberian Islands and the bordering shelf. We did not find felsic volcanics or Middle Paleozoic intrusions in the studied area of the island. The igneous rocks are mafic subvolcanic intrusions, including dikes, randomly shaped bodies, explosion breccias, and peperites. They belong to the tholeiitic series and are similar to Siberian traps in petrography and trace-element compositions, with high LREE and LILE and prominent Nb negative anomalies. The island arc affinity is due to continental crust contamination of mantle magma and its long evolution in chambers at different depths. The 252±5 Ma K-Ar biotite age of magmatism indicates that it was coeval to the main stage of trap magmatism in the Siberian craton at the Permian-Triassic boundary. The terrane including the New Siberian Islands occurred on the periphery of the Siberian trap province where magmatism acted in a rifting environment. Magma intruded semiliquid wet sediments at shallow depths, shortly after their deposition. Therefore, the exposed Paleozoic section in Bel’kov Island may include Permian or possibly Lower Triassic sediments, of younger ages than it was believed earlier.     

New data on the age of dolerites and basalts of Mendeleev Rise (Arctic Ocean)

We present results of ⁴⁰Ar/³⁹Ar isotopic investigations concerning the dating of dolerites and basalts that were sampled during the Arctica-2012 polar expedition. Basalts were sampled by means of deep underwater drilling with wells up to 2 m in outcrops on the seafloor (basalts), and dolerite samples were obtained from the bottom of an escarp of Mendeleev Rise using a manipulator on the research submarine. The analysis results of the obtained mono-mineral fractions (amphibole, plagioclase, pyroxene) from the studied rocks yielded an Early Paleozoic age of the dolerites and basalts from Mendeleev Rise. The oldest ages obtained for amphibole reach 471.5 ± 18.1 and 466.9 ± 3.3 Ma, which corresponds to the Early-Middle Ordovician. The isotopic composition of argon was measured on two mass spectrometers: the Micromass Noble Gas 5400 (UK) and the Thermo Scientific Argus (Germany). The determined Early Paleozoic age of igneous rocks of Mendeleev Rise and seismic data obtained during the last Russian expedition Arctica-2012 [2] let us suppose that this continental block of the Earth’s crust has a Precambrian basement similar to the basement identified for the New Siberian islands including the De Long archipelago.     

Upper Devonian depositional system of Bel’kov Island (New Siberian Islands): An intracontinental rift or a continental margin?

The archipelago of New Siberian Islands situated on the northeastern continental shelf of Eurasia is considered a part of an exotic terrane that collided with Siberia in the Early Cretaceous. Bel’kov Island is located close to the inferred western boundary of this terrane and thus should demonstrate attributes of its localization at the margin of the Paleozoic oceanic basin. The Upper Devonian section on Bel’kov Island is a continuous sequence of deepwater terrigenous rocks, which indicates a tendency toward deepening of the basin previously revealed on adjacent Kotel’ny Island. The lowermost Upper Devonian unit on Bel’kov Island is represented by thin Domanik-like strata resting on the Middle Devonian carbonate platform. The main body of the Upper Devonian sequence, more than 4 km in total thickness, is made up of gravity-flow sediments including turbidites, clay and block diamictites, and olistostromes in the upper part of the section, which accumulated at the slope of the basin or its rise. At many levels, these sediments have been redeposited by along-slope currents. The uppermost unit of organogenic limestone is evidence for compensation of the trough. According to conodont assemblages, the deepwater terrigenous rocks were deposited from the early Frasnian to the early Tournaisian. This time is known for extensive rifting in the eastern Siberian Platform. The data obtained allowed us to reconstruct a NNW-trending Late Devonian rift basin on the Laptev Sea shelf similar to other rifts at the eastern margin of the Siberian Platform.     

The Olkhon metamorphic terrane in the Baikal region: An Early Paleozoic collage of Neoproterozoic active margin fragments

We report data from the Khadarta, Khoboi, and Orso metamorphic complexes of the Olkhon terrane in the western Baikal region. High-grade rocks in the three complexes may have been derived from active continental margin rocks (island arc–backarc basin system). The backarc basin history possibly began at 840–800 Ma, according to SHRIMP-II U-Pb zircon ages of the Orso gneiss. Many tectonic units in the Olkhon terrane belonged to the active margin of the Barguzin microcontinent which rifted off the Aldan province of the Siberian craton in the early Neoproterozoic. The accretion of the microcontinent to the craton was accompanied by high-grade metamorphism recorded in the Khadarta and Khoboi granulites. The 507 ± 8 Ma and 498 ± 7 Ma SHRIMP-II U-Pb zircon ages of the latter complexes, respectively, may refer to the earliest evolution stage of the Olkhon metamorphic terrane. New data for the Olkhon terrane agree well with the ages of other high-grade complexes along the southern Siberian craton (Slyudyanka, Kitoikin, Derba) and correspond to the initiation of the Central Asian orogen. With these data, the Olkhon metamorphic terrane has been interpreted as an Early Paleozoic collisional collage of fragments of the microcontinent’s Neoproterozoic active margin.     

Paleozoic Tectonics and Geodynamics of the De Long Islands and Adjacent Structures of the Verkhoyansk-Chukotka Fold Belt

Doklady Earth Sciences - This work presents finalized results of our paleomagnetic study of Paleozoic rocks of Henrietta, Jeannette and Bennett islands and their implications for tectonic...     

Rhyolite–granite association in the Central Taimyr zone: evidence of accretionary-collisional events in the Neoproterozoic

The Central Taimyr accretionary belt includes two granite-metamorphic terranes: Faddey and Mamont-Shrenk, which include the oldest igneous formations of the Taimyr folded area in the Arctic framing of the Siberian craton—granitoids and granite-gneisses with U–Pb zircon ages of 900–830 Ma. The [FeO*/(FeO* + MgO)]-enriched granitoids of these terranes are products of highly fractionated I-type magmas. This paper presents results of new petrographic, geochemical, geochronological, and paleomagnetic investigations of acid rocks from a volcanic-plutonic association (in the region of the Leningradskaya River) in the Faddey terrane in the northeastern Taimyr area. These rocks formed during the final stage of continent–island arc accretion and collision that occurred at approximately 870–820 Ma. We established that the studied rocks belong to a long granitoid belt extending from Mamont-Shrenk to Faddey terrane, where all the igneous bodies are deformed and oriented uniformly. The paleomagnetic pole we calculated differs significantly from the apparent polar-wander path interval of corresponding age for Siberia. The 33.8°±5.4° angular distance between the poles indicates that the formation of this volcanic-plutonic association took place at a significant distance from the Taimyr margin of the Siberian paleocontinent.     

Middle Jurassic collision of an exotic microcontinental fragment: Implications for magmatism across the Southeast China continental margin

Thrusting, folding, and metamorphism of late Paleozoic to middle Mesozoic sedimentary rocks, together with high precision U–Pb zircon ages from Middle to Late Jurassic volcanic and granitic rocks, reveal evidence for a major deformation event in northwestern Hong Kong between 164 and 161 Ma. This episode can be linked with collision of an exotic microcontinental fragment along the southeast China continental margin determined from contrasting detrital zircon provenance histories of late Paleozoic to middle Mesozoic sedimentary rocks either side of an NE-trending suture zone through central Hong Kong. The suture zone is also reflected by isotopic heterogeneities and geophysical anomalies in the crustal basement. Detrital zircon provenance of Early to Middle Jurassic rocks from the accreted terrane have little in common with the pre-Middle Jurassic rocks from southeast China. Instead, the zircon age spectra of the accreted terrane show close affinities to sources along the northern margin of east Gondwana. These data provide indisputable evidence for Mesozoic terrane accretion along the southeast China continental margin. In addition, collision of the exotic terrane, accompanied by subduction rollback, is considered to have hastened foundering of the postulated flat slab beneath southeast China, leading to a widespread igneous flare-up event at 160 Ma.     

Tectonics of the northern part of the Lena-Yenisey oil-bearing region

This article discusses the historical tectonic development of the portion of Siberia lying within the Arctic Circle. The exposed rocks are referred to seven tectonic or geotectonic stages: Archean, Proterozoic, Sinian, lower to middle Paleozoic, upper Paleozoic to lower Mesozoic, and Mesozoic-Cenozoic. Locally on the Shorikka and Kamennaya, the nearly horizontal Lower Cambrian beds overlie the Sinian with angular unconformity. In contrast, isolated areas on the west side of the Yenisey show a gradational relationship between the Late Sinian and Early Cambrian beds in a dominantly carbonate succession. The present tectonic elements of the Siberian platform were developed in Mesozoic-Cenozoic time, and differential movements in the basement have continued into Neogene time. The sedimentary platform cover was enlarged by sedimentary overlap from Sinian to mid-Paleozoic time. The sediment came from the older fold systems. The major structures are measured in terms of variations in stratigraphic thickness, but details are unfortunately omitted. The main features are delineated on a geotectonic map embracing 42 map units and symbols. The map lacks basic reference data, geographic designations, scale, and other essential information. — B. N. Cooper.     

Paleomagnetism of Late Paleozoic,Mesozoic, and Cenozoic rocks in Mongolia

Rock complexes in Mongolia experienced two remagnetization events. Almost all secondary remanence components of normal polarity were acquired apparently in the Cenozoic, after major deformation events, and those of reverse polarity were associated with intrusion of bimodal magmas during the Late Carboniferous–Permian reverse superchron. Active continental-margin sequences in some areas of Mongolia were folded prior to the Late Carboniferous–Permian magnetic event. The primary origin of magnetization in Late Paleozoic and Mesozoic rocks has been inferred to different degrees of reliability. According to paleolatitudes derived from most reliable paleomagnetic data, the analyzed rocks were located far north of the North China block throughout the Late Paleozoic and Early Mesozoic. Mongolia, as well as Siberia, moved from the south to the north in the Paleozoic, back from the north to the south between the latest Triassic and the latest Jurassic, and remained almost within the same latitudes in Cretaceous and Cenozoic time. These paleolatitudes show no statistical difference from those for the Siberian craton at least since the latest Permian (275–250 Ma). Older Mongolian complexes (with ages of 290, 316, and 330 Ma) likewise may have formed within the Siberian continent, which makes their paleomagnetic determinations applicable to calculate the polar wander path for Siberia. The paleolatitudes of Early Carboniferous sediments in Mongolia differ significantly from those of Siberia, either because of overprints from the reverse superchron or because they were deposited away from the Siberian margin.     

New data on the structure of the Kas Block in the basement of the West Siberian Plate

A new concept concerning the structure and stages of evolution of the Kas Block of the West Siberian Plate is stated in this paper. The Kas Block is traditionally considered to be a subsided western margin of the Siberian Platform. The new concept is based on the results of the interpretation of the geophysical data recently obtained along the reference and regional profiles in this territory. The geological interpretation of the deep dynamic sections obtained by reprocessing of the CDP seismic reflection records has been performed for the first time. The structural features of the Kas Block, as well as the character of its junction with the Siberian Platform and the Paleozoic framework, are discussed. The tectonic scheme of the territory and the scheme of the pre-Late Devonian surface of the Kas Block have been compiled. The Baikalian age of the basement of the Kas Block is substantiated. The Salairian allochthonous ophiolite-basalt tectonic nappe is localized for the first time within the sedimentary cover of the Kas Block. The available information allowed us to reconstruct the development of the western margin of the Siberian continent in the Riphean and Early Paleozoic before and after the Baikalian Orogeny, respectively. The informational background of the geological and geophysical interpretation involves the results of the CDP seismic reflection profiling, including the deep dynamic seismic sections and parameters of the P-wave velocities along the reference 1-SB seismic line and the regional Vostok 10, 12, 15, and 16 seismic lines; the results of the deep seismic and magnetotelluric soundings; the gravity measurements; the magnetic exploration; and the new coherent physical geological models.     

Geochemical features,depositional settings,and provenances of Lower Paleozoic rocks in the Mamyn terrane,Central Asian Fold Belt

New data on geochemical features of the Lower Paleozoic terrigenous rocks in the Mamyn terrane (eastern Central Asian Fold Belt) and U–Pb geochronological studies of the detrital zircon from these rocks are presented. The obtained results suggest the following conclusions. 1. At present, the Kosmataya sequence includes different age Lower Cambrian terrigenous–carbonate and Lower Ordovician terrigenous rocks or represents Lower Ordovician olistostromes including limestone blocks with the Lower Cambrian fauna. Lower Ordovician terrigenous rocks were formed in an island arc or active continental margin, mainly, owing to the erosion of Cambrian–Early Ordovician plutons and volcanics that are widespread in structures of the Mamyn terrane and weakly reworked by the chemical weathering. 2. The Silurian Mamyn Formation was developed at a passive continental margin. The main sources of clastic material for this formation were the same Cambrian–Early Ordovician igneous rocks as for the Cambrian sequence, with the participation of Early Silurian and Vendian igneous complexes. The obtained data significantly refine concepts about the geological structure of the Mamyn terrane, which is a member of the Argun Superterrane, one of the largest tectonic structures in the eastern Central Asian Fold Belt.