V.A. Vernikovsky

Neoproterozoic to Early Ordovician Evolution of the Paleo-Asian Ocean: Implications to the Break-up of Rodinia

Abstract The paper reviews and integrates the recent geological and geochronological data, which allow us to recognize three stages of the evolution of the Paleo-Asian Ocean. The opening of the Paleo-Asian Ocean at 970-850 Ma is dated by the Nersin Complex in the Aldan shield, plagiogranites of the Sunuekit massif, enderbites of the Sludinsk Lake area, and passive margin sediments of the Patoma or Baikal series. The initial subduction (850-700 Ma) is marked by volcanic rocks, trondjemite and gabbro of the Sarkhoy island arc series. Collisions of microcontinents with Siberia at 660 to 620 Ma are evidenced by the exhumation of Muya eclogites (650 Ma), formation of migmatites and amphibolites of the Njurundukan belt (635 and 590 Ma), metamorphic units of the Near-Yenisei belt (640-600 Ma), and orogenic molasse (640-620 Ma). The Paleo-Asian Ocean maximally opened at 620-550 Ma, because at that time a long island arc composed of boninite volcanic rocks was formed. Primitive island arcs of that age have been reconstructed in Kazakhstan, Gorny Altai, West and East Sayan, and North Mongolia. HP and UHP rocks formed in two stages at 550-520 and 520-490 Ma. At 550-490 Ma oceanic islands and Gondwana-derived microcontinents (Kokchetav, Tuva-Mongolian, Central Mongolian and others) collided with the Cambrian-early Ordovician island arc of the Siberian continent. As a result, the island-arc system was extensively modified. Collision occurred twice at 550-520 and 520-490 Ma during which many HP and UHP rocks formed. At that time, the new oceans - the Junggar, Kazakhstan and Uralian - with an Ordovician island arc were formed.

First report of early Triassic A-type granite and syenite intrusions from Taimyr : product of the northern Eurasian superplume

Abstract Ion-microprobe U–Th–Pb analyses of zircon from three high-level syenite–granite stocks in the western part of the Taimyr fold-and-thrust belt have yielded early Triassic ages of 249–241 Ma. Those syenite–granite bodies intrude unmetamorphosed late Paleozoic to early Mesozoic terrigenous and volcanic supracrustal rocks, including the early Triassic Siberian traps. 40 Ar– 39 Ar isotopic ages of 245–233 Ma correlate well with the ion-microprobe data and define the time of closure for the K–Ar isotopic system. Limited geochemical data for the early Triassic syenite–granite plutons show that they have metaluminous compositions, high potassium, high REE and high LIL concentrations, and 87 Sr/ 86 Sr and e Nd ratios intermediate between crust and mantle, suggesting a hybrid mantle–crustal origin. We tentatively suggest that they formed in an anorogenic setting as a result of the Permo-Triassic Euroasian superplume.

Neoproterozoic accretionary and collisional events on the western margin of the Siberian craton: new geological and geochronological evidence from the Yenisey Ridge

Abstract The geological, structural and tectonic evolutions of the Yenisey Ridge fold-and-thrust belt are discussed in the context of the western margin of the Siberian craton during the Neoproterozoic. Previous work in the Yenisey Ridge had led to the interpretation that the fold belt is composed of high-grade metamorphic and igneous rocks comprising an Archean and Paleoproterozoic basement with an unconformably overlying Mesoproterozoic–Neoproterozoic cover, which was mainly metamorphosed under greenschist-facies conditions. Based on the existing data and new geological and zircon U–Pb data, we recognize several terranes of different age and composition that were assembled during Neoproterozoic collisional–accretional processes on the western margin of the Siberian craton. We suggest that there were three main Neoproterozoic tectonic events involved in the formation of the Yenisey Ridge fold-and-thrust belt at 880–860 Ma, 760–720 Ma and 700–630 Ma. On the basis of new geochronological and petrological data, we propose that the Yeruda and Teya granites (880–860 Ma) were formed as a result of the first event, which could have occurred in the Central Angara terrane before it collided with Siberia. We also propose that the Cherimba, Ayakhta, Garevka and Glushikha granites (760–720 Ma) were formed as a result of this collision. The third event (700–630 Ma) is fixed by the age of island-arc and ophiolite complexes and their obduction onto the Siberian craton margin. We conclude by discussing correlation of these complexes with those in other belts on the margin of the Siberian craton.

Central Taimyr accretionary belt (Arctic Asia): Meso-Neoproterozoic tectonic evolution and Rodinia breakup

Abstract The structure and tectonic position of the Neoproterozoic Central Taimyr accretionary belt of northwestern Siberia is dominated by the Faddey and Mamont-Shrenk granite-gneiss terranes, ophiolites, and back-arc volcanic rocks. Granites in the granite-gneiss terranes are S-type and formed between 900 and 850 Ma from 1.9 to 1.8 Ga continental crust. U–Pb and Sm–Nd isotopic studies show that the plagiogranites of the Chelyuskin ophiolite belt formed between 850 and 740 Ma. The ophiolite complex was metamorphosed to garnet amphibolite grade around 600 Ma, which is considered to be when the accretionary belt was obducted onto the Siberian continent. Comparison of principal structures of the Central Taimyr accretionary belt with similar structures in Arctic countries permits definition of the principal stages of the Neoproterozoic destruction of the supercontinent Rodinia, in the Arctic region.

Neoproterozoic Orogeny along the margins of Siberia

Abstract The Siberian Craton is bounded by fold-and-thrust belts involving Neoproterozoic (locally Mesoproterozoic) complexes on the southern (Baikal-Vitim), western (Yenisey Ridge and Turukhansk-Igarka), northern (Taimyr), and eastern (Verkhoyansk) sides. This paper focuses on the geological structure and evolution of these formations. Previous and new geochronological data show that passive continental margins existed around most of the Siberian Craton during the early Neoproterozoic and possibly the late Mesoproterozoic. Between about 850–760 Ma, the southern, western and northern passive margins of the Siberian Craton were transformed into active margins. Middle-late Neoproterozoic island arcs and ophiolites were formed between c. 750–650 Ma along these margins; they are inferred to have been obducted onto the Siberian continental margin at c. 600 Ma, prior to late Vendian deposition. New ion microprobe U-Pb ages of ophiolitic rocks from Taimyr’s Central domain are presented. The Neoproterozoic record in the Cretaceous Verkhoyansk fold-and-thrust belt indicates that the eastern part of the Siberian Craton remained a passive continental margin during the Neoproterozoic and Palaeozoic. Baltica-Siberia relationships are also discussed.

Late Riphean alkaline magmatism in the western margin of the Siberian Craton: A result of continental rifting or accretionary events?

Magmatic evolution in the western margin of the Siberian Craton has attracted the attention of many specialists in the context of debatable problems concerning the formation and breakdown of the Meso- and Neoproterozoic Rodinia supercontinent, the evolution of the Paleoasian ocean, and the origin of the Central Asian Foldbelt [1‐3]. The evolution of the Late Riphean and Vendian alkaline igneous complexes occupies a special place in this problem. According to the paleoreconstruction by Yarmolyuk et al. [3], these complexes are traced not only along the western and southern margins of the Siberian Craton, but also in North America (Laurentia). Such complexes are commonly regarded as products of anorogenic conditions related to plumes and/or continental rifting. However, models of accretion processes, when a subducted plate reaches the asthenosphere and generates a new alkaline magma source, are also discussed in the literature [4]. As has been established previously, alkaline rocks, including alkali and nepheline syenites and Li‐F granites, were formed in the Central Asian Foldbelt throughout the Late Riphean and Vendian‐Cambrian accretionary events [3].

The oldest island arc complex of Taimyr: Concerning the issue of the Central-Taimyr accretionary belt formation and paleogeodynamic reconstructions in the arctic

In this paper we provide data on the oldest island arc complex of Taimyr, which was established within the Central-Taimyr accretionary belt. We demonstrate its relationship with the mainly turbiditic back-arc basin complex. U-Pb isotopic data for zircons are presented from a plagiogranite and a plagiorhyodacite, indicating that the island arc formed 961–969 m.y. ago from a substance with a Mezoproterozoic model age: TNd(DM) varies from 1170 to 1219 Ma. Paleomagnetic investigations performed on the island arc complex rocks showed that the paleomagnetic pole of the island arc is close to synchronous poles, obtained for the south-east of the Siberian craton. Consequently, the island arc whose relicts are preserved in the modern structure of the Three Sisters Lake region was located in close proximity to the Taimyr margin of Siberia at the moment of its formation and could be separated from the continent by a back-arc basin. The data obtained have a fundamental significance for geodynamic paleoreconstructions in the Arctic sector for the Neoproterozoic.

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.

The Mesozoic Apparent Polar Wander Path for the Siberian Domain of the Eurasian Plate

Comparison of the apparent polar wander paths (APWP) is one of the most important tasks in recent paleomagnetic study. The reliability of such trajectories is largely determined by the quality and quantity of paleomagnetic data used for their construction and uniformity of distribution of these data along the APWP. Approximately 400 paleomagnetic determinations largely characterizing the Paleozoic are now available for East Siberia. The basic features of the present-day structure of northern Eurasia were formed by the end of the Paleozoic. This fact served as a basis for construction of the so-called synthetic APWP for the Eurasian continent, according to which the latter is considered as a single rigid block in the Mesozoic‐Cenozoic [1, 2]. Though paradoxical, Mesozoic strata of Siberia, except for the Lower Triassic, are insufficiently studied by the paleomagnetic method. The paleomagnetic study of Mesozoic rocks in Siberia were largely aimed at solution of stratigraphic problems, which do not need high accuracy in determination of paleomagnetic poles. Despite their reliability, such data are unsuitable for solution of tectonic tasks. The main weakness of available determinations is related to the lack of paleomagnetic tests and wide age ranges (sometimes >50 (!) Ma) obtained for paleomagnetic poles. Therefore, paleomagnetic data on Europe and China [1, 2] were used to calculate the latitudinal position and spatial orientation of the Siberian tectonic domain of the Eurasian Plate in the Mesozoic‐Early Cenozoic. At the same time, the analysis of the geological structure and paleomagnetic data available for Siberia, East Europe, and Central Asia indicates that such constructions are inconsistent

The first data on the geology of Jeannette Island (De Long Archipelago, New Siberian Islands)

This paper presents the first actual information on the geology of Jeannette Island, one of the islands of the De Long archipelago located in the East Siberian Sea. We show that Jeannette Island has a volcano-sedimentary section dominated by volcaniclastic turbidites. The sequence identified on the southwestern coast of the island has a submonoclinal plunge complicated by secondary deformation structures, which indicate a general E-W direction of tectonic transport (in present-day coordinates). The sequence is intensely cut by multiple thin (up to a few meters) gabbro-dolerite dikes that are deformed conformably with the host rocks. The general geological framework of the island bears a close resemblance to that of nearby Henrietta Island located some 70 km to the east, which consists of a volcano-sedimentary cover of Early Paleozoic age. No organic remains have been found in the studied section of Jeannette Island. The preliminary results of isotope geochronological and paleomagnetic studies confirm the Late Precambrian-Early Paleozoic age assigned to the entire rock complex of Jeannette Island. The measured paleomagnetic directions are generally consistent with the directions of Lower Paleozoic rocks of Bennett Island (De Long archipelago) and Kotelny Island (Anzhu archipelago), which confirms our earlier conclusion that the New Siberian Islands shared a common tectonic history and that this structural element of the Arctic shelf appears to have been a terrane during the Early Paleozoic. This new information can help elucidate the possible relations between the marginal-continental, shelf, island and deep-seated structures of the Eastern Arctic.