S. D. Sokolov

Stratigraphy and U-Pb detrital zircon geochronology of Wrangel Island, Russia: Implications for Arctic paleogeography

Wrangel Island represents a small but unique exposure of Neoproterozoic basement and its upper Paleozoic and Mesozoic cover within the mostly unexplored East Siberian Shelf. Its geology is critical for testing the continuity of stratigraphic units and structures across the Chukchi Sea from Alaska to Arctic Russia, for evaluating the hydrocarbon potential of this offshore region, and for constraining paleogeography and plate reconstructions of the Arctic. Upper Paleozoic platform carbonates and shales on Wrangel likely match those of the Chukchi Shelf and adjacent North Slope of Alaska (e.g., Sherwood et al., 2002), but Triassic basinal turbidites contrast with Alaskas thin shelfal units. Detrital zircon suites from upper Paleozoic strata on Wrangel reveal that local basement-derived detritus (500–800 Ma) decreases up section, replaced by 900–2000-Ma zircon populations compatible with a Baltic shield provenance. Cambrian–Ordovician–Silurian zircons (420–490 Ma) are present in lesser abundance in most samples and are inferred to have been derived from the Arctic part of the Caledonide belt. Triassic detrital zircon suites contrast with those from underlying strata: Precambrian zircons have less of an age range (1700–2000 Ma), and Devonian and younger (400 Ma) zircons are much more abundant. This change reflects breakup of the carbonate platform during Permian–Triassic rifting, with zircon age populations in Triassic strata compatible with sediment sources in the Urals, Taimyr, and Siberia. Detrital zircon data suggest that Wrangel Island, Chukotka, and northern Alaska (the Arctic Alaska-Chukotka microplate) restore against the Lomonosov Ridge upon closure of the Amerasia Basin and to the edge of the Barents Shelf after closing the Eurasia Basin. The detrital zircon data thus suggest that the Barents Shelf lays close to the paleo-Pacific margin in the early Mesozoic and that subduction-driven tectonics may have been a greater factor in the evolution of the Amerasia Basin of the Arctic than previously suspected.

Tectonics of the South Anyui Suture, Northeastern Asia

The South Anyui Suture separates the structures of the Chukotka and Verkhoyansk-Kolyma Fold Areas. The suture consists of ophiolites, island-arc rocks, deformed Upper Triassic and Upper Jurassic-Lower Cretaceous turbidites, and accretionary-type terrigenous melange with blocks of oceanic crust. Two main stages in the geological history of the South Anyui Suture are distinguished: (1) the oceanic stage (Paleozoic-onset of Late Jurassic), when the vast Protoarctic ocean with ensimatic island arcs existed, and (2) the collisional stage (Volgian Age-Early Cretaceous) that started with the transformation of the ocean into the residual and closing South Anyui turbidite basin and was completed by the formation of a fold-nappe structure in the Hauterivian-Barremian. In the course of collision, the oceanic and island complexes were thrust to the north over the passive margin of Chukchi Peninsula. The thrusting was followed by the formation of south-vergent retrocharriages and then by final strike-slip faulting. In the Aptian-Albian, collision gave way to extension with the formation of metamorphic cores and superposed orogenic basins.

Present-day structure and stages of tectonic evolution of Wrangel Island, Russian eastern Arctic Region

Present-day structure of Wrangel Island was formed during two main stages of Mesozoic-Cenozoic deformation. The general fold-thrust structural grain of the island, characterized by northern vergence and complicated by NW-trending right-lateral strike-slip faults, originated in the post-Triassic. Mesostructural data indicate a near-meridional orientation of regional compression. This deformation stage was related to the orogeny in the New Siberian-Chukchi Fold System, which occurred at the end of Neocomian in the pre-Aptian. The next stage was characterized by a near-meridional and NNW-SSE extension established by superposition of normal, right-lateral strike-slip, and pull-apart kinematics upon the former fold-thrust structure. Comparison of the structural and the published seismic data allows us to suggest the later stage of compression to be in the Late Cretacous-Paleocene, which is correlated to the Mid-Brookian angular unconformity in Arctic Alaska and North Chukchi Basin. Accordingly, the Cenozoic age (since Paleocene-Eocene) of the main extension and right-lateral transtension most likely corresponds to opening of the South Chukchi (Hope) Basin localized immediately to the south of the Wrangel-Herald Arch (High). The difference in structural patterns of the Silurian-Lower Devonian and the Upper Devonian (?)-Triassic rocks is evidence for deformation related to the Ellesmerian Orogeny in the Middle-Late Devonian.

Ophiolites in accretionary complexes along the Early Cretaceous margin of NE Asia: age, composition, and geodynamic diversity

Abstract The existing published data, combined with our own new field, petrographic, and geochemical observations and data show that ophiolites of the West Koryak fold system originated in a variety of tectonic environments. This fold system stretches along the boundary shared by two of NE Asia’s largest tectonic units, the Verkhoyansk-Chukotka and Koryak-Kamchatka foldbelts. The fold system abounds in Palaeozoic and Mesozoic ophiolites and sedimentary and volcanic island-arc assemblages. The ophiolites are Palaeozoic and Mesozoic in age. The variety of geological and geochemical signatures implies ophiolite origin in diverse tectonic settings. The Early Palaeozoic ophiolites of the Ganychalan accreted terrane and Devonian(?) ophiolites of the Ust-Belaya accreted terrane are fragments of the Panthalassan oceanic lithosphere. Serpentinite mélange in the Ust-Belaya terrane contains some blocks of island-arc provenance. They are probably Late Palaeozoic-Early Mesozoic in age as determined by K-Ar measurements, which require validation by other techniques. Mesozoic, chiefly Late Jurassic-Early Cretaceous ophiolites of the Beregovoi and Kuyul accreted terranes, originated in a suprasubduction-zone (SSZ) setting (ensimatic island arc and back-arc basin). Among the Mesozoic ophiolites, one finds blocks of oceanic assemblages in serpentinite mélanges as well. Basalt and chert blocks of clearly oceanic derivation are viewed as detached fragments of the upper part of the oceanic lithosphere. The ophiolites have experienced a variety of accretionary scenarios. Palaeozoic ophiolites docked onto the Koni-Taigonos island arc (of Late Palaeozoic-Early Mesozoic age), probably in the Late Palaeozoic or Early Mesozoic, whereas Mesozoic ophiolites accreted onto the Uda-Murgal island arc (of Late Jurassic-Early Cretaceous age) in the terminal Early Cretaceous. Sedimentary deposits, whose base is late Albian in age, make a post-accretionary sequence. These island arcs portray the overall history of the convergent boundary between the North Asian continent and NW Pacific. Ophiolites of the Ganychalan and Ust-Belaya terranes consist of thrust sheets and, jointly with Yelistratov Peninsula ophiolites, make up the basement to the forearc of the Uda-Murgal island arc, ophiolites of Cape Povorotny and Kuyul terrane being incorporated in accretionary prisms of the same arc. Ophiolites and associated metamorphic, volcanic, and sedimentary rocks of Palaeozoic-Early Cretaceous age underwent three deformation phases, each reflecting a different stage in the evolution of the NE Asian continental margin and readily correlative with principal tectonic events in the northern Circum-Pacific region.

Composition and Geodynamic Setting of Granitoid Magmatism in the Alyarmaut Uplift, Western Chukchi Peninsula

This paper reports the compositions of granitoids from the Alyarmaut Uplift in the western Chukchi Peninsula, which is interpreted as a granite-metamorphic dome. A postcollisional origin was inferred for the granitoids. Their petrographic composition, petrochemical characteristics, and the compositions of their biotite allowed us to assign them to high-K I-type granites. The trace-element composition of the granitoids is comparable with that of granite types associating with both collisional and suprasubduction settings, which may reflect magma source heterogeneity generated by previous collisional processes predating dome and granite formation. The significant scatter of ɛNd(T) and 87Sr/86Sr values in the granitoids is also indicative of the heterogeneous composition of the crustal source or variable degree of magma contamination with ancient crustal material. In addition to the dominant process of the submersion of the rim of the Chukchi microcontinent beneath the active margin of the North Asian craton, the tectonic scenario of the formation of the dome structure of the Alyarmaut Uplift should involve either slab detachment or delamination of the lithospheric mantle, which causes the invasion of asthenospheric material into the base of the crust and promotes heat transfer necessary for the derivation of granitoid magmas.

The South Chukchi Sedimentary Basin (Chukchi Sea, Russian Arctic): Age, Structural Pattern, and Hydrocarbon Potential

The South Chukchi Basin separates the late Mesozoic Chukotka Fold Belt from the Wrangel Arch and represents the northwestern continuation of the Hope Basin of the United States sector of the Chukchi Sea, which is filled with middle Eocene–Quaternary nonmarine, marine, and lacustrine rocks. The main stages of South Chukchi Basin development in the Cenozoic are comparable to those of the Hope Basin, although the analysis of onshore data from Chukotka and Wrangel Island points to the beginning of sedimentation during the Aptian–Albian–Late Cretaceous. In the South Chukchi Basin, the sediment thickness seldom exceeds 3 to 4 km (1.9–2.5 mi) but can locally reach 5 to 6 km (3.1–3.7 mi). The geometry of the faults indicates an extensional and/or transtensional setting for the South Chukchi Basin, although folds, reverse and thrust faults, pop-up and positive flower structures also occur, pointing to the local development of compressional and transpressional stress. Low-angle thrust faults predating the Aptian(?)–Paleogene extension (most likely of Late Jurassic–Neocomian age) are recognized at the base of the South Chukchi Basin. This could support the idea that the extension in the basin was driven by gravitational collapse of the Wrangel-Herald-Lisburne fold and thrust belt in the post-Neocomian. Based on the interpretation of new seismic data and analysis of published material, we believe that the hydrocarbon potential of the South Chukchi Basin may be significantly higher than what has been previously suggested.

New data on the age and genesis of igneous rocks in the Kolyuchinskaya Guba (eastern Chukotka)

New Data on the Age and Genesis of Igneous Rocks in the Kolyuchinskaya Guba (Eastern Chukotka)

Redescription of Proctophantastes gillissi (Overstreet et Pritchard, 1977) (Trematoda: Zoogonidae) with discussion on the systematic position of the genus Proctophantastes Odhner, 1911.

The redescription of Proctophantastes gillissi (Overstreet et Pritchard, 1977) (Trematoda: Zoogonidae) was made on specimens collected from Muraenolepis marmorata Gunther, 1880 (Gadiformes) caught in the Ross Sea and the Amundsen Sea (Antarctic). The fish is a new host of this parasite. Phylogenetic relations of P. gillissi were inferred by Maximum Likelihood and Bayesian inference analysis of partial sequences from 28S rDNA. The findings from analysis of the molecular data are not consistent with the traditional point of view about the position of the genus Proctophantastes Odhner, 1911 in the subfamily Lepidophyllinae. The taxonomical position of the genus needs further revision.

Tectonic zoning of Wrangel Island, Arctic region

The Northern, Central, and Southern zones are distinguished by stratigraphic, lithologic, and structural features. The Northern Zone is characterized by Upper Silurian–Lower Devonian sedimentary rocks, which are not known in other zones. They have been deformed into near-meridional folds, which formed under settings of near-latitudinal shortening during the Ellesmere phase of deformation. In the Central Zone, mafic and felsic volcanic rocks that had been earlier referred to Carboniferous are actually Neoproterozoic and probably Early Cambrian in age. Together with folded Devonian–Lower Carboniferous rocks, they make up basement of the Central Zone, which is overlain with a angular unconformity by slightly deformed Lower (?) and Middle Carboniferous–Permian rocks. The Southern Zone comprises the Neoproterozoic metamorphic basement and the Devonian–Triassic sedimentary cover. North-vergent fold–thrust structures were formed at the end of the Early Cretaceous during the Chukchi (Late Kimmerian) deformation phase.

Neoproterozoic granitoids on Wrangel Island

Based on geochronological U–Pb studies, the age of Wrangel Island granitoids was estimated as Neoproterozoic (Cryogenian). Some granitoids contain zircons with inherited cores with an estimated age of 1010, 1170, 1200, and >2600 Ma, assuming the presence of ancient (Neoarchean–Mesoproterozoic) rocks in the Wrangel Island foundation and their involvement in partial melting under granitoid magma formation.