Marianna I. Tuchkova

Tectonic evolution of the Mesozoic South Anyui suture zone, eastern Russia: A critical component of paleogeographic reconstructions of the Arctic region

The South Anyui suture zone consists of late Paleozoic–Jurassic ultramafic rocks and Jurassic–Cretaceous pre-, syn-, and postcollisional sedimentary rocks. It represents the closure of a Mesozoic ocean basin that separated two microcontinents in northeastern Russia, the Kolyma-Omolon block and the Chukotka block. In order to understand the geologic history and improve our understanding of Mesozoic paleogeography of the Arctic region, we obtained U-Pb ages on pre- and postcollisional igneous rocks and detrital zircons from sandstone in the suture zone. We identified four groups of sedimentary rocks: (1) Triassic sandstone deposited on the southern margin of Chukotka; (2) Middle Jurassic volcanogenic sandstone that was derived from the Oloy arc, a continental margin arc, along the Kolyma-Omolon block, south of the Anyui Ocean, a sample of which yielded no pre-Jurassic zircons and a single peak at 164 Ma; (3) suture zone sandstone that yielded Late Jurassic maximum depositional ages and likely predated the collision; and (4) a Mid-Cretaceous syncollisional sandstone that had a maximum depositional age of 125 Ma. These rocks were intruded by postkinematic plutons and dikes with ages of 109 Ma and 101 Ma that postdate the collision. We present a seismic-reflection line through the South Anyui suture zone that indicates south-vergence of thrusting of the Chukotka block over the Kolyma-Omolon block, opposite of most existing models and opposite of the vergence in the Angayucham suture zone, the postulated along-strike equivalent in Alaska. This suggests that Chukotka and Arctic Alaska may have different pre-Cretaceous histories, which could solve space problems with existing reconstructions of the Arctic region. We combine our detrital zircon data and interpretations of the seismic line to construct a new GPlates model for the Mesozoic evolution of the region that decouples Chukotka and Arctic Alaska to solve space problems with previous Arctic reconstructions.

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.

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.

Chapter 31 The Use of Heavy Minerals in Determining the Provenance and Tectonic Evolution of Mesozoic and Caenozoic Sedimentary Basins in the Continent-Pacific Ocean Transition Zone: Examples from Sikhote-Alin and Koryak-Kamchatka Regions (Russian Far East) and Western Pacific

Abstract This paper documents the achievements of Russian sedimentologists and mineralogists who have used heavy minerals to reconstruct the provenance and source lithologies of Mesozoic-Caenozoic sedimentary complexes of the Far East and the western Pacific Ocean, and identify their plate tectonic settings. We provide a review of publications, written mostly in Russian, which have not been available or intelligible to non-Russian speakers. Investigations concentrated mainly on the sedimentary and volcano–sedimentary rocks of the Sikhote-Alin fold belt and Koryak-Kamchatka region, but they also included the Pengina Bay and the Vanuatu Trench in the Pacific Ocean. Caenozoic sediment samples were collected during marine geological expeditions and analysed using traditional microscopy of detrital minerals, bulk sediment chemistry, and electron microprobe analysis. Distinctive heavy mineral associations have been recognised that indicated their deposition in particular plate tectonic settings. Geochemical analysis of individual heavy minerals has revealed their source lithologies in a plate tectonic context. The Sikhote-Alin sediments were derived from the continental Siberian and Chinese cratons, complemented—at the beginning and the close of the Phanerozoic—by minor input from contemporary oceanic fragments, including volcanics. In the Koryak-Kamchatka region, forearc basins were fed almost entirely by intermediate and basic rocks amongst which the products of island arc volcanism played a dominant role throughout the Phanerozoic. The principal source of detrital heavy minerals of the Middle Eocene-Pleistocene deep-sea sediments of the Vanuatu Trench was the tholeiitic basalts of the Vanuatu island arc with limited addition from ocean-floor basalts. Only insignificant amounts of terrigenous material reached the depositional area from the Australian continent.

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.

Marginal continental and within-plate neoproterozoic granites and rhyolites of Wrangel Island, Arctic region

The paper presents new data on the U–Pb zircon age, as well as results of isotopic geochemical analysis, of granites and rhyolites from Wrangel Island. The U–Pb age estimates of granites and rhyolites are grouped into two clusters (~690–730 and 590–610 Ma), which imply that these rocks crystallized in the Late Neoproterozoic. Granitic rocks dated back to 690–730 Ma are characterized by negative εNd(t) values and Paleoproterozoic Sm–Nd model age. The older inherited zircons corroborate the ancient age of their crustal source. The granitic rocks pertain to involved peraluminous granites of type I, which form at a continental margin of the Andean type and can be compared with coeval granites and orthogneisses from the Seward Peninsula in Alaska. Rhyolites and granites ~590–610 Ma in age are distinguished by a moderately positive εNd(t) and Mesoproterozoic model age. It is suggested that they have a heterogeneous magma source comprising crustal and mantle components. The geochemical features of granites and rhyolites correspond to type A granites. Together with coeval OIB-type basalts, they make up a riftogenic bimodal association of igneous rocks, which are comparable with orthogneisses (565 Ma) and gabbroic rocks (540 Ma) of Seward Peninsula in Alaska.

Deformations and Structural Evolution of Mesozoic Complexes in Western Chukotka

Detailed structural investigations have been carried out in the Pevek district to specify tectonic evolution of the Chukotka mesozoids. The earliest south-verging folds F1 formed in Triassic rocks at the first deformation stage DI. These structures are overlapped by the northern-verging folds F2 and overthrusts pertain to the second deformation stage DII. Folding structures F1 and F2 were deformed by shear folds F3, completing stage DII. The DI and DII structures are complicated by roughly NS-trending normal faults marking deformation stage DIII. It has been established that DI is related to the onset of opening of the Amerasian Basin in the Early Jurassic, or, alternatively, to the later accretion of the Kulpolnei ensimatic arc toward the Chukotka microcontinent. DII marks the collision of Siberia and the Chukotka microcontinent in the Late Neocomian. Normal faulting under the roughly E–W-trending extension during DIII is likely related to rift opening of the Podvodnikov and Makarov–Toll basins in the deep Amerasian Basin. Formation of the Okhotsk–Chukotka volcanoplutonic belt completed the structural evolution of the studied region.