Tectonic Position of the South Anyui Suture

Geotectonics - The South Anyui Fold System was formed at the end of the Early Cretaceous at the site of a closed oceanic basin as a result of the collision of the Chukotka microcontinent with the...     

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

Doklady Earth Sciences - New geochronological and geochemical data on the age and composition of undifferentiated Cretaceous volcanics from the Palyavaam River basin, Central Chukotka region, are...     

Geochemistry and geodynamic significance of the dike series of the Aluchin ophiolite complex,Verkhoyansk-Chukotka fold zone,Northeast Russia

The Aluchin ophiolites represent a tectonomagmatic complex, the upper crustal part of which is made up of two dike series. One series includes diabases and gabbrodiabases, which are exposed in the Late Triassic Atamanov Massif (226 Ma) and subdivided into low-potassium, low and moderate-titanium varieties. In terms of rare-earth element (REE) distribution pattern, these rocks correspond to the mid-ocean ridge basalts (N-MORB). At the same time, trace element composition of some samples indicates the enrichment in subduction component (Ba, Th), as well as variable depletion in Ta, Nb and other high-field strength elements (HFSE), which leads us to conclude that these rocks were formed from melts similar to back-arc basin basalts (BABB) at a sufficiently mature stage of back-arc spreading. The diabases of other series form separate dike bodies (dike swarms) that cut across a mantle ultrabasic body in the northern part of the Aluchin Massif. The most part of these rocks reveal prominent island-arc signatures, primarily, REE and trace-element distribution patterns. At the same time, they are characterized by slightly elevated contents of titanium, nickel, and chromium, and low content of aluminum. On the basis of these data, the diabases of the Aluchin Massif can be regarded as BABB basalts with distinct island-arc characteristics, which are usually termed as arc-like member. The joint geochemical evolution of the two diabase series is well consistent with that of the rocks from different structures of the Mariana trough, which, together with compositional data, indicate that the studied dike series mark the initial and mature stages of the opening of the Late Triassic suprasubduction basin.     

Geohistorical Stratigraphy and Stratigraphic Guides

A different understanding of the stratigraphic science methodology is considered. The classical geohistorical content of stratigraphy is set against the latest formal classification approach recorded in the International Stratigraphic Guide. Some provisions of the Stratigraphic Code of Russia and the International Stratigraphic Guide are studied. The described confrontation between the two concepts can be expressed by a formula: stratotype or limitotype.     

U–Th–Pb (SIMS) Dating and Formation Conditions of Volcanic Rocks in the Uyandina–Yasachnaya Volcanic Belt (Northeast Asia,Indigirka Section)

Doklady Earth Sciences - The Uyandina–Yasachnaya volcanoplutonic belt (UYVB) is located in Northeast Asia. As one of the largest volcanic belts in the region, it extends for 900 km from the...     

Correlation of Magmatic and Tectonic Events in the Evolution of West Chukotka Ophiolites

Doklady Earth Sciences - The article is an overview of the magmatic and geodynamic processes that formed Aluchin and Gromadnen-Vurguveem ophiolites in the territory of Western Chukotka. The...     

Roles of Postcollisional Granitoids and Aptian–Albian Extension in Tectonic Evolution of Mesozoic Structures on Chukchi Peninsula,Northeastern Russia

Doklady Earth Sciences - New U–Pb SIMS zircon datings from granitoid plutons and dikes of Western Chukotka, together with data obtained earlier, confirm that postcollisional granitoid...     

Geodynamic Setting,Age, and Petrogeochemical Features of Granitoids in the Chimalga Pluton,Main Batholith Belt (Verkhoyan–Kolyma Fold Area)

Geotectonics - New U?Pb SIMS and 40Ar?39Ar geochronological, petrogeochemical, and isotope geochemical data for the granitoids of the Chimalga pluton in the central part of the Main...     

Composition and geodynamic conditions of formation of the intrusive rocks of the Gromadnen-Vurguveem peridotite-gabbro massif,western Chukotka

The Gromadnen-Vurguveem peridotite-gabbro massif is confined to one of the largest ophiolite complex of western Chukotka and composed mainly of intrusive rocks. This paper reports the first comprehensive compositional data for its plutonic rocks (petrochemistry, geochemistry, and compositions of minerals). In terms of petrography, two groups of rocks can be distinguished in the Gromadnen-Vurguveem peridotite-gabbro massif. The first group includes leucocratic gabbroids (mostly gabbronorites), composing most of the massif. The second group includes olivine-bearing cumulate rocks: olivine gabbros, troctolites, plagioclase-bearing dunites, and amphibolized wehrlites. The major element variations in these rocks suggest their affiliation to low-titanium, low-potassium, and high-alumina plutonic derivatives of island-arc magmatism. According to geochemical characteristics (distribution of REEs and indicator incompatible elements), the gabbroids of the first group are akin to both island-arc tholeiites and boninites. The olivine-bearing rocks of the second groups show boninitic affinity. Based on these observations, it was concluded that the intrusive complex of the Gromadnen-Vurguveem massif was formed during an early stage of the development of an ensimatic island arc.