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...     

Composition and geodynamic setting of Late Paleozoic magmatism of Chukotka

The paper reports the results of petrogeochemical and isotope (Sr-Nd-Pb-Hf) study of the Late Paleozoic granitoids of the Anyui–Chukotka fold system by the example of the Kibera and Kuekvun massifs. The age of the granitoids from these massifs and granite pebble from conglomerates at the base of the overlying Lower Carboniferous rocks is within 351–363 Ma (U-Pb, TIMS, SIMS, LA-MC-ICP-MS, zircon) (Katkov et al., 2013; Luchitskaya et al., 2015; Lane et al., 2015) and corresponds to the time of tectonic events of the Ellesmere orogeny in the Arctic region. It is shown that the granitoids of both the massifs and granite pebble are ascribed to the I-type granite, including their highly differentiated varieties. Sr-Nd-Pb-Hf isotope compositions of the granitoids indicate a contribution of both mantle and crustal sources in the formation of their parental melts. The granitic rocks of the Kibera and Kuekvun massifs were likely formed in an Andean-type continental margin setting, which is consistent with the inferred presence of the Late Devonian–Early Carboniferous marginal-continental magmatic arc on the southern Arctida margin (Natal’in et al., 1999). Isotope data on these rocks also support the idea that the granitoid magmatism was formed in a continental margin setting, when melts derived by a suprasubduction wedge melting interacted with continental crust.     

Mesozoic and Cenozoic granitoid complexes in the stucture of the continental margin of northeast Asia

The integral data on structural position, age, and paleo-geodynamic setting of Mesozoic and Cenozoic granitoid complexes in northeast Asia make it possible to divide them into preaccretionary, accretionary, and postaccretionary groups participating in the structure of the accretionary-type continental margin. The preaccretionary granitoids are members of volcanic-plutonic associations of ensimatic island arcs or suprasubduction ophiolitic complexes, which mark the onset of growth of the granitic-metamorphic layer in the future continental crust. The accretionary granitoids emplaced during the accretion of diverse rock complexes to the continental margin and are localized in its frontal zone, where granitic-metamorphic layer grows further. The postaccretionary granitoid plutons of the marginal continental volcanic-plutonic belts seal up fold-nappe structures, determining the upper age limit of accretion and deformation. The origin of postaccretionary granitoids is related to remelting of older heterogeneous accretionary-island arc crust.     

The Stages of Formation of the Main Batholite Belt,Northeast Russia: U–Th–Pb SIMS and Ar–Ar Geochronological Data

Doklady Earth Sciences - The original and published geochronological data and the geological position of different granitoid complexes of the Main (Kolyma) Batholith Belt of Northeast Asia have...     

Carboniferous Granitoid Magmatism of Northern Taimyr: Results of Isotopic-Geochemical Study and Geodynamic Interpretation

Data on the petrography, geochemistry, and isotopic geochronology of granites from the northern part of the Taimyr Peninsula are considered. The Early–Middle Carboniferous age of these rocks has been established (U–Pb, SIMS). Judging by the results of ⁴⁰Ar/³⁹Ar dating, the rocks underwent metamorphism in the Middle Permian. In geochemical and isotopic composition, the granitic rocks have much in common with evolved I-type granites. This makes it possible to specify a suprasubduction marginal continental formation setting. The existence of an active Carboniferous margin along the southern edge of the Kara Block (in presentday coordinates) corroborates the close relationship of the studied region with the continent of Baltia.     

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.     

Age and Structure of a Fragment of the Early Cambrian Ophiolite Sequence (North Balkhash Zone,Central Kazakhstan)

Doklady Earth Sciences - A fragment of the ophiolite sequence composed of dunites, wherlites, pyroxenites, gabbro, gabbro-dolerites, and plagiogranites was described within the structure of the...