The Ordovician Gabbro–Tonalite–Trondhjemite Complex and Associated Volcanic Rocks in the Paleozoic Suture between the Urals and Kazakhstan

Doklady Earth Sciences - This paper reports new data on the Early Ordovician age established for granitoids of the gabbro—tonalite–trondhjemite complex in the Denisovka ophiolite zone...     

Early Neoproterozoic (ca. 850 Ma) Bimodal Volcanic Series in the Talas Range of the North Tianshan: Indications of the Earliest Stages of the Continental Breakup of Rodinia

Doklady Earth Sciences - The Early Neoproterozoic (851 ± 4 Ma) age of the bimodal basalt-rhyolite volcanic series, exposed on the southern slope of the Talas Alatau Range of northwest...     

Volatility inversion of silicon and magnesium oxides during the evaporation of HASP glasses on the moon

An inversion of SiO₂ and MgO volatility occurs during high-temperature melt evaporation in the CaO–MgO–Al₂O₃–SiO₂ (CMAS) system. This results in that SiO₂, which is usually more volatile than MgO, becomes less volatile during the evaporation of melts enriched in the refractory oxides CaO and Al₂O₃. The volatility inversion is adequately explained within the theory of acid–base interaction of silicate melt components developed by D.S. Korzhinskii. The compositions of high-Al₂O₃ and SiO₂-poor glasses (known as HASP glasses) from the lunar regolith show a systematic decrease in MgO/SiO₂ with increasing CaO content, which is a direct consequence of the influence of acid–base effects.     

Ophiolite sections of the Dzhalair-Nayman zone,South Kazakhstan: Their structure and age substantiation

The ophiolite complexes outcrop extending more than 700 km in the Dzhalair-Nayman zone located between the Chuya-Kendyk Tas (in the southwest) and Aktau-Dzhungar (in the northeast) Precambrian sialic massifs in South Kazakhstan. The most complete ophiolite sections are described in the central (Andassai massif) and southeastern (Dulankara massif) parts of the zone. Plagiogranites occur in a sheeted dyke complex in the upper part of ophiolite sections. A bimodal volcanic series occurs atop the section. The U/Pb zircons ages for the Andassai and Dulankara plagiogranites are 519 ± 4 and 521 ± 2 Ma, respectively. Ophiolites associated with bimodal volcanic series are also found in the north and northeast of Kazakhstan. They may form, together with the Lower Cambrian complexes of the Dzhalair-Nayman zone, a single paleostructure, whose fragments are well-traceable for over 2000 km     

Vendian Suprasubduction Magmatism in the Southern Urals

New data on the Vendian age of the volcanogenic–sedimentary sequence of the Uraltau zone (Southern Urals) were obtained. The U/Pb (SHRIMP-II) isotope age obtained for zircons from rhyolite tuffs is 591.5 ± 3.5 Ma. The sequence under consideration is intruded by Vendian granites and overlain unconformably by Ordovician terrigenous and volcanogenic deposits. The composition of Vendian volcanics and granites testifies that they were formed in a suprasubduction setting at the continental margin, complexes of which are known in the Middle and Northern Urals.     

Neoproterozoic-Early Paleozoic tectonic evolution of the western part of the Kyrgyz Ridge (Northern Tian Shan) caledonides

The conducted comprehensive study of the western part of Kyrgyz Ridge provided new data on the structure, composition and age of Precambrian and Early Paleozoic stratified and igneous complexes. The main achievements of these studies are: (1) the establishment of a wide age spectrum, embracing the interval from the Neoproterozoic to the end of the Early Ordovician, for the clastic-carbonate units composing the cover of the Northern Tian Shan sialic massif; (2) the reconstruction and dating of Early and Late Cambrian ophiolite complexes formed in suprasubduction settings;(3) the discovery and dating of the Early-Middle Ordovician volcano-sedimentary complex of island-arc affinity; and (4) proof of the wide occurrence of Late Ordovician granitoids, some of which bear Cu-Au-Mo ores. The intricate thrust-and-fold structure of the western part of the Kyrgyz Ridge, formed in several stages from the Middle Cambrian (?) until the end of the Middle Ordovician, was scrutinized; the importance of the Early Ordovician stage was demonstrated. The intrusion of large batholiths in the early Late Ordovician accomplished the caledonide structural evolution. Formation of Neoproterozoic and Early Paleozoic caledonide complexes, which were possibly related to the protracted and entangled evolution of the active continental margin, ceased by the Late Ordovician.     

Middle Devonian Age of Metamorphism of Garnet Amphibolite at the Sole of the Kempirsai Ophiolite Allochthon (Southern Urals): Results of U–Th–Pb (SIMS) Dating

Doklady Earth Sciences - Metagabbroid garnet amphibolite formed after high-pressure granulite with an estimated P–T peak of 12–16 kbar at 700–790°C occurs at the sole of the...     

Structural evolution of Vendian and early to Middle Paleozoic complexes in Uraltau Zone and Sakmara allochthons,Southern Urals

The structural evolution of the Late Precambrian and Early to Middle Paleozoic complexes is considered for the southern part of the Uraltau Zone and its extension in the Ebeta Antiform, as well as for the northeastern and northwestern frameworks of the ophiolitic Khabarny Allochthon, where the Late Precambrian and Paleozoic complexes of the continental margin in combination with ophiolites are drawn together in packets of tectonic nappes. The formation of the regional structure took place during several stages in various geodynamic settings. Five deformation stages have been recognized in the regional structural evolution from new data on mesostructural parageneses, which consist of folds that developed within outcrops and their relationships in rocks differing in age. The first stage is related to the Late Precambrian Timanian, or Cadomian Orogeny, and four subsequent deformation stages characterize Paleozoic tectonic evolution of the region. The geodynamic nature of the second stage remains unknown; the third stage is related to overthrusting of ophiolites in the Early Devonian; the fourth stage of deformations marks Late Paleozoic continental collision. The fifth stage of postcollisional strike-slip deformations completes the regional structural evolution.