Precision astrometry with schmidt telescopes

Schmidt telescopes currently provide nearly the only means to obtain positions of faint objects with respect to the standard ICRS reference system. However, the lack of adequate astrometric calibration methods to account for the specific properties of Schmidt telescopes leads to residual systematic errors of up to 1″. The main source of systematic errors is plate bending during exposure. A high-precision reduction technique to account for this effect is proposed. Application of this technique to observations acquired with the Schmidt telescopes of the Palomar and Anglo-Australian Observatories reduced the systematic errors by a factor of 2.5 and gave them a simpler structure, while simultaneously decreasing the number of unknowns in the reduction model threefold. Application of the new method, with appropriate account for the design of the particular plateholder used, will make it possible to use Schmidt telescopes to determine high-precision positions for virtually all objects detected in photographic surveys.     

Low-latitude gyrotropic waves in a finite thickness ionospheric conducting layer

The eigen-modes of electromagnetic waves in the finite depth conductive layer of the low ionosphere are considered. The dispersion properties of a discrete set of ULF waves are found taking into account the effect of their damping. The dependence of these properties on the propagation angle relative to the ambient magnetic field is analysed.     

Metabasalts of the Bryanta sequence of the Stanovoi complex of the Dzhugdzhur-Stanovoi superterrane, Central Asian fold belt: Age and geodynamic environment of formation

In this paper, we report U-Pb geochronological, Sm-Nd isotopic, and geochemical data for the basic schists of the Bryanta sequence of the Stanovoi complex of the Dzhugdzhur-Stanovoi superterrane of the Central Asian fold belt. It was shown that the protolith of the schists was composed of island-arc subalkali basalts, which crystallized at 1933 ± 4 Ma; the age of the earliest metamorphic processes is approximately 1890?C1910 Ma. This metamorphic event could be related to the collision of the Aldan and Stanovoi continental plates or accretion-collision processes at the boundary of the Ilikan and Kupurin lithotectonic zones during the formation of the latter.     

Age and tectonic position of the Stanovoi metamorphic complex in the eastern part of the Central Asian Foldbelt

Based on the results of Sm–Nd isotopic geochemical and U–Th–Pb geochronological LA–ICP–MS studies, it has been established that the formation of metamorphic rock protoliths of the Stanovoi Complex in the western Dzhugdzhur–Stanovoi Superterrane of the Central Asian Foldbelt took place over the following time spans: 2750–2860 Ma (Ilikan Group of the Ilikan Zone), 1890–1910 Ma (Bryanta Group of the Bryanta Zone), and ~2.0 Ga (Kupuri and Zeya groups of the Kupuri and Zeya zones, respectively). It has been shown that the western part of the Dzhugdzhur–Stanovoi Superterrane was formed ~1.9 Ga ago, as a result of collision of the Neoarchean Ilikan Terrane, the Paleoproterozoic island arc, and the Paleoproterozoic Kupuri–Zeya Terrane. The data make it possible to consider the Kurul’ta, and Zverevo blocks of the Stanovoi Structural Suture and the Ilikan Terrane of the Dzhugdzhur–Stanovoi Superterrane of the Central Asian Foldbelt as constituents of a common terrane.     

Early Mesozoic age of protolites of metasedimentary rocks from the Tukuringra terrane in the Mongolian–Okhotsk fold belt: Results of LA–ICP–MS U–Pb geochronological studies

This report presents the results of U–Pb geochronological LA–ICP–MS studies of detrital zircons from metasedimentary rocks of the western part of the Tukuringra terrane. The obtained data show that the Algainskaya, Garmakanskaya, and Teploklyuchevskaya series in the western part of the Tukuringra terrane are not of Middle Paleozoic but of Early Mesozoic age. It is shown that the main sources of clastic matter for these formations were Late Precambrian, Paleozoic, and Late Triassic–Early Jurassic complexes of continental massifs of the Amur superterrane.     

Sources of clastic material of Cretaceous–Paleogene deposits in the southwestern part of the Amur–Zeya Basin: results of dating U–Pb detrital zircons

The results of our study indicate that at the Late Cretaceous–Paleogene boundary in the southeastern part of the Amur–Zeya Basin, the sedimentation conditions changed drastically, namely, the change of provenance areas of debris. In the Maastrichtian, the clastic material was mainly transported from the Bureya–Jiamusi Superterrane and the volcanic–plutonic belts of Khingan–Okhotsk and East Sikhote–Alin located to the east: sedimentation occurred simultaneously with magmatic activity. During the Danian Stage, the major source of debris to the southern part of the basin was located to the south of the young mountain system of the Lesser Khingan (the uplifted part of the basement of the Songliao Block).     

Structures of degassing and fluid transport within the modern zones of the lithosphere destruction in the eastern margin of the Central Asian Fold Belt

The modern geodynamic transformations of the Amur geoblock are related to the activation of pull-apart–strike-slip and simple strike-slip movements. These movements resulted in the formation of destruction zones along ancient transregional fault systems (Nenjiang–Selemdzha, Lermontovka–Belogorsk, West Turan, Khingan, Tan Lu, and others) and young NW- and WE-trending fractures with distinctly expressed shearing displacements. These processes are fixed by earthquakes, focal magmatism, pulsed degassing of the Earth’s interior, and fluid discharge. High-permeability structures confined to the juncture of the destruction zones and young fractures served as the deep degassing drainage systems. These structures are traced by decompaction fields and anomalies of He and other gases. The most contrasting Varvarovka anomaly is located in the northeastern flank of the Yerkovtsy brown coal deposit. The paleogene coal-bearing rocks studied in the Yuzhny quarry within this deposit are characterized by high contents of noble, rare metals, and rare-earth elements, which frequently exceed their average abundances by ten orders of magnitude. Based on assay analysis, the Au content in the coals varies from trace amounts to 4.6 ppm.     

Geochemical features and sources of clastic material in Paleozoic terrigenous deposits of the northeastern flank of the South Mongolia–Khingan orogenic belt

The results of geological and geochemical studies of terrigenous rocks of the main stratigraphic subdivisions in the northeastern flank of the South Mongolia–Khingan orogenic belt and also the results of U-Pb (LА-ICP-MS) geochronological studies of detrital zircons from these deposits are presented. It is demonstrated that the studied rocks differ significantly in the nature of distribution of detrital zircon ages and, consequently, they cannot be members of a single sedimentary sequence. The data obtained confirm the standpoint according to which the northeastern flank of the South Mongolia–Khingan orogenic belt represents a “joint” zone separating the Argun and the Bureya-Jiamusi Superterranes. This joint zone was formed as the result of closure of the oceanic basin separating the specified continental massifs in the Paleozoic era. The geochemical features of the studied rocks indicate their formation in the conditions of the island arc or the active continental margin. Lack of zircon generations younger than Ordovician age in the studied samples allows assuming that the sedimentary sequences identified within the northeastern flank of the studied belt as the Necla, Dagmara, siltstone-sandstone, and Gramatukha sequences that formed from the end of the Vendian (?) to the Devonian correspond to the youngest stages of belt formation. These sediments in the current structural plan evidently represent fragments of accretion complexes cropping out in fragments among the Cenozoic sequences of the Amur-Zeya Depression.