Upper-mantle structure and nature of deep processes in island arcs and trench systems

Upper-mantle structure and heat flow and gravity data are considered. It is shown that crustal isostasy disturbance is compensated for by inhomogeneities in the density of the upper mantle; compaction beneath trenches and discompaction under island arcs. On the basis of the available data an upper-mantle density model is constructed which is represented by a seismoactive layer with a surplus density of from 0.05 to 0.1 g/cm³ and a discompacted zone overlying that layer with a density deficiency of 0.05 g/cm³ beneath the island arc and 0.01 g/cm³ in the remaining area. The available data are in poor agreement with the concept of “new global tectonics”, therefore the formation of density inhomogeneities is associated with gravity differentiation of the mantle material. A scheme of this process is proposed according to which heated differentiates of the mantle material rise along deep faults or weakened zones from depths of 700 km and more. Upper-mantle material differentiation occurs mainly in several levels, but mostly at depths down to 150–200 km within the interval of 350–450 km. Separation of heavy components as a result of differentiation and the “zone melting process” causes a high velocity and correspondingly a denser inclined layer. Discompaction of the upper mantle overlying the focal plane is associated with its being heated by high-temperature melts circulating over the inclined fault.     

Evolution of the Landscape of the Western Part of the Turan–Uyuk Basin (Tuva Highland) in the Late Pleistocene

Doklady Earth Sciences - A complex of works including geomorphological deciphering, field survey, drilling, electric prospecting, and dating of deposits using the radiocarbon method and optically...     

Silurian Granitoid Magmatism of the Rassokha Terrane (North-East Russia)

Doklady Earth Sciences - U–Pb dating of zircons from granitoids located within the Rassokha terrane show a Silurian age of their formation. Younger dates from one of the samples are related...     

Kinematics of the bottom of the Eurasia Basin near the Spitsbergen domain

Prior to extension of the lithosphere in the Eurasia Basin, the Yermak Plateau was an element of the Eurasian Arctic margin. Extension of the Barents Sea shelf culminated gradually in rifting of the continental crust with separation of this block from the continent during Chrons C25r?C26n (57.656?59.237 Ma ago) and emplacement of numerous basic dikes, which could be responsible for the formation of high-amplitude magnetic anomalies on the Yermak Plateau. The investigation included reconstruction of axes in the breakup zones along peripheral continental fragments of Spitsbergen with determination of the Euler poles and angles of rotation, which describe the kinematics of this process. It is revealed that the difference between depths of conjugate isobaths can be as large as many tens of meters, which reflects the nonuniformly scaled slide of peripheral areas of the continental crust along the plane of the crustal-penetrating fault and, correspondingly, their different subsidence during rifting.     

Acoustic stereo images of the bottom surface

In order to enhance the efficiency of the interpretation of surface images obtained with a side scanning sonar, it is proposed to supplement the standard processing software with a program for obtaining acoustic stereo images. Examples of such images synthesized with this program using the data of a bottom sonar survey with a side scanning sonar and an echo sounder are presented. The cases are considered when the information on the bottom relief contained in sonar images obtained with a standard side scanning sonar or its modifications can be used instead of the data of an echo sounding survey.     

U–Pb LA–ICP–MS Age of Detrital Zircons from the Lower Riphean and Upper Vendian Deposits of the Luga–Ladoga Monocline

The results of LA–ICP–MS U–Pb analyses of detrital zircons from the Precambrian deposits of Luga–Ladoga monocline are discussed. The age spectra of the zircons separated from the Riphean to Upper Vendian sandstones from the Shotkusa-1 well demonstrate dominance of the Paleo- and Mesoproterozoic grains while the Archaean zircons are subordinate. The Riphean debris sources were local swells of the Northern Ladoga basement. The sequence interval presumably corresponding to the Vasilieostrov Formation (Upper Vendian) has yielded not only Paleo- and Mesoproterozoic zircon ages, but Neoproterozoic as well, implying a Timanide provenance: these zircons (527 ± 9 and 516 ± 13 Ma) allow deposition of a significant part of the Shotkusa-1 sequence at the very beginning of the Cambrian.     

New Data on Geochronology of the Upper Quaternary Loess–Soil Series in the Terek–Kuma Lowland

Lithology and Mineral Resources - Drilling recovered the upper part (23 m) of the upland loess–paleosol series (LPS) on the right bank of the Kuma River near the Otkaznoe Settlement....     

The Glaciolacustrine Terrace in the Izborsk-Malskaya Valley (the North-West of Russia): Composition,Age, and Origin

Doklady Earth Sciences - Studying the Izborsk-Malskaya Valley, the authors focus on the origin of glaciolacustrine terraces in overdeepened valleys widespread in the Late Valdai (Ostashkov,...     

Structural evolution of the Main Ural Fault Zone in the western framework of the Voikar-Synya ophiolite massif

Multistage deformations in the Main Ural Fault Zone is recorded in the structural features of this zone in the southern part of the Polar Urals. The deformation of the oldest metamorphic complexes in the Khord??yus massif and Dzelyayu block developed during the precollision stage. After formation of the general nappe-thrust structure of the Urals, these blocks were squeezed to the higher crustal levels. Deformation in other tectonic units started at the early collision stage during regional thrusting. Brittle failure was superposed over the all previously formed structures at the late collision and postcollision stages.