Far fields of internal gravity waves from oscillating sources of disturbances

We considered the problem dealing with the far field of internal gravity waves generated by the source oscillating in the vertical. It is shown that, at a fixed observation point, we first record the arrival of the main wave front of a separate mode followed by the arrival of two fronts of an additional field of this wave mode, which is caused by the oscillations of the source, the asymptotics near the additional wave front being expressed via Airy function.     

Gabbro-granite intrusive series and their indicator importance for geodynamic reconstructions

One of the problems faced by researchers when paleogeodynamic reconstructions are carried out for deeply eroded orogenic terranes is the limited usage of geological and isotopic geochemical data on volcanic associations. The utilization of information on gabbroids and granitoids considered separately also fails to resolve this problem. The convergence of features of arc, collisional, and within-plate magmatic processes leads the researcher to search for indicator plutonic associations, such as paired gabbrogranite intrusive series. The latter were distinguished using geoinformation databases (including those compiled by the authors of this paper), which were composed for the Early Caledonides in the Altai-Sayan folded area and adjacent territories. This makes it possible to characterize mantle-crustal magmatism in suprasubductional and collisional environments and the conditions under which these geodynamic regimes (plate- and plume-tectonic factors) interact. This paper presents estimates of the composition of the parental basic magmas, distinctive features of their differentiation, and the compositional specifics of the accompanying extensive granite-forming processes. The example of the Altai-Sayan folded area and adjacent territories is employed to correlate the composition of the basic-ultrabasic and granitoid magmas and, on this basis, distinguish (a) differentiated gabbro-tonalite-plagiogranite intrusive series corresponding to accretionary-collisional geodynamic environments, and (b) gabbro-monzonite-granosyenite-potassic granite intrusive series, which were produced when the accretionary-collisional system was affected by a plume.     

Stratified unbounded flow past of obstacles

We studied the surface perturbations of a two-layer ideal fluid induced by a flow past a submerged obstacle (simulated by a point dipole) in the vicinity of the density-jump layer. It is shown that the formation of two different types of surface waves is possible behind the flowed past obstacle in the real conditions of the open sea. The comparison of the amplitudes of the surface perturbations induced by the obstacle located above and below the density jump revealed their significant differences, which seems to be important for the use of this effect in practical problems.     

Optical observations of gamma-ray bursts, the discovery of supernovae 2005bv, 2005ee, and 2006ak, and searches for transients using the “MASTER” robotic telescope

We present the results of observations obtained using the MASTER robotic telescope in 2005–2006, including the earliest observations of the optical emission of the gamma-ray bursts GRB 050824 and GRB 060926. Together with later observations, these data yield the brightness-variation law t ^?0.55±0.05 for GRB 050824. An optical flare was detected in GRB 060926—a brightness enhancement that repeated the behavior observed in the X-ray variations. The spectrum of GRB 060926 is found to be F _E ～ E ^?β , where β = 1.0 ± 0.2. Limits on the optical brightnesses of 26 gamma-ray bursts have been derived, 9 of these for the first time. Data for more than 90% of the accessible sky down to 19 ^m were taken and reduced in real time during the survey. A database has been composed based on these data. Limits have been placed on the rate of optical flares that are not associated with detected gamma-ray bursts, and on the opening angle for the beams of gamma-ray bursts. Three new supernovae have been discovered: SN 2005bv (type Ia)—the first to be discovered on Russian territory, SN 2005ee—one of the most powerful type II supernovae known, and SN 2006ak (type Ia). We have obtained an image of SN 2006X during the growth stage and a light curve that fully describes the brightness maximum and exponential decay. A new method for searching for optical transients of gamma-ray bursts detected using triangulation from various spacecraft is proposed and tested.     

Internal Gravity Waves in the Ocean with Multidirectional Shear Flows

Izvestiya, Atmospheric and Oceanic Physics - The problem of constructing solutions that describe internal gravity waves in a stratified medium with finite depth and multidirectional shear flows has...     

Surface effects related to the flow of a nonuniformly stratified fluid around obstacles

Doklady Earth Sciences -     

Thermochronology of the Chernorud granulite zone,Ol’khon Region,Western Baikal area

Structural-petrologic and isotopic-geochronologic data on magmatic, metamorphic, and metasomatic rocks from the Chernorud zone were used to reproduce the multistage history of their exhumation to upper crustal levels. The process is subdivided into four discrete stages, which corresponded to metamorphism to the granulite facies (500–490 Ma), metamorphism to the amphibolite facies (470–460 Ma), metamorphism to at least the epidote-amphibolite facies (440–430 Ma), and postmetamorphic events (410–400 Ma). The earliest two stages likely corresponded to the tectonic stacking of the backarc basin in response to the collision of the Siberian continent with the Eravninskaya island arc or the Barguzin microcontinent, a process that ended with the extensive generation of synmetamorphic granites. During the third and fourth stages, the granulites of the Chernorud nappe were successively exposed during intense tectonic motions along large deformation zones (Primorskii fault, collision lineament, and Orso Complex). The comparison of the histories of active thermal events for Early Caledonian folded structures in the Central Asian Foldbelt indicates that active thermal events of equal duration are reconstructed for the following five widely spiced accretion-collision structures: the Chernorud granulite zone in the Ol’khon territory, the Slyudyanka crystalline complex in the southwestern Baikal area, the western Sangilen territory in southeastern Tuva, Derbinskii terrane in the Eastern Sayan, and the Bayankhongor ophiolite zone in central Mongolia. The dates obtained by various isotopic techniques are generally consistent with the four discrete stages identified in the Chernorud nappe, whereas the dates corresponding to the island-arc evolutionary stage were obtained only for the western Sangilen and Bayankhongor ophiolite zone.     

Synkinematic granitoid magmatism of Western Sangilen,South-East Tuva

The problems of tectonic control of composition, size, and morphology of synkinematic crustal granitoids are discussed by the example of the Western Sangilen granites (South-East Tuva). Comparative analysis was performed for felsic bodies and massifs spatially confined to tectonic zone (Erzin shear zone): Erzin migmatite–granite complex (510–490 Ma), Matut granitoid massif (510–490 Ma), Bayankol polyphase gabbro-monzodiorite–granodiorite–granite massif (490–480 Ma), and the Nizhneulor Massif (480–470 Ma). It is shown that synkinematic felsic melts during the transition from collisional compression to transpression were formed at different crustal levels. An increase of shear component provided favorable conditions for the migration of felsic melts, increase of size and morphology of intrusive bodies from vein type to harploith (likely, loppoliths and laccoliths) and further to stocks. All kinematic granitoids of the Erzin tectonic zone are ascribed to the crustal S-type granites. Dispersion and average chemical composition of the synkinematic granites strongly depend on the degree of their “isolation” from protolith. From auto- and paraautochthonous granitoids to allochthonous granites, the compositional dispersion decreases and the chemical composition is displaced toward I-type magmatic rocks.     

Age of overthrust-type granites in the accretionary‒collisional system of the early Caledonides (western Baikal region)

The western Baikal region (Ol’khon region, Nutgei zone, Kharikta area) is characterized by the development of packets of thrust-type folds and synkinematic granites corresponding to the stage of thrust deformations (overthrust-type granites). Two stages in the formation of thrust-type folds separated by episodes of granite emplacement are definable. The data obtained make it possible to estimate both the time of transition from thrust to strike-slip deformations and the duration of accretionary?collisional events that resulted in regional strike-slip deformations, which terminated in the western Baikal region 460?455 Ma ago.     

Stanniferrous granites of Vietnam: Rb-Sr and Ar-Ar isotope age,composition, sources,and geodynamic formation conditions

Doklady Earth Sciences - Stanniferrous granite-leucogranite massifs in Vietnam to which the bedrock and placer commercial deposits of cassiterite are associated (Timtuc etc.) are of late Cretaceous...