Jom-Bolok volcanic field is located in the East Sayan Mts. of Siberia (Russia), a portion of the Asian convergent zone. It is located at the boundary of the Riphean Tuva-Mongolia massif, which was probably reactivated because of the interplay between far-field tectonic stress derived from the India–Asia collision zone and extension in the south-western Baikal rift system. The volcanic field comprises a number of hawaiitic lava flows, of various lengths, which flowed down paleorivers. Flows were fed by fissure eruptions and the largest lava flow field was dated as 7,130?±?140 cal 14C years BP using a buried organic sample found inside the associated cinder cone. This lava flow field is about 70 km long, ~100 km2 in area, and 7.9 km3 in volume. The area and volume of this flow field ranks this eruption highly in the global record of fissure-fed effusive eruptions. This lava flow field makes up 97% of the entire Jom-Bolok volcanic field, a fact which raises a puzzling question: why and/or how did a relatively small-volume volcanic field produce such a large-volume individual eruption? A working hypothesis is that a pond of sublithospheric melt accumulated over a relatively prolonged period. This was then rapidly drained in response of tectonic changes triggered by unloading of ice in the Early Holocene. 相似文献
During the Soviet era, Ukraine was an important industrial and agricultural region of the Soviet Union. This industrial and agricultural activity resulted in contamination of Ukraine’s estuaries with legacy anthropogenic pollutants. Investigations on the toxicological effects of this estuarine contamination have been limited. For this research, we measured the toxicity of contaminated sediments from four Ukrainian estuaries to several aquatic organisms over 3 years. Sediment chemical analyses and whole sediment toxicity identification evaluations (TIEs) were also performed to determine the classes of contaminants contributing to toxicity. Toxic sediments were observed in several of the Ukrainian estuaries and chemical analyses of the sediments demonstrated anthropogenic contaminants were widely distributed. Contaminants were also detected in macrobenthic organisms collected from the sediments. Several lines of evidence, including TIEs, indicated hydrophobic organic chemicals (HOCs) were contributing substantially to observed toxicity. This information can guide environmental managers to prioritize portions of the estuaries requiring remediation. 相似文献
Dhofar 280 recorded a complex history on the Moon revealed by high‐resolution 40Ar‐39Ar dating. Thermal resetting occurred less than 1 Ga ago, and the rock was exposed to several impact events before and afterwards. The cosmic ray exposure (CRE) age spectrum indicates a 400 ± 40 Ma CRE on the lunar surface. A unique feature of this lunar sample is a partial loss of cosmogenic 38Ar, resulting in a (low‐temperature) CRE age plateau of about 1 Ma. This was likely caused by the same recent impact event that reset the (low‐temperature) 40Ar‐39Ar age spectrum and preceded the short transit phase to Earth of ≤1 Ma. Dhofar 280 may be derived from KREEP‐rich lunar frontside terrains, possibly associated with the Copernicus crater or with a recent impact event on the deposits of the South Pole–Aitken basin. Although Dhofar 280 is paired with Dhofar 081, their irradiation and thermal histories on the Moon were different. An important trapped Ar component in Dhofar 280 is “orphan” Ar with a low 40Ar/36Ar ratio. It is apparently a mixture of two components, one endmember with 40Ar/36Ar = 17.5 ± 0.2 and a second less well‐constrained endmember with 40Ar/36Ar ≤10. The presence of two endmembers of trapped Ar, their compositions, and the breccia ages seem to be incompatible with a previously suggested correlation between age or antiquity and the (40Ar/36Ar)trapped ratio (Eugster et al. 2001; Joy et al. 2011a). Alternatively, “orphan” Ar of this impact melt breccia may have an impact origin. 相似文献
Well-developed filament channels may be present in the solar atmosphere even when there is no trace of filament material inside
them. Such magnetic systems with filament channels without filaments can result in coronal mass ejections that might appear
to have no corresponding solar surface source regions. In this case study, we analyze CMEs on 9 August 2001 and 3 March 2011
and trace their origins to magnetic systems with filament channels containing no obvious filament material on the days around
the eruptions. 相似文献
The MARS-3D model in conjunction with the particle tracking module Ichthyop is used to study circulation and tracer dynamics under a variety of forcing conditions in the eastern English Channel, and in the Boulogne-sur-Mer harbour (referred to hereafter as BLH). Results of hydrodynamic modelling are validated against the tidal gauge data, VHF radar surface velocities and ADCP measurements. Lagrangian tracking experiments are performed with passive particles to study tracer dispersal along the northern French coast, with special emphasis on the BLH. Simulations revealed an anticyclonic eddy generated in the harbour at rising tide. Tracers, released during flood tide at the Liane river mouth, move northward with powerful clockwise rotating current. After the high water, the current direction changes to westward, and tracers leave the harbour through the open boundary. During ebb tide, currents convergence along the western open boundary but no eddy is formed, surface currents inside the harbour are much weaker and the tracer excursion length is small. After the current reversal at low water, particles are advected shoreward resulting in a significant increase of the residence time of tracers released during ebb tide. The effect of wind on particle dispersion was found to be particularly strong. Under strong SW wind, the residence time of particles released during flood tide increases from 1.5 to 6 days. For release during ebb tide, SW wind weakens the southward tidally induced drift and thus the residence time decreases. Similar effects are observed when the freshwater inflow to the harbour is increased from 2 to 10 m3/s during the ebb tide flow. For flood tide conditions, the effect of freshwater inflow is less significant. We also demonstrate an example of innovative coastal management targeted at the reduction of the residence time of the pathogenic material accidentally released in the harbour. 相似文献
We report the results of a novel experimental study on eclogitic garnets with abundant inclusions of clinozoisite, quartz and rutile subjected to temperatures (T) of 800–1100 °C and a pressure (P) of 4 GPa, representative of ultrahigh-pressure (UHP) metamorphic terranes such as the Kokchetav massif, Saxonian Erzgebirge, etc. The experiments reveal extremely rapid recrystallization and partial melting of garnet interiors controlled by fluids liberated from the breakdown of the hydrous mineral inclusions. The traditional assumption that inclusions of minerals and primary fluid inclusions should be representative of the peak or even earlier metamorphic history cannot be strictly applied in this case. We argue that inclusions in UHP garnets may mirror P–T conditions postdating growth of the host crystal or even P–T conditions never actually experienced by the rock itself. The above modification of garnet interiors produces a typical patchy microstructure that occurs in natural eclogitic garnet from the diamond-bearing UHP Kokchetav massif. 相似文献
Abstract— We performed high‐resolution 40Ar‐39Ar dating of mineral separates and whole‐rock samples from the desert meteorites Dhofar 300, Dhofar 007, and Northwest Africa (NWA) 011. The chronological information of all samples is dominated by plagioclase of varying grain size. The last total reset age of the eucrites Dhofar 300 and Dhofar 007 is 3.9 ± 0.1 Ga, coeval with the intense cratering period on the Moon. Some large plagioclase grains of Dhofar 007 possibly inherited Ar from a 4.5 Ga event characteristic for other cumulate eucrites. Due to disturbances of the age spectrum of NWA 011, only an estimate of 3.2–3.9 Ga can be given for its last total reset age. Secondary events causing partial 40Ar loss ≤3.4 Ga ago are indicated by all age spectra. Furthermore, Ar extractions from distinct low temperature phases define apparent isochrons for all samples. These isochron ages are chronologically irrelevant and most probably caused by desert alterations, in which radiogenic 40Ar and K from the meteorite and occasionally K induced by weathering are mixed, accompanied by incorporation of atmospheric Ar. Additional uptake of atmospheric Ar by the alteration phase(s) was observed during mineral separation (i.e., crushing and cleaning in ultrasonic baths). Consistent cosmic‐ray exposure ages were obtained from plagioclase and pyroxene exposure age spectra of Dhofar 300 (25 ± 1 Ma) and Dhofar 007 (13 ± 1 Ma) using the mineral's specific target element chemistry and corresponding 38Ar production rates. 相似文献
SNAP, the SuperNova Acceleration Probe, is planned as a space-based telescope designed specifically to search for and monitor
cosmological supernovae and weak lensing. In this paper we propose some other mission objectives which are of great importance
in the fields of Galactic and extragalactic astronomy and which can be done as by-products with the same instrumentation and
survey strategy as currently proposed for the main SNAP mission. 相似文献
The nocturnal low-level jet (LLJ) and orographic (gravity) waves play an important role in the generation of turbulence and pollutant dispersion and can affect the energy production by wind turbines. Additionally, gravity waves have an influence on the local mixing and turbulence within the surface layer and the vertical flux of mass into the lower atmosphere. On 25 September 2017, during a field campaign, a persistent easterly LLJ and gravity waves were observed simultaneously in a coastal area in the north of France. We explore the variability of the wind speed, turbulent eddies, and turbulence kinetic energy in the time–frequency and space domain using an ultrasonic anemometer and a scanning wind lidar. The results reveal a significant enhancement of the turbulence-kinetic-energy dissipation (by?50%) due to gravity waves in the LLJ shear layer (below the jet core) during the period of wave propagation. Large magnitudes of zonal and vertical components of the shear stress (approximately 0.4 and 1.5 m2 s?2, respectively) are found during that period. Large eddies (scales of 110 to 280 m) matching the high-wind-speed regime are found to propagate the momentum downwards, which enhances the mass transport from the LLJ shear layer to the roughness layer. Furthermore, these large-scale eddies are associated with the crests while comparatively small-scale eddies are associated with the troughs of the gravity wave.
We are presenting new results on kinematics and structure of the Mrk 334 Seyfert galaxy. Panoramic (3D) spectroscopy is performed at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences using the integral-field Multi-Pupil Fiber Spectrograph (MPFS) and scanning Fabry–Pérot interferometer. The deep images have revealed that Mrk 334 is observed during the final stage of its merging with a massive companion. A possible mass ratio ranges from 1/5 to 1/3. The merger has triggered mass redistribution in the disc resulting in an intensification of nuclear activity and in a burst of star formation in the inner region of the galaxy. The circumnuclear starburst is so intense that its contribution to the gas ionization exceeds that contribution of the active galactic nuclei (AGN). We interpret the nuclear gas outflow with velocities of ∼200 km s−1 as a galactic superwind that accompanies the violent star formation. This suggestion is consistent with the asymmetric X-ray brightness distribution in Mrk 334. The trajectory of the fragments of the disrupted satellite in the vicinity of the main galaxy nucleus can be traced. In the galaxy disc, a cavern is found that is filled with a low-density ionized gas. We consider this region to be the place where the remnants of the companion have recently penetrated through the gaseous disc of the main galaxy. 相似文献