Manifestations of miocene acid intrusive magmatism on the southern slope of the Greater Caucasus: First evidence from isotope geochronology

New isotope-geochronological data (K-Ar, Rb-Sr) provide tight geochronological constraints on the history of Late Cenozoic magmatism on the southern slope of the Greater Caucasus. Several previously unknown, rhyodacite intrusive bodies with an emplacement age of 6.9 ± 0.3 Ma (Late Miocene) are reported from the Kakheti-Lechkhumi regional fault zone in the Kvemo Svaneti-Racha area. Therefore, a pulse of acid intrusive magmatism took place in a period previously considered amagmatic in the Greater Caucasus. The petrological, geochemical, and isotopic data suggest that these rhyodacites are produced by crystallization differentiation of mantle-derived magmas, which are similar in composition to Miocene mafic lavas that erupted a few hundred thousand years later in the adjacent Central Georgian neovolcanic area. The presented results allow the conclusion that the volcanic activity within the Central Georgian neovolcanic area occurred at 7.2–6.0 Ma in two discrete pulses: (1) the emplacement of acid intrusions and (2) the eruption of trachybasaltic lavas. The emplacement of rhyodacite intrusions in the Kvemo Svaneti-Racha area marked the first pulse of young magmatism on the southern slope of the Main Caucasus range and simultaneously represented the second magmatic pulse (after granitoid magmatism of the Caucasian Mineral Waters region) within the entire Greater Caucasus.     

Search for variable sources using data of “Cold” surveys

We search for variable sources, using the data of the surveys conducted on the RATAN-600 radio telescope in 1980–1994 at 3.94 GHz. To test the radio sources of the RCR (RATAN Cold Refined) catalog for variability, we estimated the long-term variability indices V of the studied objects, their relative variability amplitudes V _χ , and the χ ² probabilities p. Out of about two hundred considered sources, 41 proved to have positive long-term variability indices, suggesting that these sources may be variable. Fifteen objects can be considered to be reliably variable according to the χ ² criterion p > 0.98, three of these sources have χ ² probabilities p ≥ 0.999. The corresponding probabilities for six sources lie in the 0.95 < p < 0.98 interval, and those of the remaining 20 objects in the 0.73 ≤ p < 0.95 interval. Twenty four of 41 objects are variable or possibly variable in the optical range, and five objects are known variable radio sources. We construct the light curves and spectra for the sources with positive long-term variability indices.     

Two-Color Observations of AM Her

Observations and light curves of the variable star AM Her observed in the b and v proper color system of the Abastumani two-channel photometer are presented.     

Cluster–subcluster mergers and the formation of narrow-angle tailed radio sources

We examine the ROSAT PSPC X-ray properties of a sample of 15 Abell clusters containing 23 narrow-angle tailed (NAT) radio galaxies. We find that clusters with NATs show a significantly higher level of substructure than a similar sample of radio-quiet clusters, indicating that NAT radio sources are preferentially located in dynamically complex systems. Also, the velocity distribution of the NAT galaxies is similar to that of other cluster members; these velocities are inadequate for producing the ram pressure necessary to bend the radio jets. We therefore propose a new model for NAT formation, in which NATs are associated with dynamically complex clusters undergoing merger events. The U -shaped NAT morphology is produced in part by the merger-induced bulk motion of the ICM bending the jets.     

Subpollen Particles as Atmospheric Cloud Condensation Nuclei

Izvestiya, Atmospheric and Oceanic Physics - Bioparticles constitute a significant fraction of atmospheric aerosol. Their size range varies from nanometers (macromolecules) to hundreds of...     

Radiative association in Li+H revisited: the role of quasi-bound states

The role in radiative association of narrow resonances arising from quasi-bound levels is examined. For the rate coefficient the contribution from such levels is readily calculated in terms of the Einstein A -coefficient from bound rovibrational levels generated using a suitable alternative boundary condition. By locating systematically all the quasi-bound levels, an enhancement by more than an order of magnitude of the rate coefficient for Li(2s) + H(1s) association above about 600 K is obtained. The effect on the LiH abundance in the early Universe is no more than an increase of a factor of 3 for limited ranges of values of the redshift. For the Li(2p) state the effect of narrow resonances appears to have been taken into account in previous calculations.     

溃变图的业务操作系统简介

按溃变理论［１］的不连续或非均匀信息不仅可以预测天气系统的移动性变化和转折性变化，也可以预测降水等天气现象。并已被多次历史例案和应用实践所验证。为了便于投入业务运用，我们利用数据库系统，实现了体现资料信息非均匀和不连续的广义参数在微机、填图机上的自动化处理，完成了收报、计算和填图分析的自动化。本方法体现了预报工具的改革也充分地利用了现有的资料资源     

Changes in European precipitation seasonality and in drought frequencies revealed by a four-century-long tree-ring isotopic record from Brittany, western France

A new paleoclimatic reconstruction for western France is obtained from tree-ring cellulose stable isotopes. Living trees from Rennes Forest and beams from two ancient buildings in Rennes city have been combined to cover the past four centuries with a gap from 1730 to 1750. The cellulose ¹³C reflects the progressive changes in atmospheric CO₂ isotopic composition. The combined ¹³C and ¹⁸O measurements are used to propose a reconstruction of interannual fluctuations in local summer temperature and water stress. At the decadal time scale, the reconstructed water stress profile exhibits a significant similarity with the historical wine harvest dates, an indicator of warm and dry growth seasons, as well as with the summer central England and central Alps instrumental temperature records and climate model results. Combined with instrumental precipitation records from Paris, these reconstructions suggest a dramatic and widespread change in the seasonality of the precipitation at the beginning of the nineteenth century, with drier winters and wetter summers, which may have contributed to the Alpine glacier decline at the end of the Little Ice Age. The tree-ring isotope records also show a relationship with large-scale North Atlantic circulation changes and the interannual variability is modified between the nineteenth and twentieth centuries (7–8 year periodicities) and the seventeenth century (11–14 year periodicities). By classifying 20-year-long subsets of the reconstructed climatic parameters, we estimate that a decadal mean summer warming of 0.8±0.1°C induced extreme dry years to be 2.2±0.7 times more frequent.