The far-UV spectrum of T Tauri stars – I. The relevance of the IUE Newly Extracted Spectra

The far-UV spectrum of the T Tauri stars (TTSs) provides important clues about the structure of the stellar atmospheres, winds and accretion shocks. The IUE ( International Ultraviolet Explorer ) Final Archive contains the most complete data base for such studies. A new extraction system, the IUE Newly Extracted Spectra ( ines ), has been developed to overcome the disadvantages of the extraction system used in the IUE Final Archive, the Signal Weighted Extraction Technique ( swet ). We have compared the ines spectra of the whole sample of TTSs in the far-UV range (1200–2000 Å) with the swet low-resolution spectra available in the IUE Final Archive. Although in most of the cases there is a good agreement between both samples, an important enhancement of the ines line fluxes with respect to the swet line fluxes is reported for particular spectra. The line fluxes are enhanced by as much as a factor of ∼2.5 in some objects, which is significant for variability studies of TTSs because the variations of the UV lines are typically of this order. The emission-measure distributions built to study the atmospheres of these stars are based on the UV emission line fluxes, so the new system is susceptible to introduce changes in these models. Moreover, the non-linear enhancement of the ines line fluxes produces variations in diagnostic line ratios usually taken as temperature and density tracers in late-type stars. These line ratios can vary by as much as a factor of 3 when the ines data are compared with the swet , with the subsequent variation of the physical parameters derived from them.     

Hydrocarbons of bottom sediments at the Shtokman Field in the Barents Sea

Hydrocarbon samples taken from bottom sediments of the Barents Sea in summer 2010 in two grounds near the Shtokman Gas Condensate Field were studied. The concentration of hydrocarbons was found to increase with sampling depth along with a decrease in C_org concentration. The composition of alkanes had mixed genesis: autochthonous homologues (n-C₁₆-C₁₇) dominated in the low-molecular domain, while oil ones dominated in the high-molecular domain; light polyarenes dominated in the composition of polycyclic aromatic hydrocarbons. The seepage of hydrocarbons from the sedimentary stratum and their transformation in the surface layer of bottom sediments are considered as their major source. The relatively low hydrocarbon concentrations converted to dry mass and in the composition of C_org are supposed to be due to a decrease in the intensity of fluid flows, since the hydrocarbon reservoirs of the Shtokman Field are firmly capped by an impermeable stratum of mostly clay rocks.     

The present-day active deformation in the central and northern parts of the Gulf of Suez area,Egypt, from earthquake focal mechanism data

The average seismic strain rate is estimated for the seismotectonic zone of the northern/central parts of the Gulf of Suez. The principal strain rate tensor and velocity tensor were derived from a combination of earthquake focal mechanisms data and seismic moment of small-sized earthquakes covering a time span of 13 years (1992–2004). A total of 17 focal mechanism solutions have been used in the calculation of the moment tensor summation. The local magnitudes (MLs) of these events range from 2.8 to 4.7. The analysis indicates that the dominant mode of deformation in the central and northern parts of the Gulf of Suez is extension at a rate of 0.008 mm/year in N28°E direction and a small crustal thinning of 0.0034 mm/year. This low level of strain means that this zone experienced a little seismic deformation. There is also a right lateral shear motion along the ESE–WNW direction. This strain pattern is consistent with the predominant NW–SE normal faulting and ESE–WNW dextral transtensive faults in this zone. Comparing the results obtained from both stress and strain tensors, we find that the orientations of the principal axes of both tensors have the same direction with a small difference between them. Both tensors show a predominantly extensional domain. The nearly good correspondence between principal stress and strain orientations in the area suggests that the tectonic strength is relatively uniform for this crustal volume.     

Mineralogy and petrology of sample 67075 and the origin of lunar anorthosites

Plagioclase in cataclastic anorthosite 67075 occurs as angular matrix grains and as recrystallized clasts of micro-anorthosite. Olivines are Fe-rich and fall into two compositional groupings. Large grains of pyroxene show exceptionally well-developed exsolution lamellae analogous to those observed in pyroxenes from layered complexes. The low-Ca component in both pigeonites and augites shows varying degrees of inversion to orthopyroxene. The lattices of host and lamellae may deviate slightly (up to 2°) from the ideal orientation. Very slow cooling from magmatic temperatures is required to produce the coarse exsolution textures and inversion features. Augite macrocrystals are distinctly subcalcic indicating crystallization at temperatures around1100 ± 50°C while host-lamellae pairs and small grains in lithic clasts and matrix indicate reequilibration on a micron scale to temperatures less than 800°C. Pyroxene compositions tend to cluster into two groups both of which are among the most Fe-rich reported for highland pyroxenes. Ti and Al contents of pyroxenes are very low and Ti, Cr, and Mn follow well-established magmatic differentiation trends. The high Cr content may reflect low?O₂ conditions and/or early crystallization of olivine and plagioclase.The⁸⁷Sr/⁸⁶Sr ratios in lunar anorthosites are the lowest reported for any lunar rock. It is likely that anorthosites formed as cumulates during the major differentiation episode which occurred prior to～4.3AE. Recrystallization features are common and³⁹Ar/⁴⁰Ar ages cluster around 4.0 AE. This may be the result of the intense bombardment prior to 4.0 AE which caused repeated cycles of in-situ fracturing and granulation followed by recrystallization. The low siderophile element content and the inferred slow cooling indicate a plutonic source region (10km) not frequently plumbed by impact events. The Fe-rich silicates indicate crystallization from a melt at an advanced stage of fractionation. However, the low REE abundances are not consistent with late-stage crystallization. Plagioclase apparently crystallized relatively early and was concentrated by flotation and/or convection currents while the mafic minerals crystallized from a fractionated trapped liquid. The chemical, isotopic, and mineralogical data place stringent constraints on the nature of genetically related rocks and the relationship of anorthosites to other members of the ANT suite does not appear to be one ofsimple fractionation. The data presented in this paper are consistent with the Taylor-Jake?model of lunar evolution.     

Permian age of the Burpala alkaline pluton, Northern Transbaikalia: Geodynamic implications

This paper presents the U-Pb zircon age of pulaskite of the main phase (294 ± 1 Ma) and the rare metal syenite (283 ± 8 Ma) of the Burpala alkaline pluton. The geochronological data show that it was formed in the Early Permian. By age, it is comparable with the Synnyr pluton of the Synnyr rift zone, alkaline granitic rocks and bimodal volcanic associations of the Uda-Vitim rift zone, and carbonatites of the Saizhen rift zone of the Central Asian foldbelt. These intraplate igneous complexes were formed almost simultaneously with crustal granitic rocks of the Angara-Vitim batholite. All of this gives ground to suppose that the origination of their parental melts is a result of the influence of the mantle hot spot or mantle plume on the lithosphere that led to extensive crustal anatexis.     

The crustal continuum model for late-Archaean lode-gold deposits of the Yilgarn Block,Western Australia

Most Archaean gold ores belong to a coherent genetic group of structurally controlled lode-deposits that are characteristically enriched in Au with variable enrichments in Ag, As, W, Sb, Bi, Te, B and Pb, but rarely Cu or Zn, and are surrounded by wallrock alteration haloes enriched in K, LILE and CO₂, with variable Na and/or Ca addition. Evidence from the Yilgarn Block of Western Australia, combined with similar evidence from Canada and elsewhere, indicates that such deposits represent a crustal continuum that formed under a variety of crustal régimes over at least a 15 km crustal profile at PT conditions ranging from 180°C at <1 kb to 700°C at 5 kb. Individual deposits, separated by tens to hundreds of kilometres, collectively show transitional variations in structural style of mineralisation, vein textures, and mineralogy of wallrock alteration that relate to the PT conditions of their formation at varying crustal depths. Specific transitions within the total spectrum may be shown also by deposits within gold camps, although nowhere is the entire continuum of deposits recorded from a single gold camp or even greenstone belt. Recognition of the crustal continuum of deposits implicates the existence of giant late-Archaean hydrothermal systems with a deep source for the primary ore fluid. A number of deep fluid and solute reservoirs are possible, including the basal segments of greenstone belts, deep-level intrusive granitoids, mid-to lower-crustal granitoidgneisses, mantle lithosphere, or even subducted oceanic lithosphere, given the probable convergent-margin setting of the host greenstone terranes. Individual stable and radiogenic isotope ratios of fluid and solute components implicate fluid evolution from, or equilibrium with, a number of these reservoirs, stressing the potential complexity of pathways for fluid advection to depositional sites. Lead and strontium isotope ratios of ore-associated minerals provide the most persuasive evidence for fluid advection through deep-level intrusive granitoids or granitoid-gneiss crust, whereas preliminary oxygen isotope data show that mixing of deeply sourced fluid and surface waters only occurred at the highest crustal levels recorded by the lode gold deposits.     

Heterotrophic microbial communities on the water-sediment boundary in the Kara Sea

The qualitative and quantitative characteristics of the heterotrophic microbial communities (bacteria, flagellates, and ciliates) in the thin water-sediment layer in the Kara Sea are analyzed. The bacterial abundance correlated with the concentration of organic matter, whereas their size depended on the abundance of heterotrophic flagellates. The number of species of heterotrophic flagellates increased with the increase in the bacterial number. A positive relationship between the bacterial abundance and the ration of heterotrophic flagellates was observed at the offshore stations, probably due to the grazing pressure. The density of the ciliates on the soft silty and sandy-silty sediments was extremely low. The share of upstream filter feeding ciliate species increased with the increase in the abundance of the flagellates, probably due to the shift to less selective feeding strategies at higher values of the food concentrations. The classification of the heterotrophic microbial communities in the surface sediment layer has revealed two distinct types of the communities. The river communities are rich in species and are characterized by the high abundance of microorganisms. They are gradually replaced by marine communities at the salinity of 9%.     

Landscape–biogeochemical factors of transformation of the Cs-137 contamination field in the Bryansk region

Data are presented on the distribution of Chernobyl-derived ^137Cs in different landscapes of the Bryansk region. The role of different landscape-biogeochemical factors in the transformation of the ^137Cs contamination field is examined. The distribution of ^137Cs in the typical soil catenary junction of predpolessie, predopolje, and opolje landscapes is analyzed. The role of biogeochemical barriers in the ^137Cs accumulation is considered. It is revealed that the slope exposure affects the intensity of geochemical migration. In particular, the intensity of lateral migration of ^137Cs on the slopes of the southern and southwestern exposure is much higher than that on the slopes of the northern and northeastern exposure. The different types of geochemical lateral structure of landscape are analyzed on the basis of the catenary ^137Cs distribution.     

Evolution of latitude zonal structure of the large-scale magnetic field in solar cycles

Properties of a latitude zonal component of the large-scale solar magnetic field are analyzed on the basis of H charts for 1905–1982. Poleward migration of prominences is used to determine the time of reversal of the polar magnetic field for 1870–1905. It is shown that in each hemisphere the polar, middle latitude and equatorial zones of the predominant polarity of large-scale magnetic field can be detected by calculating the average latitude of prominence samples referred to one boundary of the large-scale magnetic field. The cases of a single and three-fold polar magnetic field reversal are investigated. It is shown that prominence samples referred to one boundary of the large-scale magnetic field do not have any regular equatorward drift. They manifest a poleward migration with a variable velocity up to 30 m s^-1 depending on the phase of the cycle. The direction of migration is the same for both low-latitude and high-latitude zones. Two different time intervals of poleward migration are found. One lasts from the beginning of the cycle to the time of polar magnetic field reversal and the other lasts from the time of reversal to the time of minimum activity. The velocity of poleward migration of prominences during the first period is from 5 m s^-1 to 30 m s^-1 and the second period is devoid of regular latitude drift.