The isotope composition of Hf in zircon from Paleoarchean plagiogneisses and plagiogranitoids of the Sharyzhalgai uplift (southern Siberian craton): Implications for the continental-crust growth

This paper presents results of U–Pb dating (SHRIMP-II) and Lu–Hf (LA–ICP MS) isotope study of zircon from Paleoarchean plagiogneisses and plagiogranitoids of the Onot and Bulun blocks of the Sharyzhalgai uplift. Magmatic zircons from the Onot plagiogneiss and Bulun gneissic trondhjemite are dated at 3388±11 and 3311±16 Ma, respectively. Magmatic zircons from plagiogneisses and plagiogranitoids of the studied tonalite–trondhjemite–granodiorite (TTG) complexes are characterized mainly by positive values of εHf indicating that felsic melts were generated mainly from juvenile (mafic) sources, which are derived from a depleted mantle reservoir. The variable Hf isotope composition in magmatic zircons and the lower average εHf values in comparison with the depleted mantle values suggest the contributions of both mafic and more ancient crustal sources to magma formation. Metamorphic zircons from the gneissic plagiogranite and migmatized plagiogneiss either inherited the Hf isotope composition from magmatic zircon or are enriched in radiogenic Hf. The more radiogenic Hf isotope composition of metamorphic zircons from the migmatized plagiogneisses is due to their interaction with melt during partial melting. Variations in the Lu–Hf isotope composition of zircon from the Bulun rocks in the period 3.33–3.20 Ga are due to the successive melting of mafic crust or the growing contribution of crustal material to their genesis. Correlation between the Lu–Hf isotope characteristics of zircon and the Sm–Nd parameters of the Onot plagiogneisses points to the contribution of ancient crustal material to their formation. The bimodal distribution of the model Hf ages of zircons reflects two stages of crustal growth in the Paleoarchean: 3.45–3.60 and ~ 3.35 Ga. The isotope characteristics of zircon and rocks of the TTG complexes, pointing to recycling of crustal material, argue for the formation of plagiogneisses and plagiogranitoids as a result of melting of heterogeneous (mafic and more ancient crustal) sources in the thickened crust.     

Uranyl molybdates in fluorites and uranium-carbonate ores from the Strel’tsovskoe ore field of the Argun deposit

Microprobe research was performed on transparent polished plates (thin sections) of samples of fluorite and uranium ore from the Argun deposit in Zabaikal’skii Krai, Russia. The composition of minerals was determined at the Center for Isotopic Study of the Russian Geological Research Institute using a Cam-Scan MX 2500 scanning electron microscope equipped with a Link Pentaflet energy-dispersion spectrometer. Certified natural and synthetic samples were used as the standards.     

Variations of the broad Hα line profile in NGC 4151 as evidence for the complex kinematics of gas in the nucleus

A great number of spectra of the Seyfert galaxy nucleus NGC 4151 were obtained in the Crimean Astrophysical Observatory in 1988–1990 using the CCD. Significant variation in continuum intensity and broad H line profile were noted. Differences between individual spectra and the spectrum taken as a standard were calculated to study this variability. It was noted that different parts of the profile are varying in different ways. Smaller changes are located at far-away regions of the wings and at the low positive velocities of the profile. Lower variations in the red part of H profile near the center of the line are interpreted by the delay effect in an expanded shell. Since the evidences for accretion in a BIR are clisting (including NGC 4151) then either the BLR is a complex system where both inflow and low velocities outflow are observed or the outflow must be referred to the inner NLR. Cross correlation analysis shows shorter delay for the higher velocities of the H profile and does not contradict to the outflow at low velocities (near the line center), but its confidence level is small. Lower response to the continuum changes at far away parts of the broad H wings evidences that the gas in the vicinity of the central engine is optically thin for the ionizing radiation.     

Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles

According to observations, the discrete auroral arcs can sometimes be found, either deep inside the auroral oval or at the poleward border of the wide (so-called double) auroral oval, which map to very different regions of the magnetotail. To find common physical conditions for the auroral-arc generation in these magnetotail regions, we study the spatial relationship between the diffuse and discrete auroras and the isotropic boundaries (IBs) of the precipitating energetic particles which can be used to characterise locally the equatorial magnetic field in the tail. From comparison of ground observation of auroral forms with meridional profiles of particle flux measured simultaneously by the low-altitude NOAA satellites above the ground observation region, we found that (1) discrete auroral arcs are always situated polewards from (or very close to) the IB of > 30-keV electrons, whereas (2) the IB of the > 30-keV protons is often seen inside the diffuse aurora. These relationships hold true for both quiet and active (substorm) conditions in the premidnight-nightside (18– 01-h) MLT sector considered. In some events the auroral arcs occupy a wide latitudinal range. The most equatorial of these arcs was found at the poleward edge of the diffuse auroras (but anyway in the vicinity of the electron IB), the most poleward arcs were simultaneously observed on the closed field lines near the polar-cap boundary. These observations disagree with the notion that the discrete aurora originate exclusively in the near-Earth portion of plasma sheet or exclusively on the PSBL field lines. Result (1) may imply a fundamental feature of auroral-arc formation: they originate in the current-sheet regions having very curved and tailward-stretched magnetic field lines.     

Optical observations of the gravitational lens SBS1 520+530 at the Ma $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l} $$ danak Observatory

Observations of the gravitationally lensed quasar SBS 1520+530 obtained in 2000–2001 on the 1.5-m telescope of the Ma $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ danak Observatory (Uzbekistan) are presented. The photometric algorithms used to observe the components of SBS 1520+530 are discussed. The images have a resolution of 0.5″–0.6″, enabling us to detect the lensing galaxy in the R and I bands and to measure its luminosity and coordinates. The results of photometric observations of components A and B of SBS 1520+530 are presented; the light curves show variability on various time scales from a few weeks to a year. A gravitational-lens model for SBS 1520+530 is constructed utilizing all currently available data.     

Recognizing of Microseismic Source Types Based on Small-Aperture Seismic Array Data

Izvestiya, Physics of the Solid Earth - Abstract—In this paper, we consider the problem of recording and processing the microseismic data with their subsequent interpretation and making the...