Geochronological constraints on Caledonian strike–slip displacement in Svalbard,with implications for the evolution of the Arctic

The timing of Svalbard's assembly in relation to the mid‐Paleozoic Caledonian collision between Baltica and Laurentia remains contentious. The Svalbard archipelago consists of three basement provinces bounded by N–S‐trending strike–slip faults whose displacement histories are poorly understood. Here, we report microstructural and mineral chemistry data integrated with ⁴⁰Ar/³⁹Ar muscovite geochronology from the sinistral Vimsodden‐Kosibapasset Shear Zone (VKSZ, southwest Svalbard) and explore its relationship to adjacent structures and regional deformation within the circum‐Arctic. Our results indicate that strike–slip displacement along the VKSZ occurred in late Silurian–Early Devonian and was contemporaneous with the beginning of the main phase of continental collision in Greenland and Scandinavia and the onset of syn‐orogenic sedimentation in Silurian–Devonian fault‐controlled basins in northern Svalbard. These new‐age constraints highlight possible links between escape tectonics in the Caledonian orogen and mid‐Paleozoic terrane transfer across the northern margin of Laurentia.     

SHRIMP zircon geochronology and geochemistry of the Orlica-Śnieżnik gneisses (Variscan belt of Central Europe) and their tectonic implications

Abstract

The Orlica-?nie?nik dome comprises large orthogneiss bodies interbedded with amphiblite-grade metasediments and minor metavolcanics. New U-Pb and Pb-Pb SHRIMP zircon ages for two major gneiss units of the dome, the ?nie?nik and Giera?tów gneiss, yielded similar ages of ca. 500 Ma. This is interpreted to reflect the magmatic crystallization age from the same or similar igneous precursors, in agreement with the geochemical characteristics of these rocks. Some zircon cores in both gneisses, interpreted to be inherited xenocrysts, have ages of ca. 530–540 Ma, and, additionally, of ca. 565 Ma and 2.6 Ga in the ?nie?nik gneiss. Igneous grains in both gneiss types have high-U rims, which are dark under cathodoluminescence. They are much better developed in the Giera?tow gneiss and they yield a well-defined weighted mean U-Pb age of 342 ± 6 Ma. These high-U rims are interpreted to have grown close to the peak of HT metamorphism which is responsible for the migmatitic texture of the Giera?tow gneiss. The Visean HT-LP metamorphism in the Orlica-?nie?nik dome is interpreted as a result of rapid uplift and decompression due to overthrusting of high grade rocks over the Moravo-Silesian nappe pile. Our data support geodynamic models that ascribe a predominant influence in the tectonic evolution of the West Sudetes to the Variscan oro- genic events. This is suggested by the inheritance of zircon xenocrysts from the Cadomian basement and by the Late Cambrian- Early Ordovician magmatic event, both typical of the Armorican terrane assemblage, as well as by the Early Carboniferous age of the metamorphism. © 2000 Éditions scientifiques et médicales Elsevier SAS     

Blueschist facies metamorphism in Nordenskiöld Land of west‐central Svalbard

Recent fieldwork in Nordenskiöld Land, Svalbard's Southwestern Basement Province, has established the presence of high‐pressure (HP) lithologies. They are strongly retrogressed blueschists consisting mainly of garnet and Ca‐amphibole with remnants of ferroglaucophane and phengite. The pressure–temperature (P–T) conditions were estimated using phase equilibrium modelling in the NCKFMMnASHTO system. P–T estimates based on the garnet, phengite and ferroglaucophane compositional isopleths and modelled paragenetic assemblage indicate peak metamorphism at 470–490 °C and 14–18 kbar. These data fall close to the 7–8 °C km^?1 geotherm, which is similar to that from Motalafjella, the only previously known occurrence of blueschists in Svalbard's Caledonides. The newly discovered blueschists could have formed during the early stage of the Caledonian Orogeny and may represent a vestige of missing marginal basins of the western Iapetus developed at the onset of subduction. The likely counterpart to Svalbard's blueschists is the ophiolitic sequence in the Pearya Terrane of northern Ellesmere Island.     

Cluster AgeS Experiment (CASE): deficiency of observed dwarf novae in globular clusters

We present the results of a search for dwarf novae (DNe) in globular clusters (GCs). It is based on the largest available homogeneous sample of observations, in terms of the time-span, number of observations and number of clusters. It includes 16 Galactic GCs and yielded two new certain DNe: M55-CV1 and M22-CV2. All previously known systems located in our fields were recovered, too. We surveyed M4, M5, M10, M12, M22, M30, M55, NGC 288, NGC 362, NGC 2808, NGC 3201, NGC 4372, NGC 6362, NGC 6752, ω Centauri (NGC 5139) and 47 Tucanae (NGC 104). The discovery of two DNe, namely M55-CV1 and M22-CV2, was already reported by Kaluzny et al. and Pietrukowicz et al., respectively. In the remaining 14 GCs, we found no certain new DNe. Our result raises the total number of known DNe in the Galactic GCs to 12 DNe, distributed among seven clusters. Our survey recovered all three already known erupting cataclysmic variables (CVs) located in our fields, namely M5-V101, M22-CV1, and V4 in the foreground of M30. To assess the efficiency of the survey, we analysed images with inserted artificial stars mimicking outbursts of the prototype DNe SS Cygni and U Geminorum. Depending on the conditions, we recovered between 16–100 per cent of these artificial stars. The efficiency seems to be predominantly affected by duty cycle/time-sampling and much less by distance/magnitude. Except for saturated tiny collapsed cores of M30, NGC 362 and NGC 6752 (and also the dense core of NGC 2808), crowding effects in the V band were avoided by our image subtraction technique augmented with auxiliary unsaturated B -band images. Our results clearly demonstrate that in GCs common types of DNe are very rare indeed. However, great care must be taken before these conclusions can be extended to the CV population in GCs.     

The impact of pyrite variability, dispersive transport and precipitation of secondary phases on the sulphate release due to pyrite weathering

The objective of this study was to investigate the impact of flow, transport and geochemical parameters in the unsaturated and saturated zones on the release of SO₄ from overburden lignite spoil piles into the adjacent lake. A vertical one-dimensional model was set up using the reactive transport simulator SULFIDOX in order to account for the unsaturated zone. The SULFIDOX model was calibrated for effective diffusion using measured O₂ in the gas phase and SO₄ concentrations in the liquid phase from the unsaturated zone of the heap. The results show high sensitivity to O₂ supply and initially present gypsum, but the inclusion of secondary mineral precipitation in equilibrium is of minor importance for the results. To account for the transport of released SO₄ from the saturated zone into the surface water, scenarios were performed by using SULFIDOX results as input concentration for a two-dimensional vertical model set up with PROCESSING MODFLOW and MT3D. These scenarios indicate a rising discharge of SO₄ into the adjacent lake due to continued pyrite weathering for 80 a. Results are highly sensitive to dispersivity, whereas the spatial variability of pyrite distribution did not show any influence on the results. The consideration of initially present gypsum shows a major effect on the modelled SO₄ release.     

Standing Alfvén waves with m ≫ 1 in an axisymmetric magnetosphere excited by a non-stationary source

As a continuation of our earlier paper, we consider here the case of the excitation of standing Alfvén waves by a source of the type of sudden impulse. It is shown that, following excitation by such a source, a given magnetic shell will exhibit oscillations with a variable frequency which increases from the shells poloidal to toroidal frequency. Simultaneously, the oscillations will also switch over from poloidally (radially) to toroidally (azimuthally) polarized. With a reasonably large attenuation, only the start of this process, the stage of poloidal oscillations, will be observed in the ionosphere.     

Long‐distance fluid migration defines the diagenetic history of unique Ediacaran sediments in the East European Craton

The diagenetic history of the Ediacaran sedimentary rocks in the East European Craton (EEC) over the area extending from Arkhangelsk (Russia) in the north to Podolia (Ukraine) in the south was revealed by means of the XRD characterization and K–Ar dating of clay fractions, mudstone porosity measurements and organic geochemistry investigations. Mudstone porosity measurements produced direct evidence of shallow maximum burial of the Ediacaran sediments on the craton (Russia, Lithuania, Belarus, Volyn), not exceeding 1.5 km, and much deeper burial at the cratonic margin, in Podolia and Poland. In general, illitization of smectite and biomarker indices indicates more advanced diagenesis at the cratonic margin. K–Ar dating of authigenic illite–smectite and aluminoceladonite revealed the Palaeozoic age of mineral diagenesis (ca. 450–300 Ma) both on the craton and its margin, with older ages generally observed in the north. When the maximum palaeotemperatures were evaluated from illite–smectite and biomarkers, based on the calibrations from the conventional burial diagenetic sections, a major mismatch was detected for the cratonic area: 100°C–130°C from illite––smectite and tens of ^oC lower from the lipid biomarkers. This diagenetic pattern was interpreted as the result of short‐lasting (in ky scale) pulses of potassium‐bearing hot fluids migrating from the Caledonian and Variscan orogens deep in the craton interior, effectively promoting illitization in porous rocks without altering the organic matter. Analogous short pulses of fluids were responsible for numerous diagenetic phenomena, including Mississippi Valley‐Type ore deposits, in the American Midwest, in front of the Appalachians. K–Ar dating indicates that the entire Proterozoic sedimentary cover of the Great Unconformity on the EEC remained untouched by measureable post‐sedimentary changes until the early Palaeozoic, thus for over 1000 My, which is an unprecedented finding.     

The Hamburg meteorite fall: Fireball trajectory,orbit, and dynamics

The Hamburg (H4) meteorite fell on 17 January 2018 at 01:08 UT approximately 10 km north of Ann Arbor, Michigan. More than two dozen fragments totaling under 1 kg were recovered, primarily from frozen lake surfaces. The fireball initial velocity was 15.83 ± 0.05 km s^?1, based on four independent records showing the fireball above 50 km altitude. The radiant had a zenith angle of 66.14 ± 0.29° and an azimuth of 121.56 ± 1.2°. The resulting low inclination (<1°) Apollo‐type orbit has a large aphelion distance and Tisserand value relative to Jupiter (T_j) of ~3. Two major flares dominate the energy deposition profile, centered at 24.1 and 21.7 km altitude, respectively, under dynamic pressures of 5–7 MPa. The Geostationary Lightning Mapper on the Geostationary Operational Environmental Satellite‐16 also detected the two main flares and their relative timing and peak flux agree with the video‐derived brightness profile. Our preferred total energy for the Hamburg fireball is 2–7 T TNT (8.4–28 × 10⁹ J), which corresponds to a likely initial mass in the range of 60–225 kg or diameter between 0.3 and 0.5 m. Based on the model of Granvik et al. (2018), the meteorite originated in an escape route from the mid to outer asteroid belt. Hamburg is the 14th known H chondrite with an instrumentally derived preatmospheric orbit, half of which have small (<5°) inclinations making connection with (6) Hebe problematic. A definitive parent body consistent with all 14 known H chondrite orbits remains elusive.     

Seasonal Variations of Water Quality in the Vostok Bay,Peter the Great Gulf,the Sea of Japan

Water Resources - Studies of 2015 were used to characterize water in Vostok Bay (Peter the Great Gulf, the Sea of Japan) in terms of phosphate concentration, biochemical oxygen demand, and pH. The...