North Atlantic Oscillation: Description,Mechanisms, and Influence on the Eurasian Climate

The present work is devoted to the characteristic of the North-Atlantic Oscillation and the analysis of the state-of-the-art of this problem. In the survey section of the work, we deal with the following issues: the definition of the North Atlantic and Arctic Oscillations, their interaction with oceanic processes, and their influence on the variations of climate in Eurasia. In addition, by using the COADS (Comprehensive Ocean Atmosphere Data Set) data and the data on the discharge of European and Asian rivers, we establish some new original results. It is confirmed that the anomalies of the sea-surface temperature are consequences of the integral response of the ocean to the preceding atmospheric actions and that the spectra of these anomalies are characterized by the presence of significant peaks within the band of periods of 10–20 yr. These periods correspond to inherent oceanic variability. The atmospheric response manifests itself in the form of abnormal conditions over the catchment areas of European and Asian rivers, which leads to oscillations of their discharges. As a result of the intensification of the North Atlantic Oscillation and the displacement of the centers of action of the atmosphere in the 60–90s of the previous century, the influence of this oscillation on the climatic conditions in the European-Asian region became more intense.     

High-precision geothermobarometry across the High Himalayan metamorphic sequence, Langtang Valley, Nepal

One of the long recognized features of Himalayan geology is the apparent inversion of metamorphic sequences, as evidenced in both metamorphic parageneses and thermobarometric data. With the aid of an extended thermobarometric dataset from the Langtang Valley section of the Higher Himalayan Crystallines, it can be demonstrated that the relatively large uncertainties associated with traditional thermobarometric techniques severely limit the tectonic interpretation of metamorphic gradients across the Himalayas. We apply the recently developed Δ PT  approach, which significantly improves the precision to which pressure and temperature differences between samples may be calculated. High-precision thermobarometric data reveal an isothermal, rather than inverted, temperature array at Langtang, while the pressure data suggest significant structural complexity, with the Higher Himalayan Crystallines in the Langtang section comprising two distinct, possibly duplicated sequences, each having experienced considerable structural attenuation following metamorphism.     

The visual double star data base

Any use of stars for astrometric purposes necessarily involves examination of their duplicity characteristics. The Washington Double Star Catalog (WDS) provides this information in a continuously updated and machine-readable format. This contribution describes the current data base and plans for its future extension.     

The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3

Mineral equilibria calculations in the system K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃ (KFMASHTO) using thermocalc and its internally consistent thermodynamic dataset constrain the effect of TiO₂ and Fe₂O₃ on greenschist and amphibolite facies mineral equilibria in metapelites. The end‐member data and activity–composition relationships for biotite and chloritoid, calibrated with natural rock data, and activity–composition data for garnet, calibrated using experimental data, provide new constraints on the effects of TiO₂ and Fe₂O₃ on the stability of these minerals. Thermodynamic models for ilmenite–hematite and magnetite–ulvospinel solid solutions accounting for order–disorder in these phases allow the distribution of TiO₂ and Fe₂O₃ between oxide minerals and silicate minerals to be calculated. The calculations indicate that small to moderate amounts of TiO₂ and Fe₂O₃ in typical metapelitic bulk compositions have little effect on silicate mineral equilibria in metapelites at greenschist to amphibolite facies, compared with those calculated in KFMASH. The addition of large amounts of TiO₂ to typical pelitic bulk compositions has little effect on the stability of silicate assemblages; in contrast, rocks rich in Fe₂O₃ develop a markedly different metamorphic succession from that of common Barrovian sequences. In particular, Fe₂O₃‐rich metapelites show a marked reduction in the stability fields of staurolite and garnet to higher pressures, in comparison to those predicted by KFMASH grids.     

The P–T record of synchronous magmatism, metamorphism and deformation at Petrel Cove, southern Adelaide Fold Belt

Porphyroblastic schists in the thermal aureole of the Victor Harbor Granite at Petrel Cove, in the southern Adelaide Fold Belt, South Australia, preserve a record of sequential cordierite, andalusite, staurolite, fibrolite, chlorite and muscovite growth (along with biotite+plagioclase+quartz+ilmenite) during progressive deformation. A P–T pseudo‐section appropriate to biotite‐saturated assemblages in KFMASH shows that the sequence of mineral reactions records increasing pressure of at least 1 kbar (from c. 3 to c. 4 kbar) during cooling from around 580 °C. Heating at pressures below c. 3 kbar is inferred for growth of early formed cordierite porphyroblasts, and is attributed in part to the thermal effects of granite emplacement, while the pressure increase is attributed to tectonic burial accruing from ongoing deformation. The ‘anticlockwise’P–T path is consistent with convergent deformation being focussed as a consequence of heating, as to be expected for a lithospheric rheology that is strongly temperature dependent.     

Tectonic transition from the Songpan-Garzê Fold Belt to the Sichuan Basin, south-western China

The formation of the Songpan-Garzê Fold Belt and the initiation of the terrestrial Sichuan Basin are related to closing of the Palaeo-Tethys during the Late Triassic Indosinian orogeny. The Songpan-Garzê Fold Belt is composed of Triassic (T₁-_-T²₃) turbiditic deposits and Palaeozoic greywacke-shale, whereas the Sichuan Basin consists of Sinian to middle Upper Triassic (T²₃) platform carbonates and Upper Triassic (T_3X to Quaternary terrestrial elastics. Three principal deformation episodes during the Late Triassic (Norian to Rhaetian) were progressively localized towards the south-eastern margin of the fold belt. D₁ was a SW-directed shortening event, related to continuous subduction of the Palaeo-Tethys, and produced NW-trending structures. Differential strain between the fold belt and the Sichuan Basin was accommodated by sinistral shearing along a NE-trending transitional zone during D₂^. D₃ SE-directed compression was the result of collision between the Cimmerian and Eurasian Continents and initiated the Longmen Mountains Thrust-Nappe Belt and terrestrial Sichuan Basin. Post-D₃ deformation, related to SE-directed thrusting in the Longmen Mountains, then propagated from hinterland to foreland. The Indosinian orogeny closed the Palaeo-Tethys and terminated the marine conditions that dominated the early evolution of the intracratonic Sichuan Basin. Tectonic loading from the exhumed fold belt and Thrust-Nappe Belt induced substantial subsidence in the Sichuan Basin, especially in the Western Sichuan Foreland Basin, resulting in the deposition of a terrestrial clastic sequence during Late Triassic (T_3X to Quaternary times. The foreland basin history comprises an early stage during the Late Triassic (T_3x^1–2), an over-fill stage during the latest Triassic to Early Cretaceous (T_3X³- K_1J), and a shrinking stage from the Late Cretaceous to the Quaternary (K_2J-Q). These can be correlated with tectonic events in the Thrust-Nappe Belt.     

Petrogenesis of carbonate-bearing nepheline syenites and carbonatites from Southern Victoria Land, Antarctica: origin of carbon and the effects of calcite-graphite equilibrium

Chemically-evolved carbonate-bearing nepheline syenites are intruded into basement metasediments of the Koettlitz Group on Dismal and Radian Ridges in the Pipecleaner Glacier region of Southern Victoria Land, Antarctica. Whole rock XRF data from the Dismal Nepheline Syenite defines a broad trend which is consistent with the removal of a cumulate fraction of approximate composition 70% hedenbergite, 15% nepheline, 10% titanite and 5% apatite. Stable isotope, major and trace element and mineralogical characteristics of the syenites are very similar to those of cross-cutting calcite-rich dykes indicating derivation from closely-related source magmas. The general association of carbonatites and nepheline syenites with extensional environments, suggests that the Dismal and Radian Ridge nepheline syenites and carbonatite dykes indicate a period of early Paleozoic (531 Ma) rifting or intrusion into localised tensional structures in an overall compressional regime. Assimilation of marble by the syenite magmas is evidenced by abundant rafts and xenoliths within the Dismal Nepheline Syenite, however, carbon and oxygen isotopic ratios from syenite and carbonatite calcites are distinctly lighter than values from the marble country rock indicating a magmatic source. Graphite and calcite commonly occur as aggregates in the Dismal Nepheline Syenite suggesting equilibrium between these two carbon-bearing phases. Isotopic fractionation between calcite and graphite, via the equilibrium: C + O₂ = CO₂ has resulted in enrichment of the ¹³C isotope in calcites from the Dismal Nepheline Syenite.     

High-precision relative thermobarometry: theory and a worked example

A number of sources of uncertainty are involved in thermobarometric calculations, the most important of which are associated with analytical precision, activity–composition ( a – x ) relationships, and thermodynamic data. Statistical treatment of these uncertainties results in relatively large uncertainties on the calculated values of pressure and temperature. Little can be done, at least in the short term, about the magnitude of such uncertainties, and any thermobarometric calculations in which they are not taken into account should be treated with caution. Given that uncertainties associated with a–x models and thermodynamic data are systematic when applied to multiple samples with the same mineral assemblage, a solution to the problem of imprecise absolute thermobarometry can be obtained via a relative thermobarometric technique referred to as the Δ PT  approach. The Δ PT  approach offers a major improvement in the precision of thermobarometry if the calculations can be presented in a Δ PT  context.     

Differential exhumation in response to episodic thrusting along the eastern margin of the Tibetan Plateau

Thermochronological data from the Songpan-Ganze˛Fold Belt and Longmen Mountains Thrust-Nappe Belt, on the eastern margin of the Tibetan Plateau in central China, reveal several phases of differential cooling across major listric thrust faults since Early Cretaceous times. Differential cooling, indicated by distinct breaks in age data across discrete compressional structures, was superimposed upon a regional cooling pattern following the Late Triassic Indosinian Orogeny. ⁴⁰Ar/³⁹Ar data from muscovite from the central and southern Longmen Mountains Thrust-Nappe Belt suggest a phase of differential cooling across the Wenchuan-Maouwen Shear Zone during the Early Cretaceous. The zircon fission track data also indicate differential cooling across a zone of brittle re-activation on the eastern margin of the Wenchuan-Maouwen Shear Zone during the mid-Tertiary, between 38 and 10 Ma. Apatite fission track data from the central and southern Longmen Mountains Thrust-Nappe Belt reveal differential cooling across the Yingxiu-Beichuan and Erwangmiao faults during the Miocene. Forward modelling of apatite fission track data from the northern Longmen Mountains Thrust-Nappe Belt suggests relatively slow regional cooling through the Mesozoic and early Tertiary, followed by accelerated cooling during the Miocene, beginning at ca. 20 Ma, to present day.

Regional cooling is attributed to erosion during exhumation of the evolving Longmen Mountains Thrust-Nappe Belt (LMTNB) following the Indosinian Orogeny. Differential cooling across the Wenchuan-Maouwen Shear Zone and the Yingxiu-Beichuan and Erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults. Thermochronological data from the Longmen Mountains Thrust-Nappe Belt reveal a greater amount of differential exhumation across thrust faults from north to south. This observation is in accord with the prevalence of Proterozoic and Sinian basement in the hanging walls of thrust faults in the central and southern Longmen Mountains. The two most recent phases of reactivation occurred following the initial collision of India with Eurasia, suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the LMTNB.     

Inclination- and dust-corrected galaxy parameters: bulge-to-disc ratios and size–luminosity relations

While galactic bulges may contain no significant dust of their own, the dust within galaxy discs can strongly attenuate the light from their embedded bulges. Furthermore, such dust inhibits the ability of observationally determined inclination corrections to recover intrinsic (i.e. dust-free) galaxy parameters. Using the sophisticated 3D radiative transfer model of Popescu et al. and Tuffs et al., together with the recent determination of the average face-on opacity by Driver et al. in nearby disc galaxies, we provide simple equations to correct (observed) disc central surface brightness and scalelengths for the effects of both inclination and dust in the B , V , I , J and K passbands. We then collate and homogenize various literature data sets and determine the typical intrinsic scalelengths, central surface brightness and magnitudes of galaxy discs as a function of morphological type. All galaxies have been carefully modelled in their respective papers with a Sérsic   R ^{1/ n}   bulge plus an exponential disc. Using the bulge magnitude corrections from Driver et al., we additionally derive the average, dust-corrected, bulge-to-disc flux ratio as a function of galaxy type. With values typically less than 1/3, this places somewhat uncomfortable constraints on some current semi-analytic simulations. Typical bulge sizes, profile shapes, surface brightness and deprojected densities are provided. Finally, given the two-component nature of disc galaxies, we present luminosity–size and (surface brightness)–size diagrams for discs and bulges. We also show that the distribution of elliptical galaxies in the luminosity–size diagram is not linear but strongly curved.