Radiometric age constraints on mineral growth,metamorphism, and tectonism of the Gummfluh Klippe,Briançonnais domain of the Préalpes,Switzerland     

Michael A. Cosca  Johannes C. Hunziker  Sylvain Huon  Henri Masson 《Contributions to Mineralogy and Petrology》1992,112(4):439-449

A combined ⁴⁰Ar/³⁹Ar, K/Ar, Rb/Sr and stable isotope study has been made of white micas from the Gummfluh klippe (Briançonnais domain of the Préalpes), Switzerland. The klippe consists mainly of Mesozoic to early Tertiary carbonate rocks metamorphosed from anchizonal to epizonal conditions. At the base of the klippe is a 10–50 m thick, ductilely deformed marble mylonite containing deformed authigenic quartz segregations. Stable isotope measurements of the coexisting calcite (¹⁸O_SMOW=24.5) and quartz (¹⁸O_SMOW=28.4) from the mylonite indicate relatively low temperatures (<300°C) during mylonitization. Analyses of white mica separates of varying size fractions from the mylonitic rocks by K/Ar and Rb/Sr techniques yield ages between 57 and 103 Ma. This variation is correlated with two parameters, the size of the mineral fraction, and the proportion of 2M₁ (more phengitic) to 1M (more muscovitic) polytype in the sample. The K/Ar and Rb/Sr ages are generally younger in the smaller size fractions, which also containless 2M₁ phengite. High precision ⁴⁰Ar/³⁹Ar age spectra from different size fractions of these micas record three distinct components, a small Hercynian component (ca. 200–300 Ma), a significant Eoalpine component (64–80 Ma) forming ⁴⁰Ar/³⁹Ar age plateaus, and a very minor Tertiary component (ca. 20–40 Ma). Characterization of the samples by SEM indicates the presence of two white mica populations, a coarser grained, deformed, detrital mica that probably corresponds to the 2M₁ phengite and a finer grained neoformed 1M mica. Collectively these observations suggest that the Gummfluh samples contain a mixture of detrital phengites of Hercynian age together with neocrystallized muscovites grown during the late Eoalpine metamorphic event followed by minor argon loss during the Tertiary. The main geologic episode recorded in the ⁴⁰Ar/³⁹Ar age spectra of white micas in the mylonite is of Late Cretaceous/Early Tertiary age (64–80 Ma), representing the first reliable Eoalpine ages ever to be reported from the Préalpes. Contrary to tectonic models, the marble mylonite at the base of the Gummfluh klippe appears to be a Cretaceous thrust plane and not the thrust surface formed during transport of the klippe into its present position from the Penninic Alps during the Tertiary. The late Cretaceous thrust developed during marine sedimentation at a depth of 800 m below the seafloor at temperatures of 280°C, facilitated by warm fluids along the tectonic discontinuity.  相似文献   

Observation-based evaluation of surface wave effects on currents and trajectory forecasts     

R&#;hrs  Johannes  Christensen  Kai H&#;kon  Hole  Lars Robert  Brostr&#;m  G&#;ran  Drivdal  Magnus  Sundby  Svein 《Ocean Dynamics》2012,62(10):1519-1533

Knowledge of upper ocean currents is needed for trajectory forecasts and is essential for search and rescue operations and oil spill mitigation. This paper addresses effects of surface waves on ocean currents and drifter trajectories using in situ observations. The data set includes colocated measurements of directional wave spectra from a wave rider buoy, ocean currents measured by acoustic Doppler current profilers (ADCPs), as well as data from two types of tracking buoys that sample the currents at two different depths. The ADCP measures the Eulerian current at one point, as modelled by an ocean general circulation model, while the tracking buoys are advected by the Lagrangian current that includes the wave-induced Stokes drift. Based on our observations, we assess the importance of two different wave effects: (a) forcing of the ocean current by wave-induced surface fluxes and the Coriolis–Stokes force, and (b) advection of surface drifters by wave motion, that is the Stokes drift. Recent theoretical developments provide a framework for including these wave effects in ocean model systems. The order of magnitude of the Stokes drift is the same as the Eulerian current judging from the available data. The wave-induced momentum and turbulent kinetic energy fluxes are estimated and shown to be significant. Similarly, the wave-induced Coriolis–Stokes force is significant over time scales related to the inertial period. Surface drifter trajectories were analysed and could be reproduced using the observations of currents, waves and wind. Waves were found to have a significant contribution to the trajectories, and we conclude that adding wave effects in ocean model systems is likely to increase predictability of surface drifter trajectories. The relative importance of the Stokes drift was twice as large as the direct wind drag for the used surface drifter.

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Earth System governmentality: Reflections on science in the Anthropocene     

Eva Lövbrand  Johannes Stripple  Bo Wiman 《Global Environmental Change》2009,19(1):7-13

This paper examines Earth System Science as a novel approach to global environmental change research. Drawing upon Michel Foucault's governmentality concept, the paper opens up the Earth System metaphor to political analysis and asks what it does to our understanding of nature and society as a governable domain. We trace the scientific practices that have produced the Earth System as a thinkable analytical category back to the International Geophysical Year in 1957. We also identify ‘the Anthropocene’ as a central and yet ambiguous system of thought for Earth System Science that harbours different strategies for sustainability in terms of (1) the persons over whom government is to be exercised; (2) the distribution of tasks and actions between authorities; and (3) contrasting ideals or principles for how government should be directed.  相似文献   

Balkanforschungen des geologischen Instituts der Universität Leipzig. 1. Reise 1926     

Johannes F. Gellert 《International Journal of Earth Sciences》1927,18(3):161-163

Ohne Zusammenfassung  相似文献   

The Characteristics of Polygonal Impact Craters on Venus   总被引：1，自引：0，他引：1  

Marko Aittola  Teemu Öhman  Johannes J. Leitner  Jouko Raitala 《Earth, Moon, and Planets》2007,101(1-2):41-53

Polygonal impact craters (PICs) are craters whose shape in plan view is more or less angular instead of being circular or ellipsoidal. This type of craters are present and often common on the Moon, Mercury, Mars and several asteroids and icy moons and after the careful analysis we found on Venus 131 impact craters, which show at least two straight rim segments. This survey proves that there are polygonal impact craters on Venus and they may provide a good tool to analyse the properties of the planet’s surface/crust/lithosphere as well as the impact process itself. This study also collaborates our previous results, that PICs are not an anomaly among craters, but an integral part of all impact craters regardless of their size or environment. We compared the polygonal impact craters to “normal”-shaped craters by using different characteristics (diameter, altitude, geologic setting, morphologic class, floor reflectance, degradation stage, and wall terracing). It turned out that the smaller crater sizes favor the formation of straight rim segments, but otherwise these craters show similar characteristics to other craters. Our study also shows that there are regions where the straight segments of the crater rims most clearly follow the orientations of the dominant tectonic features of the area. Thus, the orientations of crater walls reflect–at least in some places–the local tectonics and zones of weakness also on Venus and could thus tell us about the directions and distributions of fractures or other zones of weakness in the crust.  相似文献   

Relation between geoidal undulation, deflection of the vertical and vertical gravity gradient revisited     

Johannes Bouman 《Journal of Geodesy》2012,86(4):287-304

The vertical gradients of gravity anomaly and gravity disturbance can be related to horizontal first derivatives of deflection of the vertical or second derivatives of geoidal undulations. These are simplified relations of which different variations have found application in satellite altimetry with the implicit assumption that the neglected terms—using remove-restore—are sufficiently small. In this paper, the different simplified relations are rigorously connected and the neglected terms are made explicit. The main neglected terms are a curvilinear term that accounts for the difference between second derivatives in a Cartesian system and on a spherical surface, and a small circle term that stems from the difference between second derivatives on a great and small circle. The neglected terms were compared with the dynamic ocean topography (DOT) and the requirements on the GOCE gravity gradients. In addition, the signal root-mean-square (RMS) of the neglected terms and vertical gravity gradient were compared, and the effect of a remove-restore procedure was studied. These analyses show that both neglected terms have the same order of magnitude as the DOT gradient signal and may be above the GOCE requirements, and should be accounted for when combining altimetry derived and GOCE measured gradients. The signal RMS of both neglected terms is in general small when compared with the signal RMS of the vertical gravity gradient, but they may introduce gradient errors above the spherical approximation error. Remove-restore with gravity field models reduces the errors in the vertical gravity gradient, but it appears that errors above the spherical approximation error cannot be avoided at individual locations. When computing the vertical gradient of gravity anomaly from satellite altimeter data using deflections of the vertical, the small circle term is readily available and can be included. The direct computation of the vertical gradient of gravity disturbance from satellite altimeter data is more difficult than the computation of the vertical gradient of gravity anomaly because in the former case the curvilinear term is needed, which is not readily available.  相似文献   

Cloud radiative forcing of subtropical low level clouds in global models     

Johannes Karlsson  Gunilla Svensson  Henning Rodhe 《Climate Dynamics》2008,30(7-8):779-788

Simulations of subtropical marine low clouds and their radiative properties by nine coupled ocean-atmosphere climate models participating in the fourth assesment report (AR4) of the intergovernmental panel on climate change (IPCC) are analyzed. Satellite observations of cloudiness and radiative fluxes at the top of the atmosphere (TOA) are utilized for comparison. The analysis is confined to the marine subtropics in an attempt to isolate low cloudiness from tropical convective systems. All analyzed models have a negative bias in the low cloud fraction (model mean bias of −15%). On the other hand, the models show an excess of cloud radiative cooling in the region (model mean excess of 13 W m⁻²). The latter bias is shown to mainly originate from too much shortwave reflection by the models clouds rather than biases in the clear-sky fluxes. These results confirm earlier studies, thus no major progress in simulating the marine subtropical clouds is noted. As a consequence of the combination of these two biases, this study suggests that all investigated models are likely to overestimate the radiative response to changes in low level subtropical cloudiness.  相似文献   

Diurnal variation of outgoing longwave radiation associated with high cloud and UTH changes from Meteosat-5 measurements     

Eui-Seok Chung  Byung-Ju Sohn  Johannes Schmetz 《Meteorology and Atmospheric Physics》2009,105(3-4):109-119

Diurnal variations of outgoing longwave radiation (OLR) are examined in conjunction with diurnal variations of high cloud and upper tropospheric humidity (UTH) over the Indian Ocean and surrounding land areas using Meteosat-5 measurements. Most land areas exhibit a significant diurnal variation of OLR with the largest amplitude over the Arabian Peninsula, whereas the diurnal variation of OLR is much weaker over the Indian Ocean. While diurnal maxima of OLR are found in the early afternoon over many regions of the analysis domain following the diurnal cycle of solar heating, convectively active regions of both land and ocean where high cloud and UTH exhibit distinct diurnal variations show OLR maxima before local noon. These results indicate that high cloud development in the afternoon induces a shift in local time of OLR maxima over convective regions. In agreement with earlier studies it is shown that UTH diurnal variations are less important in regard to their impact on the OLR variations.  相似文献   

CO₂ sequestration and extreme Mg depletion in serpentinized peridotite clasts from the Devonian Solund basin, SW-Norway     

Andreas Beinlich  Håkon Austrheim  Johannes Glodny  Torgeir B. Andersen 《Geochimica et cosmochimica acta》2010,74(24):6935-6964

The conglomerates of the Solund Devonian basin of SW-Norway contain numerous (locally up to 20 vol.%) peridotitic clasts with concentric mm- to 10-cm thick zones of varying red to black color. The peridotite clasts show a clear, alteration-related textural evolution. The least-altered rocks are partly serpentinized peridotites, showing a typical mesh texture with veins of serpentine, magnesite and Ni-rich magnetite surrounding olivine (Fo₉₁) relicts and its Mg-depleted, clay-like alteration product (deweylite assemblage). In the more advanced ophicarbonate stage, the mesh cells contain calcite, silica and are surrounded by talc. In the final stage, quartz, calcite, and hematite dominate the mineralogy and occur together with minor amounts of chromite, talc, Cr-chlorite, and Cr-hydroandradite. In tandem with this textural evolution is a decrease in MgO from 40 to 2.5 wt% and a CaO increase from 1 to 35 wt%. All peridotite clasts are characterized by high Cr and Ni concentrations. The chemistry and the textural evolution show that the clasts formed by an extreme Mg-mobilization from the peridotite, with development of secondary porosity and subsequent precipitation of calcite. MgO removed from the clasts after burial is in part consumed by replacement reactions in the sediment matrix around the clasts where Mg-free minerals (e.g., almandine) are replaced by Mg-bearing minerals (e.g., talc). Calculated apparent ⁸⁷Sr/⁸⁶Sr ratios of the clasts at 385 Ma (0.7124-0.7139), corresponding to the inferred age of sediment deposition and incipient clast alteration, indicate interaction with diagenetic basinal fluids. We explain the reaction history as a three stage process involving (a) partial serpentinization of olivine in an oceanic environment (b) breakdown of olivine relicts to the deweylite assemblage resulting in mobilization of MgO under (near-) surface conditions in a tropical Devonian climate and (c) further Mg-mobilization and replacement of the deweylite assemblage by calcite and quartz after diagenesis. Sedimentary basins with abundant weathered peridotite represent potential sites for a permanent CO₂ storage by formation of calcite in a low-temperature environment.  相似文献   

Synthetic stellar and SSP libraries as templates for Gaia simulations     

Rosanna Sordo  Antonella Vallenari  Rosaria Tantalo  France Allard  Ronny Blomme  Jean-Claud Bouret  Ines Brott  Yves Fremat  Christophe Martayan  Yassine Damerdji  Bengt Edvardsson  Eric Josselin  Bertrand Plez  Oleg Kochukhov  Mary Kontizas  Ulisse Munari  Tenay Saguner  Jean Zorec  Andreas Schweitzer  Paraskevi Tsalmantza 《Astrophysics and Space Science》2010,328(1-2):331-335

ESA’s Gaia mission will collect low resolution spectroscopy in the optical range for ～10⁹ objects. Complete and up-to-date libraries of synthetic stellar spectra are needed to built algorithms aimed to automatically derive the classification and the parametrization of this huge amount of data. In addition, libraries of stellar spectra are one of the main ingredients of stellar population synthesis models, aiming to derive the properties of unresolved stellar populations from their integrated light. We present (a) the newly computed libraries of synthetic spectra built by the Gaia community, covering the whole optical range (300–1100 nm) at medium-high resolution of (0.3 nm) for stars spanning the most different types, from M to O, from A-peculiar to Emission lines to White Dwarfs, and (b) the implementation of those libraries in our SSP code (Tantalo in The Initial Mass Function 50 Years Later, 327:235 2005), exploring different stellar evolution models.  相似文献