IGCP-499 Workshop ＂Depositional Environments of the Gondwanan and Laurasian Devonian＂     

Peter Konigshof Eberhard Schindler Volker Wilde Jurga Lazauskiene M. Namik Yalcin 《《幕》》2006,29(2):135-135

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Two-Dimensional Mapping of the He D<Subscript>3</Subscript>/Hβ Emission Ratio in Solar Prominences     

Eberhard Wiehr  Goetz Stellmacher  Johann Hirzberger 《Solar physics》2007,240(1):25-36

Solar prominences have been simultaneously observed in the integrated light of the He D₃ and the Hβ emissions on two successive days, using the SST on La Palma with its tip-tilt mirror locked on a nearby white-light limb facular grain. The spatial and the temporal variation of the integrated line intensities and their ratio shows mainly two characteristics: (A) Constant emission ratio (even) in regions with substantial intensity variations and (B) varying emission ratio (often) tightly related to intensity structures of the prominence. (A) May be explained by a different number of superposing threads along the line of sight having very similar physical state. (B) Indicates threads with different intrinsic physical states; these may depend on the gas pressure or the inner structure of each thread, i.e., the “packing density,” affecting the penetration of ionizing EUV radiation, which affects the He i level populations and thus the rate of the triplet excitation.  相似文献   

Sedimentology,ichnology and hydrodynamics of strait‐margin,sand and gravel beaches and shorefaces: Juan de Fuca Strait,British Columbia,Canada     

SHANNON E. FREY  SHAHIN E. DASHTGARD 《Sedimentology》2011,58(6):1326-1346

On the south‐west coast of Vancouver Island, Canada, sedimentological and ichnological analysis of three beach–shoreface complexes developed along a strait margin was undertaken to quantify process–response relations in straits and to develop a model for strait‐margin beaches. For all three beaches, evidence of tidal processes are expressed best in the lower shoreface and offshore and, to a lesser extent, in the middle shoreface. Tidal currents are dominant offshore, below 18 m water depth (relative to the mean spring high tide), whereas wave processes dominate sediment deposition in the nearshore (intertidal zone to 5 m water depth). From 18 to 5 m water depth, tidal processes decrease in importance relative to wave processes. The relatively high tidal energy in the offshore and lower shoreface is manifest sedimentologically by the dominance of sand, of a similar grain size to the upper shoreface/intertidal zone and, by the prevalence of current‐generated structures (current ripples) oriented parallel to the shoreline. In addition, the offshore and lower shoreface of strait‐bound beach–shoreface complexes are recognized ichnologically by traces typical of the Skolithos Ichnofacies. This situation contrasts to the dominantly horizontal feeding traces characteristic of the Cruziana Ichnofacies that are prevalent in the lower shoreface and offshore of open‐coast (wave‐dominated) beach–shorefaces. These sedimentological and ichnological characteristics reflect tidal influence on sediment deposition; consequently, the term ‘tide‐influenced shoreface’ most accurately describes these depositional environments.  相似文献   

Simulation of oceanic volume transports through Fram Strait 1995–2005     

Kerstin Fieg  Rüdiger Gerdes  Eberhard Fahrbach  Agnieszka Beszczynska-Möller  Ursula Schauer 《Ocean Dynamics》2010,60(3):491-502

We discuss the model representation of volume transports through one of the most climate-relevant ocean passages, the Fram Strait. We compare results from a coupled ocean–sea ice model with different resolutions (∼1/12° and ∼1/4°) and measurements from a mooring array along 79° N. The 1/4° model delivers a realistic mean climate state and realistic net volume transports. However, this model fails to reproduce the observed intense barotropic recirculation that reaches far north in Fram Strait. This recirculation is captured in the higher resolution version of the model. Other differences exist in the circulation over the East Greenland Shelf and in the temperature of Atlantic waters in the Fram Strait region as well as in surface heat fluxes. We find that a combination of high-resolution model results and long-term measurements can improve the interpretation of measured and simulated processes and reduce the uncertainties in exchange rates between Arctic and the North Atlantic.  相似文献   

Re-Os Isotopes in the Horoman Peridotite: Evidence for Refertilization?     

SAAL  A. E.; TAKAZAWA  E.; FREY  F. A.; SHIMIZU  N.; HART  S. R. 《Journal of Petrology》2001,42(1):25-37

Re–Os isotopic data for 20 samples from a well-characterized140 m section across a layered sequence, ranging from plagioclaselherzolite through lherzolite to harzburgite, of the Horomanperidotite show: (1) a range in ¹⁸⁷Os/¹⁸⁸Os ratios (from 0·1158to 0·1283) similar to that reported for other peridotiticmassifs, thereby suggesting that the processes responsible forthe Re–Os isotopic variation at the meter-scale and thewhole-massif scale are similar; (2) that the Os isotopic ratiois controlled by the Re content through radiogenic ingrowthover a period of  相似文献   

On the influence of non-Gaussianity on turbulent transport     

Stefan Heinz  Eberhard Schaller 《Boundary-Layer Meteorology》1996,81(2):147-166

Non-Gaussianity effects, first of all the influence of the third and fourth moments of the velocity probability density function, have to be assessed for higher-order closure models of turbulence and Lagrangian modelling of turbulent dispersion in complex flows. Whereas the role and the effects of the third moments are relatively well understood as essential for the explanation of specific observed features of the fully developed convective boundary layer, there are indications that the fourth moments may also be important, but little is known about these moments. Therefore, the effects of non-Gaussianity are considered for the turbulent motion of particles in non-neutral flows without fully developed convection, where the influence of the fourth moments may be expected to be particularly essential. The transport properties of these flows can be characterized by a diffusion coefficient which reflects these effects. It is shown, for different vertical velocity distributions, that the intensity of turbulent transport may be enhanced remarkably by non-Gaussianity. The diffusion coefficient is given as a modification of the Gaussian diffusivity, and this modifying factor is found to be determined to a very good approximation by the normalized fourth moment of the vertical velocity distribution function. This provides better insight into the effect of fourth moments and explains the varying importance of third and fourth moments in different flows.  相似文献   

Constraints on the Source Components of Lavas Forming the Hawaiian North Arch and Honolulu Volcanics   总被引：4，自引：1，他引：4  

YANG  H.-J.; FREY  F. A.; CLAGUE  D. A. 《Journal of Petrology》2003,44(4):603-627

Hawaiian volcanoes, dominantly shields of tholeiitic basalt,form as the Pacific Plate migrates over a hotspot in the mantle.As these shields migrate away from the hotspot, highly alkaliclavas, forming the rejuvenated stage of volcanism, may eruptafter an interval of erosion lasting for 0·25–2·5Myr. Alkalic lavas with geochemical characteristics similarto rejuvenated- stage lavas erupted on the sea floor north ofOahu along the Hawaiian Arch. The variable Tb/Yb, Sr/Ce, K/Ce,Rb/La, Ba/La, Ti/Eu and Zr/Sm ratios in lavas forming the NorthArch and the rejuvenated-stage Honolulu Volcanics were controlledduring partial melting by residual garnet, clinopyroxene, Fe–Tioxides and phlogopite. However, the distinctively high Ba/Thand Sr/Nd ratios of lava forming the North Arch and HonoluluVolcanics reflect source characteristics. These characteristicsare also associated with shield tholeiitic basalt; hence theyarise from the Hawaiian hotspot, which is interpreted to bea mantle plume. Inversion of the batch melting equation usingabundances of highly incompatible elements, such as Th and La,requires enriched sources with 10–55% clinopyroxene and5–25% garnet for North Arch lavas. The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Ndratios in lavas forming the North Arch and Honolulu Volcanicsare consistent with mixing between the Hawaiian plume and adepleted component related to mid-ocean ridge basalts. Specifically,the enrichment of incompatible elements coupled with low ⁸⁷Sr/⁸⁶Srand high ¹⁴³Nd/¹⁴⁴Nd relative to bulk Earth ratios is best explainedby derivation from depleted lithosphere recently metasomatizedby incipient melt (<2% melting) from the Hawaiian plume.In this metasomatized source, the incompatible element abundances,as well as Sr and Nd isotopic ratios, are controlled by incipientmelts. In contrast, the large range of published ¹⁸⁷Os/¹⁸⁸Osdata (0·134–0·176) reflects heterogeneitycaused by various proportions of pyroxenite veins residing ina depleted peridotite matrix. KEY WORDS: Hawaiian plume; Honolulu Volcanics; North Arch; plume–lithosphere interaction; rejuvenated stage; trace element geochemistry; alkalic lavas  相似文献   

Involvement of Continental Crust in the Formation of the Cretaceous Kerguelen Plateau: New Perspectives from ODP Leg 120 Sites   总被引：12，自引：11，他引：12  

FREY  FREDERICK A.; WEIS  DOMINIQUE; BORISOVA  ANASTASSIA YU.; XU  G. 《Journal of Petrology》2002,43(7):1207-1239

The basaltic basement of the large igneous province formed bythe Kerguelen Plateau and Broken Ridge in the southeastern IndianOcean has been sampled by three Ocean Drilling Program cruises(Legs 119, 120 and 183). Although the Cretaceous parts of thisplateau formed in the embryonic Indian Ocean basin, presumablyby melting associated with the Kerguelen plume, trace elementabundances and isotopic ratios of Sr, Nd and Pb of Cretaceousbasalt from several drill sites indicate that continental lithospherewas involved in their petrogenesis. On the basis of relativedepletions in Nb, Ta and Th, and isotopic characteristics similarto those of EMI ocean island basalt, lavas from Leg 120 Site747 in the Central Kerguelen Plateau contain a component derivedfrom lower continental crust. On the basis of relative abundancesof Sr and Eu and EMI-like Pb isotopic ratios, the source ofbasalt from Leg 120 Site 750 in the northeastern part of theSouthern Kerguelen Plateau also contained a component derivedfrom lower continental crust; in this case, the crustal componentformed as a plagioclase-rich, clinopyroxene-bearing cumulate.Basalts from Leg 120 Site 749 define two distinct isotopic (Sr,Nd and Pb) groups which differ from the isotopic fields forSite 747 and 750 basalts. Among Site 749 lavas, there is subtleevidence for a continental component, broadly similar (i.e.moderate ²⁰⁶Pb/²⁰⁴Pb  相似文献   

Flood Basalt from Mont Tourmente in the Central Kerguelen Archipelago: the Change from Transitional to Alkalic Basalt at ~25 Ma     

FREY  F. A.; NICOLAYSEN  K.; KUBIT  B. K.; WEIS  D.; GIRET  A. 《Journal of Petrology》2002,43(7):1367-1387

The surface of the Cenozoic Kerguelen Archipelago, constructedon the Kerguelen Plateau in the southern Indian Ocean, is dominantlyflood basalt. With the objective of understanding the Cenozoichistory of the Kerguelen mantle plume, the age and geochemicalcharacteristics of this flood basalt province are being determinedby studying stratigraphic sections of basalt flows at severallocations. Sections from the NW, north–central, east andSE parts of the archipelago have been studied. Here we reportresults for a 597 m succession of lavas from Mont Tourmentefrom the Plateau Central, a region of the archipelago that hasnot been studied in detail. Mont Tourmente lavas range from  相似文献   

Thermobarometric data from a fossil zircon partial annealing zone in high pressure–low temperature rocks of eastern and central Crete, Greece     

Manfred R. Brix  Bernhard Stckhert  Eberhard Seidel  Thomas Theye  Stuart N. Thomson  Martina Küster 《Tectonophysics》2002,349(1-4)

A fossil partial annealing zone of fission tracks in zircon is described from high pressure–low temperature (HP–LT) rocks of the Phyllite–Quartzite Unit (PQ) on the island of Crete, Greece. Correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data, and with new experimental annealing results, allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples.The zircon fission track (FT) ages of samples from the PQ across Crete range from original detrital signature through reduced to completely reset. The annealing is the result of a single heating period related to the HP–LT metamorphism with near-peak temperatures lasting for only a few million years some time between 24±1 and 20±1 Ma. In eastern Crete, where rocks have experienced temperatures of 300±50 °C and pressures of 0.8±0.3 GPa, zircon FT ages range from 414±24 to 145±10 Ma. Ages above 300 Ma occur mostly near the east coast of the island in rocks which have not been heated to above ca. 280 °C and probably represent a pre-Variscan source. Track lengths are already indicative of a substantial annealing at this temperature. Most of the zircon FT ages from eastern Crete scatter within error around the stratigraphic age. Samples with apparent zircon FT ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca. 320 °C. Towards the west, a sudden decrease to very young ages ranging from 17±2 to 18±1 Ma reflects a complete resetting at ca. 350 °C. Short tracks, however, are still observed. Throughout the central and western part of the island, ages are consistently below 22 Ma. Thermobarometric data for this area indicate maximum temperatures of 400±50 °C and pressures of 1±0.3 GPa. Only samples from western Crete, which have been exposed to 400±50 °C, show exclusively long tracks. Consequently, the high temperature limit of the zircon partial annealing zone (ZPAZ) appears to be between 350 and 400 °C.A significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0.5 GPa and at different temperatures, which fit the curves previously obtained by other authors at ambient pressure.  相似文献