Origin of the Tertiary basaltic volcanism in the northern Hessian Depression   总被引：2，自引：0，他引：2  

K. Hans Wedepohl 《Contributions to Mineralogy and Petrology》1985,89(2-3):122-143

Volcanic activity started about 20 Ma before present with quartz tholeiites (QTh), had a climax with alkali olivine basalts (AOB) 13 to 14 Ma ago and ended 7 Ma ago with nepheline basanites (NB) and olivine nephelinites (ON). AOB covers 73% of the volcanic area. About 250 basalts and peridotite xenoliths were sampled for investigation. An upper mantle layer ranging from about 90 to 60 km depth has been conditioned for a preferential alkali basalt production by advection of H₂O-CO₂-fluids containing Si, Al, Ca, K, Na, P as major constituents beside numerous incompatible minor elements. At the onset of the geodynamically triggered mantle conditioning locally restricted diapirism into shallow depth has caused formation of olivine tholeiite magmas (OTh) at about 1,300° C by partial melting. All of these OTh primary melts intruded due to a favourable compressibility into granulites of the lower crust. The rare QTh basalts are their derivative magmas which have been slightly contaminated in the crust. Magmas of the subsequent alkali basaltic volcanism (AOB, bAOB, NB, ON, MON) formed by in-situ partial melting at about 75 to 90 km depth after depression of the peridotite solidi by fluids to temperatures 1,200° C. Except many AOB these magmas are primary melts as characterized by olivine/melt distribution coefficients of Mg/Fe²⁺ (K _D=0.29 to 0.34), by Ni concentrations (260 to 330 ppm) and the occurrence of peridotite xenoliths. Rapid rise of gas charged melts due to saturation in CO₂ prevented separation of olivine etc. and of xenoliths. The sequence of magmas from OTh to ON (or MON) is formed from decreasing proportions of orthopyroxene (opx) and increasing contributions of clinopyroxene (cpx) and phlogopite (ph) at almost equal proportions of spinel (sp). Incongruent melting of opx (and cpx) for OTh, AOB, NB and ON is correlated with precipitation of olivine. The average xenolith composition (73% ol, 18% opx, 7% cpx, 1.1% sp and 1.3/0.5% ph) was used to model the sources of the investigated melts by 9 incompatible elements and to calculate degrees of partial melting. The occurrence of garnet cannot be reliably excluded by modelling on the basis of HREE distribution coefficients. The average xenolith composition was used for modelling because of its resemblance with worldwide sampled depleted mantle inclusions. For avoiding to exhaust at least one mineral of the model mantle in the support of the norm composition of OTh, AOB, NB and MON magmas the degrees of partial melting cannot exceed 12.5%, 6%, 6% and 4% respectively. Mantle containing about 500 ppm K (and the correlated incompatible elements), like the average of 36 xenoliths, allows to explain the formation of OTh magmas. AOB, NB and ON melts require peridotite with slightly less than 1,500 ppm K, 670 ppm P and proportions of the correlated elements LREE, Sr, Ba, Zr, Rb, Cs, Ta, Th, Hf, U, which are higher than their abundance in primitive mantle rocks. About 20% of the xenoliths have this composition. Metasomatism of fluids with these elements must have been an immediate precursor of the alkali basaltic volcanism. Otherwise the preservation of a local disequilibrium in ⁸⁷Sr/⁸⁶Sr ratios between cpx cores and total rock at upper mantle temperatures cannot be explained.  相似文献   

U/Pb- und K/Ar-Datierungen des Uranvorkommens Höhenstein/Oberpfalz     

Dr. Claudia Carl  Dr. Harald Dill  Hans Kreuzer  Prof. Dr. Immo Wendt 《International Journal of Earth Sciences》1985,74(3):483-504

K/Ar dating of micas from rocks of Fichtelgebirge and the northern Oberpfalz (NE-Bavaria) covers the rather wide range from 330 to 300 Ma. In combination with Rb/Sr wholerock isochron ages of post-tektonic granites four Variscian events can be traced:

1. Regional metamorphism ～ 330 Ma,
2. Intrusion of the older post-deformative granite G1 about 320 Ma (Falkenberger Granit) followed by rapid cooling.
3. About 300 Ma ago the older mineral ages were more or less reset by the intrusion of younger granites (G2 to G4, Flossenbürger Granit) again followed by a rapid cooling.
4. Local influences later than 290 Ma are recorded by some white micas in fault gauges at least up to the middle Jurassic (< 150 Ma).

The different U-black ore types yielded strongly discordant U/Pb dates. Applying the three dimensional U/Pb-discordia plane method the following results have been obtained: the older pitchblende generation with an upper concordia intersection of 336±17 Ma can be correlated with the regional metamorphism as well as with the intrusion of the older post-deformative granites. The younger generation with 298±4 Ma is of equal age as the intrusion of the younger granites. The brannerite mineralisation which according to thin section evaluation must be still younger could be only roughly dated to 288±78 Ma. The low precision is due to low uranium concentration and high common lead contents of the samples. The lower concordia intersection ages are 0 to 7 Ma. They were obtained more precisely by dating of secondary U-minerals: 10 torbernite samples with extremely high²³⁸U/²⁰⁶Pb-ratios of 30 000 to 50 000 yielded a positive slope of the discordia which points to an age of (137±12)×10³a. The²³⁰Th/²³⁸U-activity ratio of 0.68 determined byα-spectrometry indicates an age of (130.4±5.0)×10³ a. Pyrite and chalcopyrite samples which had U-concentration of some 100 ppm and which according to thin section evaluation are younger than the brannerite showed a positive slope of the²⁰⁷Pb/²⁰⁶Pb vs.²³⁸U/²⁰⁶Pb discordia, too. They could not be dated because the²⁰⁷Pb/²⁰⁶Pb-ratios corrected for common lead contribution are lower than 0.046 (radiogenic lead of zero age). This may be explained by an addition of²⁰⁶Pb due to²²²Rn migration from the pitchblende in only a few cm distance.  相似文献   

The role of gravitophotophoresis for stratospheric and mesospheric particulates     

Hans rohatschek 《Journal of Atmospheric Chemistry》1984,1(4):377-389

Gravitophotophoresis, a type of photophoresis related to the direction of gravity, is examined in view of its possible importance to some aerosols in stratosphere and mesosphere. particles of various materials from about 1 to 100 m in size show levitation by photophoretic forces under laboratory simulation of irradiation by the sun at air densities of the middle atmosphere. Minimum air densities for levitation are about 2–3 g m^–3 with mineral and metallic powders, about 0.08 g m^–3 with carbonaceous powders. The fraction of rising particles can be about 0.01 to 1%. Velocities of ascent are in the range of 0.001 to 0.01 m s^–1 at a pressure of several mbar. The magnitude and the mechanical character of the force of gravitophotophoresis can be explained if it is identified with a radiometer force caused by a difference of the accommodation coefficient on the surface. It is suggested that gravitophotophoresis can be important to the residence time and the maximum altitude of carbonaceous and mineral particles, such as volcanic ash or products of meteorite impact, and to the presence of microorgnisms in the middle atmosphere.  相似文献   

Mercury pollution in the waters around Harboøre Tange and Limfjord,Denmark     

Hans Ulrik Riisgård 《Marine pollution bulletin》1984,15(4):129-133

High concentrations of mercury have been measured in mussels (Mytilus edulis) collected in two ‘hot spot’ areas: (1) near a closed-down chemical factory on the west coast of the Limfjord, and (2) on groynes in the immediate vicinity of a chemical deposit in the dunes on the Danish west coast. By collecting comparable samples of mussels from chains of buoys, the mercury pollution in the western Limfjord could be traced 50–100 km into the central and innermost parts of the Limfjord as a gradual decreasing mercury concentration gradient. By collecting mussels from groynes north and south of the chemical deposit, it was possible to monitor the relative extent of the mercury leakage to the North Sea before and after the excavation of the deposit. The investigations have demonstrated the applicability of M. edulis as a monitoring organism for mercury when importance is attached to concentration gradients and distribution patterns in well defined and homogeneous samples of mussels collected from natural populations.  相似文献   

Nature and classification of waterlain glaciogenic sediments,exemplified by Pleistocene,Late Paleozoic and Late Precambrian deposits   总被引：1，自引：0，他引：1  

C.P. Gravenor  V. von Brunn  A. Dreimanis 《Earth》1984,20(2):105-166

  相似文献   

The significance of discrete baltic nutrient samples discussed on the basis of continuous measurements     

Dr. Hans Peter Hansen 《Ocean Dynamics》1984,37(6):245-258

  相似文献   

Dependence of velocity variance on sampling time     

Gabriele C. Wollenweber  Hans A. Panofsky 《Boundary-Layer Meteorology》1989,47(1-4):205-215

The dependence of the lateral and vertical velocity variances on sampling time have been investigated, based on recent spectral models. The results have been compared with observations at Vandenberg Air Force Base and at the Boulder Atmospheric Observatory.For sampling times of l s to 1 hr, the variation of lateral variances is much smaller in neutral than in unstable conditions. In a stable atmosphere, the variances show a stronger increase with sampling time than predicted by the model. The vertical velocity variances do not increase significantly between 1 and 60 min. Again in stable conditions, the measurements show a more pronounced increase of variances as compared to the calculations, indicating significant energy between periods of a few to 20 min. This additional energy may be ascribed to gravity waves.The models cannot be applied in cases with trends in the data. The model tends to underestimate the dependence of variances on sampling time in cases when systems, such as longitudinal vortices or gravity waves exist.This work was undertaken while the authors were associated with the Scripps Institution of Oceanography, La Jolla, California.Deceased 28 February 1988  相似文献   

Regional climate simulation with a high resolution GCM: surface radiative fluxes   总被引：1，自引：1，他引：1  

Martin Wild  Atsumu Ohmura  Hans Gilgen  Erich Roeckner 《Climate Dynamics》1995,11(8):469-486

The ability of a high resolution (T106) version of the ECHAM3 general circulation model to simulate regional scale surface radiative fluxes has been assessed using observations from a new compilation of worldwide instrumentally-measured surface fluxes (Global Energy Balance Archive, GEBA). The focus is on the European region where the highest density of observations is found, and their use for the validation of global and regional climate models is demonstrated. The available data allow a separate assessment of the simulated fluxes of surface shortwave, longwave, and net radiation for this region. In summer, the incoming shortwave radiation calculated by the ECHAM3/T106 model is overestimated by 45 W m^–2 over most of Europe, which implies a largely unrealistic forcing on the model surface scheme and excessive surface temperatures. In winter, too little incoming shortwave radiation reaches the model surface. Similar tendencies are found over large areas of the mid-latitudes. These biases are consistent with deficiencies in the simulation of cloud amount, relative humidity and clear sky radiative transfer. The incoming longwave radiation is underestimated at the European GEBA stations predominantly in summer. This largely compensates for the excessive shortwave flux, leading to annual mean net radiation values over Europe close to observations due to error cancellation, a feature already noted in the simulated global mean values in an earlier study. Furthermore, the annual cycle of the simulated surface net radiation is strongly affected by the deficiencies in the simulated incoming shortwave radiation. The high horizontal resolution of the GCM allows an assessment of orographically induced flux gradients based on observations from the European Alps. Although the model-calculated and observed flux fields substantially differ in their absolute values, several aspects of their gradients are realistically captured. The deficiencies identified in the model fields are generally consistent at most stations, indicating a high degree of representativeness of the measurements for their larger scale setting.  相似文献   

Genetic implications of new lead isotope measurements on Schwarzwald vein and Upper Triassic sediment galenas     

Prof. Dr. Hans Joachim Lippolt  Ulrike Schorn  Dr. Robert T. Pidgeon 《International Journal of Earth Sciences》1983,72(1):77-104

We report the results of a lead isotopic investigation of galena from vein deposits from the Southern Schwarzwald (33 samples) and from various localities (6) from the galena horizon of the South German Keuper. The total range of isotopic ratios for the veins and the Keuper leads is:18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. The lead isotopic systems give anomalous ages when compared with lead evolution models ofHolmes (1946, 47)Houtermans (1946),Stacey &Kramers (1975) andCumming &Richards (1975). This indicates a more complex lead evolution than allowed for in these models.Small but significant variations in the isotopic ratios of lead were observed in galenas from within a number of veins and between veins. Also leads in galena from Hercynian veins within granitic host rocks in the Southern Schwarzwald were found to be more radiogenic than galena leads in veins found in gneisses in the Central Schwarzwald. These results strongly suggest a local influence on the lead isotopic compositions of the vein galenas and also place constraints on the age of the veins and models of vein formation.Galenas from Tertiary veins were found to have lower²⁰⁷Pb/²⁰⁴Pb ratios in comparison with ratios observed in Hercynian vein leads, suggesting that the Tertiary veins contain a compound of older retarded lead from a source not identified in the present study.The Keuper sedimentary galenas were found to have relatively homogenous lead isotopic ratios which fall within the range of isotopic compositions of the Hercynian vein leads. The galenas from the Upper Triassic (Keuper) are slightly more radiogenic than the more isotopically variable galena leads from the uppermost Permian (Kupferschiefer;Wedepohl et al. 1978).

---

Zusammenfassung An Bleiglanzen von Gängen des mittleren und südlichen Schwarzwaldes (33 Proben) und von verschiedenen Lokalitäten (6) der Bleiglanzbank des süddeutschen Keupers wurden massenspektrometrische Blei-Isotopen-Untersuchungen durchgeführt.Die Werte fallen in die Bereiche: 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. Aus den Blei-Isotopenverhältnissen erhält man anomale Blei-Entwicklungsalter, wenn man die Modellevon Holmes (1946, 47),Houtermans (1946),Stacey &Kramers (1975) undCumming &Richards (1975) zugrunde legt. Das zeigt, daß die Entwicklung dieses Bleis komplexer ablief, als die genannten Modelle annehmen.Kleine aber signifikante Unterschiede in der Blei-Isotopenzusammensetzung wurden für Proben eines Gangsystems und zwischen den verschiedenen Gängen beobachtet. Das Blei aus Bleiglanzen von variscischen Gängen des St. Blasien-Granits (Südostschwarzwald) ist radiogener als das der Gänge in den Gneisen des Zentral-Schwarzwaldes. Diese Beobachtung zeigt, daß die Blei-Isotopenwerte mit der lokalen geologischen Situation verknüpft sind und ist von Bedeutung für die Diskussion der Alter und Entstehungs-modelle der Bleiglanze.Bleiglanz aus den als Tertiär angesehenen Gängen zeigt niedere²⁰⁷Pb/²⁰⁴-Verhältnisse als die variscischen Gang-Bleiglanze. Daraus kann man auf eine ältere zurückgebliebene Bleikomponente schließen, deren Quelle jedoch noch nicht gefunden wurde. Die Bleiglanze aus der Keuper-Bleiglanzbank ergaben relativ einheitliche Isotopenverhältnisse, welche in die Verteilung der Schwarzwälder Bleie fallen. Sie sind etwas radiogener als die isotopisch sehr variablen Bleiglanz-Isotopenwerte des Zechsteins (Kupferschiefer;Wedepohl et al. 1978).

---

Résumé Une étude isotopique du plomb a été effectué sur des galènes provenant de filons de la Forêt Noire Centrale et du Sud (33 échantillons) et de différentes localités (6) de l'horizon à galène du Keuper du Sud de l'Allemagne.Les valeurs de plomb se situent dans les intervalles suivants: 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90.Les rapports isotopiques du plomb indiquent des âges d'évolution de plomb anormaux, si l'on prend pour base les modèles d'évolution deHolmes (1946, 47),Houtermans (1946),Stacey &Kramers (1975) etCumming &Richards (1975). Cela montre que l'évolution du plomb s'est déroulée d'une façon plus complexe que ne le supposent les modèles mentionnés. Des différences minimes mais significatives ont été observées dans la composition isotopique du plomb, pour des échantillons d'un système filonien et entre différents filons. Le plomb des galènes des filons hercyniens du granite de St. Blasien (Forêt Noire du Sud Est) est plus radiogénique que celui des filons trouvés dans les gneiss de la Forêt Noire Centrale. Cette observation montre que la composition isotopique du plomb est liée à la situation géographique locale et est d'une grande importance pour la discussion des âges et des modèles de formation des galènes.Les rapports²⁰⁷Pb/²⁰⁴Pb des galènes des filons considérés comme d'âge tertiaire sont moins élevés que ceux des galènes d'âge hercynien, ce qui permet de supposer une composante de plomb plus âgée, «retardée» dont on n'a pu jusqu'ici déceler la source. Le plomb des galènes du Keuper a une composition isotopique relativement homogène, qui se trouve dans la gamme de celle observée pour le plomb des galènes de la Forêt Noire. Leur plomb est légèrement plus radiogénique que celui des galènes du Zechstein qui a une composition isotopique très variable (Kupferschiefer;Wedepohl et al., 1978).

---

— (33 ) (6 ) - . : 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. , Holmes'a, 1946; Houterman'a, 1946, Stacey & Kramer'a, 1975 Cumming & Richard'a, 1975, . , , , ., , . St. Blasien (- ) , . , , . ²⁰⁷Pb/²⁰⁴Pb, . , . , . , , .

  相似文献   

Silver and mercury in single gold grains from the Witwatersrand and Barberton,South Africa     

K. von Gehlen 《Mineralium Deposita》1983,18(3):529-534

The contents of silver and mercury in 323 spots on gold grains from seven localities of the Witwatersrand palaeo-placer and Archaean vein deposits from Barberton were measured using an electron microprobe. The objective was to obtain information on the extent of gold alteration during fluvial transport and post-depositional geological processes. The results, however, show that Ag and Hg are distributed homogeneously in the gold grains studied. No indications were found that the gold was transported in solution nor that leaching took place in an oxidizing fluvial environment. This strongly suggests that the Ag and Hg contents in Witwatersrand gold grains represent geochemical ‘fingerprints’ inherited from their eroded primary sources. Combined analysis for Ag and Hg in Witwatersrand gold grains by electron microprobe can therefore be a valuable tool in establishing the types of primary sources for the gold.  相似文献