Hf-W chronometry of primitive achondrites     

T. Schulz  C. Münker  K. Mezger 《Geochimica et cosmochimica acta》2010,74(5):1706-2136

Metal segregation and silicate melting on asteroids are the most incisive differentiation events in the early evolution of planetary bodies. The timing of these events can be constrained using the short-lived ¹⁸²Hf-¹⁸²W radionuclide system. Here we present new ¹⁸²Hf-¹⁸²W data for major types of primitive achondrites including acapulcoites, winonaites and one lodranite. These meteorites are of particular interest because they show only limited evidence for partial melting of silicates and are therefore intermediate between chondrites and achondrites.For acapulcoites we derived a ¹⁸²Hf-¹⁸²W age of Δt_CAI = 4.1 ^+1.2/_−1.1 Ma. A model age for winonaite separates calculated from the intercept of the isochron defines an age of Δt_CAI = 4.8 ^+3.1/_−2.6 Ma (assuming a bulk Hf/W ratio of ∼1.2). Both ages most likely define primary magmatic events on the respective parent bodies, such as melting of metal, although metal stayed in place and did not segregate to form a core. A later thermal event is responsible for resetting of the winonaite isochron, yielding an age of Δt_CAI = 14.3 ^+2.7/_−2.2 Ma, significantly younger than the model age. Assuming a co-genetic relationship between winonaites and silicates present in IAB iron meteorites (based on oxygen isotope composition) and including data by Schulz et al. (2009), a common parent body chronology can be established. Magmatic activity occurred between ∼1.5 and 5 Ma after CAIs. More than 5 Ma later, intensive thermal metamorphism has redistributed Hf-W. Average cooling rates calculated for the winonaite/IAB parent asteroid range between ∼35 and ∼4 K/Ma, most likely reflecting different burial depths. Cooling rates obtained for acapulcoites were ∼40 K/Ma to ∼720 K and then ∼3 K/Ma to ∼550 K.Accretion and subsequent magmatism on the acapulcoite parent body occurred slightly later if compared to most achondrite parent bodies (e.g., angrites, ureilites and eucrites), in this case supporting the concept of an inverse correlation between accretion-age of asteroids and intensity of heating in their interiors as expected from heating by ²⁶Al and ⁶⁰Fe decay. However, the early accretion of the parent asteroid of primitive IAB silicates (∼1.0 Ma after CAIs; Schulz et al., 2009) and the possibly impact-induced melting-history of winonaites show that this concept is too simplistic. Parent body size, impact-driven melting as well as heat-insulating regolith cover also need to be considered in the early history of asteroid differentiation.  相似文献   

The impact and rotational light curves of Comet 9P/Tempel 1     

Jean Manfroid  Damien Hutsemékers  Anita L. Cochran  William M. Jackson  Rita Schulz 《Icarus》2007,187(1):144-155

UVES and HIRES high-resolution spectra of Comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C₃, CH, C₂, NH₂, and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact light curves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The impact light curves are consistent with velocities of 400-600 m/s. Their modeling requires a three-step dissociation sequence “Grand-Parent → Parent → Daughter” to produce the observed molecules. The rotational light curve for each species is explained in terms of a single model with three sources. The dust component can however not easily be explained that way.  相似文献   

Das erdmagnetische Feld im Jahr 1994 nach Messungen des Erdmagnetischen Observatoriums Wingst     

Günter Schulz 《Ocean Dynamics》1995,47(2):163-166

Ohne Zusammenfassung  相似文献   

Untersuchung zur Frage der Entstehung der Eisphase aus unterkühlten Wassertropfen     

Werner Schulz 《Meteorology and Atmospheric Physics》1958,11(1):64-83

Zusammenfassung Auf verschiedenen Metallspiegeln wurden durch Kondensation Tröpfchen mit Durchmessern zwischen 5 und 25 erzeugt und so lange unterkühlt, bis ihr Gefrierpunkt beobachtet werden konnte. Die Auswertung ergibt, daß der Erstarrungsvorgang an den Tropfen bei –10° C einsetzt und sich ab etwa –15° C verstärkt. Die Temperatur des häufigsten Umschlags von Wasser zu Eis liegt im Bereich zwischen –20°C und –24° C. In Übereinstimmung mitJacobi wird festgestellt, daß metallische Unterlagen das Gefrieren begünstigen, wofür zum Teil deren hohe Wärmeleitfähigkeit verantwortlich gemacht wird. Eine Abhängigkeit der beobachteten Gefriertemperatur von Tropfengröße oder Kühlgeschwindigkeit besteht nicht.

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Summary Droplets of 5 to 25 diameter have been produced by condensation on different metallic mirrors and supercooled until congelation, which begins at –10° C and increases from –15° on with a maximum between –20° and –24°. In concert withJacobi metal support favours the freezing process, probably because of its high thermal conductivity. The freezing temperature depends neither on the size of the droplets nor on the speed of refrigeration.

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Résumé On a obtenu par condensation sur différents miroirs métalliques des gouttelettes avec des diamètres de 5 à 25 et on les a refroidies jusqu'à congélation. Celle-ci commence à –10° C et se renforce à partir de –15° environ; elle se produit de préférence entre –20° et –24°. Le support métallique favorise, en concordance avec les résultats deJacobi, le processus de congélation en vertu probablement de sa grande conductibilité calorifique. La température de congélation ne dépend pas de la grosseur des gouttelettes ni de la vitesse de refroidissement.

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Mit 9 Textabbildungen  相似文献   

Ermittlung der Nachweis-, Erfassungs- und Bestimmungsgrenze nach DIN 32645 mit Hilfe eines Programms Calculation of Detection Limit,Identification Limit and Determination Limit according to DIN 32645 with the Aid of a Computer Programs     

M. Kolb  A. Bahr  S. Hippich  W. Schulz 《洁净——土壤、空气、水》1993,21(6):308-311

The new German standard specification DIN 32645 defines detection, identification and determination limit of analytical experiments and contains formulas for their calculation. The detection limit is a qualitative value, only at the determination limit a quantitative statement is possible. The identification limit is no limit of decision for analyses. The expenditure for calculating these parameters is considerable. Therefore, a computer program was developed and tested at the analysis of herbicides with GC-MS after enrichment with solid phase extraction (SPE). It proved that the program is also very useful at the development of analytical methods, because it allows a quick examination of changes of the analytical method. After optimization detection limits for the herbicides were achieved which amount 10–20% of the limit of the German drinking water regulation.  相似文献   

X-ray study and mössbauer spectroscopy on lunar ilmenites (Apollo 11)     

G. BayerJ. Felsche  H. Schulz 《Earth and Planetary Science Letters》1972

A comparison of lunar ilmenites (Apollo 11, 10047, 13) with terrestrial ilmenites by means of electron microprobe analysis, X-ray and Mössbauer spectrometry showed that the lunar samples contained no Fe³⁺ but excess Ti³⁺. This causes an increase of thec-axis as compared with stoichiometric ilmenite.  相似文献   

Unterdevonische Baryt-Fahlerz-Mineralisation und ihre steilachsige Verformung im Gro\kogel bei Brixlegg (Tirol)     

Dr. O. Schulz 《Mineralogy and Petrology》1972,18(2):114-128

Zusammenfassung Für die Baryt-Fahlerz-Lagerstätten im Schwazer Dolomit (Unterdevon) bei Brixlegg (Tirol, Österreich) liegen sehr differierende Altersangaben zwischen Tertiär und Oberkarbon vor. Hier werden am Beispiel des Bergbaues Großkogel Befunde dargelegt, welche hydrothermale Stoffzufuhren bereits im Unterdevon wahrscheinlich machen. Es wird submarine Entstehung mit der Anlage synsedimentärer schichtkonkordanter und-diskordanter Erzkörper angenommen. Der erzführende Sedimentkomplex liegt heute als steilachsige Großfalte vor. Die primäre Paragenese, hauptsächlich bestehend aus Quarz, Pyrit, Fahlerz und Baryt, wurde samt dem Nebengestein durch die Diagenese sowie durch die Auswirkungen der variszischen und alpidischen Orogenese und epizonalen Metamorphose im Gefüge verändert.

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Early Devonian barite-tetrahedrite mineralization and its steep axial deformation in the Grosskogel near Brixlegg (Tyrol)

Summary Very different ages are attributed to the barite-tetrahedrite deposits in the Schwazer Dolomite (Early Devonian) near Brixlegg (Tyrol, Austria), varying between Tertiary and Upper Carboniferous. In this paper observations on the ore deposit of Grosskogel indicate an introduction of hydrothermal material probably in the Early Devonian. The deposit is believed to be of submarine origin with formation of synsedimentary conformable and inconformable ore bodies. The ore-bearing sedimentary complex now forms a large, steep axial fold. The primary paragenesis (consisting mainly of quartz, pyrite, tetrahedrite and barite) together with the wallrock, was altered by diagenesis, the effect of Variscian and Alpidian orogenesis, and by epizonal metamorphism.

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Mit 4 Abbildungen  相似文献   

Platinum deposits—further thoughts: a thematic issue dedicated to Professor Eugen F. Stumpfl on the occasion of his 70th birthday     

Oskar?R.?A.?ThalhammerEmail author 《Mineralium Deposita》2003,38(3):259-260

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Summer flows in experimental catchments with different forest covers, Chile   总被引：7，自引：0，他引：7  

Andrs Iroum  Anton Huber  Kurt Schulz 《Journal of Hydrology》2005,300(1-4):300-313

Runoff and peak flows in four experimental catchments with different land uses are analyzed for summer periods. The catchments have a rainy temperate climate with annual precipitations between 2000 and 2500 mm, 70% of which is concentrated in the winter period between May and August. The final harvest of the forest plantation in one of these catchments generated increases in summer runoff. Also, differences between the maximum instantaneous discharge and the flow at the beginning of the storm then almost duplicated those registered in rainfall events of similar magnitude when the catchment was fully forested. Runoff analysis in this catchment is difficult because the two post-harvesting summer periods are much wetter than the two pre-harvesting ones but a double mass analysis shows the effect of harvesting clearly. In a paired catchment study, low cover in one of the two neighbour catchments explains higher direct runoff and base flows although lower maximum instantaneous specific discharge occurred in the less vegetated but larger catchment. Low vegetation cover explains increases in summer flows, although the size, topography, rainfall conditions, road density, extent of affected area and runoff generation processes play an important role in the hydrological effects of different land uses.  相似文献   

Dust and Gas in D/Shoemaker-Levy 9     

Ritav Schulz 《Surveys in Geophysics》1997,18(1):39-55

The spectacular impact of D/Shoemaker-Levy 9 on Jupiter in July 1994 was observed all over the world and from space, leading to many new and exciting clues to the physics of the Jovian atmosphere. However, what do we know of the impactor? There were only 16 months to study D/Shoemaker-Levy 9 between its discovery and destruction. D/Shoemaker-Levy 9 was designated as a comet at time of discovery. Then, due to the apparent absence of volatiles usually present in comets it was repeatedly discussed whether D/Shoemaker-Levy 9 was a comet or an asteroid. Although its true nature can still not be named unambigeously, a cometary origin is indicated from the observational evidence. The results of the dust analysis are consistent with D/Shoemaker-Levy 9 being a typical comet and so far this is not contradicted by any observation.  相似文献