Age and degree of metamorphism and time of nappe emplacement along the southern margin of the Damara Orogen/Namibia (SW-Africa)     

Dr. H. Ahrendt  Dr. J. C. Hunziker  Prof. Dr. K. Weber 《International Journal of Earth Sciences》1978,67(2):719-742

Along the southern margin of the Damara orogen age and degree of metamorphism were determined by means of K/Ar dating and illite crystallinity. The investigations include the following units:

1. The southwestern-most part of the east-west striking branch of the Damara orogen.
2. The nappes of the Naukluft Mountains.
3. The Nama-Group from north of the Naukluft Mountains to the Fish River in the south (including the western part of the Dwyka-Formation).

The metamorphism of the Naukluft nappes as well as the underlying Nama beds corresponds to the higher part of the anchi-zone and lower epi-zone. Between the Naukluft nappes and the folded Nama rocks adjoining the southeastern front of the nappes there is an obvious step from higher down to lower metamorphism. Further to the southeast the metamorphism in the Nama beds decreases continuously down to diagenesis. K/Ar age determinations were carried out on the three units mentioned above and also on the basement underlying the Nama sequence. Muscovites of this basement gave an age of about 1160 m. y. Determinations on white micas of the southern Damara belt, the Naukluft Mountains and the northern Nama basin define two isochrons with ages of 495 and 530 m. y The age of 530 m. y. represents the peak of metamorphism and the age of syncrystalline deformation. The age of 495 m. y. can be interpreted as a cooling age of the higher metamorphic rocks or as a dating of rejuvenation caused by a second post-crystalline deformation in parts of the Naukluft and Damara rocks. This age of 495 m. y. was also found in the mylonite of the main thrust plane of the Naukluft nappes and it represents the time of emplacement of the Naukluft nappes.  相似文献   

A Method for Characterizing Rotation Rates in the Soft X-Ray Corona     

Weber  M.A.  Acton  L.W.  Alexander  D.  Kubo  S.  Hara  H. 《Solar physics》1999,189(2):271-288

Differential rotation rates of soft X-ray features in the solar corona are quantified by a method of harmonic filtering using the Lomb-Scargle periodogram. This approach leads reasonably to a quantitative discrimination between uncertainty estimates and spectral leakage of the fundamental rotation frequency due to the presence of multiple rotating tracers. Mean rotation rates as a function of latitude and year are calculated for the years 1992–1997 (roughly the declining phase of the last solar activity cycle). The corona is found to have a small but measurable latitudinal gradient in rotation rate. The presence of multiple features places a lower bound of 1–2% on the relative uncertainties with which a `mean' rotation rate can be measured. The results are compared with autocorrelation estimates and found to agree within 1.  相似文献   

Precise U-Pb zircon ages for the Molson dyke swarm and the Fox River sill: Constraints for Early Proterozoic crustal evolution in northeastern Manitoba,Canada     

L. M. Heaman  N. Machado  T. E. Krogh  W. Weber 《Contributions to Mineralogy and Petrology》1986,94(1):82-89

Precise U-Pb zircon ages have been obtained for samples from the Molson dyke swarm and the Fox River sill in NE Manitoba, Canada. The ages determined for the Cross Lake and Cuthbert Lake dykes are 1,883.7 _–1.5 ^+1.7 and 1,883±2 Ma, respectively, and are in excellent agreement with the 1,882.9 _–1.4 ^+1.5 Ma age obtained for the Fox River sill. These results support the contention that the emplacement of the Fox River sill and the Molson Dyke swarm was contemporaneous and also demonstrate the potential for correlating mafic igneous activity in widely spaced localities. The timing of Early Proterozoic mafic magmatism in the western Superior Province appears to be synchronous with igneous activity in other parts of the Circum-Superior Belt and in the Trans Hudson orogen to the west. The emplacement of the Molson dyke swarm at 1,883 Ma indicates a 700 Ma interval of quiescence between the final igneous activity that is recorded in the Archean basement and dyke intrusion. The presence of deformed equivalents of Molson dykes in the Thompson Nickel Belt indicates that the intense deformation in this belt occurred sometime after 1,883 Ma.  相似文献   

Die Laufzeitfunktion und ihre Interpretation in der Refraktionsseismik des einachsig inhomogenen Körpers     

Priv.-Doz. Dr. Max Weber 《Pure and Applied Geophysics》1959,43(1):167-181

Zusammenfassung Es wird das Interpretationsproblem der Refraktionsseismik in einem einachsig inhomogenen Körper allgemein behandelt und exakt gelöst.

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Summary The interpretation-problem of the refraction seismic in a uniaxial inhomogeneous medium is generally treated and exactly solved.

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Bringing Time Back In: A Study on the Influence of Travel Time Variations and Facility Opening Hours on Individual Accessibility   总被引：2，自引：0，他引：2  

Joe Weber  Mei‐Po Kwan 《The Professional geographer》2002,54(2):226-240

Although recent studies of individual accessibility have used detailed representations of urban street networks, unrealistic measures of travel time based on assumptions about constant travel speeds through the network were often used. Utilizing constant travel times does not allow for daily congestion and assumes that the effects of congestion are uniform throughout the city and affect all people equally. This research measures individual space‐time accessibility in order to show that the incorporation of locally specific travel times within a street network allows a significant increase in the ability to realistically evaluate individual accessibility within cities. The results show that the accessibility of individuals within cities is not homogenous, and neither does access to employment or shopping opportunities vary according to common expectations about urban form and human behavior. Instead, the role of distance in predicting accessibility variations within cities is quite limited. This article also shows that incorporating time into accessibility measures in the form of congestion and business hours leads to additional (and highly spatially uneven) reductions in accessibility, revealing that the temporal dimension is very important to accurately assessing individual accessibility.  相似文献   

Calcmylonites and solution transfer in a Devonian reef at Warstein,Germany   总被引：1，自引：1，他引：0  

Jacob de Roo  Johannes Duyster  Klaus Weber 《International Journal of Earth Sciences》1992,81(2):333-346

Massive limestone complexes of Late Palaeozoic age are scattered across the allochthonous foreland of the Hercynides in Germany. One of these complexes is situated at Warstein. Stratigraphic facies studies have represented the Warstein complex as a reef in a coastal shelf. Our study emphasizes that at least part of the reef consists of a pile of calcmylonites.The calcmylonites have a strong foliation (S_m) and lineation (L_m) and a structural asymmetry indicating non-coaxial deformation. X-ray textures and calcite microstructures show that the mylonitization involved intracrystalline deformation and dynamic recrystallization. These processes competed with solution transfer, as the mylonites are corroded at S_m-parallel stylolites and contain carbonate veins. Cathodoluminescopy shows that some veins are parallel to S_m and have been recrystallized, whereas others are normal to S_m and retain a fibrous crackseal microstructure. The latter type created limestones showing a pair of preferred grain boundary orientations; one normal to S_m, one in S_m. This orthogonal boundary fabric is distinct from crystalplastic fabrics: the latter show only one preferred grain boundary orientation (in S_m).

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Zusammenfassung Massenkalkkomplexe spätpaläozoischen Alters liegen verstreut über das allochthone Vorland des Variszischen Gebirges in Deutschland. Einer dieser Komplexe liegt bei Warstein. Stratigraphische Faziesstudien haben den Warsteiner Komplex als ein Riff in einem küstennahen Schelf dargestellt. Die vorliegende Arbeit betont, daß wenigstens ein Teil des Riffes aus einer Stapelung von Kalkmyloniten besteht.Die Kalkmylonite haben eine starke Foliation (S_m) und Lineation (L_m), und eine strukturelle Asymmetrie die auf nicht-koaxiale Verformung hinweist. Röntgentexturen und Calcitmikrostrukturen zeigen, daß die Mylonitisierung intrakristalline Verformung und dynamische Rekristallisation beinhaltet. Diese Prozesse müssen mit Lösungstransport konkurriert haben, da die Mylonite an S_m-parallelen Styloliten korrodiert sind und Karbonatgänge erhalten. Kathodolumineskopie zeigt, daß einige Gänge (parallel zu S_m) rekristallisiert sind, während andere (senkrecht zu S_m) eine faserige crack-seal Mikro-Struktur enthalten. Der letzte Typ ist verbunden mit Konformgefügen. Diese unterscheiden sich von kristallplastischen Kornformgefügen, da sie eine zweite bevorzugte Korngrenzorientierung aufweisen, die senkrecht zur ersten (in S_m) einfällt.

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Résumé Les complexes de calcaires massifs de l'Âge paléozoîque supérieure sont repandus sur l'avantpays allochthone des Hercynides en Allemagne. Un de ces complexes est situé à Warstein. Les Études de faciès stratigraphiques ont répresenté le complexe à Warstein comme un Récif littoral. Notre étude montre que au moins partie de ce «Récif» consiste en un empilement des calcmylonites.Les calcmylonites ont une foliation (S_m) et linéation (L_m) fort, et une asymmetrie structurale indiquant de la déformation non-coaxiale. Les textures röntgenographiques et les microstructures calcitiques montrent que la mylonitization était incluse de déformation intracristalline et récristallisation dynamique. Ces processus auront été en compétition avec dissolution-cristallization («solution transfer»), car les mylonites sont corrodées aux stylolites parallel à S_m et contient des veines carbonatiques. La cathodoluminescopie montre que quelques veines (parallel à S_m) sont récristallisées, pendant que les autres (perpendiculaire à S_m) ont retenu une microstructure fibreuse («crack-seal»). Le dernier type est lié avec des fabriques de forme des grains. Ils se sont distingués des fabriques de plasticité cristalline par la présence d'une deuxième orientation préférentielle des bordures des grains, perpendiculaire à la première (dans S_m).

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. Warstein'a. , . , , , »« . (S_m) (L_m), , . , - , . , .. , S_m, . , , S_m, , , S_m, = »crack-seal«. : , S_m.

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Ein exakter Seismograph     

Priv.-Doz. Dr. Max Weber 《Pure and Applied Geophysics》1961,48(1):35-39

Zusammenfassung Es wird ein exakter Seismograph beschrieben.

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Summary An exact seismograph is described.

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Applied focused ion beam techniques for sample preparation of astromaterials for integrated nanoanalysis     

Giles A. Graham  Nick E. Teslich  Anton T. Kearsley  Frank J. Stadermann  Rhonda M. Stroud  Zurong Dai  Hope A. Ishii  Ian D. Hutcheon  Saša Bajt  Christopher J. Snead  Peter K. Weber  John P. Bradley 《Meteoritics & planetary science》2008,43(3):561-569

Abstract— Sample preparation is always a critical step in the study of micrometer‐sized astromaterials available for study in the laboratory, whether their subsequent analysis is by electron microscopy or secondary ion mass spectrometry. A focused beam of gallium ions has been used to prepare electron transparent sections from an interplanetary dust particle (IDP), as part of an integrated analysis protocol to maximize the mineralogical, elemental, isotopic, and spectroscopic information extracted from one individual particle. In addition, focused ion beam (FIB) techniques have been employed to extract cometary residue preserved on the rims and walls of microcraters in 1100 series aluminum foils that were wrapped around the sample tray assembly on the Stardust cometary sample collector. Non‐ideal surface geometries and inconveniently located regions of interest required creative solutions. These include support pillar construction and relocation of a significant portion of sample to access a region of interest. Serial sectioning, in a manner similar to ultramicrotomy, is a significant development and further demonstrates the unique capabilities of focused ion beam microscopy for sample preparation of astromaterials.  相似文献   

Airborne Fungal Spores of Subalpine Zone of the Karkonosze and Izerskie Mountains （Poland）   总被引：4，自引：1，他引：3  

Wojciech PUSZ  Wlodzimierz KITA  Andrzej DANCEWICZ  Ryszard WEBER 《山地科学学报》2013,10(6):940-952

The incidence of the airborne fungal spores was determined in the air of subalpine zone of the Karkonosze Mountains and of the Izerskie Mountains in the borderland between Poland and the Czech Republic. The experiment was conducted in 2011 and 2012 at three to four week intervals from May to October. Air samples were taken from three locations in the Karkonosze Mts. and one from the Izerskie Mts. To examine the air, the Air Ideal 3P sampler and acidified PDA medium were used. The results show that Cladosporium cladosporioides was the most abundant spore type in all the sampling locations （up to 30%）, followed by Alternaria alternata （16%-20%）, Fusarium （up to 10%） and Sclerotinia sclerotiorium （up to 6%）. The lower spore counts were recorded in May samples, compared to the other months. In this case the snow cover, that was still present in the area at the beginning of May, may be the reason for the lower, compared to June, July and August samplings, CFU （Colony Forming Unit） counts in that month.. The influx of air masses from SE, S and SW sectors in the area under study may affect dissemination of the plant-pathogenic fungi from the Czech Republic and from the South of Europe in general.  相似文献   

Effective elimination of subharmonic ghost events from vibroseis data     

M. Stiller  K.‐H. Jaeckel  M. Weber 《Geophysical Prospecting》2012,60(6):1095-1113

Harmonic or subharmonic noise is often present in vibroseis data as reverberation‐like, laterally coherent bands occurring parallel to and before or after, the main events. Such periodic noise is typically generated during the standard correlation process when the actual source signal travelling through the subsurface is, for whatever reason, different from the desired source signal, i.e., the pilot‐sweep controlling the baseplate and used for correlation. A typical cause can be that harmonic or subharmonic frequency partials are generated in addition to the vibroseis sweep's desired fundamental frequencies. These harmonics produce strong ‘ghost events’ during correlation of the geophone trace with the pilot‐sweep, originating from additional correlations between the fundamental and harmonic frequencies. Especially subharmonic ‘ghosts’ will overlap with ‘good’ fundamental signals, since for typically used up‐sweeps they are folded to later traveltimes, where the signal/noise‐ratio is already lower, thus aggravating or preventing a reliable interpretation of possible later reflections. Here, a method is introduced to remove these unwanted noise trains (with only negligible impact on the fundamental signal) by transforming the seismogram traces into a so‐called ‘(sub)harmonic domain’. In this domain, the respective harmonic noise portions are focused and separated from the fundamental signals, enabling easier detection and appropriate suppression. After back‐transformation to the x‐T domain, the records are free from the corresponding harmonic contamination and can then be processed as usual. The method operates in a data‐driven fashion, i.e., the traces are not uniformly processed but are processed depending upon their actual (sub)harmonic content. The decontamination procedure can be applied universally, i.e., to uncorrelated/correlated and/or vertically unstacked/stacked data either in a manual, semiautomated or fully automated manner. The method works perfectly for synthetic vibroseis traces with or without harmonic/subharmonic portions. The application to real, crustal‐scale vibroseis records that were acquired in 2006 in the Dead Sea region, Israel and that were severely contaminated by subharmonic ground‐roll ghosts covering reflectivity from the basement to the Moho, shows the robustness and success of the presented method.  相似文献