•Detrital zircon spectra reveal a distinct succession in the North Australian Craton.•Revised correlation of the succession has implications for uranium prospectivity.•Hf and O data indicate a period ...of juvenile crust formation at ca. 2750–2550Ma.•Hf and O data indicate that crustal reworking dominated the early Paleoproterozoic.•Detrital zircon age and Hf–O isotopes suggest Gawler or Dharwar Craton sources.
Detrital zircon age and Hf isotope patterns for the Cahill Formation and Nourlangie Schist are distinctly different from other Paleoproterozoic successions in the North Australian Craton. The Cahill Formation and Nourlangie Schist comprise the bulk of the Paleoproterozoic strata in the Nimbuwah Domain, the easternmost part of the Pine Creek Orogen on the northern margin of the North Australian Craton. They comprise micaceous and quartzofeldspathic schist, carbonaceous schist, calc-silicate rock, amphibolite and quartzite, deformed and metamorphosed during emplacement of the granitic to dioritic Nimbuwah Complex at 1867–1857Ma. The Cahill Formation hosts several world-class uranium deposits including Ranger, Jabiluka and Nabarlek. U–Pb SHRIMP and LA-SF-ICPMS detrital zircon spectra for four samples of the Cahill Formation and six samples of the Nourlangie Schist show a similar broad spectrum of ages mainly in the range 3300–1900Ma. A ubiquitous dominant peak at 2530–2470Ma matches the age of underlying Neoarchean basement, but is distinct in its dominantly mantle-like Hf and O zircon isotopic character, which shows closer similarity with possible source rocks from the Gawler Craton or alternatively from the Dharwar Craton. Common smaller age peaks occur at 2180Ma, 2080Ma and 2020Ma. The first two have no known magmatic age correlatives in the North Australian Craton. Zircons of the 2020Ma peak have distinctively unradiogenic Hf and elevated δ18O, at variance with local rocks of this age but similar to detrital zircon of the same age from the Gawler Craton. In contrast to younger Proterozoic sedimentary successions within the Pine Creek Orogen, which contain ubiquitous ca. 1870Ma detritus, the detrital spectra for the Cahill Formation and Nourlangie Schist contain almost no ca. 1870Ma detritus. A maximum deposition age of ca. 1866Ma indicates deposition within error of intrusion of the Nimbuwah Complex. We propose that the Cahill Formation and Nourlangie Schist were deposited at a plate margin immediately prior to convergent tectonism. This resulted in their burial, deformation and amphibolite facies metamorphism during orogenesis associated with the Nimbuwah Event. These findings have implications for understanding the Paleoproterozoic evolution of the Pine Creek Orogen within the context of northern Australia.
The IR light curve of the Seyfert 1.9 galaxy NGC 2992 shows a strong outburst between JD 244 7243 and 244 8734 of total energy 6 x 10 exp 43 J and having an exponential decay. The colors of the ...variable components are extracted by the method of flux variation gradients and discussed in terms of a hot dust model. (Author)
We report on the light variations of the infrared stars that were discovered recently in the Magellanic clusters NGC 419, 1783 and 1978. Their periods, of 528, 458 and 491 days, are among the longest ...known for carbon-rich Mira variables in the Clouds. All three IR stars were found to lie on the extension of the period-Mbol relation derived from the shorter-period C-rich Miras while they were 0.45–0.70 mag fainter than the extension of the period-MK relation. Their main sequence masses were determined by isochrone fitting to be 1.5–1.6 M⊙, consistent with the prediction of the evolutionary models of Vassiliadis & Wood.
The results of about 15 years of monitoring of the variable Seyfert 1 galaxy NGC 3783 in the infrared are presented. The spectrum of the variable component stays constant in shape. Changes in the ...infrared appear to lag those in the ultraviolet by about 80 to 90 d. Like the other Seyfert 1 galaxies Fairall 9 and NGC 1566, the near-infrared behavior of NGC 3783 can be modeled by a dust shell at about 1500 K whose heating depends on changes in the UV flux of the central power source.
Translated in part from the original French and annotated with figures, historical maps and commentary from the translators, this book is about a strange period in the life of the Belgian astronomer ...and journalist Jean-Charles Houzeau (1820-1888). Born into an upper-class family, he worked as an astronomer during the years 1843 to 1849 at the Royal Observatory in Brussels. He was dismissed on account of his revolutionary politics. Though he managed to obtain a contract to do survey work in 1854, in 1857 he was again fired.
For almost 100 years the photographic plate was the detector of choice for astronomical measurements, beginning ca 1880 when the technique became sensitive enough to record star images. This era ...however came to an end in the 21st century when electronic detectors supplanted plates thanks to their higher quantum efficiency and precision.In this paper I describe briefly some of the photographic era instruments used at the Cape Observatory. Some of them are still extant but others, especially the big ones, have been scrapped in the interest of saving space. Very often these instruments were interesting precision devices and state-of-the-art at the time.
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