From the Workshop Organizers     

Allan Treiman 《Meteoritics & planetary science》2003,38(12):1711-1712

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Atomistic simulation of the mechanisms of noble gas incorporation in minerals     

Z. Du  N.L. Allan  J.A. Purton 《Geochimica et cosmochimica acta》2008,72(2):554-573

Atomistic simulations have been carried out to investigate the mechanisms of noble gas incorporation in minerals using both the traditional two-region approach and the “supercell” method. The traditional two-region approach has been used to calculate defect energies for Ne, Ar, Kr and Xe incorporation in MgO, CaO, diopside and forsterite in the static limit and at one atmosphere pressure. The possibilities of noble gas incorporation via both substitution and interstitial mechanisms are studied. The favored mechanism varies from mineral to mineral and from noble gas to noble gas. In all minerals studied, the variation of the solution energies of noble gas substitution with atomic radius appears approximately parabolic, analogous to those for 1⁺, 2⁺, 3⁺ and 4⁺ trace element incorporation on crystal lattice sites. Noble gas solution energies thus also fall on a curve, similar to those previously observed for cations with different charges, but with much lower curvature.The “supercell” method has been used to investigate the pressure dependence of noble gas incorporation in the same systems. Results indicate a large variation of the solubility of the larger noble gases, Kr and Xe with pressure. In addition, explicit simulation of incorporation at the (0 0 1) surface of MgO shows that the solubility of the heavier noble gases may be considerably enhanced by the presence of interfaces.  相似文献   

Characterization and cycling of atmospheric mercury along the central US Gulf Coast     

Mark A. Engle  Michael T. Tate  David P. Krabbenhoft  Allan Kolker  Mark L. Olson  Eric S. Edgerton  John F. DeWild  Ann K. McPherson 《Applied Geochemistry》2008

Concentrations of atmospheric Hg species, elemental Hg (Hg^°), reactive gaseous Hg (RGM), and fine particulate Hg (Hg-PM_2.5) were measured at a coastal site near Weeks Bay, Alabama from April to August, 2005 and January to May, 2006. Mean concentrations of the species were 1.6 ± 0.3 ng m⁻³, 4.0 ± 7.5 pg m⁻³ and 2.7 ± 3.4 pg m⁻³, respectively. A strong diel pattern was observed for RGM (midday maximum concentrations were up to 92.7 pg m⁻³), but not for Hg^° or Hg-PM_2.5. Elevated RGM concentrations (>25 pg m⁻³) in April and May of 2005 correlated with elevated average daytime O₃ concentrations (>55 ppbv) and high light intensity (>500 W m⁻²). These conditions generally corresponded with mixed continental-Gulf and exclusively continental air mass trajectories. Generally lower, but still elevated, RGM peaks observed in August, 2005 and January–March, 2006 correlated significantly (p < 0.05) with peaks in SO₂ concentration and corresponded to periods of high light intensity and lower average daytime O₃ concentrations. During these times air masses were dominated by trajectories that originated over the continent. Elevated RGM concentrations likely resulted from photochemical oxidation of Hg^° by atmospheric oxidants. This process may have been enhanced in and by the near-shore environment relative to inland sites. The marine boundary layer itself was not found to be a significant source of RGM.  相似文献   

Instrument calibration of ocean bottom seismographs   总被引：1，自引：0，他引：1  

Allan M. Sauter  Leroy M. Dorman 《Marine Geophysical Researches》1986,8(3):265-275

To increase the accuracy of measuring sea floor motion with ocean bottom seismometers, we calibrate the seismometer system on the ocean floor. Data from the sea floor calibration, augmented with electronic and land calibration data, enables us to find the OBS transfer function to an accuracy of 0.5% in the frequency range of 0.1 to 32 Hz. We are able to distinguish between temperature, instrument and OBS ground coupling effects, all of which alter the transfer function. This paper reviews our method of calibration and discusses the effects of temperature and some of the instrument design features on the vertical seismometer transfer function.  相似文献   

An interview with Paul Witherspoon, distinguished hydrogeologist from the USA     

R. Allan Freeze  Iraj Javandel 《Hydrogeology Journal》2008,16(5):811-815

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Zircon M257 ‐ a Homogeneous Natural Reference Material for the Ion Microprobe U‐Pb Analysis of Zircon     

Lutz Nasdala  Wolfgang Hofmeister  Nicholas Norberg  James M. Martinson  Fernando Corfu  Wolfgang Dörr  Sandra L. Kamo  Allen K. Kennedy  Andreas Kronz  Peter W. Reiners  Dirk Frei  Jan Kosler  Yusheng Wan  Jens Götze  Tobias Häger  Alfred Kröner  John W. Valley 《Geostandards and Geoanalytical Research》2008,32(3):247-265

We introduce and propose zircon M257 as a future reference material for the determination of zircon U‐Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS‐determined, mean isotopic ratios (2s uncertainties) of 0.09100 ± 0.00003 for ²⁰⁶pb/²³⁸U and 0.7392 ± 0.0003 for ²⁰⁷pb/²³⁵U. Its ²⁰⁶pb/²³⁸U age is 561.3 ± 0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U‐Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ～ 840 μg g^?1 U (Th/U ～ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit‐cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the “Sri Lankan trends”, with actinide concentrations, U‐Pb age, and the calculated alpha fluence of 1.66 × 10¹⁸ g^?1. This, and a (U+Th)/He age of 419 ± 9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc‐silicate skarn.  相似文献   

Provenance of the Bosnian Flysch     

Tamás Mikes  Dominik Christ  Rüdiger Petri  István Dunkl  Dirk Frei  Mária Báldi-Beke  Joachim Reitner  Klaus Wemmer  Hazim Hrvatović  Hilmar von Eynatten 《Swiss Journal of Geoscience》2008,101(1):31-54

Sandwiched between the Adriatic Carbonate Platform and the Dinaride Ophiolite Zone, the Bosnian Flysch forms a c. 3000 m thick, intensely folded stack of Upper Jurassic to Cretaceous mixed carbonate and siliciclastic sediments in the Dinarides. New petrographic, heavy mineral, zircon U/Pb and fission-track data as well as biostratigraphic evidence allow us to reconstruct the palaeogeology of the source areas of the Bosnian Flysch basin in late Mesozoic times. Middle Jurassic intraoceanic subduction of the Neotethys was shortly followed by exhumation of the overriding oceanic plate. Trench sedimentation was controlled by a dual sediment supply from the sub-ophiolitic high-grade metamorphic soles and from the distal continental margin of the Adriatic plate. Following obduction onto Adria, from the Jurassic–Cretaceous transition onwards a vast clastic wedge (Vranduk Formation) was developed in front of the leading edge, fed by continental basement units of Adria that experienced Early Cretaceous synsedimentary cooling, by the overlying ophiolitic thrust sheets and by redeposited elements of coeval Urgonian facies reefs grown on the thrust wedge complex. Following mid-Cretaceous deformation and thermal overprint of the Vranduk Formation, the depozone migrated further towards SW and received increasing amounts of redeposited carbonate detritus released from the Adriatic Carbonate Platform margin (Ugar Formation). Subordinate siliciclastic source components indicate changing source rocks on the upper plate, with ophiolites becoming subordinate. The zone of the continental basement previously affected by the Late Jurassic–Early Cretaceous thermal imprint has been removed; instead, the basement mostly supplied detritus with a wide range of pre-Jurassic cooling ages. However, a c. 80 Ma, largely synsedimentary cooling event is also recorded by the Ugar Formation, that contrasts the predominantly Early Cretaceous cooling of the Adriatic basement and suggests, at least locally, a fast exhumation.  相似文献   

Semi-Analytic Stereological Analysis of Waste Package/Fracture Intersections in a Granitic Rock Nuclear Waste Repository   总被引：1，自引：0，他引：1  

Allan Hedin 《Mathematical Geosciences》2008,40(6):619-637

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A dipole field model for axisymmetric alfvén waves with finite ionosphere conductivities     

W. Allan  F.B. Knox 《Planetary and Space Science》1979,27(1):79-85

An axisymmetric model for approximate solution of the magnetospheric Alfvén wave problem at latitudes above the plasmapause is proposed, in which a realistic dipole geometry is combined with finite anisotropic ionosphere conductivities, thus bringing together various ideas of previous authors. It is confirmed that the axisymmetric toroidal and poloidal modes interact via the ionospheric Hall effect, and an approximate method of solution is suggested using previously derived closed solutions of the uncoupled wave equations.A solution for zero Hall conductivity is obtained, which consists of sets of independent shell oscillations, regardless of the magnitude of the Pedersen conductivity. One set reduces to the classical solutions for infinite Pedersen conductivity, while another predicts a new set of harmonics of a quarter-wave fundamental, with longer eigenperiods than the classical solutions for a given L-shell.  相似文献   

Conceptual models in exploration geochemistry: The Canadian cordillera and Canadian shield: P.M.D. Bradshaw (compiler and editor). Association of Exploration Geochemists special publication,no. 3, Elsevier Scientific Publishing Co., Amsterdam—Oxford—New York,N.Y., 1975, 223 pp., Dfl. 39.00/US $ 16.25     

R.J. Allan 《Chemical Geology》1976,18(3):245-250

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