Photoluminescence of zircon (ZrSiO4) doped with REE3+ (REE = Pr, Sm, Eu, Gd, Dy, Ho, Er)     

Henrik Friis  Adrian A. Finch  C. Terry Williams  John M. Hanchar 《Physics and Chemistry of Minerals》2010,37(6):333-342

The photoluminescence properties of synthetic zircon, ZrSiO₄, doped with REE³⁺ (REE = Pr, Sm, Eu, Gd, Dy, Ho, Er) were investigated using combined excitation and emission spectroscopy. All samples showed luminescence characteristics of intra-ion energy transitions, similar to other lanthanide-doped materials. However, the relative intensities were dependent on the energy of excitation and the presence of charge-transfer bands were inferred from excitation spectra. From the data, we conclude that the lanthanides in zircon occur in more than one type of coordination. Energy transfer between different lanthanides was observed in some co-doped samples and emissions that were unassigned in previous studies have been assigned to specific lanthanides based on excitation spectroscopy.  相似文献   

Submicroscopic accessory minerals overprinting clay mineral REE patterns (celadonite–glauconite group examples)     

Erzsébet Tóth  Tamás G. Weiszburg  Teresa Jeffries  C. Terry Williams  András Bartha  Éva Bertalan  Ildikó Cora 《Chemical Geology》2010,269(3-4):312-328

Samples of glauconite, representing different stages of glauconitisation, as well as different formation environments, were analysed for rare earth elements (REE) and other trace elements using a combination of bulk sample and spatially-resolved in situ techniques. The results indicate that the high-sensitivity, spatially-resolved technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) produces values up to two orders of magnitude lower than the bulk sample analyses. This suggests that submicroscopic rare earth element-bearing phases are distributed within the glauconite aggregates comprising the bulk samples. Analytical scanning electron microscopy (ASEM) revealed the presence of micrometre-sized grains of apatite and pore filling precipitates of an unidentified (REE, Ca)-phosphate (approximate composition Ca_0.3–0.4(Ce_0.4La_0.1–0.2Nd_0.1)PO₄) in some glauconite grains.The inherent REE concentrations of the glauconite aggregates (i.e., glauconite crystallites without accidental mechanical inclusions or authigenic, not layer silicate mineral precipitates) was found to be relatively low (e.g., typically less than 100 ppm), and this value decreased with increasing glauconitisation (smectite–mica transformation through a series of recrystallisation processes). These results suggest that the REEs substitute for Ca in the interlayer space of the layer silicate structure and, therefore, the REE content decreases as Ca is progressively removed from the interlayer (smectite–mica transition).LA-ICP-MS, when combined with electron probe microanalysis (EPMA) or ASEM, offers an opportunity to exclude submicroscopic accessory minerals from glauconite trace element analyses, and so produces reliable trace element data for the respective minerals which host those elements.These results illustrate that accessory minerals are difficult to eliminate from clay samples, and that care needs to be taken in the interpretation of clay mineral REE distributions, irrespective of the aggregation state of the studied clay (i.e., whether finely dispersed within the sedimentary rock, or forming millimetre-sized aggregates). Model calculations showed that authigenic apatite associated with the studied green marine clays tends to have higher REE content than “bioapatites”, the total REE content being above 10 000 ppm.  相似文献   

International Association of Geomorphologists Newsletter No. 18 (3/2001)     

Paul Williams  Selma Simes De Castro  Janet Hooke  Wang Ying  Vít Vilímek  Karl‐Heinz Schmidt  Anto Raukas  Tsuguo Sunamura  Algimantas Cesnulevicios  Irasema Alcntara‐Ayala  James P. Terry  Milos Stankoviansky  Carol P. Harden 《地球表面变化过程与地形》2001,26(12):1353-1360

  相似文献   

Brightness predictions for comets     

Daniel W E Green  Brian G Marsden  Charles S Morris 《Astronomy& Geophysics》2001,42(1):1.11-1.12

Daniel W E Green, Brian G Marsden and Charles S Morris write with the aim of illuminating the issue of cometary light curves and brightness predictions, following the publication in this journal last October of the letter by John McFarland (2000).  相似文献   

The use of stochastic simulations and geophysical logs to characterize spatial heterogeneity in hydrogeologic parameters     

Terry D. Lahm  E. Scott Bair  Franklin W. Schwartz 《Mathematical Geology》1995,27(2):259-278

  相似文献   

Reflections on measurement of residual stress in rock     

Terry E. Tullis 《Pure and Applied Geophysics》1977,115(1-2):57-68

Consideration of the behaviour of elastic bodies shows that it is not possible for a set of overcoring measurements that are made within isolated blocks to show residual strains or stresses that have a non-zero average, unless the size of the equilibrium volume over which the residual stresses balance is both considerably larger than the volume of the overcore and smaller than the size of the isolated block. Since some results have been reported that do not match these constraints, non-elastic behaviour must have occurred during overcoring. A possible explanation, is that oriented microcracks are somehow opened by the overcoring. In some cases, stress fields induced by microcracking near the overcoring cut may explain measured strain changes far from the cut. Consideration of various reported measurements in terms of relative sizes of overcoring and equilibrium volumes shows that care is necessary when interpreting residual stress measurements.  相似文献   

A natural example of the simultaneous operation of free-face dissolution and pressure solution     

Terry Engelder 《Geochimica et cosmochimica acta》1982,46(1):69-74

The dissolution of crinoid columnals during tectonic deformation of the Appalachian Plateau was enhanced by stress-induced changes of chemical potential of calcite in solution at the surface of the crinoid columnal. Pressure solution on the outside surface occurred within areas of highest normal stress developed at grain to grain contacts whereas free-face dissolution on the inside bore (the axial canal) of the columnal occurred where parts of the crystal lattice next to the surface were subject to the highest strain, as indicated by the presence of mechanical twins. For free-face dissolution, the chemical potential of the solute is affected more by the larger strain energy associated with mechanical twinning than strain energy from elastic strain prior to mechanical twinning of the crystal lattice. These observations suggest that free-face dissolution as well as pressure solution may contribute significantly to dissolution during rock deformation by diffusive mass transfer.  相似文献   

Geochemical distribution of hydrocarbons in sediments from mid-Narragansett Bay,Rhode Island     

Terry L. Wade  James G. Quinn 《Organic Geochemistry》1979,1(3):157-167

The concentration of hydrocarbons (saturated and aromatic) and synthetic chlorinated compounds (Chlordane, DDT, and PCBs) decreased with depth in sediment cores from mid-Narragansett Bay and reached background levels at different depths. These depths were in general agreement with those expected based on the chronological inputs of these materials to the Bay. Although the total hydrocarbons concentration decreased with depth, the biogenic n-alkanes (n-C_{25,27,29,31,33}) showed a fairly constant concentration with depth as did the organic carbon content of these sediments. The n-alkane odd/even ratio increased with depth in the cores. Size fractionation (> 45 μm and < 45 to > 0.3 μm) of two core sections showed more hydrocarbons associated with the smaller size fraction in the surface section, while the lower section had approximately equal concentrations in both fractions. These trends suggest that over the time period covered by these cores the inputs of biogenic materials has remained relatively constant, while the input of anthropogenic hydrocarbons has increased dramatically during the last 100 yr. This increase is probably due to the expanded use of petroleum over this time period and subsequent chronic inputs to this estuarine environment.  相似文献   

Cadmium levels and carbohydrate metabolism in limpets     

Roger Shore  Gordon Carney  Terry Stygall 《Marine pollution bulletin》1975,6(12):187-189

Limpets from several sites in the Bristol Channel exhibiting varying degrees of cadmium contamination have been studied. Investigations involved glucose levels and certain aspects of glucose metabolism. The results tentatively suggest that there may be a correlation between cadmium levels and reduced ability to utilize glucose.  相似文献   

Galveston Bay: Temporal changes in the concentrations of trace organic contaminants in national status and trends oysters (1986–1994)     

Thomas J. Jackson  Terry L. Wade  José L. Sericano  James M. Brooks  Jennifer M. Wong  Bernardo Garcia-Romero  Thomas J. McDonald 《Estuaries and Coasts》1998,21(4):718-730

The temporal distributions for six classes of trace organic contaminants (chlordanes, DDTs, dieldrin, PAHs, PCBs, and butyltins) in oysters from six Galveston Bay sites from National Oceanic and Atmospheric Administration’s National Status and Trends (NS&T) Mussel Watch Program are compared with other NS&T sites from the Gulf of Mexico as well as all NS&T sites of the United States (East Coast, West Coast, and Gulf of Mexico). Decreases in the median for the Gulf-wide concentration of chlordanes, dieldrin, and butyltins occurred during 1986–1994. The Gulfwide median concentrations of DDTs, PAHs, and PCBs exhibited a strong cyclic distribution with time. For Galveston Bay oysters, “high” concentration is defined as the concentration greater than the median plus one standard deviation for all Gulf of Mexico sites. The percentage of sites having high concentrations during 1986–1994 for Galveston Bay oysters are 49% for dieldrin, 45% for butyltins, 40% for chlordanes, 38% for PCBs, 30% for PAHs, and 21% for DDTs. For PCBs, 43% of Galveston Bay oyster samples analyzed over the first 9 yr have concentrations high enough for potential biological effects to be observed in oysters. The percentages in other agents were chlordanes (22%), butyltins (22%), dieldrin (5%), and PAHs (4%). National Academy of Science-proposed regulatory limits for oysters were exceeded in only 2% of Galveston Bay samples for DDTs and 1% for PCBs. All other contaminants were below proposed NAS limits.  相似文献