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861.
Geordie Mark Andy Wilde Nicholas H.S. Oliver Patrick J. Williams Chris G. Ryan 《Journal of Geochemical Exploration》2005,85(1):921-46
The Ernest Henry Fe oxide Cu–Au (IOCG) deposit (>ca. 1.51 Ga) is hosted by breccia produced during the waning stages of an evolving hydrothermal system that formed a number of tens of metres to a kilometre scale, pre- and syn-ore alteration halos, although no demonstrable patterns have been attributed to fluids expelled through the outflow zones. However, the recognition of a population of hypersaline fluid inclusions representing the ‘spent’ fluids after Cu–Au deposition at Ernest Henry provides the basis to model the geochemical characteristics of the deposit's outflow zones. Geochemical modeling at 300 °C was undertaken at both high and low fluid/rock ratios via FLUSH models involving three host rock types: (1) granite, (2) calc–silicate rock, and (3) graphitic schist. In models run at high fluid/rock ratios, all rock types are essentially fluid-buffered, and produce an albite–quartz–hematite–barite-rich assemblage, although in low fluid–rock environments, the pH, redox, and geochemical character of the host rock exerts a greater influence on the mineralogy of the alteration assemblages (e.g., andradite, Fe–chlorite, and magnetite). Significant sulphide mineralization was predicted in graphitic schist where sphalerite occurred in both low- and high-porosity models, which indicates the possibility of an association between high-temperature IOCG mineralization and lower temperature base metal mineralization.Cooling experiments (from 300 to 100 °C) using the ‘spent fluids’ predict early high-T (300–200 °C) Na-, Ca-, Fe-, and Mn-rich, magnetite-bearing hydrothermal associations, whereas with cooling to below 200 °C, and with progressive fluid–rock interaction, the system produces rhodochrosite-bearing, hematite–quartz–muscovite–barite-rich assemblages. These results show that the radical geochemical and mineralogical changes associated with cooling and progressive fluid influx are likely to be accompanied by major transformations in the geophysical expression (e.g., spectral and magnetic character) of the alteration in the outflow zone, and highlight the potential link between magnetite- and hematite-bearing IOCG hydrothermal systems. 相似文献
862.
The resolution achievable for chironomid identifications has increased in recent years because of significant improvements
in taxonomic literature. However, high taxonomic resolution requires more training for analysts. Furthermore, with greater
taxonomic resolution, misidentifications and the number of rare, poorly represented taxa in chironomid calibration datasets
may increase. We assessed the effects of various levels of taxonomic resolution on the performance of chironomid-based temperature
inference models (transfer functions) and temperature reconstruction. A calibration dataset consisting of chironomid assemblage
and temperature data from 100 lakes was examined at four levels of taxonomic detail. The coarsest taxonomic resolution primarily
represented identifications to genus or suprageneric level. At the highest level of taxonomic resolution, identification to
genus level was possible for 37% of taxa, and identification below genus was possible for 60% of taxa. Transfer functions
were obtained using Weighted Averaging (WA) and Weighted Averaging-Partial Least Squares (WA-PLS) regression. Cross-validated
performance statistics, such as the root mean square error of prediction (RMSEP) and the coefficient of determination (r
2) between inferred and observed values improved considerably from the lowest taxonomic resolution level (WA: RMSEP 1.91°C,
r
2 0.78; WA-PLS: RMSEP 1.59°C, r
2 0.86) to the highest taxonomic resolution level (WA: RMSEP 1.66°C, r
2 0.84; WA-PLS: RMSEP 1.41°C, r
2 0.89). Reconstructed July air temperatures during the Lateglacial period based on fossil chironomid assemblages from Hijkermeer
(The Netherlands) were similar for all levels of taxonomic resolution, except the coarsest level. At the coarsest taxonomic
level, reconstruction failed to infer one of the known Lateglacial cold episodes in the record. Also, the difference in reconstructed
values based on lowest and highest taxonomic resolutions exceeded sample-specific estimated standard errors of prediction
in several instances. Our results suggest that chironomid-based transfer functions at the highest taxonomic resolution outperform
models based on lower-resolution calibration data. However, transfer functions of intermediate taxonomic resolution produced
results very similar to models based on high-resolution taxonomic data. In studies that include analysts with different levels
of expertise, inference models based on intermediate taxonomic resolution, therefore, might provide an alternative to transfer
functions of maximum taxonomic detail in order to ensure taxonomic consistency between calibration datasets and down-core
records produced by different analysts. 相似文献
863.
Oliver Wetter Christian Pfister Johannes P. Werner Eduardo Zorita Sebastian Wagner Sonia I. Seneviratne Jürgen Herget Uwe Grünewald Jürg Luterbacher Maria-Joao Alcoforado Mariano Barriendos Ursula Bieber Rudolf Brázdil Karl H. Burmeister Chantal Camenisch Antonio Contino Petr Dobrovolný Rüdiger Glaser Iso Himmelsbach Andrea Kiss Oldřich Kotyza Thomas Labbé Danuta Limanówka Laurent Litzenburger Øyvind Nordli Kathleen Pribyl Dag Retsö Dirk Riemann Christian Rohr Werner Siegfried Johan Söderberg Jean-Laurent Spring 《Climatic change》2014,125(3-4):365-367
864.
865.
Michael?C.?JollandsEmail author Hugh?St.?C.?O’Neill J?rg?Hermann 《Contributions to Mineralogy and Petrology》2014,168(3):1055
The diffusion, substitution mechanism and solubility limits of Zr and Hf in synthetic forsterite (Mg2SiO4) and San Carlos olivine (Mg0.9Fe0.1)2SiO4 have been investigated between 1,200 and 1,500 °C as a function of the chemical potentials of the components in the system MgO(FeO)–SiO2–ZrO2(HfO2). The effect of oxygen fugacity and crystallographic orientation were also investigated. The solubilities of Zr in forsterite are highest and diffusion fastest when the coexisting three-phase source assemblage includes ZrSiO4 (zircon) or HfSiO4 (hafnon), and lower and slower, respectively, when the source assemblage includes MgO (periclase). This indicates that Zr and Hf substitute on the octahedral sites in olivine, charge balanced by magnesium vacancies. Diffusion is anisotropic, with rates along the crystal axes increasing in the order a < b < c. The generalized diffusion relationship as a function of chemical activity (as \(a_{{{\text{SiO}}_{2} }}\)), orientation and temperature is: \(logD_{\text{Zr}} = \frac{1}{4}loga_{{{\text{SiO}}_{2} }} + logD_{0} - \left( {\frac{{368 \pm 17\;{\text{kJ}}\;{\text{mol}}^{ - 1} }}{{2.303\;{\text{RT}}}}} \right)\) where the values of log D 0 are ?3.8(±0.5), ?3.4(±0.5) and ?3.1(±0.5) along the a, b and c axes, respectively. Most experiments were conducted in air (fO2 = 10?0.68 bars), but one at fO2 = 10?11.2 bars at 1,400 °C shows no resolvable effect of oxygen fugacity on Zr diffusion. Hf is slightly more soluble in olivine than Zr, but diffuses slightly slower. Diffusivities of Zr in experiments in San Carlos olivine at 1,400 °C, fO2 = 10?6.6 bars are similar to those in forsterite at the same conditions, showing that the controls on diffusivities are adequately captured by the simple system (nominally iron-free) experiments. Diffusivities are in good agreement with those measured by Spandler and O’Neill (Contrib Miner Petrol 159:791–818, 2010) in San Carlos olivine using silicate melt as the source at 1,300 °C, and fall within the range of most measurements of Fe–Mg inter-diffusion in olivine at this temperature. Forsterite–melt partitioning experiments in the CaO–MgO–Al2O3–SiO2–ZrO2/HfO2 show that the interface concentrations from the diffusion experiments represent true equilibrium solubilities. Another test of internal consistency is that the ratios of the interface concentrations between experiments buffered by Mg2SiO4 + Mg2Si2O6 + ZrSiO4 or Mg2SiO4 + ZrSiO4 + ZrO2 (high silica activity) to those buffered by Mg2SiO4 + MgO + ZrO2 (low silica activity) agree well with the ratios calculated from thermodynamic data. This study highlights the importance of buffering chemical potentials in diffusion experiments to provide constraints on the interface diffusant concentrations and hence validate the assumption of interface equilibrium. 相似文献
866.
IRNSS-1A: signal and clock characterization of the Indian regional navigation system 总被引:4,自引:1,他引:3
An initial characterization of the L5 and S-Band navigation signals transmitted by the first satellite of the Indian regional navigation satellite system (IRNSS) is presented. In the absence of a public signal specification, a 30 m high-gain antenna has been used to record the signal spectrum and the modulated chip sequences. For the IRNSS standard positioning service, use of a Gold ranging code is confirmed and relevant shift register parameters for the two frequencies are identified. Based on a prototype receiver, L5 single-frequency code and phase observations of IRNSS-1A have also been collected. The tracking performance is described, and the measurements are used to characterize the short-term clock stability of IRNSS-1A. 相似文献
867.
Atmospheric wet deposition of PAHs to the sea-surface microlayer 总被引:1,自引:1,他引:0
Sea-surface microlayer (SML) and subsurface seawater samples (SSW) collected from Singapore's coastal environment were analyzed for 14 polycyclic aromatic hydrocarbons (PAHs) in the dissolved (DP) and suspended particulate phase (SPM). Samples were collected prior to and after rainfall events to ascertain the contribution of wet atmospheric deposition of PAH enrichment to the SML. The concentration ranges of summation operatorPAHs in the SML before rain and after wet deposition were 2.6-46.2 ngL(-1) and 4.3-278.0 ngL(-1), respectively, for the DP and 3.8-31.4 ngL(-1) and 12.8-1280 ngL(-1), respectively, for the SPM. Load factors (i.e. concentration after wet deposition relative to before wet deposition) of the atmospheric wet deposition for DP and SPM ranged from 1.4 to 42.9 and 1.2 to 337, respectively. This study provides the first data on PAH concentration, enrichment (i.e. concentration of PAHs in SML relative to subsurface water) and load factors in the SML before and after wet deposition to the ocean surface. 相似文献
868.
High-precision high field strength element partitioning between garnet, amphibole and alkaline melt from Kakanui, New Zealand 总被引:2,自引:0,他引:2
The high field strength elements (HFSE: Zr, Hf, Nb, Ta, and W) are an important group of chemical tracers that are increasingly used to investigate magmatic differentiation processes. Successful modeling of these processes requires the availability of accurate mineral-melt partition coefficients (D). To date, these have largely been determined by ion microprobe or laser ablation-ICP-MS analyses of the run products of high-pressure, high-temperature experiments. Since HFSE are (highly) incompatible, relatively immobile, high-charge, and difficult to ionize, these experiments and their analysis are challenging. Here we explore whether high-precision analyses of natural mineral-melt systems can provide additional constraints on HFSE partitioning.The HFSE concentrations in natural garnet and amphibole and their alkaline host melt from Kakanui, New Zealand are determined with high precision isotope dilution on a multi-collector-ICP-MS. Major and trace element compositions combined with Lu-Hf isotopic systematics and detailed petrographic sample analysis are used to assess mineral-melt equilibrium and to provide context for the HFSE D measurements. The whole-rock nephelinite, ∼1 mm sized amphiboles in the nephelinite, and garnet megacrysts have similar initial Hf isotope ratios with a mean initial 176Hf/177Hf(34 Ma) = 0.282900 ± 0.000026 (2σ). In contrast, the amphibole megacrysts are isotopically distinct (176Hf/177Hf(34 Ma) = 0.282830 ± 0.000011). Rare earth element D values for garnet megacryst-nephelinite melt and ∼1 mm amphibole-nephelinite melt plotted as a function of ionic radii show classic near-parabolic trends that are in excellent agreement with crystal lattice-strain models. These observations are consistent with equilibrium between the whole-rock nephelinite, the ∼1 mm amphibole grains within the nephelinite and the garnet megacrysts.High-precision isotope dilution results for Zr and Hf in garnet (DZr = 0.220 ± 0.007 and DHf = 0.216 ± 0.005 [2σ]), and for all HFSE in amphibole are consistent with previous experimental findings. However, our measurements for Nb and Ta in garnet (DNb = 0.0007 ± 0.0001 and DTa = 0.0011 ± 0.0006 [2σ]) show that conventional methods may overestimate Nb and Ta concentrations, thereby overestimating both Nb and Ta absolute D values for garnet by up to 3 orders of magnitude and underestimating DNb/DTa by greater than a factor of 100. As a consequence, the role of residual garnet in imposing Nb/Ta fractionation may be less important than previously thought. Moreover, garnet DHf/DW = 17 and DNb/DZr = 0.003 imply fractionation of Hf from W and Nb from Zr upon garnet crystallization, which may have influenced short-lived 182Hf-182W and 92Nb-92Zr isotopic systems in Hadean time. 相似文献
869.
The global economy is currently experiencing one of its biggest contractions on record. A sharp decline in global imports and exports since 2008 has affected global merchant vessel traffic, the principal mode of bulk commodity transport around the world. During the first quarter of 2009, 10% and 25% of global container and refrigerated vessels, respectively, were reported to be unemployed. A large proportion of these vessels are lying idle at anchor in the coastal waters of South East Asia, sometimes for periods of greater than 3 months. Whilst at anchor, the hulls of such vessels will develop diverse and extensive assemblages of marine biofouling species. Once back in service, these vessels are at risk of transporting higher-than-normal quantities of marine organisms between their respective global trading ports. We discuss the potential ramifications of the global economic crisis on the spread of marine non-indigenous species via global commercial shipping. 相似文献
870.
Ehrenfreund Pascale Krafft Catherine Kochan Hermann Pirronello Valerio 《Earth, Moon, and Planets》1998,80(1-3):1-1
Earth, Moon, and Planets - 相似文献