The solubility of fluorite in hydrothermal solutions,an experimental study     

Catherine K. Richardson  H.D. Holland 《Geochimica et cosmochimica acta》1979,43(8):1313-1325

The solubility of fluorite in NaCl solutions increases with increasing temperature at all ionic strengths up to about 100°C. Above this temperature, the solubility passes through a maximum and possibly a minimum with increasing temperature at NaCl concentrations of 1.0M or less, and increases continuously with increasing temperature at NaCl concentrations above 1.0M. At any given temperature, the solubility of fluorite increases with increasing salt concentration in NaCl, KCl and CaCl₂ solutions. The solubility follows Debye-Hückel theory for KCl solutions. In NaCl and CaCl₂ solutions, the solubility of fluorite increases more rapidly than predicted by Debye-Hückel theory: the excess solubility is due to the presence of NaF^c, CaF⁺, and possibly of Na₂F⁺. The solubility of fluorite in NaCl-CaCl₂ and in NaCl-CaCl₂-MgCl₂ solutions is controlled by the common ion effect and by the presence of NaF^c, CaF⁺, and MgF⁺. The solubility of fluorite in NaCl-HCl solutions increases rapidly with increasing initial HCl concentration; the large solubility increase is due to the presence of HF^c. It seems likely that complexes other than those identified in this study rarely play a major role in fluoride transport and fluorite deposition at temperatures below 300°C.  相似文献   

Fluorite deposition in hydrothermal systems   总被引：1，自引：0，他引：1  

Catherine K. Richardson  H.D. Holland 《Geochimica et cosmochimica acta》1979,43(8):1327-1335

During the formation of fluorite deposits fluorite is precipitated either as a consequence of changes in temperature and pressure along the flow path of hydrothermal solutions or due to fluid mixing, or as the result of the interaction of hydrothermal solutions with wall rocks.A decrease in temperature in the flow direction is the most appealing, though still unproven, mechanism of fluorite deposition in Mississippi Valley fluorite deposits.Mixing can produce solutions which are either undersaturated or supersaturated with respect to fluorite. The most important parameters are the temperature, the salinity, and the calcium and fluoride concentration of the fluids prior to mixing.A variety of wall rock reactions can lead to fluorite precipitation. Among these reactions which increase the pH of initially rather acid (pH ≤ 3) hydrothermal solutions are apt to be particularly important.  相似文献   

Concentrations of polybrominated diphenyl ethers (PBDEs) in Pearl River Delta sediments   总被引：1，自引：0，他引：1  

Zheng GJ  Martin M  Richardson BJ  Yu H  Liu Y  Zhou C  Li J  Hu G  Lam MH  Lam PK 《Marine pollution bulletin》2004,49(5-6):520-524

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Confronted by Insurmountable Opportunities: Geography in Society at the AAG's Centennial*   总被引：1，自引：0，他引：1  

Douglas Richardson  Patricia Solis 《The Professional geographer》2004,56(1):4-11

Geographers at the AAG's centennial are challenged with exceptional opportunities to create a more central place for geography in society and in the university. Realizing these opportunities requires identifying and leveraging key emerging trends in the formation and uses of geographic knowledge. Better integration of geography's profound technological innovations with its core traditions also is necessary to strengthen the discipline's research capacity, and to more effectively engage with and contribute to the needs of society. Trends toward multidisciplinary research and integrative science, and the heightened need for geographic understanding in today's world, hold further promise for advancing the discipline while sustaining its historic strengths and diversity.  相似文献   

Cleaning of lake sediment samples for diatom oxygen isotope analysis   总被引：1，自引：0，他引：1  

David W. Morley  Melanie J. Leng  Anson W. Mackay  Hilary J. Sloane  Patrick Rioual  Richard W. Battarbee 《Journal of Paleolimnology》2004,31(3):391-401

Detrital grain contamination in a diatom sample can considerably influence the δ¹⁸O_diatom signal. In order to obtain a meaningful signal, pure samples must be used. This can be achieved via a series of cleaning stages including organic and carbonate material removal, sieving, differential settling and heavy liquid separation. The method described here works best for sediments with >20% diatom content. Based on testing various clean-up methods, we propose a sequence of four clean-up stages to produce pure diatom samples from a range of lake sediments types starting with a few grams of sediment. The diatom content and the oxygen isotope composition of the samples at each stage were measured in order to assess the effect of differential amounts of contamination. Results show that a four stage clean-up is necessary to produce clean diatom samples and that contamination by silt and clay causes lower δ¹⁸O values.  相似文献   

Uptake and depuration of PAHs and chlorinated pesticides by semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis)     

Bruce J. Richardson  Edmund S.-C. Tse  Sharon B. De Luca-Abbott  Michael Martin  Paul K.S. Lam 《Marine pollution bulletin》2005,51(8-12):975

Semi-batch seawater experiments were conducted to follow the uptake and release of selected PAHs (anthracene, fluorathene, pyrene and B[a]P) and organochlorine pesticides (α-HCH, aldrin, dieldrin, p,p′-DDT) in semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis). Mathematical models were applied to describe the uptake and elimination curves of the contaminants for SPMDs, and kinetic parameters, such as uptake rate constants, and equilibrium triolein/water partitioning coefficients were calculated. SPMD data showed a good fit to estimate rate constant and partition coefficient equations, but only those contaminants which partitioned mainly in the dissolved phase (α-HCH and dieldrin) were well explained for mussels. Poor conformity of the other contaminants indicated mussels uptake by routes other than diffusion, such as ingestion of algae. An apparent equilibrium state was only noted for α-HCH in mussels. Aldrin was not detected in mussels in the first few days of exposure, indicating potential metabolism of this compound. B[a]P was not detected in the triolein of SPMDs, which suggests that the membrane may act as a reservoir. Loss of spiked B[a]P from the triolein was evident in a depuration experiment, which may indicate transfer to the membrane. Rate constants for mussels were higher than those for SPMDs, but the reverse was true for partition coefficients. Overall, mussels and SPMDs had similar uptake rates for all compounds in this study, excluding p,p′-DDT and dieldrin. Contaminant elimination took place more rapidly in mussels, implying that SPMDs are better candidates for detecting episodic discharge of organic contaminants.  相似文献   

Evidence from kimberlitic zircon for a decreasing mantle Th/U since the Archean     

Robert Eugene Zartman  Stephen H. Richardson 《Chemical Geology》2005,220(3-4):263-283

A decoupling in MORB of measured Th/U (κ = 2.5) from that calculated by Pb isotopes (κ = 3.8) for the depleted asthenosphere is well established, and has been referred to as the second Pb paradox (Kramers, J.D., and Tolstikhin, I.N., 1997. Two terrestrial lead isotope paradoxes, forward transport modelling, core formation and the history of the continental crust. Chem. Geol., 139, 75–110.) or the kappa conundrum (Elliott, T., Zindler, A., and Bourdon, B., 1999. Exploring the kappa conundrum: the role of recycling in the lead isotope evolution of the mantle. Earth Planet. Sci. Lett., 169, 129–145.). More controversial has been the cause and timing of this phenomenon, although a higher return flux of U⁶⁺ relative to Th⁴⁺ and(or) the recycling of crustal Pb into the mantle have become the preferred explanations of most workers. Such a combined mechanism effectively operating over the past 2.5 Ga was modelled in plumbotectonics (Zartman, R.E., and Haines, S., 1988. The plumbotectonics model for Pb isotopic systematics among major terrestrial reservoirs—a case for bi–directional transport. Geochim. Cosmochim. Acta, 52, 1327–1339. 709.33.), and found to be quantitatively feasible.A large TIMS, SIMS and LA-ICPMS database of Th and U concentrations for kimberlite-hosted zircon, particularly from Cr-poor megacrystic suites, now exists (Kinny et al., 1989, Berryman et al., 1999, Griffin et al., 2000 and Spetsius et al., 2002; Appendix A and Appendix B, this work). Six suites comprising 10 or more zircon grains with ages between 90 and 2550 Ma reveal consistent patterns when plotted on Th/U vs. U diagrams. We interpret these patterns as resulting from fractional crystallization of a melt with kimberlite affinity presumably derived from the asthenosphere, permitting the extrapolation to an initial Th/U at the time zircon crystallization began. A two-fold decrease is seen in this ratio over the past 2.5 Ga, suggesting that during this time a similar change has occurred in the parent silicate melt. Estimates of Th and U distribution coefficients between zircon and coexisting melt permit calculation of Th/U in the melt, which, for these highly incompatible elements, presumably is the same as for its mantle source rock. Kimberlitic zircon may thus indeed give evidence of a reduction in κ, tentatively calculated as from 4 to 2, since the Archean for the depleted asthenosphere.  相似文献   

Manganese oxidation in pH and O2 microenvironments produced by phytoplankton     

Richardson LL  Aguilar C  Nealson KH 《Limnology and oceanography》1988,33(3):352-363

Pure cultures of Chlorella sp. catalyzed the oxidation of soluble Mn(II) to particulate, extracellular, manganic oxides. Manganese oxidation was dependent on photosynthetic activity: no oxidation was observed in the dark when cells were grown heterotrophically on glucose, or in the light when photosystem II was inhibited by the addition of DCMU. Manganates were not formed when media were buffered below pH 8.0, suggesting that an important driving force for manganese oxidation was the high pH resulting from photosynthesis. Field studies with minielectrodes in Oneida Lake, New York, demonstrated steep gradients of O2 and pH and the presence of particulate manganic oxides associated with pelagic aggregates of the cyanobacterium Microcystis sp. The manganese oxidation reaction apparently occurs only when photosynthesizing algae are present as dense populations that can generate microenvironments of high (>9.0) pH, either as aggregates in the pelagic zone or concentrated cell cultures in the laboratory. A large-scale transition from soluble to particulate manganese was measured in the surface waters of Oneida Lake throughout summer 1986. Removal of Mn(II) was correlated with the presence of aggregate-forming cyanobacteria that oxidize Mn(II) by the mechanism described above.  相似文献   

Lower crustal granulite xenoliths from the Pannonian Basin,Hungary. Part 1: mineral chemistry,thermobarometry and petrology   总被引：1，自引：0，他引：1  

Antal Embey-Isztin  Hilary Downes  Pamela D. Kempton  Gábor Dobosi  Matthew Thirlwall 《Contributions to Mineralogy and Petrology》2003,144(6):652-670

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Regional patterns in the paragenesis and age of inclusions in diamond, diamond composition, and the lithospheric seismic structure of Southern Africa   总被引：1，自引：0，他引：1  

Steven B. Shirey  Jeffrey W. Harris  Stephen H. Richardson  Matthew Fouch  David E. James  Pierre Cartigny  Peter Deines  Fanus Viljoen 《Lithos》2003,71(2-4):243-258

The Archean lithospheric mantle beneath the Kaapvaal–Zimbabwe craton of Southern Africa shows ±1% variations in seismic P-wave velocity at depths within the diamond stability field (150–250 km) that correlate regionally with differences in the composition of diamonds and their syngenetic inclusions. Seismically slower mantle trends from the mantle below Swaziland to that below southeastern Botswana, roughly following the surface outcrop pattern of the Bushveld-Molopo Farms Complex. Seismically slower mantle also is evident under the southwestern side of the Zimbabwe craton below crust metamorphosed around 2 Ga. Individual eclogitic sulfide inclusions in diamonds from the Kimberley area kimberlites, Koffiefontein, Orapa, and Jwaneng have Re–Os isotopic ages that range from circa 2.9 Ga to the Proterozoic and show little correspondence with these lithospheric variations. However, silicate inclusions in diamonds and their host diamond compositions for the above kimberlites, Finsch, Jagersfontein, Roberts Victor, Premier, Venetia, and Letlhakane do show some regional relationship to the seismic velocity of the lithosphere. Mantle lithosphere with slower P-wave velocity correlates with a greater proportion of eclogitic versus peridotitic silicate inclusions in diamond, a greater incidence of younger Sm–Nd ages of silicate inclusions, a greater proportion of diamonds with lighter C isotopic composition, and a lower percentage of low-N diamonds whereas the converse is true for diamonds from higher velocity mantle. The oldest formation ages of diamonds indicate that the mantle keels which became continental nuclei were created by middle Archean (3.2–3.3 Ga) mantle depletion events with high degrees of melting and early harzburgite formation. The predominance of sulfide inclusions that are eclogitic in the 2.9 Ga age population links late Archean (2.9 Ga) subduction-accretion events involving an oceanic lithosphere component to craton stabilization. These events resulted in a widely distributed younger Archean generation of eclogitic diamonds in the lithospheric mantle. Subsequent Proterozoic tectonic and magmatic events altered the composition of the continental lithosphere and added new lherzolitic and eclogitic diamonds to the already extensive Archean diamond suite.  相似文献