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  • 1
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    American Geophysical Union
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q11004, doi:10.1029/2005GC001216.
    Description: The Sr/Ca ratio of biogenic carbonate is widely used as a proxy for paleotemperature. This application is supported by empirical calibrations of Sr/Ca as a function of temperature, but it is also known that Sr uptake in calcite gauged by KdSr=(Sr/Ca)calcite/(Sr/Ca)solution is affected by other variables, including bulk precipitation rate (Kd Sr increases with increasing precipitation rate). There are no data from controlled experiments specifically addressing the effect of radial growth rate of individual crystals on Kd Sr. For this reason, we conducted two series of experiments to explore Sr partitioning at varying growth rates: (1) growth from a CaCl2–NH4Cl–SrCl2 solution by diffusion of CO2 from an ammonium carbonate source (“drift” experiments) and (2) “drip” precipitation of calcite on a substrate, using a steady flow of CaCl2–SrCl2 and Na2CO3 solutions, mixed just before passage through a tube and dripped onto a glass slide precoated with calcite (“cave-type” experiments). The growth rates of individual crystals were determined by periodic monitoring of crystal size through time or, roughly, by comparison of the final size with the duration of the experiment. Electron microprobe analyses across sectioned crystals grown in the drift experiments show that the concentration of Sr is high in the center (where radial growth rates are highest) and decreases systematically toward the edge. The center-to-edge drop in Sr concentration is a consequence of the slowing radial growth rate as individual crystals become larger. In general, high crystal growth rate (V) enhances Sr uptake in calcite due to a type of kinetic disequilibrium we refer to as “growth entrapment.” The apparent Kd Sr ranges from 0.12 to 0.35 as V increases from 0.01 nm/s to 1 μm/s at 25°C.
    Description: This work was supported by the National Science Foundation through grants EAR-9804794 and EAR-0337481 to E. B. Watson.
    Keywords: Calcite ; Partitioning ; Fluid ; Growth rate ; Strontium ; Temperature
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q03001, doi:10.1029/2010GC003322.
    Description: In situ secondary ion mass spectrometry (SIMS) analyses of δ7Li, Li/Ca, and Mg/Ca were performed on five synthetic aragonite samples precipitated from seawater at 25°C at different rates. The compositions of δ7Li in bulk aragonites and experimental fluids were measured by multicollector inductively coupled plasma–mass spectrometry (MC-ICP-MS). Both techniques yielded similar δ7Li in aragonite when SIMS analyses were corrected to calcium carbonate reference materials. Fractionation factors α7Li/6Li range from 0.9895 to 0.9923, which translates to a fractionation between aragonite and fluid from −10.5‰ to −7.7‰. The within-sample δ7Li range determined by SIMS is up to 27‰, exceeding the difference between bulk δ7Li analyses of different aragonite precipitates. Moreover, the centers of aragonite hemispherical bundles (spherulites) are enriched in Li/Ca and Mg/Ca relative to spherulite fibers by up to factors of 2 and 8, respectively. The Li/Ca and Mg/Ca ratios of spherulite fibers increase with aragonite precipitation rate. These results suggest that precipitation rate is a potentially important consideration when using Li isotopes and elemental ratios in natural carbonates as a proxy for seawater composition and temperature.
    Description: SIMS analyses were supported by U.S. NSF, EAR, Instrumentation and Facilities Program. The development of the method for bulk d7Li analysis and the MC‐ICP‐MS measurements were covered by NSF grant EAR/IF‐0318137. Precipitation experiments were supported by NSF through grants OCE‐0402728, OCE‐0527350, and OCE‐0823527 to Glenn Gaetani and Anne Cohen and through grant EAR‐0337481 to Bruce Watson.
    Keywords: Isotope ; Aragonite ; Rate ; SIMS ; Magnesium ; Lithium
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 99 (1988), S. 306-319 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Laboratory experiments near 1450° C at 1 bar (QFM) on komatiite bulk composition show olivine and liquid in cumulus textures which evolve with experiment duration. Orthocumulus texture with settled olivine crystals separated by liquid matrix is developed within a day. Experiments quenched after a few days to a week show a progression of textures which include development of columns of olivine crystals separated by channels of liquid. Olivine grain sizes increase with the cube root of time suggesting that dissolution and reprecipitation of olivine may be involved in the organization into columns and channels. Experiments quenched after two weeks have well developed adcumulus texture. The basal polycrystalline granular olivine aggregate forms from the decay of the olivine columns. Melt expulsion from the aggregate can be virtually complete, leaving 1% or less of the melt originally present. Buoyancy-driven compaction of olivine is not the mechanism responsible for this textural evolution because the final basal aggregate sometimes contains vesicles. An addition proof of the inadequacy of buoyancy is provided by raising the crucible slightly above the thermal symmetry point of the furnace. The aggregate then compacts on top of a crystal-free liquid. The thermal gradients above and below the furnace hot spot are thought to be primarily responsible for the olivine redistributions observed. Diffusion of olivine components in the liquid is driven along a saturation gradient resulting from the temperature gradient. The process, called thermal migration in geological literature, is essentially the same as traveling solvent zone refining in metallurgy. Differential solubility and Soret fractionation both contribute to olivine redistribution to the cold region of the crystal-liquid aggregate. There may be some applications of these results to natural cumulate rock petrogenesis.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 127 (1997), S. 383-390 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Diffusion rates for the three tetravalent cations U, Th and Hf have been measured in synthetic zircon. Diffusant sources included oxide powders and ground pre-synthesized silicates. Rutherford backscattering spectrometry (RBS) was used to measure depth profiles. Over the temperature range 1400–1650 °C, the following Arrhenius relations were obtained (diffusion coefficients in m2sec−1): log D Th = (1.936 ± 0.9820) + (− 792 ± 34 kJ mol−1 /2.303 RT) log D U = (0.212 ± 2.440) + (− 726 ± 83 kJ mol−1 /2.303 RT) log D Hf = (3.206 ± 1.592) + (− 812 ± 54 kJ mol−1 /2.303 RT) The data show a systematic increase in diffusivity with decreasing ionic radius (i.e., faster diffusion rates for Hf than for U or Th), a trend also observed in our earlier study of rare earth diffusion in zircon. Diffusive fractionation may be a factor in the Lu-Hf system given the much slower diffusion rates of tetravalent cations when compared with the trivalent rare earths. The very slow diffusion rates measured for these tetravalent cations suggest that they are essentially immobile under most geologic conditions, permitting the preservation of fine-scale chemical zoning and isotopic signatures of inherited cores.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 130 (1997), S. 66-80 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The diffusivity (D) of dissolved SiO2 in quartz-saturated H2O was determined at 1 GPa and ∼530–870 °C using a custom-designed Ag diffusion cell consisting of two chambers – both containing quartz + H2O – connected by a narrow capillary. During a diffusion experiment, quartz saturation was maintained at different levels in the two chambers by placing the diffusion cell in the thermal gradient of a standard piston-cylinder assembly. The diffusivity was computed from the total mass of SiO2 transported from the “hot” to the “cold” chamber during the course of an experiment. Over the temperature range investigated, the results conform to an Arrhenius-type dependence of D SiO2 (m2/s) upon T(K)−1: The significance of the constants in this equation (in particular, the ∼52 kJ/mole apparent activation energy) is uncertain, because the SiO2 content of the fluid varies markedly with temperature, due to the strong temperature dependence of quartz solubility. Nevertheless, the above expression is probably a good representation of the temperature dependence of D SiO2 in the crust, where aqueous fluids are likely to approach quartz saturation at all depths. One experimental result at 0.6 GPa suggests little dependence of D SiO2 upon pressure at crustal conditions. At the low end of the temperature range investigated, the measured diffusivities are identical to values calculated from the Stokes-Einstein equation using high P-T viscosity estimates for H2O. Disagreement between measured and calculated diffusivities at higher temperatures (a factor of ∼4 at 850 °C) may be due to one or more of the following factors: (1) inadequacy of the Stokes-Einstein relationship as a description of transport in supercritical H2O; (2) inaccuracy of viscosity estimates of H2O; or (3) concentration effects on diffusion over the temperature range investigated. Given the presence of interconnected porosity in deep-seated rocks, the diffusive transport distances for aqueous silica implied by the above equation are impressive even on a geologic scale, exceeding 0.5 km in 106 years at temperatures of 500 °C or higher. The combined effect of the high D SiO2 with the high and strongly temperature-dependent solubility of quartz at crustal conditions raises the possibility of significant diffusive fluxes through a stationary fluid in a normal geothermal gradient.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 79 (1982), S. 96-105 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Two separate series of hydrous experiments involving (1) imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite, and (2) crystallizing similar natural rock compositions progressively until apatite appears, demonstrate a close dependence between apatite saturation and silica content of the magma, and determine P2O5 levels at a given silica value and temperature at which that composition may be expected to crystallize apatite. The effect of pressure on apatite solubility is not great, and is most significant for silicic compositions. P2O5 vs SiO2 relationships of the low-K island arc suite, calcalkaline suite and high-K calc-alkaline suite, appear regular and characteristic for each suite, and when linked with the experimental work on apatite solubility, indicate the following: (1) the low-K and calc-alkaline series have low P2O5 contents (∼0.1–0.2 wt.%) and relatively flat P2O5-SiO2 patterns; they do not show evidence of reaching apatite saturation until rhyodacite-rhyolite compositions are obtained for the low-K suite, and andesite-dacite compositions for the calc-alkaline suite; (2) the high-K calc-alkaline series has higher P2O5 contents (∼0.4–0.6 wt.%) in mafic compositions, and achieves apatite saturation over a wide compositional range for the series; (3) the calc-alkaline and high-K calc-alkaline series are probably lower temperature, and more hydrous than the low-K series; (4) anomalous P2O5-SiO2 distributions may indicate non-equilibrium crystallization of apatite, magma-mixing and crystal accumulation processes active in generation of the ‘orogenic’ volcanic series.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of engineering mathematics 25 (1991), S. 115-135 
    ISSN: 1573-2703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract A number of problems are solved for the resonant frequencies of oscillation of a fluid in rectangular or circular containers having internal bodies such as surface or bottom-mounted vertical blocks or circular apertures in the top surface. The variation of these frequencies with the dimensions of the bodies is obtained. The method uses matched eigenfunction expansions and Galerkin expansions to derive explicit forms for the elementsS ijof a 2×2 matrix required in the course of the solution. An approximate formula for an arbitrary-shaped body in a container which gives good agreement with the more accurate Galerkin approach is used to solve the resonant frequencies when the internal body is a submerged cylinder.
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  • 8
    Publication Date: 2008-06-16
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 9
    Publication Date: 2015-10-02
    Description: The diffusivity of phosphorus in San Carlos olivine (SCO) was measured at near-atmospheric pressure and 650–850 °C by in-diffusion of P from a surface powder source consisting of pre-reacted SCO and AlPO 4 . The experiments were conducted in evacuated silica-glass ampoules at oxygen fugacities fixed by solid-state buffers, generally Ni-NiO but also including two experiments buffered at wüstite-magnetite. Phosphorus uptake profiles were characterized by Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA). The temperature dependence of P diffusion in SCO conforms to the expected Arrhenius relation D = D 0 exp(– E a /R T ), where the constants are as follows: log( D 0 , m 2 /s) = –10.06 ± 0.80 and E a = 229 ± 16 kJ/mol. These values characterize P as a relatively slow diffuser in olivine—slower by about an order of magnitude than Cr and Ca at basalt near-liquidus temperatures—but substantially faster than Si. With a view toward modeling P uptake during rapid growth of natural olivines, P diffusion was also characterized in dry MORB basalt melt over the temperature range 1250–1500 °C at 1 GPa, using traditional diffusion couples contained in graphite. Phosphorus diffusion profiles in the quenched and depressurized samples were quantified by laser-ablation ICP/MS. Phosphorus diffusion in basaltic melt is similar to that of Si, with log( D 0 , m 2 /s) = –6.30 ± 0.7 and E a = 147 ± 22 kJ/mol. The new data for P diffusion in olivine and basalt melt can be used to explore the acquisition of fine-scale zoning in natural olivine phenocrysts through kinetic models, as well as the survival of P zoning in olivine with time spent at elevated temperature. Models of growth entrapment of a P-enriched near-surface layer in the olivine lattice indicate that crystal growth at plausible sustained rates is indeed likely to result in regions of anomalously high P content in the resulting crystal. Phosphorus concentrations above the equilibrium partitioning value can also result from development of a diffusive boundary layer in the melt against a rapidly growing crystal, but this mechanism is ineffective at typical sustained olivine growth rates, requiring dendrite-forming growth speeds. Preservation of P zoning on the scale of a few micrometers apparently requires cooling within a few months of formation of the zoning.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
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  • 10
    Publication Date: 2013-08-20
    Description: Diffusion of helium has been characterized in natural monazite and synthetic LREE phosphates. Polished slabs of natural monazite and flat growth faces of synthetic phosphates were implanted with 100 keV 3 He at a dose of 5 x 10 15 3 He/cm 2 and annealed in 1 atm furnaces. 3 He distributions in monazites following experiments were measured with nuclear reaction analysis using the reaction 3 He(d,p) 4 He. For diffusion in monazite we obtain the following Arrhenius relation for diffusion normal to (100) \[ \hbox{ D }=1.60\times {10}^{-7}\hbox{ exp }(-150\pm 8\hspace{0.17em}\hbox{ kJ }/\hbox{ mol }/\hbox{ RT })\hspace{0.17em}{\hbox{ m }}^{2}/\hbox{ s }. \] Diffusion in natural monazite exhibits little diffusional anisotropy, as diffusion normal to (001), (100), and (010) appear similar, as do diffusivities of He in natural monazites from two different localities. Over the investigated temperature range, these diffusivities are similar to those of Farley and Stockli (2002) , and values obtained for some of the monazite grains analyzed by Boyce et al. (2005) , obtained through bulk-release of He by step heating, and are bracketed by diffusivities obtained by Farley (2007) for monazite-structure synthetic REE phosphates. Helium diffusion measured in synthetic REE phosphates (LaPO 4 , NdPO 4 , SmPO 4 , and EuPO 4 ) with the monazite structure appears to behave systematically, with diffusion in the lighter REE phosphates slightly faster than in the heavier REE phosphates. This trend is in broad agreement with the findings of Farley (2007) , but the difference in diffusivities among the REE phosphates is smaller than that reported by Farley (2007) . Activation energies for He diffusion in the synthetic LREE phosphates are similar to that for natural monazite measured in this study, but He diffusivities in synthetic LaPO 4 are about an order of magnitude faster than in the natural monazites. The differences in He diffusivities among the natural monazites and synthetic REE phosphates may be a consequence of the density and distribution of interstitial apertures in the crystal structure, which may result in differences in He migration rates. The similarities in He diffusivities for natural monazites containing varying mixtures of rare-earth elements, as well as differences in Th contents, however, indicate that the above Arrhenius relation is most relevant for describing He diffusion in monazite in nature. We use this Arrhenius relation to evaluate He retentivity in monazite experiencing thermal events, using both the closure temperature formulation of Dodson (1973) and recently developed expressions ( Watson and Cherniak 2013 ) for prograde thermal events and heating and cooling trajectories. Calculations indicate that monazite is relatively retentive of He compared with accessory mineral phases.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
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