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21.
A method to estimate the oxygen fugacity (fO2) during the crystallizationof kimberlites is developed using the Fe content of CaTiO3 perovskite(Pv), a common groundmass phase in these rocks. With increasingfO2, more Fe exists in the kimberlitic liquid as Fe3+, and thuspartitions into Pv. Experiments to study the partitioning ofFe between Pv and kimberlite liquid were conducted at 100 kPaon simple and complex anhydrous kimberlite bulk compositionsfrom 1130 to 1300°C over a range of fO2 from NNO 5 to NNO + 4 (where NNO is the nickelnickel oxide buffer),and at Nb and rare earth element (REE) contents in the startingmaterials of 05 wt % and 1500 ppm, respectively. Thepartitioning of Fe between Pv and kimberlite liquid is influencedmostly by fO2, although the presence of Nb increases the partitionof Fe3+ into perovskite at a given T and fO2. Multiple linearregression (MLR) of all the experimental data produces a relationshipthat describes the variation of Fe and Nb in Pv with fO2 relativeto the NNO buffer:
(uncertaintiesat 2, and Nb and Fe as cations per three oxygens). Over therange of conditions of our experiments, this relationship showsno temperature (T) dependence, is not affected by the bulk Fecontent of the kimberlite starting material and reproduces experimentaldata to within 1 log fO2 unit. KEY WORDS: kimberlites; oxygen fugacity; perovskite; ferric iron; magma 相似文献
22.
The abundances of the mildly incompatible elements Al, Cr, V, Sc and Yb in more than 1700 mantle peridotite bulk rock analyses are interpreted in the light of a fractional melting model based on experimentally measured partition coefficients (D) and melting reaction stoichiometries. All peridotites examined, irrespective of sample type (abyssal peridotites, orogenic massifs, ophiolites, on/off craton xenoliths), tectonic environment (divergent/convergent/passive margin, intraplate) or the pressure (P) they last equilibrated at in the mantle (plagioclase-, spinel- , or garnet facies), originated as residues at less than 3 GPa, mainly within the spinel-facies. Mantle rocks currently in the garnet facies likely were originally spinel-facies lithosphere underthrust or subducted to greater depths in convergent margins. This view is inescapable even within the widest range of D values employed in the calculations, and is furthermore strengthened when metasomatic effects on the abundances of the mildly incompatible elements in residues are considered. A pressure of origin of below 3 GPa for most mantle lithosphere creates difficulties for any model ascribing a significant volume of deep, cratonic mantle roots to plume sub-cretion or any other vertical tectonic mechanism. 相似文献
23.
Dante S. Lauretta 《Meteoritics & planetary science》2011,46(7):930-931
24.
Abstract– The study of aqueous alteration of kamacite in CM chondrites provides insight on the conditions, products, and relative timing of aqueous alteration. We studied unaltered, partially altered, and fully altered kamacite grains from Murray, Murchison, Cold Bokkeveld, and Nogoya using optical microscopy, electron microprobe analysis, scanning electron microscopy, and Raman spectroscopy. From textual evidence and chemical analysis, we established three separate microchemical environments. 1) In a microchemical environment with a high S activity, kamacite alters to form tochilinite, P‐bearing sulfides, eskolaite, and schreibersite. Mass balance calculations show that 81% of the Fe in kamacite is removed from the alteration region, making it available for the formation of other minerals or Fe‐rich aureoles. The release of Fe can alter the mesostasis of type‐I chondrules forming cronstedtite. 2) In a microchemical environment with a high Si activity and a low S activity, kamacite alters to form cronstedtite with small accessory sulfide inclusions. 3) A microchemical environment with limited S and Si activity results in kamacite alteration forming magnetite. The resulting magnetite retains associated Ni that can distinguish it from precipitated magnetite. In addition, the accessory phases of pentlandite and apatite can be formed if S or Ca are present. Finally, we note that small tochilinite grains in the matrix lack typical Ni, P, and Co levels, suggesting that they did not form from kamacite but possibly by sulfidization of magnetite. 相似文献
25.
Napolitano Dante C. Rocha Cesar B. da Silveira Ilson C. A. Simoes-Sousa Iury T. Flierl Glenn R. 《Ocean Dynamics》2021,71(3):281-292
Ocean Dynamics - South of the Vitória-Trindade Ridge, a seamount chain off East Brazil, the Brazil Current (BC) meanders cyclonically within Tubarão Bight, occasionally forming the... 相似文献
26.
Monticellite is a common magmatic mineral in the groundmass of kimberlites. A new oxygen barometer for kimberlite magmas is
calibrated based on the Fe content of monticellite, CaMgSiO4, in equilibrium with kimberlite liquids in experiments at 100 kPa from 1,230 to 1,350°C and at logfO2 from NNO-4.1 to NNO+5.3 (where NNO is the nickel–nickel oxide buffer). The XFeMtc/XFeliq was found to decrease with increasing fO2, consistent with only Fe2+ entering the monticellite structure. Although the XFe-in-monticellite varies with temperature and composition, these dependencies are small compared to that with fO2. The experimental data were fitted by weighted least square regression to the following relationship:
\Updelta \textNNO = \frac{ log[ 0.858( ±0.021)\fracX\textFe\textLiq X\textFe\textMtc ] - 0.139( ±0.022) }0.193( ±0.004) \Updelta {\text{NNO}} = \frac{{\left\{ {\log \left[ {0.858( \pm 0.021)\frac{{X_{\text{Fe}}^{\text{Liq}} }}{{X_{\text{Fe}}^{\text{Mtc}} }}} \right] - 0.139( \pm 0.022)} \right\}}}{0.193( \pm 0.004)} where ΔNNO is the fO2 relative to that of the Nickel-bunsenite (NNO) buffer and XFeliq/XFeMtc is the ratio of mole fraction of Fe in liquid and Fe-in-monticellite (uncertainties at 2σ). The application of this oxygen
barometer to natural kimberlites from both the literature and our own investigations, assuming the bulk rock FeO is that of
their liquid FeO, revealed a range in fO2 from NNO-3.5 to NNO+1.7. A range of Mg/(Mg + Fe2+) (Mg#) for kimberlite melts of 0.46–0.88 was derived from the application of the experimentally determined monticellite-liquid
Kd Fe2+–Mg to natural monticellites. The range in Mg# is broader and less ultramafic than previous estimates of kimberlites, suggesting
an evolution under a wide range of petrologic conditions. 相似文献
27.
28.
Markus Kissler-Patig Duncan A. Forbes & Dante Minniti 《Monthly notices of the Royal Astronomical Society》1998,298(4):1123-1132
The discovery of protoglobular cluster candidates in many present-day mergers allows us to understand better the possible effects of a merger event on the globular cluster system of a galaxy, and to foresee the properties of the end-product. By comparing these expectations with the properties of globular cluster systems of elliptical galaxies at the present time we can constrain merger models. The observational data indicate that (i) every gaseous merger induces the formation of new star clusters, and (ii) the number of new clusters formed in such a merger increases with the gas content of the progenitor galaxies. Low-luminosity (about M V > −21), discy ellipticals are generally thought to be the result of a gaseous merger. As such, new globular clusters are expected to form but have not been detected to date. We investigate various reasons for the non-detection of subpopulations in low-luminosity ellipticals, i.e. absence of an old population, absence of a new population, destruction of one of the populations and, finally, an age–metallicity conspiracy that allows old and new globular clusters to appear indistinguishable at the present epoch. All of these possibilities lead us to a similar conclusion, namely that low-luminosity ellipticals did not form recently ( z < 1) in a gas-rich merger, and might not have formed in a major merger of stellar systems at all. High-luminosity ellipticals do reveal globular cluster subpopulations. However, it is difficult to account for the two populations in terms of mergers alone and, in particular, we can rule out scenarios in which the second subpopulation is the product of a recent, gas-poor merger. 相似文献
29.
Auckpath Sawangsuriya Meissa Fall Dante Fratta 《Geotechnical and Geological Engineering》2008,26(5):567-578
A rapid, low-cost evaluation methodology using the wave-based techniques is proposed in this study in order to determine the
design parameters e.g., elastic modulus and Poisson’s ratio of the laboratory compacted lateritic soils. Knowing the elastic
wave velocities as measured with the wave propagation technique (i.e., a small-strain non-destructive test) and total mass
density of the specimens, the elastic moduli and Poisson’s ratio of the soil specimens can be determined. In addition, the
unconfined compression test (i.e., a large-strain destructive test) is also performed on the same specimens under the same
unconfined testing condition in order to compare the moduli corresponding to different strain levels. The experimental results
showed the potentials and limitations of using impulse signal for the determination of the elastic moduli and Poisson’s ratio
for laboratory compacted soil specimens from elastic wave propagation techniques. 相似文献
30.