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1.
D. Howell I. G. Wood D. P. Dobson A. P. Jones L. Nasdala J. W. Harris 《Contributions to Mineralogy and Petrology》2010,160(5):705-717
The pressure and temperature conditions of formation of natural diamond can be estimated by measuring the residual stress
that an inclusion remains under within a diamond. Raman spectroscopy has been the most commonly used technique for determining
this stress by utilising pressure-sensitive peak shifts in the Raman spectrum of both the inclusion and the diamond host.
Here, we present a new approach to measure the residual stress using quantitative analysis of the birefringence induced in
the diamond. As the analysis of stress-induced birefringence is very different from that of normal birefringence, an analytical
model is developed that relates the spherical inclusion size, R
i, host diamond thickness, L, and measured value of birefringence at the edge of the inclusion,
\Updelta n(R\texti )\textav \Updelta n(R_{\text{i}} )_{\text{av}} , to the peak value of birefringence that has been encountered; to first order
\Updelta n\textpk = (3/4)(L/R\texti ) \Updelta n(R\texti )\textav \Updelta n_{\text{pk}} = (3/4)(L/R_{\text{i}} ) \, \Updelta n(R_{\text{i}} )_{\text{av}} . From this birefringence, the remnant pressure (P
i) can be calculated using the photoelastic relationship
\Updelta n\textpk = - (3/4)n3 q\textiso P\texti \Updelta n_{\text{pk}} = - (3/4)n^{3} q_{\text{iso}} P_{\text{i}} , where q
iso is a piezo-optical coefficient, which can be assumed to be independent of crystallographic orientation, and n is the refractive index of the diamond. This model has been used in combination with quantitative birefringence analysis
with a MetriPol system and compared to the results from both Raman point and 2D mapping analysis for a garnet inclusion in
a diamond from the Udachnaya mine (Russia) and coesite inclusions in a diamond from the Finsch mine (South Africa). The birefringence
model and analysis gave a remnant pressure of 0.53 ± 0.01 GPa for the garnet inclusion, from which a source pressure was calculated
as 5.7 GPa at 1,175°C (temperature obtained from IR analysis of the diamond host). The Raman techniques could not be applied
quantitatively to this sample to support the birefringence model; they were, however, applied to the largest coesite inclusion
in the Finsch sample. The remnant pressure values obtained were 2.5 ± 0.1 GPa (birefringence), 2.5 ± 0.3 GPa (2D Raman map),
and 2.5–2.6 GPa (Raman point analysis from all four inclusions). However, although the remnant pressures from the three methods
were self-consistent, they led to anomalously low source pressure of 2.9 GPa at 1,150°C (temperature obtained from IR analysis)
raising serious concerns about the use of the coesite-in-diamond geobarometer. 相似文献
2.
The onset of hydrous partial melting in the mantle above the transition zone is dictated by the H2O storage capacity of peridotite, which is defined as the maximum concentration that the solid assemblage can store at P and T without stabilizing a hydrous fluid or melt. H2O storage capacities of minerals in simple systems do not adequately constrain the peridotite water storage capacity because
simpler systems do not account for enhanced hydrous melt stability and reduced H2O activity facilitated by the additional components of multiply saturated peridotite. In this study, we determine peridotite-saturated
olivine and pyroxene water storage capacities at 10–13 GPa and 1,350–1,450°C by employing layered experiments, in which the
bottom ~2/3 of the capsule consists of hydrated KLB-1 oxide analog peridotite and the top ~1/3 of the capsule is a nearly
monomineralic layer of hydrated Mg# 89.6 olivine. This method facilitates the growth of ~200-μm olivine crystals, as well
as accessory low-Ca pyroxenes up to ~50 μm in diameter. The presence of small amounts of hydrous melt ensures that crystalline
phases have maximal H2O contents possible, while in equilibrium with the full peridotite assemblage (melt + ol + pyx + gt). At 12 GPa, olivine and
pyroxene water storage capacities decrease from ~1,000 to 650 ppm, and ~1,400 to 1,100 ppm, respectively, as temperature increases
from 1,350 to 1,450°C. Combining our results with those from a companion study at 5–8 GPa (Ardia et al., in prep.) at 1,450°C,
the olivine water storage capacity increases linearly with increasing pressure and is defined by the relation
C\textH2 \textO\textolivine ( \textppm ) = 57.6( ±16 ) ×P( \textGPa ) - 169( ±18 ). C_{{{\text{H}}_{2} {\text{O}}}}^{\text{olivine}} \left( {\text{ppm}} \right) = 57.6\left( { \pm 16} \right) \times P\left( {\text{GPa}} \right) - 169\left( { \pm 18} \right). Adjustment of this trend for small increases in temperature along the mantle geotherm, combined with experimental determinations
of
D\textH2 \textO\textpyx/olivine D_{{{\text{H}}_{2} {\text{O}}}}^{\text{pyx/olivine}} from this study and estimates of
D\textH2 \textO\textgt/\textolivine D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{gt}}/{\text{olivine}}}} , allows for estimation of peridotite H2O storage capacity, which is 440 ± 200 ppm at 400 km. This suggests that MORB source upper mantle, which contains 50–200 ppm
bulk H2O, is not wet enough to incite a global melt layer above the 410-km discontinuity. However, OIB source mantle and residues
of subducted slabs, which contain 300–1,000 ppm bulk H2O, can exceed the peridotite H2O storage capacity and incite localized hydrous partial melting in the deep upper mantle. Experimentally determined values
of
D\textH2 \textO\textpyx/\textolivine D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{pyx}}/{\text{olivine}}}} at 10–13 GPa have a narrow range of 1.35 ± 0.13, meaning that olivine is probably the most important host of H2O in the deep upper mantle. The increase in hydration of olivine with depth in the upper mantle may have significant influence
on viscosity and other transport properties. 相似文献
3.
Mineral-specific IR absorption coefficients were calculated for natural and synthetic olivine, SiO2 polymorphs, and GeO2 with specific isolated OH point defects using quantitative data from independent techniques such as proton–proton scattering,
confocal Raman spectroscopy, and secondary ion mass spectrometry. Moreover, we present a routine to detect OH traces in anisotropic
minerals using Raman spectroscopy combined with the “Comparator Technique”. In case of olivine and the SiO2 system, it turns out that the magnitude of ε for one structure is independent of the type of OH point defect and therewith
the peak position (quartz ε = 89,000 ± 15,000
\textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}), but it varies as a function of structure (coesite ε = 214,000 ± 14,000
\textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}; stishovite ε = 485,000 ± 109,000
\textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}). Evaluation of data from this study confirms that not using mineral-specific IR calibrations for the OH quantification in
nominally anhydrous minerals leads to inaccurate estimations of OH concentrations, which constitute the basis for modeling
the Earth’s deep water cycle. 相似文献
4.
M. Cai 《Rock Mechanics and Rock Engineering》2010,43(2):167-184
By applying the Griffith stress criterion of brittle failure, one can find that the uniaxial compressive strength (σc) of rocks is eight times the value of the uniaxial tensile strength (σt). The Griffith strength ratio is smaller than what is normally measured for rocks, even with the consideration of crack closure.
The reason is that Griffith’s theories address only the initiation of failure. Under tensile conditions, the crack propagation
is unstable so that the tensile crack propagation stress (σcd)t and the peak tensile strength σt are almost identical to the tensile crack initiation stress (σci)t. On the other hand, the crack growth after crack initiation is stable under a predominantly compressive condition. Additional
loading is required in compression to bring the stress from the crack initiation stress σci to the peak strength σc. It is proposed to estimate the tensile strength of strong brittle rocks from the strength ratio of
R = \fracs\textc | s\textt | = 8\fracs\textc s\textci . R = {\frac{{\sigma_{\text{c}} }}{{\left| {\sigma_{\text{t}} } \right|}}} = 8{\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}}. The term
\fracs\textc s\textci {\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}} accounts for the difference of crack growth or propagation in tension and compression in uniaxial compression tests.
\fracsc sci {\frac{{\sigma_{c} }}{{\sigma_{ci} }}} depends on rock heterogeneity and is larger for coarse grained rocks than for fine grained rocks. σci can be obtained from volumetric strain measurement or acoustic emission (AE) monitoring. With the strength ratio R determined, the tensile strength can be indirectly obtained from
| s\textt | = \fracs\textc R = \fracs\textci 8. \left| {\sigma_{\text{t}} } \right| = {\frac{{\sigma_{\text{c}} }}{R}} = {\frac{{\sigma_{\text{ci}} }}{8}}. It is found that the predicted tensile strengths using this method are in good agreement with test data. Finally, a practical
estimate of the Hoek–Brown strength parameter m
i is presented and a bi-segmental or multi-segmental representation of the Hoek–Brown strength envelope is suggested for some
brittle rocks. In this fashion, the rock strength parameters like σt and m
i, which require specialty tests such as direct tensile (or Brazilian) and triaxial compression tests for their determination,
can be reasonably estimated from uniaxial compression tests. 相似文献
5.
Priscille Lesne Bruno Scaillet Michel Pichavant Giada Iacono-Marziano Jean-Michel Beny 《Contributions to Mineralogy and Petrology》2011,162(1):133-151
Experiments were conducted to determine the water solubility of alkali basalts from Etna, Stromboli and Vesuvius volcanoes,
Italy. The basaltic melts were equilibrated at 1,200°C with pure water, under oxidized conditions, and at pressures ranging
from 163 to 3,842 bars. Our results show that at pressures above 1 kbar, alkali basalts dissolve more water than typical mid-ocean
ridge basalts (MORB). Combination of our data with those from previous studies allows the following simple empirical model
for the water solubility of basalts of varying alkalinity and fO2 to be derived:
\textH 2 \textO( \textwt% ) = \text H 2 \textO\textMORB ( \textwt% ) + ( 5.84 ×10 - 5 *\textP - 2.29 ×10 - 2 ) ×( \textNa2 \textO + \textK2 \textO )( \textwt% ) + 4.67 ×10 - 2 ×\Updelta \textNNO - 2.29 ×10 - 1 {\text{H}}_{ 2} {\text{O}}\left( {{\text{wt}}\% } \right) = {\text{ H}}_{ 2} {\text{O}}_{\text{MORB}} \left( {{\text{wt}}\% } \right) + \left( {5.84 \times 10^{ - 5} *{\text{P}} - 2.29 \times 10^{ - 2} } \right) \times \left( {{\text{Na}}_{2} {\text{O}} + {\text{K}}_{2} {\text{O}}} \right)\left( {{\text{wt}}\% } \right) + 4.67 \times 10^{ - 2} \times \Updelta {\text{NNO}} - 2.29 \times 10^{ - 1} where H2OMORB is the water solubility at the calculated P, using the model of Dixon et al. (1995). This equation reproduces the existing database on water solubilities in basaltic melts to within 5%. Interpretation of
the speciation data in the context of the glass transition theory shows that water speciation in basalt melts is severely
modified during quench. At magmatic temperatures, more than 90% of dissolved water forms hydroxyl groups at all water contents,
whilst in natural or synthetic glasses, the amount of molecular water is much larger. A regular solution model with an explicit
temperature dependence reproduces well-observed water species. Derivation of the partial molar volume of molecular water using
standard thermodynamic considerations yields values close to previous findings if room temperature water species are used.
When high temperature species proportions are used, a negative partial molar volume is obtained for molecular water. Calculation
of the partial molar volume of total water using H2O solubility data on basaltic melts at pressures above 1 kbar yields a value of 19 cm3/mol in reasonable agreement with estimates obtained from density measurements. 相似文献
6.
The present work aims in discussing a principle that distinguishes between elastic parameters sets, $ \{ \Upphi \} \equiv \{ K_{0} , \, K^{\prime}, \, V_{0} ,\ldots\} The present work aims in discussing a principle that distinguishes between elastic parameters sets,
{ \Upphi } o { K0 , K¢, V0 ,?} \{ \Upphi \} \equiv \{ K_{0} , \, K^{\prime}, \, V_{0} ,\ldots\} , on the basis of an energetic criterion: once a reference set,
{ \UpphiR } \{ \Upphi_{R} \} , is given, another one can be fixed,
{ \Upphi min } \left\{ {\Upphi_{ \min } } \right\} , so that they are as close as possible to each other, but yield non-equivalent deformation energy curves
\Updelta G({ \Upphi } )\textdeform \Updelta G(\{ \Upphi \} )_{\text{deform}} , i.e. they give
\Updelta G({ \UpphiR } )\textdeform \Updelta G(\{ \Upphi_{R} \} )_{\text{deform}} and
\Updelta G({ \Upphi min } )\textdeform \Updelta G(\{ \Upphi_{ \min } \} )_{\text{deform}} such that
| \Updelta G({ \Upphi min } )\textdeform - \Updelta G({ \UpphiR } )\textdeform | 3 1×s[\Updelta G\textdeform ]. \left| {\Updelta G(\{ \Upphi_{ \min } \} )_{\text{deform}} - \Updelta G(\{ \Upphi_{R} \} )_{\text{deform}} } \right| \ge 1\times \sigma [\Updelta G_{\text{deform}} ]. ΔG
deform, calculated using the equation of state (EoS), and its uncertainty σ[ΔG
deform], obtained by a propagation of the errors affecting
{ \Upphi } \{ \Upphi \} are crucial to fix which mineral assemblage forms at P–T conditions and allow one to assess the reliability of such a prediction. We explore some properties related to the principle
introduced, using the average values of the elastic parameters found in literature and related uncertainties for di-octahedral
mica, olivine, garnet and clinopyroxene. Two elementary applications are briefly discussed: the effect of refining V
0 in fitting EoSs to P–V experimental data, in the case of garnet and omphacite, and the phengite 3T–2M
1 relative stability, controlled by pressure. 相似文献
7.
Li diffusion in zircon 总被引:2,自引:2,他引:0
Diffusion of Li under anhydrous conditions at 1 atm and under fluid-present elevated pressure (1.0–1.2 GPa) conditions has
been measured in natural zircon. The source of diffusant for 1-atm experiments was ground natural spodumene, which was sealed
under vacuum in silica glass capsules with polished slabs of zircon. An experiment using a Dy-bearing source was also conducted
to evaluate possible rate-limiting effects on Li diffusion of slow-diffusing REE+3 that might provide charge balance. Diffusion experiments performed in the presence of H2O–CO2 fluid were run in a piston–cylinder apparatus, using a source consisting of a powdered mixture of spodumene, quartz and zircon
with oxalic acid added to produce H2O–CO2 fluid. Nuclear reaction analysis (NRA) with the resonant nuclear reaction 7Li(p,γ)8Be was used to measure diffusion profiles for the experiments. The following Arrhenius parameters were obtained for Li diffusion
normal to the c-axis over the temperature range 703–1.151°C at 1 atm for experiments run with the spodumene source:
D\textLi = 7.17 ×10 - 7 exp( - 275 ±11 \textkJmol - 1 /\textRT)\textm2 \texts - 1. D_{\text{Li}} = 7.17 \times 10^{ - 7} { \exp }( - 275 \pm 11\,{\text{kJmol}}^{ - 1} /{\text{RT}}){\text{m}}^{2} {\text{s}}^{ - 1}. 相似文献
8.
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
9.
The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization 总被引:1,自引:1,他引:0
Oliver Plümper Helen E. King Christian Vollmer Quentin Ramasse Haemyeong Jung Håkon Austrheim 《Contributions to Mineralogy and Petrology》2012,163(4):701-724
Crystal-plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence
of asthenospheric mantle flow. Although crystal-plastic deformation and serpentinization are spatio-temporally decoupled,
we identified compositional readjustments expressed on the micrometric level as a striped Fe-enriched (
[`(X)]\textFe \bar{X}_{\text{Fe}} = 0.24 ± 0.02 (zones); 0.12 ± 0.02 (bulk)) or Fe-depleted (
[`(X)]\textFe \bar{X}_{\text{Fe}} = 0.10 ± 0.01 (zones); 0.13 ± 0.01 (bulk)) zoning in partly serpentinized olivine grains from two upper mantle sections in
Norway. Focused ion beam sample preparation combined with transmission electron microscopy (TEM) and aberration-corrected
scanning TEM, enabling atomic-level resolved electron energy-loss spectroscopic line profiling, reveals that every zone is
immediately associated with a subgrain boundary. We infer that the zonings are a result of the environmental Fe2+Mg−1 exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium. This
is facilitated by enhanced solid-state diffusion along subgrain boundaries in a system, which otherwise re-equilibrates via
dissolution-reprecipitation. Fe enrichment or depletion is controlled by the silica activity imposed on the system by the
local olivine/orthopyroxene mass ratio, temperature and the effect of magnetite stability. The Fe-Mg exchange coefficients
K\textD\textAtg/\textOl K_{\text{D}}^{{{\text{Atg}}/{\text{Ol}}}} between both types of zoning and antigorite display coalescence toward exchange equilibrium. With both types of zoning, Mn
is enriched and Ni depleted compared with the unaffected bulk composition. Nanometer-sized, heterogeneously distributed antigorite
precipitates along olivine subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation
relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations
support the hypothesis that serpentinization was initiated along olivine subgrain boundaries. 相似文献
10.
James M. Stroh 《Contributions to Mineralogy and Petrology》1976,54(3):173-188
The addition of Fe and Cr to the simple system MgO-SiO2-Al2O3 markedly affects the activities of phases involved in the equilibrium
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