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1.
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
2.
Rodney Grapes Sophia Korzhova Ella Sokol Yurii Seryotkin 《Contributions to Mineralogy and Petrology》2011,162(2):253-273
Sekaninaite (XFe > 0.5)-bearing paralava and clinker are the products of ancient combustion metamorphism in the western part of the Kuznetsk
coal basin, Siberia. The combustion metamorphic rocks typically occur as clinker beds and breccias consisting of vitrified
sandstone–siltstone clinker fragments cemented by paralava, resulting from hanging-wall collapse above burning coal seams
and quenching. Sekaninaite–Fe-cordierite (XFe = 95–45) is associated with tridymite, fayalite, magnetite, ± clinoferrosilite and ±mullite in paralava and with tridymite
and mullite in clinker. Unmelted grains of detrital quartz occur in both rocks (<3 vol% in paralavas and up to 30 vol% in
some clinkers). Compositionally variable siliceous, K-rich peraluminous glass is <30% in paralavas and up to 85% in clinkers.
The paralavas resulted from extensive fusion of sandstone–siltstone (clinker), and sideritic/Fe-hydroxide material contained
within them, with the proportion of clastic sediments ≫ ferruginous component. Calculated dry liquidus temperatures of the
paralavas are 1,120–1,050°C and 920–1,050°C for clinkers, with calculated viscosities at liquidus temperatures of 101.6–7.0 and 107.0–9.8 Pa s, respectively. Dry liquidus temperatures of glass compositions range between 920 and 1,120°C (paralava) and 920–960°C
(clinker), and viscosities at these temperatures are 109.7–5.5 and 108.8–9.7 Pa s, respectively. Compared with worldwide occurrences of cordierite–sekaninaite in pyrometamorphic rocks, sekaninaite occurs
in rocks with XFe (mol% FeO/(FeO + MgO)) > 0.8; sekaninaite and Fe-cordierite occur in rocks with XFe 0.6–0.8, and cordierite (XFe < 0.5) is restricted to rocks with XFe < 0.6. The crystal-chemical formula of an anhydrous sekaninaite based on the refined structure is
| \textK0.02 |(\textFe1.542 + \textMg0.40 \textMn0.06 )\Upsigma 2.00M [(\textAl1.98 \textFe0.022 + \textSi1.00 )\Upsigma 3.00T1 (\textSi3.94 \textAl2.04 \textFe0.022 + )\Upsigma 6.00T2 \textO18 ]. \left| {{\text{K}}_{0.02} } \right|({\text{Fe}}_{1.54}^{2 + } {\text{Mg}}_{0.40} {\text{Mn}}_{0.06} )_{\Upsigma 2.00}^{M} [({\text{Al}}_{1.98} {\text{Fe}}_{0.02}^{2 + } {\text{Si}}_{1.00} )_{\Upsigma 3.00}^{T1} ({\text{Si}}_{3.94} {\text{Al}}_{2.04} {\text{Fe}}_{0.02}^{2 + } )_{\Upsigma 6.00}^{T2} {\text{O}}_{18} ]. 相似文献
3.
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
4.
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
5.
Mirjam van Kan Parker Axel Liebscher Dirk Frei Jelle van Sijl Wim van Westrenen Jon Blundy Gerhard Franz 《Contributions to Mineralogy and Petrology》2010,159(4):459-473
Although orthopyroxene (Opx) is present during a wide range of magmatic differentiation processes in the terrestrial and lunar mantle, its effect on melt trace element contents is not well quantified. We present results of a combined experimental and computational study of trace element partitioning between Opx and anhydrous silicate melts. Experiments were performed in air at atmospheric pressure and temperatures ranging from 1,326 to 1,420°C in the system CaO–MgO–Al2O3–SiO2 and subsystem CaO–MgO–SiO2. We provide experimental partition coefficients for a wide range of trace elements (large ion lithophile: Li, Be, B, K, Rb, Sr, Cs, Ba, Th, U; rare earth elements, REE: La, Ce, Nd, Sm, Y, Yb, Lu; high field strength: Zr, Nb, Hf, Ta, Ti; transition metals: Sc, V, Cr, Co) for use in petrogenetic modelling. REE partition coefficients increase from $ D_{\text{La}}^{{\text{Opx}} {\hbox{-}} {\text{melt}}} \sim 0.0005
6.
Relative humidity (
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} , partial pressure of water)-dependent dehydration and accompanying phase transitions in NAT-topology zeolites (natrolite,
scolecite, and mesolite) were studied under controlled temperature and known
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} conditions by in situ diffuse-reflectance infrared Fourier transform spectroscopy and parallel X-ray powder diffraction.
Dehydration was characterized by the disappearance of internal H2O vibrational modes. The loss of H2O molecules caused a sequence of structural transitions in which the host framework transformation path was coupled primarily
via the thermal motion of guest Na+/Ca2+ cations and H2O molecules. The observation of different interactions of H2O molecules and Na+/Ca2+ cations with host aluminosilicate frameworks under high- and low-
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} conditions indicated the development of different local strain fields, arising from cation–H2O interactions in NAT-type channels. These strain fields influence the Si–O/Al–O bond strength and tilting angles within and
between tetrahedra as the dehydration temperature is approached. The newly observed infrared bands (at 2,139 cm−1 in natrolite, 2,276 cm−1 in scolecite, and 2,176 and 2,259 cm−1 in mesolite) result from strong cation–H2O–Al–Si framework interactions in NAT-type channels, and these bands can be used to evaluate the energetic evolution of Na+/Ca2+ cations before and after phase transitions, especially for scolecite and mesolite. The 2,176 and 2,259 cm−1 absorption bands in mesolite also appear to be related to Na+/Ca2+ order–disorder that occur when mesolite loses its Ow4 H2O molecules. 相似文献
7.
Sogdianite, a double-ring silicate of composition
( \textZr0. 7 6 \textTi0. 3 84 + \textFe0. 7 33 + \textAl0.13 )\Upsigma = 2 ( \square 1. 1 5 \textNa0. 8 5 )\Upsigma = 2 \textK[\textLi 3 \textSi 1 2 \textO 30 ] ( {\text{Zr}}_{0. 7 6} {\text{Ti}}_{0. 3 8}^{4 + } {\text{Fe}}_{0. 7 3}^{3 + } {\text{Al}}_{0.13} )_{\Upsigma = 2} \left( {\square_{ 1. 1 5} {\text{Na}}_{0. 8 5} } \right)_{\Upsigma = 2} {\text{K}}[{\text{Li}}_{ 3} {\text{Si}}_{ 1 2} {\text{O}}_{ 30} ] from Dara-i-Pioz, Tadjikistan, was studied by the combined application of 57Fe M?ssbauer spectroscopy and electronic structure calculations. The M?ssbauer spectrum confirms published microprobe and
X-ray single-crystal diffraction results that indicate that Fe3+ is located at the octahedral A-site and that no Fe2+ is present. Both the measured and calculated quadrupole splitting, ΔE
Q, for Fe3+ are virtually 0 mm s−1. Such a value is unusually small for a silicate and it is the same as the ΔE
Q value for Fe3+ in structurally related sugilite. This result is traced back to the nearly regular octahedral coordination geometry corresponding
to a very symmetric electric field gradient around Fe3+. A crystal chemical interpretation for the regular octahedral geometry and the resulting low ΔE
Q value for Fe3+ in the M?ssbauer spectrum of sogdianite is that structural strain is largely “taken up” by weak Li–O bonds permitting highly
distorted LiO4 tetrahedra. Weak Li–O bonding allows the edge-shared more strongly bonded Fe3+O6 octahedra to remain regular in geometry. This may be a typical property for all double-ring silicates with tetrahedrally
coordinated Li. 相似文献
8.
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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