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1.
The primary occurrence of ruby in the Mogok area, northern Myanmar is exclusively found in marble along with spinel–forsterite-bearing marble and phlogopite–graphite marble. These marble units are enclosed within banded biotite–garnet–sillimanite–oligoclase gneisses. Samples of these marbles collected for C–O stable isotope analysis show two trends of δ13C–δ18O variation resulting most likely from fluid–rock interactions. Ruby-bearing marble and phlogopite–graphite marble follow a trend with coupled C–O depletion, whereas spinel–forsterite-bearing marble follows a δ18O depletion trend with relatively constant δ13C values. Ruby formation might have resulted from CO2-rich fluid–rock interaction, while spinel–forsterite-bearing marble was genetically related to CO2-poor fluid–rock interaction. Both fluids may have arisen from external sources. Based on graphite Raman spectral thermometry, the estimated temperature for phlogopite–graphite marble, and probably ruby-bearing marble, was lower than 607 °C, and for spinel–forsterite-bearing marble, lower than 710 °C. Contrasting C/O diffusion between graphite/ruby/spinel/forsterite and calcite, local variations of isotopic compositions of newly formed minerals as a result of non-pervasive fluid infiltration, and open-system isotopic disturbance during cooling may have affected C-/O-isotopic fractionations between minerals. The estimated high formation temperatures for ruby and spinel/forsterite imply that the parental fluids may have been related to nearby igneous intrusions and/or metamorphic processes. Whether these two types of fluid were genetically related is unclear based on the present data. 相似文献
2.
This paper presents an improved generalisation of cation distribution determination based on an accurate fit of all crystal-chemical
parameters. Cations are assigned to the tetrahedral and octahedral sites of the structure according to their scattering power
and a set of bond distances optimised for spinel structure. A database of 295 spinels was prepared from the literature and
unpublished data. Selected compositions include the following cations: Mg2+, Al3+, Si4+, Ti4+, V3+, Cr3+, Mn2+, Mn3+, Fe2+, Fe3+, Co2+, Ni2+, Zn2+ and vacancies. Bond distance optimisation reveals a definite lengthening in tetrahedral distance when large amounts of Fe3+ or Ni2+ are present in the octahedral site. This means that these cations modify the octahedral angle and hence the shared octahedral
edge, causing an increase in the tetrahedral distance with respect to the size of the cations entering it. Some applications
to published data are discussed, showing the capacity and limitations of the method for calculating cation distribution, and
for identifying inconsistencies and inaccuracies in experimental data.
Received: 19 February 2001 / Accepted: 1 June 2001 相似文献
3.
The position of the transition from spinel peridotite to garnet peridotite in a simplified chemical composition has been determined experimentally at high pressures and high temperatures. The univariant reaction MgCr2O4+2Mg2Si2O6=Mg3Cr2Si3O12+Mg2SiO4, has a negative slope in P–T space between 1200 °C and 1600 °C. The experimental results, combined with assessed thermodynamic data for MgCr2O4, MgSiO3 and Mg2SiO4 give the entropy and enthalpy of formation of knorringite garnet (Mg3Cr2Si3O12). Thermodynamic calculations in simplified chemical compositions indicate that Cr shifts the garnet-in reaction to much higher pressures than previously anticipated. Moreover, in Cr-bearing systems a pressure–temperature field exists where garnet and spinel coexist. The width of this divariant field strongly depends on the Cr/(Cr+Al) of the system. 相似文献
4.
Vadim S. Kamenetsky Andrey A. Gurenko 《Contributions to Mineralogy and Petrology》2007,153(4):465-481
The origin of compositional heterogeneities among the magmas parental to mid-ocean ridge basalts (MORB) was investigated using
a single rock piece of the olivine-phyric basalt from 43°N, Mid-Atlantic Ridge (AII D11-177). The exceptional feature of this
sample is presence of very primitive olivine crystals (90–91 mol% Fo) that are significantly variable in terms of CaO (0.15–0.35 wt%).
A population of low-Ca olivine (0.15–0.25 wt% CaO) is also notably distinct from high-Ca olivine population in AII D11-177,
and primitive MORB olivine in general, in having unusual assemblage of trapped mineral and glass inclusions. Mineral inclusions
are represented by high-magnesian (Mg# 90.7–91.1 mol%) orthopyroxene and Cr-spinel, distinctly enriched in TiO2 (up to 5 wt%, c.f. <1 wt% in common MORB spinel). Glass inclusions associated with orthopyroxene and high-Ti Cr-spinel have
andesitic compositions (53–58 wt% SiO2). Compared to the pillow-rim glass and “normal” MORB inclusions, the Si-rich glass inclusions in low-Ca olivine have strongly
reduced Ca and elevated concentrations of Ti, Na, K, P, Cl, and highly incompatible trace elements. Strong variability is
recorded among glass inclusions within a single olivine phenocrysts. We argue that the observed compositional anomalies are
mineralogically controlled, and thus may arise from the interaction between hot MORB magmas and crystal cumulates in the oceanic
crust or magma chamber. 相似文献
5.
High-temperature creep behavior in Ni2GeO4 spinel was investigated using synthetic polycrystalline aggregates with average grain sizes ranging from submicron to 7.4
microns. Cylindrical samples were deformed at constant load in a gas-medium apparatus at temperatures ranging from 1223 to
1523 K and stresses ranging from 40 to 320 MPa. Two deformation mechanisms were identified, characterized by the following
flow laws:
where σ is in MPa, d is in μm and T is in Kelvin. These flow laws suggest that deformation was accommodated by dislocation creep and grain-boundary diffusion
(Coble) creep, respectively. A comparison with other spinels shows that an isomechanical group can be defined for spinels
although some differences between normal and inverse spinels can be identified. When creep data for olivine and spinel are
normalized and extrapolated to Earth-like conditions, spinel (ringwoodite) has a strength similar to olivine in the dislocation
creep regime and is considerably stronger than olivine in the diffusion creep regime at coarse grain size. However, when grain-size
reduction occurs, spinel can become weaker than olivine due to its high grain-size sensitivity (Coble creep behavior). Analysis
of normalized diffusion creep data for olivine and spinel indicate that spinel is weaker than olivine at grain sizes less
than 2 μm.
Received: 18 June 2000 / Accepted: 3 April 2001 相似文献
6.
B.?LavinaEmail author L.Z.?Reznitskii F.?Bosi 《Physics and Chemistry of Minerals》2003,30(10):599-605
A suite of vanadian magnesiochromites from the Sludyanka metamorphic complex (South Lake Baikal, Russia) were investigated by means of X-ray single-crystal structural refinements and microprobe analyses. Various morphological types of Cr–V-bearing Mg spinels are located in calc–silicate metamorphic rocks, in an assemblage that also contains other Cr–V minerals such as escolaite–karelianite, uvarovite–goldmanite, Cr–V-bearing clinopyroxene, tourmaline, amphibole, mica, etc. Along the suite there is widespread V–Cr substitution (0.14 V3+ 0.95 afu, 1.02 Cr3+ 1.80 afu), and minor, variable Al contents. The Mg content of slightly lesser than 1 afu, is almost constant. Cell parameters and octahedral bond distances increase with V3+. Unexpectedly, the Mg–O tetrahedral bond distance also increases slowly with V3+. This weak dragging effect contributes towards maintaining distortion of the oxygen array with respect to the ideal CCP, thus providing a shielding effect, which reduces V3+–V3+ repulsion. This leads to the energetic stabilization of the structure, in spite of the increase of bond strain with increasing V3+ contents. 相似文献
7.
中国大陆科学钻探CCSD-PP3钻孔地幔岩的尖晶石相部分熔融证据 总被引：1，自引：1，他引：1
CCSD PP3超镁铁岩表现为高 Mg 和 Cr,低 Ca 和 Al 特征,是中国东部和超高压变质带上极其罕见的亏损地幔岩,通过地球化学和矿物学和 Re-Os 同位素研究发现岩石来自古元古代岩石圈地幔,并在地幔浅部尖晶石相条件下发生部分熔融,最近一次部分熔融作用发生在中-晚元古代,后经岩石圈厚度加大、拆沉或深俯冲过程,岩石转变为石榴石橄榄岩。 相似文献
8.
B.?LavinaEmail author G.?Salviulo A. Della?Giusta 《Physics and Chemistry of Minerals》2004,31(1):45-51
This paper presents evaluation of cation distributions from diffraction data collected at high T, P, and is an extension of the spinel structure modelling procedure by Lavina et al. (2002). Optimised cation-to-oxygen distances are modified for thermal expansion and compressibility at T and P of interest following Hazen and Prewitt (1977) and Hazen and Yang (1999). The procedure is applied to literature data concerning hercynite, spinel s.s., Zn aluminate, Zn ferrite, magnetite and the (Fe3O4)1–
x
(MgAl2O4)
x
join. Calculated cation distribution is strongly affected by standard deviations in cell parameters and oxygen coordinates. The underestimated values often reported in the literature for powder profile refinements may strongly affect the cation distribution; however, if standard deviations are increased to physically realistic values, consistent results are obtained. For P up to 10 GPa, reasonable evaluations of cation distribution are obtained for spinel s.s., Zn aluminate and magnetite, whereas for Zn ferrite they are limited to 1.8 GPa. For P beyond 10 GPa, compressibility cannot be assumed to be linear; the relationship between cell parameter and pressure is well-defined, but the inaccuracy of oxygen coordinate prevents simple modelling of bond distances with pressure. 相似文献
9.
François Farges 《Physics and Chemistry of Minerals》2009,36(8):463-481
Cr K-edge XANES spectra were obtained for a variety of Cr-bearing model compounds containing Cr(II), Cr(III), Cr(IV), Cr(V) and Cr(VI), in which the Cr-site symmetry is D4h, Oh and Td. The centroid position of the pre-edge feature is a better indicator of the Cr valence than the edge position. In Cr-rich oxides, higher-energy transitions must be excluded in order to refine a robust valence for Cr. The pre-edge for chromates is not unique and varies as a function of the CrO4 2? moiety distortion, which is often related to Cr-polymerization (monochromate vs. dichromate). Both the analogy with the Mn K-pre-edge information and ab initio FEFF calculations of the pre-edge feature for Cr(III) and Cr(VI) confirm the experimental trends. This methodology is applied to the Cr K-edge pre-edge feature collected in gems (emerald, spinel and ruby), the layered minerals fuchsite and kämmererite, two Cr-bearing aqueous solutions and a set of sodo-calcic silicate glasses used for bottling sparkling white wine. In emerald and fuchsite, the Cr-site is differently distorted than its ruby or spinel counterpart. In a Cr(III)-bearing aqueous solution and sodo-calcic glass, no evidence for Cr(III) with Td and C3v symmetry is detected. However, minor amounts of chromate moieties (most likely monomeric) are detected in a glass synthesized in air. Preliminary spectra for the wine bottle glass suggest that only trace amounts of chromates might possibly be present in these glasses. 相似文献
10.
