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6.
Yegor D. Sinelnikov Ganglin Chen Robert C. Liebermann 《Physics and Chemistry of Minerals》1998,25(7):515-521
Polycrystalline specimens in the CaTiO3–CaSiO3 perovskite system have been hot-pressed in a 2000-ton uniaxial split-sphere apparatus (USSA-2000) at pressures up to 15 GPa
and temperature of 1550°C, for the compositions CaTiO3, Ca(Ti0.75Si0.25)O3, Ca(Ti0.5Si0.5)O3. For the specimens with the bulk densities within 1% of the X-ray density, compressional and shear wave velocity measurements
have been conducted using ultrasonic interferometry. The measured adiabatic bulk moduli (K
s
) for the CaTiO3 and Ca(Ti0.5Si0.5)O3 perovskites are 175(1) and 188(1) GPa and shear moduli (G) of 106(1) and 109(1) GPa. In situ X-ray diffraction studies at high pressure and temperature resulted in isothermal values
for K
0 of 170(5) and 185(5) GPa, respectively. For the unquenchable CaSiO3 perovskite, elasticity theory and systematics were used to predict K
0=212(7) GPa and G
0=112(5) GPa; this shear modulus is 37% less than that for (Mg,Fe)SiO3 perovskite, suggesting that CaSiO3 perovskite cannot be ignored in modeling the composition of the Earth’s lower mantle.
Received: 27 June 1997 / Revised, accepted: 25 November 1997 相似文献
8.
9.
矿物3CaO·3Al_2O_3·BaSO_4形成过程研究 总被引：1，自引：0，他引：1
ｅｏｒｅａｎｕ等［１］研究ＣａＯＡｌ２Ｏ３Ｍｘ（ＳＯ４）Ｙ［Ｍ＝Ｍｇ２＋、Ｓｒ２＋、Ｂａ２＋、Ｚｎ２＋、Ｆｅ２＋、Ｆｅ３＋、Ａｌ３］系统中,形成类似于矿物３ＣａＯ·３Ａｌ２Ｏ３·ＣａＳＯ４（硫铝酸钙）的可能性时,报道合成了新矿物３ＣａＯ·３Ａｌ２Ｏ３·ＢａＳＯ４（简写为３ＣＡ·ＢａＳＯ４）;部分学者［２,３］研究过它的胶凝性能等。在有关文献中,研究者制备研究用纯矿物的煅烧条件、获得样品的矿相组成不尽相同。如文献［１］在温度１４００℃保温２４０ｍｉｎ,制备的样品包括铝酸钙（ＣａＯ·Ａｌ２Ｏ３… 相似文献
10.
11.
Victor L. Vinograd Bjoern Winkler Daniel J. Wilson Andrew Putnis Julian D. Gale 《Physics and Chemistry of Minerals》2006,33(8-9):533-544
Static lattice energy calculations, based on empirical pair potentials, were performed for a large set of structures differing in the arrangement of octahedral cations within the garnet 2 × 2 × 2 supercell. The compositions of these structures varied between Ca3Fe2Ge3O12 and Ca4Ge4O12. The energies were cluster expanded using pair and quaternary terms. The derived ordering constants were used to constrain Monte Carlo simulations of temperature-dependent mixing properties in the ranges of 1,073–3,673 K and 0–10 GPa. The free energies of mixing were calculated using the method of thermodynamic integration. The calculations predict a wide miscibility gap between Fe-rich (cubic) and Fe-pure (tetragonal) garnets consistent with recent experimental observations of Iezzi et al. (Phys Chem Miner 32:197–207, 2005). It is shown that the miscibility gap arises due to a very strong cation ordering at the Fe-pure composition, driven by the charge difference between Ca2+ and Ge4+ cations. The structural and thermodynamic analogies between Ca–Ge and Mg–Si systems suggest that a similar miscibility gap should exist between pyrope and Mg–Si-majorite. 相似文献
12.
Six schorlomite samples with TiO2 contents varying between 9.70 and 15.34 weight percent were studied by means of Mössbauer spectroscopy and chemical analysis. The measured Mössbauer spectra have complex shapes. The spectra of these samples were fitted with six doublets, which can be assigned to VIIIFe2+, VIFe2+, VIFe3+, IVFe3+ and two electron delocalizations, IVFe3+ ? VIIIFe2+ and IVFe3+ ? VIFe2+, respectively. The assignment of iron absorption doublets and their Mössbauer parameters are discussed in terms of the single crystal structure data of one of the samples studied in this work. Cation distributions are also given. The occupancies of cations at the tetrahedral (Z) site are Fe3+>Al3+, Ti4+, and the relative enrichments at Z site are always Fe3+>Ti4+. Most of the six samples contain Ti3+. Ti3+/ΣTi ratios range from 1.43 percent to 6.40 percent. Fe2+/ΣFe ratios vary from 8.84 percent to 11.31 percent. Four types of substitution must be considered for Ti entering the garnet structure. 相似文献
13.
Ferric iron in mantle-derived garnets 总被引：4，自引：0，他引：4
Robert W. Luth David Virgo Francis R. Boyd Bernard J. Wood 《Contributions to Mineralogy and Petrology》1990,104(1):56-72
The oxidation state of a mantle assemblage may be defined by heterogeneous reactions between oxygen and iron-bearing minerals. In spinel lherzolites, the presence of Fe3+ in spinel allows use of the assemblage olivine-orthopyroxene-spinel to define f
O
2 at fixed T and P. As a first step towards establishing an analogous reaction for garnet lherzolites, garnets from mantle-derived xenoliths from South Africa and the USSR have been analyzed with 57Fe Mössbauer spectroscopy at 298 and 77K to determine Fe3+/Fe2+ and the coordination state of iron. Garnets from South African alkremites (pyrope+Mg-spinel) and eclogites, as well as garnet-spinel and low-temperature garnet lherzolites from both South Afica and the USSR, have Fe3+/Fe<0.07. In contrast, garnets from high-temperature garnet lherzolites from within the Kaapvaal craton of South Africa have Fe3+/Fe>0.10. Ferric iron is octahedrally coordinated, and ferrous iron is present in the dodecahedral site in all samples. The occurrence of significant Fe3+ in these garnets necessitates caution in the use of geothermometers and geobarometers that are applied to mantle samples. For example, the presence of 12% of the Fe as Fe3+ in garnets can increase temperatures calculated from existing Fe/Mg geothermometers by>200°C. The concomitant increase in pressures calculated from geobarometers that use the Al content in orthopyroxene coexisting with garnet are 10–15 kbar. Results of calculations based on heterogeneous equilibria between garnet, olivine, and pyroxene are consistent with the derivation of the peridotite samples from source regions that are relatively oxidized, between the f
O
2 of the FMQ (quartz-fayalite-magnetite) buffer and that of the WM buffer. No samples yield values of f
O
2 as reduced as IW (iron-wüstite buffer). 相似文献
14.
江西永平铜矿矽卡岩矿物特征及其地质意义 总被引：4，自引：3，他引：1
永平铜矿含矿岩石主要为绿帘石透辉石石榴石矽卡岩,这种岩石类型是与斑岩体有关的矽卡岩铜矿的典型赋矿岩石。通过对这一主要赋矿矽卡岩的研究,我们发现石榴石生长分为两个阶段:(1)早期石榴石:主要分布在石榴石颗粒核部,XAdr=1.0,主要以钙铁榴石为主,说明早期流体中可能含有较多的铁,是在较氧化条件下形成的;(2)晚期石榴石,沿石榴石裂隙重新成核或者在靠近流体通道的早期石榴石表面生长,出现震荡环带,XAdr=0.46~0.99,为钙铁-钙铝石榴石系列。石榴石发生变化的期间也形成新的矿物,如绿帘石、萤石、方解石和石英等。共存石榴石和绿帘石矿物中存在Fe3+-Al3+之间的替代,说明流体的氧逸度、组分浓度或aFe3+/aAl3+可能发生了变化。金属矿物也可能是在这一阶段形成的。永平铜矿矽卡岩从接触带到大理岩空间上有分带现象。从岩体到围岩的变化趋势为:石榴石含量减少,颜色存在红棕色-棕色-棕绿色-黄绿色-浅黄色的变化趋势;矿石品位降低,这与石榴石中Al2O3含量的变化较一致。我们认为这种变化是含矿热液对早期矽卡岩进行再交代改造的结果,表现为石榴石和绿帘石中Fe3+-Al3+含量的变化,并将Cu等金属沉淀下来。根据矽卡岩矿物的这些特征,在矿床勘探时,可依据棕色石榴石来追踪主矿体的位置。 相似文献
15.
在中国东部皖北地区分布着新元古代镁铁质岩,其中一些碱性基性岩为金刚石的赋矿岩石。为了确定安徽栏杆金刚石矿区的石榴子石种类,对矿区内不同类型的石榴子石进行系统采样,测定了62件石榴子石微区化学成分。结果显示,安徽栏杆石榴子石矿物化学式A_3~(2+)B_2~(3+)(SiO_4)_3中的A组阳离子由Mg~(2+)、Fe~(2+)和Ca~(2+)离子占位,B主要由Al~(3+)、Fe~(3+)、Mn~(3+)和Cr~(3+)离子占位,三价阳离子主要为Al~(3+),二价阳离子主要为Ca~(2+),表明研究区石榴子石主要为钙铝-钙铁-镁铝石榴子石系列。在62个样品中,发现了超硅石榴子石。经过计算其形成的压力范围为12.1～12.8GPa,深度可达300km。 相似文献
16.
J. Alcock 《Contributions to Mineralogy and Petrology》1996,124(2):209-215
Garnets that exhibit mixed growth and diffusion zoning are used to evaluate the effect of grossular content on garnet Fe–Mg exchange reactions. These garnets from the uppermost amphibolite-facies to granulite-facies gneiss of the Wissahickon Group, southeastern Pennsylvania, show variation in grossular content (0.035<X Ca<0.14) but nearly constant Mg? (X Mg/(X Mg+X Fe) and X Mn through the interior indicating re-equilibration of garnet and matrix minerals with respect to iron, magnesium, and manganese. Mg? is not correlated with calcium content, evidence that the effect of calcium on garnet Fe–Mg exchange reactions is small or is offset by other interactions in almandine-rich garnets. In either case, the data presented here indicate that correction for calcium content of garnets in the application of garnet-biotite geothermometry to high-grade metapelites is unnecessary and may lead to an overestimate of peak temperature. 相似文献
17.
The garnet-clinopyroxene Fe-Mg geothermometer — a reinterpretation of existing experimental data 总被引：6，自引：0，他引：6
Erling J. Krogh 《Contributions to Mineralogy and Petrology》1988,99(1):44-48
Experimental data on the partitioning of Fe2+ and Mg between garnet and clinopyroxene (Råheim and Green 1974; Mori and Green 1978; Ellis and Green 1979) have been used to construct a new expression for the garnet-clinopyroxene geothermometer, including a curvilinear relationship between In Kd and X
Ca(ga): T(°C)=((-6173(XCa)2+6731 X
Ca+1879 +10 P(kb))/(lnKd+1.393))–273Application of this geothermometer to a suite of samples of eclogites and associated omphacite-garnet-bearing gneisses from the uppermost allochthon within the North Norwegian Caledonides shows that the calculated temperatures do not vary with rather great variations in the mg number of the garnet (0.17–0.54) and Na content of the clinopyroxene (0.11–0.44). Temperatures below 900° C calculated using the present equation are somewhat lower than those obtained by the method of Powell (1985), the difference being larger for lower temperatures and lower values of X
Ca. 相似文献
18.
The three binary garnet solid solutions FeII3Al2Si3O12–XII3Al2Si3O12 (XII= MgII, MnII, CaII) have been investigated by 57Fe Mössbauer spectroscopy at 298 and 77 K and by electronic structure calculations in the local spin density approximation. The spectra yield isomer shifts and quadrupole splittings that are typical for FeII in the dodecahedral X-site of 222 point symmetry and are similar for each of the three binaries recorded. Conversely, electronic structure calculations based on the experimental crystal structure of the different end-member garnets exhibit pronounced variations in some of the electronic properties of FeII that are not reflected in the spectroscopic data. These results are interpreted as indicating that the different X–O bonds in garnet solid solutions retain to a large degree the intrinsic lengths that they possess in their respective end members, and that the Fe–O bond does not change greatly as a function of composition. This is evidence for the state of alternating bonds and not for the virtual crystal approximation in describing the X–O bond types or lengths in aluminosilicate garnet solid solutions. The observed degree and behavior of the FeII doublet asymmetry in the Mössbauer spectra for the three solid solution series do not indicate major variations in the anisotropic recoil-free fraction of FeII. Variations in doublet asymmetry are more likely a result of complex next-nearest X-site neighbor interactions and/or some degree of short-range cation ordering, though doublets representing different local X-site cation configurations cannot be resolved or fitted to the experimental spectra. 相似文献
19.
Experimental study of the stability of cordierite and garnet in pelitic compositions at high pressures and temperatures 总被引：1，自引：0，他引：1
The stability of cordierite and garnet has been studied experimentally in complex, silica oversaturated compositions (in the systems MgO-FeO-Al2O-CaO3-Na2O-K2OSiO2) in which the molecular ratio Al2O3/FeO+MgO<1. Compositions with 100 Mg/Mg+Fe2+ ratios (X) of 0, 30, 50, 70 and 100 have been used to investigate the role of this ratio in determining phase assemblages and P, T coordinates of reactions. The minimum pressure for appearance of garnet at a given temperature is strongly dependent on X
total rock.The X-values of co-existing phases (chiefly garnet, cordierite, hypersthene) in divariant equilibrium are a function of temperature and pressure and have been experimentally determined at 900° C, 1000° C and 1100° C. At high temperature (>1050° C) the phases sapphirine and spinel are stable with quartz in Mg-rich and Fe-rich compositions respectively. Experiments in the system MgO-FeO-Al2O3-SiO2 show that for a given X-value and temperature the pressure required to produce Ca-free garnet from hypersthene-cordierite assemblages is 1–2 kb greater than that required to produce garnet containing 6±2 mol percent grossular solid solution in the more complex Ca-bearing system. 相似文献
20.
J. P. BUTLER R. A. JAMIESON H. M. STEENKAMP P. ROBINSON 《Journal of Metamorphic Geology》2013,31(2):147-163
Ultrahigh‐pressure (UHP) rocks from the Western Gneiss Region (WGR) of Norway record subduction of Baltican continental crust during the Silurian to Devonian Scandian continental collision. Here, we report a new coesite locality from the island of Harøya in the Nordøyane UHP domain, the most northerly yet documented in the WGR, and reconstruct the P–T history of the host eclogite. The coesite–eclogite lies within migmatitic orthogneiss, interpreted as Baltica basement, that underwent multiple stages of deformation and partial melting during exhumation. Two stages of metamorphism have been deduced from petrography and mineral chemistry. The early (M1) assemblage comprises garnet (Pyr38–41Alm35–37Grs23–26Spss1) and omphacite (Na0.35–0.40Ca0.57–0.60Fe2+0.08–0.10Mg0.53Fe3+0.01AlVI0.40–0.42)2(AlIV0.03–0.06Si1.94–1.97)2O6, with subordinate phengite, kyanite, rutile, coesite and apatite, all present as inclusions in garnet. The later (M2) assemblage comprises retrograde rims on garnet (Pyr38–40Alm40–44Grs16–21Spss1), diopside rims on omphacite (Na0.04–0.06Ca0.88–0.91Fe2+0.09–0.13Mg0.81–83Fe3+0.08AlVI0.03)2(AlIV0.07–0.08Si1.92–1.93)2O6, plagioclase, biotite, pargasite, orthopyroxene and ilmenite. Metamorphic P–T conditions estimated using thermocalc are ～3 GPa and 760 °C for M1, consistent with the presence of coesite, and ～1 GPa and 813 °C for M2, consistent with possible phengite dehydration melting during decompression. Comparison with other WGR eclogites containing the same assemblage shows a broad similarity in peak (M1) P–T conditions, confirming suggestions that large portions of the WGR were buried to depths of ～100 km during Scandian subduction. Field relations suggest that exhumation, accompanied by widespread partial melting, involved an early phase of top‐northwest shearing, followed by subhorizontal sinistral shearing along northwest‐dipping foliations, related to regional transtension. The present results add to the growing body of data on the distribution, maximum P–T conditions, and exhumation paths of WGR coesite–eclogites and their host rocks that is required to constrain quantitative models for the formation and exhumation of UHP metamorphic rocks during the Scandian collision. 相似文献