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1.
2.
Yastami Oka Petra Steinke Niranjan D. Chatterjee 《Contributions to Mineralogy and Petrology》1984,87(2):196-204
Three Al-Cr exchange isotherms at 1,250°, 1,050°, and 796° between Mg(Al, Cr)2O4 spinel and (Al, Cr)2O3 corundum crystalline solutions have been studied experimentally at 25 kbar pressure. Starting from gels of suitable bulk
compositions, close approach to equilibrium has been demonstrated in each case by time studies.
Using the equation of state for (Al, Cr)2O3 crystalline solution (Chatterjee et al. 1982a) and assuming that the Mg(Al, Cr)2O4 can be treated in terms of the asymmetric Margules relation, the exchange isotherms were solved for Δ G
*,
and
. The best constrained data set from the 1,250° C isotherm clearly shows that the latter two quantities do not overlap within
three standard deviations, justifying the choice of asymmetric Margules relation for describing the excess mixing properties
of Mg(Al, Cr)2O4 spinels. Based on these experiments, the following polybaric-polythermal equation of state can be formulated:
, P expressed in bars, T in K, G
m
ex
and W
G,i
Sp
in joules/mol.
Temperature-dependence of G
m
ex
is best constrained in the range 796–1,250° C; extrapolation beyond that range would have to be done with caution. Such extrapolation
to lower temperature shows tentatively that at 1 bar pressure the critical temperature, T
c, of the spinel solvus is 427° C, with dTc/dP≈1.3 K/kbar. The critical composition, X
c, is 0.42
, and changes barely with pressure.
Substantial error in calculated phase diagrams will result if the significant positive deviation from ideality is ignored
for Al-Cr mixing in such spinels. 相似文献
3.
Amphibole composition in tonalite as a function of pressure: an experimental calibration of the Al-in-hornblende barometer 总被引:66,自引:3,他引:63
Max W. Schmidt 《Contributions to Mineralogy and Petrology》1992,110(2-3):304-310
The Al-in-hornblende barometer, which correlates Altot content of magmatic hornblende linearly with crystallization pressure of intrusion (Hammarstrom and Zen 1986), has been calibrated experimentally under water-saturated conditions at pressures of 2.5–13 kbar and temperatures of 700–655°C. Equilibration of the assemblage hornlende-biotite-plagioclase-orthoclasequartz-sphene-Fe-Ti-oxide-melt-vapor from a natural tonalite 15–20° above its wet solidus results in hornblende compositions which can be fit by the equation: P(±0.6 kbar) = –3.01 + 4.76 Al
hbl
tot
r
2=0.99, where Altot is the total Al content of hornblende in atoms per formula unit (apfu). Altot increase with pressure can be ascribed mainly to a tschermak-exchange (
) accompanied by minor plagioclase-substitution (
). This experimental calibration agrees well with empirical field calibrations, wherein pressures are estimated by contact-aureole barometry, confirming that contact-aureole pressures and pressures calculated by the Al-in-hornblende barometer are essentially identical. This calibration is also consistent with the previous experimental calibration by Johnson and Rutherford (1989b) which was accomplished at higher temperatures, stabilizing the required buffer assemblage by use of mixed H2O-CO2 fluids. The latter calibration yields higher Altot content in hornblendes at corresponding pressures, this can be ascribed to increased edenite-exchange (
) at elevated temperatures. The comparison of both experimental calibrations shows the important influence of the fluid composition, which affects the solidus temperature, on equilibration of hornblende in the buffering phase assemblage. 相似文献
4.
W. Schreyer D. Stepto K. Abraham W. F. Müller 《Contributions to Mineralogy and Petrology》1978,65(4):351-361
A unique clinopyroxene (En19Fs78Wo3), clinoeulite, space group P21/c, $${\text{(Fe}}_{{\text{1}}{\text{.48}}} {\text{Mg}}_{{\text{0}}{\text{.37}}} {\text{Mn}}_{{\text{0}}{\text{.08}}}^{{\text{2 + }}} {\text{Ca}}_{{\text{0}}{\text{.05}}} {\text{Al}}_{{\text{0}}{\text{.01}}} {\text{)}}_{{\text{1}}{\text{.99}}} {\text{ [Si}}_{{\text{2}}{\text{.01}}} {\text{O6],}}$$ contains sharp exsolution lamellae of ferroaugite (En17Fs43Wo40) from which the former presence of a ferropigeonite near En17Fs70Wo13 can be calculated. This two-pyroxene intergrowth is the main component of a eulysite containing also magnetite, olivine (Fo9Fa86Te5), quartz, oligoclase-K feldspar inter-growth, and retrograde cummingtonite with about 76 % grunerite end member. The occurrence of this most unusual rock type in the center of the Vredefort structure is attributed to a period of high-temperature metamorphism (at least 800 °–850 °C) which was followed by hot deformation of the rock during the Vredefort event thus probably preventing the common formation of orthopyroxene through pigeonite exsolution and inversion upon cooling. After this tectonic deformation, the rock recrystallized within the low-temperature stability range of clinoeulite to yield fine annealing textures. Late-stage equilibria at temperatures well below 500 °C include the complete unmixing of a former high-temperature anorthoclase, a Mg/Fe redistribution in the clinoeulite and olivine and, with the introduction of water, the partial formation of cummingtonite through reaction of clinoeulite, olivine, and quartz. During weathering the olivine was transformed to a nearly opaque, anhydrous ferrisilicate which, except for the change of Fe2+ to Fe3+ and the oxygen introduction, largely retained its original chemistry. 相似文献
5.
Mössbauer and polarized optical absorption spectra of the kyanite-related mineral yoderite were recorded. Mössbauer spectra of the purple (PY) and green yoderite (GY) from Mautia Hill, Tanzania, show that the bulk of the iron is Fe3+ in both varieties, with Fe2+/(Fe2++Fe3+) ratios near 0.05. Combining this result with new microprobe data for PY and with literature data for GY gives the crystallochemical formulae: $$\begin{gathered} ({\text{Mg}}_{{\text{1}}{\text{.95}}} {\text{Fe}}_{{\text{0}}{\text{.02}}}^{{\text{2 + }}} {\text{Mn}}_{{\text{0}}{\text{.01}}}^{{\text{2 + }}} {\text{Fe}}_{{\text{0}}{\text{.34}}}^{{\text{3 + }}} {\text{Mn}}_{{\text{0}}{\text{.07}}}^{{\text{3 + }}} {\text{Ti}}_{{\text{0}}{\text{.01}}} {\text{Al}}_{{\text{3}}{\text{.57}}} )_{5.97}^{[5,6]} \hfill \\ {\text{Al}}_{{\text{2}}{\text{.00}}}^{{\text{[5]}}} [({\text{Si}}_{{\text{3}}{\text{.98}}} {\text{P}}_{{\text{0}}{\text{.03}}} ){\text{O}}_{{\text{18}}{\text{.02}}} ({\text{OH)}}_{{\text{1}}{\text{.98}}} ] \hfill \\ \end{gathered}$$ and PY and $$\begin{gathered} ({\text{Mg}}_{{\text{1}}{\text{.98}}} {\text{Fe}}_{{\text{0}}{\text{.02}}}^{{\text{2 + }}} {\text{Mn}}_{{\text{< 0}}{\text{.001}}}^{{\text{2 + }}} {\text{Fe}}_{{\text{0}}{\text{.45}}}^{{\text{3 + }}} {\text{Ti}}_{{\text{0}}{\text{.01}}} {\text{Al}}_{{\text{3}}{\text{.56}}} )_{6.02}^{[5,6]} \hfill \\ {\text{Al}}_{{\text{2}}{\text{.00}}}^{{\text{[5]}}} [({\text{Si}}_{{\text{3}}{\text{.91}}} {\text{O}}_{{\text{17}}{\text{.73}}} {\text{(OH)}}_{{\text{2}}{\text{.27}}} ] \hfill \\ \end{gathered}$$ for GY. The Mössbauer spectra at room temperature contain one main doublet with isomer shifts and quadrupole splittings of 0.36 (PY), 0.38 (GY) and 1.00 (PY), 0.92 (GY) mm s?1, respectively. These values correspond to Fe3+ in six or five-fold coordination. The doublet components have anomalously large half widths indicating either accomodation of Fe3+ in more than one position (e.g., octahedraA1 and five coordinatedA2) or the yet unresolved superstructure. Besides strong absorption in the ultraviolet (UV) starting from about 25,000 cm?1, the polarized optical absorption spectra are dominated by strong bands around 16,500 and 21,000 cm?1 (PY) and a medium strong band at around 13,800 cm?1 (GY). Position and polarization of these bands, in combination with the UV absorption, explain the colour and pleochroism of the two varieties. The bands in question are assigned to homonuclear metal-to-metal charge transfer transitions: Mn2+(A1) Mn3+(A1′) ? Mn3+(A1) Mn2+(A1′) and Mn2+(A1) Mn3+(A2 ? Mn3+(A1) Mn2+(A2) in PY and Fe2+(A1) Fe3+(A1′) ? Fe3+(A1) Fe2+(A1′) in GY. The evidence for homonuclear Mn2+ Mn3+ charge transfer (CTF) is not quite clear and needs further study. Heteronuclear FeTi CTF does not contribute to the spectra. In PY, additional weak bands were resolved at energies around 17,700, 18,700, 21,000, and 21,900 cm?1 and assigned to Mn3+ in two positions. Weak bands around 10,000 cm?1 in both varieties are assigned to Fe2+ spin-alloweddd-transitions. Very weak and sharp bands, around 15,400, 16,400, 21,300, 22,100, 23,800, and 25,000 cm?1 are identified in GY and assigned to Fe3+ spin-forbiddendd-transitions. 相似文献
6.
Comparative study of dissolution rate-determining mechanisms of limestone and dolomite 总被引:2,自引:0,他引:2
The dissolution rate-determining processes of carbonate rocks include: (1) heterogeneous reactions on rock surfaces; (2) mass transport of ions into solution from rock surfaces via diffusion; and (3) the conversion reaction of CO2 into H+ and HCO
3
−
. Generally, it is the slowest of these three processes that limits the dissolution rate of carbonate rock. However, from experiment and theoretical analysis under similar conditions not only were the initial dissolution rates of dolomite lower by a factor of 3–60 than those of limestone, but also there are different dissolution rate-determining mechanisms between limestone and dolomite. For example, for limestone under the condition of CO2 partial pressures
dissolution rates increased significantly by a factor of about ten after addition of carbonic anhydrase (CA) into solution, which catalysed the conversation reaction of CO2, whereas CA had little influence on dolomite dissolution. For dolomite, the increase of dissolution rate after addition of CA into solution appeared at
Moreover, the enhancement factor of CA on dolomite dissolution rate was much lower (by a factor of about 3). In addition, when dissolution of both limestone and dolomite was determined by hydrodynamics (rotation speed or flow speed), especially under
the dissolution of limestone was more sensitive to hydrodynamic change than that of dolomite. These findings are of significance in understanding the differences in karstification and relevant problems of resource and environment in dolomite and limestone areas. 相似文献
7.
S. K. Saxena 《Contributions to Mineralogy and Petrology》1979,70(3):229-235
A garnet-clinopyroxene geothermometer based on the available experimental data on compositions of coexisting phases in the system MgO-FeO-MnO-Al2O3-Na2O-SiO2 is as follows: $$T({\text{}}K) = \frac{{8288 + 0.0276 P {\text{(bar)}} + Q1 - Q2}}{{1.987 \ln K_{\text{D}} + 2.4083}}$$ where P is pressure, and Q1, Q2, and K D are given by the following equations $$Q1 = 2,710{\text{(}}X_{{\text{Fe}}} - X_{{\text{Mg}}} {\text{)}} + 3,150{\text{ }}X_{{\text{Ca}}} + 2,600{\text{ }}X_{{\text{Mn}}} $$ (mole fractions in garnet) $$\begin{gathered}Q2 = - 6,594[X_{{\text{Fe}}} {\text{(}}X_{{\text{Fe}}} - 2X_{{\text{Mg}}} {\text{)]}} \hfill \\{\text{ }} - 12762{\text{ [}}X_{{\text{Fe}}} - X_{{\text{Mg}}} (1 - X_{{\text{Fe}}} {\text{)]}} \hfill \\{\text{ }} - 11,281[X_{{\text{Ca}}} (1 - X_{{\text{Al}}} ) - 2X_{{\text{Mg}}} 2X_{{\text{Ca}}} ] \hfill \\{\text{ + 6137[}}X_{{\text{Ca}}} (2X_{{\text{Mg}}} + X_{{\text{Al}}} )] \hfill \\{\text{ + 35,791[}}X_{{\text{Al}}} (1 - 2X_{{\text{Mg}}} )] \hfill \\{\text{ + 25,409[(}}X_{{\text{Ca}}} )^2 ] - 55,137[X_{{\text{Ca}}} (X_{{\text{Mg}}} - X_{{\text{Fe}}} )] \hfill \\{\text{ }} - 11,338[X_{{\text{Al}}} (X_{{\text{Fe}}} - X_{{\text{Mg}}} )] \hfill \\\end{gathered} $$ [mole fractions in clinopyroxene Mg = MgSiO3, Fe = FeSiO3, Ca = CaSiO3, Al = (Al2O3-Na2O)] K D = (Fe/Mg) in garnet/(Fe/Mg) in clinopyroxene. Mn and Cr in clinopyroxene, when present in small concentrations are added to Fe and Al respectively. Fe is total Fe2++Fe3+. 相似文献
8.
Solubility of Ca and Al in orthopyroxene from spinel peridotite: an improved version of an empirical geothermometer 总被引:1,自引:1,他引:0
Geothermometric equations for spinel peridotites by Fujii (1976), Gasparik and Newton (1984), and Chatterjee, and Terhart (1985) based on the reaction enstatite (en)+spinel (sp)Mg–Tschermaks (mats)+forsterite (fo) were tested using a nearly isothermal suite of mantle xenoliths from the Eifel, West Germany. In spite of using activities of MgAl2O4, en, and mats to allow for the non-ideal solution behaviour of the constituent phases, temperatures calculated from these equations systematically change as a function of Cr/(Cr+AL+Fe3+) in spinel. We propose an improved version of the empirical geothermometer for spinel peridotites of Sachtleben and Seck (1981) derived from the evaluation of the solubilities of Ca and Al in orthopyroxene from more than 100 spinel peridotites from the Rhenish Volcanic Province. A least squares regression yielded a smooth correlation between
相似文献
9.
The system Fe-Si-O: Oxygen buffer calibrations to 1,500K 总被引:1,自引:0,他引:1
The five solid-phase oxygen buffers of the system Fe-Si-O, iron-wuestite (IW), wuestite-magnetite (WM), magnetite-hematite (MH), quartz-iron-fayalite (QIF) and fayalite-magnetite-quartz (FMQ) have been recalibrated at 1 atm pressure and temperatures from 800°–1,300° C, using a thermogravimetric gas mixing furnace. The oxygen fugacity, \(f_{{\text{O}}_{\text{2}} }\) was measured with a CaO-doped ZrO2 electrode. Measurements were made also for wuestite solid solutions in order to determine the redox behavior of wuestites with O/Fe ratios varying from 1.05 to 1.17. For FMQ, additional determinations were carried out at 1 kb over a temperature range of 600° to 800° C, using a modified Shaw membrane. Results agree reasonably well with published data and extrapolations. The reaction parameters K, ΔG r o , ΔH r o , and ΔS r o were calculated from the following log \(f_{{\text{O}}_{\text{2}} }\) /T relations (T in K): $$\begin{gathered} {\text{IW }}\log f_{{\text{O}}_{\text{2}} } = - 26,834.7/T + 6.471\left( { \pm 0.058} \right) \hfill \\ {\text{ }}\left( {{\text{800}} - 1,260{\text{ C}}} \right), \hfill \\ {\text{WM }}\log f_{{\text{O}}_{\text{2}} } = - 36,951.3/T + 16.092\left( { \pm 0.045} \right) \hfill \\ {\text{ }}\left( {{\text{1,000}} - 1,300{\text{ C}}} \right), \hfill \\ {\text{MH }}\log f_{{\text{O}}_{\text{2}} } = - 23,847.6/T + 13.480\left( { \pm 0.055} \right) \hfill \\ {\text{ }}\left( {{\text{1,040}} - 1,270{\text{ C}}} \right), \hfill \\ {\text{QIF }}\log f_{{\text{O}}_{\text{2}} } = - 27,517.5/T + 6.396\left( { \pm 0.049} \right) \hfill \\ {\text{ }}\left( {{\text{960}} - 1,140{\text{ C}}} \right), \hfill \\ {\text{FMQ }}\log f_{{\text{O}}_{\text{2}} } = - 24,441.9/T + 8.290\left( { \pm 0.167} \right) \hfill \\ {\text{ }}\left( {{\text{600}} - 1,140{\text{ C}}} \right). \hfill \\ \end{gathered}$$ These experimentally determined reaction parameters were combined with published 298 K data to determine the parameters Gf, Hf, and Sf for the phases wuestite, magnetite, hematite, and fayalite from 298 K to the temperatures of the experiments. The T? \(f_{{\text{O}}_{\text{2}} }\) data for wuestite solid solutions were used to obtain activities, excess free energies and Margules mixing parameters. The new data provide a more reliable, consistent and complete reference set for the interpretation of redox reactions at elevated temperatures in experiments and field settings encompassing the crust, mantle and core as well as extraterrestrial environments. 相似文献
10.
Andreas G. Mueller 《Mineralium Deposita》2007,42(7):737-769
Five Cu–Au epidote skarns are associated with the Mt. Shea intrusive complex, located in the 2.7–2.6 Ga Eastern Goldfields
Province of the Archean Yilgarn craton, in greenstones bounded by the Boulder Lefroy and Golden Mile strike-slip faults, which
control the Golden Mile (1,435 t Au) at Kalgoorlie and smaller “orogenic” gold deposits at Kambalda. The Cu–Au deposits studied
are oxidized endoskarns replacing faulted and fractured quartz monzodiorite–granodiorite. The orebodies are up to 140 m long
and 40 m thick. Typical grades are 0.5% Cu and 0.3 g/t Au although parts are richer in gold (1.5–4.5 g/t). At the Hannan South
mine, the skarns consist of epidote, calcite, chlorite, magnetite (5–15%), and minor quartz, muscovite, and microcline. Gangue
and magnetite are in equilibrium contact with pyrite and chalcopyrite. The As–Co–Ni-bearing pyrite contains inclusions of
hematite, gold, and electrum and is intergrown with cobaltite and Cu–Pb–Bi sulfides. At the Shea prospect, massive, net-textured,
and breccia skarns are composed of multistage epidote, actinolite, albite, magnetite (5%), and minor biotite, calcite, and
quartz. Gangue and magnetite are in equilibrium with Co–Ni pyrite and chalcopyrite. Mineral-pair thermometry, mass-balance
calculations, and stable-isotope data (pyrite δ34SCDT = 2.5‰, calcite δ13CPDB = −5.3‰, and δ18OSMOW = 12.9‰) indicate that the Cu–Au skarns formed at 500 ± 50°C by intense Ca–Fe–CO2–S metasomatism from fluids marked by an igneous isotope signature. The Mt. Shea stock–dike–sill complex postdates the regional
D1 folding and metamorphism and the main phase of D2 strike-slip faulting. The suite is calc-akaline and comprises hornblende–plagioclase
monzodiorite, quartz monzodiorite, granodiorite, and quartz–plagioclase tonalite porphyry. The intrusions display a wide range
in silica content (53–73 wt% SiO2), in ratio (0.37–0.89), and in ratio (0.02–0.31). Chromium (62–345 ppm), Ni (23–158), Sr (311–1361 ppm), and Ba (250–2,581 ppm) contents are high, Sr/Y
ratios are high (24–278, mostly >50), and the rare earth element patterns are fractionated . These features and a negative niobium anomaly relative to the normal mid-ocean ridge basalt indicate that the suite formed
by hornblende fractionation from a subduction-related monzodiorite magma sourced from metasomatized peridotite in the upper
mantle. The magnesian composition of many intrusions was enhanced due to hornblende crystallization under oxidizing hydrous
conditions and during the subsequent destruction of igneous magnetite by subsolidus actinolite–albite alteration. At the Shea
prospect, main-stage Cu–Au epidote skarn is cut by biotite–albite–dolomite schist and by red biotite–albite replacement bands.
Post-skarn alteration includes 20-m-thick zones of sericite–chlorite–ankerite schist confined to two D3 reverse faults. The
schists are mineralized with magnetite + pyrite + chalcopyrite (up to 0.62% Cu, 1.6 g/t Au) and are linked to skarn formation
by shared Ca–Fe–CO2 metasomatism. Red sericitic alteration, marked by magnetite + hematite + pyrite, occurs in fractured porphyry. The biotite/sericite
alteration and oxidized ore assemblages at the Shea prospect are mineralogically identical to magnetite–hematite-bearing gold
lodes at Kambalda and in the Golden Mile. Published fluid inclusion data suggest that a “high-pressure”, oxidized magmatic
fluid (2–9 wt% NaCl equivalent, , 200–400 MPa) was responsible for gold mineralization in structural sites of the Boulder Lefroy and Golden Mile faults. The
sericite–alkerite lodes in the Golden Mile share the assemblages pyrite + tennantite + chalcopyrite and bornite + pyrite,
and accessory high-sulfidation enargite with late-stage sericitic alteration zones developed above porphyry copper deposits. 相似文献
11.
Kanonaite forms rare porphyroblasts up to 12mm long in a gahnite— Mg-chlorite — coronadite — quartz schist occurring near Kanona, Zambia. The composition is (microprobe analysis): SiO2 32.2, Al2O3 33.9, Mn as Mn2O3 32.2, Fe2O3 0.66, ZnO 0.13, MgO 0.04, BaO 0.04, TiO2 0.01, CaO 0.01, PbO 0.01, CuO 0.01, total 99.21, corresponding to $$\left( {{\text{Mn}}_{{\text{0}}{\text{.76}}}^{{\text{3 + }}} {\text{Al}}_{{\text{0}}{\text{.23}}} {\text{Fe}}_{{\text{0}}{\text{.015}}}^{{\text{3 + }}} } \right)_{1.005}^{\left[ 6 \right]} {\text{AL}}_{1.00}^{\left[ 5 \right]} \left[ {{\text{O}}_{{\text{1}}{\text{.00}}} |{\text{Si}}_{{\text{0}}{\text{.99}}} {\text{O}}_{{\text{4}}{\text{.00}}} } \right]$$ The mineral is greenish black, strongly pleochroic with X(∥a) yellow green, Y(∥b) bluish green, Z(∥c) deep golden yellow, biaxial positive, with 2V = 53°(3°), α = 1.702, β = 1.730, γ = 1.823. Vickers microhardness (100 gram load) ranges between 906 and 1017kp/mm2. The structure is orthorhombic, isotypic with andalusite, space group Pnnm, a = 0.7953(2), b = 0.8038(2), c = 0.5619(2) nm, V = 0.3592(1) nm3, a/b = 0.9895(3), c/b = 0.6990(3), S.G.(x) = 3.395 g/cm3, Z = 4. The strongest X-ray powder lines are (d in nm, I, hkl):0.5669, 100, 110; 0.4590, 75, 011 and 101; 0.3577, 90, 120 and 210; 0.2827, 94, 220; 0.2517, 90, 310 and 112; 0.2212, 83, 320, 122 and 212. Comparison of the intensities of 373 observed X-ray reflections with those calculated for several models of Mn3+-distribution indicates octahedral coordination of all or most of the manganese present. Interpretation of magnetic measurements (μeff = 3.15B.M. per Mn atom at 25 ° C) indirectly supports octahedral coordination of Mn3+. The name of the mineral is for Kanona, a town near the type locality. The name is proposed for the end member Mn3+ [6]Al[5][O¦SiO4] and for members of the solid-solution series towards andalusite with octahedral Mn3+>Al. The presently described mineral may be referred to as aluminian kanonaite. 相似文献
12.
Three independent Pb isotope homogenizing processes operating on large volumes of rock material during limited intervals in the Phanerozoic have been used to define a unique evolutionary curve for rock and ore lead isotopic compositions of the southern Massif Central, France. The model is
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