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1.
Trace element analyses of 1-atm and high-pressure experiments show that in komatiite and peridotite, the olivine (OL)/liquid (L) distribution coefficient for Al 2O 3 (
) increases with pressure and temperature. Olivine in equilibrium with liquid accepts as much as 0.2 wt% Al 2O 3 in solution at 6 GPa. Convergence to equilibrium compositions at this high level is shown by cation diffusion of Al into synthetic forsterite crystals of low-Al contents in the presence of melt. Convergence to low-Al equilibrium compositions at lower P and T is shown by diffusion of Al out of synthetic forsterite with high initial Al content. Isobaric and isothermal experimental data subsets reveal that temperature and pressure variations both have real effects on
. Variation in silicate melt composition has no detectable effect on
within the limited range of experimentally investigated mixtures. Least-squares regression for 24 experiments, using komatiite and peridotite, performed at 1 atm to 6 GPa and 1300 to 1960°C, gives the best fit equation:
Increase in
with increasingly higher-pressure melting is consistent with incorporation of a spinel-like component of low molar volume into olivine, although other substitutions possibly involving more complex coupling cannot be ruled out. High P-T ultrabasic melting residues, if pristine, may be recognized by the high
calculated from microprobe analyses of Al 2O 3 concentrations in residual olivines and estimated Al 2O 3 concentration in the last liquid removed. In general the low levels of Al in natural olivine from mantle xenoliths suggest that pristine residues are rarely recovered. 相似文献
2.
Three Al-Cr exchange isotherms at 1,250°, 1,050°, and 796° between Mg(Al, Cr) 2O 4 spinel and (Al, Cr) 2O 3 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) 2O 3 crystalline solution (Chatterjee et al. 1982a) and assuming that the Mg(Al, Cr) 2O 4 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) 2O 4 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 dT c/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.
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 MgAl 2O 4, 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+Fe 3+) 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 |
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4.
Experiments at high pressure and temperature indicate that excess Ca may be dissolved in diopside. If the (Ca, Mg) 2Si 2O 6 clinopyroxene solution extends to more Ca-rich compositions than CaMgSi 2O 6, macroscopic regular solution models cannot strictly be applied to this system. A nonconvergent site-disorder model, such as that proposed by Thompson (1969, 1970), may be more appropriate. We have modified Thompson's model to include asymmetric excess parameters and have used a linear least-squares technique to fit the available experimental data for Ca-Mg orthopyroxene-clinopyroxene equilibria and Fe-free pigeonite stability to this model. The model expressions for equilibrium conditions \(\mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction A) and \(\mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction B) are given by: 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Mg}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ W_{21} [2(X_{{\text{Ca}}}^{{\text{M2}}} )^3 - (X_{{\text{Ca}}}^{{\text{M2}}} ] \hfill \\ {\text{ + 2W}}_{{\text{22}}} [X_{{\text{Ca}}}^{{\text{M2}}} )^2 - (X_{{\text{Ca}}}^{{\text{M2}}} )^3 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{Wo}}}^{{\text{opx}}} )^2 \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Ca}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ 2W_{21} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^2 - (X_{{\text{Mg}}}^{{\text{M2}}} )^3 ] \hfill \\ {\text{ + W}}_{{\text{22}}} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^3 - (X_{{\text{Mg}}}^{{\text{M2}}} )^2 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{En}}}^{{\text{opx}}} )^2 \hfill \\ \hfill \\ \end{gathered} $$ where 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = 2.953 + 0.0602{\text{P}} - 0.00179{\text{T}} \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = 24.64 + 0.958{\text{P}} - (0.0286){\text{T}} \hfill \\ {\text{W}}_{{\text{21}}} = 47.12 + 0.273{\text{P}} \hfill \\ {\text{W}}_{{\text{22}}} = 66.11 + ( - 0.249){\text{P}} \hfill \\ {\text{W}}^{{\text{opx}}} = 40 \hfill \\ \Delta {\text{G}}_*^0 = 155{\text{ (all values are in kJ/gfw)}}{\text{.}} \hfill \\ \end{gathered} $$ . Site occupancies in clinopyroxene were determined from the internal equilibrium condition 1 $$\begin{gathered} \Delta G_{\text{E}}^{\text{O}} = - {\text{RT 1n}}\left[ {\frac{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}{{X_{{\text{Ca}}}^{{\text{M2}}} \cdot X_{{\text{Mg}}}^{{\text{M1}}} }}} \right] + \tfrac{1}{2}[(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} )(2{\text{X}}_{{\text{Ca}}}^{{\text{M2}}} - 1) \hfill \\ {\text{ + }}\Delta G_*^0 (X_{{\text{Ca}}}^{{\text{M1}}} - X_{{\text{Ca}}}^{{\text{M2}}} ) + \tfrac{3}{2}(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} ) \hfill \\ {\text{ (1}} - 2X_{{\text{Ca}}}^{{\text{M1}}} )(X_{{\text{Ca}}}^{{\text{M1}}} + \tfrac{1}{2})] \hfill \\ \end{gathered} $$ where δG E 0 =153+0.023T+1.2P. The predicted concentrations of Ca on the clinopyroxene Ml site are low enough to be compatible with crystallographic studies. Temperatures calculated from the model for coexisting ortho- and clinopyroxene pairs fit the experimental data to within 10° in most cases; the worst discrepancy is 30°. Phase relations for clinopyroxene, orthopyroxene and pigeonite are successfully described by this model at temperatures up to 1,600° C and pressures from 0.001 to 40 kbar. Predicted enthalpies of solution agree well with the calorimetric measurements of Newton et al. (1979). The nonconvergent site disorder model affords good approximations to both the free energy and enthalpy of clinopyroxenes, and, therefore, the configurational entropy as well. This approach may provide an example for Febearing pyroxenes in which cation site exchange has an even more profound effect on the thermodynamic properties. 相似文献
5.
In the Rogers Pass area of British Columbia the almandine garnet isograd results from a reaction of the form: 5.31 ferroan-dolomite+8.75 paragonite+4.80 pyrrhotite+3.57 albite+16.83 quartz+1.97 O 2=1.00 garnet+16.44 andesine+1.53 chlorite+2.40 S 2+1.90 H 2O+10.62 CO 2. The coefficients of this reaction are quite sensitive to the Mn content of ferroan-dolomite.Experimental data applied to mineral compositions present at the isograd, permits calculation of two intersecting P, T equilibrium curves. P=29088–39.583 T is obtained for the sub-system paragonite-margarite (solid-solution), plagioclase, quartz, ferroan-dolomite, and P=28.247 T–14126 is obtained for the sub-system epidote, quartz, garnet, plagioclase. These equations yield P=3898 bars and T=638° K (365° C). These values are consistent with the FeS content of sphalerite in the assemblage pyrite, pyrrhotite, sphalerite and with other estimates for the area.At these values of P and T the composition of the fluid phase in equilibrium with graphite in the system C-O-H-S during the formation of garnet is estimated as:
bars,
bars,
bars,
bars,
bars,
bars,
bars,
bars,
, bars,
bars. 相似文献
6.
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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7.
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 Fe 3+ in both varieties, with Fe 2+/(Fe 2++Fe 3+) 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 Fe 3+ in six or five-fold coordination. The doublet components have anomalously large half widths indicating either accomodation of Fe 3+ in more than one position (e.g., octahedra A1 and five coordinated A2) 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: Mn 2+( A1) Mn 3+( A1′) ? Mn 3+( A1) Mn 2+( A1′) and Mn 2+( A1) Mn 3+( A2 ? Mn 3+( A1) Mn 2+( A2) in PY and Fe 2+( A1) Fe 3+( A1′) ? Fe 3+( A1) Fe 2+( A1′) in GY. The evidence for homonuclear Mn 2+ Mn 3+ 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 Mn 3+ in two positions. Weak bands around 10,000 cm ?1 in both varieties are assigned to Fe 2+ spin-allowed dd-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 Fe 3+ spin-forbidden dd-transitions. 相似文献
8.
Near-liquidus melting experiments were performed on a high- K latite at fO 2's ranging from iron-wustite-graphite (IWG) to nickel-nickel oxide (NNO) in the presence of a C-O-H fluid phase. Clinopyroxene is a liquidus phase under all conditions. At IWG
, the liquidus at 10 kb is about 1,150° C but is depressed to 1,025° C at NNO and
. Phlogopite and apatite are near-liquidus phases, with apatite crystallizing first at pressures below 10 kb. Phlogopite is a liquidus phase only at NNO and high
. Under all conditions the high- K latites show a large crystallization interval with phlogopite becoming the dominant crystalline phase with decreasing temperature. Increasing fO 2 affects phlogopite crystallization but the liquidus temperature is essentially a function of
. The chemical compositions of the near-liquidus phases support formation of the high- K latites under oxidizing conditions (NNO or higher) and high
. It is concluded from the temperature of the H 2O-saturated liquidus at 10 kb, the groundmass: crystal ratio and presence of chilled latite margins around some xenoliths that the Camp Creek high- K latite magma passed thru the lower crust at temperatures of 1,000° C or more. 相似文献
9.
Agates of volcanic origin, containing the different quartz species, fibrous, length-fast chalcedony (CH), granular fine quartz (FQ), and fibrous, length-slow, to lepidospheric quartzine (QN), have been investigated to evaluate possible relations between microstructure, i.e. crystallite size and texture, refractive indices, densities, contents of trace elements and of water, as well as dehydration behaviour. By means of near infrared spectroscopy, total water contents
, could be differentiated quantitatively into contents of molecular water,
, and silanole-group water,
. Despite the low total water contents of the agates studied (
between 1 and 2 wt.%), near infrared spectroscopy results in reliable data on
and
.Wall-layering CH consists of fibrous quartz crystals and exhibits higher C-ratios,
, than horizontally layered FQ which consists predominantly of granular quartz crystals ( C
CH=0.45±0.11 ( N=6), C
FQ=0.36±0.10 ( N=4). This result is interpreted to be due to analogy with the behaviour of C-ratios in fluid phase-deposited opals-AN (hyalithe) and liquid phase-deposited opals-AG (non-crystalline opal) or -CT (common opal) (Langer and Flörke 1974).Translucent layers of CH show mostly lower refractive indices, when measured parallel than when measured perpendicular to the axes of the quartz fibers. The same is true for milky layers of CH. Crystallite sizes are smaller in the latter than in the former.For all samples studied, exists a positive correlation between at% (1/2Ca+1/2Mg+Na+K+Li) and at% (Al 3++Fe 3+). This indicates that at least parts of (A1 3++ Fe 3+) substitute for Si in the quartz structure. The charge is balanced by incorporation of di- and mono-valent cations in structural interstices. When the quantity at % H +, as obtained from
, is included into the sum at% (1/2 Me 2++Me +), the above correlation is destroyed. This result could be indicative for a strong concentration of the Si-OH groups in the surface of the quartz microcrystallites. 相似文献
10.
Under hydrous conditions the stability field of the assemblage Mg-cordierite+K feldspar+quartz is limited on its low-temperature side by the breakdown of cordierite+K feldspar into muscovite, phlogopite and quartz, whereas the high-temperature limit is given by eutectic melting. The compatibility field of the assemblage ranges from 530° C to 745° C at 1 kbar
, from 635 to 725° C at 3 kbars
, from 695 to 725° C at 5 kbars
and terminates at 5.5 kbars
. Most components not considered in the model system will tend to restrict this field even more. However, the condition
< P
total will increase the range of stable coexistence drastically, making the assemblage common at elevated temperatures from contact metamorphic rocks up to intermediate pressure granulites of appropriate bulk composition. 相似文献
11.
The partition of iron and magnesium between cordierite and garnet depends on
as well as temperature. The apparently conflicting experimental data on the values of K
D
may be reconciled by considering the
pertaining during the different experiments. 相似文献
12.
A wide set of aqueous chemistry data (574 water analyses) from natural environments has been used to testify and validate
of the solubility of synthetic hydroxyaluminosilicate (HAS B) , Al 2Si 2O 5(OH) 4. The ground and surface waters represent regolith and/or fissure aquifers in various (magmatic, sedimentary and metamorphic)
bedrocks in the Sudetes Mts. (SW Poland). The solubility of HAS B in natural waters was calculated using the method proposed by Schneider et al. (Polyhedron 23:3185–3191, 2004). Results confirm
usefulness and validity of this method. The HAS B solubility obtained from the field data (logK sp = −44.7 ± 0.58) is lower than it was estimated (logK sp = −40.6 ± 0.15) experimentally (Schneider et al. Polyhedron 23:3185–3191, 2004). In the waters studied the equilibrium with
HAS B is maintained at pH above 6.7 and at [Al 3+] ≤ 10 −10. Silicon activity (log[H 4SiO 4]) ranges between −4.2 and −3.4. Due to the calculation method used, the K sp mentioned above cannot be considered as a classical solubility constant. However, it can be used in the interpretation of
aluminium solubility in natural waters. The HAS B has solubility lower than amorphous Al(OH) 3, and higher than proto-imogolite. From water samples that are in equilibrium with respect to HAS B, the solubility product described by the reaction,
is calculated to be logK sp = 14.0 (±0.7) at 7°C. 相似文献
13.
The interdependence of the Fe(Mg) –1 (e.g., FeO-MgO in silicate melt; CaFeSi 2O 6-CaMgSi 2O 6 in pyroxene) and TiAl 2(MgSi 2) –1 exchange reactions between silicate melts and coexisting Ca-pyroxene has been examined. High-calcium clinopyroxenes were grown in 1 atmosphere melting and crystallization experiments on rock powders spanning the composition range tholeiite to melilitite (1,092 2+Mg2+ exchange and
suggest that at given values of
extent of Fe(Mg)–1 substitution is strongly coupled with the TiAl2(MgSi2)–1 substitution in pyroxenes near the five-component space CaMg(Si2O6-CaFe(Si)2O6-CaTi(Al)2O6-CaFe(Al,Si)2O6-CaAl(Al,Si)2O6. The inferred stabilization of Ti in iron-rich relative to magnesium pyroxene is consistent with the operation of Fe2+Ti4+ intervalence charge transfer interactions (e.g., Rossman 1980) and observations on zoning in natural titanaugites (e.g., Tracy and Robinson 1977). Although the rims of some pyroxenes grown in some melting experiments exhibit prominent zoning in TiAl2(MgSi2)–1, the average values of
inferred from the compositions of these pyroxenes, together with those of the relatively homogeneous pyroxenes produced in crystallization experiments, exhibit a 11 correlation with values of
derived from the solution model of Ghiorso et al. (1983) with a standard error of 750 calories. The Ti contents of Ca-rich pyroxenes crystallizing from a wide range of natural silicate liquids can therefore be predicted. 相似文献
14.
The occurrence of critical assemblages among antigorite, diopside, tremolite, forsterite, talc, calcite, dolomite and magnesite in progressively metamorphosed ophicarbonate rocks, together with experimental data, permits the construction of phase diagrams in terms of the variables P, T, and composition of a binary CO 2-H 2O fluid. Equilibrium constants are given for the 30 equilibria that describe all relations among the above phases. Ophicalcite, ophidolomite, and ophimagnesite assemblages occupy partially overlapping fields in the
diagram. The upper temperature limit of ophicalcite rocks lies below that of ophidolomite and ophimagnesite. The fluid phase in ophicarbonate rocks has
0.8$$
" align="middle" border="0">
, and there are indications that
during their progressive metamorphism is approximately equal to P
total. 相似文献
15.
Stability relations of Fe-Mg cordierite with K feldspar have been determined for conditions of muscovite-quartz instability, applicable to highgrade metamorphism of pelitic rocks. Fe cordierite, K feldspar, and water break down to Fe biotite, sillimanite, and quartz at pressures above a line through 640 ° C, 2kbar and 710 ° C, 2.7 kbar. A P-X diagram for the Fe-Mg analogue of this reaction at 675 ° C is consistent with a naturally occuring cordierite-biotite K
D
value of 0.53 if Al content of biotite and cordierite water of hydration are taken into account.At higher temperatures Fe cordierite breaks down alone to almandine, sillimanite, quartz and water at pressures above a line through 650 ° C, 3.41 kbar and 760 ° C, 2.9 kbar. For the Fe-Mg reaction, P-X data up to 4 kbar may be extrapolated with use of natural K
D
values increasing toward one with increasing temperatures.Lines of constant cordierite composition for the two reactions intersect in an Fe-Mg univariant reaction of sillimanite-biotite-quartz to cordieritealmandine- K feldspar-water which is metastable relative to melt at
= P
tot Reduced water pressure and impurities in the garnet and K feldspar greatly reduce the temperature of this reaction so that it becomes a reasonable reaction for upper amphibolite and granulite facies conditions.The results demonstrate that (1) cordierite may be used as a geobarometer if temperature and approximate
can be estimated, (2) almandine low in Mn and Ca does not participate in cordierite reactions where muscovite is present, and (3) the reaction which forms cordierite, almandine, and K feldspar is a possible melt-forming reaction which, under reduced
, occurs about 50 ° C above the muscovite melting reaction. 相似文献
16.
The existing experimental data [Ferry and Spear 1978; Perchuk and Lavrent'eva 1983] on Mg?Fe partitioning between garnet and biotite are disparate. The underlying assumption of ideal Mg?Fe exchange between the minerals has been examined on the basis of recently available thermochemical data. Using the updated mixing parameters for the pyrope-almandine asymmetric regular solution as inputs [Ganguly and Saxena 1984; Hackler and Wood 1984], thermodynamic analysis points to non-ideal mixing in the phlogopite-annite binary in the temperature range of 550°C–950°C. The non-ideality can be approximated by a temperature-independent, one constant Margules parameter. The retrieved values for enthalpy of mixing for Mg?Fe biotites and the standard state enthalpy and entropy changes of the exchange reaction were combined with existing thermochemical data on grossular-pyrope and grossular-almandine binaries to obtain geothermometric expressions for Mg?Fe fractionation between biotite and garnet. [T in K] $$\begin{gathered} {\text{T(HW) = [20286 + 0}}{\text{.0193P - \{ 2080(X}}_{{\text{Mg}}}^{{\text{Gt}}} {\text{)}}^{\text{2}} {\text{ - 6350(X}}_{{\text{Fe}}}^{{\text{Gt}}} {\text{)}}^{\text{2}} \hfill \\ {\text{ - 13807(X}}_{{\text{Ca}}}^{{\text{Gt}}} {\text{)(1 - X}}_{{\text{Mn}}}^{{\text{Gt}}} {\text{) + 8540(X}}_{{\text{Fe}}}^{{\text{Gt}}} {\text{)(X}}_{{\text{Mg}}}^{{\text{Gt}}} {\text{)(1 - X}}_{{\text{Mn}}}^{{\text{Gt}}} {\text{)}} \hfill \\ {\text{ + 4215(X}}_{{\text{Ca}}}^{{\text{Gt}}} {\text{)(X}}_{{\text{Mg}}}^{{\text{Gt}}} {\text{ - X}}_{{\text{Fe}}}^{{\text{Gt}}} {\text{)\} + 4441}}{{{\text{(2X}}_{{\text{Mg}}}^{{\text{Bt}}} {\text{ - 1)]}}} \mathord{\left/ {\vphantom {{{\text{(2X}}_{{\text{Mg}}}^{{\text{Bt}}} {\text{ - 1)]}}} {{\text{[13}}{\text{.138}}}}} \right. \kern-\nulldelimiterspace} {{\text{[13}}{\text{.138}}}} \hfill \\ {\text{ + 8}}{\text{.3143 InK}}_{\text{D}} {\text{ + 6}}{\text{.276(X}}_{{\text{Ca}}}^{{\text{Gt}}} ){\text{(1 - X}}_{{\text{Mn}}}^{{\text{Gt}}} )] \hfill \\ {\text{T(GS) = [13538 + 0}}{\text{.0193P - \{ 837(X}}_{{\text{Mg}}}^{{\text{Gt}}} )^{\text{2}} {\text{ - 10460(X}}_{{\text{Fe}}}^{{\text{Gt}}} )^2 \hfill \\ {\text{ - 13807(X}}_{{\text{Ca}}}^{{\text{Gt}}} )(1{\text{ - X}}_{{\text{Mn}}}^{{\text{Gt}}} {\text{) + 19246(X}}_{{\text{Fe}}}^{{\text{Gt}}} ){\text{(X}}_{{\text{Mg}}}^{{\text{Gt}}} ){\text{(1 - X}}_{{\text{Mn}}}^{{\text{Gt}}} ) \hfill \\ {\text{ }}{{{\text{ + 5649(X}}_{{\text{Ca}}}^{{\text{Gt}}} ){\text{(X}}_{{\text{Mg}}}^{{\text{Gt}}} {\text{ - X}}_{{\text{Fe}}}^{{\text{Gt}}} ){\text{\} + 7972(2X}}_{{\text{Mg}}}^{{\text{Bt}}} {\text{ - 1)]}}} \mathord{\left/ {\vphantom {{{\text{ + 5649(X}}_{{\text{Ca}}}^{{\text{Gt}}} ){\text{(X}}_{{\text{Mg}}}^{{\text{Gt}}} {\text{ - X}}_{{\text{Fe}}}^{{\text{Gt}}} ){\text{\} + 7972(2X}}_{{\text{Mg}}}^{{\text{Bt}}} {\text{ - 1)]}}} {{\text{[6}}{\text{.778}}}}} \right. \kern-\nulldelimiterspace} {{\text{[6}}{\text{.778}}}} \hfill \\ {\text{ + 8}}{\text{.3143InK}}_{\text{D}} {\text{ + 6}}{\text{.276(X}}_{{\text{Ca}}}^{{\text{Gt}}} )(1{\text{ - X}}_{{\text{Mn}}}^{{\text{Gt}}} )] \hfill \\ \end{gathered} $$ The reformulated geothermometer is an improvement over existing biotite-garnet geothermometers because it reconciles the experimental data sets on Fe?Mg partitioning between the two phases and is based on updated activity-composition relationship in Fe?Mg?Ca garnet solid solutions. 相似文献
17.
Ignimbrites from the central North Island consist mainly of glass or its devitrified product (70–95%); their phenocryst mineralogy is varied and includes plag., hyp., ti-mag., ilm., aug., hblende, biot., san., qtz, ol., with accessory apatite, zircon and pyrrhotite. The Fe-Mg minerals can be used to divide the ignimbrites into four groups with hyp.+aug. reflecting high quench temperatures and biot.+hblende +hyp.+aug., low quench temperatures. Oxygen fugacities lie above the QMF buffer curve and even in ignimbrites with low crystal contents the solid phases apparently buffered fO 2. Some ignimbrites contain the assemblage actinolite, gedrite, magnetite and hematite, reflecting post-eruption oxidation. The mineralogy also allows estimation of
using pyrrhotite and thence
,
. The assemblage biotite-sanidine can be used to estimate
and thence
. Water fugacity is calculated in a variety of ways using both biotite and hornblende as well as the combining reaction
. It is high and approaches P
total in most ignimbrites (~4kb) but is lower in unwelded pumice breccias. Comparison of temperature estimates using mineral geothermometers for the various phenocryst phases suggests that the ignimbrite magmas showed temperature differences of 60–100 °C and pressure differences of several kilobars. Individual magma chambers therefore, would have extended over several kilometres vertically. The chemical potential of water may have been constant through the magma. 相似文献
18.
To investigate the point defect chemistry and the kinetic properties of manganese olivine Mn 2SiO 4, electrical conductivity ( ) of single crystals was measured along either the [100] or the [010] direction. The experiments were carried out at temperatures T=850–1200 °C and oxygen fugacities
atm under both Mn oxide ( MO) buffered and MnSiO 3 ( MS) buffered conditions. Under the same thermodynamic conditions, charge transport along [100] is 2.5–3.0 times faster than along [010]. At high oxygen fugacities, the electrical conductivity of samples buffered against MS is 1.6 times larger than that of samples buffered against MO; while at low oxygen fugacities, the electrical conductivity is nearly identical for the two buffer cases. The dependencies of electrical conductivity on oxygen fugacity and temperature are essentially the same for conduction along the [100] and [010] directions, as well as for samples coexisting with a solid-state buffer of either MO or MS. Hence, it is proposed that the same conduction mechanisms operate for samples of either orientation in contact with either solid-state buffer.The electrical conductivity data lie on concave upward curves on a log-log plot of vs
, giving rise to two
regimes with different oxygen fugacity exponents. In the low-
regime
, the
exponent, m, is 0, the MnSiO 3-activity exponent, q, is 0, and the activation energy, Q, is 45 kJ/mol. In the high
regime
10^{ - 7} {\text{atm}}} \right)$$
" align="middle" border="0">
, m=1/6, q=1/4–1/3, and Q=45 and 200 kJ/mol for T<1100 °c=" and="> T>1100 °C, respectively. 相似文献
19.
APL computer programs for the thermodynamic calculation of devolatilization and solid-solid equilibria operate using stored values for the molar volume and entropy of solids, the free energies of H 2O and CO 2, and the free energies of formation for 110 geologically-important phases. P-T-X
CO
2 calculations of devolatilization equilibria can be made at pressures from 0.2 through 10 kb, and temperatures from 200 through 1,000° C. P-T-X calculations of solid-solid equilibria may be accomplished at pressures to 30 kb and temperatures to 1,000° C. Calculations can be extrapolations from experimental points, or direct calculations from thermochemical data alone. Options are available in these programs to consider effects of: real vs. ideal gas mixing, thermal expansion and compressibility, solid solution, fluid pressure differing from solid pressure, and uncertainties in high-temperature entropies.A collection of thermodynamic data programs accompanies the programs for calculating P-T-X
CO
2 equilibria. Over a wide range of physical conditions, the data functions report free energies, entropies, fugacities of H 2O and CO 2, high temperature entropies of solids, and activities of components in H 2O-CO 2 mixtures.List of Symbols
Activity of H 2O and CO 2
- G f
Free energy of formation of a phase from elements
- G r
Free energy change of reaction
- G
r
o
Standard state free energy change of a reaction
-
Free energies of pure H 2O and CO 2
- H
r
o
Standard state enthalpy change for a reaction
- K
Equilibrium constant
- R
Gas constant
- S
r
o
Standard state entropy change of reaction
- S
s
o
Standard state entropy change of solids in a reaction
- V s
o
Standard state volume change of a reaction
- V s
o
Standard state volume change of solids in a reaction
-
Mole fraction of H 2O and CO 2
-
Activity coefficient of H 2O and CO 2 相似文献
20.
The Gibbs free energy and volume changes attendant upon hydration of cordierites in the system magnesian cordierite-water have been extracted from the published high pressure experimental data at \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) = P total, assuming an ideal one site model for H 2O in cordierite. Incorporating the dependence of ΔG and ΔV on temperature, which was found to be linear within the experimental conditions of 500°–1,000°C and 1–10,000 bars, the relation between the water content of cordierite and P, T and \(f_{{\text{H}}_{\text{2}} {\text{O}}} \) has been formulated as $$\begin{gathered} X_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{crd}}} = \hfill \\ \frac{{f_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{P, T}}} }}{{\left[ {{\text{exp}}\frac{1}{{RT}}\left\{ {64,775 - 32.26T + G_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{1, }}T} - P\left( {9 \times 10^{ - 4} T - 0.5142} \right)} \right\}} \right] + f_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{P, T}}} }} \hfill \\ \end{gathered} $$ The equation can be used to compute H 2O in cordierites at \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) <1. Our results at different P, T and partial pressure of water, assuming ideal mixing of H 2O and CO 2 in the vapour phase, are in very good agreement with the experimental data of Johannes and Schreyer (1977, 1981). Applying the formulation to determine \(X_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{crd}}} \) in the garnet-cordierite-sillimanite-plagioclase-quartz granulites of Finnish Lapland as a test case, good agreement with the gravimetrically determined water contents of cordierite was obtained. Pressure estimates, from a thermodynamic modelling of the Fe-cordierite — almandine — sillimanite — quartz equilibrium at \(P_{{\text{H}}_{\text{2}} {\text{O}}} = 0\) and \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) =P total, for assemblages from South India, Scottish Caledonides, Daly Bay and Hara Lake areas are compatible with those derived from the garnetplagioclase-sillimanite-quartz geobarometer. 相似文献
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