共查询到20条相似文献,搜索用时 601 毫秒
1.
2.
A. Skelton J. Hode Vuorinen F. Arghe A. Fallick 《Contributions to Mineralogy and Petrology》2007,154(1):75-90
We evaluate balanced metasomatic reactions and model coupled reactive and isotopic transport at a carbonatite-gneiss contact at Alnö, Sweden. We interpret structurally channelled fluid flow along the carbonatite-gneiss contact at ~640°C. This caused (1) metasomatism of the gneiss, by the reaction: ${\hbox{biotite} + \hbox{quartz} + \hbox{oligoclase} + \hbox{K}_{2} \hbox{O} +\,\hbox{Na}_{2}\hbox{O} \pm \hbox{CaO} \pm \hbox{MgO} \pm \hbox{FeO} = \hbox{albite} + \hbox{K-feldspar} + \hbox{arfvedsonite} + \hbox{aegirene-}\hbox{augite} + \hbox{H}_{2} \hbox{O} + \hbox{SiO}_{2}}We evaluate balanced metasomatic reactions and model coupled reactive and isotopic transport at a carbonatite-gneiss contact
at Aln?, Sweden. We interpret structurally channelled fluid flow along the carbonatite-gneiss contact at ∼640°C. This caused
(1) metasomatism of the gneiss, by the reaction: , (2) metasomatism of carbonatite by the reaction: calcite + SiO2 = wollastonite + CO2, and (3) isotopic homogenization of the metasomatised region. We suggest that reactive weakening caused the metasomatised
region to widen and that the metasomatic reactions are chemically (and possibly mechanically) coupled. Spatial separation
of reaction and isotope fronts in the carbonatite conforms to a chromatographic model which assumes local calcite–fluid equilibrium,
yields a timescale of 102–104 years for fluid–rock interaction and confirms that chemical transport towards the carbonatite interior was mainly by diffusion.
We conclude that most silicate phases present in the studied carbonatite were acquired by corrosion and assimilation of ijolite,
as a reactive by-product of this process and by metasomatism. The carbonatite was thus a relatively pure calcite–H2O−CO2–salt melt or fluid. 相似文献
3.
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 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 $ D_{\text{La}}^{{\text{Opx}} {\hbox{-}} {\text{melt}}} \sim 0.0005 to $ D_{\text{Lu}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.109 $ D_{\text{Lu}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.109 , D values for highly charged elements vary from $ D_{\text{Th}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.0026 $ D_{\text{Th}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.0026 through $ D_{\text{Nb}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.0033 $ D_{\text{Nb}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.0033 and $ D_{\text{U}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.0066 $ D_{\text{U}}^{{{\text{Opx}} {\hbox{-}} {\text{melt}}}} \sim 0.0066 to $ D_{\text{Ti}}^{{\text{Opx}} {\hbox{-}} {\text{melt}}} \sim 0.058 $ D_{\text{Ti}}^{{\text{Opx}} {\hbox{-}} {\text{melt}}} \sim 0.058 , and are all virtually independent of temperature. Cr and Co are the only compatible trace elements at the studied conditions.
To elucidate charge-balancing mechanisms for incorporation of REE into Opx and to assess the possible influence of Fe on Opx-melt
partitioning, we compare our experimental results with computer simulations. In these simulations, we examine major and minor
trace element incorporation into the end-members enstatite (Mg2Si2O6) and ferrosilite (Fe2Si2O6). Calculated solution energies show that R2+ cations are more soluble in Opx than R3+ cations of similar size, consistent with experimental partitioning data. In addition, simulations show charge balancing of
R3+ cations by coupled substitution with Li+ on the M1 site that is energetically favoured over coupled substitution involving Al–Si exchange on the tetrahedrally coordinated
site. We derived best-fit values for ideal ionic radii r
0, maximum partition coefficients D
0, and apparent Young’s moduli E for substitutions onto the Opx M1 and M2 sites. Experimental r
0 values for R3+ substitutions are 0.66–0.67 ? for M1 and 0.82–0.87 ? for M2. Simulations for enstatite result in r
0 = 0.71–0.73 ? for M1 and ~0.79–0.87 ? for M2. Ferrosilite r
0 values are systematically larger by ~0.05 ? for both M1 and M2. The latter is opposite to experimental literature data, which
appear to show a slight decrease in $ r_{0}^{{{\text{M}}2}} $ r_{0}^{{{\text{M}}2}} in the presence of Fe. Additional systematic studies in Fe-bearing systems are required to resolve this inconsistency and
to develop predictive Opx-melt partitioning models for use in terrestrial and lunar magmatic differentiation models. 相似文献
4.
Yousif Osman Mohammad 《Arabian Journal of Geosciences》2011,4(1-2):69-83
Two types of serpentinized peridotites are distinguished within the Northwest Zagros Thrust Zone (NW-ZTZ) in Kurdistan region of Iraq. One is found as lower members of ophiolite sequences, such as the Mawat and Penjwin ophiolites of the upper Cretaceous age. The other is represented by intraformational isolated serpentinite bodies in Betwat, Qaladeza, and Qalander areas within the Walash–Naopurdan volcano-sedimentary unit of the Paleocene to Eocene paleo-arc tectonic setting. Serpentinites within the NW-ZTZ consist mainly of lizardite and chrysotile, with subordinate amounts of syn-serpentinization magnetite, carbonates, chromium chlorite, tremolite, and talc as secondary minerals, and olivine, clinopyroxene, and chromian spinel as primary minerals. Minor antigorite is also found in the sheared serpentinites often found in ophiolite sequences. Petrological and geochemical studies of serpentinites from the NW-ZTZ show that, of the original protoliths of serpentinites, those associated with ophiolites are residual depleted harzburgite and dunite. The $ {\text{Cr}}\# \left( {{{ = {\text{ Cr}}} \mathord{\left/ {\vphantom {{ = {\text{ Cr}}} {\left( {{\text{Cr}} + {\text{Al}}} \right){\text{ atomic ratio}}}}} \right. \kern-0em} {\left( {{\text{Cr}} + {\text{Al}}} \right){\text{ atomic ratio}}}}} \right) $ of chromian spinel is more than 0.6, and the forsterite content of olivine is 91–92. On the other hand, the original protolith of isolated serpentinite bodies is less depleted harzburgite or depleted lherzolite, which has spinel with Cr# less than 0.6 and olivine with 90–91 forsterite contents. Whole rock chemistry of major, trace, and rare earth elements shows that the serpentinites of ophiolite sequences are depleted in CaO, Al2O3, and SiO2, Sr, and Zr, and are enriched in MgO, Ni, and Cr, in comparison with the isolated serpentinites. Cr# of the disseminated unaltered chromian spinels indicates that the serpentinites of both types had been originated from the supra-subduction zone tectonic setting; the serpentinites of ophiolite sequences obducted and thrusted over the continental margin during the obduction of the Tethyth oceanic crust onto the Arabian continental margin during the upper Cretaceous period. Isolated serpentinite bodies represent serpentinized forearc mantle wedge peridotites emplaced by diapiric upwelling into non-accretionary forearc tectonic settings during the Paleocene to Eocene age. 相似文献
5.
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
6.
Yamuna Singh Anubhooti Saxena A K Bhatt R Viswanathan T S Shaji L K Nanda 《Journal of Earth System Science》2018,127(1):4
Crystallochemical data on metamict davidite from albitites and albitised rocks from the Bichun area (Jaipur district, Rajasthan, India) of Banded Gneissic Complex (BGC) are provided. Davidite occurs as euhedral, subhedral to anhedral crystals in the form of disseminated grains and also as fracture filled veins. The crystals of davidite are up to 8 cm in length and 6 cm in width. The powder X-ray diffraction (XRD) pattern of the heat-treated davidite (at \(900{^{\circ }}\hbox {C}\)) reveals well-defined reflections of crystallographic planes. The calculated unit-cell parameters of the heat treated davidite are: \(\hbox {a}_{0} = \hbox {b}_{0} = 10.3556 \, \text {\AA }\) and \(\hbox {c}_{0} = 20.9067 \, \text {\AA }\), with unit-cell volume \(\hbox {(V)} = 1941.6385 \, \text {\AA }^{3}\); and \({\upalpha }={\upbeta }= 90^{\circ }\) and \({\upgamma }= 120^{\circ }\), which are in agreement with the values of davidite standard. Geochemical data reveals that the investigated davidite contains 51.5–52.6% \(\hbox {TiO}_{2}\), 14.8–15.1% \(\hbox {Fe}_{2} \hbox {O}_{3}\), 9.8–10.2% FeO, 6.97–7.12% \(\hbox {U}_{3} \hbox {O}_{8}\), 6.72–6.92% \(\hbox {RE}_{2} \hbox {O}_{3}\), 3.85–3.61% \(\hbox {K}_{2}\hbox {O}\), 0.9–1.4% \(\hbox {Al}_{2} \hbox {O}_{3}\), and 0.8–1.2% \(\hbox {SiO}_{2}\). The calculated structural formulae of the two davidite crystals are: D-1: \(\hbox {K}_{0.0044/0.004} \hbox {Ba}_{0.0044/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.053/0.053} \hbox {Mg}_{0.14/0.14} \hbox {Pb}_{0.0076/0.008} \hbox {Fe}_{2.675/2.675} \hbox {Fe}_{1.59/1.59} \hbox {Y}_{0.1175/0.118} \hbox {P}_{0.053/0.053} \hbox {Nb}_{0.008/0.008} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.033/0.033} \hbox {U}_{0.468/0.468} \hbox {Th}_{0.009/0.009} \,\,\hbox {REE}_{0.6829/0.683})_{6.05/6.05} (\hbox {Ti}_{12.15/12.15}\,\, \hbox {Fe}_{1.9022/1.903} \hbox {Si}_{0.372/0.372}\,\, \hbox {Al}_{0.517/0.517}\,\, \hbox {Cr}_{0.018/0.018} \hbox {Co}_{0.009/0.009} \hbox {Ni}_{0.027/0.027})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.319/0.319[]1.681/1.681})_{2/2}\) and D-2: \((\hbox {K}_{0.004/0.004} \hbox {Ba}_{0.005/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.05/0.05} \hbox {Mg}_{0.094/0.094} \hbox {Pb}_{0.007/0.007} \hbox {Fe}_{2.58/2.58} \hbox {Fe}_{1.71/1.71} \hbox {Y}_{0.112/0.112} \hbox {P}_{0.106/0.106} \hbox {Nb}_{0.006/0.006} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.03/0.03} \hbox {U}_{0.48/0.48} \hbox {Th}_{0.009/0.009} \hbox {REE}_{0.665/0.665})_{6.088/6.088} (\hbox {Ti}_{12.48/12.48} \hbox {Fe}_{1.87/1.87} \hbox {Si}_{0.249/0.249} \hbox {Al}_{0.334/0.334} \hbox {Cr}_{0.019/0.019} \hbox {Co}_{0.008/0.008} \hbox {Ni}_{0.04/0.04})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.098/0.098[]1.90/1.90})_{2/2}\). The calculated structural formulae are not fully stoichiometric, which could be due to metamict nature of davidite. The characteristic feature of distribution pattern of REE in davidite is unusually high concentration of LREE and HREE and substantially low content of MREE. It may be due to the occupation of REEs in two distinct crystallographic sites in davidite structure, i.e., M(1) and M(O) sites. Chondrite-normalised plot of davidite reveals a pronounced negative Eu-anomaly (\(\hbox {Eu}/\hbox {Eu}^{*} = 0.30{-}0.39\)), which suggests extremely fractionated nature of the metasomatising fluids from which davidite had crystallized. Metamict davidite-bearing U ores not only from Rajasthan, but also from other parts of India are likely to yield very high U leachability, thereby making them attractive sources of U, which otherwise are ignored by mineral engineers as uneconomic U ores. 相似文献
7.
The thermodynamic calculation of dehydration reacton suggests very low activity of H2O during metamorphic peak of the Archaean granulite complex in the region studied.The αH2O values for Al-rich gneiss and hypersthene biotite gneiss-granulite in the Taipingzhai region are usually between 0.10 and 0.20,and those in the Louzishan region are 0.15-0.25.The fugacity of O2 in terms of lgf O2 in whole region ranges form-8to-14.The average coefficients of (δμH2O/δHMg^Bt)and(δμO2/δXMg^Bt)in the Taipingzhai region are-0.293 and-1.60 respectively,and those in the Louzishan region are-0.364and-1.420.The activity of H2O is very low in the whole region,but its values and other data mentioned above are considerably constant from place to place within a given region,even in rocks of dirrerent lithological characters.However,they show a certain gradient between different regions.Such characteristics are compatible with the genetic mechanism known as“carbonic metamorphism” put forward by Newton et al.,i.e.,the α H2O during the peak stage is controlled by permeation of pervasive CO2 influx of the mantle source,and shows features of external buffering. 相似文献
8.
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
9.
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
10.
In this paper, we, for the first time, report geochemistry of sandstone from Somanpalli Group from Pomburna area in the Eastern Belt of Pranhita–Godavari (PG) Valley, central India and studied to infer their provenance, intensity of paleo-weathering and depositional tectonic setting. Petrographic study of sandstones show QFL modal composition of arenite. Chemical results show high \(\hbox {SiO}_{2}\) and CIA but lower \(\hbox {Al}_{2}\hbox {O}_{3}, \hbox {TiO}_{2}\), Rb, Sr, \(\hbox {K}_{2}\hbox {O}\) indicating mixed sources. Major elements chemistry parameters such as, \(\hbox {K}_{2}\hbox {O/Al}_{2}\hbox {O}_{3}\) ratio and positive correlation of Rb with \(\hbox {K}_{2}\hbox {O}\), reflects a warm and humid climate for study area. The tectonic discrimination plots (\(\hbox {SiO}_{2}/20\)–\(\hbox {K}_{2}\hbox {O} + \hbox {Na}_{2}\hbox {O}\)–\(\hbox {TiO}_{2} + \hbox {Fe}_{2}\hbox {O}_{3} + \hbox {MgO};\,\hbox {K}_{2}\hbox {O}/\hbox {Na}_{2}\hbox {O}\) vs. \(\hbox {SiO}_{2}\); Th–Sc–Zr/20) indicate dominantly passive margin and slight active tectonic setting. Concentrations of Zr, Nb, Y, and Th are higher compared to the UCC values and the trends in Th/Cr, Th/Co, La/Sc and Cr/Zr ratios support a felsic and mafic source for these sandstones and deposition in passive margin basin. Chondrite normalized REE pattern reflects LREE depletion, negative Eu anomaly and flat HREE similar to UCC, felsic components. ICV value (0.95) also supports tectonically quiescent passive margin settings. CIA values (74) indicate high degree of chemical weathering and warm and humid paleoclimatic condition. 相似文献
11.
Equilibrium alumina contents of orthopyroxene coexisting with spinel and forsterite in the system MgO-Al2O3-SiO2 have been reversed at 15 different P-T conditions, in the range 1,030–1,600° C and 10–28 kbar. The present data and three reversals of Danckwerth and Newton (1978) have been modeled assuming an ideal pyroxene solid solution with components Mg2Si2O6 (En) and MgAl2SiO6 (MgTs), to yield the following equilibrium condition (J, bar, K): $$\begin{gathered} RT{\text{ln(}}X_{{\text{MgTs}}} {\text{/}}X_{{\text{En}}} {\text{) + 29,190}} - {\text{13}}{\text{.42 }}T + 0.18{\text{ }}T + 0.18{\text{ }}T^{1.5} \hfill \\ + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP = 0,} \hfill \\ \end{gathered} $$ where $$\begin{gathered} + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP} \hfill \\ = [0.013 + 3.34 \times 10^{ - 5} (T - 298) - 6.6 \times 10^{ - 7} P]P. \hfill \\ \end{gathered} $$ The data of Perkins et al. (1981) for the equilibrium of orthopyroxene with pyrope have been similarly fitted with the result: $$\begin{gathered} - RT{\text{ln(}}X_{{\text{MgTs}}} \cdot X_{{\text{En}}} {\text{) + 5,510}} - 88.91{\text{ }}T + 19{\text{ }}T^{1.2} \hfill \\ + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP = 0,} \hfill \\ \end{gathered} $$ where $$\begin{gathered} + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP} \hfill \\ = [ - 0.832 - 8.78{\text{ }} \times {\text{ 10}}^{ - {\text{5}}} (T - 298) + 16.6{\text{ }} \times {\text{ 10}}^{ - 7} P]{\text{ }}P. \hfill \\ \end{gathered} $$ The new parameters are in excellent agreement with measured thermochemical data and give the following properties of the Mg-Tschermak endmember: $$H_{f,970}^0 = - 4.77{\text{ kJ/mol, }}S_{298}^0 = 129.44{\text{ J/mol}} \cdot {\text{K,}}$$ and $$V_{298,1}^0 = 58.88{\text{ cm}}^{\text{3}} .$$ The assemblage orthopyroxene+spinel+olivine can be used as a geothermometer for spinel lherzolites, subject to a choice of thermodynamic mixing models for multicomponent orthopyroxene and spinel. An ideal two-site mixing model for pyroxene and Sack's (1982) expressions for spinel activities provide, with the present experimental calibration, a geothermometer which yields temperatures of 800° C to 1,350° C for various alpine peridotites and 850° C to 1,130° C for various volcanic inclusions of upper mantle origin. 相似文献
12.
The temperature-sensitive Fe,Mg exchange equilibrium,
|