Abstract
Use of simple mixing models of orthopyroxene and garnet solid solutions enables extrapolation of experimentally determined equilibria in the MgSiO3-Al2O3 system to uninvestigated parts of pressure-temperature-composition space. Apparent discrepancies in the experimental data for simple and multicomponent systems may be explained by considering the effect of CaO and FeO on reducing pyrope activity in the garnet solid solutions. Equilibration pressures of natural garnet-orthopyroxene assemblages may be calculated, provided temperatures are known, from a combination of the experimental data on the MgSiO3-Al2O3 system and analyses of coexisting natural phases.
Despite the presence of a compositional gap in the system, the solubility of enstatite in diopside coexisting with orthopyroxene can also be approximately treated by an ideal solution model. An empirical approach has been developed to take account of Fe2+ on the orthopyroxene-clinopyroxene miscibility gap in natural systems in order to calculate equilibration temperatures of 2-pyroxene assemblages. The model presented reproduces almost all of the available experimental data for multicomponent systems to within 60° C.
Similar content being viewed by others
References
Atkins, F. B.: Pyroxenes of the Bushveld Intrusion, South Africa, J. Petrol. 10, 222–49 (1969)
Beeson, M. H., Jackson, E. D.: Origin of Garnet-Pyroxenite Xenoliths at Salt Lake Grater, Oahu, Mineral. Soc. Amer. Spec. Pap. 3, 95–112 (1970)
Bowen, N. L., Schairer, J. F.: The system MgO-FeO-SiO2. Am. J. Sci. 29, 151–217 (1935)
Boyd, F. R.: Electron-probe study of Diopside inclusions from Kimberlite, Amer. J. Sci. 267A, 50–69 (1969)
Boyd, F. R.: Garnet peridotites and the system CaSiO3-MgSiO3-Al2O3. Mineral. Soc. Amer. Spec. Pap. 3, 63–75 (1970)
Boyd, F. R., England, J. L.: The system enstatite-pyrope. Yearbook Carnegie Inst. Wash. 63, 157–161 (1964)
Boyd, F. R., Nixon, P. H.: Ultramafic nodules from the Thaba Putsoa Kimberlite Pipe. Yearbook Carnegie Inst. Wash. 71, 382–373 (1972)
Brown, G. M.: Pyroxenes from the Early and Middle Stages of Fractionation of the Skaergaard Intrusion, East Greenland, Mineral. Mag. 31, 511–43 (1957)
Brown, G. M.: Experimental studies on inversion relations in natural pigeonitic pyroxenes. Yearbook Carnegie Inst. Wash. 66, 347–353 (1967)
Carmichael, I. S. E.: The iron-titanium oxides of salic volcanic rocks and their associated ferromagnesium silicates. Contr. Mineral. and Petrol. 14, 36–64 (1967a)
Carmichael, I. S. E.: The mineralogy of Thingmuli, a Tertiary volcano in eastern Iceland. Am. Mineralogist 52, 1815–1841 (1967b)
Chatterjee, N. D., Schreyer, W.: The reaction enstatitess+sillimanite⇌sapphiriness+quartz Contr. Mineral. and Petrol. 36, 49–62 (1972)
Davis, B. T. C., Boyd, F. R.: The join Mg2Si2O6-CaMgSi2O6 at 30 kilobars pressure and its application to pyroxenes from Kimberlites, J. Geophys. Res. 71, 3567–3576 (1966)
Evans, B. W., Moore, J. G.: Mineralogy as a function of depth in the prehistoric Makaopuhi tholeiitic lava lake, Hawaii. Contr. Mineral. and Petrol. 17, 85–115 (1968)
Green, D. H.: Conditions of melting of basanite magma from Garnet Peridotite. Earth Planet. Sci. Lett. 17, 456–465 (1973)
Green D. H., Hibberson, W.: Experimental duplication of conditions of precipitation of high pressure phenocrysts in a basaltic magma. Phys. Earth Planet. Int. 3, 247–254 (1970)
Green, D. H., Ringwood, A. E.: The genesis of basaltic magmas. Contr. Mineral. and Petrol. 15, 103–190 (1967)
Green, D. H., Ringwood, A. E.: Mineralogy of peridotitic compositions under upper mantle conditions. Phys. Earth Planet. Interiors 3, 359–371 (1970)
Hafner, S. S., Virgo, D., Warburton, D.: Cation distributions and cooling history of clinopyroxenes from Oceanus Procellarum. Proceedings 2nd Lunar Science Conference, Vol. 1, 99–108 (1971)
Heming, R. F., Carmichael, I. S. E.: High-temperature pumice flows from Rabaul Caldera, Papua, New Guinea, Contr. Mineral. and Petrol. 38, 1–20 (1973)
Himmelberg, G. R., Loney, R. A.: Petrology of the Vulcan Peak Alpine-Type Peridotite, Southwestern Oregon, Geol. Soc. Am. Bull. 84, 1585–1600 (1973)
Howie, R. A.: The geochemistry of the Charnockite series of madras, India. Trans. Roy. Soc. Edinburgh 62, 725–768 (1955)
Kushiro, I., Shimizu, N., Nakamura, Y.: Compositions of coexisting liquid and solid phases formed upon melting of natural Garnet and Spinel lherzolites at high pressures: A preliminary report. Earth Planet. Sci. Lett. 14, 19–25 (1972)
Lindsley, D. H., Munoz, J. L.: Subsolidus relations along the join hedenbergite-ferrosilite. Am. J. Sci. 267 A, 295–324 (1969)
MacGregor, I. D.: The system MgO-Al2O3-SiO2; Solubility of Al2O3 in enstatite for spinel- and garnet-peridotite compositions. Am. Mineralogist (in press) (1973)
Medaris, L. G., Jr.: High-Pressure peridotites in Southwestern Oregon. Geol. Soc. Am. Bull. 83, 41–58 (1972)
Nafziger, R. H., Muan, A.: Equilibrium phase compositions and thermodynamic properties of olivines and pyroxenes in the system MgO-“FeO” -SiO2. Am. Mineralogist 52, 1364–1385 (1967)
O'Hara, M. J., Schairer, J. F.: The join diopside-pyrope at atmospheric pressure, Yearbook Carnegie Inst. Wash. 62, 107–115 (1963)
Saxena, S. K., Ghose, S.: Mg2+-Fe2+ Order-disorder and the thermodynamics of the orthopyroxene crystalline solution. Am. Mineralogist 56, 532–559 (1971)
Skinner, B. J., Boyd, F. R.: Aluminous enstatites. Yearbook Carnegie Inst. Wash. 63, 163–165 (1964)
Smith, D.: Stability of iron-rich pyroxene in the system CaSiO3-FeSiO3-MgSiO3. Am. Mineralogist 57, 1413–1428 (1972)
Virgo, D., Hafner, S. S.: Fe2+, Mg order-disorder in heated orthopyroxenes. Mineral. Soc. Amer. Spec. Pap. 2, 67–81 (1969)
Williams, R. J.: Reaction constants in the system FeO-MgO -SiO2-O2 at 1 atm between 9000 C and 1300° C: Experimental results. Am. J. Sci. 270, 334–360 (1971)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Wood, B.J., Banno, S. Garnet-orthopyroxene and orthopyroxene-clinopyroxene relationships in simple and complex systems. Contr. Mineral. and Petrol. 42, 109–124 (1973). https://doi.org/10.1007/BF00371501
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00371501