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Clinoferrosilite-bearing kelyphite: a breakdown product of xenolithic garnet, Delegate breccia pipes, New South Wales, Australia

Published online by Cambridge University Press:  05 July 2018

W. Keankeo*
Affiliation:
Department of Geology, Australian National University, Canberra, ACT, 0200, Australia
W. R. Taylor
Affiliation:
Research School of Earth Sciences, Australian National University, Canberra, ACT, 0200, Australia
J. D. FitzGerald
Affiliation:
Research School of Earth Sciences, Australian National University, Canberra, ACT, 0200, Australia
*

Abstract

Garnet pyroxenite xenoliths from the Delegate nephelinitic breccia pipes, New South Wales, Australia, contain relict garnets (py40 alm39 gr21) which are replaced by dark kelyphitic rims resulting from garnet breakdown. The kelyphite is composed of a lamellar intergrowth of secondary minerals, in which the lamellae are <1 μm in width. Analyses by SEM and ICPMS reveal that the kelyphite has an identical bulk chemical composition to the primary garnet. Kelyphitic rims on garnet are well known from xenoliths and xenocrysts in kimberlite pipes and from tectonically-uplifted mafic and ultramafic rocks in some metamorphic terranes. Orthopyroxene occurs in metamorphic kelyphites and it has been assumed that orthopyroxene is also the breakdown product of garnet transported in basic-ultrabasic magmas. However, TEM study of Delegate kelyphite shows that the ultrafine lamellae do not contain orthopyroxene but are instead composed of magnesian clinoferrosilite (En45Fs55), and lesser ferroan spinel and anorthite. The clinoferrosilite is probably the inversion product of initially-formed magnesian protoferrosilite. The breakdown reaction is believed to result from a sudden change to lower temperature and pressure conditions when the xenoliths were transported in the Delegate magma from ∼40 km depth to the surface.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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References

Altherr, R. and Kalt, A. (1996) Metamorphic evolution of ultrahigh-pressure garnet peridotite from the Variscan Vosges Mts. (France). Chem. Geol., 134, 2747. CrossRefGoogle Scholar
Becker, H. (1997) Petrological constraints on the cooling history of high-temperature garnet peridotite massif in Lower Austria. Contrib. Mineral. Petrol., 128, 272–86.CrossRefGoogle Scholar
Burnham, C.W. (1966) Ferrosilite. Carnegie Institute Washington Year Book, 65, 285–90.Google Scholar
Deer, W.A., Howie, R.A. and Zussman, J. (1996) Chain silicates: Pyroxene group. In: An Introduction to the Rock-Forming Minerals. Addison Wesley Longman Ltd, Essex, UK.Google Scholar
Ellis, D.J. and Green, D.H. (1979) An experimental study of the effect of Ca upon garnet-clinopyroxene Fe-Mg exchange equilibria. Contrib. Mineral. Petrol., 71, 13–22.CrossRefGoogle Scholar
Garvie, O.G. and Robinson, D.N. (1984) The formation of kelyphite and associated sub-kelyphitic and sculptured surfaces on pyrope from kimberlite. Pp. 371–82 in: Kimberlite I: Kimberlite and Related Rocks (Kornprobst, J., editor). Elsevier Scientific Publishing, Amsterdam.CrossRefGoogle Scholar
Ghose, S., Wan, C. and Okamura, F.P. (1975) Site preference and crystal chemistry of transition metal ions in pyroxenes and olivines (abstract). Acta Crystallogr., A31, S76.Google Scholar
Irving, A.J. (1974) Geochemical and high pressure studies of garnet pyroxenite and pyroxene granulite xenoliths from the Delegate basaltic pipes, Australia. J. Petrol., 15, 140.CrossRefGoogle Scholar
Lindsley, D.H. (1980) Phase equilibria of pyroxenes at pressure >1 atmosphere. Pp. 289306 in: Pyroxenes (Prewitt, C.T., editor). Reviews in Mineralogy, 7, Mineralogical Society of America, Washington D.C. CrossRefGoogle Scholar
Lovering, J.F. and White, A.J.R. (1964) The significance of primary scapolite in granulitic inclusions from deep-seated pipes. J. Petrol., 5, 195218.CrossRefGoogle Scholar
Lovering, J.F. and White, A.J.R. (1969) Granulitic and eclogitic inclusions from Basic pipes at Delegate, Australia. Contrib. Mineral. Petrol., 21, 952.CrossRefGoogle Scholar
Mariano, A.N. (1989) Economic geology of rare earth minerals. Pp. 309–37 in: Geochemistry and Mineralogy of Rare Earth Elements (Lipin, B.R. and McKay, G.A., editors). Reviews in Mineralogy, 21, Mineralogical Society of America, Washington D.C. CrossRefGoogle Scholar
McDougall, I. and Wellman, P. (1976) Potassium-argon ages for some Australian Mesozoic igneous rocks. J. Geol. Soc. Austral., 23, 19.CrossRefGoogle Scholar
Messiga, B. and Bettini, E. (1990) Reactions behaviour during kelyphite and a symplectite formation: a case study of mafic granulites and eclogites from the Bohemian Massif. Eur. J. Mineral., 2, 125–44.CrossRefGoogle Scholar
Morimoto, N. (1988) Nomenclature of pyroxenes. Mineral. Mag., 52, 535–50.CrossRefGoogle Scholar
Obata, M. (1994) Material transfer and local equilibria in a zoned kelyphite from a garnet pyroxenite, Ronda, Spain. J. Petrol., 35, 271–87.CrossRefGoogle Scholar
Reid, A.M. and Dawson, J.B. (1972) Ol-Gnt reaction in peridotites from Tanzania. Lithos, 5, 115–24.CrossRefGoogle Scholar
Schrader, H., Boysen, H., Frey, F. and Convert, P. (1990) On the phase transformation proto- to clinoorthoenstatite: neutron powder investigation. Phys. Chem. Min., 17, 409–15.CrossRefGoogle Scholar
Shiraki, K., Kuroda, N., Urano, H. and Maruyama, S. (1980) Clinoenstatite in boninites from the Bonin Islands, Japan. Nature, 285, 31–2.CrossRefGoogle Scholar
Smyth, J.R. (1974) The high temperature crystal chemistry of clinohypersthene. Amer. Mineral., 59, 1069–82.Google Scholar
Sueno, S. and Prewitt, C.T. (1983) Models for the phase transition between orthoferrosilite and high clinoferrosilite. Forts. Mineral., 61, 223–41.Google Scholar
Sueno, S., Cameron, M. and Prewitt, C.T. (1976) Orthoferrosilite: high-temperature crystal chemistry. Amer. Mineral., 61, 3853.Google Scholar
Woodland, A.B. and Angel, R.J. (1997) Reversal of the orthoferrosilite – high-P clinoferrosilite transition, a phase diagram for FeSiO3 and implications for the mineralogy of the Earth's upper mantle. Eur. J. Mineral., 9, 245–54.CrossRefGoogle Scholar
Yasuda, M., Kitamura, M. and Morimoto, N. (1983) Electron microscopy of clinoenstatit e from a boninite and a chrondite. Phys. Chem. Min., 9, 192–6.CrossRefGoogle Scholar