Hostname: page-component-78c5997874-lj6df Total loading time: 0 Render date: 2024-11-10T06:44:04.214Z Has data issue: false hasContentIssue false
  • English
  • Français

Kornerupine breakdown reactions in paragneisses from southern Madagascar

Published online by Cambridge University Press:  05 July 2018

Dietrich Ackermand ,
Brian F. Windley  and
Andriantefison H. Razafiniparany
Dietrich Ackermand
Affiliation:
Mineralogisch-Petrographisches Institut, Universität, Olshausenstr. 40, 2300 Kiel, Germany
Brian F. Windley
Affiliation:
Department of Geology, The University, Leicester LE1 7RH, U.K.
Andriantefison H. Razafiniparany
Affiliation:
Service de Géologie, Université, Antananarivo, Madagascar
Get access Rights & Permissions [Opens in a new window]

Abstract

Kornerupine-rich layers up to several centimetres thick with minor sillimanite, spinel, Fe oxide and ilmenite occur in a diopsidite in sillimanite-cordierite gneiss south of Beraketa (24°27′S, 46°48′E), southern Madagascar. Kornerupine, sillimanite, spinel and hematite grains up to 1 mm across have mutual polygonal boundaries indicating textural equilibrium at their crystallisation. Kornerupine has XMg 0.67–0.80 and 0.9 to 2.6 wt.% B2O3. Sillimanite contains up to 2.0 wt.% Fe2O3. Spinel is essentially (Mg,Fe2+) Al2O4 with an XMg range of 0.29–0.40 and exsolution lamellae of Fe oxide. Textural relations demonstrate two limited reactions, each confined to areas less than 500 µm across: (1) Kornerupine and spinel reacted along grain contacts to form very fine-grained tourmaline, corundum and chlorite. The replacing phases are symmetrically zoned with a central tourmaline and hematite, bordered by an aggregate of chlorite, tourmaline and corundum, followed outwards by a rim of chlorite against the kornerupine and spinel. (2) Within kornerupine grains, zoned, round aggregates consist of very fine-grained chlorite, tourmaline and corundum of different composition than in (1). They define the terminal reaction of kornerupine breakdown.

Geothermobarometry indicates that the early kornerupine-bearing assemblage was stable at 7.0 kbar and 700 °C. This P-T point lies close to the retrograde, nearly isothermal trajectory defined independently by nearby sapphirine-bearing assemblages. The fine-grained aggregates formed most likely during further cooling, or by increasing water fugacity.

Keywords

kornerupinebreakdown productsgranulite faciesMadagascar
Type
Research Article
Information
Mineralogical Magazine , Volume 55 , Issue 378 , March 1991 , pp. 71 - 80
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Ackermand, D., Herd, R. K., and Windley, B. F. (1984) Kornerupine replacement reactions involving tourmaline, Fiskenaesset region W. Greenland. Neus Jahrb. Mineral., Mh., 490–500.Google Scholar
Windley, B. F., and Razafiniparany, A. H. (1989) The Precambrium mobile belt of Southern Madagascar. In Metamorphic Mobile Belts (Daly, J. S., Cliff, R. A. and Yardley, B. W. D., eds.) Geol. Soc. London, Spec. Publ. No. 43, pp.293–6.Google Scholar
Besairie, H. (1970) Carte gdologique No. 8; Arnpanihy, 1 : 500000. Service Géologique, Madagascar.Google Scholar
Besairie, H. (1971) Carte gdologique au 1/2000000 et notice explicative. Documentation du Bureau Géologique, Madagascar, No. 184.Google Scholar
Cahen, L. and Snelling, N. J. (1984) The Geochronology and Evolution of Africa. Clarendon Press, Oxford 512 p.Google Scholar
Finger, L. W. and Burr, D. M. (1972) REACTION: A Fortran IV computer programm to balance chemical reactions. Carnegie Inst. Washington Yearbook, 62, 616–20.Google Scholar
Grew, E. S. (1980) Sillimanite and ilmenite from highgrade metamorphic rocks of Antarctica and other areas. J. Petrol., 21, 39–68.CrossRefGoogle Scholar
Grew, E. S. and Hinthorne, J. R. (1983) Boron in sillimanite. Science, 221, 547–9.CrossRefGoogle ScholarPubMed
Holdaway, M. J. and Lee, S. M. (1977) Fe-Mg cordierite in high-grade pelitic rocks based on experimental, theoretical and natural observations. Contrib. Mineral. Petrol., 63, 175–98.CrossRefGoogle Scholar
Hottin, G. (1976) Présentation et essai d'interprétation du Precambrien de Madagascar. Bull. Bureau de Rdcherche Gdologique et MinOre, Paris, 2nd Series, 4, no. 2, 117–53.Google Scholar
Knorring, O. von, Sahama, T. G., and Lehtinen, M. (1969) Kornerupine-bearing gneiss from Inanakafy near Betroka, Madagascar. Bull. Geol. Sci. Finland, 41, 79–84.CrossRefGoogle Scholar
Kretz, R. (1983) Symbols for rock-forming minerals. Am. Mineral., 68, 277–9.Google Scholar
Lacroix, A. (1922-3) Mindralogie de Madagascar. E. Challamel, Paris, 3 vols.Google Scholar
Lacroix, A. (1941) Les gisements de phlogopite de Madagascar. Comptes Rendus Sem. G∼ol. de Madagascar, 27–37.Google Scholar
Megerlin, N. (1968) Sur une roche ∼ kornerupine du sud de Ianakafy (Centre sud de Madagascar). Ibid., 67–9.Google Scholar
Nicollet, C. (1988) Metabasites granulitiques, anorthosites et roches assocides de la croute inférièe: Exemples pris à Madagascar et dans le Massif Central franqais. Thèse d'Etat, Université Blaise Pascal, Clermont-Fd, No. d'ordre 413, 315 pp.Google Scholar
Nicollet, C. (1990) Occurrence of grandidierite, serendibite, and tourmaline near lhosy, southern Madagascar. Mineral. Mag., 54, 131–3.CrossRefGoogle Scholar
Noizet, G. (1969) Contribution à l'étude géologique des formation métamorphiques du faciè granulite dans le Sud de Madagascar. Thèse d'Etat, Université Nancy.Google Scholar
Pouchou, J. L. and Pichoir, F. (1984) A new model for quantitative X-ray microanalysis. Part I: Application to analysis of homogeneous samples. La Récherche Aérospatiale, 3, 13–36.Google Scholar
Powell, R. (1978) The thermodynamics of pyroxene geotherms. Phil. Trans. Roy. Soc. London, A288, 457–69.Google Scholar
Seifert, F. (1975) Boron-free kornerupine: a highpressure phase. Am. J. Sci., 275, 57–87.CrossRefGoogle Scholar
Seifert, F. and Schumacher, J. C. (1986) Cordieritc-spinel-quartz assemblages: a potential geobarometer. Bull. Geol. Sci. Finland, 58, 95–108.CrossRefGoogle Scholar
Thompson, A. B. (1976) Mineral reactions in pelitic rocks. Am. J. Sci., 276, 401-24, and 425–54.CrossRefGoogle Scholar
Wells, P. R. W. (1977) Pyroxene thermometry in simple and complex systems. Contrib. Mineral. Petrol., 62, 129–39.CrossRefGoogle Scholar
Wells, P. R. W. (1979) Chemical and thermal evolution of Archaean sialic crust, southern Greenland. J. Petrol., 20, 187–226.CrossRefGoogle Scholar