Advertisement

Contributions to Mineralogy and Petrology

, Volume 95, Issue 1, pp 32–43 | Cite as

Monzo-anorthosite from the Tagueï ring-complex, Aïr, Niger: a hybrid rock with cumulus plagioclase and an infiltrated granitic intercumulus liquid?

  • Christian Moreau
  • William L. Brown
  • Jean -Paul Karche
Article

Abstract

An unusual hybrid rock composed of cumulus plagioclase with the interstices occupied by abundant quartzo-feldspathic material occurs in the Tagueï ring complex, Niger. The monzo-anorthosite consists of about 75% plagioclase in large tabular to elongate crystals with interstices occupied in two stages, firstly by clinopyroxene, titanomagnetite and apatite and then by an intergrowth of quartz and alkali feldspar associated with brown-green amphibole and zircon. Secondary green amphibole, chlorite, epidote and calcite may occur. Four stages in the crystallization history were identified:
  1. (1)

    Cumulus stage represented by the cores of the plagioclase laths (An56-An66 with reversed oscillatory zoning) and rare clinopyroxene (T ∼1,150° C),

     
  2. (2)

    Early intercumulus stage with a wide overgrowth zone on plagioclase (An62-An15 with oscillatory zoning and increase in Or), clinopyroxene, apatite, titanomagnetite (T ∼1,150-1,050° C),

     
  3. (3)

    Late intercumulus stage with alkali feldspar, quartz, opaque oxide, brown-green amphibole, apatite and zircon (T ∼750-700° C). Alkali feldspar gave cryptoperthite on further cooling.

     
  4. (4)

    Deuteric stage with development of turbidity in the alkali feldspar and plagioclase rims, and formation of patch perthite with microcline and secondary minerals (T ∼400° C).

     

The contrast in mineralogy, the large gap of ∼300° C between the early and late cumulus stages and the great abundance of quartz and alkali feldspar (∼20%) suggest that the late-stage liquid of granitic composition which filled the interstices was not a simple residual liquid which crystallized in situ. From chemistry (including REE) it is almost identical to the later radial granite dykes. From gravity measurements the intrusion has the form of a pipe with less dense rocks below the present exposure level. We propose that a pulse of granite magma rose within the pipe just before complete consolidation of the leucogabbro and replaced by infiltration the denser residual intercumulus liquid.

Keywords

Apatite Oscillatory Zoning Granite Magma Alkali Feldspar Plagioclase Lath 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Barrabé ML (1943) Sur la nature et le mode de gisement des gros massifs intrusifs de l'aire anticlinale du Cap Saint-André à Ma-dagascar, et leurs relations avec les grandes coulées volcaniques voisines. Bull Soc Fr Mineral Cristallogr 66:1–24Google Scholar
  2. Black R (1965) Sur la signification pétrogénétique de la découverte d'anorthosites associées aux complexes subvolcaniques du Niger. CR Acad Sci Fr 260(D):5829–5832Google Scholar
  3. Boulanger J (1959) Les anorthosites de Madagascar. Ann Géol Madagascar XXVI: 71Google Scholar
  4. Bridgwater D, Harry WT (1968) Anorthosite xenoliths and plagioclase megacrysts. In: Precambrian intrusions of South Greenland. Medd Grønland 185, n∘ 2, p 243Google Scholar
  5. Brown WL, Parsons I (1981) Towards a more practical two-feldspar geothermometer. Contrib Mineral Petrol 76:369–377Google Scholar
  6. Brown WL, Parsons I (1984a) Exsolution and coarsening mechanisms and kinetics in an ordered cryptoperthite series. Contrib Mineral Petrol 86:3–18Google Scholar
  7. Brown WL, Parsons I (1984b) The nature of potassium feldspar, exsolution microtextures and development of dislocations as a function of composition in perthitic alkali feldspars. Contrib Mineral Petrol 86:335–341Google Scholar
  8. Brown WL, Becker SM, Parsons I (1983) Cryptoperthite and cooling rate in a layered syenite pluton: a chemical and TEM study. Contrib Mineral Petrol 82:13–25Google Scholar
  9. Demaiffe D, Hertogen J (1981) Rare earth geochemistry and strontium isotopic composition of a massif-type anorthositic-charnockitic body: the Hidra massif (Rogaland, SW Norway). Geochim Cosmochim Acta 45:1545–1561Google Scholar
  10. Demaiffe D, Duchesne JC, Michot J, Pasteels P (1973) Le massif anorthosito-leuconoritique d'Hidra et son faciès de bordure. CR Acad Sci Paris 277(D):17–20Google Scholar
  11. Donnot M (1963) Les complexes intrusifs alcalins d'Ampasidava (Madagascar). Ann Géol Madagascar XXXIII: 81–87Google Scholar
  12. Duchesne JC (1984) Massif anorthosites: another partisan review. In: WL Brown (ed) Feldspar and Feldspathoids. D Reidel Co, Dordrecht, pp 411–433Google Scholar
  13. Emeleus CH, Upton BGJ (1976) The Gardar period in southern Greenland. In: Escher A and Watt S (ed) Geology of Green-land, The Geological Survey of Greenland, pp 152–181Google Scholar
  14. Emslie RF (1978) Anorthosite massifs, rapakivi granites, and late Proterozoic rifting of North America. Precambr Res 7:61–98Google Scholar
  15. Finnerty AA, Boyd FR (1977) Pressuredependent solubility of calcium in fosterite coexisting with diopside and enstatite. Carnegie Inst Washington Yearb 77:713–717Google Scholar
  16. Ghiorso MS (1984) Activity/composition relations in the ternary feldspars. Contrib Mineral Petrol 87:282–296Google Scholar
  17. Grove TL, Baker MB, Kinzler RJ (1984) Coupled CaAl-NaSi diffusion in plagioclase feldspar: experiments and applications to cooling rate speedometry. Geochim Cosmochim Acta 48:2113–2121Google Scholar
  18. Husch JM (1982) Geology, petrology and geochemistry of anorthositic and other rocks associated with hypabyssal ring-complexes, Aïr massif, Republic of Niger. Unpublished, Ph D, Princeton Univ, p 231Google Scholar
  19. Husch JM, Moreau C (1982) Geology and major element geochemistry of anorthositic rocks associated with Paleozoic hypoabyssal ring-complexes, Republic of Niger, West Africa. J Volcanol Geotherm Res 14:47–66Google Scholar
  20. Irvine TN (1982) Terminology for layered intrusions. J Petrol 23:127–162Google Scholar
  21. Jaeger JC (1968) Cooling and solidification of igneous rocks. In: Hess HH, Poldervaart A (eds) Basalts. Wiley, New York, pp 503–536Google Scholar
  22. Kushiro I (1973) The system Diopside-Anorthite-Albite: determination of compositions of coexisting phases. Carnegie Inst Washington Yearb 72:502–507Google Scholar
  23. Lindsley D (1983) Pyroxene thermometry. Am Mineral 68:477–493Google Scholar
  24. Luth WC (1976) Granitic rocks. In: Bailey WL, Macdonald R (eds) The Evolution of the Crystalline Rocks, London, Academic Press, pp 335–417Google Scholar
  25. Miyashiro A (1978) Nature of alkalic rock series. Contrib Mineral Petrol 66:91–104Google Scholar
  26. Moreau C (1982) Les complexes annulaires anorogéniques à suites anorthositiques de l'Aïr central et septentrional (Niger). Doctoral Thesis, University of Nancy, p 356Google Scholar
  27. Moreau C, Karche JP, Trichet J (1978) Remarques sur les anorthosites des complexes subvolcaniques de l'Aïr (Niger). C R Som Soc Géol Fr 1:21–23Google Scholar
  28. Morse SA (1982) A partisan review of Proterozoic anorthosites. Am Mineral 67:1087–1100Google Scholar
  29. Murphy (1977) An experimental study of solid-liquid equilibria in the albite-anorthite-diopside system. MS Thesis, University of OregonGoogle Scholar
  30. Obata M, Banno S, Mori T (1974) The iron-magnesium partitioning between naturally occurring coexisting olivine and Carich clinopyroxene: an application of the simple mixture model to olivine solid solution. Bull Soc Fr Mineral Cristallogr 97:101–107Google Scholar
  31. Parsons I (1978) Feldspars and fluids in cooling plutons. Mineral Mag 42:1–17Google Scholar
  32. Sparks RSJ, Huppert HE (1984) Density changes during the fractional crystallization of basaltic magmas: fluid dynamic implications. Contrib Mineral Petrol 85:300–309Google Scholar
  33. Sparks RSJ, Huppert HE, Turner JS (1984) The fluid dynamics of evolving magma chambers. Philos Trans R Soc London A 310:511–534Google Scholar
  34. Simkin T, Smith JV (1970) Minor-element distribution in olivine. J Geol 78:304–325Google Scholar
  35. Tait SR, Huppert HE, Sparks RSJ (1984) The role of compositional convection in the formation of adcumulate rocks. Lithos 17:139–146Google Scholar
  36. Wager LR, Brown GM (1968) Layered igneous rocks. Oliver and Boyd, London, p 588Google Scholar
  37. Wager LR, Brown GM, Wadsworth WJ (1960) Types of igneous cumulates. J Petrol 1:73–85Google Scholar
  38. Wright JB (1975) Anorthosite — first occurrence in Nigeria and relevance to Younger Granite genesis. Mineral Mag 40:193–196Google Scholar
  39. Weill DF, Hon R, Navrotsky A (1980) The igneous system CaMg- Si2O6-CaAl2Si2O8-NaAlSi3O8: variations on a classic theme by Bowen. In: Hargraves RB (ed) Physics of magmatic processes, Princeton University Press, pp 49–92Google Scholar

Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Christian Moreau
    • 1
  • William L. Brown
    • 2
  • Jean -Paul Karche
    • 3
  1. 1.Département de GéologieFaculté des SciencesDakar-FannSénégal
  2. 2.CRPGVandoeuvre-lès-Nancy CédexFrance
  3. 3.Faculté des SciencesLaboratoire de PétrographieBesançon CédexFrance

Personalised recommendations