Hostname: page-component-586b7cd67f-dsjbd Total loading time: 0 Render date: 2024-11-30T21:41:09.471Z Has data issue: false hasContentIssue false
  • English
  • Français

Barian-titanian micas from Ilha da Trindade, South Atlantic

Published online by Cambridge University Press:  05 July 2018

J. C. Greenwood
J. C. Greenwood*
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
Get access Rights & Permissions [Opens in a new window]

Abstract

Extremely high abundances of TiO2 (up to 12.57 wt.%) and BaO (up to 7.11 wt.%) are reported from dark reddish-brown phlogopite-biotite rims around paler phlogopite cores in a lamprophyric dyke from Ilha da Trindade, South Atlantic. Both TiO2 and BaO contents increase towards the rims of the micas and in groundmass crystals. This is accompanied by corresponding increases in FeO*, MnO and Mg number; whereas SiO2, Al2O3, Cr2O3, MgO and K2O abundances all decrease. The substitution of Ba into the biotite structure can be explained by the scheme Ba + Al = K + Si. Ti-substitution schemes however are much more complex, as no general equation can account for all the Ti incorporated into the structure and therefore several schemes are proposed.

Keywords

micatitaniumbariumIlha da Trindade
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 5 , October 1998 , pp. 687 - 695
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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

Bachinski, S.W. and Simpson, E.L. (1984) Ti-phlogopites of the Shaw's Cove minette: a comparison with micas of other lamprophyres , potassic rocks, kimberlites, and mantle xenoliths. Amer. Mineral., 69, 41–56.Google Scholar
Deer, W.A., Howie, R.A. and Zussman, J. (1963) Rock-forming Minerals. Vol. 3, Sheet Silicates. Longman, London, 270 pp.Google Scholar
Edgar, A.D. (1992) Barium-rich phlogopite and biotite from some Quaternary alkali mafic lavas, West Eifel, Germany. Eur. J. Mineral., 4, 321–30.CrossRefGoogle Scholar
Farmer, G.L. and Boettcher, A.L. (1981) Petrologic and crystal-chemical significance of some deep seated phlogopites. Amer. Mineral., 66, 1154–63.Google Scholar
Fodor, R.V., Mukasa, S.B., Gomes, C.B. and Cordani, U.G. (1989) Ti-rich Eocene Basaltic Rocks, Abrolhos Platform, Offshore Brazil , 188S; Petrology with Respect to South Atlantic Magmatism. J. Petrol., 30, 763–86.CrossRefGoogle Scholar
Foley, S.F. (1990) Experimental constraints on phlogopite chemistry in lamproites: 2. Effect of pressuretemperature variations. Eur. J. Mineral., 2, 327–41.CrossRefGoogle Scholar
Furnes, H. and Stillman, C.J. (1987) The geochemistry and petrology of an alkaline lamprophyre sheet intrusion complex on Maio, Cape Verde Republic. J. Geol. Soc. Lond., 144, 227–41.CrossRefGoogle Scholar
Gibson, S.A., Thompson, R.N., Leonardos, O.H., Dickin, A.P. and Mitchell, J.G. (1995) The Late Cretaceous impact of the Trindade mantle plume: evidence from large-volume, mafic, potassic magmatism in SE Brazil. J. Petrol., 36, 189–229.CrossRefGoogle Scholar
Le Roex, A.P. (1985) Geochemistry, mineralogy and magmatic evolution of the basaltic and trachytic lavas from Gough Island, South Atlantic. J. Petrol., 26, 149–86.CrossRefGoogle Scholar
Leonardos, O.H., Ulbrich, M.N. and Gaspar, J.C. (1991) The Mata da Corda volcanic rocks. In Field Guidebook. 5th International Kimberlte Conference , Araxá. (Leonardos, O.H., Meyer, H.O.A. and Gaspar, J.C., eds.). Brasília, DF: CPRM, Special Publication 3/91, pp. 17–24.Google Scholar
Mansker, W.L., Ewing, R.C. and Keil, K. (1979) Barian-titanian biotites in nephelinites from Oahu, Hawaii. Amer. Mineral., 64, 156–9.Google Scholar
Meyer, H.O.A., Garwood, B.L. , Svisero, D.P. and Smith, C.B. (1994) Alkaline intrusions in western Minas Gerais, Brazil. In Proceedings of the 5th International Kimberlite Conference, Araxá.(Leonardos, O.H., Meyer, H.O.A. and Gaspar, J.C., eds. ). Brasília, DF: CPRM, Special Publication pp. 140–55.Google Scholar
Mitchell, R.H. (1986) Kimberlites, Mineralogy, Geochemistry and Petrology. New York: Plenum, 442 pp.Google Scholar
Mitchell-Thomé, R.C. (1970) Trindade. In Geology of the South Atlantic Islands. Berlin, Gebruder Borntraeger, pp. 67–101.Google Scholar
Rock, N.M.S. (1991) Lamprophyres. Glasgow, Blackie, 285 pp.Google Scholar
Ryabchikov, I.D., Kovalenko, V.I., Dikov, Y.P. and Vladykin, N.V. (1982) Titaniferous micas from the mantle: composition, structure, formation conditions, and possible role in the production of potassic alkali magmas. Geochem. International, 18, 124–37.Google Scholar
Thompson, R.N., Velde, D., Leat, P.T., Morrison, M.A., Mitchell, J.G., Dickin, A.P. and Gibson, S.A. (1997) Oligocene lamproite containing an Al-poor, Ti-rich biotite, Middle Park, northwest Colorado, USA. Mineral. Mag., 61, 557–72.CrossRefGoogle Scholar
Wendlandt, R.F. (1977) Barian-phlogopite from Haystack Butte, Highwood Mountains, Montana. Ann. Rept. Carnegie Inst. Wash. Ybk., 76, 534–39.Google Scholar
Wulff-Pedersen, E., Neuman, E-R. and Jensen, B.B. (1996) The upper mantle under La Palma, Canary Islands: formation of Si-K-Na-rich melt and its importance as a metasomatic agent. Contrib. Mineral. Petrol., 125, 113–39.CrossRefGoogle Scholar
Zhang, M., Suddaby, P., Thompson, R.N. and Dungan, M.A. (1993) Barian titanian phlogopite from potassic lavas in northeast China: Chemistry, substitutions, and paragenesis. Amer. Mineral., 78, 1056–65.Google Scholar