Hostname: page-component-78c5997874-g7gxr Total loading time: 0 Render date: 2024-11-04T21:36:57.045Z Has data issue: false hasContentIssue false
  • English
  • Français

The occurrence of Zr-bearing amphiboles and their relationships with the pyroxenes and biotites in the teschenite and nepheline syenites of a differentiated dolerite boss, Islay, NW Scotland

Published online by Cambridge University Press:  05 July 2018

R. J. Preston ,
M. J. Hole  and
J. Still
R. J. Preston*
Affiliation:
Department of Geology and Petroleum Geology, Meston Building, King's College, University of Aberdeen, Aberdeen AB24 3UE, UK
M. J. Hole
Affiliation:
Department of Geology and Petroleum Geology, Meston Building, King's College, University of Aberdeen, Aberdeen AB24 3UE, UK
J. Still
Affiliation:
Department of Geology and Petroleum Geology, Meston Building, King's College, University of Aberdeen, Aberdeen AB24 3UE, UK
*
* E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

The Cnoc Rhaonastil minor dolerite intrusion on Islay, NW Scotland represents a single body of alkali olivine basalt magma which differentiated in situ, from leucodolerite, through teschenite to minor nepheline syenite. The syenites occur as isolated nests and pegmatitic schlieren within the leucodolerite, and schlieren of gabbroic pegmatite also occur at the margin of the teschenite. The differentiated rocks contain pyroxene, amphibole and biotite of variable compositions which reflect both primary fractionation processes and late-stage deuteric alteration and reaction.Mafic phases within the gabbroic pegmatite, teschenite and syenite are typically rimmed and speckled with biotite, the composition of which is controlled by the local environment of crystallization. The nepheline syenites contain primary ferro-kaersutite which, where in contact with interstitial patches, has been altered to arfvedsonite, which occasionally contains up to 1.2 wt.% ZrO2. The occurrence of Zr-arfvedsonite (and of Zr-aegirine) in interstitial patches suggests that variably trace element-enriched domains existed within the residual melts on very small scales.

Keywords

doleriteamphibolezirconiumteschenitenepheline syeniteCnoc RhaonastilScotland
Type
Research Article
Information
Mineralogical Magazine , Volume 64 , Issue 3 , June 2000 , pp. 459 - 468
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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

Bailey, D.K. (1969) The stability of acmite in the presence of H2O. Amer. J. Sci., 267A, 1–16.Google Scholar
Barton, M. and Hamilton, D.L. (1978) Water-saturated melting relations to 5 kilobars of three Leucite Hill lavas. Contrib. Mineral. Petrol., 69, 133–42.CrossRefGoogle Scholar
Deer, W.A., Howie, R.A. and Zussman, J. (1997) Rock-Forming Minerals. Volume 2B Double Chain Silicates. The Geological Society, London.Google Scholar
Duggan, M.B. (1988) Zirconium-rich sodic pyroxenes in felsic volcanics from Warrumbungle Volcano, Central New South Wales, Australia. Mineral. Mag., 52, 491–6.CrossRefGoogle Scholar
Ernst, W.G. (1962) Synthesis, stability relations, and occurrence of riebeckite and riebeckite-arfvedsonite solid solutions. J. Geol., 70, 689–736.CrossRefGoogle Scholar
Farges, F., Ponander, C.W. and Brown, G.E. Jr., (1991) Structural environments of incompatible elements in silicate glass/melt systems. I. Zr at trace levels. Geochim. Cosmochim. Acta, 55, 1563–74.CrossRefGoogle Scholar
Farges, F., Brown, G.E. Jr., and Velde, D. (1994) Structural environment of Zr in two inosilicates from Cameroon: Mineralogical and geochemical implications. Amer. Mineral., 79, 838–47.Google Scholar
Finger, L.W. (1972) The uncertainty in the calculated ferric iron content of a microprobe analysis. Carnegie Institute of Washington Yearbook, 71, 600–3.Google Scholar
Hole, M.J. and Morrison, M.A. (1992) The differentiated dolerite boss, Cnoc Rhaonastil, Islay: a natural experiment in the low pressure differentiation of an alkali olivine-basalt magma. Scot. J. Geol., 28, 55–69.CrossRefGoogle Scholar
Jones, A.P. and Peckett, A. (1980) Zirconium-bearing aegirines from Motzfeldt, South Greenland. Contrib. Mineral. Petrol., 75, 251–5.CrossRefGoogle Scholar
Lamcraft, H. (1979) The geochemistry of the Tertiary dyke swarms of Mull, Islay and Jura. J. Geol. Soc., London, 139, 257 (abstract).Google Scholar
Larsen, L.M. (1976) Clinopyroxenes and coexisting mafic minerals from the alkaline Iímaussaq intrusion, South Greenland. J. Petrol., 17, 258–90.CrossRefGoogle Scholar
Leake, B.E. and 21 others (1997) Nomenclature of Amphiboles: Report of the Subcommittee on Amphiboles of the International Mineralogical Commission on New Minerals and Mineral Names. Mineral. Mag., 61, 295–321.CrossRefGoogle Scholar
Linthout, K. (1984) Alkali-zirconosilicates in peralkaline rocks. Contrib. Mineral. Petrol., 86, 155–8.CrossRefGoogle Scholar
Nash, W.P. and Wilkinson, J.F.G. (1970) Shonkin Sag laccolith, Montana. I. Mafic minerals and estimates of temperature, pressure, oxygen fugacity and silica activity. Contrib. Mineral. Petrol., 25, 241–69.CrossRefGoogle Scholar
Pearce, N.J.G. (1989) Zirconium-bearing amphibole from Igaliko Dyke Swarm, South Greenland. Mineral. Mag., 53, 107–10.CrossRefGoogle Scholar
Preston, R.J., Hole, M.J., Bouch, J. and Still, J. (1998) The occurrence of zirconian aegirine and calcic catapleiite (CaZrSi3O9.2H2O) within a nepheline syenite, British Tertiary Igneous Province. Scot. J. Geol., 34, 173–80.CrossRefGoogle Scholar
Preston, R.J., Hole, M.J. and Still, J. (in press) Exceptional REE-enrichment in apatite during the low-pressure fractional crystallization of alkali olivine basalt; an example from the British Tertiary Igneous Province. Trans. Royal Soc. Edinburgh. Google Scholar
Stephenson, D. and Upton, B.G.J. (1982) Ferromagnesian silicates in a differentiated alkaline complex: Kûngnât Fjeld, South Greenland. Mineral. Mag., 46, 283–300.CrossRefGoogle Scholar
Walker, F. and Patterson, E. (1959) The geochemistry of a boss of alkali dolerite, Cnoc Rhaonastil, Islay. Mineral. Mag., 32, 140–52.Google Scholar
Watson, E.B. (1979) Zircon saturation in felsic liquids: Experimental results and applications to trace element geochemistry. Contrib. Mineral. Petrol., 70, 407–19.CrossRefGoogle Scholar
Watson, E.B. and Harrison, T.M. (1983) Zircon saturation revisited: Temperature and composition effects in a variety of crustal magma types. Earth Planet. Sci. Lett., 64, 295–304.CrossRefGoogle Scholar