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Channelled metasomatism in Rhum layered cumulates – evidence from late-stage veins

Published online by Cambridge University Press:  01 May 2009

Alan R. Butcher
Alan R. Butcher
Affiliation:
Department of Geology, University of Manchester, Manchester, M13 9PL, U.K.
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Abstract

Late-stage veins have been studied in the Rhum layered intrusion as part of a wider investigation into postcumulus processes – in particular, to study compositions of residual liquids and their effects on host cumulates. Studies have concentrated on Unit 10 of the Eastern Layered Series (ELS), though brief investigations have also been made in the Western Layered Series (WLS).

The Unit 10 veins are generally concordant with the layering, although locally they are transgressive with dilational relationships. Two principal types can be recognized: ultrabasic and basic. Detailed microprobe studies have shown that the liquids responsible for the veins have substantially modified the compositions of the cumulus minerals in the wall-rock peridotite up to 1 cm from the vein margin.

The style of veining in the WLS is more complex than in the ELS, and several generations of vein can be identified. Both normal and harrisitic cumulates have undergone localized chemical modification near to the veins. Modification occurs regardless of the vein orientation.

The ELS and WLS veins are geochemically distinct from the numerous gabbro intrusions associated with the layered series, and it is concluded that they represent fractionated intercumulus liquids injected into early formed fractures in the cumulates. The observed chemical modification is explained by a model involving mixing of the intrusive vein melt with trapped intercumulus melt in the adjacent peridotite, followed by diffusion-controlled re-equilibration of the cumulus minerals. This type of highly localized compositional modification along fractures is termed channelled metasomatism.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 5 , September 1985 , pp. 503 - 518
Copyright
Copyright © Cambridge University Press 1985

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References

Brown, G. M. 1956. The layered ultrabasic rocks of Rhum, Inner Hebrides. Philosophical Transactions of the Royal Society of London B 240, 1–53.Google Scholar
Buening, D. K. & Buseck, P. R. 1973. Fe–Mg lattice diffusion in olivine. Journal of Geophysical Research 78, 6852–62.CrossRefGoogle Scholar
Butcher, A. R., Young, I. M. & Faithfull, J. W. 1985. Finger structures in the Rhum Complex. Geological Magazine 122, 491–502.CrossRefGoogle Scholar
Clark, A. M. & Long, J. V. P. 1971. Anisotropic diffusion of nickel in olivine. In Thomas Graham Memorial Symposium on Diffusion Processes, (ed. Sherwood, J. N., Chadwick, A. V., Muir, W. M. and Swinton, F. L.), pp. 511–21. Gordon and Breach.Google Scholar
Donaldson, C. H. 1975. Ultrabasic breccias in layered intrusions. The Rhum complex. Journal of Geology 83, 33–45.CrossRefGoogle Scholar
Donaldson, C. H. 1977. Laboratory duplication of comb-layering in the Rhum pluton. Mineralogical Magazine 41, 323–36.CrossRefGoogle Scholar
Donaldson, C. H. 1982. Origin of some of the Rhum harrisite by segregation of intercumulus liquid. Mineralogical Magazine 45, 201–9.CrossRefGoogle Scholar
Dunham, A. C. & Wadsworth, W. J. 1978. Cryptic variation in the Rhum layered intrusion. Mineralogical Magazine 42, 347–56.CrossRefGoogle Scholar
Dunham, A. C. & Wilkinson, F. C. F. 1978. Accuracy, precision and detection limits of energy-dispersive electron-microprobe analyses of silicates. X-Ray Spectrometry 7, 50–6.CrossRefGoogle Scholar
Harker, A. 1908. The Geology of the Small Isles of Inverness-shire. Memoir Geological Survey of Scotland.Google Scholar
Henderson, P. 1975. Reaction trends of chrome spinel on Rhum. Geochimica et Cosmochimica Acta 39, 1039–44.CrossRefGoogle Scholar
Irvine, T. N. 1980. Magmatic infiltration metasomatism, double-diffusive fractional crystallisation, and adcumulus growth in the Muskox intrusion and other layered intrusions. In Physics of Magmatic Processes (ed. Hargraves, R. B.), pp. 325–83. Princeton, N.J.: Princeton University Press.CrossRefGoogle Scholar
Jackson, E. D. 1961. Primary textures and mineral associations in the ultramafic zone of the Stillwater Complex, Montana. U.S. Geological Survey Professional Paper no. 358, 1–106.Google Scholar
Misener, D. J. 1974. Cationic diffusion in olivine to 1400 °C and 35 kbar. In Geochemical Transport and Kinetics (ed. Hofmann, A. W., Giletti, B. J., Yoder, H. S. Jr, and Yund, R. A.), pp. 77–98. Carnegie Institute of Washington 634.Google Scholar
Morioka, M. 1980. Cation diffusion in olivine – 1. Cobalt and magnesium. Geochimica et Cosmochimica Acta 44, 759–62.CrossRefGoogle Scholar
Palacz, Z. A. & Tait, S. R. 1985. Isotopic and geochemical investigation of unit 10 from the Eastern Layered Series of the Rhum Intrusion, Northwest Scotland. Geological Magazine 122, 485–90.CrossRefGoogle Scholar
Sparks, R. S. J., Huppert, H. E., Kerr, R. C., McKenzie, D. P. & Tait, S. R. 1985. Postcumulus processes in layered intrusions. Geological Magazine 122, 555–68.CrossRefGoogle Scholar
Tait, S. R. 1985. Fluid dynamic and geochemical evolution of cyclic unit 10, Rhum, Eastern Layered Series. Geological Magazine 122, 469–84.CrossRefGoogle Scholar
Wadsworth, W. J. 1961. The ultrabasic rocks of south-west Rhum. Philosophical Transactions of the Royal Society of London B224, 21–64.Google Scholar