Hostname: page-component-848d4c4894-m9kch Total loading time: 0 Render date: 2024-05-19T09:03:29.428Z Has data issue: false hasContentIssue false
  • English
  • Français

Fluid dynamic and geochemical evolution of cyclic unit 10, Rhum, Eastern Layered Series

Published online by Cambridge University Press:  01 May 2009

Stephen R. Tait
Stephen R. Tait
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Lithological, major element, trace element and Sr isotope data from cyclic unit 10 of the Rhum Eastern Layered Series are presented. The lower 65 metres of the unit are peridotite, subdivided on textural and geochemical grounds into a lower homogeneous portion approximately 50 metres thick and an upper heterogeneous portion approximately 15 metres thick. The uppermost 16.5 metres of the unit are allivalite. There are steep geochemical gradients across the peridotite-allivalite boundary in Ni content of olivine and whole-rock Sr isotope composition.

Calculations are presented on the geochemical evolution of a Rhum picritic liquid undergoing olivine precipitation, both when the olivines remain suspended in the residual liquid as they precipitate, and when they are continuously fractionated. Quenched groundmass and olivine compositions from the Rhum dykes and the unit 10 peridotite olivines show good agreement with the suspension model but are inconsistent with the fractionation model. The Rhum chamber is thought to have been replenished with a picritic liquid from which olivine crystallized while held in suspension; however, replenishment by a highly olivine-phyric basalt is also possible. The peridotite probably accumulated rapidly as olivines were dumped out of suspension onto the chamber floor.

The lower part of the peridotite is a poikilitic adcumulate; it is suggested that this formed by convective circulation of melt in the pores of the pile of cumulus olivines. In the latter stages of adcumulus growth, more Fe-rich and isotopically contaminated magma entered the top of the cumulus pile causing cumulus olivines to re-equilibrate and giving the intercumulus plagioclase a higher Sr isotope ratio than lower down. The olivines in the allivalite show steep stratigraphic gradients in major element composition but not in their Ni content. They also show substantial variation in major element composition laterally within the allivalite. It is suggested that these features are a consequence of postcumulus re-equilibration of olivine with migrating intercumulus magma.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 5 , September 1985 , pp. 469 - 484
Copyright
Copyright © Cambridge University Press 1985

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

Arndt, N. T. 1977. Partitioning of nickel between olivine and ultrabasic komatiite liquid. Carnegie Institute of Washington Yearbook 76, 553–7.Google Scholar
Bottinga, Y. & Weill, D. F. 1970. Densities of liquid silicate systems, calculated from partial molar volumes of oxide components. American Journal of Science 269, 169–82.CrossRefGoogle Scholar
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
Burnham, C. W. 1975. Water and magmas: a mixing model. Geochimica et Cosmochimica Acta 39, 1077–84.CrossRefGoogle Scholar
Butcher, A. R. 1985. Channelled metasomatism in Rhum layered cumulates – evidence from late-stage veins. Geological Magazine 122, 503–18.CrossRefGoogle Scholar
Cox, K. G., Bell, J. D. & Pankhurst, R. J. 1979. The Interpretation of Igneous Rocks. George Allen and Unwin, 334 pp.CrossRefGoogle Scholar
Drake, M. J. 1976. Plagioclase melt equilibria. Geochimica et Cosmochimica Acta 40, 457–65.CrossRefGoogle Scholar
Drake, M. J. & Weill, D. F. 1975. Partition of Sr, Ba, Ca, Y, Eu2+, Eu3+, and other REE between plagioclase and magmatic liquid: an experimental study. Geochimica et Cosmochimica Acta 39, 689–712.CrossRefGoogle Scholar
Duke, J. M. & Naldrett, A. J. 1978. A numerical model of the fractionation of olivine and molten sulphide from komatiite magma. Earth and Planetary Science Letters 39, 256–66.CrossRefGoogle Scholar
Dunham, A. C. & Wadsworth, W. J. 1978. Cryptic variation in the Rhum Intrusion. Mineralogical Magazine 42, 347–56.CrossRefGoogle Scholar
Gibb, F. G. F. 1976. Ultrabasic rocks of Rhum and Skye: the nature of the parent magma. Journal of the Geological Society of London 132, 209–22.CrossRefGoogle Scholar
Hamilton, D. L., Burnham, C. W. & Osborn, E. F. 1964. The solubility of water and effects of oxygen fugacity and water content on crystallisation in mafic magmas. Journal of Petrology 5, 21–39.CrossRefGoogle Scholar
Hart, S. R. & Brooks, C. 1974. Clinopyroxene-matrix partitioning of K, Rb, Cs, Sr and Ba. Geochimica et Cosmochimica Acta 38, 1799–1806.CrossRefGoogle Scholar
Hart, S. R. & Davis, K. E. 1978. Nickel partitioning between olivine and silicate melt. Earth and Planetary Science Letters 40, 203–19.CrossRefGoogle Scholar
Harvey, P. K., Taylor, D. M., Hendry, R. D. & Bancroft, F. 1973. An accurate fusion method for the analysis of rocks and chemically related materials by X-ray fluorescence spectrometry. X-Ray Spectrometry 2, 33–44.CrossRefGoogle Scholar
Huppert, H. E. & Sparks, R. S. J. 1980 a. Restrictions on the compositions of mid-ocean ridge basalts: a fluid dynamical investigation. Nature 286, 46–8.CrossRefGoogle Scholar
Huppert, H. E. & Sparks, R. S. J. 1980 b. The fluid dynamics of a basaltic magma chamber, replenished by an influx of hot, dense, ultrabasic magma. Contributions to Mineralogy and Petrology 75, 279–89.CrossRefGoogle Scholar
Irvine, T. N. 1974. Chromitite layers in stratiform intrusions. Geophysical Laboratory Yearbook 73, 300–16.Google Scholar
Irvine, T. N. 1980. Magmatic infiltration metasomatism, double-diffusive fractional crystallisation, and adcumulus growth in the Muskox and other layered intrusions. In Physics of Magmatic Processes (ed. Hargraves, R. B.), pp. 325–83. Princeton New Jersey: Princeton University Press.CrossRefGoogle Scholar
Irvine, T. N. 1982. Terminology for layered intrusions. Journal of Petrology 23, 127–62.CrossRefGoogle Scholar
Iyer, H. M. 1984. Geophysical evidence for the locations, shapes and sizes, and internal structures of magma chambers beneath regions of Quaternary volcanism. Philosophical Transactions of the Royal Society of London A 310, 473–510.Google Scholar
Kerr, R. C. & Tait, S. R. 1985. Convective exchange between pore fluid and an overlying reservoir of denser fluid: a postcumulus process in layered intrusions. Earth and Planetary Science Letters (in press).CrossRefGoogle Scholar
Kerr, R. C. & Tait, S. R. (submitted). Crystallization and compositional convection in a porous medium with application to layered intrusions. Journal of Geophysical Research.Google Scholar
Kitchen, D. E. 1985. The parental magma on Rhum: evidence from alkaline segregations and veins in the peridotites from Salisbury's Dam. Geological Magazine 122, 529–37.CrossRefGoogle Scholar
Kudo, A. M. & Weill, D. F. 1970. An igneous plagioclase thermometer. Contributions to Mineralogy and Petrology 25, 52–65.CrossRefGoogle Scholar
Leeman, W. P. & Schiedegger, K. F. 1977. Olivine/liquid distribution coefficient, and a test for crystal-liquid equilibrium. Earth and Planetary Science Letters 35, 247–57.CrossRefGoogle Scholar
McKenzie, D. P. 1984. Generation and compaction of partially molten rock. Journal of Petrology 25, 713–65.CrossRefGoogle Scholar
Moore, J. G. 1970. Water content of basalt erupted on the ocean floor. Contributions to Mineralogy and Petrology 28, 272–9.CrossRefGoogle Scholar
Nelson, S. A. & Carmichael, I. S. E. 1979. Partial molar volumes of oxide components in silicate liquids. Contributions to Mineralogy and Petrology 71, 117–24.CrossRefGoogle Scholar
Norton, D. & Taylor, H. P. 1979. Quantitative simulation of the hydrothermal systems of crystallising magmas on the basis of transport theory and oxygen isotope data: Skaergaard Intrusion. Journal of Petrology 20, 421–86.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
Roeder, P. L. & Emslie, R. F. 1970. Olivine-liquid equilibrium. Contributions to Mineralogy and Petrology 29, 275–89.CrossRefGoogle Scholar
Ryan, M. P., Koyanagi, R. Y. & Fiske, R. S. 1981. Modelling the three-dimensional structure of macroscopic magma transport systems: application to Kilauea Volcano, Hawaii. Journal of Geophysical Research 86, 7111–29.CrossRefGoogle Scholar
Scarfe, C. M. 1973. Water solubility in basic and ultrabasic magmas. Nature (Physical Sciences) 246, 9–10.Google Scholar
Shaw, H. R. 1972. Viscosities of magmatic silicate liquids: an empirical method of prediction. American Journal of Science 272, 870–93.CrossRefGoogle Scholar
Sparks, R. S. J. & Huppert, H. E. 1984. Density changes during the fractional crystallisation of basaltic magmas: implications for the evolution of layered intrusions. Contributions to Mineralogy and Petrology 85, 300–9.CrossRefGoogle Scholar
Stolper, E. & Walker, D. 1980. Melt density and the average composition of basalt. Contributions to Mineralogy and Petrology 74, 7–12.CrossRefGoogle Scholar
Tait, S. R., Huppert, H. E. & Sparks, R. S. J. 1984. The role of compositional convection in the formation of adcumulate rocks. Lithos 17, 139–46.CrossRefGoogle Scholar
Wadsworth, W. J. 1985. Terminology of postcumulus processes and products in the Rhum layered intrusion. Geological Magazine 122, 549–54.CrossRefGoogle Scholar
Wright, T. L. & Docherty, P. C. 1970. A linear programming and least squares computer method for solving petrologic mixing problems. Bulletin of the Geological Society of America 81, 1995–2008.CrossRefGoogle Scholar
Young, I. M. 1984. Mixing of supernatant and interstitial fluids in the Rhum layered intrusion. Mineralogical Magazine 48, 345–50.CrossRefGoogle Scholar