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Exceptional REE-enrichment in apatite during the low pressure fractional crystallisation of alkali olivine basalt; an example from the British Tertiary Igneous Province

Published online by Cambridge University Press:  03 November 2011

R.J. Preston ,
M.J. Hole  and
J. Still
R.J. Preston
Affiliation:
Department of Geology and Petroleum Geology, Meston Building, University of Aberdeen, Aberdeen, AB24 3UE, UK e-mail: [email protected]
M.J. Hole
Affiliation:
Department of Geology and Petroleum Geology, Meston Building, University of Aberdeen, Aberdeen, AB24 3UE, UK e-mail: [email protected]
J. Still
Affiliation:
Department of Geology and Petroleum Geology, Meston Building, University of Aberdeen, Aberdeen, AB24 3UE, UK e-mail: [email protected]
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Abstract

The Cnoc Rhaonastil dolerite boss on Islay, NW Scotland represents a body of alkali-olivine basalt magma which differentiated at low pressure and in situ, from dolerite through teschenite to minor nepheline-syenite. The syenites occur as isolated pods and pegmatitic schlieren within the leucodolerite, and have an exotic mineralogy including Zr-aegirine, Zr-arfvedsonite, Ca-catapleiite, zirconolite and aenigmatite. Fluor-apatite occurs as an accessory phase in the dolerite, but becomes more abundant within the teschenite and syenites. Total REE contents within apatites in the dolerites are typically low (σREE = 0·57–3·21 wt.% oxide), the highest REE contents occurring in irregular, deuterically altered rims and internal patches. The REE-enriched rims also have slightly elevated SiO2 contents at 0·81–0·95 wt.%, suggesting that the substitution scheme Ca2++P5+ ⇔ REE3++Si4+ was operating. These apatites have up to 0·08 wt.% Cl and 3·7 wt.% F, with most being almost pure end-member fluor-apatite. The majority of the teschenite apatites show the least REE-enrichment (σREE = 0·27–0·45 wt.%), coupled with low Na (<0·12 wt.%) and low SiO2 (<0·39 wt.%) contents. However, within the syenites two distinct populations of apatite exist. The first, most common, variety consists of unzoned, low-REE apatites (max. 3·1 wt.% σREE, again in irregular rims and patches), whereas the second variety is often complexly zoned, and has variably enriched zones up to a maximum σREE content of 42 wt.%; this is by far the most REE-enriched natural fluor-apatite so far reported from the British Isles. The REE-enriched zones are often less than 3 μm wide, and have Na content up to 5·4 wt.% Na2O, implying that the substitution scheme Na+ + REE3+⇔2Ca2+ dominated over the more typical scheme involving Si4+ which operated in the dolerites and teschenite. Other zones are either variably enriched in Y (up 2·1 wt.% Y2O3) or Th (up to 0·85 wt.% ThO2). However, there is no correlation between Y and REE contents, suggesting that crystallographic factors were involved in apatite Y and REE partitioning. The REE-rich apatites have very low Cl content (<0·04 wt.%), but high F concentrations (<2·8 wt.%). It is believed that these strongly enriched apatites crystallised under disequilibrium conditions from isolated, variably REE-enriched domains, within the fluid-rich residual syenitic magma. These domains may have been generated by the prior crystallisation of monazite, Ca-catapleiite or zirconolite, which can be found as small inclusions within albite and interstitial analcime. The dynamic process of slumping of the denser teschenite back into the leucodolerite crystal mush is believed to have played an important role in the release of deuteric fluids and the concentration of residual magmas.

Keywords

alkali olivine basaltapatitefractional crystallisationREE-enrichment
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 90 , Issue 4 , 1999 , pp. 273 - 285
Copyright
Copyright © Royal Society of Edinburgh 1999

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References

Åmli, R. & Griffin, W. L. 1970. Microprobe analysis of REE minerals using empirical correction factors. American Mineralogist 60, 599–606.Google Scholar
Arth, J. G. 1976. Behaviour of trace elements during magmatic processes–a summary of theoretical models and their applications. Journal of Research of the US Geological Survey 4, 41–7.Google Scholar
Banfield, J. F. & Eggleton, R. A. 1989. Apatite replacement and rare earth mobilization, fractionation, and fixation during weathering. Clavs and Clay Minerals 37, 113–27.CrossRefGoogle Scholar
Bouch, J. E., Hole, M. J., Trewin, N. H. & Morton, A. C. 1995. Lowtemperature aqueous mobility of the rare-earth elements during sandstone diagenesis. Journal of the Geological Society, London 152, 895–8.CrossRefGoogle Scholar
Boudreau, A. E., Love, C. & Hoatson, D. M. 1993. Variation in the composition of apatite in the Munni Munni Complex and associated intrusions of the West Pilbara Block, Western Australia. Geochimica et Cosmochimica Ada 57, 4467–77.Google Scholar
Boudreau, A. E. & McCallum, I. S. 1989. Investigations of the Stillwater Complex: Part V. Apatites as indicators of evolving fluid compositions. Contributions to Mineralogy and Petrology 102, 138–53.CrossRefGoogle Scholar
Boudreau, A. E. & McCallum, I. S. 1990. Low temperature alteration of REE-rich chlorapatite from the Stillwater Complex, Montana. American Mineralogist 75, 687–93.Google Scholar
Contini, S., Venturelli, G., Toscani, L., Capedri, S. & Barbieri, M. 1993. Cr-Zr-armalcolite-bearing lamproites of Cancarix, SE Spain. Mineralogical Magazine 57, 203–16.CrossRefGoogle Scholar
Coulson, I. M. & Chambers, A. D. 1996. Patterns of zonation in rareearth-bearing minerals in nepheline syenites of the North Qoroq Center, South Greenland. Canadian Mineralogist 34, 1163–78.Google Scholar
Drake, M. J. & Weill, D. F. 1972. New rare earth element standards for electron microprobe analysis. Chemical Geology 10, 179–81.CrossRefGoogle Scholar
Exley, R. A. 1980. Microprobe studies of REE-rich minerals: implications for Skye granite petrogenesis and REE mobility in hydrothermal systems. Earth and Planetary Science Letters 48, 97–110.CrossRefGoogle Scholar
Finch, A. A. & Fletcher, J. G. 1992. Vitusite–an apatite derivative structure. Mineralogical Magazine 56, 235–9.CrossRefGoogle Scholar
Flynn, R. T. and Burnham, C. W. 1978. An experimental determination of rare earth partition coefficients between a chloride containing vapor phase and silicate melt. Geochimica et Cosmochimica Ada 42, 685–701.CrossRefGoogle Scholar
Fujimaki, H. 1986. Partition coefficients of Hf, Zr and REE between zircon, apatite and liquid. Contributions to Mineralogy and Petrology 94, 42–5.Google Scholar
Gibb, F. G. F. & Henderson, C. M. B. 1978. The petrology of the Dippin sill, Isle of Arran. Scottish Journal of Geology 14, 1–27.CrossRefGoogle Scholar
Gibson, S. A. & Jones, A. P. 1991. Igneous stratigraphy and internal structure of the Little Minch Sill Complex, Trotternish Peninsula, northern Skye, Scotland. Geological Magazine 128, 51–66.CrossRefGoogle Scholar
Green, T. H. & Watson, E. B. 1982. Crystallization of apatite in natural magmas under high pressure, hydrous conditions, with particular reference to ‘orogenic’ rock series. Contributions to Mineralogy and Petrology 79, 96–105.CrossRefGoogle Scholar
Hole, M. J. & 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. Scottish Journal of Geology 28, 55–69.CrossRefGoogle Scholar
Hughes, J. M., Cameron, M. & Mariano, A. N. 1991. Rare-earthelement ordering and structural variations in natural rare-earthbearing apatites. American Mineralogist 76, 1165–73.Google Scholar
Jolliff, B. L., Papike, J. J. & Shearer, C. K. 1989. Inter–and intracrystal REE variations in apatite from the Bob Ingersoll pegmatite, Black Hills, South Dakota. Geochimica et Cosmochimica Ada 53, 429–41.CrossRefGoogle Scholar
Lamacraft, H. 1979. The geochemistry of the Tertiary dyke swarms of Mull, Islay and Jura. Journal of the Geological Society, London 139, 257 (abstract).Google Scholar
Mohr, D. W. 1984. Zoned porphyroblasts of metamorphic monazite on the Anakeesta Formation, Great Smokey Mountains, North Carolina. American Mineralogist 69, 98–103.Google Scholar
Pearce, J. A. & Norry, M. J. 1979. Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks. Contributions to Mineralogy and Petrology 69, 33–47.CrossRefGoogle Scholar
Pinckston, D. R. & Smith, D. G. W. 1995. Mineralogy of the Lake zone, Thor Lake rare-metals deposit N.W.T., Canada. Canadian Journal of Earth Sciences 32, 516–32.CrossRefGoogle Scholar
Preston, R. J., Hole, M. J., Bouch, J. & Still, J. 1998. The occurrence of zirconian aegirine and calcic catapleiite (CaZrSi3O9·2H2O) within a nepheline syenite, British Tertiary Igneous Province. Scottish Journal of Geology 34, 173–80.Google Scholar
Preston, R. J., Hole, M. J. & Still, J. 2000. 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. Mineralogical Magazine 64, 459–68.CrossRefGoogle Scholar
Rae, D. A., Coulson, I. M. & Chambers, A. D. 1996. Metasomatism in the North Qoroq centre, South Greenland: apatite chemistry and rare-earth element transport. Mineralogical Magazine 60, 207–20.CrossRefGoogle Scholar
Rakovan, J. & Reeder, R. J. 1996. Intracrystalline rare earth element distributions in apatite: Surface structural influences on incorporation during growth. Geochimica et Cosmochimica Ada 60, 4435–45.CrossRefGoogle Scholar
Roeder, P. L. 1985. Electron-microprobe analysis of minerals for rareearth elements: use of calculated peak-overlap corrections. Canadian Mineralogist 23, 263–71.Google Scholar
Roeder, P. L., MacArthur, D., Ma, X. P. & Palmer, G. R. 1987. Cathodoluminescence and microprobe study of rare-earth elements in apatite. American Mineralogist 72, 801–11.Google Scholar
Rollinson, H. 1993. Using Geochemical Data: Evaluation, Presentation, Interpretation. New York: John Wiley & Sons.Google Scholar
Ronsbo, J. G. 1989. Coupled substitutions involving REEs and Na and Si in apatites in alkaline rocks from Ilimaussaq intrusion, South Greenland, and the petrological implications. American Mineralogist 72, 896–901.Google Scholar
Ronsbo, J. G., Khomyakov, A. P., Semenov, E. I., Voronkov, A. A. & Garanin, V. K. 1979. Vitusite–a new phosphate of sodium and rare earths from the Lovozero alkaline massif, Kola, and the Ilimaussaq alkaline intrusion, South Greenland. Nueus Jahrbuch fur Mineralogie Abhandlungen 137, 42–53.Google Scholar
Ryerson, F. J. & Hess, P. C. 1978. Implications of liquid-liquid distribution coefficients to mineral-liquid partitioning. Geochimica et Cosmochimica Ada 42, 921–32.CrossRefGoogle Scholar
Ryerson, F. J. & Hess, P. C. 1980. The role of P2O5 in silicate melts. Geochimica et Cosmochimica Ada 44, 611–24.CrossRefGoogle Scholar
Sun, S-S. & McDonough, W. F. 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In Saunders, A. D. and Norry, M. J. (eds) London: Geological Society. Magmatism in the Ocean Basins, Geological Society Special Publication 42, 313–45, London: Geological Society.Google Scholar
Walker, F. & Patterson, E. 1959. The geochemistry of a boss of alkali dolerite, Cnoc Rhaonastil, Islay. Mineralogical Magazine 32, 140–52.CrossRefGoogle Scholar
Watson, E. B. 1976. Two-liquid partition coefficients: Experimental data and geochemical implications. Contributions to Mineralogy and Petrology 56, 119–34.CrossRefGoogle Scholar
Watson, E. B. 1979. Apatite saturation in basic to intermediate magmas. Geophysical Research Letters 6, 937–40.CrossRefGoogle Scholar
Watson, E. B. & Green, T. H. 1981 Apatite/liquid partition coefficients for the rare earth elements and strontium. Earth and Planetary Science Letters 56, 405–21.CrossRefGoogle Scholar
Wolf, M. B. & London, D. 1995. Incongruent dissolution of REE-and Sr-rich apatite in peraluminous granitic liquids: Differential apatite, monazite, and xenotime solubilities during anatexis. American Mineralogist 80, 765–75.CrossRefGoogle Scholar