Abstract
The Precambrian migmatitic gneisses at Alnö have been altered to fenite by fluids emanating from alkaline and carbonatitic magmas intruded during early to middle Cambrian times. Fenitization, related to carbonatitic sources, was promoted by peralkaline, carbonate-rich fluids, in which the main chemical components and REE were mobile. Composition-volume relationships of progressively fenitized protolith suggest mainly isovolumetric equilibration, but a modest decrease of volume (6%) did occur in the highest grade of the process. The fenitizing fluids introduced essentially CaO, CO2, Na2O, and K2O while removing SiO2 and Al2O3. Different trends of fenitization, defined as sodic, potassic and intermediate, show differing REE distribution and abundance patterns. The sodic carbonate-rich fluid introduced all the REE, but the La/Lu ratio was high. The extreme REE enrichments of high-grade fenites are associated with the widespread formation of calcite, apatite and possibly titanite. The potassic carbonaterich fluid introduced essentially light REE, but produced also the redistribution of heavy REE in the high-grade fenites. REE distribution patterns of intermediate fenites suggest the re-equilibration of fenite with a highly oxidizing alkaline fluorine-rich fluid, possibly in a later post-magmatic episode.
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References
Alderton DHM, Pearce JA, Potts PJ (1980) Rare earth element mobility during granite alteration: evidence from southwest England. Earth Planet Sci Lett 49:149–165
Åmli R (1975) Mineralogy and rare earth geochemistry of apatite and xenotime from the Gloserheia Granite Pegmatite, Froland, southern Norway. Am Mineral 60:607–620
Andersen T (1986a) Magmatic fluids in the Fen carbonatite complex, S.E. Norway: Evidence of mid-crustal fractionation from solid and fluid inclusions in apatite. Contrib Mineral Petrol 93:491–503
Andersen T (1986b) Compositional variation of some rare earth minerals from the Fen complex (Telemark, SE Norway): Implications for the mobility of the rare earths in a carbonatite system. Mineral Mag 50:503–509
Andersen T (1987a) Mantle and crustal components in a carbonatite complex, and the evolution of carbonatite magma; REE and isotopic evidence from the Fen complex, southeast Norway. Chem Geol (Isotope Geoscience) 65:147–166
Andersen T (1987b) A model for the evolution of hematite carbonatite, based on major and trace elements data from the Fen complex. In: PhD thesis Petrogenesis and geochemistry of carbonatites: the Fen complex, SE Norway, University of Oslo
Appleyard EC, Woolley AR (1979) Fenitization: an example of the problems characterizing mass transfer and volume changes. Chem Geol 26:1–15
Balashov YuA, Pozharitskaya LK (1968) Factors governing the behavior of rare-earth elements in the carbonatite process. Geochem lnt 5:271–288
Brueckner HK, Rex DC (1980) K-A and Rb-Sr geochronology and Sr isotopic study of the Alnö alkaline complex, northeastern Sweden. Lithos 13:111–119
Eby GN (1975) Abundance and distribution of the rare earth elements and yttrium in the rocks and minerals of the Oka carbonatite complex, Quebec. Geochim Cosmochim Acta 39:579–620
von Eckermann H (1948) The alkaline district of Alnö Island. Sveriges Geol Unders Ca 36:1–176
Emmerman R, Daieva L, Schneider J (1975) Petrologic significance of rare earth distribution in granites. Contrib Mineral Petrol 52:267–283
Govindaraju K, Mevelle G (1987) Fully automated dissolution and separation methodes for inductively coupled plasma atomic emission spectrometry rock analysis. Application to the determination of rare earth elements. Plenary lecture. J Anal Atomic Spectrom 2:615–621
Gresens RL (1967) Composition-volume relationships in metasomatism. Chem Geol 2:47–65
Haskin LA, Haskin MA, Frey FA, Wildeman TR (1968) Relative and absolute terrestrial abundances of the rare earth. In: Ahrens (ed) Origin and distribution of the elements. Pergamon Press, Oxford New York, pp 889–912
Humphris S (1984) The mobility of the rare earth elements in the crust. In: Henderson P (ed) Rare earth geochemistry. Elsevier, Amsterdam, pp 317–342
Jefford G (1962) Xenotime from Rayfield, northern Nigeria. Am Mineral 47:1467–1473
Kresten P (1979) The Alnö complex: discussion of the main features, bibliography and excursion guide. Nordic Carbonatite Symposium, 67 p
Kresten P (1986) Map of the Alnö complex. Sveriges Geol Unders Ser Ba 31, Specialkarta 1
Kresten P (1988) The chemistry of fenitization: Examples from Fen, Norway. Chem Geol 68:329–349
Martin RF, Whitley JE, Woolley AR (1978) An investigation of rare earth mobility: Fenitized quartzites, Borralan complex, NW Scotland. Contrib Mineral Petrol 66:69–73
Mitchell RH, Brunfelt AO (1975) Rare earth element geochemistry of the Fen alkaline complex, Norway. Contrib Mineral Petrol 52:247–259
McLennan SM, Taylor SR (1979) Rare earth element mobility associated with uranium mineralization. Nature 282:247–250
Möller P, Morteani G, Schley F (1980) Discussion of REE distribution patterns of carbonatites and alkalic rocks. Lithos 13:171–179
Morogan V, Woolley AR (1988) Fenitization at the Alnö carbonatite complex, Sweden; distribution, mineralogy and genesis. Contrib Mineral Petrol 100:169–182
Robins B (1984) Petrography and petrogenesis of nephelinized metagabbros from Finnmark, northern Norway. Contrib Mineral Petrol 86:170–177
Rubie DC (1982) Mass transfer and volume change during alkali metasomatism at Kisingiri, western Kenya. Lithos 15:99–109
Vocke RD Jr, Hanson GH, Grünenfelder M (1987) Rare earth element mobility in the Roffna Gneiss, Switzerland. Contrib Mineral Petrol 95:145–154