class display extreme fractionation and accumulation.of rare lithophile ... tiques) ddmontrent un deg6 de fractionation et d,accumu- ..... the mechanism involved at this stage, the Rb con- ...... initial (and drastic) Sr depletion was shown by.
Canadian Mineralogist Yol.23, pp. 381-421(1985)
EXTREMEFRACTIONATIONIN RARE.ELEMENTGRANITICPEGMATITES: SELECTEDEXAMPLESOF DATA AND MECHANISMS PETRdERNf, ROBERT E. MEINTZER aNn ALAN J. ANDERSON,T Departmentof Earth Sciences, tlniversity of Manitoba, Winnipeg,Manitoba R3T 2N2
ABSTRACT
rations de feldspaths de K et de Na primaires. La fractionation extrOmesevoit dans le feldspath potassique (K/Rb 1.9,K,/Cs22.4,K/T1236.Rb,zCs 6.5, Rb,zTlde 130 - Granitic pegmatitesof the rare_element(and miarolitic) classdisplayextremefractionation and accumulation.ofrare d35,K/Ba 18,000,BalRb infdrieur d 0.002),la muscovite lithophile elements, beyond the limits observed in other et la ldpidolire(K,/Rb 1.4, K,/Cs4.0, K/Tl 320,Rb/Cs 4.4, igneousand postmagmatic assemblages.Enrichment in Li Rb,zTl de 80 i 36,N/ca239),la pollucite(K,/Tl 10,Rb/Tl and -Csleadsto precipitation of rock-forming spodumene, de 60 d l3), la microlite, la simpsoniteet autres oxydestarpetalite, Li-phosphates or lepidolite, and pollucite. These difs de Ta (Nb,/Ta inf6rieur d 0.@l), la manganotantalite be interpretedascrystallochemicallyconditioned (FelMn 0.003), la spessartine(FelMn inf€rieur e 0.003), gqeoes-can Li- and-Csbasedfeldspathoids,crystallizingalong with (and la lithiophilite @e/Mn inf€rieur d 0.01),le hafnon (Zr/Hf after) the last generationsof primary K- and Nalfeldspars. 0.014) et la hawleyite et la dernjite (Zn/Cd 0.067). Les Extreme fractionation is encounteredin K-feldspar gi,znb seulsconceptscristallochimiquesclassiquesde Goldschmidt pas pour expliquer cesvaleurs. !,9.rK/Qs 22.4, K/Tt 236,Rb,zCs6.5, Rb,/Tt130 io 35, et de Ringwood ne suffisent K,/Ba 18,0@, BalRb
