Svecofennian Rare.Element Granitic Pegmatites Of
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SvecofennianSvecofennian granitic pegmatites (1.86-1.79( 1.86- 1.79 Ga) and quartz monzonite (1.87( 1.87 Ga),Ga), and theirtheir metamorphic environment inin thethe Seinäjoki region,region, western Finland Edited byby HannuHannu Mäkitie Geological Survey of Finland, Special Paper 30,9-2930, 9-29 SVECOFENNIANSVECOFENNIAN RARE.ELEMENTRARE-ELEMENT GRANITIC PEGMATITES OF THE OSTROBOTHNIAOSTROBOTHNIA REGION,REGION, WESTERN FINLAND; THEIR METAMORPHIC ENVIRONMENT AND TIME OF INTRUSION by Alviola, R.,R. , Mänttäri,I.,Mänttäri, 1. , Mäkitie, H. and Vaasjoki, M. Alviola, Reijo, Mänttäri, Irmeli, Mäkitie, HaHannu,nnu, & Vaasjoki, Matti 2001. Svecofennian rarerare- element granitic pegmatites ofofthe the Ostrobothnia region, western Finland; theirmetamorphictheir metamorphicenviron environ- ment and time of intrusiintrusion. on. Geological Survey of Finland,Finland, Special Paper 30, 9-29,9-29, 10l0 figures, 5 tables and one appendix. Ostrobothnia isis situated in western Finland along the coast of the Gulf of Bothnia. It consists of the Ostrobothnia Schist BeltBelt,, the Vaasa Migmatite Complex and part of the Central Finland Granitoid Complex, and is part of the Paleoproterozoic 1.90-1.871 .90- | .87 Ga SvecofennjanSvecofennian accretionary arc complex of central and western FinlandFinland.. The Ostrobothnia SchiSchistst Belt consists of turbiditic metapelites exhjbitingexhibiting Paleoproterozoic ((-Archean)-Archean) provenance,provenance , and local metavolcanic rocks as interlayers. The large Central Finland GrGranitoidanitoid Complex, which contajncontainss sysyn-n- and post-kinematic granitoids occurs east of the schjstschist belt and to the west of the scrustsschists are the diatexites of the Vaasa Migmatite ComplexComplex.. Most of the Ostrobothnian supracrustal rocks were metamorphosed under low-pressure ampruboliteamphibolite faciesfacies,, locally granulite facies, conditions 1.89-1.881 .89- 1.88 Gaago. The metamorprucmetamorphic grade is lowestlowestinthe in the central and eastem parts of the Ostrobothnia Schist Belt.Be1t. The grade increases towards the Vaasa Migmatite Complex and also southwards in the southern part of the schist belt. The rare-element (RE) granitic pegmatites oftheof the region are divided into 12l2 groupsgroups.. All pegmatites belong to the LCT (Li(Li,Cs,Ta),Cs,Ta) family except the Alavus NYF (Nb,(Nb,Y,F) Y,F) pegmatites. Most pegmatites are beryl pegmatites of the beryl-columbite subtype, but three groups belong to the spodumene subtype and one group to the albite-spodumene subtype of complex pegmatites. Two groups of the beryl-beryl columbite ssubtypeubtype areare topaz/andalusite-topazlandalusite- and fluorite-bearing with biotite predominant over muscovite and without tourmaline. All the RE-pegmRE-pegmatitesatites of the schist belt occur in the lower to medium amphibolite facies rocks with the exception of the topaz/andalusite-topazlandalusite- and fluoritfluorite-bearinge-bearing pegmatitespegmatites,, which are in upper amphibolite facies mica gneisgneisses ses ssurroundingurrounding the Vaasa Migmatite Complex. The pegmatitepegmatitess aatt Alavus lie within the Central Finland Granitoid ComplexComplex.. U-Pb ages have been determined from LCT pegmatite hosted Nb-Ta mineralsminerals.. Columbites from the KaatialaKaatiala,, Ullava, Haapaluoma, and Korvenniemi pegmatites and tapiolitetapiolite from thethe SeinäjokjSeinäjoki pegmatite yielded ages between 1.80-1.79 Ga. The dated columbites are ferro- and manganocolumbites. The Alavus NYF pegmatites do not contain Nb-Ta minerals applicable forfor U-Pb dating. The dated monazite fromfrom thesethese pegmpegmatitesatites gives an age of 1.86 Ga andand,, thusthus,, thesethese dykes may be linked to the evoevolutionlution of thethe 11.89-1.87.89-1.87 Ga Central Finland Granitoid Complex. The 11.80-1.79.80-1 .79 Ga old RE-pegmatites indicateindicate a tectono-magmatic episode distinct from thethe culmination (c.(c. 1.88 Ga) of thethe Svecofennian orogeny. Key words ((GeoRefGeoRef ThesaurusThesaurus,, AGI): pegmatitepegmatite,, absolute ageage,, U-Pb, columbitecolumbite,, monazitemonazite,, metameta- morphismmorphism,, metapelitemetapelites,s, Svecofennian, ProterozoicProterozoic,, OOstrobothnia,strobothnia, Bothnia BeltBelt,, Seinäjoki, Finland RReijoeijo AlviolaAlviola,, lrmIrmelieli Mänttäri,Mänttöri, Hannu MäkitiMcikitiee & Matti Vaasjoki GGeologicaleological SurveSurveyy of Finland, P.P.O. O. Box 9696,, FIN-02150 EspooEspoo,, F1NLANDFINLAND E-mail:E -mail : rr ee ijij o.ao. alvlv iiolaola @gsf.f@ g sf.fii 9 GeoloGeologiangian tutkimututkimuskeskus,skeskus, SpSpecialecial PapPaperer - GGeologicaleological SSurveyurvey oofi FFinland,inland, SSpecialpecial PapPaperer 3300 RReijoeijo AAlvioln,lviola, lrmIrmelieli MMänttöri,änttäri, HannuHannu MäkitiMökitie- e andand MattiMatti VaaVaasjokisjoki CONTENTSCONTENTS Introduction ............... .. .................................................. ................................................ 11 Lithology of (>strobothniaOstrobothnia .............................. ..... ................... .. .. .. .. ...... .. ........ ............................ 12I2 Central FinhmdFinlmd Granitoid Complex .............................. ........ .................................... 12I2 Ostrobothnia Schist Belt8e1t............................................ .. .............. .................... .... .... .. .............. 12 Vaasa MigMigmatitematite Complex .. .. ................... .. .. .. .. .. ................... ... .. ..... ..................... .... 1t3 3 MetamorphisnlMetamorphism and tectonictectonicss ....... .. .. .................. .. ........................................................ 1313 MetamorphiMetamorphismsm ....................................... ... ............ ......... .. .... .. ... ................... .. ..................... ... 13t3 Tectonic setting and deformation ................. .. ... ................................. ........... ........ ....... ....... .... 14I4 Pegmatite granites and RERE-pegmatite-pegmatite groupgroupss .............. ...................... ........ .................. 17l7 U-Pb dating of01' pegmatites ................... .. ......................... ........ ........ .............. .. .. .. ...... .. .......... .. ....... 20 SampSampleie material .. ......... .. ....... ..... .... ............... ............... ... .... .... ... ............. .. ... .......... .... 212l Analytical methods ........ ..... .. ............. .. ....... ............. .. .... .. .. ...................... ... .. ............. 212l U-Pb isotopic resultsresults ...... ...... .. .................... .................. ....... .. ...... .. ............ ............ .... 22 Discussion ........... ..................... ................... .................. .. ......................................... .... 24 AcknowledgementsAcknowledgernents ................ .... ................. ......................... ....... ........ .. ................... .... 26 References ........................ .. ....................................... .... ... ........ .. .. ......... .. .................. ... 27 Appendix l:1: Summary of thethe published isotopicisotopic age data available form Osffobothnia,Ostrobothnia, western Finland 10 GeologianGeologian tutkimuskeskus,tutkimuskeskus, SpecialSpecial PaperPaper - GeologicalGeological SurveySurvey of0/ Finland, Finland, SpecialSpecial PaperPaper 3030 - SvecofennianSvecofennian rare-elementrare-element graniticgranitic pegmatites...pegmatites .. INTRODUCTIONINTRODUCTION OstrobothniainOstrobothnia in westernwestern FinlandFinland lieslies roughlyroughly attheat the minorminor RE-pegmatiteRE-pegmatite populationspopulations werewere detected,detected, andand centrecentre of thethe PrecambrianPrecambrian Fennoscandian (Baltic)(Baltic) thethe Seinäjoki tintin pegmatitespegmatites werewere found inin 1979. Shield. The mainmain geologicalgeological unitsunits of thethe regionregion are Only twotwo RE-pegmatiteRE-pegmatite groups, namely thethe ((1) 1) thethe marginalmarginal areas of the the Central FinlandFinland Granitoid Haapaluoma-KaatialaHaapaluoma-Kaatiala and thethe Seinäjoki groups, havehave Complex inin thethe south and east, (2)(2) thethe arcuate been studied inin detail (Haapala(Haapala 1966, NieminenNieminen I1978, 978, Ostrobothnia Schist Belt inin thethe centre, and (3)(3) thethe Oivanen 1983, Nurmela 1985, Alviola 1989a). Vaasa Migmatite Complex inin thethe northwest (Fig. 1). Granitic pegmatites are classifieddassified intointo (l)(1) abyssal, All thesethese rocksrocks belong toto thethe Paleoproterozoic 1.90- (2) muscovite, (3) rare-element and (4) miarolitic 1.87 Ga Svecofennian accretionary arc complex of according toto theirtheir metamorphic environment, typicaltypical central and western Finland (Korsman et al. 1997). minor elements, nature of their parental gtanitesgranites and The prominent Kaatiala pegmatite was probably relation to theirtheir parental granites (see Ginsburg et al. v the first pegmatite known from Ostrobothnia. It was 1979, Cerny 1990). Pegmatites of thethe rare-element quarried for quartz on a small scale for a long timetime classdass are broadly divided intointo threethree families:farnilies: LCT before industrial quartz production started in 1942. (Li,Cs,Ta),(Li,Cs,Ta),NYF(Nb,Y,F)andararemixedLCT+NYF NYF (M,Y,F) and arare mixedLCT+NYF The production of feldspar for the domestic ceramiccerarnic family. These are further classifieddassified into 5 types and 9 industry commenced soon afterwards. subtypessubtypes