Geo log ical Survey of Finland. Spec ial Paper 28 Thomas t smdqvist and Sill; Autio (eds. ), Reiduiv Boe et al.

the west. Rock-forming events during three major the rifted and tecto nically shortened margin ofBaltica. orogenies and tectonically more quiet (anorogenic) Units accreted to Baltica, emanating from exo tic and evolutionary intervals have contributed to the pres­ outboard terranes,e.g . from Laurentia, havealso been ently exposed bedrock. Two of these orogenies oc­ iden tified in the higher Ca ledonian structural units. curred in Precambri an time: the Lopian orogeny of Sedimentary, inter montanedeposits of Devonian a nd Archaean age (c. 2.9-2.6 Ga), co ntaining remn ants of Late Silurian age , which have been affected by Ca l­ still older ('Saa mian', up to c. 3.1 Ga) rocks, and the edonian deformation, also occur in the Ca ledo nides. Svecokarelian (or Svecofennian) orogeny of Palaeo­ The westernmost parts of the Mid -Norden bed rock, proterozoic age (c. 1.9-1.8 Ga). The third and young­ in the shelf area ofthe Norwegian Sea, are do minated est orogeny is the Caledonian, the major tectonic by sedimentary cover sequences of Mesozoic and events of which fall in the Silurian and Devonian. Cenozo ic age . Older sedimentary cover rocks, of The eastern and ce ntral parts of the bedrock of the Mesoproterozoic to Ca mbrian age, occuron top of the Mid-Norden area belong to the Fennoscandian (or Pro terozoic and Archaean co mplexe s in the Gulf of Baltic) Shield. The west-central parts, mai nly in the Bothnia and adjo ining land areas. Scandi navian mountain region, are composed of Four imp act craters have been identified in the nappes formed by plate collision of the Precamb rian Mid -Norden area.Threeofthese (Lappajarvi,Lockne bedrock of northern Europe (Baltica) with that of and Soderfjarden) were formed in Phanerozoic tim e, No rth America (Laurentia) during the Caledonia n whereas the age ofthe fou rth (Suvasvesi)still remains orogeny. These nappes are composed ofPrecambria n unknown. to Silurian rocks and have been thrus t in a southeast­ Th e interested reade r will find short, rela tive ly erly direction over the older craton (Baltica) and its popular overviews ofthe geology of the Mid-Norden thin autochthonous Vendian to Lower Ordovician area on pp. 161-174 . T hese descriptions are given in sedimentary cover. They mainly include rocks of the Finni sh, Norwegian and Swedish, as well as Engli sh. crystalline basem ent and its sedimentary cover from

3. FEN NOSCANDIAN SHIELD AND COVER RO CKS

3.1 Archaean basement complex Heikki Lukkarinen

3.1.1. General features mig matitic gneiss and granitoid lithologies surrounded by Palaeoproterozoic unit s, especially within the In the Mid-Norden area, Archaean rocks occur Karetian Dom ain between Joensuu and Kuopio. mainly in Finland. In Sweden, Archaean rocks are The main rock types in the Archaean co mplexes are present in a small area c. 20 km southwes t of Lulea, m igmatitic, generally medium- to fine-grained and are referred to as the 2.7 Ga old Vallen-Alhamn tonalitic, trondhjemitic to granodioritic gneissesa nd granitoids (VAg). Th e western borderofthe Archaean gra nitoids with amphibolite enclaves of varied si ze. (the Archaean-Proterozoic palaeoboundary), as de­ On the Bedrock Map these gneisses and granitoids fined by ENd values of Protero zoic granitoids and fall into an age gro up of 3 140-2500 Ma. All ages volcanic rocks, runs northwestward from Lulea. It is referred to on the Bed rock Map and in this ten are named the Lulea-Jokkmokk Zo ne (O hlander et a!. publi shed U-Pb zircon ages, unless othe rwise Slated. 1993; cf. Fig. 24, p. 49 ). Migmatitic gneisses display variably stromatic-ph le­ On the Bedrock Map the Arc haean basement in bitic to schlieren-nebulitic structures (Fig. 2a). Their Finland is subdivided into migm atitic gneiss and paleosome co ns ists of to nalite, mica gneiss or gra nitoi d complexes with supracrusta l rocks as well amphibo lite, whereas the co mposition ofthe neosorne as younger granitoids intruded into the olde r litholo­ is most ly trondhjemitic to granodioritic, and ro a gies. The followin g complexes, named in order from lesser extent granitic. The granitoids related to the north to south, are present (Fig. I): the Pudasjarvi migmatitic gnei sses are tonalites, leucotonalites or (PuC), Kuhmo (KuC), Manamansalo (MaC), Iisalmi leucogranodiorites; however, a few ofthem are quartz (liC), Rautavaara (RaC), Lieksa (LiC), Nurmes (NuC) diorites. They differ fro m the migmatites by havin g a and Il omantsi (IlC) Complexes. Besides these com­ more homogeneou s structure (Fig. 2b ), althoughtb ey plexes, there are many basement gneiss domes with are foliated and , in places, co ntain abundant selI ist,

12 Geological Survey of Finland, Speci al Paper 28 Description to the Bedr ock Map of Centr al Fenn oscandia (Mid -Norden)

PuC

EUy oI80thnW

Finnish Mid-Norden area

Archaean basement

N A

Lithology

Proterozo ic lithologies Uthotog ies of the CPG Metagreywackes of the Npg §Greenstone belt lithologies c::J Granodiorite.granite D Carbonatite-syenite CJ Migmatites and granitoids

CPG =Central Puotanka Group Npg = Nurmes paragneiss

Russia Comp lexes Domes Greenstone belts PuC = Pudasjiirvi Kod = Kontiolahti SGB = Suomussalmi KuC=Kuhmo Sod = Sotkuma KGB = Kuhmo MaC = Manam ansalo Jud = Juoj Arvi T GB = Tlpasjarvi PpC = Pilperinmaki Knd = Kon nuslahti 1GB = lIomantsi Pm C = Pirttimaki Ktd = Kotalahti IiC = lisalmi Pad = Paukarlahti Shear Zones nee = Raulavaara Ved = Vehmasmaki UC = Ueksa Kud = Kuoplo HSZ = Hirvaskoski NuC= Nunnes OSZ = Oulujarvi IIC = lIomants i RSZ = Rautavaara Koi = Konere ____ Complex boundary Mid-Norden boundary

Fig. 1. Main lithol ogic al uni ts of the Archaean basement in the Mid-Norden area in Fin land.

] 3 Geological Survey of Finland, Special Paper 28 Thomas Lundqvist and Sini Aut io (eds .), Reidulv ROe et af.

Fig. 2a. Migmatlti c tonalitic- trondhjemitic basement gneiss of the Iisalmi complex. Oinasjarvi, Sonkajarvi. Photo, J. Paavola.

Fig. 2b. Gneissic tonalite of the Kuhmo complex . Saynaja vaara, Suomussalmi. Photo, H. Lukkarinen. gneiss and amphiboliteinclusions. The contacts to the metasedimentary rocks, and belts of paragneiss that migmatites are transitional. Thus, and because of in­ contain mainly greywacke metamorphosed to mica completemapping, onlya limited numberofgranitoid gneiss. In the Kuhmo Complex, there are from north units have been displayed on the Bedrock Map . For to south the Suomussalmi (SGB), Kuhmo (KGB) and similar reasons, amphibolite inclusions within the Tipasjarvi (TGB) GreenstoneBelts.Supracrustalrocks rnigrnatitic gneisses and granitoids are not shown on of the Ilomantsi Complex are referred to as the the BedrockMap. In the Kuhmo Complex, migmatitic Ilomantsi Greenstone Belt (1GB). On the Bedrock gneisses and related granitoids have been referred to Map the greenstone belt rocks are placed in the age as a first-generation TTG orthogneiss series with a group 2800---2740 Ma. Mostrecent age determinations, tonalitic-trondhjemitic-granodioritic composition by however, show that in the Suomussalmi Greenstone Gaal et al. (1978), Martin et al. (1983), and Homeman Belt there are felsic volcanic rocks as old as 2970Ma et aL (1988). (Vaasjoki et al. 1999). The main paragneiss belt, Supracrustal units within these complexes form referred to as the Nurmes paragneisses (Npg), is greenstone belts consisting of metavolcanic and situated between the Kuhmo and the Lieksa COIlL-

14 Geological Survey of Finland. Speci al Paper 28 Description tv (he Bedrock Map of Central Fennoscand ia (Mid-No rden)

plexes. The ages of these paragneisses are between fluid concentration of the rocks protected hornblendes 2750 and 2700 Ma. and biotites from Proterozoic resettin g, e.g. in the Younger granitoid intrusions in these complexes granulite high-grade rocks within the lisalmi Com­ are generally medium- to coarse- grained with little or plex (MSIA Map 72, 76, 81), in the Taivalkoski area no migmatisation.They occur as intrusions of various (MSIA Map 2) , and in the area so utheast of size and as cross-c utting dykes. Their composition Amrnansaari (MSIA Map I I). varies from quartz diorite to leucogranite. The y can The greenstone belt rocks in the Kuhmo Complex be divided into a second-generation TTG series with have been affected by medium-grade, in places, low­ tonalitic-trondhj emitic-granodiori tic composi tion grade metamorphism ofArchaean (Tuisku & Sivonen (Gaal et al. 1978, Martin et a1. 1983, Horneman et al. 1984, Luukkonen 1992) or Proterozoic age (Taipale 1988, O' Brien et al. 1993) and a GG series with et al. I980,Tuisku & Sivonen 1984). Sm-Nd isotopic granodioritic-granitic composition (Hornernan et al. mineral isochrons show pervasive medium-grade 1988). These younger granitoids have been intruded metamorphic resetting of the komatiites in the Kuhmo into the migmatitic gneisses and related granitoids, Greenstone Belt at 1850 Ma (Gruau et al. 1992 ). and also into the greenstone belts and paragneisses. Metamorphism of the supracrustal rocks in the On the Bedrock Map they are shown as a group of Ilomantsi Greenstone Belt varies from low- to me­ 2750-2650 Ma age, except for the Kutsu granite dium-grade (Tuukki et al. 1987, O'Brien et al. 1993). (Kut) in the Ilornantsi Complex and an unlabelled On the MSIA Map, younger granitoids are classi­ granite intrusion in the Pudasjarvi Complex east of fied as intrusions, although they were metamorph osed Kemi , which were placed in a group of 2600-2500 and foliated during Archaean time, K-Ar hornblend e Ma age. The alkaline rocks of the Siilinj arvi and biotite ages (e.g. MSIAMap references 14, 19, Carbonatite Complex (SCC) were formed at 2600 70,95, I 15) suggest a metamorphic resetting of these Ma, and constitute a separate lithological unit within mineral s also during Proterozoic time (Konrinenet al. the Archaean basement complex. 1992). In the Ilomantsi Complex, Archaean K- Ar The Archaean basement complexes have under­ hornblende ages (e.g. MSIA Map 127, 130) and U- Pb gone polyphase deformation and metamorphism dur­ titanite ages (Vaasjoki et al. 1993) from the granito id ing the Lopian orogeny (Gaal et al. 1978, Gaal & intrusions and migmatites to the south and east of the Gorbatschev 1987, Luukkonen 1992). Fault, thrust Ilomantsi Gree nstone Belt indicate that the metamor­ and shear zones shown on the Metamorphic, Struc­ phic temperature in that area did not exceed c. 500°C tural and Isotope Age (MSIA)Map are mainly based during the Palaeoproterozoic Svecokarelian orogeny on published data, but in poorly mapped areas, e.g. in (Kontinen & Paavola 1996). On the other hand, K-Ar the Lieksa, Nurmes and Pudasjarvi Complexes, and biotite and muscovite ages of gold-bearing samples in places also in the Kuhmo Complex, they have been from the Uomantsi Greenstone Belt are 1800-1700 drawn using low-altitude aeromagnetic maps. These Ma (O' Brien et al. 1993). These data are consistent zones are Archaean and/or Proterozoic in age. Some with those published by Kontinen et al. (1992) a nd Archaean NW-SE trending zones have been reacti­ Kontinen and Paavola (1996), anddisplay Proterozoic vated in Proterozoic time (Luukkonen 1985, 1992). thermal resetting of the biotite atc. 1800 Ma throug h­ On the MSIAMap, migmatitesandrelatedgranitoids out almost the entire area of the Archaean basement areclassified as high-grade metamorphic rocks, based in eastern Finland. on their migmatitic structures. Their mineral assem­ blages, however, com monly indicate a medium-grade 3.1. 2 Migmatitic gneiss and granitoid corn­ metamorphism, due to metamorphic retrogression of plexes either Archaean and/or Proterozoic age. K-Ar horn­ blende and biotite ages (e.g. MSIA Map references The P udasj ar vi Complex is bounded to the we st 10, 39, 46, 47, 58, 60, 98, I l l, 125, 138) reflect a and southwest by Palaeoproterozoic units, to the tecton othermal recrystallisatio n of these minerals southeas t by the Oulujarvi Shear Zone (OSZ), and to during the Svecokarelian orogeny c. 1900-1800 Ma the east by the HirvaskoskiShear Zone (HSZ; seeFi g. ago Over large areas in the Archaean basement com­ I).Besides the common migmatitic gnei sses an d plex (Kontinen et al. 1992). The KIAr ages shown on granitoids, it also contains some amphibolite an d the MSIA Map are only selected examples of the total paragneiss inliers which probably represent meta­ data fro m the Archaean area in eastern Finland. morphosed remn ants of Archaean volcanic rocksan d Hornblende and, in places, biotite in these rocks greywackes of unknown depositional age, respe c­ inherit their Archaean K-Ar isotopic signature partly tively. Up to the present there is very little publishe d or comp letely only in areas where rigidity and low information on these rocks (Enkovaara et al. 195 3,

] 5 Geo logical Surveyor Finland, Special Paper 28 Thomas Lundqvist and Sini Autio (eds.) , Reidulv Bee et at.

see also Perttunen 1991). and Pirttimaki (see Fig. I), respectively, were previ­ The Kuhmo Complex is bordered to the west by ously classified as Proterozoic gneisses by Laajoki Palaeoproterozoic units referred to as the Kainuu and Luukas (1988), butare now regardedas Archaean. Schist Belt (Fig. I) and to the south by the Nurmes The area referred to as the Iisalmi Blockby Vayrynen paragneisses (Npg). On the Nordkalott Map (Geo­ (1939) has been divided on the Bedrock Map into a logical Map, Northern Fennoscandia, I:I million western lisalmi Complex and an eastern Rautavaara 1987), the continuation of the Kuhmo Complex to the Complex. The former is bordered by Proterozoic north is referred to as the Kuusamo Complex (KuC). units to the west, north and south. The latter is limited The greenstone belts -the Suomussalmi, Kuhmo and to the eastby the Rautavaara ShearZone (RSZ), while Tipasjarvi Belts - divide the complex into a western the boundary between these complexes follows the and an eastern part. The main greenstone belts and eastern margin of granulite high-grade rocks of the many minor greenstone lithologies interfinger with Iisalmi Complex (Fig. I). In this complex, ages of migmatites and granitoids in the eastern part, but the 3136±20Ma(MSIAMap 82) and 3095±18Ma(MSIA main belts have sharp, fault-bounded contacts against Map 79) for quartz-dioritic paleosomes of the migmatites and granitoids of the western part. migmatitic TTG gneisses register the oldest ages Proterozoic metamorphism and deformation have known at the moment in the Archaean basement affected the migmatites and granitoids in the western complexes ofeastern Finland. They suggesteither the part of the complex more than the rocks east of the time of the primary crystallisation or the age of an greenstone belts, resulting in their ubiquitous early high-grade metamorphism (Paavola 1986). mylonitisation. The age of a tonalitic paleosome Narrowbands and belts ofamphibolites, less than one within a migmatitic gneiss in the eastern part of the metre up to hundreds of metres wide, are present complex is 2843±18 Ma (MSIA Map 22, Luukkonen within the migmatites and granitoids (Paavola 1984a, 1985), while a quartzo-feldspathic neosome material 1988a,b). They seem to be contemporaneous with the ofthe same migmatitic gnei ss is 2657±32 Ma (MSIA 3100 Ma old quartz-dioritic gneisses (J. Paavola, Map20, Luukkonen 1985).The Haasianvaaratonalite unpublished data). In the Iisalmi Complex there are (Haa), west of the Tipasjarvi Greenstone Belt, and a also blocks with granulite high-grade lithologies tonalitic granitoid (known as Huuskonvaara) east of (Paavola 1984a, 1988a; Holtta 1997). These blocks it, contain zircons with an age of 2830±2 Ma (MSIA are sharply bordered by fault zones with blasto­ Map 41) and 2808±8 Ma (MSIA Map 43), respec­ mylonitic rocks (Paavola 1988b, 1991). Ages ofigne­ tively (Hyvarinen 1989, Vaasjoki et al. 1999). On the ous enderbitic rocks within these blocks, i. e. 2693±2 Bedrock Map, the Vieksinjoki tonalite (Vie) is inter­ Ma (MSIA Map 73) and 2682±6 Ma (MSIA Map 75), preted to belong to the same granitoid group as the document the igneous crystallisation ages (Paa­ Haasianvaara tonalite. Presently available age data volaI986). The age of the latest Archaean metamor­ suggest that, within the errorlimits, the paleosomes of phism in this area is c. 2630 Ma (Huhma et al. 1995). the migmatitic gneisses and related granitoids are K-Arhornblende ages ofthe enderbitic rock (Fig. 3a), contemporaneous, indicatingwidespreadigneous and amphibolite (Fig . 3b) within the granulite high-grade metamorphic events at about 2840 Ma in the Kuhmo block and quartz dioritic gneiss outside the granulite Complex (Luukkonen 1985, 1992). The ageof2784±4 high-grade block, i.e. 2638±80 Ma (MSIA Map 76) , Ma (MSIA Map 31) for a leucocratic tonalite near the 2747±82(MSIAMap 72)Maand2666±80Ma(MSIA contact ofthe Viiksimo granite (Vii), east of Kuhmo, Map 81), respectively, demonstrate that Proterozoic is interpreted as the time of segregation of this metamorphismdidnot stronglyaffect the hornblendes, leucocraticmaterial from oldertonalitic-trondhjemitic while biotites ofthe last mentioned rock (MSIA Map gneisses (Luukkonen 1989). 81) are Proterozoic (2088±63 Ma) in age (Kontinen et The Manamansalo Complex is bounded to the aI. 1992). west and north by the Oulujarvi ShearZone, andto the The Rautavaara Complex mainly contains TTG east and south by Proterozoic rocks. An available age migmatites and granitoids, but differs from the Iisalmi of2675±1 Ma (MSIA Map 24) ofa tonalitic granitoid Complex by having, in addition to amphibolitic within the migmatites indicates either the time of the mesosomes, a lot ofgranitised mica gneiss andquartz­ intrusion or the age of an Archaean metamorphism feldspargneiss mesosomes, which probably are meta­ (Kark] et al. 1995). The migmatites and granitoids of morphosed remnants of Archaean greywackes and this complex were also pervasively deformed and arkosites, respectively. In places, there are feldspar­ recrystallised later, during Palaeoproterozoic time. augen gneisses (Fig. 4) with an age of 2727±34 Ma Two migmatitic gneiss complexes west and south­ (MSIA Map 85, Paavola 1984b). The rocks of the west of Lake Oulujarvi, referred to as Piiparinmaki Rautavaara Complex have undergone penetrative

16 Geological Survey of Finland. Special Paper 28 Desc ription tc the Bedrock Map of Cemral Fennoscandia (Mid-Norden)

Fig . 3a. Ender bite of the gran uli te high -grad e bloc k in the li sal mi comp le x. Maaselankangas. v arpa isjarvi . PhOlO . J. Paavol a.

Fig. 3b. Garnet amphibolite of the granulite high-grade block in the Iisalmi comp lex. Kurnisevanmaki. Sonkajarvi. PhOl O, J. Paavola. deformation and metamorphism also during Proter­ lineated. At the moment, there is little updated infor­ ozoic time, e.g. most of the known Protero zoic mation on these rocks. metadiabase dykes within that complex have an in­ The Lieksa Complex is situated between the Kuh­ tensive foliation or lineation, and a K-Ar hornblen de mo Complex and the Koitere granodiorite (Koi), and age of the hornblende gneisses 1871±60 Ma (MSIA extends eastwards from Lake Pielinen.Within the Map 84, Kontinen et al. 1992). main components-tonalitic-trondhjemitic-granodior­ The Nurmes Complex extends westwards to the itic migmatites and granitoids (Fig. 5) - small rem­ Raut avaara Shear Zone. It is bounded to the north by nants of a greenstone belt composed of mafic and the N urmes paragneisses and continues eastwards to ultramafic amphibolitic rocks are present scattered Lake Pielinen. The southern border is formed by over the whole Lieksa Comple x. In places, intermedi­ Proterozoic units. It consists of migmatitic gneisses ate-mafic gneisses contain ortho- and clinopyroxene. and granitoids similar to the complexes mentioned which suggests an earlier Archaean high-grade before, and the rocks have been strongly deformed metamorphism. There is little updated information on during Proterozoic time,e.g. manyknownmetadiabase the rocks of the Lieksa Complex. dykes within that complex are intensively foliated or The Ilomantsi Complex. to the south and south-

17 Geological Surve y of Finland, Special Pape r 28 Thomas Lundqvist and Sini Autio (eds. ), Reidulv Bee et at.

Fig. 4. Augen gneiss of the Rautavaara complex. Raatti, Nilsia. Photo, J. Paav ola. east of the Koitere granodiorite, is bordered to the lated occurrences of Archaean granitoids (Fig. 6). west by Proterozoic lithologies of the Karelian Do­ Thi s belt extends from Vallen-Alhamn in the south to main. It comprises mainly supracrustal rock s of the c. 25 km northwest of Lulea (Mellq vist 1997), and is Ilomantsi Green stone Belt and younger granitoids situated nearthe Archaean-Proterozoic palaeo-bound­ intruding the supracrus tals. ary of Ohlander et al. (1993). In the Vallen-Alhamn area southwest of Lulea in Sweden, more or less gneissic tonalites and gran ites to granodiorites with K-feldspar megacrysts (the 3.1.3 Basement gneiss domes Vallen-Alharnn granitoids, Vag) have been shown to be ofArchaean age . A tonalite at Alhamn has yielded In the area between Joensuu and Kuopio, several aU-Pb age of2710±3 Ma (MSIA Map 262, Lundqvist roundish migmatite and granitoid windows ofvarious et al. 1996, Lundqvist et al. 2000). It has also been size occur (Wilkman 1938, Huhma 1975, Gaal 1980, demonstrated that the Vallen-Alhamn gran itoids in Koistinen 1993). They consist of migmatitic TTG fact form part of a NNW-SSE trending belt of iso- gneisses and granitoids similar to those of the com-

Fig. 5. Migmatitic tonalite-trondhjemite gneiss of the Lleks a complex. Varpo vaara, Lieksa. Photo, H. Lukkarinen.

18 Geo logical Survey o f Finland.Special Paper 28 Description to the Bedrock Map of Central Fennoscandia (Mid-Norden)

Fig. 6. Archaean granodioritic augen gneiss, forming a megaxenolith in the Balingc 'co nglom­ erate' (see text). Balingsbcrget . W of Lulea. Photo, A. Wikstrom. plexes described above, but, in contrast to the latter, Arc haean gree nstone belts - the Suom ussalmi (SGB), they are surro unded by Proterozoic rocks, i.e. they Kuhm o (KGB) and Tipasjarvi (TGB) Greensto ne form mantled gneiss domes (Eskola 1949). Th ese Belt s. Th ese belts are co mposed mainl y ofmafic a nd relationships dem onstrate that Archaean basement ultramafic met avolcanic rocks , to a lesser extent of rocks exten d westwards as far as Kuopio beneath the intemnediate to felsic metavolcanic and meta-sedi­ Proterozoic Karelian Domain. Wheth er these domes mentary rocks, and some mafic and ultramafic intru­ belong to the Ilomantsi Complex as parts of its exten­ sive rocks.Their petrology, stratigraphy and geologi­ sio n below the Karelian Domain, or for m alloch­ cal evolution have been de scrib ed by, e.g. Gaal et al. thonous nappes from some unknown source west of (1978), Han ski (19 80), Taipale et al. ( 1980), Taipale the Karelian Domain and the Ilomantsi Complex, is and Tuokko (198 1), Hypponen (1983), Piirainen still an open question. The largest gneiss domes are (1988), T aipale (19 88), Engel and Diez (1989), the Kontiolahtidome (K od) , the Sotkumadome(Sod), Luukkonen (1988, 1992), Halkoaho et al. (1997) and the Juojarvidomes (Jud), the Konnuslahti dome (Knd), in several papers ofa research group from the Univer­ the Kotalaht i dome (Ktd), the Vehrnasmaki dome sity of Renn es, France (see reference s above and (Ved), the Pau karlaht i dome (Pad) and the Kuop io Martin 1989). domes (Kud). Geological mapping carried out aft er Th e mafic volcanic rocks consist of met amor­ the printin g of the Bedrock Map has shown that the phosed tholeiitic and Fe- tholeiitic lavas and tuffs.T he dome labelled Kmd (the Kolunrnaki dome) is actually lavas are mainly pill owed, indicating submarine v ol­ a strongly defor med Palaeoproterozo ic granitoid in­ canic activ ity, but massive flows also occur. T he trusion.Agedata show that the Sotku rna,Juojarvi and ultramafic metavolcanites, peridotitic ko rnatiites, are Pau karlaht i do mes contain tonalitic to granodioritic predo minantly laye red, spinifex-textured or pillowed gne isses with ages of 2635 Ma (MS IA Ma p 128 lavas with pyroxenitic to basaltic komatiitic interflo ws We therill et aI.1962), 2683±32 Ma (MSIA Map 132, of variolitic pillowed lavas. There are also som e Huhm a 1976) and 2795±19 Ma (MSIA Map 141, komatiitic metatuffs. The felsic and intemnediate Gaal 1980 ), respectively.In the Kuopio domes, zir­ met avolcanites are mostly pyroclastic rocks. Mafic cons yield an age of c. 2500-2400 Ma for a tonalitic intrusive rocks occur in the volcanic succession as gneis s, due to episodic lossoflead in zirco n during the gabbro bodies and sills. The largest serpentinitcs, Svecokarelian orogeny c. 1900-1800Ma ago(Ko uvo which are co llectively labelled Kel (the Kellojarvi & T ilt on 1966). serpentinite) on the Bedrock Map, represen t layer ed metacumulates ofkomatiitic metavolc ani tes (Halko­ aho et al. 1997 ). The metavolcanic rock s are interca­ 3.1.4 Greenstone belts lated with black schists and banded iron formations showing evidence of hydrothermal acti vi ty. Sericite In the Kuhmo Complex, a more tha n 200 krn-l ong qu art zites, in places with po lymictic metacong­ and generally 1-15 km-w ide zone co nsists of the lom erate interbeds, are present within the volcanic

19 Geological Survey of Finland. Special Paper 28 Thoma s Lundqvist and Sini Autio (eds.) . Reidut v Boe et al. rocks ma rk ing breaks in the volcanic ac tivity . ogenic metasedimentary rocks and met agreywackes Turbiditic greywackes metamorphosed into mica (Sorjonen-Ward 1993 ). Metamorphosed lavas of schists and mica gneisses are the most widespread tholeiitic and komatiitic composition occur as a few rocks of sedimentary origin in these greenstone belts. narrow intercalations, whereas intermediate meta­ They cover the vo lcanic sequences ofthe Kuh mo and volcanic rocks are scarce (O' Brien et al. 1993). Be­ Ti pasjarvi Greenstone Belts. sides metagreywacke, the sedimentary rocks in this Ages of the felsic metavolcanic rocks lie between schist belt include subarkosite, black schist, ban ded c. 2980and2780Ma (MSIAMap4,27,33,42,Hypponen iron formation and polym ictic meta-conglomerate. In 1983, Vaasjoki et al. 1999). A ural ite gabbro sill (the the eas tern part of the Kovero Schist Belt, meta­ Moisiovaara Sill, MoS), which intrudes the mafic sedimentary rocks predominate (Tuukki at al. 1987, metavolcanic rocks, has yielded an age of 279 0± 18 Piirainen & Vu ollo 1991 ). The western part of this Ma (MSIA Map 17, Luu kkonen 1988). A minimum belt mainly co nsists of massive to pi llowed meta­ age (2739±8 Ma , MS IA Map 25) for closure of the tholeiitic lavas with minor tuff interbeds. The mafic volcanic activity within the gree nsto ne belts is set by rocks also contain some intercalations of meta­ a porphyritic quartz diorite dyke that cuts thro ugh the volcanites with komatiitic and rhyolitic-rhyodacitic mafic metavolcanic rock(Hypponen 1983). Based on compositions, as well as serpentinite bodies.In places, chemical composition and vari ous discriminant dia­ the komatiites show spinifex tex ture . Arkosite, black grams, it has been suggested that the greenstone belts schist and banded iron formation (oxides and sili­ in the Kuhmo Complex are remnan ts ofan Archaean cates) occ ur as intercalations in the met avolcanic proto-oceanic rift environ ment (Martin et al. 1983), rocks. subduction-related magmatic arcs or marginal basin The meta-andesi te and mica gneiss within the Hat tu settings (Piirainen 1988, Taipale 1988), or intra­ Schist Belt hav e given ages of 2754±6 Ma (MSIA continental rift systems (Luukkonen 1992). Map 87) and 2761±1 1 Ma (MS IA Map 92), respec­ The Ilomantsi Greenstone Belt (F ig. 7), within the tive ly (Vaasjoki et al. 1993). Sm-Nd isotopic data on Ilomantsi Co mplex, has been divided into the eastern these rocks (MS IA Map 86, 92, 117) give no clear Hattu Schist Belt (HSB) and the western Kovero evidence forsources much olderthan 3000Ma (Huhma Sch ist Belt (KS B) (Tuukki et al. 1987; see also 1987, O'Brien et al. 1993). The age of a felsic So rjonen-Ward 1993 ).The dominant rocks of the metavolcanic rock within the KSB is 2666±51 Ma Hattu Schist Belt are felsic metavolcanites, volcan- (MSIA Map 134). It doc uments either the age of

ILOMANTSI GREENSTONE BELT

Proterozoic lithology • Karjalite (Metadiabase) o Metagreywacke (Hoytiainen schists) o Metavoicanite o Quartzite

Archaean lithology o Granite o Keitere Granodiorite o Granodiorite - Tonalite Russia Quartz diorite o Metagreywacke ] o Felsic-intennediate metavolcanite 1GB N o Mafic-ultramafic metavolcanite A o Tonaiitic-trondhjemitic-granodioritic gneisses o 5 10 km ~ and granitoids

Fig. 7. Subdivi sion of the Ilomantsi Greenstone Belt (1GB). The map is modified after the Bed rock Map of Central Fennosca ndia.

20 Geological Survey of Finland. Speci al Paper 28 Description to the Bedrock Map of Ce ntral Fcnno scundl a (Mid-Norde n) volcanic activity or the timing of a later, strong Kainuu Schi st Belt and the Kuhmo Greenstone Belt. deformation that has affec ted the rock (Vaasjoki et al. The main rock type is a stromatic-phlebitic to nebulitic 1993),The chemical composition of the metavolcanic migmatite (Fig. 8). The compos ition of the leuco some rocks is predomi nantly similar to Archaean meta­ is leucotonalitic to leucogranodioritic, while the volcanic rocks overall, and various discriminant dia­ paleosome is a fine-grained, granoblastic, biotite­ grams suggest that the rock s in the Hattu Schist Belt plagioclase gneiss . In spite of the high grade meta­ have formed either in an island arc or continental-arc morphism and deform ation, relict bedd ing is visible tecto nic setting (O' Brien et aL 1993), The thol eiitic in many places. The chemical composition of the meta volcanic rocks in the Kovero Schist Belt have paleosome suggests a calc-alkaline, igneous prov­ been interpreted to have a marginal basin affinity enance for the original material in the paragneiss. The (Tuukki et al, 1987). chemical homogeneity and widespread extension of Besides these major greenstonebelts, the Archaean the paragneisses indicate sedimentation in a major basementcomplexes contain somesmallergreenstone turb idite basin. Based on age data ofthe paragneisses belts. The minor Archaean schist belt referred to as and the granitoids cutting them , sedimentation prob­ the Ipatti For mation, southwest of Lieksa on the ably occurred at 2750-2700 Ma (MSIA Map 50, 5 1, western shore of Lake Pielin en, consists of mafic, 53, 54, 55). Sm-Nd isotopic studies south of the intermediate and felsic metavolcanic rocks and vol­ Kuhmo (MSIA Map 37) show that the metagreywackes cano-sedimentary schists (Vayrynen 1933, Piirainen do not contain material much older than 3000 Ma et al. 1974). West of this area, the Nunnanlahti Schi st (Huhrna 1987). Belt (Kohonen et al. 1989, Piirainen & Vuollo 199 1), incorrectly labelled paragneiss on the Bedrock Map 3.1.6 Younger granito ids (label 139 should be 143), consists mainly of meta­ morphosed mafic lavas, with some felsic meta­ Granites that intrude the Pudasjarvi Complex east volcanites and mica gneiss. Ultrama fic rocks occur as of Kemi have been placed in the same age group small bodies of soapstone and serpentinite, and are (2500- 2600 Ma ) as the Kutsu granite (Kut; MSlA cut by Palaeoproterozoic metadiabase dykes. Map 147) on the Bedrock Map, based on an age deter- . minat ion of the Sornpujarvi granite in the area north 3,1.5 Nur mes paragneisses of the Mid-Norden area (K ouvo & Tilton 1966, see also Pert tunen 1991).Th e ages of a tonalitic intrusion Th e Nurmes paragneisses (Npg) cover an area and a tonalite dyke that have intruded into amigmatitic approximately 40-10 km wide and 90 km long be­ gneiss in the southeastern part of the Pudasjarvi tween the Kuhm o and Liek sa Complexes (Konti­ Complex are 2721±25 Ma (MSIAMap9)and 2731±24 nen 1991).Smalleroccurrences ofsimilar paragneisses Ma (MSIA Map 13), respectively (Karki et al. 1995). occur west of Nurmes and between the Proterozoic Presently availabl e age dete rmination s (Hy pponen

Fig. 8. Migmathi c greywacke of the Nurmes paragne isses. Pieni Loytosuo. Ristlja rvl. Photo, A. Konti nen.

2 1 Geo logical Survey of Finland. Special Paper 28 Thomas l.undoviss and Sin; Autio (eds. ), Reidull' HO e ct al .

1983, Luuk konen 1985 , Luukkonen 1988, and (e.g. Sorjonen-Ward 1993). The Hoikan Kylkeinen Vaasjoki et ai. 1999) demonstrate that the younger (Hoi),Pogosta (Pog), Silvevaara (Sil) and Viluvaara granitoids and a quartzo-fel dspathic neosome mate­ (Vii) intrusive rocks are biotite granodiorites . The rial within the migmatitic gnei sses of the Kuhmo two last-mentioned intrusions also contain K-feld­ Complex fall into two age groups: 2750-2730 Ma and spar phenocrysts, and the Silvevaara gra nodiori te is 2710-2650 Ma. The former consists ofa 2739±8 Ma hornblend e-bearing (Sorjonen-Ward 1993). Deter­ porphyritic quartz diorite dyke (MS IA Map 25), a minations using the SHRIMP method show that this 2745±8 Ma old tonalite (MSIA Map 54) and a 2734±2 granodiorite contains inherited zircon cry stals with Ma porphyritic granodiorite (Hypponen 1983). The an age of 3180 Ma, whereas the emplacement of the main rock type of the latteris referred to as Konivaara­ intrusion occurred at 2757±4 Ma (MSIA Map 109, type granitoids (Ko n), with a quartzdioriti c-tonalitic­ Sorjonen-Ward & Claoue-Long 1993). Porphyritic granodioritic-granitic composition, being typi cally a tonalit e dyke s (the Vehk avaara dykes), which cut K-feldspar and/or plagioclase megacryst-bearing through mafic volcanic rocks, contain inherited zir­ tonalite or granodiorite. These granitoids, including co nsasoldas3027±43 Ma (MSIAMap 114; Vaasjok i the porphyritic Viiksimo granite-granodiorite (Vii), et al. 1993).The ages oftwosamples fro m the Pogosta were emplaced during an Archaean 0 3 deformation granodiorite (Pog) are 2724±5 Ma (MSIA Map 123) stage and have been referred to as the 0 3 granitoids and 2733±6 Ma (MSIA Map 120. Vaasjoki et ai. by Luukkonen (1992 ). The age of the granodiorite at 1993). The Lukanvaara (Luk) and Naarva (Naa) Kon ivaara is2697± 10 Ma (MSIAMap 15,Luukkonen intrusions are leucogranitic and typic ally contain 1988 ). Other rocks belonging to this age group are the tourmaline and garnet (Sorjonen-Ward 1993). The 2657±32 Ma quartzo-feldspathic neosome material Kartitsa (Kat) and Longanvaara (Lon) intrusions are within migmatitic gneisses (MSIAMap 20), a 2675±T: granitic, whereas the Hakovaara(Hak) intrusion isa horn ­ Ma granodioritic dyke cutting the same migmatitic blend e-bearingquartz diorite (Sorjonen-Ward 1993). gneiss (MSIA Map 21), a 2694±1 3 Ma old gneissic The large, composite, Koitere granitoid intrusion granodiorite (MSIAMap 26), a gneissic granodiorite (Koi), north of the Ilomantsi Greenstone Belt, com ­ and a gneissic granite intruded into the Nurmes prises hornblend e ± clinopyroxene-bearin g monzon ­ paragnei sses, with ages of 2660±5 Ma (MSIAMap ites, gra nodiorites and granites, typically with large 5 1) and 2683 ± 13 Ma (MSIA Map 55), respecti vely. K-feldsparphenocrysts (Sorjo nen-Ward 1993).There Besides those granitoids, there are also leucogranitic­ are several inclusions of mafic and ultramafic rocks leucogranodioritic intrusions of unknown age. e.g. ofvolcanic origin, migmatitic gneiss, mica gneiss and the Honkivaara (Hon), Isovaara (Iso) and Pitkakangas quartz -bande d iron formation within this intrusion, (Pit) granites.They are mixed with migmatitic gneisses which have not yet been mapped in detail. Accord ing and related granitoids , and contain variable amounts to preliminary V-Pb zircon age data (J. Paavola, H. of K-feldspar megacrysts. Huhma, oral communication 1997), the Koitere Along the northern border of the Lieksa Complex, granitoid is as old as the younger granitoids intru sive extending from Nurm es towards the Viiksimo gran­ into the Ilomantsi Compl ex. ites in the east, many even-grained to porphyritic The gneissic Kutsu granite (Kut) ofNykanen (1968) leucogranitic-Ieucogranodioritic intru sion s of un­ is much younger than the other granitoids of the known age occur, e.g. the Kopras (Kop), Suolajoki Ilomantsi Complex, and has an age of 2647±28M a (Suo), Jonkeri (Jon) and Ulvin salo (Ulv) granites. (MSIAMap 147, Lavikainen 1989). Within these massifs there are also syenogranitic to syenitic rocks, e.g. th e Jonkeri (Jos) and Vaskivaara 3.1.7 Siilinjarvi Carbonatite Complex (Vas) syenites . Gneissic tonalites of unkn own age, e.g. the Mustinvaara (Mus) and Nevonsuo (Nev) The Siilinj arvi Car bonat ite Com plex, 25 km north tonalites, are interpre ted to belong to the older ITG of Kuopio, is c. 16 km long and 1 km wide. It consists granitoids, based on th e compositions and struc tures of a series of rocks in whic h the end members are of the rock s. magmatic carbonatite and glimmerite (Puusti nen In the Ilomant si Complex, the Kuittila (Ku i), 1971). The complex contains apatite enough to sup­ Korpivaara (Kor) and Ta sanvaara (Tas) intru sive port mining activity.The carbonatite-glimmerite rocks rocks display a biotite-tonalitic composition (Sor­ (Fig. 9) are rimmed by syenite-fenite rocks grading jonen-Ward 1993). The rocks at Kuittila and Tasan­ into the surrounding Archaean migmatite gneisses. vaara are 2746±9 Ma (MSIA Map 104) and 2748±6 Patchett et al. (1981 ) have published a V-Pb zircon Ma (MSIA Map 90), respectively (Vaasjoki et ai. age of 2580±20 Ma (MSIA Map IOJ) for the com ­ 1993) . The form er contains gold-beari ng shear zones plex. However, accord ing to more recent age

22 J Geologi cal Surveyor Finland. Special Paper 28 Descri ption to the Bedrock Map of Central Fennoscandia (Mid -Norden)

Fig. 9. Carbonatite layers (light) in gIimmerite rock (dark). Kemira mine. Siilinjarvi. Photo, H. Lukkarinen. determinations, a more precise age is 2609±6 Ma Dial SGA Meeting. Turku / Finlandll l -13 Au gust 1997 . (Geological Survey of Finland, unpublished data), Rott erdam: A.A. Balkema, 431-4-34. Hanski, E. 1980. Komatiitic and tholeiitic metavolcanics of the Sfivikkovaara area in the Archea n Kuhmo greensto ne belt . eastern Finland . Bullet in of the Geological Soc iety of 3.1.8 References Fin land 52 (I ), 67-100. HOIUa, P. 1997. Geochem ical cha racteristics of granu lite Engel, W.W. & Diez, G~ T. 1989. A modified stra tigraphy facies rocks in the Arch ean Varpaisjrirvi area, central and tectonomagmatic model for the Sucmussalm i green­ Fennoscandian Shield. Lithos 40, 3 1- 53. stone belt. ea stern Finland . based on the remapping of the lI orneman, R., Hyva rtnen, T. & Niskan en, P. 1988.The Ala-Luoma area. Bulletin of the Geological Soc iety of gra nitoids surro unding and intruding the Kuhmo greensto ne Finland 61 (2 ), 143- 160. belt. eastern Finland . Geological Survey of Finl and. S pe­ Enkovaa ra , A., Harme, 1\'1. & Vayrynen, H. 1953. Oul u ­ cial Paper 4. 97- 12L Ta enia . Explanation to the map of rocks. Gener al Geol ogi­ Huhma, A . 197 5. Ou toku mm un, Pol vijiirve n j n Siv ak­ cal Map of Fi nland I : 400 000. Pre-Qua ternary rocks. kavaa ran kartta-alue iden kalliopera. Summary: Precambr­ Sheets C5 - B2. Geo logica l Sur vey of Finland. 153 p. ian rocks of the Outokumpu. Polvijarvi and Siv akkavaara Es kola, P. 194 9. The problem of mantled gneiss domes. map-s heet areas. Geo logical Map of Fin land 1 : 100 000, Quarterly Journal ofthe Geo logical Society ofLondon. vol. Explanatio n to the maps of pre-Qu atern ary rocks. Sheets crv (4), 46 1-476. 4222 ,4224, 43 11. Geological Survey of Finland.151p . Gaal, G. 1980. Geo logical setting and intru sio n tectonics of Huhma, A. 1976. New as pects to the geology of the Ou to­ the Kotalahti nickel-copper dep osit. Fin land. Bulletin of kump u region. Bulletin of the Geologica l Society ofF in­ the Geological Socie ty of Fin land 52 (I ), 10 1- 128. land 48 ( 1-2),5- 48. Gaal, G. & G orbatsch ev, R. 1987. An outline of the Huhma, H. 1987. Provenance of early Proterozoic and Precambrian evolution of the Baltic Shield. Precambrian Archaean metasediments in Finland: a Sm-Nd isotopic Research 35, 15-52. study. Precambrian Research 35. 127- 143. Gaal, G., M ik kol a, A. & Soderho lm, B. 1978. Evolution of Huhma, II ., Holttii, P. & Pa avola, J. 1995. Isotopic stud ies the Archean crust in Finland. Precambrian Research 6. on the Archae an Vurpai sjarvi granulites in Finland. In: 199- 215. Glebovitsky, V. A. & Kotov, A. B. (eds.) Precambrian of Geo logica l Map, Nor the r n Fe nnoscandia. 1 : 1 millio n Europe: Stra tigraphy. Structu re. Evolution and Minerali za­ 1987. Geological Surveys of Finland, Norway and Sweden. tion. MAEGS 9. 9th Meeting of the Associati on of Euro­ Helsinki. pean Geological Soc ieties 4- 15 September 1995. 51. Pe­ Gr uau, G., Tou r -pi n, S., Fo urcade , S. & Blais, S. 1992. Loss tersburg, Russian Federation. Abstracts. 4 1 ~4 2 . of isotopic (Nd, 0 ) and chemical (REE) mem ory during Hy ppdne n. V. 1983. Ont oj oen, Hiisijarvenja Kuhmon kar-tta­ metamorphism of komat iites: new evidence from eas tern alueide n kall iopera. Summary: Pre-Quaternary rocks of the Finland. Con tri butions to Mineralogy and Petrology 112. Ontojoki , Hiisijarvi, and Kuhmo map-sheet areas. Geologi­ 66-82. cal Map of Fin land ] : tOO 000. Explan ation to the maps of lIalkoa ho, T ., Liimata inen, J., Papunen , H & Valima a , J. pre-Quaternary rocks, Shee ts 44 11. 4412 and 4413. Geo­ 1997. Cr-rich basalts in kc matiitic volcanic association of logical Survey of Finl and. 60 p. the Archaean Kuhmo greensto ne belt, Finlan d: Evidence Hyvar'inen, T. 1989. Gran itoids on the Puukari map-she et. for redu cing conditions during magma ge neration. In: In: Gaal. G.(ed.) Arc haean gra nitoids and associ atedM o. Papunen. H . (ed.) Mineral Deposits: Research and ex plora­ Wand Au mineralization in eastern Finland. Symposium: tion. Whe re do they meet? Proceedings of the Fourth Bien- Precamb rian granitoids . Petrogenesis, geoc he mistry a nd

23 Geological Survey of Finland. Special Paper 28 Tho mas l.undqvist and Sini A utio (eds. ), Reidulv Boe et ill.

metallogeny. August 14-17. 1989, University of Helsinki, ety of Finla nd 6 1 (2), 161- 187. Finland . IGCP Projects 217, 247. Geological Survey of Luukko ne n, E.J . 1992. Late Archaean and earl y Proterozoic Finland, Guide 25. 2- 32 . structural evolution in the Kuhmo-Suomussulmi terrain. Karki, A., Laajoki, K. & Vaasjoki, M. 1995. Tectonic eastern Finland. Turun yliopis ton julkaisuja - Annales Uni­ settings and isotopic datings of late Archaea n and Palaeo­ versi tatis Turkuensis. Ser. A, 78. l13 p. proterozoic granitoids in the Central Fenn oscandian Shield. Martin, H., Cha uvel, C., J ahn, B ~ l\1. & Vidal, P. 1983. Rh­ Finla nd. In: Karki, A. Palaeoprotcrozoic shear tectonics in Sr and Sm-Nd ages and isotopic geoche mistry of Archaean the Central Fennosc andian Shield. Finland . Publications of granodioritic gneisse s from eastern Fin land. Prec amb rian the Department ofGeology University of Oulu, Res Terrae, Research 20, 79- 9 1. Scr. A (10 ), Paper III, 1- 24. Martin, H. 1989. Archaean chronology in the easter n part of Kohonen, J.J ., Tuukki, P.A . & Vuollo, J.I. 1989. Nun­ the Baltic Shi eld: a synthesis . Precambrian Research 43. nanla hden-Kuhnustan-Ahmovaaran alueen geologia. Poh­ 63-77. jois-Karjalan malmiprojekti. Oulun Yliopislo. Rapo rtti 23. Mellqvist, C. 1997. Proterozoic crustal growth along the 132 p. (In Finni sh) Archaean cont inental margin in the Lute d area . northern Koi stinen, T. 1993. Hein aved en knrtta-alueen kalliopera . Sweden. Unpub lished licent iate thesis, Lulef Unive rsity of Summary: Pre-Qu aternary rocks of the Hcin uvesi map ­ Technology. Depart ment of Environmental Planning and shee t area. Geo log ica l Map of Finland I : 100000. Expla­ Design. Division of App lied Geo logy. (unpag inated} nat ion to the ma ps of pre-Quater nary rocks.Sheet 422 1. Nyka ne n, 0 .1968. Toh rnajarvi. Geological map of Finla nd Geological Survey of Finland. 64 p. I : 100 000. Explanation to map ofrocks . Shee t 4232-4234. Kontinen, A. 1991. Evide nce for significa nt paragneiss com­ Geological Survey of Finland. 66 p. po nent within the late Archaean Nurm es gneiss com plex , O'Brien, H., Huhma, II. & Sorj onen -ward. r-, 1993. eastern Finland . In: Autio, S.(ed.) Geo logical Survey of Petroge nesis ofthe late Archean Hattu schist belt . Ilomantsi. Finland. Current Research 1989- 1990. Geological Survey eastern Finland: Geoc hemistry and Sr, Nd isoto pic co mpo­ of Finland. Special Paper 12. 17- 19. sitio n. In: Nurmi , P.A. & Sorjonen-Ward. P. (eds .) Geo­ Kontinen,A., Paa vola, J. & Lukkarinen, ll. 1992. K-Ar logical deve lopment , gold mineralization and ex plo ration ages of hornblende and biot ite from Late Archaean rocks of methods in the Archaean Hattu schist belt. Ilomantsi. east­ eastern Finland - interpretation and discussion of tectoni c ern Finl and. Geol ogical Survey of Finland. Spec ial Pape r imp lications. Geological Survey of Finl and. Bulletin 365. 17.147- 184. 31 p. O'Brie n, R. , Nurmi, P. & Ka rh u, J. 1993 . Oxygen. hydro­ Ko ntinen, A. & Paavola, J . 1996. Svccokarelian (Palaeo­ gen and strontium isotopic compositions of gold minera li­ proterozoic) tecton o-th ermal effect on the Archaean bed­ zat ion in the Late Archean Hattu schist belt . Ilomantsi, rock ofNorth Karelia, eastern Finland . In: Ekdahl, E. & Au­ eastern Finland . Geological Survey of Finl and , Specia l tio. S.(eds.).GlobalGeoscience Transect/SVEKA -Prcceed ­ Paper 17, 29 1- 306. ings of the Kuopi o Seminar. Fin land 25.-26 . 11.1993. Geo­ O hla nder, R., SkiOld, T., Elm ing, S.-A., BABEL \Vor king logical Survey of Finland, Reportof lnvestigation 136. 7- 8. G roup. Claesson, S. & Nisca, D.H . 1993. Del ineation and Kouvo, O. & Tilto n, G. R . 1966. Mineral ages from the cha racte r of the Archaean-Proterozoic bound ary in north­ Finnish Precambrian. Journal ofGeology 74 (4), 421-442. ern Sweden . Precambrian Research 64. 67-84. Laajoki, K. & Luukas,J.1 988. Early Proterozoic stratigraphy Paa vola, J . 1984a.On the Arc haean high-grade metamorphic of the Salahmi-Pyhanta area. cen tral Finland, with an em­ rocks in the Vurpaisjarvi area. Cent ral Finland. Geological phasis on applying the principl es of lith odernic stratigraphy Survey of Finland. Bulletin 327. 33 p. to a complexly deformed and metamorphosed bedrock. Bul­ Paa vola, J . 1984b . Nitslan kartta-alueen kulliopera. Sum­ letin ofthe Geological Society of Finland 60 (2). 79-106. mary: Pre-Qua ternary rocks of the NilsHi map-sheet area. La vikainen, S. 1989. The granitoid rocks of the lIomantsi Geological Map of Finland I : 100 000. Explanation to the re gion. In: Gaul. G. (cd.) Archean granit oid s and associated maps of pre-Quaternary rocks. Sheet 3334. Geo log ical Mo. Wand Au mineralization in eastern Finland. Excur sion Surv ey of Fin land . 57 p. C3 .Geological Survey of Finland. Gu ide 25, 69-75. Paavola, J. 1986.A communication on the V-Pb and K-Ar Lu ndqvist , Th ., Vaasjoki, M. & SkiOld , T. 1996. Prelim i­ age relations of the Archaean basement in the Lapin lahti ­ na ry note on the occurrence of Archaean rocks in the Varpai sjarvi area. central Finland . Geological Survey of Va llen-Alhamn area. northern Sweden . In: Lundqvist. Th. Finland , Bulletin 339 , 7- 15. (ed.) Radiometri c datin g results 2. Division of Bedrock Paavola, .J. 1988a. The Archaean bedrock of Lapi nlahti ­ Geology.Geological Survey of Sweden. Sveriges geologiska Varpai sjarvi area. Central Finland. Geological Survey of undersokning C 828, 32-33. Fin land . Special Paper 4. 161-169. L un d q vist, Th.•S kiOld, T. & Vaasjoki, M. 2000. Archaean­ Paavola, J . 1988b. Lapinlahden kartta-a lueen kalliopera . Proterozoic Geochronolog y of the Vallen-Alhamn Area. Summ ary: Pre-Q uatern ary rocks of the Lapinlahti map­ northern Sweden. GFF 122,273- 280 . sheet area. Geological Map of Finland 1 : 100 000. Expla­ Luu k k one n, E.J. 1985. Structural and V-Pb isotopic study of nat ion to the maps of pre-Quaternary rocks. Sheet 3332. late Archaean rnigm atiric gn eisses of the Presvecokarelides, Geological Sur vey of Finland . 60 p. Lylyvaara. easte rn Finland. Transactions of the Royal So­ Paav ola, J . 1991. Iisalm en kartta -alueen kalliopcra. Sum­ ci e ty of Edinburgh: Earth Sciences 76 . 401-410. mary: Pre-Quatern ary rocks of the Iisalm i map-sheet area. Luu k konen.Ei.l. 1988 . Moisionvaaran j a Ala-Vuokin kartta­ Geo logical Map of Finland I : 100000. Explanati on (Q the alueen katlioper tt. Summary: Pre-Quaterna ry rocks of the maps of pre-Quaternary rocks. Sheet 334 1. Geological Moisionvaara and Ala-Vuo kki map-sheet areas. Geolog ical Su rvey of Fin land . 57 p. Map of Finland 1 : 100 000, Explanatio n to the maps of pre­ Pa tch ett, P.J ., Kouvo, 0 .•Hedg e, C.E. & Tatsumoto , M. Qua ternary rocks. Sheets 442 1, 4423 + 4441. Geol ogica l 198 1. Evo lution of continental crust and mantl e heterog e­ Survey of Fin land. 90 p. neity: evide nce from Hf isotopes. Contribu tion s to Miner­ Lu ukkonen, E.J . 1989. The early Proterozoic Saari-Kiekki alogy and Petrology 78. 279- 297 . gree ns tone belt: A represe ntat ive of the Sariola Group at Perttunen, V.1991. Kcrn!n. Karuu gin, Simonja Runkauk sen KUhrno. Eastern Fin land . B ulletin of the Geo logical Soci- kartta-alueiden kalliopcra. Summary: Pre-Quaternary rocks

24 Geological Survey of Finland. Special Paper 28 Descript ion (0 the Bedrock Map of Central Fennoscandia (Mid-Norden)

of the Kemi. Karunki, Simo and Runka us map-sheet areas. Nickel sulfide field conference. Excursion guide.Finland . Geological Map of Fin land 1 : 100 000. Explanation to the IGCP Project no. 161 Sulfide deposits in mafic and ultra­ maps of pre-Quaternary rocks. Sheets 2541 , 2542 + 2524, mafic rocks, 37- 73. 2543 and 2544 . Geologica l Sur vey of Finl and. 80 p. Tuisku, P. & Slvonen , S. 1984. Paine -ja lhrnpotilaolosuhteet Pllralnen, T. 1988. The geology of the Archaean greenstone Kuhmon vihredkivivyohykkeen metamorfoosissa (with an - granitoid ter rain in Kuhmo, east ern Fin land. Geological Engli sh summary ). Arkeei sten alueiden malmiprcjekti. Survey of Finland . Specia l Paper 4. 39- 5 1. Oulun yliopisto. Rapcrtti 19. 59 p. Piirainen, T., Honkamo, M. & Rossi, S. 1974. A prelimi­ Tuukki, P.A.• .Mannikkd, K.H , Oj ala, V.J . & Pitkaj iir vi, nary report on the geology of the Koli area . Bulletin of the J .T. 1987. Kovero n liuskejakson geologia (Geo logy of the Ge ologi cal Society of Finland 46 (2), 16 1- 166. Kovero schist belt] . Oulun ylio pisto , Pohjois-Karjalan Piirainen, T. & Vuollo,J.1991. Arkeeinen ja proterotsooinen malmiprojekti. Raportti 9. 123 p. (In Finnish) geologin en cvoluutio ja malminmuodo stus: Pohjois-Kar­ Vaasjoki, M., Sorjonen-Ward, P. & Lavikainen, S. 1993. jalan loppuraportti. Pohjois-Ka rjalan rnalmip rojekti.Oulun U· Pb age deter minations and sulfide Pb-Pb characteristics yliopistc. Raportti 3 1. 145 p. (1n Finnish) from the late Archean Hattu schist bell, Ilomantsi. eastern Puustinen , K. 1971. Geo logy of the Siilinj arvi carbo natite Finland. In: Nurm i. P.A. & Sorjonen-Ward, P. (eds.)Geo­ complex. eastern Finland . Bulletin de la Commiss ion logical development. gold mineralization and exploration geologique de Finl ande 249. 43 p. meth ods in the Arc haean Hattu schist belt. Ilomantsi, eas t­ Sorjonen-\Vard, P. 1993.An over view of structural evolu ­ ern Finland. Geological Surv ey of Finland . Special Paper tio n and lithic units within and intruding the late Arc hean 17, 103-131. Hattu schist belt, Ilomantsi , eastern Finland. In: Nurmi, Vaasjoki, M., Taipale, K. & Tuokko, 1. 1999. Radiom etr ic P.A. & Sorjo nen-Ward. P. (eds.) Geological develo pment. ages and other isotopic data bear ing on the evo lution of gold mineralization and exploration methods in the Archaean Archaean cru st and ores Kuhmo-Suomussal mi Area, East­ Hatt u schist belt , llomantsi. eastern Finland. Geological ern Finland . In: Kahkonen. Y. & Llndq vist, K. (cds.) Stud­ Su rvey of Finland, Special Paper 17. 9-102. ies on the evolu tion of the Precambrian in Finland contrib­ Sorj onen-\Vard, P. & Clao ue-Long. J. 1993. A preliminary utedbythe Global Geoscience Transect/ SVEKA · Project. Bul­ no te on ion mic roprobe results for zirc on s from the letio of the Geological Society of Finland 71 (I ). 155-176. Si lvev aara Gra nodiorit e. Itomamst. ea stern Finland. In: vayryn en, H. 1933. Uber die Stratigraphie der kare lischen Autio, S. (ed.) Geological Survey of Finland ,Current Re­ Form ation. Comptcs Rend us de la Societe geo logique de se arch 1991·1992. Geo logica l Survey of Fin land. Special Finlande 6. Bulletin de la Commission geologique de Paper 18, 25- 29. Finlande 10 1, 54-78. Ta ipa le, K. 1988. Volc anism in the Archaean Kuhmo Vayrynen, H. 1939.On the geology and tectonics of the greenstone bell . eastern Fin land. Geol ogical Survey of Outokumpu ore field and region. Bulletin de la Comm ission Fi nland, Special Paper 4, 151-1 60. geologique de Finlande 124. 91 p. Taip a le, K. & Tuokko, I. 1981. Kuhmon arkeei sen \Vetherill, G.\"., Kouvo, 0., Tilton, G.R . & Ga st , P.,,"'. vihreakivi vyohyk keen geologiasta j a ma lmiminerali ­ 1962. Age measur ements on rocks from the Finnish saatioista (On the geology and ore mineralisations of the Precambrian. Journ al of Geo logy 70 ( 1).74-88. Ku hmo gree nstone bell]. Oulun Yliopisto , Kuhmon ja Wilkman, W.\V.\V. 1938. Kuopio. Kivilajikarta n selitys Kittilan malmiprojektit. Rapo rtti 47.65 p. (In Finnish) (with an Eng lish summary). Explanation to the map of Taipale, K., Tuokko, I. & Piirain en, T. 1980. A brief rock s. General Geological Map of Finland I : 400 000 , Pre­ int roduction to the geology and geochemistry ofthe Kuhmo Quartern ary rock s, Shee t C3. Geo logical Survey of Pin­ greenstone belt. eastern Finland. In: Papunen. H. (ed.I land.Ffl p.

3,2, Proterozoic crystalline rocks

Jukka Kousa, Heikki Lukkarinen and Thomas Lundqvist

3,2.1 General features age determinations ofparticularly the plutonic rocks, have shown that both orogenic belts contain coeval The Proterozoic crystalline rocks ofthe Finnish and plutoni c rocks. An increase in our knowledge of Pre­ Swedish Mid-Norden area range between c. 2500 and cambrian sedimentation and tectonics led to the inter­ 1100 Ma in age. Until the middle of the century.it was pretation that Ihe Svecofennian lithologies (Sveco­ commonly believed that Ihe Proterozoic rocks in fennides) form a geosynclinal facies and the Karelian Finland are products of two orogenic cycles, during formations (Karelides) the foreland facies of a single which two mountain chains, the Karelides and the orogenic belt (or an orogen), referred to as the Svecofennides, were formed (e.g. Eskola 1941). The Svecokarelides. This belt was formed during the Karelian schists in eastern and northernFinland, known Svecokarelidic (or Svecokarelian) orogeny c. 1900­ also as the Karelian Formations (Eskola 1925), we re 1800 Maago (Simonen 1986, andreferences therein). cons idered younger than the Svecofennian schists in Gaal and Gorbalschev (1987) have suggested that the the western panofFinland. In the 1960' s. radiometric tennSvecokarelian orogeny is misleading and should

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