Geological Survey of Finland
Bulletin 357
Paleoproterozoic volcanism in the Kühtelysvaara - Tohmajärvi district, eastern Finland
by Lauri J. Pekkarinen and Heikki Lukkarinen
Geologian tutkimuskeskus Espoo 1991 ------
Geological Survey of Finland, Bulletin 357
P ALEOPROTEROZOIC VOLCANISM IN THE KIIHTELYSVAARA - TOHMAJÄRVI DISTRICT, EASTERN FINLAND
by LAURI J. PEKKARINEN AND HEIKKI LUKKARINEN
with 17 figures, 1 table and 3 appendices
GEOLOGIAN TUTKIMUSKESKUS ESPOO 1991 Pekkarinen, L.J. & Lukkarinen, H., 1991. Paleoproterozoie volcanism in the Kiih telysvaara - Tohmajärvi distriet, eastern Finland. Geological Survey 0/ Finland, Bulletin 357,30 pages, 17 figures, I table and 3 appendiees. The numerous episodes of Paleoproterozoie volcanism and assoeiated sedimen tation preserved in the Kiihtelysvaara - Tohmajärvi distriet represent both prolonged and episodie rifting of eratonie erust. V-Pb zireon age determinations from two mafie dykes intruded in eonjunetion with the basalmost lava flows indieate an age of ca. 2120 - 2100 Ma for this earliest mafie magmatism. However, no informa tion is yet available eoneerning the age of the younger flows, dykes or sills. Pyroclastie units are also present and have, along with the mafie lava flows and intrusions, been metamorphosed under greenschist facies eonditions. Volcan ism took plaee in an intraeratonie, within-plate setting, with predominantly basal tie eompositions. Hydrothermal alteration oeeurred both during and after erup tion. This affeeted the chemical composition of the earlier lava in particular, the younger lava flows as weil as the dykes and sills generally showing less evidence of ehemical alteration. The volcanogenic and sedimentary formations of the Kiihtelysvaara area have been renamed according to local geographical place names and regional correla tions and comparisons have been made between the study area and similar sequences elsewhere in Finland, particularly with respect to the mafie units.
Key words: metavolcanic rocks, metabasite, hydrothermal alteration, rifting, absolute age, stratigraphy, correlation, Paleoproterozoic, Proterozoic, Kiihtelys vaara, Tohmajärvi, North Karelia, eastern Finland
Pekkarinen L.J., Outokumpu Finnmines Oy, Exploration, P.O. Box 67, SF-83501 Outokumpu, Finland Lukkarinen H., Geological Survey 0/ Finland, P. O. Box 1237, SF-70701, Kuopio, Finland
ISBN 951-690-446-7 ISSN 0367-522X
Vammalan Kirjapaino Oy 1991 CONTENTS
Introduction ...... 5 General geology and stratigraphy ...... 7 Metabasite petrography ...... 10 Older metabasites ...... 10 Y ounger metabasites ...... 10 Metabasite geochemistry ...... 11 Sampling and analytical methods ...... 11 Alteration and effects on whole-rock geochemistry ...... 11 Major element geochemistry ...... 13 Trace element geochemistry ...... 16 Radiometrie ages of metabasites ...... 19 Disdussion ...... 19 Alteration and petrogenesis ...... 19 Tectonic setting ...... 22 Dyke rocks in the Archaean craton ...... 24 Correlation ...... 24 Conciuding remarks ...... 26 Acknowledgments ...... 26 References ...... 27 Appendices: 1. Major (wt-OJo) and trace (ppm) element compositions of metabasites from the Kiihtelysvaara - Tohmajärvi district 2. Sampling sites and short descriptions of sampies 3. Sampling sites for Nd-Sm and U/ Pb-age measurements and short descriptions of sampies
INTRODUCTION
The Archaean basement gneiss complex in (1971 a) nevertheless considered that the meta North Karelia is bounded in the west by a se diabase dykes cutting the basement gneis ses cor quence of Paleoproterozoic sediments and vol respond to Fe-rich tholeiites, whereas lava flows canogenic lithologies. In addition to lavas, within the Proterozoic sequence apparently be pyroclastic deposits and tuffaceous sediments, long to the spilite-keratophyre association. the metavolcanic sequence includes metadiabase The purpose of this study is to describe the dykes and sills (Nykänen, 1971a,b; Piirainen petrography, stratigraphy and chemical charac et al. , 1974; Pekkarinen, 1979). This so-called teristics of the metavolcanites and related intru Jatulian phase of volcanism took place between sives in the Kiihtelysvaara - Tohmajärvi districL 2200-2000 Ma (Sakko, 1971; Kouvo, 1976; The stratigraphieal scheme of Pekkarinen (1979) Simonen, 1980; Meriläinen 1980a,b; Huhma, has been modified somewhat, such that forma 1986a). Piirainen (1968) divided the Jatulian mafie tions and groups (Figure 3) have been named dykes intruding both basement gneisses and after geographieal place names (cf. Hedberg, cover quartzites in the Koli area into two sepa 1976). It is suggested that the terms Sariola, Jatuli rate types - a 'drier', tholeiitic association and and Kaleva (cf. Meriläinen, 1980a,b; Luukkonen & a more volatile-rich spilitic group. According to Lukkarinen, 1986) be used with reference to tec Hanski (1986b), the earlier (ca. 2200 Ma) Jatulian tofacies rat her than as formallithostratigraphi intrusions constitute a distinct gabbro-wehrlite cal units (cf. Laajoki, 1988). Because all volcano association which represents a more primitive genic lithologies and dykes in the study area have parent magma than that of later magmatism. been to some extent metamorphosed and are in The geology of the Kiihtelysvaara - Toh many instances intensely deformed, they may col majärvi region is comparatively weil known, lectively be referred to as metabasites. However, having been described earlier in some detail by, for convenience the prefix meta- will not be used among others, Nykänen (1968, 1971a,b), Pekka here further . rinen (1979) and Ward (1987, 1988). However, Both authors have participated in interpreta there has been rather less information available tion and preparation of the manuscripL Lukka concerning the geochemistry of the metavol rinen however was responsible for producing the canites and associated mafic dykes (cf. Nykänen, chemical variation and discrimination diagrams, 1968, 1971a; Pekkarinen, 1979). Likewise, their while Pekkarinen summarized these results, de origin, tectonie setting and alteration system veloped a model for describing alteration effects atics have not been examined in detail. Nykänen and revised the stratigraphical terminology. 6 Geologieal Survey of Finland, Bulletin 357
A '. USSR '\ N \ \. '\ '-. " Bas"m"nl \ , '\ '\ '\ \ ) '\ ' 11 ;' \\ 11 .•1)... 1\ / 40 km \ 11 ~ Iloma~isl i ~ ~- ~---- +,"A"r,,- - 11 ,\'\ ~~ l~telysvoa ra ;'1\ ~ Formations of ~/~ the Viesimo, Raatevaara and " ' Hyypiä Groups r=:-=l Formations of the "=-=-=J Tohmajärvi Group
Metadiabase dykes and sills
Area In Fig B
r- I Area In Fig. 3 I
EARLY PROTEROZOIC FORMATIONS o 2km
HelnQvoarQ end Koljola Fm ~ Kartel/aara Fm ~' . *":' ARCHAEAN BASEMENT EJ Dttala Fm D Haukilampi Fm Vltstola end Sarkllampl end Migmatites, gneisses ~ Petolkko Fm ~o 0 Polkkylampl Fm I-",~ 1and granitaids Mptadlobase dyke Kalkunmakl Fm Metapelites and mafie 0- - \" Metadlobase sill IlIlIj volcanic rocks
Fig. I. Stratigraphie map of North Karelia (A) modified after Luukkonen ja Lukkarinen (1986) and (B) simplified geologi eal map of the Hyypiänvaara - Raatevaara area. Line A-B eorresponds LO seetion in Fig. 10. Numbers refer LO sites sampled for analyses. Geological Survey of Finland, Bulletin 357 7
GENERAL GEOLOGY AND STRA TlGRAPHY
The Kiihtelysvaara - Tohmajärvi district is 10- elast conglomeratic intercalations in its lower cated in eastern Finland, along the boundary part. Both the Viesimo and Raatevaara Groups zone between the Archaean basement complex have been intruded by numerous mafic dykes. and the Proterozoic Karelidic schist belt (Sirno Volcanic activity in the Kiihtelysvaara district nen, 1980). The Archaean craton (Figure 1) con commenced with the eruption of mafie lavas onto sists of greenstone belts and granitoids that Haukilampi Formation quartzites. The latter formed between 2.9-2.5 Ga (Wetherill et al., were evidently already consolidated by this stage, 1962; Kouvo & Tilton, 1966; Tilton & Grünen• since lava has been found occupying fissures in felder, 1968; Nykänen, 1968, 1971a,b; Simonen, the quartzites and conversely, quartzite enelaves 1980; Proskuryakov, 1983; Lavikainen, 1986, occur within the lavas (Nykänen, 1971a). The 1989; Ward & Nurmi, 1989). Paleoproterozoic mafic sequence, designated as the Koljola For mafic dykes and dyke swarms are very abundant mation, varies from 30-80 m in thickness and within the craton (Nykänen, 1968, 1971a,b; Pek consists of numerous lava flows as weIl as, in the karinen, 1979; Lavikainen, 1986), typically oc uppermost part, pyroclastic deposits and tuffa curring with a frequency of 2-3 dykes/ km' ceous sediments. The formation can be traced, (Pekkarinen, unpublished data). Those dykes at the present erosion level, from north of the vil causing magnetic anomalies are evident from the lage of Kiihtelysvaara to south as far as the Finn gray-tone aeromagnetic pixel map shown in Fig ish - Soviet border. The mafic volcanic rocks ure 2. In general the dykes are subvertical and exposed in the Tohmajärvi culmination (Nykä• 0 0 0 strike preferentially towards 285 -295 , 320 - nen, 1968; Tohmajärvi igneous complex of 0 0 0 325 and 075 -085 , with widths typically be Ward, 1987, 1988) are considered here to be cor tween 10-30 m, although in some cases they may relative in time with the Koljola Formation vol exceed 100 m in thickness. canism. The petrography and stratigraphieal sequence The Koljola Formation is overlain by the Hyy of formations in the Kiihtelysvaara area (cf. Fig piä Group (Upper latulian group of Meriläinen, ure 3), has been dealt with in detail by Pekkari 1980a and Upper latuli Subgroup of Luukkonen nen (1979). Directly overlying the Archaean base & Lukkarinen, 1986). This sequence begins with ment, or in places separated from it by a locally the quartzites of the Kalkunmäki Formation preserved paleoregolith, is the riftogenic Viesi which is in places carbonate-bearing. The lower mo Group (synonymous with the Sariolian part of the formation contains sporadic interca Group of Meriläinen, 1980 and Sariola Group of lations of quartz-pebble conglomerate while to Luukkonen & Lukkarinen, 1986), comprising the wards the top of the unit some tuffaceous and breccia conglomerates of the Pölkkylampi For pelitic horizons are present. The Kalkunmäki mation and arkoses of the Särkilampi Formation. Formation is succeeded by dolomites of the The upper surface of this arkose formation is also Viistola Formation, which also has some minor characterized by a regolith, again recording intercalations of lavas and pyroclastic deposits. chemical weathering. The overlying Raatevaara These are in turn overlain by the Annala Forma Group (corresponding to the Lower latulian tion, consisting of a quartz-hematite lithology in Group of Meriläinen, 1980a, and Lower latuli addition to quartzites, followed by the Petäikkö Subgroup of Luukkonen & Lukkarinen, 1986) Formation, which comprises a diverse sequence represents shallow-water deposition and ineludes of dolomites, carbonaceous pelites and phyllites. the Haukilampi Formation, which consists A younger phase of volcanism at Kiihtelys predominantly of orthoquartzites, with quartz- vaara is represented by several lava flows and 8 Geological Survey of Finland, Bulletin 357
..'"
••fr •
N I
o 10 20
km
Fig. 2. Low-a1titude aeromagnetic data image of the Kiihtelysvaara - Tuupovaara area provided by Outo kumpu Co, enhanced with high-pass (91 x91 window) and edge enhancement (5x5 window) filtering, and linear stretching. Processed from the aeromagnetic data of Geological Survey of Finland using the method described by Aarnisalo (1984). Subareas: K = Kortevaara, H = Hyypiä, R = Raatevaara, V = Valkea vaara, W = Värtsilä, T = Tohmajärvi. Other symbols: Ar = Archaean area, g = Archaean greenstones, pz = Proterozoic area, v = metavolcanics, d = metadiabase dykes. Geological Survey of Finland, Bulletin 357 9
FORMATIONS AC CORDING REDEFINED TE CTOFACIES LlTHOLOGY GROUPS TO PEKKARINEN 1979 FORMATIONS
MICA SCHIST FM ~ ~ ~ ~ ~ HEINÄVAARA FM ~ - KALEVA - - TOHMAJÄRVI ~ .~ TURBIDITE-CONGLOMERATE- ..~ ~.- = . 6 - = 6 KORTEVAARA FM QUARTZITE FM ' C? . .e::>,' . 6 -~-.:::::.;;:------DOLOMITE-CARBONACEOUS OTTOLA FM ~ -'r-- ~ SLATE-VOLCANITE FM r---+- --',- -+- -+- -'r- PETÄIKKO FM .. -:- ;;- .---: -:- -;~-:-;-7 ~.-~..... :-.x: .: . HEMATITEROCK-QUARTZITE FM ...... :. : :io. ', ,': oe · ',::.: ,, ' ANNALA FM -+- -+- HYYPIÄ ~ --'r- DOLOMITE-VOLCANITE FM -'r- VI/STOLA FM JATULI -'r- --'r- -'r- .' . UPPER QUARTZITE FM : ~ ""'.'. KALKUNMÄKI FM t>:~~;;~,=,~ i?~.p . ~. "2'. v v v v v vy VOLCANITE FM v v v v v KOLJOLA FM .=. = . = . = =.= RAATEVAARA LOWER QUARTZITE FM HAUKILAMPI FM p.·=·.c,.o. 9.6 .0 : 0 oT7T7TT/77TTn7TT1 7T 000 0 '6' 'lm;z>", 0 ARKOSITE FM 0 0 0 0 o 0 0 0 SÄRKILAMPI FM SARIOLA VIESIMO GO • BRECCIA-CONGLOMERATE FM :.o .. ~~.:?~ ... c: \J ....~ . . :G.? MAJOR UNCONFORMITY UNCONFORMITY AND OLDER t7O/T/1 AND YOUNGER UNCONFORMITY ~ WEATHERING CRUST WEATHERING CRUST E3 Fig. 3. Lithostratigraphic units of the Kiihtelysvaara area. pyroclastic deposits within the Petäikkö Forma glomerates of the Kortevaara Formation and the tion. These are collectively grouped within the mi ca schists of the Heinävaara Formation and Ottola Formation although they are relatively its associated graphite pelite intercalations. thin and discontinuous compared to the fIows of Sedimentation and volcanism was followed the Koljola Formation. They are however charac by deformation and metamorphism during the teristically accompanied by bedding-concordant ca. 1.9-1.8 Ga Svecokarelidic orogeny (cf. diabase intrusions such as the Hyypiä and Pekkarinen, 1979, p. 16), during which the Valkeavaaara Sills. Dykes associated with these Paleoproterozoic sequence was folded against the sills have been observed to truncate dykes belong rigid Archaean basement to the east. Sediments ing to the earlier Koljola Formation magmatism of the Tohmajärvi Group were metamorphosed (Pekkarinen, 1979, p. 116), suggesting that they under amphibolite facies conditions (Nykänen, used in part the same feeder channels or frac 1968, 1971a; Pekkarinen, 1979; Campbell et al. , tures. 1979), whereas the Viesimo, Raatevaara and The Hyypiä Group is overiain by the Toh Hyypiä Groups, including the metabasites were majärvi Group (Kalevian Group of Meriläinen, metamorphosed to somewhat lower, greenschist 1980a, and Kaleva Group of Luukkonen & Luk facies grade (Pekkarinen, 1979). karinen, 1986), which includes the turbidite con- 10 Geological Survey of Finland, Bulletin 357 METABASITE PETROGRAPHY Older metabasites On the basis of isotopic age determinations as The pyroclastic units overlying the Koljola For weil as stratigraphic position, the earlier group mation lavas are generally highly schistose and of metabasites can be defined to include (i) la banded and consist predominantly of chlorite, vas and pyroclastic deposits of the Koljola For plagioclase (albite-andesine), opaques and quartz. mation; (ii) the vo1canogenic sequence at Toh Plagioclase phenocrysts are absent. majärvi, and (iii) those mafic dykes which trun Diabase dykes within the Archaean basement cate basement gneisses and sediments of the complex consist principally of hornblende and Viesimo and Raatevaara Groups. plagioclase (oligoclase-andesine), together with Lava flows in the Koljola Formation are typ i additional minor amounts of biotite, quartz, epi cally fine-grained and schistose and commonly dote, carbonate, chlorite, sphene and opaque ox contain amygdales filled with quartz, epidote or ides. Margins of the dykes, while sharing the carbonate (cf. Pekkarinen, 1979, Figure 66, p. same mineral assemblage, te nd to be somewhat 117). Pillow lavas are not known from the strained and finer-grained. Dykes > 50 m in Kiihtelysvaara area, although they have been width tend to display internal differentiation, found within the Tohmajärvi sequence (Nykä• with a central part richer in plagioclase and nen, 1968, p. 30). The Koljola Formation has quartz (Nykänen, 1968, Figure 11, p. 29). Those been subdivided into upper and lower units, with dykes that can be traced across from the base the latter consisting predominantly of the miner me nt into sediments of the Viesimo and als biotite and/ or chlorite, plagioclase (albite Raatevaara Groups (such as the Piippolanmäki oligoclase), quartz and opaque oxides (ilmenite). Dyke), typically show a mineralogical transfor Plagioclase occurs both as relict phenocrysts mation from hornblende to chlorite and (10-15070) < 1. 5 mm in size and within the plagioclase to a mixture of albite, carbonate and groundmass. Phenocrysts are generally strongly sericite. In spite of these changes, original ophitic sericitized or sausseritized. Hornblende also oc magmatic textures are often weil preserved. curs as sporadic phenocrysts. The upper unit is The metabasites of the Tohmajärvi area, such essentially the same mineralogically except that as the coarse-grained Oravaara basalt (Huhma, chlorite tends to dominate over biotite and quartz 1986a), originally consisted of lavas, pyroclastic too is somewhat more abundant. Plagioclase deposits and hypabyssal intrusions; mineralogi phenocrysts, while present, are gene rally smaller eally they are very similar to the older Kiihtelys than those in the lower unit. Both units contain vaara metabasites as deseribed above (cf. Nykä• accessory sphene and apatite; carbonate and epi nen, 1968). dote are also present, typically as amygdales. Younger metabasites The younger metabasites at Kiihtelysvaara in whieh truncate Koljola Formation metabasites clude (i) the lavas and pyroclastie deposits of the and overlying sediments, such as the Vii stola For Ottola Formation, (ii) sills, and (iii) those mafie mation dolomites (cf. Pekkarinen, 1979, p. 42). dykes which have truncated earlier dykes and The lavas of the Ottola Formation are fine- Geological Survey of Finland, Bulletin 357 11 grained and consist of amphibole (hornblende narrower than this are fine-grained throughout. or cummingtonite), plagioclase albite-ande Of the dykes examined in this study, the Hyy sine), biotite, opaque oxides and quartz. Amphi piä Sill (Figure 1), which is some 80 m wide and bole is also present as prismatic phenocrysts has intruded between dolomites and carbona 0.5-1.5 mm in length, but plagioclase ceous sediments of the Petäikkö Formation, is phenocrysts are lacking. Accessory sphene and composed principally of hornblende and plagio apatite are present, along with some small clase (andesine), with accessory biotite, car amounts of carbonate and tourmaline. These bonate, chlorite, sphene and opaque oxides. The lavas are also associated with graphite-bearing central part of the dyke is coarser-grained than banded tuffs. the margins, although this does not correspond Mafic dykes that truncate dykes of the earlier to any change in mineral composition. The magmatic phase or Viistola Formation dolomites Valkeavaara Sill which, based on fjeld observa consist predominantly of hornblende and plagio tions and diamond drilling is not continuous with clase (oligoclase-andesine), with additional the Hyypiä Sill, has intruded between the Kalkun amounts of biotite, epidote, sphene and opaque mäki and Petäikkö Formations (Pekkarinen, oxides. Dykes exceeding 1 m in width generally 1979, p. 38). Mineral compositions are the same have distinctly finer-grained margins, but dykes as for the Hyypiä Sill. METABASITE GEOCHEMISTRY Sampling and analytical methods Analyses were made from sampies weighing (cf. Danielsson & Saikkonen, 1985). Major and 0.5-1.0 kg collected either from outcrop or drill trace element abundances of some sampies were core material. Sampies were chosen so as to avoid measured at the Rautaruukki laboratories, using the effects of weathering or secondary quartz or pressed powder pellets and a Philips PW 1400 carbonate fissure and amygdale fillings. Sam pie XRF spectrometer. REE, Th and U abundances locations are indicated in Figure 1 and Appen were determined by the INAA method (Rosen dix 2. berg, 1972; Rosenberg and Zilliacus, 1977, 1980) Major elements and Ba, Zr and Sr were ana at the Reactor Laboratory of the Technical Iyzed by XRF at the Geological Survey of Fin Research Centre of Finland. land using lithiumtetraborate fused discs and a Analytical data are presented in Appendix 1. Philips PW 1420/ AHP XRF spectrometer. Other All major elements have been recalculated to trace elements, including Cr, Ni and Y were de 1000J0 on a volatile-free basis and with total Fe termined by optical emission spectrophotometry expressed as Fe20 3 before plotting. Alteration and effects on whole-rock geochemistry Following extraction and separation of a melt during cooling and solidification, porous zones from its parent magma, it may undergo numer in lavas and pyroclastic deposits are favourable ous episodes of fractionation or contamination sites for the percolation of hydrothermal fluids before finally reaching the surface. Moreover, which both remove and introduce various co m- 12 Geological Survey of Finland, Bulletin 357 KEY Volcanic rocks _ lava } Otlola Fm + tuff } T lava (upper unitl Koljola Fm v lava (lower unitl Diabase intrusions Younger group (Ca .2.06 Ga? ) o diabase sill (The Valkeavaara Sill) o diabase sill (The Hyypiä Sill ) x diabase (dyke in dolomite ) • diabase (internal dyke, fine - grained ) Older group ( Ca 2. 11 Ga ) o diabase dyke (anci ent feeder channel) for lower lavas • diabase (Iess altered dykes in ) basement area and Tohmajärvi * leucocratic diabase differentiate MgO/lO S iOz/100 Fig.4. Ternary system (after Davis et al. 1979) for recognizing alteration on the basis of MgO, CaO, AIP3 and SiOz data from the metabasites in the Kiihtelysvaara and Tohmajärvi areas. ponents in solution. If the rocks also remain Valkeavaara Sill (Appendix 1, analyses 31 and permeable during subsequent deformation and 32) also plot within the unaltered field. metamorphism, then metasomatie ehanges may take plaee that modify ehemieal eompositions still further. The MgO-CaO/ AI20 3-Si02 diagram (Davis et al., 1979) presented as Figure 4 indieates the 10 extent to whieh Ca-depletion and possible Si02 ;!- and MgO addition have taken plaee in lavas and I ~ tuffs of the Koljola (Appendix 1, analyses 10- o o 23) and Ottola (Appendix 1, analyses 33-35) u Formations. In eontrast, the older generation of 5 o mafie dykes, including their more leueoeratie vari \I I ~. ants (Appendix 1, analyses 1-6), as weIl as those \I --- interpreted as feeder ehannels to lava flows (Ap pendix 1, analyses 7-9) all plot within the field eharaeteristie of unaltered eompositions. An ex eeption to this however is the sam pie 7, taken o 0.2 0 .4 0.6 0.8 1.0 from the vieinity of the inferred vent, wh ich groups with the lava sam pies outside the un alte red field. The younger mafie dykes (Appen Fig. 5. CaO vs. Nap/ (NazO + KzÜ) diagram für the meta dix 1, analyses 24-27) and sampies from the basites considered in this study. Symbols as in Fig. 4. Geologieal Survey of Finland, Bulletin 357 13 According to the CaO vs. Na20/(Nap + K20) • diagram (Figure 5), Ca depletion in the Koljola 20 • Formation lavas and tuffs (Appendix 1, analyses c!- 10-23) was possibly concomitant with alkali ad I dition. This is reflected mineralogicaBy by the al 3 15 bitization of feldspar and the relative abundance M o of micas. Abundances of Ca and alkalis in the N .0.A\/ ·:0 .. (j) o dyke near the presumed vent (Analysis 7) cor LL 10 + + B respond very weB to those in the Koljola Forma tion lavas. Ca contents in the Ottola lavas (Ap pendix 1, analyses 33-35) are somewhat higher c than those in the Koljola Formation (Appendix 1, analyses 10-23). Albitization of plagioclase is also less apparent in the Ottola Formation lavas 10 8 6 4 o than in the those of the Koljola Formation and MgO wt- Ofo hornblende is also more typical, even though it Fig. 6. Fep3T vs. MgO eovariation diagram (after Pharaoh is commonly chloritized and metamorphic in and Pearee 1984) for Kiihtelysvaara and Tohmajärvi meta origin. basites. General trends for oeeanie and eontinental tholeiite The relative abundances of MgO and total Fe suites (A), island are tholeiite suites (B) and island are ea1c alkaline suites (C). Symbols as in FigA. (expressed as Fe20 3) within the metabasites of the study area have evidently been affected by secondary alteration, as is indicated by the con (Figure 6), as weB as in the abundance of chlo siderable scatter observed in variation diagrams rite in the sampies. Major element geochemistry The effects of alteration have generally not basites gene rally fall within the high-Fe tholeiite been sufficient to obscure the essentially subal field (Figure 8B). kalic character of both the older and the younger In unaltered volcanics, the Mg' -number (= 2+) metabasites on the Na20 + K20 vs. Si02 dia Mg/ (Mg + Fe atomic ratio with Fe20 / gram of Irvine & Baragar (1971), even though FeO = 0.15) is a useful indicator of degree of so me sampies, as a result of alkali addition, do differentiation. However, since it has already in fact plot in the alkaline field (Figure 7 A). Ac been shown that Fe and Mg contents in the cording to the Ti02 vs. Zr/ P20 5 diagram of metabasites of the study area have been modi Floyd & Winchester (1975), the metabasites are fied to some extent, it is unlikely that the trends tholeiitic (Figure 7B), whereas some of the Kol observed in the variation diagram (Figure 9) are jola Formation metabasites, including both lavas, attributable entirely to differentiation. Neverthe tuffs and the feeder channel sam pIe are, due less, Mg' -numbers for the Koljola Formation again to alkali addition, located within the calc (Figure 9A) tend to fall between 0.62 (10.2 wtOJo alkaline field on the AFM (Irvine & Baragar, MgO) and 0.32 (2.5 wt% MgO), with a mean of 1971) diagram (Figure 8A) . On the cation plot 0.49 (3.9 wt% MgO). Mafic dykes on the other of Jensen (1976), in which less mobile alumin hand appear to be in general somewhat richer in ium is used instead of alkali elements, meta- Fe, with Mg'-numbers between 0.47 (6.5 wt% 14 Geological Survey of Finland, Bulletin 357 A 8 A i! alkaline I 0 '\0 ~ 6 '\Z 0 ~ N • ><::. ~ .+ 0 + 4 N 0 Z .r -• 2 subalkaline Si02 wt- O/o calc - a lkatme 40 50 60 70 B 3 OlkO',,; tholelltlc Mg O i! ..!. T ~ Fe + Ti N 0 t~~ 0 8 2 ,:: . 0 ~ HFE=h,gh-lran thalellt le HMG= hlgh- magneslu m ..,. ba sa l t s tholellt lc basalts J °-0 o 0 .05 0.10 0.15 Fig.7. (Nap+Kp) vs. Si02 diagram (A) and Ti02 vs. Zr/ P20 S diagram (B) for metabasites from Kiihtelysvaara and Tohmajärvi. Dividing li ne in A after Irvine and Baragar (1971) and in B after Floyd and Winchester (1975) . Symbols as in Fig. 4. AI Mg Fig. 8. AFM diagram (A) and Jensen Cation Plot (B) for Kiihtelysvaara and Tohmajärvi metabasites. Di viding line in A after Irvine and Baragar (1971) and in B after Jensen (1976). MgO) and 0.22 (3.2 wt070 MgO) and a mean value Symbols as in Fig. 4. of 0.42 (3 .9 wt% MgO). The uppermost lavas of the Koljola Formation show inereasing SiOz and K20 abundanees with inereasing Mg' -number, whereas TiOz, Alz0 3 and FePitotaI) abun danees eonversely deerease; lavas from the lower The variation diagram for the younger meta part of the formation however show no syste basites (Figure 9B) cIearly shows the Hyypiä Sill matie eorrelation with Mg' -number. CaO and as being rieher in MgO (mean Mg' -number = K20 eontents are also appreeiably smaIler in the 0.57, eorresponding to 7.9 wt% MgO) than the upper lavas, as is the degree of seatter in Na20 Valkeavaara Sill (mean Mg'-number = 0.34, and P20 S abundanees. 4.0 wt% MgO). However, dykes interpreted as Geological Survey of Finland , Bulletin 357 15 A B 65 4 65 S i 02 Ti 0 2 Si 0 2 T i 02 60 60 fit, I I I I 55 55 I I I I .. x.~\ <:} 50 50 ~ : X. ~ \ ~ 18 25 18 25 Al203 Fe203TOT Al203 Fe203 TOT 16 16 20 20 14 14 15 )(' 12 12 t"',O ' ~ \ 0.6 12 06 12 MnO MgO MnO 10 / / ..... \j1 10 I ~ 0.4 8 ~ ~ I 0.4 8 I 6 .- I ~ 0.2 4 /"./ / // 0.2 'ti!/'2 _/ / ~ 10 10 CaO Ca O Na20 8 8 ...... - ..... , 4 ~9- t \ \ . ,., '~~f'C\ ,y/ \ / \ / \ / '''2/ 0.4 0.4 KZO KZO P 20 5 /'V' // \J', 0.3 0.3 I " h 'V \ h 'V 0.2 0. 2 X c I I ~ / . I~ '\O 0. 1 0. 1 / '" ~\ \ -...;. ~..... :~ I ~: \ ~ \~ I 02 0.4 0.6 0.2 0.4 06 0.3 0.5 07 0.3 0.5 0 .7 Mg Mg' Fig.9. Variation diagram for major elements in the older (A) and younger (B) Kiihtelysvaara and Tohmajärvi metabasites. Solid line separates dykes and dashed line metalavas. Symbols as in Fig. 4. having been feeder channels to these sills are The degree of compositional variation across similar to one another, with mean Mg'-numbers wide mafic dykes is indicated by a traverse of 0.45 (6.1 wtOJo MgO). Ottola Formation lavas through the strongly differentiated Piippolan do not differ significantly in composition from mäki intrusion (A-B in Figure 1) , about 200 m their intrusive counterparts. from the inferred point of eruption (Figure 10). 16 Geological Survey of Finland, Bulletin 35 7 A B 301 f::::::::,:::j < 15 1:: ::::1 ~ ; : ; :;:;: ; :;:;I 15-18 ~:;:;:;:;:; :;:l 302 !::::::::::::::::I > 18 % !::::::::::::::::I LEGEND D ~ 5 ~2 ~ 6 ~3 t ();g-: ,~ 7 Bi! 4 8 ~02 1:;: ':::':' :1 1;:;:;:;:;:;:;:1 4-7 50 100m o (::::::::::::::::1 Fig . 10. Geological cross-section (Li ne A- B in Fig.l) looking west through Piippolanmäki Dyke and showing distribution , T , of Si02 CaO, MgO, FeO Na20 and Kp. Symbols: 1 = quartzite; 2 = fine-grained mica-rich schist at contact; 3 = medium grained diabase; 4 = medium-grained, loca1ly coarse-grained biotite-rich and magnetite-bearing diabase; 5 = leucocratic diabase; 6 = fine-grained and chlorite-rich amygdaloidal rock; 7 = overburden; 8 = drill hole. Sampies were assayed semiquantitatively by emission spectrophotometer. Trace element geochemistry Metabasite trace element abundances are plot Lavas within the Ottola Formation charac ted with respect to Mg' -number in the variation teristically have Ni, Cr, Y and Zr contents almost diagram in Figure 11 . Lavas and associated dykes as high as those in the Hyypiä Sill (Figure IIB), of the Koljola Formation have similar and rather whereas Sr values are distinctly lower, suggest low Ni and Cr contents, of less than 50 and ing either secondary loss or else the relatively 100 ppm respectively (Figure lIA). Moreover greater proportion of plagioclase as a crystalliz they are not entirely in agreement with the Mg' ing phase in the lava magma. The scatter in Ba numbers of the rocks, suggesting the possibility abundances probably results from secondary of Ni and Cr loss and concomitant Mg gain dur mobilization. Two analyses from the Hyypiä Sill ing hydrothermal alteration. Strontium values indicate that Ni and Cr are more abundant (mean fall sympathetically with decreasing Mg' -number, values 105 ppm and 230 ppm respectively) than while conversely, Ba and K both show a consist in the Valkeavaara Sill (mean values 35 ppm and ent inverse correlation with Mg' -number. This 40 ppm respectively). Conversely, the Valkea mayaIso be the case for Zr, although there is con vaara Sill has higher Y and Zr abundances (mean siderable scatter in the data. Yttrium is margin values 35 ppm and 215 ppm respectively) com ally less abundant in the uppermost lavas com pared to the Hyypiä Sill (25 ppm and 80 ppm). pared to the lower flows . Mean trace element abundances in these sills Geological Survey of Finland, Bulletin 357 17 A 150 300 800 Ni Cr Ba 600 100 200 - - " ~ 'V "" 400 \ 'V ' \ \ 50 ~'i ---iJ 100 ', 'V \ // I 200 ~ 'V E / ~ / "" 'V ~ a. // 'V / ~ " / a. ~- " - y / (l;-;___ '~~y / 500 Sr 50 Y 300 Zr 400 40 //fj'" //-'fj",- 200 300 30 I ~'Y7 ""~ ~" 'V ", / • y ...... / '',-\j~~~ " ! l 200 20 (y -- )9J.;?-- - ~ "'-- 100 " -Y_-/ '" / / 100 / I 10 I / ~ _w_ 'V y /'" 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 8 150 300 800 Ni Cr Ba 0 600 100 200 Ji ."" 400 50 100 200 E 0 a. 0 a. i' 500 Sr 50 Y 300 Zr 400 40 200 300 30 200 20 U• ___ I 100 100 ~CI ", 10 ' .... !I!.I 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0,7 Mg . Fig. 11 . Variation diagram for selected trace elements from the older (A) and younger (B) Kiihte- Iysvaara and Tohmajärvi metabasites. Symbols as in Fig. 4. 18 Geological Survey of Finland, Bulletin 357 generally correspond closely to those in the as times greater than chondritic abundances sociated fine-grained dykes that cut across the «La/ Yb)N 3.6-7.0). They also have a earlier generation of dykes. distinct positive Eu anomaly, which reflects the Chondrite-normalized REE distributions for abundance of plagioclase phenocrysts in the the metabasites indicate fractionation of Koljo lavas. A solitary exception to this is sampie la Formation lavas (Figure 12A) such that La H103, taken from the uppermost unit of the values are 70-80 times greater and Yb 12-15 formation, for which La is only 25 times and Yb 11 times the chondritic abudances «La/ Yb)N = 1.8), and which also lacks any significant Eu enrichment. Lanthanide abundances in the Hyy piä Sill are lower than those in associated lava flows (Figure 12B) and fractionation of both Koljola Fm A LREE and HREE is also significantly less - La 'V H 103 } upper uni! is 24 times and Yb 13 times chondritic abudances H 101 } •0 H 10 7 . 0 R 10 3 lower um! «La/ Yb)N = 2.0-2.2). 100 • R 104 Figure 13 shows a comparison of Nd and Sm values for Koljola Formation lavas from Kor 50 UJ tevaara, Hyypiä, Raatevaara and Valkeavaara I- a:: with those from the coarse-grained Oravaara 0 z 0 basalt from the Tohmajärvi region (Huhma, :r: 10 u 1986) - the Oravaara sam pie is distinctly LREE depleted, whereas Koljola Formation lavas are >:: 5 ""u 0 clearly LREE enriched. a:: Metadiabase s i ll 100 • H 104 Fm o H 106 50 METABASITES ~ KOATEVAARA HYYPIA RAATEVAARA I VALKEAVAARA OAAVAARA Ci ~ 100 I 0 10 r u 58~ 50 18IC~ 282C~ :~~ 5C "- I. La Ce Nd Sm Eu Tb Vb 2'~ ~6~ 5'---'; u" 0 Fig. 12. Chondrite-normalized REE abundances of selected '" 10 AJ9S -- metabasites (Hickey and Frey 1982). Lavas from the Koljola Formation (A) and two sampies from the Hyypiä Sill (B). ,I ,I 1 For comparison the ranges of volcanic rocks from the Jout Nd Sm Nd Sm Nd Sm Nd Sm Nd Sm tiaapa Formation in the Peräpohja area (after Perttunen 1986) are shown in A and volcanic rocks from the Vaivanen For Fig. 13 . Chondrite-normalized Sm-Nd concentration patterns mation in the Kuopio area (Lukkarinen; in prep.) are shown of some sampies from Koljola Fm (H. Huhma; unpublished in B. Average value of ocean floor tholeiites (OFT) after data). For comparison data from sam pie A398 (Huhma 1986, BVSP (1981) The symbols and numbers refer to analyses pre p. 337), which is a coarse-grained basalt or diabase dyke. Nor sen ted here (Appendix 1). malization values are: Nd = 0.597, Sm = 0.192. Geological Survey of Finland, Bulletin 357 19 RADIOMETRIC AGES OF METABASITES In an attempt to ascertain the age of volcan ism in the Kiihtelysvaara - Tohmajärvi district, 0,40 ./ one sampie (A427) was analyzed from a dyke cut 2113=-/.4 / ting Archaean gneisses at Kutsu (Nykänen, 1968), and two more were taken from the Piippolan 20004 / 6'./426 G mäki Dyke, which terminates against, and 190Q/ / D presumably fed a lava flow (Figure 1). Sampie / /Os A426 is from the western end of the dyke near the inferred point of eruption, while Sampie / /0c ~: ~;65A .Zr PliPPOLANM ÄK l A465 is from the eastern part where it cuts 0.30 ° Zr KU TSU, A 427 Archaean basement (Figure 1) . Analytical results 6' F E and ages are listed in Table 1. J" 368" 46 Mo Zircons from the Piippolanmäki Dyke are eu 5,0 207P b/ 235 U 7,0 hedral, transparent - though somewhat yellow Fig. 14. Concordia diagram for zircons of the Piippolanmäki ish in color, and rather acicular, sometimes Dyke (A 426 and A 465) and the Kutsu Dyke (A 427). having length to width ratios L/ B in excess of 10. The sam pie from Kutsu represents the more strongly differentiated central phase of the dyke, in which zircons are euhedral, with a length to width ratio such that L/ B > 7. Crystals poor in uranium are clear and glassy, while U-rich and then the upper intercept becomes 2123 ± 10, with metamiet grains are rather turbid. the lower intercept at 513 ± 60 Ma, although in A regression based on both sam pies gives this case the sampies define a curved line. an upper concordia intercept of 2113 ± 4 Ma The U-Pb zircon age of the coarse-grained (2a standard deviation) and a lower intercept Oravaara basalt at Tohmajärvi is 2105 ± 15 Ma of 368 ±46 Ma (Figure 14). A regression based (Huhma, 1986a) which, within error limits, over only on the three Piippolanmäki zircon fractions laps with that of the above-mentioned dykes. On yields an upper intercept of 2115 ± 6 Ma (2a the basis of these age determinations it is there standard deviation) and a lower intercept of fore reasonable to deduce that the first major 368 ± 52 Ma. Using the six concordant frac phase of volcanism in the Kiihtelysvaara and tions from the Kutsu Dyke (A, B, C, D, G and Tohmajärvi region took place around 2120- H), form a chord intersecting the concordia 2100 Ma. So far there is no direct information at 2113 ± 5 Ma (2a standard deviation) and available concerning the age of the younger vol 380 ± 57 Ma. If all eight fractions are included, canic phase. DISCUSSION Alteration and petrogenesis The spilitization of marine basalts is consid seawater and basalt either ne ar the seafloor it ered to result from chemical interaction between self (Humpris & Thompson, 1978) or at low 20 Geologieal Survey of Finland, Bulletin 357 Table I. U-Pb data for zireons from Kiihtelysvaara and Tohmajärvi metadiabase dykes. Sampie Fraetion Coneentration 206Pb Isotopie eomposition of lead Atom ratios and radiometrie 206Pb = 100 ages, Ma No (g/ em' ) Ilg/ g 204 Pb 0 = grain size, 238U 206Pb 206Pb 2°'Pb 2°'Pb measured 204 207 208 Ilm 238U 23l U 206Pb A426: metadiabase dyke; Piippolanmäki, Kiihtelysvaara A426A total 407 .7 125 .31 789.1 .10154 14.348 76 .089 .3552 6.368 .13004 ± 21 ± 60 ± 69 1959 2027 2098 A465: metadiabase dyke; Piippolanmäki, Kiihtelysvaara A465A d>3.8 343 .2 96.66 511.1 .17004 15 .113 35 .276 .3255 5.77 1 .12858 0>50 ± 20 ± 57 ± 73 1816 1942 2078 B d>3.8 400.0 109 .97 626.3 . 12303 14.465 32.356 .3177 5.621 . 1283 0<50 ± 20 ± 70 ± 10 1778 1919 2075 A427 : leukoeratie diabase dyke; Kutsu, Tohmajärvi A427A d>4.2 274.4 76 .20 733.2 .04440 13.430 19 .371 .3210 5.69 .1285 0>70 ± 25 ± 15 ± 24 1794 1929 2077 B d > 4.2 205 .6 59 .22 365 .9 . 18958 15.427 24.127 .3329 5.93 .1291 0<70 ± 25 ± 15 ± 23 1852 1965 2086 C 4.0 238U = 1.55125xl(}lo/ a 23SU = 9.8485xl(}lo/a atomic ratio 238 U / 23lU = 137 .88 air abraded: Krogh, T. (1973) grades of burial or hydrothermal metamorphism dote and albite-chlorite-actinolite-quartz-ca1cite (Cann 1960; Stakes and O'Neil, 1982). In a rock have been demonstrated to be stable (Stakes & dominated hydrothermal system, having a waterl O'Neil, 1982). Mottl (1983) on the other hand rock ratio < 50 and at temperatures between 200 0 concluded that pillow lavas, consisting of the as and 350 0 C, the assemblages chlorite-quartz-epi- semblage chlorite-albite-epidote-actinolite or Geological Survey of Finland, Bulletin 357 21 chlorite-albite-epidote-quartz, generally represent alteration under conditions in which the Seawa ter water/ rock ratio < 35 and at temperatures straddling the greenschist facies boundary (250- 400 C). Giggenbach (1984) suggested that Na metasomatism (and also Mg and Ca alteration) results from downwards circulation and heating of fluids. Potassium metasomatism takes place in a wide range of hydrothermal settings, at tem peratures between 100°-600° C (cL Naboko, 1962; Sheppard et al. , 1971). Naboko (1962) also identified a vaporization zone at depths of 30-100 m, in which temperatures dropped from 190° C to 100° C, with a concomitant rise in pH leading to K-metasomatism and the formation of Fig. 15. Tentative model illustrating hydrothermal alterati orthoclase. According to Giggenbach (1984), K on in the older metabasites. Symbols: 1= quartzites of the metasomatism is promoted by upwards circula Kalkunmäki Fm, 2 = tuffs of the Koljola Fm, 3 = upper lava unit of the Koljola Fm, 4 = lower lava unit of the Koljola Fm, tion and cooling of hydrothermal fluids. 5 = diabase dykes (feeder for the lavas), 6 = quartzites of the Haukilampi Fm, 7 = arkosites and conglomerates of the Vie The changes in CaO, Na20, KP, MgO, simo Gr, 8 = Archaean basement. Fe(total) and Si02 abundances observed in the Kiihtelysvaara district (Figur es 3, 9, 10) some what resemble those described by Hellingwerf sumably was lost from the system at a later sta (1986) from the Bergslagen district of Sweden. ge, during hydrothermal metamorphism fol The marked loss of CaO is compensated for by lowing burial beneath younger sediments. It is addition of alkalis, such that Nap has in possible too that Fe was to some extent removed creased 1 •• OSt of all in the uppermost lavas of the during this process, to be subsequently precipi Koljola Formation (as indicated by the albitiza tated as matrix in overlying conglomeratic units tion of plagioclase), while Kp shows most sig (cL Pekkarinen, 1979, p. 88). Continuing hyd nificant enrichment in the lower lavas. The CaO rothermal activity may have leached K from ar contents of the feeder dykes also falls progressi kosites lying beneath the lavas and, because of vely where they intrude Proterozoic rocks, until the ambient thermal gradient, K migrated in the vicinity of the vent, where abundances are upwards, resulting in K being preferentially en similar to those in associated lavas. K20 also riched in the lowermost lavas of the Koljola For decreases markedly at the margins of the dyke mation. (Figure 10). The MgO contents of the lavas have Although a slight CaO enrichment is discern relatively increased with respect to FeO, presum ible, neither the lavas and pyroclastie deposits of ably relating directly to Mg addition (reflected in the Ottola Formation, nor the younger dykes and the abundance of chlorite). Evidence of silicifica sills show such substantial alteration as observed tion is commonly found, for instance in the form in the Koljola Formation metabasites. This sug of quartz-filled amygdales. gests therefore that the hydrothermal alteration Adopting the model of Hellingwerf (op. cil.), of the Koljola Formation took pI ace before the it seems reasonable to propose (Figure 15) that younger phase of volcanism. the intrusion of mafie tholeiitic lavas through In spite of the effects of alteration, the meta weakly lithified arkosic and quartzose sediments basites of the Kiihtelysvaara and Tohmajärvi areas caused so me Si and K contamination. CaO pre- are clearly subalkaline and tholeiitic in charac- 22 Geologieal Survey of Finland, Bulletin 357 ter (Figures 7, 8), with the ENd (2100) value of K, La and Ce (Figure 16, cf. Holm, 1985), (ii) + 2.6 for the Oravaara basalt (Huhma, 1986a) Nd and Sm chondrite-normalized ratios for Kol suggesting a LREE depleted mantle source. Sialic jola Formation sam pIes from Kortevaara, Hyy crustal contamination took place at least during piä, Raatevaara and Valkeavaara showing LREE the eruption of the tholeiites of the Koljola For enrichment (Figures 12, 13), and (iii) the ENd mation, as indicated by (i) the increased abun (2100) value of -1.7 for a sampIe (2B, Figure 13) dances of the hygromagmatophile elements Rb, from Hyypiä (Huhma, 1987). Tectonic setting Amongst trace elements, Ti, Zr and Y have A been demonstrated to be relatively immobile dur ing secondary alteration processes and thus rather 10 reliable indicators of original tectonomagmatic > settings (cf. Pearce & Norry, 1979; Pearce, 1980). 5 N Metabasites of the Kiihtelysvaara area lie prin cipally in the within-plate (WPB) field (Figure 16A) on the Zr/Y vs. Zr diagram of Pearce & Norry (1979), while on the Ti vs. Zr diagram of Pearce (1980), they lie in both the within-plate and mid-ocean ridge (MORB) fields, although the partial overlap between these two fields should be borne in mi nd (Figure 16B). The Kiihtelys vaara metabasites also overlap the continental / B / and oceanic basalt trends on the Fe20 (total) vs. / 3 / MgO diagram of (Pharaoh & Pearce, 1984) al E though, as a result of Fe and Mg metasomatic a. a. changes, some of lavas actually approach the is ,:: 10000 land arc tholeiite field (Figure 6, p. 13). Hygromagmatophile elements (H-elements) 5000 from Kiihtelysvaara metabasites when normal / ized with respect to primordial mantle abun / dances (Holm, 1985) yield curves that closely resemble that for mean continental tholeiites (Figures 17 A, B). The LREE contents of Koljo la Formation lavas are clearly greater than those 50 100 500 of marine tholeiites (cf. OFT-trend in Figure 12A). Such LREE enrichment may be a conse Fig. 16. Zr/ Y vs . Zr diseriminant diagram (A) and Ti - Zr quence of contamination by sialic crust but evi diseriminant diagram (B) for the Kiihtelysvaara and Tohma dence also exists for significant LREE enrichment järvi metabasites. Fields in A refer to mid-oeean ridge ba during hydrothermal processes (Dostal & Strong, salts (MORB), island are basalt (lAB) and within plate ba salts (WPB) affinities after Pearee and Norry (1979). Fields 1983; Hellman et al. , 1983; Kay & Hubbart, in B after Pearce (1980), basic-evolved line after Pharaoh and 1978; Langmuir et al. , 1977; Seifert et al. , 1985). Pearee (1984). Symbols as in Fig. 4. Geological Survey of Finland, Bulletin 357 23 early mafic dykes into these sediments and the Koljola Fm • H 103 ( upper unit) Archaean basement, and the associated extrusion 'V Average } H 10 1, H 107 lower of the Koljola Formation lavas was presumably R 103, R 104 umt related to tectonic instability and the initiation of intracratonic rifting (cL Ward, 1987, 1988). The relative scarcity of pillow structures and 10 comparative abundance of amygdales and brec W cias within the lavas of the Koljola Formation -l f suggests that they were formed partlyon dry land Z « and partly in shallow water (Nykänen 1968, L Average va!ues · • Continental tholeiite (CT) 1971a; Pekkarinen, 1979). The presence of pil -l « • Ocean floor tholeiite (OFT) low lavas at Tohmajärvi (Nykänen, 1968) indi o 0:: cates that volcanism there took place in a sub o B L 100 Metadiabase sill marine setting. With the progression of rifting, 0:: o Average a.. HI04, HI06 the metabasites of the Koljola Formation were '-... covered by the quartz arenites, carbonates and ::c: U carbonaceous pelites of the Hyypiä Group. The o 0:: eruption of the younger volcanites and erosion 10 of earlier volcanics was apparently coeval with this sedimentation, as was the intrusion of the Average value • Con tlnenta l tholeiite (CT) mafic sills. Although sedimentation gene rally ap pears to record a transition from continental to more marine conditions, it is nevertheless pos 1 :g ~ 0 o o'C '"-' sible that, fQr example, the Viistola Formation Rb Ba Th U K Nb La Ce Sr P Zr Sm TI carbonates were deposited in separate small rift related depocenters rather than in a continental Fig. 17. H-element abundances of selected lavas in the Kol platform or shelf setting (cL Pekkarinen, 1979). jola Formation (A) and in the Hyypiä Sill (B). Primordial mantle va lues for normalization after Wood et al. (1 979). For The rifted basin or basins were then filled with comparison average values of N-MORB (OFf) and continen the turbiditic rudites, arenites and lutites of the tal tholeiites (CT) after Holm (1985). The symbols and num Kortevaara and Heinävaara formations (Pekka bers refer to analyses presented here (Appendix I). rinen, 1979; Ward, 1987, 1988), reflecting a major phase of erosion. It is significant that no volcanic intercalations have been found within On the basis of both chemistry and the cratonic this sequence and that detritus is typically de to epicratonic nature of associated sediments, the rived from the craton, including in particular metabasites of the Kiihtelysvaara and Tohmajär• those areas from which J atulian sediments and vi region are more likely to have formed in a volcanics had been eroded (cL Huhma, 1986a). within-plate continental setting rather than at a Deposition of the Tohmajärvi Group is inferred mid-ocean ridge. Deposition of the Viesimo and to have begun around 2000 Ma (cL Meriläinen, Raatevaara groups evidently took place under 1980a, b) but more precise estimates are not yet quiescent conditions whereas intrusion of the available (cL Huhma, 1990). 24 Geological Survey of Finland, Bulletin 357 Dyke rocks in the Archaean craton The Archaean basement in the Kiihtelysvaara is related to the Kutsu monzogranite, dated at - Tohmajärvi region has been intruded by 2547 ± 28 Ma (U-Pb zircon concordia upper in numerous diabase dykes whose predominantly tercept) (Lavikainen, 1989). Dykes belonging to NW -SE orientation presumably re fleets exten Group B trend at 270°-295° and cut the Loitimo sional opening along a NE-SW direction (cf. monzogranite, while terminating within the Ga;:il, 1986; Kontinen, 1987a). Field observa J atulian sequence. Pekkarinen (unpublished tions, diamond drilling and geophysical data all data) has nevertheless found that so me dykes show that so me of these dykes terminate within sharing the Group A trend do in fact intrude the the Koljola Formation and therefore may Loitimo monzogranite, as weIl as terminate with represent feeder channels. Other dykes demon in the Proterozoic metabasites. It is thus plau strably cut Koljola Formation lavas and over sible that at least some of the Group A dykes lying sediments and may be feeder channels for are younger than the age proposed by Korhonen the younger volcanics and sills (Pekkarinen, (1987) and may instead represent to the same (ca. 1979). Some of these dykes strike sub parallel to 2120-2100 Ma) phase of rifting as the Group the volcanic units, at least at the present erosion B dykes and the Koljola Formation lavas. Some level, thus making it difficult to demonstrate a of the Group A dykes may in fact be related to direct relationship between dykes and flows. It an older (> 2300 Ma) phase of rifting, during is further possible that some of these dykes were which, according to the interpretation of Pekka feeder channels to lava flows that have subse rinen (1979) the conglomerates (Pölkkylampi quenti:' been eroded from the craton. Formation) and arkosites (Särkilampi Forma Korhonen (1987) has subdivided the mafic tion) of the Viesimo Group were deposited. Vol dykes o. l\[orth Karelia into two groups on the canic units connected with this phase of rifting basis of their magnetic properties. Dykes belong have been described from elsewhere in eastern ing to Group A tend to strike between 305°- Finland, at Saari-Kiekki (Luukkonen, 1989) and 330°. Korhonen (op. cit.) inferred an age of in Soviet Karelia (Sokolov & Heiskanen, 1985), 2630-2640 Ma for these dykes since they do not but are not present in the Kiihtelysvaara area. appear to cut the Loitimo monzogranite, which Correlation Correlation of the Koljola Formation with The quartzites underlying the Koljola Forma similar units outside the study area is hindered tion can be traced as an effectively continuous by their lack of contiguity. At the present level unit northwards as far as Koli, although it has of erosion, Koljola Formation metabasites can proved difficult to determine which of the quartz only be traced as far as so me kilometers N of the ite units at Koli actually correlates best with village of Kiihtelysvaara (Nykänen, 1971a; Pek those at Kiihtelysvaara (cf. Marmo et al. , 1988). karinen, 1979) . The paucity of isotopic age de Moreover, there are no volcanic units at Koli, al terminations also limits the possibilities for though several generations of mafic dykes and chronostratigraphical correlation, so that the fol layered intrusions intrude both quartzites and the lowing suggestions and discussion is of necessity underlying Archaean basement (Piirainen, 1968; tentative. Piirainen et al., 1974, Hanski, 1986a, b; Vuol- Geological Survey of Finland, Bulletin 357 25 10, 1988; Vuollo et al. , in prep.). Some of these Kiihtelysvaara may indeed correlate with voIcan dykes could perhaps represent hypabyssal feeders ism at Kuopio and SiiIinjärvi. Further support to subsequently eroded lava fIows (Piirainen for this suggestion comes from the similarities in et al., 1974). Hanski (1986a, b) has termed the the isotopic composition of carbonate sam pIes differentiated mafie sills of northern and eastern from the Petäikkö Formation at Kiihtelysvaara Finland the gabbro-wehrlite association (GW A), and those from Kuopio and SiiIinjärvi, with while a related group of intrusions in the Koli re Jouttiaapa Formation, which overlies the Kivalo obtained for the Piippolanmäki Dyke at Kiihte Formation, have an Sm-Nd age of 2090 ± 70 Ma, lysvaara. Although both chronostratigraphical which agrees, within error limits, with the age of and lithostratigraphical evidence thus support the Koljola Formation (2120-2100 Ma). Furt correlation of the Jouttiaapa and Koljola Forma hermore, the Sipojuntti mafic dyke which cuts tions, differences in chemical composition (eg. the Archaean Pudasjärvi basement gneisses has REE patterns in Figure 12, p. 18) nevertheless yielded a V-Pb zircon age of 2114 ± 14 Ma (Pert suggest that they formed in different environ tunen, 1987) which is effectively identical to that ments. CONCLUDING REMARKS Volcanism in the Kiihtelysvaara - Tohmajärvi vaara Sills. After an intense period of erosion, district apparently records a prolonged phase of all these units were buried beneath turbiditic de rifting, with the oldest volcanics of the Koljola posits of the Tohmajärvi Group. Formation having erupted upon the cratonic Two of the dykes associated with Koljola For quartzites of the Haukilampi Formation, at the mation volcanism and also the coarse-grained margin of the rift, or rifts. The penecontem Oravaara basalt within the Tohmajärvi meta poraneous Tohmajärvi volcanics presumably basites have been dated isotopically at around formed within the central part of the rift basin. 2120-2100 Ma, wh ich gives a reliable estimate With the waning of volcanic activity in the basin for the age of the earlier phase of volcanic ac or basins, a sedimentary sequence was deposited, tivity. The age of the younger metabasites has yet commencing with quartzites and epiclastic to be determined, but would appear from indirect deposits (Kalkunmäki Formation), and followed evidence to be considerably younger than the by predominantly calcareous and carbonaceous earlier metabasites. pelites and dolomites (Viistola and Petäikkö For The metabasites of the Kiihtelysvaara and Toh mations). Sedimentation was nevertheless accom majärvi district were tholeiitic in character and panied by sporadic volcanic activity, culmina were erupted and intrude within a continental set ting in the Ottola Formation lavas and pyro ting. Their chemical compositions have however clastics, which were coeval with the Petäikkö For been affected by subsequent hydrothermal al mation carbonates. Mafic sills were also intruded teration and also to so me extent, by sialic crustal at this stage, including the Hyypiä and Valkea- contamination during ascent and eruption. ACKNOWLEDGMENTS Professor Atso Vorrna, Dr. Olavi Kouvo, Dr. the Geological Survey were performed by Mr. Ilkka Laitakari, Dr. Kauko Meriläinen, Dr. Han Väinö Hoffren and the optical emission spectrog nu Huhma, Mr. Juha Karhu, Mr. Jukka Kousa raphy measurements were made by Ms . Ringa and Mr. Olli Äikäs all offered valuable comments Danielsson. Isotopic age determinations were on an earlier draft and valuable suggestions for done at the Geological Survey of Finland under improvment. The XRF analyses undertaken at the direction of Dr. Olavi Kouvo. Mrs. Anni Geologieal Survey of Finland, Bulletin 357 27 Vuori (Geological Survey of Finland) and Mrs. The Rautaruukki chemical laboratory and the Rauha Turunen (Outokumpu Finnmines Oy) Reactor Laboratory at the Finnish National drafted the diagrams and the text was translated Technical Research Center. Financial support for by Dr. Peter Sorjonen-Ward. We express our REE analyses by the Academy of Finland via gratitude to all the above people and the staff of IGCP-project 179 is gratefully acknowledged. the Isotope Laboratory at the Geological Survey, REFERENCES Aarnisalo, J., 1984. Image proeessing and integration of geo Floyd, P.A. and Winchester, J.A., 1975. Magma type and physieal, landsat and other data as a tool for mineral tectonic setting discrimination using immobile elements. exploration in glaeiated Preeambrian terrain. In Proeeed Earth Planet. Sei. Lett. 27, 211-218. ings of the International Symposium on Remote Sensing Ga:il, G., 1986. 2200 million years of erustal evolution: The of the Environment, Third Thematie Conferenee: Remote Baltic shield. Bull. Geol. Soe. Finland 58 (I), 149-168. Sensing for Exploration Geology. Colorado Springs, Giggenbach, W.F., 1984. Mass transfer in hydrothermal al Colorado, April 16-19, 1984, 107-128. teration systems - A eoneeptual approach. Geoehimiea Aumo, R., 1983. The Proterozoie metasedimentary and et Cosmoehimiea Acta 48,2693-2711. metavolcanie mantle of the Kuopio domes. In K. Laajoki Hanski, E., 1986a. The gabbro-wehrlite aeeoeiation in the and J. Paakkola (eds.), Exogenie processes and related eastern part of the Baltie Shield.In G.H. Friedrieh, A.D. metallogeny in the Sveeokarelian geosynclinal eomplex. Genkin, A.J. Naldrett, J .D. Ridge, R.H. Sillitoe and F.M. Guidebook of the field trip for the IGCP projeets 91 and Vokes (eds.), Geology and metallogeny of copper deposits. 160 to eastern, eentral and southern Finland, August Springer-Verlag Berlin Heidelberg, 151-170. 17-26, 1983 . Geologieal Survey of Finland, Guide 11, Hanski, E., 1986b. Intrusions of the gabbro-wehrlite assoei 86-99. ation and their stratigraphie implieations in Finland. In BVSP, 1981. Basaltie volcanism on the terrestial planets. V.A. Sokolov and K.1. Heiskanen (eds.), Early Pro Basaltie volcanism study projeet. Pergamon Press, Ine., terozoie of the Baltie Shield. Proceedings of Finnish-So New York. 1286 p. viet Symposium held in Petwzavodsk 19th-27th Au Campbell, D.S., Treloar, P.J. and Bowes, D.R., 1979. Meta gust, 1985 . The Commitee for Scientific and Teehnical morphie his tory of staurolite-bearing sehist from the Co-operation between Finland and the Soviet Union. Sveeokarelides, near Heinävaara, eastern Finland. Geol. Petrozavodsk 1986, 123-136. Fören. Stock holm Förh. 101, 105- 118 . Hedberg, H.D. (ed.) 1976. International stratigraphie guide. Cann, J.R., 1960. Spilites from the Carlsberg Ridge , Indian A guide to stratigraphie classification, terminology, and Oeean. Journal of Petrology 10, 1-19. proeedure by International Subeommission on Strati Danielsson, R. and Saikkonen, R., 1985. Chemieal analysis graphie Classifieation of lUGS Commission on Stratig ofUSGS-W-2, USGS-DNC-I and USGS-BIR-I standard raphy. Wiley & Sons. New York. 200 p. rocks. Geologieal Survey of Finland, Report of Investi Hellingswerf, R.H., 1986. Contributions to the geology and gation 70. 12 p. ore genesis of western Bergslagen, Sweden. GUA Papers Davis, A., Blackburn, W.H., Brown, W.R. and Ehmann, of Geology, Series I, No. 25. Amsterdam. 255 p. W.D., 1978. Traee element geoehemistry and origin of Hellman, P.L., Smith, R.E. and Henderson, P., 1979. The late Preeambrian - early Cambrian Catoetin greens tones mobility of the REE: evidence and implictions from selected of Appalaehian Mountains. Univ. of California at Da terrains affeeted by burial metamorphism. Contrib. vies, Davies, Calif., Rep. (unpublished). Referenee in Mineral. Petrol. 71, 23-44. Sehweitzer, J. and Kröner, A., 1985. Geoehemistry and Hickey, R.L. and Frey, F.A., 1982. Geoehemieal eharaeteris petrogenesis of early Proterozoie intraeratonie volcanie ties of boninite series volcanies: implieations for their rocks of the Vendersdorp Supergroup, South Afriea. source. Geochimiea et Cosmoehimica Acta 46, 2099- Chemieal Geology 51, 265-288. 2115. Dostal, J . and Strong, D.F., 1983. Traee-element mobility Holm, P.E., 1985. The geochemieal fingerprints of differ during low-grade ' metamorphism and silieifieation of ent teetonomagmatic environments using hygromag basaltie rocks from Saint John, New Brunswiek. Can. J. matophile element abundances of tholeiitie basalts and Earth Sei . 20, 4341-435. basaltie andesites. Chemieal Geology 51, 303-323. 28 Geological Survey of Finland, Bulletin 357 Huhma, H., 1986a. Sm-Nd, U-Pb and Pb-Pb isotopic evi Krogh, T.E., 1973. A low-contamination method for dence for the origin of the Early Proterozoic Svecokarelian hydrothermal decomposition of zircon and extraction of crust in Finland. Geol. Surv. Finland, Bull. 337,48 p. U and Pb for isotope age determinations. Geochim. Cos Huhma, H., 1986b. Nd-isotopic composition and age of the mochim. Acta 37, 485-494. Jatulian Juottiaapa vo1canite formation in the Peräpoh• Laajoki, K., 19110. Karjalaisten muodostumien alaosat Puo ja schist area, Finland. In V.A. Sokolov and K.l. Heiska langan tutkimusten valossa. (Suomen geologisessa seu nen (eds.), Early Proterozoic of the Baltic Schieid. rassa 25.10.1979 pidetty esitelmä). Abstract: The lower Proceedings of Finnish-Soviet Symposium held in most Karelian formations on the basis of the studies in Petrozavodsk 19th-27th August, 1985. The Commitee Puolanka (Lecture delivered on 25.10.1979 to the Geo for Scientific and Technical Co-operation between Fin logical Society Finland). Res Terrae, Ser. B, No. I. 18 p. land and the Soviet Union. Petrozavodsk 1986,27-30. Laajoki, K. 1988. Karjalaisten muodostumien ryhmittely tek Huhma, H., 1987. Provenance of early Proterozoic and Ar tofasieksiin. In V. Lappalainen and H. Papunen (eds.), chaean metasediments in Finland: a Sm-Nd isotopic study. Tutkimuksia geologian a1a1ta. Turun yliopiston julkaisuja Precambrian Res. 35, 127-143. - Annales Universitatis Turkuensis. Sarja - Ser. C, Osa Huhma, H., 1990. Isotopic studies on early Proterozoic - Tom. 68, 21-30. (in Finnish with English summary) metasediments in Finland. In Y. Kähkönen (ed.), Pro Laajoki, K., Ervamaa, P., Havola, M., Heino, T., Kangas, terozoic Geochemistry, Helsinki '90. Abstracts of the R. and Strand, K., 1983. The Proterozoic Kainuu Schist Symposium held in the Department of Geology, Univer Belt. In K. Laajoki and J. Paakkola (eds.), Exogenic sity of Helsinki December 13-14, 1990. IGCP Project processes and related metallogeny in the Svecokarelian 217 Proterozoic Geochemistry. Helsinki, Finland, 19-20. geosynclinal complex. Guide to fjeld trips for IGCP Humpris, S.E. and Thompson, G., 1978. Hydrothermal al projects 91 and 160 in eastern, central and southern Fin teration of oceanic basalts by seawater. Geochemica et land, August 17-18,1983. Geological Survey of Finland, Cosmochimica Acta 42, 107-125. Guide I I, 34-85. Irvine, T.N. and Baragar, W.R.A., 1971. A guide to the Langmuir, C.H., Bender, J.F., Bence, A.E., Hanson, G.N. chemical classification of the common vo1canic rocks. and Taylor, S.R., 1977. Petrogenesis of basalts from the Can. J. Earth Sci. 8, 523-548. FAMOUS area: Mid-Atlantic ridge. Earth Planet Sci. Jensen, L.S., 1976. A new cation plot for classifying subalkalic Leu. 36, 133-156. volcaruc rocks. Ontario Div. Mines., Misc. Paper 66.22 p. Lavikainen, S., 1986. Oskajärven kartta-alueen kallioperä. Kay, R.W. and Hubbart, N.J., 1978. Trace elements in ocean Summary: Pre-Quaternary rocks of the Oskajärvi map ridge basalts. Earth Planet. Sci. Leu. 38, 95-116. sheet area. Kallioperäkarttojen selitykset - Explanation Koistinen, T.J., 1981. Structural evolution of an early Pro to the maps of Pre-Quaternary rocks. Lehti - Sheet 4243. terozoic strata-bound Cu-Co-Zn deposit, Outokumpu, Suomen geologinen kartta - Geological map of Finland Finland. Trans. Royal Soc. Edinburgh: Earth Sci. 72, I : 100 000. Geologian tutkimuskeskus - Geological Sur 115-158. vey of Finland. 42 p. Kontinen, A., 1986. Early Proterozoic stratigraphy and sedimentation in the Hyrynsalmi area, eastern Finland. Lavikainen, S., 1989. The granitoid rocks of the Ilomantsi In V.A. Sokolov and K.l. Heiskanen (eds.), Early Pro region. In: G. Gaal (ed.), Precambrian granitoids. Petro terozoic of the Baltic Shield. Proceedings of Finnish-So genesis, geochemistry and metallogeny, August 14-17, viet Symposium held in Petrozavodsk 19th - 27th Au 1989, Helsinki. Excursion C3: Archean granitoids and as gust, 1985. The Commitee for Scientific and Technical sociated Mo, Wand Au mineralisation in eastern Finland. Co-operation between Finland and the Soviet Union. Geologian tutkimuskeskus - Geological Survey of Fin Petrozavodsk 1986, 75-103. land, Opas - Guide 25, 69-72. Kontinen, A., 1987a. Early Proterozoic mafic rocks in the Lukkarinen, H. (in prep.). Paleoproterozoic volcanism in the Hyrynsalmi area northeastern Finland. Geologian tut Kuopio area, eastern Mid-Finland. kimuskeskus - Geological Survey of Finland, Tutkimus Lukkarinen, H., Huhma, H. and Kousa, J. (in prep.). raportti - Report of Investigation 76, 13-20. (in Finn Paleoproterozoic vo1canism in the Siilinjärvi area, east ish with English abstract) ern Mid-Finland. Kontinen, A., 1987b. An early Proterozoic ophiolite - The Luukkonen, E.J., 1989. The early Proterozoic Saari-Kiekki Jormua mafic-ultramafic complex, nonheastern Finland. greenstone belt: a representative of the Sariola group at Precambrian Res . 35, 313-341. Kuhrno, eastern Finland. Bull. Geol. Soc. Finland 61 (2), Korhonen, J., 1987. On the petrophysical properties of the 161-187. mafic dyke rocks and corresponding aeromagnetic anoma Luukkonen, E. and Lukkarinen, H., 1986. Explanation to lies in Finland. Geologian tutkimuskeskus - Geological the Stratigraphic Map of Middle Finland. Geological Sur Survey of Finland, Tutkimusraportti - Repon of Inves vey of Finland, Report of Investigation 74. 47 p. tigation 76,221-254. (in Finnish with English abstract) Marmo, J., Kohonen, J., Sarapää, O. and Äikäs, 0 ., 1988. Kouvo, 0., 1976. Kallioperämme kronostratigrafiasta. Suo Sedimentology and stratigraphy of the lower Proterozoic men Geologinen Seura & Geologiliitto r.y., Koulutus Sariola and Jatuli Groups in the Koli - Kaltimo Area, moniste 2, 1-13 (in Finnish). eastern Finland. In K. Laajoki and J. Paakkola (eds.), Kouvo, O. and Tilton, F.R., 1966. Mineral ages from the Sedimentology of the Precambrian in eastern and north Finnish Precambrian. J. Geol. 74 (4), 421-442. ern Finland. Proceedings of IGCP 160 Symposium at Geological Survey of Finland, Bulletin 357 29 Oulu, January 21-22, 1986. Geological Survey of Fin nary report on the geology of the Koli area. Bull. Geol. land, Special Paper 5, 11-28. Soc. Finland 46, 161-166. Meriläinen, K., 1980a. On the stratigraphy of the Karelian Proskuryakov, V.V. (ed.), 1983. Objasnitelnaja zapiska karte formations. In A. Silvennoinen (ed.), Jatulian geology poiskovyh prixnakov na zeleznye rudy dlja territorii in the eastern part of the Baltic Shield. Proceedings of Finljandii masstaba I : 400 000 - Suomen rautamalmien a Finnjsh - Soviet symposium held in Finland 21st-26th I : 400000 -mittakaavaisen etsintäkohdekartan selitys. August 1979. The Committee for Scientific and Techni Unpublished report. V/ 0 Tehnoexport. 311 p. (in Rus cal Co-operation between Finland and the Sowiet Union. sian) Rovaniemi 1980,97-112. Rosenberg, R.J., 1972. Instrumental activation analysis of Meriläinen, K., 1980b. Stratigraphy of the Precambrian in Lunar sampies. Suomen Kemistilehti B 45, 399-404. Finland. Geologiska Föreningens i Stockholm Förhand• Rosenberg, R.J. and Zilliacus, R., 1977. Improving accura lingar 102, 177-180. cy in routine instrumental activation analysis. Journal of Mottl, M.J., 1983. Metabasalts, axial hot springs, and the Radioanalytical Chemistry 39, 189-200. structure systems at mid-ocean ridges. Geol. Soc. of Am. Rosenberg, R.J. and Zilliacus, R., 1980. Instrumental neu Bull. 94, 161-180. tron activation determination of 23 elements in 8 new Naboko, S.I., 1962. Conditions of the present-day hydrother USGS Standard Rocks. Geostandards Newsletter 4 (2), mal metamorphism of volcanic rocks. Internat. Geology 191-198. Review 5, 850-858. Sakko, M., 1971. Varhais-karjalaisten metadiabaasien radio Nykänen, 0., 1968. Kallioperäkartan selitys - Explanation metrisiä zirkoni-ikiä. Summary: Radiometric zircon ages to the map of rocks. Lehti - Sheet 4232-4234, Toh of the Early-Karelian metadiabases. Geologi 23, 117-119. majärvi. Suomen geologinen kartta - Geological Map Seifert, K.E, Cole, M.R.W. and Brunotte, D.A., 1985. REE of Finland 1 : 100000, 66 p. mobility due to alteration of Indian Ocean basalt. Can. Nykänen, 0., 1971a. Kallioperäkartan selitys - Explanation J. Earth Sci. 22, 1884-1887. to the map of rocks. Lehti - Sheet 4241, Kiihtelysvaara. Suomen geologinen kartta - Geological map of Finland, Sheppard, S.M.F., Nielsen, R.L. and Taylor, H.P., Jr .. 1971. I : 100 000. 68 p. Hydrogen and oxygen isotope ratios in minerals from por Nykänen, 0., 1971b. On the Karelides in the Tohmajärvi area, phyry copper deposits. Econ. Geol. 66, 515-542. Eastern Finland. Bull. Geol. Soc. Finland 43, 93-108. Simonen, A., 1980. The Precambrian in Finland. Geologi Pearce, J.A., 1980. Geochemical evidence for the genesis and cal Survey Finland. Bull. 304. 58 p. eruptive setting of lavas from Tethyan ophiolites. In Sokolov, V.A. and Heiskanen, K.I., 1985. Evolution of Opruolites. Proceerungs international opruolite symposium, Precambrian vo!canogenic-sedimentary lithogenesis in the Cyprus 1979, Nicosia: Geological Survey Department, south-eastern part of the Baltic Shield. In K. Laajoki and 1980, 261-272. J. Paakkola (eds.), Proterozoic exogenic processes and Pearce, J.A. and Norry, M.J., 1979. Petrogenetic implica related metallogeny. Proceedings of symposium held in tions of Ti, Zr, Y and Nb variations in volcanic rocks. Oulu, Finland, August 15-16, 1983. Geological Survey Contrib. Mineral. Petrol. 69, 33-47 of Finland, Bull. 331,91-106. Pekkarinen, L.J., 1979. The Karelian formations and their Stakes, D.S. and O'Neil, J.R., 1982. Mineralogy and stable depositional basement in the Kiihtelysvaara - Värtsilä isotope geochemistry of hydrothermally altered oceanic area, East Finland. Geol. Surv. Finland, Bull. 301. 141 p. rocks. Earth Planet. Sci. Lett. 57, 285-304. Perttunen, V., 1986. Geochemistry of Karelian mafic effu Strand, K., 1985. Alaproterotsooisten Kurkikylän ryhmän ja sive rocks in the Peräpohja area, NW Finland. In V.A. sen päällä olevien karjalaisten muodostumien stratigra Sokolov and K.I. Heiskanen (eds.), Early Proterozoic of fia, paleosedimentologia ja rakenne. Res Terrae, Ser. B. the Baltic shield. Proceedings of the Finnish-Soviet sym 7. 170 p. (in Finnish) posium held in Petrozavodsk 19th - 27th August, 1985. Tilton, G.R. and Grunenfelder, M.H., 1968. Sphene: Ura The Commitee for Scientific and Technical Co-operation nium-Iead ages. Science 159, 1458-1461. between Finland and the Soviet Union. Petrozavodsk Vuollo, J ., Piirainen, T. and Huhma, H., (in prep.). Early 1986, 5-14. Proterozoic tholeiitic diabase dykes in Koli - Kaltimo Perttunen; V., 1987. Mafic dykes in the northwestern part area, North Karelia, eastern Finland: geological sig of the Pudasjärvi Granite Gneiss Complex. Geologian tut nificance. kimusmuskeskus - Geological Survey of Finland, Tut Ward, P., 1987. Early Proterozoic deposition and deforma kimusraportti - Report of Investigation 76, 29-34. (in tion of the Karelian Craton margin in southeastern Fin Finnish with English abstract) land. Precambrian Res. 35, 71-93. Pharaoh, T.C. and Pearce, J.A., 1984. Geochemical evidence Ward, P , 1988. Early Proterozoic Kalevian lithofacies and for the geotectonic setting of early Proterozoic metavol their interpretation in the Hammaslahti - Rääkkylä area, canic sequences in Lapland. Precambrian Research 25, eastern Finland. In K. Laajoki and J. Paakkola (eds.), 283-308. Sedimentology of the Precambrian in eastern and north Piirainen, T., 1969. Initialer Magmatismus und seine Erzbil ern Finland. Proceedings of IGCP 160 Symposium at tung in der Beleuchtung des Koli-Kaltimogebietes. Bull. Oulu, January 21-22, 1986. Geological Survey of Fin Geol. Soc. Finland 41, 21-45. land, Special Paper 5, 29-48. Piirainen, T., Honkamo, M. and Rossi, S., 1974. A prelimi- Ward, P. and Nurmi, P., 1989. Geology and gold minerali- 30 Geological Survey of Finland, Bulletin 357 zation in the Hattu schist belt. In G. Gaal (ed.), Precam Wetherill, G.W., Kouvo, 0., Tilton, G.R. and Gast, P.W., brian granitoids. Petrognesis, geochemistry and metalloge 1962. Age measurements on rocks from the Finnish ny. August 14-17, 1989, Helsinki. Excursion C3: Precambrian. J. Geol. 70 (1), 74-88. Archean granitoids and associated Mo, Wand Au miner Wood, D.A., Joron, J.L., Treuil, M., Norry, M. and alization in eastern Finland. Geologian tutkimuskeskus Tarney, J., 1979. Elemental and Sr-isotope variations in - Geological Survey of Finland, Opas - Guide 25, basic lavas from Iceland and the surrounding ocean floor. 41-59. Contrib. Mineral. Petrol. 70, 319-339. Appendix 1. Major (wt-%) and trace (ppm) element compositions of metabasites from the Kiihtelysvaara - Tohmajärvi district. 2 3 4 5 6 7*) 8 9 10 11*) 12x) 13*) 14*) 15*) 16x) 17x) Sam pie Tl03 TlOI 1101 TI02 1102 WI0l RllO VIOI KIOI VI03 HI07 RI02 RI03 RI04 HIOI RI06 RI05 Si02 64.40 48.32 48.29 52.08 49.20 49.55 58.72 50.45 49.91 52 .50 48.24 54.69 50.41 57.96 52.48 63.90 63.87 Ti02 0.82 3.07 2.59 2.16 2.01 1.80 2.35 1.64 1.24 1.57 2.16 2.22 2.39 2.28 2.37 1.70 1.70 AIPJ 13.30 12.19 13 .81 11.00 12.50 12.57 13 .31 15 .58 14.49 16.46 16.40 12.99 15 .17 12.86 13.50 13.29 12.86 FepJT 10.31 22.40 17.84 18.10 15.30 16.31 14.31 14.31 15.04 14.98 15.48 14.21 14.94 13.22 14.32 12.09 12.07 MnO 0.17 0.50 0.24 0.27 0.21 0.27 0.03 0.22 0.25 0.14 0.18 0.12 0.14 0.07 0.08 0.03 0.05 MgO 1.32 4.07 3.63 4.93 5.01 6.47 3.62 4.82 5.05 4.81 5.90 5.51 6. 16 5.60 7.72 2.50 3.67 CaO 3.40 6.53 8.42 7.77 8.81 8.78 0.71 6.94 5.05 1.68 1.96 4.09 3.36 0.83 1.55 0.40 0.31 Nap 5.67 3.00 3.74 3.10 2.08 2.40 4.21 3.39 4.65 3.96 0.90 2.35 3.01 3.86 2.53 3.54 3.76 Kp 0.16 0.15 0.42 0.20 0.82 1.30 2.77 1.27 1.73 2.05 3.88 2.49 3.54 1.25 2.51 2.14 1.30 P20S 0.14 0.17 0.22 0.11 0.36 0.08 0.24 0.22 0.09 0.15 0.26 0.26 0.27 0.23 0.24 0.21 0.21 Total 99.69 100.40 99.20 99.72 96.30 99.53 100.27 98 .84 97.50 98 .30 95.36 98.93 99.39 98 .16 97.30 99.80 99.80 Ba 290 700 360 170 300 500 400 200 460 280 Cr 65 17 20 n.d. 20 36 n.d. 18 n.d. n.d. Ni 22 n.d. 30 n.d. 20 44 n.d. n.d. 10 10 Sr 460 n.d. 140 n.d. 50 170 n.d. n.d. 20 10 Y 31 20 31 30 39 33 24 20 20 Zr 200 170 80 230 210 150 130 170 180 180 0 Rb n.d. n.d. 140 n.d. 80 "0 Ö (JQ Th 7.4 1.7 5.1 5.3 i'). U 3.2 0.4 1.02 1.14 ec La 28 18.2 27 25 C/) Ce 81 44 50 69 Ei Nd 39 23 35 35 '<" Sm 8.4 6.7 9.1 6.6 0...., 'I1 Eu 3.0 1.91 4.7 3.0 S· Tb 0.97 1.03 1.12 1.06 p;- ::> Yb 2.7 3.4 2.9 3.0 ?- Mg' 0.22 0.29 0.31 0.38 0.42 0.47 0.36 0.43 0.43 0.42 0.46 0.47 0.48 0.49 0.55 0.32 0.41 =.tI:I Analyses 1-6; metadiabase dykes (older group), 7-9; metadiabase dykes (older group, feeder channels), 10-15; lavas of the Koljola Fm (lower unit), 16-17; meta- ~ S· = = 2+) = = = lavas of the Koljola Fm (upper unit). Fe20 JT tot. Fe as Fe20 J, Mg' Mg/(Mg + Fe with Fe20/FeO 0.15, - not analysed, n.d. not detected. Analyses c.> V> made at *) Geologica1 Survey of Finland, Espoo, x) Rautaruukki Co., Raahe, for others see Appendix 2. -J Appendix L (continued). 0 0'" Sampie 18") 19') 20 21") 22') 23 ') 24 25 26 27 28") 29 30") 31 ') 32') 33') 34') 35') Ö No (JQ;::;. HI03 RI07 RI02 HI02 RI08 RI09 V 102 K103a KI03b K102 HI04 H105 H106 V105 V104 V107 V108 V 106 e Vl Si02 48.40 60.19 56.37 50.20 66.33 65 .51 50.75 47.28 48 .15 49.38 50.33 50.66 49.40 49.45 49.90 51.21 55.73 49 .88 ~ Ti0 2.21 1.80 1.84 2.17 1.68 1.77 1.72 1.48 1.46 1.46 1.36 1.09 1.54 2.25 1.98 1.50 0.89 1.54 < 2 '<'" AI 0 11.87 12.66 16.00 12.75 15.41 2 3 13 .65 13 .55 13 .63 14.00 12.96 13 .08 13.25 13.58 13.48 13.70 15.78 16.47 15.37 0..., Fe20 3T 19.72 11.87 12 .76 13 .76 9.13 9.16 15 .17 17.37 16.48 15.24 12.58 11.30 13.93 17.31 17.77 13 .79 11 .62 13 .36 '"Tl MnO 0.14 0.08 0.09 0.14 0.06 0.07 0.25 0.25 0.25 0.24 0.20 0.16 0.33 0.24 0.24 0.14 0.23 0.22 5· j;i MgO 7.94 5.45 7.14 10.18 3.64 5.14 6.19 5.92 5.87 6.39 6.84 7.21 9.68 3.84 4.12 6.90 6.78 6.92 :l po CaO 0.71 1.32 0.43 0.45 0.58 0.48 8.44 8.25 8.63 7.86 7.77 8.36 3.94 7.75 7.52 3.68 2.84 5.81 Ol Na20 3.83 4.44 2.75 3.26 4.17 3.45 2.78 3.16 3.47 3.74 3.96 3.12 4.09 2.72 2.94 2.91 3.48 2.67 S Kp 0.89 0.71 0.52 2.29 1.02 0.84 0.51 1.08 0.69 0.65 0.98 0.70 0.56 1.11 1.21 1.68 0.54 1.53 1r P20 l 0.19 0.22 0.35 0.21 0.21 0.21 0.16 0.12 0.12 0.12 0. 12 0.12 0.15 0.23 0.21 0.14 0.05 0.14 5· w Total 97.68 99.63 95.88 96.66 99.78 99.71 99.22 98.49 98.60 98.78 99.92 99 .19 98.99 96.77 98.55 97.94 94.91 97.48 u. -.l Ba n.d. 80 30 200 190 220 160 120 140 500 700 490 540 490 140 430 Cr 28 n.d. 29 n.d. n.d. 140 140 150 250 220 30 50 210 270 220 Ni 40 10 52 10 10 80 80 80 110 100 30 40 110 100 120 Sr n.d. 20 140 30 30 120 120 120 250 n.d. 120 120 60 40 80 Y 23 n.d. 28 10 10 20 20 20 28 23 40 30 20 20 20 Zr 100 200 300 140 180 190 90 100 100 90 70 240 190 120 50 120 Rb n.d. n.d. 110 n.d. n.d. Th 2.4 1.41 1.41 U 0.4 0.3 0.3 La 7.6 7.9 7.1 Ce 15.6 19.9 19.3 Nd 8.6 12.8 12.9 Sm 3.2 3.8 4.3 Eu 1.24 1.30 1.51 Tb 0.8 0.68 0.78 Yb 2.8 2.4 2.4 Mg' 0.48 0.51 0.56 0.62 0.47 0.56 0.48 0.43 0.44 0.49 0.55 0.59 0.61 0.33 0.34 0.53 0.57 0.54 Analyses 18-21; metalavas of the Koljola Fm (upper unit), 22-23; metatuffs of the Koljola Fm, 24; metadiabase dyke, cutting dolomites of the Viistola Fm, 25-27; fine-grained metadiabase dykes (younger group), 28- 30; The Hyypiä Sill (younger group), 31-32; The Valkeavaara Sill (younger group), 33-35; metalavas of the Ottola Fm . Analyses made at ") Geological Survey of Finland, Espoo, ,) Rautaruukki Co., Raahe, for others see Appendix 2. Geological Survey of Finland, Bulletin 357 Appendix 2. Sampling sites and short descriptions of sampies. Sampie Location Map- x/ y- Description Reference / sam pie for No sheet coordinates analyses collected by T103 Kutsu, 4232 6909.00/ 531. 00 Leucocratic middle portion of a Nykänen 1968, p. 28 Tohmajärvi di fferentiated metadiabase dyke Pekkarinen 1979, p. 123 from the basement area. TlOI Kemie, 4232 6901.00/517.50 Metadiabase dyke from the Tohma- Nykänen 1968, p. 28 Tohmajärvi järvi area. IlOI Havukka, 4243 6949.25/547.80 Metadiabase dyke from the basement Lavikainen 1986, p.40 Ilomantsi area. TI 02 Kemie, 4232 6899.50/ 516.00 Metadiabase dyke from the Tohma- Nykänen 1968, p. 28 Tohmajärvi järvi area. Il 02 Hattuvaara, 4244 6976.95/ 564.68 Medium-grained metadiabase dyke Pekkarinen 1987 Ilomantsi from the basement area (DH 22). W101 Tervavaara, 4232 6906.50/ 531.00 Medium-grained metadiabase dyke Nykänen 1968, p. 28 Värtsilä from the basement area. Pekkarinen 1979, p.123 RIIO Raatevaara, 4241 6922.97/ 516.51 Altered medium-grained metadiabase Lukkarinen Kiihtelysvaara dyke from from the Kalkunmäki area (an ancient feeder channel). VIOI Valkeavaara, 4232 6917.35/518.55 Medium-grained metadiabase dyke Pekkarinen 1979, p. 123 Kiihtelysvaara from the Silmuvaara area (an ancient feeder channel). KIOI Kortevaara, 4241 6929.48/ 514.78 Medium-grained metadiabase dyke Pekkarinen (see also Kiihtelysvaara from the Kortevaara area Pekkarinen 1979, p. 21) (an ancient feeder channel). VI03 Valkeavaara, 4232 6918 .37 / 519.97 Slightly altered metalava from the Pekkarinen 1979, p. 123 Kiihtelysvaara Koljola Fm (lower unit). HI07 Hyypiä, 4241 6926.52/515.34 Slightly altered metalava from the Lukkarinen Kiihtelysvaara Koljola Fm (lower unit). RI02 Raatevaara, 4241 6922 .70/ 516.62 Moderately altered metalava from Pekkarinen Kiihtelysvaara the Koljola Fm (lower unit). RI03 Raatevaara, 4241 6922.70/516.61 Slightly alte red metalava from the Lukkarinen Kiihtelysvaara Koljola Fm (lower unit). R104 Raatevaara, 4241 6922.70/516.60 Moderately altered metalava from Lukkarinen Kiihtelysvaara the Koljola Fm (lower unit). H101 Hyypiä, 4241 6924 .56/ 516.34 Slightly altered metalava from the Lukkarinen Kiihtelysvaara Koljola Fm (lower unit). RI06 Raatevaara, 4241 6922.75/ 516.57 Strongly altered metalava from the Pekkarinen Kiihtelysvaara Koljola Fm (upper unit). RI05 Raatevaara, 4241 6922.75 / 516.57 Strongly altered metalava from the Pekkarinen Kiihtelysvaara Koljola Fm (upper unit). HI03 Hyypiä, 4241 6924.82/516.16 Slightly altered metalava from the Lukkarinen Kiihtelysvaara Koljola Fm (upper unit). RI07 Raatevaara, 4241 6822.75/ 516.75 Strongly altered metalava from the Pekkarinen Kiihtelysvaara Koljola Fm (upper unit). R102 Raatevaara, 4241 6922 .20/ 516.72 Moderately altered metalava from Nykänen 1971, p.40 Kiihtelysvaara the Koljola Fm (upper unit). Pekkarinen 1979, p.123 H102 Hyypiä, 4241 6924.79/ 516.21 Slightly altered metalava of the Lukkarinen Kiihtelysvaara Koljola Fm (upper unit). RI08 Raatevaara, 4241 6922.75/ 516.56 Strongly altered metatuff of the Pekkarinen Kiihtelysvaara Koljola Fm (upper unit). Geological Survey of Finland, Bulletin 357 Appendix 2. (continued). Sampie Location Map- x/ y- Description Reference 1 sam pIe for No sheet coordinates analyses collected by RI09 Raatevaara, 4241 6922.75 / 516.56 Strongly altered metatuff of the Pekkarinen Kiihte1ysvaara Koljola Fm (upper unit). V102 Valkeavaara, 4232 6917 .35/ 518.08 Medium-grained metadiabase dyke Pekkarinen 1979, p. 123 Kiihtelysvaara cutting dolomite of the Viistola Fm. KlO3a Kortevaara, 4241 6929.40/ 514.70 Fine-grained marginal part of ca. Pekkarinen (see also Kiihtelysvaara 40 cm wide metadiabase dyke Pekkarinen 1979, p. 21) cutting the older metadiabase dyke (KI01) at Kortevaara. KlO3b Kortevaara, 4241 6929.40/ 514.70 Fine-grained middle part of ca. Pekkarinen (see also Kiihtelysvaara 40 cm wide metadiabase dyke Pekkarinen 1979, p. 21) cutting the older metadiabase dyke (K101) at Kortevaara. K102 Kortevaara, 4241 6929.42/514.70 Fine-grained ca. 4 m wide Pekkarinen (see also Kiihtelysvaara meta diabase dyke cutting the older Pekkarinen 1979, p. 21) metadiabase dyke (K101) at Kortevaara H104 Hyypiä, 4241 6925.98/ 515.24 Coarse-grained middle part of the Lukkarinen Kiihtelysvaara Hyypiä Sill. HlO5 Hyypiä, 4241 6926.05 / 515.05 Coarse-grained middle part of the Nykänen 1971, p.40 Hyypiä Sill. Pekkarinen 1979, p.123 H106 Hyypiä, 4241 6926.43/ 515.07 Deformed lower part of the Hyypiä Lukkarinen Kiihtelysvaara Sill. V 105 Valkeavaara, 4232 6918 .97/ 517.43 Medium-grained middle part of the Pekkarinen 1979, p. 38 Kiihtelysvaara Valkeavaara Sill (DH 306/ 80.85- 81.05 m). V104 Valkeavaara, 4232 6918 .97 / 515.43 Medium-grained middle part of the Pekkarinen 1979, p. 38 Kiihtelysvaara Valkeavaara Sill (DH 306/ 85.80- 86.00 m). V 107 Valkeavaara, 4232 6918.97/ 517.43 Basaltic metalava from the Ottola Pekkarinen 1979, p. 38 Kiihtelysvaara Fm (DH 306/ 51.40-51.60 m). V108 Valkeavaara, 4232 6918.97/ 517.43 Slightly altered metalava from the Pekkarinen 1979, p. 38 Kiihtelysvaara Ottola Fm (DH 305/ 52.75-52.90 m). V106 Valkeavaara, 4232 6918.97/517.43 Basaltic meta lava from the Ottola Pekkarinen 1979, p. 38 Kiihtelysvaara Fm (DH 306/ 59.55-59.80 m). Geological Survey of Finland, Bulletin 357 A ppendix 3. Sampling sites for Nd-Sm and U/ Pb-age measurements and short descriptions of sampies. Sampie Location Map x / y Description Reference 1 sampie for No sheet coordinates analyses collected by Sam pies for Nd-Sm measurements lA,B,C Kortevaara, 424 1 6928.83/ 514.50 Basaltic metalava from the Huhma Kiihtelysvaara Koljola Fm 2A,B,C Hyypiä, 4241 6926.501515.35 Basaltic metalava from the Huhma 1987, p. 132 Kiihtelysvaara Koljola Fm 4A,B,C,D Raatevaara, 4241 6922.701516.62 Basaltic metalava from the Huhma Kiihtelysvaara Koljola Fm 5A,B,C Valkeavaara, 4232 6918.90/ 517.80 Basaltic metalava from the Huhma Kiihtelysvaara Koljola Fm A398 Oravaara, 4232 6900.401517.30 Coarse meta basalt or Nykänen 1968 Tohmajärvi metadiabase dyke from the Huhma 1986, p. 25 Tohmajärvi igneous complex. Sampies for U/ Pb-age measurements A427 Kutsu, 4232 6909.501530.00 Medium-grained leucocratic Nykänen and Kouvo Tohmajärvi middle part of the Kutsu dyke. A426 Hyypiänvaara, 4241 6926.701515.60 Keratophyric middle part of Nykänen and Kouvo Kiihtelysvaara the Piippolanmäki dyke (western end). A465 Hyypiänvaara, 4242 6926.25/ 516.55 Medium-grained part of the Räisänen and Kouvo Kiihtelysvaara Piippolanmäki dyke (eastern part). Tätä julkaisua myy Denna publikation säljes av This publication can be obtained from GEOLOGIAN GEOLOGISKA GEOLOGICAL SURVEY TUTKIMUSKESKUS (GTK) FORSKNINGSCENTRALEN (GFC) OF FlNLAND (GSF) Julkaisumyynti Publikationsrlirsäljning ublication sales 02150 F..spoo 02150 Esbo SF·02150 Espoo, Finland ~ 90-46931 rn 90-46931 ~ 90-46931 Teleksi: 123185 geolo sf Telex: 123 185 geolo sf Telex: 123 185 geolo sr Telekopio: 90-462 205 Telefax: 90-462 205 Telefax: 90-462 205 GTK. Väli·Suomen GFC, Mellersta Finlands GSF, Regional office of aluetoimisto distriktsbyrA Mid·Finland Kirjasto Biblioteket Library PL 1237 PB 1237 P.O. Box 1237 70701 Kuopio 70701 Kuopio SF-70701 Kuopio. Finland rn 971-205111 ~ 971-205 III ~ 971-205 111 Telekopio: 971-205 215 Telefax: 971-205 215 Telefax: 971-205215 GTK, Pohjois·Suomen GFC, Norra Finlands GSF, Regional office or aluetolmisto distriktsbyrä Northern Finland Kirjasto Biblioteket Library PL77 PB 77 P.O. Box 77 96101 Rovaniemi 96101 Rovaniemi SF·96101 Ro\Oanlemi, Finland ~ %0-297 19 ~ 960-297219 rn 960-297219 Teleksi: 37 295 geolo sf Telex: 37 295 geolo sf Telex: 37 295 geolo sr Telekopio: %0-297 289 Telefax: 960-297 289 Telefax: 960-297 289 ISBN 951-690-446-7 ISSN 0367-522X