Painting the Volcanic Landscape of Early Fennoscandia

Home , Suomussalmi

Painting the volcanic landscape of early Fennoscandia – Geochronology of the Meso- and Neoarchaean Suomussalmi-Kuhmo-Tipasjärvi greenstone complex, Karelia Province, Finland

ELINA LEHTONEN

ACADEMIC DISSERTATION To be presented, with the permission of the Faculty of Science of the University of Helsinki, for public examination in lecture room B123, Exactum, Kumpula campus, on June 17th, 2016, at 12 o’clock noon.

DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40 / HELSINKI 2016 © Elina Lehtonen (synopsis) 5HSULQWHGZLWKWKHNLQGSHUPLVVLRQRI(OVHYLHU 3DSHU,,, © Reprinted with the kind permission of Springer (Paper III)

&RYHUSKRWR(/HKWRQHQ%DFNFRYHUSKRWRE\-+HLQRQHQ

Author´s address: Elina Lehtonen )LQQLVK0XVHXPRI1DWXUDO+LVWRU\ P.O.Box 44 8QLYHUVLW\RI+HOVLQNL)LQODQG HOLQDOHKWRQHQ#KHOVLQNL¿

6XSHUYLVHGE\ 'RFWRU3HQWWL+|OWWl *HRORJLFDO6XUYH\RI)LQODQG)LQODQG

&RVXSHUYLVHGE\ 'RFWRU-DDQD+DOOD )LQQLVK0XVHXPRI1DWXUDO+LVWRU\)LQODQG

Reviewed by: Adjunct Professor Phillips Thurston /DXUHQWLDQ8QLYHUVLW\&DQDGD

Doctor Kristoffer Szilas 6WDQIRUG8QLYHUVLW\8QLWHG6WDWHVRI$PHULFD

Opponent: Doctor Wouter Bleeker *HRORJLFDO6XUYH\RI&DQDGD&DQDGD

&XVWRV 3URIHVVRU7DSDQL5lP| Department of Geosciences and Geography 8QLYHUVLW\RI+HOVLQNL)LQODQG

ISSN 1798-7911 (paperpack) ISSN-L 1798-7911 ISBN 978-951-51-1351-1 (paperpack) ISBN 978-951-51-1352-8 (PDF) KWWSHWKHVLVKHOVLQNL¿

8QLJUD¿D+HOVLQNL Lehtonen E.Painting the volcanic landscape of early Fennoscandia – Geochronology of the Meso- and Neoarchaean Suomussalmi-Kuhmo-Tipasjärvi greenstone complex, Karelia Province, Finland8QLJUD¿D+HOVLQNLSDJHVWDEOHVDQG¿JXUHV

Abstract

Archaean cratons contain the oldest parts of the age groups based on pre-existing and new geo- Earth’s crust that have survived crustal recycling FKURQRORJLFDOGDWD*D*D*D processes. Archaean greenstone belts are vital DQG±*D7KH6XRPXVVDOPLJUHHQVWRQH parts of these cratons and preserve the oldest EHOWFRQWDLQVWKHROGHVWYROFDQLFSKDVH *D volcanoclastic and sedimentary rocks on Earth. DQGWKH7LSDVMlUYLDQG.XKPRJUHHQVWRQHEHOWV They play an important part in the study of the WKH\RXQJHVWYROFDQLFSKDVH ±*D 7KH evolution of the early Earth and formation of sta- new age determinations validate a chronostrati- ble continental crust. One of the most important graphic interpretation for each belt. The updated questions related to Archaean greenstone belts is chronostratigraphic model of the Suomussalmi how they were initially formed. Various tectonic greenstone belt comprises four volcanic units: processes have been suggested and the pertinent FD*D /XRPDXQLW *D DJHIURPD geological environments remain open for sci- PD¿FURFN7RUPXDXQLW *D $KYHQODKWL HQWL¿FGHEDWH$EVROXWHDJHGHWHUPLQDWLRQVRI unit) and 2.82 Ga (Mesa-aho unit). The Kuh- plutonic and supracrustal rocks provide an es- mo greenstone belt is interpreted to contain two sential tool for understanding crustal evolution units comprised of mainly volcanic rocks (Siivik- of the early Earth. kovaara and Nuolikangas) and a unit containing This thesis focuses on the largest Archae- sedimentary material deposited after the end of an greenstone association in eastern Finland: WKHYROFDQLVP 5RQNDSHUl %RWKWKH1XROLNDQ- WKH6XRPXVVDOPL.XKPR7LSDVMlUYLFRPSOH[ gas unit (ca. 2.84 Ga) and the Siivikkovaara unit which belongs to the Karelia Province of the FD±*D DOVRFRQWDLQPD¿FDQGXO- Fennoscandian shield. The main objective of the WUDPD¿FURFNV7KH7LSDVMlUYLJUHHQVWRQHEHOW thesis is to constrain a detailed geochronology for comprises three volcanic units with ages of ca. WKHIHOVLFDQGLQWHUPHGLDWHYROFDQLFURFNVDVZHOO *D 7DODVVXRXQLW *D +LHWDSHUlXQLW DVVHGLPHQWDU\URFNVRIWKHJUHHQVWRQHFRPSOH[ *D .RLYXPlNLXQLW DQG.RNNRQLHPLXQLW and associated plutonic rocks. The ages of the mainly composed of sedimentary rocks depos- selected samples were determined with second- ited after the end of the volcanism. ary ion mass spectrometry (SIMS) and laser-ab- %DVHGRQDYDLODEOHGDWDWKHFD*DYRO- lation multi-collector inductively-coupled-mass- canic rocks of the complex register an older con- VSHFWURPHWU\ /$0&,&306 DQGZKROHURFN tinent. The younger volcanic rocks with ages of samples were analyzed for their major and trace FD±*DIRUPHGYLDLQWHUDFWLRQEHWZHHQ element compositions. WKHROGHUFRQWLQHQWDQGRFHDQLFOLWKRVSKHUHRU The felsic and intermediate volcanic rocks during rifting of the older continent. RIWKH6XRPXVVDOPL.XKPR7LSDVMlUYLJUHHQ- stone complex can be divided into four distinct DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

Tiivistelmä (in Finnish)

$UNHHLVHWYLKUHlNLYLY\|K\NNHHWRYDWPHUNNHMl WXQHLWDYXONDQLLWWHMDO|\W\\XXVLHQWXWNLPXNVHQ NDOOLRSHUlPPHYDQKLPPLVWDWXOLYXRULSHUlLVLVWl SHUXVWHHOOD MRNDLVHOWD HULOOLVHOWl Y\|K\NNHHOWl NLYLVWl$UNHHLVLDYLKUHlNLYLY\|K\NNHLWlO|\W\\ ,NlU\KPl*DO|\W\\6XRPXVVDOPHQMD7L- OlKHVMRNDLVHQPDQQHUDOXHHQYDNDLVWDRVLVWDMDQH SDVMlUYHQYLKUHlNLYLY\|K\NNHLOWlMDRVD.XK- PXRGRVWDYDWWlUNHlQRVDQPDDSDOORQNHKLW\VWl PRQYLKUHlNLYLY\|K\NNHHQSLQWDNLYLVWlVLVlOWll Q\N\LVHQNDOWDLVHNVLHOLQNHOSRLVHNVLSODQHHWDNVL ]LUNRQLNLWHLWlMRLGHQLNlRQQRLQ*D Nykyaikaisen laattatektoniikkaprosessien alka- 7lVVlYlLW|VNLUMDW\|VVlHVLWHWllQHWWlVDDWD- PLVDMDQNRKWDDHLNXLWHQNDDQYLHOlWDUNNDDQWLH- villa olevan geologisen tiedon perusteella Suo- GHWlYDLNNDPRQHWJHRORJLVLVWDWRGLVWHLVWDYLLW- PXVVDOPHOWDO|\W\YlW*DLNlLVHWNLYHWRYDW WDDYDWQLLGHQDONDQHHQDUNHHLVHOODDMDOOD1lLGHQ WRGHQQlN|LVHVWLRVDYDQKHPSDDPDQQHUWDMDQXR- YDQKLPSLHQWXOLYXRULSHUlLVWHQNLYLHQNHKLW\NVHQ UHPPDWYXONDDQLVHWNLYHW ±*D V\QW\- WXWNLPXNVHQNDQQDOWDRQWlUNHlWLHWllPLOORLQ LYlWMRNRWlPlQYDQKHPPDQPDQWHUHHQMDPHUHO- YLKUHlNLYLY\|K\NNHLWlPXRGRVWDYDWSLQWDNLYHW OLVHQOLWRVIllULODDWDQYXRURYDLNXWXNVHVVDWDLYDQ- NHUURVWXLYDW7lKlQWDUYLWDDQDEVROXXWWLVLDLlQ- KHPPDQPDQWHUHHQUHSHlPLVHVVl PllULW\NVLlY\|K\NNHLGHQNLYLVWl 7lVVlYlLW|VNLUMDW\|VVlNlVLWHOOllQ6XRPXV- VDOPHQ.XKPRQMD7LSDVMlUYHQDOXHLOOHOHYLW- Acknowledgements Wl\W\YLHQ DUNHHLVWHQ YLKUHlNLYLY\|K\NNHLGHQ WDUNHPSDDNHUURVMlUMHVW\VWlMDLNlMDNDXPDD NUR- This great time travelling experience into the era QRVWUDWLJUD¿QHQWXWNLPXV 6XRPXVVDOPL.XK- of the oldest volcanoes of Finland would have not PR7LSDVMlUYL YLKUHlNLYLY\|K\NNHHQ DOXH RQ been possible without the helping hands around PLHOHQNLLQWRLQHQWXWNLPXVNRKGHVLOOlVLOWlO|\- PH+HUH,ZRXOGOLNHWRH[SUHVVP\VLQFHUH W\YlW6XRPHQYDQKLPPDWQRLQPLOMDUGLD gratitude to everyone involved. YXRWWDYDQKDWWXOLYXRULSHUlLVHWNLYHW

“I am not the one to tell the truth Not the one to tell a lie ...I’m just a grain of sand.” - Ghost Brigade: Grain 5 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40 Contents

Abstract ...... 3 7LLYLVWHOPl LQ)LQQLVK ...... 4 Acknowledgements ...... 4 List of original publications ...... 7 Abbreviations ...... 8 /LVWRIWDEOHVDQG¿JXUHV ...... 9

1 Introduction ...... 1.1 What are greenstone belts ...... 1.2 In search of a (plate) tectonic model and the origin of the greenstone belts 12 1.3 Geologic setting ...... 14 1.4 Previously suggested tectonic models for the SKT greestone complex .....14 1.5 Aims of the study ...... 17

6DPSOLQJPHWKRGRORJ\DQGWHUPLQRORJ\ ...... 17 2.1 Sampling ...... 17 7KH8±3EPHWKRGDQGVWDWLVWLFVRIJHRFKURQRORJ\ ...... 17 2.3 Stratigraphic terminology ...... 19 2.4 Geochemistry and discrination diagrams ......

3 Review of the original publications...... 21 3DSHU,7LSDVMlUYLJUHHQVWRQHEHOW ...... 21 3.2 Paper II: Kuhmo greenstone belt ...... 21 3.3 Paper III: Suomussalmi greenstone belt ...... 22

4 Discussion ...... 22 4.1 Geochronology and spatial variation of the volcanic rocks ...... 22 4.2 Geochemistry of the felsic and intermediate volcanic rocks ...... 25 4.3 Detrital zircon analyses of the SKT greenstone complex ...... 28 4.4 The tectonic models for the SKT greenstone complex ...... 29 4.5 Future studies ...... 33

5 Conclusions ...... 34

References ...... 35

Appendices: Publications I±III

6 List of original publications

The thesis is based on the following peer-reviewed original publications:

, $VPDOO$UFKDHDQEHOW±GLYHUVHDJHHQVHPEOH$8±3EVWXG\RIWKH7LSDVMlUYL JUHHQVWRQHEHOW.DUHOLD3URYLQFHFHQWUDO)HQQRVFDQGLDQ6KLHOG)LQODQG/LWKRV ±±

,, 8±3E JHRFKURQRORJ\ RI $UFKDHDQ YROFDQLFVHGLPHQWDU\ VHTXHQFHV LQ WKH .XKPRJUHHQVWRQHEHOW.DUHOLD3URYLQFH±0XOWLSKDVHYROFDQLVPIURP0HVRWR 1HRDUFKDHDQDQGD1HRDUFKDHDQGHSRVLWLRQDOEDVLQ"3UHFDPEULDQ5HVHDUFK ±

III The temporal variation of Mesoarchaean volcanism in the Suomussalmi greenstone EHOW.DUHOLD3URYLQFH(DVWHUQ)LQODQG,QWHUQDWLRQDO-RXUQDORI(DUWK6FLHQFHV '2,V\

The publications are referred to in the text by Roman numerals.

Author’s contribution

7KHUHVHDUFKSURMHFWZDVSODQQHGE\(/HKWRQHQ3+|OWWlDQG-+DOOD(/HKWRQHQZDV in charge of planning and performing the sampling and conducting the isotopic analyses of all three papers.

, 7KHVWXG\ZDVSODQQHGE\(/HKWRQHQLQFRRSHUDWLRQZLWK$.lS\DKR8±3E DQDO\VHVZHUHGRQHLQFRRSHUDWLRQGDWDZDVLQWHUSUHWHGDQGWKHDUWLFOHZDVZULW- ten jointly by both authors with the main responsibility on E. Lehtonen.

,, 7KHVWXG\ZDVSODQQHGE\(/HKWRQHQLQFRRSHUDWLRQZLWK7+DONRDKR(+HL- OLPR3+|OWWlDQG$.lS\DKR(/HKWRQHQKHOGWKHPDLQUHVSRQVLELOLW\IRU8± 3EDQDO\VHVLQWHUSUHWLQJWKHJHRFKURQRORJ\GDWDDQGZULWLQJWKHDUWLFOHDQGRWKHU DXWKRUVHGLWHGDQGFRPPHQWHGWKHDUWLFOH(/HKWRQHQDQG(+HLOLPRLQWHUSUHWHG and wrote the elemental geochemistry part in co-operation.

,,, 7KHVWXG\ZDVSODQQHGE\(/HKWRQHQLQFRRSHUDWLRQZLWK7+DONRDKR(+HL- OLPR3+|OWWlDQG++XKPD(/HKWRQHQKHOGWKHPDLQUHVSRQVLELOLW\IRU8±3E DQDO\VHVLQWHUSUHWLQJWKHJHRFKURQRORJ\GDWDDQGZULWLQJWKHDUWLFOHDQGRWKHUDX- WKRUVHGLWHGDQGFRPPHQWHGWKHDUWLFOH(/HKWRQHQDQG(+HLOLPRLQWHUSUHWHG and wrote the elemental geochemistry part in co-operation.

7 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

Abbreviations

SIMS secondary ion mass spectrometry LA-MC-ICPMS laser-ablation multi-collector inductively coupled plasma mass spectrometry the KGB the Kuhmo greenstone belt the SGB the Suomussalmi greenstone belt WKH7*% WKH7LSDVMlUYLJUHHQVWRQHEHOW WKH6.7 WKH6XRPXVVDOPL.XKPR7LSDVMlUYL 8+3 XOWUDKLJKSUHVVXUH ACM active continental margin WPVZ within plate volcanic zone WPB within plate basalt MORB mid ocean ridge basalt BIF banded iron formation

8 /LVWRIWDEOHVDQG¿JXUHV

Table 1 Summary of the studied samplesSDJH Table 2 Tectonic settings for the SKT greenstone complexSDJH

Fig 1 Distribution of the Archaean cratons,SDJH Fig 2 Examples of pillow basalt and spinifex texture in komatiiteSDJH Fig 3 Suggested initiation times for the plate tectonics on EarthSDJH Fig 4 Models for tectonic regime for the ArchaeanSDJH Fig 5 6LPSOL¿HGOLWKRORJLFDOPDSRIWKH.DUHOLD3URYLQFHSDJH )LJ Example of a concordia diagramSDJH Fig 7 The chronostratigraphic interpretation of the SKT greenstone complexSDJH Fig 8 Compilation of the age results from the SKT greenstone complex, page 24 Fig 9 Elemental geochemistrySDJH )LJ *HRWHFWRQLFFODVVL¿FDWLRQSORWVSDJH Fig 11 La/Sm versus Sm/Lu plot of the volcanic rock samplesSDJH Fig 12 Examples of zircon grains from the quartz sandstoneSDJH

9 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

1 Introduction RFHDQLFFUXVW 'DYLHV 7KH$UFKDHDQFUDWRQV )LJHJ%OHHNHU UHSUHVHQWSDUWVRIWKH(DUWK¶VFUXVWWKDW 1.1 What are greenstone belts? have survived crustal recycling processes. Some The early Earth was very different compared RIWKHROGHVWVXSUDFUXVWDODVVHPEODJHV$UFKDHDQ with the modern Earth. No rocks are known JUHHQVWRQHEHOWVWHOOXVDVWRU\RIKRZWKHHDUO\ IURPWKH¿UVWPLOOLRQ\HDUVRIWKH(DUWK¶V Earth evolved towards the modern dynamic plate KLVWRU\DOWKRXJKWKHROGHVWFUXVWDO]LUFRQVSUH- V\VWHP,QDQXWVKHOOWKHWHUP³JUHHQVWRQHEHOW´ served in the detrital record are 4.4 Ga old (e.g. is used to describe a metamorphosed supracrustal :LOGHHWDO9DOOH\HWDO DQGWKHLU EHOW &RQGLH 8VXDOO\WKHJUHHQVWRQHEHOWV trace-element compositions suggest that conti- IRUPHORQJDWHGWHQVWRWKRXVDQGVRINLORPHWHUV QHQWDOFUXVWDOIRUPLQJSURFHVVHVRSHUDWHG long rock assemblages comprising both volcanic million years after Earth’s accretion (Grimes et and sedimentary rocks. Greenstone belts have DO 'XULQJWKH+DGHDQWKH(DUWKDFFUHWHG IRUPHG WKURXJKRXW WKH (DUWK¶V KLVWRU\ IURP and the mantle and the core differentiated (e.g. the Archaean greenstone belts to Phanerozoic :DOWHUDQG7U¡QQHV 7KHROGHVWNQRZQ VXSUDVXEGXFWLRQRSKLROLWHV HJ'LOHNDQG3RODW rocks are the ca. 4 Ga orthogneisses found from EXWWKHFKDUDFWHULVWLFVEHWZHHQ$UFKDHDQ $FDVWD6ODYH&UDWRQ %RZULQJDQG:LOOLDPV DQGSRVW$UFKDHDQEHOWVDUHGLIIHUHQW &RQGLH )LJ 7KH\RXQJ(DUWKZDVDOVRKRWWHU 7KH \RXQJHU JUHHQVWRQH EHOWV WKDQWKHSUHVHQW HJ&RQGLHDQG%HQQDQG contain larger amounts of syn- to postvolcanic UHIHUHQFHVWKHUHLQ DQGLWKDVDOVREHHQVXJJHVW- sedimentary rocks compared with the Archaean ed that the Archaean oceanic crust was thicker greenstone belts. Dominating rock types in and more buoyant compared with modern day Archaean greenstone belts are mafic and

Figure 1. Distribution of Archaean cratons and greenstone belts on Earth, with selected cratons/provinces and JUHHQVWRQHEHOWVPDUNHG)LJXUHPRGL¿HGDIWHU%OHHNHU *% JUHHQVWRQHEHOW

10 Figure 2. ([DPSOHVRISULPDU\YROFDQLFWH[WXUHVSUHVHUYHGLQ$UFKDHDQJUHHQVWRQHEHOWVD VSLQLIH[WH[WXUHLQD NRPDWLLWHRIWKH.XKPRJUHHQVWRQHEHOWDQGE FURVVVHFWLRQRIDSLOORZVWUXFWXUHLQDWKROHLLWLFEDVDOWRIWKH6XRPXVVDOPL greenstone belt. Notice the chilled margins and preserved remnants of gas vesicles in pillows. The diameter of the lens cap is ca. 6 cm and the length of the compass is 12 cm. Photographs by E. Lehtonen.

XOWUDPD¿FYROFDQLFURFNVLHNRPDWLLWHVZLWK well-studied Archaean greenstone belts are the 0J2FRQWHQWRYHUZW $UQGWDQG/HVKHU greenstone belts of the Pilbara craton in Austra- ,WLVJHQHUDOO\DFFHSWHGWKDWWKHIRUPDWLRQ OLDWKH%DUEHUWRQJUHHQVWRQHEHOWLQ6RXWK$I- of high MgO melts requires higher ambient ULFDDQGWKH$ELWLELJUHHQVWRQHEHOWLQ&DQDGD PDQWOH WHPSHUDWXUHV WKDQ WKH PRGHUQ (DUWK VHHHJ&RUIXHWDO9DQ.UDQHQGRQNHW and this might explain why there are not that DO+LFNPDQ)XUQHVHWDO many komatiitic rocks formed after the Archaean Archaean greenstone belts record evidence of the 1LVEHW HW DO $QGHVLWLF FRPSRVLWLRQV $UFKDHDQDWPRVSKHUHDQGK\GURVSKHUHDQGDOVR are rare in Archaean volcanic rocks in general FRQWDLQWKHHDUOLHVWVLJQVRIOLIHDWFD±*D &RQGLH EXW QRW WRWDOO\ ODFNLQJ IURP VHH6FKRSIHWDO 7KHROGHVWVWURPDWROLWH $UFKDHDQJUHHQVWRQHEHOWV HJ3XFKWHOHWDO (ca. 3.43 Ga) are found in a chert from Pilbara 7KXUVWRQDQG.R]KHYQLNRY3DSHU FUDWRQ )LJ$OOZRRGHWDO I and II). Archaean greenstone belts are a key Archaean greenstone belts also bear econom- target in studying the evolution of the early LFLPSRUWDQFHIRUH[DPSOH$X$J&XDQG1L (DUWKDQGWKLVWKHVLVIRFXVHVRQWKHVXSUDFUXVWDO GHSRVLWV HJ&RQGLH 7KHIRUPDWLRQRI sequences formed during the Archaean eon. some of these deposits is linked to volcanic or Greenstone belts were coined owing to the sedimentary processes at certain time period(s) of greenish tint of the volcanic rocks (e.g. Vearn- the evolution of the greenstone belt succession(s) FRPEHHWDO FUHDWHGE\JUHHQPHWDPRU- HJ7KXUVWRQDQG&KLYHUV3DSXQHQHW SKLFPLQHUDOVVXFKDVHSLGRWHFKORULWHDQGDP- DO.LUNHWDO/HFOHUFHWDO phibole formed during greenschist to low am- %OHHNHU/LQGERUJHWDO 6\VWHPDW- phibolite metamorphic conditions. The Archaean LFFKURQRVWUDWLJUDSKLFUHVHDUFKLVEHQH¿FLDODOVR greenstone belts are surrounded by gneissic gran- from the economic point of view. Although the LWRLGVZKLFKUHSUHVHQWYROXPLQRXVO\ODUJHUSUR- Archaean greenstone belts are metamorphosed portion of Archaean lithologies compared with DQGGHIRUPHGSULPDU\IHDWXUHVVXFKDVVSLQL- WKHJUHHQVWRQHEHOWV &RQGLH 7RJHWKHU fex textures in komatiite and pillow structures in these granite-greenstone assemblages form the WKROHLLWLFEDVDOWKDYHEHHQORFDOO\SUHVHUYHG )LJ nuclei of Archaean cratons sharing similar char- 2). Many primary textures and structures imply acteristics on a global scale (Fig. 1). Examples of that the volcanic rocks erupted in subaqueous

11 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

HQYLURQPHQWEXWHYLGHQFHIRUVXEDHULDOHUXS- WKH$UFKDHDQ &DZRRGHWDO DQGVHYHUDO tions have also been reported (e.g. Ransom et WLPHSHULRGVIURPWR!*DKDYHEHHQVXJ- DOVHHGLVFXVVLRQLQ+RIPDQQDQG.XVN\ gested for the initiation time of modern-like plate ,QDGGLWLRQWKHUHVHDUFKRQ$UFKDHDQWHF- tectonics (see references in Fig. 3). Most of the WRQLFVGRHVQRWEHQH¿WRQO\RXUXQGHUVWDQGLQJ models suggest that the plate tectonic processes RIWKHHYROXWLRQRIWKHHDUO\(DUWK HJ.U|QHU started to operate sometime during the Archaean EXWDOVRSURYLGHVHVVHQWLDONQRZOHGJHWR HJGH:LW9DQ.UDQHQGRQNHWDO study the evolution of other terrestrial planets %URZQ'LOHNDQG3RODW6KLUH\HW .RUHQDJD DO DQGLQJHQHUDOLWLVDFFHSWHGWKDWWKH plate tectonics operated throughout the Protero- 1.2 In search of a (plate) ]RLF HJ&RQGLHDQG.U|QHU +RZHYHU tectonic model and the origin questions related to the Archaean tectonics are of the greenstone belts still open and some authors argue that plate tec- The processes responsible for the genera- WRQLFVGLGQRWVWDUWXQWLO3URWHUR]RLFEDVHGRQ tion of the Archaean greenstone belts and the the lack of Archaean ophiolite sequences and surrounding plutonic rocks are under continu- XOWUDKLJKSUHVVXUHPHWDPRUSKLVP 6WHUQ RXVVFLHQWL¿FGHEDWH$QLPSRUWDQWTXHVWLRQLV +DPLOWRQ whether greenstone belts are autochthonous or The predominant tectonic models for the Ar- allochtonous in origin compared with each other chaean Earth can be divided into horizontal and and surrounding plutonic rocks (e.g. Van Kranen- YHUWLFDO+RUL]RQWDOWHFWRQLFPRGHOVDUHVLPLODUWR GRQN9DQ.UDQHQGRQNHWDO ,Q the modern-day tectonic processes and contain the autochthonous models greenstone belts are IHDWXUHVOLNHLVODQGDUFVVXEGXFWLRQ %HQQDQG IRUPHGLQSODFHRQEDVHPHQWURFNVZKHUHDVLQ 0R\HQ DQGODWHUDODFFUHWLRQRIRFHDQLF allochtonous models the volcanic rocks are con- SODWHDXV HJ9RJWDQG*HU\D 9HUWLFDO VLGHUHGWRUHSUHVHQWH[RWLFWHUUDQHVIRUPHGLQ models usually suggest that the lithosphere was unknown locations and later juxtaposed with the WRRZDUPDQGVRIWWRVXEGXFWDQGLQVWHDGVDJ- basement rocks. In order to answer these ques- GXFWLRQZLWKGRZQZDUGGLUHFWHGGLDSLUVODUJH tions geochronology is required. The term “plate mantle overturns or mantle plume upwellings tectonics” is usually used to refer to modern- RSHUDWHG HJ6WHLQDQG+RIPDQ%pGDUG OLNHVXEGXFWLRQGULYHQSODWHWHFWRQLFVZLWKOLWKR- 7KHPRVWSRSXODUPRGHOVIRUWKHWHFWRQLF spheric plates subducting under one another and UHJLPHGXULQJWKH$UFKDHDQDUH VWDJQDQWOLG slab-pull as the main driving force (see discus- ÀDWVXEGXFWLRQDQG HSLVRGLF VXEGXFWLRQ VLRQLQ6WHUQ :KHQDQGKRZVXEGXFWLRQ driven tectonic models (Fig. 4). process initiated on the Earth is one of the main In the stagnant-lid model )LJ D WKH questions related to the evolution of the planet movement of material in the mantle is mainly HJ6WHUQYDQ+XQHQDQG0R\HQ vertical and the crust is not moving horizontally %HUFRYLFLDQG5LFDUG5H\HWDO on a large scale nor is recycled back into the And if the subduction-driven plate tectonics did Earth’s mantle. Upwelling of hot mantle material QRWRSHUDWHLQWKH$UFKDHDQKRZGLGWKHJUHHQ- towards lithosphere creates extension and forms stone belts and the surrounding plutonic rocks QHZ OLWKRVSKHUH ZKHUHDV VPDOO SURSRUWLRQV IRUP"%DVHGRQSDOHRPDJQHWLFGDWDLQGLYLGXDO of older lithosphere might be recycled back pieces of lithosphere were moving laterally in into the mantle via delamination. Nd isotopic

12 Figure 3. Selection of suggested times for the initiation of plate tectonics on Earth, and arguments which they are EDVHGRQ0RGL¿HGIURP.RUHQDJD data from the Abitibi greenstone belt and and mantle wedge would not form (Smithies et +I LVRWRSH GDWD IURP +DGHDQ DQG $UFKDHDQ DO +RZHYHUWKHÀDWVXEGXFWLRQPRGHO zircon grains support the interpretation that the during the Archaean has been challenged by VWDJQDQWOLG PRGHO ZDV RSHUDWLYH EHIRUH QXPHULFDOPRGHOOLQJ YDQ+XQHQHWDO *D 'HEDLOOHHWDO*ULI¿QHWDO According to WKH VXEGXFWLRQ PRGHO 7KHÀDWVXEGXFWLRQPRGHOargues that due to subduction was operating during the Archaean SK\VLFDOSURSHUWLHVRIWKH$UFKDHDQOLWKRVSKHUH )LJ F HJ )XUQHV HW DO \HW VRPH VXEGXFWLRQRIOLWKRVSKHULFSODWHVZDVÀDWUHVXOWLQJ authors suggest that it took place only as episodic LQGLVSHUVHGYROFDQLVPDERYHWKHÀDWVXEGXFWLRQ “protosubduction” and was not continuous (e.g. ]RQH )LJE$EERWHWDO6PLWKLHVHW 6WHUQ YDQ +XQHQ DQG 0R\HQ DO0DUWLQHWDO )ODWVXEGXFWLRQ Based on extensive geochemical comparison would have produced melts at shallow depths of immobile elements of basaltic rocks from

13 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

$UFKDHDQJUHHQVWRQHEHOWVRIGLIIHUHQWFUDWRQV )RUWKLVWKHVLVWKH6XRPXVVDOPL.XKPR7LSDV- )XUQHV HW DO VXJJHVWHG WKDW RI MlUYL KHUHDIWHU6.7 JUHHQVWRQHFRPSOH[ )LJ the belts were formed in a subduction-like 5) was selected because it is the largest Archae- HQYLURQPHQWDQGRQO\DPLQRULW\LQVXEGXFWLRQ an greenstone complex in Finland and has been XQUHODWHGHQYLURQPHQWVVXFKDVSOXPHVHDÀRRU PDSSHGLQGHWDLO+RZHYHUWKHUHVHDUFKRQWKLV spreading or continental rift environments. A FRPSOH[KDVFRQFHQWUDWHGPDLQO\RQPD¿FDQG remnant of a subducted slab has been found XOWUDPD¿FYROFDQLFURFNV HJ+DONRDKRHWDO ZLWKVHLVPLFLPDJLQJEHORZWKHFD± 0DLHUHWDO $OVRVHYHUDOGLIIHUHQW Ga Archaean Abitibi greenstone belt (Calvert stratigraphic interpretations have been suggest- HW DO &DZRRG HW DO DQG WKH ed for the SKT greenstone complex (e.g. Tai- geochemical signatures of the volcanic rocks SDOH3LLUDLQHQ3DSXQHQHWDO there carry a subduction-like signature (see +XKPDHWDOD/LQGERUJHWDO3D- GLVFXVVLRQLQ%HQQDQG0R\HQ ,WKDV SHUV,±,,, 7KH6.7JUHHQVWRQHFRPSOH[FRQ- EHHQDUJXHGKRZHYHUWKDWXVLQJJHRFKHPLVWU\ tains the oldest recorded volcanic rocks (ca. 2.94 for interpreting tectonic regimes might not be *D LQ)LQODQG 9DDVMRNLHWDO+XKPD VR UHOLDEOH EHFDXVH LW UHÀHFWV WKH SURSHUWLHV HWDOD3DSHU,,, 7KH\RXQJHVWYROFD- RI WKH VRXUFH DQG PHOWLQJ FRQGLWLRQV UDWKHU nic rocks in the other parts of the complex have WKDQLQGLYLGXDOWHFWRQLFSURFHVVHV YDQ+XQHQ \LHOGHGDJHVRIFD±*DDQGWKHUHIRUH DQG0R\HQ&RQGLH $QDO\VHVRI the whole complex seems to preserve geologi- large global geochemical datasets have shown FDOKLVWRU\RYHUDWLPHSHULRGRIFDPLO- that even classifying modern-day basalts in OLRQVRI\HDUV +XKPDHWDOD3DSHUV,± GLIIHUHQWWHFWRQLFUHJLPHVLVGLI¿FXOW /LHWDO ,,, +XKPDHWDO DE FRQ¿UPHGWKDW DQGWKH(DUWK¶VG\QDPLFVLQWKH+DGHDQ DJHYDULDWLRQEHWZHHQDQGSRVVLEO\DOVRZLWKLQ and Archaean might have been different different individual greenstone belts can be ob- IURP WKRVH RQ PRGHUQ (DUWK &RQGLH served. The results emphasized the importance of absolute ages from the felsic volcanic rocks 1.3 Geologic setting of these belts in search of detailed understand- The Archaean nucleus of the Fennoscandian ing of the geochronology and chronostratigra- 6KLHOGLVGLYLGHGLQWR¿YHSURYLQFHV.DUHOLD phy of the SKT greenstone complex. With new 1RUUERWWHQ.ROD%HORPRULDQDQG0XUPDQVN DJHGHWHUPLQDWLRQVWKLVWKHVLVDLPVWRSURYLGH )LJ6ODEXQRYHWDO+|OWWlHWDO a more detailed chronostratigraphic interpreta- 7KH.DUHOLDSURYLQFH KHUHDIWHU.DUHOLD tion of the supracrustal rock assemblages from is further divided into three subprovinces: Vod- the SKT greenstone complex. By combining OR]HUR&HQWUDO.DUHOLDDQG:HVWHUQ.DUHOLD7KH SUHYLRXVO\ SXEOLVKHG DQG QHZ GDWD LW LV DO- 6XRPXVVDOPL.XKPR7LSDVMlUYLJUHHQVWRQHEHOW so possible to more closely evaluate the rela- belongs to the Western Karelia subprovince. tionships between individual greenstone belts. The Archaean greenstone belts of Finland have been studied in detail during the past de- 1.4 Previously suggested tectonic models for the FDGHV HJ +DQVNL /XXNNRQHQ Suomussalmi-Kuhmo-Tipasjärvi 3LLUDLQHQ9DDVMRNLHWDO+DONR- greenstone complex DKRHWDO3DSXQHQHWDO+XKPD Literature related to the tectonic environments HWDODE/XXNNRQHQHWDO of the greenstone belts of Karelia is extensive.

14 Figure 4. 0RGHOVIRUWKH$UFKDHDQWHFWRQLFUHJLPHD SOXPHVWDJQDQWOLGWHFWRQLFVE VKDOORZÀDWVXEGXFWLRQSODWHWHFWRQLFV 77* WRQDOLWHWURQGKMHPLWHJUDQRGLRULWH DQGF HSLVRGLF VXEGXFWLRQSODWHWHFWRQLFVFRPSDUDEOHWRWKHPRGHUQ(DUWK )LJXUHPRGL¿HGDIWHU&DZRRGHWDO

Almost all the modern-like tectonic settings 3LLUDLQHQ 7KH¿UVWVWDJHRIJUHHQVWRQH have been applied to the Karelian greenstone EHOWIRUPDWLRQZDVGRZQZDUSLQJVXEGXFWLRQ EHOWVRFHDQLFSODWHDXV HJ3XFKWHOHWDO DQGSDUWLDOPHOWLQJRIWKHRFHDQLFFUXVWIROORZHG 0DLHUHWDO+|OWWlHWDO LVODQG by a failed rift and bimodal volcanism. The failed DUFV DQG EDFNDUF EDVLQV HJ 3XFKWHO HW DO ULIWZDVDJDLQIROORZHGE\VXEGXFWLRQDQGWKH DQGDUFVHWWLQJVZLWKFRQWLQHQWDOLQSXW last phase of evolution was isostatic elevation HJ7KXUVWRQDQG.R]KHYQLNRY+|OWWl of the crust. HWDO 7KHWHFWRQLFPRGHOVVXJJHVWHGIRU the SKT greenstone complex are the following: 2) Plume-related rift environment Another model for the formation of the SKT 1) Failed rift followed by the formation of a greenstone complex is a plume-related continen- subduction zone WDOULIWHQYLURQPHQW /XXNNRQHQ3DSXQHQ Piirainen (1988) interpreted the volcanic rocks HWDO ,QWKLVPRGHODWKHUPDOSOXPHZDV of the SKT greenstone complex having been introduced under an older sialic crust (which was formed in a failed rift environment followed by interpreted to comprise the volcanic rocks that subduction. According to this model the Kuhmo have in later studies been shown to be ca. 2.94 greenstone belt can be divided into two groups *D DQGWKH¿UVWFDOFDONDOLQHYROFDQLFURFNV based on lithostratigraphy: one with mainly ZHUHIRUPHG$VWKHVLDOLFFUXVWFRQWLQXHGULIWLQJ tholeiitic-komatiitic rocks and another with WKROHLLWLFEDVDOWLFODYDVZHUHHUXSWHGIROORZHGE\ ELPRGDOYROFDQLFURFNV$FFRUGLQJWRWKLVPRGHO komatiitic lavas and minor felsic volcanic rocks. all three greenstone belts share the same history $IWHUWKHGHFOLQLQJRIWKHWKHUPDOSOXPHORZ-

15 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

Figure 5. 6LPSOL¿HGOLWKRORJLFDOPDSRIWKH.DUHOLD3URYLQFH0DSPRGL¿HGDIWHU.RLVWLQHQHWDO $JHGDWD IURP3DSHUV,±,,,.R]KHYQLNRYHWDO 6YHWRYHWDO 0DWUHQLFKHYHWDO +XKPDHWDO D DQG$UHVWRYDHWDO 6.7 6XRPXVVDOPL.XKPR7LSDVMlUYL

HUFUXVWZDVUHPHOWHGZKLFKSURGXFHGWKHODVW 3) Oceanic plateau (Kuhmo-Tipasjärvi) and con- phase of calc-alkaline volcanism. The sedimen- tinental rift (Suomussalmi) tary cover was deposited after the end of the vol- The most recent proposed tectonic model for FDQLVP+RZHYHU6P1GLVRWRSHGDWDVXJJHVW formation of the komatiitic rocks of the SKT that when the volcanic rocks of the Kuhmo and greenstone complex is based on their geochem- 7LSDVMlUYLEHOWVIRUPHGVLJQL¿FDQWO\ROGHUFRQWL- LVWU\ 0DLHUHWDO %DVHGRQWKHSULPLWLYH QHQWDOFUXVWZDVQRWSUHVHQWFRQWUDU\WRWKH6XR- =U1EDQG1E7KUDWLRV0DLHUHWDO VXJ- PXVVDOPLJUHHQVWRQHEHOW +XKPDHWDOE JHVWHGWKDWLQWKH.XKPRDQG7LSDVMlUYLJUHHQ- stone belts the komatiitic rocks erupted in an oce- DQLFSODWHDXVHWWLQJZKHUHDVLQWKH6XRPXVVDOPL

16 greenstone belt they erupted in a continental rift- RXVURFNVDPSOH +\WWLPlNLPLFURJUDQXODUIHO- related environment. The oceanic plateau setting VLFURFN$3DSHU,, ZDVGLI¿FXOWWRGH¿QH is challenged by felsic xenoliths that have been DQGWKHUHIRUHLWKDVEHHQOHIWRXWRIWKH¿QDO IRXQGLQXOWUDPD¿FDQGPD¿FYROFDQLFURFNVRI interpretation. All plutonic rock samples were the Kuhmo greenstone belt and are suggested to collected from the Kuhmo greenstone belt in or- derive from pre-existing felsic crust (Papunen et der to study the relationships of the plutonic and DO %DVHGRQ6P1GLVRWRSHGDWDKRZHY- volcanic rocks in the area. The sedimentary rocks HUWKH[HQROLWKVUHSUHVHQWMXYHQLOHVRXUFH +XK- were collected in order to compare their zircon PDHWDOE age populations with the adjacent volcanic rocks The suggested tectonic models for the SKT and estimate the maximum deposition age of the greenstone complex will be discussed more de- sedimentary rocks. For planning of the sampling tail in Chapter 4.4 in the light of the new results VLWHVPDSSLQJDQGGULOOFRUHORJJLQJLQIRUPDWLRQ 3DSHUV,±,,, previous geochronological studies (e.g. Vaasjoki HW DO +XKPD HW DO D DV ZHOO DV 1.5 Aims of the study structural interpretations (e.g. unpublished drill The aims of this thesis are: core reports by Geological Survey of Finland to constrain detailed chronostratigraphic in- DQG2XWRNXPSX2\7DLSDOH ZHUHXWLOL]HG terpretation from the STK greenstone com- 3DSHUV,±,,,LQFOXGHGHWDLOHGGHVFULSWLRQRIWKH SOH[ 3DSHUV,±,,, zircon grain separation methods used. to provide neutral stratigraphic nomenclature Mainly felsic and intermediate volcanic and for the SKT greenstone complex for form- plutonic rock samples were collected in order to ing as basis for future stratigraphic research maximize the probability of gaining zircon grains 3DSHUV,±,,, for age determinations. Almost half of the sam- to study the detrital zircon record from the ples from the Kuhmo and Suomussalmi green- sedimentary rocks within the greenstone stone belts were collected from the drill cores EHOWV 3DSHUV,±,,, DQGWKHQHZVDPSOHVIURPWKH7LSDVMlUYLJUHHQ- to compare the age and geochemistry of the stone belt from outcrops. The drill cores offer a volcanic rocks from different belts (this the- window to the bedrock in areas that are largely sis) FRYHUHGE\4XDWHUQDU\WLOODQGPRUDLQH+RZHY- to evaluate suggested tectonic models for the HUVDPSOLQJGULOOFRUHVLVQRWZLWKRXWSUREOHPV SKT greenstone complex in the light of the because contacts between different rock units can QHZUHVXOWV 3DSHUV,,DQG,,,WKLVWKHVLV usually be observed only on a centimetre scale.

2.2 The U–Pb method and 2 Sampling, methodology statistics of geochronology and terminology Geochronological studies from Archaean greenstone belts can be used for reconstructing con- 2.1 Sampling WLQHQWDOJURZWK .U|QHU 'DWLQJ$UFKDH- )URPWKUHHVHSDUDWHJUHHQVWRQHEHOWVLQWRWDO DQHYHQWV]LUFRQLVWKHPRVWLPSRUWDQWPLQHUDO VDPSOHV YROFDQLFSOXWRQLFVHGLPHQWDU\ because it is chemically and mechanically dura- URFNVDQGRQHPHWDLJQHRXVURFN7DEOH ZHUH EOHFRPPRQLQIHOVLFDQGLQWHUPHGLDWHPDJPDW- studied. The primary nature of one metaigne- ic rocks and as a detrital mineral in sedimentary

17 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

URFNVXVXDOO\KDVKLJK8FRQWHQWDQGGLVFULPL- PRQUDSLGSUHFLVHDQGDFFXUDWH%RWKVHFRQG- nates the daughter isotopes of Pb during crystal- ary ion mass spectrometry (SIMS) and laser-ab- OL]DWLRQ 'DYLVHWDO 7KH8±3EPHWKRG lation multi-collector inductively coupled plas- is based on the decay of 238U to Pb (half-life ma mass spectrometry (LA-MC-ICPMS) tech- *D DQG235U to 3E KDOIOLIH niques are suitable for geochronological studies Ga). Both of these systems should give the same of the Archaean greenstone belts. In the SIMS age if there was no gain or loss of U or Pb af- PHWKRGLVRWRSHFRPSRVLWLRQRIDVPDOOGLDPH- WHUWKHIRUPDWLRQRIWKHURFN3UDFWLFDOO\8±3E WHUDUHD P LVDEODWHGZLWKDKLJKHQHUJ\ JHRFKURQRORJ\LVWKHUPRFKURQRORJ\LQD]LUFRQ LRQEHDPXQGHUYDFXXP ,UHODQGDQG:LOOLDPV grain the age indicates the temperature in which VHHDOVRGLVFXVVLRQLQ6FKRHQH 7KH the system cooled under the temperature where VDPSOLQJGHSWKLVW\SLFDOO\ P7KHVHSDUDP- GDXJKWHULVRWRSHV 3E FHDVHWRVLJQL¿FDQWO\GLI- eters give a good spatial control and possibility fuse from the crystal structure of the zircon grain to analyze different parts of grains individually. anymore. The magmatic closure temperature of Ablated material is introduced into a mass spec- ]LUFRQLVFD&DQGWKHUHVHWWLQJWHPSHUDWXUH trometer with high mass resolution. In LA-MC- LVHYHQKLJKHU HJ/HHHWDO*DUGpVDQG ,&306PHWKRGODVHULVXVHGIRUDEODWLQJWKH 0RQWHO VXUIDFHRIWKHDQDO\]HGPDWHULDOZKLFKLVWKHQ 'XULQJWKHSDVWIHZGHFDGHVWHFKQLTXHVDQG carried by a carrier gas into inductively coupled UHVHDUFKPHWKRGVKDYHDGYDQFHGDQGGLYHUVL¿HG plasma which ionizes the material (see discus- and analysis methods that can analyze parts of VLRQLQ6FKRHQH 7KHPDVVGLIIHUHQFHVRI the individual grains have become more com- the ionized material are then analyzed with mass

Table 1. Summary of the samples studied from the greenstone belts and related methods.

Suomussalmi Kuhmo Tipasjärvi

Volcanic rock VDPSOHV Q 65 10

Plutonic rock VDPSOHV Q 5

Sedimentary rock VDPSOHV Q 2* 2 2

Metaigneous rock VDPSOHV Q 1

Analysis method SIMS, SIMS, SIMS LA-MC-ICPMS LA-MC-ICPMS Paper III II I

*including one volcanogenic sedimentary rock sample

6,06 VHFRQGDU\LRQPDVVVSHFWURPHWHU

/$0&,&306 ODVHUDEODWLRQPXOWLFROOHFWRULQGFXWLYHO\FRXSOHGSODVPDPDVVVSHFWURPHWHU

18 VSHFWURPHWHU7KH8±3E]LUFRQDQDO\VHVIRU3D- ,IWKH06:'LVKLJKHUWKDQRQHLWLPSOLHVWKDW SHUV,±,,,ZHUHFDUULHGRXWZLWK&DPHFD,,,06 the scatter in the analytical result is higher than 6,06DWWKH1RUGVLPODERUDWRU\6ZHGLVK what can be explained with analytical errors. If 0XVHXPRI1DWXUDO+LVWRU\DQGIRU3DSHUV,, WKH06:'RIFRQFRUGDQFHLV!WKHSURED- and III also with LA-MC-ICPMS at the Finn- ELOLW\RIFRQFRUGDQFHLV /XGZLJ LVK,VRWRSH*HRVFLHQFHV/DERUDWRU\*HRORJLFDO MSWD value for concordance can be also re- 6XUYH\RI)LQODQGLQ(VSRR'HWDLOHGWHFKQLFDO ported as MSWD for combined concordance and GHVFULSWLRQVRIWKH8±3EDQDO\VLVPHWKRGVDUH ;

19 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

,QIRUPDO FODVVL¿FDWLRQ LV XVHG LQVWHDG RI S\UR[HQHVSLQHODQGLQJDUQHWDQGWKXVQRWWUDQV- IRUPDOOLWKRVWUDWLJUDSKLFFODVVL¿FDWLRQEHFDXVH fer from solid into liquid in the melting process stratigraphic positions and lithological charac- of the mantle. Lu is compatible in garnet and teristics of different age phases are unclear in do not transfer from solid into liquid if source SODFHV7KHUHIRUH LQ WKH LQWHUSUHWDWLRQV PDGH FRQWDLQJDUQHW'XULQJORZGHJUHHPHOWLQJWKH LQWKLVWKHVLVDQGRULJLQDOSDSHUVDXQLWEDVHG amount of incompatible elements in the melt is FODVVL¿FDWLRQLVFRQVLGHUHGWREHDQHXWUDODS- KLJKFRPSDUHGWRFRPSDWLEOHHOHPHQWVEXWGH- proach to assemble the age groups together to crease with increasing amount of melting. In low enable clear comparison and discussion of the GHJUHHPHOWV/DDQGRWKHUOLJKW5(( /D(X UHVXOWV,QWKHQDPLQJRIWKHVHXQLWVSUHYLRXV DUHHQULFKHGPRUHHI¿FLHQWO\LQWRWKHPHOWFRP- lithostratigraphic nomenclature has been used SDUHGWRWKHKHDY\5(( +R/X 7KHUHIRUH/D ZKHUHUHDVRQDEOH+RZHYHUIRUH[DPSOHLQWKH Sm and Sm/Lu ratios can be used to evaluate FDVHRIWKH7LSDVMlUYLJUHHQVWRQHEHOWGHSHQGLQJ melt evolution. RQWKHDXWKRURQO\RQHRUWZRIHOVLFLQWHUPHGLDWH Tectonic discrimination diagrams by Schandl volcanic formations were previously described DQG*RUWRQ XWLOL]HKLJK¿HOGVWUHQJWKHOH- DQGQDPHG .RLYXPlNLDQG7DLYDOMlUYL)RUPD- PHQWUDWLRV 7K7D7K+I7D+IDQG7K

20 in drawing interpretations based on trace ele- stone belt is the Kokkoniemi unit and consists PHQWJHRFKHPLVWU\RQO\)XUWKHUPRUH6FKDQGO RIVHGLPHQWDU\PDWHULDOGHSRVLWHG*D DQG*RUWRQ HPSKDVL]HGWKHLPSRUWDQFH of high-quality analytical data in the case of low 3.2 Paper II: Kuhmo greenstone belt FRQFHQWUDWLRQHOHPHQWV HJ+I7DDQG7K 3DSHU,,SUHVHQWV8±3EJHRFKURQRORJLFDOGDWD (SIMS and LA-MC-ICPMS) and geochemical GDWDRQWKHIHOVLFLQWHUPHGLDWHYROFDQLFURFNV 3 Review of the original sedimentary rocks and granitoids in the Kuhmo publications greenstone belt. Whole-rock geochemistry is al- VRSUHVHQWHGIURPWKHYROFDQLFVHGLPHQWDU\DQG 3.1 Paper I: Tipasjärvi granitoid rocks. The objective of the study was greenstone belt to resolve the age range of the volcanism and 3DSHU,SUHVHQWV8±3EJHRFKURQRORJ\ 6,06 decipher in detail 1) whether the main belt con- and geochemical data on the felsic-intermedi- WDLQVYROFDQLFURFNVRI*D ZKDWLVWKH ate volcanic and sedimentary rocks of the Ti- age of the youngest volcanic phase containing SDVMlUYLJUHHQVWRQHEHOW:KROHURFNJHRFKHP- KLJK&UEDVDOWV DQGZKDWDUHWKHPD[LPXP istry was used to characterise the volcanic rock deposition ages for the sedimentary material at samples and to compare them to the tonalitic the immediate vicinity of the belt. The age re- URFNVDURXQGWKH7LSDVMlUYLJUHHQVWRQHEHOW7KH sults on the volcanic rocks revealed that the fel- aim of the paper was to study the age range of sic-intermediate volcanism occurred in two ma- the felsic-intermediate volcanism in the Tipas- MRUHSLVRGHVFD*DDQGFD±*D MlUYLJUHHQVWRQHEHOW*HRFKURQRORJLFDOUHVXOWV Both episodes were interpreted to comprise also from the volcanic rocks revealed that the felsic- PD¿FDQGXOWUDPD¿FYROFDQLVP7KHDJHUHVXOWV intermediate volcanism has occurred in three dis- from the granitoid rocks revealed that the ma- WLQFWHSLVRGHVFD*D*DDQG*D jority of the granitoid magmatism in the imme- 7KLVVWXG\ZDVWKH¿UVWRQHWRUHFRUG*D diate vicinity of the belt was contemporaneous YROFDQLFURFNVIURPWKH7LSDVMlUYLJUHHQVWRQH ZLWKWKH\RXQJHVWYROFDQLFSKDVHFD± Based on these age results and spatial relation- *D7KH\RXQJHVWGHWULWDO]LUFRQSRSXODWLRQVFD VKLSVRIWKHGLIIHUHQWYROFDQLFURFNVXOWUDPD¿- *DDQG*DLQWKHFRQJORPHUDWHDQG FDQGPD¿FYROFDQLFURFNVZHUHIRUPHG TXDUW]ULFKVDQGVWRQHUHVSHFWLYHO\LPSO\WKDW *DDQG*D$JHUHVXOWVRIWKHVHGLPHQ- WKHVHGLPHQWDU\PDWHULDOZDVGHSRVLWHGFD± WDU\URFNVLQWHUSUHWHGWRUHSUHVHQWWKH\RXQJ- 0\UDIWHUWKHFHVVDWLRQRIWKHYROFDQLVP7KH HVWSKDVHRIWKHJUHHQVWRQHEHOWVXFFHVVLRQFRQ- VHGLPHQWDU\PDWHULDODOVRFRQWDLQV]LUFRQJUDLQV ¿UPHGWKDWROGHUFUXVWDOPDWHULDO !*D SUR- which pre-date the oldest volcanism along the duced part of the detritus. Based on the young- belt and imply that older crustal material was HVWGHWULWDO]LUFRQDJHSRSXODWLRQWKHGHWULWXV available during their deposition. The combina- was deposited tens of millions of years after tion of previously published and new results sug- the end of the volcanism. These results suggest gest a chronostratigraphic interpretation for the WKDWWKH7LSDVMlUYLJUHHQVWRQHEHOWFRQWDLQVWKUHH Kuhmo greenstone belt comprise two volcanic felsic and intermediate volcanic units (Talassuo and one mainly sedimentary unit: the Nuolikan- *D+LHWDMlUYL*D.RLYXPlNL JDV *D 6LLYLNNRYDDUD ±*D DQG *D 7KH\RXQJHVWXQLWLQWKH7LSDVMlUYLJUHHQ- 5RQNDSHUl *D XQLWVUHVSHFWLYHO\

21 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

WHUSUHWDWLRQV HJ7DLSDOH3LLUDLQHQ 3DSXQHQHWDO+XKPDHWDOD/LQG- 3.3 Paper III: Suomussalmi ERUJHWDO 7KHVHDUHUHYLHZHGDQGGLV- greenstone belt FXVVHGLQWKHRULJLQDOSDSHUV 3DSHU,,,DQG,,, 3DSHU ,,, SUHVHQWV 8±3E JHRFKURQRORJLFDO One of the main goals of this thesis was to con- (SIMS and LA-MC-ICPMS) and geochemical struct a chronostratigraphic model for the green- data on the felsic and intermediate volcanic and VWRQHEHOWVZLWKV\VWHPDWLFSUR¿OHVDPSOLQJ(DU- the sedimentary rocks from the Suomussalmi OLHUZRUNE\+XKPDHWDO D RQWKH6.7 greenstone belt. The aim of this paper was to JUHHQVWRQHFRPSOH[DOUHDG\LGHQWL¿HGDJHYDULD- study the relationship of the volcanic rocks tion in the felsic and intermediate volcanic rocks. in the Kiannanniemi area with the other parts New geochronological results reported in Papers of the Suomussalmi greenstone belt. The ,±,,,VXSSRUWWKHLQWHUSUHWDWLRQWKDWDJHYDULDWLRQ geochronological results from the volcanic rocks FDQEHREVHUYHGQRWRQO\EHWZHHQGLIIHUHQWEHOWV revealed that the felsic-intermediate volcanism in EXWDOVRZLWKLQWKHEHOWV)XUWKHUPRUHWKHFRP- the Kiannanniemi area occurred in three separate bined data from earlier works and from Papers HSLVRGHV*D*DDQG*D7KH ,±,,,SHUPLWDPRUHGHWDLOHGJHRFKURQRORJLFDO 2.84 Ga volcanic phase has not previously been comparison between the different belts. In con- recognized from the Suomussalmi greenstone WUDVWWRSUHYLRXVVWXGLHV 3DSXQHQHWDO EHOW 6SDWLDO UHODWLRQVKLSV EHWZHHQ PD¿F DQG +XKPDHWDOD/LQGERUJHWDO 3D- ultramafic volcanic rocks of different age SHU,VKRZVWKDWWKH7LSDVMlUYLJUHHQVWRQHEHOWLV JURXSV VXJJHVW WKDW WKH PD¿F DQG XOWUDPD¿F comprised of three felsic-intermediate volcanic volcanism was also episodic. The youngest SKDVHV*D*DDQG*D7KHUH- detrital zircon population from a greywacke-like sults in Paper II support the previous suggestion sedimentary rock implies that the sedimentary +XKPDHWDOD WKDWWKH.XKPRJUHHQVWRQH PDWHULDOGHSRVLWHGFD*D7KLVVDPSOH belt contains ca. 2.84 Ga intermediate volcanic DOVR FRQWDLQHG ]LUFRQ JUDLQV ZKLFK SUHGDWH URFNVDQGWKLVDJHSKDVHLVQRZLQFOXGHGWREH WKH ROGHVW YROFDQLVP DORQJ WKH EHOW DQG a part of the evolution of the Kuhmo greenstone imply that while the sedimentary material was EHOW 1XROLNDQJDVXQLW)LJ 5HVXOWVRI3DSHU EHLQJ GHSRVLWHG ROGHU FUXVWDO PDWHULDO ZDV III also indicate that the previously unknown 2.84 available. Paper III divides the Suomussalmi *DYROFDQLFSKDVHFRQWHPSRUDQHRXVZLWKVRPH greenstone belt into four chronostratigraphic RIWKHYROFDQLFURFNVLQWKH7LSDVMlUYLDQG.XK- XQLWV /XRPD *D 7RUPXD *D PRJUHHQVWRQHEHOWVLVIRXQGDOVRLQWKH6XR- $KYHQODKWL *D DQG0HVDDKR *D mussalmi greenstone belt. Based on the geochronological results of Pa- SHUV,±,,,DQGSUHYLRXVO\SXEOLVKHGVWXGLHV HJ 4 Discussion +XKPDHWDODDQGUHIHUHQFHVLQWKHUHLQ four major felsic and intermediate volcanic epi- 4.1 Geochronology and spatial sodes can be observed in the SKT greenstone variation of the volcanic rocks FRPSOH[FD*D*D*DDQG Previous stratigraphic interpretations from the ±*D,QDGGLWLRQWRWKHLQWHUSUHWDWLRQV SKT greenstone complex have mainly been based on the ages from the felsic and intermedi- lithostratigraphic or rock type stratigraphic in- DWHURFNVDWKROHLLWLFSODJLRFODVHXUDOLWHSRUSK\-

22 ULWLFURFN\LHOGHGDQDJHRIFD*D +XKPD The *DIHOVLFDQGLQWHUPHGLDWHYRO- HWDOD DQGLWKDVEHHQLQFOXGHGLQWKH FDQLFHYHQW is recognized from all three green- chronostratigraphic model of the Suomussalmi stone belts. These volcanic rocks are found in greenstone belt (Paper III). Compilation of chro- the western and eastern margins of the Tipas- nostratigraphic interpretations of the SKT green- MlUYLDQG.XKPRJUHHQVWRQHEHOWVUHVSHFWLYHO\ stone complex is presented in Figure 7. )LJVDQGFG+XKPDHWDOD3DSHUV ,DQG,, DQGLQWKHHDVWHUQPDUJLQRIWKH.L- The events are as following (Figs. 7 and 8): annanniemi area (the Suomussalmi greenstone Ca. *DIHOVLFDQGLQWHUPHGLDWHYROFD- EHOW)LJE3DSHU,,, 7KH*DYROFDQLF QLFURFNVhave only been found only in the Suo- event in the Suomussalmi and Kuhmo green- PXVVDOPLJUHHQVWRQHEHOW )LJVDQG+XKPD VWRQHEHOWVLQFOXGHVDOVRVHGLPHQWDU\LQWHUOD\HUV HWDOD3DSHU,,, 6SDWLDOO\WKLVDJHJURXS komatiitic rocks and tholeiitic basalts (Papers II is found in the eastern margins of the Luoma area DQG,,, DQGIRUWKH7LSDVMlUYLJUHHQVWRQHEHOW DQGWKH.LDQQDQQLHPLDUHD )LJE9DDVMRNLHW PD¿FDQGXOWUDPD¿FYROFDQLFURFNVGHSRVLWHG DO+XKPDHWDOD3DSHU,,, 6SD- EHWZHHQ*DDQG*D 3DSHU, tial relationships of the felsic-intermediate and The *DIHOVLFDQGLQWHUPHGLDWHYROFD- PD¿FXOWUDPD¿FYROFDQLFURFNVLQGLFDWHWKDWWKLV QLFURFNVDUHUHFRUGHGIURPWKH7LSDVMlUYLDQG YROFDQLFSKDVHDOVRLQFOXGHVPD¿FDQGXOWUDPD¿F 6XRPXVVDOPLJUHHQVWRQHEHOWV )LJVDQG volcanic rocks (Paper III). +XKPDHWDOD3DSHUV,DQG,,,VHHDO-

Figure 7. Chronostratigraphic interpretation of the Suomussalmi-Kuhmo-Tipasjärvi greenstone complex. More detailed FKURQRVWUDWLJUDSKLFLQWHUSUHWDWLRQVDUHVKRZQLQ3DSHUV,±,,,'DWDIURP9DDVMRNLHWDO +XKPDHWDO D and Papers I–III. Grey bars mark possible hiatus/unconformity.

23 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40 so discussion in Paper II). The 2.82 Ga volca- mo greenstone belt suggest that the Nuolikangas nic phase of the Suomussalmi greenstone belt XQLWLVGLUHFWO\LQFRQWDFWZLWKXOWUDPD¿FURFNV was interpreted to also contain komatiitic and LQWHUSUHWHGWREHORQJWRWKH±*D6LLYLN- EDVDOWLFURFNVDQGWKHVHYROFDQLFURFNVFDQEH NRYDDUDXQLW 7+DONRDKRSHUVFRPP found across the greenstone belt (Fig. 8b). On- This might imply that the 2.82 Ga age group is ly one sample yielded an age of ca. 2.82 Ga in QRWSUHVHQWLQWKH6LLYLNNR.HOORMlUYLDUHDRIWKH WKH7LSDVMlUYLJUHHQVWRQHEHOW )LJG 2EVHU- .XKPRJUHHQVWRQHEHOWHYHQWKRXJKVRPHVX- vations from a new drill core that pierces the pracrustal felsic rocks of the northern part of the *DDQG*DYROFDQLFXQLWVLQWKH.XK- Kuhmo greenstone belt contain 2.82 Ga mate-

Figure 8. Compilation of the age results of volcanic and plutonic rocks from the Suomussalmi-Kuhmo-Tipasjärvi greenstone FRPSOH[D ZKROHFRPSOH[E WKH6XRPXVVDOPLJUHHQVWRQHEHOWF WKH.XKPRJUHHQVWRQHEHOWDQGG WKH7LSDVMlUYL JUHHQVWRQHEHOW'DWDIURP3DSHUV,±,,,9DDVMRNLHWDO .lS\DKRHWDO +HLOLPRHWDO 0LNNROD HWDO DQG+XKPDHWDOD)LJXUHVKDYHEHHQVLPSOL¿HGDIWHU/XXNNRQHQDQG6RUMRQHQ:DUG 0LNNROD 3DSXQHQHWDO DQG+DONRDKRDQG1LVNDQHQ )RUPRUHGHWDLOHGOLWKRORJLFDOPDSVDQGGULOOFRUH VHFWLRQVVHH3DSHUV,±,,,6HGURFN VHGLPHQWDU\URFN%,) EDQGHGLURQIRUPDWLRQ

24 ULDO VDPSOHV$DQG$)LJD+XKPD PDHWDOD 7KH.RVWRPXNVKDJUHHQVWRQH HWDOD belt (Figs. 5) shares similarities with the young- The ±*DIHOVLFDQGLQWHUPHGLDWH est volcanic rocks of the Kuhmo greenstone belt YROFDQLFURFNVDUHIRXQGLQWKH7LSDVMlUYLDQG LQWKHVHQVHWKDWD8±3EDJHRI0D .XKPRJUHHQVWRQHEHOWVEXWQRWLQWKH6XRPXV- has also been reported from a silica-rich inter- VDOPLJUHHQVWRQHEHOW )LJVDQG+XKPDHW layer in a section comprised of basaltic and kom- DOD3DSHUV,DQG,,, ,QWKH7LSDVMlUYL atiitic rocks as well as banded iron formations DQG .XKPR JUHHQVWRQH EHOWV YROXPHV RI WKH .R]KHYQLNRYHWDO FD*DYROFDQLFURFNVVHHPWREHJUHDWHU compared to the other age groups. Because these 4.2 Geochemistry of the felsic volcanic rocks are the youngest found in the Ti- and intermediate volcanic rocks SDVMlUYLDQG.XKPRJUHHQVWRQHEHOWVLWLVSRV- The main geochemical features of the studied sible that the older volcanic sequences are bur- volcanic rocks of the SKT greenstone complex ied under these volcanic rocks and therefore are DUH LOOXVWUDWHG LQ )LJXUH 7KH VDPSOHV DUH not represented in the geochronological data so PHWDPRUSKRVHGDQGWKHUHIRUHPRELOL]DWLRQRI SURIXVHO\,WZDVLQWHUSUHWHGWKDW±*D some elements may have occurred. Analyses are 6LLYLNNRYDDUDXQLWDOVRFRQWDLQ&UULFKEDVDOWV plotted in the conventional TAS (total alkali ver-

NRPDWLLWLFURFNVWKROHLLWLFEDVDOWVDQGEDQGHG VXVVLOLFD GLDJUDPRI/H%DVHWDO 6L22

LURQIRUPDWLRQV %,)V3DSHU,, LQWKH.XKPR versus Zr/TiO2 diagram of Winchester and Floyd greenstone belt. DQGLQ-HQVHQ¶VFDWLRQSORW -HQVHQ When the geochronology of the SKT green- The volcanic rock samples show a wide range stone complex is compared with other green- of SiO2 )LJDE 7KHPRVW6L22-rich sample VWRQHEHOWVLQWKH.DUHOLD3URYLQFH )LJ LW is from a hydrothermally altered kyanite-quartz can be concluded that apart from the Suomus- URFN $)LJVFDQG DQGGRHVQRWUHSUH- VDOPLJUHHQVWRQHEHOWWKH*DDJHJURXSLV VHQWSULPDU\FRPSRVLWLRQ+RZHYHUVRPHRWKHU rare in the volcanic rocks of the Western Kare- SiO2-rich rocks contain quartz phenocrysts and it lia and Central Karelia subprovinces. Contem- ZDVLQWHUSUHWHGWKDWWKHFRPSRVLWLRQUHÀHFWVWKH SRUDQHRXV FD *D DQGHVLWLF EDVDOWLF DQG primary composition for these samples (Paper I). komatiitic rocks have been reported from the ,PSRUWDQWO\JHRFKHPLFDOFRPSRVLWLRQDQGDJH 9RGOR]HURVXESURYLQFH $UHVWRYDHWDO do not correlate with each other. For example 7KHPD¿FYROFDQLFURFNVIURPWKH.RVWRPXN- WKHUK\ROLWLFURFNVRIWKH7LSDVMlUYLJUHHQVWRQH VKDJUHHQVWRQHEHOWKDYH\LHOGHG6P±1GDQG EHOW\LHOGHGDJHVRI*DDQG*DDQG 3E±3ELVRFKURQDJHVRIFDDQG*D the dacitic volcanic rocks of the Suomussalmi .R]KHYQLNRYHWDODQGUHIHUHQFHVWKHUH- JUHHQVWRQHEHOWDJHVRIFD*D*DDQG in). These are contemporaneous with the 2.84 *D )LJ ,Q-HQVHQ¶VFDWLRQSORW -HQVHQ Ga felsic and intermediate volcanic rocks of the DOOVDPSOHVH[FHSWRQHPD¿FYROFDQLF 6.7JUHHQVWRQHFRPSOH[EXWRWKHUZLVHWKLVDJH URFNRIWKH7LSDVMlUYLJUHHQVWRQHEHOWDUHFDOF group seems to be unknown in the Karelia Prov- alkaline (Fig. 9c). ince (Fig. 5). In addition to the SKT greenstone Tectonic discrimination diagrams have been FRPSOH[WKHGDFLWLFURFNRIWKH2LMlUYLJUHHQ- used to classify and study the formation envi- stone belt yielded an age of ca. 2.82 Ga (Figs. 5 ronments of the Archaean magmatic rocks (e.g. DQG3DSHU,,.R]KHYQLNRYHWDO+XK- 3HDUFH6FKDQGODQG*RUWRQ +HUH

25 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40 the felsic and intermediate volcanic rocks from WLRQIRUWKHNRPDWLLWLFURFNVRIWKH7LSDVMlUYLDQG WKH7LSDVMlUYLJUHHQVWRQHEHOW 3DSHU, DUHSORW- .XKPRJUHHQVWRQHEHOWVIRUZKLFKDQRFHDQLF ted in the tectonic discrimination plot by Schan- plateau setting has been proposed based on their GODQG*RUWRQ )LJ ,QDGGLWLRQGDWD SULPLWLYH=U1EDQG1E7KUDWLRV 0DLHUHWDO IURPWKH+DDVLDYDDUDWRQDOLWH )LJG )LJXUHVKRZVWKDWWKHPD¿FDQGXO- 0D.lS\DKRHWDO.lS\DKR WUDPD¿FYROFDQLFURFNVSORWLQDFWLYHFRQWLQHQ- DQGPD¿FDQGXOWUDPD¿FURFNVIURPWKH7LSDV- WDOPDUJLQZLWKLQSODWHYROFDQLFDQGPLGRFHDQ MlUYLDQG.XKPRJUHHQVWRQHEHOWV 0DLHUHWDO ULGJHEDVDOW¿HOGV'DWDIURPWKH+DDVLDYDDUD ZHUHSORWWHGIRUDFRPSDULVRQ$OOWKHIHO- tonalite plots in active continental margin and sic and intermediate volcanic rock samples plot ZLWKLQSODWHYROFDQLF¿HOGV7KHDJHRIWKHNRP- LQWKHDFWLYHFRQWLQHQWDOPDUJLQ¿HOGDQGWKH DWLLWLFURFNVRIWKH7LSDVMlUYLJUHHQVWRQHEHOWLV WZRPD¿FYROFDQLFURFNVZLWKXQNQRZQDJHV XQNQRZQ VHHGLVFXVVLRQLQ3DSHU, EXWLWKDV VDPSOHV$DQG$)LJG SORWLQWKH been interpreted from the Kuhmo greenstone belt ZLWKLQSODWHDQGDFWLYHFRQWLQHQWDOPDUJLQ¿HOGV WKDWVRPHRIWKHPD¿FDQGXOWUDPD¿FYROFDQLF These results differ from the previous interpreta- URFNVDUHUHODWHGWRWKHFD±*DLQWHU-

Figure 9. 9ROFDQLFURFNVIURPWKH6.7JUHHQVWRQHFRPSOH[DUHSORWWHGLQD 7$6GLDJUDP /H%DVHWDO E 6L22 versus Zr/TiO2GLDJUDP :LQFKHVWHUDQG)OR\G DQGF LQ-HQVHQFDWLRQSORW -HQVHQ ZKHUH7+ WKROHLLWH DQG&$ FDOFDONDOLQH'DWDIURP3DSHUV,±,,,DQG3LHWLNlLQHQHWDO

26 Figure 10. *HRWHFWRQLF FODVVL¿FDWLRQ RI WKH YROFDQLF URFNV IURP WKH7LSDVMlUYL JUHHQVWRQH EHOW 'DWD IURP 3DSHU , GLDJUDPVDIWHU6FKDQGODQG*RUWRQ %ODFNFLUFOHVDUHPD¿FYROFDQLFURFNVZLWKXQNQRZQDJHV LQWHUSUHWHGWR EH *DDQG!*DVHHGLVFXVVLRQLQ3DSHU, JUH\FLUFOHVDUHYROFDQLFURFNVZLWKDJHV±*D)RU a comparison, areas where data from komatiitic basalts, high-Cr basalts and komatiites in the Tipasjärvi and Kuhmo JUHHQVWRQHEHOWV GDWDIURP0DLHUHWDO DQGFD*DWRQDOLWHQHDUWKH7LSDVMlUYLJUHHQVWRQHEHOW GDWDIURP .lS\DKR IDOODUHPDUNHG

mediate volcanic rocks (Paper II). The relationships between the komatiitic and intermediate volcanic rocks are discussed in more detail in &KDSWHU+RZHYHUDVQRWHGDOUHDG\HDUOLHU the use of tectonic discrimination diagrams is VRPHZKDWDPELJXRXV &RQGLH/LHWDO DQGTXHVWLRQUHODWHGWRJHRFKHPLFDO¿Q- gerprinting of the tectonic environment of the felsic and intermediate volcanic rocks remains open in the SKT greenstone complex. ,QWKH/D6PYHUVXV6P/XSORWWKHYROFD- QLFURFNVDPSOHVIURP3DSHUV,±,,,GRQRWVKRZ correlation with age or individual belt (Fig. 11). Figure 11. La/Sm versus Sm/Lu plot of selected 7KH/D6PUDWLRVHHPVWREHKLJKHULQWKH volcanic rock samples, data from Papers I–IIII. For a comparison, areas where data from komatiitic basalts, *DROGYROFDQLFURFNVRIWKH7LSDVMlUYLJUHHQ- high-Cr basalts and komatiites in the SKT greenstone stone belt compared to the volcanic rocks of this FRPSOH[ GDWDIURP0DLHUHWDO DQGWKH*D Haasiavaara tonalite near the Tipasjärvi greenstone belt DJHIURPWKH.XKPRJUHHQVWRQHEHOWDSDUWIURP GDWDIURP.lS\DKR)LJG IDOODUHPDUNHG6*% sample A2321. WKH6XRPXVVDOPLJUHHQVWRQHEHOW.*% WKH.XKPR JUHHQVWRQHEHOW7*% WKH7LSDVMlUYLJUHHQVWRQHEHOW

27 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

FL¿FDJHSRSXODWLRQVFDQEHIRXQGLQDURFND VPDOOHUGDWDVHWLVIHDVLEOH 9HUPHHVFK $WRWDORIVHGLPHQWDU\URFNVDPSOHVZHUH 4.3 Detrital zircon analyses of VWXGLHGLQ3DSHUV,±,,,DTXDUW]VDQGVWRQH VDP- the SKT greenstone complex SOH$ )LJ D D FRQJORPHUDWH VDPSOH ,Q WKH VHGLPHQWDU\ SURYHQDQFH DQDO\VLV WKH $)LJD JUH\ZDFNHOLNHPLFDVFKLVWVDQG youngest zircon population can be considered JQHLVVHV VDPSOHV$$$)LJV WRUHÀHFWWKHPD[LPXPDJHRIGHSRVLWLRQ HJ EG DQGDYROFDQRJHQLFVHGLPHQWDU\URFNFRO- .QXGVHQHWDO'LFNLQVRQDQG*HKUHOV OHFWHGEHWZHHQWZRYROFDQRFODVWLFXQLWV $ ,Q RUGHU WR REWDLQ PRUH SUHFLVH GHWHU- Fig. 8d). The main aim of the detrital zircon stud- PLQDWLRQIRUWKHPLQLPXPDJHRIGHSRVLWLRQ ies was to compare the ages of detrital zircon other evidence such as age data for intersect- grains with the ages of volcanic rocks in the ing dikes or plutons or other supracrustal rock greenstone belts and to constrain the possible units younger than the sedimentary rock have to maximum age of the deposition of the sedimen- be utilized. Detrital zircon analysis is subject to tary material. Selecting the grains and analyses ERWKQDWXUDODQGDUWL¿FLDOELDVHV HJ6LUFRPEH was done randomly choosing grains with vari- DQG6WHUQ$QGHUVHQ0RHFKHUDQG able grain sizes and morphologies. 6DPVRQ&DZRRGHWDO6OiPDDQG ,Q3DSHUV,±,,,WKHQXPEHURIDQDO\VHG]LU- .RãOHU ZKLFKVKRXOGEHNHSWLQPLQG con grains of sedimentary rock samples varied when interpreting the results. The recommend- from 21 to 57. It should be noted that especial- ed amount of randomly analysed detrital zircon ly in the case of the samples with small amount grains for sedimentary provenance analysis var- RIDQDO\VHVDOODJHSRSXODWLRQVDUHPRVWOLNHO\ LHVIURPWRGHSHQGLQJRQWKHFRPSOH[- not included. These datasets proved to be ad- ity of the age distribution of the sample (Ver- HTXDWHKRZHYHULQVKRZLQJWKDWVWXGLHGVHGL- PHHVFK$QGHUVHQ +RZHYHULIWKH PHQWDU\URFNVIURPWKH7LSDVMlUYLDQG.XKPR PDLQDLPLVWR¿QGRXWZKHWKHURQHRUPRUHVSH- greenstone belts were deposited after the end

Figure 12. ([DPSOHVRIWKH]LUFRQJUDLQVIURPDTXDUW]VDQGVWRQH VDPSOH$)LJD3DSHU,, $JHV 0D shown with analysed grains.

28 of volcanism. Most sedimentary rock samples WKHJUHHQVWRQHEHOWHYROXWLRQDQGWKH\PLJKW from SKT greenstone complex have heteroge- contain hydrothermal activity and contempora- QHRXV]LUFRQSRSXODWLRQVDQGWKHVDPSOHVFRQ- neous volcanism. For the purpose of an exten- tain both younger and older zircons are recorded VLYHSURYHQDQFHDQDO\VLVWKHDPRXQWRIH[LVW- from the volcanic rocks along the belts. Only LQJGDWDRQWKHVHGLPHQWDU\URFNVLVUDWKHUORZ RQHVHGLPHQWDU\URFNVDPSOH $3DSHU,,, and other probable environments of deposition contained a homogeneous zircon age population VKRXOGEHFRQVLGHUHG+RZHYHUWKHUHVXOWVHQ- of a same age with the volcanic rocks related to courage to perform more detailed studies also the sedimentary rock. on the sedimentary rocks within these belts. Es- Although the applicability of detrital zircon pecially the sedimentary rock interlayers within VWXGLHVLVOLPLWHGWKHIHZVHGLPHQWDU\URFNVDP- different volcanic age groups could shed light SOHVUHSRUWHGLQ3DSHUV,±,,,LPSO\WKDWWKHLU to the tectonic environment in which the supra- detritus originated from heterogeneous sources. crustal rocks were formed. The detrital zircon studies suggest that during the \RXQJHVWVHGLPHQWDWLRQSKDVH FD *D 4.4 Tectonic models of the different blocks of the Karelia Province were SKT greenstone complex assembled. This interpretation is made with the It has been suggested that the 2.94 Ga volcanic assumption that the detritus in the sedimentary rocks in the Suomussalmi greenstone belt are URFNVUHÀHFWVWKHVXUURXQGLQJOLWKRORJLFXQLWVRI separated by an unconformity or a shear zone the depositional basin and that the material was from other volcanic rocks within the belt (En- not transported from exotic sources by aeolian JHODQG'LHW]6RUMRQHQ:DUGDQG/XXN- processes. The rounded grain morphologies im- NRQHQ 7KHSHWURJHQHWLFUHODWLRQVKLSEH- ply that some of the grains represent multicycle tween the 2.94 Ga volcanic event and younger detritus (for example grain with the age of 3345 volcanic rocks in the area is not yet well under- 0D)LJ 6RPHJUDLQVKRZHYHUDUH VWRRG 6RUMRQHQ:DUGDQG/XXNNRQHQ HXKHGUDO VHHJUDLQZLWKWKHDJHRI The suggested eruption settings for the 2.94 Ga 0D)LJ LPSO\LQJUDSLGWUDQVSRUWDWLRQDQG volcanic rocks are shallow water and possibly or deposition from a proximal source. subaerial environments based on primary struc- The zircon age populations and structures WXUHVIRUH[DPSOHODFNRISLOORZVWUXFWXUHVLQWKH of the sedimentary rocks from the SKT green- YROFDQLFURFNV (QJHODQG'LHW] 6P1G stone complex are very similar to those found isotope data of the volcanic rocks of the Suo- from the greenstone belts of the northern and mussalmi greenstone belt indicate involvement eastern parts of the Karelia Province (e.g. Thur- RIHYHQROGHU !*D FUXVWFRPSDUHGZLWK VWRQDQG.R]KHYQLNRY.R]KHYQLNRYHW WKH.XKPRDQG7LSDVMlUYLJUHHQVWRQHEHOWV FD DO+XKPDHWDOD 3DSHU,,GLV- *D+XKPDHWDOE +RZHYHUWKH cusses the possibility of a succession basin for- data concerning the oldest volcanic rocks is not mation during the evolution of the greenstone extensive and thus do not allow a detailed in- belts. The rocks deposited in extensional basins terpretation for the formation environment. In have been proved to be economically important WKHIROORZLQJGLIIHUHQWIRUPDWLRQVFHQDULRVIRU in other Archaean greenstone belts (e.g.Thurston the volcanic rocks of the SKT greenstone com- HWDO%OHHNHU 7KHVHEDVLQVDUH plex are evaluated based on the available data interpreted to have formed in the last phases of (Table 2).

29 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

DEOHYROFDQLFVXFFHVVLRQVDW±*DFRXOG Oceanic plateau setting and relationship be- be the accretion of several individual arcs and tween komatiitic and calc-alkaline rocks oceanic plateau-type volcanic assemblages (Ta- $VDOUHDG\QRWHGWKHNRPDWLLWLFURFNVRIWKH EOH VLPLODUWRZKDWKDVEHHQVXJJHVWHGIRU 7LSDVMlUYLDQG.XKPRJUHHQVWRQHEHOWVPD\KDYH example for the Abitibi greenstone belt in Canada EHHQGHSRVLWHGLQDQRFHDQLFSODWHDXVHWWLQJDQG 'HVURFKHUVHWDO +RZHYHUWKLVPRGHO those of the Suomussalmi greenstone belt in a VHHPVLPSUREDEOHEHFDXVHWKHURRPWR¿WVHY- FRQWLQHQWDOULIW 0DLHUHWDO $IWHUWKH eral individual tectonic environments within the QHZDJHUHVXOWVLWVHHPVSUREDEOHWKDWDWOHDVW JUHHQVWRQHFRPSOH[LVTXLWHVPDOO)RUH[DPSOH the Kuhmo and Suomussalmi greenstone belts LQWKHFDVHRIWKH7LSDVMlUYLJUHHQVWRQHEHOWWKUHH contain more than one komatiitic succession and GLIIHUHQWYROFDQLFSKDVHVFDQEHLGHQWL¿HGIURP that the komatiitic rocks are spatially linked to WKHEHOWZLWKLQDZLGWKRIFDNP 3DSHU, WKH±*DFDOFDONDOLQHYROFDQLFURFNV 7KHH[DFWDJHVRIWKHPD¿FDQGXOWUDPD¿FURFNV 3DSHUV,,DQG,,, .RQQXQDKRHWDO DO- DUHXQNQRZQLQWKLVEHOW\HWEDVHGRQ¿HOGDQG so reported that the sulphur isotope signatures GULOOFRUHREVHUYDWLRQVWKHPD¿FDQGXOWUDPD¿F from komatiite-hosted sulphide deposits vary in rocks were probably formed between 2.84 Ga WKH6XRPXVVDOPLJUHHQVWRQHEHOWLPSO\LQJWKDW DQG*D,IWKHPD¿FDQGXOWUDPD¿FYROFD- they had different parental magma composition nic rocks represent slivers of oceanic plateau and and/or different emplacement history. The an- the felsic volcanic rocks formed in arc-type envi- desitic volcanic rocks seem to spatially be re- URQPHQWWKLVZRXOGPHDQWKDWSDUWVRIWKUHHRU lated to the younger phase of komatiites in the four individual tectonic blocks should be juxta- .XKPRJUHHQVWRQHEHOW 3DSHU,, +RZHYHUDQ- posed within the narrow greenstone belt. Paper desitic compositions are rare in oceanic plateau II suggests that the 2.84 Ga Nuolikangas unit and VHWWLQJV HJ.HUUDQG0DKRQH\ ,QDG- ±*D6LLYLNNRYDDUDXQLWRIWKH.XKPR GLWLRQWKHIHOVLFYROFDQLFURFNVRIWKH7LSDVMlUYL greenstone belt might have formed in different greenstone belt plot within the active continental WHFWRQLFVHWWLQJVDQGODWHUJRWMX[WDSRVHG+RZ- PDUJLQ¿HOGLQWHFWRQLFGLVFULPLQDWLRQGLDJUDPV HYHUZKHQWDNLQJLQWRFRQVLGHUDWLRQDOOWKHWKUHH )LJ ZKLFKLVRSSRVLWHWRWKHUHVXOWVIURP JUHHQVWRQHEHOWVRIWKLVFRPSOH[WKHK\SRWK- WKHNRPDWLLWLFURFNV$VQRWHGHDUOLHUWKHWUDFH esis of several different tectonic environments element discrimination diagrams have been criti- LVUDWKHUYDJXH7KHUHIRUHEHFDXVHRIWKHFORVH FL]HG &RQGLHHWDO/LHWDO DQG proximity of the belts and partial similarity of therefore these interpretations should be treated DJHSDWWHUVLQ±*DYROFDQLFURFNVDF- ZLWKFDXWLRQ+RZHYHULIWKHFDOFDONDOLQHURFNV cretion of individual arcs and oceanic plateaus of the SKT greenstone complex represent inter- is an improbable explanation for the SKT green- action with continental crust and the interpreta- stone complex. tion of spatial and temporal relationship between WKHPDQGNRPDWLLWLFURFNVLVFRUUHFWWKHRFHDQLF Continental rifting plateau setting seems an unlikely explanation for 6HYHUDO VWXGLHV VHH HJ 3LLUDLQHQ the formation environment (Table 2). /XXNNRQHQ3DSXQHQHWDO KDYH suggested that the SKT greenstone complex was Constraints against arc-plateau accretion formed when older continental crust started to One explanation for the formation of the vari- ULIW 7DEOH ,QWKLVUHJDUGWKHYROFDQLFDQG

30 Table 2. Comparison of different tectonic settings for the volcanic rocks of the SKT greenstone complex.

Setting Hypothesis Pros Cons Probability

6FDOHIRU¿WWLQJVHYHUDOLQGLYLGXDO formation environments within the greenstone complex is small Different volcanic age JURXSV *D*D *D UHSUHVHQW Based on the spatial relation- Arc(s) and Explains the differences in individual volcanic succes- ships, komatiitic rocks are oceanic geochemical compositions VLRQVMX[WDSRVHGWRJHWKHU UHODWHGWR VRPH IHOVLFLQWHU- plateua(s) between the andesitic- Improbable felsic-intermediate volcanic mediate volcanic successions mix and rhyolitic volcanic rocks and rocks might have formed in 3DSHUV,,DQG,,, match komatiitic rocks DUFW\SHVHWWLQJXOWUDPD¿F volcanic rocks in oceanic plateau type setting Study area represents polym- etamorphic part of crust, and mobilization of elements in later metamoprhic events is probable !UHOLDELOLW\RIJHRFKHPLVWU\"

Primary structures of some Andesitic rocks are rare in mod- All volcanic rocks < 2.84 Oceanic volcanic rocks indicate ern oceanic plateau type settings Ga were formed in an Improbable plateuau VXEDTXHDVHUXSWLRQHQYL- &RQGLH.HUUDQG oceanic plateua setting ronment 0DKRQH\

/RQJGXUDWLRQ FD0\U Sm-Nd isotope signature of and cyclicity of volcanism some volcanic rocks suggest a is suitable for continental MXYHQLOHVRXUFH +XKPDHWDO rift environment E The volcanic rocks with Protoconti- ages of 2.84-2.79 Ga were nent split in formed in same rifting Probable half HYHQWRIWKHROGHU ш 2.94 *D SURWRFRQWLQHQW Both subaerial and sub- Trace elements of the komatiitic DTHRXVYROFDQLFFHQWHUV rocks in the Kuhmo and Tipas- HJ(QJHODQG'LHW] järvi greenstone belts do not 6RUMRQHQ:DUGDQG show input of older continental /XXNNRQHQ FUXVW 0DLHUHWDO

The 2.84-2.79 Ga-old Sm-Nd isotope signature of Explains geochemical volcanic rocks formed via some volcanic rocks suggest a variation and cyclicity of interaction of continental MXYHQLOHVRXUFH +XKPDHWDO YROFDQLFURFNV 3DSHUV,,,, and oceanic lithosphere E Interaction between con- Probable tinent-ocean boundary Possible scenarios: arc- Trace elements of the komatiitic type setting with subduc- Average pressure ca. 16- rocks in the Kuhmo and Tipas- tion, continental collapse 17 kbar at 600-700 °C for järvi greenstone belts do not and resulting episodic albite inclusions in garnet show input of older continental subduction, or edge-driven .*%+|OWWlHWDO FUXVW 0DLHUHWDO convection

31 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

SOXWRQLFURFNVRI*DLQWKH6XRPXVVDOPL probable. greenstone belt could represent part of a conti- A failed rift followed by subduction (Piirain- nent that started to rift. The ages of the volca- HQ LVDQXQOLNHO\PRGHOIRUWKH6.7JUHHQ- nic rocks within the whole complex indicate that VWRQHFRPSOH[LWWDNHVFD±PLOOLRQ\HDUVIRU ULIWLQJZRXOGKDYHVWDUWHGEHIRUHFD± the lithosphere to get dense enough to subduct *D +XKPDHWDOD3DSHUV,±,,, DQGFRQ- DIWHULWVIRUPDWLRQ 6WHUQDQGUHIHUHQFHV WLQXHGDWOHDVWXQWLOFD*DDVLQGLFDWHGE\ in therein). The ca. 2.84 Ga andesitic rocks in the youngest ages from the volcanic rocks of the WKH7LSDVMlUYLJUHHQVWRQHEHOW 3DSHU, VXJJHVW Kuhmo greenstone belt (Paper II). that if the andesitic composition is considered The Red Sea region is an example of an active RIDVLJQRIDVXEGXFWLRQWKHVXEGXFWLRQZRXOG ULIWLQWKH0LGGOH(DVW :HLQVWHLQDQG*DUIXQNHO have commenced shortly after rifting. 7KHYROFDQLFUHFRUGWKHUHVWDUWHGFD 0DDJRDQGFRQWLQXHGWRSUHVHQWGD\+RZHYHU Different scenarios for continental and oceanic the age of volcanism is changing spatially across lithosphere interaction WKHDUHDWKDWLVRYHUNPORQJDQGLQGLYLG- Volcanic rocks can be formed by the inter- ual parts of the rift have been volcanically active action of continent-ocean boundary by several RQO\GXULQJWLPHSHULRGVRIPLOOLRQ\HDUV$Q ZD\V 7DEOH 3RVVLEOHVFHQDULRVDUHIRUH[- example of episodic rifting comes from the Neo- DPSOHPRGHUQOLNHDUFYROFDQLVPZLWK HSLVRG- SURWHUR]RLF

32 observed in modern continental arcs (Jicha and tems that produced also the tholeiitic rocks of -DJRXW]3DWHUVRQDQG'XFHD $O- WKHJUHHQVWRQHEHOWV7KH±*DYROFDQLF bite inclusions in garnet in a tholeiitic rock from rocks of the SKT greenstone complex could be the Kuhmo greenstone belt have yielded high H[SODLQHGDOVRZLWKWKLVPRGHOLIWKH*D DYHUDJHSUHVVXUHV FD±NEDU+|OWWlHWDO rocks are again interpreted to be part of older ZKLFKFRXOGLQGLFDWHDVXEGXFWLRQLQWKH Archaean crust. 6.7JUHHQVWRQHFRPSOH[6LPLODUO\JDUQHWDO- bite-bearing mineral assemblages yielding high Summary remarks for the tectonic evolution of SUHVVXUH ±NEDU DQGORZWHPSHUDWXUH ± the SKT greenstone complex & FRQGLWLRQVKDYHEHHQLQWHUSUHWHGWRUHS- When evaluating the available data in the resent subduction ca. 3.2 Ga ago in the Archaean OLJKWWKHSUHVHQWHGPRGHOVLWLVHYLGHQWWKDWWKH %DUEHUWRQJUHHQVWRQHEHOW6RXWK$IULFD 0R\HQ SKT greenstone complex does not represent vol- HWDO canism related to a single tectonic event. The In WKHHGJHGULYHQFRQYHFWLRQPRGHOD LQWHUSUHWDWLRQ LV KRZHYHU WKDW WKH LQGLYLGXDO small-scale convection cell is formed in the up- greenstone belts are related to each other and the per mantle area where the lithosphere has vari- following conclusions about the tectonic evolu- DEOHWKLFNQHVVIRUH[DPSOHLQFUDWRQERXQGDULHV tion of the SKT greenstone complex are allowed: DQGUHVXOWLQLQWUDSODWHYROFDQLFDFWLYLW\ .LQJ ± 7KH*DPDJPDWLFURFNVZHUHIRUPHG DQGUHIHUHQFHVWKHUHLQ %DVHGRQQXPHUL- LQDQXQNQRZQWHFWRQLFHQYLURQPHQW V UHS- cal modelling the edge-driven convection model UHVHQWLQJDQROGHUFRQWLQHQW has been proposed for the Moroccan Atlas Moun- ± 7KHYROFDQLFURFNVZLWKDJHVRIFD± WDLQVLQWKHQRUWKHDVW$IULFDZKHUHZLGHVSUHDG Ga formed via interaction between the older volcanism took place in two phases separated FRQWLQHQWDQGWKHRFHDQLFOLWKRVSKHUHRULQ E\ FD PLOOLRQV RI \HDUV .DLVODQLHPL DQG DULIWVHWWLQJ+RZHYHUWKHLQWHUDFWLRQZLWK YDQ+XQHQDQGUHIHUHQFHVWKHUHLQ 7KH continental lithosphere is probable also for DQGHVLWLFURFNVRIWKH&RORUDGR3ODWHDX8QLWHG the younger generation of volcanic rocks in 6WDWHVKDYHEHHQH[SODLQHGZLWKWKLVPRGHO YDQ the SKT greenstone complex. :LMNHWDO %DVHGRQWKHDYDLODEOHJHR- FKHPLFDODQGDJHGDWDLHFD0\UF\FOLFLW\ 4.5 Future studies LQYROFDQLVPWKHHGJHGULYHQFRQYHFWLRQPRG- This thesis adds on to the knowledge of the Ar- el is also suitable for the evolution of the SKT chaean geology of the Karelia Province. Con- greenstone complex. cerning the age and evolution of the Archaean 7KH VXEFUHWLQJ PRGHO by Bédard et al. JUHHQVWRQHEHOWVKRZHYHULPSRUWDQWTXHVWLRQV VXJJHVWVWKDWWKH$UFKDHDQFUDWRQVDFWHG still remain unanswered. Considering the SKT DVDFWLYHWHFWRQLFDJHQWVDFFUHWLQJDQGVXEFUHW- JUHHQVWRQHFRPSOH[LWZRXOGEHLQWULJXLQJWR LQJWKHRFHDQLFSODWHDXVDQGSURGXFLQJV\QWHF- get more information from the 2.82 Ga volca- tonic tonalite-trondhjemite-granodiorites via in- nic rocks and their spatial variation across the WHUDFWLRQEHWZHHQPDQWOHÀRZDQGFUDWRQNHHOV greenstone complex. All three belts contain ev- This model profusely criticizes the arc signature idence of supracrustal material being deposited of Archaean volcanic rocks and suggests that the GXULQJWKLVWLPHSHULRGEXWFRPSDUHGWRRWKHU andesitic volcanic rocks were formed by mix- age groups it appears to be less abundant. In the ing processes in heterogeneous plumbing sys- 7LSDVMlUYLJUHHQVWRQHEHOWPRUHHODERUDWHVWXG-

33 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

LHVDORQJWKH7DODVVXRSUR¿OHFRXOGKHOSWRGH- JUHHQVWRQH EHOWV DQG SURYLGHV WKH IROORZLQJ ¿QHWKHDJHRIWKH%,)VDQGPD¿FDQGXOWUDPD¿F conclusions for the formation of greenstone belts volcanic rocks (see discussion in Paper I). De- in the Karelia Province of the Fennoscandian tailed studies about the stratigraphic position of Shield: WKHPD¿FDQGXOWUDPD¿FYROFDQLFURFNVVKRXOGEH done also in the Suomussalmi and Kuhmo green- 1. The SKT greenstone complex comprises of VWRQHEHOWVLQRUGHUWRVROYHWKHLUUHODWLRQVKLSV VHYHUDOYROFDQLFSKDVHVFD*D*D with the different-aged felsic and intermediate *D±*D volcanic cycles. Also high-quality geochemical VWXGLHVRIDOOYROFDQLFURFNVZRXOGEHEHQH¿- 2. The ages of the volcanic rocks become younger cial. A detailed detrital zircon research from the from the north to the south along the greenstone youngest sedimentary rocks could provide more complex. The northernmost Suomussalmi understanding about the evolution of the belts af- greenstone belt hosts the oldest 2.94 Ga volcanic ter the cessation of the volcanism and possible SKDVHZKHUHDVWKH\RXQJHVWSKDVHFD± economically important depositional basins. An *DVHHPVWREHODFNLQJ extensive detrital zircon study of the sedimentary rocks that are found as interlayers in the volca- 3. The age results and geochemical composition QLFURFNVWRVHHZKHWKHUWKH\FRQWDLQLQGLFDWRUV of the felsic and intermediate volcanic rocks of RIVLJQL¿FDQWO\ROGHUGHWULWXVFRPSDUHGWRWKH WKHZKROH6.7JUHHQVWRQHFRPSOH[QRUZLWKLQ YROFDQLFURFNV6P1GDQG/X+ILVRWRSHDQG LQGLYLGXDOEHOWVGRQRWVKRZFRUUHODWLRQ trace element work from volcanic and detrital zircon grains might provide a more detailed picture 4. The age difference between individual belts IRUWKHRULJLQRIWKH]LUFRQJUDLQV±DQGDOVRWR implies a different formation history between the the tectonic processes in which the supracrust- volcanic rocks of the SKT greenstone complex. al rocks of the STK greenstone complex were 7KHDYDLODEOHGDWDVXJJHVWVWKDWWKHFD± formed. Geochemical modelling of the volcanic 2.79 Ga volcanic rocks of the SKT greenstone URFNVDQGQHZDJHDQG6P1GDQG/X+ILVR- complex formed via interaction between the WRSHZRUNIURPWKHYROFDQLFURFNVFRXOGEHQH¿W ROGHUFRQWLQHQW *D DQG\RXQJHURFHDQLF the discussion of the formation environment of OLWKRVSKHUHRULQDFRQWLQHQWDOULIWVHWWLQJ the volcanic rocks of the SKT greenstone belt. ,QDGGLWLRQFRPSDUDWLYHVWXGLHVIURPRWKHU$U- 7KH\RXQJHVWYROFDQLFURFNVRIWKH7LSDVMlUYL cheaen greenstone belts of the Karelia Province and Kuhmo greenstone belts are overlain by ZRXOGEHQH¿WWKHGLVFXVVLRQUHODWHGWRWKHLUIRU- \RXQJHU VHGLPHQWDU\ PDWHULDO ZKLFK ZDV mation and possible relationships. deposited tens of millions of years after the youngest volcanic rocks. The detritus of the sedimentary rocks contains zircon grains with 5 Conclusions DJHV RI ! *D$VVXPLQJ WKDW WKH GHWULWXV UHÀHFWVWKHFKDUDFWHULVWLFVRIWKHEHGURFNQHDUWKH The work presented here demonstrates the GHSRVLWLRQDOEDVLQWKH]LUFRQJUDLQSRSXODWLRQV potential of detailed chronostratigraphic studies LPSO\WKDWGXULQJWKHGHSRVLWLRQWKHGLIIHUHQW of Archaean supracrustal rocks to act as a tool subprovinces of the Karelia Province had already for understanding the evolution of Archaean been assembled.

34 References tectonics begin on planet Earth? Geological Soci- HW\RI$PHULFD6SHFLDO3DSHU &DOYHUW$-6DZ\HU(:'DYLV:-DQG/XGGHQ $EERW''UXU\5DQG6PLWK:+))ODW J.N. 1995. Archaean subduction inferred from to steep transition in subduction style. Geology seismic images of a mantle suture in the Supe- ULRU3URYLQFH1DWXUH $OOZRRG$&:DOWHU05%XUFK,:DQG.DP- &DZRRG3$.U|QHU$3LVDUHYVN\63UH- EHU%6ELOLRQ\HDUROGVWURPDWROLWH cambrian plate tectonics: Criteria and evidence. reef from the Pilbara Craton of Western Australia: *6$WRGD\ Ecosystem-scale insights to early life on Earth. &DZRRG3$+DZNHVZRUWK&-DQG'KXLPH% 3UHFDPEULDQ5HVHDUFK 'HWULWDO]LUFRQUHFRUGDQGWHFWRQLFVHWWLQJ $QGHUVHQ7'HWULWDO]LUFRQVDVWUDFHUVRIVHGL- *HRORJ\GRL* mentary provenance: limiting conditions from sta- &RQGLH.&$UFKHDQJUHHQVWRQHEHOWV(OVH- tistics and numerical simulation. Chemical Geol- YLHU6FLHQWL¿F3XEOLVKLQJ&RPSDQ\$PVWHUGDP RJ\ The Netherlands. 434 p. $UHVWRYD1$&KHNXODHY93/REDFK=KXFKHQNR &RQGLH .& *UHHQVWRQH WKURXJK WLPH ,Q 6%DQG.XFKHURYVNLL*$)RUPDWLRQRI &RQGLH.& (G $UFKHDQ&UXVWDO(YROXWLRQ the Archean Crust of the Ancient Vodlozero Do- 'HYHORSPHQWVLQ3UHFDPEULDQ*HRORJ\YRO main (Baltic Shield). Stratigraphy and Geological (OVHYLHU$PVWHUGDPSS &RUUHODWLRQ &RQGLH.&DQG%HQQ.$UFKHDQ*HRG\QDP- $UQGW1DQG/HVKHU&0.RPDWLLWH(QF\FOR- ics: Similar to or different from modern geodyam- SHGLDRI*HRORJ\(OVHYLHUSS± LFV$UFKHDQ *HRG\QDPLFV DQG (QYLURQPHQWV %pGDUG-+$FDWDO\WLFGHODPLQDWLRQGULYHQ *HRSK\VLFDO0RQRJUDSK6HULHV model for coupled genesis of Archaean crust &RQGLH.&DQG.U|QHU$:KHQGLGSODWH and sub-continental lithospheric mantle. Geo- tectonics begin? Evidence from the geologic re- FKLPLFDHW&RVPRFKLPLFD$FWD FRUG,Q&RQGLH.&DQG3HDVH9 (GV :KHQ GRLMJFD did plate tectonics begin on planet Earth? Geologi- %pGDUG-++DUULV/%DQG7KXUVWRQ3& FDO6RFLHW\RI$PHULFD6SHFLDO3DSHU The hunting of the snArc. Precambrian Re- GRL VHDUFK GRLM SUHFDPUHV &RQGLH.&KDQJLQJWHFWRQLFVHWWLQJVWKURXJK time: Indiscriminate use of geochemical discrimi- %HQQ.DQG0R\HQ-)7KHODWH$UFKHDQ QDQWGLDJUDPV3UHFDPEULDQ5HVHDUFK $ELWLEL2SDWLFDWHUUDQH6XSHULRU3URYLQFH$PRG- 591. L¿HGRFHDQLFSODWHDX,Q&RQGLH.&DQG3HDVH &RUIX).URJK7(.ZRN<<-HQVHQ/6 9 (GV :KHQGLGSODWHWHFWRQLFVEHJLQRQSODQHW 8±3E]LUFRQJHRFKURQRORJ\LQWKHVRXWKZHVWHUQ (DUWK"*HRORJLFDO6RFLHW\RI$PHULFD6SHFLDO $ELWLELJUHHQVWRQHEHOW6XSHULRU3URYLQFH&D- 3DSHUGRL QDGLDQ-RXUQDORI(DUWK6FLHQFHV %HUFRYLFL'DQG5LFDUG<3ODWHWHFWRQLFV *URYH7/DQG3DUPDQ6:7KHUPDOHYROX- GDPDJHDQGLQKHULWDQFH1DWXUH tion of the Earth as recorded by komatiites. Earth GRLQDWXUH DQG3ODQHWDU\6FLHQFH/HWWHUV %OHHNHU:7KHODWH$UFKHDQUHFRUGDSX]]OH 'DYLHV*)2QWKHHPHUJHQFHRISODWHWHFWRQ- LQFDSLHFHV/LWKRV LFV*HRORJ\ %OHHNHU:7DUJHWHG*HRVFLHQFH,QLWLDWLYH 'DYLV'::LOOLDPV,6DQG.URJK7( Lode gold deposits in ancientdeformed and meta- 5HYLHZV LQ 0LQHUDORJ\ DQG *HRFKHPLVWU\ morphosed terranes: the role of extension in the GRL formationof Timiskaming basins and large gold 'HEDLOOH92¶1HLOO*%UDQGRQ$'+DHQHFRXU GHSRVLWV$ELWLELJUHHQVWRQHEHOW±DGLVFXVVLRQ 3

35 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

ages of detrital zircons to infer maximum depo- +HLOLPR(+DOOD-DQG+XKPD+6LQJOH sitional ages of strata: A test against a Colorado JUDLQ]LUFRQ8±3EDJHFRQVWUDLQWVRIWKHZHVWHUQ Plateau Mesozoic database. Earth and Planetary and eastern sanukitoid zones in the Finnish part of 6FLHQFH/HWWHUV WKH.DUHOLDQ3URYLQFH/LWKRV 'LOHN<DQG3RODW$6XSUDVXEGXFWLRQ]RQH +HLQRQHQ -6 &DUOVRQ 5: DQG /XWWLQHQ$9 RSKLROLWHV DQG$UFKHDQ WHFWRQLFV*HRORJ\ ,VRWRSLF 6U1G3EDQG2V FRPSRVLWLRQ GRL)RFXV RIKLJKO\PDJQHVLDQGLNHVRI9HVWIMHOODZHVWHUQ GH:LW0-2Q$UFKHDQJUDQLWHVJUHHQVWRQHV 'URQQLQJ0DXG/DQG$QWDUFWLFD$NH\WRWKH cratons and tectonics: does the evidence demand origins of the Jurassic Karoo large igneous prov- DYHUGLFW"3UHFDPEULDQ5HVHDUFK LQFH&KHPLFDO*HRORJ\ (QJHO::DQG'LHW]*-$PRGL¿HGVWUD- +LFNPDQ$+7ZRFRQWUDVWLQJJUDQLWHJUHHQ- tigraphy and tectonomagmatic model for the Suo- VWRQH WHUUDQHV LQ WKH 3LOEDUD &UDWRQ$XVWUDOLD PXVVDOPLJUHHQVWRQHEHOWHDVWHUQ)LQODQGEDVHG evidence for vertical and horizontal tectonic re- on the remapping of the Ala-Luoma area.Bulleting JLPHVSULRUWR0D3UHFDPEULDQ5HVHDUFK RI*HRORJLFDO6RFLHW\RI)LQODQG )XUQHV+GH:LW0DQG5RELQV%$UHYLHZ +RIPDQQ$DQG.XVN\707KH%HOLQJZH RIQHZLQWHUSUHWDWLRQVRIWKHWHFWRQRVWUDWLJUDSK\ JUHHQVWRQHEHOWHQVLDOLFRURFHDQLF",Q.XVN\ geochemistry and evolution of the Onverwacht 70 (G 3UHFDPEULDQRSKLROLWHVDQGUHODWHG 6XLWH%DUEHUWRQ*UHHQVWRQH%HOW6RXWK$IULFD rocks. Developments in Precambrian Geology *RQGZDQD5HVHDUFK )XUQHV+'LOHN<GH:LW03UHFDPEULDQ +RSNLQV0+DUULVRQ7DQG0DQQLQJ&( greenstone sequences represent different ophiolite /RZKHDWÀRZLQIHUUHGIURP!*\U]LUFRQVVXJ- W\SHV*RQGZDQD5HVHDUFK JHVW+DGHDQSODWHERXQGDU\LQWHUDFWLRQV1DWXUH *DUGpV(DQG0RQWHO-02SHQLQJDQGUH- GRLQDWXUH setting temperatures in heating geochronological +RSNLQV0+DUULVRQ7DQG0DQQLQJ&( systems. Contributions to the Mineralogy and &RQVWUDLQVRQ+DGHDQJHRG\QDPLPFVIURPPLQ- 3HWURORJ\ HUDOLQFOXVLRQVLQ!*D]LUFRQV(DUWKDQG3ODQ- *ULI¿Q:/%HORXVRYD($2¶1HLOO&2¶5HLOO\ HWDU\6FLHQFH/HWWHUV 6<0DONRYHWV93HDUVRQ1-6SHWVLXV6DQG +|OWWl3%DODJDQVN\9*DUGH$0HUWDQHQ6 :LOGH6$7KHZRUOGWXUQVRYHU+DGHDQ 3HOWRQHQ36ODEXQRY$6RUMRQHQ:DUG3DQG Archean crust-mantle evolution. :KLWHKRXVH0$UFKHDQRI*UHHQODQGDQG *ULPHV&%-RKQ%(.HOHPHQ3%0D]GDE )HQQRVFDQGLD(SLVRGHV± ).:RRGHQ-/&KHDGOH0-+DQJK¡M. +|OWWl3+HLOLPR(+XKPD+-XRSSHUL+.RQ- DQG6FKZDUW]--7UDFHHOHPHQWFKHPLVWU\ WLQHQ$.RQQXQDKR-/DXUL/0LNNROD3 of zircons from oceanic crust: A method for dis- 3DDYROD-DQG6RUMRQHQ:DUG3$UFKDH- tinguishing detrital zircon provenance. Geology an complexes of the Karelia Province in Finland. GRL*$ ,Q+|OWWl3 (G 7KH$UFKDHDQRIWKH.DUHOLD +DONRDKR7/LLPDWDLQHQ-3DSXQHQ+DQG9lOL- Province. Geological Survey of Finland Special PDD-([FHSWLRQDOO\&UULFKEDVDOWVLQWKH 3DSHU komatiitic volcanic association of the Archaean +|OWWl3+HLOLPR(+XKPD+.RQWLQHQ$0HU- .XKPRJUHHQVWRQHEHOWHDVWHUQ)LQODQG0LQHUDO- WDQHQ60LNNROD33DDYROD-3HOWRQHQ3 RJ\DQG3HWURORJ\ 6HPSULFK-6ODEXQRY$DQG6RUMRQHQ:DUG +DONRDKR7DQG1LVNDQHQ07XWNLPXVW\|VHO- 37KH$UFKDHDQ.DUHOLDDQG%HORPRULDQ RVWXV.XKPRQNDXSXQJLQ.HOORMlUYHQ3lUVlPlQ- 3URYLQFHV)HQQRVFDQGLDQ6KLHOG,Q'LOHN<DQG suo 1 valtausalueella (kaivosrekisterinumero )XUQHV+ (GV (YROXWLRQRI$UFKHDQ&UXVWDQG 8344/1)suoritetuista nikkelimalmitutkimuksista (DUO\/LIH6FLHQFH%XVLQHVV0HGLD'RUGUHFKW YXRVLQD ± *HRORJLFDO 6XUYH\RI )LQ- SS± ODQG ([SORUDWLRQ 5HSRUW SS LQ +XKPD+0lQWWlUL,3HOWRQHQ3.RQWLQHQ$ Finnish). +DONRDKR7+DQVNL(+RNNDQHQ7+|OWWl3 +DQVNL(.RPDWLLWLFDQGWKROHLLWLFPHWDYRO- -XRSSHUL+.RQQXQDKR-/D\DKH</XXN- canics of the Siivikkovaara areain the Archean NRQHQ ( 3LHWLNlLQHQ. 3XONNLQHQ$ 6RU- .XKPRJUHHQVWRQHEHOWHDVWHUQ)LQODQG%XOOHWLQ MRQHQ:DUG39DDVMRNL0:KLWHKRXVH0 RI*HRORJLFDO6RFLHW\RI)LQODQG D7KHDJHRIWKH$UFKDHDQJUHHQVWRQHEHOWV +DPLOWRQ:%$QDOWHUQDWLYH(DUWK*6$7R- LQ)LQODQG,Q+|OWWl3 (G 7KH$UFKDHDQRIWKH GD\ Karelia Province. Geological Survey of Finland +DPLOWRQ:%3ODWHWHFWRQLFVEHJDQLQ1HRSUR- 6SHFLDO3DSHU WHUR]RLFWLPHDQGSOXPHVIURPGHHSPDQWOHKDYH +XKPD+.RQWLQHQ$0LNNROD3+DONRDKR7 QHYHURSHUDWHG/LWKRVGRLM +RNNDQHQ7+|OWWl3-XRSSHUL+.RQQX- OLWKRV QDKR-/XXNNRQHQ(0XWDQHQ73HOWRQHQ3

36 3LHWLNlLQHQ.3XONNLQHQ$E1GLVRWRSLF cow/Espoo. evidence for Archaean crustal growth in Finland. .RQQXQDKR-+DQVNL(:LQJ%%HNNHU$/XN- ,Q+|OWWl3 (G 7KH$UFKDHDQRIWKH.DUHOLD NDUL6DQG+DONRDKR77KH+LHWDKDUMX Province. Geological Survey of Finland Special 3*(HQULFKHGNRPDWLLWHKRVWHGVXO¿GHGHSRVLWLQ 3DSHU WKH$UFKHDQ6XRPXVVDOPLJUHHQVWRQHEHOWHDVW- ,UHODQG75DQG:LOOLDPV,6&RQVLGHUDWLRQV HUQ)LQODQG2UH*HRORJ\5HYLHZV in zircon geochronology by SIMS. Reviews in .RPL\D70DUX\DPD60DVXGD71RKGD6 0LQHUDORJ\ DQG 3HWURORJ\ GRL +D\DVKL0DQG2NDPRWR.3ODWHWHFWRQ- LFVDW±*D)LHOGHYLGHQFHIURPWKH,VXD -DQRXãHN9)DUURZ&0DQG(UEDQ9,Q- DFFUHWLRQDU\FRPSOH[VRXWKHUQZHVW*UHHQODQG terpretation of whole-rock geochemical data in 7KH-RXUQDORI*HRORJ\ igneous geochemistry: introducing Geochemical .RUHQDJD-,QLWLDWLRQDQG(YROXWLRQRISODWHWHF- 'DWD7RRONLW *&'NLW -RXUQDORI3HWURORJ\ tonics on Earth: Theories and Observations. Annu- 1255-1259 DO5HYLHZRI(DUWKDQG3ODQHWDU\6FLHQFHV -HQVHQ/6$1HZ&DWLRQ3ORWIRU&ODVVLI\LQJ GRLDQQXUHYHDUWK Subalkalic Volcanic Rocks. Ontario Geological .R]KHYQLNRY91%UH]KQD\D 1* 3UHVQ\DNRY 6XUYH\0LVFHOODQHRXV3DSHU 6//HSHNKLQD(1$QWRQRY$9DQG6HU- -LFKD%5DQG-DJRXW]20DJPDSURGXFWLRQ JHHY6$*HRFKURQRORJ\ 6+5,03,, UDWHVIRULQWUDRFHDQLFDUFV(OHPHQWV of zircons from Archean strato-tectonic associa- .DLVODQLHPL/DQGYDQ+XQHQ-'\QDPLFVRI WLRQVRI.DUHOLDQJUHHQVWRQHEHOWVVLJQL¿FDQFH lithospheric thinning and mantle melting by edge- for stratigraphicand geodynamic reconstructions. driven convection: Application to Moroccan Atlas 6WUDWLJU*HRO&RUUHO PRXQWDLQV*HRFKHPLVWU\*HRSK\VLFV*HRV\V- .U|QHU$7KHUROHRIJHRFKURQRORJ\LQXQGHU- WHPVGRL*& VWDQGLQJFRQWLQHQWDOHYROXWLRQ,Q.\VN\70 .lS\DKR $ :KROHURFN JHRFKHPLVWU\ RI =KDL0*DQG;LDR: (GV 7KHHYROYLQJ VRPH WRQDOLWH DQG KLJK 0J)H JDEEUR GLRULWH continents: Understanding processes of continen- and granodiorite plutons (sanukitoid suites) in WDOJURZWK*HRORJLFDO6RFLHW\/RQGRQ6SHFLDO WKH.XKPRGLVWULFWHDVWHUQ)LQODQG%XOOHWLQRI 3XEOLFDWLRQV WKH*HRORJLFDO6RFLHW\RI)LQODQG /H%DV0-/H0DLWUH5:6WUHFNHLVHQ$DQG .lS\DKR $ 0lQWWlUL , DQG +XKPD + =DQHWWLQ%$FKHPLFDOFODVVL¿FDWLRQRI *URZWKRI$UFKDHDQFUXVWLQWKH.XKPRGLVWULFW YROFDQLFURFNVEDVHGRQWKHWRWDODONDOL±VLOLFDGLD- HDVWHUQ)LQODQG8±3EDQG6P±1GLVRWRSHFRQ- JUDP-RXUQDORI3HWURORJ\ straints on plutonic rocks .Precambrian Research /HH-.::LOOLDPV,6DQG(OOLV'-3E 8DQG7KGLIIXVLRQLQQDWXUDO]LUFRQ1DWXUH .lS\DKR$+|OWWl3DQG:KLWHKRXVH0- 8±3E]LUFRQJHRFKURQRORJ\RIVHOHFWHG$UFKDHDQ /HFOHUF)%pGDUG-++DUULV/%0F1LFROO9- migmatites in eastern Finland. Bulletin of Geo- *RXOHW15R\3DQG+DXOH37KROHL- ORJLFDO6RFLHW\RI)LQODQG± itic to calc-alkaline cyclic volcanism in the Roy .HUU$&DQG0DKRQH\--2FHDQLFSODWHDXV *URXS&KLERXJDPDXDUHD$ELWLEL*UHHQVWRQH 3UREOHPDWLFSOXPHVSRWHQWLDOSDUDGLJPV&KHPL- %HOW±UHYLVHGVWUDWLJUDSK\DQGLPSOLFDWLRQVIRU FDO*HRORJ\ 9+06H[SORUDWLRQ&DQDGLDQ-RXUQDORI(DUWK .LQJ6'+RWVSRWVDQGHGJHGULYHQFRQYHF- 6FLHQFHVGRL( WLRQ*HRORJ\ /L&$UQGW177DQJ45LSOH\(07UDFH .LUN-5XL]-&KHVOH\-:DOVKH-DQG(QJODQG HOHPHQWLQGLVFULPLQDWLRQGLDJUDPV/LWKRV *$PDMRU$UFKHDQJROGDQGFUXVWIRUP- LQJHYHQWLQWKH.DDSYDDO&UDWRQ6RXWK$IULFD /L=;/L;+.LQQ\3:DQJ-=KDQJ6 6FLHQFH =KRX+*HRFKURQRORJ\RI1HRSURWHUR]RLF .QXGVHQ7/$QGHUVHQ7:KLWHKRXVH0-DQG V\QULIWPDJPDWLVPLQWKH

37 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

$FWD 0R\HQ-)6WHYHQV*DQG.LVWHUV$5HFRUG /XGZLJ.58VHU¶VPDQXDOIRU,VRSORW*D of mid-Archaean subduction from metamorphims %HUNHOH\*HRFKURQRORJLFDO&HQWHU5LGJH LQWKH%DUEHUWRQWHUUDLQ6RXWK$IULFD1DWXUH 5RDG%HUNHOH\&$S GRLQDWXUH /XXNNRQHQ (- DQG 6RUMRQHQ:DUG 3$U- 1$6& 1RUWK $PHULFDQ 6WUDWLJUDSKLF FRGH NHHLQHQNDOOLRSHUl±LNNXQDPLOMDUGLQYXRGHQ $$3* %XOOHWLQ GRL WDDNVH,Q/HKWLQHQ01XUPL3DQG5lP| 27 (GV 6XRPHQNDOOLRSHUl±YXRVLPLO- 1LVEHW(*&KHDGOH0-$UQGW17DQG%LFNOH MRRQDD6XRPHQ*HRORJLQHQ6HXUDSS M.J. 1993. Constraining the potential temperature (in Finnish) of the Archaean mantle: A review of the evidence /XXNNRQHQ(-/DWH$UFKDHDQDQGHDUO\3UR- IURPNRPDWLLWHV/LWKRV WHUR]RLFVWUXFWXUDOHYROXWLRQLQWKH.XKPR±6XR- 1XWPDQ $3 )ULHQG &5/ DQG %HQQHWW 9& PXVVDOPLWHUUDLQHDVWHUQ)LQODQG7XUXQKainuu. .RVWRPXNVKDJUHHQVWRQHEHOW1:%DOWLF6KLHOG *HRORJLFDO6XUYH\RI)LQODQG5HSRUWRI,Q- (DUWKDQG3ODQHWDU\6FLHQFH/HWWHUV YHVWLJDWLRQSS 3XFKWHO,6+RIPDQQ$:$PHOLQ<9*DUEH 0LNNROD3+XKPD++HLOLPR(DQG:KLWHKRXVH 6FK|QEHUJ&'6DPVRQRY$9DQG6KFKLSDQ- 0$UFKHDQFUXVWDOHYROXWLRQRIWKH6XR- VN\$$&RPELQHGPDQWOHSOXPHLVODQG PXVVDOPLGLVWULFWDVSDUWRIWKH.LDQWDFRPSOH[ arc model for the formation of the 2.9 Ga Sumoze- Karelia: constraints from geochemistry and iso- UR.HQR]HURJUHHQVWRQHEHOW6(%DOWLF6KLHOG WRSHVRIJUDQLWRLGV/LWKRV isotope and trace element constraints. Geochimica 0RHFKHU'3DQG6DPVRQ6''LIIHUHQWLDO HW&RVPRFKLPLFD$FWD± zircon fertility of source terranes and natural bi- 5DQVRP%%\HUO\*5DQG/RZH'56XE- as in the detrital zircon record: Implications for DTXHRXVWRVXEDHULDO$UFKHDQXOWUDPD¿FSKUHDWR- sedimentary provenance analysis. Earth and Plan- PDJPDWLFYROFDQLVP.URPEHUJ)RUPDWLRQ%DU- HWDU\6FLHQFH/HWWHUVGRLM EHUWRQ*UHHQVWRQH%HOW6RXWK$IULFD,Q/RZH HSVO '5DQG%\HUO\*5 (GV *HRORJLFHYROXWLRQ

38 of the Barberton Greenstone belt. Geological So- ranes that the modern episode of subduction tec- FLHW\RI$PHULFD6SHFLDO3DSHU WRQLFVEHJDQLQ1HRSURWHUR]RLFWLPH*HRORJ\ 5H\3)&ROWLFH1)ODPHQW16SUHDGLQJ GRL* FRQWLQHQWV NLFNVWDUWHG SODWH WHFWRQLFV 1DWXUH 6WHUQ5-0RGHUQVW\OHSODWHWHFWRQLFVEHJDQLQ ± Neoproterozoic time: An alternative interpretation 6FKDQGO(6DQG*RUWRQ03$SSOLFDWLRQRI of Earth’s tectonic history. GSA Special Papers KLJK¿HOGVWUHQJWKHOHPHQWVWRGLVFULPLQDWHWHF- tonic settings in VMS environments. Economic 6YHWRY6$6YHWRYD$,1D]DURYD719H- *HRORJ\ GOR]HUR6HJR]HURJUHHQVWRQHEHOW&HQWUDO.DUH- 6FKRHQH%87K3EJHRFKURQRORJ\7UHDWLHV lia: new geochronological data and interpretation RQ*HRFKHPLVWU\ 6HFRQG(GLWLRQ RIUHVXOWV,Q*ROXEHYȺ,DQG9RORGLFKHY2, 6FKRSI-:.\GU\DYWVHY$%&]DKD$'7ULSD- (GV *HRORJ\DQGXVHIXOPLQHUDOVRI.DUHOLD WKL$%(YLGHQFHRI$UFKHDQOLIH6WURPDW- Issue 13. Petrozavodsk:KarRC RAS. 5-12. (ab- ROLWHVDQGPLFURIRVVLOV3UHFDPEULDQ5HVHDUFK stract in English) ± 7DLSDOH.7KHJHRORJ\DQGJHRFKHPLVWU\RIWKH 6KLUH\67.DPEHU%6:KLWHKRXVH0-0XHOOHU $UFKHDQ.XKPRJUHHQVWRQHJUDQLWHWHUUDLQLQWKH 3$DQG%DVX$5$UHYLHZRIWKHLVRWRSLF 7LSDVMlUYLDUHDHDVWHUQ)LQODQG$FWD8QLYHUVLW\ and trace element evidence for mantle and crustal 2XOXHQVLV6HULHV$*HRORJLFD SURFHVVHVLQWKH+DGHDQDQG$UFKHDQ,PSOLFD- 7DQJ0&KHQ.DQG5XGQLFN5/$UFKHDQ tions for the onset of plate tectonic subduction. XSSHUFUXVWWUDQVLWLRQIURPPD¿FWRIHOVLFPDUNV ,Q&RQGLH.&DQG3HDVH9 (GV :KHQGLG WKHRQVHWRISODWHWHFWRQLFV6FLHQFH plate tectonics begin on planet Earth? Geologi- GRLVFLHQFHDDG FDO6RFLHW\RI$PHULFD6SHFLDO3DSHU 7KXUVWRQ3&DQG&KLYHUV.06HFXODUYDULD- 6LUFRPEH.1DQG6WHUQ5$$QLQYHVWLJDWLRQ tion in greenstone sequence development empha- RIDUWL¿FLDOELDVLQJLQGHWULWDO]LUFRQ83EJHR- VL]LQJ6XSHULRU3URYLQFH&DQDGD3UHFDPEULDQ chronology due to magnetic separation in sample 5HVHDUFK preparation. Geochimica et Cosmochimica Acta 7KXUVWRQ3&DQG.R]KHYQLNRY91$Q$U- chean quartz arenite-andesite association in the 6OiPD-DQG.RãOHU-(IIHFWVRIVDPSOLQJDQG HDVWHUQ%DOWLF6KLHOG5XVVLDLPSOLFDWLRQVIRUDV- mineral separation on accuracy of detrital zircon semblage types and shield history. Precambrian VWXGLHV*HRFKHPLVWU\*HRSK\VLFV*HRV\VWHPV 5HVHDUFK 4GRL*& 7KXUVWRQ3&$\HU-$*RXWLHU-DQG+DPLOWRQ 6PLWKLHV5+&KDPSLRQ'&DQG&DVVLG\.) 0$'HSRVLWLRQDOJDSVLQ$ELWLELJUHHQ- )RUPDWLRQRI(DUWK¶VHDUO\$UFKDHDQFRQ- stone belt stratigraphy: A key to exploration for WLQHQWDOFUXVW3UHFDPEULDQ5HVHDUFK syngenetic mineralization. Economic Geology GRL6 6ODEXQRY$,/REDFK=KXFKHQNR6%%LELNRYD 7VLNRXUDV%3H3LSHU*3LSHU'-:+DW]LSDQDJ- (96RUMRQHQ:DUG3%DODJDQVN\999R- LRWRX.7ULDVVLFULIWUHODWHGNRPDWLLWHSL- ORGLFKHY2,6KFKLSDQVN\$$6YHWRY6$ FULWHDQGEDVDOW3HODJRQLDQFRQWLQHQWDOPDUJLQ &KHNXODHY93$UHVWRYD1$DQG6WHSDQRY *UHHFH/LWKRV 967KH$UFKDHDQQXFOHXVRIWKH%DOWLF 9DDVMRNL07DLSDOH.DQG7XRNNR,5DGLR- )HQQRVFDQGLDQ6KLHOG,Q*HH'*DQG6WHSKHQ- metric ages and other isotopic data bearing on the VRQ5$ (GV (XURSHDQ/LWKRVSKHUH'\QDP- evolution of Archaean crust and ores in the Kuhmo LFV*HRORJLFDO6RFLHW\RI/RQGRQ0HPRLU 6XRPXVVDOPLDUHDHDVWHUQ)LQODQG%XOOHWLQRI WKH*HRORJLFDO6RFLHW\RI)LQODQG 6RUMRQHQ:DUG3DQG/XXNNRQHQ($UFKHDQ YDQ+XQHQ-DQG0R\HQ-0$UFKHDQVXE- URFNV,Q/HKWLQHQ01XUPL3$5lP|27 duction: Fact or Fiction? Annual Review of Earth (GV 7KH3UHFDPEULDQ*HRORJ\RI)LQODQG.H\ DQG3ODQHWDU\6FLHQFHVGRL to the Evolution of the Fennoscandian Shield. De- DQQXUHYHDUWK YHORSPHQWVLQ3UHFDPEULDQ*HRORJ\YRO(O- YDQ +XQHQ - YDQ GHU %HUJ$3DQG9ODDU 1- VHYLHU$PVWHUGDPSS± 9DULRXVPHFKDQLVPV WR LQGXFH SUHVHQW 6WHLQ 0 DQG +RIPDQ 0DQWOH SOXPHV DQG GD\VKDOORZÀDWVXEGXFWLRQDQGLPSOLFDWLRQVIRU HSLVRGLF FUXVWDO JURZWK 1DWXUH the younger Earth: a numerical parameter study. GRLD 3K\VLFVRIWKH(DUWKDQG3ODQHWDU\,QWHULRUV 6WHUQ5-6XEGXFWLRQLQLWLDWLRQVSRQWDQHRXV 179-194. and induced. Earth and Planetary Science Letters 9DQ.UDQHQGRQN 0-9 3UHIDFH$UFKDHDQ WHFWRQLFV$UHYLHZ3UHFDPEULDQ5HVHDUFK 6WHUQ 5- (YLGHQFH IURP RSKLROLWHV EOXH- VFKLVWVDQGXOWUDKLJKSUHVVXUHPHWDPRUSKLFWHU- 9DQ.UDQHQGRQN 0- +LFNPDQ$+ 6PLWKLHV

39 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A40

5+DQG1HOVRQ'5*HRORJ\DQGWHF- :LOGH6$9DOOH\-:3HFN:+ *UDKDP& tonic evolution of the Archean North Pilbara Ter- 0(YLGHQFHIURPGHWULWDO]LUFRQVIRUWKH UDLQ3LOEDUD&UDWRQ:HVWHUQ$XVWUDOLD(FRQRPLF existence of continental crust and oceans on the *HRORJ\ (DUWK*\UDJR1DWXUH± 9DQ.UDQHQGRQN 0- 6PLWKLHV 5+ +LFNPDQ :LQFKHVWHU-$DQG)OR\G3$*HRFKHPLFDO $+DQG&KDPSLRQ'&5HYLHZVHFXODU discrimination of different magmaseries and their tectonic evolution of Archean continental crust: in- differentiation products using immobile elements. terplay between horizontal and vertical processes &KHPLFDO*HRORJ\ LQWKHIRUPDWLRQRIWKH3LOEDUD&UDWRQ$XVWUDOLD 7HUUD1RYD 9DQ.UDQHQGRQN0-,YDQLF7-:LQJDWH07' .LUNODQG&/DQG:\FKH6/RQJOLYHG autochthonous development of the Archean 0XUFKLVRQ 'RPDLQ DQG LPSOLFDWLRQV IRU