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Laale1 of the Plate Teetonie Evolution of GEOLOGIAN TUTKIMUSKESKUS GEOLOGICAL SURVEY of FINLAND TUTKIMUSRAPORTTI REPORT OF INVESTIGA TION 133 laale1 of the plate teetonie evolution of GEOLOGIAN TUTKIMUSKESKUS GEOLOGICAL SURVEY OF FINLAND Tutkimusraportti 133 Report of Investigation 133 Tapio Ruotoistenmäki A SCHEMA TIC MODEL OF THE PLA TE TECTONIC EVOLUTION OF FINNISH BEDROCK Geologian tutkimuskeskus Espoo 1996 Ruotoistenmäki, Tapio 1996. A schematic model of the plate tectonic evolution ofFinnish bedrock. Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Report o/Investigation 133. 23 pages and 13 figures. The evolution of Finnish bedrock du ring the time interval from about 2.9 - 1.86 Ga is divided into three main stages: I) Kuhmoan (- Belomorian) orogeny (ca. 2.8 - 2.6 Ga), 2) Svecobaltian orogeny (ca. 2.2 - 2. 1 - 2.0 Ga) and 3) Kainuan-Svecofennian orogeny (ca. 1.97 - 1.86 - ... Ga). The beginning and closing stages of these orogenies are recorded by increases in intracratonic mafic magmatism that are attributed to increased thermal activity beneath the crust. Culminations in orogenie felsic magmatism and tectonic activity are evident as sharp statistical modal peaks in the age distribution of Fennoscandian detrital zircons. By combining the various episodic culminations in mafic and felsic activity it has been possible to propose aseries of plate tectonic models to explain the main evolutionary trends in the development of the Finnish bedrock in both time and space. The main emphasis of this paper has been the evolution of central and southern Finland. Therefore, the applicability ofthese models becomes less certain further to the north - northeast, where it seems that simultaneous but separate large scale processes were operating giving rise to the Belomorian and Kola orogens. Key words: (GeoRef Thesaurus, AGI): crust, bedrock, evolution, plate tectonics, models, orogeny, igneous activity, Precambrian, Proterozoic, Finland Tapio Ruotoistenmäki Geological Survey 0/ Finland Betonimiehenkuja 4 FIN-02150 ESPOO, FINLAND ISBN 95 1-690-621-4 rSSN 0781-4240 Vammalan Kirjapaino Oy 1996 Ruotoistenmäki, Tapio 1996. A schematic model of the plate tectonic evolution of Finnish bedrock [Suomen kallioperän laattatektoninen kehitysmalli]. Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Report o/lnves­ tigation 133. 23 sivua ja 13 kuvaa. Suomen kallioperän kehitys aikavälillä 2.9 - 1.86 Ga on jaettu kolmeen päävaiheeseen: 1) kuhmolainen (-belomorinen) orogenia (aikavälillä n. 2.8 - 2.6 Ga), 2) svekobalttilainen orogenia (n. 2.2. - 2.1 - 2.0 Ga) ja 3) kainuulainen-svekofennialainen orogenia (n. 1.97 - 1.86 - ... Ga). Näiden orogenioiden alku- ja loppuvaihetta kuvastaa mantereellisen emäksisen magmatismin lisääntyminen,joka voidaan yhdistää kuorenalaiseen lämpötilan kasvuun. Orogenian kulminaatio­ vaiheeseen liittyy tektoninen aktiivisuus ja hapan magmatismi,joka kuvastuu maksimeina sedimenttisten zirkoni en ikäjakaumassa. Happamen ja emäksisen magmatismin ikäjakaumista voidaan siten päätellä Suomen kallioperän kehityksen päävaiheet. Pääpaino tässä työssä on Etelä- ja Keski-Suomen kallioperän kehityksessä. Mallien sovellettavuus pohjoiseenja itään päin mentäessä on epävarmempaa, sillä niillä alueilla on ilmeisesti ollut samanaikaisia, mutta osittain erillisiä tektonisia prosesseja Kuolan ja belomoridien alueilla. Asiasanat (Fingeo-sanasto,GTK): maankuori, kallioperä, kehitys, laattatektoniikka, mallit, orogenia, magmaattinen toiminta, prekambri, proterotsooinen, Suomi Tapio Ruotoistenmäki Geologian tutkimuskeskus Betonimiehenkuja 4 02150 ESPOO CONTENTS Introduction .................................................................................................................................................... 7 Closing stage of the Archaean sea (ca. 2.97 Ga) ....................................................................................... 9 Kuhmoan (-Be1omorian) orogeny: opening stage ofthe Karelian sea (ca. 2.8 Ga) .................................. 9 'Svecobaltian' orogeny (ca. 2.2-... Ga) ................................................... ................................................. 11 Svecofennian orogeny « 2 Ga) ............................................................................................................... 13 Conclusions ........... ...................... ..... .. .................................... .. .... .... ... ... ...................................................... 20 Acknowledgements ...................................................................................................................................... 20 References .. .. .................................................................................. .. .................... .. ................... ............. ...... 21 Abbreviations: AS: Archaean sea BMS: Belomorian sea BS: Baltian sea CG+SS: Central Finland granite island arc and Savo schist belt back-are basin DB: Diabase dykes EC: Eastern continent Gr: Granitoids GSF: Geological Survey of Finland H: Haveri seamount I: Iisalmi block IG: Greenstone volcanism 1+0: Jormua and Outokumpu ophiolites K+O: Kainuan-Outokumpu intracontinental sea KC: Karelian continent KG: Kuhmo greens tones KS: Karelian sea LBZ: Ladoga-Bothnian Bay fracture zone Lgb: Lapinlahti gabbro Mf: Mafic magmatism MORB: Mid-ocean ridge basalts NA: Näränkävaara-Auho fracture zone P: Pielavesi block Rgr: Rautavaara granulite SBC: Svecobaltian continent Sf: Svecofennian processes in Sweden and Estonia SfS: Svecofennian sea SG+TS: Southern Finland island arc and Vaasa-Tampere back arc basin SL: Karjalitic sills TH: Tervo-Haaparanta fracture zone To: Tonalitic magmatism Vgr: Varpaisjärvi granulite Vt: Vaasa overthrust H ", I have just one more question .. , H (Columbo) Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Report o/Investigatioll 133, 1996 A schematic model of the plate tectonic evolution of Finnish bedrock INTRODUCTION Since the pioneering paper of Anna Hietanen main basis for this work is in Fig. 1, which shows (1975) the plate tectonic theory has been widely the distributions of the ages of Fennoscandian invoked and applied in explaining the evolution of detrital zircons from central and southern Sweden the Proterozoic S vecofennian crust. Piirainen (1975) and Finland (Claesson et al., 1993), and zircon ages interpreted the Svecofennian metallogeny on basis of the principal rock components of the Belomo­ of plate tectonic theory. Gaal (1982, 1986) and rides (Bogdanova and Bibikova, 1993). The Fen­ GaaI and Gorbatschev (1987) applied the plate noscandian ages in the figure have been analyzed tectonic theory in explaining the evolution of late by SHRIMP ion microbrobe thus reducing the Archaean and Proterozoic crust in Finland and possibility of mixed ages. Because the sampIes are Russian Karelia. Ekdahl (1993) considered the from metagreywackes and quartzites from througout evolution of ore controlling Raahe-Ladoga zone central and southern parts of Finland and Sweden (Ladoga-Bothnian Bay zone, LBZ) in central Fin­ they can be taken as representative random sampies land using the plate tectonic theory. Lahtinen (1994) of felsic crustal blocks supplying material to Sve­ presents a comprehensive plate tectonic picture of cofennian sediments. Their age distribution is also the evolution of the Proterozoic bedrock of south­ wide, including all the known main periods of ern Finland. Korja (1995) examined the Svecofen­ evolution recorded in the Finnish bedrock with the nian crustal evolution using the large amount of exception of significant 2.1 - 2.0 age interval, deep seismic sounding data available from Fenno­ which indicates the existence of previously undoc­ scandian region. Park et al. (1984), Ward (1987) urnented, 'exotic' felsic crust close to the Fennos­ and Kohonen (1995) have considered the plate candian shield ca. 1.9 Ga ago (Huhma et al. , 1991 ; tectonic evolution in eastern Finland. Claesson et al. , 1993). The conventional multi­ In this paper I present a relatively simple series grain zircon ages given by Bogdanova and Bibi­ of plate tectonic models covering the evolution of kova (1993) represent the latest and, probably, the the Finnish bedrock from ca. 2.9 Ga to 1.86 Ga. The most reliable information of the evolution of Be- 30 90 25 80 70 20 15 10 I. 0 340033003200310030002900280027002600250024002300 2200 2100 2000 1900 1800 Age [Mal _ Svecofennian c=::JBelomorian - . - Svecofennian - 0 - Belomorian Fig. 1. V-Th-Pb isotopic age distribution for zircons from Svecofennian metasediments ana lyzed by SHRIMP ion microprobe by C laesson et al. ( 1993) and Belomorian intrusive ages (Bogdanova and Bibikova, 1993). Bars: frequencies, lines+circles: cumulative frequencies. 7 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Finland, Report of In vestigation 133, 1996 Tapio Ruotoistenmäki lomorian belt bordering the Archaean craton in the Fennoscandian orogenic processes appear to have east. Another important paper in this context is that of had both systematic and chaotic characteristics. Huhma (1986) which defined the location of the Although processes are considered here at a Archaean-Proterozoic boundary in Finland using Sm­ relatively local scale, i.e. from the viewpoint of the Nd, U-Pb and Pb-Pb isotopic analyses. Besides the Finnish region, one must keep in mind that in most above age data, the large number of multi-grain cases these processes have been related to global zircon ages produced by the Geological Survey of scale tectonics, even in Archaean time, as pointed Finland and those
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