OUTOKUMPU OY 020/Baltian kilpi/TJK ym./1985 MALMINETSINTÄ Tapio KOistinen/LAP 8.3.1985
ABSTRAKTIKOKOELMA; Helsinki symposium on the Baltic Shield, 4-6/1985
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JAKELU OKME/Etelä-Suomi, OKME/LäTIsi-Suomi, OKME/ltä-Suomi 1 I I 1 Prof. R. Gorbatschev Dr. G. Gaal Dept. of Mineralogy and Geological Survey of Petrology Finland Institute of Geology Kivimiehentie 1 Lund University SF~02150 ESPOO 15 Sölvegatan 13 FINLAND S-223 62 LUND SWEDEN
Dear Colleague,
In order to activate international. cooperation on the Pre cambrian of northern Europe within .the framework of the Internationa1 Lithosphere Program(ILP), particu1arly its ) working groups WG 3 and WG 4, we wou1d 1ike to suggest a fact finding and prob1em-defining workshop to review the present state of knowledge and p1an future joint research efforts.
The problems concerned wi1l be particu1arly the formation of the Proterozoic 1i thosphere, the co~tinua tion of ArcheanlTEhoge·I}e'El.c processes- in - ~- Proterozoic, and the~ve~opment~I:the-Soundary 1fetween tne PioteroZOlcärid the Archean in the central Baltic :.s1iie ld, i. e. tne-S-vecokarel lan-··-an-cf Archean- -reg ions- ef Finiand and Sweden. In addition, these aspects wi1l be related to the general Proterozoic development of the shie1d.
Since this is the first effort at such a co-operation attempting to knit together more c1ose1y the treatment of Ear1y and Mid Proterozoic prob1ems in Finland, Sweden and Norway, it is our idea to limit participation in this pioneer workshop to a number of invited workers who are personal1y invo1ved in research on the subject, encouraging them to give reviewsof their particu1ar fields of work. We wou1d also 1ike to keep the workshop as informal as possib1e, not, at this stage, involving governmenta1 organizations as such. ) To get things gOing, we suggest that we meet already on March ) 4-6th, 1985 in Helsinki. Housing at reduced prices in shared double rooms wil1 be arranged in Helsinki and we have good hopes of being ab1e to raise funds to subsidize travel1ing particularly for participants from continental Europe and Britain.
Please indicate your interest to participate on the enclosed form and return it before September 1, 1984 to R. Gorbatschev.
atschev · i Helsinki Symposium on the Central Baltic Shield Helsinki March 4 - 6, 1985
LIST OF PARTICIPANTS
BARBEY, Pierre, Dr. FRIETSCH, Rudyard, Prof. Laboratoire de Petrologie Högskolan i Luleå Universite de Nancy I Avd. för ekonomisk geologi C.O. n:o 140 S-951 87 LULEA 54037 NANCY CEDEX Sweden France FRONT, Kai, M.Sc. BERTHELSEN, Asger, Prof. Dept. of Geology Geologisk Central Institut Div. of Geology and Mineralogy 0. VOldg. 10 University of Helsinki DK-13S0 COPENHAGEN K Snellmaninkatu 5 Denmark SF-00170 HELSINKI Finland BJÖRKLUND, Alf, Prof. Geological Survey of Finland GAÄL, Gabor, Dr. SF-02150 ESPOO Geological Survey of Finland Finland SF-02150 ESPOO Finland CLAESSON, Lars-Ake, FK Sveriges Geologiska Ab GORBATSCHEV, Roland, Pro=. Box 801 Dept. of Mineralogy & Petrology S-951 28 LULEA University of Lund Sweden Sölvegatan 13 S-22362 LUND CLAESSON, Stefan, Dr. Sweden Naturhistoriska riksmuseet Section for Mineralogy HAAPALA, Ilmari, Prof. Laboratory for Isotope GeologJDept. of G~ology Box 50007 Div. of Geology a~d Mineralogy S-1 04 05 STOCKHOIJ.l University of Helsinki Sweden Snellmaninkatu 5 SF-00170 HELSINKI EHLERS, Carl, Prof. Finland Geologiska institutionen Aho Akademi HENKEL, Herbert, Dipl. geofys. 20500 ÅBo Sveriges Geologiska Undersökning Finland Geofysiska sektionen Boy. 670 S-751 28 UPPS~. Sweden \" \ 2 1, KORHONEN, Heikki, Prof. HJELT, Sven-Erik, Prof. Institute of Seismology University of Oulu University of Helsinki Linnanmaa Et. Hesperiankatu 4 SF-90570 OULU SF-00100 HELSINKI Finland Finland HUBBARD, Fred, Dr. KORHONEN, Juha, L.Eng.Sc. Geology Department Geological Survey of Finland The University SF-02150 ESPOO DUNDEE, 001 4HN Finland Scotland Great Britain KORSMAN, Kalevi, Dr. Geological Survey of Finland HUHMA, Hannu, M.Sc. SF-02150 ESPOO Geological Survey of Finland Finland SF-02150 ESPOO Finland KOUVO, Olavi, Dr. Geological Survey of Finland HYVÄRINEN, Lauri, Prof. SF-02150 ESPOO Geological Survey of Finland Finland SF-02150 ESPOO Finland
HÖLTTÄ, Pentti, M.Sc. Geological Survey of Finland SF-02150 ESPOO Finland KÄHKöNEN, Yrjö, L.Ph. Dept. of Geology Div. of Geology and Mineralogy KAORANNE, L.K., Director University of Helsinki Geological Survey of Finland Snellmaninkatu 5 SF-02150 ESPOO SF-00170 HELSINKI Finland Finland K..~UTSKY, Gunnar, Dr. LAAJOKI, Kauko, Prof. Sveriges Geologiska Undersökning University of Oulu Box 670 Dept. of Geology 5-75128 UPPSALA Linnanmaa Sweden SF-90570 OULU Finland von KNORRING, Mary, U.Sc. Geological Survey of Finland LINDH, Anders, Doc. SF-02150 ESPOO Lunds Universitet Finland Avd. för Mineralogi och Petrolo~J Sölvegatan 13 KOISTINEN, Tapio, Dr. S-222 36 LUND Outokumpu Oy Sweden SF-83500 OUTOKUMPU Finland LUND, Carl-Erik Avd. för fasta jordens fysik KORPELA, Kauko, Prof. Uppsala universitet Geological Survey of Finland Box 556 SF-021S0 ESPOO 5-751 22 UPPSALA Finland Sweden 3
LUNDQVIST, Thomas, Dr. PHARAOH, Tim, Dr. Sveriges Geologiska Undersökning British Geolcgical Survey Box670 Keyvorth 5-75128 UPPSALA NOTTINGHAM NG12 5GG Sweden • Great Britain LUNDSTRÖM, Ingmar, Fil.lic. Sveriges Geologiska Undersökning PESONEN, Lauri, Dr. Berggrundssektionen Geological Survey of Finland Box 670 SF-02150 ESPOO S-751 28 UPPSALA Finland Sweden PIPPING, Fredrik, L.Ph. Geological Survey of Finland SF-02150 ESPOO .... . Finland
MARKER, Martin RICKARD, David, Prof. Geologisk Centralinstitut Department of Mineral Exploitation 0ster Voldgade 10 University College DK-1350 COPENHAGEN K Newport Road Denmark CARDIFF, CF2 1TA Great Britain MARTIN, Herv~, Dr. Universit~ de Rennes I SIGMOND, Ellen M., F~rstestatsgeol c c Institut de Geologie Campus de Beaulieu Norges Geologiske Unders~kelse Avenue du General Leclerc Postboks 3006 35042 RENNES Cedex N-7001 TRONDHEIM France Norge MERILÄINEN, Kauko, Dr. SILVENNOINEN, Ahti, Dr. Geological Survey of Finland Geological Survey of Finland SF-02150 ESPOO Box 77 Finland SF-96101 ROVANIEMI Finland NURMI, Pekka, Dr. Geological Survey of Finland TAIPALE, Kalle, Dr. SF-02150 ESPOO Geological Survey of Finland Finland SF-02150 ESPOO OEN, I.S. Prof. Finland University of Amsterdam Geological Institute TALVITIE, Jouko, Prof. Nieuwe Prinsengracht Geological Survey of Finland AMSTERDAM SF-02150 ESPOO The Netherlands Finland PAOGET, .Peter, Dr. TIAINEN, Markku, loi. Se • Norges Geologiske Unders~kelse : Geological Survey of Finland Postboks 3006 SF-02150 ESPOO N-7001 TRONDHEIM Finland Norge TONTTI, Mikko, L.Ph • PAPUNEN, Heikki, Prof. . Geological Survey of Finland Dept. of Geology SF-02150 ESPOO University of Turku Finland SF-20500 TUR.T{U Finland •
WELIN, Eric, Prof. Naturhistoriska riksmuseet Sektionen för mineralogi Laboratoriet för isotopgeologi Box 50 007 S-104 05 STOCKHOLM Sweden WESTRA, Laszlo, Dr. Instituut voor Aardwetenschappen Vrije Universiteit 1007 me AMSTERDAM De Boelelaan 1085 Postbus 7161 The Netherlands, VORMA, Atso, Prof. Geological Survey of Finland SF-02150 ESPOO Finland ÖHLANDER, Björn, Bergsingenjör Högskolan i Luleå Avd. för ekonomisk geologi S-951 87 LULEA Sweden · /
P R 0 G R A M M E
HELSINKI SYMPOSIUM ON THE BP~TIC SHIELD
4-6. March 1985
A Finnish-Swedish contribution to the International Lithosphere Proqram. Working Group 3: Proterozoic Lithospheric Evolution Working Group 4: Archean Lithosphere
j
Conveners: Gabor Gaal (WG 3, 4), Roland Gorbatschev (WG 3 and chairman of the Swedish ILP committee) and Mary von Knorring (secretary of the Finnish ILP-committee) Monday 4.3.85
8.30 Visit to the Geologieal Survey of Finland
10.00 Opening of the Symposium
10.10 G. Gaal: Evolu ion ef the Arehaean and Proterozoie erust in the n rthern and eastern Baltie Shield 10.30 R. Gorbatsehev Crustal evolution in the western and Bal tie Shield seen against the baekgr()]Jnd . an and Proterozoie Ii thoge!1esis f~ f AL 10.50 C.E. geophysieal results of Fennolora 79
11. 10 H. Korhonen: V loei ty strueture of the Earth' s erus~: in Finl d ( _el--- 11 . 30 S.E. Hjelt: As eets ef the geoeleetrie models of th~e~ ____~ Baltie S ield ( ----e.J 0..;;;11 11 .50 Lunch
12.50 Eriksson & Henkel: Regional geophysieal studies in ~, t Seandinavia ~ ~ . ~
13.10 J. Korhonen: Geomagnetie modelling of upper and lower _~_ erust in Finland 13.30 o. Kouvo: Geologieal ehronogram, Finland: A eomparative study CE 1 a.-b:ji, 13.50 Diseussion
14.00 Coffee
14.25 Ellen Sigmond: Review of Preeambrian ge~logy in SW Norway
14.45 T. Falkum: The relationship between syn- and preofO~n~_!~ . roeks in the Sveeonorwegian orogeny L ~ _~ . 15.05 A. Lindh: Westward growth of the Baltie Shield in SW Sweden j 15.25 Diseussion
15.35 Break 10 min.
15.45 G. Kautsky: The Nordkalott Prejeet
16.05 A. Silvennoinen: The voleanite projeet in northe~_t~~.' Finland l ~ 16.25 A. Björklund: Large-seale struetures ef Preearnbrian on the Nordkalott as refleeted by geoehemistry 16.45 Dinner 2
17.45 Discussion and a contribution by M.A. Etheridge: "An Early Proterozoic tectonic model from Northern Australian Provinces"
20.00 Sauna and evening snack at VKK
Tuesday
5.3.85
8. 15 H. Martin and P. Barbey: Contrasting Archaean and Early Proterozoic evolutions of the eastern part of the Baltic Shield 8.35 B. Barbey: Early Proterozoic lithogenetic processes as exemplified by the Belomorian Mobile Belt 8.55 A. Berthelsen and M. Marker: The teetonies of the Lapland Granulite Belt and the Kola Suture 9.15 H. Martin: Genesis and evolution of the continental Archaean crust of East Finland 9.35 Discussion
9.45 Coffee
10.10 T. Skiöld: Comments on the geochronoloqy of northern Västerbotten and Norrbotten, Sweden (written contribution to be read)
10.20 T.C. Pharaoh: Geochemical evidence for the origin of Early Proterozoic volcanic suites in the Northern part of the Baltic Shield 10.40 K. Laajoki: The Early Proterozoic Kainuu Schist Belt and its relationship to the Late Archaean basement 11. 00 T. Koistinen: On the sequential fragmentation in the Karelides region, eastern Finland
) 11 .20 K. Korsman: Metamorphism as an indicator of the evolution .' of the crust 11.40 Discussion
11 .50 Lunch
12.50 I. Haapala and K. Front: Petrology of Nattanen-type granites, northern Finland 13.10 B. öhlander: Contrasting granite types in northernmost Sweden 13.30 R. Gorbatschev: Development problems of the Svecofennian lithosphere juvenile or regenerated~ntinental crust? ~! /~fn,tr 3
13.50 Discussion
14.00 Coffee
14.20 H. Huhma: Proterozoic crustal evolution in Finlanö: Sm-Nd isotopic evidence 14.40 S. Claesson: Sm-Nd data on Proterozoic mafic rocks from central Sweden 15.00 R. Frietsch: Proterozoic volcanism in central and northern Sweden 15.20 L.A. Claesson: Geochemistry of volcanites in the Skellefte Field, Northern Sweden ~) 15.40 Discussion 15.50 Break 10 min.
16.00- Work-shop 18.30
19.00 Dinner on HoteZ DipoZi (70 FIM)
Wednesday
6.3.85
8.30 E. Welin: Svecofennian sedimentation 8.50 C. Ehlers: The geochemistry and stratigraphic position of the volcanic rocks in the Svecofennides of SW Finland 9.10 Y. Kähkönen: General geochemical features of the meta volcanics of the Proterozoic Tampere Schist Belt \ 9.30 Discussion
9.40 Coffee ) 10.00 I. Lundström: Current problems in Bergslaqen geology, central Sweden 10.20 Th. Lundqvist: Geology in central Norrland, Sweden 10.40 K. Front and P. Nurmi: Characteristics of the syn kinematic Svecokarelian granitoids in southern Finland
11 .00 F. Hubbard: High-crustal level, late-orogenic magmat1sm and tectonism in the central segment of Aland 11 .20 L. Westra: Thermo-tectonic control of low-pressure granulites in southern Finland 4
11 .40 • Discussion 11.50 Lunch
12.45 I.S. Oen: Geology and rnetallogenesis in the Proterozoic of central Sweden
13.05 D. Richard: Irnplication of the setting Pb-Nd-S~ isotopic systerns at Kiruna, Sweden ~ ____ I 13.25 I. Haapala: Petrogenetic and rnetallogenetic aspects of the rapakivi granites \~ ~r 13.45 Discussion
13.55 Coffee ) 14.15- Final discussion 15.00
15.10 Bus leaving for airport
) "
G. Gaal
EVOLUTION OF THE ARCHEAN AND PROTEROZOIC CRUST IN THE NORTHERN AND EASTERN BALTIC SHIELD
Helsinki Symposium on the Baltic Shield, 4-6 March, 1985
INTRODUCTION
The extension of the plate tectonic concept down the Pre cambrian time scale during the past ten years has completely changed our thinking in Precambrian geology. Thanks to this development, and the major advances in various branches of geoscience, much progress has been made in understanding - the Precambrian geology of the Baltic Shield. This symposium aims at a representative cross section of the state of the art and we have convened experts who will express their ideas also on the crustal evolution of the eastern and northern parts of the Baltic Shield. As an introduction I shall give you a broad review of the subject and some of the views I present may have to be corrected in the light of evidence presented in the forthcoming talks. I am prepared for this. Broad regional concepts should be looked at with open mind and I personally hope that this symposium will succeed in building up a constructive and positive spirit of cooperation.
THE MAJOR TECTONIC UNITS OF THE BALTIC SHIELD
Fig. 1 The Baltic Shield exhibits geochronological zoning with younging ages from east to west within the time span between 3100 Ma and 900 Ma. The 2200 Ma crustal evolution occurred in five tectonic cycles: - 2 -
( 1 ) The Early Archean cycle (> 2900 Ma) (2 ) The Late Archean cycle (2900 - 2500 Ma) ( 3) The Svecokarelian cycle (2200 - 1550 Ma) (4 ) The Southwest Orogen (1780 - 1550 Ma) (5) The Sveconorwegian cycle (1200 - 1000 Ma)
The first three cycles affected the eastern part of the Baltic Shield, where the following tectonic units can be distinguished: Low-grade terrain (green) with the granitoid -greenstone belt association; High-grade terrain (red) with the Kolan and Belornorian gneisses Early Proterozoic intracratonic belts, e.g. the Petsenga-Irnadra-Varzuga belt and the Granulite Cornplex of Lapland; Early Proterozoic geosynclinal cornplex (blue) sub divided into the Karelides on the continental rnargin the Suture Zone and the Svecofennides.
DEVELOPMENT OF THE ARCHEAN CRUST
Fig. 2a According to available evidence the evolution of the Archean crust started with granitoids sorne 3000 - 3100 Ma ago. Granitoids and greenstone belts forrn a typical low-grade terrain with rnajor green stone belts nurnbered here 1 - 21. The age of the greenstone belts in the northern part of the
Baltic Shie~ d is currently in dispute. The Archean age is plausible for the Sodankylä greenstone belt (no. 20 on the rnap) , where the layered gabbro cornplex of Koitelainen, dated by the U-Pb rnethod at 2450 Ma, intrudes the surrounding supra crustals. The sarne lithology continues in the Karasjokk belt. - 3 -
~ The Kittilä greenstone belt and the "older greenstones" of Kiruna, on the other hand, are depicted as Early Proterozoic.
The greenstone-belt rocks deposited between 2900 Ma and 2700 Ma either on older ensialie basement or on limited oceanic crust in rift environments. The greenstone-belt lithologies vary substantially from belt to belt and strati graphic correlations are problematic. The lowermost unit of the belt may be basal conglomerate, quartzite, komatiite or graywacke. In some green stone belts komatiitic and tholeiitic volcanics predominate (Kuhmo, no. 17, Sodankylä no. 20) in others calc-alkaline volcanics (Hautavaara, no. 1).
Fig. 2b The high-grade terrain of the Belomorian gneisses is in juxtaposition to the greenstone belts of Soviet Karelia. The boundary is a mylonite and fault zone dipping northeast. The Belomorian gneisses are chiefly supracrustals of geo synclinal derivation metamorphosed at an early stage under high- to mediurn-pressure granulite faeies conditions and folded in four deformational phases. The assumed depositional age is 2900 - 2700 Ma, and U-Pb ages on zircons indicate an event of intensive metamorphism and magmatism 2700 Ma ago and episodic loss of lead 1850 Ma ago. The age, lithology, and deformational and metamorphic history of the Kolan gneisses are similar to those of the Belomorian gneisses.
Fig. 3 This diagram reconstructs the crustal evolutionary stage 2800 Ma ago: Archean ensialie crust older than 2900 Ma existed in the west, in the area now adjoining the Svecokarelian orogenic belt. This environment formed a protocontinent that can justifiably be referred to as the nucleus of the Baltic shield. About 2900 Ma ago a geosynclinal system, underlain by a hypothetical oceanic crust, evolved on the eastern side of the protocontinent. The collisional stage might have started some 2800 Ma ago, resulting in the development of a - 4 -
subduction zone or a subparallel system of subduction zones dipping to the west or southwest. A N-NW-trending island arc system was formed with tholeiitic and calc-alkaline volcanism. In marginal basin environments komatiitic magma ascended from the upper mantle. The westernmost greenstone belts in Finland and Norway were generated in a back-arc rift system environment. Farther west the Archean proto continent was covered by Archean platform-type sediments as described from the Kotalahti area.
PROTEROZOIC HISTORY OF THE ARCHEAN CRUST
Fig. 2c Significant Proterozoic tectonic-magmatic reactivation is a special feature of the Baltic Shield. After the intensive Late Archean crust-forming event the newly formed crust had consolidated by 2500 Ma. Tectonic quiescence was, however, not achieved and soon after consolidation a period of block faulting started and the terrestrial volcano-sedimentary sequence of the Sumi-Sariola group deposited in N-NW and E-W trending rift zones 2500 - 2300 Ma ago. Where tholeiitic volcanics of this group overlie Archean greenstone belts the Archean-Proterozoic bounday becomes obscured and it has proved difficult to draw the boundary, for example, in Finnish Lapland, in Finnmark and in Vetrenyy Poyas. The Sumi-Sariola group was followed by a short quiet period marked by subaerial weathering. This in turn was followed by the deposition of the platform sediments and volcanics of the Jatulian group 2300 to 2000 Ma ago.
Fig. 2d Towards the end of the Jatulian time the tensional deforma tion of the continental crust accelerated, leading finally, about 2000 Ma ago, to the splitting up of the Archean continent. The major lines of separation, depicted on this figure, are characterized by belts of mafic-ultramafic rocks - 5 -
marking either intracratonic or marginal sutures:
• In the Ladoga-Bothnian Bay - Skellefteå zone a passive continental margin evolved (1);
• A continental basin opened up behind the margin, setting the depositional environment of the Outokumpu rock association (2);
• The NW-trending branch (3) has characteristics of an aulacogene;
• The Granulite complex of Lapland has been inter preted by Barbey (1982) to have evolved as an intercontinental collision belt (4);
• The Petsenga - Imadra - Varzuga belt (5) has been interpreted by Berthelsen (1984) to be the result of a continent-continent collision preceded by the development of a wide rift zone or Red-Sea type of ocean (= "Kola Suture").
Fig. 2e Proterozoic magmatic reactivation continued until the end of the Early Proterozoic, when the northern part of the Baltic Shield was invaded by diapiric granitoid bodies during the Svecokarelic cycle 1900 - 1700 Ma ago. The ultimate cause of this magmatism might be subduction of the oceanic crust towards the NE under the Archean crust. - 6 -
DEVELOPMENT OF THE PROTEROZOIC CRUST
Since the development of the Proterozoic crust will be subject of Roland Gorbatschev's talk, I shall restrict the time I have left to a short review of the eastern margin of the Svecokarelian complex.
The western limit of the Archean basement has been delineated, mainly by geochronological studies, along a NW-trending line north of the Skellefteå belt and south of Kuopio. The old division into Karelides and Svecofennides is nowadays seen in a new light: The Karelides are part of the Svecokarelian orogen underlain by Archean continental crust and the Sveco fennides have no Archean basement but were forrned on fresh oceanic crust. The junction between the Karelides and the Svecofennides is a crustal feature of the first order known as a "suture".
Fig. 2f The continental shelf and marginal basin are the dominant environments of the Karelides. We shall probably be given a detailed description of the Outokumpu region in the talk by Tapio Koistinen and of the shelf environment in the talk by Kauko Laajoki. Perhaps the most prominent feature of the Karelides is the presence of ophiolite nappes testifying to the closing of the marginal basin.
Fig. 2g The evolution of the marginal basin is a consequence of the transformation of a passive continental margin into an active continental margin with subduction of oceanic crust under the Archean craton in the east. The first subduction re sulted in the developrnent of a tholeiitic island-arc system right at the edge of the craton. This environment is charac terized by bimodal tholeiite-trondhjemite/tonalite magmatism. Scattered gecchronological data along the suture zone indicate the interval 1930 Ma - 1880 Ma for the age of the - 7 -
development of the tholeiite-island arc system. The system contributed comparatively little to the formation of new Proterozoic crust. The really effective crust-forming process culrninated somewhat later, around 1880 Ma, when the extensive calc-alkaline island-arc system wasformedfartherwest.
Fig. 4 This sketch attempts to explain and illustrate the generation of the tholeiite island arc system (above) and the calc -alkaline island arc system (below).
CONCLUSION
Integrated models explaining both Archean and Early Protero zoic lithosphereric evolution are based on plate tectonic concepts. I see no reason why plate tectonic processess should notalready have acted in the Early Precambrian. What should be important in the future is how to apply the plate tectonic concept to the Precambrian of the Baltic Shield. The generalized models should now be replaced by refined versions which take into account alI the progress made in the fields of isotope geology, metamorphic and magma petrology, structural geology, sedimentology, geochemistry and geophysics. AlI these branches of geoscience have led to remarkable achievements in our knowledge of the Baltic Shield and it is up to us now to coordinate these efforts to make out of the Baltic Shield a model for Precambrian lithospheric evolution. ."
- 8 -
FIGURE CAPTIONS
Fig. 1. Major units of the Precambrian of the Baltic Shield. Explanations: 1. Phanerozoic platform cover, 2. Caledonides, 3. Rapakivi granites anc porphyry belt, 4. Early Proterozoic greenstone belts: 1-6 (1. Petsenga, 2. Imadra Varzuga, 3. Vet=enyy Poyas, 4. Central Soviet Karelia, 5. Suisaari, 6. Kiruna, Kittilä etc. green stone belts), 5. Inferred western boundary of the Archean crust, 6. Protogine zone, 7. Thrust fault.
Fig. 2. The Precambrian of the Baltic Shield. Explanations: 1 . Ar c h ean gran••;to;ds, 2. Belomorian and Kolan gneisses, 3. Late Archean greenstone belts: 1-18 (1. Hautavaara, 2. Manga, 3. Jalonvaara, 4. Himola, 5 . Koikari, 6. Matkalahti, 7. Sumozero-Kemozero, 8. South Vygozero, 9. Bergaul, 10.Parandova, 11. Kostomuksha, 12. Tikshozero, 13. Paana- järvi, 14. Kuolajärvi, 15. Ilomantsi, 16. Tipasjärvi, 17. Kuhmo, 18. Suomussalmi, 19. Jauratsi, 20. Sodankylä, 21. Karasjokk). 4. Early Proterozoic infracratonic greenstone belts, 5. Early
Proterozoic mafic intrusions, 6. Platfor~ cover (Jatulian and
S~~i-Sariola groups), 7. Shelf sediments and proximal tur~idites, 8. Ophiolite nappes, 9. Metagraywackes (micaschists anä mica gneisses), 10. Island arc volcanites and related sediments: 19-27 (22. Aijala-Orijärvi, 23. Hämeenlinna, 24. Tampere schist belt, 25. Haukivesi, 26. Kiuruvesi-Pyhäsalmi, 27. Pihtipudas, 28. Ylivieska, 29. Skellefteå, 30. Bergslagen province) • 11. High-grade rocks (mostly metapelites), 12. Granulite complex of Lapland, 13. Synoroge."'lic te postorogenic Svecokarelian granitoids, 14. Rapakivi granites, 15. Värmland-Småland porphyry granite, 16. Jotnian and Sub-Jotnian rocks, 17. Sveconorwegian gneisses, 18. Telemark suite, Dal group, Kapebo group, 19. Late P=otero zoic granites, 20. Caledonides, 21. Sedimentary cover of the East European platform, 22. Oslo graben, 23. Paleozoic'alkaline intrusions, 24. Eocambrian autochton, 25. Cataclastic zone, 26. Thrust fault, 27. Strike slip fault, 18. Fault in general. - 9 -
Fig. 3. Plate tectonic model for t~e Late Archean cycle of the Baltic shield c. 2800 Ma ago, not to scale. ,Explanations: 1. Upper mantle, 2. Archean platforrn cover, 3. Oceanic crust, 4. Geosynclinal sedirnents, 5. Komatiitic and tholeiitic volcanics, 6. Rift-stage sediments, 7. Granitoid diapirs, 8. Calc-alkaline volcanics.
Fig. 4. Plate tectonic rnodel for the Svecokarelian cycle of the Baltic shield c. 1920 Ma ago (above) and c. 1880 Ma ago (below), approximately to scale. Explanations: 1. Oceanic crust, 2. Upper mantle, 3. Archean granitoids, 4. Archean greenstone belts, 5. Early Proterozoic platforrn cover, 6. Eugeosynclinal sediments, 7. Younger proximal turbidites, 8. Volcanic rocks, 9. High-grade met arnorphi sm , 10. Trondhjemite-tonalite magma, 11. Tholeiite magma, 12. Ni bearing gabbro-peridotite, 13. Calc-alkaline rnagma, 14." Porphyritic granite-granodiorite, 15. Alkaline magma, 16. Generation depth of trondhjemite-tonalite (Tr), tholeiitic (Tho) , calc-alkaline (Cal) and alkaline(Alk) magma, 17. Faults: A. Haukivesi fault, B. Suvasvesi fault, C. Pihlajavesi/Kolkon järvi fault. Fig.1
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58"
~~t::~:·A.~ M> I Y ~1-t+J~-o 1 ~ 8 c:zJ 15 0 22 r:8 w E c.2800 Ma Archean Back-arc rift Calc-al'kaline Geosynclinal Continent platform cover green stone belts island arc domain (Kotalahti) (Kuhmo-Suomussalmi) (Hautavaara) (Belomorian and Kolan .gneisses) + + + + + + + + + + + + + + + + \ / .... \' \ .... , \. I I '_1 " , "~\I"'I"'\ ...... / " ,. , -/\-, .... \1 '" \ / ... ;;. "', ...... I \ \ ,,~- I - \ ' ~ I / /_,1"'" _1... 1 2 ~3§4 Ei35 1:.-.:::-:, 6 le017 ~ 8 6 ."_. co c.u• • WSW ENE 50km Okm I + + + +~~~++ + + + v v v '-50 100 WSW ~Q) ;:,C ENE Svecofennldes -0 en;:'N Karelldes ® 50km ••••• •• 0 km + + + + AA + + v v 50 JITr v v v v lITi!ill!j 1 ..:q~J~ v ~~ ~. ~ yvl" • '~J v ~ v .'. v TT'Tho • · ~2 [2J 10 v '1hi>;"... vf.\ v v _ v v v 100 3 • •• 11 c::::2J Cl • "%" J v ~~ v "%~ • GEOPHYSICAL RESULTS OF FENNOLORA Carl-Erik Lund Based on the Fennolora results the crust along the profile can mainly be devided into 3 areas with different velocity-depth models.The northern area,mainly confining the archean and the sveco-karelidic basement,is characterized by pronounced velocity reversals in the upper crust.Oown to a depth of c.15 km up to three velocity reversals have been recorded,with apparent velocties as high as 6.8 km/s.The high velocity in the upper crust seems to be azimuth dependent.The central segment,confining the northern centralpart of the svecofepnian basement is charachterized by smoothly increasing velocity with depth.The velocity is not asimuth dependent.Along the remaining southern part of the profile the velocity-depth models are charachterized by modest velocity reversals in the upper part of the crust. The -! crustal thickness varies between c.37 km beneaththe southermost end of the profile and c.53 km in the central lsvecofennian part of the profile.ln the archean part the crust seem to be about 45 km thick. - The Mandal - Ustaoset line, a newly dfscovered major-fault zone fn :: . .South Norway. B·~~ ; ~ .. ~ .... . r :~ · : ;.; ::: : ~ ..:. - . .. Ellen M.O. Sigmond Norges geologiske undersekelse P.O.Box 3006, 7001 Trondheim, Norway ABSTRACT. Survey mapping and compilation in connection with the new 1:1 mil1ion geological bedrock map of Norway have revealed that the Precambrian rocks of South Norway can be divided into two blocks by a large tectonic line, the Mandal-Ustaoset Fault Zone. The 10cation of such a tectonic line is indicated by the presence of ultracataclasites and mylonites along fts central and northern parts; by a belt of post tectonic granites west of the fault zone; by the distribution af the Telemark supra-crustals; and by the higher and more irregular magnetic -field, and more numerous radiometric anomalies, west of the fault. It is uncertain whether the tectonic line represents a continent-continent col1ision suture, a col1ision which in this case must have taken place before the deposition of the Bandak Group of the Telemark supracrustals (pre-1200 Ma), or a mega-fault zone. The latest movements along the fault zone took place in its central and northern parts along low angle faults, after intrusion of the past-tectonic granites (1000-800 Ma) and before depositian of the Cambrian shales...... _' . < • • Westwards growth of the Baltic Shield Anders Lindh, Institute of Geology, Sölvegatan 13, 5-223 62 Lund, Sweden Abstract At the end of the Svecokarelian Orogeny roughly 1750 Ma ago, meta morphosed granitic crust already existed in the area that now makes up the western growth zone of the Baltic Shield. However, nothing is known of the actual extent of such crust. Neither is anything known about the relation between the Svecokarelian rocks and these "con tinental fragments". The opening stage of the westwards growth, 1650 - 1700 million years ago, was characterized by massive plutonic activity. In the eastern part of the growth zone, this early plutonism was alkali-calcic but in the western part it was calc-alkalic. Simultaneously, the intrusion period of the Rapakivi rocks began in the Svecokarelian part of the Shield. Possibly, a period of metamorphism followed in the growth zone immediately after the intrusion of this second generation of plutonics. The next period of plutonism produced granites in the west that were more alkalic. Only small amounts of granites were formed farther in the east. These latter granites are almost unseparable from their neigh bours of the earlier generations. There are clear indications of a meta morphic period following this third phase of plutonics. In the western part of the growth zone migmatites were probably formed. The fourth period of plutonic activity, roughly 1225 - 1275 Ma ago, produced extensive amounts of granites in the west but no or only subordi nate amounts closer to the Svecokarelian part of the Shie1d. A1so these rocks are metamorphosed and at 1east loca11y migmatized. The p1utonics of the fifth and last period are confined to the western sector. They intruded about 900 Ma ago. They are unmetamorphosed, unfo1iated granites. 18 The development of the 87Sr /86Sr initia1 ratios and of the ö 0 with time suggests that most of this long endogenic history was ensia1ic, reworking older crust. The p1utonic activity first ceased in the east and successive1y 1ater in the west. Most rocks are po1ymetamorphic. Supracrusta1s both volcanics and c1astic sediments from the growth period are rare, either because they never formed, or because they have not been preserved. ABSTRACT THE NORDKALOTT PROJECT BY GUNNAR KAUTSKY The Nordka10tt project covers Fennoscandia north of 1atitude 660. It is a co11aborative venture invo1ving the Geo10gica1 Surveys of Finland, Norway, Sweden and Green1and and is cosponsoredby the Nordic counci1 of ministers. The aim of the project is to identify ore-bearing structures in the area by the app1ication of geological, geophysica1, geochemica1 and photogeo10gical investigations. Thus, it is the most comprehensive earth science project in Norden today. The project is producing a wide variety of maps over the area. These inc1ude a set of 1:1 M compi1ations portraying aeromagnetic anomalies, gravimetric anomalies, geophysicalinterpretation, 1itho10gy and stratigraphy, structures, metamorphism, metal10geny, resource potential and quaternary geo10gy. In addition, thematic maps in smal1er scales showing other Quaternary phenomena such as deglaciation, moraine -stratigraphy and movement of the ice sheets are also being prepared. The geochemical data will be presented in a large number of small sca1e maps with one for every element and type of samp1e (i.e. stream sediment, til1, water, humus, dead organic matter and 1iving organic matter in streams). These geachemical maps are based on a samp1e density af one per 30 km 2• Databanks far most af the maps and the geochemical data, are being prepared; they will be kept at the Geo10gical Surveys. A datafile will be produced for occurrences of ores and industrial minera1s in the area. The project has a working group responsible for the computer storage and treatment of information. This group will use the avai1able data for minera1 resource assessment. The various geological, geophysica1 and geochemica1 products af the Nordka1ott project wil1 provide a unique basis for most future geoscience activities in the area. They wi11 be particu1arly suitable as background information for I.L.P. investigations. Extended abstract for "SYNPOSIUM ON '!HE CENTRAL BALTIC SHIELD AND AruOINING AREAS" , ;' to be held in Helsinki on March 4-6, 1985. ~-SCALE STROC'lURES OF PREX:AMBRIAN BEDROCK IN FINIAl'ID AND 00 'JBE NJRDKAID'IT AS REFLECTED BY GEXX:HEMIS'mY A. Björklund Geological survey of Finland SF~21S0 Espoo, Finland Metal contents of sorne 1000 composi te tilI sarrples over Finland and sorne 5000 corrposi te tilI sarrples mainly over the Precambrian basernent of northern Finland, Norway, and Sweden (north of 660N) were used to study the large geochernical patterns of the bedrock. A zone of strong mafic signature (high contents of Cr, Ni, Mg, etc.) trends northwest from west of Salla at the eastern border of 'Finnish Lapland through northern Norway up to the Early Paleozoic complex af the Caledonides (Fig. 1). This mafic signature decreases slightly to the northeast. Tb the southwest it decreases stepwise. Contents of elernents of felsic association (Sn, La, Nb etc.) are low over northern Finland and northeastern Norway and increase stepwise over northern SWeden and southern Finland. This stepwise decrease is well-demonstrated by the ratio Rb/Na, the pattern of which has discontinuities along the lines Lappeenranta-Seinäjoki, OUtokumpu-OUlu (northern edge of the Main sulfide Ore Zone), and Kemijärvi-Enontekiö (Fig. 2). The line OUtokurnpu-Gällivare forms a major boundary of significant change in the geochemical character with strong felsic geochernical signatures to the southwest and strong mafic geochernical signature to the northeast. The felsic signature makes a bulge across this line over the western part of the granitoid cornplex of central Finnish Lapland. - 2 - The northwest-trending zonal geochernical pattern is interrupted by a weaker northeast-trending zonal pattern seen only in the contents of a few elernents. No systernatic change in the level of contents in this pattern can be seen in any direction. Over central and southern Finland there is tendency for large ring-shaped patterns of the contents of many element. The partially extracted component (hot aqua regia attack) of the elements also shows a northwest-tranding zonal pattern interrupted by a weaker northeast-trending zonal pattern. Some elements (P, La) show a strong increase to the southwest, while others form three northwest-trending zones of high contents (Fig. 3): a zone from west of Salla to northern Norway; a 50 - 70 km wide anomaly along the Main Sulfide Ore Zone; and an arcuate anomaly over part of the Svecokarelian schist belts of southwestern Finland. The contents of some elernents are very high in a northeast-trending zone over western Kittilä and northern Sodankylä in northern Finland. High-density sarnpling over parts of Finland shows, that the discontinuities in the pattern are very sharp and forrn broken lines in detail. The large paterns are built up of srnaller angular to subangular blocks delinited mainly by northwest- and northeast-trending lines. Especially the srnall-scale pattern is strongly correlated with gravimetric patterns, while the pattern of the rnagnetic field partly intersect the geochernical pattern. The rnafic geochernical signature reveals three northwest-trending zones: The northeastern Lapland zone to the line Kernijärvi-Enontekiö; the central zone to the line Kotalahti-Hitura; and the southern zone . In some parts of this zone contents of elernents of the mafic signature are as high as in the central zone. The felsic - 3 - .. signature reveals four zones: The north-eastern Lapland zone to the line Kemijärvi-Enontekiö (with strong Rb/Na anomaly south of Ivalo); the northern central zone to the line OUtokumpu-Qulu (Gällivare); the southern central zone to the line Lappeenranta-Seinäjoki; and the southwestern zone. The northeastern edge of the southern central zone overlaps the southwestern edge of the central zone of rnafic signature by sorne 70 km along the Main Sulfid Ore Zone. Including - this zone of overlap, Finland is devided into five northwest-trending zones of specific geochemical signature. The zonal pattern supports the view that the Baltic Shield was formed by accretion from the southwest, accorrpanied by evolution toward more felsic magmatism. The line OUtokumpu-OUlu (Gällivare) forms the most obvious transition from mafic to felsic geochernical signature and can be trend in th~ geochemical maps of the Nordkalott Project. This through the Gällivare are in northern SWeden may be the junction between mainly Archean terrain to the Northeast and Proterozoic crust to the Southwest. High values of Pd clustered along this line, may indicate deep fracturing and penetration of upper mantle material to higher levels in the crust. Barium-richhypersten monzonites, surrounded by rocks metamorphosed by high temperatures to granulite facies occur on the Kotalahti-Hitura and the Lappeenranta-Seinäjoki discontinuities. This indicates fracturing accompanied by intrusion from great depths. The continuation of the Kotalahti-Hitura line can be traced in the geochemical pattern in the southwestern corner of the Nordkalott Project area and a straight continuation into Norway goes over Sulitjelma. - 4 - , . The obvious ring-formed geochemical pattern in the zone between the Kotalahti-Hitura and the Lappeenranta-Seinäjoki lines indicate considerable Proterozoic granitoid activity. The zone southwest of the Lappeenranta-Seinäjoki line has a curved apperance in the pattern of most partially extracted elements, which may indicate that an originally straight pattern has been affected by granitoid intrusions in its northeastern part. The strong felsic geochemical signature over the western parts of the large granitic area of Central Finnish Lapland may indicate a large granitoid diapire associated with the Proterozoic intrusive activity south of the line OUtokumpu-Gällivare. The northeast-trending zonal pattern is interpreted as reflecting different erosional levels of rifted crust which formed as a result of Proterozoic tectonic activity. The pattern of aulacogenes in the Baltic Shield, especially over USSR Territory, filled with Late Proterozoic sediments, exhibit a straight northeast- and northwest-trending pattern which indicates, that the rifting has been acti ve long after the Proterozoic time. In the three zones of high contents of the easily extractable component of most elements (Sodankylä in Finnish Lapland, the Main Sulfide Ore Zone of Finland and parts of the Svecokarelian schist bel ts of southwestern Finland) hydrothermal and other processes associated with large-scale tectonic activity were probably responsible for formation of large orebodies. The anomaly over the Main Sulfide Ore Zone coincide with a gravimetric anomaly and is situated to the northeast of a zone of thickened granitic crust. This may indicate that the geochemical pattern is related to deep structures of the crust. .' 100 km .,.,,,,, ,.,.,1>0 . ~{: 7"",1'1 I~. ;-~.. - . ~. ·:~f ~:: ~. - _ .. _ ~ t • • 71\"0 I .-. ".ron ~M · .. · .-- ...... ~~ · . ·.. ~ ~ ., •. ' ·• . · .... '- •... . ,."., ,""" T~· - . .. - ... r '41 ••·~t·· •. ._.~ r Cr • • • ~~"~ . • • IN TILL .. ..:.~ •.;. I{ 7_ 1•. · -...... ·· . · ..'. -:;-~. I . • .. I I ' . ... 50 100 300•• . .. . . '. •• · • ...... ppm • \ .. . • •• ~. 4 7300 1- ... .- \ '-- • · .. ' . ""..... •• •• •• 10. '. • • •• • • • • ••••• . (. ' .. · ... . .,.,.,., ~L~ • • • '1 noo u ·. .. • · ...... · ...... • • ·...... ·• • •• :\• • ...... · . 7\00 - / ~A- · ~Tt . · . C"'. . · • · . · . · . . · . · • • · . · . . · · · · · . . • ·• :( .. .. .· •• · • · . . . . . · . · · · · .. . . · . . . . .J: · · . .. \. ?OOO · . · · ·. · . · - . · ...... · ... ..--' · .. lJ-I" • · ~...... •• • •• . .. . • T' · .. .. ,oautIPV •• 411 • . . . · . · . • • • • Ii • .... ,'lodl • ~ · ...... :-~ ...... · ...... ' ...... · . . i ': . · . • •••• J u · · · · · ...... · . · ·. · . · · . . . . - ~ ...... • ...... · ...... · . · .' .. . t • · . · . · .. : ...... • ... . . · ...... · .:/ . • · . . · ...... · ...... · . . V · · ...... - . ' . · . · · . . · ·...... ·. .. · : ..· .. .. . • . . · . . :~ . ' . · ...... v:s'';' . .~ .. ./ ....,., ...... ~ . . · · ~~ 7 . .. • • ~. .)~ ~- ,. \00 ------.' , 1~~r-__r- ______,- ______-r __ ~==I=OO~km===----r~~--~------r-~,n ~, 1.,.,,,,, .!~v.. "._...... _.+-.-f-----t----1 I","" O • . •" .• rr· .~~ . .. •. •.. . . ) .. '. .. 1\ 1,_ " ~ . : : .. '. II Rbx1000/Na IN TILL ~~\~~<_·::~:..~·~~·~~ .. (~--rll,- ...... • -e. ~ _. .• •• ~ I I I ...... 2_--.-. 5 10• . . : : ...... I~JL---L------~------~~--~~·+_~·-.·--~~~·-\ · ~·~·-· :t~jr--~j_~~ -.-. . '--~. . .: .. ' '. .'. ':.{ ,. • . '. . .0 •... . (...... ~--~----+-----+---~~~~·~·~~·~·~·~~~--~I~ 1-- , /1 0 : • : • 0 ,: :o. ~: ~\• .- :-.::-..1 ~~: .. I~7.ool._--!--_-+-:- ~--, 1-...I~~----~----~~----~----~----~----~~- .. __ , 100 km l~~ __-+ ______-+______~~ ______~ ____ -+-r~~~--~~~------~r---~nw HQ~ ____+- ______~ ______~~~ ____ ---4----~-4~~~.. ru~--~------+---~7~ • • • • Ba . IN TILL . . . . . • I I • ·. 60 100 ! pp'" • • • • •• • . • • . ••• • • • • • • • •••• • • • Mm~ __~ ______~ ______~ ______~~ ______~~ ______~~ ______~~ __~" 1------· I CONTRASTING ARCHAEAN AND EARLY PROTEROZOIC EVOLUTION OF THE EASTERN PART OF THE BALTIC SHIELD. H. MARTIN (1) _ P. BARBEY (2) (1) Centre Armoricain d'Etude Structurale des Socles - Campus de Beaulieu Institut de Geologie - 35042 - RENNES Cedex (FRANCE). (2) Laboratoire de Petrologie, Universite de Nancy I, Boite Postale 239, 54506 - VANDOEUVRE-LES-NANCY (FRANCE). The compared evolution of the Archaean greenstone belts of Karelia and of the early Proterozoic Belomorian fold belt may be surnrnarized in three points : (1) similar initial stages characterized by rifting of an older continental crust mainly composed of TTG rocksi (2) in Karelia large volumes of komatiitic and tholeiitic lavas were emplaced in ensialic basins whereas the Belomorian geosyncline was floored with oceanic crust and filled with flysch-like terrigenous material arising from the sedimentary recycling of the adjacent continental crusti (3) strongly different final stages corres ponding either to the sagduction of the Archean greenstone basins connected with crustal recycling via partial melting (calc-alkaline magmatism) or to the closure of the Belomorian geosyncline through subduction of the oceanic crust and subsequent continental collision. The preferred evolution through sagduction rather than subduction may be clearly correlated to : (1) the nature of the volcanic material, (2) the nature of the substraturn on whlch the greenstones were emplaced and (3) the mantle plume activity, and more particularly the spreading extent. The nature of both the volcanic rocks and the substratum determines the intensity of the gravity anomaly. The required conditions are : high geother mal gradients wnich can induce in short times the genesis of large volurnes of komatiites and the deposition of these high density volcanics over a low density continental crust. The reduction of the Earth heat· production through time pre cludes the genesis of great amounts of komatiites after the early Proterozoic. Consequently, high 6d values are no longer realized, leading to sagduction disappearance. The second determinant factor is the extent of spreading related to the intensity of the asthenospheric diapirs. At first during the Archaean, ultramafic lavas produced by high degree of melting in the mantle accumulated in ensialic greenstone basins. If spreadinq extents was not sufficient to induce continental breakup, the gravity anomaly may have been maintained for a long time and sagduction succeeded to failed rifts. No oceanic crust was created and thus none could have been subducted. At the opposite if the spreading extent was high enough, the sialic crust was able to break apart and the dormation of small oceanic basins followed. The emplacement of komatiites over oceanic crust does not generate high Öd values. Owing to evidences for plate motion and interaction since the early Archaean and considering the comparative evolution of these two domains in light of recent models for Precambrian plate teetonies, it is suggested that in the Archaean crustal evolution, sagduction and subduction were two competitive processes, one prevailing over the other depending on the nature of both the volcanic pile and its substratum and on the spreading extent. The changes in global tectonic style towards the Archaean - Proterozoic boundary, is a logical consequence of the progressive cooling of the Earth, which induces the disappearance of the kamatiitic volcanism and of the related sagduction. A.Berthelsen and M.Marker: (Institut for almen Geologi, 0ster Voldgade 10, DK-1350 Cph. K (+ 45.1.112232)) The teetonies of the Granulite belt and the Kola collision suture Based on field work in northern Norway and Finland and study of available maps and litterature from the northeastern part of the Baltic shield, a tectonic division is performed (fig. 1), the crustal structures discussed (fig. 2), and a plate-tectonic model proposed (fig. 3). Fig. 1: Tectonic map of the northeastern part of the Baltic shield. The following tectonic units are differentiated: 1: The Murmansk unit; 2: the Sydvaranger unit; 3: the Kola suture belt, a continent-continent collision suture; 4: the Inari unit; 5: the Granulite belt; 6: the Tana belt, and 7: the Southern foreland. Fig. 2: Palinspastic sketch of the western Kola Peninsula north of the head of the White Sea. The crustal structures have been restored to their pre-faulting position (the arrows indicate the sense of movement used in the restoration). Fig. 3: Plate-tectonic model for the c. 2000-1900 Ma old evolution of the Granulite belt and the Kola collision suture. The tectonic units are numbered as in fig. 1. In the upper the position of subsequently formed ductile thrust zones is indicated. Calc-alkaline intrusives south of the Kola suture are obliquely ruled; 3a is an supposed island arc complex north of the Inari microcontinent, 3b and c supposedly Jatulian shelf-type to continental sedimentary -volcanogenic formations. I"la rch the 1.mt;- 1985 ro Q) Cf) E • .:t(. . --Cl U. o ... . o 100 I I km 2 7 Fig 2 I Fig 3 GENESIS AND EVOLUTION OF THE ARCHAEAN CONTINENTAL CRUST EXAMPLE OF EASTERN FINLAND. H. MARTIN Centre Armoricain d'Etude Structurale des Socles - Campus de Beaulieu Institut de Geologie - 35042 - RENNES Cedex (FRANCE). In the eastern part of central Finland (Kainuu) vast areas of granodioritic gneisses surround the 2.65 Ga. Kuhmo-Suomussalmi greenstone belt. They can be subdivided into two chronological and lithological units : (1) a gneissic basement and (2) la te granodioritic and granitic intrusions. The gneissic basement has a typical Archaean TTG (Trondhjemite Tonalite-Granodiorite) composition. It wasformed during at least 2 episodes (1) TTG of Kivijärvi (2.86 Ga) and (2) TTG of Naavala(~ 2.65 Ga). The field, petrological and geochemical (major and trace elements, isotopes) data lead to a 3 stages petrogenetic model. (a) formation of a tholeiitic crust by partial melting of the mantle .. (b) melting of this crust (transformed into garnet bearing amphibolite) to generate the TTG parental magma. (c) fractional crystallization of the parental magma to produce the various rock type of the TTG series. This appears to be not only a finnish but a world wide process of Archaean TTG genesis. The comparative study of Archaean and post Archaean granitoids shows significant changes in course of time. For instance the high REE frac tionation (La!Yb) and the low Yb content of the Archaean TTG indicate the major role of garnet and hornblende, when the se two minerals do not take a pr.aninent part in the genesis of modern granitoids. This main difference is interpreted as a direct consequence of the cooling of the Earth. In Archaean time the subducted oceanic crust was "young and warm", so it reached the conditions of melting before deshy dratation had occured, leaving a residue where garnet and hornblende were the main phases. At the opposite, the modern subducted oceanic crust is "old • and cold", 50 it is deshydrated before it reachs the melting conditions of an hydrous tholeiite : it cannot melt at shallow depth. The fluids produced by deshydratation reactions, rehydrate the mantle wedge, which can undergo partial melting and gives rise to calc-alkaline magmatism; hybridation processes can also take place. 1n these conditions the modern calc-alkaline magmas cannot be directly produced by the partial melting of the subducted oceanic crust, the most important residual phases are, in this case, olivine and pyroxene. The location of calc-alkaline magma genesis in subduction zone environments has migrated in course of time and this is a direct consequence of the cooling of the Earth. .. \..." I Comrnents upon the Proterozoic chronostratigraphy of ... northern Sweden Torbjörn Skiöld The different phases of Svecokarelian orogenic deforrnation and metarnorphisrn are intirnately connected with the intrusion of plutonic rocks. Recent radiornetric dating of zircons from some granitoids in northern Sweden has made it possible to delimit the tirne intervals of the major orogenic and metamorphic episodes of the Svecokarelian in that area. In Norrbotten County, large scale deforrnation and granitization apparently ended with the emplacement of the migmatite-forrning, potassium-rich granites about 1800 Ma ago. Thus, it now seems clear that the Svecokarelian orogeny did not continue for another 250 Ma as has been deduced from earlier Rb-Sr datings of both folded volcanics and rnigmatite granites. The young Rb-Sr ages of some of the so-called Lina granites, syenites, perthite granites and felsic volcanics probably are the result of anorogenic metarnorphic events with respect to the Svecokarelian and must be interpreted with caution. Svecokarelian thermal and deformational metamorphism are likely to have been different both in extent and in time from one area to the other. The early orogenic plutonies often are sub-circular or elongated massifs and have intruded during folding of the supracrustal belts. They seem t~ have a fairly common crystallization age of about 1880 Ma. In some cases a somewhat younger age of 1860 Ma has been calculated, which either reflects a successive emplacement or is the effect of 2 therma1 metamorphism. An inf1uence of this kind has been noted in zircons from early Proterozoic gneisses. Here the datings have been carried out on textural1y we1l controlled crysta1s. Some of the zircons are homogeneous detrital grains yielding the age of the Archaean crustal source while others show total recrysta1lization or prominent overgrowth on zircon cores indicating a peak of metarnorphism at approximately 1840 Ma ago. The fact that zircon ages of about 1840 Ma have been obtained from essentially unfoliated perthite granites and syenites (Skiöld, unpublished data) supports the idea of a thermal event at about this time. Furthermore, it indicates that fo1ding, at 1east in some areas of Norrbotten, was not effective after 1840 Ma. The fina1 phase o·f region~l metamorphis~ which, apart from a tectonic influence, severely has granitized the country rocks was connected with the formation of the migmatite granites at about 1800 Ma. In some areas, these granites constitute the 1arger part of the present erjosional level. There they appear in the form of rounded, dome-1ike bodies leaving compressed and fo1ded gneisses at their margins. In higher crusta1 1eve1s and where the granite intrusions are associated with faults, the metamorphic imprint on the remaining gneisses is less pronounced. In the Archaean area north of Kiruna, the Rb-Sr systems of the gneisses have been reset while titanite and zircon ages are partia11y unaffected (Welin et al 1971) . The early and 1ate Svecokare1ian plutonic activity of northern most Sweden thus encompass the main metamorphic events of that orogeny to the time intervai be·tween 1880 and 1800 Ma ago. 3 The early orogenic plutonics often show a magmatic differentiation from gabbros to granodiorites. Textural investigations of zircons from the dated occurences seldom show rernnants of ancient magmatic or detrital cores, which may indicate that major ,volurnes within these rocks originate from the lower crust or upper mantle. As the time of rock crystallization is known from previous zircon work, it is thought that calculations of initial neodyrniurn isotope ratios and REE analysis on whole rock and zircon samples will provide more conclusive evidence upon rock genesis. Such an investigation is also proposed for the migmatites and the post orogenic granitoid stocks. South of the continental craton and within the Skellefte field the final stage of regional metamorphism was linked to the for.mation of the migmatite granites of the Revsun~ type. Zircon concentrates from this type of rock include a notable arnount of zircon zenolites. Zircon populations devoid of such zenolites indicate a rock-for.ming age of about 1760 Ma, which is some 40 Ma younger than for migmatites of the continental area further north. When trying to establish a chronostratigraphy covering the continental craton from southern Norrbotten to northern most Sweden, it is of great inte~~ to investigate the volcanic rocks. Atternpts have frequently been made to corre1ate the terrestrial, andesitic to rhyo1itic, volcanics of the Kiruna area with those of the Arvidsjaur area. Zircons from two rhyolites south-west of Kiruna satisfy an age of about 1910 Ma, whi1e a syenite porphyry near Gä11ivare has a minirnurn age of 1860 Ma. 4 Contrary to the situation in northern Norrbotten, contacts in the Arvidsjaur field show early orogenic Sveco- karelian plutonics, the Jörn granite serie, cross-cutting and brecciating felsic terrestrial volcanics. According to Wilson (1982) these granitoid intrusions have an age of about 1890 Ma, which means that at least parts of the Arvidsjaur volcanics are older. This should, however, be compared with a fairly precise zircon age (Skiöld, unpublished data) on a feldspar porphyry situated 10 km east of Sorsele and north-west of the Skellefte field proper. The dated porphyry overlies greywackes, schists and mafic volcanics, which probably form the oldest volcano-sedimentary sequence - the Skellefte Group. The calculated age is 1864 ± 12 Ma (2 sigma) with a low MSWD- value of 0.4, indicating an exellent fit to the isochron. Thus, judging from present state of knowledge, there are reasons to believe that, apart from the Dobblon and sirnilar occurences, the terrestrial volcanics from Kiruna in the north alI the way to the northern front of the Skellefte field have extruded during a relatively long period~ of time - about 40 Ma. They share a certain tirne interval with the early orogenic plutonics and both rock types may conceivably be different products of a common, repeatedly active source/force. , A Sm-Nd mineral isochron from the basaltic volcanics underlying the felsic volcanics of the Kiruna area indicate an age of 1932 +- 45 Ma. The age is believed to reflect isotopic equilibration during the crystallization of a greenschist facies assemblage, which probably is the result of a hy~otherrnal circulation in the marine environrnent. Previous tirne correlations between the Jatulian greenstones 5 of the Karelidic Schist belt in northern Finland and the basaltic volcanism in the Kiruna area are not supported by this age determination. It is not surprising, however, that discrepancies upon the chronostratigraphic position of seemingly similar sequences mayarise, especially when correlating over large distances in geologically complicated terrains. Concerning the mafic volcanics of northernmost Sweden, additional Sm-Nd and U-Pb zircon investigations on basaltic lavas, amphibolites and hypabyssal rocks, in \ particular from the Kiruna and Pajala regions, have recently J ~ been initiated. References.- Welin, E., Christiansson, K. & 'Nilsson, ö., 1971: Rb-Sr radiometric ages of extrusive and intrusive rocks in northern Sweden I. Sveriges geologiska undersökning C666. Wilson, M. R., 1982: The Jörn granitoid complex: a multi disciplinary study. Geologiska Föreningens i Stockholm Förhandlingar 104, 379-381. Torbjörn Skiöld, Naturhistoriska riksmuseet, Box 500 07, S-105 05 Stockholm, Sweden • . Co h r~ II\() sl- t'.. n'~ r .. f '" ~ fro~ ; n-.e. ~o~.f.. f\e.hf.~t ~~eA. of t\o~"'e"''''' r;r-to K · "'JtS (~ .. ) 1M-'-plti s"" I ;"!I-,.,.rlolt tf) ~4 /. &>0 l1e". t lti~e - fo fOs~ tP,01''''''c dC),,"~s I pt/,nt~ fl a" "", ,,,-. "./-J.u Unto/, e,-J~tJI r'fe",,'I~r 4"~ ,e, .JI" , -".. , ,.. "" ,'" ~:.~ 11~.J."..rt;;I.''r'''' -f"ltI,'''1 ""e( r~ C"'''$f'''-'''. ~ .~"" . . . t#t~/'I ""..,tl'ti c. . d;II~"'.~1-"4k) plu.",.",'e t F~/t"c VO/Cd"'''~M .. ... ;, /. 9'3 ( !".. - ~eI. ) 1'14" 'c. t/.ltiIt h/r,., P.r'~ ,,;,,,.~ I ~ r w;/!-t ei ~ -/-,./ fA I .", ,,"4I-AI'HIJ;phi'c, -ti,.e,ol1 S H '~'J:t• .~ ,olit'! .f.~~"tI~ 1-, ~i~~.~s . .. . . Drlfto .. .,.,.J f~".,~e"rr~~ ... .. - . • ' "... ...... , r GF..ocHEMlCAL EVIDENCE FOR nm GEOTECTONIC SETTING OF EARLY PROTEROZOIC METAVCLCANIC SEQUENCES IN LAPLAND 1 2 Tim Pharaoh and Julian A. Pearee 1. Deep Geology Researeh Group, British Geological Survey, Keyworth, Notts NG12 ,5GG. 2. Department of Geology, The University, Newcastle upon Tyne, NE1 7RU. A systematie geoehemical study of Early Proterozoie metavolcanie rocks from the northenl part of the Baltie Shield supports the eoneept that a eomplex mosaie of eontinental masses, volcanie ares and marginal basins were welded into one eratonie massif during the Sveeokarelian Orogeny (1900-1750 Ma). In the north, in Finnmark and Northenl Norrbotten, tholeiitie metabasalts, together with thick shallow-water elastie metasediments, form the main part of the Karelian supraerustal sequenees, whieh in tUnl overlie Archean base ment. The traee element signatures of these metabasalts are eomparable to those of post-Phanerozoic eontinental tholeiites whieh erupted in zones of lithosphere attenuation and whieh suffered contamination by sialie erust. It i8 not however possible to determine by geoehemistry alone whether the eontinental rift-basin in question lay in an intraplate or back-are setting. Metabasalts with a volcanie-are geochemical signature become an inereasingly important component of supraerustal sequenees as the diffuse southenl margin of the Karelian continent is approached. In the Skellefte Field, an ensialic volcanie arc developed and fed eonsiderable quantitiea of immature claatic sediment into the deep water 'Norrland Geosyneline', whieh may have been fully oceanic in charaeter. Subduction magmatism continued during the Svecokarelian Orogeny, giving rise to synorogenic metavolcanie auitea auch as the Kiruna porphyries. The evidence for marked apatial variation of magmatic activity in the Early Proterozoic ia in contraat to the rather monotonoua pattern of greenstone belt development reporled from the Archean. We believe that this apatial variability is a consequence of geotectonic proceases aimilar to those of modenl day piate tectonica, and present a plate tectonic model tor the Early Proterozoie development of the Baltic Shield. FINNMARK FINNMARKS - I NORTH SKELLEFTEÄ I I NORRLAND SOUTH WINDOWS VIDDA NORRBOTTEN ARJEPlOG SWEDEN ALA PORPHYRIE POSTOROGENIC NOT NOT I ~ " - ; _ " .. ·t<>~6j .. ;t38 :· SUPRACRUST AL AND RECOGNISEO RECOGNISEO INTRUSIVE SUITES LATE . STOCKHOLM . SVECOKARElIAN . GRANITE ETC "" OROGENY WITH EMPlACEMENT OF SYNOROGENIC + MAGMA TIC SUITES EARLY LATE ' UPPER "RAIPAS a'p : . ' " .. ' ." " .. : .: ." "PAHAKURKIO . " . . ._------...... " .. " . . " ". CARAVARRI "" . -: "ANO . ""·"·" -: -: -:- =~~-:' " --== " :-.:: ": DEVELOPMENT P~RS;( GAÖtIF>::::~ ~~"- ~ ~ ___-~} ;j:~~~:c~ ~~ : ~_I~!-_'{ ~~c~~. c <,l'p-~· -;__ := _" ": c:~~-.=::=.--=~:- OF EARL Y PROTEROZOIC SUPRACRUSTAL SEQUENCES OF KARElIAN (N) AND SVECOFENNIAN (5) w FACIES ~ r-- EARLY VASTERVIK PRE-KARElIAN NOT NOT ZIRCON BASEMENT COMPLEX EXPOSEO RECOGNISED RECOGNISED I SOURCE SOUTH NORTH -SPACE ~ . ' K. Laajoki: The Early Proterozoic KainuJ Schist Belt I and its relationship to the Late Archaean basement. (Helsinki symposium on the Central Baltic Shield 4-6. March 1985) Abstract The Kainuu Schist Belt consists of two parts separated by a tectonic fault zone. The eastern part presents a traditionaI Sariola-Kainuu-Jatuli-Kaleva-type sequence deposited nonconformably on the Late Archaean basement of the Kuhmo province stabilized about 2600 Ma aga. This part is mainly autachthonaus-parautochthanaus. The west ern part, narth af Oulujärvi, cansists af a Lappani-Ja tuli-Kaleva-type sequence whose western, lawermast parts are migmatized and folded ta paragneisses. The cantact between the paragneisses and the basement of the Pudas järvi black is not expased. At Jarmua aphiolite-type rocks are in clase (tectanic?) cantact with basement racks, while the southernmost western parts af the belt shaw an autochthanaus relationship to the basement af the Iisalmi black. The basic unanswered questions are 1) da the western and eastern parts represent fragments af the ance caherent epi- or pericontinental cover af the Archaean basement, 2) are they remnants af twa indi vidual sedimentary prisms af separate Archaean nucleii and3) what is the nature and age af the uncanfarmity below the western paragneisses. K. Laajaki, University of Oulu, Department of Geology, Linnanmaa, SF-90570 Oulu. 4.3.1985 T.J.Koistinen: On the sequential fragmentation in the Karelides region, eastern Finland A very long period of tectonic evolution is recorded by the Karelian part of the Svecokarelides. It starts with the rifting of the older crust, cratonized in late Archaean times, and culminates in the reverse processes in the orogenic phase .(over 1900 -co 1800 MA ago) . A number of recent publications deal with the structures related to the complex evolution in the orogenic phase, others study fault and fracture patterns. There are different approaches depending on the purpose of the work and on the source material. The present contribution is, rather than a presentation of new evidence, a review combining and correlating published data. These point to a successive fragmentation of the basement together with the evolving cover. Some blocks were active late (less than 1000 MA ago) • Kalevi Korsman, Geological SUrvey of Finland MEI'AM)RPHISM AS AN INDICATOR OF THE E.VOIm'IOO OF THE CRUsr '!he Savo schist belt b:>rdering the Archean tonalite area is characterised by metatrorphic blocks. Wi thin the blocks metam:::>rphic features may be unifonn, but between the blocks there is a sharp change in the nature of rretanorphisrn. Progressive rnetarrorphic phases mk place between 1930 Ma - 1980 Ma ago. Signs of a progressive phase younger than 1880 Ma have not been detected in the Savo Schist belt. The rretarrorphic features of the Savo Schist belt reflects the rnetarrorphism of a rift zone in which the heat flow has increased as a result of magrratic activity. Granulite faeies rnetarrorphisrn of Proterozoic rnetapelite area is cormected with zonal rnetam:::>rphism of the andalusite-sillimanite type. '!he granulite faeies rretam:::>rphisrn toak place at high o temperature (750 C), but pressure lower (4.3kb) than that in the o inmediate enrivonnent (T = 680 C, P = 4.8kb). The crust undeIWent intense rneltin3" in the high temperature zane and was subject to gravitative uplifting. Metanorphic evolution began before the granitoids of the 1880 Ma age group were ~laced, rut intense recrystallisation was still cantinuing 1810 Ma ago. The features of zonal rnetanorphism reflect metanoq:h.i.sm of the tectonically thickened crust. . i PETROLOGY OF THE NATTANEN-TYPE GRANITES, NORTHERN FINLAND -Ilmari Haapala and Kai Front University of Helsinki, Department of Geology, P.O. Sox 115, SF-00170 Helsinki . ' -, ' . The Nattanen-type granites form a group of postkinemat~c (age, about 1.77 Ga) multipleintrusions (Tepasto, Pomovaar:a, Riestovaara; Nat- . . tanen, Juvoaivi) in central Lapland. These rounded batholiths and stocks intruded the granulite belt and gneissose granites." In :kola Peninsula, the Litsa River - Ara Fjord granites have similar . characteristics, but their first intrusion phase, composed of diorites and lamprophyres, has not been found in association ~ith the Natt~nen group of granites. The Nattanen-type complexes are composed of various biotite granites which contain magnetite, sphene, apatite, allanite and zircon as typical accessories. The magnetite content of some. " , granite phases is anomalously high. Geochemically, the granites are characterized by high SiOi,Na20+K20, FeO/MgO and Th/U -aswell as by low Sr. They are slightly peraluminous and have higher Na 20/K20 ratio than rapakivi granites and late-kinematic microcline granites in southern Finland. The granite complexes show marked internal differ- entiation with Sa decreasing and Rb increasing towards the latest intrusive phases. The Tepasto aplite granite, the host of a Mo showing, has the highest Rb content. Sr, Nd, Hf and Pb isotope studie~ of Kouvo, Patchett and co-workers indicate that the Archean crust was a major source of the Nattanen-type granites. 1/ , I , 4 Helsinki Symposium on the Baltic Shield, 4-6. March 1985 1 (2) GEODYNAMIC SIGNIFICANCE OF CONTRASTING GRANITOlD TYPES IN NORTHERN SWEDEN M. R. Wil son Swedish Geological Company, Box 801, S-951 28 Luleå, Sweden B. öhlander Department of Economic Geology, University of Luleå, S-951 87 Luleå, Sweden M. Cuney CREGU B.P. 23 54501 Vandoeuvre-les-Nancy, Cedex, France P.J. Hamilton SURRC, East Kilbride, Glasgow, G75 OQU Scotland Early Proterozoic granitoid suites in northern Sweden fall into two main groups, an early phase 1.89-1.84 Ga and a later phase 1.80-1.75 Ga. The older suites generally have a wide range of composition, the younger suites are more restricted. Sm-Nd isotopic studies show that the older granitoids are derived from sources with relatively short average crustal residence times, suggesting rapid evolution from mantle-derived material, while the younger granitoids are derived from sources with long average crustal residence times, - i.e. dominantly crustal sources. The older granitoids can be subdivided geochemically into the calcic Jörn complex within the Skellefte district, the calc-alkalic Haparanda suites, and the alkali-calcic to alkalic intrusions of the Arvidsjaur alkaline province. Both the Jörn complex and the Haparanda suite have very low Gä, Nb and Y contents (Jörn also has low Yb and Ta)and low Rb contents and are similar to Phanerozoic volcanic arc granites. The intrusions of the Arvidsjaur region have significantly higher Ga, Nb, Y, Ta and Yb contents and slightly higher Rb contents, suggesting a significant 'within-plate' contribution. However, they do not show the marked Ba depletion of mature alkali provinces, such as Nigeria. It is therefore suggested that the Skellefte district Jörn complex represents a granitoid in a rather immature volcanic arc environment (cf. Panama), the Haparanda suite a more mature volcanic arc environment, while the Arvidsjaur province is similar to the type of sub-alkalic to alkali pro vince developed in the Andes, inland of the main calk-alkaline belt and possibly related to ensialie spreading. The younger granitoids have more restricted major element chemistry but still vary significantly both in major and trace elements, depending on their geological environment. For example, the Vettasjärvi (Lina-type) granite is near the minimum melting composition for granites, while the Arvidjaur granite is similar but of a much more alkali character. Intru sions in the metasedimentary environment of the Storuman area have higher oxygen isotope ratios than the other granitoids and can be relatively peraluminous, although intrusions with highly restricted compositional ranges (e.g. Joran) are less peraluminous. 2 All the younger granitoids show the high Rb and low Sr contents typical of evolved granites with a major crustal component, but vary consi derably in their Ga, Nb, Y, (Ta and Yb) contents. The Vettasjärvi (Lina) granite is similar to Phanerozoic syn-collision granites, while Arvidsjaur and Jörn seem to inherit a 'within-plate' characteristics, and may be compared to Phanerozoic 'post-collision' granites. The geology, palaeogeography, chemistry and isotope geology of northern Sweden strongly supports a hypothesis involving subduction-related magmatism and ensialie rift magmatism in the earlier period, followed by crustal anatexis related to continental collision in the later period. --~~ ._ ._------ PROTEROZOIC CRUSTAL EVOLUTION IN FINLAND: NEODYMIUM ISOTOPIC EVIDENCE. HANNU HUHMA (Geological Survey of Finland, SF-02150 Espoo, F~nland) Sm-Nd systematics have been used to investigate the involvement of old recycled material versus juvenile additions during the Svecokarelian oro geny. This study consentrates on the granitoids with known U-Pb zircon ages, and on metasediments from Kalevian and Svecofennian major piles. Analyses from primitive preorogenic basic rocks indicate the existence of a depleted mantle reser voir during the evolutionary stage of the Svecoka relian orogeny. Granitoids from Southern and Central Finland, not close to the Archean, have epsilon-Nd close to ze ro, indicating high proportion of juvenile mate rial in their genesis. In contrast, the contribution of Archean crust is substantial in the Svecokarelian granites from Northern Finland, as well as close to the Archean in the East. Epsilon-Nd values from -6 to -9 at 1.8 Ga have been measured from the North. The contribution of older material in Svecofennian metasediments from Tampere is low, and similar to the granitoids from Southern Finland • Th~ mean chondritic Nd-model age from ten Kalevian metasediments in North Karelia is about 2.17 Ga. The likely explanation is that Kalevian sediments have a substantial component with short crustal residence time, mixed with Archean material. The Nd data indicates that in vast areas the newly r mantle derived material was the major component in the generation of Svecokarelian crust. In the North and close to the existing craton the involvement of the Archean is substantial. HELSINKI SYMPOSIUM ON THE CENTRAL BALTIC SHIELD 4.-6. March 1985 Geochemistry of volcanites in the Skellefte District, Northern Sweden Lars-Ake Claesson, SGAB, Box 801,951 28 LuleA. The Skellefte district, an early Proterozoic massive sulphide ore province, contains a well preserved volcanic-sedimentary rock association, referred to as the "Skellefte Group". The massive sulphide hosting rocks comprise a bimadel suite of meta-volcanics -- a calc-alkaline group of rhyolites and a midly tholeiitic group of basalts and basaltic andesites. Stratigraphically above the metavolcanic rocks occur metasediments associated with ultramafic rocks, basalts and basaltic andesites. These rocks are in certain geochemical aspects comparable with basaltic komatiites and boninites. The present geochemical study shows a volcanic arc setting for the calc alkaline rhyolites as well as for the midly tholeiitic basalts and basaltic andesites. Back-arc spreading has been initiated by splitting of the volcanic arc. Thisspreading initiated eruptions of ultramafic rocks, basalts and basaltic andesites with a transitional volcanic arc to mid-ocean ridge affinity. Deposition of these rocks occur in several small basins throughout the southern margin of the Skellefte arc. It is surmised that the setting of the Skellefte arc was of an oceanic rather than an ensialie environment, shown by the presence of a mid-ocean ridge component in the transitional rock types. The present results are part af a wider study in order ta establish a geotectonic model for the Skellefte district. Definitions of different stratigrafic levels and their solution on the problem with massive sulphide deposits in certain positions throughout the volcanic pile are included in this study. Proterozoic volcanism in central and northern Sweden Rudyard Frietsch The ore-bearing Early Proterozoic volcanics and their tectonic setting are discussed. The felsic comoosition of the V01C&lics of central Swe den contradicts ån or~gin by an island-arc vclcanism in a subduction zone. Large-scale metasomatic alteration of ore-existing mafic-interme diate volcanics may present an exnlanation for this feature. The Skellefte volcanics lying at a transition zone between a continental mass and a marine envircrunent are commonly considered to reoresent an island-arc. The vclcanics of the Porohyry grouo towards the north are terrestrial and the volcanics of the Greenatone grouo 10 the same area are formed by intracratonic rifting. Support for considering the Skellefte district as island-arc over a towards north dipo1og subduc tion zone ia de live red by the metal zonation resembling that found in association with Andean magmatic belts. The arc com~rises Cu-Zn and porphyry Cu-(Ho) deposits and in the back-arc 10 thrust belts there are CU-Zn-Pb, Mo-W and Udeoosits. Nv; and N-S major fault zones delimit the mineralized area. Uorth of the Mv fault zone there are deoosits with Fe and Cu which 10 oart are controlled by rift1og. !m~ort~nt for the metallogenetic evolution are some large areas of low ma~etic granites and migmatites (react~vated Ärchean basement?) around which the Proterozeic magmatic ·processes took olace. Sm-Nd data on Proterozoic mafic rocks fran central Swe::1en Stefan Claesson, Naturhistoriska riksmuseet, Box 50 007, S-104 05 Stockholm. At the M.lseum of Natural History, Stockholm, an isotope project focussing on Nd isotopes is in progress. Three areas with different geological settings are studied; the Haparanda area at the margin of the Karelian continent in rortheasternrrost Sweden, Våsternorrland in the central parts of the large greywacke basin in central Swe::1en and Finland, and the FOlymetarrorphic terrane in southwestern Swe::1en. The project includes investigation of selected m:mtle derivatives. Nd data on well-preserved mafic rocks can provide insight into the evolution of the Proterozoic m:mtle under1ying the Ba1tic Shie1d. In Västernorr1and, different rocks with suitable geochemistry and wi th the age known ei ther fran direct dating or fran indirect age constraints, have been se1ected fran the age interval 1900-1200 Ma. These inc1udeamphil::olite which occurs interlayered with greywackes, ear1y orogenic gabbros, old FOstorogenic do1erite and Jotnian dolerite. The results available so far, from ear1y orogenic gabbro and from older and Jotnian dolerite, indicate derivation fran mantle reservoirs with similar I m:x1erately dep1eted Nd characteristics. Presently, only few initial Nd ratios for rnafic rocks fran the Baltie Shie1d are available. The data indicate a LIL-dep1eted Protero zoic m:mtle, similar to what has been sha.-m fran other cratons. Et'ic Welin '! Welin , E., The depositional evolution of the Svecofennlan supt'act'ustal sequence. On the basis of six new zit'con ages of metavolcanic t'ocks. othet' isotopic and geophysical data and geologlcal ebset'va- tions, the cht'onoloqical and tectono-stt'atigt'aphic evolution of the eat'ly Pt'otet'ozoic Svecofennian supt'act'ustal recks in Finland and Sweden is discussed. It has been established that a NW-SE displacement from the 8ethnian Bay te Lake Ladoga ana a sinking of the southwestet'n block was initiated 1950-2000 Ma aqo. Accumulations of pelitic sediments and qrevwackes en the subsided At'chean basement continued until about 1860 Ma. In south- centt'al and not'thet'n Sweden shallow marine and terres~- ri. a 1 velcanics extruded 1880-1890 Ma aqo. The t hick accumula- 'tions and th~ volcanic rocks were subsequently i ntruced OY plutonic rocks formlng large batholiths 1860 te 1891 Ma ago. Radiometric dating. zircons. U-Pb. Svecoiennian. meta- volcanics. metasediments, Proterozoic. Finland. Sweden . Eric Wel i n. Natut'historiska riksmuseet. 80x 50007. S-104(]S Stockholm. Sweden. 1 SI'RATIGRAPHY ANn GBXHEMISI'RY rn THE PROI'EROZOIC VOLCANIC ROCKS OF THE NAGU-KCRPO AREA, SW FINlAND. Carl Ehlers, Alf Lindroos, Mirja Jaanus~ärkk.älä. ABSTRAcr The volcanic rocks of the Nagu-Korpo area fom a thin «1000 m) layer that is folded into narrow synforms separated by migmatite-filled antifarms. In Nagu the volcanic forrration comprises three units: a lower unit of subvolcanic banded gatbro sills, a miOOle unit of arnphiJ:olitic volcanic rocks and an upper tmit ronsisting of a thin mafic to ultramafic volcanic rock layer. The volcanic rocks occur interlayered with a much thicker sequence of metasedirnentary rocks. Geochemically the metalavas are tholeiitic and plots based on Ti-Y-Zr and other trace elements show that they resemble recent within-plate lavas. REE analyses show that the upper, nore mafic lavas are enriched in I.REE relative to the lavas of the much thicker amphibolitic miOOle unit below. Most trace elements show patterns differing fran those of recent arc lavas, which rould lead te alternative m::dels for the initial forrration of the volcanic rocks of the Sverofennian fold belt. Carl Ehlers and Alf Lindroos Geologisk-mineralogiska institutionen Aho Akademi, 20500 Åbo 50, Finland. Mirj a Jaanus~ärkkälä Nuolihaukantie 6A 25 90250 Oulu 25, Finland. GENERAL GEOCHEMICAL FEATURES OF THE METAVOLCANICS OF THE PROTEROZOIC TAMPERE SCHIST BELT Yrjö Kähkönen, Department af Geology, University af Helsinki, P.O. Box 115, SF-00171 Helsinki, Finland Helsinki Symposium on the Central Baltic Shield 4.-6. March 1985 ILP WG 3 and ILP WG 4 The Early Proterozoic (about 1900 Ma) Tampere schist belt is a synclinal volcanic-sedimentary belt characterized by greywackes pelites among the sedimentaryrocks, and by wide compositional variations among the volcanigenic rocks. The volcanic rocks af the belt are typically intermediate medium-K and high-K rocks (SiO made is about 60-63 %, ADR-index about 70) with calc-alkaline af~inities • . A slight tendency towards bimodal - Si0 frequency distribution exists and this is caused mainly by the 2Upper Volcanic Unit af Ylöjärvi. The volcanic rocks studied are divided into units and, partly, into subunits which have as their typical geochemical features: At Orivesi (in the east) 1) The Intermediate Unit af Orivesi is about 1 km thick. It is characterized by calc-alkaline high-K dacites and andesites. This unit contains the so far oldest dated volcanic rocks near Tampere. 2) The Subalkaline Basaltic-to-Rhyolitic Unit af Orivesi obviously overlies the former and is about 150 m thick in the profile inves tigated. It has mainly calc-alkaline affinities but, e.g., its andesites tend ta be lower in K than its basalts. 3) The Alkaline Unit af Orivesi occupies a position near the hinge zone af the major syncline, overlies the former and is 100-230 m thick in the profile studied. The unit is divided into two subunits; (a) the Basaltic-to-Andesitic Subunit (constant FeO:MgO ratios) and (b) the Trachytic Subunit (overlies the former, displays highly variable FeO:MgO ratios). The Alkaline Unit is o~erlain by cong lomerates-greywackes-pelites. At Vaavujärvi 4) the Vaavujärvi sill (up ta 400 m thick) is cha racterized by high-K (or nearly so) andesites. At Kämmenniemi 5) the volcanic rocks are dominated by high-K dacitesand rhyolites which have calc-alkaline affinities. This area is up ta 2 km wide in N-S direction. At Ylöjärvi (in the west) 6) The Lower Volcanic Unit af Ylöjärvi contains on the N limb af the major syncline typically medium-K/high-K basaltic andesites, andesites and dacites which have mostly calc-alkaline affinities. 7) On the southern limb af the syncline the Lower Volcanic Unit contains a subunit (100 m thick in the profile studied) which is characterized by nearly low-K tholeiitic andesites-dacites. Basing on earlier studies and greywackes associated with the overlying Veittijärvi conglomerate the Lower Volcanic Unit contains here also high-K and very high-K andesites and basalticandesites. 8) The Upper Volcanic Unit of Ylöjärvi is 'characterized by low-K and medium-K basalts, basaltic andesites and andesites which have tholeiitic affinities. The v ole a n i c s i n v e s t i 9 a ted h a v emo s t 1 y, t h 0 u 9 h ' n 0 t n ec e s s ari 1 y a 1 - ways, arc affinities. ADR-index and Zr contents (exceeding 100 ppm regularly) suggest similarities with arcs near or at continental margins but lack af significantly older crust in the Svecafennides in general makes these comparisons questionable at present. CURRENT PROBlEMS IN BERGSlAGEN GEOlOGY Abstract Ingmar lundström The Bergslagen area proper is generally understood to comprise the metallogenic province to the west of lake Mälaren in south central Sweden. Here a large num ber of iron as well as base metal ores occur in a succession of volcano-sedimen tary rocks, including the famous leptites and hälleflintas of the Swedish geo logical literature. Since a continuation of this geological environment can be discerned eastwards to the coastal areas of the Baltic Sea, these eastern areas should also be taken into consideration when the geology of Bergslagen is dis- cussed. ~ In the western part of the area ("Bergslagen proper"), the supracrustal succes sion is clearly transgressive as the lowermost tuffs are overlain by tuffites, which in turn are covered by metaargillitic sediments. Here, metavolcanites clearly dominate the stratigraphic column. In the eastern, coastal areas, some lateral variations on this pattern are evident. Thus, metavolcanites are clear ly less frequent, and an underlying sedimentary formation also occurs. This general shift towards a more sedimentary environment in the east is corraborated by some observations of a westerly sedimentary provenance, as well as an easter ly deepening of the depositional basi ns in the Örebro area. In neither area has any basement to the supracrustal succession been identified. The volcanites of both areas are predominatly rhyolitic, but minor intrusive and extrusive mafic rocks also occur. However, dacitic and more mafic compositions appear ta in crease towards-the east. Thus, the alleged bimodality of the volcanites of wes tern Bergslagen may meet some restrictions in the east. However, the general preponderance of felsic compositions is thought to testify to some kind of con tinental margin volcanic situation. The chemistry of the metavolcanites frequently deviates from that of unaltered eruptive rocks. Thus, the lowermost rhyolitic tuffs are frequently clearly en riched in Na, while the superposed rhyolitic tuffites may show a corresponding K accumulation. In both cases, Ca tends to be rather low. These features are thought to be due to a large scale, probably hydrothermal, metasomatic, synvol canic alteration. The same process is also held responsib1e for 1arge zones of mica quartzites, preferably enriched in Mg and K. These zones mostly occur with in the 10wermost, Na-enriched tuffs. The most complete deve10pment of alI these a1teration patterns occur in western Bergslagen, while Na and Mg enrichments appear to be 1ess frequent in the east. The numerous ore occurrences of Berg slagen tend to occur preferab1y in formations affected by such synvolcanic al terations. for this reason, the latter are thought to have a meta1logenetic significance. The supracrustal rocks are intruded by severa1 generations of intrusive rocks. The oldest of the se is a suite of about 1.9 G.a. old gabbros to granites. They are commonly referred to as "gneiss-granites", "ur-granites" or primorogenic intrusives. Unlike the ensuing ca 1.7 G.a. old serorogenic granites, pegmatites and ap1ites and the ca 1.6 G.a. postorogenic granites, the primorogenic intru sives are genera1ly concordant with the fold pattern of the supracrustals. The primorogenic intrusives are also mostly penetratively lineated or foliated. AlI these intrusions are cut by a set of about l G.a. old postorogenic dolerite dykes. ______~ ______. ~~.~_. ______~, .~, ____ _.~~ __ ~.~,~----~-P~.. ~. (~..------e~ . __ ~._u~.-__p-e~ __~.* ~-~- ~. ~-- - -_._--_ .. _ .__ ._ - _. ~-- . ::-_ .. _------_._.~ The macroscopic fold pattern can be described as an interplay of north-south and east-west trending folds with steeply dipping axial surfaces. The orienta tion of the macroscopic structures has been suggested to reflect relict rift patterns in the west and stress directions araund large bodies of primoragenic intrusives in the east. Curiausly, the mesoscapic lineations and fald axes af the area alI plunge in an easterly directian, regardless of the arientatian af the macroscapic falds. The regianal metamorphism af the area is of law pressure type as testified e.g. by the almost ubiquitous presence af andalusite/sillimanite and cordierite in argillitic metasediments. The metamorphism reaches high amphibolite facies in the central parts of the area where migmatites are common. Towards both the east and west, however, a regional metamorphic gradient towards greenschist faeies is evident. As the amphibolite facies alteration"of the central area has affected even the uppermost stratigraphic units, the high metamorphic area clearly is not the basement of the lower metamorphic rocks. In the regionally low metamorphic areas, vestiges of older contact metamorphic patterns can be found. The regional metamorphic minerals generally show post-defarmation tex tural relationships. Thus, the regional metamorphism has outlasted the regional deformation. A pervasive retrogression is hawever often apparent even in post metamarphic intrusive rocks. As it tends to fallow post-metamarphic fracture zanes, it evidently reflects a separate metamorphic event. Early Svecofennian stratigraphy of central and southern Norrland, Sweden 8y Thomas Lundqvist, Geological Survey of Sweden The early Svecofennian stratigraphy (from the literature and from unpublished investigations) is presented for a selection af seven regions in central and southern Norrland: the Nappikoski area, the Los-Hamra region, the northern Hälsingland, western Medelpad and northern Angermanland regions, the Naggen areaand the Skellefte-Arvidsjaur fields. Stratigraphic schemes are supported by U-Pb ages on zircons in acid metavolcanics (E. Welin, personal communication). The following features are af special importance: No basement (Archaean?) has been identified for the sedimentary and volcanic rocks. Metarhyolites and metadacites, often ignimbritic, usually occur at high strati graphic levels (exception: the Skellefte volcanics). Quartzites and meta-arkoses also generally occur at high stratigraphic levels (exception: the Noppikoski area), and are rare or lacking in the north. This may be taken to indicate a provenance region in the south-west. Future research s,hould aim at improving stratigraphic schemes by field mapping in critical areas, supported by radiometric dating. The provenance af quartzites, meta-arkoses, metagrey wackes and metapelites should be investigated by, e.g. studies on zircons (morphology, U-Pb dating) and Sm-Nd isotope analyses. Special attention should be given ta the possibility that the ratio between Archaean and early Proterozoic material could vary along a NE-SW line. ------~----_ . _--_ ... '. 1 •. " , •••••. • 1 ! . CHARACTERISTICS OF SYNKINEMATIC SVECOKARELIAN GRANITOIDS IN SOUTHERN FINLAND FRONT, K., University of Helsinki, Department of Geo10gy, P.O. Box 115, SF-00170 Helsinki NURMI, P.A., Geo10gica1 Survey of Finland, ·SF-01250 Espoo Synkinematic granitoids (SKG) ·are the predominant component of the Svecokarel1an crust. Their U-Pb ages on zircons vary from 1.92 to 1.86 Ga, being genera11y 1.89 to . 1.88 Ga. SKG occur as p1utons 1n schist be1ts (G5B), and form the gran1to1d complex of central . 2 ' Finland (GCF) with ·a tota1 area in excess of 35 000 km • GSB occur u contonnableplutons with sharp and 10ca11y cross~cutting contacts, and crystallized soon .atter the peak of major regiona1 d~fonmation and metamorphism, but before younger defonnation phases. GSB are' composed of granodiorites, tona lites and trondhjemites. Vo 1um1nous granites are 1acking. Composite p1utons are often zoned with gabbros, diorites, tona1ites and trondhjem ites at their margins and with granodiorites and minor granites at the1r centres. Porphyry-type minera1ization is associated with some 1ate granit01d phases. GCF 1s composed of an 1ndefinite number .of intrusions ·ranging in composition from gabbro .. to . grantte. The 1atter covers large parts of. the comp1ex. Coarse grain size of the gran1toids in GCF - 1s common as we11 as po1yphase defonnation . Hajor minera1s of SKG are pl~gioclase, potassium fe1dspar, quartz, biot1te and hornb1ende, and typical accessories are sphene, apatite, magnetite and z1rcon. Chemical analyses of ca. 150 SKG from southern f1nland show calc~ alka1ine characteristics with var1able 5102, high Na 20/K20 and low mol. A1203/(CaO+Na20+K20). lnitial 87Sr/86Sr ratios are around 0.703. GCF has higher feOto~/M90 and ~0/Na20 than GSB. Geologica1 and geochemical character1stics of SKG correspond to those of Phanerozo1c I-type granito1ds. SKG are cogenetic with mafic plutonic rocks, which ev1dently ca.used major " . . remelting 1n the lower crust giving rise to granHo1d magmas. Var10us degrees of mixing of , mantle~derived and crustal magmas is probable. Nd 1sotope studies show that Archean material was 1nsignif1cant 1n the source of SKG, wh1ch refers to fast recycl1ng of new mantle~derived material. The geochemical features of GCF may indicate th1cker crust 1n central finland than in surrounding areas dur1ng the generat10n of the gran1toid~. Compared to C1rcumTPac1fic granitofds 5KG. ·lack a major old crusta1 component in the1r source and do not .show linear be1ts w1th a marked difference in age. HELSINKI SYMPOSIUM ON THE BALTIC SHIELD (4-6. March .1985): A finnishTSwedish contr1bution to the International Lithosphere Program. HIGH CRUSTAL LEVEL, LATE OROGENIC MAGMATISM AND TECTONISM IN THE CENTRAL SEGMENT OF ALAND Fred Hubbard and Nick Branigan Department of Geology, The University, Dundee DDl 4HN, Scotland. The Group 111 granites of Sederholm (Ava, Seglinge, Mosshaga and Lemland) form discrete complexes distributed along a NE-SW line across the Aland Archipelago. They were emp1aced after cessation of the main Svecofennian orogeny, during the subsequent long period of continuing mant1e/crust interaction and repeated crustal adjustment by shearing which cu1minated in the major Rapakivi Granite event. Current investigations on the is1and of Seglinge suggest that these com plexes were emplaced at high crustal levels with, at least in part, an exp10sive diatremic mode. Over a short time interva1, a composite pipe of pi1lowed hybrids was emp1aced and, with the surrounding country rocks, was subsequently explosive1y disrupted and invaded by porphyritic/porphyroclastic granite to form breccia screens and ring dykes. Field re1ationships and textures suggest that the granite was emplaced 1argely as gas-borne solids. A hybrid suite, such as constitutes the central pipe, could be produced by contact anatexis/assimilation if hot, basic melts were impounded beneath porphy ritic granite sheets. The granite phase at Seglinge may be a samp1e of the roof of such a source complex, mobi1ised by vo1ati1e-discharge when the surface was breeched. Compositional change in transit wou1d be minimal. The compositional simi1arity of the Seglinge granite and the rapakivi granites is so close as to suggest some genetic kinship. The Group 111 "proto-rapakivi" complexes may represent 10ca1, premature, tappings from the deve10ping rapakivi source region. The source granite composition, as indicated by the Seglinge granite, is quite distinct from the Svecofennian synorogenic granites but c10se1y simi1ar to granite sheets in S.W. Sweden deve10ped during lower crusta1 depletion associated with basic intrusion. Similar lower crust/mantle processes may have operated during the long, spasmodica11y eventfu1, period which fo110wed the main Svecofennian orogenic activity in S.W. Finland. The thermotectonic evolution of the West Uusimaa low pressure granulite dome, SW Finland L. Weatra and J. Schreura Free University Institute of Earth Sciencee De Boelelaan 1085 1081 HV AMSTERDAM The Netherlands The Svecokarelian metamorphlc belts ln Finland show two linear zones with high grade, amphlbolite to granuIite facies rocks • . The . West Uusimaa Granulite Complex occurs ln the E-W running Svec?fennian branche, possibly associated with Rapakivi granites. The metamorphic anq structural history of West Uusimaa ia complex. Three successive fold generations have been recognized. The first one (D1) is tentatively related to thrusting and imbrication tectonics at plate collision contacts. The main deformation (D2) is probably a N-S compression, which created atfirst E-W trending upright folds. Further crustal shortening tightened theae F2 folds ln the weatern part of the belt, whereas conjugate ~ear zones and mega-boudins or tectonic Ienses of competent' rock bodies developed in the eastern part. Teetonies in this phase are possibly controlled by ~ifferential movement between large scale,synkinematic K-granitoid masses. The Svecofennian rocks are largely metamorphosed under amphibolite-facies conditions, but ln the eastern part of the belt the main (D2) deformation culminated in granulite-facies metamorphism. The amphibolite- to granulite facies transition zone along the western boundary of the granulite-facies complex, in which a number of prograde reactions and mineralogical changes are telescoped, crosscuts alI major structures and rock unita and is only affected by late-D3 folding (open disharmonic folds with approximately N-S trending axial pIanes) and young ahear zone activity, associated with pseudotachylite generation. Structural evidence suggests that the whole region represents one crus t al level. The appliaation of varioue indep~ndend geothermometers indicate a tem8erature increase from .550-650 °c in the amphibolite-facies domain to 100-825 C in the granulite-facies domain, associated with a slightly decreasing water activity (0.1< aH20<0.4) and a generally incre~sirlg C02 activity. FIuid inclusions and varlous independend geobarometers indicate that the temperature increase is isobaric at an extremely Iow-pressure of about 4 Kbar. The transition zone 1s only 2-3 Km wide. It 1s concluded that the granulites represent a low-pressure thermal dome. Whole rock chemical data show that the granulite facies metamorphism is isochemical, in other words : the West Uusimaa Complex classifies as an undepleted granulite-facies region. The Uusimaa granuIite rocks, therefore, can not be regardedas refractory rocks from which Rapakivi melta were extracted. The high metamorphic temperatures and dominancy of C02 fluid inclusions could be expIained b y the lnflux of hot C02-bearing flulds from an external · aource such as mafic intrusives at deeper crustal levels. · Any plate tectonic model for the origin 0 f the Svecofennian beIt in Finland should incorporate a heat source to account for the the exceptional geothermal gradåents of about 50 °C/km for the amphibolite-facies domain up to about 60 C/km for the granulites. Such a modeloould be lithospheric doubling; subhorizontal subduction ofyoung, hot oceanic lithosphere. 1.5. cOen· - Geology and metallogeny of the Bergslagen Supra crustal Serles ln the Fl1lpstad-Kopparberg sectlon Abstract The Bergslagen-Supraerustal Series in the Filipstad-Kopparberg area is defined as a 1900-1800 Ma old ehronostratigraphie unit forming the filling of the NNE Bergslagen basin. The Bergslagen Supraerustal Series eomprise four roek groups: (1) the Voleano sedimentary Supergroup, (2) the Older Granite Group, (3) the Metabasie Roek Group, (4) the Gabbro-Tonalite Group. The Voleano-sedimentary Supergroup ean be divided into: (a) the Lower Leptite Group of felsic voleanies deposited in th~ Early Voleanie Stage, (b) the Middle Leptite Group of banded felsie tuffs, . marbles and iron formations, deposited in EW, NNE and NS branehing basins in the lnitial Rift Stage, (e) the Upper Leptite and Slate Group deposited in the youngest NS basins in the Rift Stage. A phase of eompressive deformation affeeting the basin sediments and the post-deformation intrusion of the Gabbro Tonalite Gro~p mark (d) the Post-rift Stage. The lnitial Rift and Rift Stage extensional teetonies is eharaeterized by bimodal felsie and mafie magmatism. Mafie dykes of eontinental tholeiitie eharaeter intruded parallel to the EW, NNE and NS axes of rifting in and along graben zones, whereas subvoleanie Older Granites, interseeting mafie dykes and interseeted by other mafie dykes, were preferentially emplaeed in the pile of felsie voleanies in the horst zones. lntensive sOdium-, potassiurn- and magnesium metasomatism assoeiated with iron, manganese and sulfide skarns oeeurin the Voleano-sedimentary Supergroup in spatiotemporal relationship to the lnitial Rift and Rift Stage felsie and mafie magmatism. These mineralizations are believed to be related to sub-seafloor hydrothermal eonveetion systems generated by the mafie and felsie magmas, intruding and extruding synehronously with the development of ~he Bergslagen Supraerustal Series in a zone of erustal extrusion and basin subsidenee. * Geologiseh lnstituut Universiteit van Amsterdam Nieuwe Prinsengraeht 130 1018 VZ Amsterdam - The Netherlands