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M.V.Mints, V.N.Glaznev, A.N.Konilov, N.M.Kunina, A.P.Nikitichev, A. B. Raevsky, Yu.N.Sedikh, V.M.Stupak, V.I.Fonarev THE EARLY PRECAMBRIAN OF THE NORTHEASTERN BALTIC SHIELD: PALEOGEODYNAMICS, ...

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5 - amphibolites, migmatites, gneisses, 6 - felsic and basic granulites, migmatites, 7 - G rt-B t gneisses (felsic metavolcanics) and A eg-A rf gneisses ("alkaline granites" felsic alkaline metavolcanics); 8 - migmatites with amphibolite and gneiss xenolites; 9 - gabbro, gabbro-anorthosites. 10-29 - Paleoproterozoic: 10 - G rt-Stv-K y schists, amphibolites; 11 - alkaline gabbro, 12 - layred mafite-ultramafites. 13 - alkaline granites (.remelted alkaline gneisses), 14 - dom es formed by rhemorphosed alkaline gneisses, 15 - mafic volcanics and sediments o f riftogenic type; 16 - mafic volcanics o f oceanic type, partially - volcano-clastic rocks; 17 - mafic and moderateacid volcanics o f island-arc type, volcano-clastic and volcano-sedimentary assemblages; 18 - sedimentary-volcanic assemblages (mostly m afic volcanics) o f unknown geodynamic settings; 19 - granites, diorues, 2 0 - felsic and mafic granulites, 21.21 - gabbro-anorthosites and gabbro: partially eclogitized {21) or transformed into Grt amphibolites (22); 23 - Alpine-type ultramafics (dunites, harzburgites); 2 4 - bimica-Ky gneisses, Grt-bearing amphibolites; 25 - K y-G it gneisses, Grt amphibolites (Late Ajchean Belomorian assemblage secondary metamorphosed in Paleoproterozoic). 2 6 -2 8 - migmatites, gneisses and granitoids forming domes and arches: with predominance of: rheomorphosed gneisses (26), migmatites (27), granitoids {28). 2 9 - porphiritic granites, granodiorites (intrusive bodies and domes). 30 - Neoproterozoic - sandstones, gristones, schists 3 1 -33 - Paleo zoic.


31 - southern boundary o f Norwegian caledonides. 3 2 - nepheline syenites, 33 alkaline ultramafics, carbonatites. 3 4-40 - geological boundaries and fa u lts : 34 - stratigraphic and intrusive boundaries; 35 - dome and arch restrictions, 36 - Paleozoic strike-slip faults, partially Paleoproterozoic ones reachvized in Paleozoic, 3 7 Late A rchean faults: arc-shaped upthrusts (37), arc-shaped normal faults (35), main and secondary thrusts (35); 4 0 - Paleoproterozoic thrusts Fig. 1.21. The reconstructed succession o f geodynamic settings in the Late Archean history o f the NEBS collision structures (plan) Compression settings: subduction o f the Titovka-Keivy microocean lithosphere, active margins development, collision o f the Central-Kola, Keivy and M urmansk m icrocontirents, front tectonic nappes origin Fig. 1.22. The reconstructed succession o f geodynamic settings in the Late Archean history o f the NEBS collision structures; approach and collision: a - Central-Kola and Murmansk microcontinents. 6 - Keivy and Murmansk microcontinents (cross-sections) Com pression settings: Titovka-Keivy microocean lithosphere subduction. active margins development, front thrust nappes origin 1 - continental crust, 2 - lithospheric mantle (e), asthenosphere (6); 3 - oceanic crust; 4 - volcanic activities (a) and sedimentary-volcanic assemblages (6) o f active margins; 5 - eruptions (a) and deposits (6) o f pyroclastic flows in back-arc extension area; 6 gabbro (a) and granitoid (6) intrusive bodies and granite-gneiss domes (e); 7thrust-nappes; 8 - metagabbro-ancrthositc bodies in the thrust-nappe sole Fig. 2.26. P aleogeodynam ic d em arcation o f the N EB S P aleoproterozoic structures / Late Archean units; 2 Paleoproterozoic units: 2 sutures, 3 volcano-sedimentary belt of unestablished geodynamic nature, 4 - back thrust belt, 5 - outcroped subnappe area, 6 - plulonic arc granitoids, 7 - granite-gneiss and graniie-migmatite domes o f Kola-Belomonan belt (without special sign at the scheme);

8 - Neoproterozoic structures; 9 - thrusts; 1 0 - geological boundaries o f unestablished geodynamic nature Fig. 2.28. T h e reconstructed succession o f geodynam ic settings in the Paleoproterozoic history o f the NEBS collision stru c tu re s (plan) Extension settings continent rifting, layred mafic-ultramafic bodies emplacement (a); opening of

Pechenga-Vaxzuga and Circum-Karelia microoceans and oceanic lithospere origin (6). Compression settings:

oceanic lithospere subduction, origin o f the active margin (island arc*5 systems back-arc spreading and related ) oceanic lithosphere together with oceanic island chains origin (e); the closure o f Pechenga-Vaizuga and CircumKarelia microoceans as a result o f subduction, creation o f accretion prisms including the fragments o f oceanic lithosphere and oceanic island assemblages (Pechenga gabbro-wherliie bodies are understood as root parts o f those islands), starting o f back thrusting (?); collision o f the Kola, Karelia and Bebm orian microcontinents, formation o f back thrust-nappe system, rheomorphism and doming, epigenetic C u-N i ore origin (d) Present erosion level (e) Fig. 2.29. The reco n stru cted succession o f geodynainic settings in the Paleoproterozoic history o f the NEBS collision stru c tu re s (cross-sections) Legend for fig.2.29 and 5.4 I - sedimentary assemblages mainly terrigenous; 2 - alkaline volcanism; 3 sedimentary-volcanic assemblages of intiacontinent and back-arc rifts, 4 - gabbro-anorthositcs; 5 - layered mafic-ultramafic bodies;

- granulite metamorphism, granulites, 7 - Archean granulites, 8 - oceanic crust, 9 - E-MORB type volcanism, 10- oceanic island volcanoes; II - calc-alkaline volcanism. 1 2 -1-, partially S-type granitoids; 13 - granosyenites, K-gramtes, S-type granites; 14 - granitc-migmatite and granite-gneiss domes, 15 - mantle plume; 16 - asthenosphenc material displacement Fig. 3.2. Geological schem e o f Kola-SD refractio n seismic profile a rea Legend for fig 3.2 and 3.3 / - mostly Late Archean high-grade assemblages, 2 -1 2 Paleoproterozoic: 2 -8 sedimentary-volcanic Pechenga succession. 2 - Majarvi andesibasalts, 3 - Pirttijarvi alkaline basalts, 4 - pillowed tholeutes o f Zapolamy and M ated suites, 5 - imbricated ensemble o f "Productive layer- tuffogenic-sedimentary assemblage with lens shaped inclusions o f pillowed tholeines and gabbro-wherlites, 6 - subvolcanic andesite-dacite bodies o f Poritash Mountain, 7 - Bragino andesibasalts, 8 - picrite-basalts, basalts and ryiolites of Kaplya and Mennel suites, Talia gneisses; 9 - granitoids; 10 - migmatite-granites and granite-gneisses, 11-12 - Lapland belt assemblage.

11 - granulites, 1 2 -s u b n a p p e melange zone, gneiss-blastomilonites, amphibolites; 1 3 - Litsa-Aragubagranitoids;

1 4 - thrust faults; 15 - normal faults, 16 - Kola superdeep well; 1 7 - Kola-SD profile Fig. 3.3. T he in te rp re ta tio n o f Kola-SD profile reflection seismic d a ta (together w ith seismic data northw ard from the Kola su p er deep well) For position o f Kola-SD profile see fig.3.1. a - seismic cross-section, 6 - seismic data together with geological interpretation, e - reconstructed geological cross-section For additional legend see fig.3 2 / upthrusl-underthrusi faults according to seism ic reflections, a - main ones that form the assemblage restrictions, 6 - secondary ones, 2 Pechenga succession lower boundary; 3 - reflections, dipping ( a ) and subhorizontal (6); 4 - depth interval o f refraction discontinuity (after [Mints, Kolpakov ei al., 1987]), 5 - subhorizontal reflection system; 6 - Kola superdeep well Fig. 3.4. T he in te rp re ta tio n o f E G G I-9010 profile reflection seismic data For position o f EGGI-9010 profile see fig 3.!

a - seism ic cross-section, 6 - seismic data together with geological interpretation, e - reconstructed geological cross-section I - Archean gneiss-amphibolite-migmatite complex; 2-11 - Paleoproterozoic. 2 - 8 - Lapland granulite belt 2 -te c to n ic melange zone (amphibolites, Ky-bearmggneisses), 3 - metagabbro-anorthosiies, Grt amphibolites, 4 - undivided (2 ) and (3) type assemblages o f Kaskama and Talia suites), 5.6 - felsic granulites (5 - khondalites, 6 - G rt-B t with Si I and C or gneisses), 7 - 9 - mafic granulites ( 7 - two-pyroxene ones, 8 - Amp-CPx-PI schists, 9 - enderbites), 10 - Pechenga-lmandra-Vaizuga sedimentary-volcanic belt: mafic volcanics, terrigenous sediments, 1 1 - m igmaiites, granites Fig. 4 3. The formation history o f Pechenga-Alaka ore d istrict structure

- plans, 6 - cross-sections; ages - in Ga) (a / - the riftogenic and transform faults in back-arc basin area (sec fig.2.28); 2 - spreading axis;

3 transform faults and oceanic island chains; 4 accretion prism; 5 - crust: a - oceanic (at plans), 6 - continental;

6 - oceanic crust (at cross-sections); 7 - oceanic island volcanoes with sediments on their slopes; 8 - active-margin volcanism (a) and related assemblages (6); 9 - granite-migmatite and granite-gneiss domes; 10 - tectonic transporl direction; I I - Pechenga-Alaka arch structure (at lower cross-section) Fig.





5.1. P -T conditions o f crustal high-grade metamorphism a - Phanerozoic and Neoproterozoic metamorphic assemblages; 6 - Palecproterozoic and Archeam granuhte-gneiss assemblages; - thermal structure o f high-grade (granulite and amphibolite facies) crustal metamorphic areas / - 5 - metamorphic assemblages (ages o f assemblages at fig.S.l,a: filled signs - Phanerozoic, open ones Neoproterozoic, at fig.5.1,6 filled signs - PaJeoproterozoic, open ones Archean): I eclogites and high-grade granulites and amphibolites o f subducted continental crust and subnappe assemblages overthrusted by thick crustal tectonic slices, 2 - granulite-gneiss (granulite-amphibolile) o f thrust-nappe assemblages, 3 - mafic and ultramafrc intrusive bodies metamorphosed under granulite-eclogite facies conditions; 4 - P -T intervals o f referred assemblages (in case o f averaged data dotted lines are used); 5 - numbers related to granulite-gneiss assemblages that include synmetamorphic gabbro-anorthosite o r mafic-ultramafic bodies; 6 -1 0 - metamorphic areas in P-T coordinates: 6 - eclogite-greenschist facies o f subdueiion zones (after: [Dobreisov. 1995]), 7 - eclogite (highpressure and ultrahigh-pressure) facies rocks o f subducted continental crust, 8 - amphibolite-gran ulite-eclogite facies o f subnappe complexes; 9,10 - the boundaries o f granulite-amphibolite facies metamorphic crustal area (including subnappe complexes): 9 - approxim ate position o f the crust-mantle discontinuity in ArcheanPaleoproterozoic (a), in Neoproterozoic-Phanerozoic (6 ), 10 approximate position ol granulite-amphibolite metamorphic boundary in upper crust; I I - approximate geotheims in the crustal area o f high-grade meta morphism: in Archean-Paleoproterozoic (a), in Neoproterozoic-Phanerozoic 16 ); geotherms for "cold" and "warm" subductiDn after [Peacock, 1993]; 12 - averaged geotherm for present crust o f the Baltic Shield (after [Glaznev et ah, 1989].

There are references in the Russian text Fig. 5.2. The model o f Archean evolution - hypothetic cross-sections im itating the granitization and granulite metamorphism settings, evolution and tectonic relationships o f granulite belts and granite-greenstone areas I - continental crust; 2 - oceanic crust that formed by: tholeiites (a), tholeiites and komatiites (6);

3 - oceanic crust fragments included in: continental crust (a), mantle (6); 4 - volcanic activities of: within-plate (komatiitic) (a), island-arc and active margin (tholeiitic and calk-alkaline) (6), within-plate (tholeiites) (e) types;

5 - volcanic assemblages o f continental rift and other within-plate (a) and subduction (6) settings; 6 - basal sedimentary assemblages o f riftogenic depressions; 7 - terrigenous and chemogenic sediments; 8 - m afic (mainly gabbro-anorthosite) intrusives; 9 high-grade metamorphism o f granulite and amphibolite facies: in the lower and middle crust (a), in subnappe complexes (6); 10 - granitization (granite-migmatite complexes) (r), granitoid plutors (6), I I - granite-migmatite and granite-gneiss domes; 12 - fluid flows, mainly water (a), mainly carbomcmethanic and water-carbonic (6); 13 - mantle plums; 14 - convective m ovements in aslhenocphere Fig. 5 3. Pflleoproterozoic orogens o f the North America craton and Fen no-Scandinavian (Baltic) Shield (platform cover removed) (based on P.HofTman materials [The Geology o f North..., 1989| and other data (there are references in the Russian legend fo r fig.5.5) I - Archean crust; 2 - 6 - Paleoproterozoic crust: 2 - 4 - accretion orogens: 2 - 2.3 -2 1 Ga juvenile (?) crust and 2.0-1.8 Ga continental margim magmatic arcs, 3 - 1.9-1.8 G a juvenile crust and 2.0-1.8 Ga continental margim magmatic arcs, 4 - 1.8-1.6 G a juvenile crust and; 5.6 collision orogens: 5 - 2.4-1.8 Ga juvenile crust and continental margim magmatic arcs, 6 - granulite-gneiss belts thrust-nappes formed by rocks o f the Archean or Paleoproterozoic lower-middle crust (the completion o f tectonic emplacement - c.1.8 Ga ago); 7 - poslPaleoproterozoic crust; 5 - Tectonic restrictions o f the Paleoproterozoic crust; 9 - strike-slip faults (e) and thrusts (6).

Upper case names are Archean orogens, lower case names are Paleoproterozoic ones CK - Circum-Karelia belt system, C S Cape Smith belt, L - Lapland granulite belt, PV - Pechenga-lmandra-Varzuga belt, S - granulites in the Snowbird strike-slip zone Fig. 5.4. The reconstructed succession o f geodynamic settings in the Paleoproterozoic history o f the North America craton (cross-sections) For legends see fig.2.29 Fig.5.5. The main events correiarion in evolution o f the Palcoproterozoic orogens 1-13 - igneous assemblages: 1-17 - riftogenic: / - layred mafic-nltramafics, 2 - diabase dikes, 3 layered gabbro-anorthosites, 4 - alkaline granites, syenites, 5 - alkaline basalts, rhyolites, 6 - leucocratic granites (S-type), 7 - terrigenous sediments, mafic lavas and sills; 8.

9 o f spreading zones and oceanic islands: 8 pillowed tholeiites (T -M O R B ), ophioliteS, 9 - picrites, gabbro-wherlites (mainly oceanic volcanoes), 10-12- calk-alkaline assemblages o f subduction zones: 10 - volcanics, 11 - granitoids, 13 - anorogcnic (granites, syenites, rhyolites, pegmatites). 1 4 - grannlites. 15- rheomoiphism and doming.

P1V - Pechenga-lm andra-V arzuga belt, LKGB - Lapland-Kolvitsa granulite belt, Y - Yormua belt, CS - Circum-Superior belt system (Trans-Hudson, Cape Smith, New Quebeck belts), TT - Taltson-Thelon belt, sTT - surrounding o f Taltson-Thelon belts (Slave province, Queen Maud uplift. Snowbird zone), S - Svecofennian orogen, sS - Svecofennian margin o f the Kola-Karelian continent.

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