Jl geol. Soc. Lond. Vo1.135, 1978, pp. 597--610, 6 figs., 1 table. Printed in Northern Ireland.

The Finnmarkian phase of the Caledonian Orogeny

B. A. Sturt, 1. R. Pringle & D. M. Ramsay

SUMMARY: The Kalak nappe complex of N involves late Precambrian to Middle Cambrian sediments and a Precambrian gneiss basement on which the sediments were depo- sited. While the uppermost nappe in Finnrnark was emplaced during the Silurian the members of the Kalak nappe complex were emplaced in late Cambrian/early Ordovician times during the Finnmarkian orogenic stage--probably the analogue of the Grampian stage of the British Caledonian. The tectonic-metamorphic events of the Finnmarkian stage were broadly coeval with the emplacement of basic and alkaline igneous bodies of the Seiland Igneous Province which were introduced from 552+17Ma (syn-D1) until 501+27Ma (late D2) and which themselves reflect magmatic evolution from tholeiitic to alkaline types.

Attention has recently been focussed on the Caledo- framework for this magmatic evolution, and to con- nian Nappe Complex of northernmost Norway (Gayer sider the timing of orogenic development of the Kalak 1974, Gayer & Roberts 1974, Sturt et al. 1975) and Complex in relation to that of the lower nappes and preliminary plate tectonic models have been proposed foreland. for its orogenic evolution (Ramsay 1973, Robins & Gardner 1975). It has been claimed (Ramsay & Sturt 1976) that the metamorphism and emplacement of the The general geological setting nappes occurred in two discrete stages. Firstly a lower of the Kalak Complex group of nappes was emplaced in late Cambrian/early Ordovician times and the upper or MagerCy Nappe in Many of the essential features of the region have been late Silurian times (Table 1). reviewed in a previous article (Sturt et al. 1975). The older or lower group of nappes (Gaissa, Laksef- Detailed published maps include the 1:250 000 map- jord and Kalak) form an extensive tract from N Troms sheet Hammerfest (Roberts 1974) and the 1:50 000 through most of (Fig. 1). The results pre- map-sheet Alta (Zwaan 1975). Important evidence sented in this account indicate that the metamorphic has recently been discovered which confirms the pres- development occurred in the general time interval ence of Precambrian gneisses in the Kalak Nappe 550-500Ma. It is considered that Finumarkian Complex (Ramsay & Sturt 1978). These gneisses are orogenic activity in the allochthonous Kalak Complex present both as basement to the Kalak cover sequence records a more extended sequence of events than in in several of the constituent nappes and as discrete the foreland autochton and parautochthon. The age of gneiss nappes bounded by extensive mylonite zones. the metamorphism is broadly coeval with the Gram- The metasediments of the Kalak Nappe Complex pian metamorphism of Scotland and Ireland (Dunning comprise a great thickness of predominantly shallow- 1972). Recent work reveals that the Kalak Nappe water elastics, of Eocambrian to Middle Cambrian Complex contains Precambrian gneisses with a com- age, which form a well differentiated stratigraphic plex pattern of cover/basement relationships. This pat- succession (Ramsay 1971). A number of local stratig- tern has similarities with the Moine Complex of Scot- raphic successions have been established and are cor- land (van Breemen et al. 1974, Brook et al. 1976, related with the sequence of SOrcy (Ramsay 1971). 1977). Ramsay proposed that the SCrCy succession should be Pankhurst (1974), following Dewey & Pankhurst considered as a standard sequence as it is confirmed by (1970), proposed that the Grampian orogenic stage of abundant sedimentary structures and the presence of the Scottish and Irish Caledonides, was relatively the only identified fossils (Holland & Sturt 1970). short-lived, perhaps not exceeding 10-20Ma. The Roberts (1971) suggested that this sequence repre- Finnmarkian was apparently more protracted and oc- sents a progressive vertical change from littoral and cupied an interval of approximately 50 Ma. The Kalak sublittoral deposits to deeper water turbidites in a Nappe Complex contains the Seiland Petrographic progressively evolving geosyncline. The SCrcy succes- Province with its unusual assemblage of igneous rocks sion is as follows: which were emplaced into the deforming orogene. The Hellefjord Schist Gp. parent magmas of the gabbros display an evolution -Meta turbites, mica schists from tholeiitic eventually to alkaline-olivine basalt types (Robins & Gardner 1975). The principle objec- Aafjord Pelite Gp. tives of the present study are to present a time -Mica schists, graphitic schists

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25" I : i I ! I LOCATION MAP ~ROKA~,p NORO~N

sO~ °

! I

I ......

Autachtho~ous late Pre- 0 50kin cambrcon/Tremodoc sedi- Kak3k noppe complex L,~==mm===~J ments and D=vidal Group

i Batents Sea Group

NOROKYN METAMORPHIC COMPLEX D Magereynoppe and nappes [~ 9 Ka|ak nopp~ complex "~ of equivalent age Raogo group Laksefjor d noppe

I i I L i I 25" 30' FIG i. General map of the tectonic units of . Place names: D--Diggermul, F--Friarfjord, H--Honingsvag, G---Gjesvaer, Sn--Sncfjord, Hm--Hammerfest, Hv--, BrmBreivikbotn (also Haraidseng and Baarvik), Sg--Stangnes, L-Lerisfjord, A--AIta, O---Oksfjord, K--Kvaenangen, Ly--Lyngen, ArwArncy. A--A' and B--B' represent lines of section for Fig. 2.

Falkenes Marble Gp. part, of Precambrian age and represent segments of a -Marbles and calc-silicates continental basement on which the essentially shallow- (contains archaeocyathids) water late Precambrian and Cambrian meta-sediments were deposited. Storelv Schist Gp. Ramsay & Sturt (1977) showed that the Klubben -Pelitic and semi-pelitic Psammite rests with primary stratigraphic unconfor- mica schists mity on Precambrian gneisses at Stangenes on Kvalcy. This contact was folded by easterly overturned folds Klubben Psammite Gp. during Finnmarkian deformation, and the gneisses -Psammite, semi-pelitic mica suffered both tectonic and metamorphic reworking. schists (contains trace- On KvalCy the cover sediments, in the lower or Kval- fossils of interconnecting sund Nappe, are truncated by a thick nappe of myloni- tic gneisses (Fig. 2). This gneiss nappe is termed the burrow type in upper part) Kvaloy Nappe, and extends, at least, from the south- eastern part of Seiland northeastwards to Snofjord, on the Porsanger Halvcy (Fig. 1). The uppermost part of This distinctive sequence can be traced from the the Kvalcy Nappe is a complex imbricate zone, where north of the Porsanger Halv0y southwestwards for a repetitions of metasediments and gneisses are overlain distance of approximately 250 km to Lyngenfjord (Fig. by the Hammer[est Nappe. In this latter, gneisses are 1), where it is apparently truncated by nappes bearing unconformably overlain by the Klubben Psammite. the Nordland sequence (Gustavson 1972). Within the The contact is folded by easterly overturned folds Kalak Nappe Complex a sequence of nappe units can which are locally recumbent, as is the case with the be recognised which contain both gneisses and the Hammer[est Syncline (Fig. 2). Jansen (1976) demon- metasediments of the characteristic Kalak succession, strated in the Lerrisfjord region, that a complex sequ- i.e. that established for S0rcy. The gneisses are, in ence of nappes overlies the low-grade Karelian rocks of

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Ho mmer f es t Hammer fest Kvaley Kvo i sund I Noppe ~ Syncline Nappe | Nappe

." "." " . ~1 -I" ~ - I ~ ~ / ' ~ " " " " - " / " ~ ". x ~ I - " - / " ~ ~ /~/ - / ::':::::::~;:~;,7-'--, - ~.,, ..':'"'" ."-'" , ,- ,'- ,'~;\~/,- ," -"'(-(-"" -'-':':':.!~. " /'~ ~ )' 7.7// ~; .: .... ",,x-'x \/~ ~"('~.r "/~x/ -r\- " / ~_~/ - ~/-/ / ..-:-:-::-:.:.7/ / / / /// , :::~,, ~-:<~:,_ ,"," .~/,~l"'/ / ,t --, ,/._,,."/- .',. " '")-."~/.L~~f¢.- / ' ~''.1" "':'"" :///~,.,,qq~./L//////~-{~i/~/~///././-'" - ,~//<-- -

if < -. -p .,.,-.// Oividal I I I ~ Group 0 ;.,~ --; ,'--'.;' x'. (_,.. -', d,, (. -,, :. '.-. ~..-JZr~-; ~.;~'z,'.~ *,~,~1~/.~-,~,~¢~//_~. ~_.~.~-./-. ;.p)'/-~ ;,~:

- "" xz'f~/ ~ -t" -'- ~ " ///,- //i //z /// /// /.~.4~,,~..---~ ',-. - ~,, ,-.T.,~//z ,-'(~ - \7 .~ \-~.-- - "" .-.." "..';.'-;:,.,.:.,-¢-T=~,~;.-:'. ,;~,.~ ,~-2~;;, ~----,.,.'.':.,'--',-,.',-,;?.',.%, k',",,-,'', k ~V-" " -- 7..i7,-,-?,.,-, ...... ,.,., .,,-,._,.,,-, -:...-,-.,,,.-.-...-.,-., ....

~~ Katok metasedlmentary sequence ,,, ,-'] Gneisses in Katak NctppeComplex ///~~, ~.-/~/ Low-grade Precambrion Raipas Suite ~,---.,-'t.,,~.t?~- x- ; Presumed substrate to Rctipas Suite

FIG. 2. Sketch sections for lines A--A', B--B' on Fig. 1. Not drawn to scale.

the Komagijord window. This nappe sequence con- stones occur within the Ankerlia Schist (Hellefjord tains parautochthonous elements of the Karelian, Schist). The Kalak sedimentary sequence suggests the gneisses probably of Precambrian age and Kalak sedi- progressive differentiation of an Atlantic-type conti- ments. Preliminary studies of Rb/Sr whole-rock geo- nental margin during late Precambrian and Cambrian chronology of the gneisses (Sturt, Jansen & Pringle, times. unpubl, data) shows that granitic dykes which cut the The tectono-metamorphic evolution of the Kalak gneissic foliation yield an age in the order of 1500 Ma. Nappe involved essentially two major deformation Work in progress by the authors in the Alta and cycles (D1 and D2) which pre- and post-dated the Kvaenangen regions indicates that similar nappe sequ- metamorphic peak. During each cycle polyphasal se- ences are present. The only other age determination quences of deformation episodes were imposed on the on gneisses is a Rb/Sr isochron of 1035 Ma for quartz- rocks, although only one major regional fold- rich gneisses in the Oksfjord area (Brueckner 1973). producing episode occurred in each cycle. The Thus the general tectono-stratigraphical pattern is tectono-thermal evolution in the Seiland region, was one of a sialic basement with a cover of the Kalak interspersed by the emplacement of mafic and ul- metasedimentary sequence. There has been considera- tramafic plutons and a variety of other igneous rocks. ble shuffling of this basement/cover during Caledonian The regional metamorphism within the Kalak Nappe thrusting and much interfolding. In some areas origi- is of Barrovian type, generally within the almandine nal basement/cover relations remain virtually intact, amphibolite facies. ~1 migmatite complexes de- while elsewhere the cover has been detached from veloped within the region and small areas of granulite- basement and in overriding it, has eliminated parts of facies metamorphism have been reported (Hooper & the cover succession. Gronow 1970, Roberts 1974). Large areas of Recent compilations (Gayer 1974, Gayer & Roberts granulite-facies rocks are present on Seiland, StjernCy 1974, Sturt et al. 1975) show that the sedimentary and the Oksfjord peninsula, and apparently relate to a successions of the Kalak and the underlying Laksef- local magmatic heat source in the plutonic centres. jord and Gaissa nappes are stratigraphical equivalents The metamorphic maximum through most of the reg- of the foreland autochthon. Palimpspastic reconstruc- ion was attained during a relatively static interval tion demonstrates (Gayer & Roberts 1974) that in late between D1 and D2 (Sturt & Ramsay 1965, Roberts Precambrian and Cambrian times the region had an 1968, Hooper & Gronow 1970). In Seiland, Stjern0y extremely wide continental shelf receiving shallow- and parts of the Oksfjord peninsula, where the major- water elastic sediments. The possibility of a deepening ity of the major mafic and ultramafic plutons were trough during the deposition of the rocks which are emplaced during D2, high grade metamorphic condi- now Hellefjord Schist, has been indicated by Roberts tions continued. This was probably due to magmati- (1971). There is little evidence of volcanic activity, caUy related heat-flow, in a generally declining re- although in the Kvaenangen/Reisadalen area green- gional temperature field.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/135/6/597/4885687/gsjgs.135.6.0597.pdf by guest on 01 October 2021 600 B. A. Sturt, L R. Pringle & D. M. Ramsay Igneous history o| the Geochronology ot the Kalak Kalak Nappe Nappe Complex The major igneous activity within the Kalak Nappe Traditionally the deformation and metamorphism of Complex is restricted to the NW-SE trending elliptical the region was related to a late Silurian Caledonian area of the Seiland Province, some 90x 55 km. This phase. This was apparently confirmed by the Llan- area lies close to, though offset from, a major positive doverian fauna on Mager~y (Henningsmoen 1961), gravity anomaly--the StarCy Anomaly (Brooks 1970). but it has been shown (Ramsay & Sturt 1976) that the The offset was interpreted by Brooks as representing Silurian rocks of Mager0y lie above the Kalak rocks, thrust translation some 40 km southeastwards. Several in the MagerCy Nappe (Table 1). lines of evidence indicate that thrust translations of Sturt et al. (1967) published a series of K-Ar min- and within, the Kalak Nappe Complex occurred at eral ages (Table 1) from the alkaline rocks of the successive stages. Worthing (1970) records a major Seiland Province. The ages fall into two groups, i.e. belt of amphibolite-facies blastomylonitic rocks in micas 384-421 Ma and nephelines 480-491 Ma. It was eastern Seiland, which is folded by the D2 folds and concluded that the nepheline ages indicate a minimum cut by some members of the late igneous suite. age for high-grade metamorphism in the Kalak Nappe Around the Komagfjord Window blastomylonites at which thus approximately coincided with Grampian the base of the Kalak Nappe are in upper orogenesis in Scotland. A Rb/Sr isochron yielded an greenschist/amphibolite facies though the final move- age of 530+ 35 Ma for anatectic veins associated with ments produced intense diaphthoresis. Gayer (1974) the syn-metamorphic Hasvik Gabbro on S~r¢y also records blastomylonites of D2 age from the lower (Pringle & Sturt 1969). Two isochron plots (Pringle & part of the Kalak Nappe in the Porsangerfjord area. Roberts 1973) suggest ages of 500+ 100 Ma for grani- Many papers have dealt with aspects of the plutonic tic gneisses from northeastern S¢rCy. Sturt et al. development of the Seiland region, which represents (1975) considered that the slaty cleavage in the one of the most unusual elements in Caledonian geol- parautochthon and marginal autochthon was approxi- ogy both in terms of the range of igneous rocks and mately coeval with the metamorphism. Thus a wide- their emplacement during the progressive tectono- spread age province of Finnmarkian orogenic defor- metamorphic evolution. The igneous rocks include mation and metamorphism is indicated. ultramafic, mafic and alkaline types, diorites and rarely granites. The pioneer work of Barth (1927, 1953, 1961) established the existence of most of these rock Analytical techniques types, though he and others (Krauskopf 1953, Oos- All samples were analysed by standard isotope dilu- teroom 1963) considered that they had essentially a tion techniques using S2Rb and ~Sr spikes. The analy- deep-crustal, metamorphic origin. Recent studies ses were carried out using an Atlas CH4 mass spec- (Sturt & Ramsay 1965, Speedyman 1972, Robins trometer equipped with a digital output. 1971, Sturt & Taylor 1972, Bennett 1974, Robins & All Sr isotopic data were normalized to g6Sr/SVSr= Gardner 1974), however, demonstrate that the gab- 0.1194 and ages were calculated by York's model II broic, ultramafic and alkaline rocks are products of (York 1969) regression analyses using )t87Rb= mantle-derived magmas. Layered gabbroic and ul- 1.39 x 10 -1~ a -1. The experimental uncertainties used tramafic plutons (Bennett 1974, Hooper 1971, Robins in this regression were 1.5 per cent and 0.1 per cent & Gardner 1974) exhibit many features characteristic for the 87Rb/s6Sr and STSr/S6Sr ratio respectively and of such bodies in non-orogenic terrains. The alkaline the resultant uncertainties in the calculated ages given rocks include carbonatites, nepheline syenites, shonki- at the 95 per cent confidence level. nites and alkaline pyroxenites (Sturt & Ramsay 1965, Robins 1974). The plutons of the Seiland Province constitute a The Gabbro complex sequence extending throughout the tectono- The Brevikbotn Gabbro (Sturt & Ramsay 1965)was thermal evolution of the Kalak Complex (Sturt & emplaced late in D1. Around the gabbro a metamor- Ramsay 1965, Sturt & Taylor 1972, Robins & Gard- phic aureole is partially preserved in schists and psam- ner 1974, 1975). Robins & Gardner (1975) showed mites, which were fine-grained prior to gabbro emp- that the parent magmas of the successive gabbroic lacement. High-temperature pseudomorphs after gar- plutons follow a systematic evolutionary trend (Fig. 3), net occur in the inner part of the aureole (Sturt & changing from sub-alkaline through calc-alkaline to Taylor 1972) implying that at least upper greenschist- alkaline-olivine basalt. Certain deviations occur, how- facies conditions obtained prior to gabbro emplace- ever, as is seen in the relatively late emplacement of ment. As the result of late-D1 strain the hornfelses the tholeiitic Lille Kufjord gabbro in southern Seiland. and gabbro suffered strong flattening which produced The plutons were emplaced successively as syn-D1, a marked foliation and partially destroyed the contact inter D1/D2 and syn-D2 intrusions. metamorphic mineral assemblages and textures. This

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west SEILAND PROVINCE Kva~rx~ngen-Bargsfiord W. Serey S.E. 5erey Seiland- Stierney I 12 ' I1 ,25,23, 24, II II (9, 30, 45) J

[Baslc dykes l Loca I I Deforma t i on Alkaline rocks Alkaline rocks ] J ALKALINE L Litchfieldite peg. ] [[ Carbonatite 1 Carbonatite SUBP ROV I NCE I u. Kofi~,d g.bb,o I

Cpx. gabbeos BASALT SUBPROVINCE

Vatna galobro [ Syen~bbro, l ] : TRANSmONAL Second BASALTSUBPROWNCE Phase of Deformation MOnzogronlte IVIonzon~te CALC-AL KALINE /V~,onzonlte ~enodlotl te Diorite Havnefjord diorite BASALT Relnfiord complex |i Langstrand gaI~oro SUBPROVINCE Kobberfjord norite

Regional Sandland-Middag- J Diorites J Metamorphic sfjell gobbro Hasvik Balero J J Olanes gabbro Peak Olderfiord norite Basic dykes J SUBALKALINE BASALT SUBPROVINCE First J Phase of l Basic dykes J Breivlkbotn & Def°rmati°nI / Storelv gabbro Husfjord BabOo Henseby gabbro

i eJ i O Basic dykes ]

FIG. 3. Magmatic sequence of the Seiland Igneous Province (reproduced from Robins & Gardner 1975, with permission of Elsevier Scientific Publishing Co. J.)

flattening fabric pre-dates the main regional por- the regional field. The static interval was probably of phyroblast metamorphism. some considerable duration as the temperatures in the In the highest grade hornfelses, many anatectic aureole had declined into those of regional granitic dykes and veins occur. Where complete melt- amphibolite-facies conditions prior to D2. As the ing occurred such veins are almost ideal for Rb/Sr gabbro was intruded at a peak of regional metamorph- whole-rock age determination of the thermal event ism, its emplacement age is critical for dating which produced anatexis. An aplitic granodiorite vein Finnmarkian metamorphism. yielded an isochron plot (Fig. 4) which gives an age of Pringle & Sturt (1969) presented their first Rb/Sr 552+17Ma, with an initial ratio of 0.712. It is results on an anatectic granite dyke which cuts the concluded that this age represents the time of em- marginal part of the gabbro. This gave an age of placement of the Breivikbotn Gabbro. Three biotite 530+35 Ma. To improve the accuracy of this result, whole-rock ages from the same vein (Fig. 4) gave 440, further samples were collected from the dyke. The 425 and 410 Ma respectively. resultant isochron plot of all data gives 539±27 Ma, with an initial ratio of 0.7108 (Fig. 4). An aplograno- The Hasvik Gabbro phyre dyke from the central part of the gabbro was also analysed and gives an isochron age of 542+ The Hasvik Gabbro (Sturt 1969, 1971, Robins & 16 Ma and an initial S6Sr/STSr ratio of 0.706 (Fig. 4). Gardner 1974) was emplaced, during the static inter- The low initial S6sr/a7Sr ratio for this dyke suggests val between D1 and D2, into rocks undergoing that it is a late derivative of the Hasvik Gabbro. amphibolite-facies metamorphism (Sturt 1971), and The two isochrons at 539 and 542Ma are consi- superimposed a high-grade metamorphic aureole on dered to represent the age of emplacement of the

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TEC TONO- STRA TIGRAPHIC STRATIGRAPHIC AGE OF PALAEON TOLOGICAL DEFORMATION /METAMORPHISM RA DIOME TR {C UNi T SEQUENCE AND MAIN EVIDENCE AND IGNEOUS ACTIVITY AGE DETERMINATIONS LITHOLOGIES

C)rdovicion(?) - Silurian L Iondoverian Fauna Geeenschist - om~ibolite facies No~ yet doted Greywockes, shales, phyll;tes, regional metamorphism. Progrode Managrop tids matamoq~hism and thrust fabric. MAGEROY schists, limestones, conglo- Corals merates. Mc~c, ulrromafic and wan;tic NAPPE Brnchiogods rocks Crinoids Trace fossils

Vv~,vv~vvvvv' vvvvvvvvvvvvvvvvvvvvvvv ivvvvvvvvvvvvvvvvvVvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv THRUST - CONTACT/PROGRADE METAMORPHISM

A^^AA^^^^^^^^^^^^ kAAA A AAAAAAAAAAA A AA A A A AAA A AAAAAAA AA AAAAA A AA A ", A A A A A A A A AAAAAAA A AAA AAAAA~,J AAAAAAAAAAAAAA AAAAAAAAAA

Late Precambrian - Cambrian Archaeocyoth;ds of o Complex defom',atlon history. High- 402Ma. K-Ar whole ,ack. (Da,e T Psammites, schists, limestones Lr-mid Cambrion age grade regional ry~etomorphism (main- ~-Jote metamorphic even1~ A - with turbidites at top of in Falkenes Marble Gr~Jp ly omphibolite focies) with local 384-420Ma. K-At micas (Dote KA LAK K S succession (S~eya) development of migmatites, of late rnelornorph;c evenlt A E No gloclogene ~diments Trnce fossils ;n Klu~n Plutonic rnaflc, u{tramaflc, d;or{t{c, 480-491Mka. K-At nephe{ines L D recora%,d. Psamm|te Group g~nitic, and alkaline rocks ;n (Date of main high grade A I (S~0yo) W. Finnmark and N. Trams. metamorphism) K M .S0|-552Ma. Rb-Se ;tochron ages. (Date of medium°high E grade metamorphism) N T S NAPPE IN SOME CASES THRUST-CONTACT; IN OTHERS PRIMARY UNCONFORMITY

P Precambrian None Poizphose Precambrlan deformation {$00Ma. Rb-Sr, on granite dyke R Two different types of basement and metamorphism (amphlbolite facies cutting gneisses (preliminary isochron E with relics of grar~Jlite facies) from Lerrisfjord area) E L involved in Kalak Nappe C E Complex. PoJyphose ~o{~.donion reworking. A (i) Rocks of Raipas Suite {n iMatamorph;sm from greenschist to high M E para~ tachthenaus nappes ~mphibolite facies. COMPLEX B h (ii) Para- and ortho-gneisses ;n gr',eo~s rock{: Precambr;on granites, R T internal thrust sheeh within abbros, doler;tes, etc. I S Kolak Nappe Complex, ~oledonion - as {n Kalak matasediments A either as gneiss units or to- N gether with the Knick sediments.

vvvv vvvvvvvvvvvv v vvvvvvvv vvv', vvvvvvvvvvvv~ THRUST CONTACT/DiAPHTHORITIC METAMORPHISM AND CATACLASIS

,A~ A ~ A A A AA AA AAAAAAAAAAAAAAAAAAAAAAAA~ A^A, Rb-Sr isochron o~s__ Late Precambrian - Corrgoeion(?) No loss{is recorded Strongly def~'rn~l low gre~sch{st .503Mo. Slates - Fr;arfiord Son, tortes, schists, phyHites, facies rnetasedlments. Formotlon (age of cleavage) limestones, glaciogene sediments Local I~:nic dykes. etc. LAKSEFJORD ~~ ~~

N A P PE UNCONFORMITY AT BASE OF LAKSEFJORD GROUP

Basement gneisses Not yet dated vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv 'vvvvvv vvvv vvvvvvvvvvvvvv THRUST - CONTACT/DIAPHTHORIT{C METAMORPHISM AND CATACLASIS

'kAAAAAAAAAA^^AAA^^AAAAA.AAAAA^A^ AAAAAAAAAAAAAAAAA ~AAAAAAAAAAAAAAAAA y~ AAAAAAAAAAAAA^AAAAAAA^A^/' ,~.AAAAAAAAAAAAAAAAAAAAAAA

G A JS S A Lot, Precambrlan - Cambrian(?) Stromatolit~ in Little memmorl~a6~l - $1;gt~tly Not yet ~NKI Sandstones, shales, limestones, Porsangee dolomite recrystollized sedirmmts. N A P P E glocia~ sediments etc. Variably folded or cleaved.

wvvvvvvvvvvvvvvvvvvvvvvvv~,vvvvvvvvvvvvvvvvvvvvvvgvvvvvvvvvvvvvvvvvVvvvvvvvvvvvv vv v v v vvvvvvv~ vvvvvvvvvvvvvvvvvvvvvvvv THR UST - CON TACT/CATACLASI S W. AAAAAAAAAAAAAAAAAAAA ^ A ^ ^ A ^ ^ A A AA A AAAAAAA.%AAAAAAAAAAA^^A^^ ^^AAA^AAAAAAA AAAAAAAAAAA/ A A A A A A A A A A/'.AA A A A A AA AAAAA

Late Pr~ambrian - Trernadoc Cambrian and Tremed~- Little metomoq>ho~d - slightly Rb-Sr i,~:hron o~e_s Continuc~t sequence of ion macro- and trace- recrylltolliz~l sediments. 515Mo. Shales - S~geidd~ AUTOC HTHONOUS =r~tones, d~ales, glaciogene fms;I favnas. Vaeiably folded and cleaved. Formation (age of cleavage) sediments etc. 668Mo. S~alet - Nybor~ Form- at on (age of diogenes{$)

TREMADOC - ~ "~- ~ UNCONFORMITY AT BASE OF VESTERTANA GROUP

LATE PRECAMBRIAN No fossils recorded Little melomorpho~d - slightly 825Ma. Shales - Voclse G¢oup rtcrystallized l~dirnents. (age of di~lenetis ) Sandstones, shales etc. Voriably folded and Cleaved.

REGIONAL UNCONFORMITY

KARELIAN AND OLDER CRYSTALLINE BASEMENT

TABLE 1: The main features of the Finnmark Nappe sequence

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BA~ARV~IK SYENITE DYKE AGE- SOl:1: 27M.v IJI.- 0.7316t .0065

I A,tO RANITE 0,,, I~1 CUTTINGHASVIK GAB~ NEPHELINE SYENITE PEGMATITE ~,,gPluotne /

:g . pm~uaum ~ /

ANATECTIC GRANITE /

VEto4 Rb(/Sr mineral whole-rock ajres- Haralcisenggranite vein, biotite (three samples), 440 +- 15 My.,425 + 15 My. and 410 My. For otherm|neral ages see Sturt et al (1967) and Brueckner (1973).

/ ,ae: m ~:~-,. o h,o~P°' h"t" ,o,, °" ~'g'~

~ i a S s 7 i t k ~1 t'2 ~

FIG. 4. Rb-Sr whole-rock isoehrons, and mineral ages.

Hasvik Gabbro, and the peak of the regional nepheline mineral ages in the range 480-491 Ma amphibolite-facies metamorphism. though the micas all are consistently younger. The youngest member of the alkaline suite in the Breivikbotn complex is a single syenite-aplite dyke, The alkaline rocks which cuts the carbonatite at Baarvik. The Rb/Sr The Breivikbotn alkaline complex represents the isochron age for this dyke is 501+27Ma with an last major igneous event on SCrcy (Sturt & Ramsay initial ~6Sr/S7Sr ratio of 0.7316 (Fig. 4). A nepheline- 1965). Work by Robins (1971, 1974), Appleyard syenite pegmatite, from Haraldseng, gave a mineral (1974) and the authors shows that, with local excep- isochron (essentially a biotite age) at 415 + 12 Ma. tions, the alkaline complexes represent the closing It is concluded that the whole-rock isochron at stages of magmatic activity and were emplaced in late 501+27Ma dates the emplacement of the Breivik- D2. The studies of Sturt et al. (1967) gave K/Ar botn alkaline complex.

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The slates of the parautochthon and age of slaty cleavage formation in the parautochthon autochthon and autochthon is in the range 500-520 Ma. The proposed ages for slaty cleavage development The foreland cover sequence is continuous from late lie on the younger side of the maximum metamorph- Precambrian through Cambrian time into the foss- ism in the Kalak Nappe Complex, and closer to that of iliferous Tremadoc (Reading 1965). A Caledonian the late syn-D2 Breivikbotn alkaline complex. This slaty cleavage ($1) is well developed in the suggests that the tectono-metamorphic development parautochthon nappes and in the foreland especially of the sub-Kalak units corresponds to the D2 defor- close to the thrust-front. Pringle (1973) obtained an mation of the Kalak Nappe Complex. Rb/Sr isochron age of 668+7 Ma for the intertillite shales of the Innerelr Member, and concluded that Summary of the geochronological results this represented the age of diagenesis. He also pre- sented an Rb/Sr isochron age of 515 + 7 Ma for slates The first feature apparent from the new data is the of the Stappogeidde Formation at Tanafjord. The rocks confirmation of a late Cambrian/early Ordovician age of this formation lie clearly beneath the base of the for the tectono-metamorphic development of the fossiliferous Cambrian, and it was concluded (Pringle Kalak Nappe Complex. This orogenic event has been 1973, Sturt et al. 1975) that the isochron represents termed the Finnmarkian Phase by Ramsay & Sturt the age of slaty cleavage development. The slates in (1976). The Rb/Sr isochron pattern also indicates that the Laksefjord Nappe were also sampled and give an the Caledonian magmatic history was of considerable Rb/Sr isochron age of 503 +45 Ma with an initial ratio duration, i.e. of the order of 50 Ma. Unfortunately, no of 0.7242 (Fig. 5). Although this isochron plot has a precise statigraphical controls are available to place larger error it coincides well with the age obtained for constraints upon this. The authors are of the opinion the Stappogeidde slates. It is thus considered that the that the time difference is both real and significant and

AGE 503 + z.5 m.y. 875r IR .721.2±-0031 865r 7 Slates, Friarfjorden 1017C 1017 B 10~17K~17 i

87Rb 0 i 2 3 ¼ 5 6 865r

FIG. 5. Rb-Sr whole-rock isochron, slate from Friarfjord.

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shows a sequence: of tectonic windows. The parautochthonous nappes show differences from east to west, with the Gaissa 1. Syn-D1 Breivikbotn gabbro 552 ± 17 Ma and Laksefjord nappes representing slices of the au- tochthon cover-sequence, while in the west the 2. Interkinematic (D1-D2) Hasvik 539 ± 27 Ma parautochthon contains material of the Raipas Suite. Gabbro 542 ± 16 Ma The Precambrian gneissic basement to the Kalak sedi- ments, and the major thrust nappes involving signific- 3. Late-D2 Breivikbotn Alkaline 503 ± 16 Ma ant amounts of gneiss indicate the former westward Complex extension of the Baltic Shield beneath the continental This pattern corresponds to the sequence of tec- shelf on which the Kalak clastic sediments accumu- tonic, metamorphic and magmatic events established lated. The nappe units can be traced with reasonable by purely geological criteria. The ages from slates continuity from HavCysund in the north, to Lyngerd- (503-515 Ma) are believed to date the formation of jord in the south, where the Finnmarkian Nappes are slaty cleavage and to correlate with Kalak D2. truncated by a younger nappe sequence. The K/Ar and Rb/Sr mineral ages fall into distinct The authors suggest the following sequence of groups, which coincide with the Finnmarkian and the events during the Finnmarkian: main Scandinavian phases of the Caledonian orogeny. 1. Deposition of clastic sediments (including late Pre- In the earlier group of ages the nephelines at 480- cambrian glacial deposits) occurred on a wide con- 491 Ma are apparently later than the whole-rock tinental shelf, with transition from fluviatile to shal- Rb/Sr age of 501 +27 Ma for the Baarvik syenite, and low marine conditions in E Finnmark. During presumably represent cooling/uplift ages attained on Cambrian times progressive deepening of a basin in passing through the nepheline blocking temperature. the west, culminated in a thick greywacke accumu- This would presumably be during the phase of active lation (Hellefjord Schist (N), Ankerlia Schist (S)). uplift and erosion of the Finumarkian mountain belt. Local submarine volcanism occurred in the south There are only two biotite ages at 440--445 Ma and (Reisadalen) (Fig. 6A). although the blocking temperature for biotite is con- 2. The early deformation (D1) took place in late siderably lower than that of nepheline it is unlikely Middle Cambrian to Upper Cambrian times of the that these represent part of a continuous unroofing Kalak rocks. This encompassed a complex sequ- period. In the younger group of ages, muscovite dates ence of superimposed strains, together with the (421 Ma) are older than biotite (384-416 Ma) which is early basic magmatism of the area though preced- in order of decreasing blocking temperature with ing the regional metamorphic maximum. The late younger age. These presumably reflect the reheating D1 fabric is marked by strong extensional strains, during the main Scandinavian phase, and coincide with implying that lateral translation of Kalak rocks may the metamorphism of the rocks of the Mager~y Nappe have begun at this time. This stage of orogenic (Ramsay & Sturt 1976); although the mineral ages development occurred some distance west of the probably represent cooling ages obtained successively present coastline (Fig. 6B). during uplift and erosion in late Silurian/early Devo- 3. During and subsequent to D1, in the Kalak rocks, nian times. sedimentation continued in the 'foreland basin' into Tremadoc times (Fig. 6B). Within the Finnmarkian orogenic segment temperatures continued to rise, The Finnmarkian in a regional producing the main inter-D1/D2 metamorphic context maximum. 4. At the beginning of D2 major eastward translation The Finnmarkian Orogenic Phase is seen to involve of the Kalak rocks over the foreland occurred, polyphase deformation, metamorphism and plutonism marked by the development of the East Seiland during late Cambrian to early Ordovician times. On blastomylonite belt and the syn-D2 blastomylonites the basis of correlation of events in the Kalak Nappe at the base of the Kalak Nappe. The important Complex with the underlying parautochthon and au- syn-D2 magmatism occurred, and there are indica- tochthon, it appears that the initial emplacement of tions that amphibolite-facies temperatures locally the nappe units on to the Baltic Shield occurred during continued into D2. An implication of the early the D2 deformation. This proposition would indicate thrusting is that the complex suite of syn-D2 plu- the establishment during the Finnmarkian of a major tons was emplaced through crystalline continental Caledonian thrust-front, forming the eastern margin of crust (Fig. 6C). During Kalak D2, orogenic strains the orogenic belt. spread eastwards and slaty cleavage was developed The basement to the Finnmarkian Nappes shows a in the parautochthonous nappes and the adjacent diversity from the high-grade Karelian and pre- autochthon. Karelian to the east of the thrust-front to the low-grade 5. The late major translation of the Kalak Nappe Raipas Suite, probably Karelian, in the western group Complex, occurred in a declining temperature field

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Hellefjord Schist Storelv-Aafjord Klubben Varanger Tillite Group Groups Psammite / S.L. __~ ..... ~ ...... ~-~.~.~ ~.-..~ :!::::::'.:-'.-:~:~:!~ ~:: ...... ~ ...... i:i:~::.:i~:!:~:::~ ".:;->' • ...... -:.:."::::':"FF~ 0..-...-.-. ;~ !.f...L.~======::::::::::::::::::::::::::::::::::::::~:.::: ::::::;:::: .... ! ,,: ,::i""-~:J~::""" ...... ~-: ...... ~i~i~!'~:";::~ i* .~~~--~ ~~:.i...-:.! m'.:-"-" ...... ':. ~ ' ..~~:"::':'....-:~'~- :::::~: ..~(~?~:i?.~:~:.i:::::::::::::::::'.:.:.:.::::::'.::-: • •: . ~::::.:.:...-:~,::~bb'.~:~']::;:.. ======• ...... ,..:~ ~.~'-'.":'.;.!:~::-'::::::".':...... [..~.-.-~.-...... Raipas Suite Crystalline Basement

lB. UPPER CAMBRIAN,] Kalak Thrust

~4~..

[C. LOWER ORDOVICIAN Pre D21gneous Rocks

':!i~ "~'t't't't'l

....~:~:~ t "t" t" t" t, Syn D2 Igneous Rocks I D. UPPER ORDOVICIAN I

M. Ordovician- Silurian Sediments ~~

...... - - - :-~_ _ = _ _ ...... ----: - -...... :.:.::ii:.~i!~!~i~!i!:::~::':" ...... '.-...-Z- -'"" ~ ...... ~~::~ ~:~,~:~#i!i!i'~ii',iHii'~ii',!i!ili!i!S...... :;! i~,:" .....

I E. END SILURIAN ] F" FIG. 6. Proposed evolutionary sequence of the north Norwegian Caledonides.

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as the nappe front encroached upon progressively alkaline magmatism of the foreland was probably tem- less metamorphosed units. Strong retrogression in porally related to the beginning of strong deformation greenschist facies can be observed at the contacts, in the orogenic belt. It is interesting that the Fen, Alno together with brecciation. During D2 the 'foreland and Livaara alkaline complexes and the Holla and basin' was dosed and the Finnmarkian mountain Kaliz kimberlites, of the Baltic Shield, form a belt chain established (Fig. 6D). marginal to the Caledonian front. Future models for 6. To the west of the emergent Finnmarkian mountain Caledonian plate reconstruction should take account range an Ordovician-Silurian sedimentary basin of this feature. was established, the sedimentary sequence now Apart from the northernmost part, the Scandinavian being seen in the MagerOy Nappe. During Caledonides are dominated by late Silurian (Scandina- Ordovician-Silurian times deep erosion of the vian) deformation, metamorphism and plutonic activ- Finnmarkian mountain range occurred (Fig. 6D). ity (Gee 1975), and only relics correlatable with the 7. During late Silurian orogenesis, of the Scandina- Finnrnarkian are present. Such relics are variably re- vian phase, the rocks forming the MagerCy Nappe worked by the later deformation and metamorphism. were subjected to Barrovian-type regional In western Norway clear evidence is available for a metamorphism. There was a renewal of mafic and major phase of pre-AshgiU orogeny, involving poly- ultramafic plutonism, and major overthrusting of phase deformation, metamorphism and plutonic activ- the MagerCy nappe across a Kalak substrate occur- ity. This is demonstrated by the major unconformity at red. During this phase of orogenesis reactivation of the base of the Moberg Conglomerate, at Bergen, and the underlying thrust planes cannot be ruled out. its stratigraphical correlatives in Vestlandet (Sturt & South of Lyngenfjord and in the Birtevarre/Skibotn Thon 1976, Naterstad 1976). Beneath the unconfor- areas rocks of the Nordland Facies (probable equi- mity is an older Caledonian metamorphic complex, valents of the MagerOy Nappe) were thrust over the but as yet there is no reliable geochronological evi- nappe sequence of the Kalak Complex (Fig. 6E). dence available. The Dalradian rocks of Scotland show many This sequence conforms well with those indicated by similarities to the Kalak Complex of northern Norway, Ramsay (1973) and Robins & Gardner (1975) in their and to the older Caledonian complexes of western models for the progressive plate tectonic evolution of Norway. In general terms, the Kalak and Dalradian the region. Robins & Gardner (1975), however, ap- sequences both range up through tillite-bearing late peal to major overthrusting initiated in late D2. This Precambrian clastic sediments into Cambrian basinal they relate to a model of an eastward-dipping, then assemblages. The Dalradian apparently extends into steepening and eventually overturning subduction the Arenig, setting a higher stratigraphic limit than zone which resulted in the thrusting of the Kalak rocks that for the Kalak sequence. The timing of orogenic across the Baltic Shield. deformation and metamorphism is broadly similar, Attention has been drawn to the unusual character, though the time-span of Finnmarkian orogenesis was in an orogenic setting, of the magmatic evolution in apparently greater. Dewey (1961) and Skevington the Seiland Province. This is particularly seen in the (1971) suggested on the basis of stratigraphical evi- development of synorogenic alkaline complexes con- dence that the amphibolite-facies metamorphism of taining carbonatites. In recent papers (Doig 1970, the Dalradian rocks of western Ireland occurred at Vartiainen & Woolley 1974) the close grouping by age latest in early Ordovician times. Phillips (1974), how- of major alkaline complexes in the North Atlantic ever, considers that the Connemara Dalradian under- region has been emphasized. Vartiainen & Woolley went its principal deformation and metamorphism in (1974) show that, with the exception of the Seiland mid-Ordovician times, supported by the proposed age Province, the 'Grenvillian' and 'Caledonian/ for D1 deformation of 487+6Ma at Slieve Gamph Appalachian' alkaline complexes lie outside but fairly (Pankhurst et al. 1976). The considerable volume of close to the margins of the respective orogenic belts. reliable radiometric data now available shows the In Scandinavia and Canada there is a consistent pat- Grampian stage of orogenic evolution in Scotland and tern of ages in the range 585-560Ma for the Ireland to have occurred in the general time-span 'Caledonian/Appalachian' alkaline complexes. Doig 490-530 Ma (Dunning 1972, Pankhurst 1974, Pank- (1970) considered that such complexes related to the hurst et al. 1976, Dewey & Pankhurst 1970. Brad- formation of early graben structures in the North bury et al. 1976). Microfossil evidence suggests that Atlantic, though Vartiainen & Woolley (1974) view the younger rocks of the Scottish Dalradian are of them as relating to 'sporadic deep-faulting within the Arenig age or even slightly yoimger (Harris & Pitcher forelands, thus tapping relatively deep levels in the 1975). Bradbury et al. (1976) show that the post-D2 mantle'. The syn-D1 magmatism in the Seiland Pro- Ben Vuirich granite gives UfPb zircon and Rb/Sr vince is dated at 552+ 17 Ma, implying a close tem- whole-rock ages of 514+6 Ma, considered to be an poral relationship between this and the slightly older emplacement age. They also conclude that a 491+ (?) alkaline magrnatism in the foreland. Thus the 15 Ma radiometric age for the syn-D3 Dunfallandy

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Hill granite is an emplacement age. Thus it appears plexes east of the orogene. The two major deforma- that the age of the Grampian orogenic phase had a tion cycles of the Finnmarkian, were separated by a lower stratigraphic constraint in the Arenig and that relatively long interval and the second major move- an Arenig/Llandeilo ago is most probable for the ment period (D2) occurred in the early Ordovician, deformation and metamorphism. Recent work by involving also deformation of the foreland and the Flinn & Pringle (1976) on the East Mainland in Shet- thrusting of parautochthonous nappes. It is also pro- land, shows that the migmatites in the Colla Firth posed that the substrate to the Kalak sedimentary permeation belt yield an isochron of 530±25Ma, sequence was a continental basement of varied charac- giving an overlap with the age quoted for the Ben ter and age, and that these Precambrian rocks are now Vuirich granite. From the non-metamorphic segment involved in a variety of basement/cover relationships of the British Caledonides O'Nions et al. (1973) have within the mobile belt. recently presented an isochron age of 505~7Ma, The results presented in this paper, taken together considered to be the age of slaty cleavage in the with data from the literature, show that the time Ingletonian of northern England. This corresponds represented by Finnmarkian orogenesis was an impor- closely with the slaty cleavage ages presented from the tant period of tectono-thermal development in a 'foreland region' of northern Norway. number of segments within the Caledonian orogene. It Evidence is increasingly available concerning the is apparent, however, that the orogenic development complex history of deformation and metamorphism in had diverging patterns in other segments of the the Moine of Scotland. It is apparent that parts of the orogene, e.g. in Wales where sedimentation was virtu- Moine, particularly the Ballachulish area, the Central ally uninterrupted during the Lower Palaeozoic. It is Highlands and according to Soper & Williamson perhaps also significant that, as yet, no positive evi- (1975) also the northernmost Moine, have suffered dence of late Cambrian/early Ordovician metamorph- only Caledonian metamorphism. In the Morar area, ism is forthcoming from East Greenland. Considerable however, it appears that Moine rocks have undergone differences in the timing of orogenic development are Precambrian deformation and metamorphism. Brook seen in different parts of the Caledonides. This is et al. (1976, 1977) show how the Ardgour Gneiss expressed by the restricted occurrence of the late gives an Rb/Sr whole-rock isochron age of 1050± Precambrian zone of Avalonian deformation, and by 46 Ma, and that pelitic schists of Morar provide an the development of the Finnmarkian/Grampian Rb/Sr isochron age of 1024±96Ma. These results orogenic phase only in certain segments of the were interpreted as demonstrating Grenville Caledonides. The effects of Taconic deformation were metamorphism. The ages are very similar to that pre- also apparently of limited extent. Late Silurian sented by Brueckner (1973) for gneisses in the Kalak orogenic deformation and metamorphism was wide- Nappe Complex. Brook et al. (1977), in reviewing the spread in the northern part of the orogene, whilst the literature, show how this Grenvillian metamorphism is maximum expression of Acadian orogenesis was in the post-dated by pegmatites in the time range 800-- Appalachians. Thus during Caledonian development 700 Ma prior to the Caledonian. Thus, as Brook et al. certain zones were apparently characterised by sepa- (1977) indicate, the Moines possibly represent more rate and distinctive patterns of tectono-thermal de- than one stratigraphic sequence separated in time by velopment which do not find significant expression in orogeny and pegmatite emplacement, and which were other segments. welded together during the course of Caledonian evolution. In this context analogies can be made with ACKNOWLEDGEMErCrs. This paper represents work done in the zone of Finnmarkian development in northern relation to the IGCP Project 27--Caledonian Orogen. Norway. The authors wish to acknowledge grant support by the Norwegian Research Council for Science and the Humanities (NAVF) project No. D. 48.22-18, and by the Natural En- Conclusions vironment Research Council (NERC). We wish to thank the Elsevier Scientific publishing company for permission to The present work indicates that the tectono-thermal reproduce Fig. 3. We especially thank Statsgeolog K. B. development of the Kalak Nappe Complex probably Zwaan who has generously allowed access to his unpublished began in mid-Cambrian/Upper Cambrian times, and compilations for the 1 : 250 000 map-sheet Nordreisa, and the coincided with the emplacement of major alkaline com- 1 : 50 000 map-sheet Kvaenangen.

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Received 24 June 1977; revised typescript received 7 December 1977. BRIAN A. STtJRT, Geologisk Institutt ard. A, Joachim Frielesgt. 1, 5014 Bergen, Norway R. PRtNGLE, Dept. of Geology & Geophysics, University of Cambridge, Madingley Road, Cambridge CB3 0EZ D. M. RAMSAY, Dept. of Geology, The University, Dundee DDt 4HN, Scotland

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