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 Norway 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 Finnmark (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 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/135/6/597/4885687/gsjgs.135.6.0597.pdf by guest on 01 October 2021 598 B. A. Stun, L R. Pringle & D. M. Ramsay 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 northern Norway. Place names: D--Diggermul, F--Friarfjord, H--Honingsvag, G---Gjesvaer, Sn--Sncfjord, Hm--Hammerfest, Hv--Hasvik, 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 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/135/6/597/4885687/gsjgs.135.6.0597.pdf by guest on 01 October 2021 Finnmarkian phase, Caledonian Orogeny 599 Ho mmer f es t Hammer fest Kvaley Kvo i sund I Noppe ~ Syncline Nappe | Nappe ." "." 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"..';.'-;:,.,.:.,-¢-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