Interpretation of the Proterozoic Kautokeino Greenstone Belt, Finnmark, Norway from combined geophysical and geological data

ODLEIV OLESEN & JAN SVERRE SANDSTAD

Olesen, O. & Sandstad, J.S. 1993: Interpretation of the Proterozoic Kautokeino Greenstone Belt, Finn­ mark, Norway from combined geophysical and geological data. Nor. geol. unders. Bull. 425, 41-62.

Processed images of aeromagnet ic, gravimetric and topographical data and geological maps combined with EM helicopter measurements, petrophysical data and digitised geological field observations have been used in a geological interpretation and structural analysis of the Kautokeino Greenstone Belt, KGB. The data were analysed with an image-processing system (geophysical data) and a geographic informati­ on system (geological data and interpretations).

The bulk of the mafic volcanic rocks in the Kautokeino Greenstone Belt is situated within a NNW-SSE­ trending, 35 km wide and up to 5-6 km deep trough which is thought to represent an Early Proterozoic rift deformed by strike-slip faulting along the Bothnian-Kvcenangen Fault Complex, BKFC.The margins of the Alta-Kautokeino Rift, AKR, can be outlined from the geophysical data. The CiegljaljAkka-Boaganjavri Lineament and the Soadnjujavrt-Bajasjavri Fault are the main bordering fault zones and are continuous along the entire greenstone belt. The supracrustals between these two zones are continuous to great depth (5-6 km) and the contacts along these bordering zones are steeply dipping. Gravity interpretations show that the outer amphibolite-fac ies rocks are just as deep as the central greenschist-facies unit. Results of the present study suggest that the amphibolit e-facies volcano-sedimentary rocks situated along the flanks of the KGB should also be included in the rift.

The mudstones and limestones in the Bikkacakka Formation may have been formed during thermal sub­ sidence as a result of cooling of upwelled asthenosphere after a phase of rifting. The above-lying deep and narrow Caravarri Formation contains abundant coarse-grained sandstones and conglomerates deri­ ved from a granitic source. We believe the Caravarri Formation to have been the result of late-stage uplift of the margins, subsequent erosion of the exposed basement, and deposition of the sediments in deep internal basins. Strike-slip movements may be incorporated in this model. Large-scale sinistral displace­ ment along the BKFC embraced the AKR which was already a zone of weakness in the Karelian continen­ tal block. This strike-slip movement may have allowed the Caravarri Formation to form in a pull-apart basin within the rift.

The 230 km long Mierujavri-Svcerholt Fault Zone, MSFZ, is the main fault zone which separates the f1at­ lying volcanosedimentary sequences in the Masi area from the Jergol Gneiss Complex to the southeast. The MSFZ extends from Mierujavri 30 km north of Kautokeino in a northeasterly direction through Masi, lesjavri and Lakselv and then beneath the Caledonian nappes on the Svcerholt Peninsula. A system of duplexes can be delineated along the MSFZ from the geophysical images. An extension of the MSFZ can be found to the southwest into northern Sweden. An apparent sinistral offset of the MSFZ can be obser­ ved along the margins of the BKFC.

Odleiv Olesen & Jen Sverre Sands/ad, Norges geologiske unders okelse, Boks 3006 -Lade, N-7002 Trond­ tieim, Norway.

Introduction prospecting have been made by Olesen et al. (1992d) and Sandstad et al. (1992).

The purpose of this study has been to com­ The Finnmarksvidda area is heavily cover­ pile a geological bedrock map of the Kauto­ ed with glacial drift. Regional geophysical keino Greenstone Belt, KGB (Siedlecka et data are therefore a necessary prerequisite al. 1985), in Finnmark, northern Norway, to structural analysis and geological inter­ and to evaluate areas favourable for pro­ pretation. High-frequency (spatial resoluti­ specting of Bidjovagge-type gold-copper on) and shaded-relief images have proved deposits. The geological and geophysical particularly effective forms of enhancing interpretations , with special emphasis on information from regional data (Henkel et al. the structural geology, are presented in this 1984, Henkel 1988, Lee et al. 1990). Pro­ paper. Evaluations of promising areas for cessed images of aeromagnetic, gravime- 44 Odleiv Otosen & Jan Sverre Sands/ad NGU - BULL 425. 1993

tric and topographic data combined with EM assumed to be related to movements along helicopter measurements, petrophysical shear zones, it is of great importance to out­ data and digitised geological field observati­ line the structural geology of the KGB toget­ ons have been used. The data were analy­ her with the lithological compilation. The sed with an Erdas image-processing sys­ main structural elements (Fig. 8), such as tem (geophysical data) and an Arc/into geo­ the Alta-Kautokeino Rift, AKR (Bergh & Tor­ graphic information system (geological data ske 1986), the Baltic-Bothnian megashear and interpretations). The Erdas system (Berthelsen & Marker 1986) which has earli­ allows data to be swapped in and out of the er been renamed the Bothnian-Kvcenangen image buffer, thus permitting easy compari­ Fault Complex, BKFC (Olesen et al. 1992a) son of data-sets. By the use of the Erdas­ and the Mierujavri-Sveerholt Fault Zone, Arc/lnfo Live-link module, the geological MSFZ (Olesen et al. 1990), will be interpre­ information and interpretations are kept in ted in more detail. the graphics plane while swapping the geophysical images. The present study is a continuation of the interpretation by Olesen & Solli (1985) utili­ Since the mineralisations at Bidjovagge are sing improved techniques and more detai-

Col

Ca ledonian roc ks Granitoids Meta ga bbro Diabase/metadiabas Metased. psammitic Metased. pelitic .- Metavolcanite I:':,:I"!;:::":j Gneiss Lithologic al boundary Fault/shear zone o 10km

Fig. 1. Simplified bedrock geology map of western Finnmarksvidda. JGC - Jergol Gneiss Complex; RGC -Raiseatnu Gneiss Com­ plex; GAF - Goldinvarri Formation; MsF - Masi Formation; CsF - Caskijas Formation; SuF - Suolovuopmi Formation; LiF- LikCa For­ mation; BiF -Bikkacakka Formation; CaF - Caravarri Formation; Cal - Caledonian nappes and Dividal Group. B- Bidjovagge; K ­ Kautokeino. M - Masi. NGU - BULL 425, 1993 Odfeiv Otesen & Jan Sverre Sandstad 45

led data-sets. The magnetic dislocation 1985) or migmatised equivalents of the map of Olesen & Solli (1985) has also been Kautokeino Greenstone Belt. Opinions dif­ transferred to the image-processing system. fer on the stratigraphy of the greenstone The images of the more detailed data dis­ belt: from two cycles (Siedlecka et al. 1985, play, as expected, the previously recogni­ Solli 1983, Sandstad 1983,1985, Olesen & sed regional faults of the area (Olesen & Solli 1985, Hagen 1987) to four main volca­ Solli 1985). Petrophysical sampling and in nic cycles (Olsen & Nilsen 1985). We do situ susceptibility measurements have been not think that the evidence for the latter carried out. more complex stratigraphy is compelling and will therefore continue to advocate the As a consequence of the new interpretation former interpretation. fault-bounded borders of the AKR and duplex structures along the MSFZ have The Kautokeino Greenstone Belt can be been identified. The present study also subdivided into a number of formations. helps to resolve the ongoing controversy The oldest of these are the Goldinvarri For­ concerning the formation of the AKR, espe­ mation (Solli 1983) and the correlative Vuo­ cially the extent of the rift within the KGB. megielas Formation (Siedlecka 1985), Another intriguing question is to what extent which consists of mafic volcanic rocks the faulting is related to rifting or to the sub­ metamorphosed in amphibolite facies. sequent strike-slip deformation. Delineating They have been found only along the eas­ the fault tectonics in the KGB also has a tern margin of the greenstone belt, to the bearing on our understanding of the formati­ south and northeast, respectively. The Masi on of gold deposits of the Bidjovagge-type Formation lies above the Goldinvarri Forma­ and may be a valuable aid for gold explora­ tion with a supposed angular unconformity tion in adjacent areas. and consists of quartzitic rocks. The main body of the greenstone belt is occupied by the Caskijas, Likca and Suolovuopmi For­ Geological setting mations (Siedlecka et al. 1985) each of which consists mainly of basic metavolcani­ The Kautoke ino Greenstone Belt tes (Fig. 1, Plate 4). They can, on a broad The Kautokeino Greenstone Belt (KGB) is scale, be correlated to the Avzi, Stuorajavri the westernmost of three Early Proterozoic and Baharavdojavri Formations in the greenstone belts within inner Finnmark and southern part of the KGB (Olsen & Nilsen is overlain by Caledonian rocks (Fig. 1, Pla­ 1985), but the detailed relationships are still te 4). The KGB comprises a 40-80 km wide controversial. The volcanic rocks are domi­ synclinorium of Early Proterozoic volcano­ nated by basic tuffs and tuffites, but basaltic sedimentary rocks (Solli 1983, Siedlecka et lavas and concordant diabases are also al. 1985, Krill et al. 1985, Olesen & Solli present. In some places, komatiitic metavol­ 1985, Olsen & Nilsen 1985, Hagen 1987) canites are present. Mica schists interpre­ and is situated between two culminations of ted as metamorphosed, fine-grained, clas­ gneisses, the Haiseatnu' Gneiss Complex tic, terrigenous sedimentary rocks are inter­ and the Jergol Gneiss Complex to the west bedded with the volcanites, but only in the and east, respectively (Fig. 1). These Suolovuopmi Formation to the northeast do gneisses are partly of Archaean age (Olsen they make up a considerable portion of the & Nilsen 1985) and form the basement to rocks. The Suolovuopmi Formation in the the greenstone belt. However, no clear Masi area is therefore interpreted to have depositional contact has been found betwe­ formed on a platform at the margin of a rift. en the gneisses and the supracrustals, pre­ The youngest rocks of the greenstone belt sumably since the contacts are either fault­ are found in the central northern parts. bounded or have been obliterated by Here it can be demonstrated that the volca­ younger felsic intrusions. The Haiseatnu nism in the Caskijas Formation gradually Gneiss Complex may comprise partly remo­ decreased and that the formation is concor­ bilised Archaean gneisses (Olsen & Nilsen dantly overlain by pelites (Bikkacakka For-

, The official spellings of many Lappish (sami) geographical names, including several used e.g. for lithostratigraphi c units, have recently been changed. The old and new forms are listed in an appendix (p.62). 46 Odleiv Olesen & Jan Sverre Sands/ad NGU• BULL 425. 1993

mation) and sandstones (Caravarri Formati­ Marker 1986 , Hen kel 1988 , 1991, Olesen et on; Sandstad 1985). According to Bergh & al. 1990). In the Kautokeino area, 3-4 regio­ Torske (1 986, 1988) the Caravarri Formati­ nal NNW-SSE fau lt zone s have been deli­ on and the greenschi st-facies volcan osedi­ neated (Olesen & Solli 1985, Olesen et al. mentary rocks within the eastern part of the 1990). Local Iaul tinq along these zones has Caskijas Format ion were formed within the been mapped by Holmsen et al. (1957). gradually subs iding Alta-Kautokeino Rift (AKR) along the margin of the Karelian con­ Albite diabases have intruded one section tinental block. We argue below that the of the BKFC borde ring the eastern side of whole of the Caskijas and Likca Formations the Cara varri Formation in the area of map­ should be included in the AKA. sheet Carajavri 1833 I (Solli 1990). The BKFC can be traced on aeromagnetic maps Defo rmation and metamorphism are of low from the Finnmarksvidda area below the intensity in the central parts of the KGB and Caledon ian nappes to the Alta-Kvre nangen increase towards the gneiss complexes to tectonic window in the north (Olesen et al. the west and to the east. As see n fro m Pla­ 1990). The western and eastern term inati­ tes 1 & 4, the general structural trend of the ons of the Juvr i Nappe, which is the low er­ western and southern part of the KGB is most unit within the Caledonian nappe suc­ NNW-SSE. Within this area both the bed­ cession in western Finnmark (Sandstad ding and the foliation are generally steep. In 1985 , Zwaa n 1988), coincide with extensi­ the northeastern part of the KGB the struc ­ ons of faults within the BKFC. This indica­ tural trend is NE-SW and the dip flattens out tes that the BKFC may have been active (Solli 1988). during the Caledon ian orogeny.

To the northwest, mudstones of the Upper The 230 km long Mierujavr i-Svesrholt Fault Proterozoic/Lower Cambrian Dividal Group Zone (MSFZ, Fig. 8) extends from Mierujav­ unconforma bly overli e the rock s of the gre­ ri 30 km north of Kautokeino in a northeas­ ensto ne belt. Above this are the Caledoni­ terly direction through Masi, lesjavri and an nappes which , in this area , consist main ­ Lakselv and then subsurface bene ath the ly of feldspathic metasandstones (Zwaan Caledonian nappes on the Svre rholt Penin­ 1988). sula. In the Masi-les javr i area the MSFZ is para llel to the northwestern marg in of the Jergol Gne iss Comp lex and is mostly situa­ Regional fault zones ted within or at the border of the Masi For­ The western area of the KGB is dom inated mation. Based on interpretation of aero­ by NNW-SSE trend ing faults interpreted by magnetic and grav ity data the MSFZ trunca­ Olesen & Solli (1 985). Berthelsen & Mark er tes the Proterozoic Levajok Granulite Belt (1986) and Henkel (1 988, 1991) include beneath the Caledon ian nappes (Olesen et these faults in the regional Baltic-Bothnian al. 1990). The Archaean-Lower Proterozoic megashear and Bothn ian-Seiland shear Goldinvarri Formation and the correlative zone , respectively. We think that the name Vuomegielas Formation (Siedlecka et al. Botbruen-Kveenenqen Fault Complex , 1985) have been dextra lly displaced 20 km BKFC (Fig. 8), will be a more appropriate along the MSFZ (Olesen et al. 1990). In the name since the zone can be traced from the Masi area , intrusions of 1815±24 Ma albite Bay of Bothn ia to Kvrenangen; and its cont­ diabases (Krill et al. 1985 ; U-Pb zircon date) inuation to the the Baltic Sea in the south is are related to the NE-SW trending MSFZ. poorly defined. The BKFC is composed of To the southwest, the MSFZ is truncated by several fault segments which are well defi­ the Proterozoic BKFC. The MSFZ was the­ ned from both geological and geophysical refore mainly active befor e the last major data (Holmsen et al. 1957, Olesen & Solli deformation of the Alta-Kautokeino Rift. 1985 , Geol. Surveys of Finland, Norway Brecciation is common along the faults wit­ and Sweden 1986b, 1987 , Berthelsen & hin both the BKFC and the MSFZ. NGU - BULL 425, 1993 Odleiv Olesen & Jan Sverre Sandstad 47

The postglacial Stuoragurra Fault (Olesen medium-altitude data has been published in 1988 and Olesen et al. 1992a,b) is situated the scale of 1:500,000 (Olesen et al. within the MSFZ and is consequently paral­ 1992c). lel to the northwestern margin of the Jergol Gneiss Complex. The fault line is shown in During 1979-85 most of the area was Plate 3. It can be traced for 80 km, from reflown at a profile spacing of 200-250 m south of Biggejavri in a northeasterly directi­ and a flight altitude of 50 m (Habrekke on through Masi. The fault is made up of 1979, 1980a,b, 1981, 1983, 1984, Dvorak numerous segments of faults with up to 10 1982, Mogaard & Skilbrei 1986). These m of reverse displacement. The Stuoragur­ measurements are much more detailed ra Fault is situated mainly within quartzites than the former . The low-altitude surveys of the Masi Formation. North of Masi, older than 1985 were compiled , levelled and however, the Stuoragurra Fault cross-cuts interpreted by Olesen & Solli (1985), but amphibolites within the Suolovuopmi For­ because of confident iality only the interpre­ mation and an albite diabase. Brecciation is tations were published. Skilbrei (1986) observed in all the locations where the included the survey by Mogaard & Skilbrei bedrock is exposed in the fault escarpment (1986) in the compilation and levelled the (Olesen et al. 1992a) and such brittle defor­ data-sets using the 'orthognostic' mapping mation is also observed along the entire technique of Kihle (1992). In the present length of the MSFZ in the Precambrian on study an additional survey flown by Dighem Finnmarksvidda. The brittle deformation is (Dvorak 1982) on the 1:50,000 map-sheet consequently believed to have occurred 1833 IV Mallejus has been included, and during the formation of the MSFZ and not the total of 29,000 profile-km of low-altitude the younger Stuoragurra Fault. measurements have been interpolated to a square grid of 100 x 100 m using the mini­ The earliest detectable displacements along mum curvature method (Swain 1976). The the MSFZ are inferred to be Proterozoic final grid was slightly smoothed using a 3 x (Olesen et al. 1990) and the latest took pla­ 3 point Hanning filter. The data-set has ce less than 9,000 years ago (Olesen 1988, been superimposed on the medium-altitude Olesen et al. 1992b). Along the MSFZ to 500 x 500 m grid to generate the coloured the northeast of lesjavri, a syn-sedimentary map shown in Plate 1. Because of the diffe­ movement during the deposition of the rent flight altitudes, there are some discre­ Cambrian Dividal Group and a post/late­ pancies at the border of the medium- and Caledonian displacement which cuts the low-altitude data-sets. The final map shown Gaissa Thrust have been reported (Town­ in Plate 1 was produced using the shaded send et al. 1989). Furthermore, the offsho­ relief technique (Lee et al. 1990, Kihle re extension of the MSFZ coincides with 1992) with illumination from the east. one of the major basement faults on the continental shelf (Lippard & Roberts 1987). Gravity data The MSFZ must consequently represent an The gravity map in Plate 2 is based on mea­ extremely long-lived fault-zone . surements from 2,500 gravity stations. A regional gravity survey was carried out on Finnmarksvidda within the Finnmark Pro­ Data used in the interpretation gramme during the years 1980-1988 (Ole­ Aeromagnetic data sen & Solli 1985, Olesen et al. 1993), most­ The aeromagnetic measurements were car­ ly using a snow scooter and helicopter for ried out in two periods. In 1959-62, the area transportation . Measurements were made was drape-flown at an altitude of 150 m with at stations located 1 - 4 km apart. The com­ a profile spacing of 1 km. Maps in the scale plete Bouguer reduction (Mathisen 1976) of of 1:50,000 have been digitised in a 500 x the gravity data has been computed using a 3 500 m grid, from which the Definite Geo­ rock density of 2,670 kg/m , the Internatio­ magnetic Reference Field 1965 was subse­ nal Gravity Standardization Net 1971 quently removed. A printed map of the (I.G.S.N. 71) and the Gravity Formula 1980 48 Odleiv Olesen & Jan Sverre Sands/ad GU . BUl 425. 1993 for normal gravity. A total of 250 measure­ had an original contour interval of 20 m. ments from the Norwegian Mapping Autho­ The use of digital topography in tectonic rity (Statens kartverk) are included in the studies has been demonstrated by Henkel survey. (1988). Glacial processes will enhance or obliterate pre-glacial tectonic imprints Since the grid was calculated at 500 m depending mainly on the direction and intervals the variable areal distribution of the intensity of ice flow. The map shown in Pla­ primary observations has been homogeni­ te 3 has been produced using the shaded sed by extracting stations with a minimum relief technique (Lee et al. 1990, Kihle spacing of 300 m from the original data-set. 1992) with illumination from the east. This reduced data-set (ea. 2,200 stations) was gridded using the minimum curvature Digital topographical and hydrographical method, and then smoothed using a 3 x 3 data in vector-form delivered by the Norwe­ point Hanning filter. The final step in the gian Mapping Authority, series N250-vector, process was to separate the data into a were used in the compilation of the geologi­ regional field associated with the mountai­ cal map. The data are adapted for use in nous Caledonian area to the northwest, and the scale 1:250,000, but are also suitable a residual component using the method by for the scale 1:100,000; they consist of Olesen et al. (1990). The contour interval of automatically and manually generalised and the residual field in Plate 2 is 1 mGal, and is digitised data from 'Norway 1:50,000 believed to be larger than the error in the (M711 )'. Administrative borders, drainage gravity data. The locations of the gravity systems, communications, settlements, stations are shown on the residual map. superficial deposits and elevation contours and points are included. Electromagnetics Electromagnetic data were collected during the helicopter-borne surveys (Habrekke Petrophysical data 1979, 1980a,b, 1981, 1983, 1984, Dvorak Olesen & Solli (1985) and Hoist (1986) have 1982, Mogaard & Skilbrei 1986). Discrete reported petrophysical data for 1,1 50 and electromagnetic responses have been ana­ 114 rock samples, respectively. An additio­ lysed to map conductors using the vertical nal 1,100 rock samples were collected sheet model. The conductance (i.e. con­ during geological mapping and the follow up ductivity-thickness product) in ohm-1 (mho) of geophysical anomalies (1986-1989). The of the vertical sheet model was calculated rock samples (weighing 0.3 - 1.0 kg) have by computer in all of the surveys. This is been measured with respect to density, done regardless of the interpreted geome­ magnetic susceptibility and remanent mag­ tric shape of the conductor. This was not an netisation. The sample locations are shown unreasonable procedure, because the com­ in Fig. 2. The measuring procedure is des­ puted conductance increases as the electri­ cribed by Torsvik & Olesen (1988). The cal quality of the conductor increases, densities used in the gravity modelling are regardless of its true shape. Strong con­ shown in Table 1. In addition, a large num­ ductors are characteristic of graphite or ber of in situ determinations of magnetic massive sulphides. Conductors with con­ susceptibility have been made in selected ductance higher than 5 mhos are plotted in areas. These results are presented as his­ Plates 1 - 4. tograms in Fig. 3. Measurements of natural remanent magnetisation (NRM) directions on rock samples of reversed magnetised Digital topographical and hydrologi­ diabase are shown in Fig. 4. cal data The Norwegian Mapping Authority (Statens kartverk) has provided a 100 x 100 m grid of Geological data digital topography from the area. This data­ Outlines of bedrock exposures, with their lit­ set was derived from digitised 1:50,000 sca­ hological information, from 12 preliminary le topographical maps (M711 series), which and printed geological maps in the scale NGU · BULL 425, 1993 Odleiv Olesen & Jan Sverre Sandstad 49

N

O.

o

0 =336 ° 1= _ 56° a. l p ha. = 9 0

Fig. 4. Plot of natural remanent magnetisation (NRM) directi· ons of a reversed magnetised diabase on a Wulff net (lower hemisphere). Open circles show negative inclination. Dashed line displays the cone of 95 per cent confidence (alpha). The Fig. 2.Sample locations, 2,400 rock samples measured with plot shows a condensed distribution except one outlier which is respect to density, susceptibility and remanence. ignored in the calculation of the statistics.

CASKIJAS FORMATION WEST CASKIJAS FORMATION EAST AMPH IBOLlTE FACIES GREENSCH IST FACIES

TUFFITE TUFFITE n ' 203 n -396

METADIABASE METADIABASE n- l08 n· 400

ARGILlITE METASEDIMENTS n-268 n" 36 ::' f - ~.' f~~~

lO·S 10'" 10·] 10-2 10.1 1 IO·S wl. 10-) Fig. 3. Susceptibility spectra of in situ measurements on amphibolite- and greenschist-facies tuffite, metadiabase and metasedi­ ments within the Caskijas Formation. 50 Odleiv Otesen & Jan Sverre Sands/ad GU - BULL 425. 1993

1:50,000 (Lindahl & Mikalsen 1975, Olsen Geographic information system 1987 a.b.c.d, 1988 a,b,c, Sandstad 1985, The geographic information system Solli 1987,1988,1 990) were digitised. Total­ pcArc/lnfo , version 3.40, was used for the ly, about 6,300 exposures were transmitted interpretation and compilation of the geolo­ to the geographic information system gical map (Plate 4) in combination with the Arc/lnfo , representing approximately one image-processing system Erdas. A detailed 2 exposure pr. km . The area is heavily description of the compilation and presenta­ covered by glacial drift and contains relati­ tion of the map is given by Sandstad (1992). vely few exposures. The exposures are most numerous in the northern part of the A uniform legend based on lithology and KGB and decrease southwards (Plate 4). A metamorph ic grade was set up for use in few limited areas in the southern part are the interpretation. The formational legends well exposed. used in the preliminary and printed bedrock maps were neglected due to the uncertain Methods of interpretation correlation between different formational units. By this system the screen contains up to 16 different colours and a simplified Image processing legend was used during the interpretation The data were analysed with an Erdas ima­ (Sandstad 1992). The outlines of the expo­ ge-processing system (Erdas 1990) running sures of the lithological units were shown in on a PC with an Intel 80386 processor and different colours on the screen. an IMAGRAPH 1024 x 1024 image-proces­ sing card. The system can hold three raster The Erdas system is driven within the images, each with a positive 8-bit range of Arc/lnfo software with the aid of an Erdas 0-255 and one 4-bit graphic plane for over­ Live-link module which allows easy swap­ lays of vector data. The Erdas system ping of different images. Processed images allows data to be swapped in and out of the of the geophysical data, mainly different image buffer and thus allows multiple data­ processings of the magnetic data, and the sets to be easily compared. The gridded electromagnetic indicators were kept in the gravity, aeromagnetic and topograph ical graphic plane as background for the geolo­ data-sets were rescaled into the 0-255 gical data in the overlay plane. The inter­ range. Histogram-equalised colour, high­ pretations of the Iithological boundaries and frequency filtered and shaded-relief images faults are digitised directly on the video have been used to enhance the information monitor using a mouse-controlled cursor of the regional data-sets. Shaded-relief pre­ within the Arc/lnfo . The interpretation of sentations, which treat the grid as topograp­ the faults was compared with the geophysi­ hy illuminated from a particular direction, cal interpretations. Once completed, the have the property of enhancing features final geological interpretation map was plot­ which do not trend parallel to the direction of ted on a Calcomp electrostatic plotter at the illumination. The interpretation of magnetic scales of 1:100,000 (Sandstad 1992) and dislocations by Olesen & Solli (1985) and 1:250,000 (Olesen et al. 1992d). preliminary interpretations of aeromagnetic data, the location of VLF ground profiles and VLF anomalies have been digitised and transferred to the Erdas system. These Structural interpretation interpretations and the computed electrical The structural interpretation utilising the conductors from the helicopter-borne elec­ image-processing technique is similar to the tromagnetic measurements are represented method of Henkel et al. (1984) and Henkel as vector data in the image-processing sys­ (1988). In Henkel's method, fault zones tem. Figs. 5 and 6 show shaded relief ima­ occurring within magnetic rock units are ges of the low-altitude aeromagnetic mea­ interpreted from: 1. Linear discordances in surements and digital topography , respecti­ the anomaly pattern. 2. Displacement of vely. reference structures. 3. Linear or slightly NGU - BULL 425, 1993 Odleiv Olesen & Jan Sverre Sandstad 51

Fig. 5. Shaded relief image of the low- altitude aeromagnetic measuremen ts from the Kautokeino Greenstone Belt ('illumination' from the east). For scale and location of the image ; see Plate 1. curved magnetic gradients. 4. Discordant more, emerge as intermittent linear gradi­ linear or curved minima (Henkel & Guzrnan ents in the gravity image. 1977). The digital elevation data can be used to corroborate the interpretation of the Ground VLF and magnetic profiles with magnetic data since fault zones commonly lengths varying from 400 m to 4 km have coincide with linear depressions in the topo­ been measured on 28 selected locations graphy. Regional fault zones will, further- across fault zones in the Masi area (Olesen 52 Odleiv Olesen & Jan Sverre Sandstad NGU - BULL 425. 1993

Fig. 6. Shaded relief image of the digita l topograph y from the Kautokeino Gree nstone Belt ('illumi nation' from the eas t). For scale and location of the imag e; see Plat e 3 . et al. 1992a). The purpose of these measure­ The magnetic banding within the KGB is ments was to check and correct the interpre­ generally found to represent the primary tations based on the method just outlined. In layering of the volcano-sedimentary sequ­ regions of resistive soil and bedrock the VLF ences and metadiabase sills which now method can be used to detect large water­ mostly show up with steep dips. The dip of containing fracture zones in the bedrock albite diabases in the Masi area has been (Eriksson 1980, Henkel & Eriksson 1980). modelled using the aeromagnetic data NGU - BULL 425. 1993 Odleiv Olesen & Jan Sverre Sandstad 53 recorded along helicopter-profiles and the Table 1. Rock densities employed in the gravity modelling. Kautokeino Greenstone Bell. measured magnetic properties of the bedrock (Olesen et al. 1992a). Roc k unit No . Density (la) k g /m ) Me a n st . dev . We have used the computer programme by Rai ' sednc Gneiss Comple x 8 6 2. 69 . 1 4 Torsvik (1 992) to compute the gravity Jer' q u I Gneiss Comple x 457 2.69 .11 response of a model along one profile Gal ' de nvarri Form ation 8 0 2 .96 . 11

across the Kautokeino Greenstone Belt Masi Formation 117 2 . 65 . 07 (Plate 2). The basic model in the program­ Cas' ke j a s Fo rmation 1 9 8 2 .96 . 1 0 me comprises bodies of polygonal cross­ (Amphibolit e f a c i e s ) section with limited extension in the strike Cas ' k e jes Formation 65 2 .88 .12 direction. The interpretation is shown in (Greenschist f ac Les I Profile A-C in Fig. 7. This profile is an Suoluvuobmi Fo rmation 1 44 2 .97 . 1 0 Metavolcanics extension of the profile interpreted by Ole­ Suoluvuobmi Fo rmat.ion 72 2 .73 . 0 6 sen & Solli (1 985) and is continuous across Metasediments the whole of the greenstone belt. The den­ Lik ' ce Fo rmation 182 2.85 .19 sities used in the gravity modelling are shown in Table 1. Caravarri Fo rmat i o n 52 2 .66 . 06 Al bite d iaba se 55 2 .91 . 1 0

PRO FILE A- [ GRAVI TY FIELD mGal 40

30

20

10 ......

00 A

1 Caskljas Formalion (amphlbolite facles) 2960 AmbIent density 2690 kg/m' 2 t askiJas Formation (greenschist tacles) 2860 3 BikkaUkka Formation 2760 Inferred model boundary 4 taravarrlFormation 2660 5 Ukta Formallon 2850 ObservedBouguer anomaly 6 Suolovuoprnl Formation, micaschist 2730 Regionalgravity field frombodyno. 11 7 Suolovuopml Formation, amphibolite 2970 r-----. Calculated gravity effect 8 Suolovuopmi Formation, amphibolile 2970 9 Masi Formation 2650 10 Galdinvarri Formation 2960 11 Intermediate gneiss 2800 o Albite diabase 2910

Fig. 7. Gravity section across the Kautokeino Greenstone Bell. Location of the profile shown in Plate 2. 54 Odleiv Olesen & Jan Sverre Sandstad NGU . BULL 425. 1993

Results ments exist. Geophysically the formations are characterised by a lack of electromag­ Lithological compilation netic indicators and low magnetic field. The western and eastern gneiss complexes were readily distinguished during the inter­ The 'Sedimentary and volcanic rocks of pretation. Most characteristic is the diffe­ supposed Early Proterozo ic age' are divided rent magnetic patterns of the complexes. into medium- and higher-grade metamor­ While the Haiseatnu Gneiss Complex phic rocks and low- and very-Iow grade (RGC) has a weak, but pronounced banded metamorphic rocks (Plate 4). The amphibo­ magnetic appearance similar to the supra­ lite-tacies supracrustals constitute the most crustals of the greenstone belt, the magne­ abundant rock-type within the map area tic signature of the Jergol Gneiss Complex (Plate 4). The stratigraphically lowermost (JGC) is more irregular (Plate 1). Bodies of Masi Formation consists mainly of quartzi­ supracrustal rocks are mapped within the tes and feldspathi c quartzites and minor RGC, while intrusive granitoids are more conglomerates (Siedlecka et al. 1985). The common within the eastern complex (Plate psammitic metasediments which are belie­ 4). We suggest that the RGC mainly con­ ved to constitute the lowermost part of the sists of migmatised parts of the greenstone overlying metavolcanic formations (Olsen & belt and that the JGC represents an older Nilsen 1985) are also included. The meta­ and probably Archaean basement. This sediments commonly define dome-shaped interpretation agrees with Olsen (in press) structures. These dome structures have a who claims that only the southern part of the low and smooth magnetic pattern compared RGC can be correlated with the JGC. Grant to similar structures caused by granitic intru­ (1985) has also shown that migmatisation is sions which give a low but irregular magne­ likely to reduce the susceptibility of the tic pattern. The quartzites are intruded by bedrock and this may explain why the several diabases/metadiabases which com­ amplitude of the banded anomalies in the monly occur as sills surrounding the dome RGC is reduced when compared with the structures. anomalies representing the greenstone belt. The contact between the metasediments One of the major controversies bearing on and the overlying metavolcanites is usually our understanding of the geology of the a primary depositional contact (Siedlecka et Kautokeino Greenstone Belt relates to the al. 1985). The lowermost parts of the meta­ number of major volcanic cycles and hence volcanic formations consist of carbonates, the stratigraphy of the belt. During this mica schists and graphite schists. The combined interpretation we were able to metamorphic boundaries between the use the more simple model with two major amphibolites and greenstones on Plate 4 volcanic cycles. The oldest volcanic unit is are arbitrary and mark the transititional the Goldinvarri Formation (Solli 1983) and zones. In most places gradually changes in the correlative Vuomegielas Formation metamorphic grade are observed. The lack (Siedlecka 1985) northeast of Plate 4. We of abrupt breaks in metamorphic grade, and have correlated these formations with the similar chemical compositions and magnetic Sotnabeaiiavrit Formation (and partly the susceptibilities are among the major argu­ Baharavdojavri Formation) in the south ments why we favour one major volcanic (Olsen &Nilsen 1985). They occur along cycle overlying the Masi Formation within the eastern margin of the KGB and repre­ the Alta-Kautokeino Rift (AKR). The meta­ sent the 'Sedimentary and volcanic rocks of volcanites are characterised by a banded proba ble Late Archaean age ' on Plate 4. magnetic pattern . The basaltic am phiboli­ The dominating amphibolite-facies metavol­ tes consist mainly of metatuffs and metatuf­ canites are basaltic and have relatively high fites. In addition there are metamorphosed MgO and low Ti02 contents (Solli 1983). lavas and diabases and metasediments; Minor occurrences of ultramafic metavolca­ mica schists, marbles and graphite schists. nites, and psammitic and pelitic metasedi- The low-grade metamorphic metabasalts NGU - BULL 425. 1993 Odleiv Olesen & Jan Sverre Sandstad 55 along Stuorajavri and agglomeratic layers where brittle faulting is most intensive west of Kautokeino are strongly magnetic (Sandstad et al. 1992). and readily distinguished. Only in the nor­ theastern part of the KGB, within the Suolo­ The 'Intrusive rocks of supposed Early Pro­ vuopmi Formation, and centrally in the KGB terozoic age' have retained the classificati­ do the pelitic metasediments make up a ons used in the preliminary and printed considerable portion of the rocks. The bedrock maps in the scale 1:50,000. The graphite schists are outlined by the EM con­ major granites are located mainly in the ductors, especially within the AKR where eastern part of the map area (Plate 4), with­ the rocks are steeply dipping. The nume­ in both the Jergol Gneiss Complex and the rous EM indicators in the northeastern part greenstone belt. The granites are occasio­ of the map-area are partly due to weakly fol­ nally highly differentiated and weakly defor­ ded and almost flat-lying rocks. Komatiitic med to undeformed. They have intruded metavolcanites, partly consisting of pillow the supracrustals and are assumed to lavas (Olsen & Nielsen 1985), occur at diffe­ represent post-orogenic intrusions. In are­ rent stratigraphic levels along the eastern as where a mixture of exposures of granites margin of the AKR and within the Masi area. and other non-magnetic felsic rocks occur, the borders are arbitrary. A similar simplifi­ A gradual decrease in volcanic activity with cation is also shown for granodiorites within accompanying deposition of pelitic sedi­ the JGC. The granodiorites are weakly to ments has been mapped in the north-cen­ moderately foliated and represent syn- to tral part of the AKR (Sandstad 1985, Sied­ post-orogenic intrusions. Xenoliths of gneis­ lecka et al. 1985). The border between peli­ ses and supracrustal rocks of the KGB are tes with layers of graphite schist (Caskijas found within the larger granodioritic massif Formation) and pelites with layers of siltsto­ east and south of Masi (Solli 1988). The ne (Bikkacakka Formation, Sandstad 1985) large Riednjajavri quartz monzonite occur­ is mapped with the use of the EM conduc­ ring in the extreme southwest of the green­ tors. Above these rocks are situated feld­ stone belt is massive to weakly foliated and spathic sandstones constituting the young­ has a minor angular discordance against est supracrustal unit within the KGB (Cara­ the metavolcanites. Major bodies of gab­ varri Formation, Siedlecka et al. 1985). bro/metagabbro are assumed to represent subvolcanic intrusions and are mapped Albite felsites and albite-carbonate altered mainly along the eastern part of the green­ rocks occur locally within the greenstone stone belt. In the northeast they cover large belt (e.g. Holmsen et al. 1955, Gjelsvik areas partly due to the presence of concor­ 1958, Padget 1959). They often constitute dant intrusions within the flat-lying supra­ thin layers or irregular zones associated crustals. A minor peridotite is spatially with tectonic activity, and just a few major associated with regional faults east of the areas dominated by albite-rich rocks are Caravarri Formation. It is the only ultrabasic shown on the map (Plate 4). Very fine-grai­ intrusion known within the KGB, but similar ned albite felsites representing altered peli­ intrusives are found within correlative rocks tic metasediments and metatuffites occur within the Alta-Kvesnanqen tectonic window primarily in the lower or upper part of the (Vik 1985). basaltic metavolcanic sequences. They are assumed to be formed in association with The basaltic dykes are subdivided into the intrusion of diabase sills in the unconso­ several groups (Plate 4). The clearly most lidated sedimentary sequence (Vik 1985, distinctive of these are the diabases with Bjerlykke et al. 1993) and are commonly reverse magnetisation. They are the young­ associated with copper-gold mineralisations est rocks within the greenstone belt and as observed in the Bidjovagge Mine. Medi­ paleomagnetic studies indicate an age of um- to coarse-grained albite-carbonate around 900-950 mill. years (Mertanen et al. rocks are common in the central part of the 1990). They have retained an ophitic texture AKR, surrounding Kautokeino, in areas and are orientated NE-SW parallel to the 56 Odleiv Olesen & Jan Sverre Sandstad NGU • BULL 425, 1993

Mierujavri-Sveerholt Fault Zone (MSFZ). press) describes gradual transititions from Most of the albite diabases which occur fre­ ordinary diabase to reddish albite-bearing quently along the MSFZ have a similar ori­ diabase.More detailed mapping shows that entation . They have a high content of mag­ NE-SW orientated albite diabases occur netite (up to 10 %, Solli 1983) giving a just north of Kautokeino (Sandstad et al. charcteristic anomaly pattern on the aero­ 1992). Most of the albite diabases have this magnetic map (Plate 1). They are supposed NE-SW orientation, but such intrusions are to represent intrusive rocks with a high albi­ also found along N-S trending faults, e.g. te content (Solli 1983, Olsen in press). south of Carajavr], The further classification However, it is likely that some of the other of the basaltic dykes based on deformation mapped diabases/metadiabases may be follows the mapping of Olsen (in press) in classified as albite diabase. Olsen (in the southern part of KGB. Olsen considers

70·

FINLAND

B

LEGEND

AEROMAGNETICALlY INDICATED REGIONAL FAULTS

GREENS TONE S

AlBITE OIABAse

B BASEME NT CULM INATION B ...... J50. KM

Fig, 8. Sketch map of regional structural elements interpreted from aeromagnetic and gravity data in Finnmark and adjacent areas ir, northern Finland and northern Sweden (Modified from Geological Surveys of Finland, Norway and Sweden 1986b, Olesen et al. 1990. Henkel 1991). BKFC - Bothnian-Kvcenangen Fault Complex; KAFZ -Karesuando-Arjeplog Fault Zone; MSFZ - Mierujavri. Svcerholt Fault Zone; LVFZ - Langfjord-Vargsund Fault Zone. Odleiv Olesen & Jan Sverre Sandstad 57 NGU - BULL 425. 1993 that the different dykes are associated with eastern block being downthrown or (c) an different volcanic cycles. In disagreement oblique movement consisting of both sinis­ with this interpretation, as discussed in the tral and dip-slip movement. previous section, we have, however, cho­ sen to map diabases with preserved ophitic The western zone, the CBL, appears on the texture in the southern part of the KGB. aeromagnetic image as the border between Both low- and high-magnetic basaltic dykes the high-amplitude, banded magnetic pat­ occur independently of the degree of defor­ tern to the east and the low-amplitude, ban­ mation. In general they are assumed to be ded pattern to the west. The CBL coincides associated with the basaltic volcanism and with the eastern margin of the migmatised commonly occur as sills. Haiseatnu Gneiss Complex. This border is intruded by granites and pegmatites (Holm­ sen et al. 1957 , Sandstad 1983, Olsen in The Bothnian-Kvcenangen Fault press). However, faulting along the northern Complex part of this lineament has been observed by The NNW-SSE trending Alta-Kautokeino Holmsen et al. (1957), and Sandstad (1983) Rift is bounded to the west and east by ste­ reported strong deformation along the zone. eply dipping fractures, the Cieg1laljakka­ Shear deformation has been observed by A. Boaqanjavri Lineament, CBL, to the west Bjerlykke (pers. comm. 1990) to the west of and the Soadnjuiavrf-Baiasiavri Fault, SBF, the Bidjovagge Mine. Shear-heating at gre­ to the east (Plate 3). These structures are ater depth along strike-slip faults can continuous along the entire greenstone belt enhance crustal anatexis (Michard-Vitrac et and constitute part of the BKFC. Especially al. 1980 , Sylvester 1988), and the original along the eastern fault, the SBF, cross-cut­ fault rock along the rift-fault may therefore ting relationships to magnetic reference not be recognisable. From the geophysical structures can be observed. A striking fea­ images, we conclude that the CBL repre­ ture seen in Plate 1 is the change in the sents the most distinct dislocation along the magnetic pattern from NE-SW-trending western border of the AKR. We interpret structures 5 km north of Mlerujavri to the this lineament as a continuous fault zone NNW-SSE-trending structures at the margin from the better exposed area north of Hais­ of the AKR. This indicates that the NE-SW javri to the south . In this southern area , structures are apparently transected by which is to a great extent covered by glacial sinistral displacement along the SBF. drift, a steep fault bordering the Haiseatnu Immediately to the south of the Caledonian Gneiss Complex has also been described front north of Soadnjujavri there is a similar by Holmsen et al. (1 957, Fig. 16). Several discordance between the E-W-trending large fault zones also occur within the rift structures within the Suolovuopmi Formati­ (Plate 4). These, however, are not continu­ on and the N-S-trending structures in the ous along the entire rift. One interesting Likca Formation. Holmsen et al. (1 957) result is that the electrical conductors repre­ reported N-S-trending faults with brecciation senting mainly graphite schists (Plate 4) and mylonitisation of the rocks at both loca­ seem to coincide with some of the fault tions. Further to the south, Olsen (in press) zones which are interpreted from the aero­ has reported shearing along this zone. A magnetic and topographical data. Note that reversed magnetised dyke (Plates 1 - 4) the VLF-EM method could not be used to has an apparent sinistral offset of 1 km control the location of these faults. These along the SBF. Measurements of natural zones may represent the same type of she­ remanent magnetisation on samples from ar zones as those appearing in the Bidjo­ the dyke are shown in Fig. 4. Modelling of vagge Mine, which to a great extent control aeromagnetic profiles across this dyke the gold mineralisations within this mine shows that it dips 60-70° to the southeast. (Bjerlykke et al. 1993). The true movement along the SBF after the intrusion of the dyke is therefore either (a) 1 The gravity field in Plate 2 is composed of km sinistral or (b) 2-3 km dip-slip with the anomalies of different wavelengths. The 58 Odleiv Olesen & Jan Sverre Sandstad NGU - BULL 425, 1993 central area, the Kautokeino Greenstone AKR continues further NNW onto the conti­ Belt, consists of alternatin g high and low, nental shelf of the Norwegian Sea. short-wavelength (5-10 km) anomalies. The local lows correspond to basement Fig. 3 shows the frequency distributions of rocks, felsic intrusion s and quartzites in in situ susceptibility measurements of the antifo rms, and sandstones within the basi­ main lithologies of the Caskijas Formation in nal Caravarri Formation. The gravity highs the area of 1:50,000 map-sheet 1833 IV correspond to the basic metavolcanites. Mallejus, As described above, the eastern Within the rift, both bedding and schistosity part of this map area contains mostly gre­ are generally steeply dipping. Flat-lying enschist-facies rocks while the western part structures occur where the underlying base­ contains their amphibolite-facies equiva­ ment forms dome structures (Olesen & Solli lents (Sandstad 1983,1985). It has long 1985) . Four antiformal structures in the Mie­ been a matter of dispute whether or not the­ rujavri area have been defined in addition to se two units represent one and the same those previously identified by Holmsen et al. formation as stated by Sandsta d (1 957) and Olesen & Solli (1985). These (1983,1985) and Siedlecka et al. (1985), or structures (Plates 2 & 3) can be interpreted two different units with regard to time of for­ either as gravity-driven diapirs (Olesen & mation and depos itional environmen t Solli 1985), as fold-interference phenomena (Olsen & Nilsen 1985, Bergh & Torske (Olsen in prep.) or as folds within shear­ 1988). The histogram s in Fig. 3 show a induced strike-slip duplexes (flower structu ­ very similar pattern for the correlative rock­ res). The largest gravity highs are interpre­ types in the two areas. The bimodal distri­ ted as accumulations of strongly folded bution of the susceptibility is respons ible for and/or faulted amph ibolites with depths of the typical banded anomaly pattern which up to 6 km (Olesen & Solli 1985). can be seen within the greenstone belt on the aeromagnetic map in Plate 1. There is The western part of Profile A - C in Fig. 7 is no difference with regard to major element dominated by a synclinorium of amphiboli­ chemistry between the low-magnetic and tes from the Caskijas Formation. The volu­ the high-mag netic volcanites (Sandstad me of these rocks is significantly larger than 1983).The difference in magnetite content that of the Goldinvarri Formation. There is a must therefore be a result of different oxida­ prominent gravity low related to the Cara­ tion states inherited from the pre-metamor­ varr i Formatio n. The mudstone underlying phic state (Grant 1985). The source of the the Caravarri Formati on is interpreted to volcanic rocks and the depos itional environ­ have a depth of 5-6 km. Since the Caravar ­ ment is therefore likely to be similar in the ri Formation is depos ited on top of the two areas. In this context it should be poin­ mudstone, the depth of these sandstone s is ted out that the Caskijas Formation and cor­ likely to be similar. The depth of the Car a­ relative units in the southern part of the varri Formation , however, cannot be deter­ KGB are unique among the volcanosedi­ mined from the gravity data because of a mentary format ions in the Proterozoic on lack of density contrast with the underlying Finnmarksvidda in terms of high magnetite basement. The gravity data do not allow content. The aeromagnet ic anomal ies cau­ the presence of any greenstones below the sed by the Caskijas Formation resemble Caravarri Formation. those of the Kiruna and Kittila greenstones in northern Sweden and northern Finland, From the aeromagnetic and gravity data, respectively, with regard to amplitude and the AKR and the BKFC can be traced bene­ wavelength (Geological Surveys of Finland, ath the Caledonian nappe s to the Alta-Kvee­ Norway and Sweden 1986a). nangen window , where they were deforme d during the Caledo nian orogeny (Zwaan & The Mleruje vri-Sveemott Fault Zone Gautier 1980, Olesen et al. 1990). From the The prom inent, NE-SW-trending, characte­ aeromagnetic and gravity maps of Olesen ristic high-magnetic anoma lies in the Masi et al. (1990) there is also evidence that the area are due to Proterozoic albite diabas es NGU - BULL 425, 1993 Odleiv Olesen & Jan Sverre Sands/ad 59

that have intruded along faults within the opmi Formation increases continuously to MSFZ (see Plates 1 & 4), Outside this fault the west of the Masi Formation. The Bigge­ zone the albite diabases have intruded regi­ varri Duplex to the east of Biqqejavr] (Plates onally as sills along layering and foliation 3 & 4) is therefore interpreted to continue surfaces, Locally, deformation of these dia­ beneath the amphibo lites to the north of the bases can be observed , for instance along Mazejakka river. The albite-carbonate the main road between Masi and Kautokei­ alteration along the Mazejakka is thought to no (UTM coord. 602400-7698500) where represent a gently northward-dipping roof of the diabase has been transformed to the Biggevarri Duplex structure mainly loca­ arnphibollte. From the aeromagneti c and ted within the quartzite. The Biggejavri topographical images, a complex system of REE-Sc mineralisation (Olerud 1988, Sand­ duplexes (Woodcock & Fischer 1986) can stad 1989) located within an albitite is situa­ be delineated along the MSFZ from Mieru­ ted in the amphibolites shortly above this javri to lesjavrl (Plates 1 & 3), Local, weak, duplex interface and the mineralisation may magnetic anomalies are caused by small be related to faultinq along the MSFZ. amounts of magnetite in quartzite beds with­ in the Masi Formation. The interpretations The gravity low in Plate 2 to the northwest have been followed up in the till-covered of Biggejavri is caused by the absence of area with electromagnetic , VLF, ground pro­ amphibolites in an anticlinal structure of files (Olesen et al. 1992a). quartzites of the Masi Formation. A magne­ tic anomaly (Plate 1), which is composed of Magnetic model calculations along aero­ short- and long-wavelength components, is magnetic profiles indicate that the albite dia­ related to the same structure and is inter­ base has either intruded into a positive flo­ preted as sill-like intrusions of albite diaba­ wer structure (Wilcox et al. 1973) or has se, a relation that is generally valid in the been involved in the deformat ion along a Masi area (Olesen & Solli 1985), When similar structure (Olesen et al. 1992a). The interpreting the negative gravity anomaly in wedge-shaped structure bordered by faults this area it was necessary to take into along Fidnajakka , Biqqejavri, Mazejakka account the gravity effect of the amphiboli­ and the Kautokeino River has been inter­ tes in the Suolovuopmi Formation located 2 preted as a duplex which Olesen et al. km to the north of Profile A-B (Plate 2). (1992a) proposed to name the Biggevarri Duplex. In the eastern part of the gravity Discussion and conclusions Profile A-C (Fig. 7) there is an increase in the regional field towards the Jergol Gneiss The bulk of the mafic volcanites in the Kau­ Complex. This long-wavelength anomaly is tokeino Greenstone Belt is located within a interpreted to be caused by a layered base­ NNW-SSE-trending, 35 km wide and up to ment consisting of an upper felsic unit and a 5-6 km deep structure which is thought to lower intermediate unit. On Finnmarksvid­ represent the AKR modified by later folding, da, this layered basement is interpreted to faulting and shearing along the BKFC. The form two large culminations with amplitudes borders of this sheared rift can be outlined of 5-7 km in the Haiseatnu and Jergol from the geophysical images. The CBL and Gneiss Complexes , as demonstrated by SBF in Plate 3 are the main bordering faults Olesen & Solli (1985). The western flank of and are continuous along the entire length the latter is visible on the profile. The gradi­ of the greenstone belt. As can be seen ent of the regional field is larger in the Masi from the three northernmost gravity profiles area than in the Kautokeino area further to by Olesen & Solli (1985), the supracrustal s the south (Plate 2). The gravity anomaly between these two zones are continuous to caused by the Goldinvarri Formation is situ­ great depth and the contacts along these ated on the flank of the regional anomaly. bordering zones are generally steeply dip­ ping. The southern most profile in Olesen & According to the gravity modelling of Profile Solli (1985) does not reveal a steep contact A-C in Fig. 7, the thickness of the Suolovu- and is interpreted as the southern terminati- 60 Odleiv Olesen & Jan Sverre Sandstad NGU . BULL 425. 1993 on of the rift at the Finnish border. The 1985). This is most likely caused by late­ quartzites within the Masi Formation along stage uplift of the margins, subsequent ero­ the Finnish border are characterised by sion of the exposed basement and depositi­ their high metamorphic grade and migmati­ on of the sediments in deep internal basins. sation (Olsen & Nilsen 1985). The high One mode l for the formation of the KGB metamorphic grade is also characteristic was proposed by Olesen & Solli (1985); to further north at the western and eastern re-establish gravitational equilibrium after margins of the rift. We therefore favour the the depos ition of the dense volcanic rocks, interpretation by Bergh & Torske (1 984, the layered crust culminated on both sides 1988) of a southwa rd-propagating rift into of the belt and form ed the Haiseatnu and the Karelian continental block . Olsen & Nil­ Jergo l Gneiss Complexes. In this late stage sen (1985) and Bergh & Torske (1988) pre­ the uplifted basement was expose d to erosi­ fer to exclusively incorporate the low-grade on and the sediments were deposited in volcan ic rocks of the Caskijas Format ion in basins within the greenstone belt. A similar the AKR. From the geophys ical images model was proposed in northeastern Swe­ there is no evidence of these low-grade den by Lindroo s & Henkel (1978). Howe­ rocks of the Caskijas Formation represen­ ver, in this they incorporated marginal sedi­ ting a separate fault-bounded rift. On the mentary basins and not a central basin. contrary, gravity interpretations by Olesen & Solli (1985) and Fig. 7 show that the outer An alternative model, following the thermal amphibolite-facies rocks are just as deep as mode l for basin evo lution proposed by the central greenschist-facie s unit. The pre­ McKenzie (1 978), involves the format ion of sent study consequently suggests that the the mudstones and limestones in the Bikka­ amph ibolite-facies volcanosed imentary cakka Formation during thermal subsidence rocks along the flanks of the Kautokeino as a result of cooling of upwelled asthenos­ Greenstone Belt should also be included in phere after a phase of rifting. Specifically, the rift. Detailed mapping in the map area horizontal heat flow could cause additional 1833 IVMallejus by Sandstad (1 983) shows cooling within the rift and uplift of its shoul­ that the two units represent the same strati­ ders (Ingersoll 1988). Strike-slip move­ graph ic succession with a gradual change ments may be incorporated in the model. in metamorphic facies from one unit to the The large-scale sinistral displacement other. Sandstad (1983) could not detect reported by Berthelsen & Marker (1986) and any abrupt break with regard to lithology, Henke l (1988) along the 1.9-1.8 Ga-o ld chem istry, metamorphism or tecton ic style Bothnian-Kvrenangen Fault Comp lex between the two units. embraced the 2.2-1.9 Ga Alta-Kautoke ino Rift which was already a zone of weakness Bergh & Torske (1987) include the Berg­ in the Karelian continental block. This stri­ mark area in the west ern part of the Alta­ ke-slip movement may have produced pull­ Kvrenangen Window in the rift. The strati­ apart basins within the rift.The Caravarri graphy in this area (Vik 1981) is similar to Formation has been interpreted to be the the stratigraphy described by Sandstad youngest unit within the greenstone belt. (1983) for the western most part of the Cas­ The strike-slip movements could also have kijas Formation on the map-sheet Mallejus. triggered the formation of the gravity-indu­ This observation also supports our interpre­ ced diapirs which were delineated by Ole­ tation that the whole of the Caskijas Forma­ sen & Solli (1985). tion should be included in the rift. The flat-lying, thin (up to 2 km) sequences The mode l for the development of the KGB to the west of Masi (Plate 4) are interpreted must explain why the formation of the deep as having been deposited on a platform at and narrow Caravarri Formation contains the margins of the deep rift. This is suppor­ abunda nt coarse-grained sandstones and ted by the increased volume of sediments in conglomerates derived from a granitic sour­ this area (Olesen &Solli 1985). The arnphi­ ce (Holmsen et al. 1957, Siedlecka et al. bolites occur adjacent to the AKR . The NGU-BULL 425,1 993 Odleiv Olesen & Jan Sverre Sands/ad 61

MSFZ constitutes the border between this beneath the Caledonian nappes (Olesen et flat-lying sequence to the northwest and the 0.1. 1990). On the Kola Peninsula a similar more deformed Goldinvarri Formation and large-scale fault, the Mokhtozerckaya Fault Jergol Gneiss Complex to the southeast Zone, MFZ (Barzhitzky 1988), has been (Plate 4), Holmsen et 0.1. (1957) and Solli reported to terminate the eastern end of the (1983) reported that the Masi Formation has Lapland Granulite Complex which is the locally been inverted and thrusted above continuation of the Levajok Granulite Belt the Suolovuopmi Formation to the west. In through Finland into Russia. During or after the present model of the MSFZ we interpret the emplacement of the Levajok Granulite the thrusting and imbrication of the Masi Belt in the continent-continent collision (Krill Formation to have occurred internally within 1985), the MSFZ and the MFZ may have the formation , as a result of dextral strike­ acted as dextral and sinistral transform slip movements along the MSFZ. The faults, respectively. 'Indentor tectonics' thrusting of the quartzite consequently (e.g. Tapponier et al. 1986) may also developed mainly underneath and along the explain these large-scale strike-slip faults border of the Suolovuopmi Formation. adjacent to continent-continent collision zones. Watterson (1978) suggested that In the area of map-sheet 1933 IV Masi (Sol­ indent-linked faults may be the main cause li 1988), foliation and layering steepen of the pervasive lineament networks in Pre­ towards the Kautokeino River; from the cambrian continental crust. geophysical data this river valley area is interpreted to represent the central part of Proterozoic albite diabases have intruded the MSFZ (Plates 3 & 4). A palm tree struc­ the MSFZ in the Masi area. Locally, defor­ ture (Sylvester & Smith 1976) slightly tilted mation features can be observed in these to the northwest, can be inferred along the diabases. In the Masi area, Olesen (1988) MSFZ by combining the geophysical inter­ reported that the Stuoragurra Fault follows pretation and the geological observations. one old fracture zone and then cuts across This type of structure typically occurs along to follow another. Interpretations of more strike-slip faults (Sylvester 1988). Two detailed geophysical images have resulted minor, fault-bounded blocks representing in the delineation of a system of duplexes the Suolovuopmi Formation on Arvusvarri along the MSFZ from Mierujavri to Skogan­ and Haigadancakka (Solli 1988), immedia­ varre. Albite-carbonate alteration occurs tely east of Masi and 15 km south of Masi along the borders of the Biggevarri Duplex. respectively, are situated close to the centre Slight tilting of the MSFZ towards the north­ of the MSFZ. These blocks are interpreted west may have been caused by the doming to be emplaced by normal faulting , which of the Jergol Gneiss Complex. Since the may represent extension across the top of deformation increases towards the MSFZ, the uplifted and laterally spreading blocks the folding and imbrication in this area may (Sylvester 1988). The S-shaped MSFZ, be associated with movement along the representing a restraining bend, is consist­ MSFZ. ent with the observed accumulated dextral displacement of 20 km along the fault zone. To the southwest into northern Sweden, an The wedge-shaped positive Biggevarri extension of the MSFZ can be found; the Duplex, interpreted from geophysical ima­ Karesuando-Arjeplog Fault Zone, KAFZ ges, may have been formed as a conse­ (Fig. 8), reported by Henkel (1991). This quence of this dextral strike-slip component. fault zone occurs in the Tjarra Formation Internal thrusting of the Masi Formation which is correlated with the Masi Formation within this structure was reported by Holm­ (Geological Surveys of Finland, Norway and sen et 0.1. (1957). Sweden 1987) and is intruded by highly magnetic albite diabases. The MSFZ and Based on the interpretation of aeromagnetic KAFZ have an apparent sinistral offset of and gravimetric data the MSFZ truncates 10-15 km along the BKFC (Fig. 8). the Proterozoic Levajok Granulite Belt 62 Odleiv Olesen & Jan Sverre Sandstad GU- BULL 425. 1993

Acknowledgements Gjels vik, T. 1958: Alb ittrike bergarter i den arelske fjellkjede This work was part ially financed by Norsulfid a.s, the Roya l pA Finnmarksvidda . ord-Norge. Nor. geol . unders . 203. Norwegian Council for Scient ific and Industrial Research. 60-72 . NTN F (Grant 13220 to Odleiv Olesen) and the Geological Sur ­ Grant, F.S. 1985: Aeromagnetics . geo logy and ore environ­ vey of orway. The study benefitted from collaboration with ments. I. Magnetite in igneous, sed imentary and rnetamor­ the NTN F project 'Ore genesis with in the Kautokeino Green­ phic rocks : an overview . Geoexpiotetion 23.303·333. stone Belt'. conducted by Professor Arne Bjorlykke at the Uni­ Hagen, R. 1987. Kautokeino gronnsteinsbelte, unpubl. bedrock versity of Oslo. The gravity measurements and much of the geology map 1:100,000. AlS Prospektering, Oslo. petrophysical laboratory work have been performed by several Henkel, H. 1988 : Tectonic stud ies in the Lansjarv region. colleagues within the Finnmark Programme and the Geophysi­ Svens k kii mbranslehanrering AB Technical Report 88-07. cal Department of the Geo logical Survey of Norway. Herbert 166 pp. Henkel, David Roberts and Peter Walker have read an earlier Henkel, H. 199 1: Magnetic crusta l structures in northern Fen­ version of this paper and made suggestions towards its impro­ noscandia. In: Was ilews i, P. & Hood, P.(eds.), Magnetic vement. Ola Kihle . Jan Reidar Skilbrei, Arne Solli and Trond anomalies - land and sea. Tectonophysics 192.57·79. Tors vik have contr ibuted with valuable adv ice and discussions . Henke l, H. in Ambros, . 1980 : Desc ription of the geological and Randi Blomsoy, Gunnar Gronli and Bjorg Inger Svend­ maps Lanna vaara V. O. SV, SO and Karesuando SV . gArd have prepared the figures. Tim Pharaoh and Arne Solli SO . Sver. geol. unders. At25-30 .57-111. provided constructive comments dur ing their refereeing of the Henkel. H. & Guzrnan, M. 1977 : agnetic features of fracture manuscript. To all these persons and institutions we express zones. Geoexp loration 15. 173-181 . our sincere than ks. Henkel, H. & Eriksson , L. 1980: Interpretation of low altitude airborne magnetic and VL F measurements for ident ificati· on of fracture zones. In: Bergman, M. (ed.) Subsurface Space. Pergamon Press, Oxford , 9 13-918 . Henkel, H., Aaro, S., Hultstrorn, J., Kero . L., Mellander, H. & Andersson, C. 1984: Filipstadprojektet - en test av bitdebe­ handlingssysteme t EBBA· l for regionala geofysiske data. Unpubl. SGU Geophysical Report 8408 , 93 pp. Hois t, B. 1986 : Kombin ert tolkning av geofysikk og geologi p/l kartblad 1832 I Siebe i Keinok emo-omduiet. Finnmark. Unpubl. thes is, NTH . Univer sity of Trondheim, 109 pp. Holmsen, P.. Padget. P. & Pehkonen, E. 1957 : The Precarn- brian geo logy of Vest-Finnrnark . orthern orway. or. References geol . unoers. 201, 106 pp. Habrekke, H. 1979: Magnetiske-, etektrornacnetrske-, rac iorne­ Barzhilzky.V.V. 1988 : Kosmogeologicheskaya karta, Dochet­ triske· og VLF-mAlinger fra helikopter over et ornrade syd vertichnyh obrasovaniy. Servero-vostochnoy chasti Baltii­ for Kautokeino, Finnmark. Unpubl. GU Report 1734. 12 skogo shtshita. Masshtab 1:1 000 ODD, ob'yasnitel'naya pp. zap iska . Ministerstro geologii SSSR. Kiev, 86 pp. Habrekke , H. 1980a : Magnetiske- , elektrornaqnetiske- , VL F· Bergh , S.G. & Torske. T. 1986 : The Proterozoic Skoadduvarri og radiometriske malinger fra helikopter over Kautokeino Sandstone Formation. Alta . northern Norw ay: A tecton ic syd , Kautokeino. Finnmark. Unpubl. GU Report 1782. 12 fan-delta complex. Sediment. Geo/. 47, 11-25 . pp. Bergh . S.G& Torske, T. 1988: Palaeovolcanology and tectonic Habrekke, H. 1980b : agnetiske- , elektromagnetis e-, VLF- sett ing of a Proterozoic metatholeiitic sequence near the og rad iometriske mAlinger fra heli opter over Bidjovagge­ Baltic Shield margin. northern orwa y. Precambrian Res. ornradet, Kauto eino, Finnmark. Unpub l. GU Report 39,227-246. 1783.12 pp. Berthelsen . A. & Marker. . 1986: 1.9-1.8 Ga old stri e-sl ip Habrekke. H. 1981 : agnetis e-, e1e rornaqnetiske-. VLF- og megashears in the Baltic Shield, and the ir plate tectonic radiometriske mAlinger fra heli opt er over Bidjovaggeom­ implications. In: Galson , D.A & Mueller, S.(eds.), The radet , Kauto eino , Finnmark. Unpubl. GU Report 1833. European Geotraverse, Part 2. Tectonophysics 128. 163­ 12 pp. 181. Habre ke . H. 1983 : Geofysis e mAlinger fra heli opter 0 er et Bjorlykke, A., Nilsen , K.S ., Anttonen, R. & Ekberg. M. 1993 : ornrade rundt Mas i, Kauto eino . Finnmark. Unpub l. GU Geological sett ing of the Bidjo vagge deposit and related Report 1902. 15 pp. gold-copper deposits in the northern part of the Baltic Shi­ Habrekke, H. 1984 : Geofysiske mAlinger fra helikopter over eld. Proceedings tram the 8th IAGOD Symposium 1990. kartbladene Carajav'ri og Jiesj av'ri , Finnmark. Unpubl. Ottawa, Canada, 667·680. NGU Report 1886/8. 15 pp. Dvorak , Z. 1982 : DIGHEM" survey of the Finnmark area, Ingersoll, R.V. 1988: Tectonics of sed imentary bas ins.Geol. Norway for N S Sydvaranger. Dighem Ltd. Report 706, 69 Soc. Am. Bull. 100, 1704·1719. pp. Kihle , 0 .1992: TH EMA P - et Unir as-b asert produksjonssystem Erdas 1990 : Image processing module, vers ion 7.4, January for fargerasterkart. Unpubl. NGU Internal Report 92.068. 1990. ERDAS Inc.. Atlanta . 217 pp. 92 pp. Eriksson, L. 1980: Elektriska och magnetiska metoder for pavr­ Krill , A.G . 1985 : Svecokarelian thrus ting with thermal inversion sande av svaghetszoner i berg (Abstract in En9Iish). in the Karasjok-Levajok area of the northern Baltic Shield. Unpubl. Geophys. Report. Sveriges geologiska unders6k­ Nor. geo/. unders. Bull. 403. 89-101. ning, 80 12. 17 pp. Krill, A.G ., Berg, S , Und ahl, I., Mearns , EW ., Often , M., Olerud , Geological Surveys of Finland, Norway and Sweden 1986a: S.• Olesen, 0 ., Sandstad, J.S., Siedlecka, A. & Solli, A. Aeromagnetic anomaly map , Northern Fennosca ndia, 1:1 1985 : Rb·Sr, U· Pb, and Sm-Nd isoto pic dates from the mill , Helsinki. /SBN·9 1·7158·375·0 . Precambrian rocks of Finnmark, Nor. geol . unoets. Bull. Geologica l Surveys of Finland, Norway and Sweden 1986b: 403,37-54. Aeromag netic interpretation map, Northern Fennoscandia, Lee. M.K.. Pharaoh, T.C. & Soper, N.J. 1990 : Structural trends 1:1 mill , Helsinki. /SBN-9 1-7158·376-9. in central Britain from images of gravity and aeromagn etic Geological Surveys of Finland, Norway and Sweden 1987: fields . Journ. Geot. Soc . London 147. 241·258. Geological map , Northern Fennoscandia, 1:1 mill , Helsinki. Undahl, I. & Mikalsen, T. 1975 : Raisjav'ri. Foreloig berggrunns­ ISBN-91-7158-370-X. geologisk kart 1833 111- 1:50.000. or. gea . unders . NGU - BULL 425, 1993 Odleiv Olesen & Jan Sverre Sandstad 63

Lippard, S.J. & Roberts, D. 1987: Fault systems in Caledonian the Kautokeino Greenstone Belt: Rb-Sr geochronology and Finnmark and the southern Barents Sea. Nor. geol. unders. geochemistry of associated gneisses and late intrusions. Bull. 410, 55·64. Nor. geo/. unders. Bull. 403,131-160. Lindroos , H. & Henkel, H. 1978: Regional geological and geo­ Padget, P. 1959: Leucodiabase and associated rocks in the physical interpretation of Precambrian structures in north­ Karelidic zone of Fennoscandia. Geol. For. Stockh. For­ eastern Sweden. Sver. geol. unders. C751, 19 pp. hand. 81, 316-332. Mathisen, O. 1976: A method for Bouguer reduction with rapid Sandstad , J.S. 1983: Berggrunnsgeologisk kartlegging av pre­ calculation of terrain corrections. Geogr. Surv. Norway kambrisk grunnfjell innen kartbladet Mallejus, Kvrenang­ geodetic publications 18, 40 pp. en/Kautokeino, Troms/Finnmark. Unpub/. NGUReport McKenzie, D. 1978: Some remarks on the development of 1886/5, 28 pp. sedimentary basins. Earth Planet. Sci. l.ett. 40, 25-32. Sandstad, J.S. 1985: Mallejus.Forelobig berggrunnsgeologisk Mertanen, S., Pesonen, L.J., & Leino, M. 1990: Uusia paleo ­ kart 1833 IV - 1:50, 000. Nor. geo/. unders. magneettisia tuloksia Fennoskandian diabaaseista. Sum­ Sandstad, J.S. 1989: Geology of the Biggejavri Sc-REE occu­ mary: New paleomagnetic results of diabase dykes in Fen­ rence in Finnmark, North Norway. 3GAC·MAC Annua/ noscandia. Ge%gi 42, 55-56. Meeting; Program with Abstracts; Montreal, May 1989, p. Michard-Vitrac, A , Albarede, F., Dupuis, C., & Taylor, HP . 1980: A2. The genesis of Variscan plutonic rocks - Inferences from Sandstad, J.S., 1992: Beskrivelse av digitalt framstilt berggrunns­ Sr, Pb, and U studies on the Maladeta Igneous Complex, kart over Kautokeinogronnsteinsbeltet, Finnmark. Unpubl. central Pyrenees, Spain. Contr. Miner. Petr. 72, 57-72. NGU Report 92.250, 37pp. Mogaard, J.O. & Skilbrei, J.R. 1986: Geofysiske malinger fra Sandstad, J.S., Bjorlykke, A , Olesen, O. & Nilsen, K S. 1992: helikopter over kartbladene Kautokeino, Lappuluobbal, Vurdering av malmpotensialet etter samtolkning av geoda­ Siebe og Addjit, Finnmark fylke. Unpubl. NGU Report ta i deler av Kautokeinogronnsteinsbeltet. Unpub/. NGU 86.054, 22 pp. Report 92.255, 23 pp. Olerud, S. 1988: Davidite·loveringite in Early Proterozoic albite Siedlecka, A 1985: Geology of the lesjav'ri - Skoganvarre felsite in Finnmark, North Norway. Min. Mag. 52,400-402. area, Northern Finnmarksvidda, North Norway. Nor. geol. Olesen, O. 1988: The Stuoragurra Fault, evidence of neotecto­ unders. Bull. 403 , 103-112. nics in the Precambrian of Finnmark, northern Norway. Siedlecka, A , Iversen, E., Krill, A. G., Lieungh, B., Often, M., Nor. Geo/. Tidsskr. 68,107-118. Sandstad, J.S. & Solli, A 1985: Lithostratigraphy and cor­ Olesen, O. & Solli, A 1985: Geophysical and geological inter­ relation of the Archean and Early Proterozoic rocks of Finn­ pretation of regional structures within the Precambrian marksvidda and the Sorvaranger district. Nor. geo/. Kautokeino Greenstone Belt, Finnmark, North Norway. unders . Bull. 403, 7-36. Nor. geo/. unders . BUll. 403, 119-129. Skilbrei, J.R. 1986: Magnetisk residualfeltkart, Finnmarksvid­ Olesen, 0. , Roberts, D., Henkel, H., Lile, O.B. & Torsvik, T. H.1990: da, M 1:250,000. Unpubl. NGU Report 86.158, 13pp. Aeromagnetic and gravimetric interpretation of regional Solli, A. 1983: Precambrian stratigraphy in the Masi area, structural features in the Caledonides of West Finnmark Southwestern Finnmark, Norway. Nor. geol. unders. 380, and North Troms, northern Norway. Nor. geo/. unders. BUll. 97-105. 419,1 -24. Solli, A. 1987: Lappuluobbal. Forelopig berggrunnsg eologisk Olesen, 0 ., Henkel, H., Lile, O.B., Mauring, E. & Ronning J.S. kart 1933 III - 1:50 000, Nor. geo/. unders. 1992a: Geophysical investigations of the Stuoragurra post­ Solli, A. 1988: Masi, 1933 IV - berggrunnsgeologisk kart - M glacial fault, Finnmark, northern Norway. Journ. Appl. 1:50,000. Nor. geol. unders. Geophysics 29, 95-118. Solli, A. 1990: Carajavri, 18331 - berggrunnsgeologisk kart - M Olesen, 0 ., Henkel, H., Lile, O.B., Mauring, E., Ronning, J.S & 1:50 000. Nor. geo/. unders. Torsvik, T.H. 1992b: Neotectonics in the Precambrian of Swain, C.J. 1976: A Fortran IV program for interpolating irregu­ Finnmark, northern Norway. Nor. Geol. Tidsskr. 72, 301­ larly spaced data using the difference equations for mini­ 306. mum curvature. Computers & Geosciences 1, 231-240. Olesen, 0. , Habrskke, H., Kihle, O. & Smethurst, MA 1992c: Sylvester, A G. 1988: Strike-slip faults. Geol. Soc. Am. BUll. Finnmark fylke, aeromagnetisk anomalikart. M. 1:500.000. 100, 1666-1703. Nor. geo/. unders. Sylvester, AG. & Smith, R.R. 1976: Tectonic transpression and Olesen, 0 ., Sandstad, J.S. & Bjorlykke, A 1992d: basement-controlled deformation in the San Andreas fault Samtolkning av geodata i Kautokeino-Masi-ornradet, Finn­ zone, Salton Trough, California. Am. Ass. Petr. Geol. Bull. mark. Unpubl. NGU Report 92. 143, 22 s. 60, 2081-2102. Olesen, 0 ., Gellein, J., Kihle, O. & Sindre, A 1993: Finnmark Tapponier, P., Peltzer, G. & Armijo, R. 1986: On the mechanics fylke, tyngdeanomalikart, M. 1:500.000. Nor. geol. unders. of the collision between India and Asia. In Covard, MP. & Olsen, KI. 1987a: Roaw oai'vi. Forelopig berggrunnsgeolo­ Reis, A C. (eds.) Collision tectonics. Geo/. Soc. London gisk kart 1832 11 - 1:50,000. Nor. geol. under. Spec. Pub/. 19, 115-157. Olsen, K.I. 1987b: Ur'devarri. Forelopig berggrunnsgeologisk Torsvik, T.H. 1992: IMPS - Interactive modelling of potential kart 1832 11 1- 1:50,000. Nor. geol. unders. field data (Release 5). Unpubl. NGU Report 92.305, 75 pp. Olsen, K.I. 1987c: Addjit. Forelopig berggrunnsgeologisk kart Torsvik, T.H. & Olesen, 0.1988: Petrophysics and palaeo­ 1832 IV - 1:50,000. Nor. geo/. unders. magnetism initial report of the Norwegian Geological Sur­ Olsen, K I. 1987d: Suvcaganvarri. Forelopig berggrunnsgeolo­ vey Laboratory. NGU Report 88. 17t, 108s. gisk kart 1932 III - 1:50,000. Nor. geo/. unders. Townsend, C., Rice, A H.N. & Mackay, A. 1989: The structure Olsen, KI. 1988a: Siebe. Forelopig berggrunnsgeologisk kart and stratigraphy of the southwestern portion of the Gaissa 1832 I • 1:50,000. Nor. geol . unders. Thrust Belt and the adjacent Kaiak Nappe Complex, Finn­ Olsen, K.I. 1988b: Kautokeino.Forelopig berggrunnsgeologisk mark, N. Norway. In: Gayer, RA (ed.) The Ca/edonide kart 1833 11 - 1:50,000. Nor. geol. unders.. Geology of Scandinavia. Graham & Trotman, London, 111­ Olsen, KI. 1988c: Law oai'vi. Forelopig berggrunnsgeo logisk 126. kart 1932 IV - 1:50,000. Nor. geol. unders. Vik, E. 1981: Bergmark gruvefelt, Kvrenangen, Troms. Forelo­ Olsen, KI. in press: Beskrivelse til de berggrunnsgeologiske pig rapport fra geologiske og geofysiske undersokelser kart: Kautokeino 18331, Addjit 1832 IV, Siebe 1832 1, Urde­ 1979-1980. Unpubl. NGU Report 1800/46C , 50 pp. oai'vi 1832 Ill, Hoavvoal'vi 1832 11 M 1:50,000, Finnmark. Vik, E. 1985: En ge% gisk utidersoketse av kobbermine ra­ Unpubl. NGU Report. liseringene i Alta-Kvrenangen omrsdet, Troms og Finnmark. Olsen, K.I. & Nilsen, K.I. 1985: Geology of the southern part of Unpubl. dr.ing. thesis, NTH, University of Trondheim, 300 pp. 64 Odleiv Olesen & Jan Sverre Sandstad GU -BULL 425. 1993

Waner son, J. 1978 : Proterozoic intraplate deform ation in the Journ. Struct. Geol. 8. 725-73 5. light of southeast Asian neotectonics . Nature 2 73. 636­ Zwaa n, K.B. & Gautier, A.M . 1980: A1taog Gargia. Beskrivelse 640 . til de berggrunnsgeologiske kart 1834 I og 1934 IV, M Wilcox, R.E., Harding, T.P. & Seely, D.R. 1973 : Basic wre nch 1:50,000. Nor. geol. unders 35 7, 1-47 . tectonics. Am. Ass. Petr. Geol. Bull. 5 7, 74-96. Zwaa n, K.B. 1988: Nordreisa, berggrunn sgeologisk kart - M Woo dcoc k. N.H. & Fischer, M. 1986: Strike-slip duplexes . 1:250,000. Nor. geol. unders .

Manuscript received March 1993; revised typescript accepted August 1993.

Appendix Many ....appish geographical names have mendations of the Norwegian Committee been used in stratigraphic nomenclature, for Stratigraphy, we have adopted the revi­ especially for formations, groups, comple­ sed spellings decided by the 'Navnekonsu­ xes, etc., in the Proterozoic and Archaean lenttjenesten for samiske navn'. The old and of Finnmarksvidda: Following the recom- new names are here listed alphabetically.

Old spelling New spelling Baharavduiavri Formation Baharavdojavri Formation Caskejas Formation Caskijas Formation Galdenvarri Formation Goldinvarri Formation Jer'gul Gneiss Complex Jergol Gneiss Complex Raiseedno Gneiss Complex Haiseatnu Gneiss Complex Suoluvuobmi Formation Suolovuopmi Formation Sadnabei Formation Sotnabeaijavarit Formation