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Jerzy Czerny, Adam Kieres, Andrzej Manecki, Maciej Manecki, Jacek Rajchel XX Polar Symposium Lublin, 1993 University of Mining and Metallurgy, Faculty of Geology, Geophysics and Environmental Protection, Kraków THE GEOLOGICAL MAP (1:25 000) OF THE SW PART OF WEDEL JARLSBERG LAND The map presented here concludes geological mapping carried out between 1985 and 1990 in the Hornsund area by teams of geologists from the University of Mining and Metallurgy. Basic information was collected during polar expeditions organised by the University of Mining in summer seasons of 1985, 1986, and 1988, during XII Polar Expedition of the Polish Academy of Sciences in 1989/90, and during the summer expedition of the Norsk Polarinstitutt in 1990. The map covers a fragment of the western coast of Spitsbergen north of the Hornsund, among Torellbreen, Vrangpeisbreen and Hansbreen. Rocks cropping out in the area are of metamorphic origin and Precambrian age, and belong to the Caledonian basement of Svalbard. Their map is in part uncovered, ie. the Quaternary deposits has only been shown on Elveflya and on the foreland of Torellbreen. During geological mapping new data were collected what allowed to complete and change — in some degree — former opinions on geologic structure and development of the area under study (Birkenmajer 1975, 1981, 1990, 1992). A substantial innovation has been made by identification of two big tectonic units (tectonic blocks) which contain unconnected rock sequences of different ages. The two blocks are separated by a major dislocation with the WNW-ESE trend that displays features of a thrust. It extends from the Vimsodden towards Kosibapasset. Different geological developments of the rock complexes situated on both sides of the recognized dislocation make the major argument supporting the idea presented above. In the rocks of the southern tectonic block, there are distinct signes of two stages of metamorphic alterations, at first of progressive nature under conditions of amphibolite and epidote-amphibolite facies but followed by retrogressive metamorphism under conditions of greenschist facies. Only one phase, that of progressive metamorphism (greenschist facies), has been registered in the rocks of the northern tectonic block. The diaphthoritic changes within the rocks of the southern block can be traced 305 both in the field and in thin sections. They were looked into and described in details by Smulikowski (1965). In amphibolites of the Eimfjellet Group the alterations cumulate in bands of chlorite and chlorite-biotite schists, containing sometimes pseudopebbles of unchanged amphibolites. In paragneisses, mica and carbonate-mica schists of the Isbjórnhamna Group, the diaphthoritic bands (sericite and sericite-chlorite schists) are equally abundant and can be distinguished by their different, ie. greenish colour. Within quartzites, marbles and metagranitoids, diaphthoresis induced cataclasis and created mylonitic zones. The idea of two tectonic blocks is supported by another argument, namely by lithologic correlation. Only the southernmost part of the Vimsodden sequence (ie. quartzites, metatuffs and rhyolitic conglomerates cropping out on Pyttholmen) can be compared with similar rocks occurring on the foreland of Werenskioldbreen and on Kvartsittsletta. The upper part of the Vimsodden Subgroup {sensu Birkenmajer 1975), situated north of the inferred here dislocation zone, cannot be correlated with rocks of the southern tectonic block. Among others, the Jens Erikfjellet greenstones do not form a facial equivalent of the Skalfjellet amphibolites what is proved by results of chemical analyses of both volcanic rock series. In turn, when analysing orientation of the tectonic structures in the southern tectonic block it can be noticed that they are oblique to the direction of the dislocation zone. Axes of the big folds follow the NW-SE trend while the strike of the dislocation zone is close to 300° (i.e. WNW-ESE). The only area where such a diagonal orientation of the rock strata can be directly observed in thefield was found on the foreland of Werenskioldbreen. It should also be noted that the rocks situated immediately north of the thrust zone display the monoclinal structure with schistosity surfaces being parallel to the direction of the dislocation. The tectonic structure of the area must have been coeval with and formed by thrust movements which took place along the boundary between the two blocks. The dislocation zone itself is, however, of the key importance to prove validity of the idea presented here. The zone can be studied in two places: on Vimsodden and on the foreland of Werenskioldbreen, being there relatively wide (100-300 m). It is composed of diaphthoritic schists (sericite-chlorite and chlorite-biotite ones) containing better or worse preserved lenses of preexisting rocks, belonging to the Eimfjellet Group and displaying more advanced metamorphism (amphibolites and metagranites, Smulikowski 1968). The strike and dip of the diaphthorite schistosity (ca. 300°/60-807SW) reflects the current orientation of the whole dislocation zone, but its original dip could be quite different. Considering the significant thickness of this zone with predominace of plicative deformations, it is quite probable that the dislocation forms a steep thrust while shearing and thrusting movements took place under p-T conditions of greenschist facies with simultaneous diaphthoresis of rocks forming the southern tectonic block. 306 In light of new data collected during geological mapping, it seems viable to propose some changes in the lithostratigraphic division of the Precambrian part of the Hecla Hoek Succession atHornsund (Birkenmajer 1975,1981,1990,1992) as shown on Figure 1. The basic change results from the presence of the two distinguished, independent tectonic units (blocks). The southern region is built of rocks belonging to the I s b j ó r n h a m n a and Eimfjellet groups. The latter is limited here to quartzites and metavolcanites occurring south of the dislocation which separates the two blocks. Within the northern tectonic block the boundary separating the whole complex into two structural units is formed by the natural surface of unconformity (Torellian) which lies at the base of the Slyngfjellet conglomerates. A thick sequence of metasediments occurring below this unconformity has been included into the D e i l e g g a G r o u p and a new internal division of this group has been based on distinguished sedimentary megacycles (metaarenites -> metapelites -» carbonate rocks). In turn, the lithologically differentiated series of metasediments and metavolcanites of the upper structural unit has been included into the Sofiebogen G r o u p which contains — as accepted here — all rocks resting above the Torellian unconformity. To the I s b j ó r n h a m n a G r o u p , there belongs a clastic-carbonaceous sequence, metamorphosed under conditions of amphibolite facies, consisting of mica and carbonate-mica schists, paragneisses and marbles. In the mica schists, along with almandine there appears disthene or staurolite, and in carbonate-mica schists and Ca-rich paragneisses the presence of Ca-scapolite has been confirmed. Rocks rich in carbonate minerals occur in the middle part of the profile, what has enable division of the group into three formations (Skoddefjellet, Ariekammen, Revdalen). During field work, a concordant contact of sedimentary nature was observed in many places between the Isbjórnhamna and Eimfjellet groups (intercalation of mica schists with garnets in the lowermost part of the feldspar quartzite sequence in the Skjerstranda Formation). Hence, the Isbjórnhamna Formation cannot be regarded as the crystalline basement of the remaining part of the Hecla Hoek Succession. Extent of the E i m f j e l l e t G r o u p has been here limited to the quartzite-amphibolite series of the southern tectonic block. Detailed mapping has allowed to present a slightly different internal division of this group. First of all, it has been found that quartzites building the Gulliksenfjellet massif occur within a vast syncline, so they rest both structurally and stratigraphically above metavolcanites. In turn, the position below amphibolites (and above the Revdalen schists) occupies another metaarenite complex, lithologically definitely different from the Gulliksenfjellet Formation. Therefore, it has been decided to include grey quartzites rich in K-feldspars, underlying the amphibolites, into a separate lithostratigraphic unit — the Skjerstranda Formation, and to limit the extent of the Gulliksenfjellet Formation to the white and greenish, monomictic quartzites, occupying the position in the upper part of the group profile. 307 The Skjerstranda quartzite is overlain by a schist-quartzite-amphibolite sequence with the first metagranitoid horizon. The sequence resembles lithologically the Steinvikskardet Formation of Birkenmajer (1975) but does not occur close to the pass of that name. Therefore, it seems necessary to define the described here rock series with a new term—Eimfjellbreane Formation, relevant to the position of its stratotypic profile. Additionally, it was revealed during mapping that the lower (the Torbjórnsenfjellet Formation) and upper (the Brattegga Formation) parts of the Skalfjellet Subgroup cannot be clearly defined. In practice, amphibolites cropping out on the slopes of Torbjórnsenfjellet and Brattegga are indistinguishable, and — what is more important — it is not possible to identify without ambiguity the boundary between the two formations. The Gangpasset granitization zone is to separate them but it does not form a single, continuous stratigraphic horizon. Lenses of granitoid rocks occur in the lower part of the metabasites as two thin levels. They can be characterized as enclaves, elevated from deep parts of a magma chamber and deposited in different basalt flows. Genesis of anorthosite metagabbro blocks with the plagioclase cummulative structure (the Angellfjellet amphibolites) could be similar. They contain bands of ultramafic cummulates rich in magnetite and ilmenite, and separate blocks display the presence of irregular aplite veins. The division of the whole metavolcanite sequence into two parts (formations) seems to be more viable. The lower one (amphibolites with the two metagranitoid horizons plus the discontinuous level of anorthosite metagabbros) correspond petrographically with the Skalfjellet Subgroup and, therefore, it is proposed to preserve that name but ranked only as a formation (the Skalfjellet Formation). In the upper part of the metavolcanite sequence, there occur acid volcanites (metarhyolites, feldspar-quartz felses, muscovite and biotite schists). This bimodal volcanic series crops out mainly in the Bratteggdalen area therefore it has been distinguished under that name (the Bratteggdalen Formation). Withdrawal of the Werenskiold glacier made accessible many good outcrops on its foreland what has enabled correlation of the Eimfjellet Group profile with the lower fragment of the Vimsodden Subgroup (sensu Birkenmajer 1975). Due to that, the series of acid pyroclastic rocks (muscovite schists and rhyolite metaconglomerates) lying above the Gulliksenfjellet quartzites has been discerned as a separate lithostratigraphic unit with a proposed name of the Pyttholmen Formation. When analysing spatial distribution of the distinguished formations as well as variability of their thicknesses and lithological compositions, it has been concluded that the Eimfjellet Group metavolcanites form a paleostructure of the central volcano type. The metavolcanites reach their maximum thickness and variability in the Eimfjellet area and just there a center of volcanic activity should be localized. In peripheral areas (Skjerstranda-Gulliksenfjellet, Fugleberget) the 308 amount of quartzites increases in both the Skjerstranda and Gulliksenfjellet formations. Thus, sources of clastic material for those formations should be traced somewhere south-west or south of the paleovolcano. The volcanic Eimfjellet series is bimodal and its metabasites are of the continental tholeitic type. They represent differentiates of at least two primordial magmas, formed from remelting of mantle rocks, depleted to a different degree with incompatible elements. An intraplate, continental character of the Eimfjellet series is additionally underlined by the presence of exceptionally K-rich rhyolite lavas and enclaves of the A-type granitoids. Differentiation of geochemical features of metabasites, the presence of numerous enclaves (granitoids and gabbros, including anorthosite gabbro) and also bimodality of the whole series can prove its connection with deep-seated magma sources, probably in the lower part of the lithosphere, on its boundary with the mantle. Rocks of the D e i l e g g a G r o u p build the lower structural stage of the northern tectonic block and cropp out in the eastern part of the mapped area. The group is composed of a thick series of various phyllites (metapelites) and laminated quartzite schists (metamudstones, metasiltstones), with numerous intercalations of quartzites (metaarenites) and with three thick intercalations of carbonate rocks. The three horizons have just made possible not only establishing in the field the succession of rock strata but also recognition of general features of the tectonic structure. Thefirst horizon crops out in the Slyngfjellet, Strypegga and Solheimfjellet massifs and consists of yellow-weathered dolostones, grey and black calcite marbles and subordinate carbonate schists. The second one is built entirely of carbonate schists — yellow at the base with leaf-like fissibility, getting brown-weathered and plate-like upwards. The third level is made up of grey dolostones and black and grey calcite marbles, being accompanied by characteristic black phyllites with chloritoid and rich with metaanthracite substance. Thick layers of quartzites border dolostones of the first and third horizons. The quartzites in question gradually pass into layered quartzite-phyllite series in which both the amount and thickness of metaarenite beds decrease. These observations formed a basis of distinguishing three sedimentary cyclothems with the following succession: metaarenites -* metapelites -» carbonate rocks within the sequence of the Deilegga Group. Accepting this division, the lithologic profile of the group has been constructed. Independently, among rocks of the quartzite-phyllite series of the 2nd cyclothem (in outcrops on the western arete of Syngfjellet), there were found relics of the cross bedding. The succession of strata, recognized due to this bedding corresponds well with that resulting from identification of sedimentary cyclothems. As the result, three formations have been distinguished (Strypegga, Skilryggbreen and Deileggbreen), equivalent to the three successive cyclothems, of which only the middle one is fully developed. Having established the succession of strata, it must be accepted that the whole sequence of the Deilegga Group are lying in the overturned position. Im309 mediately below the Torellian unconformity, there occur the oldest rocks, and structurally below them follow younger and younger one. In light of that, the Skilryggen-Vrangpeisen antiform forms a false anticline within the range of Deilegga Group otucrops. In the northern part of Wedel Jarlsberg Land a similar structure has been recognized (Bjornerud 1990). The youngest rocks, lying above the Torellian unconformity, were included into theSofiebogen G r o u p . Within the stratotype area, the group consists of three different rock-type units: metaconglomerates -» dolostones -> phyllites. Directly on rocks of the Deilegga Group, there rest the Slyngfjellet conglomerates, overlying in various places different lithosomes of the group in question. In the north-western part of the studied area, the conglomerates occur as two or three thick layers, separated by massive sequences of greenstones. Those metavolcanites, synchronic with the Slyngfjellet Formation, have been distinguished as an independent formation (the Jens Erikfjellet greenstones). There are three units recognized within the profile of the greenstones. The lower one consists mainly of greenschists of tuffogenic origin and a single layer of black greenstones, pigmented by Fe-Ti oxides. The middle one can be distinguished by intercalations and laminae of multicoloured metacherts and lenses of plagiophyric greenstones. In the upper unit, bedded and laminated, mostly tuffogenic greenstones prevail, with lenses of characteristic epidotites and intercalations of light-grey „porphyrites". The Jens Erikfjellet greenstones occur as a prism, with a maximum thickness in its southern part (close to the Vimsodden-Kosibapasset dislocation), wedging out northwards. The metabasites are uncommonly unique as far as their geochemistry is concerned, they show tholeitic differentiation trend and carry significant traces of contamination with a material of the continental crust. They were fractionated in a shallowseated magma chamber which was being emptied in a sudden manner: the most differentiated lavas rest at the bottom of the volcanic series, and rocks less differentiated can be found in its uppermost part. The Jens Erikfjellet greenstones display features of continental basalts, associated with rifting (as inferred by the presence of conglomerates). On the slopes of the Wernerknatten, a system of greenstone dykes has been found; they intersect prefolded phyllites and dolostones of the Deilegga Group. Sometimes, the dykes have both-sided thermal contacts well preserved. The greenstones form textural and chemical analogues of the Jens Erikfjellet metavolcanites, most probably the former acted as feeders to the latter. These observations set indirectly the age of the Jens Erikfjellet Formation volcanites as younger ones than the rocks of the Deilegga Group. Above the Slyngfjellet metaconglomerates and Jens Erikfjellet greenstones, there rest a relatively thin series of grey dolostones with intercalations of black calcite marbles and carbonate schists. The series increases its thickness northwards and is more diversified in the same direction. Among the dolostones on the 310 slopes of Bratthó, there appear minute lenses of cherts and intercalations of sedimentary breccias of several types (fragments of cherts in dolostone, fragments of dolostones in cherts, and ordinary dolostone breccias). Despite some differences in their lithology and thickness, the rocks can be compared with and identified as the Hóferpynten Formation. The differences result, most probably, from facial variability. Above the carbonate rocks, there occurs a thick complex of dark-grey and black phyllites, with a sequence of greenish phyllites in the middle, and with few thin intercalations of grey and black quartzites. The complex has been included into the Gashamna Formation, from which it differs only in lesser amount of quartzite intercalations and in higher degree of recrystallization. In particular, the characteristic intercalation of greenish phyllites strongly resembles the rock cropping out in Soflebogen. In the approach presented here, also the middle part of the Vimsodden sequence (the Vimsodden Subgroup sensu Birkenmajer 1975) has been included into the Soflebogen Group. This refers to the rocks situated between the belt of diaphthoritic schists, separating the northern and southern tectonic blocks, and greestones and metaconglomerates cropping out on the western foreland on the Jens Erikfjellet. The basic argument supporting such an idea is seen in relics of the cross bedding, identified in layers of metaarenites, exposed on Elveflya. The relics indicate a reverse succession of strata (they are getting younger southwards, not northwards), contrary to the previously suggested opinion. It has also been found that sizes of pebbles, occurring in numerous here layers of conglomerates with fractional bedding, decrease from north to south. The observation prove that the Vimsodden sequence lies stratigraphically above the Syngfjellet metaconglomerates and Jens Erikfjellet greenstones, hence it is younger than the two rock units. The distinguished part of the Vimsodden sequence has been described as the Elveflya Formation. It consists successively of: (1) green and black carbonate-mica schists with intercalations of yellow quartzites; (2) black muscovite-paragonite schists with chloritoid, and subordinate, thin layers of quartzites; (3) carbonate-mica schists with intercalations of grey marbles and yellow quartzites, and with two thick complexes of metaconglomerates at the top; (4) again black muscovite-paragonite schists with chloritoid. The amount and thickness of quartzites intercalations increase eastwards while the thickness of marbles increases westwards. In the middle part of the Elveflya Formation in the carbonate-mica schists, there were observed singular, isolated minute pebbles — they can be interpreted as dropstones. In such a case, at least a part of the Elveflya Formation can correspond stratigraphically to the Kapp Lyell tillites, known from the Bellsund area and correlated with glaciation of the Wendian age. The Vimsodden-Kosibapasset dislocation, separating the northern and 311 southern tectonic blocks, represents probably a deep-seated fracture which displayed multiphase tectonic and igneous activity. It is the matter of discussion whether this disjunction formed a boundary between various terranes. From the spatial distribution of the Eimfjellet and Jens Erikfjellet volcanites it can be guessed that in two different geological periods the disjunction served as a passage for ascending magmas. During sedimentation of rocks of the Sofiebogen Group, the dislocation formed a boundary between a more stable block just south-west of the dislocation (Hóferpynten, Dunóyane, Isóyane) and a tectonically active area to north-east of it which was being subsided (Fannytoppen, Tonedalen, Krakken). In the area of the southern block, where the Slyngfjellet conglomerates either does not exist or are very thin, carbonate rocks of the Hóferpynten Formation reach great thicknesses and are developed as shallow-water facies on a stromatolitic carbonate platform. Thick series of conglomerates were deposited north-east of the dislocation having been accompanied by tholeitic lava flows (the Jens Erikfjellet Formation). Carbonate rocks, equivalents of the Hóferpynten Formation, are here not so thick, do not contain stromatolites, and are characterized by numerous breccias and schist intercalations (a slope of the carbonate platform?). During Caledonian movements, the Vimsodden-Kosibapasset dislocation acted as a thrust zone. Rocks of the northern block was being progressively metamorphosed under conditions of greenschist facies while in the southern block zones of diaphthorites, arranged parallel to the dislocation, were formed simultaneously. Igneous and tectonic reactivation of the area took place in Cretaceous what was associated with an early stage of opening of the northern Atlantic. The following data indicate that the Vimsodden-Kosibapasset dislocation behaved as a sinistral strike-slip fault at that time. (1) Three thick dolerite dykes with latitudinal strikes (Hyttevika-Eimfjellet, Eimfjellet-Tuva, Flatryggen-Princessetoppen) are arranged en echelon. Such a system of tensional fractures, later filled up by a magma, could be connected with a sinistral strike-slip zone. (2) Dolerite dykes with longitudinal strikes on Vimsodden are intersected by faults and displaced in a manner indicating just a sinistral strike-slip movement. However, some segments of the dykes display also the NW-SE strikes. (3) Sets of small faults and fractures in schists on Vimsodden (with the WNW-ESE and SW-NE strikes), found by Birkenmajer (1986), can be interpreted as — respectively — low- and high-angle sets of shear fractures associated with a NW-SE strike-slip zone. (4) Minute folds with axes dipping to SW at 50-70° (Birkenmajer 1986), also occurring on Vimsodden, result — most probably — from tension characteristic of strike-slip movements. A simple compression along WSW-ENE would create also minute folds but rather with horizontal axes. Cretaceous dolerite dykes within the southern tectonic block are intersected 312 by normal faults trending NNW-SSE with fault faces dipping steeply to SW. These faults seem to be the only signes of the Tertiary tectonic rejuvenation in the Hornsund area. Thees disjunctions together with smaller accompanied fractures carry mineralization of quartz and Fe-bearing carbonates with lesser pyrite and Cu, Pb, and Zn ores. These observations contradict previously presented opinions on the age of the carbonate-polymetallic mineralization (Birkenmajer & Wojciechowski 1964). REFERENCES Birkenmajer, K., 1975: Caledonides of Svalbard and plate tectonics. Bull. Geol. Soc. Denmark, 24: 1-19. Birkenmajer, K., 1981: The geology of Svalbard, the western part of the Barents Sea and the continental margin of Scandinavia. In: Nairn, A. E. M., Churkin, M. Jr. & Stehli, F. G. (eds.). The Ocean Basins and Margins, 5: 265-329. Plenum Press. New York. Birkenmajer, K., 1986: Tertiary tectonic deformations of Lower Cretaceous dolerite dykes in a Precambrian terrane, south-west Spitsbergen. Stud. Geol. Pol., 89: 31-44. Birkenmajer, K., 1990: Geology of the Hornsund area, Spitsbergen. Explanations to the map 1:75,000 scale. (3-42). Uniwersytet Śląski, Katowice. Birkenmajer, K., 1992: Precambrian succession at Hornsund, south Spitsbergen: a lithostratigraphic guide. Stud. Geol. Pol., 98: 7-66. Birkenmajer, K. & Wojciechowski, J., 1964: On the age of ore-bearing veins of the Hornsund area, Vestspitsbergen. Stud. Geol. Pol., 11: 179-184. Bjornerud, M., 1990: Upper Proterozoic unconformity in northern Wedel Jarlsberg Land, southwest Spitsbergen: Lithostratigraphy and tectonic implications. Polar Research, 8 (2): 127-140. Smulikowski, W., 1965: Petrology and some structural data of lower metamorphic formations of the Hecla Hoek Succession in Hornsund, Vestspitsbergen. Stud. Geol. Pol., 18: 1-107. Smulikowski, W., 1968: Some penological and structural observations in the Hecla Hoek Succession between Werenskioldbreen and Torellbreen, Vestspitsbergen. Stud. Geol. Pol., 21: 97-161. Addresses of the authors: mgr inż. Jerzy Czerny, mgr inż. Adam Kieres, prof, dr hab. Andrzej Manecki, mgr inż. Maciej Manecki, dr hab. inż. Jacek Rajchel, University of Mining and Metallurgy, Faculty of Geology, Geophysics and Environmental Protection, al. Mickiewicza 30,30-059 Kraków, Poland MAPA GEOLOGICZNA SW CZĘŚCI ZIEMI WEDELA JARLSBERGA W SKALI 1:25 000 Streszczenie Prezentowana mapa stanowi końcowy efekt prac kartograficznych wykonywanych w latach 1985-1990 w rejonie Hornsundu przez zespół geologów z AGH. Mapa obejmuje fragment wybrzeża Spitsbergenu na północ od fiordu Hornsund, pomiędzy lodowcami Torella, Vrangpeisa i Hansa. W obszarze tym odsłaniają się skały metamorficzne wieku prekambryjskiego, należące do kaledońskiego fundamentu Svalbardu. Podczas prac kartograficznych zebrano nowe dane pozwalające uzupełnić dotychczasowy obraz budowy i historii geologicznej badanego obszaru. 313 S£rkapp Land Group Sofiokammen Croup K a p p Lyoll T l l l i t e s C&shamna Phyllites Sofiebogen (Fm) Group Conglomerates (F«. ) Delleggbreen Deilegga Group Formation Formation Pyttholmen J e n s E r i k f j e l l e t G r e e n s t o n e s (Fm. ) Formation Skilryggbreen Strypegga < C T u v a Carbonates (Hb.) Tuva Phyllites (Hb.) Koslbapasset Hecber Skllryggen Calcareous Shlsts Tonefjellet НешЪег Slyngfjellbreen Dolostones (Mb. Broddegga Quartzltes (Hb.) Formation G u l l i k s e n f j e l l e t Q u a r t z l t e s (Fn. ) Eimfjellet Group Bratteggdalen Skilfjellet Formation Formation ElmfJellbreane Skjerstranda Bevdalen IsbJQrnhamna Group Formation Formation Formation Ariekammen Formation Skoddefjellet (Mb.) Formation Fig. 1. Lithostratigraphy of the Hecla Hoek Succession in Wedel Jarlsberg Land ) Vlmsa Member Tonefjellbreen Hb. Rundlngen Member