NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 305

Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone, , , North

Tore Herrevold, Roy H. Gabrielsen & David Roberts

Herrevold, T., Gabrielsen, R.H. & Roberts, D.: Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone, Varanger Peninsula, Finnmark, North Norway. Norwegian Journal of Geology, vol. 89. pp. 305-325, Trondheim 2009, ISSN 029-196X.

Structural studies in the Late Riphean to Vendian succession of the southeastern part of the Trollfjorden-Komagelva Fault Zone on Varanger Peninsula, Finnmark, have revealed the presence of two main sets of contractional structures, here grouped into D1 and D2 events. These folding and cleavage-forming episodes are superseded by two, separate extensional events, D3 and D4. Although only one of these four events (D3) has been directly dated in the actual study area, the probable ages of the disparate, contractional deformation episodes can be deduced from published geochronological data in neighbouring parts of Varanger Peninsula or Northwest Russia. The deformation history of this area shows the following sequence of main events: (1) Inversion of the pre-existing, , basinal regime occurred during an episode of SW-directed shortening, folding and associated cleavage development, with reverse faulting and minor sinistral strike-slip movements along the Trollfjorden-Komagelva Fault Zone. By comparison with the situation on the nearby Rybachi and Sredni Peninsu- las in NW Russia, this D1 deformation and low-grade metamorphism is likely to have occurred during the Timanian orogeny at about 570-560 ± 10 Ma. (2) The D2 event represents the main Caledonian deformation and is characterised by SE-directed shortening (NE-SW-trending folds and NW-dipping cleavage) that gave rise to a moderate dextral strike-slip displacement along the Trollfjorden-Komagelva Fault Zone. Based on recent geochronology from NW Varanger Peninsula, this major contractional, epizone event is considered to be late-Finnmarkian, c. 470-460 Ma. It is likely that Siluro-Devonian Scandian deformation in the study area and along the fault zone was largely of brittle character. (3) A regional, extensio- nal event, D3, is reflected in N-S fracturing and dolerite dyke intrusion. The dyke intrusion is dated to Late Devonian time at c. 375-370 Ma. (4) A younger extensional event, D4, is manifested in dip-slip normal faulting along and adjacent to the main fault zone, with breccias, gouge and quartz- calcite veining. The age of this episode is open to speculation – from Carboniferous to Cretaceous – but a Mesozoic reactivation seems highly likely based on our knowledge of offshore geology.

Tore Herrevold, Total E & P AS, PO Box 168, 4001 Stavanger, Norway ([email protected]). Roy H. Gabrielsen, Department of Geosciences, University of Oslo, P.O. Box 1047, NO-0316 Oslo, Norway. David Roberts, Geological Survey of Norway, NO-7491 Trondheim, Norway.

Introduction The peninsula is divided into two distinctive northern and southern regions by the NW-SE- to WNW-ESE- The geology of Varanger Peninsula in East Finnmark, trending Trollfjorden-Komagelva Fault Zone (TKFZ) , is now well known through the (Siedlecka & Siedlecki 1967) (Fig. 1). The southern, systematic mapping, and stratigraphic and sedi- Tanafjorden-Varangerfjorden Region (TVR) comprises mentological studies of Siedlecka & Siedlecki (1967, 1971, what is mostly an autochthonous/parautochthonous, 1972), Banks et al. (1971, 1974), Siedlecka (1972, 1985), pericratonic/platformal, diagenetic to mid-anchizone, Siedlecki (1980), Pickering (1981, 1982, 1985), Edwards sedimentary succession ranging in age from Late (1984), Rice (1994) and Røe (2003). Complementing Riphean (Tonian-) to Early Cambrian this work there have been diverse investigations on (Banks et al. 1971, Siedlecka et al. 1995a) (Fig. 2). Close metamorphism (Bevins et al. 1986, Rice et al. 1989a), to Tanafjorden, however, these same rocks occur in micropaleontology (Vidal 1981, Vidal & Siedlecka 1983), allochthonous position, as part of the anchizone Gaissa palaeomagnetism (Kjøde et al. 1978, Bylund 1994a, b, Nappe Complex (Lower Allochthon), and the succession Torsvik et al. 1995) and mafic dykes (Beckinsale et al. 1975, reaches up to Early Tremadoc on the nearby Digermul Roberts 1975, Rice & Reiz 1994, Rice et al. 2004), as well Peninsula (Reading 1965, Nikolaisen & Henningsmoen as structural geology and tectonics (Roberts 1972, Rice et 1985). In innermost Varangerfjorden the diagenesis- al. 1989b, Karpuz et al. 1993) and 40Ar/39Ar geochronology grade succession lies unconformably upon a Neoarchaean (Dallmeyer & Reuter 1989, Guise & Roberts 2002, Rice & crystalline basement (Føyn 1937, Siedlecki 1980, Rice et al. Frank 2003, Kirkland et al. 2008). A detrital zircon study of 2001), and is disrupted by several internal unconformities. several of the formations occurring on Varanger Peninsula In contrast, the northern Region (BSR) – also is also in progress (Roberts et al. 2008). called the Northern Varanger Region by some authors 306 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 1. Principal structural elements of the Varanger Peninsula, Finnmark, northern Norway (mainly after Siedlecki (1980) and Karpuz et al. (1993)). BSR – Barents Sea Region (Barents Sea and Løkviksfjellet groups, and Berlevåg Formation). TVR – Tanafjorden-Varangerfjorden Region (Vadsø, Tanafjorden and Vestertana groups). The grey ornamented area in the extreme northwest is the Berlevåg Formation of the Tanahorn Nappe. The lined area in the extreme southwest is the Archaean crystalline basement. TKFZ – Trollfjorden-Komagelva Fault Zone. The inferred eastward extension of the sole thrust-fault to the Parautochthon is taken from Sygnabere (1997). The inset map in the upper right corner shows the Trollfjorden-Komagelva Fault Zone and its southeastern continuation (SRFZ) onto the Rybachi and Sredni Peninsulas in Northwest Russia. SRFZ – Sredni-Rybachi Fault Zone. The study area is indicated by the rectangle. NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 307

Fig. 2. Lithostratigraphic successions, Varanger Peninsula. Columns 1 and 2 are from the Tanafjorden-Varangerfjorden Region, southwest of the TKFZ, and column 3 from the Lower Allochthon of the Barents Sea Region. Note that two amendments have been proposed for the strati- graphy shown in Column 1; the Ekkerøya Formation may possibly be raised to group status (Rice & Townsend 1996); and it has been suggested that the Veidnesbotn Formation may be equivalent to the Gamasfjellet Formation (Røe 2003).

(e.g. Rice 1994) – consists largely of slightly higher-grade revealed that structures ascribed to the Vendian-age (epizone), allochthonous, basinal to deltaic successions Timanian orogeny are almost certainly represented in of Late Riphean-Vendian () age in western the northeastern parts of Varanger Peninsula (Roberts and central areas (Siedlecka & Roberts 1995, Siedlecka 1995, 1996, Roberts & Olovyanishnikov 2004). The et al. 1995b) (Fig. 2). These rocks are considered to TKFZ extends southeastwards along the coastline represent a thrust sheet (Rákkočearru thrust sheet: of Kola Peninsula, NW Russia (known there as the Roberts 2009) of the Lower Allochthon, and are overlain Karpinskiy Line), and farther southeast into the Timans by middle greenschist-facies, mostly turbiditic rocks of as the Central Timan Fault (Olovyanishnikov et al. the Tanahorn Nappe (part of the Middle Allochthon) 2000). To the northwest of Varanger, the fault zone can in the extreme northwest (Laird 1972, Levell & Roberts be traced offshore north of Magerøya as a system of 1977, Rice et al. 1989a, Rice & Frank 2003). These thrust WNW-ESE-trending fault segments transecting the units are clearly imaged immediately offshore on newly Finnmark Platform, and passing across the Hammerfest acquired aeromagnetic data (Gernigon et al. 2008, Basin towards the southern flank of the Loppa High Barrère et al. 2009). where it seems to terminate (Lippard & Roberts 1987, Gabrielsen & Færseth 1989, Jensen & Sørensen 1990). The TKFZ thus constitutes a major, crustal lineament and Clearly, this fundamental crustal lineament has been there is evidence to suggest that its deep-seated precursor multiply reactivated from Precambrian to Cenozoic time, fault may have originated in Archaean time and formed and along segments of the fault in parts of NW Russia a major terrane boundary (Karpuz et al. 1995, Roberts it is seismically active even today. The principal phase et al. 1997). Subsequently, it functioned as a normal of dextral strike-slip translation along the TKFZ is now fault during a long period of Late Mesoproterozoic to considered to be of Ordovician age (Rice & Frank 2003). Neoproterozoic, passive-margin sedimentation, and was later reactivated several times in contractional, On Varanger Peninsula, the only published, structurally strike-slip and extensional regimes (Siedlecka & oriented study undertaken along the TKFZ is that of Siedlecki 1967, Rice et al. 1989b, Karpuz et al. 1993). Karpuz et al. (1993) from central parts of the fault zone. The fault is most commonly cited as a dextral strike-slip This involved a synergistic approach integrating multiple lineament by virtue of the difference in metamorphic datasets from the entire peninsula. In addition to this grade and intensity of folding across the structure, work, discussion of the evidence for dextral strike-slip and both duplexes and positive flower structures have was presented by Rice et al. (1989b), and structural been reported by Lippard & Roberts (1987), Rice et information from a small area along the southern margin al. (1989b) and Karpuz et al. (1993). Although the of the TKFZ inland from the present study area has been metamorphism and folding had earlier been considered reported by Sygnabere (1997). The present contribution as wholly Caledonian (e.g., Roberts 1972, Bevins et al. serves to report the results of an investigation of folds, 1986, Rice et al. 1989a), work on the Rybachi and Sredni cleavages, fractures and vein arrays concentrated in the peninsulas in nearby Northwest Russia during the 1990s southeastern part of the fault zone in the Komagelva- 308 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 3. Principal structural features of the Komagelva- area (the study area), based on the present fieldwork with some information from Siedlecki (1980). Symbols for some of the structures are enlarged, and are therefore not to scale. Encircled numbers are localities referred to in the text.

Komagnes area (Fig. 3), and thus aims to provide a better based on regional structural correlations, to suggest the coverage and understanding of the entire fault zone. likely orogenic ages of particular fold generations and Here, it has been possible in many outcrops to discern associated cleavages. the relative ages of certain structures and, moreover, NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 309

main sets oriented ENE-WSW and WNW-ESE, with a Structures associated with the subordinate set trending NNE-SSW (Fig. 4c). On outcrop Trollfjorden-Komagelva Fault Zone scale, the lineaments of the two main sets are commonly seen to represent either a close jointing or shear zones which generally show minor dextral displacements. On Varanger Peninsula, the Trollfjorden-Komagelva Fault Zone defines a regional lineament approximately Mesoscopic and even smaller-scale folds are best 75 km in length and varying between 1 and 5 km in developed along and close to the southwestern width (Fig. 1). Its internal structure is characterised by an escarpment to the main fault zone. Open to close, anastomosing or braided lineament pattern (Gabrielsen upward-facing folds trending between NE-SW and & Ramberg 1979, Gabrielsen 1984, Rice et al. 1989b, ENE-WSW with southeasterly vergence and an axial Karpuz et al. 1993). The main lineaments are mostly planar, spaced cleavage in pelitic lithologies are the topographic, and most of the escarpments along the most common structures, but a few NW-SE-trending fault zone coincide with fracture sets or faults which folds verging southwest are also present. Some of these are parallel or slightly oblique to the main fault (Karpuz folds (both NE-SW and NW-SE trending fold axes) et al. 1993), producing lensoid, contractional duplex have associated low-angle or high-angle reverse faults structures (Rice et al. 1989b). with small offsets. Also present along this fault zone margin are quartz- and calcite-filled vein arrays, the In the study area (Fig. 3) the river Komagelva flows most common being a steep to moderately dipping set roughly parallel to the trend of the main fault zone, striking parallel to the main trace of the TKFZ (Fig. 5b). and deflections along its course are partly structurally Calcite veinlets along the surfaces of the fold-related, controlled (Karpuz et al. 1993). The fault zone is NE-SW-oriented reverse faults show slickensides and topographically defined by a broad, approximately steps indicative of top-to-the-southeast transport. There 5 km-wide, alluvial plain, narrowing inland to the are also lenses of intensely brecciated rock trending northwest, and bordered by escarpments both to the NW-SE and up to 15 m in length, with steeply dipping northeast and to the southwest. Along these opposing sheared margins. The comminuted matrix to these lenses escarpments the degree of exposure is fairly good, is cemented by baryte and iron oxides. Here it can be particularly along the northeastern margin. In contrast, mentioned that baryte mineralisation has been reported exposures are rare along the river course, which defines from similar cataclasites and breccias in northwestern the assumed central part of the fault zone. parts of the trasé of the TKFZ (Sandstad 1987).

The coastal section of the study area offers excellent The coastal exposures and raised cliffs in the vicinity exposure at every headland, but again, the central of Komagnes (Fig. 2) offer the best opportunities for fault zone is unfortunately not exposed. North and studying meso-scale shear zones, cleavages and a few south of the TKFZ in the study area, the topography small-scale folds. There, several ENE-WSW-striking is characterised by an undulating terrain that offers shear zones are exposed, with local micro-brecciation only scattered exposures. The inland part of the fault and rare development of duplex and flower structures zone is separated from its less deformed northeastern (Fig. 6). Both transpressional and transtensional dextral and southwestern margins by prominent, topographic displacements have been recorded, and some of the faults escarpments with elevations varying between a few tens are reactivated by dip-slip normal movements. Along of metres to more than 100 metres. this c. 600 m-long shore section, the most prominent structures in the thin-bedded, maroon mudstones and In the following, we first describe the structures and vein grey silty are spaced cleavages, one oriented arrays observed in different parts of the study area, and NE-SW to ENE-WSW and dipping at a moderate angle to then discuss the various structures in terms of stages, i.e., the northwest (Fig. 7a), and the other striking c. WNW- relative ages, of deformation in a kinematic framework. ESE and dipping north-northeast. At this shoreline Finally, suggestions are made with regard to the likely locality, the two cleavages show clear intersection ages of these structures in a more regional context. lineations on bedding surfaces (Fig. 7b) with the c. NE-SW-trending cleavage being the more penetrative The area south of the TKFZ of the two. This feature is particularly noticeable at low tide. These cleavages clearly correlate with the folds An E-W-trending, upright, gentle to open syncline, with and cleavages noted above from outcrops along the thin-bedded, cleaved shales and silty sandstones of the southwestern escarpment. Moreover, at Komagnes the Innerelva Member of the Stappogiedde Formation in its NW-dipping cleavage is axial planar to small-scale, core dominates the geology of the southern part of the SE-verging folds, some of which carry cleavage-parallel study area (Fig. 3). A smaller, parallel anticline is also reverse faults with offsets of a few centimetres. present closer to the main fault zone. In this southern area, lineaments marking topographic features and The Komagnes locality is also well known from the mapped from aerial photographs are grouped into two presence of 3-4 mafic dykes, most clearly seen in the 310 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 4. Contoured, equal-area, lower-hemisphere projection and azimuth-frequency rose dia- grams of fractures measured in the field; (a) the region northeast of the Trollfjorden-Komagelva Fault Zone, (b) the northeastern fault margin, (c) the southwestern fault margin, and (d) the region southwest of the fault zone.

old raised cliff just north of the road but also exposed cleavage; and the dyke itself is cut by transverse joints. on the shore at low tide. The main dyke, which actually Various earlier investigations, geochronological and consists of at least two parallel dykes, trends c. N-S paleomagnetic, have resulted in differing ages for these and dips 75º east, but in the intertidal zone it splits dykes, either Devonian (Beckinsale et al. 1975) or Late into several thinner dykes and dykelets. Adjacent to Vendian (Torsvik et al. 1995), but a Late Devonian age the main composite dyke in the raised cliff there is a has been confirmed by 40Ar/39Ar dating of plagioclase prominent NNW-SSE-trending close jointing or fracture separates (Guise & Roberts 2002). NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 311

Fig. 5. Contoured, equal-area, lower- hemisphere projection and azimuth- frequency rose diagrams of quartz- and calcite-filled veins found along (a) the northeastern margin and (b) the southwestern margin of the Troll- fjorden-Komagelva Fault Zone.

Fig. 6. Secondary shear zones with flower structures at the southern border of the Trollfjorden-Komagelva Fault Zone, developed in siltstones of the Innerelva Member of the Stappogiedde Formation at locality 2 (Fig. 3) just southwest of Komagnes. The two, vertical faults strike at N50°E and belong to one and the same strike-slip system. They can be followed along strike over a distance of more than 100 m. (a) The northern fault, looking northeast. Note the series of half-flowers developed at restraining bends. The half-flower structure in the central part of the photo is 30 cm in width. (b) Positive flower structure developed along the southern fault, looking northeast. This structure is not associated with a restraining bend, demonstrating the dextral transpressional nature of the strike-slip system. Side of compass in the foreground is 12 cm.

Figure 6 312 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 7. (a) Strongly cleaved (S2), thin-bedded and laminated pelitic rocks of the Stappogiedde Formation, Komagnes; looking northeast. (b) Photo looking down onto a near-horizontal bedding surface at the Komagnes locality showing intersections on bedding of the S1 (yellow pencil) and S2 (green pencil) cleavages. The narrow end of the white pen is pointing almost due north. (c) Penetrative spaced cleavage (S1) in interban- ded sandstones and silty claystones of the lower member of the Båsnæringen Formation, Grunnes; looking northwest. The notebook is lying on a bedding surface. (d) Strongly developed spaced cleavage (S1) in silty claystones in the hinge zone of a large-scale D1 fold, from the foreshore in the bay Laukvika, 2 km east of Grunnes; looking southeast. In the underlying , S1 is more of a fracture cleavage but the cleavage is poorly developed in, or swings around, the two ball-and-pillow type structures in the upper part of the sandstone unit.

The area north of the TKFZ common folds strike between NNW-SSE and NW-SE; Regional maps of the northern part of the study area and the folds verge southwest with a steep, NE-dipping, (Siedlecki 1980, Siedlecka & Siedlecki 1984) depict open, tightly spaced cleavage parallelling their axial surfaces NNW-SSE- to N-S-trending folds that also extend farther (Fig. 7c). In some dark grey to black mudstone beds this north to the area between Vardø and is more akin to a slaty cleavage. A few small, NE-SW- (Fig. 1). Gentle, long-wavelength, cross folds of ENE- trending, open to close folds have also been recorded. WSW trend are also present producing dome-and-basin These also carry an axial planar spaced cleavage outcrop patterns (Siedlecki 1980, Gjelsvik 1998). Along and postdate the more common NW-SE folds. This the eastern coast between Komagvær and Svartnes (Fig. deformation sequence, with the NW-SE folds predating 3), NNW-SSE to NW-SE-trending, close to tight folds the NE-SW folds, has also been reported from a with a steep NE-dipping axial planar cleavage are the wider area of NE Varanger Peninsula (Gjelsvik 1998). most prominent structural features on macro- and meso- Several steeply dipping, WNW-ESE-striking faults scale (Fig. 7c, d) and are associated with southwesterly show indications of sinistral shear, but some surfaces directed reverse faults. Quartz- and calcite-filled within the fault cores (some of which contain a 1-2 cm veins are developed in many places, and are especially thickness of gouge) denote reactivation during later, common along shear zones and reverse faults. extensional, dip-slip movements. Quartz and quartz- calcite veins are prominent features of this margin (Fig. As compared with the southwestern margin, the 5a), and dilation veins, commonly with en échelon northeastern escarpment margin is characterised by geometry, are seen in connection with flexural slip on more extensive meso-scale folding. Axes of the most macroscopic folds. NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 313

Fracture and vein populations within and adjacent to the events, here designated D1 to D4. Although each of TKFZ these may have involved more than one pulse of broadly The contrast in structural pattern between the coaxial deformation, any further subdivision into Trollfjorden-Komagelva Fault Zone and its surrounding separate deformational phases based on trend analysis areas is clearly reflected by the contoured plots and would seem inappropriate since the development of rose diagrams of fractures (Fig. 4a, b). In the region to some of the minor structures may have been controlled the south of the southwestern escarpment, NW-SE- by local factors rather than reflecting a regional stress striking fractures are far less common (Fig. 4d), whereas regime. fractures parallel to the regional lineament are abundant along the southwestern fault margin and to the north of D1 deformation the fault zone (Fig. 4a, b, c). Of particular interest is the dissimilarity in the main fracture trends between the areas This is a prominent contractional deformation event north and south of the fault margins, and the differences that affected both the northern (BSR) and the southern between these areas and the fault margins proper. (TVR) regions, though to differing degrees. Folds and associated cleavage ascribed to D1 are more common North of the fault zone, three principal sets of fractures and extensively developed in the BSR than in the area are recognised, striking NW-SE, N-S and ENE-WSW, south of the TKFZ. of which the first set is dominant (Fig. 4a). Along the northeastern fault margin, fractures striking NNW-SSE, NW-SE- to NNW-SSE-trending folds (F1). Folds of ENE-WSW and NNE-SSW are the most abundant (Fig. this generation and trend are ubiquitous along the 4b). It is particularly interesting to note the differences northeastern fault margin and in the area to the north between the northeastern and southwestern fault and northeast of the escarpment. Farther to the northeast, margins where, in the latter case, ENE-WSW, NW-SE towards Vardø and Persfjord, there is a tendency for and NNE-SSW trends predominate (Fig. 4c). In the area macrofolds and related cleavage to trend more NNW-SSE south of the southwestern fault margin, three main sets or, locally, even N-S (Roberts 1972, 1996, Siedlecki 1980, of fractures are developed, striking NNE-SSW, ENE- Rice et al. 1989b, Gjelsvik 1998). Across the northern WSW and WNW-ESE (Fig. 4d). part of the study area, the metasandstones and cleaved mudstones of the Båsnæringen Formation are deformed Stereographic plots of quartz- and calcite-filled veins into open, parallel folds with wavelengths of up to 8-10 registered along the northeastern fault margin (Fig. 5a) km. Whilst there is no pronounced asymmetry to the display mainly similar patterns to those of the fractures folds on a macro-scale, almost all mesoscopic folds are devoid of mineral growth (cf. Fig. 4b). Along this margin, asymmetric and verge to the southwest, as reflected in veins striking NNW-SSE are extremely common and the well developed, NE-dipping, axial planar cleavage appear to follow the trend of the main folds and associated (S1) described earlier (Fig. 7c, d). Locally developed cleavage. One difference, however, is that the ENE-WSW SW-directed thrusts are found in the vicinity of ramp- fracture trend (Fig. 4b) is not represented in the vein and-flat structures (Fig. 8a) and minor, steeply dipping, population. In the case of the southwestern margin, the reverse faults also indicate transport to the southwest. prevalent trend for veins is WNW-ESE (Fig. 5b), whereas Along the northeastern fault margin, contractional the dominant fracture trend is ENE-WSW (Fig. 4c). duplexes in the Godkeila Member of the formation are characterised by gently E-dipping, layer-parallel flats and The common occurrence of quartz and/or calcite veins E-W to WNW-ESE-striking ramps dipping at 50-80º to along and close to the TKFZ is generally indicative of the north. Fold axes here plunge gently WNW. Along the the presence and strong influx of hydrothermal fluids ramp faults the fine-grained sandstones are brecciated along the trace of the fault. In general, the intensity of and impregnated with segregations and veins of quartz. fracturing parallel to the fault zone diminishes markedly Quartz and quartz-calcite veins are commonly developed to the south of the southwestern margin, implying that across this northern area and appear to be associated the southern region has been relatively less affected by with the F1 folding. The most conspicuous features are the increments of semi-ductile and brittle deformation layer-parallel veins and conjugate sets of en échelon, associated with movement along this major crustal rotated, sigmoidal gash veins (Fig. 8b). At Svartnes, low lineament. angle reverse faults show well developed slickensides indicating SW directed transport (Fig. 8c).

Main deformational episodes Along the southwestern fault margin (locality 3 in Fig. 3), NW-SE to WNW-ESE-trending F1 folds in Based on the field mapping of folds, cleavages and sandstones of the Lillevatnet Member are of parallel fracture sets, the observed superposition of folds type with subhorizontal axes, wavelengths of 5-10 m and and cleavages, and the analysis of these data in this amplitudes of 3-4 m. Axial planes are generally vertical southeastern part of the TKFZ, it is possible to ascribe or dip steeply to the northeast. In map view, the axial these structures to at least four different deformational traces display a left-stepping, en échelon geometry with 314 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 8. (a) Fault-propagation fold above a ramp-and-flat thrust surface in the Godkeila Member of the Båsnæringen Formation northeast of the Trollfjorden-Komagelva Fault Zone. Fold vergence indicates transport to the southwest. Brecciation and segregations of quartz can be seen along the steep ramp fault. View to the southeast. (b) Several sets of quartz veins in the Næringselva Member of the Båsnæringen Formation along the northeastern margin of the Trollfjorden-Komagelva Fault Zone. Two conjugate sets of rotated en échelon veins are cut by arrays of non-rotated veins. In the lower left part of the photo, the rotated quartz veins are deformed by several shear bands associated with layer- parallel movement, e.g. top to the left. View to the northwest. (c) Low-angle reverse fault (ramp in a ramp-and-flat structure) with quartz vein showing prominent slickensides. Båsnæringen Formation, Svartnes, looking southeast. The pencil is pointing towards 234°. (d) Equal-area, lower-hemisphere projections of bedding (great circles), fracture cleavage (dashed great circle) and fold axes from structures found in the Vagge Formation approximately 2 km northwest of Komagnes along the southwestern fault margin. The asymmetric, S- to SW-verging folds were generated during the D1 deformation episode (e) Structural data associated with D1 contractional faults from the study area. Poles to low- angle to steeply dipping, reverse-fault planes are indicated by triangles, and plunges of slickenside lineations by stars.

respect to the TKFZ. In the mudstone units of the Vagge Stress tensors have been calculated based on fault Formation, a well developed, axial planar, tightly spaced plane orientation and slickenside information using cleavage (S1) dips at moderate angles to the NE-NNE the program Fault Kin v.3.25 (Allmendinger 1989- (Fig. 8d) and reflects the overall SW- to SSW-directed 1992). Stereographic projections of contractional and shortening in this particular subarea. In the Komagnes extensional stress axes based on fault plane data from all area (locality 2, Fig. 3), F1 folds are rare but there is a localities in the investigated area are presented in Fig. 9. clearly identifiable spaced cleavage striking WNW-ESE A contoured plot of shortening axes shows a bimodal and dipping NNE (Fig. 7b). Farther southwest, well distribution with a major cluster of mainly NE-SW- away from the fault zone, folds and cleavage of this D1 striking axes with horizontal to sub-horizontal plunges, generation appear to be lacking. and a minor cluster of mainly NNW-SSE-trending axes NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 315 with moderate to steep plunges towards both NNW and along the fault zone at this time (Fig. 10a). North of SSE (Fig. 9a). The NE-SW-trending clusters reflect the the TKFZ, on the other hand, in the eastern part of D1 palaeostress situation, and the NNW-SSE clusters the BSR, F1 macrofolds dominate the map pattern, the D2 palaeostress situation (see description of D2 thereby indicating the imposition of a more regional below). A similar plot of the stretching axes displays SW- to WSW-directed compression not confined to the a cluster of steeply and partly southerly plunging axes proximity of the actual fault zone. Another explanation (Fig. 9b). for the gradual swing in fold axial trend, from NW-SE in the Komagvær-Svartnes area to NNW-SSE or close D1 deformation: synthesis and age relations to N-S between Vardø and Hamningberg, may be as a result of drag along the main fault zone associated with Structures of the D1 event are most common along the minor sinistral movements arising from a principal fault margins and in areas to the north and northeast SW-directed compressive stress impinging on the of the Trollfjorden-Komagelva Fault Zone. South WNW-ESE-trending TKFZ (Fig. 10b). of the fault zone, the F1 folds are confined to an area quite close to the trace of the TKFZ, but even there D2 deformation they are subordinate to structures ascribed to the D2 event. It is difficult to say with certainty whether The second episode of deformation identified in the these particular F1 folds have been rotated from their study area is also contractional and represented mainly original orientation into sub-parallelism with the fault by folds and an associated axial-surface cleavage, reverse zone during a component of strike-slip movement faults and dextral shear zones. along the TKFZ, or whether they reflect a contraction directly normal to the fault trace. However, the axes NE-SW to ENE-WNW-trending folds (F2). Folds of of F1 folds occurring along the southwestern fault this generation are particularly common along the margin display an en échelon configuration, which southwestern fault margin where they occur as gentle to may suggest that anticlockwise rotation was associated open, buckle folds (Fig. 11a) with wavelengths of 2-4 m with a small component of sinistral shear movement and amplitudes less than 30 cm. Tighter, chevron-type

Fig. 9. Contoured equal-area lower- hemisphere projection of estimated short- ening (a) and stretching axes (b) based on fault plane slickenside orientations and conjugate sets of shear fractures. Contour intervals are 2s.

A B

Fig. 10. Schematic representation of pos- sible fold development along the margins of the Trollfjorden-Komagelva Fault Zone during the D1 deformation event. (a) Rotated folds arising from roughly SW- directed compression with a component of sinistral strike-slip movement adding to the reverse slip along the fault zone. (b) Folds that show a gradual rotation into parallelism with the fault zone due to WSW- to SW-directed compression and with the fault zone acting as a barrier. 316 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 11. (a) Siltstones of the Innerelva Member affected by layer-parallel buckling around NE-SW to ENE-WSW-striking axes (locality 2 in Fig. 3), with a weakly developed box-fold; looking northeast. (b) Tight to close similar folds of chevron type with a SSE vergence, in the Innerelva Member at Komagnes. (c) Large-scale asymmetric fold with a SE vergence in the Godkeila Member of the Båsnæringen Formation, at the nor- theastern margin of the Trollfjorden-Komagelva Fault Zone; locality along the river Komagelva, looking approximately north. (d) Equal-area, lower-hemisphere projections of structural data associated with the D2 contractional deformation from the above-mentioned localities. Circles – fold axes, squares – poles to dip-slip-reactivated, dextral strike-slip faults, great circles – axial planes of folds.

Fig. 12. Contoured equal-area lower-hemisphere projection of all bedding planes measured in the study area. Overlain are b-axes and poles, indicating statistical fold axes, based on four map-scale folds of the D1 (stars and dashed lines) and D2 (circles and simple lines) deformations. NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 317 folds with axial planes dipping steeply to the northwest D2 deformation: synthesis and age relations and axes plunging gently towards northeast are also Within the study area, folds belonging to the D2 present (Fig. 11b), especially in the thin-bedded, more deformation are best developed along the fault margins pelitic lithologies, and there are low- to high-angle of the TKFZ. The NE-SW to ENE-WSW-trending thrust faults characterised by slickensides where calcite and SE- to SSE-verging folds and reverse faults are veins accompany the faults, thus confirming top-to-the- clearly indicative of a broadly SE-directed principal southeast transport. Top-to-the-southeast movement compressive stress. Seen in relation to the main NW-SE is also evident from quartz growth fibres and climbing to WNW-ESE-trending fault trace, this compression arrays of calcite veins. A spaced cleavage (S2) axial planar would be expected to have generated dextral strike-slip to these F2 folds is a prominent feature just south of the movement along this major lineament. In the Komagelv TKFZ (Fig. 7a). area, there is evidence to suggest that this was of a transpressional character with local transport to the SE North of the fault zone, NE-SW-trending folds with to ESE. There, the tightly folded siltstones were rotated related cleavage are uncommon, but there are SE-vergent, clockwise with respect to the main fault trace and show map-scale F2 folds along the northeastern fault margin easterly plunging fold axes, and thus support the idea of where sandstones of the Båsnæringen Formation are right-lateral transpression during the D2 deformation weakly deformed into asymmetric, open, parallel folds episode. (Fig. 11c). A stereographic projection of bedding planes, with a statistical best-fit great circle and b-axis, indicates This compressional event seems to have been of a regional a gentle NE-plunging statistical fold axis (Fig. 12). These character across the Tanafjorden-Varangerfjorden particular folds are accompanied by steep conjugate Region, as structures ascribed to this deformation are fracture sets clearly coeval with the mesoscopic folding. not confined to the vicinity of the TKFZ but are also Bedding-parallel quartz fibres associated with D2 found over most of the region south of the fault zone flexural slip are mostly undeformed, in contrast to a wavy (Siedlecka 1980, Chapman et al. 1985, Townsend 1986, or crenulated, layer-parallel, mineral lineation associated Sygnabere 1998). In general, although mesoscopic and with the SW-vergent folds of the D1 deformation event, map-scale folds are far more common in the western half and thus provides evidence that the F2 folds post-date of the TVR, smaller-scale SSE- to S-vergent folds can the D1 structures. be followed eastwards along and above one particular décollement horizon as far east as the coastline between NE-SW-striking reverse faults north of the TKFZ Ekkerøya and Komagnes (Sygnabere 1998). indicate transport to the southeast and are considered to belong to the same deformational event as the F2 D3 deformation folds. These meso-scale faults cross-cut and displace the mineral fibre lineation associated with the layer- An event which we designate as D3 is a phase of parallel slip that occurred during the D1, SW-vergent extensional deformation represented by features such as transport. dolerite dykes, extensional dip-slip faults and associated master joints. In the study area, direct evidence of such NE-SW to ENE-WSW-trending dextral shear zones features is confined to the area south of the TKFZ, but that can be ascribed to the D2 compressional regime this does not preclude the possibility that D3-related are extensively developed along the southwestern structures may occur in parts of the BSR. margin of the TKFZ. These display rare duplexes, flower structures and calcite-filled breccias indicative N-S-striking dolerite dykes are found along parts of of both transpressional and transtensional dextral the southwestern fault margin (Fig. 3) and another shear. The shear zones are steeply dipping, segmented similar dyke occurs c. 20 km farther south on Ekkerøya zones traceable for 40-50 m along strike. Farther south, (Beckinsale et al. 1975, Siedlecka & Roberts 1992, Guise vertical NE-SW-striking fractures are topographically & Roberts 2002, Rice et al. 2004). In the Komagnes area, well expressed in the sandstones of the Gamasfjellet three steeply east-dipping dykes (Fig. 3) display a right- Formation. Riedel-shear fractures and corrugation stepping, en échelon geometry in map view (Fig. 13a). marks and steps on the master fracture surfaces suggest Locally where the middle dyke terminates towards the dextral strike-slip movements. These right-lateral south, along the foreshore, a left-stepping geometry is faults of the D2 deformation were later reactivated by seen. Close inspection reveals that some of the dykes extensional dip-slip, as indicated by lineations defined are composite, dyke-in-dyke intrusions; and the thickest by chlorite-coated growth fibres of calcite, and vertical dyke is 2.5 m in thickness (by comparison, the Ekkerøya offsets of bedding. This later extension is especially dyke is c. 16 m thick). In thin-section, the dolerite evident in outcrops along the southwestern fault dykes show little signs of alteration and have an ophitic margin. In addition to these reactivated faults, new to subophitic texture dominated by plagioclase and faults were initiated and in some places there are weak clinopyroxene (Roberts 1975). The country rock (banded flexures of bedding which may reflect the presence of mudstones and siltstones of the Innerelv Member) shows blind normal faults at shallow depth. a c. 4 cm-wide, baked contact zone. 318 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 13. (a) Steep, N-S-trending dolerite dyke (locality 2 in Fig. 3) cutting Innerelva Member siltstones at the southwestern fault margin of the TKFZ; view looking north. At the southern termination of this dyke along the foreshore, the dyke splits into thinner dyke segments displaying a left-stepping en échelon geometry, and where the relay zones are characterised by brecciation of the siltstone. (b) Equal-area, lower-hemisphere projections of structural data associated with the D3 extensional deformation in the Komagnes area. Squares – poles to extensional dip-slip fault planes; great circles – dolerite dykes.

The Komagnes composite dykes can be followed in area, the N-S normal faults post-date shallower dipping outcrop for 325-625 m along strike. Using a handborne reverse faults which are likely to have formed during the proton-magnetometer, it was possible to trace the D2 contractional event. northernmost dyke for a further 250 m into the southwestern marginal part of the fault zone beneath D3 deformation: synthesis and age relations Pleistocene and recent deposits, until its signature eventually faded (Herrevold 1993). No lateral offset or The dolerite dykes clearly transect and post-date the change in strike could be detected in tracing the dyke earlier folds and cleavages related to the D1 and D2 northwards into the fault zone. Whilst this suggests that deformations, but are themselves cut by two sets of steep, its emplacement may have post-dated all significant NE- to N-dipping, extensional, calcite-filled fractures strike-slip movements associated with the earlier D1 and and minor faults striking NW-SE to WNW-ESE. Since D2 events, we cannot be absolutely sure about this as the we now know that the main Komagnes and Ekkerøya dyke has not been detected in or adjacent to the actual dykes are almost certainly of Late Devonian age (Guise & fault core. The dykes may have intruded along either pre- Roberts 2002), confirming the K-Ar study of Beckinsale existing or contemporaneous N-S-trending fractures, et al. (1975), then the dyke intrusion event may signify since these appear to be particularly abundant close to the imposition of a regional E-W to WNW-ESE-oriented the dykes and some show dip-slip extensional offsets. extensional stress field at or just before this time, at least Intersection between cleavages and fractures in the in the TVR. There is evidence to suggest, however, that Komagnes area has given rise to the formation of ‘pencil this extensional regime also influenced the northeastern cleavage’ with the longest axes of the horizontal, elongate BSR (Guise & Roberts 2002) where NE-SW trending ‘pencils’ trending E-W. This feature is found in steeply faults were reactivated (Rice et al. 2004), thus allowing N-dipping zones with intense fracturing. the sporadic intrusion of mafic dykes. Farther to the northwest in the BSR, several such normal faults (some of The dykes are cut by at least two sets of steeply dipping which are conceivably rejuvenated oblique-slip faults or joints, locally faults, striking NW-SE and WNW-ESE. minor thrusts) are also indicative of a NW-SE-oriented Many of these later, open fractures or minor faults are extensional regime (Siedlecki 1980, Lippard & Roberts filled or smeared with calcite, and show evidence of 1987), but a more detailed analysis of faulting and fault normal, dip-slip movement. Just to the south of the study reactivation is required in this particular region. area, conjugate sets of steep, N-S-trending, normal faults have been reported by Sygnabere (1998). These have The age of dyke emplacement and lack of any visible downthrows of up to 20 cm and would appear to relate to strike-slip offsets of the main Komagnes dyke along the D3 extensional event documented here. In this same and adjacent to the southwestern margin of the fault NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 319 zone would also indicate that all major strike-slip displacement along the TKFZ is likely to have ceased by Late Devonian time. A brief discussion of the dyke intrusion in a wider regional context is presented later.

D4 deformation

In the study area, this phase of deformation is represented by extensional structures developed just south of the TKFZ and along the northeastern fault margin.

ENE-WSW-striking tensile fractures are present south of the fault zone, both along the escarpment, where they are common, and in the area farther south. In alternating siltstones and mudstones, in several places, these fractures are filled by calcite, whereas quartz provides the fracture fill in the coarser-grained, thick-bedded sandstones. Late joints of this trend form a subordinate population along the northeastern fault margin, but there they are devoid of either quartz or calcite mineralisation.

WNW-ESE-striking extensional faults. Along the northeastern fault margin, this extensional phase is more pronounced and reflected in reactivation of larger WNW-ESE-striking shear zones that cross-cut map- scale D1 folds. The late reactivation of these faults by extensional dip-slip movements (Fig. 14) is characterised by brittle deformation with incohesive breccia and gouge along the fault cores. Normal drag close to the fault planes indicates a consistent downthrow of the northern Fig. 14. A steep, WNW-ESE-striking, normal fault in the blocks. The mode of deformation here is in clear contrast Næringselva Member of the Båsnæringen Formation along the nor- to that recorded in the two, earlier, contractional events, theastern fault margin of the Trollfjorden-Komagelva Fault Zone, in being much more brittle in character. Along the looking west. Drag indicates downthrow to the north. Fault breccia southwestern margin, the WNW-ESE fracture pattern and gouge are found along the fault plane, but no slickensides have is accompanied by quartz and calcite veining, with been detected. indications of minor, dip-slip normal movement in several cases. Dip-slip reactivation of NE-SW-trending, dextral faults is also quite common in these southwestern areas.

D4 deformation: synthesis and age relations Ages of deformation

Effects of this latest recognisible deformation in the The sequence of deformation events outlined above, as study area, reflecting NNE-SSW to NE-SW oriented recorded in this southeasternmost part of the TKFZ and extension, are most pronounced along the northern its surroundings, is clearly a relative chronology based margin of the TKFZ. The nature of the deformation on the long-standing notion of superposition of folds, products along these dip-slip reactivated faults indicates cleavages and other structures and fault-rock products. that deformation occurred at a shallower crustal depth In only one case – that of D3 – do we have a reasonably than was the case with any of the structures seen in secure idea of the absolute age of an event (Fig. 15). In connection with the earlier deformational events. This the other three cases we are forced to rely on structural extension may be seen in terms of a late, post-Caledonian correlations, partly within the confines of Varanger reactivation of the Trollfjorden-Komagelva Fault Zone, Peninsula but also with events registered in nearby areas since most of the extensional structures are found in of Northwest Russia. Biostratigraphic evidence also proximity to the fault zone and its margins. However, provides some lower constraints, and our knowledge of this does not necessarily imply that reactivation is offshore geology along the northwestward prolongation localised preferentially along the TKFZ. Within the BSR of the TKFZ helps in suggesting a likely age, or ages, for as a whole, several of the map-scale normal faults are our youngest D4 structural event. In the brief paragraphs suspected to have earlier histories of reverse- to oblique- that follow, we therefore attempt to pin actual ages, or slip movement. age ranges, on the four main events which have affected 320 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY this multiply reactivated crustal lineament and adjacent Stappogiedde Formation close to Komagnes was areas. acquired at c. 570-560 Ma (Gorokhov et al. 2001). This age coincides with the time of a reversal in palaeocurrent D1: During a period of collaborative Norwegian- vectors (Banks et al. 1971), with sediment suddenly Russian fieldwork and research in the early 1990s, it deriving from a rising landmass in the northeast and soon became clear that the lithostratigraphies and filling a small foreland basin (Gorokhov et al. 2001). If structural development observed on the Rybachi and the of the subjacent Mortensnes Formation Sredni Peninsulas of NW Russia (Fig. 1, inset map) had are reflecting part of the Gaskiers glaciation (Halverson much in common with what we see in eastern Varanger et al. 2005), i.e., at c. 580 Ma, then the 570-560 Ma Peninsula. On Rybachi Peninsula in particular, a major illites in the Stappogiedde Formation may be recording Late Riphean turbidite system (Siedlecka et al. 1995b) the approximate age of the Timanian deformation on revealed many of the features seen in the Kongsfjord Varanger. Submarine Fan of the Barents Sea Group of the BSR (Siedlecka 1972, Pickering 1981, 1985). Moreover, the In the eastern BSR, a dolerite dyke near Hamningberg low-grade lithostratigraphic succession on Rybachi is provided a U-Pb zircon, upper-intercept age of c. 567 strongly folded and cleaved along a NW-SE (to NNW- Ma and a lower intercept of c. 392 Ma (Roberts & Walker SSE) axial trend, with fold vergence towards southwest 1997). The dyke cuts a penetrative cleavage related to (Roberts 1995, Roberts & Karpuz 1995). These N-S-trending folds, a cleavage which, nearby at Finnvika, structures, part of the local (Rybachi) D1 deformation, trending NNW-SSE, had yielded an imprecise, Rb-Sr abut against a major steeply dipping fault – the Sredni- whole-rock, isochron age of 520 ± 47 Ma (Taylor & Rybachi Fault Zone (SRFZ) – which is a southeastward Pickering 1981). At c. 2.5 km southeast of Finnvika, continuation of the TKFZ. On Sredni Peninsula, in lower this same cleavage is strongly deformed through a c. diagenesis-grade rocks, open NW-SE-trending folds are 60° arc around later, ENE-WSW-trending, upright restricted to a narrow zone immediately adjacent to the folds. The three fractions of zircon analysed from the SRFZ. Accordingly, the D1 deformation on Rybachi and Hamningberg dyke are discordant and the authors then close to the SRFZ has been interpreted as a form of basin favoured an interpretation that the upper discordia inversion. intercept indicated the approximate age of crystallisation (Roberts & Walker 1997), notwithstanding the presence The structural scenario on Rybachi and Sredni is, of variable amounts of inheritance in the fractions. thus, highly reminiscent of the situation observed in Later, based on a review of mafic dyke geochemistry in the eastern part of the Varanger Peninsula, notably in northern Finnmark, Rice et al. (2004) argued that the the BSR, in terms of lithologies, fold axial trend and lower-intercept age of 392 +25/-36 Ma was probably closer vergence, cleavage development and metamorphic grade. to the true age of intrusion. Taking into consideration In NW Russia, the NW-SE-striking folds and cleavage the geochemistry of the Hamningberg dyke and another, have long been known to constitute part of the Vendian- chemically similar, dolerite dyke at Finnvika (with a age, ‘Timanian mountain chain’ (Tschernyschev 1901) or robust 40Ar-39Ar plateau age on plagioclase of 369 Ma: ‘Timanides’ (Schatsky 1935), also referred to in Russian Guise & Roberts 2002), we consider that the upper literature as the ‘Baikalian’ orogeny but now replaced intercept is likely recording an inheritance signature and by the more appropriate term ‘Timanian’ (Puchkov now favour the re-interpretation of Rice at al. (2004), 1997, Gee et al. 2000, Roberts & Olovyanishnikov 2004). i.e., that the dyke is Late Devonian in age, similar to the Isotope dating constraints indicate that the principal dykes at Finnvika, Komagnes and Ekkerøya. phase of the Timanian orogeny occurred during the time interval 590-560 Ma, generally oldest in the hinterland The question of the age of the NNW-SSE-trending, pre- and youngest along the frontal ranges and their foreland dyke cleavage in the Finnvika-Hamningberg area, and basins (see review in Roberts & Olovyanishnikov 2004; wider Vardø-Komagelva region, thus remains open. also Grazhdankin 2004). New data from southernmost Currently, the only secure lower and upper constraints Novaya Zemlya, however, are suggesting that the latest are provided, respectively, by the earliest Vendian age pulses of Timanian accretionary collision probably (Vidal & Siedlecka 1983) of the youngest rocks in the continued well into Cambrian time (Pease & Scott 2009). Barents Sea Group affected by the D1 folds and cleavage, and by the Devonian age of the mafic dykes. Accepting We therefore consider that the D1 contractional that the ENE-WSW-trending folds which locally structures in eastern Varanger Peninsula are almost deform the D1 cleavage and become dominant farther certainly Timanian, i.e., of probable Vendian age, and to the northwest are of Early Ordovician age, as in the indicative of basin inversion. As yet it has not been northwestern BSR (Rice & Frank 2003), this narrows possible to date the very low-grade S1 cleavage, but down the constraints; but they are still poor. Clearly, more there is indirect evidence which serves to provide precise geochronological data are needed before any safe loose constraints. In the TVR, Rb-Sr studies on conclusion can be reached. As things stand, however, and illite subfractions have suggested that an interpreted taking all regional evidence into account, i.e., including compactional fabric in the Innerelva Member of the structural trends and isotopic dating in Northwest Russia NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 321

Fig. 15. Summary of the main tectonic events that have affected the rocks along and adjacent to the Trollfjorden-Komagelva Fault Zone in the study area, with their suggested approximate ages. The strain ellipsoids and double arrows illustrate subhorizontal contraction for D1 and D2, and extension arising from subvertical shortening for D3 and D4.

(Gee & Pease 2004, and papers therein), we suggest that transpression and right-lateral strike-slip movement the D1 deformation and low-grade metamorphism in along the TKFZ. In western parts of Varanger Peninsula, this eastern part of the Barents Sea Region of Varanger folds of this trend, with NW-dipping slaty cleavage, are Peninsula is likely to have occurred in Vendian time, and far more abundant and dominate the structural picture probably at around 570-560 ± 10 Ma. in the parautochthon and Gaissa Nappe Complex (Roberts 1972, Siedlecka 1980, Johnson et al. 1978, Rice D2: In our study area, mesoscopic folds trending et al. 1989b). Until quite recently, the precise age of this NE-SW to ENE-WSW and verging SE to SSE represent contractional deformation, involving southeastward the second, main deformation episode, a regionally thrusting, was not known. Earlier, in a Rb-Sr whole- extensive, SE-directed shortening that involved rock study of cleaved mudstones from the Stappogiedde 322 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

Formation in the southwestern part of the TVR, Pringle together with the ages accorded to the D1 and D2 events, (1973) had reported an isochron age of 504 ± 7 Ma (see would therefore infer that the suggestion of a Vendian also Sturt et al. 1975), interpreted as dating the cleavage to Early Cambrian age for the Komagnes dyke based and folding and regarded as reflecting latest Cambrian on a palaeomagnetic study (Torsvik et al. 1995) must be to Early Ordovician Finnmarkian deformation. The rejected. The dykes are aligned parallel to a prominent reliability of this isochron, however, was questioned by N-S open fracture set, and the Komagnes dyke has been Dallmeyer & Reuter (1994). followed into the main fault zone without any detectable strike-slip offset, implying that all major strike-slip Subsequently, Bylund (1994b) reported an Early movement along the TKFZ had ceased by Late Devonian Ordovician remagnetisation event in rocks of the Gaissa time. Nappe Complex along the eastern coast of Tanafjorden, and Sundvoll & Roberts (2003) presented Rb-Sr data The Devonian dykes, and the D3 extensional event from strongly cleaved pelites in the Gaissa southwest (Fig. 13), fit into a well documented pattern of Mid of Tanafjorden pointing to a Sr-isotopic resetting event Devonian to Early Carboniferous rifting and sporadic at around 500-480 Ma. In a 40Ar/39Ar study of cleaved mafic magmatism reported from nearby parts of the rocks from northwestern Varanger Peninsula, Rice & Kola Peninsula and Timan-Pechora region (Ziegler Frank (2003) concluded that, in the Tanahorn Nappe, 1988, Nikishin et al. 1996; see discussion in Guise & the penetrative (S2) cleavage formed at c. 460 Ma “during Roberts 2002). On the Kola Peninsula, there are also the last stages of the SE-directed Finnmarkian event”; Pb-Zn mineralisations of Late Devonian age associated and in rocks of the Løkviksfjellet Group in the footwall with some of the N-S trending dolerite dykes (Juve et al. of the Tanahorn Nappe, inferred ages of equivalent folds 1995). and pervasive cleavage range from pre-470 to 450 Ma. A later crenulation cleavage in the Tanahorn Nappe yielded D4: Within the confines of the study area, the D4 plateau ages of c. 425 Ma, indicating that this younger, extensional event is manifested in dip-slip reactivation ESE- to E-directed, brittle overprint is of Mid to Late of earlier shear zones and faults, with fairly consistent Silurian, Scandian age (Rice & Frank 2003). Kirkland et northeastward downthrows. Calcite and quartz veining al. (2008) have also provided Ar-Ar geochronological along fractures is common, and along the northeastern evidence for a Late Silurian-Early Devonian event in margin there are breccias and gouge in fault cores. rocks of the Berlevåg Formation. Just to the southeast, Although there are no constraints on the timing of D4 in rocks of the Løkviksfjellet Group, plateau ages for extension, and no known mineral growth amenable to a late spaced cleavage are c. 443 Ma, suggesting that a radiometric dating, there is evidence from the offshore separate pulse of weak deformation may have occurred prolongation of the TKFZ on the Finnmark Platform of towards the very end of the Ordovician period. In a crustal extension, rifting and faulting in Carboniferous, Rb-Sr investigation of illites in the TVR, Gorokhov et Permo-Triassic and Jurassic to Early Cretaceous time al. (2001) reported that finer (0.1 μm) subfractions of (Gabrielsen & Færseth 1989, Dengo & Røssland 1992, authigenic illite range in age from 440 to 390 Ma, and Roberts & Lippard 2005). In addition, on the island of were interpreted by them to reflect phases of early- to Magerøya (Fig. 1), there are NW-SE-trending mafic dykes late-Scandian deformation, fluid migration and uplift. (Roberts et al. 1991) of Early Carboniferous age (Lippard & Prestvik 1997), and one WNW-ESE-trending dyke of The geochronological evidence currently available similar geochemistry and age occurs on the Digermul from Varanger Peninsula is thus suggesting that our Peninsula (Beckinsale et al. 1975, Rice et al. 2004). D4 SE-verging, D2 structures are likely to have formed in a deformation could therefore have occurred in any one Finnmarkian-related, Early Ordovician event (Fig. 15). It of these rifting episodes, or even include increments of also indicates that polyphase deformation in the Lower movement from more than one of these events. Allochthon of the BSR extended well into the Ordovician period, and that the main dextral strike-slip translation along the TKFZ also occurred during this prolonged, conclusions Early to Late Ordovician time interval. Scandian deformation, on the other hand, including possible late Based on structural studies in the southeastern part of pulses of strike-slip, is likely to have been of a more the Trollfjorden-Komagelva Fault Zone on Varanger brittle character in this particular study area. Peninsula, two main sets of contractional structures can be identified, grouped into D1 and D2 events. These D3: As noted above, the N-S-trending dolerite dykes that deformational episodes are superseded by two, separate, transect the F1 and F2 folds and cleavages have yielded extensional events, D3 and D4, characterised by brittle Late Devonian, 40Ar/39Ar mineral ages (Komagnes 378 structures, fault breccias and quartz-calcite veining. Ma, Ekkerøya 375 Ma; Guise & Roberts 2002). These The actual ages of the two contractional events can be ages correspond closely with earlier, K-Ar whole-rock deduced from published geochronological data either in ages of c. 360 Ma for these same dykes (Beckinsale et other parts of the Varanger Peninsula or in neighbouring al. 1975, but recalculated after Dalrymple 1979) and, areas of Northwest Russia. The first extensional event, NORWEGIAN JOURNAL OF GEOLOGY Structural geology of the southeastern part of the Trollfjorden-Komagelva Fault Zone 323

D3, has a fairly secure, Late Devonian age, based on References Ar-Ar mineral data from dolerite dykes. The age of the latest D4 event, on the other hand, is unknown, with Allmendinger, R.W., Marrett, R.A., Cladouhos, T. 1989-1992. FaultKin (formerly Fault Kinematics), version 3.25. A program for analyzing diverse options available ranging from Late Palaeozoic to fault slip data for the Macintosh computer. Mesozoic. Banks, N.L., Edwards, M.B., Geddes, W.P., Hobday, D.K. & Reading, H.G. 1971: Late Precambrian and Cambro-Ordovician sedimenta- The sequential deformation history in the study area may tion in East Finnmark. Norges geologiske undersøkelse 269, 197-236. be summarised as follows (Fig. 15): Banks, N.L., Hobday, D.K., Reading, H.G. & Taylor, P.N. 1974: Stratigraphy of the Late Precambrian ’Older Sandstone Series’ of the (1) Inversion of the Neoproterozoic basinal regime area, Finnmark. Norges geologiske undersøkelse 303, 1-15. Barrère, C., Ebbing, J. & Gernigon, L. 2009: Offshore prolongation of during a pre-Caledonian, low-grade, and inferred Caledonian structures and basement characterisation in the western Timanian (Vendian), contractional deformation Barents Sea from geophysical modelling. Tectonophysics 470, 71-88. (D1) event. This earliest episode is characterised by Beckinsale, R.D., Reading, H.G & Rex, D.C. 1975: Potassium-argon SW-directed shortening, folding and coeval cleavage ages for basic dykes from East Finnmark: stratigraphical and struc- development, with reverse movements along the tural implications. Scottish Journal of Geology 12, 51-65. Trollfjorden-Komagelva Fault Zone. By comparison Bevins, R.E., Robinson, D., Gayer, R.A. & Allman, S. 1986: Low-grade with the Timanides in NW Russia, this deformation metamorphism and its relationship to thrust tectonics in the Cale- donides of Finnmark, North Norway. Norges geologiske under- and metamorphism is likely to have occurred at søkelse Bulletin 404, 33-44. around 570-560 ± 10 Ma. Bylund, G. 1994a: Palaeomagnetism of the Late Precambrian Vadsø (2) Caledonian deformation (D2) with SE-directed and Barents Sea Groups, Varanger Peninsula, Norway. Precambrian shortening and dextral strike-slip displacement Research 69, 81-93. of unknown magnitude along the Trollfjorden- Bylund, G. 1994b: Palaeomagnetism of Vendian-Early Cambrian sedi- Komagelva Fault Zone. Based on recent geo- mentary rocks from E. Finnmark, Norway. Tectonophysics 231, chronology from NW Varanger Peninsula, this major 45-57. Chapman, T.J., Gayer, R.A. & Williams, G.D. 1985: Structural cross- contractional to transpressional event is considered sections through the Finnmark Caledonides and the timing of the to be late-Finnmarkian, pre-470 to 460 Ma (Arenig- Finnmarkian event. In Gee, D.G. & Sturt, B.A. (eds.) The Caledo- Llanvirn), but pulses of deformation are believed to nide orogen – Scandinavia and related areas. John Wiley & Sons, have occurred throughout Ordovician time. Scandian Chichester, 125-137. deformation in the actual study area and along the Dallmeyer, D. & Reuter, A. 1989: 40Ar/39Ar whole-rock dating and the fault zone was probably only of brittle character. age of cleavage in the Finnmark autochthon, northernmost Scandi- (3) A regional, E-W-oriented, extensional event (D3) navian Caledonides. Lithos 22, 213-227. Dalrymple, G.B. 1979: Critical tables for conversion of K-Ar ages from with intrusion of dolerite dykes. Dyke emplacement is old to new constants. Geology 7, 558-560. dated to Late Devonian time, at c. 375-370 Ma. Edwards, M.B. 1984: Sedimentology of the Upper Proterozoic glacial (4) A later, NE-SW-oriented, extensional event (D4) record, Vestertana Group, Finnmark, North Norway. Norges geolo- along and adjacent to the Trollfjorden-Komagelva giske undersøkelse Bulletin 394, 76 pp. Fault Zone, reflected in normal faults with breccias, Faleide, J.I., Gudlaugsson, S.T. & Jacquart, G. 1984: Evolution of the gouge and quartz-calcite veins. The age of this episode western Barents Sea. Marine Petrology and Geology 1, 123-150. is open to speculation, but Late Palaeozoic-Mesozoic Føyn, S. 1937: The Eo-cambrian series of the Tana district, northern Norway. Norsk Geologisk Tidsskrift 17, 65-164. reactivation along the fault zone is highly likely based Gabrielsen, R.H. 1984: Long-lived fault zones and their influence on on our knowledge of offshore geology. the tectonic development of the southwestern Barents Sea. Journal of the Geological Society, London 141, 651-662. Gabrielsen, R.H. & Færseth, R.B. 1989: The inner shelf of North Cape, Acknowledgements Norway and its implications for the Barents Shelf - Finnmark Cale- The first author would like to thank Signe-Line Røe for hospitality, donide boundary. A comment. Norsk Geologisk Tidsskrift 69, 57-62. help with identification of some of the lithostratigraphic units, and Gabrielsen, R.H. & Ramberg, I.B. 1979: Fracture patterns in Norway guidance in the field. During fieldwork, T.H. received financial support from Landsat imagery: results and potential use. Proceedings Nor- from Finnmark Fylkeskommune, and enthusiastic help from former wegian Sea Symposium, Tromsø 1979, Norwegian Petroleum Society, Fylkesgeolog Sigmund Johnsen. Sadly, Sigmund Johnsen passed away NSS/123, 1-23. during the course of our work, such that he never saw its final result. Gee, D.G. & Pease, V. (editors) 2004: The Neoproterozoic Timanide We would like to dedicate this article to his memory. Orogen of Eastern Baltica. Geological Society, London, Memoirs Financial support for fieldwork for M.R.K. from the Norwegian 30, 255 pp. Research Council, from a joint Norwegian-Russian project ”Lineament Gee, D.G., Beliakova, L., Pease, V., Dovshikova, L. & Larionov, A. 2000: and fault system analysis in Finnmark and western Kola Peninsula, Vendian intrusions in the basement beneath the Pechora Basin, Russia”, led by D.R., is acknowledged with thanks. We would also like to thank Ridvan Karpuz for collaboration during fieldwork and northeastern Baltica. Polarforschung 68, 161-170. for fruitful discussions of the manuscript. Rodney Gayer, Hugh Gernigon, L., Marello, L., Barrère, C., Skilbrei, J.R. & Roberts, D. 2008: Rice and Anna Siedlecka kindly commented on an early version of Significance of the new BAS-06 aeromagnetic survey for a better the manuscript. The final typescript has benefited from helpful and understanding of salt tectonics and basin structure in the Barents constructive reviews by Stephen Lippard and Hugh Rice. In particular, Sea. (Abstract and poster). 33rd International Geological Congress, we thank Hugh Rice for his brusque yet correct insistence that we sort Oslo, August 2008. out ambiguities relating to questionable, published, isotopic dates in the Gjelsvik, T. 1998: Nye aspekter ved forhold mellom den baikalske og den section on ages of deformation. kaledonske deformasjonen og dets betydning for deformasjonshisto- 324 T. Herrevold et al. NORWEGIAN JOURNAL OF GEOLOGY

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Varanger Peninsula, Finnmark, and coastal areas of Kola Peninsula, Norway and Russia. (extended abstract) Norges geologiske undersø- NW Russia. Norges geologiske undersøkelse Bulletin 431, 59-65. kelse Special Publication 7, 331-332. Roberts, D. 2009: Berggrunnskart Berlevåg 2336-1, 1:50 000, revidert Siedlecka, A., Lyubtsov, V.V. & Negrutsa, V.Z. 1995a: Correlation bet- foreløpig utgave. Norges geologiske undersøkelse, Trondheim. ween Upper Proterozoic successions in the Tanafjorden-Varanger- Roberts, D. & Karpuz, M.R. 1995: Structural features of the Rybachi fjorden Region of Varanger Peninsula, northern Norway, and on and Sredni Peninsulas, Northwest Russia, as interpreted from Sredni Peninsula and Kildin Island in the northern coastal areas Landsat-TM Imagery. Norges geologiske undersøkelse Special Publi- of Kola Peninsula in Russia. Norges geologiske undersøkelse Special cation 7, 145-150. Publication 7, 217-232. Roberts, D. & Walker, N. 1997: U-Pb zircon age of a dolerite dyke from Siedlecka, A., Negrutsa, V.Z. & Pickering, K.T. 1995b: Upper Protero- near Hamningberg, Varanger Peninsula, North Norway, and its zoic turbidite system of the Rybachi Peninsula, northern Russia – regional significance. Norges geologiske undersøkelse Bulletin 432, a possible stratigraphic counterpart of the Kongsfjord Submarine 95-102. Fan of the Varanger Peninsula, northern Norway. Norges geologiske Roberts, D. & Siedlecka, A. 2002: Timanian orogenic deformation undersøkelse Special Publication 7, 201-216. along the northeastern margin of Baltica, Northwest Russia Siedlecka, A., Roberts, D., Nystuen, J.P. & Olovyanishnikov, V.G. 2004: and Northeast Norway, and Avalonian-Cadomian connections. Northeastern and northwestern margins of Baltica in Neoprotero- Tectonophysics 352, 169-184. zoic time: evidence from the Timanian and Caledonian orogens. 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