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NORWEGIAN JOURNAL OF GEOLOGY Provenance and correlation of sediments in Telemark, South Norway 57 Provenance and correlation of sediments in Telemark, South Norway: status of the Lifjell Group and implications for early Sveconorwegian fault tectonics Jarkko Lamminen Lamminen, J: Provenance and correlation of sediments in Telemark, South Norway: status of the Lifjell Group and implications for early Sveconorwegian fault tectonics. Norsk Geologisk Tidsskrift, Vol 91, pp. 57-75. Trondheim 2011, ISSN 029-196X. The Telemark Supracrustals are a thick, well preserved, greenschist facies, Mesoproterozoic sediment and volcanic rock sequence exposed in the Telemark area in South Norway. From 1500 to 1347 Ma intracontinental rifting, followed by a long period of tectonic quiescence left a bimodal volcanic sequence, the Rjukan Group, overlain by a mainly quartzitic sedimentary succession, the Vindeggen Group. From c.1170 to 1000 Ma, a dynamic, probably largely strike-slip, tectonic regime leading to the Sveconorwegian Orogeny resulted in the deposition of laterally discontinuous groups of sediments, commonly conglomeratic, and bimodal volcanic to sub-volcanic magmatic rocks above a major unconformity, called the Subsvinsaga unconformity. Here, we report detrital zircon U-Pb data from three sandstone units that have been alternatively placed below and above this unconformity. The Lifjell Group was regarded as correlative to the Vindeggen Group by J.A. Dons, as part of his classical Seljord Group (now obsolete). Then it was reassigned to a much higher level, overlying the 1155 ± 2 Ma Brunkeberg porphyry. It includes prominent c. 1780 and 1500 Ma detrital zircon age modes and lacks any zircons younger than 1350 Ma. the age distribution is similar to the Brattefjell Formation in the Vindeggen Group, supporting the original correlation between these units. Another set of samples was taken from an elongated sandstone-conglomerate unit near Høydalsmo. Detrital zircon shows typical Palaeoproterozoic and c.1500 Ma ages, but 1300-1200 Ma and c.1130 Ma ages are also abundant. This unit is coeval with the Eidsborg Formation and confirms for the first time that the Eidsborg Formation is separated from underlying deposits by an angular unconformity. Depositional contacts with the Rjukan, Oftefjell and Høydalsmo groups indicate that the Eidsborg Formation once covered large areas in Telemark, and that all the earlier formations were already exposed to erosion. A survey of different conglomerates in the Sveconorwegian succession in Telemark reveals a trend from quartzite clasts in the oldest Svinsaga conglomerates to polymictic conglomerates in the younger formations and a general lack of granitic clasts until the very uppermost parts of the succession. This can be explained by exhumation of a thick quartzite cover and repeated burial, uplift and recycling of earlier deposits, until the basement was exposed. The activity of basin-bordering faults is clearly demonstrated by the changing conglomerate clast lithologies. The Sveconorwegian succession in Telemark was probably deposited in a strike-slip tectonic environment. The stratigraphic status of the Lifjell Group still remains enigmatic, but most likely it is part of the Vindeggen Group. Jarkko Lamminen ([email protected]), Department of Geosciences, University of Oslo,P.O. box 1047 Blindern, N-0316 Oslo, Norway. Introduction U-Pb age determination of allochthonous basement The Telemark Supracrustals are exposed in the Telemark area in South Norway. They consist of volcanic and sedimentary rocks that partly preserve their original stratigraphic relationships. They were faulted, folded and metamorphosed under greenschist facies conditions, and contrast with the high-grade gneisses that dominate the rest of the Southwest Scandinavian Domain. Their genesis and stratigraphy have been studied for more than 200 years (e.g. Törnebohm 1889; Werenskiold 1910; Bugge 1931; Wyckoff 1934). The whole area was mapped by J.A. Dons (Dons 1959, 1960a, 1960b, 1962, 1972), who established a tri-partite stratigraphy consisting of the Rjukan, Seljord and Bandak groups, from bottom to top. Over the years the area was studied geochemically (Menuge & Brewer 1996; Brewer & Menuge 1998; Knudsen et al. 1997; de Haas et al. 1999; Andersen et al. 2002; Köykkä 2010). The geochronology of the magmatic rocks was established by Dahlgren et al. (1990a, 1990b), Laajoki et al. (2002), Bingen et al. (2003, 2005) and Andersen et al. (2007). In recent years, new detailed mapping of the area lead to a significant improvement of our understanding of the lithostratigraphy and sedimentology of the supracrustal rocks (Andersen et al. 2004a; Laajoki 2002a,b, 2005, 2006a, 2006b; Laajoki & Lamminen 2006; Laajoki & Corfu 2007, 2008; Köykkä & Laajoki 2009; Köykkä 2010; Lamminen & Köykkä 2010). The rocks in Telemark have archived almost 500 million years of geological history. They occupy a unique time interval between two orogenies, the Gothian Orogeny (c.1650-1520 Ma) and the Sveconorwegian Orogeny (c.1140-900 Ma). During this large time span, the style of tectonism changed from simple rifting via tectonic quiescence to a more complex and dynamic behaviour before the Sveconorwegian Orogeny. The original stratigraphic 58 J. Lamminen scheme for Telemark, established by J.A. Dons, survived for 40 years until a new scheme was informally proposed by Laajoki et al. (2002), based on fieldwork and geochronological data. Problems still exist with this scheme and some of these are highlighted in this study. The early Sveconorwegian deposits in Telemark are characterised by abundant conglomerates that indicate high relief and the presence of fault-bounded depositional basins. Defining individual basins is difficult in highly deformed supracrustal successions, but field observations show that the early Sveconorwegian basins in Telemark probably were small, intermontane pull-apart basins. This study presents new detrital zircon U-Pb data from some early Sveconorwegian sedimentary units in Telemark. The objective is to test parts of the new lithostratigraphic scheme by Laajoki et al. (2002), addressing the problematic status of the Lifjell Group and the unconformable status of the Eidsborg Formation. The data for individual samples are compiled in appendix 1 and 2 in the electronic supplement that accompanies this article. Geological setting and regional lithostratigraphy The Fennoscandian Shield is composed of an Archaean core in the northeast and progressively younger Proterozoic crustal domains towards the southwest. Summaries of the regional Precambrian geology are given by Gaál & Gorbatschev (1987), Gorbatschev & Bogdanova (1993) and Bogdanova et al. (2008), and a map of the entire shield has been published by Koistinen et al. (2001). The area including southwest Sweden and southwest Norway is the youngest part of the Shield and has been called The Southwest Scandinavian Domain (SSD, Gaál & Gorbatschev 1987), the Sveconorwegian Belt (Bingen et al. 2008) or the Sveconorwegian orogen (e.g. Corfu & Laajoki 2008). We choose to use the first of these names. The area is structurally complex, including several Precambrian fault- and shear zones that strike in a general N-S direction and that subdivide the area into several structural domains (Fig. 1). In the literature, the Precambrian bedrock areas bordered by these fault and shear zones have been called sectors, terranes and blocks. A nongenetic block-terminology (Andersen 2005a) is used here. The Southwest Scandinavian Domain (SSD) The SSD is bordered in the east by the c.1400 km long, 1850-1650 Ma Transscandinavian Igneous Belt (TIB), consisting mainly of alkali-calcic granitoids and their volcanic equivalents, as well as minor mafic rocks. The TIB is interpreted as a continental magmatic arc, which developed along the NNW-SSE running central axis of the present day Fennoscandian Shield. The magmas of TIB rocks formed by re-melting older Svecofennian NORWEGIAN JOURNAL OF GEOLOGY rocks with minor mafic additions (Högdahl et al. 2004). The exact duration or geographical extent of the TIB magmatism is not known because a large part of the plutonic belt is covered by Caledonian nappes. The Eastern Segment is the easternmost crustal block of the SSD connected to the TIB along a fault contact (the Protogine Zone). It consists of reworked TIB rocks. Sveconorwegian, c.970 Ma high-pressure granulites and eclogite facies metamorphism is recorded in the Eastern Segment (Johansson et al. 2001). Other crustal blocks west from the Eastern Segment are called Sveconorwegian allochthons (Stephens et al. 1996). They are bordered by the “Mylonite Zone”, a Sveconorwegian oblique thrust zone (Viola & Henderson 2010). The first allochthonous block westwards is the Idefjorden Block. It consists of diverse calc-alkaline volcanic and plutonic rocks and sedimentary rocks developed in island arc settings and accreted to the Fennoscandian Shield during the Gothian Orogeny (i.e. c.1720-1520 Ma, Åhäll & Connelly 2008). Westwards, the Bamble-Lillesand and Kongsberg-Marstrand blocks are thought to have been connected originally but are now separated by the Permian Oslo Rift (Starmer 1996). These two blocks structurally overlie other blocks to the west in the SSD. The BambleLillesand Block consists of paragneisses and orthogneisses, gabbros and quartzites (Starmer 1993; Padget & Brekke 1996). The Bamble-Lillesand Block may be composed of two lithotectonic terranes: the mainland Bamble area with a pre-Sveconorwegian crustal history, and a Sveconorwegian island arc fragment along the central part of the coast (Tromøy and adjacent islands) (Andersen et al. 2004b). The Bamble-Lillesand Block is separated from the Telemark Block (see below) by the Sveconorwegian Porsgrunn-Kristiansand Shear Zone (Fig. 1), along which upper amphibolite-facies to granulite facies gneisses and metasediments of the BambleLillesand Block (Nidelva and Kragerø complexes) have been thrust over the amphibolite-facies granitic gneisses of the Telemark Block (Starmer 1993). The KongsbergMarstrand Block consists mainly of 1700-1500 Ma calcalkaline meta-igneous rocks and coeval metasediment ary rocks (Modum Complex), and younger intrusions. The rest of the SSD further to the west in southwest Norwaycomprises the Telemark and the Hardangervidda-Rogaland blocks. The Mandal-Ustaoset Shear Zone (Sigmond 1985) separates the two blocks, but they are generally considered to be genetically similar. Bingen et al. (2005) coined the term “Telemarkia” to pool these two blocks together. The Telemark Block is the focus of this study. It consists of a well preserved volcanic-sedimentary suite in the north, called the Telemark Supracrustals, and gneisses in the south, called the Vrådal gneiss complex. The Hardangervidda-Rogaland Block consists mostly of orthogneisses and granites with some supracrustal rocks. These are Mesoproterozoic and NORWEGIAN JOURNAL OF GEOLOGY Provenance and correlation of sediments in Telemark, South Norway 59 Figure 1. Geological map of central Telemark. The study areas are framed. Stratigraphic scheme follows Laajoki et al. (2002). Dashed lines are unconformities. include the sedimentary Hettefjorden and Festningsnutan groups and the volcano-sedimentary Sæsvatn-Valldal sequences (Bingen et al. 2002). They are potentially correlative to the Telemark supracrustal rocks (Torske 1985; Bingen et al. 2002; Lamminen & Köykkä 2010). The Telemark Supracrustals A suite of well-preserved, Mesoproterozoic volcanic and sedimentary rocks, called the ‘Telemark Supracrustals’, form a prominent feature in the Telemark Block (Dons 1960a, b, 2004; Sigmond et al. 1997; Laajoki 2000, 2003; Laajoki et al. 2002; Bingen et al. 2001, 2005). They form a supracrustal succession approximately 10 km thick, metamorphosed under low-grade greenschist-amphibolite facies (Brewer & Atkin 1987; Atkin & Brewer 1990). Dons (1960a) divided the Telemark supracrustal rocks into three groups: Rjukan (oldest), Seljord and Bandak (youngest), separated by major unconformities. The Heddal Group was introduced by Dahlgren et al. (1990a) for correlative rock unit of the Bandak Group in the eastern part of the Telemark Block. Laajoki et al. (2002) proposed to abandon the original tri-partite division, keeping only the Rjukan Group, following new radiometric dating results and the uncovering of several unconformities. Especially important is the dating of the Brunkeberg porphyry at 1155 ± 2 Ma (Laajoki et al. 2002) and its interpretation. Today, the Telemark supracrustal rocks have been shown to consist of two main successions, a lower succession deposited between c.1510-1347 Ma, referred to as the “Vestfjorddalen Supergroup” by Laajoki & Lamminen (2004), and one overlying succession, deposited between c.1170-1010 Ma and separated by a major unconformity (sub-Svinsaga unconformity, Dons 2004; Laajoki 2000, 2003, 2009). This Sveconorwegian succession corresponds to the Bandak Group in the old stratigraphic scheme. Its type area around Lake Bandak was probably the site of a basin, which is referred to below as the “Bandak rift basin”. Another depocentre was located in the northeast, where the Heddal Group was deposited in a separate basin, “the Heddal basin”. The Rjukan rift basin The Vestfjorddalen Supergroup (the Rjukan rift basin) starts with the Rjukan Group (Fig. 1). No depositional basement for the Rjukan Group has been clearly identified in the field. The group consists of the Tuddal Formation, made up of c.1.51 Ga continental felsic volcanic rocks (Dahlgren et al. 1990a; Nordgulen 1999; Bingen et al. 2005), overlain by a c.2 km thick succession of the volcanic-sedimentary Vemork Formation (c. ≤1495 ±2 Ma, Laajoki & Corfu 2007), characterised mainly by mafic volcanism (Fig. 1). The stratigraphic relations between the Tuddal and the Vemork formations has been a matter of debate (cf. Dahlgren et al. 1990a; Dahlgren & Heaman 1991; Brewer & Menuge 1998; Laajoki & Corfu 2007; Köykkä 2010). In this work, the traditional interpretation 60 J. Lamminen is followed, where the Vemork Formation is part of the Rjukan Group (see Laajoki et al. 2002). The Rjukan Group is overlain unconformably by the c.7 km thick sedimentary-dominated Vindeggen Group (Fig. 1). The Vindeggen Group consists of several sandstone and mudstone formations deposited in various environments including alluvial, tidal flat and open marine. The group is complexly faulted into several internally folded blocks (Fig. 1). For this reason, individual formations within the group are discontinuous and may be missing in some areas. The true thickness of the Vindeggen Group is unknown because it is abruptly cut by the sub-Svinsaga unconformity. NORWEGIAN JOURNAL OF GEOLOGY under the Eidsborg Formation. The Heddal Group in the northeast and the Kalhovd Formation in the northwest (Bingenet al. 2003) are probably correlative to the Eidsborg Formation. The Lifjell Group The Lifjell Group was introduced by Laajoki et al. (2002) to describe a wedge-shaped quartzite unit east of the town of Seljord (Figs. 1 and 2), originally part of Dons’ Seljord Group (Dons 1960a). It was defined on the basis of mapping and U-Pb zircon dating. Mapping of the quartzites southeast of Seljord revealed that they overlie felsic volcanic rocks assigned to the Brunkeberg The Bandak rift basin Formation(Fig. 2). The Brunkeberg Formation was origThe c.2000 m thick Sveconorwegian succession, defining inally correlated with the Rjukan Group. This placed the the Bandak rift basin, corresponds to the Bandak overlying rock unit as correlative with the Seljord Group. However, U-Pb zircon dating of this volcanite at 1155 ± Group, sensu Dons 1960a. An angular unconform 2 Ma by Laajoki et al. (2002) showed that it was much ity (the sub-Svinsaga unconformity; Köykkä & Laajoki younger than the Rjukan Group. This meant that the 2009; Laajoki2009) separates the Vestfjorddalen Superoverlying unit must be significantly younger than the group from the overlying supracrustal succession, which Seljord Group, and thus it was named the Lifjell Group. has a depositionalage that coincides with the earlyThe remaining part of the Seljord Group was renamed middle Sveconorwegian Orogeny (or c.1200-1000 Ma). the Vindeggen Group. It was also suggested that the traThis supracrustal succession is more diverse, consisting ditional name of the Bandak Group be abandoned; two of coarse sedimentary rocks interlayered with bimodal magmatic rocks. On a regional scale, the formations new groups, the Høydalsmo and Oftefjell, were introduced and the Lifjell Group was correlated with these. are laterally restricted and variable, which suggests that they were laid down in separate basins, or subThe Lifjell Group consists of intensively deformed basins (Laajokiet al. 2002; Bingen et al. 2003), possibly quartzites, in places isoclinally folded, and a strongly in a transtensional tectonic regime (Bingen et al. 2003; deformed conglomerate and sandstone succession in its Lamminenet al. 2009; this study). The type area for the basal part, called the Vallar Bru Formation (see below). Sveconorwegian succession is around Lake Bandak, but In the east, it is cut by the Skogsåa porphyry (Laait correlates with the Heddal Group in the northeast and joki et al. 2002), which is the lowest part of the Heddal the Kalhovd Formation in the northwest (Bingen et al. Group. In the west, a large fault system runs through 2003). Generally, the oldest Sveconorwegian deposits are Seljordfrom NE to SW, and is called the Slåkådalen- volcanic-sedimentary whereas the youngest formation Grunningsdalen fault zone (Fig. 2) (Laajoki 2002a; lacks volcanic rocks. Laajoki2006b). It forms a valley between the Lifjell mountain range and the mountains west of it. The fault The Sveconorwegian succession starts with the Oftezone has a completelydifferent geology compared to fjell Group (Fig. 1) (Laajoki 2006a), which is sediment the rocks around it. It includes at least two types of ary in the basal part and volcanic-sedimentary in the conglomerateand various quartzites and volcanic rocks upper part. The Svinsaga Formation lies at the base of including the Brunkebergporphyry. The Seljord conthe Oftefjell Group, unconformably above theVindeggen glomerate (de Haas et al. 1999) forms a distinct lithotype Group around Lake Bandak in the south. but conformin this succession. It was renamed as Vallar Bru conglomable near mount Gausta in the north. This unconformity erate by Laajoki (1998). In the south the Lifjell Group is is named the sub-Svinsaga unconformity and includes a bordered by a similar conglomeratic-volcanic lithology. heavily brecciated zone (Köykkä & Laajoki 2009; Laajoki The rocks in the western and southern borders are tightly 2009), which probably represents a regolith. It has been folded and deformed, and the conglomerates are usually shown that a hiatus of at least 150 m.y. is associated with highlydeformed. The rheologically incompetent quartzthis unconformity (Lamminen et al. 2009). The bulk ite and volcanite clasts are stretched, while some rare of the Svinsaga Formation is composed of feldspathic granite clasts have resisted. Detailed field descriptions of sandstone withsome pebbly units. Above the Svinsaga the lower contact of the Lifjell Group and the associated Formation, the Ofte Formation consists of bimodal volconglomerates (including the Vallar Bru Formation) are canic rocks and coarse, mainly volcaniclastic sediments. given in Laajoki (2002a, 2006b). The sedimentological The Ofte Formation is unconformably overlain by the characteristics of the main quartzite of the Lifjell Group volcanic-sedimentary Høydalsmo Group. The Sveco are in many places masked by intense deformation. Hownorwegian succession ends with the Eidsborg Formaever, in places one can find wave ripples, heterolithic tion, which consists only of sedimentary rocks. Around units and tabular cross bedding. The sandstone is also Lake Bandak, no angular unconformity is observed NORWEGIAN JOURNAL OF GEOLOGY Provenance and correlation of sediments in Telemark, South Norway 61 Figure 2. Simplified geological map of the Lifjell-Seljord region. Sampling sites are marked. Map is modified from geological maps available at www.ngu.no in 2010. well sorted. These features suggest a shallow marine origin for the main part of the Lifjell Group. The lower part of the Lifjell Group, the Vallar Bru Formation, is interpreted to represent a typical alluvial fan massflow type conglomerate. Sedimentologically it is in striking contrast with the shallow marine part of the Lifjell Group. The Garvik quartzite At the southern margin of the Telemark Supracrustals, the rocks are highly deformed and divided into thrust sheets. The pre-rift basement for the Telemark Supracrustals has never been identified, but originally it was thought to be the Bø granite in the south (Dons 1960b; Fig. 2). The gneisses in the Vrådal gneiss complex were studied by Andersen et al. (2007), who obtained an age of 1208 ± 6 Ma for a granitic gneiss in the Kviteseid area. The Bø granite is probably of similar age. The contact between the supracrustals and the Bø granite is very sharp. A parallellaminated quartzite with numerous amphibolite veins and dykes is the first supracrustal unit that comes in contact with the Bø granite in the south. This and similar gneissic rocks further to the west were collectively named “Transtaulhøgdi supracrustals” by Laajoki et al. (2002). In the newly revised stratigraphic scheme the status of this thin quartzite has not been definitively established. Here we call it informally the Garvik quartzite from the locality where it is observed close to Lake Seljord. of a c.1 km thick succession of mainly feldspathic sandstones with some conglomerates. The sedimentary structures are well preserved. At least four different types of conglomerates can be defined (Figs. 4-6), based on their clast population. The unit was originally included in the Seljord Group (Dons 1962, 1963, 1972), later in the underlying Rjukan Group (Dons 2004), and most recently in the Sveconorwegian Røynstaul Formation (Høydalsmo Group) by Laajoki & Lamminen (2006). The Snaunetten basin In the west the Snaunetten basin is bounded, from north to south, by the Vemork Formation basalt, Tuddal Formation rhyolite and the Oftefjell Group. The contact with the Vemork Formation is unambiguously depositional (Fig. 5a), while the contact with the Tuddal Formation is not exposed. The contact with the Oftefjell Group is locally observed to be depositional. For a detailed description of the western contact, see Laajoki & Lamminen (2006). The eastern margin is defined by a major fault called the Raudsinutan fault, which juxtaposes the basin succession against the sandstones of the Vindeggen Group (Gausta Formation). The Raudsinutan fault is interpreted as syn-sedimentary fault due to the lithology of the conglomerates in the sediments (details are given later). Later this fault was reactivated, causing right-lateral displacement and folding in the Snaunetten basin (insets in Fig. 3). In the north the basin margin is a hook-fold, whereas in the south the sedimentary strata are mostly locally folded and dissected by NW-trending faults. The Snaunetten basin (Figs. 3-4) is a palaeobasin defined by a NE-SW oriented, elongated rock body consisting Lithostratigraphic columns of the Snaunetten basin are shown in Fig. 4. The variety of conglomerates found is 62 J. Lamminen NORWEGIAN JOURNAL OF GEOLOGY Figure 3. Geological map of the Snaunetten basin region. Insets show detailed mapping in the north and south. Sampling sites are marked in the insets. Basemap after Dons 2004. Figure 4. Simplified lithostratigraphical columns from northern and southern parts of the Snaunetten basin. The basin is mainly made of sandstone, but contains various conglomerates, probably of alluvial fan origin. The conglomerates vary in composition. Sampling sites are marked. NORWEGIAN JOURNAL OF GEOLOGY Provenance and correlation of sediments in Telemark, South Norway 63 Figure 5. The conglomerate variability in the northern Snaunetten basin. For relative stratigraphical positions of the conglomerates , see Fig. 4. UTM coordinates (WGS84/zone 32V) are provided in the lower right corners of the pictures. (A) Depositional contact of the Snaunetten basin with Vemork Formation basalts. (B) Mass-flow bouldery conglomerate in the northernmost tip of the Snaunetten basin (Fig. 3b). Clasts are generally c.15 cm in size. Largest quartzite clasts are up to 1.5 m. (C) Polymictic massflow conglome rates interbedded with sheet sandstone. This conglomerate comes on top of the conglomerate in Fig. b. Two clusters of larger clasts are seen, which is typical for ephemeral rivers. See compassfor scale. (D) Very poorly sort ed conglomerate consisting of basic volcanic and acid volcanicclasts. These deposits are associated with large scale sets of tabular crossbeds (eolian?). Size of nameplate is c.15 cm. (E) Conglomerate consisting solely of acid volcanic clasts. The apparent orientation of the clasts is tectonic. shown in Figs. 5-6. Sedimentologically the Snaunetten basin contains conglomerates of probable alluvial fan origin and monotonous sandstones with very minor mudstones. The conglomerate beds are laterally restricted and occasionally soft-sediment deformation structures can be seen. In the north, the basement of the Vemork Formation is overlain by a polymictic conglomerate consisting of poorly sorted boulders up to 1.5 m in size (Fig. 5b and c). Further to the south the conglomerate is comprised only of basaltic and acid volcanic clasts (Fig. 5d). Higher in the stratigraphy, the clast composition changes rapidly to become monomictic acid volcanic in composition (Fig. 5e). In the southern part of the basin, the polymict variety is missing. The conglomerate is mainly acid volcanic (Fig. 6a) becoming quartzite-dominated further up in the stratigraphy (Fig. 6b). Sedimentary structures in the sandstones commonly include large-scale tabular cross-beds, parallel lamination and some large-scale trough cross-beds. The rock has a characteristic and delicate pin-stripe lamination, defined by hematite grains. There is a lack of well-defined channel structures. The sedimentary facies of the conglomerates and sandstones suggest episodic and unconfined flow. Large scale dunes with pin-stripes could be eolian in origin (Fryberger & Schenk 1988). Analytical methods Material studied Samples analysed in this study are summarised in Table 1. Two sandstone samples from the Snaunetten basin were chosen for analysis. Sample JL-04-30.1 was taken from near the base of the basin succession in Haugset (inset B in Fig. 3). The host rock consists of a horizontally laminated quartz-rich sandstone interbedded with poorly sorted, bouldery and polymictic conglomerates of acid volcanic, mafic volcanic and quartzitic composition. Sample JL-04-75.2 was taken from near the top of the basin package in Førstøyl (inset A in Fig. 3), c.10 km southwest from Haugset. It was collected from a massive silty sandstone which also contains quartzite conglomerate clasts. 64 J. Lamminen NORWEGIAN JOURNAL OF GEOLOGY Two samples were collected from the Lifjell Group and one sample from the Garvik quartzite. Sample JL-0914 from the Lifjell Group is from a thick sandstone bed between quartzite clastic conglomerates that occurs on the northwest side of Nordfjell. Under the microscope, the rock is seen to be an extremely deformed schistose quartz-muscovite rock, which was probably originally a quartz arenite. Almost all the framework minerals are recrystallised. Sample JL-09-13 was collected from the main Lifjell quartzite, just 10 metres above the previous sample. It was collected at the fault contact and is a highly sheared orthoquartzite. Sample JL-09-12 was collected in the southern part of the Lake Seljord area near Garvik and belongs to the Garvik quartzite. The rock restsdirectly on top of the sheared Bø granite and is a sheared orthoquartzite, as the contact is tectonically altered by strong shear deformation. U-Pb zircon method Provenance of the sampled sediments is evaluated from detrital U-Pb zircon analyses and conglomerate clast lithology. Zircon grains were separated by standard methods including crushing, milling and heavy liquids. U–Pb dating was performed using a Nu Plasma HR multi collector ICPMS and a New Wave/Merchantek LUV-213 laser microprobe at the Department of Geosciences, University of Oslo. Analytical methods are described briefly here. A full account is given in Røhr et al. (2008) and Rosa et al. (2009). Masses 204, 206, 207 and 238 were measured and 235U was calculated from 238U using a natural 238 U/235U=137.88. Mass number 204 was used as a monitor for common 204Pb. Raw data were reduced to U and 206 Pb concentrations and U–Pb isotope ratios by a sample -standard bracketing routine similar to that of Jackson et al. (2004). Figure 6. Conglomerates in the southern Snaunetten basin (Fig. 3a). Coordinates are in UTM/WGS84/zone 32V. (A) Acid volcanic conglomerates dominate the lower part of the succession. This conglomerate is similar to the one pictured in Fig. 5e. (B) Conglomerate consisting almost entirely of white quartzite clasts. Some acid volcanic clasts may be found as well. Note similar sedimentary facies association, typical for alluvial fans, in both photographs.. The U-Pb ages for samples JL-04-30.1 and JL-04-75.2 were calculated in 2005 using a single standard bracket ing technique. This method gives good precision, but >1500 Ma old zircon tends to get inversely discordant. An improved 2-3 standard method was developed later and the rest of the samples follow the new routine. The zircon used for calibration included zircon standards Table 1. Summary of samples analysed in this study. Sample Name* Unit Locality UTM coordinates (WGS 84, zone 32V) Notes JL-04-30.1 orthoquartzite Eidsborg Formation Haugset 460974 6610459 Gneissic recrystallized texture. JL-04-75.2 orthoquartzite Eidsborg Formation Førstøyl 455961 6600787 Gneissic recrystallized texture. JL-09-12 orthoquartzite Garvik quartzite Garvik 485822 6587558 Gneissic recrystallized texture. JL-09-13 orthoquartzite Lifjell Group/main quartzite Nordfjell 488482 6599947 Gneissic recrystallized texture. JL-09-14 muscovite schist Lifjell Group/Vallar Bru Fm. Nordfjell 488461 6600023 Gneissic recrystallized texture. NORWEGIAN JOURNAL OF GEOLOGY GJ-01 (609 ± 1 Ma; Jackson et al. 2004), 91500 (1065 ± 1 Ma; Wiedenbeck et al. 1995), in-house Palaeoproterozoic standard A382 (1876 ± 2 Ma; Patchett & Kouvo 1986) and an in-house standard Ceylon (553 ± 2 Ma; F. Corfu pers. comm.). In our laboratory the GJ standard gave a concordia age of c.601 Ma and the 91500 gave a concordia age of c.1059 Ma. These standards are known to be slightly discordant, hence the discrepancy of concordia age from the upper intercept age. These values were used in calculations. IsoplotEx 3.0 (Ludwig 2003) was used to plot concordia and probability density diagrams. Zircon standard 91500 was also run as an unknown for checking the accuracy of the method. Outlier standard analyses were rejected based on the outcome of the standard run as unknown. This data can be found in Appendix 1. Laser settings were: c.32 % power, 40 µm spotsize and 10 Hz repetition rate. Results All the U-Pb results are listed in Appendix 2 and in Figs. 7 and 8. In order to have statistical confidence, at least 60 zircons (Dodson et al. 1988) should be analysed and preferably 100 or more (Vermeesch 2004, 2005; Andersen 2005b). Analysing over 100 grains is unrealistic in most cases. It must be kept in mind that there is a slight probability that geologically significant small zircon populations have gone undetected. However, major populations show up early and c.30 grains should be enough to detect them. The relative heights of the peaks in diagrams reflect the relative abundance of an age population in the Figure 7. Conventional concordia plots and probability density plots of the detrital zircon samples from the Snaunetten basin. The 1480-1520 Ma peaks in both diagrams are most likely related to the Tuddal Formation. In both samples the Palaeoproterozoic is rather minimal. For sample JL-0475.2, this could be due to the small number of grains studied. The young, 1123 Ma peak is missing in the lower probability density diagram. The so called “interorogenic” ages of 13001200 Ma are present in these samples. Provenance and correlation of sediments in Telemark, South Norway 65 sample, but interpretations based on low grain counts should be applied with caution. Natural factors add another complexity. There is no way of knowing whether certain age-populations consisted of metamict grains that are now gone. The zircon fertility of rocks (felsic vs. mafic rocks) is important too (Moecher & Samson 2006), even some granites can be low in zircon. Although these uncertainties are always present, other criteria, such as conglomeratic clast lithology and palaeocurrent measurements can be used to support zircon data. The Snaunetten basin Two samples from the Snaunetten basin represent different sedimentary facies. Sample JL-04-30.1 from the northern part is associated with polymictic alluvial fan conglomerates. Detrital zircon shows pronounced peaks at 1123 Ma and 1482 Ma (Fig. 7). It is notable that the Palaeoproterozoic signal is very low, which is the opposite that is typically found in the older (Vindeggen Group) sediments from Telemark (Lamminen & Köykkä 2010). Sample JL-04-75.2 from the southern part of the basin succession shows a distinctive 1518 Ma peak and minor peaks at c.1300 Ma, as well as a range of Palaeoproterozoic and Archaean ages (Fig. 7). Although the amount of analysed grains in this sample is low, it can be stated confidently that the 1518 Ma is the dominant population. The 1123 Ma peak found in the north, was not detected, which could be a statistical issue. It also indicates that the provenance in this part of the basin is different than in the north. 66 J. Lamminen NORWEGIAN JOURNAL OF GEOLOGY Figure 8. Samples from the Lifjell Group and Garvik quartzite analysed in this study compared with those from the Vallar Bru Formation (Lifjell Group) analysed by de Haas et al. (1999). (A) The c.1155 Ma age of the Brunkeberg porphyry is absent from all samples. (B) The 1200-1300 Ma interval is common in young sediments from Telemark (see Fig. 7), but is missing here. (C) The c.1500 Ma is found in all except one sample. This is probably just due to low grain count. (D) The c.1730-1750 Ma interval is common for the Vindeggen Group (Lamminen & Köykkä 2010). This is found in all except one sample. The Lifjell Group Probability density diagrams of samples from the Lifjell Group are presented in Fig. 8. Sample JL-09-14 from a sandstone bed in a conglomeratic succession at Nordfjell shows a distinctive c.1500 Ma peak. Some Palaeoproterozoic ages are present and the youngest peak is 1387 Ma. Results from the main orthoquartzite of the Lifjell Group at Nordfjell (sample JL-09-13) are similar to the Upper Brattefjell Member of the Brattefjell Formation (Fig. 9) (Lamminen & Köykkä 2010). The Palaeoproterozoic is most abundant in the age spectra and even Archaean grains are relatively common. Major peaks can be found at 1760, 1884, 2700, 1626 and 1500 Ma. The 1500 Ma peak is much smaller than the 1760 Ma peak. When the amount of analysed grains exceeds about 60, there is more confidence that the observed highest and lowest peaks are real. The 1760 Ma peak is important, since it is not present in sample JL-09-14 that, according to the new stratigraphic scheme, should underlie the main Lifjell quartzite (Fig. 10). This c.1760 Ma age is very common in the Vindeggen Group and other quartzites in Telemark, for example the Blefjell quartzite (Bingen et al. 2001; Andersen et al. 2004a; Lamminen & Köykkä 2010) (Fig. 9). The Garvik quartzite Sample JL-09-12 from the southern contact of the Telemark Supracrustals at Garvik shows also a major c.1500 Ma mode (Fig. 8), and smaller but distinct Palaeoproterozoic modes peaking at 1703 and 1837 Ma (Fig. 8). The youngest peak at 1320 Ma is defined by a single analysis only. More grains were analysed from this sample than from sample JL-09-14, but these samples are virtually indistinguishable. It is likely that sample JL-09-12 is just a more deformed correlative to sample JL-09-14. NORWEGIAN JOURNAL OF GEOLOGY Provenance and correlation of sediments in Telemark, South Norway 67 Figure 9. Probability density diagrams comparing the main quartzite of the Lifjell Group with the Vindeggen Group and the Blefjell quartzite. (A) The c.1550 Ma “Gothian gap” is characteristic for the Vindeggen Group (Lamminen & Köykkä 2010) and is also present in the Lifjell Group and Blefjell quartzite. (B) The c.1730-1750 Ma age is a major mode in all diagrams. The c.1500 Ma Tuddal signature is minor. Figure 10. Schematic column across the conglomeratic lower part of the Lifjell Group (Vallar Bru Formation) in the Grunningsdalen-Slåkådalen fault system. Brecciated depositional surface is exposed at Heksfjellet. The detrital zircon age pattern obtained from the sandstone (JL-09-14) interbedded with conglomerates does not contain the same ca. 1760 Ma peak as in the sample from the Lifjell Group shallow marine sequence (JL-09-13) only 10 m above in the stratigraphy. Also the Archean is missing in sample JL-09-14. Fieldmapping strongly suggests the presence of a fault between the sampling sites. Zircon evidence supports this. 68 J. Lamminen Provenance and correlation The Snaunetten basin The Snaunetten basin succession in the north contains three different conglomerate types. The basal conglomerate is polymictic in the northernmost tip of the basin (Figs. 3, 5b and c). The sandstone sample (JL-04-30.1) analysed from a bed in the conglomeratic deposit has distinctive age modes at 1123 Ma and 1480 Ma. Palaeoproterozoic zircons are rare. The facies is a parallel-laminated sheetflood sandstone, interpreted to commonly accompany mass-flow conglomerates in alluvial fan settings (e.g. Blair & McPherson 1994). Since Palaeoproterozoic are typically abundant in the Gausta quartzites (Lamminen & Köykkä 2010), this suggests that the nearby Gausta quartzites were not sourced extensively, but that the material came mainly from an area lying to the present northwest. The presence of quartzite clasts similar to the Gausta Formation of the Vindeggen Group in the conglomerates indicates some sourcing from the east, too. Further up in the stratigraphy, the composition of the conglomerate changes rapidly to contain only acid volcanic clasts, which is the most abundant clast type in the entire basin. This means that the fault bounding the basin to the west became more active than the one in the east. Alluvial fans are typical in fault bordered basins and their evolution is commonly directly related to the activity of the fault. Detrital zircon from the southern part of the basin (sample JL-04-75.2) shows a major 1520 Ma peak, and the rest of the peaks are more or less equally abundant. The complete absence of a 1123 Ma peak is a notable difference from the north. Also the 1520 Ma peak is older than the 1480 Ma found in the north, which may be related to local differences in the age of the Tuddal Formation. The Tuddal Formation is large and its age-structure is unknown. The c.1500 Ma ages are probably related to the Tuddal volcanism and the younger c.1123 Ma age is early Sveconorwegian magmatism. The northern part of the Tuddal Formation has some igneous intrusives (The Uvdal plutonic belt), from which the Tinn granite has been dated at 1476 ± 13 Ma (Andersen et al. 2002). No age determinations have been made from the southern part of the Tuddal Formation. The youngest dated porphyry in Telemark is the Skogsåa porphyry at 1145 ± 4 Ma (Laajoki et al. 2002), which is somewhat older than the youngest age peak found in the Snaunetten basin. The youngest volcanic rocks in Telemark, sources of the 1123 Ma peak, may have been eroded away. An enigmatic feature of the Mesoproterozoic sediments in South Norway is the presence of Archaean zircon. No unambiguous solution to this problem exists, but the Lewisian of Scotland or Baltic Shield origins are most likely. The Snaunetten basin has recently been included in the 1155-1150 Ma Røynstaul Formation (Høydalsmo NORWEGIAN JOURNAL OF GEOLOGY Group), mainly because of lithological similarity (Laajoki & Lamminen 2006). The polymictic conglomerate draping the basal contact in its northern part, in Haugset, is lithologically similar to the conglomerates of the Røynstaul Formation around Lake Bandak (Fig. 1) and in a number of other localities nearby (Laajoki & Lamminen 2006). New detrital zircon data place new constraints on the stratigraphic position of the Snaunetten succession. Field data show that the thickness of sediments in the Snaunetten basin is more than 1 km and that there are no interlayers of volcanic rocks. Detrital zircons from the sample close to the bottom of the Snaunetten succession constrain deposition to be younger than 1123 Ma. The Eidsborg Formation is the only regional unit which shares these characteristics. The maximum sedimentation age for the Snaunetten basin is equivalent to the 1118 ± 38 Ma youngest detrital zircon age from the Eidsborg Formation in the small dataset of de Haas et al. (1999). The type locality of the Eidsborg Formation is situated some 5 km southeast from the Snaunetten basin at Lake Bandak (Fig. 1); the Snaunetten basin thus represents an outlier of the Eidsborg Formation preserved from erosion in a down-faulted crustal block. An unconformity below the Eidsborg Formation was predicted by Laajoki et al. (2002), but not supported by data. The present study shows for the first time that the Eidsborg Formation overlies both the Vemork and the Tuddal formations, and also the Oftefjell Group. At Lake Bandak it overlies the Høydalsmo Group. A schematic model of the Snaunetten basin is shown in Fig. 11. The Lifjell Group and the Garvik quartzite Sample JL-09-14 from the Vallar Bru Formation at Nordfjell has a major peak at c.1500 Ma (Fig. 8). The strong 1500 Ma peak indicates Tuddal Formation as the principal source. This is supported by the presence of felsic clasts in the conglomerate in the lower part of the succession (Heksfjellet conglomerate, Laajoki et al. 2002). Laajoki et al. (2002) dated one clast from the nearby Heksfjellet and also obtained a c.1500 Ma age indicating derivation from the Tuddal Formation. The Palaeoproterozoic signature in sample JL-09-14 is most likely recycled from the Vindeggen Group quartzites. Sample JL-09-13 from the main Lifjell Group quartzite at Nordfjell contains a significant amount of Palaeoproterozoic and older grains. The c.1500 Ma peak is minor. The sample itself was sampled close to the sampling site of JL-09-14, on the eastern side of an apparent fault contact. The provenance signature is drastically different and such a rapid change is not likely to be sedimentary. Lamminen & Köykkä (2010) found a trend in the detrital zircon population in the Vindeggen Group where the uppermost parts contained the largest amount of Palaeoproterozoic and older zircon, while the lowermost parts were dominated by c.1500 Ma zircon directly related to the Tuddal magmatism. Due to the covering NORWEGIAN JOURNAL OF GEOLOGY Provenance and correlation of sediments in Telemark, South Norway 69 Figure 11. Basin model for the Snaunetten basin. The Raudsinutan fault is a major boundary between two contrasting lithologies: Rjukan Group volcanics and Vindeggen Group quartzites. The basin history is characterised by episodic activation and de-activation of the boundary faults, reflected in variable conglomerate compositions in the basin. of local rocks by shallow shelf sediments, the local (c.1500 Ma) signal becomes strongly reduced. If the Lifjell Group is correlated with the Vindeggen Group, then the Lifjell Group would fit in this trend and even contain a significant Archaean population to signify distant sources. Based on this and on sedimentological similarity, the part of the Lifjell Group analysed in the present study seems to correlate with the Upper Brattefjell Member (Lamminen & Köykkä 2010) of the Bratte fjell Formation. In the study area, the Upper Bratte fjell Member is located on the NW side of Nordfjell, on the other side of the Slåkådalen-Grunningsdalen fault system(Fig. 2). Many isolated orthoquartzite units occur in the Precambrian bedrock of South Norway (Bingen et al. 2001). Among them the Blefjell quartzite (Andersen et al. 2004a) is a strongly deformed mature sandstone unit in eastern Telemark close to the Heddal Group. This unit poses a similar problem as the Lifjell Group. Field studies have suggested that it either underlies a porphyry dated at 1159 ± 8 Ma (Sørkjevatn Formation, Bingen et al. 2003), or overlies it (Andersen et al. 2004a), but no detrital zircon younger than 1404 ± 11 Ma has been found from the sandstone (Andersen et al. 2004a). The contact between the Blefjell quartzite and the Sørkjevatn Formation is also similar to that of the Lifjell Group and its supposed basal contact with the Brunkeberg Formation porphyry. Also here one can find a quartzite conglomeratic unit (Surtetjørn Formation; Andersen et al. 2004a) and several amphibolites. Thus the setting is analogous to the southern contact of the Telemark Supracrustals; see Andersen et al. (2004a) for detailed descriptions of this area. No distinctive evidence for a volcanic origin has been detected from the Sørkjevatn porphyry, so a subvolcanic origin for the rock is not excluded (Bingen et al. 2003; Andersen et al. 2004a). In Fig. 9 the detrital zircon age pattern from the Blefjell quartzite shows a striking similarity with the Lifjell Group. The Vallar Bru Formation and associated deposits have probably survived from later erosion in a fault zone. It is possible that the Slåkådalen-Grunningsdalen fault is an early sign of Sveconorwegian activity in the bedrock, before the more dynamic period began. Deep fault systems are ideal for preservation of rocks from erosion, which is probably the reason why today we find these conglomerates only within the fault zone. Although previous field evidence has suggested that the Lifjell Group overlies the Brunkeberg porphyry, critical examination of the field descriptions (Laajoki 2002a; Laajoki 2006b) and the author’s own field studies reveal that many of the contacts are in fact not exposed, are strongly sheared, or their syndepositional status is otherwise unclear. As the Vallar Bru and correlative conglomerates bordering the Lifjell Group are intensively sheared and stretched, the younging direction for the beds is impossible to determine. The entire southern part of the Telemark Supracrustals appears to be cut into numerous thrust sheets, which is also evident from the terraced landscape around the Seljord. Two important questions arise. (1) Are the Vallar Bru and correlative conglomerates overturned and in fact underlying the Brunkeberg porphyry? (2) Is the Lifjell Group completely allochthonous and its apparent position above the conglomerates due to tectonism rather than sedimentation? 70 J. Lamminen Diabase dykes in Telemark The Telemark Supracrustals contain several diabase (dolerite) dykes at almost all stratigraphic levels. They are especially abundant in the Vindeggen Group where two have been dated. Near the town of Rjukan, the Hesjåbutind gabbro was dated at 1145 +3/-2 Ma by (Dahlgren et al. 1990b) and near the town of Høydalsmo, the Sandvik diabase was dated at 1347 ± 4 Ma by Corfu & Laajoki (2008). Both basaltic volcanism and the appearance of a dyke swarm in a region indicate crustal extension. The dykes are commonly oriented parallel to the original bedding, resembling sills, or parallel to the regional structural grain. It is not known how many generations of dykes exist in Telemark. However, diabase dykes are very rare in the Bandak basin. As diabase dykes usually denote a distinct event in geological history, they could be used to correlate problematic rock units in southwest Norway. For example the Lifjell Group and the Vallar Bru conglomerates are heavily penetrated by dykes, which is also true for the Blefjell quartzite further in the east. This reasoning would make the Vallar Bru conglomerates and the Lifjell Group older than most of the Bandak Group. Discussion If heavy minerals are going to be used for correlation purposes, the sedimentary environment needs to be well known. A multi-mineral approach including garnet, zircon and rutile has been used successfully in the correlation of Palaeozoic sediments of the North Sea (e.g. Morton 2009). Ideally the sampled sediments are from a facies that represents a sedimentary environment where the sediment has beenwell mixed and homogenised. Lateral variability in the provenance could lead to erroneous correlations. The present study illustrates this phenomenon. In a shallow marine shelf sedimentary environment, homogenisation is very likely due to continuous wave and tidal action and presence of alongshore currents. Conversely, in alluvial environments, rivers have tributaries that may have different provenances. Also mixing in a fluvial environment is not necessarily efficient. Statistical representativity of the samples and random phenomena itself add another complication. The detrital zircon method gives fundamentally different information than field mapping, but has a clear advantage in being an objective method. In a complexly deformed area like Telemark, field relationships are difficult to establish and key lithological contacts are almost always deeply covered by vegetation or are strongly sheared, thus it is possible to misinterpret tectonically formed contacts between adjacent different lithologies to be primary depositional contacts, and vice versa. The Lifjell Group was elevated to group status by Laajoki et al. (2002), after U-Pb dating of the Brunkeberg porphyry to 1155 ±2 Ma. This placed paramount importance on the nature of the porphyry and especially its field relationships. Several observations nevertheless question NORWEGIAN JOURNAL OF GEOLOGY the interpretation of Laajoki et al. (2002): 1) Deposition of the mineralogically mature sandstones of the Lifjell Group are governed by marine processes, while all the other known sediments of the Sveconorwegian succession are continental and alluvial 2) The Lifjell Group is thick, while individual formations in the Sveconorwegian succession are relatively thin; 3) The Lifjell Group does not contain any detrital zircons around 1155 Ma, in spite of the fact that the Brunkeberg porphyry is interpreted to underlie the Lifjell Group via a weathering crust. The weathering crust itself argues for prolonged subaerial exposure and recycling of zircon in the overlying sediment; 4) Several zircon age modes at around 1250 Ma are widely abundant in the Sveconorwegian succession (Bingen et al. 2003; Lamminen et al. 2009; this study), but are completely lacking in the Lifjell Group. If the Lifjell Group was indeed deposited at the same time as the continental Sveconorwegian succession, it should have been deposited on a shallow shelf or/and in a tidal flat environment. This kind of environment gets its detritus from continents by rivers, which according to such a timing would have been a Sveconorwegian mountain range at that time. Thus, it would be logical to think that those rivers were eventually discharged into the sea carrying some < 1350 Ma zircons that would have ended up in the shallow shelf where the Lifjell Group should have been deposited. The abundance of diabase dykes in the Lifjell Group supports the detrital zircon findings that it must correlate with the Vindeggen Group, considered here to have been deposited between 1500 and 1350 Ma. Dating one of these dykes would solve this problem conclusively. The variety of early Sveconorwegian conglomerate deposits in Telemark The Sveconorwegian succession in Telemark is known for its lithological variability. It is almost completely continental and includes diverse conglomerates that change even within the same formation. Most conglomerates are mass flow type deposits that were laid down in alluvial fans, some are interpreted as gravelly braided streams (Köykkä & Laajoki 2009; Köykkä 2011). A gallery of different conglomerates is shown in Fig. 12. It shows that the oldest known Sveconorwegian conglomerate, the Svinsaga conglomerate, consists only of quartzite clasts (Fig. 12a-b). Most of the clasts are red and can be readily traced to the Brattefjell Formation of the Vindeggen Group. The upper member of the Brattefjell Formation is an unusually bright red quartzite unlike any other in Telemark. The Vallar Bru conglomerate is dominated by white quartzite clasts, but include some felsic clasts too (Fig. 12c). Younger conglomerates include acid volcanic clasts and basalt clasts. The Langelinutane Member of the Ofte Formation (Oftefjell Group) has typically only porphyry clasts (Laajoki 2006a) (Fig. 12d). The Røynstaul and Eidsborg conglomerates are polymictic containing various porphyry types, epidotised basalt clasts and white quartzites (Laajoki & Lamminen 2006) (Fig. NORWEGIAN JOURNAL OF GEOLOGY Provenance and correlation of sediments in Telemark, South Norway 71 Figure 12. A gallery illustrating conglomerate clast variability from the Sveconorwegian succession in Telemark. The photographs have been slightly color-enhanced to bring out detail better. (A-B) Conglomerates of the Svinsaga Formation are only made of quartzites, mostly the red quartzite which is characteristic for the Upper Brattefjell Member of the Brattefjell Formation (Photos by J. Köykkä). The stick is c.1 m long. (C) The Vallar Bru Formation is mainly made of white quartzite clasts, but includes some reddish porphyry clasts as well. (D) The Langelinutane Member of the Ofte Formation is almost solely made of various porphyry clasts. (E) The Eidsborg Formation is characteristically polymictic in the basal part including quartzite, porphyries, basalt and schist clasts. (F) A conglomeratic unit called the Kultankriklan conglomerate, can be found as an outlier deposited on top of tilted Vindeggen Group. This unit was originally correlated with the Røynstaul Formation by Laajoki & Lamminen (2006). It can also be correlative with the Eidsborg Formation. Size of nameplate is c.15 cm long. (G) The Eidsborg Formation contains white quartzite and grey granite clasts in its uppermost part. 12e-g). The Eidsborg Formation is especially varied and its clast composition varies over short distances. The uppermost conglomerates of the Eidsborg Formation include abundant granite clasts, which could reflect basement exposure. The change of conglomerate clast composition within a short distance is an indication of a dynamic sedimentary environment, probably a pull-apart basin regime with drainage areas of restricted extent, reflecting local bedrock source rocks. Fault-block tilting and the activation and deactivation of faults lead to changes in the hinterland, exposing different rocks for erosion. In pullapart basins, large lateral movements may move the basin from one source area to another. The same fault activity also changes the sediment dispersal pattern. For the majority of the conglomerates in Fig. 12, the clasts are either quartzites or acid volcanics, but polymictic varieties with basic volcanite clasts are present too. Granite clasts are extremely rare in most of the conglomerates, which suggests that the crystalline basement was not well exposed. Most of the quartzites are probably recycled from the Vindeggen Group and the porphyries are either from the Tuddal volcanics or younger. Pull-apart basins 72 J. Lamminen are usually short-lived and rapidly subsiding basins. They occur in many tectonic settings. A Basin and Range analogy has been suggested for the Telemark area (Dahlgren et al. 1990a; Bingen et al. 2003). The geochemistry of the bimodal magmatic rocks supports this analogy (see discussion in Bingen et al. 2003). Early Sveconorwegian basin developmentin Telemark A model for the development of the Telemark Supracrustals is presented in Fig. 13. The Mesoproterozoic history of the Telemark Supracrustals starts with the Rjukan rift basin, which contains a volcanic core and a thick NORWEGIAN JOURNAL OF GEOLOGY sedimentary cover. At the end of the post rift development in the Rjukan rift basin, South Norway was covered by a shallow sea that left thick quartzitic deposits. These are now found in Telemark (upper part of the Vindeggen Group), Hardangervidda (Hettefjorden and Festningsnutan groups) and possibly in Bamble and Kongsberg (Kragerø and Modum complexes). A detailed account of the Rjukan rift basin is given in Lamminen & Köykkä (2010). If we consider the Lifjell Group as being part of the Vindeggen Group, then the early Sveconorwegian starts with the deposition of the Vallar Bru Formation. The quartzitic cover, left from a long tectonically quiet period, was dissected by faults, and small basins were formed where alluvial fans sourced almost exclusively the old Figure 13. Schematic model for the evolution of the Telemark Supracrustals. (A) Extensional period. The start of the Rjukan Rift Basin involved an enormous amount of bimodal volcanism. It was followed by a long period of sedimentation without volcanism. (B) It is likely that the whole of S Norway was covered by shallow marine sediments and the Rjukan Rift Basin was buried under these. (C) The Vindeggen Group sedimentation was terminated at c.1350 Ma, which is constrained by a diabase sill. A deep regolith was developed on the Vindeggen Group. (D) The thick cratonic cover started to rift apart giving rise to the Svinsaga Formation, and probably the Vallar Bru Formation (V) was deposited first during this period. The first Sveconorwegian volcanic rock overlies the Svinsaga Formation. (E) Extension was concentrated at the southern part of Telemark, where the Bandak basin was formed. It was rapidly filled with bimodal volcanics and coarse sediments. The Oftefjell and Høydalsmo groups were deposited at this time. Occasional periods of rift inversions might have taken place. (F) The extensional period changed into compressional regime and new pull-apart basins were formed. The Snaunetten basin (S) was initiated. NORWEGIAN JOURNAL OF GEOLOGY Vindeggen quartzites. The Tuddal Formation was locally exposed and subjected to erosion. Probably simultaneously, the Bandak rift basin started to form in the south, creating accommodation space for the sediments of the Svinsaga Formation. The conglomerates of the Svinsaga Formation contain solely quartzites and lack porphyries. The tectonic activity increased and was concentrated in the Bandak rift basin and further to the northeast in the Heddal basin. The basin widened and was subject to bimodal magmatic episodes and possibly basin inversion, creating angular unconformities and erosion of previous deposits. The numerous diabase dykes in the Vindeggen Group could have been feeder dykes for the Sveconorwegian magmatism, as suggested by Dons (1962). Basin inversions led to the more polymictic character of the conglomerates. Gradual crustal thickening did not allow the fractures to penetrate to the mantle anymore. The evolution changed from “thin-skinned” to “thick skinned” tectonism (sensu Allen & Allen 2005). The polymictic Eidsborg conglomerates and sandstones were deposited all over Telemark. This study shows indirectly that the Raudsinutan fault bordering the Snaunetten basin succession and the Slåkådalen-Grunningsdalen fault zone bordering the Lifjell Group, were likely synsedimentary and already active in early Sveconorwegian times and have been preserved until today. The Lifjell Group and the SlåkådalenGrunningsdalen fault zone are overlain by the 1145 ± 4 Ma Skogsåa porphyry (Laajoki et al. 2002; Laajoki 2002b) at the base of the Heddal Group (Fig. 2). This places time constraints on the faulting event in the Slåkådalen-Grunningsdalen fault zone and supports the model where the Vallar Bru Formation is the oldest unit in the Sveconorwegian succession. Conclusions U-Pb zircon from a sandstone-conglomerate unit, the Snaunetten basin, in central Telemark, shows abundant zircon with ages: c.1120, 1300 and 1480-1510 Ma and some Palaeoproterozoic and Archaean ages. This rock unit unconformably overlies the Rjukan Group and is correlative to the youngest stratigraphic units of the Telemark Supracrustals, which are the Kalhovd and Eidsborg formations. The c.1500 Ma aged zircon comes from the Tuddal volcanics or associated plutonic rocks in the north, and the younger grains can be matched with rocks in south and southwest Telemark. The Snaunetten basin shows a rapid switching of provenance which indicates a dynamic tectonic environment. The Lifjell Group and its basal conglomerates show no evidence of detrital zircon younger than c.1350 Ma. Based on detrital zircon U-Pb ages, sedimentological similarity, and the abundance of diabase dykes, it is concluded that the Lifjell Group represents a highly Provenance and correlation of sediments in Telemark, South Norway 73 deformed and probably dislocated part of the Vindeggen Group whereas the conglomeratic basal part, the Vallar Bru conglomerate, is probably much younger, correlative to the Sveconorwegian succession. The Garvik quartzite at the southern border of the Telemark Supracrustals is also probably correlative to the Vallar Bru conglomerate and coeval units. The Lifjell Group does not contain any zircon from the c.1155 Ma Brunkeberg Porphyry that has been mapped to underlie the conglomeratic basal part, or from any other volcanic rock of early Sveconorwegian time. It is possible that the Brunkeberg porphyry is a subvolcanic dyke, or that the Vallar Bru conglomerate was deposited earlier than the porphyry was emplaced. 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