The Sveconorwegian orogen of southern Scandinavia: setting, petrology and geochronology of polymetamorphic high-grade terranes

Transcription

1 33 IGC excursion No 51, August 2 5, 2008 The Sveconorwegian orogen of southern Scandinavia: setting, petrology and geochronology of polymetamorphic high-grade terranes Organizers: Jenny Andersson, Geological Survey of Sweden, Uppsala Bernard Bingen, Geological Survey of Norway, Trondheim David Cornell, Göteborg University, Sweden Leif Johansson and Ulf Söderlund, Lund University, Sweden Charlotte Möller, Geological Survey of Sweden, Lund

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3 TABLE OF CONTENTS Abstract... 5 Logistics... 6 Dates and location... 6 Travel arrangements... 6 Accommodation... 6 Field logistics... 6 General Introduction... 7 Regional Geology... 8 The Eastern Segment The Idefjorden Terrane Excursion Route and Road Log Excursion Stops Day 1 Transect across the Sveconorwegian orogenic front Introduction Stop No 1.1: Lu-Hf geochronology of mafic cumulates, example from the old quarry of Taberg Location Introduction Description Stop No 1.2: The Protogine Zone and the Transscandinavian Igneous Belt of the pre-sveconorwegian Fennnoscandian craton Location Introduction Description Stop No 1.3: Zircon formation during metamorphism and deformation of mafic rocks, example from petrology and U-Pb chronology applied to a metabasic intrusion in the Protogine Zone Location Introduction Description Optional stop: Mafic magmatism and mafic dyke swarms along the eastern boundary of the Sveconorwegian orogen Location Introduction Description Stop No 1.4: Direct dating of Sveconorwegian folding in the southern Eastern Segment Location Introduction Description Day 2 Eclogites, high-p granulites and charnockites Introduction Stop No 2.1: Charnockitisation and polyphase metamorphism in the Eastern Segment of the southwest Swedish Gneiss Region. Incipient charnockitization in discrete dehydration zones Location Introduction Description Söndrum zirconology Stop No 2.2: Högabjär: Ion probe zircon dating of polymetamorphic Hallandia gneiss Location Introduction Description Stop No 2.3: Lilla Ammås: Decompressed Sveconorwegian eclogites Location... 46

4 Introduction Description Stop No 2.4: Buskabygd: High-grade tectonites in the Ullared Deformation Zone Location Introduction Description Stop No 2.5: On the occurrence of 1.4 Ga old charnockites in the Southwest Swedish Granulite Region; igneous or metamorphic charnockitisation - or both?...49 Location Introduction Description Day 3 Terrane boundaries and tectonic build up of the Sveconorwegian Orogen Introduction Stop No 3.1: The Mylonite Zone: a major Sveconorwegian structural, metamorphic and lithological terrane boundary in the Fennoscandian Shield Location Introduction Description Stop No 3.2: Age and emplacement conditions of the Chalmers Metagabbro Location Introduction Description Stop No 3.3: Migmatisation in Stora Le Marsstrand graywackes driven by mafic intrusions. Composite dyke development and the origin of calc-alkaline magma series by back-veining and assimilation. Archaean and Early Proterozoic zircon xenocrysts in Mesoproterozoic crust Location Introduction Description Day 4 Terrane boundaries and tectonic build up of the Sveconorwegian Orogen (continued)65 Stop No 4.1: The fate of zircon in crustal processes: ion probe U-Pb-Th (SIMS) and ICP-MS REE and U-Th analyses guided by Cathodoluminescence imaging Location Introduction Description Stop No 4.2: U-Pb, Sm-Nd, Lu-Hf geochronology of Mesoproterozoic mafic intrusions in the Sveconorwegian Province Location Introduction Description Stops 4.3 and 4.4: The Idefjorden terrane west of the Oslo Rift Introduction Stop No 4.3: Preserved Bouma sequences in amphibolite-faces metagreywacke, with garnetamphibolite dykes Location Introduction Description Stop No 4: Pervasive amphibolite-facies garnet blastesis in HP amphibolite-facies conditions Location Introduction Description References... 80

5 Abstract The Sveconorwegian orogen in southern Scandinavia is the result of a collision between Fennoscandia (the southwestern continental segment of Baltica) and another continent in late Mesoproterozoic time. The orogenic province is composed of five distinct Proterozoic gneiss segments that were displaced and reworked during a succession of compressional (and extensional) orogenic phases at between Ga. Sveconorwegian orogenesis culminated in a continent-continent collision phase at Ga that involved regional scale high-pressure granulite metamorphism and local emplacement of eclogites in the southeasternmost part of the orogen. The principal lithotectonic units of the orogen are internally separated by crustal scale deformation zones along which final crustal reconfigurations and tectonic adjustments took place at about Ga. Today, the southwestern Fennoscandian shield areas offers exposures of an exquisite traverse through a partly deep-seated Precambrian continent-continent collision zone(s). The 33IGC premeeting excursion No 51, to the eastern part of the Sveconorwegian orogen, will involve a traverse from well preserved rocks of the pre-sveconorwegian Fennoscandian craton across the Sveconorwegian deformation front into the high-grade gneiss complex of the partly parautochthonous Eastern Segment and further west into the Sveconorwegian allochthon. The excursion participants will be taken to well exposed high-grade metamorphic domains, including the Southwest Swedish granulite region that exhibits a polymetamorphic high-grade gneiss complex with charnockites, high-pressure granulites and tectonically emplaced eclogites. A special focus is set on the timing and character of metamorphism and deformation associated with the orogenic evolution of the eastern part of the orogen. Different aspects on the age and character of protolith rocks in different parts of the orogen will also be highlighted. The excursion to the Sveconorwegian orogen aims to highlight the combination of field geology, metamorphic petrology and different applications of geochronological-geochemical analytical techniques to constrain the timing and character of metamorphic and tectonothermal events in high-grade metamorphic complexes. The individual excursion stops have been selected to include key localities that have been used to construct, characterise and directly date the P-T evolution and tectonic build up of this part of the orogen. A primary goal with the excursion is to bring together structural geologists, metamorphic petrologists, isotope geochemists, geochronologists, and other geoscientists to combine their expertise and discuss how to model tectonic cycles and thereby, how to understand the crustal evolution of our continents. The excursion is prepared as a four days field trip arranged to cover three principal themes regarding the tectonic build up of this part of the Sveconorwegian orogen. (I) Transect across the Sveconorwegian orogenic front, deals with the tectonic build up of the orogenic front and the geochronology of structures and metamorphism related to the tectonic evolution of the easternmost high-grade parts of the orogen. (II) Eclogites, high-p granulites and charnockites, focus on the timing and tectonic setting of high-p and high-p-t metamorphic events in the high-grade gneiss complex of the Eastern Segment. (III) Tectonic boundaries and lithotectonic build up of the Sveconorwegian orogen, concerns the age and tectonic style of metamorphic terrane boundaries and the crustal evolution of allochthonous lithotectonic units overlying the high-p rocks of the Eastern Segment.

6 Logistics Dates and location Timing: From morning on the 2 nd to the evening on the 5 th of August Start location: Participants will be picked up at the Landvetter Airport, Gothenburg from which pre-paid fee starts to apply End location: Participants are dismissed at the Gardemoen Airport outside Oslo for their own return travel arrangements Travel arrangements The excursion is organised as a 4 days pre-meeting field tour in the Sveconorwegian orogen of Scandinavia. The excursion starts in the morning of Saturday 2 nd of August at Landvetter Airport, Gothenburg/Göteborg [one hour flight from any of the Scandinavian capitals (Oslo, Copenhagen or Stockholm). The town of Gothenburg can also easily be reached by train from Copenhagen or Stockholm, a journey of 2.5 to 3.5 hours. The participants will be picked up by the excursion leaders at the Landvetter Airport (Gothenburg Airport). This is a small airport, and participants will be picked up just outside the arrival gates. Transportation from there on will be done by mini buses. The Landvetter airport can also be reached by both domestic and international flights. Please refer to the web for further information at aspx Airport bus from central Gothenburg takes about 30 minutes. During peak hours, air port buses to central Gothenburg depart every 15 minutes. More information available at The excursion ends in the evening of Tuesday 5 th of August in Oslo. Accommodation Overnight accommodation will be in reasonably priced guesthouses or hostels that will provide basic hotel standard (no need to bring sheets or towels). Two nights (2 nd through 4 th of August) will be spent at the Bråtadal hostel in Svartå ( It is an environmental friendly hostel, simple but with an excellent organic food kitchen and located in a picturesque district in the central part of the excursion area. The third night will be spent at the charming Skäret guesthouse on the traffic-free island of Styrsö in the Gothenburg archipelago ( Both guesthouses are rather small and we will be the only guests during our stay there. The guesthouses also have room and equipment for evening seminars. All meals will be provided during the excursion. Dinner and breakfast will be served in at the guesthouses where we stay overnight. Lunch and coffee breaks will be brought along from the guesthouses, to be eaten outdoors if the weather permits. Field logistics During the excursion, transport on mainland will be done by minibus. On the third excursion day we will leave the minibuses on the mainland to take a ferry to visit the traffic free islands of Vrångö and Styrsö (overnight at Styrsö) in the Gothenburg archipelago. Excursion stops do not involve long hikes but participants should have adequate footwear and suitable clothing for walking in rainy weather and in rough and uneven terrain. Rock outcrops may be slippery in rainy weather and always along shorelines. The weather in August is on average, warm and pleasant, with midday temperatures between 15 and 25 C and occasional showers.

7 General Introduction This pre-conference excursion will be held in the Sveconorwegian orogen of southern Scandinavia, a tectonic counterpart to the Grenville orogen in Canada. Here, the shield area exposes an exquisite traverse through a deep-seated Precambrian continent-continent collision zone(s). The orogen is composed of several Proterozoic gneiss segments attached along the southwestern margin of the Baltica proto-continent during a succession of compressional orogenic phases at between Ga. A final continent-continent collision phase at Ga involved high-pressure granulite metamorphism and emplacement of eclogites in the southeastern part of the orogen. The excursion participants will be taken to well exposed highgrade metamorphic domains, including the Southwest Swedish granulite region that exhibits a polymetamorphic high-grade gneiss complex with charnockites, high-pressure granulites and tectonically emplaced eclogitised units. The excursion aims to highlight the combination of field geology, metamorphic petrology and application of different geochronological-geochemical analytical techniques to pin down the metamorphic conditions and the timing of tectonothermal events of high-grade metamorphic complexes. The individual excursion stops have been selected to show key localities used to construct, characterise and directly date the P-T evolution and tectonic build up of the eastern Sveconorwegian orogen in Scandinavia. Our purpose with the excursion is to bring together structural geologists, metamorphic petrologists, isotope geochemists, geochronologists, and other geoscientists to combine their expertise and discuss how to model tectonic cycles and thereby, understand the crustal evolution of our continents. The outline of the excursion follows three main themes: (I, day one) Tectonic build up of the orogenic front; the transition between weakly to unmetamorphosed rocks of the pre-sveconorwegian craton and the high-grade gneisses of the Sveconorwegian Southwest Swedish granulite complex. (II, day two) Geochronology and setting of eclogites, granulites, and charnockites. (III, day three and four) Terrane boundaries and lithotectonic build up of the Sveconorwegian orogen. This pre-conference excursion is thematically linked to a symposia on Geochronology and Isotope geology held in the IGC 2008 meeting, sub-session entitled Geochronology of metamorphic reactions and deformation in high-grade orogenic settings (sub-section MPC- 02). Convenors: Jenny Andersson, Bernard Bingen, David Cornell and Ulf Söderlund

8 Regional Geology At the end of the Mesoproterozoic, the Fennoscandian margin (the present day southwestern segment of continent Baltica) was reworked by orogenic activity that resulted from collision with at least one other major continent, possibly Amazonia (Fig. 1; Hoffman 1991). This orogenic activity is attributed to Sveconorwegian orogensis, and is bracketed in time at between Ga. Today, the imprint of Sveconorwegian orogenic activity remains as a c. 500 km wide, partly deeply eroded, orogenic belt in southwestern Scandinavia. This orogenic province is referred to as the Sveconorwegian orogen (Fig. 2). The orogen is delimited in the east by the Sveconorwegian Frontal Deformation Zone (Wahlgren et al. 1994), a tentative zone outlined by discrete brittle- ductile deformation zones that marks the eastern boundary for Sveconorwegian tectonothermal reworking in Fennoscandia. East of the Sveconorwegian Frontal Deformation Zone are Palaeproterozoic rocks of the c Ga Svecokarelian orogen and largely unmetamorphosed and undeformed rocks of the Ga Transscandinavian Igneous Belt (Fig. 3). Fig. 1. Classical plate reconstruction at the end of the Grenvillian-Sveconorwegian orogeny, with the Sveconorwegian orogen restored to the right of the Grenville orogen (Cawood et al. 2007). The map shows the first order tectonometamorphic correlation between the two belts following compilations and data by Rivers and Corrigan (2000), Rivers et al. (2002), Bingen et al. (2008c), and Söderlund et al. (2008a).

9 The internal parts of the Sveconorwegian orogen includes five principal lithotectonic units (Bingen et al. 2005) separated by roughly N-S-trending crustal scale deformation zones of Sveconorwegian age (Park et al. 1991; Andersson et al. 2002). The principal Sveconorwegian lithotectonic units are, from east to west, the Eastern Segment, the Idefjorden Terrane, the Bamble Terrane, the Kongsberg Terrane and the Telemarkia Terrane (Figs. 2 and 3). These units differ from one another in their Pre-Sveconorwegian as well as their Sveconorwegian crustal evolution, regarding both timing and style of crustal growth, deformation and metamorphism. Rocks affected by orogenic reworking of Sveconorwegian age are present also north of the Caledonian Front. Since these rocks were later reworked during the Caledonian orogeny ( Ma) their tectonic relation to rocks within the Sveconorwegian orogen south of the Caledonian front is at present unclear. Fig. 2. Situation map of southwestern Scandinavia showing the main lithotectonic units and shear zones of the Sveconorwegian orogen. Sveconorwegian orogenesis resulted in widespread high-grade metamorphism, partial melting and deformation of the Fennoscandian crust. Available data and observations provide evidence for a sequence of events covering at least 240 million of years, between c and 900 Ma, including both compressional and extensional tectonic events (Figs. 4 and 5; see review in Bingen et al. 2008a; 2008c). The period prior to the onset of Sveconorwegian orogenesis is characterized by bimodal magmatism at between 1280 to 1140 Ma, variably associated with sediment basins. This magmatism is abundant in the western Sveconorwegian orogen, in the Telemarkia terranes (Laajoki et al. 2002), but extends also deeply into the Fennoscandia craton (Söderlund et al. 2005). It is possibly related to a subduction off-board the Fennoscandian continent. The earliest dated Sveconorwegian high-grade metamorphism is recorded between 1140 and 1125 Ma in the classical Arendal granulites in the Bamble Terrane (Figs. 4 and 5; Smalley et al. 1983). This orogenic phase is referred to as the Arendal phase and may relate to a local collision or accretion at the margin of Fennoscandia. The main

10 Sveconorwegian orogenic event included regional deformation, metamorphism and partial melting in both the eastern and western parts of the orogen between 1050 and 980 Ma. This orogenic phase is called the Agder phase and metamorphism related to this stage varies from lower amphibolite facies to high-pressure granulite facies (Figs. 4 and 5; Bingen et al. 2008b; Söderlund et al. 2008a). Both the tectonic style and the metamorphic grade vary widely between the different lithotectonic units. The Sveconorwegian orogenic evolution included a major compressional event at Ma that resulted in high-pressure granulite and eclogite facies metamorphism in the Eastern Segment of the southeasternmost part of the orogen, (Figs. 4 and 5; Möller 1998; Johansson et al. 2001). This event is referred to as the Falkenberg phase and reflects final convergence related to the main continent-continent collision. Late- Sveconorwegian gravitational collapse took place between c. 970 and 900 Ma during the Dalane phase (Figs. 4 and 5; Bingen et al. 2006). Exhumation and unroofing of the deeply buried crustal domains, extensional reactivation of major shear zones and post-collisional magmatism increasing in volume westwards characterize this stage. This post-collisional magmatism includes the classical Rogaland anorthosite complex at the southwestern end of the Telemarkia terrane (Schärer et al. 1996), that also associated with high- to ultrahightemperature granulite-facies metamorphism of the surrounding gneisses (Tobi et al. 1985; Bingen & van Breemen 1998; Möller et al. 2003). Final relative motion between the Sveconorwegian terranes is estimated at about Ma. Fig. 3. Cummulative probability curves of geochronological data on magmatic events in the five lithotectonic units of the Sveconorwegian orogen. Figure following Bingen et al. (2008c).

11 In terms of thermal and metamorphic evolution, two first order trends emerge from the presently available data. (1) A record of high-pressure metamorphism is preserved in the east of the Sveconorwegian orogen, in the Eastern Segment and Idefjorden Terrane, while low to medium pressure metamorphism prevails in the west. (2) Sveconorwegian magmatism, including syn-collisional and post-collisional magmatism, increases tremendously in volume towards the west, with a sharp increase in the western part of the Idefjorden terrane (the Flå and Bohus granite plutons). This first order zoning of the orogen is analogous to the magmatic and tectonometamorphic zoning of the Grenville belt of Laurentia (Fig. 1). The 33 IGC excursion No 51 covers the eastern parts of the Sveconorwegian orogen which includes the Eastern Segment and Idefjorden terrane and the geology of these two units is reviewed below. The geology of the central and western parts of the Sveconorwegian orogen, including the Telemarkia, Bamble and Kongsberg terranes is reviewed in Bingen et al. (2008a; 2008c). Fig. 4. Summary of geochronological data on high-grade metamorphism in the Sveconorwegian orogen, following Bingen et al. (2008b).

12 Fig. 5. Summary of the distribution of metamorphism, magmatism and sedimentary basins during the Sveconorwegian orogeny. For each time slice, the conditions of metamorphism are summarized in the pressure-temperature space. Figure following Bingen et al. (2008c).

13 The Eastern Segment The Eastern Segment is the easternmost lithotectonic unit of the Sveconorwegian orogen and it forms the parautochthonous basement (at least parts of it) of the orogen. It is composed of Ga orthogneisses of the same age and composition as largely unmetamorphosed and undeformed intrusives of the Transscandinavian Igneous Belt (Fig. 3; Connelly et al. 1996; Söderlund et al. 1999; Söderlund et al. 2002; Möller et al. 2007; Bingen et al. 2008c; Söderlund et al. 2008b). The northern part of the Eastern Segment, north of lake Vänern and the Hammarö Shear zone (Fig. 2), is largely composed of penetratively to semi-penetratively deformed felsic plutonic rocks. Metamorphic conditions are in the amphibolite to greenschist facies. Titanite ages date cooling after Sveconorwegian metamorphism at about c. 960 Ma, but preserved Paleoproterozoic igneous titanite are also found in these rocks (Söderlund et al. 1999). Metamorphism and deformation attributed to pre-sveconorwegian orogenic activity have, so far, not been recorded in the northern parts of the Eastern Segment. The southern part of the Eastern Segment, south of lake Vänern and the Hammarö Shear Zone (Fig. 2), is composed of largely migmatitic orthogneisses commonly interlayered with amphibolite, garnet amphibolite and mafic granulites. Sveconorwegian metamorphism in the southern Eastern Segment reached upper amphibolite to high-pressure granulite conditions. P-T estimates obtained from metabasic rocks in the region yield temperatures between 680 and 770 C and corresponding pressures of 9-12 kbars (Johansson et al. 1991; Wang & Lindh 1996; Möller 1998; Möller 1999; Söderlund et al. 2004). Some of the high-pressure mafic granulite boudins show evidence for being decompressed eclogites (Möller 1998, 1999). Metamorphic zircon from a number of localities brackets Sveconorwegian metamorphism and migmatitization between c. 990 and 960 Ma (Figs. 4, 5; Falkenberg phase; Andersson et al. 1999; 2002; Söderlund et al. 2002; Möller et al. 2007). Zircon inclusions in garnet provide a maximum age of 972 ±14 Ma for the ecolgite-facies metamorphism (Ullared locality; Johansson et al. 2001). Titanite U-Pb data range from 960 to 920 Ma (Connelly et al. 1996; Söderlund et al. 1999; Johansson et al. 2001). The internal parts of the southern Eastern Segment is structurally characterised by large scale upright to moderately overturned E-Wtrending folds with wavelengths of between c km, and sub-horizontal, undulating commonly south-vergent fold axis. The regional scale fold pattern is also easily recognised in high-resolution aeromagnetic anomaly maps (Fig. 6; Möller et al. 2007). Due to a general penetrative Sveconorwegian overprint, pre-sveconorwegian minerals have, as a rule, recrystallised or re-equilibrated. Consequently, little is known about the pre- Sveconorwegian tectonothermal evolution of the Eastern Segment. Robust mineral isotope systems like the U-Pb system in zircon, however, have in places a preserved record of a pre- Sveconorwegian metamorphism. Regional scale migmatisation and in places gneissic layering have been dated at between c and 1420 Ma (Söderlund et al. 2002; Austin Hegardt et al. 2005; Möller et al. 2007). This event is referred to as the Hallandian event. There is increasing geochronological, petrographic and structural evidence that the Hallandian event included substantial high-grade reworking of the southern Fennoscandia in Mesoproterozoic time. The Hallandian event is partly co-eval with orogenic reworking attributed to the Dano-Polonian orogeny described from areas south and southeast of the Sveconorwegian orogen (Bogdanova et al. 2008). The Hallandian event was followed at c Ma by intrusion of partly charnockitic granite and syenitoid rocks, and contemporaneous charnockitisation of side rock gneisses around felsic dyke intrusions at about 1400 Ma (Hubbard 1975; Åhäll et al. 1997; Andersson et al. 1999; Rimsa et al. 2007).

14 The youngest rocks in the southern Eastern Segment are high-angle discordant pegmatitic and granitic dykes dated at about c. 950 Ma (Möller & Söderlund 1997; Andersson et al. 1999; Möller et al. 2007). Structurally young metabasic dykes occur at high-angle discordance to veined gneissic fabrics in the country rocks but are themselves metamorphosed in the highpressure granulite facies. The igneous emplacement age of these dykes is at present unknown. Fig. 6. Aeromagnetic anomaly map of southern Sweden. Abbreviations: PZ=Protogine Zone, MZ=Mylonite Zone, GÄZ=GötaÄlv Zone, e=sveconorwegian eclogite. Part of the airborne magnetic map (total field) over SW Sweden. Data source: Geological Survey of Sweden. Map compiled by Leif Kero, Geological Survey of Sweden, Uppsala.

15 The Sveconorwegian Frontal Deformation Zone (Figs. 2 and 6; Wahlgren et al. 1994; Söderlund et al. 2004) delimits the Eastern Segment in the east. It forms a tentatively outlined border zone for the eastern extension of the Sveconorwegian orogen and is outlined by discrete brittle- ductile deformation zones that mark the eastern boundary for Sveconorwegian tectonothermal reworking in Fennoscandia. South of lake Vättern, the Sveconorwegian Frontal Deformation Zone borders the eastern parts of the Protogine Zone, a prominent deformation zone system that marks a conspicuous boundary between high-grade orthogneisses of the Eastern Segment, and non-penetratively deformed and unveined rocks of the Transscandinavian Igneous Belt (Figs. 2 and 6). The Protogine Zone it self forms a c. 25- km wide structural and metamorphic transition zone composed of numerous discrete, subvertical, N-S-trending deformation zones. It played a central role for the tectonic juxtaposition of previously deeply buried rocks of the Eastern Segment in late Sveconorwegian time. In the west, the Eastern Segment is separated from overlying Sveconorwegian allochthonous terranes by the Mylonite Zone (Figs. 2 and 6). The southern section of the Mylonite Zone is a shallowly west-dipping prominent deformation zone that forms a major lithological, metamorphic and structural terrane boundary (Andersson et al. 2002). The Mylonite Zone north of lake Vänern is interpreted as a sinistral transpressional thrust zone with an overall top-to-the-southeast transport direction (Park et al. 1991; Stephens et al. 1996). The Mylonite Zone is reworked as a normal extensional shear zone in late Sveconorwegina time (Berglund 1997). Zircon U-Pb data in the southern section of the Mylonite Zone and its direct hangingwall and foot-wall record amphibolite-facies metamorphism and migmatitization at between 980 and 970 Ma (Larson et al. 1999; Andersson et al. 2002). This interval is equivalent, within error, to the age of high-grade metamorphism in the Eastern Segment. Indirect estimates for extensional tectonics along the southern sections of the Mylonite Zone are provided by hornblende 40 Ar/ 39 Ar plateau ages between c. 920 and 910 Ma, a titanite age at c. 920 Ma and a zircon age in a stromatic migmatite at c. 920 Ma (Johansson & Johansson 1993; Page et al. 1996; Scherstén et al. 2004). The Idefjorden Terrane The Idefjorden Terrane (Fig. 2) is made up of c Ma plutonic and volcanic rocks, associated with greywacke-type metasedimentary sequences (Fig. 3; Åhäll et al. 1998; Brewer et al. 1998; Åhäll & Larson 2000; Bingen et al. 2001; Andersen et al. 2004; Åhäll & Connelly 2008). The magmatic rocks generally have calc-alkaline and tholeiitic compositions, typical for supra-subduction zone magmatism. The lithologies show a general younging towards the west. The Horred metavolcanic rocks (c Ma) are exposed in the southeastern part of the terrane close to the Mylonite Zone. The Åmål supracrustal rocks and the coeval Göteborg granite suite (c Ma) form a belt situated to the east of the c Ma Stora Le-Marstrand Formation and the Hisingen plutonic suite. These lithologies were assembled during the Gothian accretionary orogeny (Andersen et al. 2004; Åhäll & Connelly 2008; Bingen et al. 2008a). Amphibolite-facies metamorphism and deformation associated with Gothian orogenesis have been constrained at about 1540 Ma (Connelly & Åhäll 1996; Åhäll & Connelly 2008; Bingen et al. 2008b). The Ma "Gothian" lithologies were intruded by the bimodal plutonic Kungsbacka suite between 1340 and 1250 Ma (Austin Hegardt et al. 2007), and by Sveconorwegian post-collisional norite-granite plutons between 960 and 920 Ma (Eliasson & Schöberg 1991; Scherstén et al. 2000; Årebäck & Stigh 2000; Hellström et al. 2004; Bingen et al. 2006). These include the Flå and Bohus plutons. West of Lake Vänern, the Gothian and Kungsbacka metaintrusive rocks are overlain by the poorly dated supracrustal Dal Group (Brewer et al. 2002).

16 The Idefjorden Terrane shows a general N-S to NW-SE Sveconorwegian structural trend. It contains several amphibolite-facies orogen-parallel shear zones, including the Ørje Shear Zone (Norway) or Dalsland Boundary Zone (Sweden) and the Göta Älv Shear Zone (Fig. 2; Park et al. 1991). These shear zones are interpreted as transpressive thrust zones (Park et al. 1991). One zircon date at 974 ±22 Ma records metamorphism in the vicinity of the Göta Älv Shear Zone, and may record deformation along this shear zone (Ahlin et al. 2006). Sveconorwegian metamorphism is variable in the Idefjorden Terrane and ranges from greenschist-facies to amphibolite-facies and locally granulite-facies conditions. East of the Göta Älv Shear Zone and Dalsland Boundary Zone, the Åmål supracrustal rocks are well preserved and partly show greenshist-facies metamorphism only. In contrast, high-pressure mafic granulite boudins occurs in a high-grade gneiss complex located immediately south of lake Vänern (Gaddesanda locality, stop 4:2; Figs. 4 and 7; Söderlund et al. 2008a). The gneiss protoliths are dated at about 1.6 Ga (they are thus coeval with the Åmål supracrustals) and the high-pressure granulite-facies metamorphism is dated between 1050 and 1025 Ma (Agder phase; Söderlund et al. 2008a). West of the Göta Älv Shear Zone and Dalsland Boundary Zone, amphibolite-facies metamorphism is dated between c and 1020 Ma, according to zircon and titanite data (Hansen et al. 1989; Austin Hegardt et al. 2007). West of the Oslo rift, high-pressure amphibolite-facies conditions are locally recorded (Hensmoen locality; Figs. 4, 5; Bingen et al. 2008b). Monazite and titanite dates in these rocks range from c to 1025 Ma (Bingen et al. 2008b). High-pressure conditions are dated at c Ma in a kyanitebearing metapelite. To the west, the Idefjorden Terrane is separated from the Telemarkia Terrane by the southwest dipping Vardefjell Shear Zone. It is characterized by amphibolite-facies banded gneiss rich in amphibolite-layers and amphibolite boudins. The timing of amphibolite-facies metamorphism in the banded gneiss is estimated at c Ma according to zircon data (Bingen et al. 2008b), implying that ductile deformation along the Vardefjell Shear Zone is coeval or younger than c Ma. Fabric-parallel titanite may record continued deformation at 985 ±5 Ma (Bingen et al. 2008b). The Vardefjell Shear Zone is tentatively interpreted as a thrust zone.

17 Excursion Route and Road Log Fig. 7. Simplified geological outline of the Sveconorwegian orogen in southern Scandinavia (southern Baltic Shield). Locations of excursion stops are shown in magnified inset to the right. The excursion to the Sveconorwegian orogen of Scandinavia is organised as a four days field trip arranged to cover three principal themes on the tectonic build up of the eastern part of the orogen. The first theme, Transect across the Sveconorwegian orogenic front, (day 1, stop ) deals with the tectonic architecture of the orogenic front and the geochronology of structures and metamorphism connected to the tectonic evolution of the easternmost highgrade parts of the orogen. The second theme, Eclogites, high-p granulites and charnockites, (day 2, stop ) focus on the timing and tectonic setting of high-p and high-p-t metamorphic events in the high-grade gneiss complex of the Eastern Segment (the easternmost, partly parautochthonous part of the Sveconorwegian orogen). The third topic, Tectonic boundaries and lithotectonic build up of the Sveconorwegian orogen, (day 3 and 4, stop ) deals with the age and tectonic style of metamorphic terrane boundaries and the crustal evolution of allochthonous lithotectonic units that are overlying the high-p rocks of the Eastern Segment. The three different topics of the excursion will be presented in more detail below in introductory sections preceding the descriptions of the excursion stops. The locations of the individual excursion stops are indicated on detailed maps included in the description for each stop (in addition to co-ordinates for the outcrops given in UTM Zo33 and Zo32, Northern Hemisphere). A geological outline of the eastern part of the Sveconorwegian orogen, with the individual excursion stops indicated on the map, is given in figure 7.

18 Day 1. Transect across the Sveconorwegian orogenic front The excursion starts in the morning of the 2 nd of August at Landvetter airport. We will drive highway R40 to Jönköping and continue on highway E4 towards the south (towards Helsingborg) to reach Smålands Taberg and Stop 1.1. Here we will look at classical out crops of early Sveconorwegian mafic cumulates and discuss Lu-Hf geochronological and petrological data, and ore geology of these rocks and the implications for the tectonic evolution of the Protogine Zone. We will continue southwards along highway E4 to the Hok valley and Stop 1.2 where we will look at the onset of Sveconorwegian deformation in metagranites of the Transscandinavaina Igneous Belt. These out crops are located in the eastern Protogine Zone that forms the boundary for penetrative and non-penetrative Sveconorwegian deformation in the Fennoscandian shield. Thereafter we will drive westwards, across highway E4 and take road 152 towards Gnosjö to look at variously metamorphosed and deformed metabasic rocks in the westernmost parts of the Protogine Zone at Åker (Stop 1.3). This stop will highlight aspects on the tectonic evolution of the eastern boundary of the Sveconorwegian orogen and different techniques to directly date metamorphic reactions in mafic rocks. Continue westwards along road 27 for an optional stop in the partly well preserved mafic dolerites (Hyperites) at Herrestad (Optional stop). These are examples of the mafic magmatism and mafic dyke swarms that occur along the eastern boundary of the Sveconorwegian orogen. Continue westwards along roads 27 and 153 to reach Stop 1.4 where we will look at Sveconorwegian migmatitic gneisses at Oxanäset. These gneisses have been used for U-Pb-Th ion probe zircon analytical work intimately integrated with geological and aeromagnetic bedrock mapping for direct dating of migmatisation and synchronous conspicuous regional scale E-W folding characteristic for the internal parts of the southern Eastern Segment. We continue towards the west for dinner and overnight at the Svartrå, Bråtadal hostel. Day 2: Eclogites, high-p granulites and charnockites In the morning, we drive southwards towards Halmstad to reach the harbour and the old abandoned quarry at Söndrum (stop 2.1). Here we will look at incipient charnockitization in dehydration zones in the well-exposed walls of the quarry as well as excellent coastal exposures of patchy charnockites along the shoreline. The locality will highlight aspects on the geochemistry, isotope geochemistry and geochronology of charnockitisation and polyphase metamorphism in the Eastern Segment. Continue to stop 2.2, and the abandoned quarry at Högabjär, just east of Halmstad, where we will look at key localities for polymetamorphic gneisses used to define 1.44 Ga migmatisation, 1.40 Ga granitic dyke intrusion, and post-1.40 Ga folding in the Eastern Segment. We drive back towards the north along highway E6 and at Falkenberg we turn eastwards at road 154 to Ullared. Here we will visit localities with decompressed Sveconorwegian eclogites at Lilla Ammås (stop 2.3) and the high-grade tectonites in the Ullared Deformation Zone at Buskabygd (stop 2.4). These localities include out crops of former eclogite, deformed and recrystallised into granulite facies mylonitic gneiss and intercalated with felsic gneiss. The outcrops are key localities for studies of the petrology, geochronology and tectonic evolution (extent and mode of emplacement) of relict eclogite mafic boudins in the Ullared Deformation Zone. Focus of these two excursion stops is also aspects on the tectonic role of the Ullared Deformation Zone, and the timing and character of deformation in the eclogite-bearing parts of the zone. We continue towards the west on road 153 to Varberg to look at coastal exposures of 1.4 Ga old charnockites at Getterön (igneous or metamorphic charnockitisation - or both? stop 2.5). Drive back towards the east on road 153 for dinner and overnight at Bråtadal, Svartrå hostel,

19 Day 3: Terrane boundaries and lithotectonic build up of the Sveconorwegian orogen Drive towards the west on road 153 to Varberg and then northwards on the old highway E6 to reach the Årnäs peninsula where rocks in the Mylonite Zone are exposed along the southern shore of the Klosterfjord (stop 3.1). Here we will look at rocks used to constrain the age and tectonic role of the Mylonite Zone; a major structural, metamorphic and lithological Sveconorwegian terrane boundary that separates rocks of the parautochthonous Eastern Segment from overlying allochthonous lithotectonic units in the west. We continue northwards on highway E6 to central Gotheburg and the university of Chalmers (stop 3.2). Here we will look at an about 1.3 Ga old metagabbro that have been in focus for studies of diapiric wall rock melts, ion probe geochronology of xenocryst zircon and metamorphic titanite and constraints of P-T conditions from cation partition thermobarometry. Drive to the harbour at Saltholmen to catch a ferry to the Vrångö island in the southern Göteborg archipelago (stop 3.3). Here we will look at migmatisation of Stora Le Marsstrand graywackes driven by mafic intrusions and composite dyke development and the origin of calc-alkaline magma series by back-veining and assimilation. Catch the ferry to Styrsö for dinner and overnight at Guesthouse Skäret, Day 4: Terrane boundaries and lithotectonic build up of the Sveconorwegian orogen (continued) In the morning, ferry to mainland and the Saltholmen harbour. Drive across Gothenburg towards Stora Lundby and stop 4.1. Here we will look at metamafic rocks that have been in focus for ion probe U-Pb-Th (SIMS) and ICP-MS REE and U-Th analyses of zircon guided by Cathodoluminescence imaging to explore the fate of zircon in crustal processes. Continue northwards on road 45 towards Trollhättan and Gaddesanda (stop 4.2). Here we will look at high-p granulite facies metadolerites analysed for U-Pb, Sm-Nd, Lu-Hf isotopes to date and characterise Mesoproterozoic mafic intrusions and their metamorphic history in the Idefjorden terrane. Drive towards the west on road 44. At the intersection with highway E6, turn north towards Oslo. Drive to Veme in the Hönefoss area to look at preserved Bouma sequences in amphibolite-faces metagreywacke, with garnet-amphibolite dykes in the western Idefjorden Terrane (stop 4.3). Continue to Hensmoen to look at pervasive amphibolite-facies garnet blastesis in HP amphibolite-facies conditions (stop 4.4). Drive back to Oslo. Excursion ends in Oslo. The minibuses will return to Gothenburg in the evening of day four, immediately after the excursion and participant are welcome to follow us back to Gothenburg.

20 Excursion Stops Day 1 Transect across the Sveconorwegian orogenic front Introduction The first day we will visit localities within and west of the Protogine Zone. The scope of the day is the tectonic role of the Protogine Zone; the border zone between unmetamorphosed to moderately metamorphosed rocks of the Transscandinavian Igneous Belt in the pre- Sveconorwegian craton and high-p granulite facies rocks in the Sveconorwegian Orogen. Focus will be on structural and metamorphic terrane boundaries across the Protogine Zone and geochronology and isotope geochemistry of metamorphic and igneous events associated with these structures. The first excursion stop is made within the c Ga Småland Taberg ultra mafic body, which belongs to a suite of Ga mafic to syenitoid and granitic igneous rocks located along the Protogine Zone. The magmatic activity confined to the Protogine Zone may reflect intracratonic tension in response to tectonic activity at the continental Fennoscandian margin and thus marks the onset of Sveconorwegian orogenic activity. The second excursion stop is made within non-penetratively deformed rocks of the Transcandinavian Igneous Belt to look at the onset of Sveconorewgian deformation in the Protogine Zone. The third stop is made in the westernmost parts of the Protogine Zone, and immediately west thereof, where detailed zircon geochronology and petrography of metamafic intrusions testify of the tectonic evolution of the eastern part of the Sveconorwegian orogen. The third stop is an optional locality within a metamafic intrusion that belongs to one (or several) generation(s) of mafic dyke swarms found in the easternmost parts of the Sveconorwegain orogen. Isotope geochronology and isotope geochemistry of these mafic rocks combined with petrography and field data are used for models of the crustal evolution of this part of the shield area. The forth ands last stop of the day is located well within the lower western level of the Eastern Segment which is typically composed of migmatite gneisses intercalated with high-p granulite facies and upper amphibolite facies metabasic rocks. The structural grain is here dominated by large scale E-W to NW-SE trending folding of the lithological and gneissic banding. The locality exhibits folded migmatite gneiss intercalated with garnet amphibolite boundins, and is a typical representative of the gneiss complex that compose the internal lower level parts of the southern Eastern Segment. Stop No 1.1: Lu-Hf geochronology of mafic cumulates, example from the old quarry of Taberg Location Smålands Taberg (UTM Zo33 NH: / ). Outcrop in the old quarry of Taberg. Drive from Landvetter airport towards Jönköping along highway R40. From Jönköping, take the E4 highway towards the south (direction Helsingborg). Turn right at Torsvik and then left towards Taberg (road no 93).

21 Introduction The Smålands Taberg is an ultramafic intrusion located within the Protogine Zone. It belongs to a generation of c Ga old mafic, syenitoid to granitic intrusions located within and along the southern parts of the Protogine Zone. These intrusions testify to the early onset of Sveconorwegian tectonic activity in Fennoscandia. A simplified map of the main lithologies at Taberg is given in Figure Topics of interest: - Emplacement, petrology, and ore geology of the Taberg mafic cumulates implications for the tectonic evolution of the Protogine Zone - The use of the Lu Hf apatite chronometer Description Smålands Taberg is famous for its Fe-Ti ore deposits (in magnetite-rich melatroctolite). The mineralization is depleted in incompatible elements which precludes the use of minerals (baddeleyite, zircon, titanite or apatite) commonly used for dating the emplacement of igneous rocks. Patches of leucogabbro in the melatroctolite have REE patterns and initial Hf and Nd isotope compositions identical with the host melatroctolite (Fig ). These characteristics are conclusive evidences for a common parental magma such that the leucogabbro crystallized after fractionation of olivine and titanomagnetite; two major mineral phases in the melatroctolite. The age of this ultramafic body was recently determined by Lu-Hf apatite chronology (Fig.1.1.3; Larsson & Söderlund 2005). Apatite and plagioclase separated from the leucogabbro plus a whole rock sample define a Lu-Hf isochron with a slope corresponding to an age of 1204 ± 2 Ma. This result falls into the lower group of a magmatic syenite-granite suite in southern Sweden (Söderlund & Ask 2006). Clearly, the Lu-Hf isotope system offers an important technique for dating Si-unsaturated rocks that lack baddeleyite or zircon. Guides: Ulf Söderlund (Geobiosphere Science Centre, Lund University). Literature: Larsson & Söderlund (2005)

22 Pegmatite Melatroctolite Gabbro Amphibolite (metagabbro) Gneiss granite Mylonite Strike and dip Fault 275 Leucogabbro inclusions 100m Taberg 341. A Modified from Hjelmqvist 1950 Fig Simplified map showing the main lithologies at Taberg. Modified from Hjelmqvist (Larsson & Söderlund 2005).

23 Fig REE-diagram showing parallel trends of various lithologies that indicate a common source. Figure taken from Larsson & Söderlund Fig Lu-Hf isochrone diagram including three apatite fractions of strongly elevated Lu/Hf ratios (outside diagram). Note wr D7 (Melatroctolite) plot just outside the 1204-Ma isochrone. Figure from Larsson & Söderlund (2005). 23

24 Stop No 1.2: The Protogine Zone and the Transscandinavian Igneous Belt of the pre- Sveconorwegian Fennnoscandian craton Location Hok valley, Hok manor. (UTM Zo 33 NH: / ). Drive southwards along highway E4 from Jönköping towards Helsingborg. At Skillingaryd, turn east towards Hok. Introduction The Transscandinavian Igneous Belt forms a roughly N-S trending magmatic belt that intrude rocks of the Palaeoproterozoic Svecofennian Province east of the Sveconorwgeian orogen. South of Lake Vättern, the Transscandinavian Igneous Belt is mainly composed of Ga old granites, monzonites and quartzmonzodiorites. The more intermediate compositions characteristically contain mafic enclaves. Gabbroic rocks are sparse and typically show magma mingling and mixing with their side rock along the contacts. E-W-trending belts dominated by felsic volcanic rocks, mainly rhyolites, are also present. A transection across the Protogine Zone, from east to west, exposes a transition of non-metamorphosed to weakly metamorphosed intrusives of the Transscandinavian Igneous Belt into high-grade orthogneisses to the west of the zone. Major lithological changes are bound by deformation zones. The migmatitic orthogneisses in the southern Eastern Segment are of the same age and composition as rocks in the western parts of the Transscandinavian Igneous Belt. It is suggested that these gneisses are reworked equivalents to rocks of the Transscandinavian Igneous Belt of the pre-sveconorwegian Fennoscandian craton and that these rocks, at least in part, form the parautochthonous basement of the Sveconorwegian orogen. Description The area of the Hok valley exhibit outcrops with near isotropic granite (Barnarp granite) typical for felsic intrusives of the Transscandinavian Igneous Belt of the pre-sveconorwegian Fennoscandian craton. The Hok valley also exposes out crops in which the onset and progressive development of Protogine Zone deformation can be studied. In this area, near isotropic megacrystic granite with mantled feldspars (Barnarp granite) pass into shear zones 24

25 with pervasively foliated (schistose) metagranite. These rocks also contain a conspicuous steeply west plunging stretching lineation (290/60), defined by K-feldspar and quarts. Rotated K-feldspars and C-S-fabrics indicate a top to the east sense of shearing. (Description of the Hok Valley granites is based on unpublished excursion guide by Per- Gunnar Andreasson, Lund University, Lund, Sweden, NorFa Field Seminar 1999, day 1 the Protogine Zone ). Guides: Charlotte Möller and Jenny Andersson (Geological Survey of Sweden) Literature: Andreasson & Dallmeyer (1995) Stop No 1.3: Zircon formation during metamorphism and deformation of mafic rocks, example from petrology and U-Pb chronology applied to a metabasic intrusion in the Protogine Zone Location Åker (on the boundary between the Eastern Segment and the Protogine Zone). (UTM Zo 33 NH: / ). Drive south from Jönköping on highway E4 towards Helsingborg. At Skillingaryd, c. 50 km south of Jönköping, turn right (west) at road no 152 towards Gnosjö. The Åker metabasite crops out in an about 20 m long road cut along the road. Introduction At least three different generations of mafic intrusions occur along the eastern border of the Sveconorwegian orogen emplaced at about 1.6, 1.4, 1.2 and 0.9 Ga respectively. The Åker metabasic intrusion belongs to the oldest generation (c. 1.6 Ga old) and records petrographic and geochronological evidence of a prolonged igneous and tectonic evolution of this easternmost part of the Sveconorwegian orogen. The road cuts at Åker exhibit metabasic rocks in various state of reworking ranging from well preserved isotropic gabbro to penetratively oliated garnet amphibolite (Fig.1.3.2). The metamorphic reactions are associated with release of Zr and growth of metamorphic zircon (Fig.1.3.3). Four stages of zircon growth have been recognised and directly dated the Åker locality (Fig.1.3.3). The behaviour and robustness of the Sm-Nd and Lu-Hf isotope systems during metamorphism have also been studied at this locality. 25