Pressure, Temperature and Time Constraints on Tectonic Models for Southwestern Sweden 2010 ISBN 978-91-628-8211-2 ISBN

Home , Gothian orogeny

Ph.D. thesis Ph.D. UniversityGothenburg of Eric Austin Hegardt HegardtEric Austin Department Earth of Sciences for Southwestern Sweden Constraints Models on Tectonic Pressure, Temperature and Time Time and Temperature Pressure,

Eric Austin Hegardt Pressure, Temperature and Time Constraints on Tectonic Models for Southwestern Sweden 2010 ISBN 978-91-628-8211-2 ISBN

University of Gothenburg Faculty of Science 2010

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Eric Austin Hegardt

Göteborg University Department of Earth Sciences Geology BOX 460 SE-405 30 Göteborg SWEDEN

Göteborg 2010 Earth Sciences Centre Doctoral Thesis A134

Pressure, temperature and time constraints on tectonic models for southwestern Sweden Eric Austin Hegardt

Abstract

In this work, a number of key localities have been investigated in detail in order to provide precise constraints on models for the tectonic evolution of southern Sweden. The new data presented in this thesis show that there are large differences in terms of pre-Sveconorwegian tectonic evolution between the Eastern and Median-Western Segments situated on either side of the Mylonite Zone, a major shear zone as well as a structural and lithological boundary. This has a direct influence on the possible tectonic scenarios that can be suggested when reconstructing the formation of the south-western part of the Fennoscandian Shield.

At Viared in the central Eastern Segment, Sveconorwegian eclogite facies metamorphism is dated at 0.97 Ga using mainly U-Pb on zircon. This is similar to other localities showing high-pressure granulite or eclogite facies metamorphism in the Eastern Segment and suggests that this high grade event was a regional feature east of the Mylonite Zone.

On the well exposed Nordön Island in the Western Segment, both pre-Sveconorwegian and Sveconorwegian metamorphism and deformation was dated using several isotope methods, including U-Pb SIMS zircon and Sm- Nd garnet dating. In the Median Segment, veining was dated using U-Pb SIMS zircon methods. In addition to age determinations, thermobarometry was done on several samples and the results compared with published data. The results show that Sveconorwegian peak metamorphism reached amphibolite to granulite facies west of the Mylonite Zone at 1.02-1.04 Ga. This is 50-70 Ma before the orogenic activity started in the Eastern Segment.

In the central Eastern Segment, Pre-Sveconorwegian veining is dated at 1.42 Ga, thus belonging to the 1.42-1.46 Ga Hallandian veining found elsewhere in the Eastern Segment. Pre-Sveconorwegian veining and isoclinal folding in the Western Segment is dated at 1.55 Ga. Neither the 1.55 Ga nor the 1.02-1.04 Ga events have been found in the Eastern Segment. Further, the 1.42-1.46 Ga veining event documented in the Eastern Segment has not been found in the Western or Median Segments. Only a few 0.97 Ga zircon U-Pb ages have been found in the Western and Median Segments west of the Mylonite Zone. In the Western Segment, Ar-Ar dating of muscovite related to late Sveconorwegian uplift gives 981±4 Ma, interpreted to reflect the crystallization of muscovite below 400 °C. This indicates that the Western Segment already was exhumed at the time when the Eastern Segment experienced its Sveconorwegian high-pressure peak metamorphism.

Additionally this work shows that there is an age difference between the 1.34 Ga Askim, the 1.30 Ga Göta and 1.31 Ga Kärra granites west of the Mylonite Zone and the 1.38-1.40 Ga granites and monzonites east of the Mylonite Zone, thus disproving the previous concept of “stitching granites” that was used as an argument for a pre-Sveconorwegian correlation between the Eastern and Western Segments. The differences in pre- Sveconorwegian history between the segments east and west of the Mylonite zone suggest that the zone originally formed as a Sveconorwegian first order crustal suture. However, no ophiolites have been found along the zone and no calk-alkaline magmatism related to subduction of oceanic crust slightly before 0.97 Ma has yet been documented. If such features were found it would strengthen the idea that the Mylonite Zone is a crustal suture, however their lack does not preclude it.

Geothermobarometry on retrograde eclogite facies rocks exposed at Viared indicates that those rocks experienced metamorphic conditions of 15.0–16.7 kbar at temperatures of 719 to 811°C. The equivalent burial depth of ~50 km is compatible with metamorphism in a subduction setting. The partial preservation of a high pressure paragenesis indicates rapid exhumation after burial. A two-dimensional model involving continental subduction of the Eastern Segment is proposed to explain the cycle of eclogite and high-pressure granulite facies that took place during the ~0.97 Ga Falkenberg phase of the Sveconorwegian Orogeny.

Keywords: Sveconorwegian, Gothian, Hallandian, U‐Pb zircon ion probe dating, Sm-Nd garnet dating, thermobarometry, continental subduction, Eastern Segment, Median Segment, Western Segment

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Included in this thesis are five papers (four as first author, one as co-author) of which three are published in GFF, one has been submitted and one is not yet submitted. The papers are:

Eclogites in the central part of the Sveconorwegian Eastern Segment of the Baltic Shield: Support for an extensive eclogite terrane. By Austin Hegardt, E., Cornell, D., Claesson, L. Simakov, S., Stein, H. & Hannah, J., 2005: GFF, Vol. 127, pp. 221–232. Reprinted with permission from GFF

Emplacement ages of the mid-Proterozoic Kungsbacka Bimodal Suite, SW Sweden. By Austin Hegardt, E., Cornell, D., Hellström, F.A. & Lundqvist, I., 2007: GFF, Vol. 129, pp. 227–234. Reprinted with permission from GFF

Nature and stratigraphic position of the 1614 Ma Delsjön augen granite-gneiss in the Median Segment of south-west Sweden. By Ahlin, S., Austin Hegardt, E. & Cornell, D., 2005: GFF, Vol. 128, pp. 21–32. Reprinted with permission from GFF

Relative and Absolute Temporal Relationships between Folding, Foliation and Metamorphism of the Stora Le-Marstrand Formation in the Sveconorwegian Province, Baltic Shield. By Austin Hegardt, E., Stigh, J., Cornell, D., Sjöström, H., Anczkiewicz, R., Page, L., Finger, F. Submitted to Mineralogy and Petrology.

An exhumation model for the eclogite-bearing Eastern Segment in the Sveconorwegian Province of the Baltic Shield. By Austin Hegardt, E., Cornell, D. Manuscript.

Authors are indicated in order of their contributions with the first author as the main writer. I have contributed to both field work and analytical work including isotope work (ion-probe U- Pb zircon and titanite dating, wet chemical methods for Sm-Nd and Lu-Hf garnet dating and sample preparation for Ar-Ar hornblende and muscovite dating). My contributions also include petrography, geochemistry, SEM-EDS work, interpretations, writing and the preparation and submission of the manuscripts. My estimated contributions to the specific papers are: Paper I, 60 %, paper II, 70%, paper III and IV 50% and paper V, 80%.

The Re-Os analyses in paper I were done by co-authors H. Stein and J. Hannah and garnet- clinopyroxene pressure calculations were done by co-author S. Simakov. The Ar-Ar analyses in paper III were done by co-author L. Page and the U-Pb electron-probe U-Pb isochron dating on xenotime was done by co-author F. Finger.

Austin Hegardt 2010

Contents

Introduction ...... 1 Summary of the papers ...... 5 Paper I...... 5 Paper II...... 6 Paper III...... 6 Paper IV ...... 7 Paper V ...... 8 Summary of the Sveconorwegian Orogeny ...... 9 Sveconorwegian tectonic units ...... 9 The Eastern Segment ...... 9 Western and Median Segments ...... 12 The Kongsberg and Bamble Terranes ...... 14 The Telemarkia Terrane ...... 14 Sveconorwegian Shear Zones in SW Sweden ...... 15 The Protogine Zone and Sveconorwegian Frontal Deformation Zone ...... 15 The Mylonite zone ...... 15 Constraints on tectonic models for the Sveconorwegian Orogeny ...... 16 Terrane analysis ...... 16 Is the Mylonite Zone a Sveconorwegian crustal suture? ...... 16 Presence of ophiolites ...... 16 Differences in rock ages ...... 17 Differences in metamorphic history ...... 17 Closure of an ocean, subduction and related magmatism...... 17 Structural aspects ...... 18 Does the Mylonite Zone need to be a Sveconorwegian suture? ...... 18 Tectonic models for the Sveconorwegian orogeny ...... 20 Conclusions ...... 21 Acknowledgements ...... 22 References ...... 23

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

geological features. Such a model is a way Introduction to visualise a tectonic sequence of events, linking cause and effects (Paper V). The 1.15-0.9 Ga Sveconorwegian Province occupies the polymetamorphic region of Traditional models describing the southwestern Sweden and southern formation of the Fennoscandian Shield Norway (Fig. 1). The region is, with only envisage successive growth from an minor differences, also commonly referred Achean nucleus located in the present to as the Southwest Scandinavian Domain northeastern part of the shield (Gaal & (SSD). The complex history of this area Gorbachev, 1987). In this model, the during and before the Sveconorwegian Southwest Scandinavian Domain has been orogeny has been a matter of debate for part of the Fennoscandian shield since the more than 100 years. In 1936, Wahl end of the Gothian cycle which was introduced the name Gothian for the completed at about 1.5 Ga (Åhäll & orogenic cycle that caused folding in Connelly, 2008). southwestern Sweden and southwest Norway, at that time considered to be Understanding the pre-Sveconorwegian Archean in age. When radiometric dating history is of utmost importance as it became available, rocks in the region gave provides possible starting points for any ages younger than 1130 Ma, which led Sveconorwegian tectonic model. For this Magnusson (1960) to introduce the name reason, the doctoral research has not Sveconorwegian, then described as “a been limited to the Sveconorwegian period of regeneration”. The orogeny. For example, the magmatic and Sveconorwegian regeneration period was metamorphic ~1.4 Ga event affecting the later described as an orogeny, roughly Eastern Segment of the Southwest coeval with the well-known Grenvillian Scandinavian Domain was described by orogeny of North America and many other Hubbard (1975) as the Hallandian orogen. structural provinces on other continents, Although Hubbard´s (1975) original commonly referred to as Grenvillian. description of Hallandian veining was actually Sveconorwegian in age, the This doctoral thesis presents and discusses widespread migmatites in the region now new and published data that are relevant dated at 1.46-1.41 are referred to as the when constructing tectonic models for the Hallandian orogeny (Möller et al., 2007). Swedish part of the Sveconorwegian orogeny. Localities investigated are shown Table 1 summarises some key features of in Figure 2, together with some of the each Proterozoic orogeny thought to have most important geological features in this affected the Southwest Scandinavian region, such as shear zones and Domain. A few other features not ascribed documented observations of to the main orogenic events are also Sveconorwegian high-pressure mineral given. assemblages. Based on the data, I suggest a plausible tectonic scenario that can explain many (but not all) of the observed

Austin Hegardt 2010

Figure 1. Outline of the Sveconorwegian orogeny showing the shear zones and main tectonic units.KPZ=Kristiansand-Porsgrunn Shear Zone, SSZ=Saggrenda-Sokna Shear Zone, ÅVT= Åmot-Vardefjell Shear Zone, GZ= Göta Älv Shear Zone, DBT=Dalsland Boundary Thrust, MZ=The Mylonite Zone, PZ=The Protogine Zone, SFDZ=Sveconorwegian Front Deformation Zone. Redrawn from Bingen et al. (2008)

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Figure 2. Map showing localities with documented high-pressure rocks and sample sites investigated in this work. Numbers in the map refer to the sites listed in the inset table.

Austin Hegardt 2010

Table 1. Summary of orogenies and events that affected the Swedish part of the Sveconorwegian Province.

Orogeny/ Event Age Location Metamorphism Metamorphic Selected grade reference Gothian Orogeny 1.75– Western, Median Folding and Amphibolite Gorbatschev 1.55 Ga and Eastern Veining facies 1980; Åhäll & Segments Gower 1997; Åhäll & Conelly 2008 Hallandian aged 1.40- Eastern Segment Granulite- High Christoffel et al. granite-monzonit 1.38 Ga Charnockites temperature 1999; Söderlund intrusions et al. 2002 Hallandian Orogeny 1.46- Eastern Segment Veining and syn- High Christoffel et al. 1.41 Ga deformation temperature 1999; Söderlund migmatite et al. 2002, formation Paper I, Möller et al 2007 1.47-1.44 Ga Dykes and 1.47- Eastern Segment - - Bogdanova et 1.55-1.45 Ga AMCG 1.44 Ga and western East al. 2001, 2006; magmatism related to European Craton Brander & the Danopolonian (and possibly the Söderlund 2009 Orogeny Western Segment). Kungsbacka Bimodal 1.34- Western and - - Welin & Suite 1.31 Ga Median Samuelsson Segments 1987; Paper II

Central Scandinavian 1.28- Western - - Söderlund et al. Dolorites and 1.25 Ga Fennoscandia 2006 equivalents Sveconorwegian The Telemark, Regional folding, greenshist - Berthelsen Orogeny Bamble and foliation and high-P 1980; Bingen et Kongsberg veining granulite- al. 2008 terranes and the eclogite Western, Median and Eastern Segments

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

conditions. Summary of the papers Geothermobarometry indicates that the Paper I rock experienced metamorphic conditions Austin Hegardt, E., Cornell, D., Claesson, L. of 15.0–16.7 kbar at temperatures of 719 Simakov, S., Stein, H. & Hannah, J., 2005: to 811°C. Calculations using the existing Eclogites in the central part of the retrograde assemblage of clinopyroxene- Sveconorwegian Eastern Segment of the garnet-plagioclase-quartz give values of Baltic Shield: Support for an extensive 10.5–12.5 kbar and 700–770°C, reflecting eclogite terrane. GFF, Vol. 127, pp. 221– conditions during rapid exhumation. The 232. Stockholm. ISSN 1103-5897. textural and mineralogical features, together with the calculated P–T This paper presents new pressure- conditions, show that the mafic boudins at temperature and time data from a locality Viared were subjected to eclogite facies situated near Viared in the central Eastern conditions at ~50 km depth, evidence for a Segment, well north of the high pressure subduction process. The Ullared eclogites granulite region in the southern Eastern found by Möller (1998) are thus not a Segment. Work was done on mafic unique occurrence in the Eastern Segment boudins found along a road cutting, close and high pressure metamorphism is to Viared in the central Sveconorwegian shown to be widespread in this tectonic Eastern Segment. The locality was unit. originally investigated by Claesson (2002) who showed that the mafic boudins To date the boudin formation, display both mineralogical and textural molybdenite in quartz-plagioclase veins features demonstrating that these rocks that formed after boudin formation were were once eclogites. sampled and dated using the Re-Os method. The results give 974±3 Ma. The The paper presents the extended work, age thus represents a minimum age for including additional petrographic and boudin formation. The results are also pressure-temperature calculations and a supported by U-Pb dating of titanite from range of age determinations using several an inter-boudin pegmatitic granite melt isotopic methods. that gave a 961±26 Ma age. Two related molybdenite samples gave ages at 957±4 The mafic boudins at Viared comprise and 949±4 Ma respectively, representing largely hornblende-plagioclase either protracted amphibolite facies amphibolite, but their clinopyroxene and conditions or a low grade 230–320°C garnet-bearing interiors indicate that they alteration event. retrogressed from eclogite. Clinopyroxene grains contain exsolved plagioclase. From The host rock surrounding the boudins electron microscope images and EDS comprises a veined orthogneiss. The analyses it was possible to calculate the veining event was dated at 1426±18 and original clinopyroxene composition which 1415±15 Ma from two separate samples indicates original omphacite. Plagioclase using ion-probe zircon dating. The age coronas surrounding garnets (with a indicates that Hallandian veining is a kyanite inclusion) also indicate widespread feature in the Eastern retrogression from high-pressure Segment. The intrusive age of the country

Austin Hegardt 2010 rock was dated at 1701±10 Ma from the that the Kungsbacka Bimodal Suite, which zircon cores. seems restricted to the Western and Median Segments, is significantly younger Paper II than the 1.38 Ga Tjärnesjö and Torpa Austin Hegardt, E., Cornell, D.H., granites east of the Mylonite Zone (Åhäll Hellström, F.A. & Lundqvist, I., 2007: et al. 1997; Andersson et al. 1999) in the Emplacement ages of the mid-Proterozoic Eastern Segment of the Sveconorwegian Kungsbacka Bimodal Suite, SW Sweden. Province. This age difference disproof the GFF, Vol. 129 (Pt. 3, September), pp. 227– concept of pre-Sveconorwegian stitching 234. Stockholm. ISSN 1103-5897. granites and allows the Mylonite Zone to be interpreted as a first order This paper originated from the re-dating of Sveconorwegian tectonic boundary, the Mesoproterozoic Askim Granite in the separating crustal segments with distinct Western Segment at 1336±10 Ma, pre-Sveconorwegian histories. presented in Austin Hegardt (2000). The dating was done to test the age The paper also presents new age-data on correlation with similar aged granites east Sveconorwegian migmatite formation in of the Mylonite Zone. The previous Askim the Western Segment. Metamorphic Granite age of 1362±9 Ma had been an overgrowths on zircons from the Kärra important argument for a pre- pegmatite are dated at 1043±11 Ma and Sveconorwegian assembly of the Eastern confirm the age of Sveconorwegian and Median-Western Segments, now metamorphism at 1.04 Ga in the Western shown to be invalid. The paper includes Segment. This indicates that the peak of dates from the 1311±8 Ma Kärra Granite Sveconorwegian metamorphic evolution and the ≥1304±6 Ma Göta Granite. In in the Western Segment differs by about addition, oscillatory zoned magmatic 70 Ma from the ~970 Ma metamorphic zircon grains in a pegmatite dyke in the peak in the Eastern Segment. Kärra Granite were dated at 1325±8 Ma, within analytical uncertainty of the age of This study also documents the occurrence the host granite and not related to a of penetrative deformation and high- different metamorphic event as had been grade metamorphism including partial thought. melting in the Western and Median Segments, after 1.3 Ga, which was The dated granites are part of a 1.34–1.30 previously thought to be of >1.5 Ga Ga bimodal magmatic suite for which the Gothian age. It also proves that in some name Kungsbacka Bimodal Suite is areas it is impossible to distinguish post- proposed. The suite forms a N–S trending Gothian from older units, based only on linear belt from Kungsbacka in the south their degree of deformation. to Trollhättan in the north. Other possible members are the 1.32 Ga Ursand Granite and 1.33 Ga Hästefjorden Granite (Piontek Paper III et al. 1998), the 1.31 Ga Veddige augen Ahlin, S., Austin Hegardt, E. & Cornell, D., gneiss and 1.33 Ga Stråvalla augen gneiss 2005: Nature and stratigraphic position of (Andersson 2001) and the 1.33 Ga the 1614 Ma Delsjön augen granite-gneiss Chalmers Mafic Intrusion (Kiel et al. 2003). in the Median Segment of south-west Sweden. GFF, Vol. 128 (Pt. 1, March), pp. The suite probably formed in a continental 21–32. Stockholm. ISSN rift environment. This study demonstrated 1103-5897. 6

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

The paper reports on the age and tectonic related mafic source rocks. The K-feldspar setting of the Delsjön augen granite- megacrysts might be accounted for by a gneiss, a rock which is unique to the moderate increase in water content Median Segment. It occurs as elongated, before crystallization during magma up to 50 km long bands which in some ascent, which moved the cotectic lines so cases are associated with the Härsjön that mainly orthoclase crystallized from supracrustal gneiss. The rock generally the melt. The non-megacrystic samples contains 25–30% megacrysts of probably did not experience this hydration recrystallized microcline aggregates in a process. matrix of quartz, plagioclase, microcline and biotite. Ion probe U–Pb zircon dating of the Delsjön augen granite-gneiss gives a The Delsjön augen granite-gneiss is part of 1614±5 Ma date. This age is interpreted to the mainly ~1.6 Ga plutonic calc-alkaline date the intrusion of the suite as bodies granodioritic to granitic rocks and dacitic and dykes along a zone of magma volcanic belonging to the Göteborg Suite chambers. (e.g. Åhäll & Connelly 2008). Note, in Paper III, the alternative name Kallebäck Sveconorwegian metamorphic zircon rims Suite (Mell 2005) is used for the granitic-to from a migmatised Delsjön augen granite- granodioritic rocks of the suite. gneiss were dated at 974±22 Ma, indicating movement in a major shear Even though the Delsjön augen granite- zone between the Western and Median gneiss is interpreted to belong to the Segments at the same time as high grade Göteborg Suite rocks, field relationships metamorphism occurred in the Eastern indicate that the Delsjön augen granite- Segment. Noteworthy is that no sign of gneiss is probably older than most of the Pre-Sveconorwegian (Gothian or non-megacrystic members of the suite, Hallandian) veining events are found in the granitoid gneisses which dominate the this part of the Median Segment. region. Paper IV The work included geochemical Austin Hegardt, E., Stigh, J., Cornell, D. H., comparisons between the Delsjön augen Sjöström, H., Anczkiewicz, R., Page, L., granite-gneiss and the non-megacrystic Finger, F.: Relative and Absolute Temporal Kallebäck Suite granitoids. The comparison Relationships between Folding, Foliation shows that the rocks have overlapping and Metamorphism of the Stora Le- chemical characteristics, although the Marstrand Formation in the non-megacrystic members show a much Sveconorwegian Province, Baltic Shield. larger compositional spread than the Submitted to Mineralogy and Petrology. uniform Delsjön augen granite-gneiss. The Delsjön augen granite-gneiss and the non- Paper IV originated from the detailed megacrystic granitoids also have structural and geologic investigation of the remarkably similar trace element Nordön Island which was led by Jimmy characteristics and both plot as volcanic Stigh in the late 1970s. The several arc granites. Comparing only samples with generations of amphibolite and pegmatite >65% silica, both groups may be explained intrusions that occur on the island provide as water-unsaturated eutectic melts good structural markers and made it ideal derived by partial melting of subduction- for further studies of the polymetamorphic evolution that affected 7

Austin Hegardt 2010 this region. The island is small, only 1 x 1 by recrystallisation of muscovite, dated at km but the rocks are very well exposed. 981±4Ma by Ar-Ar. The work included dating of several metamorphic events and pressure- Paper V temperature calculations from mineral Austin Hegardt, E. & Cornell, D.: An analyses. exhumation model for the eclogite- bearing Eastern Segment in the Meta-greywackes belonging to the Stora Sveconorwegian Province of the Baltic Le-Marstrand formation are the most Shield. common rock type on the island but a major folded amphibolite dyke, the This paper originated from the tectonic Nordön Amphibolite Dyke, is also a model and ideas presented in my Master´s dominant feature. thesis (Austin Hegardt, 2000). In this study, new pressure-temperature and Four major phases of deformation (D1-D4) time data were combined with published were previously recognised and three of data to investigate the distribution and them (D2-D4) could be dated. In addition, origin of high-pressure rocks in south- U-Pb SIMS analyses on detrital zircons western Sweden. Metabasic rocks with constrain deposition of the Stora Le- partially preserved eclogite facies Marstrand Formation to before 1575±21 paragenesis have now been found at Ma and a maximum age at 1596 Ma. several localities in the Sveconorwegian Province. This profoundly influences Sedimentation was followed by D1/S1 models for tectonic evolution in the foliation resulting from sediment Eastern Segment of the Sveconorwegian compaction. U-Pb ion probe zircon Province. In particular, the paper analyses dates partial melting conditions addresses the question whether the and isoclinal folding M2/F2 at 1545±13 occurrence of retrograde eclogites is an Ma, followed by intrusion of the Nordön indicator of the former presence of a Amphibolite Dyke at 1548±11 Ma. subduction zone, now seen as a crustal suture along the Mylonite Zone. The Sm-Nd garnet analyses date metamorphic discontinuities across the Sveconorwegian D3 peak metamorphic two major terrane boundaries, the conditions and F3 folding at 1029±6 Ma, Mylonite and Protogine Zones were also within error of the 1043±11 Ma evaluated. The results indicate that a metamorphism documented in the Kärra significant part of the Eastern Segment has granite (Paper III). been through a high-pressure eclogite facies event, followed by retrogression at Thermobarometry calculated on D3 ~10 kbar and 700-800ºC to amphibolite or metamorphic paragenesis indicates high-pressure granulite facies. conditions at ~11.5 kbar and ~750ºC. A post-D3 pegmatite, probably formed by The eclogite facies and retrograde heating of the post- orogenic metamorphism took place within a short overthickened crust gives an Ar-Ar period close to 970 Ma. This sequence of muscovite age at 994±4 Ma which is events is not seen in the neighbouring interpreted as the intrusion age. Sub- Western and Median Segments to the horizontal F4 folding reflecting late west, nor in the Trans-Scandinavian Sveconorwegian uplift was accompanied Igneous Belt to the east.

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Migmatite formation in the Median or terranes, separated by roughly N-S Segment is dated at 1017±7 Ma, trending zones of ductile deformation comparable to published dates of 1.03- (Berthelsen, 1980; Wahlgren et al., 1994, 1.04 Ga for the main metamorphic event Andersen 2005; Bingen et al. 2008). The in the Western and Median Segments. Sveconorwegian tectonic units have been This shows that the Western and Median referred to as Segments, Sectors, Terranes Segments experienced a very different or Blocks. The nomenclature used in this Sveconorwegian tectonometamorphic work is based on the work by Berthelsen history compared to the Eastern Segment, (1980), Starmer (1996) and Bingen et al. with a >50 Ma difference in the timing of (2001; 2008). From west to east, the the peak metamorphic conditions. A names used for tectonic units which lie crustal subduction and exhumation model, west of the late Palaeozoic Oslo rift are based on the physical experiments by the Telemarkia, Kongsberg and Bamble Chemenda et al. (1996), is applied to the Terranes following Bingen et al. (2008). region and presented as a possible Units east of the Oslo rift are from west to explanation for the 970 Ma event that east referred to as the Western, Median affected the Eastern Segment. and Eastern Segments in accordance with Berthelsen (1980). The Begna sector is Summary of the interpreted as the Western and Median Sveconorwegian Orogeny Segment’s continuation west of the Oslo rift following Bingen et al. (2001). The ~1.14-0.90 Ga Sveconorwegian Alternative nomenclatures were reviewed province (Fig. 1) forms a ~500 km wide by Andersen (2005). belt, bounded to the west and north by The Eastern Segment sea or Caledonian nappes (Bingen et al. The Eastern Segment and Sveconorwegian 2008). It forms the Scandinavian province (Fig. 1 and 3) is delimited to the counterpart of the Grenville orogeny and east by a metamorphic break at the resulted from a continent-continent Protogine Zone and structurally by the collision between Baltica and another Sveconorwegian Frontal Deformation large continent, possibly Amazonia. Figure Zone (Wahlgren et al. 1994). The Mylonite 3 shows a simplified lithology map of the zone (Magnusson 1937) is a major west- Sveconorwegian Province. dipping shear zone which forms the

western boundary of the Eastern Segment To the east, the Sveconorwegian province (Fig. 1). Eastern Segment mainly comprises is delimited by a metamorphic break at orthogneisses, with several generations of the Protogine Zone (PZ), followed by the minor mafic rocks (Fig. 2). In the northern Sveconorwegian Front Deformation Zone The Eastern Segment, 1.67 Ga granitoid (SFDZ) in which the Sveconorwegian rocks can be traced across the deformation is seen in shear zones which Sveconorwegian Frontal Deformation die out eastwards (Wahlgren et al. 1994). Zone into the Trans-Scandinavian Igneous East of the Protogine Zone are the only Belt (TIB). In the southern Eastern slightly deformed granitoids and Segment, orthogneisses with porphyries of the 1.85-1.66 Ga Trans- emplacement ages between 1.73-1.66 Ga Scandinavian Igneous Belt (TIB). show similar chemical characteristics to Sveconorwegian tectonic units coeval The Sveconorwegian province is made up of large 1.68 to 1.59 Ga lithotectonic units 9

Austin Hegardt 2010

Figure 3. Geologic map of the Sveconorwegian Province (modified from Koistinen et al. (2001). This page shows SW Norway, opposite page shows SW Sweden using the same scale.

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Austin Hegardt 2010 undeformed TIB rocks (Connelly et al. km. Zircon inclusions inside garnets are 1996; Andersson 2001; Söderlund et al. dated at 972 ±14 Ma interpreted to reflect 2002; Möller et al. 2007). This implies that eclogite formation (Johansson et al. 2001). the bulk gneisses of the Eastern Segment Hornblende 40Ar-39Ar dates around 0.93 comprise reworked TIB rocks. Ga are interpreted to reflect cooling through 500-550 ºC (Page et al. 1996a, Pre-sveconorwegian Hallandian migmatite 1996b). formation is dated at 1.46-1.42 Ga and occurs on a regional scale in the Eastern In the Eastern Segment, the gentle folding Segment (Christoffel et al. 1999, with roughly east-west oriented fold axes Söderlund et al. 2002, Möller et al. 2007, (Larson & Stigh 1987) is visible on the Paper I). It is probable that deformation detailed aeromagnetic map published by was connected with migmatisation during the Swedish Geological Survey (Fig. 4). The convergent tectonism (Bogdanova et al. pattern results from the tectonic banding 2006; Möller et al. 2007). This was of alternating gneisses, migmatites and followed by granite and monzonite metabasic rocks. magmatism at 1.40-1.38 Ga (Hubbard 1975; Åhäll et al. 1997; Andersson et al. Western and Median Segments 1999; Rimsa et al. 2007) The Median and Western Segments (Fig. 1 and 3) are separated by the Dalsland Granites, syenites and dolerites intruded Boundary Thrust in the north and the Protogine Zone at ~1.2 Ga and bounded to the east by the Mylonite zone dolerites also intruded along the and to the west by the Åmot-Vardefjell easternmost Sveconorwegian border at Shear Zone (Berthelsen 1980; Bingen et al. 0.98-0.97 and at 0.95 (Söderlund et al. 2001). The boundary between the Median 2005 and references therein). and Western Segments south of the Dalsland Boundary Thrust is less clear. In Sveconorwegian metamorphic grade this thesis, the Göta Älv Shear Zone is used increases from north to south. It generally as it roughly separates the Stora Le- reached upper amphibolite to high- Marstrand Formation and 1522-1588 Ma pressure granulite facies in the southern Hisingen Suite granitoids (named Frölunda Eastern Segment around 970 Ma Suite by Mell 2005) from the 1634–1594 (Johansson et al., 1991; Johansson & Ma Göteborg Suite (named Kallebäck Suite Kullerud, 1993; Wang & Lindh, 1996; by Mell 2005) of calc alkaline granites to Söderlund, 1999; Möller 1998, 1999; granodiorites and its volcanic equivalents Paper I). Pressure and temperature (Åhäll et al. 1995, 1998; Åhäll & Connelly estimates range between 8-12 kbar and 2008; Mell 2005; Paper III). The southern 680-800 °C for the amphibolite to part of the Göta Älv Shear Zone also granulite facies rocks. constitutes the eastern border for ~1.5 Ga Evidence of Sveconorwegian high-pressure Gothian veining as well as being a metamorphism has been documented at Sveconorwegian metamorphic break, several localities (Paper I, V). Eclogites separating greenschist facies granites west formed at >15 kbar in mafic rocks were of the zone from veined amphibolite documented at Ullared (Fig. 2), showing facies rocks east of the zone. garnets with preserved prograde zonation (Möller 1999). This indicates rapid burial and exhumation from depths of at least 45

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Figure 4. Map of the total magnetic field showing the different structural aspects in the segments. Map from the Geological Survey of Sweden)

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

The Western Segment is dominated by trending and thus show a clear contrast in ~1.59 Ga Stora Le-Marstrand Formation the observed total magnetic field comprising metamorphosed lithic wackes compared to the east-west trends in the with minor metabasic rocks (Åhäll et al. Eastern Segment (Fig. 4). 1998). These sediments were intruded by granites at 1.59-1.52. An andesitic dyke on The Kongsberg and Bamble Terranes Orust, coeval with the mafic Orust dykes, The Kongsberg and Bamble Terranes (Fig. is dated at 1.46 Ga (Åhäll & Connelly 1 & 3) mainly comprise 1570-1460 Ma 1998). Emplacement of the Kungsbacka metapelites, metagraywackes, quartzites Bimodal Suite occurred along the Göta Älv and orthogneisses with a strong N-S to NE- Shear Zone at ~1.3 Ga (Paper II). Along the SW deformation pattern, forming two north coast of the Western Segment lies tectonic wedges overlying the Telemarkia the 0.92 Ga late Sveconorwegian Bohus Terrane. Mafic magmatism in the Granite (Eliasson & Schöberg 1991). Kongsberg Terrane is dated at 1.2 Ga. In Gothian veining and deformation is dated the Bamble Terrane, the gabbro-tonalite at ~1.55 Ga (Åhäll & Connelly, 2008; Paper Tromøy complex is dated at 1.20-1.18 Ga IV) and Sveconorwegian metamorphism and Granite-charnockite plutons at 1.17- reached amphibolite facies at ~1.04-1.03 1.15 Ga. (Bingen et al. 2008 and Ga in the Western Segment east of the references therein). Oslo rift (Johansson 1993; Romer & Smeds 1996; Åhäll et al. 1998; Paper II, IV). West Two Sveconorwegian metamorphic events of the Oslo rift in the Begna Sector, high are documented. Upper amphibolite to grade metamorphism is dated at 1.09 Ga, granulite facies metamorphism is dated at at 1.05-1.04 and at 1.03-1.02 (Bingen et al. 1.14-1.13 Ga in the Bamble Terrane and 2008). Veining near the Göta Älv Shear amphibolite facies conditions are dated at Zone dated at 0.97 Ga (Paper III) indicates 1.11-1.08 Ga in the Bamble and Kongsberg that this zone was active after the general Terranes (Bingen et al. 2008, and 1.05-1.02 event. references therein). Neither of these events have a direct age correlation to The Median Segment comprises mainly those documented in the Swedish ~1.6 Ga plutonic calc-alkaline granodioritic Western, Median and Eastern Segments. to granitic rocks and dacitic volcanic rocks The Telemarkia Terrane (Åhäll et al. 1995, 1998; Paper III and V). The Telemarkia Terrane is limited to the No pre-Sveconorwegian veining has so far east by the Kristiansand-Porsgrunn Shear been documented in the Median Segment. Zone and to the west by sea or Caledonian Sveconorvegian metamorphism is dated at nappes (Fig. 1 & 3). It is mainly made up of ~0.92 Ga to ~1.04 Ga (Jarl 1992; Larson et a >10 km thick supracrustal sequence, al. 1999; Scherstén et al. 2004; Paper III metamorposed at greenschist to and V). Migmatites developed near the amphibolite facies conditions and 1.52- Mylonite Zone at ~0.97 Ga (Larson et al. 1.48 Ga orthogneisses. Several 1999). High-pressure granulite facies generations of Sveconorwegian granitoids metamorphism, dated at 1.05-1.03 Ga, intruded the Telemarkia Terrane between was documented near Trollhättan by 1.05 and 0.92 Ga (Bingen et al. 2005; 2008 Söderlund et al. (2008). and references therein).

Structures in the Western and Median The Sveconorwegian metamorphism starts Segments are generally north-south at 1035 Ma in most of the Telemarkia

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Terrane but the metamorphic grade varies Eastern Segment moved up and over the between different areas. Upper Trans-Scandinavian Igneous Belt. amphibolite facies dates are more or less continuous from 1035 Ma to c. 950 Ma in The Mylonite zone southern Telemarkia. The Mylonite zone is a 400 km long major lithological and tectonostratigraphic Sveconorwegian Shear Zones in boundary. The southern part of the zone SW Sweden divides less-veined gneisses and The Sveconorwegian tectonic units are supracrustal rocks, of the Western and divided by major shear zones that cut the Median Segments, from more intensely main 1.7–1.2 Ga gneisses. The main two migmatised gneisses in the Eastern zones that separate the Swedish tectonic Segment. Stephens et al. (1996) describes units are the Protogine Zone (including the it as a west-dipping left-lateral Sveconorwegian Frontal Deformation transpressive ductile shear zone. It has a Zone) and the Mylonite Zone. steep dip of 70-90° in the northern parts that becomes gentler to the south. The Protogine Zone and Approximately 60 km south of Lake Sveconorwegian Frontal Deformation Vänern the zone becomes narrower and Zone near Varberg it splits into several branches The Protogine Zone is a before disappearing into the sea (Fig. 1). tectonostratigraphic boundary between the Trans-Scandinavian Igneous Belt and Berglund (1997) describes the Mylonite the Sveconorwegian Province (Fig. 1). Zone movements as compressional with South of Lake Vättern it is steeply dipping top-to-the-east shear sense in the Vänern and 25-30 km wide. It exhibits a fan-like area and extensional, top-to-the-west, in structure between Karlstad and Karlskoga, the southern part. He also suggested that with a foliation dip changing from steep extension followed compression. This westerly in the east, to easterly in the contradicts a recent investigation by Viola west. Top-to-the-east shear sense is seen & Henderson (2010), who explain the zone in Värmland north of Lake Vättern as a simple Sveconorwegian thrust. In this (Wahlgren et al. 1994). The sense of recent investigation it is noteworthy that movement is more complex to the south strike-slip components only exist in the but the overall displacement is oblique northern and southern part of the zone, dextral (Berglund et al. 1992). The thus the geological differences across the Protogine Zone is also a Sveconorwegian zone cannot be explained by a several 100 metamorphic discontinuity, separating km strike slip movement. high-grade rocks to the west from low- grade rocks to the east (Johansson 1992), In the southern part of the Mylonite Zone, implying a large vertical movement. a metamorphic break is seen between the

amphibolite-facies hanging-wall (Median Wahlgren et al. (1994) described the Segment) and high-pressure granulites of Sveconorwegian Frontal Deformation the adjacent Eastern Segment (Stephens Zone, in which Sveconorwegian shear et al. 1996). zones are recognised east of the Protogine

Zone. It is structurally younger than the The Mylonite Zone is not only a lithological Protogine Zone, with steep westerly or boundary, but also marks a significant vertical dip and the dominant shear sense change of structural and geophysical is top-to-the-east, showing that the fabric. The Western and Median Segments 15

Austin Hegardt 2010 have dominantly north-south trending American west coast involve closure of structures while the Eastern Segment is four basins with changes in subduction dominated by east-west trending direction (Moors & Twiss, 1995). structures (Fig. 3). According to the principle of uniformitarianism, there is no reason to Constraints on tectonic believe that continent-continent collisions models for the were less complicated in the late Sveconorwegian Orogeny Mesoproterozoic. Is the Mylonite Zone a The results obtained in this research Sveconorwegian crustal suture? project have implications for the tectonic Do the tectonic units west of the Mylonite evolution during the Sveconorwegian Zone share a pre-Sveconorwegian history orogeny. Important aspects are discussed with the Fennoscandian Shield? Below is a below and a possible tectonic model to compilation of geologic criteria which explain the high-pressure metamorphism characterise an exotic terrane: in the Eastern Segment at 970 Ma is suggested. Presence of ophiolites Ophiolites are the undisputed geological Terrane analysis features that prove an ancient suture zone Reconstructing the tectonic history of a and closure of an ocean basin. Ophiolites Precambrian structural province such as are common in modern orogenic belts, but the Sveconorwegian is complicated by the rare in Precambrian ones. For example in fact that it is too old for any ocean floor the 1.2-1.0 Ga Namaqua-Natal orogeny of spreading record to be preserved, because southern Africa, only one possible the oceanic crust has disappeared down a ophiolite is found in the boundaries subduction zone. Remnants of oceanic between nine established terranes with crust can only be preserved as rare different pre-Grenvillian histories and occurrences of ophiolites. Interpreting well-established collisions (Cornell et al., tectonic units as exotic terranes and 2006). Many Phanerozoic ophiolites are establishing the location of possible suture now interpreted as having formed in back- zones that represent the closure of arc basins rather than in major ocean ancient oceans can however be done, basins. This is because the obduction of using a terrane analysis in which the ophiolites onto the crust is more likely if differences and similarities between the the oceanic crust is relatively young and units are compared. More recent or warm. The mafic rocks near the Mylonite ongoing orogenic belts involving a Zone at Kedum, which show evidence of a continent-continent collision, where the high-pressure metamorphic history, could ocean floor spreading record is preserved be the remains of an (Gothian?) ophiolite, and with remaining mountain chains, but this is highly speculative. The lack of reveal that the tectonic sequence of well-preserved ophiolites along the events during an orogeny is complicated. Mylonite Zone is an argument against the An example is the Himalayan orogeny, interpretation of the Mylonite Zone as a which involved the late Cretaceous crustal suture, but does in no way collision between Tibet and the Kohistan- disprove it. Ladakh island arc before the main collision involving India (O’Brian 2001). Models for the Cordilleran orogeny along the North

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Differences in rock ages correlation east of the Mylonite Zone. A A sharp boundary separating domains similar interpretation was made by Larson with distinct differences in crustal ages is et al. (1998) in a study further north, in suggestive of an ancient crustal suture. the Värmland county. There are no signs The Mylonite Zone effectively separates of ~1040-1020 Ma metamorphism and the 1.73-1.66 Ga Eastern Segment from veining in the Eastern Segment east of the the 1.63-1.55 Ga Median and Western Mylonite Zone despite these being Segments. No pre-Sveconorwegian predominant in the Western and Median metamorphism has been dated in the Segments. Thus the timing of peak Mylonite Zone. The present crustal metamorphic events differs by 50-70 Ma architecture is mainly a Sveconorwegian across the Mylonite zone. feature, although the protolith ages do Regarding the 970 Ma Sveconorwegian not exclude the units east and west of the metamorphism found in the Eastern Mylonite Zone having come together Segment, subordinate ~970 Ma during the Gothian orogeny, as proposed metamorphism and veining is recorded in for example by Åhäll & Connelly (2008). a few localities west of the Mylonite Zone which can be correlated with the peak The 1.46 Ga Orust and Koster-Kattsund metamorphism in the Eastern Segment. dykes in the Western Segment (Åhäll & This leads to the suggestion that the Connelly 2008; Åhäll et al. 2004) might be Eastern Segment collided with the units correlated with mafic dykes which occur west of the Mylonite Zone after 1020 Ma east of the Mylonite Zone. These are the and close to 970 Ma. 1.46 Ga Valaam dykes (Rämö et al. 2001), the 1.47–1.46 Gustafs- and Tuna dykes Closure of an ocean, subduction and (Lundström et al. 2002), the 1.46 Ga related magmatism. Bunkris dyke (Söderlund et al. 2004, 2005) Subduction-related magmatism is and the 1.46 Ga Jönköping Anorthositic expected in the overriding plate of a Suite (Brander & Söderlund 2009; see subduction zone, with a volcanic front table 1). In the Western Segment the 100-300 km from the trench axis Orust dykes and the Koster-Kattsund depending on the subduction angle of the dykes have been dated at 1.46 Ga and down-going slab. If subduction-related 1.42 Ga respectively, although only Rb-Sr magmatism did occur, it would have been dating was used for the Koster-Kattsund in a region now covered by the Skagerrak dykes. The rare occurrence of 1.46 Ga Sea or (further north) in southern Norway. dykes in the Eastern Segment immediately Any volcanic rocks would most likely have west of the Mylonite Zone questions the been eroded away, but one would expect significance of this age-correlation. to find mafic dykes or calc-alkaline plutonic rocks. No Sveconorwegian calc- Differences in metamorphic history alkaline magmatism has been In the Eastern Segment, Hallandian 1.46- documented close in time to 970 Ma in 1.42 Ga migmatitic veining is widespread any of the Sveconorwegian terranes but and this event cannot be correlated across numerous granites, regarded as post the Mylonite Zone. No pre- tectonic were emplaced in southern Sveconorwegian veining has so far been Norway from ~1000 Ma. The lack of dated in the Median Segment. In the typical subduction-related magmatism Western Segment, 1.55 Ga veining and above subduction zones was explained for folding is dated in the Stora Le-Marstrand the western Mediterranean part of the Formation and this veining has no Alpine orogeny by the young oceanic crust

Austin Hegardt 2010 being too warm to subduct to the ~100km models interpreting the Mylonite Zone as depths required for magma generation a purely intra-cratonic shear zone need to (Moores & Twiss, 2005). If closure of explain the driving mechanism for massive Sveconorwegian ocean basins took place crustal thickening. Furthermore, recent in a similar setting, then this has work near Borås in the central Eastern implications on tectonic models involving Segment indicates 22-25 kbar at 600 °C, subduction of continental crust, e.g. the corresponding to a minimum depth of 75 Chemenda model in paper V. A young and km during initial garnet growth at 956 ±9 relatively buoyant sub-oceanic mantle Ma (Cornell et al. 2008; Danielsson 2008; lithosphere would not as easily pull down Mohammad et al. submitted). Such great the continental crust as an older and depths at such a low temperature are heavier sub-oceanic mantle lithosphere. typical in a subduction zone setting. Figure 5 shows the Viared eclogites in a P-T Structural aspects diagram with typical geothermal gradients The aeromagnetic map of southern for a modern subduction zone and an Sweden in Fig. 4 shows that the main intra-continental setting. Typical structures are north-south directed in the metamorphic facies fields are included for Western and Median Segment and east- comparison. The Viared eclogites plot at west directed in the Eastern Segment. The the high temperature side of the 20 °C/km Mylonite Zone is seen as a sharp boundary line, just inside the field of an inter- between these two units. The east-west continental geothermal gradient. structures have been explained as the However, the Proterozoic age and the result from an east-west extension related granitic composition of the Eastern to Sveconorwegian exhumation of the Segment results in a comparatively high Eastern Segment (e.g. Berglund, 1997). heat production which disallows a direct Ideas involving N-S compression and comparison with modern oceanic crustal shortening at ~970 Ma have also subduction zones. been mentioned to explain the east-west structures (Möller et al. 2007). Bingen et al (2008) suggested that the Does the Mylonite Zone need to be a Bamble and Kongsberg Terranes could Sveconorwegian suture? represent the remnants of a The eclogites and high pressure granulites Sveconorwegian basin followed by an in the Eastern Segment formed at least 50 early 1140-1080 Ma collision between the Ma after the main Sveconorwegian event Telemark Terrane and the Western- in the Western and Median Segments. By Median Segment. Looking at modern this time the Eastern and Western-Median orogenic belts, it is likely that such a long- Segments must have been exhumed to lived orogeny as the Sveconorwegian near their present level. That is probably involved the closure of more than one why the 970 Ma event is not well ocean basin. An early 1140-1080 Ma represented west of the Mylonite Zone. collision west of the Western Segment is The work by Möller (1998) indicates a likely, although it does not satisfactory rapid burial and exhumation of the relict explain deep burial of the Eastern eclogites. The recognition of relict Segment close to 970 Ma. A collision close eclogites at four localities in the Eastern to 970 Ma in the proximity of the Eastern Segment (Ullared, Skene, Viared and Segment seems needed to explain the Borås, Fig. 2) means that much of the observed high pressure metamorphism in segment had been at >30 km depth. Thus the Eastern Segment. A model

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

zone. Two lines of evidence against this

Figure 5. The estimated pressure-temperature conditions for the Viared rocks in relation to typical geothermal gradients for common tectonic settings. Pressure and temperature fields for metamorphic facies shown as reference. Figure modified from Spear (1993) and Turner (1968). envisaging east-west compression from an interpretation are that documented indentor off the present west coast of subduction-related magmatism in Norway southern Norway seems unlikely, because or the Kattegat at 970 Ma is lacking and high-grade metamorphism is lacking in the that well-preserved Sveconorwegian tectonic units west of the Mylonite Zone ophiolites are not found along the during the time when stacking of crustal Mylonite Zone. However these are not slices in the Eastern Segment was seen as compelling. Alternative required. interpretations need to explain the occurrence of several localities in the The rock protolith ages, the metamorphic Eastern Segment which show high- history of the rocks and the structural pressure metamorphism, such that a pattern support the idea that the Mylonite subduction-exhumation tectonic cycle Zone is a late Sveconorwegian suture seems difficult to exclude. 19

Austin Hegardt 2010

3. Falkenberg phase, 980-970 Ma Tectonic models for the Crustal thickening propagates towards the Sveconorwegian orogeny east giving rise to granulite and eclogite facies metamorphism in the Eastern Austin Hegardt (2000) suggested a Segment. possible model to explain the 4. Dalane phase, 970-900 Sveconorwegian high-pressure Relaxation and post collisional metamorphism in the Eastern Segment. gravitational collapse exhuming the The model was based on the physical Eastern Segment and the Telemark experiments by Chemenda et al. (2006) Terrane. and involved subduction of continental crust along the Mylonite Zone. The same For the 980-970 Ma Falkenberg phase, Chemenda-based model is included in Möller et al. (2007) suggested that the paper V in this thesis. initial extrusion of the eclogites at Ullared in the southern Eastern Segment was Bingen et al. (2008) presents a four stage contemporaneous with formation of the model for the whole of the E-W folding seen on the aeromagnetic Sveconorwegian orogeny describing the map (Fig. 2). Möller et al. (2007) also relative position and timing and suggested that the E-W structures could metamorphic conditions of the involved have formed during a N-S directed tectonic units. A scenario having an exotic compression but points out that a Telemark Terrane is discussed as an substantial strike-slip component along alternative to an indigenous Telemark the Protogine Zone is needed if this Terrane but the Mylonite Zone is regarded scenario is correct, as no crustal as an intra-cratonic shear zone in both shortening is observed in the Trans- cases. Regardless of an exotic or Scandinavian Igneous Belt. If true, as indigenous origin of the Telemark Terrane, shown in this work, a similar strike-slip the model by Bingen et al. (2008) involves component must be taken up by the four stages: Mylonite Zone as the Sveconorwegian 1. Arendal phase, 1140-1080 Ma metamorphism in the Western and The Arendal phase is interpreted as an Median Segments pre-dates the 970 Ma early collision at 1140 Ma between the extrusion of eclogites by >50 Ma. So far, Telemark Terrane and Western-Median no E-W directed 970 Ma structures have Segments forming the Kongsberg and been dated in the neighboring segments Bamble Terranes. west of the Mylonite Zone.

2. Agder phase, 1050-980 Ma The Chemenda based model that is This is interpreted as the main proposed by Austin Hegardt (2000) and in Sveconorwegian orogenic event following Paper V suggests a tectonic driving collision between Fennoscandia and mechanism for the burial of the Eastern another large continent, causing the 1.05- Segment during the Falkenberg phase. The 1.02 Ga amphibolite-granulite facies Chemenda model does not contradict the metamorphism in the Western and model by Bingen et al. (2008), although Median Segments. In the Telemark Bingen implies that the Mylonite Zone is Terrane, crustal thickening is documented not a crustal suture. from 1035 Ma.

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

The work presented in this thesis Conclusions establishes that the Western and Median 1. Segments with 1.05-1.02 Ga Eclogite facies metamorphism at 970 Ma Sveconorwegian metamorphism have is documented at several localities in the more in common with the Bamble, central Eastern Segment, suggesting that Kongsberg and Telemark Terranes than Sveconorwegian high grade metamorphic with the Eastern Segment and that the conditions are a regional feature in much Eastern Segment did not participate in the of the Eastern Segment. Retrograde main Sveconorwegian event (the 1050- eclogite facies rocks exposed at Viared 980 Ma Agder phase of Bingen et al. were buried to depths of ~50 km before 2008). being rapidly exhumed. The rapid burial- exhumation cycle is compatible with The uniqueness of the Eastern Segment metamorphism in a continental supports the essential principles behind subduction setting. the Chemenda model presented in paper V, and the interpretation of the Mylonite 2. Zone as a Sveconorwegian crustal suture. Pre-Sveconorwegian high grade However the model does not address metamorphism including veining is dated north-south variations in the metamorphic at 1.42 Ga in the central Eastern Segment. gradient in the Eastern Segment. The 1.04- The results extend the region where 1.02 Ga metamorphism documented in veining related to the Hallandian Orogeny the Western and Median Segments is also is documented. In the Median Segment not covered by the model. Crustal west of the Mylonite Zone, thickening could have resulted from a Sveconorwegian veining is dated at 1.02 collision with the Telemark Terrane as Ga, thus significantly older than the 0.97 suggested by Bingen et al (2008), although Ga Falkenberg phase in the Eastern it seems problematic with an increasing Segment. However, 0.97 Ga metamorphic grade from west to east in metamorphism is dated in the Göta Älv the Western and Median Segments. Also, Shear Zone between the Western and the high grade granulites east of Median Segments suggesting some Trollhättan (Söderlund et al. 2008) and the tectonic movements west of the Mylonite possibly retrograded eclogites at Kedum Zone during the Falkenberg phase. The occur in the vicinity of the present veined gneisses west of the Mylonite Zone Mylonite Zone, an area interpreted as the show no sign of a 1.46-1.41 Ga Hallandian eastern border of an exotic terrane at that event. time. 3. Re-dating of 1.36-1.31 Ga granites in the Alternative models having the Eastern and Western Segment disproves the previous Western-Median Segments together since age correlation with 1.40-1.38 Ga granites pre-Sveconorwegian times must however and monzonites in the Eastern Segment, explain the paradox of the complete lack suggesting that the segments on either of 1.04-1.02 Ga ages east of the Mylonite side of the Mylonite Zone had different Zone, still considering the position of the pre-Sveconorwegian histories. high grade rocks in the Median Segment and the dip and age of the Mylonite Zone.

Austin Hegardt 2010

4. and inspiration in my daily work. All my In the Western Segment, peak former Ph.D. colleagues and friends at the Sveconorwegian metamorphism is dated Department of Earth Sciences, in at 1.04-1.03 Ga, thus similar in age to particular Åsa Pettersson, Lena Sultan, crustal thickening in the Median Segment Johan Hogmalm, Anna Pontén, Sofia and in the Telemark Terrane. Holmgren, Olof Larsson, Karin Appelquist, Linus Brander, Henrik Drake, Björn 5. Sandström and Anita Turesson for great Pre-Sveconorwegian syn-deformational discussions, superb coffee breaks and Gothian veining is dated at 1.55 Ga in the many happy moments. Western Segment. No veins with a similar age have so far been found in the Eastern All my colleagues at Bergab for support, in Segment, thus establishing that the particular Thomas Wallroth for accepting Mylonite Zone is the eastern limit of my somewhat flexible working hours Gothian veining. needed to finish this thesis. 6. A 2-dimensional tectonic model involving All my friends at Dannemora Mineral for continental subduction along the Mylonite continuously pushing me towards my goal; Zone can explain the metamorphic Kjell Klippmark, Peter Svensson, Lena evolution including eclogite facies Landersjö, Mikael Eriksson, Tommy conditions documented in the Eastern Persson, Gunnar Rauseus Lars Alm, Stig Segment. Variations in metamorphic grade Johansson and in particular Elisabet Alm within the Eastern and Western-Median for the last minute help…..(it is now 21:56, Segments, with metamorphic grade the day before printing). increasing northwards in the Western- Median Segments but decreasing My special thanks to Stellan Ahlin and to northwards in the Eastern Segment, will Lennart Falk for your inspiration and your require a more complex scenario to enthusiasm that helped me get the work explain the 3-dimensional configuration. done. Ulf-Bertil Andersson is greatly acknowledged for all the support during Acknowledgements my early struggle. Inger Lundqvist and Thomas Eliasson at SGU for your help and It is a pleasure to thank those who made for giving me the opportunity to do this thesis possible. First of all, I owe my extended field work in exactly the right deepest gratitude to my supervisor Prof. place! My special thanks also to Petra David Cornell whose endless Brinkhoff for all the help support during encouragement made me finish this stressful but happy moments at Panterra thesis. My mum Birgitta Hegardt, my late that made it possible for me to finish this dad Ruddy Austin and my brother David work. Hegardt are greatly thanked for all your unconditional support during this work. I Owe Gustafsson and Ali Firoozan at the am also grateful to Bridget Austin for all Department of Earth Sciences , Göteborg the support and non-geologic discussions University; Dr. Martin Whitehouse and Lev during my stay in Brussels . Ilyinsky at NordSIM , Swedish Museum of Natural History; Dr. Robert Anczkiewicz at Secondly, there are many people, who I the Institute of Geological Sciences, Polish would like to thank for providing both help Academy of Sciences and Prof. Dominique

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Weis, EOS UBS are greatly acknowledge Southwest Scandinavian Domain of the for the help with laboratory work and Fennoscandian Shield. GFF 127, 159-168. isotope analyses. Andersson, J., 2001: Sveconorwegian orogenesis in I thank the Swedish Geological Survey for the southwestern Baltic Shield. Zircon financial support SGU grant 1119/2000 to geochronology and tectonothermal setting of David Cornell. The Science Faculty at orthogneisses in SW Sweden. Doctoral Thesis, Lund University of Gothenburg for salary University, Lund, SWEDEN. funding. Adlebertska Stiftlesen and Sven Andersson, J., Söderlund, U., Cornell, D., Lindquists resestipendium at the Johansson, L., Möller, C., 1999: Sveconorwegian (- University of Gothenburg are thanked Grenvillian) deformation, metamorphism and contributing financially to laboratory work leucosome formation in SW Sweden, SW Baltic abroad. Shield: constraints from a Mesoproterozoic granite intrusion. Precambrian Research 98, 151-171.

Finally I would like to thank my near and Austin Hegardt, E., 2000: A Sveconorwegian crustal dear for putting up with me! subduction and exhumation model for the Eastern Segment, south-western Sweden. M.Sc. thesis, Earth Sciences Centre, Göteborg University, References Göteborg, Sweden, Publ. B220, 38pp.

Åhäll, K.-I., Persson, P.-O., Skiöld, T., 1995: Berglund, J., 1997: Mid-Proterozoic evolution in Westward accretion of the Baltic Shield: south-western Sweden. Ph.D. thesis, Earth implications from the 1.6 Ga Åmål-Horred Belt, SW Sciences Centre, Göteborg University, Göteborg, Sweden. Precambrian Research 70, 235-251. Sweden, Publ. A15, 71pp.

Åhäll, K.-I., Samuelsson, L., Persson, P.-O., 1997: Berglund, J., Larson, S. Å., Stigh, J., 1992: Features Geochronology and structural setting of the 1.38 of the Protogine Zone, south central Sweden. Ga Torpa granite; implications for the charnockite Geologiska Föreningens i Stockholm Förhandlingar formation in SW Sweden. GFF 119, 37-43. 114, 337-339.

Åhäll, K.-I., Cornell, D. H., Armstrong, R., 1998: Ion Berthelsen, A., 1980: Towards a palinspastic probe zircon dating of metasedimentary units tectonic analysis of the Baltic Shield. Colloque C6: across the Skagerrak: new constraints for early Géologie de l’europé du Précambrien aux Bassins Mesoproterozoic growth of the Baltic Shield. sédimentaires post-hersyniens. Congrés Precambrian Research 87, 117-134. Géologique International, Paris, 5-21.

Åhäll, K.-I., Connelly, J.N., 1998: Intermittent 1.53– Bingen, B., Bikerland, A., Nordgulen, Ø., Sigmond, 1.13 Ga magmatism in the western Baltica; age E.M.O., 2001: Correlation of supracrustal constraints and correlations within a postulated sequneces and origen of terranes in the supercontinent. Precambrian Res 92, 1–20 Sveconorwegian orogen of SW Scandinavia: SIMS data on zircon in clastic sediments. Precambrian Åhäll, K.-I., Connelly, J.N., Brewer, T.S., 2004: Two Research 108:293-318. extraordinary magmatic records in Proterozoic Baltica; 330Ma of near-continuous growth and Bingen, B., Skår, Ø.,Marker, M., Sigmond, E. 460Ma of episodic additions of mantel-derived th M.O.,Nordgulen, Ø., Ragnhildstveit, J.,Mansfeld, J., components. The 26 Nordic Geological Winter Tucker, R. D. & Liégeois, J.-P., 2005: Timing of Meeting. GFF 126, 15 (Abstract volume). continental building in the Sveconorwegian orogen, SW Åhäll, K.-I., Connelly, J., 2008: Long-term Scandinavia. Norwegian Journal of Geology,Vol. 85, convergence along SW fennoscandia: 330 m.y. of pp. 87-116. proterozoic crustal growth. Precambrian Research 161 (2008) 452–474 Bingen, B., Nordgulen, Ø., Viola, G., 2008: A four- phase model for the Sveconorwegian orogeny, SW Andersen, T., 2005: Terrane analysis, regional Scandinavia. Norwegian Journal of Geology 88, 43- nomenclature and crustal evolution in the 72

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Cornell, D.H. Thomas, R.J. Gibson, R. Moen, H.F.G. Bogdanova, S. V., Page L.M., Skridlaite, G., Taran, Moore J.M. and Reid D.L. 2006: Namaqua-Natal L.N., 2001: Proterozoic tectonothermal history in Province. in Johnson, M.R., Anhauesser, C.R., the western part of the East European Craton: Thomas, R.J (eds) Geology of South Africa. Geol. 40Ar/39Ar geochronological constraints. Soc.S. Afr and Council Geoscience, Pretoria, p. 325- Tectonopysics 339, 39–66 379.

Bogdanova, S.V., Gorbatschev, R., Grad, M., Janik, Danielsson, E., 2008: Kyanite and Mg-rich T., Guterch, A., Kozlovskaya, E., Motuza, G., staurolite as inclusions in garnet; more evidence of Skridlaite, G., Starostenko, V., Taran, L., a high pressure event in the Swedish Eastern EUROBRIDGE, Polonaise Working Groups, 2006: Segment. Masters Thesis, Department of Earth EUROBRIDGE: new insights into the geodynamic Sciences, Göteborg University, evolution of East European Craton. In: Gee DG, Stephenson RA (eds) European Lithosphere Eliasson, T., Schöberg, H., 1991: U-Pb dating of the Dynamics. Geol Soc Lond Mem 32, 599–625 post-kinematic Sveconorwegian (Grenvillian) Bohus granite, SW Sweden: evidence of restitic zircon. Brander, L., Söderlund, U., 2009: Mesoproterozoic Precambrian Research 51, 337-350. (1.47–1.44 Ga) orogenic magmatism in Fennoscandia; Baddeleyite U–Pb dating of a suite Gaàl, G. & Gorbatschev, R., 1987: An outline of the of massif-type anorthosite in S. Sweden. Precambrian evolution of the International Journal of Earth Sciences (Geol Baltic Shield. Precambrian Research 35, 15–52. Rundsch) 98, 499–516 Hubbard, F. H., 1975. The Precambrian crystalline Chemenda, A. I., Matauer, M., Bokun, A. N., 1996: complex of south-western Sweden; the geology Continental subduction and a mechanism for and petrogenetic development of the Varberg exhumation of high-pressure metamorphic rocks: region. Geologiska Föreningens i new modelling and field data from Oman. Earth Stockholm Förhandlingar, 97, 223–236. and Planetary Science Letters 143, 173-182. Jarl, L.-G., 1992: New isotope data from the Christoffel, C., Connelly, J., Åhäll, K.-I., 1999: Timing Protogine Zone and south-western Sweden and characterization of recurrent pre- (Abstract). Geologiska Föreningens i Stockholm Sveconorwegian metamorphism and deformation Förhandlingar 114, 349-350 in the Varberg-Halmstad region of SW Sweden. Precambrian Research 98(3-4), 173-195 Johansson, L., 1992: The late Sveconorwegian metamorphic discontinuity across the Protogine Claesson, L. 2002. Discovery of eclogite relics well zone. Geologiska Föreningens i Stockholm inside the Eastern Segment of the Sveconorwegian Förhandlingar 114, 350-353. Province. Masters Thesis, Department of Earth Sciences, Göteborg University B320, 43pp, ISSN Johansson, Å., 1993:U-Pb dating of titanites from 1400-3821. Southwest Sweden. Sveriges geologiska undersökning, rapporter och meddelanden, 76, 12- Connelly, J. N., Berglund, J., Larson, S. Å., 1996: 13 Thermotectonic evolution of the Eastern Segment of southwestern Sweden: tectonic constraints from Johansson, L., Kullerud, L., 1993: Late U-Pb geochronology. In: Brewer, T. S. (ed.), Sveconorwegian metamorphism and deformation Precambrian Crustal Evolution in the North Atlantic in southwestern Sweden. Precambrian Research Region, Geological Society Special Publication No. 64, 347-360. 112, 297-313. Johansson, L., Lind, A., Möller, C., 1991: Late Cornell, D., Danielsson, E., Austin Hegardt, E., Sveconorwegian (Grenville) high-pressure granulite 2008: Magnesian staurolite and kyanite in garnet facies metamorphism in southwest Sweden. inclusions: Further evidence of a high-pressure Journal of Metamorphic Geology 9, 283-292. event in the Swedish Eastern Segment. Abstract: Annual Meeting Mineralogical Network, Natural Johansson, L., Möller, C., Söderlund, U., 2001: History Museum, University of Oslo, June 2008 p.4. Geochronology of eclogite facies metamorphism in the Sveconorwegian Province of SW Sweden. Precambrian Research 106, 261-275.

Pressure, temperature and time constraints on tectonic models for southwestern Sweden

Möller, C., 1998: Decompressed eclogites in the Kiel, H. M., Cornell, D.H. & Whitehouse, M. J., Sveconorwegian (-Grenvillian) orogen of SW 2003: Age and emplacement conditions of the Sweden: petrology and tectonic implications. Chalmers Mafic Intrusion deduced from contact Journal of metamorphic Geology 16, 641-656. melts. GFF 125, 213-220 Möller, C., 1999: Sapphirine in SW Sweden: a Koistinen, T., Stephens, M.B., Bogatchev, V., record of Sveconorwegian (-Grenvillian) late- Nordgulen, orogenic tectonic exhumation. Journal of Ø., Wennerström, M. & Korhonen, J., Metamorphic Geology 17, 127-141. 2001: Geological map of the Fennoscandian Shield, scale 1:2 000 000. Geological Survey of Möller, C., Andersson, J., Lundqvist, I., Hellström, Finland, Geological Survey of Sweden, Ministry F., 2007: Linking deformation, migmatite formation of Natural Resources of Russia, Geological and zircon U–Pb geochronology in Survey of Norway polymetamorphic orthogneisses, Sveconorwegian Province, Sweden. Journal of Metamorphic Larson, S.-Å., Stigh, J., 1987: Lithology and Geology 25, 727-750. structure of the SW-Swedish granitoids and the significance of the Protogine Zone (Grenville O'Brien, P-.J., 2001: Subduction followed by Front). In: International symposium on Granites Collision: Alpine and Himalayan examples. In: and associated mineralizations. Super. Geol. e Rubie, D.C. & van der Hilst, R. (eds), Processes and Recur. Min., Brazil. Consequences of Deep Subduction, Physics of the Earth and Planetary Interiors, 127, 277-291. Larson, S.Å., Stigh, J. & Lind, G., 1998: Constraints for a structural subdivision of the Southwest Page, L.M., Möller, C. & Johansson, L., 1996a: Scandinavian Domain in Sweden. GFF 120, 85‐90. 40Ar/39Ar geochronology across the Mylonite Zone and the Southwestern Granulite Province in Larson, S.-Å., Cornell, D. H., Armstrong, R. A., 1999: the Sveconorwegian Orogen of S Sweden. Emplacement ages and metamorphic overprinting Precambrian Research 79, 239-259. of granitoids in the Sveconorwegian Province in Värmland, Sweden – an ion probe study. Norsk Page, L.M., Stephens, M.B. & Wahlgren, C.H., Geologisk Tidskrift, 79, 87-96 1996b: 40Ar/39Ar geochronological constraints on the tectonothermal evolution of the Eastern Lundström, I., Persson, P.-O., Ahl, M., 2002. Ages of Segment of the Sveconorwegian Orogen, south- post-tectonic dyke porphyries central Sweden. In: Brewer, T.S. (ed.), Precambrian and breccias in Bergslagen, south-central Sweden. crustal evolution in the North Atlantic Region. In: Bergman, S. (Ed.), Radiometric dating results 5. Geological Society, London, Special Publications SGU Research Papers C 834, pp. 43–49. 112, 315-330.

Magnusson, N.-H., 1937: Den centralvärmländska Piontek, J.E., Connelly, J.N. & Åhäll, K.I., 1998: 1.3 mylonitzonen och dess fortsättning i Norge, Ga anorogenic magmatism in Southwest Sweden, Geologiska Föreningens i Stockholm Förhandlingar Geological Society of America, 1998 annual 59: 2, 205-228. meeting. Geological Society of America (GSA), Boulder, CO, United States, pp. 293. Magnusson, N.-H., 1960: Age Determinations of Swedish Precambrian rocks. Geologiska Rimsa, A., Johansson, L. & Whitehouse, M.J. 2007: Föreningens i Stockholm Förhandlingar, 82, 407- Constraints on incipient charnockite formation 432. from zircon geochronology and rare earth element characteristics. Contributions to Mineralogy and Mell, S., 2005: A geochemical investigation of 1600 Petrology 154, 357-369. Ma and 1560 Ma Granitoids, Western Segment, SW Sweden. M.Sc. Thesis, Göteborg University, Romer, R.L., Smeds, S.A., 1996: U-Pb columbite Göteborg, Sweden. 36pp. ages of pegmatites from Sveconorwegian terranes in Southwestern Sweden. Precambrian. Research Moors, E.M., Twiss, R.J., 1995: Tectonics W.H. 76, 15-30. Freeman and Company, New York Rämö et al 2001. Age and significance of Mesoproterosoic CFB, Lake Ladoga. Abstract

Austin Hegardt 2010

Geological Society of America 33(6) A-139 5, 539-560.

Scherstén, A., Larson, S.-Å., Cornell, D., Stigh, J., Turner, F.J., 1968: Metamorphic Petrology, 2004: Ion probe dating of a migmatite in SW Mineralogical and Field Aspects. New York, Sweden: The fate of zircon in crustal processes. McGraw Hill. Precambrian Research 130 (1-4), 251-266. Wahlgren, C.-H., Cruden, A. R., Stephens, M. B., Spear, F.S., 1993: Metamorphic phase equilibria 1994: Kinematics of a major fan-like structure in and pressure-temperature-time paths. Washington, the eastern part of the Sveconorwegian orogen, DC, Mineral. Soc. Am. Baltic Shield, south-central Sweden. Precambrian Research 70, 67-91. Starmer, I.C., 1996: Oblique terrane assembly in the late Paleoproterozoic during the Labradorian- Wahl, W., 1936: Om granitgrupperna och Gothian Orogeny in southern Scandinavia. Journal bergskedjeveckningarna i Sverige och Finland. of Geology 104(3), 341-350 Geologiska Föreningen i Stockholm Förhandlingar, 58(1), 90-101. Stephens, M. B., Whalgren, C.-H., Weijermars, R., Cruden, A. R., 1996: Left-lateral transpressive Wang, X.-D., Lindh, A., 1996: Temperature- deformation and its tectonic implications, pressure investigation of the southern part of the Sveconorwegian orogen, Baltic Shield, Southwest Swedish Granulite Region. European Southwestern Sweden. Precambrian Research 79, Journal of Mineralogy 8, 51-67. 261-279. Viola, G. & Henderson, I. H. C., 2010: Inclined Söderlund, P., Söderlund, U., Möller, C., transpression at the toe of an arcuate thrust: an Gorbatschev, R., Rodhe, A., 2004: Petrology and example from the Precambrian "Mylonite Zone" of ion microprobe U/Pb chronology applied to a the Sveconorwegian orogeny. In: Law, R. D., Butler, metabasic intrusion in southern Sweden; a study R. W. H., Holdsworth, R. E., Krabbendam, M. & on zircon formation during metamorphism and Strachan, R. A. (eds.) "Continental tectonics and deformation. Tectonics, 23, 1-16. Mountain building: The Legacy of Peach and Horne", Geological Society, London, Special Söderlund, U., 1999: Geochronology of Publications, 335, 707-727 Tectonothermal Events in the Parautochthonous Eastern Segment of the Sveconorwegian (Grenvillian) orogen, Southwestern Sweden. Thesis for Ph.D. degree, Lund University, ISBN 91-86746- 29-4.

Söderlund, U., Möller, C., Andersson, J., Johansson, L., Whitehouse, M., 2002. Zircon geochronology in polymetamorphic gneisses in the Sveconorwegian Orogen, SW Sweden; ion microprobe evidence for 1.46-1.42 and 0.98-0.96 Ga reworking. Precambrian Research, 113, 3-4, 193-225.

Söderlund, U., Isachsen, C.E., Bylund, G., Heamna, L.M., Patchett, P.J., Vervoort, J., Andersson, U.B., 2005: U/Pb baddeleyite ages and Hf, Nd isotope chemistry constraining repeated mafic magmatism in the Fennoscandian Shield from 1.6 to 0.9 Ga. Contributions to Mineralogy and Petrology, 150, 2, 174-194.

Söderlund, U., Hellström, F., Kamo, S., 2008: Geochronology of high-pressure mafic granulite dykes in SW Sweden; tracking the P-T-t path of metamorphism using Hf isotopes in zircon and baddeleyite. Journal of Metamorphic Geology, 26,