Brendan Dyck a Key Fold Structure

A key fold structure within a Sveconorwegian eclogite-bearing deformation zone in Halland, south-western Sweden: geometry and tectonic implications

Brendan Dyck Masters thesis in Geology at Lund University, no. 279 (45 hskp/ECTS)

Department of Earth- and Ecosystem Sciences Division of Geology Lund University 2011

A key fold structure within a Sveconorwegian eclogite-bearing deformation zone in Halland, south-western Sweden: geometry and tectonic implications

Master Thesis Brendan Dyck

Department of Earth and Ecosystem Sciences Division of Geology Lund University 2011

Contents

1 Introduction ...... 1 2 Geological setting ...... 2 3 Methods ...... 3 3.1 Mapping and structural analysis 5 3.2 Petrography, Scanning Electron Microscope-Energy Dispersion Spectroscopy (EDS) and P-T-calculations 5 3.3 U-Pb zircon analysis 6 4 Results...... 6 4.1 Rock types/lithologies in the Ätran area 6 4.1.1 Grey gneiss (Gällared type) 6 4.1.2 Leucocratic gneiss 6 4.1.3 Porphyritic granite-augen gneiss (Tjärnesjö type) 7 4.1.3.1 Sample (26-0) porphyritic granite 7 4.1.3.2 Sample (26-1) augen gneiss 7 4.1.3.3 Sample (26-4) migmatized gneiss 7 4.1.4 Retro-eclogite 8 4.1.5 Garnet-rich gneiss 16 4.1.6 Migmatization 16 4.2 Metamorphic assemblages and P-T conditions 17 4.2.1 Eclogite facies 17 4.2.2 Medium-pressure granulite facies 17 4.2.3 Greenschist facies 17 4.3 P-T estimation using TWQ 19 4.4 Structure 22 4.4.1 Structural map and the Ätran closure 22 4.4.2 Folding 25 4.4.3 Fabrics 25 4.4.4 Shearing spatially associated with folding 26 4.4.4 Sense of shear in the bulk rock mass 26 4.4.5 U-Pb zircon analysis 27 4.5 Zircon geochronology 27 4.5.1 Sample descriptions and isotopic results 27 4.5.1.1 Undeformed granite 27 4.5.1.2 Deformed granite 27 4.5.1.3 Migmatized granite 27 4.5.1.4 Grey gneiss 28 4.5.1.5 Pegmatite 28 5 Interpretations ...... 33 5.1 Metamorphism 33 5.1.1 1.39 Ga granite 33 5.1.2 Stabilities of mineral assemblages 35 5.2 Structure and strain 35 5.2.1 Heterogeneous strain distribution 35 5.2.2 Shearing and folding relations 35 5.2.3 Strain model 35 5.2.4 Tectonostratigraphic marker 36 5.3 Geochronology 37 6 Tectonic interpretation and discussion ...... 37 6.1 Suggestions for future studies 39 7 Conclusions ...... 39 8 Acknowledgments ...... 40 9 References ...... 40

A key fold structure within a Sveconorwegian eclogite-bearing deformation zone in Halland, south-western Sweden: geometry and tectonic implications

BRENDAN DYCK

Dyck, B., 2011: A key fold structure within a Sveconorwegian eclogite-bearing deformation zone in Halland, south -western Sweden: geometry and tectonic implications. M.Sc. Thesis in geology at Lund University, Nr. xxx, 42 pp. 45 hskp/ECTS.

Abstract:

Retro-eclogites and associated high-pressure rocks are found in the Ullared area, southwest Sweden. These rocks are evidence of the high-pressure deformation which occurred during the formation of the c. 500 km long Sveconorwegian orogenic belt around one billion years ago. Their presence is restricted to a domain north of the towns Ätran, Gällared and Ullared.

Detailed structural, petrographic and geochronologic studies of the Ätran area were made with the aim of further understanding the regional structure and metamorphic history, with particular focus on a fold closure suggested by airborne magnetic anomaly maps. A cylindrical inclined south-vergent isoclinal fold with fold axis parallel stretching lineations forms a c. 4 km wide fold closure around the town of Ätran. The southern demarcation of the Ätran closure is a lithotectonic boundary where eclogites are restricted to the area north of the boundary. U-Pb zircon SIMS geochronology of a granitic meta-intrusion (Ätran granite) found just south of the Ätran closure yields an igneous intrusive age of 1388±7 Ma and a Sveconorwegian migmatization & amphibolitization age of 955±15 Ma. The intrusive age of the Ätran granite is coeval to those of the nearby Torpa and Tjärnesjö granitic meta- intrusions, which are now recognized as tectonostratigraphic markers to the aforementioned lithotectonic boundary.

P-T estimates for microdomains with biotite+hornblende+garnet indicate post-eclogite re-equilibrium at conditions of 8.5±1.1 kbars and 690±50°C. Thermodynamic modelling using Domino-Theriak software, combined with petrological data from samples within the Ätran area suggest decompression from a peak metamorphic pressure of c. 17 kbars. Pseudosection calculations describe a c. 2 kbar (6 km Δ depth) zone where eclogite assemblages are stable in mafic and not felsic rocks. The recognition of this eclogite facies variable zone serves as a plausible explanation for the observation of eclogite mineral relicts in the mafic but not the felsic rocks found north of the lithotectonic boundary.

The parallelism of the fold axes and stretching lineations of the cylindrical folding near Ätran prompt a wrench shear component in the regional strain model. Following the regional strain model, the Ätran fold is interpreted as the lateral tip of a proposed ≥50 km wide fold nappe that propagated at least 75 km into the Eastern Seg- ment. A probable tectonic scenario for the formation of this fold nappe and related regional deformation is a Sveco- norwegian late-orogenic deformation with a present day E-W shortening.

Keywords: Sveconorwegian, fold nappe, eclogite, Ätran area, U-Pb geochronology, Domino-Theriak

Brendan Dyck, Division of Geology, Department of Earth and Ecosystem Sciences, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden. E-mail: [email protected]

1. Introduction al, 2001). This orogen has tectonic counterparts around the world, including the Grenville Orogen in Canada The Sveconorwegian Orogen in southwestern and USA. The Sveconorwegian Orogen is composed Scandinavia exposes deep sections of a mountain cha- of metamorphosed and deformed, Proterozoic intrusi- in that formed by continent-continent collision one ve and supracrustal rocks and resulted from a collision billion years ago. It is the tectonic counterpart to the between Baltica and at least one other major continent. Grenville Orogen in North America and was built du- One tectonic interpretation suggests Amazonia is the ring the formation of Supercontinent Rodinia. The other colliding continent, but subsequent evidence is southern parts of the Eastern Segment (counties still lacking to confirm this theory (Hoffman, 1991). Halland and Västergötland), host remnants of very The Sveconorwegian Orogen has been divided into high-pressure rocks – eclogites - that formed by deep five distinct lithotectonic units (Bingen et al, 2005). crustal metamorphism around 0.97 Ga. These units are all N-S-trending and are separated by Field data (Möller and Andersson, unpublished) deeply rooted deformation zones (Park et al, 1991). suggest that the eclogites are bound to a specific struc- The primary lithotectonic units from west to east are; tural domain within the Eastern Segment; one example the Telemarkia terrane, the Kongsberg terrane, the of this is that eclogites are lacking east of Ätran, cen- Bamble terrane, the Idefjorden terrane and the Eastern tral Halland. The ―disapperance‖ of eclogites east of Segment (figure 1). The foreland of the Sveconorwegi- Ätran coincides with an apparent fold structure shown an orogenic belt to the east, in Sweden and Finland, is by the airborne magnetic anomaly map. The present made up of Paleoproterozoic rocks predominantly af- study was initiated in order to investigate the field re- fected by orogenic activity between 1.9 and 1.8 Ga; lations and structural geology of the Ätran area, with more or less undeformed rocks that formed around and particular focus on the suggested fold closure. after 1.7 Ga are also present. Geochronological data Objectives: from a multitude of samples taken in the past forty years confines the Sveconorwegian orogeny to 1140- To document the structure and deformation 900 Ma (Bingen et al, 2008). The ages interpreted as fabrics in a presumed fold hinge in a part of the peak metamorphic ages youngs from c. 1140 Ma in the eclogite-bearing Ullared Deformation Zone western units to c. 970 Ma in the Eastern Segment To document the deformation fabrics and kine- (Johansson et al, 2001; Bingen et al, 2008). matic indicators at a few selected high-strain The Eastern Segment is considered to be a parau- localities within the same deformation zone. tochthonous unit that contains rocks similar in compo- To describe the metamorphic mineral assembla- sition and age to the 1.9-1.7 Ga rocks in the foreland to ges and microtextures in tectonites. the east. The protolith to the majority of the Eastern To provide a structural and metamorphic inter- Segment is 1.7 Ga granites and syenitoids with associ- pretation of the study area. ated basic intrusive rocks, similar to the younger phase To discuss plausible tectonic models. of igneous activity in the so-called Transscandinavian A Nordsim study titled ―Tracing of a major isocli- Igneous Belt (Söderlund et al, 2002; Möller et al, nal nappe-like fold structure that encloses eclogite- 2007). Metamorphic conditions vary within this major bearing units in the Sveconorwegian orogen: U-Pb-Th tectonic unit. The northern portion underwent green- spot dating of the critical structural marker‖ was per- schist and amphibolite facies metamorphism, whereas formed in connection with this thesis. The focus of this the southern portion is predominately composed of study was to confirm or deny the presence of a litho- upper amphibolite and high-pressure granulite facies tectonic boundary south of the mapped fold structure orthogneisses and metabasic rocks, locally with eclogi- via age relations. Structural geology often accompani- tes (Möller 1998; Söderlund et al, 2004). Pressure tem- es geochronology to establish igneous and meta- perature estimates for the southern part of the Eastern morphic phases. Structural evidence usually supports Segment fall in the range 680- 800°C and 8-12 kbar or denies the proposed ages of rocks or their deforma- (Wang and Lindh, 1996). In southern areas, remnant tion by means of age relations. This study is unique in eclogite boudins indicate high-pressure conditions that the inverse of that principal is employed; geochro- (>15 kbar , >50km; Möller, 1998). nology is used to determine a structural model. Due to the high-temperature metamorphism of the Sveconorwegian orogeny, nearly all minerals have re- 2. Geological setting equilibrated and/or recrystallized. This makes interpre- ting the Sveconorwegian versus pre-Sveconorwegian

metamorphism challenging. Söderlund et al (2002) and The Sveconorwegian orogen extends for at least Möller et al (2007) presented evidence from zircon U- 500 km from south-western Sweden to the Norwegian Pb geochronology that shows regional scale migmati- Sea along the south-west coast of Norway. The orogen zation dated between 1460 and 1420 Ma. This event is is confined in the east by the Sveconorwegian Frontal termed the Hallandian event. Following the Hallandian Deformation Zone (SFDZ) and in the north and west event, there were 1400-1380 Ma intrusions of granitic by thrust nappes belonging to the Caledonian orogen and syenitoid rocks with an associated charnockitisa- (Berthelsen 1980; Wahlgren et al., 1994; Koistinen et tion of surrounding gneiss units (Andersson et al,

1999; Harlov et al, 2006). crustal levels. Parts of this exhumation have been in- An eclogite-bearing, composite deformation zone, terpreted to have taken place during general relaxation originally coined as the Ullared Deformation Zone and gravitational collapse of the orogenic belt (e.g. (UDZ), was discovered in the Falkenberg-Ullared area Möller et al, 2007; Bingen et al, 2008). (Möller et al., 1997). Unpublished data suggests that the UDZ actually is made up of two different deformation zones: the Ullared Zone and the Svarten Zone (figure 2), where the Ullared zone is E-W to NW-SE trending and eclogite-bearing. Both zones appear as intensely banded units on the airborne magnetic anomaly map; strongly deformed and mylonitic gneisses are present within both zones. There is a marked increase in gravity, show by the airborne gravity anomaly map, from north to south across the Ullared Zone. The Svarten Zone trends approximately NNW and can be followed southwards from the lithotectonic boundary (the ―Mylonite Zone‖, MZ) between the Idefjorden Terrane and Eastern Segment. The Svarten Zone appears to cut and reorient structures in the Ulla- red Zone and is thus considered the younger of the two zones. Compositionally, the UDZ is heterogeneous and similar to other portions of the Eastern Segment containing felsic to intermediate orthogneisses, augen gneisses and subordinate metabasic lenses and units, which range in size from a few centimeters to several Figure 2. Airborne magnetic anomaly map showing kilometers and are generally less deformed than the the location of the Ullared Zone and the Svarten Zone, surrounding gneisses. U-Pb dating of zircon inclusions the two were originally coined the Ullared Deforma- in kyanite and garnet in eclogites from the UDZ has tion Zone. a= kyanite bearing eclogites (Ammås type), yielded a maximum age of 972 ± 14 Ma for the eclogi- o= obbhult unit (intermediate-pressure mafic granuli- tization (Johansson et al, 2001). Following the eclogite) map source SGU. tization there was rapid exhumation of the eclogites and surrounding strongly deformed rocks to mid- 3. Methods

3.1 Mapping and structural analysis

Chosen area field mapping was carried out during September and October 2010. Mapping was direc- ted by the airborne magnetic anomaly map (SGU), and availability of outcrop. Lithological and structural observations were made at eighty-six localities. Folia- tions, mineral stretching lineations and fold axis were plotted in Stereonet 6.3.3. True dip calculations were performed trigonometrically when in the field, and using Stereonet 6.3.3 afterwards. For plots with a large data set, Kamb contours with 1% bins are used to emphasize data density. Shear indicators were identified and documented and samples were orientated for microscopy studies.

3.2 Petrography, Scanning Electron Microscope- Energy Dispersion Spectroscopy (EDS) and P-T- Figure 1. Map of southwest Scandinavia showing the calculation locations of the Sveconorwegian units and important Twenty rock samples were investigated both shear zones with respect to the Fennoscandia foreland, with polarizing microscopy and with scanning electron Oslo rift and Caledonian overprint. Modified from microscopy (SEM; using a Hitachi S3400N fitted with Bingen et al, 2008. an EDS analyser (Link INCA) at the Department of 5

Earth and Ecosystem Science, Lund University and calculations were made using the Isoplot 3.7 software Department of Earth Sciences, University of Gothen- provided by Ludwig (2003). burg). An acceleration voltage of 15-25 kV was used on polished and carbon coated samples. 4. Results Pressure and temperature conditions were modelled using the Domino-Theriak software developed by Capitani and Brown (1987). All Domino-Theriak 4.1 Rock types/lithologies in the runs were performed using the internally consistent Ätran area database presented by Berman (1988); the preset solution models were unchanged. A range of bulk rock The mapped area (figure 3) is composed of a compositions where modelled to represent mineral heterogeneous gneiss complex, where the outcrops are assemblages from all compositions found within the compositionally layered; with the degree of strain and study area. H2O and oxygen was considered in excess partial melting that is common throughout the area, it for all calculations. P-T pseudosections calculated on is not possible to determine the protoliths or their com- Domino show the thermodynamically stable mineral positions with certainty. Contacts are commonly not assemblages of a defined composition over a range of exposed or gradual, so the mapped boundaries involve P-T conditions. Theriak calculates molar and volume some degree of interpretation. For simplicity, rocks percents of stable phases of a defined rock composi- where divided into five different lithological units; tion at a defined pressure and temperature. End mem- grey gneiss, retro-eclogite, garnet rich gneiss, leucoc- ber quantities of minerals that exhibit solid solution ratic gneiss, and porphyritic granite – augen gneiss are also calculated in the Theriak program. (Tjärnesjö type). These units are folded by a 4 km Equilibrium P-T estimates were done using the wide isoclinal antiformal structure that has an east TWEEQU (Thermobarometry With Estimation of dipping fold axis. Equilibration State) programs TWQ1.02 and TWQ2.02 (Berman 1988, 1997). Equilibrium was es- 4.1.1 Grey gneiss (Gällared type) tablished first optically, then by spectrum comparison The grey gneiss, recognized by its dull colour between multiple domains of a single grain. and banded appearance is the outermost unit in the mapped fold structure. Relative to the other units 3.3 U-Pb zircon analysis found within the study area, the grey gneiss shows moderately high strain (figure 4a). Alteration of folia- Zircons from five samples were handpicked for tion parallel layering of reddish leucosomes and local- dating. Samples were first crushed on a clean anvil, ly amphibolitic layers c. 0.5-1 cm thick is responsible and then powdered using a swing-mill. Zircon along for the banded appearance. Some varieties contain with other similar sized heavy mineral grains were feldspar megacrysts up to 4 cm in diameter (figure 4b). separated and collected following standard procedure The grey gneiss is identified as the Gällared gneiss, on a Wilfley wet separation table. Hematite and mag- described by Söderlund et al (2001). The sample taken netite was then removed with a pen magnet, and the for microscopy studies is an intermediate variety with remaining apatite and zircon grains were separated by sparse K-feldspar megacrysts. The sample (70-1) con- hand under magnification. Zircons selected for analyti- sists of quartz, plagioclase and biotite with lesser cal work were handpicked and mounted on double amounts of K-feldspar, garnet and ilmenite. Grain si- faced tape. About 100-200 crystals from each sample zes vary from medium to fine grained, with the less were selected, except for sample 70-2, from which fine-grained grains existing together in domains only 10 crystals were recovered. The selected crystals (figure 4 e,f). Plagioclase rich domains are fine grai- were embedded in epoxy together with the Geostan- ned, with a neoblastic appearance (figure 4 c,d). Me- dards zircon 91500 (Wiedenbeck et al, 1995). The gacrysts of plagioclase are strained as seen by the ben- epoxy mount was polished to expose the central parts ding of twinning and in some cases subgrains are for- of the zircon crystals and thereafter studied in back- med. Microdomains that are predominantly quartz are scattered electron images using a Hitachi S3400N fit- coarse grained with a near granoblastic texture. Biotite ted with an EDS analyser (Link INCA) located at the has a preferred orientation parallel to foliation and Department of Earth and Ecosystem Science, Lund only exists in association with ilmenite. University. High-spatial resolution secondary ion mass 4.1.2 Leucocratic gneiss spectrometer analysis (SIMS) were made using a Ca- The leucocratic gneiss, named for its quartz rich meca IMS 1280 at the Nordsim facility at the Swedish composition and light colour in the field is the highest Museum of Natural History in Stockholm. The instru- strained unit (figure 5a). Composed of 55% quartz and ment was operated with a spot size less than 25 µm. 30% feldspars some of which are anti-perthitic, this is Analytical procedures followed the protocol described the most felsic of all units (figure 5 b,c). Sample (68- in Whitehouse et al (1999) and Whitehouse & Kamber 1) contains millimetre wide quartz ribbons as long as 4 (2005). Re-imaging of the zircon mount was done with cm. The remaining 15% of the sample is small-grained a standard c. 25 µm carbon coat. Diagrams and age 6

Figure 3. Lithological map of the study area with select structural observations based on 84 observation points. garnets, anhedral hornblende, scapolite and small sub- Plagioclase crystals have bent twinning planes. Hornb- hedral biotite with associated ilmenite. Minor amounts lende and biotite have no preferred orientation and are of a clinopyroxene, and orthopyroxene exist in equi- clustered in mafic domains. librium with the major phases (figure 5 d,e). Garnet is fine-grained anhedral and has indented and irregular 4.1.3.2 Sample (26-1) augen gneiss shapes indicative of resorption. This sample shows A foliation is visible in both hand sample and very little evidence of recrystallization (i.e. grain thin section (figure 6 a,e,f), defined by the preferred boundary migration, subgrain rotation) although other orientation of biotite and quartz ribbons. The assemb- felsic gneiss localities appear sugary in the field and lage is the same as in sample (26-0), the only differen- are highly recrystallized. Sericite alteration of plagioc- ce is the presence of rutile in the sheared sample. Ruti- lase produces a locally ‗dusty‘ appearance. le appears to have grown at the expense of ilmenite

(figure 6 g,h). Fine-grained plagioclase and quartz rich 4.1.3 Porphyritic granite and augen gneiss domains are parallel to the foliation. Augens of orthoc- (Tjärnesjö type) lase and medium sized plagioclase and quartz grains A 400 x 200m granite body was found just are strained. Some orthoclase grains are perthitic with south of the Ätran closure hinge. The body is hetero- exsolution of plagioclase. geneously deformed with highly sheared augen gneiss domains occurring mere meters from nearly undefor- 4.1.3.3 Sample (26-4) migmatized gneiss med porphyritic domains (figure 6a). Even with vary- Foliation and leucosome development is visible ing degrees of strain, the granite is easily recognised in hand sample; in thin section there are mafic and by its centimetre sized orthoclase grains and a distinct felsic domains but no preferred crystal orientation. reddish hue. The granitic body found in this study is Orthoclase and microcline exists as megacrysts with a undistinguishable from the Tjärnesjö granite located myrmekite-like sympectite growing at the expense of immediately north of the fold structure. orthoclase (figure 6 i,j). Quartz rich domains are medium-grained and granoblastic. Hornblende and biotite 4.1.3.1 Sample (26-0) porphyritic granite are euhedral and weakly orientated. Bent twinning There is a weak foliation seen in hand sample, planes and other signs of strain is visible in some fine- but no fabric is visible in thin-section (figure 6b). The grained plagioclase and K-feldspar domains rich in rock is characterized by a porphyritic texture compo- myrmekite. Titanite is a minor phase and exists in as- sed of 25% plagioclase, 25% quartz, 35% orthoclase sociation with ilmenite (figure 6 k,l). and 15% hornblende/biotite aggregates (figure 6 c,d). 7

A B

C D

E F Figure 4. Grey gneiss: A) Strongly strained grey gneiss (locality 76), with deformed and foliation parallel, reddish, granitic leucosomes. B) Orthoclase megacryst bearing grey gneiss (locality 31). Note: the photo is of a wet surface that appears darker than it would dry. C) Photomicrograph of sample 70-1, plane-polarized light; Fine grained quartz and plagioclase neoblastic texture in grey gneiss. D) Photomicrograph of sample 70-1, cross-polarized light; Fine grained quartz and plagioclase neoblastic texture in grey gneiss. E) Photomicrograph of sample 70-1, plane- polarized light; Less fine-grained aggregate of quartz and plagioclase in grey gneiss. F) Photomicrograph of sample 70-1, cross-polarized light; Less fine-grained aggregate of quartz and plagioclase in grey gneiss. 4.1.4 Retro-eclogite sorted into groups based on what mineral they form a An example of a well preserved retro-eclogite, pseudomorph of. Two different symplectites occur: taken from locality 80, is described with minor modifi- clinopyroxene+hornblende+plagioclase symplectite cations from previous work (Dyck, 2010). This sample (cpx-symplectite) resulting from the breakdown of is made up of garnet, hornblende, quartz, plagioclase, large clinopyroxene grains and biotite+plagioclase clinopyroxene, and biotite with accessory phases of symplectite (biotite-symplectite). Grain outlines of the rutile and opaques (figure 7). These minerals can be clinopyroxene from which the cpx-symplectite has

Figure 5. Leucocratic gneiss, locality 68, sample 68-1: A) Leucocratic gneiss with quartz ribbons up to 5 cm in length. B) Photomicrograph in plane-polarized light; Quartz ribbons, plagioclase, anti-perthite and scattered garnet. C) Photomicrograph in cross- polarized light; Quartz ribbons, plagioclase, anti- perthite and scattered garnet. D) Photomicrograph in plane-polarized light; Mafic sub-domain with anhedral clinopyroxene, orthopyroxene, biotite and scapolite. E) Photomicrograph in cross-polarized light; Mafic sub- domain with anhedral clinopyroxene, orthopyroxene, A biotite and scapolite.

B C

D E formed are still visible, and are 7-12 mm in length. rest quartz and plagioclase nearest garnet (figure 8e). The cpx-symplectite minerals have grown in a cros- Garnet makes up approximately 25 percent of this shatched 90° pattern and there is a very tight intersection and it occurs as 3-6 mm diameter crystals. The growth of the clinopyroxene and hornblende (figure 8 garnet crystals are mostly subhedral, but in some in- a,b). Other localities of the cpx-symplectite show a stances the garnet looks disaggregated and resorbed; parallel pattern, but remain the same chemically plagioclase and hornblende has grown between the (figure 8 c,d). In the areas where two large cpx- grains. Inclusions of quartz and plagioclase with dis- symplectite grains meet, there is an increase in the tinctly tapered twinning exist in the larger garnet gra- amount of plagioclase occurring as small rounded grains. Hornblende also occurs as medium sized subhed- ins. Quartz exists as large 5-10 mm long euhedral ral and anhedral crystals. Isolated grains are anhedral, crystals, with patchy undulose extinction. There is not but grains that form an aggregate of hornblende are a very prominent undulose extinction, the difference in subhedral. The biotite-symplectite is characterized by extinction angles between the subgrains of quartz are a vermicular intergrowth of biotite and plagioclase c. 8°. A corona texture around the quartz occurs near (figure 8 f,g). In the center of the largest biotite- garnet. It consists of two phases, clinopyroxene nea- symplectite present in this section there are multiple

A B

C D

E F

G H

I J

K L Figure 6. Porphyritic granite-augen gneiss, locality 26: A) Variably strained augen gneiss, finely laminated rock (top left) lies less than a meter from augen gneiss (bottom right), location of sample 26-1. B) Porphyritic granite, location of sample 26-0. C) Photomicrograph of sample 26-0, plane-polarized light; Orthoclase megacryst surrounded by medium grained feldspars and quartz. D) Photomicrograph of sample 26-0, cross-polarized light; Orthoclase megacryst surrounded by medium grained feldspars and quartz. E) Photomicrograph of sample 26-1, plane- polarized light; Horizontal foliation planes defined by mafic aggregates and quartz ribbons, and orthoclase augen (bottom). F) Photomicrograph of sample 26-1, cross-polarized light; Horizontal foliation planes defined by mafic aggregates and quartz ribbons, and orthoclase augen (bottom). G) Photomicrograph of sample 26-1, plane-polarized light; Small rutile grains nucleating at ilmenite grain boundaries. H) Photomicrograph of sample 26-1, cross- polarized light; Small rutile grains nucleating at ilmenite grain boundaries. I) Photomicrograph of sample 26-4, plane-polarized light; Recrystallized microcline, undulose quartz and plagioclase. Orthoclase is not present in this photomicrograph, but is sometimes present in cores of microcline crystals. J) Photomicrograph of sample 26-4, cross-polarized light; Recrystallized microcline, undulose quartz and plagioclase. Orthoclase is not present in this photomicrograph, but is sometimes present in cores of microcline crystals. K) Photomicrograph of sample 26-4, plane-polarized light; Titanite and ilmenite intergrowths surrounded by biotite, plagioclase and quartz. L) Photomi- crograph of sample 26-4, cross-polarized light; Titanite and ilmenite intergrowths surrounded by biotite, plagioclase and quartz. small quartz grains. A second phase of biotite has also revealed some reaction sites which were previous- grown over part of the symplectite, and is distingui- ly unnoticed. There is a c. 5μm wide reaction rim of shed by its different orientation showing the cleavage amphibole which separates the clinopyroxene and pla- planes. Rutile exists in a few locations throughout the gioclase on the aforementioned garnet quartz reaction sample, everywhere in contact with an opaque phase. site. The opaque phase associated with rutile is ilmeni- The largest rutile grain is located within a cpx- te, which also occurs in smaller quantities scattered symplectite and there is a rim of hornblende surroun- throughout the rock. ding the rutile crystal (figure 8h). Two 200 x 300m mafic bodies were mapped as SEM retro-eclogites. This unit is the most mafic of all com- A look at this section in the scanning electron micros- positions within the fold structure, and can be recogni- cope helped to confirm the composition of phases and zed in the field by a dark (red and green) appearance.

The bodies are compositionally layered with dark gar- mafic bodies are mostly gabbroic in composition, but net and pyroxene-rich rocks grading to anorthositic the mineral assemblages vary between layers. Thin compositions (figure 9 a,b). Strain is partitioned section (30-3) is from one of the more mafic layers among the layers with the large garnet-pyroxene rock and it shows the most common eclogite textures. A showing the lowest strain, and the anorthositic rock high-pressure assemblage of coarse-grained garnet, showing the highest degree of strain (figure 9c). The omphacite and quartz is overprinted with intergrowths Rtl/Ilm 8 h

8 c,d

Cpx-Sym

8 a,b Bt-Sym Qtz 8 f,g

8 e

Grt

1 cm Hbl

Figure 7. Retrogressed eclogite, sample CHM09020A: Scanned thin section showing pseudomorphs of large grains, and mineral relations and textures. Rtl/Ilm = rutile (brown) and ilmenite, Cpx-sym = clinopyroxene-symplectite, Bt-Sym = biotite-symplectite, qtz = quartz, Grt = garnet, Hbl = hornblende. Boxes denote locations where photos were taken. 12

A B

C D

E F

G H 13

Figure 8 (previous page). Retrogressed eclogite, CHM09020A: A) Photomicrograph of crosshatched cpx - symplectite, plane-polarized. B) Photomicrograph of crosshatched cpx-symplectite, cross-polarized. C) Photomic- rograph of parallel cpx-symplectite in contact with a quartz grain, plane polarized. D) Photomicrograph of parallel cpx-symplectite in contact with a quartz grain, crossed polarized. E) Retrogressed eclogite decompression reaction: clinopyroxene+ plagioclase corona between garnet and quartz. F) Photomicrograph under plane-polarized light; Biotite-symplectite in contact with garnet (top left and right), note the second phase of biotite occuring right of center. G) Photomicrograph under cross-polarized light; Biotite-symplectite in contact with garnet (top left and right), note the second phase of biotite occuring right of center. H) Photomicrograph under cross-polarized light; Rutile/ilmenite grain with hornblende rim inset in a parallel cpx-symplectite.

A B

Figure 9. A) Vertical south facing outcrop showing a boudinaged mafic garnet and pyroxene-rich retro- eclogite layer surrounded by a garnet-rich gneiss, location 30. B) Close-up of the retro-eclogite layer in 9A red grains are garnet, green grains are clinopyroxene, and light green specs are scapolite. C) High-strained meta-anorthosite (plagioclase 80-85%) with elongate dark mineral aggregates. Photo taken at locality 34.

A B Figure 10. Retro-eclogite, sample 30-3; Plagioclase, hornblende and clinopyroxene symplectite. A) plane-polarized light. B) cross-polarized light.

A B

C D

100 μm

E F

Figure 11. Retro-eclogite from locality 30, sample 30-3: A) Photomicrograph under plane-polarized light; Garnet grain surrounded by margarite (colourless) and chlorite (light green) intergrowths. B) Photomicrograph under cross -polarized light; Garnet grain surrounded by margarite and chlorite intergrowths. C) Symplectitic intergrowth of plagioclase, hornblende and diopside. D) Coronitic quartz inclusion in garnet, corona phases are plagioclase and hedenbergite clinopyroxene. E) Two compositions of plagioclase: lighter plagioclase has an anorthite content of 32%, the darker plagioclase has an anorthite content of 38%. F) Fibrous intergrowth of chlorite (dark) and margarite (light).

of white mica, plagioclase, scapolite and hornblende. Various symplectitic and coronitic textures exist, parti- A cularly around garnet and omphacite grains. (figure 11d) shows a quartz inclusion in garnet where the quartz and garnet have reacted to form a composite corona of plagioclase An49 and hedenbergite. Symplectitic intergrowths of plagioclase, hornblende and diopside seen in (figure 10 a,b & 11c) show hornblende growing at the expense of diopside. Microprobe analyses of the white mica confirm two phases: a coloured Mg rich chlorite intergrown with colourless margarite (figure 11 a,b,f). Scapolite is common throughout the sample; its distinct texture is attributed to the remnant plagioclase domains existing within the grains. Plagi- oclase rich domains have a granoblastic texture and the individual grains have tapered twinning planes. B SEM analysis of the plagioclase domains reveals multiple plagioclase phases (figure 11e) shows what looks like a texturally younger lighter phase An38 overgrowing the darker phase An32.

4.1.5 Garnet-rich gneiss (08-1) The term ‗garnet rich gneiss‘ is used for intermediate gneisses with ≥10% visible garnets that do not qualify as a ‗retro-eclogite‘. This unit has many varieties particularly in terms of garnet volume percent and the size of garnets (figure 12a). Irrespective of the variations within the unit, the garnet gneiss is intermediate in composition. Garnet and orthopyroxene pseudomorphs (figure 12 b,c) make up about 25% of sample (figure 19). Biotite and hornblende each comprise about 15% of the sample with the remaining being C plagioclase and quartz. Biotite grains appear in close relation to oxides. Similar to the felsic and grey gneiss, the plagioclase and quartz rich domains show high degrees of strain through shearing and grain size reduction.

4.1.6 Migmatization Migmatization varies considerably, even on a local outcrop scale. Anatexis of all rock compositions within the study area produced net and stromatic metatextites (figure 13 a,b). In no domains larger than 2 m3 is the rheologically critical melt percent (c. 30%) tho- ught to have been exceeded. A general trend was recognized with increasing volume % of leucosomes to Figure 12. Garnet-rich gneiss, locality 08, sample 08-1: the north. Unpublished ongoing mapping by the Geo- A) South facing vertical outcrop showing a garnet- logical Survey of Sweden and excursions to areas pyroxene-hornblende aggregate 10 cm in diameter sur- north of the herein investigated area around Ätran con- rounded by smaller garnets. B) Photomicrograph in pla- firm an increase in migmatization to the extent that ne-polarized light; Strongly altered orthopyroxene and microscale structures are no longer visible and field subhedral hornblende grains surrounded by plagioclase structures are ‗blurred‘. and quartz. C) Photomicrograph in cross-polarized light; Strongly altered orthopyroxene and subhedral hornblende grains surrounded by plagioclase and quartz.

A B Figure 13. Metatextites: A) Net metatextite with garnet rich gneiss paleosome found at locality 63. B) Migmatitic retro-eclogite with a strong linear fabric from locality 61. 4.2 Metamorphic assemblages and 690°C for both a mafic and felsic composition. The P-T conditions felsic bulk rock composition calculation results in a quartz, plagioclase and K-feldspar rich rock. The ma- The aforementioned mineral phases belong to fic bulk rock composition yields a rock, which is com- three metamorphic assemblages representing eclogite posed of plagioclase, omphacite clinopyroxene, garnet facies, medium-pressure granulite facies and green- and hornblende. Figure 14 is a pseudosection calcula- schist facies metamorphic conditions. ted in Domino, which shows how the ratio of the plagioclase end-members varies according to P-T condi- 4.2.1 Eclogite facies tions. Following an isothermal decompression path from the plagioclase free domain, the first plagioclase Garnet and clinopyroxene, omphacite in parti- stable is An12. As pressure decreased, the amount of cular, are the two phases most indicative of high- anorthite in plagioclase increases. pressure conditions. Minor amounts of clinopyroxene and garnet were observed in the leucocratic gneiss. In 4.2.3 Greenschist facies all lithologies except for the grey gneiss, the amount of garnet and clinopyroxene progressively increases with There are no completely equilibrated meta- the decrease in silica and subsequent increase in Fe morphic mineral assemblages, which could have for- and Mg. The high-pressure phases garnet and pseudo- med at low pressures and temperatures, but there are morphs after omphacite are abundant in the retro- alteration of high grade minerals by late mineral pha- eclogite unit. There is no igneous plagioclase in the ses that have formed at low grade conditions. Many retro-eclogite sample, as determined by the mineral samples contain late sericite alteration of plagioclase, textures. Theriak calculations for both a mafic and appearing ‗dusty‘ in texture. Chlorite alteration of felsic composition (table 1 a,b), suggest that the volu- orthopyroxene is a late low-grade feature observed in me percent of all stable phases at 17 kbar and 700°C. the garnet-rich gneisses. Intergrowths of chlorite and The felsic bulk rock composition yields a rock rich in margarite, both low-grade mica group minerals, were quartz, white mica, plagioclase and omphacite. The found in the retro-eclogite samples. mafic bulk rock composition yields a rock composed mostly of almandine-rich garnet and omphacite clinopyroxene.

4.2.2 Medium-pressure granulite facies A pervasive re-equilibration that has affected Table 1. Theriak results, calculated for bulk rock com- all rock types occurred under granulite to upper- positions of an amphibolitized mafic boudin and a amphibolite facies metamorphic conditions. In the leucocratic (felsic) gneiss. For minerals that exhibit more mafic varieties, garnet, plagioclase, hornblende solid solution, the most voluminous endmember is and clinopyroxene with lesser amounts of quartz, bio- denoted following the solid phase name. Tephroite tite and scapolite are the phases that appear stable with (Mn2SiO4) is a Mg silicate, used by Theriak to express one another. In the more felsic gneisses, quartz, plagi- excess Mg content. The tephroite component is often oclase, hornblende, K-feldspar and biotite coexist in negligible and occurs as a component of an oxide pha- equilibrium. Where scapolite occurs, it appears in se. Molar amounts N, volume/mol, cubic volume and equilibrium with the amphibolite facies minerals. Re- volume % are calculated: A) Felsic gneiss at 700°C sults from Theriak computations (table 1 c,d), give the and 17 kbar, B) Mafic rock at 700°C and 17 kbar, C) volume percent of all stable phases at 8.5 kbar and Felsic gneiss at 690°C and 8.5 kbar, D) Mafic rock at 690°C and 8.5 kbar. 17

Figure 14. Domino plot with anorthite (An) isopleths with An content ranging from An12 to An52, the composition used in the calculation is from a mafic boudin sampled within the study area.

4.3 P-T estimation using TWQ profile was performed. Reactions used as geothermo- (Berman 1992) meters have Fe-Mg ion exchange between biotite, garnet and amphiboles. The ratios of Fe-Mg between pha- Microprobe analysis (table 2) of a garnet rich ses in equilibrium are dependant on temperature. Net gneiss sample from within the fold structure (locality transfer reactions (ie. amphibole + quartz + garnet = 79) were performed in the aim of determining the PT plagioclase + amphibole) were used as barometers conditions of the Sveconorwegian amphibolite facies since they involve a significant change in volume, overprint, which has re-equilibrated many of the as- which is dependent on pressure conditions. Backscat- semblages that were formed at an earlier stage of the ter images of the analytical spot locations shows the orogeny. Microdomains were chosen where garnet, equilibrium textures of the phases used for P-T calcu- biotite and amphibole are in equilibrium. Equilibrium lations (figure 15 a,b). was established first optically, then by analysing spots The amphibole-garnet reactions plot similarly in the grains that were in contact with the other chosen within each microdomain (Figure 16 a,b). The biotite- phases and comparing the analysis spectrums to other garnet yielded higher temperatures than expected for spots within the same grains that were farther from the both microdomains, an indication garnet has been par- chosen contact sites. This method was used on the tially resorbed to form new biotite (Spear & Florence, amphibole, biotite, plagioclase and later ilmenite. Gar- 1991). Resorbtion of garnet and re-distribution of Fe net cores and rims were in equilibrium thus, no zoning and Mg to form new biotite via a net transfer reaction

produces biotite that is Fe rich and will therefore give of the Eastern Segment fall in the range of 680- 800°C a higher temperature estimate if used in equilibrium and 8-12 kbar (Johansson et al, 1992; Wang and with garnet. If biotite and garnet had late diffusional Lindh, 1996; Möller, 1998). The results of this study exchange, an even lower T than that yielded by the are within that range, on the lower pressure and tempe- amphibole-garnet equilibrium would be expected. Pre- rature end. viously published P-T estimates for the southern part

A B

Figure 15. Backscatter electron images of microdomains analysed for P-T determination: A) Microdomain 1; hornblende, garnet and biotite triple point with no signs of disequilibrium. B) Microdomain 2; hornblende, biotite, and garnet in equilibrium with eachother. Note: the hornblende has a 2 micron wide rim at the contact with biotite, disequilibrium features such as this were avoided.

Figure 16. A) TWQ results for domain 1; intersections at 8.3 kbar and 700°C for the amphibole-garnet thermometer and 9.6 kbar and 777°C for the biotite-garnet thermometer. B) TWQ results for domain 2; intersection at 8.2 kbar and 685°C for the amphibole-garnet thermometer and 10.2 kbar and 785°C for the biotite-garnet thermometer.

Garnet 1 Biotite 1 Number of Number of Element Compund% Formula ions Element Compund% Formula ions Na 0 Na2O 0 Na 0.18 Na2O 0.05 Mg 4.4 MgO 0.52 Mg 11.65 MgO 2.63 Al 21.29 Al2O3 1.97 Al 14.6 Al2O3 2.6 Si 37.56 SiO2 2.96 Si 35.48 SiO2 5.37 Cl 0 0 Cl 0 0.02 K 0.03 K2O 0 K 9.15 K2O 1.77 Ca 6.59 CaO 0.56 Ca 0.11 CaO 0.02 Ti 0.1 TiO2 0.01 Ti 5.9 TiO2 0.67 Mn 1.42 MnO 0.09 Mn 0.05 MnO 0.01 Fe 29.6 FeO 1.95 Fe 19.25 FeO 2.44 O 12 O 21.98 Totals 100.97 Totals 96.37 Cation Cation sum 8.05 sum 15.55

Hbld 1 Garnet 2 Number of Number of Element Compund% Formula ions Element Compund% Formula ions Na 1.8 Na2O 0.53 Na 0.14 Na2O 0.02 Mg 9.71 MgO 2.18 Mg 4.51 MgO 0.52 Al 12.62 Al2O3 2.24 Al 21.9 Al2O3 1.98 Si 41.45 SiO2 6.24 Si 38.54 SiO2 2.96 Cl 0 0.03 Cl 0 0 K 1.45 K2O 0.28 K 0 K2O 0 Ca 11.6 CaO 1.87 Ca 7.41 CaO 0.61 Ti 1.89 TiO2 0.21 Ti 0 TiO2 0 Mn 0.15 MnO 0.02 Mn 1.29 MnO 0.08 Fe 17.84 FeO 2.25 Fe 29.36 FeO 1.89 O 22.97 O 12 Totals 98.51 Totals 103.15 Cation Cation sum 15.8 sum 8.06

Hbld 2 Biotite 2 Number of Number of Element Compund% Formula ions Element Compund% Formula ions Na 1.9 Na2O 0.52 Na 0.29 Na2O 0.08 Mg 10.3 MgO 2.16 Mg 12.07 MgO 2.67 Al 13.12 Al2O3 2.18 Al 14.66 Al2O3 2.57 Si 41.86 SiO2 5.9 Si 36.2 SiO2 5.38 Cl 0 0.03 Cl 0 0.02 K 1.67 K2O 0.3 K 9.24 K2O 1.75 Ca 11.96 CaO 1.8 Ca 0 CaO 0 Ti 2.58 TiO2 0.27 Ti 6.83 TiO2 0.76 Mn 0.1 MnO 0.01 Mn 0 MnO 0 Fe 16.8 FeO 1.98 Fe 18.16 FeO 2.26 O 21.97 O 21.98 Totals 100.29 Totals 97.45 Cation Cation sum 15.12 sum 15.47

Table 2. Microprobe analysis of garnet, hornblende and biotite from domain 1 and 2 used for TWQ P-T calculations.

4.4 Structure cross-sections (figure 18) show the structure to be south vergent, with axial surfaces inclined to approxi- 4.4.1 Structural map and the Ätran closure mately 50° from horizontal and dipping towards the north. The cross-sections both have apparent dip cal- The primary focus of mapping and fieldwork culated for since they do not strike perpendicular to was to confirm or deny the presence of a km scale fold the foliations. closure, which was indicated by the airborne magnetic anomaly map and a few structural measurements. Compilation of structural observations assertively con- firms the existence of a fold closure (figure 17b). The closure, which terminates in the east around the town of Ätran is termed the ‗Ätran closure‘. The interlimb angle approaches zero west of the closure, therefore the fold is classified as isoclinal. Structural complexiti- es and a topographical cutting effect have led to variations in the mappable width of the Ätran closure; a width of 4 km was measured across the hinge zone (the portion of the structure that was most extensively mapped). Field observations confirm that the limbs continue west of Ätran for at least 9 km, although when comparing to the magnetic anomaly data a length of 15 km or more is suspected. The Ätran closure is the surface trace of an isoclinal fold with a fold axis plunging 22° to the east (088°). Of the ten fold- axis measurements; the average orientation was 22/088 with a median orientation of 20/088 (figure 17a). Multiple identical fold axis measurements confirm the fold axis is straight and so the fold is not a B sheath fold but in essence cylindrical. All rocks within the Ätran closure are strongly deformed and have a mineral stretching lineation ranging between 18/068 and 30/102 with the majority within 2° of 21/090, parallel to the fold axis (figure 17a). A stereonet plot of all the poles to the planes of the measured foliations shows that the fold structure has an essentially cylindrical shape with a fold axis that plunges gently to the east (figure 17a). Compilation of foliations, lineation and location of kinematic indicators in a structural map (figure 17b), as well as in the two presented

C Figure 17a. Equal area stereonet plots of structural measurements taken within the Ätran area: A) plot of measured fold axes, mean orientation 22/088. B) plot of mineral stretching lineations, mean lineation 21/090. C) plot of foliation poles to planes with Stereonet 6.3.3 calculated 1% kamb density contours and cylindrical best fit girdle. The orientation of the pole to the girdle is calculated at 21/084.

Stretching lineations Stretching

Foliation poles to to planes poles Foliation

Figure 17b. Structural map showing: select foliations and lineations, 4th and 3rd order fold axial traces, transects used for cross-sections and location of kinematic indicators. Inset: (Fig. 17b) Equal area stereonet plot of foliation poles to planes with Stereonet 6.3.3 calculated 1% kamb density contours and cylindrical best fit girdle. The orientation of the pole to the girdle is calculated at 21/084; (Fig. 17c) Equal area stereonet plot of mineral stretching lineations, mean lineation 21/090.

sections showing fold geometry and location the of mapped units.

- Figure Figure 18. Cross

4.4.2 Folding Four magnitudes of fold structures are suspected to have formed during the same deformation phase. Two magnitudes (1st and 2nd order) can be seen on outcrop scale, one (3rd order) is interpreted by the presence of ‗backfolded shear structures‘ and the fourth (4th order) being the mapped structure. The term ‗backfolded shear structures‘ is used to describe shear planes that have been folded and inverted by a later order of folding resulting in an apparent reversed kinematics. The magnitude of the 3rd order folds that are interpreted by backfolded shear structures is interpreted to have an amplitude on the order of many 10‘s A of meters. Although folding on this scale cannot be directly documented due to the limited size of outcrops; one hinge zone was found west of the study area (figure 19a). All magnitudes of structures have the same characteristics; being tight to isoclinal, cylindrical and exhibiting fold axis parallel stretching lineations, a prime example of the fractal nature of structural geology. The vergence of all magnitudes of folds is southwards, exemplified in figure 19b which represents the smallest magnitude of folding. Figure 19b also shows the asymmetry of the 1st and 2nd order folds, there are long shallow dipping limbs and shorter steeply dipping limbs. The symmetry of 3rd and 4th B order folds is not observable, but based on the fractal Figure 19. A) Fold hinge, interpreted to be 3rd order nature of folding it is likely they are similarly asym- folding. The fold axis is orientated 03/108, sub parallel metric. 1st and 2nd order folds have an amplitude- to the large scale structure‘s fold hinge. Picture loca- width ratio of c. 5:1. tion is west of study area. B) West facing vertical outcrop showing south vergent isoclinal 1st and 2nd order 4.4.3 Fabrics folds, picture location west of study area. Foliation measurements were taken from gneissic foliation planes and parallel gneissic layering planes (figure 20a). The gneisses in the Ätran area have a strong penetrative planar fabric. There is c. 0.5-1 cm visible spacing between fabric elements (foliation planes). Colour banding between dark locally amphibolitic layers and light felsic mineral rich layers is common and often chaotic. Foliations are often folded resulting in isoclinal structures. Foliation planes often form a planar anisotropic weakness, so the rocks will preferentially fracture along foliation planes, thus a compass measurement could be taken directly from the plane. A A linear fabric was identified at most localities, although it was often not as penetrative as the planar fabric. Elongate mineral grains or grain clusters define the linear fabric. Mineral stretching lineations are best seen in quartz ribbons, but they can also form in nearly all types of minerals and mineral aggregates (figure 20b). The stretched minerals typically had an aspect ratio ≥5:1.

Figure 20. A) South facing vertical outcrop (locality 08) of garnet rich gneiss with foliation parallel gneissic layering. B) Mineral stretching lineation seen in quartz ribb- bons (diagonal), the surface on which the lineation is seen is a sub-horizontal foliation plane. Picture from locality 31. B

4.4.4 Shearing spatially associated with folding inverts shear planes, giving an opposite shear sense Two distinct sets of shear planes were obser- (figure 22d). Folding was carefully deconstructed ved. A well defined set is oriented 000/15, sub hori- using vergence of parasitic folds to determine which zontal and a dip congruent with measured fold axes limb is exposed. The overall sense of shear of the and stretching lineation (Figure 21a). Shear planes north dipping limbs of the 4th order fold structure is within this set are observed to only affect the smallest top to the east, and the shear sense within the granite outcrop scale of folds. The second set of shear planes body found south of the hinge is also top to the east. are parallel to the axial planes of the fold structures and are oriented c. 270/40. These are often observed to be partially developed, and can be seen in all observable magnitudes of folding. This set of shear planes are developed near-parallel to the axial planes of the south vergent folds, and have accommodated oblique displacement, as seen by the deflection of foliation, with only a minor reverse fault component apparent. The resulting fold geometry suggests the majority of displacement across these shear planes is in an E-W lateral direction (Figure 21b). A

A B

B Figure 21. Shear planes: A) Vertical west facing outc- C rop cut by a sub horizontal shear plane with top to the east displacement. B) Vertical west facing outcrop with an axial plane parallel shear plane with oblique displacement, picture location west of study area.

4.4.5 Sense of shear in the bulk rock mass The types of kinematic indicators that were documented in the study area were: δ-augens, σ- augens (figure 22 a,b), S-C‘ fabrics (figure 22 a,d) and S-C fabrics (figure 22e) in net migmatites. Complica- tions arose when both dextral and sinistral shear indicators could be seen in an outcrop. Parasitic folding D 26

C Figure 22. Kinematic indicators: A) σ-type indicators and weakly developed S-C‘ fabric (locality 26), sense of shear is sinistral. B) σ-type indicator in megacrystic grey gneiss, shear sense is sinistral (location 31). C) The right limb of the center fold is a ‗backfolded‘ limb with inverted shear planes (location 31). D) S-C‘ fabric showing top to the S east (dextral) shear in an augen gneiss domain of the gran- S itic body (location 26). E) Vertical, south facing outcrop C (locality 62) with an S-C type fabric developed in a metatextite, sense of shear is dextral. E average 2 07 Pb/ 20 6 Pb age of 1388±11 Ma (2s, 4.5 Zircon geochronology MSWD=0.43, prob. 0.86; Figure 24a), for the same analyses. The igneous crystallization of the least defor- Two new occurrences of potential 1.39 Ga gra- med granite sample is here dated at 1388±7 Ma. nitic gneisses were found while mapping the Ätran closure: one extending the southern tip of the Tjärne- 4.5.1.2 Deformed Granite sjö granite, and one in the overturned southeastern part (augen gneiss; sample 26-1, n3785) of the fold closure. A confirmation of a 1.39 Ga intru- Zircons from the deformed granite are clear, sive age of the newly discovered granites is critical for colourless and subhedral. Some grains are fractured the structural interpretation. The 1.39 granites behave along their rims. These zircons are 0.5-1.5 mm in size as competent bodies and are also important as they with length to width ratios c. 3:1. In back-scattered allow separation of 1.43 Hallandian and 0.97 Ga Sve- (BSE)-images the crystals are similar to those from the conorwegian deformation (e.g. Andersson et al 1999). undeformed granite sample. Many grains show a faint Five samples were selected for geochronological zonation only, sometimes a faint sectorial zonation or work. Three samples, representing different states of are dominated by virtually unzoned domains. No dis- strain, were from an internally structurally concordant tinct rims are observed. variably deformed and migmatized granitic body. One Nine analyses were done in zircon from the from a pegmatite dyke and one from the side rock grey moderately deformed granite (figure 24b). One analy- gneiss. All isotopic data is presented in table 3 and in sis, n3785-04, has a slightly higher U content than the figures 23-25. All age calculations include decay cons- other analyses, and is more than 2% discordant. One tant errors. analysis, n3785-06, was displaced and hit the crystal- epoxy interface. The remaining seven spots, which 4.5.1 Sample descriptions and isotopic results were placed well within the zircon grains, are concordant (<0.5% discordant within 2s errors), and have U 4.5.1.1 Undeformed Granite contents between 116-439 ppm, normal for igneous (porphyritic; sample 26-0, n3783) zircon, and conformal U/Th ratios between 0.33-0.61. Zircons from the undeformed granite are clear, The U-Pb data from these spots do, however, not con- colourless and subhedral. Most grains are un-fractured, form to a common concordant age and the weighted and are 0.5-1.0 mm in size with length width ratios c. average 207Pb/206Pb age of these spots is quite impreci- 3:1. In back-scattered (BSE)-images the crystals typi- se at 1372 ± 26 Ma (95% conf. and a high MSWD of cally show weak oscillatory zonation that appears so- 3.3; Figure 24c). mewhat blurred. Many grains show a faint zonation only, sometimes a faint sectorial zonation or are domi- 4.5.1.3 Migmatized Granite nated by virtually unzoned domains. (sample 26-4, n3782) Ten analyses were done in zircon from sample Zircons from the migmatized granite are trans- n3783 (Figure 23a, Table 3). All analyses are <1% lucent and sub-hedral. Most grains are un-fractured, concordant (within 2 sigma errors), are low in com- and are 0.5-1.5 mm in size with length width ratios c. mon Pb and have similar Th/U contents in the 0.88- 3:1. In contrast to the other two samples described 0.54 interval. Analysis n3783-05, 06 and 09, however, above, BSE images of the zircons from the migmati- give distinctly younger ages. These analyses do not zed granite sample show faint oscillatory and sector conform to a simple recent Pb-loss model and may zoning in the cores with a distinct BSE bright rim that indicate a post igneous crystallization disturbance of is typically 10-20 μm wide. the U-Pb system of these zircon domains so these ana- Thirteen concordant analyses were obtained lyses were excluded from age calculation. The remai- from zircon of the migmatized variety of the granite. ning seven analysis yield a concordant age of 1388±7 All data from sample n3782 is shown in figure 24d. Ma (2s, MSWD of equivalence and concordance=1.2, The data cluster in two age groups, one c. 1.4 Ga old probability 0.27; Figure 23b), identical to the weighted

representing spots in oscillatory zoned core domains, with a faint yellow tint. Crystals are c. 0.5 mm in and one c. 1.0 Ga old hitting rims. Spots n3782-05r length, with a 2:1 length to width ratio. Oscillatory and n3782-03 are excluded from age-calculation since zoning is pronounced in the cores, and rims vary in they show an obvious mixing of rim and core data due BSE brightness. The cores often exhibit a distinct po- to incorrect spot placement. BSE imaging of spots lygonal zonation pattern and are not rounded. n3782-11 and 13 does not show any core-rim mixing, Eleven analyses were aimed at oscillatory zo- but hit a pits and cracks in the zircon, which may ex- ned core domains. Four spots are >1.5% discordant. plain their discordance. The concordant spots in oscil- They represent spots misplaced into cracks or spots latory zoned core domains defines a common Concor- that cross-cut the crystal-epoxy interface and are di- dant age of 1387±10 (95% conf., MSWD of equiva- scarded from age calculation. Analysis n3784-9 is lence and concordance=0.17, probability 0.68; Figure slightly younger than the other spots and does not con- 24d) and a weighted average 207Pb/206Pb age of form to a common concordant age. If this analysis is 1386±10 (2s, MSWD =1.14, probability 0.34; Figure excluded, a concordant age of the remaining six spots 24e). This data dates igneous crystallization of the is defined at 1699±10 Ma (95% conf., MSWD of equi- migmatite protolith at 1387±10 Ma. valence and concordance=2.0, probability 0.12; Figure Four analyses were set in BSE-light zircon rims 25c). The weighted average 207Pb/206Pb age for the and together they define a younger phase. One analy- same six spots is 1703±6 Ma (2s, MSWD=0.88, pro- sis cross-cut a texturally older domain (n3872-3) and bability=0.49; Figure 25d). Crystallization of oscillato- was excluded from age calculations. The remaining ry zoned zircon in the grey gneiss is here dated at three analyses define a common concordant age of 1699±10 Ma. 952±8 Ma (2s, MSWD of equivalence and concordance=0.20, probability 0.65; Figure 24f), identical to a 4.5.1.5 Pegmatite weighted average 207Pb/206Pb age of 955±15 Ma (2s, (sample 70-2, n3786) MSWD=0.07, probability 0.94) for the same analyses There was a low yield in zircons from the peg- (figure 25a). A scatter plot of Th/U versus 207Pb/206Pb matite sample, the separation process was repeated age of all analysis is useful for distinguishing the low once and still only ten grains were recovered. Zircons Th/U metamorphic rims from the high Th/U igneous from the pegmatite sample are highly fractured and cores (figure 25b). The texturally young zircon phase altered. Optically these zircons are ‗cloudy‘ and have a is here dated at about 955 Ma. yellow tint. The Crystals are c. 0.5mm in length with a 2:1 length to width ratio. Where there is oscillatory 4.5.1.4 Grey Gneiss zoning, it is distinct and polygonal. (sample 70-1, n3784) BSE-imaging of the spots in sample n3786 The grey gneiss zircons are more equal dimen- shows that the analytical spots hit cracks and five of sional than the ones found in the granite samples, they totally six analyses gave discordant data (figure 25f). also exhibit more cracks and alteration features. Opti- The 207Pb/206Pb ages also vary greatly (figure 25e). cally the zircons from the grey gneiss are translucent

n3783 - cluster 3 1460 n3783 - cluster 3 1460 undeformed granite Concordia Age = 1388.4 6.3 Ma 0.091 undeformed granite 0.091 (2 , decay-const. errs ignored) MSWD (of concordance) = 1.2, Probability (of concordance) = 0.27 1420 1420 0.089 0.089

2 2

10 Pb 10 Pb 7

1 7 4 3 1 4 3 206 206 1380 1380 8 8

0.087 0.087

Pb/

207 207 51340 51340 6 9 6 9 0.085 0.085

1300 1300

0.083 0.083 3.9 4.1 4.3 4.5 4.7 3.9 4.1 4.3 4.5 4.7 238U/206Pb A 238U/206Pb B Figure 23. A) Undeformed granite, Tera-Wasserburg plot of all analyses. B) Undeformed granite, concordant age plot, dashed data omitted from age calculation.

1440 0.093 n3783 - cluster 3 n3875 - deformed granite undeformed granite 1420 1460 0.091

1400 n3783-02r n3783-10 1420 n3785-02 0.089 n3785-06 n3785-04

n3783-07 Pb n3783-03 n3783-04 1380 n3783-01r 06 cross-cut 206 crystal-epoxy n3785-01 n3783-08 interface 1380

Pb/ n3785-05 1360 0.087 n3785-07 207 n3785-03 n3785-09 n3785-08r1340 1340 0.085 Discordant data shown with Mean = 1388 11 [0.76%] 2 1300 dashed lines 1320 Wtd by data-pt errs only, 1 of 8 rej. MSWD = 0.43, probability = 0.86 (error bars are 2 ) 0.083 3.8 4.0 4.2 4.4 4.6 4.8 1300A B 238U/206Pb 0.10 Old group: BLUE 1450 n3785 - deformed granite, N=7 of 9 analysis Concordia Age = 1387.2 10 Ma excluding analysis 06 (cross cut crystal-epoxy 1550 (95% confidence, decay-const. errs ignored) interface) and analysis 4 >2% discordant MSWD (of concordance) = 0.17, 1430 Probability (of concordance) = 0.68 0.09 1450 7 1410 n3785-02 10 1128 11 13509 Young group: RED 13 Concordia Age = 955.9 6.7 Ma 1390 Pb (2 , decay-const. errs ignored)

206 1250 5 MSWD (of concordance) = 1.5, n3785-01 0.08 Probability (of concordance) = 0.22 1370 n3785-05 Pb/ 1150

n3785-07 3 207 1350 n3785-03 n3785-09 1050 0.07 1330 n3785-08r 950 264 n3782 migmatized granite 1310 Mean = 1372 26 [1.9%] 95% conf. Wtd by data-pt errs only, 0 of 7 rej. 1290 MSWD = 3.3, probability = 0.003 0.06 (error bars are 2 ) 3.5 4.5 5.5 6.5 1270C D 238U/206Pb 0.075 1500 Concordia Age = 951.6 7.6 Ma (2 , decay-const. errs included) Mean = 1386 10 [0.73%] 2 MSWD (of concordance) = 0.20, 1480 Wtd by data-pt errs only, 0 of 6 rej. Probability (of concordance) = 0.65 MSWD = 1.14, probability = 0.34 0.073 1460 (error bars are 2 )

1440 Pb 970

206 0.071

1420 n3782-07r 950 Pb/

930 207 1400 n3782-10

n3782-08 1380 0.069 n3782-01 n3782-12 n3782-09 1360 n3782 - migmatized granite excluding analysis 03, missplaced spot 1340 0.067 n3782- migmatized granite 6.05 6.15 6.25 6.35 6.45 6.55 1320E F 238U/206Pb Figure 24. A) Undeformed granite, weighted average 207Pb/206Pb plot, the data in grey is omitted from the calculation. B) Deformed granite, Tera-Wasserburg plot of all analyses, discordant data denoted with dashed lines. C) De- formed granite, weighted average 207Pb/206Pb plot. D) Migmatized granite, Tera-Wasserburg plot of all analyses, data in the old group is coloured blue, data in the young group is coloured red, uncoloured data omitted from calculations. E) Migmatized granite, weighted average 207Pb/206Pb plot of old group data. F) Migmatized granite, concordant age plot of young group data.

1040 10.00 Mean = 955 15 [1.6%] 2 n3782-migmatized granite 1020 Wtd by data-pt errs only, 0 of 3 rej. MSWD = 0.066, probability = 0.94 (error bars are 2 ) 1000

1.00 980

960 n3782-02 n3782-06r n3782-04 940 1382.8

calc 0.10 958.2 920 1011.9

Th/U 951.9 900 1221.3 n3782 - migmatized granite 957.4 excluding analysis 03, missplaced spot 880 1428.5 0.01 1390.4 1373.7 A860 1403.6 1385.9 1383.8 All concordant points except for n3784-09a 1318.4 1740 N=6 Concordia Age = 1700.5 8.6 Ma 0.106 0.00 (95% confidence, decay-const. errs ignored) 600.0 700.0 800.0 900.0 1000.0 1100.0 1200.0 1300.0 1400.0 1500.0 MSWD (of concordance) = 2.5, 207 206 1720 Probability (of concordance) = 0.12 B Pb/ Pb Age (Ma) 1740

5 Mean = 1703.2 6.4 [0.38%] 2 117 1700 Wtd by data-pt errs only, 0 of 6 rej. Pb 0.104 10 1730 MSWD = 0.88, probability = 0.49

3 8 206 4 (error bars are 2 ) 6

Pb/ 1680

9 1720 207 1 0.102 1660 1710 n3784-05 n3784-07 n3784-11 n3784- grey gneiss 1640 1700 n3784-10 n3784-08 0.100 1690 n3784-04 3.0 3.2 3.4 3.6 3.8 C 238U/206Pb 1680

1.00 1670 n3784- grey gneiss 1660D

1750 n3786- pegmatite dyke 0.105 n3786-05 1650 n3786-04 n3786-01 1550 0.10 n3786-06

Pb 0.095 206

Th/Ucalc 1450

Pb/ n3786-03 207 1350 0.085 n3786-02

1250

1150 0.075 0.01 1200.0 1300.0 1400.0 1500.0 1600.0 1700.0 1800.0 2 3 4 5 6 7 8 E 207Pb/206Pb Age (Ma) F 238U/206Pb Figure 25. A) Migmatized granite, weighted average 207Pb/206Pb plot of young group data. B) Migmatized granite, Th/U versus 207Pb/206Pb Age (Ma) plot of all analyses. C) Grey gneiss, concordant age plot, uncoloured analyses omitted from age calculations. D) Grey gneiss, weighted average 207Pb/206Pb plot. E) Pegmatite, Th/U versus 207Pb/206Pb Age (Ma) plot of all analyses. F) Pegmatite, Tera-Wasserburg plot of all analyses.

0.7 2.6 0.5

- - -

lim.

Disc. % Disc.

9.8 9.6 9.7

7.3 8.2 8.0 8.6 7.0 9.6 9.7

11.1 10.3 10.1 10.1 10.0 10.0 10.3 10.9 10.5 10.3 10.6 10.0 11.0 11.1 10.0 10.0

10.2 10.5 10.1 10.4 10.2 11.7

238

206

955.3 964.5 944.3 951.0

1407.2 1402.3 1364.3 1376.2 1365.5 1299.3 1389.7 1381.3 1277.9 1398.6 1384.2 1368.4 1343.2 1344.6 1391.3 1422.1 1326.2 1373.2 1288.7 1406.7 1198.3 1364.7 1395.3 1399.9 1364.7 1335.1 1395.8 1342.3

8.4 9.5

16.8 12.7 14.9 14.5 10.3 13.3 13.6 11.8 12.8 15.6 16.3 13.2 12.1 21.3 11.1 16.4 16.3 15.4 10.4 32.2 17.6 11.3 25.9 11.3 28.2 11.6 14.6 19.3 13.1 11.4

(Ma)

Age ± Age

Pb Pb

207 206

958.2 951.9 957.4

1387.3 1399.3 1387.4 1388.4 1343.7 1336.4 1390.1 1373.8 1334.3 1396.3 1385.6 1417.5 1358.2 1413.3 1374.4 1415.6 1366.8 1339.1 1351.5 1382.8 1011.9 1221.3 1428.5 1390.4 1373.7 1403.6 1385.9 1383.8 1318.4

1.24 1.05 1.13 1.11 0.97 1.09 1.09 1.07 1.07 1.17 1.19 1.10 1.04 0.90 1.42 1.05 1.20 1.17 1.15 0.97 1.79 1.26 1.07 1.54 0.97 1.72 1.01 0.96 1.13 1.29 1.16 0.99

Pb Pb

2.96741 2.97452 2.86731 2.89657 2.80549 2.64544 2.93080 2.88641 2.59446 2.96111 2.91088 2.92238 2.77564 2.85963 2.91045 3.04688 2.74890 2.81645 2.64219 2.95937 1.56431 1.62281 1.54027 2.28143 1.55623 2.93029 2.94440 2.92937 2.89253 2.79697 2.93530 2.71690

207 206

0.87832 0.81325 0.82230 0.81531 0.81080 0.84829 0.82335 0.87835 0.84184 0.83398 0.82224 0.85699 0.82246 0.78766 0.88183 0.87090 0.83573 0.80696 0.82828 0.80272 0.82434 0.91494 0.91119 0.78338 0.78980 0.85114 0.80644 0.82615 0.82981 0.79887 0.93261 0.79885

238

206

0.24395 0.24301 0.23571 0.23799 0.23592 0.22331 0.24059 0.23897 0.21924 0.24230 0.23952 0.23649 0.23167 0.23192 0.24088 0.24682 0.22842 0.23741 0.22130 0.24386 0.15973 0.16140 0.15777 0.20429 0.15897 0.23578 0.24167 0.24254 0.23578 0.23011 0.24175 0.23149

Ratios Ratios

0.18 0.03 0.11 0.63 0.51 0.50

206

{0.03} {0.02} {0.06} {0.07} {0.03} {0.02} {0.03} {0.03} {0.02} {0.08} {0.02} {0.02} {0.96} {0.10} {0.08} {0.04} {0.04} {0.03} {0.03} {0.07} {0.00} {0.03} {0.07} {0.06} {0.01} {0.06}

Pb Pb

1945 2946 3667 3764

206 204

67818 90056 32622 28153 68790 65524 60583 74954 23654 10345 70565 53800 18562 24545 52494 50539 61846 66711 28278 70291 25880 32290 33777

101896 102318 119605 542851 141534

0.56 0.28 0.65 0.58 0.59 0.70 0.66 0.75 0.47 0.67 0.51 0.33 0.61 0.64 0.47 0.50 0.39 0.44 0.54 0.60 0.01 0.01 0.01 0.32 0.01 0.56 0.32 0.80 0.67 0.52 0.52 0.90

[U]

ppm 70.5 89.3

107.9 282.2 130.8 142.8 273.8 232.1 154.9 230.0 186.3 113.5 156.8 162.4 302.2 715.1 135.5 438.8 116.2 243.4 136.8 270.2 107.4 182.0 470.7 118.2 478.8 227.1 295.4 126.7 322.0 225.0

[Pb]

ppm 32.9 80.4 39.6 42.8 81.3 67.4 47.9 71.8 50.3 35.4 46.6 45.7 88.8 39.9 32.1 70.0 38.0 83.1 18.4 31.6 79.7 28.4 81.8 21.0 65.0 94.5 38.7 25.7 96.7 70.2

213.8 134.0

rim rim core core core core core core core core core core core core core core core rim core old young old young young young old old old old old old old

textural textural domain

area

Analysed Analysed

exempt exempt exempt exempt epoxy mix mix fracture fracture

validity

01r 02r 03 04 05 06 07 08 09 10 01 02 03 04 05 06 07 08r 09 01 02 03 04 05r 06r 07r 08 09 10 11 12 13

------

n3783 n3783 undefor- grani- med te n3785 deformed granite n3782 migmatized granite

Sample # spot n3783 n3783 n3783 n3783 n3783 n3783 n3783 n3783 n3783 n3783 n3785 n3785 n3785 n3785 n3785 n3785 n3785 n3785 n3785 n3782 n3782 n3782 n3782 n3782 n3782 n3782 n3782 n3782 n3782 n3782 n3782 n3782 31

3.1 1.7 1.5 0.7 4.6

- - - -

29.2 31.5 14.4 16.3

- - - -

7.4 6.5 8.7

11.7 15.1 14.5 12.0 13.0 13.1 12.2 11.6 11.9 11.9 10.9 10.5 12.3 10.2

866.4

1578.6 1018.4 1759.9 1648.5 1706.8 1620.1 1693.3 1717.6 1645.2 1678.9 1699.3 1528.9 1181.5 1502.7 1719.3 1267.9

5.5 8.6 7.6 9.2 7.3 8.7 8.7 6.1 9.7 8.7

10.4 13.7 11.4 11.5 14.9 12.8 11.2

1671.3 1468.7 1696.8 1691.5 1710.5 1687.5 1709.1 1697.4 1683.1 1700.4 1708.0 1586.8 1306.1 1416.5 1611.9 1694.8 1543.9

1.01 1.07 1.03 1.10 0.90 1.03 1.08 0.90 0.93 0.93 0.86 1.01 1.11 1.05 0.94 0.94 1.07

3.92444 2.17256 4.50139 4.16670 4.37945 4.07675 4.33657 4.37963 4.13814 4.27457 4.35160 3.61739 1.67776 2.48443 3.59587 4.37859 2.87107

0.83156 0.78467 0.98175 0.99881 0.80184 0.90467 0.88054 0.80676 0.80150 0.80553 0.79325 0.80050 0.79573 0.80971 0.77999 0.81186 0.88635

0.27747 0.17115 0.31390 0.29139 0.30313 0.28572 0.30040 0.30531 0.29073 0.29750 0.30161 0.26766 0.14385 0.20116 0.26251 0.30566 0.21735

0.24 0.44 0.12 0.06 1.02 0.38 0.21 0.62

{0.01} {0.03} {0.02} {0.04} {0.02} {0.03} {0.00} {0.01} {0.02}

7724 4272 1837 4923 8789 2995

66707 86554 15670 48946 94373 74312 32599 98136

136389 200536

>1e6

0.52 0.30 1.06 0.62 0.66 0.62 0.57 1.18 0.62 0.67 0.84 0.49 0.18 0.05 0.78 0.62 0.26

226.4 425.0 541.0 226.7 274.8 230.6 154.3 302.3 267.1 235.7 440.0 290.3 630.3 738.0 281.0 218.1 740.2

79.5 89.0 85.2 85.1 59.0 91.4 97.4 99.2 85.5

237.7 108.1 133.3 100.1 179.3 106.0 164.4 190.9

rim rim core core core core core core core core core core core core core core core

fracture epoxy exempt fracture fracture fracture fracture fracture

01r 02r 03 04 05 06 07 08 09 10 11 01 02 03 04 05 06

------

Tableanalytical 3.data All

n3784 n3784 gne- grey iss n3786

n3784 n3784 n3784 n3784 n3784 n3784 n3784 n3784 n3784 n3784 n3784 n3786 n3786 n3786 n3786 n3786 n3786 32

5 Interpretations lower-pressure biotite and hornblende assemblage. At 17 kbar and 700°C Theriak calculations predicts 9 vol% garnet and 13 vol% omphacite for a felsic gneiss 5.1 Metamorphism (table 2). When compared to the Theriak results for the 5.1.1 1.39 Ga granite same composition at 8.5 kbar and 690°C, suggested by Strain and migmatization has heterogeneously P-T determinations from the mafic assemblages (cp. P- affected different domains of the granite body. The T estimations), there is a reduction in the stability of composition of all samples is identical; it is just the garnet to 5 vol% and clinopyroxene is no longer stab- crystal size and form that has changed. From a compa- le. These observations support the interpretation of the rison of the unstrained, strained and migmatized samp- felsic gneiss having once equilibrated at conditions les the following conclusions can be drawn. As a result near 17 kbar and 700°C followed by a decompression of strain, perthite formed from the exsolution of plagi- and subsequent retrogression at 8.5 kbar and 690°C. oclase in K-feldspar. Migmatization has resulted in The retroeclogite sample 30-3 has the largest recrystallization of the quartz domains and the forma- compositional contrast to the felsic gneiss, represented tion myrmekite. Orthoclase crystals have recrystallized in both the high-pressure phases and medium-pressure to microcline. Rutile is found only in the strongly stra- phases observed. Previous petrographic work (BSc ined rocks; titanium may have been released from stra- thesis) as well as support from previous studies of ec- ined biotite and amphibole. Titanite is only found in logites in the Ullared area (Möller 1998, 1999) allow the migmatized domains, and likely formed from ilme- for confident recognition of a high-pressure eclogite nite and rutile during reaction with a Ca-bearing mine- assemblage, even with varying amounts of lower- ral, possibly simultaneous with the introduction of a pressure retrogression. The high-pressure phases, re- fluid. The presence of titanite in the migmatized as- cognized by their large grain sizes or in the case of semblage indicates migmatization occurred at pressu- omphacite the large outline of sympletic reactions are, res below 14 Kbar (Kylander-Clark et al 2008). Kylan- garnet, omphacite and quartz with minor rutile. At 17 der-Clark et al (2008) calculated the stability of titanite kbar and 700°C Theriak predicts 42 vol% almandine for a granodiorite composition using the same inter- rich (53 mol%) garnet, 41 vol% omphacite and 9% nally consistent database used for Domino-Theriak quartz for a gabbroic composition. Theriak results for calculations. Since neosomes are foliation parallel, the same composition at 8.5 kbar and 690°C yield a migmatization is interpreted as occurring in a dynamic reduction of garnet to 17 vol% and omphacite to 22 environment, although biotite and hornblende have vol% with a formation of 32 vol% plagioclase An40 grown with no preferred orientation in some samples. and 13 vol% hornblende. The plagioclase + hornblen- Compared to other rocks in the study area, the granite de + diopside symplecites, a common feature of retro- body contains unusually well preserved domains, like- gressed mafic eclogites, form when omphacite breaks ly due to its competence with K-feldspar-rich and down, first to form plagioclase and diopside and at porphyritic interlocking crystal texture. lower pressures and temperatures continue with diopside breaking down to form hornblende. Symplectitic 5.1.2 Stabilities of mineral assemblages and corona textures around garnets demonstrate chemical instability during uplift. During decompression The pseudosections presented in this study from eclogite pressures to granulite and amphibolite show what was first forwarded by Green and Ringwo- pressures, calculations suggest that the first plagiocla- od (1972); eclogite assemblage stability is strongly se stable is albitic (An ); as decompression continues dependent on bulk rock chemistry. So long as minerals 12 the plagioclase will re-equilibrate to a more anorthitic do not exist in a metastable state during compression, composition (Figure 14). Plagioclase in sample (30-3) then the eclogite stabilization will be dependent on provide a snapshot of this re-equilibration process, bulk rock chemistry. Austrheim (1987) stressed the with a lower-pressure phase An overgrowing the importance of fluid availability and deformation in 38 higher-pressure An phase. Scapolite, which forms at triggering the forward high-pressure metamorphic 32 medium to high temperatures when the metamorphic reactions, serving as an explanation for the (counter- fluids are CO and S-rich, appears in equilibrium with intuitive) eclogite facies assemblages forming along 2 the amphibolite facies assemblage. The chlorite and viens in a granulite host in the Caledonian Bergen margarite reflect the rocks low-grade fluid and meta- Arcs. The field relations in the present study area do morphic history. not suggest the rocks have behaved in a non-ideal The well-preserved retro-eclogite had a high- manner during prograde motion, on the other hand pressure assemblage composed of large clinopyroxene, there is very little of the prograde stages preserved. garnet and quartz. Retrogression at lower pressures A common feature in all compositions studied replaced much of the clinopyroxene and outermost is the remnants of both a high-pressure assemblage as rims of the garnet. The cpx-symplectite resulted as a well as a medium-pressure assemblage. The most fel- breakdown of the typical high-pressure phase ompha- sic sample (68-1) contains minor amounts of the high- cite, as described by Anderson and Moecher (2007). pressure phases clinopyroxene and garnet, both of The different patterns seen in the cpx-symlectites may which appear resorbed and unstable in relation to the represent the original orientation of omphacite, as the 33

exsolution processes are expected to follow mineral The garnet gneiss is interpreted to have never cleavage planes. The crosshatched symplectite pattern been plagioclase free, and therefore never been an formed from an omphacite grain with an orientation eclogite. With a composition intermediate compared to perpendicular to the z-axis. The large hornblende crys- the retro-eclogite and felsic gneiss, it is expected to tals unassociated with the symplectites possibly for- have had a high-pressure assemblage of about 30% med at a later metamorphic event, their presence and garnet, 25% omphacite, 15% orthopyroxene, 15% qu- apparent stability suggests retrogression took place artz and 15% albitic plagioclase at 700°C and 17kbar. under amphibolite facies conditions. The textures sug- The omphacite has broken down to form plagioclase gest that plagioclase, although now occurring with and hornblende, there may also be some reduction in nearly every phase was not present alongside garnet the garnet volume percent. Biotite likely formed at the and omphacite. There are no plagioclase inclusions expense of oxides, as it is only seen in oxide bearing within the center of the garnet grains, suggesting no domains. Further retrogression following the equilibri- prograde plagioclase is preserved. The spatial relation um of amphibolite facies assemblage is responsible for between rutile and ilmenite could indicate a prograde the sericitation of plagioclase and the alteration of reaction from ilmenite to rutile. The amphibole rim garnet. around the rutile/ilmenite reacion sites could be expla- Bulk rock chemistry plays a fundamental role ined by consumption of rutile during amphibolitiza- in determining which minerals are stable at any P-T tion. The equilibrium between garnet, clinopyroxene, condition. When the pseudosections are compared it is plagioclase, quartz is useful as a geobarometer and clear that at nearly all P-T conditions, the mafic and common in retrogressed eclogites. Moecher et al felsic rocks will have different mineral assemblages. (1988) as well as Anderson and Moecher (2007) revi- The stability of plagioclase is of particular importance ew the various possible reaction paths these phases can since its absence at high pressures defines the eclogite take, but a simplified version is as follows; garnet assemblage. Figure 26 clearly shows a rock with a (grossular and pyrope) + quartz = clinopyroxene mafic composition will be eclogitized at lower pressu- (diopside) + plagioclase (anorthite). The origin of the res than a rock with a more felsic composition. The biotite-symplectite is uncertain, but its formation un- more mafic the composition is, the lower the pressure der similar conditions as the cpx-symplectite is sug- needed for the plagioclase out reaction to occur. At gested. One possible origin is a high-pressure phengi- any particular temperature, the difference in pressure tic white mica with a low stability in mid-pressure for plagioclase stability in the mafic compared to the conditions. Wimmenauer and Stenger (1989) proposed felsic rock is a minimum of 2 kbar that corresponds to a formation of biotite, plagioclase and spinel from the c. 6 km of depth. When a normal continental geotherm decomposition of phengite. Spinel has not been identi- is considered (Artemieva 2006) the pressure difference fied in this section; the reaction in the present retroec- increase to c. 3.5 kbar or c. 10 km in depth. In terms of logite may have been different due to the presence of a natural deep-crustal environment, there is a depth free SiO2. range ≥6 km where mafic compositions will be plagioclase free and felsic compositions will still contain plagioclase.

Figure 26. Domino pseudosection calculated for a mafic boudin composition, the plagioclase-out reaction is outlined. Overlain in orange is the same plagilocase-out reaction for a felsic gneiss composition.

5.2 Structure and strain

5.2.1 Heterogeneous strain distribution Heterogeneous strain distribution is seen on different scales. On the map scale, retro-eclogite bodies are boudinaged and felsic gneisses are the most strained (cp. Lithological map). On outcrop scale there is uneven strain between layers of varying compositions (ie. figure 9a), and even in some homogeneous outcrops strain is unevenly distributed (ie. figure 6a). Small scale features such as foliation wrapping around garnet porphyroclasts (figure 12a) is another sign of heterogeneous strain distribution. On the microscale, A felsic domains are weaker and more easily deformed than those containing garnet and pyroxenes. In areas of high shear grain size reduction is common. At ele- vated temperatures, when the strain rate exceeds the possible rate of crystal plastic flow then dynamic recrystallization processes like neoblast nucleation dominate. In the most quartz rich unit, the leucocratic gneiss, strain is evenly distributed among all domains resulting in a stretched out rock with minimal grain size reduction (figure 27). In more mafic units like the garnet rich gneiss, strain is unevenly partitioned among weaker felsic and stronger mafic domains. To accom- modate the same amount total strain (only retro- eclogite unit was boudinaged) the strain rate must increase in the weaker (felsic) units (figure 28). B 5.2.2 Shearing and folding relations Figure 27. Strain distribution: A) Quartz ribbons deve- A study of the kinematic indicators yielded loped in leucocratic gneiss. B) Grain size reduction of little information due to the difficult to interpret sym- quartz along a micro shear plane; mafic-rich domains metry that most indicators had. Top to the east shear were less affected by shearing. indicators were observed on both limbs of the 4th order fold structure, indicating shearing occurred simul- taneously with or following the folding. The sub- horizontal shear planes (figure 21a) are penetrative on an outcrop scale, but cannot be followed or correlated between outcrops. Some shear planes have been folded (ie. figure 22c) indicating some phases of shearing occurred before folding. In a more detailed study of kinematics, Ekdahl (2001) observed a top to the east trend in a part of the Ullared area northeast of the present study area.

5.2.3 Strain model The two shear regimes most commonly discussed are pure shear and simple shear. Pure shear (irrotational strain) has two opposing displacement vectors that are defined by the same principal stretching axis. Simple shear (rotational strain) has one displacement vector defined by the principal stretching Figure 28. Figure showing the relation between com- axis. The combined force of simple and pure shear can petency and strain rate. be termed ‗general shear‘, the force responsible for displacement along shear zone parallel planes. Neither of these two shear types are capable of defining a strain regime in which un-curved fold axis lie nearly parallel to stretching lineations, without suggesting a

radically changing stress field that produces a late phase of shortening perpendicular to the displacement direction. Cobbold and Quinquis (1980) showed that a shear zone parallel fabric will not fold in any amount of progressing simple shear. Therefore the folding commonly accompanying shear zones is most often attributed to heterogeneities in the rock. The conside- ration of a third shear type ‗wrench shear‘, which in- volves a rotational component similar to the physical force of torque combined with rheological differences within the rock allows for a variety of complex models capable of explaining folding that occurs in some shear zones (figure 29). Ridley and Casey (1989) modelled the effects of combined wrench and thrust shear and compared the results to simple shear with shortening parallel to Figure 30. Sketch model for the spatial distribution of the shear direction (a two step process). In the combi- fabrics and folds with respect to shear direction (mineral ned wrench and thrust model, after a total strain of γ=4 stretching lineation), view from NNE; modified from the fold axis is sub-parallel (within 15°) and parallel Ridley (1986). beyond γ=6 where γ represents the stretching ratio (stretching along principal stretching axis divided by stretching perpendicular to the principal stretching axis). In the shear and shortening model it takes consi- 5.2.4 Tectonostratigraphic marker derable more shear strain to produce sub-parallel fold Previous work (Möller et al. unpublished data) axis and the resultant fold shape still had a curved fold suggests that the eclogites of the eastern Sveconorwe- axis. gian Orogen are restricted to a position structurally A fold nappe can be viewed as a ductile analo- above the deformed 1.39 Ga Torpa and Källsjö grani- gy to a surface thrust sheet. When the bow and arrow tic metaintrusive bodies. The identification of the Ät- model for thrust displacement presented by Elliot ran fold closure connects this structural level with the (1976) is applied to ductile shear zones, it becomes southern tip of the Tjärnesjö granitic metaintrusion, so evident the degree of strain will vary along the fold that the eclogite-bearing domains are entirely enclosed nose, that is the propagating hinge of a fold structure. by a major nappe-like fold structure. The closure prov- The frontal and lateral tips will experience very high ides a structural explanation for the lack of eclogites degrees of strain, and in some circumstances complex found east of Ätran, and the understanding of this strain patterns will develop (Coward and Potts, 1983). structure is critical for explaining and developing a The term lateral tip is used by Coward and Potts kinematic model of the eclogite emplacement. The (1983) to describe to outermost sides of a nappe with a presence of deformed and ‗in-folded‘ meta-intrusions bow structure. In the Ullared zone, the Ätran closure that belong to the structurally underlying 1.40-1.38 Ga likely represents the lateral tip of a large fold nappe Torpa, Källsjö and Tjärnesjö meta-intrusive bodies in (figure 30), and high strain is expected in this part of a parts of the fold structure suggests that these rocks large fold nappe as a result of the fold geometry rather indeed are traceable tectonostratigraphic markers. than a increase in the stress regime. In a uniform stress field with no wrench shear component, shearing and folding will progress in a ‗normal‘ fashion creating ever tighter folds and eventually non-cylindrical sheath folds will develop (Cobbold & Quinquis, 1980).

Figure 29. Effect of simple and wrench shear on a rock with a planar anisotropy, modified from Ridley (1986).

5.3 Geochronology Torpa and Tjärnesjö bodies. The granite mapped in this study is interpreted to be a boudinaged portion of U-Pb analysis of igneous zircon in three diffe- the Tjärnesjö granite, which may have once been rent samples of variously strongly metamorphosed and structurally connected to the farther west Torpa grani- deformed porphyritic granites found south of the Ätran te. The rigid granite bodies have been deformed and closure affirms c. 1.39 Ma intrusion age of the newly displaced by the Ätran fold, and so define an outer discovered granite body (Ätran metaintrusion).The boundary to the fold closure. A comparison of the ob- most pristine granite sample for dating the igneous served fold structures in the Ätran area, with the fab- protolith age of the granite body is the sample from ric/fold distribution map (figure 30) places the Ätran the undeformed granite, here dated at 1388±7 Ma. The closure on the lateral tip of a large c. 50 km wide non- igneous crystallization age of moderately deformed cylindrical fold nappe. At Ätran the fold axis is paral- granite sample is less precise at 1372±26 Ma but lel to the stretching lineation and the small scale folds within statistical errors overlapping with the well pre- are cylindrical and asymmetric, both features that are served granite sample. Igneous crystallization of the expected to develop on the lateral tips. The position of migmatitic variety was dated at 1387±10 Ma. The pro- the Ätran closure in a proposed large scale thrust tolith age of the Torpa and Tjärnesjö granites have structure can be seen in (figure 31). The outline of the been determined by U-Pb-Th analysis of zircon at c. proposed structure can be followed along areas with 1.39 Ga (Andersson et al 1999, 2002). The igneous low magnetic anomalies. The large structure is visuali- zircon in megacrystic metagranites/augen gneiss dated sed as an easterly propagating thrust/channel flow in this project are similarly complex and give identical ‗nappe‘ that is cut by the Mylonite Zone in the west. igneous crystallization ages at about 1.39 Ga. The eastward propagation of the nappe deformed and displaced the Tjärnesjö, Torpa and Ätran granites at c. Although the granite shows a wide range of 955 Ma in the late stages of the Sveconorwegian oro- strain in local domains, it appears that metamorphic geny. Deformation cross-cutting pegmatites from the zircon rims grew only when there was some degree of Gällared area, c. 15 km west of Ätran have been dated anatectic melting such as the migmatization of sample at 956±7 Ma, giving a minimum age to the regional 26-4. New zircon growth in the migmatitic granite was Sveconorwegian deformation (Möller & Söderlund, dated at 955±15 Ma. Since migmatization is interpre- 1997). A present day E-W shortening is needed to ted to be coeval to the deformation of the granite body, create an east propagating nappe, such as the continu- the 955±15 Ma age gives a Sveconorwegian age to the ed collision and eastward propagation of the Sveco- deformation and migmatization of the granite. The norwegian orogeny. The development of the mylonite position and deformation of the granite is also structu- zone post-dates the nappe formation, as it crosscuts the rally linked to the formation of the Ätran fold structu- west end of the structure. Only a general trend of top re, now confirmed to be Sveconorwegian. Furthermo- to the east displacement has been observed in the stu- re, textural observations from the area (MSc thesis dy area, similar to what was suggested by Möller et al, herein, BSc thesis) of the pervasive amphibolite over- (1997) and Ekdahl (2001). Anatexis is observed to print in the region can also be tied to the migmatiza- increase north from the Ätran closure, so the centre of tion and deformation age. Igenous crystallization of the nappe may have experienced significant partial the grey gneiss side rock was constrained at 1699±10 melting. A melt percent beyond 30% generally super- Ma. This age is similar to orthogneiss protolith ages of sedes the rheologically critical melt percent and forms the regionally abundant side rock grey gneisses that diatextites capable of flowing like igneous melts, if are interpreted to have formed in connection with the this is the case in the proposed structure then the term younger phases of magmatism belonging to the ‗channel flow‘ is more appropriate than ‗thrust nappe‘. Transscandinavian Igneous Belt (Söderlund et al 2002). Ages from the pegmatite zircons indicate they Irrespective of whether the proposed structure are likely xenocrystic and no crystallization age was is a thrust nappe or a channel flow, its south boundary, recovered from this rock. mapped in this study, is a lithotectonic boundary. All known retro-eclogite occurrences are north of the Ät- ran closure; south of the closure boundary rocks exhi- 6 Tectonic interpretation bit upper amphibolites or medium-high pressure gra- and discussion nulite facies assemblages without eclogite relicts (Möller & Andersson unpublished data). The mapped The Torpa and Tjärnesjö bodies are key rock fold structure, and in connection, the proposed large units for understanding the Sveconorwegian deforma- fold nappe have exhumed rocks from eclogite facies tion in the eastern segment. Their c. 1.39 Ga intrusion conditions and juxtaposed them structurally above postdates the c. 1.43 Ga ‗Hallandian‘ deformation upper-amphibolite and high-pressure granulite facies event (cp. Geological setting), making them a mono- rocks. Figure 32 is a proposed PT-time path for the metamorphic unit hosted by a poly-metamorphic c. 1.7 rocks within the fold closure, based on a collaboration Ga ‗grey gneiss‘. The 1388±7 Ma protolith age of the of results from this study and previous findings granite at Ätran is coeval to the intrusion age of the (Möller, 1999 and references therein). The peak press- 37

sure conditions for both the felsic and mafic units was ints on the low-grade metamorphism responsible for c. 17 kbar and 700°C; at these conditions eclogite faci- the formation of margarite and chlorite in the retro- es assemblages will only form in the basic/mafic com- eclogite sample and the sericite alteration of plagiocla- positions. Eclogitization of the mafic units has a maxi- se in all samples. A fluid influx during erosion and mum age of 972±14 Ma (Johansson et al, 2001). By subsequent uplift, when the rocks were under green- dating the migmatization age of the granite, the age of schist facies conditions is likely responsible for such amphibolitization is known to have occurred late in the low-grade features. orogenic event at c. 955 Ma. There are no age constra-

Figure 31. Aeromagnetic anomaly map of SW Sweden, the dashed white line marks the proposed outline of large scale eclogite bearing fold nappe. Inset bottom: 2.5 x magnifications showing location of the Ätran closure, Tjärnesjö granite (black), Torpa granite (black) and here in described Ätran granite (yellow). Inset top: Sketch showing the geometry of the proposed fold nappe. References: Aeromag map (SGU), Varberg map (Lundqvist, 2008), Kungsäter (SGU unpublished data, Möller personal commu- nication), Källsjö (Ekdahl, 2001), Tjärnesjö (Andersson et al, 1999) 38

Figure 32. Proposed PT-time path for mafic and felsic compositions within the UDZ. Peak pressure suggested at 17 kbar and 700°C, within the mafic-eclogite stability field (red line) and below the felsic-eclogite stability field (orange line). The maximum age of eclogitization is 972±14 Ma (Johansson et al, 2001). Exhumation and re- equilibrium at upper-amphibolite facies conditions c. 8.5 kbar and 690°C is dated to 955±7 Ma. The late low-grade assemblage likely formed during erosion-induced uplift to greenschist conditions c. 4 kbar and 400°C. Kyanite - andalusite-sillimanite stability denoted by the dashed black line. Compare to figure 26 for assemblage stability.

6.1 Suggestions for future studies geometry it is unlikely any high-pressure mineral relicts are present east of the Tjärnesjö body. Following the model for shear induced folding A quantitative study of strain should yield a in high-grade terrains presented by Ridley (1986) and decrease in total strain at sites 1 and 2 relative to the discussed in the structural interpretations of the thesis present study area and site 3, and a substantial decrea- herein, predictions about the spatial distribution of se in towards site 4 and the core of the fold nappe. deformation fabrics can be made. Thus, the proposed fold nappe geometry in figure 30 can be treated as a 7 Conclusions hypothesis and tested. At site 1 (figure 31) the fold axis will trend Detailed structural, petrography and geochro- 045-060° with fold-hinge sub-parallel stretching linea- nology studies of the Ätran fold structure in the Sveco- tions (a significant angle to the bulk transport direc- norwegian eclogite-bearing deformation zone have tion). Folds will be cylindrical, asymmetric and in the produced the following findings: right conditions they may be extremely rodded. The fold geometry at site 2 depends most on A c. 4 km wide cylindrical inclined south- the local heterogeneities within the rocks. Fold hinges vergent isoclinal fold with a gently east dipping should trend c. 000°, and the mineral stretching linea- fold axis forms a fold closure around the town tions should be hinge-perpendicular. Folds at site 2 of Ätran. will be recumbent with axial planes representative of A granitic meta-intrusion found just south of the large-scale fold axial plane. the Ätran closure has been displaced by top-to- Site 3 should closely resemble the features east shear associated with the formation of the described in this study. Small variations in the inter- Ätran fold. preted bulk transport direction may result in cylindri- U-Pb zircon dating of the granitic meta- cal upright folds rather than the asymmetric folding intrusion yields an intrusive age of 1388±7 Ma, described. Similar to the present study area, the stret- and allows correlation with the Tjärnesjö and ching lineation will be strongly pronounced in defor- Torpa granites. med rocks. The southern demarcation of the Ätran closure Site 4 represents the innermost portion of the is a lithotectonic boundary, where retro- fold nappe, the total strain will be substantially lower eclogites are restricted to the domain north of than what is described in the present study area. The the boundary. degree of anatexis is expected to increase towards site Pseudosection calculations describe a c. 2 kbar 4 and diatextites may dominate the centre of the fold (6 km Δ depth) zone where eclogite assembla- nappe. High-pressure mineral relicts are expected at ges are stable in mafic and not felsic rocks. site 4. Based on what is known about the fold nappe This serves as a plausible explanation for the

observation of eclogite mineral relicts in the plications for lithosphere secular evolution. mafic but not the felsic rocks found north of the Tectonophysics 416, 245-277. lithotectonic boundary. Migmatization of the rocks within the study Austrheim, H., 1987: Eclogitization of lower crustal area took place at c. 955 Ma. This age also ser- granulites by fluid migration through shear zo ves as a minimum age for the retrogression and nes. Earth and Planetary Science Letters 81, re-equilibration that took place under medium- 221-232. pressure granulite and upper-amphiboilte facies conditions. Berthelsen, A., 1980: Towards a palinspastic analysis P-T conditions of the pervasive medium- of the Shield. International Geological Cong pressure retrogression were estimated at c. 8.5 ress, Colloquium C6, Paris, 5–21. kbar and 690°C ± 1.1 kbar and 50˚C. The Ätran fold is interpreted as the lateral tip of Berman, R.G., 1988: Internally-consistent thermody a proposed ≥50 km wide fold nappe that propa- namic data for minerals in the system Na2O- gated east c. 75 km into the Eastern Segment K2O-CaO-MgO-FeO-Fq03 -Al2O3-Si02-TiO2- and is crosscut in the west by the Mylonite H2O-CO2. Journal of Petrology 29, 445-522. Zone. Bingen, B., Nordgulen, O. & Viola, G., 2008: A fourphase model for the Sveconorwegian oro 8 Acknowledgments geny, SW Scandinavia. Norwegian Journal of Geology 88, 43-72 I would like to express my deepest gratitude to Charlotte Möller for her extensive work as my super- Bingen, B., Skår, Ø., Marker, M., Sigmond, E.M.O., visor. Her support and insights were invaluable. Nordgulen, Ø., Ragnhildstveit, J., Mansfeld, J., Thanks to my co-supervisor Jenny Andersson, who Tucker, R.D. & Liégeois, J.P., 2005: Timing of greatly assisted me in my Nordsim study as well as continental building in the Sveconorwegian with valuable discussions and comments in the field orogen, SW Scandinavia. Norwegian Journal of and during manuscript preparation. Thanks to Michael Geology 85, 87-116. Stephens for his review and comments. I also wish to thank Martin J. Whitehouse and the staff at the Nord- Cobbold, P. R. & Quinquis, H., 1980: Development of sim Laboratory for all their help and for giving me the sheath folds in shear regimes. Journal of Struc opportunity to use their lab. Finally, to my friend‘s tural Geology 2, 119-126. here in Lund and my family back home, Thank you for all the love and support you have given me throughout Coward, M.P. & Potts, G.J., 1983: Complex strain the years. patterns developed at the frontal and lateral tips to shear zones and thrust zones. Journal of Structural Geology 5, 383-399. 9 References de Capitani, C. & Brown, T. H. 1987: The computa Andersson, J., Söderlund, U., Cornell, D., Johansson, tion of chemical equilibrium in complex sy L. & Möller, C., 1999: Sveconorwegian (- stems containing non-ideal solutions. Geochi Grenvillian) deformation, metamorphism and mica et Cosmochimica Acta 51, 2639–2652. leucosome formation in SW Sweden, SW Bal tic Shield: constraints from a Mesoproterozoic Dubey, Ashok K., 1980: Late stages in the develop granite intrusion. Precambrian Research 98, ment of folds as deduced from model experi 151-171. ments. Tectonophysics 65, 311-322

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Löfroth, Elin, 2010: A Greenland ice core of early land plants from upper Silurian perspective on the dating of the Late strata in Klinta 1 well, Skåne, Sweden. (45 Bronze Age Santorini eruption. (45 hskp) hskp) 255. Ellingsgaard, Óluva, 2009: Formation 240. Bjärnborg, Karolina, 2009: The copper Evaluation of Interlava Volcaniclastic sulphide mineralization of the Zinkgruvan Rocks from the Faroe Islands and the deposit, Bergslagen, Sweden. (45 hskp) Faroe-Shetland Basin. (45 hskp) 241. Stenberg, Li, 2009: Historiska kartor som 256. Arvidsson, Kristina, 2010: Geophysical and hjälp vid jordartsgeologisk kartering – en hydrogeological survey in a part of the pilotstudie från Vångs by i Blekinge. (15 Nhandugue River valley, Gorongosa hskp) National Park, Mozambique. (45 hskp) 242. Nilsson, Mimmi, 2009: Robust U-Pb 257. Gren, Johan, 2010: Osteo-histology of baddeleyite ages of mafic dykes and Mesozoic marine tetrapods – implications intrusions in southern West Greenland: for longevity, growth strategies and constraints on the coherency of crustal growth rates. (15 hskp) blocks of the North Atlantic Craton. (30 258. Syversen, Fredrikke, 2010: Late Jurassic hskp) deposits in the Troll field. (15 hskp) 243. Hult, Elin, 2009: Oligocene to middle 259. Andersson, Pontus, 2010: Hydrogeological Miocene sediments from ODP leg 159, site investigation for the PEGASUS project, 959 offshore Ivory Coast, equatorial West southern Skåne, Sweden. (30 hskp) Africa. (15 hskp) 260. Noor, Amir, 2010: Upper Ordovician 244. Olsson, Håkan, 2009: Climate archives and through lowermost Silurian stratigraphy the Late Ordovician Boda Event. (15 hskp) and facies of the Borenshult-1 core, 245. Wollein Waldetoft, Kristofer, 2009: Sveko- Östergötland, Sweden. (45 hskp) fennisk granit från olika metamorfa miljöer. 261. Lewerentz, Alexander, 2010: On the occurrence of baddeleyite in zircon in 272. Andersson, Josefin, Hybertsen, Frida, 2010: silica-saturated rocks. (15 hskp) Geologi i Helsingborgs kommun – en 262. Eriksson, Magnus, 2010: The Ordovician geoturistkarta med beskrivning. (15 hskp) Orthoceratite Limestone and the Blommiga 273. Barth, Kilian, 2011: Late Weichselian glacial Bladet hardground complex at Horns Udde, and geomorphological reconstruction of Öland. (15 hskp) South-Western Scania, Sweden. (45 hskp) 263. Lindskog, Anders, 2010: From red to grey 274. Mashramah, Yaser, 2011: Maturity of and back again: A detailed study of the kerogen, petroleum generation and the lower Kundan (Middle Ordovician) application of fossils and organic matter ‘Täljsten’ interval and its enclosing strata for paleotemperature measurements. (45 in Västergötland, Sweden. (15 hskp) hskp) 264. Rääf, Rebecka, 2010: Changes in beyrichiid 275. Vang, Ina, 2011: Amphibolites, structures ostracode faunas during the Late Silurian and metamorphism on Flekkerøy, south Lau Event on Gotland, Sweden. (30 hskp) Norway. (45 hskp) 265. Petersson, Andreas, 2010: Zircon U-Pb, 276. Lindvall, Hanna, 2011: A multi-proxy study Hf and O isotope constraints on the growth of a peat sequence on Nightingale Island, versus recycling of continental crust in South Atlantic. (45 hskp) the Grenville orogen, Ohio, USA. (45 277. Bjerg, Benjamin, 2011: Metodik för att hskp) förhindra metanemissioner från avfalls- 266. Stenberg, Li, 2010: Geophysical and deponier, tillämpad vid Albäcksdeponin, hydrogeological survey in a part of the Trelleborg. (30 hskp) Nhandugue River valley, Gorongosa 278. Pettersson, Hanna, 2011: El Hicha – en National Park, Mozambique – Area 1 and studie av saltstäppssediment. (15 hskp) 2. (45 hskp) 279. Dyck, Brendan, 2011: A key fold structure 267. Andersen, Christine, 2010: Controls of within a Sveconorwegian eclogite-bearing seafloor depth on hydrothermal vent deformation zone in Halland, south- temperatures - prediction, observation & western Sweden: geometry and tectonic 2D finite element modeling. (45 hskp) implications. (45 hskp) 268. März, Nadine, 2010: When did the Kalahari 280. Hansson, Anton, 2011: Torvstratigrafisk craton form? Constraints from baddeleyite studie av en trädstamshorisont i Viss U-Pb geochronology and geo-chemistry mosse, centrala Skåne kring 4 000 - 3 000 of mafic intrusions in the Kaapvaal and cal BP med avseende på klimat- och Zimbabwe cratons. (45 hskp) vattenståndsförändringar. (15 hskp) 269. Dyck, Brendan, 2010: Metamorphic rocks 281. Åkesson, Christine, 2011: Vegetations- in a section across a Svecnorwegian utvecklingen i nordvästra Europa under eclogite-bearing deformation zone in Eem och Weichsel, samt en fallstudie av Halland: characteristics and regional en submorän, organisk avlagring i Bellinga context. (15 hskp) stenbrott, Skåne. (15 hskp) 270. McGimpsey, Ian, 2010: Petrology and 282. Silveira, Eduardo M., 2011: First precise lithogeochemistry of the host rocks to the U-Pb ages of mafic dykes from the São Nautanen Cu-Au deposit, Gällivare area, Francisco Craton. (45 hskp) northern Sweden. (45 hskp) 283. Holm, Johanna, 2011: Geofysisk 271. Ulmius, Jan, 2010: Microspherules from utvärdering av grundvattenskydd mellan the lowermost Ordovician in Scania, väg 11 och Vombs vattenverk. (15 hskp) Sweden – affinity and taphonomy. (15 hskp)

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