NTNU Norwegian University of Science and Technology Faculty of Engineering Department of Geoscience and Petroleum
Vanja
Vanja Skålnes Haugsnes
Structural analysis and titanite U-Pb petrochronology of major
Sveconorwegian shear zones in Telemark, southern Norway
Master’s thesis in Technical Resource Geology Supervisor: Espen Torgersen
June 2021
Master ’s thesis
Vanja Skålnes Haugsnes
Structural analysis and titanite U-Pb petrochronology of major
Sveconorwegian shear zones in Telemark, southern Norway
Master’s thesis in Technical Resource Geology Supervisor: Espen Torgersen
June 2021
Norwegian University of Science and Technology Faculty of Engineering
Department of Geoscience and Petroleum
i
Abstract
Can titanite petrochronology be used to constrain the timing of deformation along crustal scale shear zones?
This study investigates this question through geological mapping of a structurally complex area in the Sveconorwegian orogen of Southern Norway, and by linking structural analysis, the growth of temperature sensitive minerals, and recrystallization of rock forming minerals with titanite U-Pb petrochronology within two large scale shear zones; the extensional Nisser Detachment Zone (NDZ) and the Hestkås Thrust Zone (HTZ). The overall goal is to unravel the tectonic evolution of the Nissedal–Drangedal area in Telemark.
This study combines field mapping, remote sensing, structural analysis, geochronology, and petrography with titanite petrochronology. Selected titanite grains were characterized and analysed by optical microscopy, Backscatter Electron microscopy (BSE), Electron Probe Micro Analyzer (EPMA), Electron Backscatter Diffraction microscopy (EBSD) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The analyses suggest multiple generations of titanite associated with Sveconorwegian orogenic events. These analyses are compared with 40Ar–39Ar ages in hornblende, biotite, and feldspar from the same area.
Overall, the field area comprises three tectonostratigraphic units, from bottom to top: 1) The Vråvatn complex composed of amphibolite- to granulite-facies granitic gneiss. 2) The Nisser Detachment zone (NDZ), a >100 m wide, crustal-scale, top-to-the SE mylonitic to cataclastic shear zone that juxtaposes the underlying Vråvatn complex against the overlying 3) Nissedal complex. Which comprises c. 1200 Ma sub-volcanic felsic and mafic rocks, intruded by medium- to coarse-grained gabbro, granitic dykes, and porphyritic granite, shortly after 1200 Ma. The porphyritic granite is, in places, strongly deformed by the top-to-the NW amphibolite facies compressional HTZ, which was active around 1080 Ma, demonstrated by recrystallized titanite rims. The northern part of the Nissedal complex experienced non-penetrative lower amphibolite facies metamorphism at c. 1000 Ma, as documented by recrystallized titanite rims and cores from all analysed rocks at 1016–990 Ma. The rocks from the Vråvatn complex were emplaced and metamorphosed at about the same time as in the Nissedal complex, but they experienced high-grade amphibolite facies metamorphism.
The study shows that the Nissedal and Vråvatn complexes have separate cooling histories until c. 900 Ma, wherein the Vråvatn complex remained at higher metamorphic conditions than the Nissedal complex. The two complexes where juxtaposed as the Vråvatn complex was rapidly exhumed in the footwall of the shallow-dipping, top-to-the SE amphibolite- to sub-greenschist facies extensional NDZ between 945 and 900 Ma. After 900 Ma, the cooling histories of the two complexes coincides, at temperatures <325°C and some cataclastic deformation along the NDZ until c. 860, demonstrated by recrystallized titanite rims in cataclastic rocks overprinting mylonitic foliation.
Within the field area, five events are recognized as being related to the Sveconorwegian orogeny: (A) 1220–1145 Ma; formation of both gneiss- and supracrustal complexes in Telemarkia Lithotectonic Unit (LU). (B) 1110–1088 Ma; SW–NE compression (including the HTZ) leading to crustal thickening at the start of the main orogenic period. (C) 1016–990 Ma; high-grade metamorphism in gneiss complexes and low-grade metamorphism of supracrustal complexes in Telemarkia LU. (D) 960–940 Ma; emplacement of widespread HBG-granites in Telemarkia LU. (E) 945–860 Ma; SE–NW extension (including the NDZ), related to crustal thinning, resulting in rapid exhumation of amphibolite- to granulite facies gneiss complexes
This study shows that titanite petrochronology may be applied to unravel the temporal and deformational evolution of shear zones. It requires, however, careful in-situ thin section analysis to have a better control on the internal zoning patterns and the spatial associations of the titanites, and through structural and microstructural analyses to identify mineral assemblage, cross cutting relations, shear deformation, and possible recrystallization, to understand what the obtained ages represent. The combined analyses have help to unravel the tectonic evolution of the Nissedal–Drangedal area and shed new light on the late Sveconorwegian evolution in Telemarkia LU.
Further work focused on other contacts between supracrustal and gneiss complexes in the Sveconorwegian orogen is necessary to test the model of orogen-scale extension and exhumation of gneiss complexes.
Key words: Sveconorwegian orogeny, titanite U-Pb petrochronology, LA-ICP-MS, EPMA, compressional and extensional shear zones.
ii
Kan titanitt petrokronologi bli brukt til å fastslå tidsspennet for deformasjon langs stor-skala skjærsoner? Denne studien vil undersøke dette spørsmålet gjennom geologisk kartlegging av et strukturelt komplekst område i det Svekonorvegiske orogenet i Sør-Norge, ved å linke strukturanalyse, vekst av temperatursensitive mineraler og re-krystallisering av bergartsdannende mineraler, sammen med U-Pb petrokronologi av titanitt, i to stor-skala skjærsoner; Nisser ekstensjonssone (NDZ) og Hestkås kompresjonssone (HTZ). Det overordnede målet er å forstå den tektoniske utviklingen i Nissedal–Drangedal området i Telemark.
Denne studien kombinerer felt kartlegging, fjernmåling, strukturanalyse, geokronologi og petrologi med titanitt petrokronologi. Utvalgte titanitt korn var karakterisert og analysert med optisk mikroskopering, tilbakesprednings Elektronmikroskopering (BSE), Elektronmikrosonde (EPMA), Elektron Tilbakesprednings Diffraksjon (EBSD) and Laser Ablasjon Induktivt koblet plasma Massespektrometri (LA-ICP-MS). Analysene foreslår at det er flere generasjoner av titanitt assosiert med hendelser knyttet til det Svekonorvegiske orogenet.
Disse analysene er sammenlignet med 40Ar–39Ar aldre i hornblende, biotitt og feltspat fra samme område.
Overordnet består feltområdet av tre tektonostratigrafiske enheter, fra bunn til topp: 1) Vråvatn komplekset som består av amfibolitt- til granulitt facies granittiske gneiser. 2) Nisser ekstensjons skjærsonen (NDZ), en >100 m bred, stor-skala, top-mot sørøst mylonittisk til kataklastisk skjærsone som sidestiller det underliggende Vråvatn komplekset mot det overliggende 3) Nissedal komplekset. Som består av ca. 1200 Ma sub-vulkanske felsiske og mafiske bergarter, som er intrudert av grov- til middelskornet gabbro, granittiske gangbergarter og porfyrisk granittiske gneiser, kort tid etter 1200 Ma. Den porfyriske granitten er stedvis sterkt deformert av den top-mot nordvestlige, amfibolitt facies, kompresjons skjærsonen HTZ, som var aktiv rundt 1088 Ma, demonstrert av re-krystalliserte titanitt rander. Nordlige deler av Nissedal-komplekset opplevde en ikke-penetrerende lav amfibolitt facies metamorfose rundt ca. 1000 Ma, dokumentert av re-krystalliserte titanitt rander og kjerner fra alle analyserte korn som gir aldre i tidsspennet 1016–990 Ma. Bergartene fra Vråvatn komplekset var plassert og metamorfosert omtrent samtidig som i Nissedal komplekset, men opplevde høy-grads amfibolitt facies metamorfose.
Denne studien viser at Nissedal- og Vråvatn kompleksene hadde separate avkjølingshistorier frem til ca. 900 Ma;
hvor Vråvatn-komplekset var under høyere metamorfe forhold enn det Nissedal-komplekset. De to kompleksene ble sidestilt da Vråvatn-komplekset ble raskt avkjølt i ligg-blokken av den slakt fallende, top-mot sørøstlige amfibolitt til grønnskifer facies ekstensjons skjærsonen NDZ mellom 945 og 900 Ma. Etter 900 Ma var avkjølingshistorien til de to kompleksene like, ved temperaturer <325°C og det var noe kataklastisk deformasjon langs NDZ frem til ca. 860 Ma, demonstrert av re-krystallisert titanitt rander i kataklasitter som overprinter mylonittisk foliasjon.
I feltområdet er det gjenkjent fem hendelser som er relatert til den Svekonorvegiske fjellkjedeformingen: (A) 1220–1145 Ma, dannelsen av både gneis- og vulkanske komplekser i Telemarkia litotektoniske enhet (LU). (B) 1110–1088 Ma, sørvest–nordøst-kompresjon (inkludert HTZ) som førte til fortykning av jordskorpen i starten av fjellkjedens hovedperiode. (C) 1016–990 Ma, høygrads metamorfose i gneiskompleksene og lavgrads metamorfose i de vulkanske kompleksene i Telemarkia LU. (D) 960–940 Ma, dannelse av HBG-granitter spredt i Telemarkia LU. (E) 945–873 Ma, sørøst–nordvest-ekstensjon (inkludert NDZ), relatert til skorpetynning og resultering i rask ekshumering av amfibolitt- til granulitt facies gneis komplekser.
Denne studien viser at titanitt petrokronologi kan bli brukt til å forstå tids- og deformasjonshistorien til skjær soner. Men det trengs nøye in-situ tynnslips analyser, for å ha bedre kontroll på interne soneringsmønstre og romlige assosiasjoner for titanittene, og grundige strukturelle og mikro-strukturelle analyser for å identifisere mineralselskap, kryssende forhold, skjærdeformasjon og mulig re-krystallisering, for å forstå hva den oppnådde alderen representerer. Kombinasjonen av alle analysene har hjulpet til å avdekke den tektoniske utviklingen i Nissedal–Drangedal området og kastet nytt lys over den sene Svekonorvegiske utviklingen i Telemarkia LU.
Videre arbeid fokusert på andre kontakter mellom vulkanske- og gneis-komplekser i det Svekonorvegiske orogenet er nødvendig for å teste modellen av fjellkjede-skala ekstensjon og ekshumering av gneis komplekser.
Nøkkelord: Svekonorvegisk fjellkjedefolding, titanitt U-Pb petrokronologi, LA-ICP-MS, EPMA, kompresjons og ekstensjons skjærsoner
iii
Acknowledgments
This thesis is the final work in a series of 3, including a specialization project on the Sveconorwegian orogeny and a course of learning to characterize titanite. The projects have been founded by NTNU and NGU and has together stretched over 2 years (2019–2021), including three weeks of field work together with the BITE-team. During this work I have done and learned a great deal, all thanks to a lot of skilled people, to whom I would like to give my thanks.
Firstly, I want to thank my supervisor Espen Torgersen for giving me the opportunity to work on such an inspiring project. He has supervised both specializing projects and master thesis, which have included field work, several rounds in the lab, and many hours of discussions with valuable explanations and clarifications. In addition to all the great supervision on geology, I want to thank for all the valuable tips, comments, and corrections regarding scientific writing, I have improved a lot on my writing skills and increased the joy of writing. I would also like to use this opportunity to thank for the really good course “Advanced Structural Geology”, which is a great course.
Furthermore, I want to thank Bernard Bingen for thorough explanations and clarifications concerning concepts and theories of the Sveconorwegian orogen, showing the preparation method for titanite whole-crystal analysis, and for helping with writing corrections and comments in the thesis.
I would like to thank the whole BITE-team for making the field work an instructive, enjoyable, and inspiring experience. A special thanks to Iain Henderson for assisting in the field, it is amazing how much there is to see when he is accompanying in the field. And I want to thank Vebjørn Røvde for valuable discussions and company when preparing and sawing the samples.
Thanks to Trond Slagstad and Anette Granseth for explaining the accretion/subduction models of the Sveconorwegian orogeny.
Thanks to everyone at the thin section preparation lab and EM lab at NTNU, especially thanks to Kjetil Eriksen and Håkon Fjærli for efficiently making and preparing the thin sections prior to all analyses, to Kristian Drivenes for supervising and helping on the EPMA, and Bjørn Eske Sørensen for guiding through the work on the EBSD and finalizing the EBSD-data. Also, thanks to the lab-staff at NGU for doing the chemical and petrophysical analyses.
A large thanks to Graham Peter-Hagen ang Yue Wang for helping and explaining the use of the La-ICP-MS at NGU, thanks for being curious and wanting to try something new. Especially thanks to Graham for processing the data, I appreciate that he always took the time to thoroughly explain the process and including me in every step.
Also, a large thanks to Morgan Granerød for preparing and doing the Ar-Ar analysis, and making the Ar-Ar age spectra, and to Vebjørn Røvde who helped preparing for analysis, but could not include the data in his thesis because of delays in the analysis.
Finally, I would like to thank my fellow students and teachers for teaching me so much prior to the thesis and for making the time at NTNU such a great and memorable time. I also want to give a special thanks to Eric Thörn for making the time during writing of the thesis a good time, even thru lockdowns and home-office.
Vanja Skålnes Haugsnes Trondheim, June 2021
iv
Abstract ... i
Sammendrag ...ii
Acknowledgments ... iii
Table of Contents ... iv
List of Figures ... vi
List of Tables ... xii
Abbreviations ... xiii
1 Introduction ... 1
2 Methods ... 3
2.1 Analysis of published work ... 3
2.2 Digital field mapping... 3
2.3 Sample preparation and bulk rock analysis ... 4
2.4 Optical microscopy ... 4
2.5 Electron Backscatter Diffraction (EBSD) ... 4
2.6 Electron Probe Micro-Analyzer (EPMA) ... 5
2.7 Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) ... 6
2.8
40Ar-
39Ar analysis ... 9
3 Regional geology ... 11
3.1 Sveconorwegian orogen ... 12
3.2 Sveconorwegian orogenic evolution ... 14
3.2.1 Pre-orogenic evolution, c. 1280–1080 Ma ... 14
3.2.2 The main orogenic phase, c. 1065–990 Ma... 15
3.2.3 Late Sveconorwegian evolution, c. 990–860 Ma ... 15
3.3 Geological framework of study area ... 17
4 Results: Bedrock mapping and structural analysis ... 19
4.1 Field area ... 20
4.2 Lithological descriptions ... 27
4.2.1 Nissedal complex ... 27
4.2.1.1 Metarhyolite ... 27
4.2.1.2 Sub-volcanic felsic dykes ... 30
4.2.1.3 Amphibolite ... 32
4.2.1.4 Metagabbro ... 34
4.2.1.5 Hestkås augen gneiss ... 38
v
4.2.2 Vråvatn complex ... 41
4.2.2.1 Vråvatn granitic gneiss ... 41
4.3 Structural geology ... 44
4.3.1 Hestkås thrust zone (HTZ) ... 47
4.3.2 Nisser Detachment Zone (NDZ) ... 54
5 Results: Titanite analysis ... 69
5.1 Titanite characterization ... 70
5.1.1 Protomylonitic Vråvatn gneiss (BITE_308) ... 70
5.1.2 Nisser mylonite (BITE_722) ... 74
5.1.3 Nisser cataclasite (BTE_760)... 76
5.1.4 Hestkås augen gneiss (BITE743) ... 78
5.2 Titanite U-Pb analysis ... 82
5.2.1 Proto-mylonitic Vråvatn gneiss (BITE_308) ... 82
5.2.2 Nisser cataclasite (BITE_760)... 86
5.2.3 Hestkås augen gneiss (BITE_743) ... 88
6 Results:
40Ar/
39Ar data ... 91
7 Discussion ... 99
7.1 Geological evolution of the field area ... 100
7.1.1 1220–1145 Ma; Formation of the Nissedal and Vråvatn complexes ... 100
7.1.2 1088 Ma; Hestkås Thrust zone (HTZ) ... 102
7.1.3 1016–990 Ma; Regional metamorphism ... 103
7.1.4 945–860 Ma; Nisser Detachment zone (NDZ) ... 103
7.2 The field area in a Sveconorwegian perspective ... 105
A. 1220–1145 Ma; formation of gneiss- and supracrustal complexes in Telemarkia LU. ... 106
B. 1110–1088 Ma; SE–NW Compression ... 106
C. 1016–990 Ma; metamorphism in Telemarkia LU ... 107
D. 960–940 Ma; emplacement of HBG-granites ... 107
E. 945–860 Ma; SE–NW Extension ... 110
7.3 The use of in-situ titanite in petrochronological analysis of shear zones ... 111
8 Conclusions ... 112
9 Recommendations for further work ... 113
10 References ... 114
Appendices ... 118
Appendix A–EPMA results ... 118
Appendix B–
40Ar/
39Ar data ... 128
vi
FIGURE 2.1:ILLUSTRATION OF DOWNHOLE FRACTIONATION CORRECTION. A)THE RAW DATA BEFORE COMMON PB CORRECTION, AND B) THE COMMON PB CORRECTED DATA. ... 7 FIGURE 2.2:AN EXAMPLE DATASET PLOTTED IN AN INVERSE TERA-WASSERBURG DIAGRAM, WITH NOMENCLATURE USED IN THIS REPORT. ... 8 FIGURE 3.1:SKETCH MAP OF THE SVECONORWEGIAN OROGEN, WITH NOMENCLATURE OF LITHOTECTONIC UNITS (LU) AND THE MAIN
FAULT- AND SHEAR ZONES.COORDINATES GIVEN HERE IN LAT/LON.MAP RECREATED AFTER HAUGSNES (2019)&BINGEN ET AL. (2020).BLACK SQUARE SHOWS AREA OF 40AR/39AR DATA PRESENTED IN THIS STUDY, RED SQUARE SHOWS THE MAIN STUDY AREA... 12 FIGURE 3.2: ILLUSTRATION EXPLAINING THE TWO MAIN THEORIES REGARDING THE SVECONORWEGIAN OROGENIC EVOLUTION. ILLUSTRATIONS ARE COPIED FROM SLAGSTAD ET AL.(2020)(SUBDUCTION THEORY) AND BINGEN ET AL.(2020)(COLLISIONAL THEORY). ... 16 FIGURE 3.3: TELEMARKIA LU WITH TRANSPORT DIRECTION OF THE LARGE FAULT- OR SHEAR ZONES, INCLUDING THE NISSER
DETACHMENT ZONE (NDZ) AND THE HESTKÅS THRUST ZONE (HTZ).NOMENCLATURE FOR LITHOLOGIES IN ASSOCIATION WITH THE FIELD AREA IS ALSO PRESENTED.FIELD AREA MARKED WITH RED SQUARE.BLACK SQUARE MARKS AREA FOR 40AR/39AR ANALYSIS. ... 18 FIGURE 4.1:LITHOLOGICAL OBSERVATIONS FROM FIELDWORK, PRESENTED WITH FIELD NAMES. THE BLACK SQUARE MARKS THE FIELD
AREA... 21 FIGURE 4.2:GEOPHYSICAL MAPS FROM STAMPOLIDIS AND OFSTAD (2014) USED DURING FIELD WORK AND WHEN MAKING THE
FINALIZED MAP.THE FIELD AREA IS MARKED WITH BLACK SQUARE. A)RADIOMETRIC TERNARY GROUND CONCENTRATION MAP (TH,U,K), B) TOTAL MAGNETIC ANOMALY MAP (NT=TOTAL FIELD ANOMALY). ... 21 FIGURE 4.3:SAMPLE MAP, WITH ASSOCIATED SAMPLE NUMBER, SHOWING ALL SAMPLES COLLECTED DURING FIELD WORK, IN ADDITION
TO ONE SAMPLE COLLECTED BY IAIN HENDERSON (BITE_308). ... 22 FIGURE 4.4: PETROPHYSICAL DATA FROM ALL SAMPLES, SHOWING A LARGE VARIATION IN DENSITY AND MAGNETIC PROPERTIES
THROUGHOUT THE FIELD AREA.THE MYLONITIC SAMPLES SEEMS TO HAVE A SLIGHTLY HIGHER MAGNETIC COMPOSITION COMPARED TO THE UNDEFORMED SAMPLES... 24 FIGURE 4.5:MAJOR ELEMENT COMPOSITION OF ALL DATA, SHOWING A GREAT VARIATION BETWEEN MAFIC AND FELSIC ROCKS.THE
FELSIC CATACLASITE SAMPLES HAVE LESS SIO2 CONTENT COMPARED TO THE UNDEFORMED FELSIC SAMPLES. ... 24 FIGURE 4.6:CHONDRITE NORMALIZED REE SPIDER DIAGRAM OF ALL SAMPLES.FELSIC AND MAFIC SAMPLES HAVE A NEGATIVE AND
POSITIVE EU-ANOMALY, RESPECTIVELY. THERE IS NO SYSTEMATIC CHANGE IN REE COMPOSITION CORRELATED WITH DEFORMATION.ALL MAFIC SAMPLES ARE RELATIVELY SIMILAR IN REE CONTENT.THE FELSIC SAMPLES ALL HAVE A CLEAR NEGATIVE EU-ANOMALY BUT VARY GREATLY IN REE CONCENTRATION.THE UNDEFORMED VRÅVATN GNEISS SAMPLES HAVE A LOW REE CONCENTRATION, WHICH IS MUCH HIGHER IN THE MYLONITIC AND CATACLASTIC SAMPLES OF THE VRÅVATN GNEISSES.THE FELSIC ROCKS FROM THE NISSEDAL COMPLEX HAVE A RELATIVELY HIGH CONCENTRATION IN REE, WITH NO OBVIOUS DIFFERENCE BETWEEN DEFORMED AND UNDEFORMED ROCKS. ... 25 FIGURE 4.7:FINALIZED BEDROCK MAP OF FIELD AREA, WITH INTERPRETED LITHOLOGICAL BORDERS, BASED ON FIELD OBSERVATIONS AND
GEOPHYSICAL MAPS.WITH A SELECTION OF STRUCTURAL MEASUREMENTS AND TOPOGRAPHIC LINEAMENTS.RED LINE,A-A’, CORRELATES WITH CROSS SECTION IN FIGURE 4.8. ... 26 FIGURE 4.8:CROSS SECTION,A-A’ CORRELATES WITH MARKINGS IN THE BEDROCK MAP (FIG.5.7), SHOWING A SHALLOWLY SE DIPPING
STRUCTURAL GRAIN, DOMINATED BY THE TWO LARGE SHEAR ZONES, THE NDZ AND HTZ, DIVIDING THE FIELD AREA.THE FOOTWALL OF THE HTZ IS SLIGHTLY MORE DEFORMED COMPARED TO THE HANGING WALL. ... 26 FIGURE 4.9:DIFFERENT OCCURRENCES OF METARHYOLITE, A)BITE_713; MASSIVE WITH LITTLE TO NO BANDING OR FOLIATION, B) BITE_705; BANDED WITH AREAS OF COARSE GRAINS, C)BITE_720; EXTREMELY BANDED, BUT NO DYNAMIC RECRYSTALLIZATION. ... 28 FIGURE 4.10: A) METARHYOLITE WITH COLOURS VARYING FROM LIGHT GREY, GREEN AND DARKER GREY, B) ALTERNATING BANDS OF FINE
AND COARSE-GRAINED METARHYOLITE, C) FIELD PHOTO OF CONTACT BETWEEN METARHYOLITE AND AMPHIBOLITE, SHOWING IRREGULAR BUT RELATIVELY SHARP BORDER, D) LAMINATED ROCK WITH ALTERNATING MAFIC AND FELSIC COMPOSITION. ... 28
vii FIGURE 4.11: A)THIN SECTION SCAN OF BANDED METARHYOLITE (BITE_720), CROSS POLARIZED LIGHT, SHOWING FELSIC/MAFIC SEGREGATION AND NO SIGNIFICANT DYNAMIC RECRYSTALLIZATION, B) PHOTOMICROGRAPH OF METARHYOLITE (BITE_713) WITH GENERAL COMPOSITION. ... 29 FIGURE 4.12: A) HAND SPECIMEN OF MEDIUM-GRAINED FELSIC ROCK (BITE_709) B) XENOLITHS OF MEDIUM GRAINE METAGABBRO
WITHIN MEDIUM GRAINED FELSIC ROCK, C) CONTACT BETWEEN MEDIUM-GRAINED FELSIC ROCK AND COARSE-GRAINED METAGABBRO, SHOWING SMALL XENOLITHS OF METAGABBRO IN THE FELSIC DYKE, INDICATING THAT THE FELSIC ROCK INTRUDED INTO THE METAGABBRO. ... 30 FIGURE 4.13: A) FELSIC DYKE INTRUDED INTO METAGABBRO, WITH LATER FOLDING OF BOTH LITHOLOGIES, FOLDS HAVE SE-DIPPING AXIAL
PLANES, B) COARSE-GRAINED SUB-VOLCANIC DYKES INTRUDING A FINE-GRAINED AMPHIBOLITE, C) FELSIC DYKE INTRUDED INTO METAGABBRO, WITH SHOOTING VEINS IN SEVERAL DIRECTIONS. ... 31 FIGURE 4.14: A) FIELD PHOTO OF UNDEFORMED AMPHIBOLITE, WITH CHARACTERISTIC SALT/PEPPER TEXTURE, B) SHARP CONTACT
BETWEEN FINE-GRAINED AMPHIBOLITE AND COARSE-GRAINED METAGABBRO. ... 32 FIGURE 4.15:SAMPLE BITE_745, A FOLIATED AMPHIBOLITE ASSOCIATED WITH THE HTZ, A)HAND SPECIMEN SHOWING GENERAL
TEXTURE, B) THIN SECTION SCAN (PLAN POLARIZED LIGHT) SHOWING GENERAL TEXTURE, C) PHOTOMICROGRAPH SHOWING GENERAL COMPOSITION WITH SMALL, ELONGATED AMPHIBOLE AND ROUNDED CLINOPYROXENE, D) PHOTOMICROGRAPH SHOWING TWO TYPES OF AMPHIBOLE, YELLOW-BROWN IS HORNBLENDE WITH SHARP EDGES AND CLEAVAGES, GREEN IS ACTINOLITE WITH DIFFUSE EDGES AND NO CLEAVAGES. ... 33 FIGURE 4.16: A) METAGABBRO WITH SUB-OPHITIC TEXTURE, B) METAGABBRO INTRUDING AMPHIBOLITE, C) VEINS OF INTRUDING
METAGABBRO IN A RHYOLITE, D) INTRUDING METAGABBRO IN A METARHYOLITE SEQUENCE, WITH A XENOLITH OF METARHYOLITE IN THE METAGABBRO. ... 35 FIGURE 4.17: A) XENOLITHS OF METARHYOLITE IN METAGABBRO, B) METAGABBRO INTRUDED BY A COARSE-GRAINED FELSIC ROCK. . 36 FIGURE 4.18: A)THIN SECTION SCANS OF METAGABBRO WITH OPHITIC- TO SUB-OPHITIC TEXTURE (BITE_753), PLANE POLARIZED AND
B) CROSS POLARIZED LIGHT, C) PHOTOMICROGRAPH OF GENERAL TEXTURES OF BITE_753, NORTH OF THE HTZ, AND D) BITE_712,SOUTH OF THE HTZ, E,F) PHOTOMICROGRAPHS OF BITE_712, PYROXENE WITH SECONDARY AMPHIBOLE RIMS. .. 37 FIGURE 4.19:BITE_743, SHOWING GENERAL TEXTURE OF HESTKÅS AUGEN GNEISS. ... 38 FIGURE 4.20: A) FIELD PHOTO OF RELATIVELY UNDEFORMED AUGEN GNEISS, SHOWING PORPHYRITIC TEXTURE, B) AUGEN GNEISS BORDER
TO MEDIUM-GRAINED METAGABBRO, WITH AUGEN WITHIN THE METAGABBRO UNIT, INDICATING INTRUSION OF METAGABBRO INTO THE AUGEN GNEISS, C) MAFIC INTRUSION INTO AUGEN GNEISS, D) BANDS OF ALTERNATING AUGEN GNEISS AND FINE-GRAINED MAFIC ROCK, E) FLOW TEXTURE OF AUGEN GNEISS AROUND METAGABBRO, INDICATING THAT AUGEN GNEISS INTRUDED THE METAGABBRO. ... 39 FIGURE 4.21: A) PHOTOMICROGRAPH OF AUGEN GNEISS (BIT_743), B) THIN SECTION SCAN OF MYLONITIC AUGEN GNEISS (BITE_743), SHOWING HETEROGENEOUS STRAIN DISTRIBUTION WITH LOWER STRAIN IN THE UPPER PART, ORANGE SQUARE INDICATE POSITION OF PHOTOMICROGRAPH C, C) PHOTOMICROGRAPH OF FELDSPAR PORPHYROCLAST WITH SAUSSURITIC ALTERATION, D) AMPHIBOLE ELONGATED MOSTLY PARALLEL TO THE FOLIATION (RED LINE) AS IT BENDS AROUND A PORPHYROCLAST. ... 40 FIGURE 4.22:VRÅVATN GRANITIC GNEISS (BITE_754), SHOWING GENERAL TEXTURE. ... 41 FIGURE 4.23: A)VRÅVATN GRANITIC GNEISS TEXTURE, B) THE VRÅVATN GNEISS IS ABUNDANT AND HARD, STANDING OUT IN THE FIELD. ... 42 FIGURE 4.24: A)THIN SECTION SCAN (XPL) OF PROTO-MYLONITIC VRÅVATN GRANITE (BITE_754), ORANGE SQUARE MARKS ZOOMED
IN PHOTOMICROGRAPH, B) PHOTOMICROGRAPH OF PROTO-MYLONITIC VRÅVATN GRANITIC GNEISS (BITE_754), SHOWING GENERAL MINERAL ASSEMBLAGE, C) SECONDARY AMPHIBOLE WITH FRACTURES ALONG CLEAVAGE PLANES (MARKED WITH WHITE DOTTED LINES) IN HIGH ANGLE TO THE FOLIATION (MARKED WITH RED LINES).MATRIX MINERALS ARE CAPTURED BY THE AMPHIBOLE ALONG THE CLEAVAGES IN A POIKILOCLASTIC TEXTURE. ADJACENT FELDSPAR GRAINS HAVE UNDULOSE EXTINCTION AND DEFORMATION TWINNING. ... 43 FIGURE 4.25:STRUCTURAL MEASUREMENTS WITHIN THE FIELD AREA.ALL STRUCTURAL MEASUREMENTS ARE DIRECTLY TRANSFERRED FROM DIGITAL FIELD WORK. ... 45 FIGURE 4.26:STEREONET SHOWING A) FOLIATION IN VOLCANIC AND METAGABBRO SEQUENCES (GREY = PRIMARY FOLIATION, PURPLE = TECTONIC FOLIATION, PURPLE DOTS = MINERAL LINEATIONS), B) FOLIATION ASSOCIATED WITH HTZ(YELLOW DOTS = CRENULATION LINEATIONS, PURPLE DOTS = MINERAL LINEATIONS), C) TECTONIC FOLIATION AND LINEATIONS ASSOCIATED WITH NDZ, D) FOLIATION IN VRÅVATN COMPLEX (BLUE = GNEISSIC BANDING, RED = TECTONIC FOLIATION), E) BRITTLE FRACTURE PLANES WITHIN
viii
ALL LITHOLOGIES (GREY =NDZ, ORANGE =HTZ), F) FOLD AXIAL PLANES AND FOLD AXIS OF ALL LITHOLOGIES (PURPLE =NISSEDAL COMPLEX, ORANGE =HTZ, GREEN =NDZ, PINK =VRÅVATN COMPLEX). ... 46 FIGURE 4.27:SIMPLIFIED MAP SHOWING POSITION OF HESTKÅS AUGEN GNEISS AND HTZ IN NISSEDAL COMPLEX.ORANGE SQUARE
COVERS HESTKÅS AUGEN GNEISS IN FIELD AREA (FIG.5.28). ... 47 FIGURE 4.28:APPROXIMATE PATH OF HIGH STRAIN ZONE IN THE HTZ(BLACK LINE).KEY LOCATIONS ARE MARKED WITH YELLOW DOTS
AND LOCATION NUMBER, MEASUREMENTS OF FOLIATION (RED), MINERAL LINEATIONS (PURPLE), AND CRENULATION LINEATIONS (ORANGE) ARE SEEN IN THE STEREONET AND IN THE MAP SHOWING LOCATION OF MEASUREMENTS.A-A’ INDICATES DIRECTION OF CROSS SECTION SHOWN IN FIGURE 29. ... 48 FIGURE 4.29:THE TECTONIC FOLIATION ASSOCIATED WITH HTZ HAS TWO MAIN FOLIATION DIPPING DIRECTIONS, INTERPRETED AS
LARGE-SCALE OPEN FOLDS, A) ILLUSTRATIONAL CROSS SECTION CUT PARALLEL TO THE STRIKE OF THE HTZ, SHOWING SEVERAL LARGE-SCALE FOLDS WITH FOLD AXIS (BLUE LINE) AND MINERAL LINEATIONS (PURPLE LINE) PLUNGING SUB-PARALLEL TO MAIN SHEARING DIRECTION OF HTZ, B) STEREONET SHOWING TWO MAIN FOLIATION DIPPING DIRECTIONS (INDICATED BY GREEN AND ORANGE LARGE CIRCLES AND POLES TO PLANES), INTERPRETED AS LARGE-SCALE OPEN FOLDS WITH FOLD AXIS EQUAL TO THE Β-AXIS: 30–>155. ... 48 FIGURE 4.30: A) PROTO-MYLONITIC AUGEN GNEISS WITH FOLIATION (RED LINES) AND K-FELDSPAR PORPHYROCLASTS, B) MINERAL
LINEATIONS (PURPLE LINES) ON A FOLIATION SURFACE, C) MYLONITIC AUGEN GNEISS, WITH FOLIATION AND SOME CLASTS, D) ULTRA-MYLONITIC MAFIC ROCK ASSOCIATED WITH THE HTZ, WITH HIGHLY DEVELOPED FOLIATION AND ONLY MICRO- PORPHYROCLASTS, AND SEGREGATION OF FELSIC AND MAFIC MINERALS. ... 49 FIGURE 4.31:PHOTOMICROGRAPHS OF SAMPLE BITE_743, SHOWING A)SGR OF QUARTZ, WITH EPIDOTE AND AMPHIBOLE IN MATRIX, B)BLG OF FELDSPAR PORPHYROCLASTS WITH SERICITIC INCLUSIONS, C,D)SPO OF MATRIX MINERALS, WITH SGR OF QUARTZ RIBBON. ... 50 FIGURE 4.32:LOCALITY CLOSE TO ROVTJØRNBØTAN (VAH_400), A)OUTCROP WITH ALTERNATING LAYERS OF AUGEN GNEISS AND
MELANOCRATIC FINE-GRAINED AMPHIBOLE-RICH ROCK, AND STEREONET OF FOLIATIONS AND CRENULATION LINEATION, INDICATING A SHEAR MOVEMENT AXIS IN SE–NW DIRECTION, B) ZOOMED IN ON ORANGE BOX IN FIG. A, SHOWING CRENULATION LINEATIONS PERPENDICULAR TO DIP DIRECTION OF FOLIATION PLANE, AND CRENULATION FOLDS IN DARK FOLIATED LAYER. ... 52 FIGURE 4.33:LOCALITY ØSTJORDDALEN, CLOSE TO SNØÅS (VAH_25), INCLUDES A) ASYMMETRIC FOLD WITH GENTLY SE DIPPING AXIAL
PLANE IN ASSOCIATION WITH THE HESTKÅS THRUST, B) ORIENTED SAMPLE (BITE_704)(114/24,22–>125), WITH AUGEN GNEISS INTERTWINED AND FOLIATED TOGETHER WITH A MAFIC FINE-GRAINED ROCK, ORANGE SQUARE INDICATES POSITION OF PHOTOMICROGRAPH, C) PHOTOMICROGRAPH OF SIGMA CLAST INDICATING SINISTRAL KINEMATIC, CONSISTENT WITH TOP-TO-THE NE MOVEMENT. ... 52 FIGURE 4.34:LOCALITY VAH_792; A) ISOCLINAL OVERTURNED FOLD, WITH SE DIPPING AXIAL PLANE (YELLOW), UPPER LIMB (GREEN), LOWER LIMB (PINK), FOLD AXIS (BLUE DOT), B)3D VIEW OF FOLD HINGE WITH FOLD AXIS MARKED WITH BLUE LINE, AND STEREONET OF FOLD GEOMETRY. ... 53 FIGURE 4.35: LOCALITY KVERNHUSHAUGEN (VAH_371); A) THIN SECTION OF ORIENTED SAMPLE (BITE_743) WITH FOLIATION
134/40 AND LINEATION 37–>130, B)PHOTOMICROGRAPH OF ORANGE BOX, DELTA- AND SIGMA CLASTS INDICATING SINISTRAL MOVEMENT, CONSISTENT WITH A TOP TO THE NW THRUST MOVEMENT. ... 53 FIGURE 4.36: MAP OF NDZ, WITH FOLIATION (RED) AND MINERAL LINEATION (PURPLE) MEASUREMENTS, IN ADDITION TO KEY
LOCALITIES (YELLOW) AND SAMPLES (ORANGE), AND STEREONET OF ALL MEASUREMENTS. ... 54 FIGURE 4.37:A SIMPLIFIED ILLUSTRATION OF A CROSS SECTION, APPROXIMATELY FOLLOWING THE INTERSECTION A-A’ IN THE MAP IN FIGURE 5.36, SHOWING THE COMPLEXITY OF THE NDZ.WITH VRÅVATN GNEISSES IN THE FOOTWALL AND VARIATING ROCKS FROM THE NISSEDAL COMPLEX IN THE HANGING WALL, WITH INCREASING STRAIN TOWARDS THE MIDDLE.CATACLASTIC DEFORMATION AND FAULTING OVERPRINT THE MYLONITIC FOLIATION. REPRESENTATIVE SAMPLES FROM EACH LITHOLOGY ARE LISTED UNDERNEATH THE RESPECTIVE LITHOLOGY IN THE CROSS SECTION. ... 55 FIGURE 4.38: A,B)L-S TECTONIC TEXTURE WITH FOLIATION (RED LINES) AND MINERAL LINEATIONS (PURPLE LINE), C)LOCALITY
VAH_840 ALONG FJÅGESUNDVEGEN, SHOWING A CORRELATION BETWEEN STRAIN AND CHLORITE ALTERATION BECAUSE OF WATER INFILTRATION, WITH A SHARP AND LOCALIZED TRANSITION FROM 1. GNEISS WITH ONLY LITTLE STRAIN AND ORIGINAL FELDSPAR CRYSTALS,2. SOME STRAIN AND BOTH FELDSPAR AND SECONDARY CHLORITE, TO 3. HIGH STRAIN ZONE WITH ALMOST ONLY CHLORITE, THIS INDICATES RAPID STRAIN TRANSITION, D) ORIGINAL FELDSPAR BEING CHLORITIZED... 56
ix FIGURE 4.39: A) PROTO-MYLONITIC METARHYOLITE (BITE_759), WITH MINERAL ASSEMBLAGE, B,C) MYLONITIC AMPHIBOLITE (BITE_724),(B – XPL) CHLORITE OVERPRINTING AMPHIBOLE AND EPIDOTE,(C – PPL) WITH FOLIATION AND S-C’ SHEAR BANDS. ... 57 FIGURE 4.40: A) PROTO-MYLONITIC METAGABBRO (BITE_758), PYROXENE CLASTS WITH SECONDARY AMPHIBOLITE RIMS, B) SECONDARY AMPHIBOLE ALIGNED WITH TECTONIC FOLIATION, INDICATING PRE- OR SYN SHEAR DEFORMATIONAL GROWTH. ... 58 FIGURE 4.41: A)PROTO-MYLONITIC VRÅVATN GNEISS (BITE_754), SHOWING TWINNING IN FELDSPAR AND SGR I QUARTZ, B) PSEUDOTACHYLITE BAND IN VRÅVATN PROTOMYLONITE (BITE_308), SUB-PARALLEL TO THE TECTONIC FOLIATION (RED LINE), CUTTING THE OBLIQUE FOLIATION (YELLOW LINE). ... 60 FIGURE 4.42:ULTRAMYLONITE (BITE_721), SHOWING A CLEAR SPO. ... 60 FIGURE 4.43:MINERAL VEINS AND TENSION GASHES INDICATING POST-MYLONITIC BRITTLE DEFORMATION. ... 60 FIGURE 4.44: A)PHYLLONITE TEXTURE, SHOWN IN HAND SPECIMEN AND THIN SECTION SCANN OF BITE_755, B) PHYLLONITE AT
OUTCROP, SHOWING EXTENSIVE FOLIATION AND PENETRATIVE CLEAVAGES, C) EXTENSIVE CHLORITIZATION, OVERPRINTING EPIDOTE, AMPHIBOLE AND TITANITE GRAINS. ... 61 FIGURE 4.45: A) FRACTURED CATACLASITE WITH ANASTOMOSING FOLIATION, B) SLICKENSIDES ON FRACTURE PLANE, C) HAND SPECIMEN OF BITE_741, SHOWING TEXTURE WITH CHLORITE ALTERATION AND FRACTURES, D) PHOTOMICROGRAPH OF HIGHLY FRACTURED CATACLASITE (BITE_741), E) CATACLASITE IN FIELD, SHOWING EXTENSIVE GREENSCHIST FACIES METAMORPHISM, F) PHOTOMICROGRAPH SHOWING EXTENSIVE CHLORITE ALTERATION (BITE_760). ... 62 FIGURE 4.46: A)CATACLASITE WITH RELICT MYLONITIC TEXTURE IN FIELD, B) SCAN OF CATACLASITE (BITE_741) WITH RELICT MYLONITIC
TEXTURE, SOME OF THE BRITTLE FRACTURE PLANES (WHITE LINES) AND RELICT MYLONITIC TEXTURE (YELLOW LINES) ARE MARKED. THERE IS EXTENSIVE EPIDOTE ALTERATION ALONG THE BRITTLE FRACTURES. ... 63 FIGURE 4.47: A,B) MYLONITE FROM NISSEDAL COMPLEX (BITE_722), SHOWING BLG RECRYSTALLIZATION OF FELDSPAR AND SGR TO
SLIGHT GBM RECRYSTALLIZATION OF QUARTZ, C,D) PROTOMYLONITE FROM VRÅVATN COMPLEX (BITE_308; BITE_754), SHOWING UNDULOSE EXTINCTION, DEFORMATIONAL TWINNING AND BLG RECRYSTALLIZATION OF FELDSPAR AND SGR AND GBM OF QUARTZ, E) CATACLASITE WITH SECONDARY CHLORITE GROWTH ALONG FRACTURES (BITE_761), F) BRITTLE DEFORMATION OF FELDSPAR (BITE_761). ... 64 FIGURE 4.48:PROTOMYLONITIC VRÅVATN GRANITIC GNEISS WITH TECTONIC FOLIATION (RED) SUB-PARALLEL TO THE GNEISSIC BANDING
(GREEN), AND HIGH STRAIN ZONES WITH SHEAR BANDS (YELLOW) MAKING AN OBLIQUE FOLIATION, AT DIFFERENT SCALES, INDICATING EXTENSIONAL MOVEMENTS AS A TOP-TO-THE SE DETACHMENT, A,B) LOCALITY VAH_837, C) THIN SECTION FROM SAMPLE BITE_308, ALSO INCLUDING A PSEUDOTACHYLITE (PINK) CROSSCUTTING THE OBLIQUE SHEAR BAND FOLIATION. ... 66 FIGURE 4.49:INCLINED FOLD WITH NW DIPPING AXIAL PLANE AT LOCALITY VAH_846, INDICATING SE VERGENCE, B) STEREONET
SHOWING FOLD GEOMETRY WITH UPPER LIMB (GREEN), LOWER LIMB (PINK), AXIAL PLANE (YELLOW), AND FOLD AXIS (BLUE)... 66 FIGURE 4.50: A)C-S SHEAR BAND IN PROTOMYLONITIC METAGABBRO, AT LOCALITY VAH_842, B) ORIENTED SAMPLE OF PROTO- MYLONITIC METAGABBRO (BITE_758), C) THIN SECTION SCAN OF ORIENTED SAMPLE SHOWING ASYMMETRIC CLASTS AND FOLDS, D) ASYMMETRIC FOLD SHOWING DEXTRAL MOVEMENT, E) DELTA CLASTS, INDICATING TOP-TO-THE SE DETACHMENT MOVEMENT. ... 67 FIGURE 4.51: A)THIN SECTION SCAN OF ULTRAMYLONITIC FELSIC ROCK (BITE_722), WITH MICRO-PORPHYROCLASTS IN FINE-GRAINED
MATRIX, B,C) ASYMMETRIC SIGMA CLASTS WITH SINISTRAL KINEMATICS, D) DELTA CLAST INDICATING SINISTRAL KINEMATICS, INDICATING TOP-TO-THE SE DETACHMENT. ... 68 FIGURE 5.1:THIN SECTION SCAN OF BITE_308, WITH THE POSITION OF THE TITANITE CLUSTERS. ... 70 FIGURE 5.2: BITE_308, A)EBSD IMAGE OF TITANITE-1, SHOWING GROWTH TWINNING (YELLOW) IN THE SUBHEDRAL GRAIN, B) THIN
SECTION IMAGE OF TITANITE-1, SHOWING GROWTH TWINNING, AND CONCENTRIC ZONING, C)EBSD IMAGE OF TITANITE-3, SHOWING DEFORMATIONAL TWINNING, D)BSE IMAGE OF TITANITE-3, WITH PATCHY ZONING PATTERN E) THIN SECTION IMAGE OF TITANITE-3, SHOWING KINK BANDS AND UNDULOSE EXTINCTION. ... 71 FIGURE 5.3:BSE IMAGES OF TITANITE CLUSTERS FROM THE PROTOMYLONITIC VRÅVATN GRANITE (BITE_308), GREEN SPOTS ARE
CLASSIFIED AS CORE-COMPOSITION, RED ARE RIMS, AND RED SPOTS WITH BLACK RIM AROUND MARKS OUTER-RIM POPULATION FOUND WITH U-PB ANALYSIS, A) TITANITE-1; SHOWING ONE SUBHEDRAL GRAIN WITH CONCENTRIC ZONING, CONTAINING TWO CORES SURROUNDED BY RIM AND OUTER-RIM COMPOSITION, CLOSELY ASSOCIATED WITH ZR, B) TITANITE-3; PATCH ZONING WITH CORE AND RIM COMPOSITIONS, C,D) TITANITE-5; BOTH PATCHY AND CONCENTRICALLY ZONED WITH CORE AND RIM COMPOSITIONS. ... 72
x
FIGURE 5.4:EPMA DATA FOR TITANITE IN BITE_308, SHOWING A DISTINCT DIFFERENCE IN COMPOSITION BETWEEN CORE (GREEN) AND RIM (RED) AREAS.RED AREA WITH BLACK OUTLINE MARKS AN OUTER-CORE, RECOGNIZED FROM U-PB ANALYSIS, AND IN THE MAJOR ELEMENT MAPS (FIG.5.5).MORE MAJOR ELEMENT COMPOSITION DIAGRAMS ARE FOUND IN APPENDIX A(FIG.A1). .. 73 FIGURE 5.5:EPMA MAP OF TITANITE-1A FROM BITE_308, SHOWING VARIATIONS IN ALL MAJOR ELEMENTS.A CLEAR DIFFERENCE
BETWEEN THE CORE (BLACK OUTLINE) AND RIM ARE SEEN, THERE ARE ALSO RECOGNIZED AN OUTER CORE IN THE TOP OF THE GRAIN, WITH HIGH AL AND LOW TI... 73 FIGURE 5.6: A)THIN SECTION SCAN OF BITE_722, SHOWING LOCATION OF ANALYSED TITANITE GRAINS, B) REFLECTED LIGHT
PHOTOMICROGRAPH OF TITANITE-1B, SHOWING ILMENITE AS A REACTION PRODUCT OF TITANITE. ... 74 FIGURE 5.7:BSE IMAGES OF TITANITE FROM BITE_722, GREEN MARKS GROUP 1 WITH LIGHT BSE HUE, RED POINTS HAVE CHEMISTRY
OF GROUPS 2 AND DARK BSE HUE, AND YELLOW SPOTS HAVE BRIGHT BSE HUE. A) TTN-1A, B) TTN-1B1, C) TTN-3, D) TTN-1B-2.
... 75 FIGURE 5.8:EPMA DATA OF TI VS FE FOR BITE_722, PLOTTING IN CLUSTERS CORRELATING WITH LIGHT BSE HUE (GREEN COLOUR) AND DARK BSE HUE (RED COLOUR). ... 75 FIGURE 5.9:THIN SECTION SCAN OF BITE_760, A CATACLASTIC MAFIC ROCK FROM THE MIDDLE OF THE NDZ, WITH MARKINGS OF THE
ANALYSED TITANITE GRAINS. ... 76 FIGURE 5.10: A,B,C)BSE IMAGES OF BITE_760, WITH EPMA SPOTS, GREEN SPOTS INDICATE CORE COMPOSITION, RED SPOTS INDICATE
RIM COMPOSITION, THERE ARE MOSTLY RIM COMPOSITIONS, THE CORES ARE SMALL BUT DISTINCTLY BRIGHTER IN BSE HUE,(A: TTN-7, B: TTN-6, C: TTN-5), D)EPMA SPOTS FOR BITE_760, SHOWING CLEAR CORE VS RIM COMPOSITIONAL DIFFERENCES. 77 FIGURE 5.11:THIN SECTION SCAN OF BITE_743, A MYLONITIC AUGEN GNEISS FROM THE HTZ, WITH MARKINGS OF THE ANALYSED
TITANITE GRAINS. ... 78 FIGURE 5.12:PHOTOMICROGRAPH OF TITANITE-2(BITE_743), SHOWING CLOSE RELATIONSHIP WITH SULPHIDE MINERALS. ... 79 FIGURE 5.13:BSE IMAGES OF TITANITE GRAINS IN BITE_743, WITH EPMA SPOTS CORRELATED TO CORE=GREEN, RIM=RED, INNER- CORE=WHITE, AND OUTER-RIM= RED WITH BLACK OUTLINE, A) TTN-2, B) TTN-1, C) TTN-2, D) TTN-3. ... 80 FIGURE 5.14:EPMA ANALYSIS FOR BITE_743, SHOWS DIFFERENT TITANITE COMPOSITIONS FOR CORE (GREEN SPOTS) AND RIM (RED
SPOTS).WHITE SPOTS ARE INNER-CORE AND RED WITH BLACK OUTLINE IS OUTER-RIM COMPOSITIONS RECOGNIZED BY LA-ICP-MS U-PB ANALYSIS.THE INNER CORE GROUP PLOTS WITH SIMILAR COMPOSITION AS THE CORE GROUP FOR ALL MAJOR ELEMENTS.THE OUTER RIM GROUP HAS DISTINCTLY DIFFERENT F CONTENT COMPARED TO THE RIM GROUP. ... 81 FIGURE 5.15: BSE IMAGES SHOWING POSITIONS FOR LASER ABLATION SPOTS DURING LA-ICP-MS. CORRELATED WITH EPMA CHEMICAL DATA AND COLOUR CODED BASED ON CORE (GREEN), MIX (WHITE), RIM (RED), AND OUTER-RIM (BRIGHT RED) COMPOSITIONS. ... 83 FIGURE 5.16:U-PB DATA FROM LA-ICP-MS ANALYSIS OF TITANITE IN BITE_308, SHOWING THREE TITANITE GROUPS OF DIFFERENT
AGES, A CORE OF C.993MA, A RIM OF C.927MA, AND AN OUTER RIM OF C.884MA. ... 84 FIGURE 5.17:BSE IMAGES OF TITANITE IN NISSER CATACLASITE, SHOWING THE POSITION OF LA-ICP-MS ANALYTICAL SPOTS, COLOUR
CODED BASED ON CORE AND RIM COMPOSITIONS.THE WHITE SPOTS MARK ANALYSES WHICH ARE UNCERTAIN. ... 86 FIGURE 5.18:TERA-WASSERBURG DIAGRAM SHOWING U-PB DATA FROM LA-ICP-MS ANALYSIS OF TITANITE IN BITE_760, SHOWING
TWO DISTINCT MIXED POPULATIONS, A CORE POPULATION OF C.1005MA AND A RIM POPULATION OF C.830MA. ... 87 FIGURE 5.19:BSE IMAGES OF TITANITE IN BITE_743, SHOWING THE POSITION OF LA-ICP-MS ANALYTICAL SPOTS, COLOUR CODED
BASED ON CORE AND RIM COMPOSITIONS, A)TTN-2, WHITE SPOTS MARK AN INNER CORE GROUP, WHICH GIVES OLD INTERCEPT AGE, POSSIBLY CONTAMINATED BY THE SULPHIDES CLOSE BY, B) TTN-1, MAINLY CORE COMPOSITION, SURROUNDED BY A THIN RIM, C) TTN-2 CONTINUED, D) TTN-3, BRIGHT RED SPOTS MARK OUTER CORE WITH A YOUNGER INTERCEPT AGE. ... 89 FIGURE 5.20:TERA-WASSERBURG DIAGRAM FOR LA-ICP-MS DATA OF BITE_743.SHOWING THREE TITANITE POPULATIONS, A CORE
OF C.1144MA, A RIM OF C.1088MA, AND AN OUTER RIM OF C.1005MA. ... 90 FIGURE 6.1:AGE OF ALL SAMPLES OLDER THAN 700MA, ALONG THE CROSS-SECTION A-A' IN THE MAP IN FIGURE 6.2.ILLUSTRATION
MODIFIED AFTER TORGERSEN (2021 PERS.COMM.). ... 92 FIGURE 6.2:MAP SHOWING SAMPLES DATED BY 40AR/39AR.A SIMPLIFIED BEDROCK MAP INDICATES WHAT LITHOLOGICAL UNIT THE
SAMPLES ARE FROM.THE RED LINE MARK POSITION OF CROSS SECTION (FIG.6.1). ... 93 FIGURE 6.3:AGE SPECTRA FOR SAMPLES ASSOCIATED WITH THE NDZ, SHOWING % RADIOGENIC 40AR,K/CA RATIO, AND APPARENT
AGE, ALL IN RESPECT TO THE CUMULATIVE %39AR RELEASE. ... 96 FIGURE 6.4:AGE SPECTRA FOR SAMPLES ASSOCIATED WITH THE NDZ AND THE HTZ, SHOWING % RADIOGENIC 40AR,K/CA RATIO, AND
APPARENT AGE, ALL IN RESPECT TO THE CUMULATIVE %39AR RELEASE. ... 97
xi FIGURE 7.1:TEMPERATURE VS AGE DIAGRAM OF THE UNITS IN THE FIELD AREA,NISSEDAL COMPLEX,NDZ, AND VRÅVATN COMPLEX.
THE DIAGRAM IS MADE BY LINKING THE GROWTH OF TEMPERATURE-SENSITIVE MAJOR MINERALS (SUCH AS AMPHIBOLE, EPIDOTE, AND CHLORITE), WITH RECRYSTALLIZATION OF QUARTZ AND FELDSPAR, AND THE AGE DATA FROM TITANITE (U-PB),HORNBLENDE (40AR/39AR), BIOTITE (40AR/39AR), AND FELDSPAR (40AR/39AR), WHICH ARE PLOTTED WITH THEIR CLOSURE- OR RECRYSTALLIZATION TEMPERATURE.CLOSURE TEMPERATURE FOR EACH MINERAL IS FOUND IN TABLE 9 AND TABLE 10.ORANGE ARROW, RED STIPPLED ARROW, AND BLACK STIPPLED ARROW, SHOWS AVERAGE TEMPERATURE GRADIENT OF THE NISSEDAL COMPLEX,VRÅVATN COMPLEX, AND THEIR COMMON COOLING GRADIENT, RESPECTIVELY.THE DOTTED GREY BOXES INDICATE TEMPERATURE INTERVALS OF 1. RECRYSTALLIZATION IN HTZ (SGR OF QUARTZ AND BLG OF FELDSPAR), 2. REGIONAL METAMORPHISM IN A. NISSEDAL COMPLEX (LOW-AMPHIBOLITE FACIES, <500°C), B. VRÅVATN COMPLEX (HIGH-GRADE AMPHIBOLITE FACIES,600–800°C),3.RECRYSTALLIZATION IN NDZ(SGR+GBM OF QUARTZ,BLG+SGR OF FELDSPAR),4.
CATACLASTIC DEFORMATION IN NDZ,<300°C). ... 101
FIGURE 7.2:ILLUSTRATION OF GEOLOGICAL EVOLUTION IN A REGIONAL SCALE.A. EMPLACEMENT OF BOTH VOLCANIC- AND GNEISS COMPLEXES, SHORTLY FOLLOWED BY INTRUSION OF MEDIUM-GRAINED MAFIC AND FELSIC ROCKS, IN TELEMARK LU, AND METAMORPHISM IN BAMBLE LU, THE ASSOCIATION BETWEEN BAMBLE AND TELEMARKIA LUS IS NOT CERTAIN,B. COMPRESSIONAL SHEARING LEADING TO THRUSTING OF BAMBLE LU OVER TELEMARKIA LU ALONG THE KPSZ, AND ACTIVATION OF THE HTZ,C. REGIONAL METAMORPHISM IN TELEMARKIA LU,D. EMPLACEMENT OF GRANITE INTRUSIONS, E. EXTENSION, LEADING TO JUXTAPOSITIONING OF TELEMARKIA AND BAMBLE LUS ALONG THE KPSZ, AND EXHUMATION OF THE VRÅVATN COMPLEX, LEADING TO JUXTAPOSITIONING OF VRÅVATN COMPLEX AGAINST TELEMARK SUPRACRUSTAL- AND NISSEDAL COMPLEXES, ALONG THE NDZ AND THE “UNNAMED SZ” ... 105
FIGURE 7.3:OVERVIEW OF THE U-PB TITANITE AGES (TABLE 9) AND 40AR/39AR AGE-INTERVALS (TABLE 10) OBTAINED IN THIS STUDY, TOGETHER WITH THE MAIN EVENTS WITHIN THE AREA, AND ASSOCIATED EVENTS OTHER PLACES IN THE OROGEN. A–E CORRESPONDS TO THE PHASES OF THE EVOLUTION PRESENTED IN THIS CHAPTER. ... 108
FIGURE A1:EPMA DATA FROM BITE_308 ... 118
FIGURE A2:EPMA DATA FROM BITE_722 ... 119
FIGURE A3:EPMA DATA FROM BITE_760 ... 120
FIGURE A4:EPMA DATA FROM BITE_743 ... 121
Front photo: “Vågakallen” by Torgeir Schjølberg
xii
List of Tables
TABLE 1:OVERVIEW OF THE ANALYSED ELEMENTS, WITH THE DETECTOR CHAMBER AND DIFFRACTION CRYSTAL USED, IN ADDITION TO
COUNTING TIMES FOR THE DIFFERENT ELEMENTS, AND AVERAGE DETECTION LIMIT. ... 5
TABLE 2:OVERVIEW OF THE MEASURED IONS, WHICH DETECTORS WERE USED, AND THEIR DETECTION LIMITS. ... 6
TABLE 3:INSTRUMENT PARAMETERS USED DURING LA-ICP-MS ANALYSIS ... 6
TABLE 4:OVERVIEW OF ALL SAMPLES COLLECTED IN THE FIELD AREA, COORDINATES, WHERE PICTURED, AND THEIR USE.OTS–ORIENTED THIN SECTION,TS–THIN SECTION,CH–CHEMISTRY AND PETROPHYSICS,U-PB–TITANITE U-PB DATING,HS–HAND SPECIMEN IDENTIFICATION. ... 23
TABLE 5:LA-ICP-MS,U/PB DATA, FROM TITANITE IN VRÅVATN PROTOMYLONITE (BITE_308). ... 85
TABLE 6:LA-ICP-MS,U/PB DATA, IN TITANITE FROM NISSER CATACLASITE (BITE_760), RED=RIM, GREEN=CORE. ... 87
TABLE 7:LA-ICP-MS,U/PB DATA, FROM TITANITE IN HESTKÅS THRUST (BITE_743). ... 90
TABLE 8:ALL HORNBLENDE, BIOTITE, AND FELDSPAR SAMPLES DATED BY 40AR/39AR ISOTOPES, WITH AGES OLDER THAN 700MA. ORGANIZED BY AREA, INCLUDING COORDINATES, AGES AND SQUARE ERROR, AGE TYPE AND SPECTRUM, AND MSWD.ALL SAMPLES ARE PRESENTED IN APPENDIX B(TABLE A6). ... 94
TABLE 9:TITANITE U-PB AGES, WITH GEOLOGICAL SIGNIFICANCE AND TEMPERATURE ESTIMATES ... 109
TABLE 10:40AR/39AR AGE INTERVALS OF HORNBLENDE, BIOTITE, AND FELDSPAR WITHIN EACH UNIT ... 109
TABLE A1:AVERAGE DETACTION LIMIT FOR ALL ANALYSES ... 122
TABLE A2:EPMA RESULTS FROM BITE_308.ALL ELEMENT DATA IS PRESENTED AS WEIGHT %(WT%).GREEN=CORES, RED=RIM, ORANG=OUTER-RIM. ... 123
TABLE A3:EPMA RESULTS FROM BITE_722.ALL ELEMENT DATA IS PRESENTED AS WEIGHT %(WT%).GREEN=AREAS WITH LIGHT BSE HUE, RED=AREAS WITH DARK BSE HUE, YELLOW=BRIGHT AREAS... 124
TABLE A4:EPMA RESULTS FROM BITE_760.ALL ELEMENT DATA IS PRESENTED AS WEIGHT %(WT%).GREEN=CORES, RED=RIM. ... 125
TABLE A5:EPMA RESULTS FROM BITE_743.ALL ELEMENT DATA IS PRESENTED AS WEIGHT %(WT%).GREEN=CORES, RED=RIM, WHITE=”INNER CORE”, ORANGE=OUTER-RIM. ... 126
TABLE A6:ALL HORNBLENDE, BIOTITE, AND FELDSPAR SAMPLES DATED BY 40AR/39AR ISOTOPES, AND FAULT GOUGE DATED BY K-AR. ORGANIZED BY AREA, INCLUDING COORDINATES, AGES AND SQUARE ERROR, AGE TYPE AND SPECTRUM, AND MSWD. ... 128
xiii
Abbreviations
Methods: Local:
EBSD = Electron backscatter diffraction
BITE = Bedrock Infrastructure in Telemark
BSE = Back-scattered electrons NDZ = Nisser Detachment Zone EPMA = Electron probe microanalyzer HTZ = Hestkås Thrust Zone
SEM = Scanning electron microscope
KPSZ = Kristiansand–Porsgrunn shear zone
LA-ICP-MS = Laser ablation–inductively coupled plasma–mass spectrometry
LU = Lithotectonic Unit
TIB = Transscandinavian igneous belt HBG = Hornblende-biotite-granite MSWD = Mean Square of Weighted
Deviates General:
XRF = X-ray fluorescence Ma = Million anno
xpl = Cross-polarized light Myr = Million years ago ppl = Plan polarized light
Elements:
Microstructures: Si = Silicon
BLG = Bulging recrystallization Al = Aluminium SGR = Sub Grain Rotation
recrystallization
Fe = Iron Ti = Titanium GBM = Grain Boundary Migration
recrystallization
Mg = Magnesium Na = Sodium SPO = Shape preferred Orientation K = Potassium CPO = Crystal preferred orientation F = Fluor
Ca = Calcium
Minerals: Zr = Zirconium
Qtz = Quartz U = Uranium
Bt = Biotite Mn = Manganese
Ms = Muscovite Pb = Lead
Fld = Feldspar Th = Thorium
Kfs = Alkali feldspar Ar = Argon
Pl = Plagioclase Hg = Mercury
Hbl = Hornblende He = Helium
Act = Actinolite P = Phosphorus
Ep = Epidote Ttn = Titanite Rt = Rutile Zrn = Zircon Py = Pyrite Ilm = Ilmenite
Px = Pyroxene Cpx = Clinopyroxene
1
1 Introduction
The late-Mesoproterozoic Sveconorwegian orogen is a large and well-exposed orogenic belt in southwestern Scandinavia that is not yet completely understood. The crustal-scale architecture of the orogenic province is defined by tectonic juxtaposition of distinct lithotectonic units (LUs) divided by crustal-scale shear zones. A lot of the previous work done in the Sveconorwegian province have been focused on petrologic, geochemical, isotopic, and geochronological data (Andersen et al., 2002; Andersen et al., 2004; Bingen et al., 2008b; Bingen et al., 2005; Bingen et al., 2003; Bingen et al., 2008c; Granseth et al., 2020; Slagstad et al., 2020; Slagstad et al., 2012). But lately there have been more focus on the structural aspects as well (Henderson & Ihlen, 2004; Torgersen et al., 2018; Viola et al., 2013; Viola et al., 2011), with extensive mapping and analyses of a selection of the largest shear zones. The structural aspect is crucial to constrain a comprehensive geodynamic model for the Sveconorwegian orogen, and the main results of the large-scale structural mapping shows that there have been episodes of compression followed by extension in most of the shear zones across the whole orogenic province (Heaman & Smalley, 1994; Henderson &
Ihlen, 2004; Scheiber et al., 2015). Although the structural aspects of the Sveconorwegian orogen have recently gained more focus, there is still more work needed to get a complete overview of the geodynamics of the orogen.
The goal of this study is to increase the understanding of the compressional and extensional history of the Sveconorwegian orogenic event as evident in the central parts of the orogenic belt.
The master thesis has been part of a multi-disciplinary geological mapping project conducted by the Geological survey of Norway (NGU) in the Nissedal–Drangedal area in Telemark between 2017 and 2021 (Fig. 1.1). The project is called “Bedrock Infrastructure in Telemark” (BITE) and the main aims of the project are to 1) construct a new 1:100 000 bedrock map of the Nissedal–Drangedal area, which has been one of the poorest mapped areas in Norway, 2) to make easy-accessible thematic maps of high relevance to the society, and 3) improve the understanding of the geometrical and temporal relations of the geology in the area. The mapped area comprises mostly Mesoproterozoic rocks and structures related to the Sveconorwegian orogen (Bingen et al., 2008c; Bingen
& Viola, 2018; Granseth et al., 2020; Slagstad et al., 2012). During the first field season of the project in 2017 a new major shear zone, the Nisser detachment zone (NDZ), was discovered (Bingen, 2021 pers. comm.; Torgersen et al., 2018). It is situated between a low-grade supracrustal complex, the Nissedal complex (Mitchell, 1967), and a high- grade gneiss complex, the Vråvatn complex (Laajoki et al., 2002). Although major shear zones in the Sveconorwegian orogen are generally known and mapped, this one was entirely unknown and unreported on any map. Rapidly it became clear that its geological significance and evolution are key to understand the geological history of the whole region, and more specifically the relations between low-grade upper crustal rocks and high-grade middle crustal gneiss complexes.
For the current study, a field area was chosen that extends across the NDZ from the Nissedal complex to the Vråvatn complex (Fig. 1.1). The area has not been thoroughly mapped before, only mentioned as part of more regional scale studies (Andersen et al., 2007; Cramez, 1970; Laajoki et al., 2002; Mitchell, 1967; Thomsen, 2000), or sporadically mapped without associated descriptions and analyses (Bergstøl & Strand, 1973). This study provides a bedrock map with associated cross section, lithological descriptions, and structural analysis. It also includes petrochronological analysis of two large shear zones; in addition to the NDZ also the Hestkås Thrust Zone (HTZ).
Petrochronology is the union of petrology and geochronology; the science of linking rock-forming processes to the time rate, and time, at which they occurred (Engi et al., 2019; Engi et al., 2017). Age data are combined with compositional and deformational data to recover temperature vs time diagrams of the main lithological units.
To understand the temperature-time history of a rock it is useful to link the growth of temperature-sensitive major minerals and deformation structures to datable accessory minerals (Chris Yakymchuk, 2017).
