Geological and Petrographical Investigations in the Kongsberg— Bamble Formation
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NORGES GEOLOGISKE UNDERSØKELSE NR. 160. GEOLOGICAL AND PETROGRAPHICAL INVESTIGATIONS IN THE KONGSBERG— BAMBLE FORMATION BY JENS A. W. BUGGE WITH 7 PLATES AND 26 FIGURES, It TABLES IN THE TEXT 081.0 1943 I KOMMISJON HOS H. ASCHEHOUG & CO 4 v f (!ontentB. Preface 7 Intro6uction g I. The Old Complex l l 1. Quartzites (mainly Arenaceous Sediments) 11 2. Micaschists, Cordierite-Sillimanite-Carrying Rocks (Mainly Argil laceous Sediments) 15 a. Sillimanite-Biotite-Cordierite Gneiss 16 b. Sillimanite-Biotite Gneiss 17 c. Muscovite-Sillimanite-Biotite Gneiss 17 d. Microcline-Sillimanite-Biotite Gneiss 17 e. Microcline-Sillimanite-Garnet Gneiss 18 3. Limestones (Mainly Calcareous Sediments) 18 4. Effusives 19 5. Oldest Plutonic Rocks in the Kongsberg District 20 6. Banded Gneisses 7 21 a. Description 21 b. Genesis 24 7. Rocks of the Hyperite Group 38 a. Description 38 b. Petrography and Genesis 44 11. The Younger Complex 53 1 . Metataxites 55 2. Arendalites 60 a. Geological Investigations in the Field 62 b. Microscopic Studies 64 a. The Light Minerals 64 p. The Dark Minerals 69 c Petrology 73 d. Comparison with Other Regions 77 3. Cordierite-Anthophyllite-Carrying Rocks 82 a. Mineralogy 82 b. Petrography 87 a. Gedrite-Cordierite-Carrying Amphibolites 89 |3. Gedrite-Cordierite-Carrying Plagioclase Gneisses 91 y. Gedrite(Anthophyllite)-Cordierite Rocks without Plagioclase 94 c. The Genesis of the Cordierite-Anthophyllite-Carrying Rocks 99 4 Nodular Granites 103 a. Petrography ; 106 b. The Application of the Facies-Principle on the Sillimanite- Carrying Rocks 109 c. The Genesis of the Nodular Granites 111 5. Synkinematic Granites 114 a. Porphyre Granites 116 b. Fine- to Mediumgrained Granites 117 c. The Genesis of the Granites 119 6. Granite Pegmatites 123 a. Petrography 123 b. Genesis 125 7. Postkinematic Granites 129 8. Skarn Rocks 129 111. Facies Series in the Arendal District 133 IV. Comparison with Sweden and Finland 135 Summary 137 List of References 145 IlluBtrationB. Figure l. Map illustrating the location of the Kongsberg— Bamble Formation 10 » 2. Distribution of sedimentary rocks in the southern part of the Kongsberg— Bamble Formation 12 » 3. The geology of parts of the Søndeled District 13 » 4. Amphibolite band showing signs of transgressive structures . 27 » 5. Geology of the Kongsberg District <repr«6uce6 after C. Bugge) 30 » 6. Profile from Kongens Grube, Kongsberg (reproduced after C. Bugge) 31 » 7. Banded gneiss, SE side ok Gjervoldsø, Øiestad 35 » 8. Microphoto of banded gneiss, SE side of Gjervoldsø, Øiestad 37 » 9. Distribution ok hyperites in the southern part of the Kongs berg—Bamble Formation 39 » 10. The Niggli-values al, fm, c, alk of gabbroid rocks from the Kongsberg— Bamble Formation plotted in atetrahedron diagram 52 » 11. Strongly deformed amphibolite band from the migmatite zone of banded gneisses, SE side of Gjervoldsø, Øiestad 56 » 12. "Migmatite river", Ytre Halvorsholmen, Øiestad 57 » 13. Ptygmatites, Ytre Halvorsholmen, Øiestad 58 » 14. Nebulitic amphibolite band from the migmatite zone of banded gneisses, 200 m E of Morvigen, Landvig 59 » 15. Pegmatite-schlieren in amphibolite, NW side of Ærø, Øiestad 60 » 16. Geology of parts of the Arendal District 63 » 17. Grain of hypersthene with inclusions ok partly resorbed biotite flakes 71 » 18. The Niggli-values al, fm, c, alk of different silicate-rocks in the Kongsberg— Bamble Formation plotted in a tetrahedron diagram 74 » 19. Variation-diagram of the Niggli-values mg, si ok different sili cate rocks from the Kongsberg— Bamble Formation 75 » 20. Composition of normative feldspars ok different silicate rocks 77 » 21. Cordierite replacing plagioclase; amphibolite Søndeled 93 » 22a, b. Nodular granite, W side of Brøbørvann, Søndeled 105 » 23. A" K F diagram of aluminous rocks in tne Kongsberg— Bamble Formation 111 » 24. Distribution of granites in tne southern part of the Kongs berg—Bamble Formation 115 » 25. Pegmatite, Ramskjær, Søndeled 128 » 26. Map illustrating facies-series in the Arendal District 134 Table 1. Chemical analyses of metamorphic argillaceous rocks from the southern part of the Kongsberg— Bamble Formation 16 2. Chemical analyses of banded gneisses from the southern part of the Kongsberg—Bamble Formation 22 » 3. Norm of banded gneisses given in table 2 23 4. Chemical analyses of gabbroid rocks 51 5. Chemical analyses of different silicate rocks krom the Kongs berg—Bamble Formation 72 6. Chemical analysis of anthophyllite, Vormlitjern, Søndeled.... 83 7. Chemical analyses of anthophyllites from different parts of the Kongsberg— Bamble Formation 84 8. Chemical analysis of cordierite, Tvedestrand 86 » 9. Chemical analysis of a cordierite-anthophyllite rock SE of Vormlitjern, Søndeled 97 • 10. Chemical analysis and mode of nodular granite, Bærø, Kragerø 107 » 11. A tentative stratigraphical scheme ok the Kongsberg— Bamble Formation 138 Plate I. Fig. 1. Microphoto of cordierite-micaschist, Sandvika, Søndeled. » 2. Muscovitization of sillimanite aggregates, sillimanite gneiss, Sandvika, Søndeled 11. » 3. Microphoto of sillimanite gneiss, Skutterud, Modum. • 4. Microphoto of antiperthite in arendalite, Sjælvika, Tvede strand. » 111. » 5. Microphoto of "relic perthite" in arendalite, Flosta, Tvede strand. » 6. Microphoto ok corroded border between albite and micro perthite, hypersthenegranite, Langsev, Arendal. » IV. » 7. Microphoto of myrmekite in arendalite. » 8. Microphoto of biotite surrounded by small grains of hyper sthene, arendalite, Voksnes, Tromøy. » V. » 9. Microphoto of recrystallized grains ok quartz and hypersthene in arendalite, Voksnes, Tromøy. » 10. Microphoto showing amphibole replacing biotite, Markevigen, Tromøysund. » VI. » 11. Microphoto of cordierite with polysynthetic twins parallel to (110), Hasleøen, Søm, Arendal. » 12. Microphoto of nodular granite, west side of Brøbørvann, Søndeled. - VII. » 13. Microphoto of nodular granite, 600 mNW of Braaten, Søndeled. » 14. Microphoto of microcline with inclusions of plagioclase and myrmekite, granite N of Kilancl, Åmli. Preface. The—1939.field investigationsThe investigationswere carnetwere madeout duringfor thethe yearsGeological1937 3urvev of Norway on the initiative of Director Carl Bugge, who entrusted me with the task to give a general survey of the geology in the Arendal district of the Kongsberg—Bamble Formation. The present paper deals with the petrology of the district, and besides, intends to give a survey of the main geological features. The main researches have been limited to the region between Risør and Grimstad, but Bpecial inv6Btl^ationB have keen extended to other parts of the Kongsberg—Bamble Formation. paper encleavoul-8 to 6eBcl-id>e tne rock material witn vvnicn wc nave to cio, ancl to analv?e tne tunctionB exerciBeo! by tne metamorpmc ancl metaBomatic ploceBBeB an 6tne cnan^eB tnereb^ mclucecl in tne roclcB. Accurate knowleciFe of the rock material iwelt is a necessary prerequisit for drawing conclusions regarding the larver struc tural and architectural features, and for giving a tectonic analysis ot the region. These problems will be discussed in a second part which is to appear later. Dr. Carl Bugge kindly placed all his collections of rock specimens, slides, and diaries at my disposal. He was the first to introduce me to geological working method and tor his great personal interest and the many valuable suggestions and discus sions I am deeply indepted. conBiclerable part ot tne laborator^ re«earck waB carrie6 out in at tne Oeolo^ical InBtitute ot I^s^lcole, ancl ProteB3or Vo^t kincllv placecl all tlie equip mentB ot tne InBtitute at mv cliBpoBal. 8 I owe great thanks to my former teacher Professor Tom. F. W. Barth for man)" inspiring discussions and for valuable assist ance botn in my present work and previously. Certain parts of the laboratory research were carried out at his Institute. To a certain extent the present paper refers to older collec tions from the Kongsberg ßamble Formation. Through the kind ness of Dr. C. W. Carstens I was allowed to study the collections of Videnskabernes Selskab, Trondheim. The rock specimens and slides from Kragerø, collected by Professor Dr. W. C. Brøgger was kindly placed at my disposal by the Director of Geologisk mineralogisk Museum, Professor V. M. Goldschmidt. I want to express my thanks for his kind help and for stimulating discus sions on various problems. Grants have been received from the Nansen foundation and from cand. jur. Halvdan Bjørum's foundation. Ninelalo^jBl( InBtitutt, 08w, 31, 1943. Intro6uction. The geological investigations of the map "Arendal" were systematically started by the Geological Survey of Norway about 1921, preliminary investigations håving been carrie^ out still earlier by several Norwegian geologists. Minerals from the well-known skarn-ironore deposits at Arendal were Btuclie6 already in the eighteenth century, and o!etaile6 6eBcriptionB have been 6elivere6 by >Veibve, Scheerer, M. Kjerulf, T. Dahll, and others. The general geology of the district has ben 6iBcuBBeo! bv Xjerult and Danll as well as by David Forbes, W. C. Brøgger, J. H. L. Vogt; more recent!> by Th. Vogt and Arne Bugge. In the xealB 1921—1928 the geological mapping was carried out by O. Andersen. His investig ations were chiefly restricted to the region be.tween Risør and Lyngør. More detailed investigations on the map "Arendal" has been carried out by Carl Bugge who travelled in tniB cllBtrict several weeks during the years 1928 1939. The Kongsberg ßamble Formation is separated from the noltnweBtel-n Telemark Formation by a prominent friction breccia running from Modum in the north to Kristiansand in the south (35). A wedge of overlain post-archean rocks from the Oslo ViBtl-ict c!ivia'eB the formation into a noltnern and a Boutnern branch (fig. 1). The rocks are all Pre-Cambrian and belong to the deeper parts of an ancient mountain-range. The first section of the present publication deals with rocks of the Old Complex, i. e. rocks which were formed before the culmination of the revolutionary phase. Evidence is cited to show that the Old Complex comprises rocks which represent meta 10 Fig. 1. Map illustrating the location of the Kongsberg—Bamle Formation.