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Geological Survey of Norway Postboks 6315 Sluppen NGU ~ NO-7491 Trondheim, Norway ,,,'" '''',,'sk, "'";ok,,,, fill Tel.:-47 'l3 90 40 00 REPORT (J(o,'ookGf5<JrveyofNorway Telefax 4773 92 1620 Report no.: 2008.064 ISSN 0800-3416 Grading: Open Title: A tectonostratigraphi c transect across the central Scandinavian Caledonides, Storlien-Trondheim-Leps0)' . Part II: Excursion guide in Norway Guidebookfor the Norwegian part of Excursion #34 ofthe 33,d International Geological Congress, Oslo, Norway, August 2008, 30 participantsjrom 13 nations Authors: Client: Peter Robinson & David Roberts County: Commune: Map-sheet name (M- I :250.000) Map-sheet no. and -name (M- I :50.000) Deposit name and grid-reference: Number of pages: 160 Price (NOK): 364.- Map enclosures: Fieldwork carried out: Date of report: Project no.: Person responsible: August 8, 2008 3251.00 ~ Ie . E "",?,._, ' l~ Summary: This guidebook was prepared for the Norwegian part (seven days) of Excursion #34 ofthe 33" IGC, Oslo, 2008, to give participants from outside the region as comprehensive a view as possible within 10 days of the stratigraphy, paleontology, tectonostratigraphy, structural geology, igneous and metamorphic petrology, geochronology, tectonics and geophysics, in a traverse across this major thrust-assembled orogen from the foreland in Sweden to places deep in the hinterland in coastal Norway with evidence of ultra-high-pressure metamorphism and melting. The flrst three days in Sweden (Part [ofreport 2008 .064) were led by David Gee l and Per-Gunnar Andreasson', with co- leaders Erik Sturkell' and Anna Ladenburgerl. The last seven days (Part II: this report) were led by Peter Robinson' and David Roberts' with co-leaders Arne Solli', Kurt 5 4 4 6 8 Hollocher , Per Terje Osmundsen , Tor Grenne , Herman Van Roermund , Michael Terry7 and Hans Vrijrnoed , with lO 12 contributions by David Gee, Bob Tucker', Tom Krogh , Alan Krill", Emily Walsh" and Megan Regel . It was divided by day as follows: Day 4: Trondheim Nappe Complex and subjacent units: Storlien to Trondheim. Day 5: Scandian geology ofthe Outer Trondheimsfjord region. Day 6: Part I: Geology ofthe H@londa-Horg-L@kken area. Day 6: Part II: Geology of Trollheimen. Day 7: Garnet peridotites in the northern UHP domain afthe West ern Gneiss Region, Otrey. Day 7: Mafic dikes and basement-cover relationships, southern coast afthe islands ofMidsund. Day 8: Structural and metamorphic relationships between Caledonian nappes and Fennoscandian basement on the mainland near Brattvag. Day 9: Geology ofHarams@y , Flems@y ond Leps@y Day 10: Geology on the rOllte Leps@ya-Brattvag-Solholmen-Svartberget-Atlantic Highway-Aver@y-Halsa-Trondheim. The introduction to this excursion guide, in Norway, includes a dedication to the late Professor Tom Krogh, who died suddenly in the spring of2008. A full list of references pertaining to the geology of the areas covered by the seven days of excursions in Norway is given at the end of the report. IUppsala University, Sweden; ' Lund University, Sweden; ' Technical University of Tallinn, Estonia; 'Geological Survey of Norway, Trondheim; 'Union College, Schenectady, NY, USA; 'Utrecht University, Utrecht, The Netherlands; ' South Dakota School of Mines, Rapid City, SD, USA; 'University of Oslo, Norway; 'U.S.Geological Survey, Reston, VA, USA; 10 Deceased 2008, University of Toronto, Ontario, Canada; "Norwegianlnstitute of Science and Technology, Trondheim, Norway; 12Cornell College, Mount Vernon, Iowa, USA. Keywords: Caledonian orogen Tectonostratigraphy Structural geology Metamorphism Tectonics Geochronology Paleontology Geochem.istry Ophiolites Tom Krogh On the outcrop beside a kyanite-zoisite eclogite with coesite pseudomorphs at Fjørtoft, July 1, 2003, on the Post-meeting Excursion of the Alice Wain Field Symposium. Tom sampled this outcrop in 1998, both the eclogite and the cross-cutting extensional pegmatite. On the latter he obtained a U-Pb zircon age of 394.5 +/-2 Ma (Fig. 9.23, this guidebook), but on the former, despite his best efforts, he was unable to find any zircon. This is now explained by the very low Zr content, because the protolith was a plagioclase-rich cumulate rock (see Stop 9-7 and Fig. 9-11, this guidebook). Tom's zircon knowledge in the lab was profound, but he was also aware of all aspects in the field and with the use of a heavy hammer, so that a collecting tour with him was an experience never to be forgotten. (Photograph courtesy of Helen Lang) Fig. 0.1 Tectonostratigraphic map of the central Scandinavian Caledonides showing the general route of 10- day Post-meeting Excursion #34. Day 4 1 Day 4, Monday, 18 August Trondheim Nappe Complex and subjacent units: Storlien to Trondheim. David Roberts (with contributions by David Gee to Stops 1, 2 and 3, and Peter Robinson to Stop 11) Summary of route We leave Åre at 08.00 hours and drive west on the E14 road, arriving at the Customs Station near Storlien just before 09.00 (there is no need to stop here). Proceed to Stop 4.1 (Fig. 4.1). From there, after two more stops just inside Sweden, we will drive west along the wide valley of Teveldalen and, after Stop 4.6, along the narrow, incised valley of Stjørdalen. We continue on the E14 until we reach the E6 road junction on the outskirts of the town of Stjørdal. There, we turn right (north) for stops 4.9 and 4.10 (Fig. 4.1), thereafter returning (south) on the E6 highway, passing Stjørdal, and continuing on to Trondheim. After a short break at the Geological Survey of Norway (NGU) in Lade we visit nearby coastal exposures of higher levels of the Bymarka ophiolite, and then continue to the Trondheim Vandrehjem – arriving at c. 17.45. Introduction On this fourth day of the transect we will continue our gradual upward climb in the Caledonide tectonostratigraphy with the focus now shifting to representative rocks of the Köli Nappes as we cross the border from Sweden into Norway. To refresh our memories, however, we begin the day with two stops on the Swedish side, one in the Seve and the other in rocks of the Lower Allochthon at a locality that affords an excellent view to the west, weather permitting, into the Norwegian county of Nord-Trøndelag. As we approach the border, and especially clear at Stop 2, west of Storlien, we will see that the tectonostratigraphy is deformed across a major, N-S-trending antiform. This structure can be followed over several tens of kilometres, roughly parallel to the Norwegian-Swedish border. Known as the Skardøra Antiform (Hurich et al. 1988), it has previously been referred to as the Sylarna or Riksgrense Antiform. This antiformal structure is one of several such open folds that deform the tectonostratigraphy of the Scandinavian Caledonides, and clearly developed during and/or post- dating the principal Scandian thrusting but prior to the extensional deformation that accompanied the late-Scandian collapse of the orogen. Looking southwest from the vantage point of Stop 2, the prominent escarpment of Steinfjellet marks the eastern limit of the Köli rocks of the Trondheim Nappe Complex (TNC), floored by the Steinfjell Thrust which was later reactivated as a normal fault during the late-Scandian extensional deformation (Sjöström & Bergman 1989). This composite, contractional/extensional structure is clearly seen on the seismic reflection profile (Hurich et al. 1988, Palm et al. 1991) (Fig. 4.2), and its mylonitic rocks will be examined briefly at Stop 3. It has been suggested that the late extensional fault at the top of the Steinfjell Thrust may be a continuation of a detachment fault exposed beneath the Devonian rocks at Røragen, 100 km farther south (Norton 1987, Gee et al. 1994). Another contender for the prolongation of the Røragen detachment might be the Kopperå fault, just east of Meråker (Hurich & Roberts 1997, in prep., Mosar 2000), which is also prominent on the seismic reflection imagery (Fig. 4.2). Thereafter we drive westwards down the valley Teveldalen, initially in low-grade, Lower Ordovician to Llandovery (and possibly Wenlock), turbiditic rocks of the Meråker Nappe, part of the TNC, which we will examine at two stops. At the base of the Meråker Nappe there is a bimodal but largely mafic, amphibolite-facies, magmatic complex (Fundsjø Group) of inferred Cambrian to 1 Day 4 2 transect with Day 4 stops marked as encircled numbers. encircled transect with Day 4 stops marked as ig. 4.1. Simplified geological map of the Storlien-Trondheim F Tremadoc age. This has provided detritus to a basal conglomerate, above an important unconformity, in the overlying Sulåmo Group (Chaloupsky & Fediuk 1967). Most of the succession in the Meråker Nappe shows westerly dips but the greater part is inverted, except in the east (east of a major syncline exposing the Llandovery-age Slågån Group) where the strata are disposed 2 Day 4 3 Fig. 4.2. Interpretation of the vibroseis reflection profiles, Storlien (east) to Trondheimsfjord (west), and across Fosen Peninsula (c. NNW-SSE), taken from Hurich & Roberts (1997). B/C – Basement-cover contact, generally tectonised; BUA – Base of Upper Allochthon; H – Hitra-Snåsa Fault; KF – Kopperå Fault; SA – Skardøra Antiform; ST – Steinfjell Thrust; STZ – Stadland shear zone; V – Verran Fault. normally (Siedlecka 1967). In another interpretation, from an area 30 km farther northeast, inferred younger rocks (?Wenlock, but no fossils) occur in another syncline east of the Slågån Group (Hardenby 1980). Continuing westwards we pass into the locally higher-grade rocks of the Gula Nappe which are intensely folded in this area and are characterised by a near-vertical foliation. Although the internal structure of the Gula Complex (formerly termed Group) has been controversial, in the far northeast of the Trondheim Region the rocks and the major thrusts define an antiform that is deformed around a younger synformal fold (Roberts 1967).