4. Tectonics and structural geology
4.1. Trans-Atlantic correlation of Proterozoic collisional belts and Paleoproterozoic Metallogeny of the Arctic
The Amitsoq Plutonic Suite – a newly discovered suite in the Ketilidian Orogen, South Greenland
Katrine Baden1, Leon Bagas2, Jochen Kolb3, Tonny B. Thomsen1 and Tod E. Waight4
1Geological Survey of Denmark and Greenland, 2China University of Geosciences, 3Karlsruhe Institute of Technology, 4University of Copenhagen
The study area is situated in the ca. 1855-1735 Ma Ketilidian Orogen of South Greenland. Six fine- to medium-grained felsic rocks from the northeast coast of Amitsoq Island were dated by LA-ICPMS (U/Pb zircon). Observations from fieldwork show show complex mixing and mingling structures of feldspar-phyric monzonite and leucogranite. Both rocks have an intrusive contact with granodiorite, which itself intrudes a metasedimentary rock. North of the metasedimentary rocks, a banded, porphyroclastic felsic gneiss occurs.
The gneiss yields an age of 1784±7 Ma, that is interpreted as the intrusion age of a felsic precursor. This age overlaps with regional peak metamorphism (1790-1770 Ma) and the late stage of the Julianehåb Igneous Complex (1781-1807 Ma). The fine-grained metasedimentary rock gives a spread of concordant ages from ca. 1800-2800 Ma, supporting its sedimentary origin. The feldspar-phyric monzonite has an intrusion age of 1680±8 Ma, which is indistinguishable from the 1704±11 Ma intrusion age of the granodiorite. Homogeneous monzonite from the same site yields an intrusion age of 1735±6 Ma. This ca. 45 Ma older age falls in the range of the Illua Plutonic Suite (1755-1728 Ma).
The Amitsoq Island is underlain by a complex set of igneous and metamorphic rocks with intrusive ages (ca. 1700 Ma) never reported for the Ketilidian Orogen before. The new data indicate that its geology is more complex than previously thought, which highlights the need for remapping and reinterpretation, to improve our understanding of the geological history and economic potential for gold deposits.
A new configuration of crustal-scale shear zones controlling copper-gold mineralization in northern Sweden
Tobias E Bauer1 and Edward P Lynch2
1Division of Geosciences and Environmental Engineering, Luleå University of Technology, Sweden, 2Department of Mineral Resources, Geological Survey of Sweden
Northern Sweden is a well-mineralized area in Europe and contains three major metallogenic belts; namely, the Gold Line, Skellefte and Northern Norrbotten ore districts. Gold and/or copper deposits occur in all three belts as orogenic Au, Au-rich VMS and IOCG-style mineralization. Regardless of mineralization style, however, most deposits appear to be spatially controlled by a set of crustal-scale Paleoproterozoic shear zones, which share similar structural characteristics and deformation histories.
Reappraisal of regional geological and geophysical data, coupled with structural mapping, suggests crustal-scale shear zones form continuous, c. N-S-trending zones extending from the Gold Line in the south to Northern Norrbotten. An example from Norrbotten is a zone that extends SSW from Karesuando in the north towards Svappavaara. While this zone has traditionally been inferred to continue SW towards Arjeplog (i.e. the KADZ, Karesuando-Arjeplog deformation zone, Bergman et al. 2001), we favour its deflection SSE into the Nautanen-Aitik trend, which mimics the configuration of analogous zones to the east and west. Furthermore, we tentatively suggest splays of this major zone continue south through the Laver area and terminate in the Skellefte district close to Björkdal and Boliden.
Crustal-scale shear zones show a long-lived deformation history with several reactivation-hydrothermal events. The most important ore forming events along these zones can be assigned to an early phase of crustal extension at c. 1.90 Ga (Skyttä et al. 2012), and two phases of crustal shortening at around 1.87 and 1.80 Ga, coinciding with major Svecofennian-cycle tectonothermal events (c.f. Bauer et al. 2016, 2017).
Bauer, T.E., Sarlus, Z. & Tavakoli, S. 2016: Poly-phase structural controls on ore deposits in northern Sweden. Proceedings of the Nordic Geological Winter Meeting 2016, Helsinki, Finland.
Bauer, T.E., Sarlus, Z., Lynch, E., Martinsson, O., Wanhainen, C., Drejing-Carroll, D., Coller, D. 2017: Two independent tectonic events controlling AIO and IOCG deposits in the Gällivare area, Sweden. Proceeding of the 14th SGA Biennial Meeting, 20-23 August 2017, Québec City, Canada, 839-842.
Skyttä, P., Bauer, T.E., Tavakoli, S., Hermansson, T., Andersson, J. & Weihed, P. 2012: Pre-1.87 Ga development of crustal domains overprinted by 1.87 Ga transpression in the Palaeoproterozoic Skellefte district, Sweden. Precambrian Research 206-207, 109-136.
Paleoproterozoic volcanogenic massive sulfide mineralization, Karrat Group, Central Kangiusap Kuua, West Greenland
Yvonne Michelle DeWolfe1, Jochen Kolb2 and Diogo Rosa3
1Mount Royal University, Department of Earth and Environmental Sciences, Calgary, Canada, 2Karlsruhe Institute of Technology, Institute of Applied Geosciences, Geochemistry and Economic Geol, 3Geological Survey of Denmark and Greenland, Copenhagen, Denmark
The Karrat Group of Central West Greenland is composed of the Qeqertarssuaq (Lower Karrat Group), Qaarsukassak, Mârmorilik, Kangilleq, and Nûkavsak formations (Upper Karrat Group). All volcanic rocks of the Karrat Group are placed in the Kangilleq formation (informal), which is defined as a package of meta-volcanic (greenschist) rocks that unconformably overlie meta-sedimentary rocks of the Qeqertarssuaq Formation and are conformably overlain by meta-sedimentary rocks of the Nûkavsak Formation. The Kangilleq formation shows dominantly within-plate, alkali basalt geochemical signatures.
A unique sequence of meta-volcanic rocks (~100 m) occurs in the Central Kangiusap Kuua. These rocks differ from all other rocks of the Kangilleq formation in that they: 1) show tholeiitic arc-like affinities; 2) contain felsic volcanic rocks; and 3) contain VMS-type sulfide mineralization. The basal ~60 m consist of pillow basalt lava containing flow top breccias and hyaloclastite indicating subaqueous eruption. Overlying the pillows is an ~30 m sequence of mafic volcaniclastic rocks where normal to reverse grading, massive to crudely bedded, and channel/scour structures suggest emplacement by mass debris flows. The mafic volcaniclastic beds are overlain by a rhyolite breccia ~5 m), which is capped by a strongly silicified rock (~2 m). The felsic breccia hosts stringer to massive sulfide (pyrite, pyrrhotite ± sphalerite, chalcopyrite).
Our work documents the first occurrence of a tholeiitic, bi-modal volcanic sequence with arc-like signature, and VMS-type mineralization within the Karrat Group. Thus, it has important implications for mineral exploration, and the interpretation of the geodynamic setting of the Kangilleq formation.
A new reef-type PGE-enriched zone in the early Paleoproterozoic Näränkävaara Layered Intrusion, northeastern Finland
Ville Järvinen1, Tapio Halkoaho2, Jukka Konnunaho2 and O. Tapani Rämö1
1University of Helsinki, Finland, 2Geological Survey of Finland
The 2.44 Ga Näränkävaara layered intrusion is located 100 km south of the Arctic Circle. It belongs to a belt of 2.45-2.43 Ga mafic layered intrusions formed during continental extension (Lauri et al. 2012). These intrusions contain contact-, reef- and offset-type PGE deposits (Rasilainen et al. 2010).
The intrusion is 25 km long and 5 km wide. Geophysical modelling infers a triangular keel extending up to a depth of 10 km. Wall rocks are Archean TTG, migmatites, gneisses and metavolcanic rocks (Alapieti 1982). The intrusion consists of four principal units (stratigraphic thickness in parentheses): a basal dunite (2 km), a peridotitic-pyroxenitic unit (700 m), a gabbroic unit (400 m), and a quartz-dioritic unit (200 m). Parental magma has boninitic or siliceous high magnesium basalt affinities except for the basal dunite, which is komatiitic.
Five drill holes intersect a 10–25 meter thick PGE-enriched zone located at the border zone between the pyroxenitic and gabbroic units (Lahtinen 2005). Average intersection is 15 meters with 0.25 ppm Pt+Pd+Au. Highest assay is 0.39 ppm Pt+Pd+Au in a 1 meter long sample. The Pd/Pt is 2.5–8.7. Sulfides are rare (highest analyzed S at 2440 ppm and Cu at 262 ppm). The PGE-enriched zone is continuous along strike for at least 5 km.
This type of PGE-enriched zone has not been found in similar stratigraphic position from other Finnish 2.43-2.45 Ga layered intrusions (e.g. Iljina et al. 2015). Lithologically it resembles the PGE mineralization in the Munni Munni Complex (Barnes & Hoatson 1994).
Alapieti, T.T. 1982: The Koillismaa layered igneous complex, Finland – its structure, mineralogy and geochemistry, with emphasis on the distribution of chromium. Geological Survey of Finland, Bulletin 319, 116 pp.
Barnes, S.J. & Hoatson, D.M. 1994: The Munni Munni Complex, Western Australia: stratigraphy, structure and petrogenesis. Journal of Petrology 35, 715–751.
Iljina, M., Maier, W.D.& Karinen, T. 2015: PGE-(Cu-Ni) deposits of the Tornio-Näränkävaara belt of intrusions (Portimo, Penikat, and Koillismaa). In: Maier, W.D., Lahtinen, R. & O’Brien, H. (eds.): Mineral Deposits of Finland, 133–164. Amsterdam: Elsevier.
Lahtinen, J. 2005: Tutkimustyöselostus Näränkävaaran–Murtovaaran ultramafisella–mafisella kompleksilla valtauksilla Murtovaara 6, 8–19, 21–26, 32–34 vuosina 2001-2003 suoritetuista malmitutkimuksista. Dragon Mining NL, Raport 080/4523/JJL/05, 9 pp.
Lauri, L., Mikkola, P. & Karinen, T. 2012: Early Paleoproterozoic felsic and mafic magmatism in the Karelian province of the Fennoscandian shield. Lithos 151, 74-82.
Rasilainen, K., Eilu, P., Halkoaho, T., Iljina, M. & Karinen, T. 2010: Quantitative mineral resource assessment of platinum, palladium, gold, nickel, and copper in undiscovered PGE deposits in mafic- ultramafic layered intrusions in Finland. Geological Survey of Finland, Report of Investigation 180, 338 pp.
Linking the Umivik and Scourie dyke swarms tighter into a pre-Iapetus plate configuration
Martin Klausen1, Riaan Bothma1 and Thomas Kokfelt2
1Department of Earth Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa, 2Geological Survey of Denmark and Greenland, GEUS, Oester Voldgade 10, 1350 København K, Denmark
The mafic Umivik dyke swarm in SE Greenland (64˚10-30’N) was sampled during the GEUS 2012 ‘SEGMENT’ expedition and mapped in Google Earth for structural and petrological investigations. This approximately 40-km-wide exposed part of a much more extensive igneous province is made up of more than 160 roughly E-W trending dykes, which constitute 5-15 % of the outcrop. Within Umivik we recognize at least two slightly oblique cross cutting sub-swarms with similar geochemical signatures. Their compositions are comparable to those of the Scourie dyke swarm, across the conjugate rifted margin in Scotland (Myers, 1987), which may all have been derived from the same metasomatised sub-continental lithospheric mantle source (Hughes et al., 2014). According to Nilsson et al (2013) and Davies & Heaman (2014), these dykes were emplaced between 2.42-2.36 Ga, during the break-up of the Superia supercontinent. Subsequently, dykes were variably deformed through a combination of conjugate shear and thrust zones during the Nagssugtoqidian/Laxfordian orogeny, with the southernmost extent of this orogen’s deformation front coinciding with the Umivik area. With the exception of a few less deformed ‘crustal enclaves’, mafic intrusions become progressively more deformed and metamorphosed across this nearly 150 km wide deformation front, exemplified by four case study areas up along the coast. The Atlantic Ocean eventually separated the Greenlandic and Scottish part from each other and our primarily aim is to use both structural and petrological evidence provided by mafic intrusions to bring these two craton fragments tighter together within their post-Nagssugtoqidian and pre-Atlantic configuration.
Davies, J.H.F.L. & Heaman, L.M., 2014: New U–Pb baddeleyite and zircon ages for the Scourie dyke swarm: A long-lived large igneous province with implications for the Paleoproterozoic evolution of NW Scotland. Precambrian Research 249, 180–198.
Hughes, H.S.R., McDonald, I., Goodenough, M., Ciborowski, T.J.R., Kerr, A.C., Davies, J.H.F.L., Selby, D., 2014: Enriched lithospheric mantle keel below the Scottish margin of the North Atlantic Craton: Evidence from the Palaeoproterozoic Scourie Dyke Swarm and mantle xenoliths. Precambrian Research 250, 97–126.
Myers, J.S., 1987: The East Greenland Nagssugtoqidian mobile belt compared with the Lewisian complex. In: Park, R.G. & Tarney, J. (eds), Evolution of the Lewisian and Comparable Precambrian High Grade Terrains. Geological Society Special Publication 27, 235–246.
Nilsson, M.K.M., Klausen, M.B., Söderlund, U. & Ernst, R.E., 2013: Precise U–Pb ages and geochemistry of Palaeoproterozoic mafic dykes from southern West Greenland: linking the North Atlantic and the Dharwar cratons. Lithos 174, 255–270.
Architecture of the Rinkian Orogen between Svartenhuk and Holm Ø, western Greenland
Jochen Kolb1, Crystal LaFlamme2, Annika Dziggel3 and Kristine Thrane4
1Institute of Applied Geosciences, Karlsruhe Institute of Technology, Germany, 2ARC Centre of Excellence in Core to Crust Fluid Systems (CCFS), University of Western Australia, Aus, 3Institut für Angewandte Mineralogie und Lagerstättenlehre, RWTH Aachen University, Germany, 4Geological Survey of Denmark and Greenland
The Paleoproterozoic Rinkian Orogen extends from Nuussuaq to north of Holm Ø along the Greenlandic western coast. It has recently been interpreted as northern extension of the Nagssugtoqidian Orogen that continues west in the Trans-Hudson Orogen of Canada. We concentrate on the high-grade metamorphic northern part of the Rinkian Orogen.
The rocks are characterized by Archean orthogneiss, ultramafic rocks, amphibolite, Paleoproterozoic paragneiss, charnockite of the 1.90-1.87 Ga Prøven Igneous Complex (PIC), and ca. 1.82 Ga granite. The PIC has a diameter of ~100 km, with increasing foliation intensity towards the outer contact. In the south, rocks of the PIC are thrust E on top of Paleoproterozoic paragneiss, which records peak metamorphic conditions at 750-800°C and < 4 kbar. In the north, contact relationships between the igneous rocks of the PIC and paragneiss are complex. The near-vertical, several km wide Tussaaq shear zone marks the boundary between the PIC and Paleoproterozoic paragneiss. From this shear zone to the N, the fabrics flatten progressively, turning into a NW-vergent fold-and-thrust structure. Leucosomes are ubiquitous, most abundant around the Tussaaq shear zone and form syn-deformational structures, indicating high temperature metamorphism. These leucosomes coalesce into pegmatites and plutons, which are dated at 1.82 Ga. Similar ages for peak metamorphism indicate a tectonothermal event some 50 m.y. after emplacement of the PIC, exhuming rocks of the middle crust. The fact that the youngest of the ca. 1.82 Ga granites crosscut the high-T fabrics, indicates that exhumation was a fast tectonic process and not driven by erosion.
Sniffs of ‘IOCG-style(?)’ chalcopyrite mineralisation in northwestern Greenland
Crystal LaFlamme1, Kathleen Bathgate1, Jochen Kolb2, Diogo Rosa3, Marco Fiorentini1 and Kristine Thrane3
1Centre for Exploration Targeting, University of Western Australia, 2Karlsruhe Institute of Technology, 3GEUS
The Nutaarmiut Complex was identified during a 2016 field campaign in the Paleoproterozoic Rinkian Orogen. It is notable for: 1) blebby chalcopyrite and extensive malachite staining, and 2) being low grade and undeformed compared to the adjacent strongly deformed and granulite-facies lithologies. Field mapping defined locally chalcopyrite mineralized, gabbro and syenite layers. Further petrologic, geochronological, geochemical, and isotopic investigation has since demonstrated that these lithologies rather form locally mineralized metasomatic rocks.
The ‘felsic’ layers comprise sericitised orthoclase and albite. At least two generations of assemblages are observable in the ‘mafic’ layers: 1) quartz+albite+epidote+biotite+chlorite+sericite, and 2) an overprinting assemblage of hematite+ilmenite+chalcopyrite+apatite+monazite+zircon. The second assemblage contains abundant iron oxides that are intimately associated with blebs and stringers of chalcopyrite. Sulfur isotope measurements of chalcopyrite yield δ34S of +10‰, indicating sourcing of sulfur from an oxidised fluid. A‘felsic’ layer yielded metamict uraniferous (up to 8000 ppm) zircon. The zircon with the lowest uranium content (<2000 ppm) are used to constrain a 207Pb/206Pb age of ca. 1783 Ma. Regionally, this hydrothermal event follows peak high-T metamorphism by about 40 m.y., coinciding with the timing of metamorphic titantite and resetting of hornblende Ar-Ar ages. In the Churchill Province, this age corresponds to magmatism of the post-orogenic Nueltin Suite, which is sourced from lower crustal and mantle melts. Petrological observations, geochronology, sulfur isotopes and mineralisation style define a package of metasomatic rocks that is consistent with fluids that, in other areas, form IOCG-style mineralisation. This remote area of northwestern Greenland could be prospective for IOCG mineralisation.
Structural inheritance and basement-cover linkages within the Palaeoproterozoic Peräpohja Belt, Northern Finland
Pietari Skyttä1 and Simo Piippo2
1Dept. of Geography and Geology, University of Turku, Finland, 2Dept. of Geosciences and Geography, University of Helsinki, Finland
Correlation of regional-scale bedrock structure and stratigraphy within the Peräpohja Belt (PB), Northern Finland, shows that the evolution of the Palaeoproterozoic cover sequences have an intimate relationship with the underlying Archaean basement. By recognizing the basement control the heterogeneous nature of the contractional structural overprint within PB may be explained by one progressive south-verging thrusting event instead of several compressional events with highly contrasting palaeostress orientations. Compressional deformation was additionally controlled by strain localization into a basin-wide basal detachment zone accommodated by a mechanically weak unit. Hard linkages between the basement and the cover is shown by exposure of the deepest parts of the PB stratigraphy in the hanging walls of reverse faults, which consequently must continue down to the basement and represent reactivated basement structures. By contrast, soft linkages are shown by deviations from the typical thrust-and-fold belt fold patterns, such as abrupt fold terminations. The recognized major basement structures comprise fault-bound, approximately E-W trending horsts and an orthogonally cross-cutting central graben. The basement structures were generated under synchronous extension in both NE-SW and NW-SE orientations, which we attribute to development of a pull-apart basin with pre-existing basement weakness zones, at an overstepping zone between two major N-S deformation zones. This indicates that the N-S structures experienced lateral slip during the break-up of the Archaean continent at around 2.45 Ga, and the inferred setting explains why PB did never progress into a proper rift. Recognition of the major basement structures significantly improves targeting of mineral exploration in PB.
Linking orogenesis across the North-Atlantic; the Grenvillian and Sveconorwegian orogens, different in style, but geodynamically coupled
Trond Slagstad1, Nick M. W. Roberts2 and Evgeniy Kulakov3
1Geological Survey of Norway, Trondheim, Norway, 2NERC Isotope Geosciences Laboratory, Keyworth, UK, 3Centre for Earth Evolution and Dynamics, University of Oslo, Oslo, Norway
The Sveconorwegian orogeny in SW Fennoscandia comprised a series of geographically and tectonically discrete events between 1140 and 920 Ma (Slagstad et al., 2017). Thrusting and high-grade metamorphism at 1140–1080 Ma in central parts of the orogen were followed by long-lived arc magmatism and ultra-high-temperature metamorphism at 1070–920 Ma in the westernmost part of the orogen. In the eastern part of the orogen, crustal thickening and high-pressure metamorphism took place at 1050 in one domain and at 980 Ma in another. These discrete tectonothermal events are best explained as series of accretionary events of fragmented and attenuated crustal blocks of the SW Fennoscandian margin behind an evolving continental-margin arc. In contrast, the coeval Grenvillian orogeny is ascribed to long-lived collision with Amazonia. We argue that roughly coeval, but tectonically different events in the Sveconorwegian and Grenville orogens may be linked through the behaviour of the Amazonia plate. Subduction of Amazonian oceanic crust, and consequent slab pull, beneath the Sveconorwegian may have driven long-lived collision in the Grenville. Conversely, the development of a major orogenic plateau in the Grenville may have slowed convergence, thereby affecting the rate of oceanic subduction and thus orogenic evolution in the Sveconorwegian. Our model shows how contrasting but coeval orogenic behaviour can be linked through geodynamic coupling along and across tectonic plates, and cautions against comparing and correlating orogenic belts mainly based on geochronological data.
Slagstad, T., Roberts, N.M.W. & Kulakov, E. 2017: Linking orogenesis across a supercontinent; the Grenvillian and Sveconorwegian margins on Rodinia. Gondwana Research 44, 109-115.
Paleoproterozic volcanism of the Karrat Group
Erik Vest Sørensen1, Michelle Y DeWolf2 and Simon Mose Thaarup1
1Geological Survey of Denmark and Greenland, 2Mount Royal University
Exceptionally well exposed and preserved meta-volcanic rocks of the Paleoproterozoic Kangilleq formation (informal), Upper Karrat Group. are found throughout the Karrat region. This allows us to characterize the Kangilleq formation and the volcanic environment prior to- and during the early formational stages of the Nukavsak Formation that comprises the bulk of the Paleoproterozoic stratigraphy.
Through field-observations and 3D-mapping we document that the stratigraphy of the Kangilleq formation varies from one dominated by mafic tuff breccias with subordinate pillow and massive basalt lavas to one dominated by alternating, thin (1 – 10 m) pillow and massive basalt lava flows with lesser mafic volcaniclastic rocks. This suggest a dynamic subaqueous environment for the emplacement of the Kangilleq formation volcanic rocks, one in which active, synvolcanic faulting caused the formation of one or more basins restricting both the deposition of volcaniclastic debris, and the distribution of lava flows.
The meta-volcanic rocks of Kangilleq formation are greenschist facies consisting of amphibole and chlorite with variable proportions of carbonate, quartz, feldspar, titanite, apatite, Fe-oxides +- biotite. Immobile element lithogeochemistry characterize these rocks as alkali basalt, with minor tholeiitic basalt, that display significant light REE enrichment and high field-strength element concentrations suggestive of within-plate basalts. Volcanic lithofacies and structures, combined with lithogeochemistry suggest the Kangilleq formation erupted in a localized intracratonic rift, possibly associated with mantle plume activity.
Indicator minerals obtained by gold sluicing in Lapland, a clue to possible deposit types in the area
1University of Oulu
Lapland gold rush started 150 years ago, when visible gold was panned at Ivalojoki in September 1868. A wide spectrum of ore minerals has been obtained since then as byproduct of gold sluicing. Astonishingly, only few studies have been made to use this material as exploration tool in the area. The reason for this might be, that the claims are usually small and many times run by manpower. There are also societal and nature conservation reasons that possibly repulse explorers interest in the region. Also, the Lapland Granulite Belt (LGB) bedrock is quite monotonous. The indicator minerals may be grouped to PGMs and associated minerals as chromian magnetite; Fe-Ti-oxides together with some silicates; different types of corundum; tantalite, columbite, ferberite and related minerals; different gold nuggets sometimes together with pieces of parent rock; REE minerals, especially abundant monazite; and objects with possibly extraterrestrial origin.
A variety of PGMs has been found but the study has mostly targeted to new species rather than using the mineral compositions and assemblages to identify the parent deposit type(s). Isoferroplatinum is the most common of the PGMs. The inclusions indicate enrichment of Ru, Ir and Os which is usual to chromitite associated deposits. This is reinforced by the occurrence of chromian magnetite and chromite in the concentrate. Some mineral associations as kashinite-laurite-cooperite could indicate Alaskan-type intrusion parent.
Tantalite-columbite etc. and possibly monazite, could be derived from the marginal zone of the LGB, which is characterized by anomalous REE concentration.
Drone-borne mineral exploration in Central-West Greenland: New insights from the Paleoproterozoic Karrat group
Robert Zimmermann1, Rosa Diogo2 and Richard Gloaguen1
1Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute for Resource Technology, 2Geological Survey of Denmark and Greenland, Department of Petrology and Economic Geology
During the last two field seasons, two different types of Unmanned Aerial Systems were tested and evaluated for mineral mapping in central West Greenland. A fixed-wing system turned out to be more suitable as large areas can be covered faster and more efficiently.
In 2017, a sensefly ebeePlus fixed-wing system with a 4 channel multispectral Sequoia camera (4 channels in VIS-NIR with 1.2 MP and an additional 16 MP RGB camera) was deployed. Flight altitude was set to achieve 11cm ground sampling distance (GSD). Processing followed in-house routines using Structure-from-Motion photogrammetry to get Digital Surface Models (DSM) and geometrically corrected orthomosaics. In total 6.4 km2 of the VMS showings in Kangiusap Kuua at Svartenhuk were covered. The VMS showings are hosted in the Nûkavsak Formation of the Paleoproterozoic Karrat Group. In certain stratigraphic horizons within the meta-turbidites, meta-basalt with associated sulfide-rich sea-floor alteration occurs. Flight plans were set to cover both alteration and host rock. A validation dataset includes sampling and spectral characterisation of selected hand specimens.
Gossan and associated alteration of host rock is easily mappable by integrated morphological and spectral analysis as they form ridges with a distinct iron feature. Moreover, traces of fractures and faults, their spatial distribution and relation to the altered horizon are retrieved.
This further highlights the capability of drone-borne application for high-resolution reconnaissance mapping within short turn-around times. Intermediate insights from the project Multi-sensor drones for geological mapping (MULSEDRO) will facilitate the application of drones under unfavourable conditions.
New U-Pb geochronology for the Archean basement, Karrat Group cover sequence and later intrusions of the Ray Province, West Greenland.
1Geological Survey of Denmark and Greenland
The Ray Province of West Greenland comprises Archean orthogneisses and overlying Paleoproterozoic supracrustal rocks, the Karrat Group. The Karrat Group is traditionally divided into a lower Qeqertarssuaq Formation that is overlain by the Nukavsak Formation . The Archean basement and the Karrat Group are intruded by the Prøven Igneous Complex at 1.90-1.87 Ga and all were reworked to varying extents and metamorphic grades during the Paleoproterozoic [1,2,3].
New U-Pb data from the Archean orthogneisses yield ages of ca 3.1-3.0 Ga in the central Rae Province of West Greenland, which give way to younger ages of ca. 2.7 Ga to the north. This apparent progressive younging either reflects a different terrain to the north or northward growth of the craton.
The Qeqertarssuaq and Nukavsak formations yield distinctly different detritus patterns. The Qeqertarssuaq Formation is dominated by ages corresponding to the underlying Archean basement, whereas the Nukavsak Formation yields detritus pattern dominated by Palaeoproterozoic ages, typically with a significant mode at ca. 2.00-1.95 Ga .
Metamorphic monazite ages from the Nukavsak Formation reveal multiple metamorphic events, the earliest being coeval with the intrusion of the Prøven Igneous Complex at 1.90-1.87 Ga. A later metamorphic event ranges in age from ca. 1.83-1.80 Ga. Granitic intrusions of similar age are also present in the northern part of the Province. The young ages may be related to convergence and eventual collision of the Superior and Rae provinces.
 Henderson G and Pulvertaft TCR (1987). Descriptive text to 1:100 000 sheets Mârmorilik 71 V. 2 Syd, Nûgâtsiaq 71 V.2 Nord and Pangnertôq 72 V.2 Syd, 72 pp. Copenhagen: Grønlands Geologiske Undersøgelse.
 Thrane K et al. (2005.) Contrib. Min. petrol. 149: 541-555
 Sanborn-Barrie M, Thrane K, Wodicka N and Rayner N (2017). The Laurentia – West Greenland connection at 1.9 Ga: New insights from the Rinkian fold belt. Gondwana Research 51: 289-309.
4.2. Caledonian orogenic cycle: the Greenland-Svalbard-Scandinavia connection
Chemistry, age and tectonic evolution of the western Trondheim Nappe Complex in the Oppdal area, Central Norway
Bjørgunn H. Dalslåen1, Deta Gasser2, Tor Grenne3, Lars Eivind Augland1, Fernando Corfu1 and Arild Andresen1
1University of Oslo, 2Western Norway University of Applied Sciences, 3Geological Survey of Norway
The evolution of, and along-strike correlations within the Iapetus-derived western Trondheim Nappe Complex (TNC) have been debated for almost a century. The area close to Trondheim is best studied. It consists of the Løkken, Vassfjellet and Bymarka (LVB) ophiolitic fragments in the NW, and the Støren s.s. greenstones in the SE, which both are unconformably overlain by Mid-Ordovician to Silurian volcanic and sedimentary rocks of the Hovin and Horg successions. Until recently, the TNC in the Oppdal area to the south has been less studied, but metabasaltic and metasedimentary rocks have been correlated with the LVB/Støren, Hovin and Horg units, and a large-scale tectonic inversion has been inferred. Here we present new lithological and structural field observations, geochemical data, and detrital and magmatic zircon ages from the Oppdal area, and suggest a new tectonic model for this southern part of the TNC. Our results indicate that the area consists of four different units: (1) a ~480-472 Ma volcanic and sedimentary succession comprising submarine basaltic and minor rhyolitic flows, (2) a ~472-469 Ma volcanic unit dominated by intermediate to rhyolitic pyroclastic deposits, (3) a <450 Ma sedimentary and volcanic succession, and (4) an unconformably overlying <430 Ma sandstone and volcanic succession. The rocks in the area record the change from marginal basin or ocean floor spreading to subduction-related and continental volcanism. The study has consequences for along-strike correlations within the TNC and offers further insight to the complexity of the Iapetus Ocean closure preserved in this part of the Scandinavian Caledonides.
The Seve subduction system in the Scandes
David G. Gee1, Per-Gunnar Andreasson2, Håkan Austrheim3, Christoph Hieronymus1, Iwona Klonowska1, Jaroslaw Majka1 and Remi Vachon
1Uppsala University, Sweden, 2Lund University, Sweden, 3Oslo University, Norway
The Seve Nappe Complex (SNC) in the Scandinavian Caledonides provides some of the best exposed evidence on land for the character of a highly attenuated, magma-intruded, outer margin of a continent (including the continent-ocean transition zone). The last forty years of research has shown that this Baltoscandian margin of continent Baltica was initially rifted and locally intruded during the late Tonian and Cryogenian and subsequently extensively injected by mafic magma during break-up and separation of Baltica from Laurentia in the early Ediacaran at c 600Ma. Partial eclogitization of the SNC was recognized in the late 1960s and more recent studies of the metamorphic history have shown that Ordovican UHP metamorphism, with microdiamonds in garnets, is widespread in the host metasediments of the SNC over a vast area, apparently related to subduction beneath outboard volcanic arcs during closure of the Iapetus Ocean (now preserved in the overlying Köli Nappe Complex). It is suggested here that the increase in density related to eclogitization of the mafic magma-rich margin, promoted the subduction process. The SNC is dominated by upper crustal components – psammitic and pelitic metasediments, hosting the dolerites and gabbros; most of the underlying attenuated, magma-intruded, lower crustal “basement” was apparently eclogitized and lost into the mantle. Our preferred hypothesis is that most of this subducted basement was of Sveconorwegian age and included a substantial, granulite facies component.
The North Atlantic Caledonides – from Scandinavia and Greenland to Svalbard and the high Arctic
David G. Gee1 and Jaroslaw Majka1
1Uppsala University, Sweden
The type area of the Caledonides in the UK and Ireland is disrupted by major late- to post-orogenic, orogen-parallel faults. Western Scandinavia provides a more coherent section through the orogen and, together with complementary parts of northeastern Greenland, comprise an excellent laboratory for understanding this collisional orogen. The southernmost Scandes also suffer from similar problems to those in Scotland, with the Oslo rift disrupting the Caledonian foreland basin. Nevertheless, the whole 1700 km long Scandian mountain belt provides an amazingly coherent eastern flank of the Orogen, with well-preserved Ordovician and Silurian foreland basin successions, abundant evidence of Ordovician HP/UHP subduction of the outermost Baltoscandian margin during accretion of Iapetus-related terranes, and culminating Siluro-Devonian, Scandian underthrusting of Laurentia by Baltica, involving vast lateral displacement of allochthons. Northeastern Greenland, providing the complementary western flank of the Orogen, is also dominated by major thrust systems, all comprising parts of the Laurentian margin, emplaced at least 200 km westwards onto the platform.
In the deep hinterland of both the Scandinavian and Greenlandian Caledonides there is abundant evidence of late-orogenic, early Devonian axial extension, superimposed on the nappe pile; also, hinterland-vergent extension. Both these phenomena are prominent in the Svalbard Caledonides, where the rock units and tectonic history of deposition and thrusting is so similar to northeast Greenland; only in southwestern Spitsbergen, in the domain of the Cenozoic fold-and-thrust belt, is there a Caledonian terrane with affinities to northernmost Greenland, Pearya and the Timanides, providing key evidence for understanding Caledonian orogeny in the Arctic.
Remnants of the pre-Caledonian Baltica rifted margin preserved in a lithologically mixed unit between Bergen and Tynset, Scandinavian Caledonides, South and Central Norway
Johannes Jakob1, Joost M. van den Broek1 and Torgeir B. Andersen1
1The Centre for Earth Evolutions and Dynamics, Department of Geosciences, University of Oslo, Norway
Remnants of the magma-poor and magma-rich pre-Caledonian rifted margin of Baltica are preserved in the allochthons of the Scandinavian Caledonides. The transition from magma-poor to the magma-rich domain corresponds to the northern termination of the Jotun Nappe Complex. Solitary metaperidotite bodies abound in the magma-poor segment and the transition zone.
The metaperidotite bodies display a characteristic early flattening fabric. The flattening fabric is well-developed in the ultramafic bodies enclosed in the metasedimentary units structurally below the large crystalline basement nappes of Southern Norway including the Jotun, Lindås, and upper Bergsdalen nappe complexes, but can also be found in the metaperidotite lenses between Vågåmo and Tynset. Pre-Scandian contact relationships between those deformed metaperidotites and the metasediments have been obliterated during the Scandian Orogeny. However, well-recrystallised, pre-Scandian, extensional and sedimentary “ghost structures” within the metaperidotite bodies are locally preserved and can be found on favourably weathered surfaces.
The interpretation of the lithologically mixed unit between Bergen and Tynset is challenging, because, no geochronological evidence of the early rift stages from within the unit have yet been reported. Moreover, the unit may have been reworked between the latest Cambrian and early Mid-Ordovician (Jakob et al. 2017). However, an original lithostratigraphic succession of the ancient Baltica rifted margin may be preserved in a thrust nappe north of Lesja (Jakob et al. this volume) and may help to shed light on the origin and pre-Scandian history of the mixed unit between Bergen and Tynset.
Jakob, J., Alsaif, M., Corfu, F., & Andersen, T.B. 2017: Age and origin of thin discontinuous gneiss sheets in the distal domain of the magma-poor hyperextended pre-Caledonian margin of Baltica, southern Norway. Journal of the Geological Society 174, 557-571.
Jakob, J., Mohn, G., Closset, P., Andersen, T.B. this volume: The lithostratigraphy of a hyperextended domain in the magma-rich to magma-poor transition zone in the southern Pre-Caledonian LIP, Scandinavian Caledonides, Norway
Subduction and thrust emplacement of the Lower Seve Nappe in the Scandinavian Caledonides: Pressure-Temperature-Deformation constraints along the COSC-1 borehole in Åre
Pauline Jeanneret1, Johanna Holmberg1, Iwona Klonowska1, Jaroslaw Majka1, Henning Lorenz1, Bjarne S.G. Almqvist1, Anna Ladenberger2, Karolina Kośmińska3 and David G. Gee1
1Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden, 2Geological Survey of Sweden, Villavägen 18, 751 28 Uppsala, Sweden, 3Faculty of Geology, Geophysics and Environmental Protection, AGH – University of Science and Technol
The Scandinavian Caledonides comprise thrust sheets transported onto the Paleozoic platform successions of the Baltoscandian margin. These thrust sheets are subdivided into the Lower, Middle, Upper and Uppermost allochthons. The tectonostratigraphically highest part of the Middle Allochthon is the Seve Nappe Complex, the target for the Collisional Orogeny in the Scandinavian Caledonides (COSC-1) scientific drilling project. A continuous ~2.4 km long drill core through the metamorphic Lower Seve Nappe (LSN) has been retrieved. The Seve nappes are considered to have been still hot when emplaced and, consequently, the COSC-1 profile provides a unique opportunity to relate the pressure-temperature-deformation (P-T-D) history of this critical allochthon to the tectonic structures that formed during emplacement under mid-crustal condition. Moreover, this research will endeavor to establish a coherent model of mid-Palaeozoic (Scandian) mountain building. Our research focuses on deciphering the complete P-T-D evolution of the LSN based on a combination of established and innovative methodologies of P-T estimates (QuiG barometry and TitaniQ thermometry). The finite ductile strain pattern of the LSN results from the superposition of two major tectono-metamorphic events M1-D1 and M2-D2. M1-D1 features are interpreted as the consequence of the LSN subduction, and M2-D2 event corresponds to the final exhumation and thrusting of the LSN above the underlying allochthons.
A new tectonic model for the Seve Nappe Complex in Norrland, Sweden
Hans Jørgen Kjøll1, Torgeir Andersen1 and Loic Labrousse2
1Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Norway, 2Universite Pierre et Marie Curie, Paris, France
The Seve Nappe Complex (SNC) in Norrbotten, Sweden has classically been mapped as a series of nappes formed by the telescoping of the rifted margin of Baltica. Typically, the SNC is sub-divided into the lower, middle and upper nappe-series. The lower Seve generally constitutes slivers of basement and are overlain by meta-sedimentary and meta-igneous rocks representing both the middle and upper Seve nappes. The peak metamorphism varies considerably within the Seve from local eclogite facies to a more regional amphibolite facies and domains where original pre-Caledonian contact metamorphism related to dolerite intrusions are preserved. This has led to the norm of subdividing the SNC in different thrust nappes. We propose, however, a model where the Seve in Norrbotten represents a more continuous section through the magma-rich, attenuated margin of Baltica and that the metamorphic overprint, rather than representing decoupling and re-stacking, represent differential reactivity of individual lithologies with different reaction potential. High strain zones are present throughout Seve but the need for large internal thrusts juxtaposing older rocks on top of younger is not present internally in the Seve. This has dramatic consequences for, not only the understanding of the mountain building in the Caledonides, but may also open a new interest for the Seve as a place to study the deep processes of magma-rich passive margins, which are often lost in subduction and in general difficult to study in seismic lines due to masking of high velocity mafic intrusive and extrusive rocks.
UHP metamorphism in the Seve Nappe Complex in the Scandinavian Caledonides
Iwona Klonowska1, Jaroslaw Majka1 and Marian Janák2
1Uppsala University, Sweden, 2Slovak Academy of Sciences
Evidence for ultrahigh-pressure metamorphism (UHPM) and deep subduction of the Baltican outer margin in provided by diamond-bearing gneisses in three localities, on Tväråklumparna and Åreskutan in west-central Jämtland and near Saxnäs in southern Västerbotten. These UHP gneisses are found within the Middle Seve Nappe.
Microdiamonds are identified by microRaman spectroscopy and are found as inclusions in garnet as well as in zircon. The UHPM within this rocks is also confirmed by the phase equilibrium modelling. The peak pressure conditions of the Åreskutan gneiss are estimated to 4.1-4.2 GPa and 830-840ºC, whereas of the Marsfjället gneiss (Saxnäs) to ~3.6 GPa and 750ºC. Monazites from all three localities were chemically dated and they yielded Ordovician ages of migmatization (post-UHP stage). The dating for Åreskutan and Tväråklumparna gneisses shows that the diamond-bearing gneisses underwent partial melting between 445 and 435 Ma, whereas the post-UHPM in Marsfället gneiss is older (ca. 470Ma). The timing of the UHPM and diamond formation still remains to be resolved, however the recent studies provide important information about the tectonometamorphic evolution of the Seve Nappe Complex in the Swedish Caledonides.
A review of magmatic and metamorphic events recorded by crystalline basement of Southwestern Svalbard
Karolina Kośmińska1 and Jarosław Majka2
1AGH Univeristy of Science and Technology, Kraków, Poland, 2Uppsala University, Uppsala, Sweden
Svalbard’s Southwestern Basement Province (SBP) consists of numerous tectonic units juxtaposed by major strike-slip faults and thrust zones of early Paleozoic (perhaps also Neoproterozoic) to Cenozoic age. Felsic and mafic igneous rocks of various affinities are of Ectasian-Stenian, Tonian and Cryogenian-Ediacaran age. Sedimentary successions were deposited during Mesoproterozoic, Neoproterozoic and early Paleozoic. Majority of both igneous and metamorphic rocks have been affected by at least one metamorphic event. Metamorphic events were associated with the Torellian (c. 640 Ma), Caledonian and Ellesmerian (c. 360 Ma) orogenies. The grade of metmorphism varied from greenschist and amphibolite to blueschist and eclogite facies. The SBP is definitely a composite terrane assembled piece by piece during the aforementioned orogenic events as well as the Eurekan orogeny that shaped final tectonic framework observed nowadays. Comprehensive recognition of the geological complexity of the SBP is a key for understanding of whole Svalbard together with adjacent area.
This work was supported by the National Science Centre (Poland) through the “NAC” project no. 2015/17/B/ST10/03114.
Syn-collisional Scandian extension and magmatism on the Orkney Islands, Scotland
Anders Mattias Lundmark1, Lars Eivind Augland1 and Audun Dalene Bjerga1
1University of Oslo, Department of Geosciences, PO Box 1047 Blindern, 0316 Oslo, Norway
The Orkney Islands, NW Scotland, are dominated by sedimentary rocks of the Devonian Orcadian basin. The sparsely outcropping basement has received less attention than its cover, but is typically interpreted as Grampian or Scandian granites intruding Neoproterozoic Moine schist. New structural, TIMS age and geochemical data demonstrate that a grey and a pink granite intruded metasedimentary gneiss at 432 ± 0.5 Ma and 430 ± 1 Ma, respectively, to form the Orkney granite complex during the Scandian phase of the Caledonian orogeny. Inherited zircons in the granites give ages typical of Moine schist. Both granites display geochemical characteristics of the Scandian high Ba-Sr granite suite in the northern British Isles. Both the granites and the gneiss are cut be previously undocumented extensional mylonite zones, which are overprinted by similarly oriented extensional phyllonites, and in one case by similarly oriented extensional brittle faults. Three such deformation zones are observed: in the north, the Yesnaby shear zone display top-to-north extensional shear sense and in the south the Stromness and the Graemsay shear zones display top-to-south extensional shear sense. Successive emplacement of granite, pegmatite and aplite into the shear zones, cross-cutting some structures while being deformed by others, allow dating of the deformation. We propose that the ductile to brittle evolution of the shear zones reflect deformation during emplacement and cooling of the granite complex at a relatively shallow crustal depth. The N-S extension on Orkney during Scandian overall NW-SE directed collision likely reflects transcurrent faulting associated with the nearby Great Glen Fault.
Are Southwestern Svalbard and the Pearya Terrane counterparts?
Jarosław Majka1 and Karolina Kośmińska2
1Uppsala University, Uppsala, Sweden, 2AGH University of Science and Technology, Kraków, Poland
Svalbard’s Southwestern Basement Province (SBP) and the Pearya Terrane of northern Ellesmere Island are thought to be possible counterparts dismembered by long-distance strike-slip faults. Both terranes indeed share some similarities including Mesoproterozoic to Neoproterozoic igneous rocks and associated sedimentary successions locally intruded by younger mafic dykes as well as thick Neoproterozoic sedimentary successions that include horizons of diamictites of possible glacial origin. However, there are also dissimilarities between the two terranes. The SBP bears a record of the Torellian orogeny (c. 640 Ma), which is hitherto lacking in Pearya. Also, clearly subduction related Caledonian blueschist facies rocks are known only from the SBP. On the other hand the Pearya Terrane comprises a vestige of the Ordovician island arc, which could have been a part of the same subduction system. The Pearya Terrane also hosts Devonian intrusives which do not occur in the SBP. Despite these dissimilarities, it can be stated that both the SBP and the Pearya Terrane form a coherent system of tectonically juxtaposed sub-terranes, but much more comprehensive tectonic, petrological and geochronological research in both terranes is needed to decide whether they are true counterparts or not.
This work was supported by the National Science Centre (Poland) through the “NAC” project no. 2015/17/B/ST10/03114.
Integration of palaeomagnetic, isotopic and structural data to understand Svalbard Caledonian Terranes assemblage
Krzysztof Michalski1, Geoffrey Manby2, Krzysztof Nejbert3, Justyna Domańska Siuda3 and Mariusz Burzyński1
1Institute of Geophysics, Polish Academy of Sciences – Centre for Polar Studies KNOW, 2Natural History Museum, London, Great Britain, 3Department of Geology, University of Warsaw, Poland
During the PALMAG project (2012-2016) a total number of 828 palaeomagnetic specimens of metacarbonates and metabasites from 46 sites representing all three of Svalbard’s Caledonide Terranes were demagnetized in the Laboratory of Palaeomagnetism (Institute of Geophysics Polish Academy of Sciences) to recognize their NRM patterns. Simultaneously, 13 samples of mica schists and amphibolites from the Western and Eastern Terranes and mylonites from the Kongsfiord, Billefiord and Eolussletta Fault Zones were subjected to in situ laser ablation 40Ar/39Ar age determinations at the CEPSAR (The Open University, UK). Integration of palaeomagnetic and isotopic experiments accompanied by detailed structural observations lead to the following palaeogeographic and tectonic conclusions: (a) the results confirm the complete remagnetization of the investigated metamorphic complexes of Spitsbergen (West of Hinlopenstretet) during Caledonian tectono-genesis (Burzyński et al. 2017); they also confirm the amalgamation of Svalbard with Baltica in Late Silurian time (Michalski et al. 2012, 2014); (b) the results indicate a significant reorganization of the geometry of the sampled sectors of the West Spitsbergen basement by listric faulting related to the opening of the North Atlantic-Arctic Ocean Basins (Michalski et al. 2017); (c) In Nordaustlandet (East of Hinlopenstretet), relicts of a pre-Caledonian (primary?) magnetization appears to have survived; (d) analyses of the palaeolatitudes derived from the Murchisonfiord (Nordaustlandet) samples do not confirm the positioning of Eastern Svalbard near to Eastern Greenland in Neoproterozoic time, the results suggest, rather, that Eastern Svalbard constituted a separate microplate or could have been located near the N. Greenland/Pearya blocks. (manuscript in revision).
Burzyński M., Michalski K., Nejbert K., Domańska-Siuda J., Manby G. 2017 „High-resolution mineralogical and rock-magnetic study of ferromagnetic phases in metabasites from Oscar II Land, Western Spitsbergen – toward reliable model linking mineralogical and palaeomagnetic data.”- Geophysical Journal International: https://doi.org/10.1093/gji/ggx157
Harland, W.B. & Wright, N. 1979. Alternative hypothesis of the evolution of pre-Carboniferous evolution of Svalbard. Norsk Polarinstitutt Skrifter 167, 89–117.
Michalski, K., Lewandowski, M. & Manby, G.M. 2012. New palaeomagnetic, petrographic and 40Ar/39Ar data to test palaeogeographic reconstructions of Caledonide Svalbard. Cambridge University Press. Geological Magazine, 149, 696–721.
Michalski K., Nejbert K., Domańska-Siuda J., Manby, G. 2014. New palaeomagnetic data from metamorphosed carbonates of Western Spitsbergen, Oscar II Land. Polish Polar Research, v.35(4), p. 553-592.
Michalski, K., Manby, G., Nejbert, K., Domańska-Siuda, J. & Burzyński, M. 2017. Using palaeomagnetic and isotopic data to investigate late to post-Caledonian tectonothermal processes within the Western Terrane of Svalbard. Journal of the Geological Society, published online 23 February, 2017. doi: 10.1144/jgs2016-037
The Siljan Ring; A Lower Paleozoic petroleum system with kitchens in a Telychian rift basin, disrupted by meteor impact and rejuvenated by biological and Quaternary glacial processes
John Michelsen1, Ganjavar Khavari-Khorasani and Jollinus Salehy
1Gigawiz Ltd. Co
The oils in Siljan are thought to have formed by Frasnian impact heating of the Katian Fjäcka shale (Vlierboom et al., 1986). However, oil remains are not unique to the Siljan crater and occur throughout the subsurface of central Sweden (Sandström et al., 2006). By reexamining published seismics (Juhlin et al., 2012; Muhamad 2017), well descriptions (Lehnert et al., 2012; Muhamad et al., 2015) together with our own source rock observations, we demonstrate that the oil formed in kitchens in a Telychian rift basin prior to the impact. We see no evidence of NW-SE oriented Ordovician facies belts (Lehnert et al., 2013), and imaged major normal faults and the Mora structural high are Telychian rather than impact related. The major unconformity seen in the Mora 1 well (Lehnert et al., 2012) is the base of a 200m+ deep NNW-SSE oriented 600m+ wide incised valley, triggered by associated normal faulting. We suggest the rift basin formed due to extension over the flexural bend in front of the Caledonian orogeny. We also observe younger incised valleys, possibly related to the Sheinwoodian glacially triggered regression. We explain the post-Ordovician deformation as a combination of the Telychian extension, and the meteor impact. The gas produced in the Siljan Ring is biogenic and likely from biodegradation of residual oils (Rouchon et al., 2015). The gas seeping activity however, is likely due to the decompression (around 200 bar) from the withdrawal of the Weichselian ice cap and the associated subglacial basement water flow patterns.
Juhlin, C., Sturkell, E., Ebbestad, J.O.R., Lehnert, O., Hogstrom, A.E.S. & Meinhold, G. 2012. A new interpretation of the sedimentary cover in the western Siljan Ring area, central Sweden, based on seismic data. Tectonophysics 580, 88–99.
Lehnert, O. et al. 2012: New Ordovician–Silurian drill cores from the Siljan impact structure in central Sweden: an integral part of the Swedish Deep Drilling Program. GFF 134, 87–98.
Lehnert, O., Meinhold, G., Arslan, A., Berner, U., Calnar, M., Huff, W.D., Ebbestad, J.O., Joachimski, M.M., Juhlin, C. & Maletz, J. 2013: The Siljan impact structure of central Sweden: an unique window into the geologic history of western Baltoscandia. IODP/ICDP Kolloquium Freiberg, March 27, 2013.
Muhamad, H., Juhlin, C., Lehnert, O., Meinhold, G, Anderson, M., Juanatey, M.G. & Malehmir, A. 2015: Analysis of borehole geophysical data from the Mora area of the Siljan Ring impact structure, central Sweden. Journal of Applied Geophysics 115, 183–196.
Muhamad, H. 2017: Geophysical studies in the western part of the Siljan Ring impact crater. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1468. 69 pp. Uppsala: Acta Universitatis Upsaliensis.
Rouchon, V., Beaumont, V., Deville, E., Scélin, L. & Gidlund, A. 2015: Light methane and heavy oil from the Siljan Ring impact structure, Sweden – the fingerprints of a non-conventional petroleum system. Abstract, 27th International Meeting on Organic Geochemistry. Prague, September 13-18, 2015.
Sandström, B., Tullborg, E.-L., de Torres, T. & Ortiz, J.E. 2006: The occurrence and potential origin of asphaltite in bed-rock fractures, Forsmark, central Sweden. GFF 128, 233–242.
Vlierboom, F.W., Collini, B. & Zumberge, J.E. 1986: The occurrence of petroleum in sedimentary rocks of the meteor impact crater at Lake Siljan, Sweden. Organic Geochemistry 10, 153–161.
Timing of collision initiation and location of the orogenic suture in the Scandinavian Caledonides
Trond Slagstad1 and Christopher L. Kirkland2
1Geological Survey of Norway, Trondheim, Norway, 2Centre for Exploration Targeting–Curtin Node, Curtin University, Perth, Australia
The Scandinavian Caledonides formed during Baltica–Laurentia continent-continent collision in the late Silurian. We propose that initial contact along continental-margin promontories led to a drop in convergence rate, resulting in increased slab roll-back along parts of the margin still undergoing oceanic subduction. Slab roll-back caused extension of the overlying lithosphere with orogen-wide emplacement of mafic layered intrusions, ophiolite formation and bimodal magmatism at 438–434 Ma, in what immediately thereafter became the upper plate (Laurentia) in the Scandian collision. Initial collision at promontories may be challenging to identify due the metamorphic effects of full-fledged collision shortly thereafter. However, rapid deposition of sediments from eroding orogenic highs just prior to or during the 438–434 Ma period may represent a tell-tale sign of early collision. An example of such early Silurian deposits may be present on Magerøya, in the northernmost Scandianavian Caledonides (Corfu et al., 2006), where the sediments appear penecontemporaneous with mafic intrusive units likely formed in a back-arc setting. This model provides a tight constraint on the timing of collision initiation, and provides a framework by which some tectonic units comprising the Scandinavian Caledonides can be assigned a Baltican or more exotic heritage, where other methods, such as detrital zircon (DZ) chronology cannot, as proved by DZ statistical similarity right across the entire North Atlantic region (e.g., Slagstad & Kirkland, in press). Tracking the suture through the intrusive model highlights that many units conventionally ascribed a Baltican heritage are in fact much more far travelled.
Corfu, F., Torsvik, T.H., Andersen, T.B., Ashwal, L.D., Ramsay, D.M. & Roberts, R.J. 2006: Early Silurian mafic-ultramafic and granitic plutonism in contemporaneous flysch, Magerøy, northern Norway: U-Pb ages and regional significance. Journal of the Geological Society of London 163, 291-301.
Slagstad, T. & Kirkland, C.L. in press: The detrital-zircon fingerprint of the Scandinavian Caledonides: a non-unique answer to tectonstratigraphic position. Lithosphere.
The age of metagabbro from the Bangenhuk unit, Atomfjella Complex, Ny-Friesland, Svalbard
Jakub BAZARNIK1, Jarosław MAJKA2, Jarosław MAJKA3, Karolina KOŚMIŃSKA3, William C. MCCLELLAND4, Karsten PIEPJOHN5, Zbigniew CZUPYT6 and Tomáš MIKUŠ7
1Polish Geological Institute – NRI, Carpathian Branch, Skrzatow 1, 31-560 Krakow, Poland, 2Department of Earth Sciences, Uppsala University, Villavägen 16, 752-36 Uppsala, Sweden, 3Faculty of Geology, Geophysics and Environmental Protection, AGH–UST, Krakow, Poland, 4Department of Earth and Environmental Sciences, University of Iowa, Iowa City, Iowa 52242, USA, 5Bundesanstalt fur Geowissenschaften und Rohstoffe, Geologie der Energierohstoffe, Hanover, Germany, 6Polish Geological Institute – NRI, Address 4, Rakowiecka Street, 00-975 Warszawa, Poland, 7Earth Science Institute, Slovak Academy of Sciences, Ďumbierska 1, 974 01 Banská Bystrica, Slovakia
The Bangenhuk unit is a part of the Atomfjella Complex and belongs to the Svalbard’s Eastern Basement Province. Whole Complex has been metamorphosed in amphibolite facies during the Caledonian Orogeny (Witt-Nilsson et al. 1998). The rocks of the Atomfjella Complex crop out in western Ny-Friesland and form north-south trending antiform, which includes metagranitic basement covered by younger metasediment (Gee & Tebenkov, 2004).
The Bangenhuk unit of the Nordbreen Nappe is composed mainly of granitic gneisses whose age was estimated to c. 1750 Ma (Johansson et al. 1995, Bazarnik et al. 2017). However, older (c. 2709 Ma) quartz-monzonite has also been found (Hellman et al. 2001). Both gneisses and metasedimentary covers are intruded by mafic dykes of unknown age.
A sample of metamorphosed gabbro was collected from the southern coast of Mosselbukta, near a small cottage on the Bangenhuken peninsula, during the CASE 18 Expedition in 2015. It forms a dyke cutting thorough gneisses and striking approximately north-south. The gabbro is composed mainly of plagioclase, pyroxene, amphibole and garnet with minor amount of apatite, ilmenite, quartz and zircon.
U-Pb zircon dating was performed in the Micro-Analyses Laboratory in Polish Geological Institute in Warszawa using SHRIMP IIe/MC. About 40 fragments of euhedral zircon grains with oscillatory zoning have been analyzed. The obtained result ca. 1382 Ma has not been recorded in the Ny Friesland area before. Similar ages were noticed in Zig-Zag Dal Formation in eastern North Greenland (Upton et al. 2005).
Acknowledgments: This research is supported by the NCN grant 2015/19/N/ST10/02646.
Bazarnik, J., McClelland, W.C., Majka, J., Kośmińska, K. & Piepjohn, K. 2017: Detrital zircon provenance from the Atomfjella Complex and Mosselhavøya Group, northern Ny Friesland, Svalbard. Geophysical Research Abstracts 19, 3860.
Gee, D.G. & Tebenkov, A.M. 2004: Svalbard: a fragment of the Laurentian margin. In: Gee, D.G. & Pease, V. (eds): The Neoproterozoic Timanide Orogen of Eastern Baltica. Geological Society of London, Memoir 30, 191-206.
Hellman, F.J., Gee, D.G. & Witt-Nilsson, P. 2001: Late Archean basement in the Bangenhuken Complex of the Nordbreen Nappe, western Ny-Friesland, Svalbard. Polar Research 20, 49-59.
Johansson, Å., Gee, D.G., Björklund, L. & Witt-Nilsson, P. 1995: Isotope studies of granitoids from the Bangen- huken Formation, Ny Friesland Caledonides, Svalbard . Geological Magazine 132, 303–320.
Upton, B. G. J., Rämö, O. T. , Heaman, L. M., Blichert-Toft, J., Kalsbeek, F., Barry, T. L. & Jepsen, H. F. 2005: The Mesoproterozoic Zig-Zag Dal basalts and associated intrusions of eastern North Greenland: mantle plume–lithosphere interaction. Contribution to Mineralogy and Petrology 149, 40–56.
Witt-Nilsson, P., Gee, D.G. & Hellman, F.J. 1998: Tectonostratigraphy of the Caledonian Atomfjella Antiform of northern Ny Friesland, Svalbard. Norsk Geologisk Tidskrift 78, 67-80.
Detrital zircon signatures of the metasedimentary rocks of the Lower Seve Nappe in the COSC-1 drillhole, Åre, Sweden.
Yuan Li1, David G. Gee2 and Anna Ladenberger3
1State Key Laboratory for Continental Tectonics and Dynamics, Chinese Academy of Geological Sciences,, 2Department of Earth Sciences, Uppsala University, Sweden., 3Geological Survey of Sweden
The ICDP- “Collisional Orogeny in the Scandinavian Caledonides” (COSC) drilling project, targeted the Lower Seve Nappe, located in the footwall of the microdiamond-bearing Åreskutan Nappe of the Seve Nappe Complex (SNC) in western Jämtland; it penetrated 2500m of mainly psammitic metasediments, amphibolites and a few felsic, usually pegmatitic intrusions. U-Pb dating by LA-ICPMS of zircons in these lithologies provides evidence of a mainly Mesoproterozoic provenance of the metasedimentary rocks and it also confirms evidence of mid Ordovician felsic magmatism (Li et al. 2014). The age of the mafic rocks is difficult to constrain because they have all been subject to a complex metamorphic history (Jeanerette et al, this volume). Over twenty samples of the psammitic schists and gneisses have been analysed. As in previous investigations of the SNC (Gee et al 2014) and underlying Särv Nappes (Be´eri-Schlevin et al 2011) in central Jämtland, and farther north near the border to Västerbotten (Kirkland et al 2011) and also southern Norrbotten (Gee et al 2015), the zircon populations are nearly all dominated by Sveconorwegian signatures; many also by a strong late Palaeoproterozoic component. At the base of the hole, there is a significant late Archean zircon population. Along with the data from the Kalak Nappe Complex correlatives of the SNC and Särv Nappes in northernmost Norway (Kirkland et al 2007), the new data emphasize the common character of the provenance of the sediments in all these nappes, derived from the outer margin of Baltica.
4.3. Evolution of the North Atlantic margin: from Mesozoic rifting to Cenozoic inversion
Deltaic growth-faults of the Triassic Barents Shelf; structural style and deformation mechanisms controlling basin configuration
Alvar Braathen1, Mark Mulrooney1, Aleksandra Smyrak-Sikora2, Beyene Haile1, Ingrid Anell1, Kei Ogata3, Harmon Maher4, Per Terje Osmundsen5 and Ivar Midtkandal1
1Department of Geosciences, University of Oslo, Norway, 2Department of Arctic Geology, UNIS, Norway, 3Vrije University, Amsterdam, Holland, 4University of Nebraska at Omaha, USA, 5Geological Survey of Norway
Deltas represent major sedimentary accumulation zones with distinct subaqueous, sigmoidal geometry and principal deposition concentrated near the top, which are inherently prone to instability that leads to mass wasting and/or structural collapse. We compare tectonic and collapse-related faults associated with delta progradation of the upper Triassic succession of Edgeøya (SE Svalbard), to collapse structures in a more “typical” Last Chance Delta (Utah). Common for both investigated delta systems is that faults have listric geometries instigated by linkage of variously oriented segments above well defined detachment zones. Hanging walls form rollover folds, locating accommodation in the half-grabens towards faults. Infill is characterized by wedge-shaped, sand prone bodies that attest to rapid slip increments on faults contemporaneous to mild erosion along the crests of fault blocks. In the footwall (underneath) of listric faults, mud pillows or triangle-zones are developed. Related smaller structures attest to a transition from hydroplastic shear to brittle, frictional flow deformation along with diagenesis and cementation.
Edgeøya half-grabens arrested high amounts of sand in the prodelta realm, whereas the Last Change delta records deposition mainly in the deltatop. The trigger and driving mechanism for delta collapse by faulting is the localized, differential loading of the sand bodies of channels/mouth bars and fault-controlled basins. Faults move material towards the free surface of the delta-front. Complementary, compaction of prodelta muds offers localized and gradual mechanical decoupling from overlying denser sand. Further, the compaction front below deltas can trigger faulting in the prodelta realm, with land-ward dipping faults facing the prograding delta-front.
The Mesozoic basin of Ramså in Northern Norway: Characteristics, Development and regional impact
Marco Brönner1, Tor Arne Johansen2, Børre Davidsen3, Håkon Rueslåtten3, Bent Ole Ruud2 and Tormod Henningsen4
1Geological survey of Norway, Trondheim; Department for Geoscience and Petroleum, NTNU, Trondheim, 2University of Bergen, Bergen, Norway, 3Geological survey of Norway, Trondheim, Norway, 4University of Tromsø, Tromsø, Norway
The Ramså Basin on Andøya, Northern Norway gives a unique insight into the Mesozoic sedimentary strata onshore the mainland of Norway. It experienced a great deal of attention since the 19th century and was studied geologically several times. However, extensive geophysical mapping was missing and the tectonic development of the basin itself is still disputed.
Moreover, the basin is part of the well developed strandflat of eastern Andøya where remains of deeply weathered basement around and underneath the sedimentary strata indicate a history of repeated uplift and erosion which makes it to a key location to understand the development of this remarkable landscape widely observed along the Norwegian coast. In a cooperation project of NGU and the University of Bergen we carried out extensive geophysical and geological profiling including seismic and potential field measurements to investigate the characteristics and settings of the Ramså Basin. Specimens were analyzed sedimentologically, petrologically/mineralogically and geochemically. Four new boreholes were core-drilled and are currently subject to further analyses.
This integrated study provides an enhanced understanding of the geometry and tectonic settings of the Ramså Basin as a set of a NE-SW oriented normal faulted half-graben, which developed in the latest stage of the opening of the Andfjorden Basin. Our results indicate weathering in a tropical to sub-tropical climate, and K/Ar dating reveals Late Triassic age. Two newly found Mesozoic sub-basins south of the Ramså Basin confirm repeated erosion and transgression phases with a burial depth of the sediments not exceeding more than 2 km.
Correlation of the Oligocene – Pliocene succession in Norway, Denmark & UK
Tor Eidvin1, Erik S. Rasmussen2, Fridtjof Riis1 and Karen Dybkjær2
1Norwegian Petroleum Directorate (NPD), P. O. Box 600, N-4003 Stavanger, Norway, 2Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350, Copenhagen K, Denmark.
The almost complete, mainly deltaic, upper Paleogene-Neogene succession from Jylland, Denmark was investigated for Sr-isotopes, micro-fossils, and palynology in order to make a robust stratigraphic framework for the North Sea area. The investigation shows that the Danish succession correlate readily with lithological units, in the Norwegian North Sea, the Norwegian Sea shelf and the East Shetland Platform. In particular, Bolboforma and dinocyst correlations show that the upper part of the Danish Gram Formation correlates with the base of the Molo Formation in it’s southern part, and that this part of the Molo Formation corresponds to the middle/upper part of the Kai Formation (Norwegian Sea shelf). The new robust correlation between the North Sea and North Atlantic realm is fundamental in the understanding the palaeogeography during the late Paleogene and Neogene. For instance, The Bolboforma assemblages have their origin in the Norwegian Sea and therefore, due to the presence in the Danish area, confirm that it was an open strait in the northern North Sea (the only seaway passage into the North Sea Basin during the Miocene). The glauconitic Utsira Formation (approximately 5.7-5 Ma), in the threshold area close to the opening to the Norwegian Sea, overlie erosional unconformities comprising 21 and 13 my. We believe that this unconformity was partly related to the activity of strong currents in the narrow strait between Norway and the Shetland platform and partly related to the Messinian glacio-eustatic level drop.
Late Cretaceous basin inversion in the Kattegat – Skagerrak segment, Sorgenfrei – Tornquist Zone, Denmark, and Mesozoic – Cenozoic crustal tectonics of the eastern North Sea Basin
1Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark.
The Sorgenfrei – Tornquist Zone is a NW-SE trending, 50-100 km wide fault zone that cut off the East North Sea Block (ENSB), i.e. the Mesozoic basement of the Eastern North Sea Basin, from the Baltica Palaeozoic platform. The break was established in the Triassic, where the ENSB was established as the hangingwall block in the Kattegat area; by contrast, the Baltica platform develloped as the hangingwall block in the Fjerritslev halfgraben to the northwest (1).
In the Kattegat area, the Triassic faulting established a staircase fault block trajectory with downfaulting towards the southwest into the Danish Basin. In the Jurassic – Early Cretaceous, the Kattegat segment changed into an asymmetric, northeast dipping graben, the Kattegat Graben. In the Late Cretaceous, maximum subsidence returned to the southwest into the Danish Basin, while the Kattegat Graben was inverted during backward tilt of the graben block.
The ENSB formed the northeast flank of the Central North Sea Dome (2). The Jurassic – Cenozoic structural evolution of the ENSB was governed by the rise and fall of the Central Graben rift dome: 1) synrift rise in the Jurassic – Early Cretaceous, 2) Late Cretaceous transition phase with collapse of the Central Graben rift, 3) Cenozoic postrift subsidence (3). A model of the Mesozoic crustal tectonics associated with the ENSB illustrates the interrelationship between the evolution of the Kattegat – Skagerrak segment and the Central Graben Dome across the eastern North Sea Basin (4).
(1) Vejbæk, O.V. 1997: Dybe strukturer i danske sedimentære bassiner.
Geologisk Tidsskrift 4, 1-31.
(2) Ziegler, P.A. 1990: Geologcal Atlas of Western and Central Europe, Shell Internationale Petroleum Maatschappij B.V.
(3) Graversen, O. 2006: The Jurassic-Cretaceous North Sea Rift Dome and associated basin evolution. American Association of Petroleum Geologists, Search and Discovery, article 30040.
(4) Graversen, O. 2002: A structural transect between the central North Sea
Dome and the South Swedish Dome: middle Jurassic–Quaternary uplift–
subdidence reversal and exhumation across the eastern North Sea Basin.
Geological Society, London, Special Publications 196, 67-83.
Mesozoic basin inversion governed by crustal extension in the Bornholm area, Sorgenfrei-Tornquist Zone, Denmark
1Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark
Basin inversion describes the deformation of asymmetric grabens characterized by folding and thrusting, i.e. horizontal shortening, associated with uplift of the sedimentary graben fill above regional (1). The compressive stress field has been interpreted in a plate tectonic concept as a result of continent-continent collision that established a compressive stress field in the orogenic foreland (2, 3).
However, structural analysis of basin inversion in the Sorgenfrei – Tornquist Zone illustrates, that basin inversion was the result of superposition of asymmetric extensional fault basins dipping in opposite directions. The evolution of the graben basins, took place during successive extensional tectonic regimes separated by stillstand intervals. During subsidence of the superposed, extensional basin, the primary basin was tilted backward, and the basin was inverted during local compression between the primary footwall blocks.
The Mesozoic fault block pattern of the Bornholm area illustrates, that the NW-SE trending Sorgenfrei – Tornquist Zone was extended in two directions: The main extension was in a NE-SW direction across the strike of the fault zone, and a secondary NW-SE extension along the fault zone trend.
Based on the changing graben activity, the Mesozoic has been divided into Triassic, Jurassic – Early Cretaceous and Late Cretaceous extensional tectonic regimes. Graben subsidence started in the Triassic, and basin inversion was active in the Jurassic – Early Cretaceous and again in the Late Cretaceous (4, 5). The tectonic regimes were separated by turnover intervals characterized by only minor tectonic activity in the late Late Triassic and the early Late Cretaceous.
(1) Ziegler, P.A. 1987: Compressional intra-plate deformations in the Alpine foreland – an introduction. Tectonophysics 137, 1-5.
(2) Ziegler, P.A. 1987: Late Cretaceous and Cenozoic intra-plate compressional deformations in the Alpine foreland – a geodynamic model. Tectonophysics 137, 389-420.
(3) Kley, J. & Voigt, T. 2008: Late Cretaceous intraplate thrusting in central Europe: Effect of Africa-Iberia-Europe convergence, not Alpine collision. Geology 36, 839-842.
(4) Graversen, O. 2004: Upper Triassic–Lower Cretaceous seismic sequence stratigraphy and basin tectonics at Bornholm, Denmark, Tornquist Zone, NW Europe. Marine and Petroleum Geology 21, 579–612.
(5) Graversen, O. 2004: Upper Triassic – Cretaceous stratigraphy and structural inversion offshore SW Bornholm, Tornquist Zone, Denmark. Bulletin of the Geological Society of Denmark 51, 111–136.
Evidence of post-breakup tectonism on the Northeast Greenland shelf: Implications for “passive” margin conditions
Thomas Guldborg Petersen1
1Technical University of Denmark, DTU
The break-up between the Eurasian and North American plates during the Paleogene is well constrained by geophysical data. The structural history of Northeast Greenland following the breakup is on the other hand still very much an area of discussion. Here, analysis of seismic data offshore Northeast Greenland constrains the timing of the post-breakup tectonic events by correlation with the well-dated magmatic intrusions in the region and their associated thermal uplift and venting of gasses. Previous studies have mapped large-scale faulting along the western margin of the Thetys Basin where extensional faulting with an offset exceeding 1s TWT on the seismic profiles is observed. This is often associated with dramatic failure of the uplifted footwall where vast quantities of sediment slid into the Thetys Basin, apparently instantly, which suggests relatively fast propagation of the fault system. The time of breakup is constrained in the seismic data by magmatic intrusions dated to peak in the earliest Eocene. Both a southwards deepening erosional incision, as well as several vents associated with the de-gassing of intruded magma coincides with the continental breakup. This seismic marker is clearly truncated by the failure of the footwall as well as offset by the fault, which shows that the faulting occurred in post-breakup times, during a tectonic phase where no faulting on the “passive” margin is expected. Significant progradation associated with tilting and erosion superseded the observed faulting. This indicates that active tectonism may explain the exhumation and progradation observed on the Northeast Greenland margin during the Neogene.
Petersen, T. G., Hamann, N. E. and Stemmerik, L. 2015: Tectono-sedimentary evolution of the Paleogene succession offshore Northeast Greenland, Marine and Petroleum Geology 67, 481–497.
Reynolds, P. et al. 2017: Hydrothermal vent complexes offshore Northeast Greenland: A potential role in driving the PETM, Earth and Planetary Science Letters, 467, 72–78.
The late Cenozoic evolution of the mid Norwegian Margin
Helge Løseth1 and Eilert Hilde1
1Statoil ASA, R&D Trodnehim
Even though North Atlantic post break-up sediments are well recorded on the structural rather simple mid Norwegian passive margin, the unconstrained ages and uncertain paleo-geographic reconstructions has led to debate. The aim of this paper is to constrain the late Cenozoic geological evolution with focus on vertical movements of the inner margin and positions of coast-lines. The database consists of regional 2D and 3D seismic and well data.
Prior to the Miocene compression phase, Eocene to lower Miocene coastlines were located landward of the subcrop with an unresolved eastward extent. The mid to late Miocene compression phase, which formed inversion structures more than 1000m high and 300km long, also caused dramatic shifts in base levels along the inner passive margin. The base level fell 100’s of meter at onset of compression and the coastline shifted ocean-ward. The Mid Miocene Unconformity developed and the syn-tectonic Kai Formation was deposited. Upon termination of the compression phase the base level rose in the order of 500m. Sediments from the following transgression (lower Molo Formation) is documented for the first time. The younger coast-parallel 600km long upper Molo Formation shelf delta is overlain by the Quaternary glacio-marine Naust Formation. The inner shelf was tilted 0.5° westward during the glacial period due to isotatic adjustments from onshore erosion and offshore deposition.
The observed vertical base level fall and subsequent rise of the inner passive margin occurred with the onset and termination of the compression phase. Similar shifts may occur along any passive margin.
Palaeostress analysis and hydrocarbon leakage potential of disparate fault sets within the Swaen Graben
Nathalia Mattos1, Kamaldeen Omosanya2, Ståle Johansen3 and Tiago Alves1
13D Seismic Lab, School of Earth and Ocean Sciences, Cardiff University, 2Department of Geoscience and Petroleum, Norwegian University of Science and Technology, 3Geoscience and Petroleum, Norwegian University of Science and Technology
The Swaen Graben represents one of the Cretaceous structural elements of the SW Barents Sea whose growth and development remains poorly described in the literature. Majority of the previous works undertaken in the study area proposed a close connection between the Swaen Graben and the Eastern Loppa High with the likelihood of a strike-slip tectonics being the dominant process for fault growth on the western section of the graben. In this work, we assessed the palaeostress and slip tendencies of five fault types in the Swaen Graben. These faults were selected based on the assumption that they are strike-slip faults, flower structures, riedel shears, isolated-erosionally decoupled faults, and small-scale transfer faults. The principal palaeostress tensor associated to the faults, was determined based on the relationship between the slip tendency values and the measured displacement. Our model shows a sub-vertically oriented σ1 plunging 76.9º along a N246.4º azimuth for all the five fault types. The orientations of σ2 and σ3 are sub-horizontal. Slip tendency values for the faults varies from 0 to 1. Most of the Type 1 faults show slip tendency values 0 to 0.67. Type 3 and 5 faults have the highest slip tendency values. Hydrocarbon leakage factor ranges from 0.16 to 1 and is highest within the Type 3 and 5 faults. We show that these faults are extensional with the Type 5 faults acting as transfer faults connecting two disparate fault systems. The studied faults are analogous to modern day examples in the East African Rift Systems.
Influence of late Cenozoic erosion and deposition on temperature distribution beneath the north-eastern part of the Mid-Norwegian continental margin (the Lofoten-Vesterålen area)
Yuriy Maystrenko1, Laurent Gernigon1, Odleiv Olesen1, Dag Ottesen1 and Leif Rise1
1Geological Survey of Norway, Trondheim, Norway
A 3D thermal pattern beneath the north-eastern part of the Mid-Norwegian continental margin (the Lofoten-Vesterålen area) and adjacent areas of the continent has been investigated to understand the thermal effect of relatively high erosional and depositional rates observed during the Pleistocene.
A lithosphere-scale 3D structural model of the Lofoten-Vesterålen area from Maystrenko et al. (2017) has been used as a realistic approximation of the geometries of the sedimentary infill, crystalline crust and lithospheric mantle during a 3D thermal modelling. The 3D thermal modelling has been performed by use of the commercial software package COMSOL Multiphysics. The Earth’s surface and sea floor have been taken as an upper thermal boundary condition with taking into account palaeoclimatic changes during the Cenozoic. The lithosphere-asthenosphere boundary has been used as a lower thermal boundary. The erosion and deposition have been also included in the 3D thermal calculations.
The modelled thermal influence of the late Cenozoic erosion within the Lofoten-Vesterålen margin segment is reflected by a positive thermal anomaly within the areas where sedimentary and/or crystalline rocks were eroded. A negative thermal effect has been modelled in the areas affected by deposition of sedimentary rocks. The erosion-induced, positive, temperature anomaly is up to +27 oC at depths of 17-22 km beneath the eastern part of the Vestfjorden Basin. Two deposition-induced, negative, temperature anomalies have minimal values of around -70 oC at 17-20 km depth and -48 oC at 12-14 km depth beneath the oceanic Lofoten Basin and the north-eastern part of the Vøring Basin, respectively.
Maystrenko, Y.P., Olesen, O., Gernigon, L., Gradmann, S., 2017. Deep structure of the Lofoten-Vesterålen segment of the Mid-Norwegian continental margin and adjacent areas derived from 3D density modeling. Journal of Geophysical Research: Solid Earth, 122 (2), 1402-1433, doi: 10.1002/2016JB013443.
Extensional detachments, breakaway complexes and supradetachment basins in rifted margin formation: examples from offshore Mid Norway
Per Terje Osmundsen1 and Gwenn Péron-Pinvidic2
1Geological Survey of Norway, 7491 Trondheim, Norway & Dept. of Geosciences, P.O. box 1047, Universit, 2Dept. of Geosciences, P.O. box 1047, University of Oslo, 0316 Oslo, Norway
The large-magnitude faults that control crustal thinning and excision at rifted margins combine into laterally persistent structural boundaries that separate margin domains of contrasting morphology and structure. We term them breakaway complexes. At the Norwegian rifted margin, the constituent faults operated on the crustal scale, cut large thicknesses of heterogeneously layered lithosphere and facilitated fundamental margin processes such as post-orogenic equilibration, deformation coupling and eventual excision or near excision of continental crust. Many of them can be classified as extensional detachment faults, and they performed different types of work on the lithosphere and occupy different locations in the margin architecture. The array of associated synrift basins thus record the changing state of the continental lithosphere as the crystalline crust was nearly or wholly excised in a series of major deformation stages. The association of synrift supradetachment basins with fundamental modes of crustal thinning explains the particular locations of distinct basin styles in the margin architecture and provides the basis for a broad classification. Supradetachment basins appear to dominate the population of synrift basins on the margin scale. They were draped by a basin that post-dated local block rotation but pre-dated breakup, and that was still strongly affected by a subsidence pattern that much reflected the earlier large-magnitude faulting.
The source area of the Miocene Ribe Group, Eastern North Sea basin: the control of climate and tectonism.
Erik S. Rasmussen1, Mette Olivarius1, Karen Dybkjær1, Torsten Utescher2 and Peter Japsen1
1Geological Survey of Denmark and Greenland (GEUS), esr [at] geus [dot] dk, 2Steinmann Institute, University of Bonn, Nußallee 8, 53115 Bonn and Senckenberg Research Institute,
The sediment provenance was investigated by comparing radiometric age dating of the sink area to the comprehensive data available from the source area. The basement in southern Norway and southwestern Sweden, and possibly its derived sediments, is the primary source of the Miocene sand. However, smaller age populations show that the rivers had a larger catchment area. Overall, it is the same type of sediment that was fed from source to sink during the early Miocene, but heavy mineral analyses show that the maturity of the sediment varies, presumably in response to changes in the erosion rate. The study of the source area encompasses investigations of clay minerals, flora, and fission track data, in order to unravel the climate and uplift history. The initial topography of the source area (Fennoscandian Shield) was relatively low, less than 500 m in the earliest early Miocene when a pronounced phase of uplift and erosion in this region began according to interpretation of apatite fission-track data. The elevation of the source area during the early Miocene is coincidence with a major reorganisation of sediment routing systems in the eastern North Sea region. This occurred during a period of climatic stability and thus most likely an indication of tectonic activity in the source area. An increased relief of the hinterland is revealed from steadily higher contents of mountain elements in the pollenflora and by the end of the early Miocene, at app. 15 Ma, the highest peaks in the source area likely exceeded 1500 m.
Miller, K.G., Fairbanks, R.G. and Mountain, G.S. 2987: Tertiary oxygen isotope synthesis, sea-level history, and continental margin erosion. Palaeoceanography, 2, 1-19.
Deep crustal structures in the northern North Sea rift: observations from new 3-D seismic reflection data
Thilo Wrona1, Haakon Fossen1, Robert L. Gawthorpe1, Jan Inge Faleide2 and Marit Stokke Bauck3
1Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway, 2Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway, 3CGG, P.O.Box 43 Lilleaker, 0216 Oslo, Norway
Pre-existing basement structures can affect the nucleation, growth and linkage of normal faults in rifts and rift systems. The northern North Sea rift developed on top of an extremely heterogeneous crust containing structures from the Caledonian orogeny to Devonian extension. Our understanding of these structures has long been limited by poor imaging of the basement with conventional 2-D seismic reflection data. New broadband 3-D seismic reflection data allow us to study the extent, geometry and orientation of these deep crustal structures in unprecedented detail. The data contain a wide range of frequencies (2.5-155 Hz) and provides high-resolution, three-dimensional images of deep crustal reflectors. The improved imaging allows us to map a high-amplitude lower crustal reflection package over an area of more than 4000 km2. The package varies in depth from 20 to 30 km with elevations coinciding with footwalls of major N-S trending normal faults.
Deep crustal reflectivity observed in the northern North Sea has been explained by eclogized continental crust using a combination of 2-D seismic, gravity and magnetic data. This study explores alternatives to this explanation. More precisely, we examine the role that igneous intrusions, Caledonian thrusts and Devonian extensional shear zones could have played in the generation of the observed reflection package. Moreover, we examine the timing and interaction between these structures and subsequent tectonic faults.
Pliocene Pockmarks in the eastern Danish Central Graben, North Sea – Formation and Significance
Kaziwa Mohammadi1 and Katrine J. Andresen2
In this study, we describe abundant Pliocene circular depressions from the Danish Central Graben, mapped using 3D-seismic data which are courtesy of Maersk Oil, Operator of DUC. We interpret the depressions as buried pockmarks formed due to focused fluid-venting to the seafloor during the Pliocene. The origin of the fluids and the significance of the fluid-venting are not fully understood. Our preliminary analyses show that the majority of the pockmarks occur on one distinct surface suggesting a very confined timing of formation. The distinct pockmarked surface is comprised within a westward prograding set of clinoforms suggesting that the pockmarks may have formed in response to sea-level changes and/or climatic fluctuations. The pockmarks furthermore occur spatially clustered in a large pockmark field, which could be controlled by lithology variations along the clinoforms. Alternatively, deeper structural elements vertically below the pockmark field such as the Coffee Soil Fault, which marks the eastern edge of the Danish Central Graben, could have focused migration of deep thermogenic fluids and controlled the spatial distribution of the pockmarks. Hence, our seismic observations point towards a combined control of pockmark formation from both deep structures and depositional environment. Our further analysis of the pockmarks will include borehole data and will focus on constraining the timing and the controlling factors in more detail. We will investigate the origin of the escaped fluids and the possible relations with regional events in the Late Neogene-Quaternary such as climatic fluctuations and maturation of thermogenic source rocks in the Central Graben.
SeisLab Aarhus, Department of Deparment of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C
Origin and sediment budget of an early Neogene – early Quaternary contourite drift system on the SW Barents Sea margin
Tom Arne Rydningen1, Gert Høgseth1, Amando Lasabuda2, Jan Sverre Laberg2 and Polina A. Safronova3
1Dep. of Geosciences, University of Tromsø, 2Dep. of Geosciences, University of Tromsø; Research Centre for Arctic Petroleum Exploration (ARCEx), 3ENGIE E&P Norge AS
Alongslope ocean currents distribute sediments across continental slopes surrounding ocean basins, making contourite drifts deposited from such currents important paleoceanographic archives. Furthermore, on high-latitude margins submarine failures often relate to contourites, as they may act as weak layers due to their lithological character and/or physical properties. Although identified several places along the Norwegian-Barents Sea-Svalbard margin, contourites are not described from the SW Barents Sea. Using 2D-seismic data, we here describe a contourite drift covering a substantial part (~20,000 km2) of the SW Barents Sea slope, located mainly beneath the Bear Island Trough Mouth Fan. From correlation to commercial well data, this mounded drift covers a time span from early Neogene to early Quaternary. This drift therefore likely started to form at the onset of alongslope flow similar to the present circulation following the opening of the Fram Strait gateway and the subsidence of the Scotland – Faroe – Iceland – Greenland ridge. It continued to accumulate sediments following the onset of the northern hemisphere glaciations in late Neogene until glacigenic deposits completely dominated this part of the slope. Parts of the drift has been remobilized, thus it has influenced on the stability of the continental slope, most likely because of stress exerted by up-flank accumulation of glacigenic sediments causing the drift deposits to fail. We will discuss the onset of drift growth and its implications for the evolution of the margin, and – for the first time, present sedimentation rates and sediment volume for a high-latitude contourite drift.
4.4. Vertical movements, changes in plate motion and mantle dynamics: observations and models in the north-east Atlantic domain
An undereexplored method for determination of paleotemperature and burial depth.
A number of methods are used to estimate palaeotemperatures. Fluid inclusions studies give a direct measure of the palaeo temperature. Other methods are based on changes in mineralogy, e.g. Quartz cementation at 70°C. Clay transformation from smectite to potassium rich illite happens in several stages with increasing temperatures. Fission track analysis is based on formation of damage trails formed by radioactive decay in apatite and subsequent annealing as a
function of temperature. Methods based on blocking temperatures are based on diffusion of a gas out of the crystal lattice at certain temperatures.
Other methods are based on the combined effect of temperature and the time of exposure to this temperature. One such method is a hitherto underdeveloped method based on the magnetisation of a sediment or rock. If the magnetic grain size is favourable, the rock may acquire and preserve a magnetisation which will be added to the already present magnetisation. If a rock changes position by folding at a certain point in time, this new magnetisation will have a different direction and may be easily defined. Knowing the temperature, the duration of the rock being in its present position may be calculated. Knowing the time period, the temperature may be calculated. In addition, the age of the component may be calculated from the palaeopole to which the magnetic component points. Examples were determination of burial depth (approx. 5km) during Carboniferous of a suevite from the Ritland impact crater, Norway, and determination of palaeotemperatures of sediments in the Barents Sea.
Beyer, C. 2012 .: Palaeomagnetic determination of palaeotemperature and burial of the impact
structure at Ritland. EAGE Geoinformatic konference in Kiev, extended abstract
Beyer, C. & Spassov, S.2012: Remagnetised rocks from two localities, Norway,
Contributions to Geophysics and Geodesy,special issue 2012, p10-12.
Beyer, C., Pia Buchholtz Hansen, Atle Mørk, 2014, Chronostratigraphy of the Triassic in the Nordkapp Basin. CB-Magneto Multiclient report.
Early postglacial rebound tectonics within the Tjörnes Fracture Zone, North-Iceland.
Bryndís Brandsdóttir1, Sigríður Magnúsdóttir1, Neal Driscoll2, Robert Detrick3 and Jeffrey Karson4
1Institute of Earth Science, University of Iceland, Reykjavik, Iceland, 2Scripps Institution of Oceanography, UC San Diego, USA, 3Incorporated Research Institutions for Seismology, Washington DC, USA, 4Syracuse University, Syracuse NY, USA
The multi-branched plate boundary across Iceland is made up of divergent and oblique rifts, and transform zones, characterized by complex tectonics. The Tjörnes Fracture Zone (TFZ) links the northern rift zone (NVZ) on land with the Kolbeinsey Ridge off shore. The TFZ lacks the clear topographic expression typical of oceanic fracture zones and consists of broad zone of deformation roughly 150 km wide (E-W) by 50-75 km long (N-S), involving a complex array of oblique-slip faults bounding (NS) rifts and right-lateral (WNW) strike-slip faults, active throughout Holocence. The magma-starved southern extension of the KR, the ~80 km NS and 15-20 EW Eyjafjarðaráll rift (ER), is made up of dominantly extensional faults merging southwards a system of right-lateral strike-slip faults with vertical displacement up to 15 m.within the Húsavík Flatey Fault Zone (HFFZ). A 500-700 m deep asymmetric rift, with 20-25 m vertical displacement on normal faults characterizes the northern ER whereas transform along the HFFZ has created a NW- striking pull-apart basin with frequent earthquake swarms. We present the tectonic framework of the ER and Skjálfandadjúp (SK) basins multibeam bathymetry, high-resolution seismic reflection data (Chirp) and seismicity. Both basins contain post-glacial sediments of variable thickness. Correlation of Chirp reflection data and tephrachronology from a sediment core within the SK basin reveal major rifting episodes between 10-12.1 kyrs BP activating both basins, followed by smaller-scale fault movements throughout Holocene. These vertical fault movements reflect increased tectonic activity during early postglacial time coinciding with isostatic rebound enhancing volcanism within Iceland.
The surface below ca 900 m altitude in southern Norway was probably buried by late Mesozoic sediments and re-exposed by Neogene uplift and erosion
1Geological Survey of Denmark and Greenland
Analysis of the ASTER DEM over southern Norway confirms that the landscape of southern Norway above an altitude of about 900 m consists of 3 sub-horizontal surfaces separated by steeper slopes and incised by deep glacial valleys (Lidmar-Bergstöm et al., 2000). The surface of the Pre-Cambrian basement rocks below 900 m in southwest and south Norway consists of a uniform rough slope dipping to sea-level or to the strandflat, also incised by deep glacial valleys. Field work shows that the landforms below 900 m asl and between the deep glacial erosion consist of “hilly relief” and “joint valleys” as interpreted onshore in southern Sweden where they were buried below Late Cretaceous limestone (Lidmar-Bergstöm, 1994). Similar structures observed on seismic sections offshore western Norway and south-west Sweden have been buried by Late Jurassic and Cretaceous rocks respectively. Hilly relief and joint valleys formed during warm wet climates during the Late Mesozoic by weathering of feldspars in fractures to produce kaolin. Subsequent erosion of the kaolin produces joint valleys where the fractures are aligned and hilly relief where there are intersecting sets of fractures. Burial and later erosion are required to preserve these landscapes. Norway south of Hardangervidda must therefore have been buried below Mesozoic sediments that have subsequently been removed. No kaolinitic weathering of the Pre-Cambrian rocks of Hardangervidda took place because they were covered during the Mesozoic by Caledonian metamorphic rocks.
Lidmar-Bergström, K., Ollier, C.D. & Sulebak, J. 2000: Landforms and uplift history of southern Norway. Global and Planetary Change 24, 211–231.
Lidmar-Bergström, K. 1995: Relief and saprolites through time on the Baltic Shield. Geomorphology 12, 45–61.
Burial and exhumation history of the Upper Jurassic sediments on Andøya, northern Norway based on AFTA and VR data
Peter Japsen1, Paul F. Green2, James A. Chalmers1 and Johan M. Bonow3
1GEUS, 2Geotrack International, 3Geovisiona
Outliers of Middle–Upper Jurassic sediments occur onshore and in the coastal zone of Norway near Bergen, Trondheim and in the Lofoten archipelago (Bøe et al. 2010). But only on the island of Andøya (Lofoten) do they crop out; here a coal-bearing Jurassic–Cretaceous succession of 900 m occurs in a small, partly fault-bounded area on the eastern part of the island. We have measured vitrinite reflectance (VR) on samples from Norminoil well B (courtesy of the Norwegian Petroleum Directorate) that penetrated the entire Jurassic sequence on Andøya (Petersen et al. 2013); the mean VR value is 0.48% for 6 samples from depths between 218 and 520 m. This value corresponds to a palaeotemperature of 78°C, and for any reasonable palaeogeothermal gradient this implies that a km-thick cover of Jurassic and younger sediments must have covered the Jurassic–Cretaceous sediments exposed on Andøya; e.g. around 2 km for 25°C/km and a palaeo-surface temperature of 20°C. New apatite fission-track analysis (AFTA) data from samples of Jurassic sediments and basement from the Lofoten region provide results that are consistent with the interpretation of the VR and provide information about when cooling (exhumation) from maximum palaeotemperatures (burial) began. Our results thus suggest that thermal subsidence following rift climax in the late Middle Jurassic (Hansen et al. 2012) led to burial of Lofoten and the adjacent region by a thickness of sedimentary cover equivalent to the altitude of the highest peaks in the present-day landscape.
Bøe, R., Fossen, H. & Smelror, M. 2010: Mesozoic sediments and structures onshore Norway and in the coastal zone. Norwegian Journal of Geology 450, 15-32.
Hansen, J.-A., Bergh, S.G. & Henningsen, T. 2012: Mesozoic rifting and basin evolution on the Lofoten and Vesterålen Margin, North-Norway; time constraints and regional implications. Norwegian Journal of Geology/Norsk Geologisk Forening 91.
Petersen, H.I., Overland, J.A., Solbakk, T., Bojesen-Koefoed, J.A. & Bjerager, M. 2013: Unusual resinite-rich coals found in northeastern Greenland and along the Norwegian coast: Petrographic and geochemical composition. International Journal of Coal Geology 109, 58-76.
Neotectonics in Norway
Odleiv Olesen1, John Dehls1, Sofie Gradmann1, Yuriy Maystrenko1, Lars Olsen1, Conrad Lindholm2, Ilma Janutyte2, Halfdan Kierulf3, Jan Michalek4, Lars Ottemöller4, Dag Ottesen1, Lei Rise1, Maria Ask5, Tom Rune Lauknes6 and Fridtjof Riis7
1Geological Survey of Norway, 2NORSAR, 3Norwegian Mapping Authority, 4University of Bergen, 5Luleå University of Technology, 6Norut, 7Norwegian Petroleum Directorate
We summarize results of the 2013-2017 NEONOR2 project (Neotectonics in Nordland – implications for petroleum exploration) and compare it to previous research projects (e.g. NEONOR project 1997-2000) and other recent relevant discoveries. The NEONOR2 project is a collaboration project between NGU, Kartverket, NORSAR, Norut, NPD and the universities in Bergen and Luleå. The project is sponsored by the Norwegian Research Council and ten petroleum companies. The project investigates neotectonic phenomena onshore and offshore through a multidisciplinary approach including geological, seismological and geodetic studies combined with rock mechanics, applied geophysics and numerical modeling.
Within this project, a 26 seismograph network monitored the seismicity within a 2.5 year period. More than 1000 earthquakes were registered and 123 focal mechanisms have been derived. An updated compilation of all geodetic stations in Norway and Fennoscandia were analyzed for regional and local present-day strain patterns. Numerical modelling of the present-day stress field evaluated the effect of ridge push, sediment loading/unloading, glacial isostasy and topography. The effect of the Pleistocene sediment redistribution on the subsurface temperature has also been modelled. The occurrence of earthquake swarms is to some degree correlating with high mountains located along the wide Nordland strandflat.
Two presumably postglacial faults (Stuoragurra F. and Nordmannvikdalen F.) have been subject to more detailed studies such as trenching, ground penetrating radar and resistivity profiling. The Stuoragurra F. in Finnmark and the Grønna F. in Nordland are seismically active faults in Norway. These results are entering an updated neotectonic map of Norway.
4.5. Open Session: Structural Geology and Tectonic
Coupling of the ductile and brittle structures of the bedrock in Hyvinkää, Southern Finland
Bence Balogh1, Eemi Ruuska1 and Pietari Skyttä1
1University of Turku, Department of Geography and Geology, FI-20014 Turun yliopisto
There is a general difficulty in understanding the attitudes of the inherently discontinuous fractures of the bedrock in contrast to the continuous ductile structures. This study aims at linking the ductile and brittle features and, consequently, getting a better control over the fracture occurrence and orientation within the poorly-exposed bedrock. This study relates to studying the relationship between the bedrock and the overlying glacifluvial aquifers of the First Salpausselkä formation in Hyvinkää, Southern Finland. The results provide input data for the ongoing implicit modelling, and bedrock DEM interpolation development in the future. Based on existing geological and geophysical data, and new mapping observations, three principal, structurally homogeneous domains were defined. Brittle and ductile data from two of the domains correlate with the E-W main branches and NE-SW splays of the regional-scale shear zone, whereas fracturing within the third domain is more irregular, controlled dominantly by a regional scale, upright fold and secondarily by N-S structural trends. On individual outcrops, mutually parallel fractures were assigned into fracture sets. The sets were then correlated with the regionally dominant fracture and foliation orientations, and reassigned into representative sets within the respective structural domains. Fracturing is dominantly of cubic type with the main fracture set (R1) orientation strongly controlled by the foliation. The second most abundant set (R2) tends to be approximately at a right angle to R1 and the third group (R3) consists of horizontal to sub-horizontal fractures. Deviations from this pattern are attributed to fracturing caused by non-coaxial deformation along shear zones.
Sand tectonics – sand mobility linked to faulting and the influence on depositional systems
Kristine Halvorsen1, Susanne Tveterås1, Alvar Braathen1, Ivar Midtkandal1 and Valentin Zuchuat1
1University of Oslo
Mobility of sand by fluidisation, so-called sand tectonics, can drive surface movements and implicity have a significant impact on sediment distribution and sand body geometries. Although similarities between sand- and salt tectonic-related structures exist, substantial differences in deformation style and geometries occur. We adress the understanding of sand tectonic processes. Three outcrops in the Upper Jurassic Entrada Sandstone and Curtis Formation in Utah (USA) have been used to characterise the structural and sedimentary response to the underlying mobilisation of sand. Key observations are assembled from mapping of sag-upwarp and fault geometries, as well as from logging and description of growth succession. The latter deposits attest to channelised sub- to inter-tidal depositional environments. Data show that mild sand mobilisation results in meter-scale gentle sag and upwarps (sand pillows). Increased sand mobility leads to progressively higher and steeper relief between upwarps and sags, which links to nucleation of faults and thereby development of small fault-bound grabens. During fault activity, growth sequences attest to repeated fault movement events, demonstrating the strong structural control on the basin fill. After graben formation, many of the faults in higher positions of the grabens are truncated and removed by erosion. Subsequent lenticular-shaped basin fill reflects a wider channelized depositional body than that of the grabens. However, the grabens seem important in locating these channels. The result from our analysis may provide important input applicable to both CO2 storage operations and the petroleum industry.
Brittle fault systems of deep geological nuclear waste repository at Olkiluoto, SW Finland
Nicklas Nordbäck1 and Jussi Mattila2
1Geological Survey of Finland, 2Posiva Oy
Olkiluoto Island has been selected as the site for deep geological repository for high-level nuclear waste. This study aims to improve the characterisation of the brittle structures intersecting the repository. The objective is to gain a better understanding of the structural evolution of the site, with the ultimate goal of enhancing the understanding of the reactivation potential of different fault systems and associated seismic hazard.
The structural complex of Olkiluoto is composed of ductile and brittle structural systems, which both have a long and complex history. The ductile systems comprise ductile structures, formed during several different phases of Paleoproterozoic ductile deformation. The ductile deformation has affected the bedrock properties, resulting in prominent anisotropy and manifested by ductile structures such as foliation, folding and ductile shear zones, which all form planes of weakness in the bedrock. These type of structures have also played an important role in the localisation and development, of the brittle structures in Olkiluoto. The brittle structural system is composed of brittle structures such as joints, veins, single plane faults and fault zones. The faults were in this study classified into fault systems, with each system being composed of fault zones with similar tectonic history and structural properties. The classification can be employed in the assessment of the reactivation potential of the faults at the site, as the faults in each fault system are considered to have similar properties and thus, a similar chance for reactivation in either current or future stress states.
Target-rock weakening mechanisms during peak-ring formation of the Chicxulub impact crater inferred from IODP-ICDP Expedition 364
Ulrich Riller1, Felix Schulte1, Michael Poelchau2, Auriol Rae3, Richard Grieve4, Joanna Morgan3, Naoma McCall5 and Sean Gulick5
1Institut für Geologie, Universität Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany, 2Universität Freiburg, Geologie, Albertstr. 23b, 79104 Freiburg, Germany, 3Department of Earth Science and Engineering, Imperial College London, UK, 4Earth Sciences Sector, Natural Resources Canada, Ottawa, Ontario, Canada, K14 0E4, 5Institute for Geophysics, University of Texas, Austin, TX, USA
The floors of large impact craters are largely flat and contain one or more morphological rings. The formation of the innermost ring, the so-called peak ring, and the causes of target rock weakening leading to the observed flat crater floors are not well understood. Constraining these mechanisms is the prime structural geological objective of Expedition 364 “Drilling the K-Pg Impact Crater”, using the Chicxulub crater, Mexico, as a terrestrial analogue for the formation of planetary impact basins. The target rocks of the crater are replete with cratering-induced, microscopic to mesoscopic deformation structures including: (1) pervasive grain-scale fractures, (2) centimeter-thick cataclasite zones, (3) striated shear faults, (4) crenulated mineral foliations, and (5) ductile band structures. Structural overprinting criteria point to a relative age for these structures. Specifically, cataclasite zones cut grain-scale fractures displaying jigsaw geometry and are consistently displaced by shear faults. Impact melt was emplaced in zones of dilation, often localized by shear faults. These observations indicate that pervasive fragmentation was respectively followed by localized cataclastic deformation, shear faulting, and emplacement of melt into dilation zones. This succession of deformation mechanisms is corroborated by the observation that melt bodies are devoid of shear faults. As melt bodies were viscous during formation of ductile band structures, these structures formed after the shear faults. Based on the overprinting relationships, we relate the deformation structures to cratering stages known from impact mechanics.
3D model of the lithotectonic units and regional deformation zones in the bedrock of Sweden
Phil Curtis1, Carl-Henric Wahlgren1, Stefan Bergman1, ldikó Antal Lundin1, Claes Mellqvist1, Stefan Luth1 and Sverker Olsson1
A three-dimensional model has been created representing the lithotectonic units and their bounding regional deformation zones in the bedrock of Sweden. The model, including a brief description and basis for modelling of each modelled deformation zone and lithotectonic unit, is a development of the existing lithotectonic subdivision included in the bedrock map of Sweden at the scale 1:1 million (Bergman et al. 2012). The aim is to visualize the interpretation of the overall geometrical relationships between the various lithotectonic units on a national scale and provide a basic framework and background for more detailed regional and local scale models. The aim is to link the model to general geological descriptive texts aimed at schools and other interested parties as well as scientific presentations.
East Greenland 72-74° N Inland to Coast Thermo-tectonic Evolution
Peter Klint Jensen1
1Peter Klint Jensen
East Greenland 72-74° N Inland to Coast Thermo-tectonic Evolution
Jensen, Peter K.1; Hansen, Kirsten2
1Strandparksvej 12, 1 MF, DK-2900 Hellerup, Denmark; klint [at] geologi [dot] com
Fission track analysis of eight samples from East Greenland yields information of the exhumation history. Modelling the thermal evolution of the samples indicates that essential elements of the recent landscape were established before 250 Ma. Thus, altitude variations of 2-3 km at that time are like present values. From before 350 Ma to before 200 Ma, starting form SW, deep valleys were incised into a plateau being more than 3 km above the present landscape. After about 200 Ma the exhumation rate of the overall area was moderated, however with an increase especially in the valleys after 50 Ma.
Our interpretation is based on a simulation of temperature history through time intervals derived from the track length distribution. We use signal analysis theory to enhance the resolution of the time-temperature information of the fission tracks. Statistical noise and biases such as track annealing anisotropy are taken care of. We calculate the thermal history backwards in time and analyse the results as erosion/burial depths, which leads to our interpretation of the gradual inland erosion.
All measurements are performed in transmitted light on prismatic faces, however, horizontal track lengths are measured without angle to the c-axis.
Key words: Fission tracks, thermochronology modelling, East Greenland.
Modelling the fracture characteristics of crystalline bedrock for the purposes of bedrock surface interpolations
Eemi Ruuska1, Antti Kallanranta2, Pietari Skyttä1 and Michael Hillier3
1Department of Geography and Geology, University of Turku, FI-20014 Turun yliopisto, 2Dept. Geosciences and Geography, University of Helsinki, PL-64 00014 Helsingin yliopisto, 3Geological Survey of Canada, Ottawa
The purpose of the study is to characterize the bedrock fracturing and its spatial variability which may be subsequently used in interpolating the digital elevation models (DEMs) of the glacially eroded bedrock surface. The work focusses at testing and developing the implicit modelling approach and tools, validating the results by using explicit models and compared to fracture networks defined with the Discrete Fracture Network modelling tool (DFN). The used implicit modelling approach, by contrast to the conventional explicit approach, allows generation of more objective, time-efficient and repeatable 3D-models.
This study is conducted in the Hyvinkää area, southern Finland, under an umbrella of a broader Salpausselkä project investigating the relationship between the bedrock structures and the overlying glacifluvial aquifers. The principal input data of this study are fractures, correlated with foliation data and regrouped into sets as determined within a parallel ongoing study.
As a central tool, a new functionality “Local Anisotropy Interpolator” of SURFE plug-in for GOCAD has been developed. With this tool, we are able to generate a grid with an interpolated fracture plane at each grid cell displaying the local variations within the anisotropy of the bedrock across the study area. The resulting anisotropy will provide improved control over the fracture orientations, and the results of the DFN models will provide constraints on the fracture densities. These together may be used to evaluate the existing DEMs of unexposed bedrock surfaces based on sparse data, and as input data in future development of the DEM interpolation tools.
Mechanical separation of crust from slabs subducted below the transition zone
Anders Vesterholt1, Thorsten Nagel1 and Kenni Dinesen Petersen1
1Department of Geoscience, Aarhus University
As oceanic crust subducts into the mantle, it eclogitizes and becomes negatively buoyant relative to the peridotitic upper mantle. However, experimental studies indicate that, at depths between 660 km to 800 km, below the mantle transition zone, MORB compositions are positively buoyant at certain conditions. This has raised the possibility that oceanic crust can become mechanically separated during subduction below the 660 km discontinuity. Several conceptual and simple physical models have been proposed for such crustal segregation. Here we present a 2D thermomechanical model that employs recent experimental constraints that indicate that majoritic garnet is relatively weak at transition zone conditions. We show that channel-like upward flow within oceanic crust can occur in the density-inversion window between 650 and 750 km depth. Depending on geometric and thermal boundary conditions, this flow is sufficient to cause runaway instabilities, episodic mechanical separation of crust from the downgoing slab and thus the formation of stable crustal patches at the lower-upper mantle boundary. Our results have far-reaching implications for our understanding of the compositional stratification of the mantle, its convective circulation and the seismic velocity structure near the mantle transition zone.