The post-Caledonian tectono-thermal evolution of Western Norway

En riftet kontinentalmargin viser ofte et karakteristisk landskap som domineres av høye og flate fjell som er separert fra en lavtliggende kyststripe av en tydelig skrent. Mye av vår nåværende forståelse av disse områdene er basert på omfattende seismiske studier og data fra borehull samlet inn fra havbunnen utenskjærs, hvor innsamlingen av data er motivert av kontinentalmargin potensiale som kilde til hydrokarboner. Kunnskapen innhentet på land, derimot, blir ofte begrenset av forløpende komplekse berggrunnstrukturer og mangel på overliggende sedimenter som ville gjort innsikten i tektonisk bevegelse lettere. For å få en god forståelse av en riftet kontinentalmargin må kunnskapen vår om den tektoniske og termiske utviklingen på land forbedres. Vest-Norge er et godt eksempel på en riftet kontinentalmargin. Her har dannelsen og utviklingen siden den Kaledonske fjellkjeden har vært en pågående debatt gjennom mange år. Målet med denne avhandlingen er å utvikle en integrert tektonisk og termisk modell for utviklingen av et feltområde som ligger i de nordlige deler av Vest-Norge. For å få til dette, kombineres detaljerte feltstudier av sprø deformasjonsstrukturer med ulike geokronologiske og termokronologiske metoder. Artikkel I fokuserer på utviklingen av sprø deformasjonsstrukturer gjennom tid og rom for det valgte studieområdet. Ved å kombinere fjernanalyser av lineamenter med et omfattende datasett som består av feltobservasjoner av sprekker og forkastninger, gir denne artikkelen ny innsikt i forståelsen av sprø deformasjon for regionen og hvordan denne deformasjonen er påvirket av forløpende duktile strukturer. I tillegg gjennomføres K-Ar datering av sleppemateriale fra seks ulike forkastninger. Studien påviser fire forskjellige spenningsfelt som dominerte i tiden etter den Kaledonske fjellkjeden: 1) NV-SØ kompresjon i silur som ble etterfulgt av NV-SØ ekstensjon i tidlig til midt devon. 2) Sen devon og tidlig karbon var karakterisert av et dominerende sidelengs spenningsfelt, hvor σ1 roteres fra N-S i den nordlige delen av studieområdet, til NØ-SV i den sørlige delen. 3) Et mindre utpreget spenningsfelt som viser Ø-V ekstensjon som trolig sammenfaller med riftfaser i perm-trias eller i sen jura. 4) K-Ar datering av sleppemateriale viser to perioder med økt forkastningsaktivitet i midtre (123-115 Ma) og sen (86-77 Ma) kritt under VNV-ØSØ transtensjon. Artikkel II beskriver resultater fra de første U-Pb dateringer gjennomført på sprekkefyllende kalsitt i Norge. Disse dateringene gir informasjon om subtile tektoniske hendelser som dekker både høye og lave temperaturer, som blant annet er for kalde til å dateres med K-Ar datering av sleppemateriale. I denne studien beskrives det fire regionale tektoniske hendelser ved å kombinere 15 U-Pb kalsittaldre med informasjon fra sprø strukturell deformasjon tilhørende sprekker og forkastninger, samt stabile isotop analyser: 1) Dalsfjord forkastningen, som er en dal av Nordfjord-Sogn skjærsonen, viser reaktivering i trias-jura og som relateres til riftepisoder utenskjærs. 2) Sprekker parallelle med Møre-Trøndelag forkastningskomplekset dateres til sen kritt (90-80 Ma) og kobles til strekking av litosfæren og normal reaktivering langs forkastningskomplekset. 3) Kalsitt fra sprekker som viser varierende orientering er datert til sen kritt – tidlig paleocen alder (70-60 Ma) og relateres til oppløft av en strukturell dom som følge av ankomst av den proto-Islandske manteldiapiren. 4) Kalsitter fra sprekker som viser NØ-SV strøk er datert til ulike aldere yngre enn 50 Ma. Disse alderne kobles til flere episoder av sprekke-utvidelse etter oppbruddfasen av Nord-Atlanteren, noe som indikerer en langvarig kenozoisk deformasjonshistorie. Artikkel III presenterer lav temperatur termokronologiske data fra et høydeprofil fra indre Nordfjord. Denne studien viser den første termiske modellen som inkluderer flere prøver av et høydeprofil fra regionen. Høyden på profilet er 1841 meter (fjellet Skåla) og inkluderer 12 prøver analysert med apatitt fisjonsspor datering (AFT) og 4 prøver analysert med apatitt (U-Th)/He datering. Prøvene viser økende alder med høyde, hvor AFT prøvene viser aldre fra 159 ± 11 Ma til 256 ± 21 Ma og apatitt (U-Th)/He prøvene viser aldre fra 80 ± 4 Ma til 277 ± 15 Ma. Ved å kombinere flere AFT og (U-Th)/He prøver sammen i en flerprøve termisk modell, begrenser vi modellen og reduserer datastøy sammenlignet med modeller som bare inkluderer en prøve. Når modellen testes for ulike termisk avkjølingshistorier, viser modellen en foretrukket utvikling med rask avkjøling fra den Kaledonske fjellkjeden til øvre nivåer i skorpen (~3 km dypt) i tidlig til midtre trias, etterfulgt av langsom og stødig avkjøling gjennom store deler av mesozoikum til sen kritt, hvor avkjølingen igjen øker til den når dagens temperaturer. Flerprøve-modellen tillater også avkjøling til overflatetemperaturer i sen jura om utviklingen etterfølges av oppvarming i kritt og begravelse av omtrent 1,5-3 km med sedimenter. Denne artikkelen understreker at for indre Nordfjord ble de høytliggende og flate fjellpartiene sannsynligvis dannet i kenozoikum og representerer ikke et mesozoisk peneplan. Artikkel IV presenterer et nytt regionalt datasett av lav temperatur termokronologiske data fra studieområdet. Prøver som ble samlet fra hele området resulterte i 29 AFT analyser og 45 apatitt (U-Th)/He analyser av enslige korn. Hverken AFT eller (U-Th)/He aldre viser en korrelasjon mellom alder og høydemeter over havet på prøvelokalitetene. AFT aldere varierer fra 323 ± 27 til 140 ± 4 Ma og (U-Th)/He aldere varierer fra 228 ± 12 til 57 ± 3 Ma. Regionalt sett viser prøver yngre aldre innerst i fjorder og langs Mørekysten, mens de eldre prøvene finnes i nærheten av Hornelen devonbasseng ved havnivå. Prøvene viser stedvis stor spredning i alder over korte avstander, noe som her relateres til sprang langs reaktiverte forkastninger ved Nordfjord-Sogn skjærsonen. Regionen viser en kompleks utvikling i tid og rom, hvor 1) regionen ved indre Nordfjord viser sakte avkjøling gjennom mesozoikum og økt avkjøling fra sen kritt-kenozoikum frem til i dag, som sammenfaller med funn fra artikkel III. 2) Regionen ved Sognefjorden viser liknende avkjølingstrend som indre Nordfjord, men med mindre ned-til-vest normal forkastningsreaktivering i trias/jura langs sprø forkastninger ved kysten som er en del av Nordfjord-Sogn skjærsonen. 3) Regionen rundt Hornelen viser store variasjoner i alder over korte avstander, som relateres til forkastningsaktivitet i sen jura-kritt langs forkastninger med Ø-V strøk. Termiske modeller viser at prøvene ble avkjølt til øvre skorpe (<8 km) fra sen karbon-perm og tillater avkjøling til overflatetemperaturer i sen Jura etterfulgt av oppvarming i kritt. Vi viser at lokale sedimentære bassenger muligens kan ha blitt dannet i hengblokken på disse forkastningsstrukturene i kritt. 4) Møreregionen nord for Nordfjord viser avkjøling til øvre skorpe (<8 km) i jura som kobles til heving av fotvegg under reaktivering i jura av Møre-Trøndelag forkastningskompleks under rifting utenskjærs. Denne studien viser at Vest-Norge har vært gjennom en kompleks tektonisk og termisk utvikling i tid og rom siden den Kaledoniske fjellkjeden for omtrent 400 millioner år siden. Ved å bruke nye tilgjengelige metoder innen termokronologi og geokronologi, og ved å kombinere disse med veletablerte metoder, konkluderer vi blant annet med å vise 1) fremtredende system av strøkforkastninger som ikke tidligere er blitt beskrevet, 2) flere subtile perioder med tektonisk aktivitet i kenozoikum, 3) en robust flerprøve termisk modell som danner et sterkt grunnlag for regionale termiske tolkninger, og 4) at avkjøling langs en riftet kontinentalmargin ikke er kontinuerlig og homogen, men varierer langs strøk og er kontrollert av langvarige forkastningssystem.The onshore areas of rifted margins are often characterized by high elevation and low-relief landscapes separated from a low laying coastal strip by a distinct escarpment. A lot of our current understanding from these areas is today based on extensive seismic studies and well data information from the offshore realm motivated by the margins high potential as a source for hydrocarbons. The knowledge gain from the onshore regions has often been hampered by the complex basement structural architecture and the often lack of overlaying sedimentary records. In order to fully understand the evolution of a rifted margin, however, our understanding of the tectonic and thermal evolution of onshore areas needs to be improved. The margin of Western Norway is one example of a rifted margin where its formation and development since the Caledonian orogeny has been a long lived debate. The aim of the thesis is to develop a integrated tectonic and thermal model for the evolution of the field area located in the northern part of Western Norway by combining detailed field work on brittle structures, with various geo- and thermochronological methods. Paper I of this thesis focuses on the brittle structural temporal and spatial evolution of the study region. By combining an extensive field dataset of fracture and fault information with remote sensing analysis and K-Ar fault gouge dating of six faults, the paper gives new insight into the brittle architecture of the region and how it is influenced by ductile precursor structures. Following the Caledonian orogeny, four major stress fields were resolved: 1) NW-SE Silurian compression was followed by Early to Mid-Devonian NW-SE extension. 2) The late Devonian to early Carboniferous was characterized by a dominant strike-slip stress field, with σ1 rotating from N-S to NE-SW from the northern to the southern study area. 3) A minor E-W extensional stress field was possibly related to the Permian-Triassic or the Late Jurassic offshore rift phases. 4) K-Ar fault gouge dating revealed two periods of fault activity in the mid (123-115 Ma) and the late (86-77 Ma) Cretaceous under a WNW-ESE transtensional stress field. Paper II provides the first ever U-Pb dating of fracture filling calcite from Norway. These data provide information about subtle tectonic events covering both high and low temperature domains, which generally are too cold to be dated by K-Ar fault gouge dating. Based on 15 U-Pb calcite ages, related brittle structural information of the fractures and faults, and stable isotope analysis, four regional tectonic events were deciphered: 1) A Triassic-Jurassic reactivation of the Dalsfjord fault, a fault strand of the Nordfjord-Sogn detachment zone, broadly relates to offshore rift episodes. 2) Late Cretaceous ages (90-80 Ma) of fractures parallel to the Møre-Trøndelag fault complex relate to lithospheric stretching and normal fault reactivation along the fault complex. 3) Late Cretaceous-early Paleocene ages (70-60 Ma) are detected on fractures and faults with various orientations and are related to a domal exhumation following the arrival of the proto-Icelandic mantle plume. 4) Ages younger than 50 Ma, all from fractures and faults with a NE-SW strike, are related to several episodes of fracture dilation during the post-breakup period, indicating a long-lived Cenozoic deformation history. Paper III presents low-temperature thermochronological data from an elevation transect located in the inner Nordfjord. Here, we show the first multi-sample thermal history model of an elevation transect from the region. The elevation transect reaches 1841 masl, includes 12 samples analysed by Apatite Fission Track (AFT) dating and 4 samples analysed by (U-Th)/He dating, and shows increasing ages with elevation; AFT samples yield ages from 159 ± 11 Ma to 256 ± 21 Ma and apatite (U-Th)/He samples yield ages from 80 ± 4 Ma to 277 ± 15 Ma. By combining the AFT and (U-Th)/He data into a multi-sample thermal history model, we increase the constraints on the model and reduce data noise compared to single-sample models. Testing the model for various thermal cooling histories, the model shows a preferred evolution with fast cooling following the Caledonian orogeny to upper crustal levels (~3 km depth) in the Early-Middle Triassic, slow and steady cooling throughout the Mesozoic until the Late Cretaceous, where the cooling again increases until present day surface temperatures. The multi-sample model also allows for cooling to surface temperatures in the Late Jurassic if followed by Cretaceous reheating and reburial by 1.5-3 km of sediments. This paper highlights that for the inner Nordfjord, at least, the high-elevation low-relief surfaces most likely formed during the Cenozoic and do not represent a simply uplifted Mesozoic peneplain. Paper IV provides a new regional dataset of low-temperature thermochronological data from the study area. Samples collected across the region resulted in 29 AFT analyses and 45 single grain apatite (U-Th)/He analyses. Neither the AFT nor the (U-Th)/He samples show a correlation of age and elevation. AFT ages vary from 323 ± 27 to 140 ± 4 Ma and the (U-Th)/He analysis vary from 228 ± 12 to 57 ± 3 Ma. Regionally, the ages are youngest in the inner fjords and along the onshore Møre margin, whereas the oldest ages are found close to the Hornelen Devonian basin at sea level. The ages show large offset over short distances, related to fault offset along reactivated fault strands of the Nordfjord-Sogn detachment zone. The region shows a complex spatial and temporal evolution, where 1) the inner Nordfjord subregion shows slow cooling throughout the Mesozoic and increased cooling by the Late Cretaceous-Cenozoic until present, corresponding to the findings from paper III. 2) The Sognefjord subregion shows a similar general cooling history as the inner Nordfjord, with minor offsets along brittle faults, such as along brittle fault strands of the Nordfjord-Sogn detachment zone, indicating down-to-the-west normal fault reactivation in the Triassic/Jurassic. 3) In the Hornelen basin subregion, large age variations over short distances are related to Late Jurassic-Cretaceous fault offset along steep E-W striking faults. The thermal models reveal that the samples cooled to the upper crust (<8 km) by the Carboniferous-Permian and allow for cooling to surface temperatures in the Late Jurassic followed by Cretaceous reheating. We suggest that local Cretaceous sedimentary basins could have formed in the hanging block of these fault structures. 4) The region north of the Nordfjord shows cooling to the upper crust (<8 km) during the Jurassic and we relate this to footwall uplift from fault reactivation of the Møre-Trøndelag fault complex during Jurassic rifting. This study shows that Western Norway has undergone a complex tectono-thermal spatial and temporal evolution since the Caledonian orogeny. In conclusion, by using newly available methods within thermochronology and geochronology, and combining them with established methods, we here 1) describe prominent strike-slip fault systems not been properly described earlier, 2) detect several pulses of tectonic activity in the Cenozoic, 3) produce robust multi-sample thermal models forming a strong basis for regional thermal interpretations, and 4) highlight that cooling along a rifted margin is not continuous and homogenous but vary along strike, controlled by long lived detachment and fault systems.Doktorgradsavhandlin

Norwegian demands on avalanche safety - legislation, quality policy and judicial practice

Avalanche Workshop, Davos 13-17 May 1990The Building and Planning Act and the Working Environment Act both have demands concerning avalanche safety. The legal demands concerning avalanche safety were first established in the Building Act of 1924. The act was put into force for the whole country in January 1966

Constitutionality of State Income Taxes

The constitutionality of state income taxation has been considered by several courts with the result that some have held state income tax laws constitutional and some have held them unconstitutional. The courts which have passed upon the question have been confined to a consideration of the provisions of the constitution of the particular state and have held that such a tax is in conflict with the constitutional limitations or that such a tax is permissible as not being prohibited by the constitution. The decision in each instance in which the income tax was held unconstitutional has been based upon the conclusion that an income tax is a property tax within the meaning of the term as used in the constitution under consideration. The Supreme Court of Washington has fallen in line with several jurisdictions in holding that such a tax is a property tax within the definition in our constitution that, \u27property\u27 as used herein shall mean and include everything, whether tangible or intangible, subject to ownership. If it is truly determined that a tax on net income is fundamentally a property tax there can be no quarrel with the conclusion that a graduated income tax is m violation of the uniformity clause and must therefore be held unconstitutional. A review of the cases holding a net income tax to be a property tax would seem to indicate that all courts which have so held have failed to take into full consideration the fundamental factors which determine the proper classification of any given tax. Such cases have also disregarded certain well recognized rules of constitutional construction in that limitations on the taxing power not expressly stated have been read into the constitution by an all inclusive definition given to the word property

A contribution to the prediction of slush avalanches

Symposium on Snow and Ice Processes at the Earth's Surface. Sapporo 1984Slush avalanches, primarily known from uninhabited arctic and mountainous regions, every year cause damage to man and property in Norway. Seeking objective criteria to identify their hazard zones, and methods for their prediction and control, the Norwegian Geotechnical In stitute (NGI) has started a research program on these topics. Thirty-four slush avalanches with known loca tions of crown surface have been investigated with regard to geomorphic and climatic characteristics. Starting zones, crown surfaces and tracks were classified according to geomorphic conditions important to avalanche release and motion. Weak cohesionless snowpacks of coarse grain s, and hard la yers or crusts of ice in snow cover or on the ground, are cr itica l conditions for slush avalanche release. Intense rain, falling on cohesionless new snow on these substrata, is the most striking feature of current weather sit uations. The main starting zones were drainage channels, sloping bogs, depressions and open fields. Channel-like, scar-like or bowl-like features appeared in the snow cover due to avalanche release. Three main types of release were identified: I) Sudden release from crown surface, 2) drainage of snow-emba nked , water-satu rated snowfields through narrow outlets and 3) rapid head ward growth from first point of release. En largements and confinements along Ihe avalanche tracks were caused by distinctly defined features in the tracks

Impact of rapid mass movement and drifting snow on the infrastructure and development of Longyearbyen, Svalbard

The thermal regime and hydrological conditions in arctic regions are a threat and a challenge to human activity. In the Longyearbyen area, Svalbard, snow avalanches, slushflows, debris flows , creep and drifting snow interfere with the location and design of construction works - buildings, roads, ditches, pipes, masts etc., and during winter and spring, popular skiing areas and routes for snowcats can in periods be hazardous. Svalbard Samfunnsdrift AIS has sought professional help from the Norwegian Geotechnical Institute, to evaluate risks and safety measures for existing housing and reduce operational problems caused by drifting snow. Future development will take place in areas which fulfill the safety requirements of the Norwegian Building and Planning Act. A review of problems and recommendations is presented. Limited time-series of relevant meteorological data from Longyearbyen, as weIl as sparse knowledge of the processes influencing mass stability in permafrost areas, have proved to complicate both risk analysis and accomplishment of mitigative measures. Better knowledge of local wind direction and speed are the key to improve the location and design of roads, production areas and buildings with regard to drifting snow. Research projects within these fields of arctic hydrology are proposed.publishedVersio

Slushflow hazard - where, why and when? 25 years of experience with slushflow consulting and research.

Slushflows — flowing mixtures of water and snow — are a major natural hazard in Norway. Knowledge gathered by the Norwegian Geotechnical Institute during 25 years of slushflow consulting and research is presented. The variation in regional occurrence is described and related to climatic premises and ground conditions. The principal ideas about slushflow release, down-slope propagation and run-out are outlined. They are closely related to the rate and duration of water supply, snowpack properties and geomorphic factors. Slushflow release is caused by basal shear failure aided by water pressure to cause loss of basal support and finally tensile failure through the snowpack. Our methods of hazard evaluation and acute hazard prediction and warning are summarized, including the estimation of water supply based on meteorological data. The results of a worldwide questionnaire on slushflows, literature studies and scientific contacts, indicate that slushflows occur in all countries having a seasonal snow cover and that the results of our studies in Norway have a general validity

Slushflow questionnaire

Questionnaires concerning slushflows were distributed globally. The purpose of the questionnaire was to determine the geographic distribution of slushflow activity as well as to collect information concerning most common nomenclature, release conditions, period of occurrence, type of terrain upon which they occur, the characteristics of starting zones, paths and run out zones, geomorphic activity, type of damage and hazard control

Prediction of slushflow hazard based on data from local meteorological stations.

Seeking objective criteria for slushflow prediction and warning, meteorological data has been recorded at two slushflow sites in Rana District, North Norway, during a 10 years period. The two starting zones were equipped with standard meteorological devices. In addition, the fluctuation of water level in snowpack was monitored by pressure transmitters. The measurements were performed automatically every ten minutes. Within a distance of 20 km from the slushflow sites there are one standard climatological station and two precipitation stations. One of the main topics of the research project is to evaluate the possibility of using neighbouring meteorological stations in the prediction of current slushflow hazard and slushflow releases. Correlation of in situ measurements with records from the local meteorological stations is the basic input to the evaluation. The analysis has documented that observations at the meteorological stations can be used as a base for predicting slushflow hazard in the Rana District. The temperature and humidity are well correlated in slushflow situations while the wind speed and precipitation measurements had to be adjusted by simple models taking into account topographic characteristics, distance and elevation differences. Generally, the result indicates that slushflow prediction might be based on observations at local meteorological stations if the necessary models for parameter transformation are established