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Mid-Norden Project

GEOPHYSICS SUB-PROJECT

Gravity and magnetic maps of Central Fennoscandia:
Norway, Sweden and Finland;

Combinations with Data and Maps of Northern Fennoscandia (Nordkalott Project)

 

 

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Introduction to Mid-Norden Project
by Gunnar Kautsky, (Project Leader)

Geophysics: Abstract, Introduction
Availability of Data and Maps, Location Map

 

Gravity
(Intro / Maps)

Magnetics
(Intro / Maps)

Seismic Maps
(Intro / Map)

Petrophysics
(Finland)

Digital Maps

References

 

Compiled by Tapio Ruotoistenmäki (GSF)

Mid-Norden Geophysics Sub-Group:

Tapio Ruotoistenmäki (sub-project leader; GSF), Sven Aaro (SGU), Seppo Elo (GSF), Jomar Gellein (NGU), Nils Gustavsson (GSF), Herbert Henkel (SGU), Kajsa Hult (SGU), Esa Kauniskangas (GSF), Leif Kero (SGU), Ola Kihle (NGU), Matti Lehtonen (GSF), Jouni Lerssi (GSF), Atle Sindre (NGU), Jan Skilbrei (NGU), Timo Tervo (GSF) and Leif Thorning (GEUS)


Geological Survey of Finland (GSF; Espoo, Finland)
Geological Survey of Denmark and Greenland (GEUS; Copenhagen, Denmark)
Geological Survey of Norway (NGU; Trondheim, Norway)
Geological Survey of Sweden (SGU; Uppsala, Sweden)

Contact persons:
Finland: Tapio.Ruotoistenmaki at gsf.fi
Norway: Jan.Skilbrei at ngu.no
Sweden: Sven.Aaro at sgu.se

Version 02.11.1998.

This is an Internet version of Mid-Norden Project products. More detailed data and maps are available from the Geological Surveys.

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Mid-Norden Project and its Products; Introduction
by Gunnar Kautsky, Project Leader

The MID-NORDEN PROJECT is a joint venture between the Geological Surveys of Finland, Norway, and Sweden aimed at compiling modern, regional geoscientific information in the central part of Finland, Norway and Sweden. The Geological Survey of Denmark has participated in the steering group of the project and in the geophysical work. The project has been sponsored by the Nordic Council of Ministers and covers an area in central Fennoscandia between latitudes 62o50'N and 65o50'N. Information has been compiled in numerical databases and in both cartographic and report form, and is available from the Geological Surveys of Finland, Norway and Sweden.

The MID-NORDEN PROJECT has been financed by governmental funds at the Geological Surveys in the three countries, and by support from the Nordic Council of Ministers. The project leader has been Gunnar Kautsky (Sweden) and the project has been steered by a group composed of the directors of the Nordic Geological Surveys, the project leader and one national coordinator for each country (Finland: Pekka Kallio, Norway: Rognvald Boyd. Sweden: Naz Ahmed Shaikh). Caj Kortman (Finland) was responsible for editorial work. A data group with members from each of the three countries has assisted in the compilation of topographic base data and in the digitization of the various products.

The geoscientific work has been organized in five subprojects:

·  Bedrock geology

·  Mineral deposits (metallic ores and industrial rocks and minerals)

·  Quaternary geology

·  Geophysics

·  Environmental geology

The results of the MID-NORDEN PROJECT will be presented as printed maps, published descriptions which accompany the bedrock and Quaternary geology maps, and digitized information on a CD-ROM. The products of the various subprojects are described briefly here:

·  Bedrock geology: One bedrock geological map and one metamorphic- structural-isotope age map, the latter including a complete list of radiometric age determinations. A published description to the maps.

·  Ore deposits and industrial minerals: One map of metallic ores and mineralizations and one map of industrial rocks and minerals. A short overview is presented in the description to the bedrock maps.

·  Quaternary geology: One map of Quaternary deposits and Quaternary stratigraphy, and one map of glacial geomorphology, paleohydrography and ice flow indicators. A published description to the maps.

·  Geophysics: One aeromagnetic anomaly map and one gravity anomaly map including general descriptions.

·  Environmental geology: A published volume with maps from a number of selected areas in each of the three countries, including descriptions.

The MlD-NORDEN PROJECT is a southerly continuation of the previously completed NORDKALOTT PROJECT. The data compiled in both of these projects cover approximately half of Fennoscandia and provide a comprehensive overview of a wide range of geoscientific disciplines in northern and central Fennoscandia. Together, these projects provide information on bedrock geology, structural geology, metamorphism, Quaternary geology, aeromagnetic and gravity anomalies, and occurrences of metallic ore deposits and industrial minerals The bedrock and geophysical maps of the Mid-Norden area cover not only areas on land but also most of the offshore areas along the Norwegian continental shelf as well as in the Gulf of Bothnia

1996-11-26/GK

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location map

Geophysical maps of Mid-Norden project;
Abstract, Introduction, Availability of data and maps, Location Map

ABSTRACT

During the years 1986 - 1996 the internordic Mid-Norden geophysics subgroup prepared geophysical gravity and magnetic data matrices and maps covering central Fennoscandia. The data matrices were further combined with the corresponding Nordkalott data covering northern Fennoscandia. The maps and their derivatives have been produced as paper versions, and as digital versions to be browsed by PC. The digital maps can further be combined with any vector or location data; e.g. ore showings, seismic profiles and fracture information. The advantage of the maps is that geophysical and corresponding lithological features can be continued across the national borders which is necessary when modelling the large tectonic processes that created the Fennoscandian crust. The understanding of bedrock evolution is further needed e.g. when predicting and modelling the location of ore showings and evolution of fracture zones around radioactive waste repositories.

INTRODUCTION

The Mid-Norden Project is a joint venture between the Geological Surveys of Finland, Norway and Sweden providing regional geoscientific information. The project is sponsored by the Nordic Council of Ministers. It covers an area in central Fennoscandia between latitudes 62°45'N and 66°N (see Location Map). The information has been compiled as both numerical databases and in map form available from the geological surveys.

Combining the results of the Mid-Norden Project with those of the previously published Nordkalott Project (e.g. Kautsky, 1986) offers a comprehensive overview of a wide range of geoscientific data from northern and central Fennoscandia. It includes information on bedrock, structural geology, Quaternary geology, magnetic and gravity anomalies and occurrences of ore deposits and industrial minerals. The bedrock and geophysical maps of the Mid-Norden area cover not only areas on land but also most of the offshore areas along the Norwegian continental shelf as well as parts of the Bothnian Bay. Both projects have involved valuable contributions from individual scientists at the Geological Survey of Denmark and Greenland.

Eight thematic maps at a scale of 1 : 1 000 000 covering the Mid-Norden area will be produced in 1996 - 1997, as well as a volume containing a series of environmental geology test cases and descriptions to the bedrock maps and the Quaternary geology maps.

Geophysics Sub-Project

The main goal of the Mid-Norden geophysics sub-project is to prepare gravity and magnetic data matrices and maps covering central Fennoscandia. The data used is the airborne magnetic data provided by the Geological Surveys of Finland, Norway and Sweden and gravity data provided by the Geological Surveys of Finland, Norway and Sweden, Finnish Geodetic Institute, Norwegian Mapping Authority and National Land Survey of Sweden. The maps have been published as paper maps (Ruotoistenmäki et al., 1996 a, b) showing anomalies in colours and the regional trends emphasized using hillshading. The maps also include general description of the data, statistics, index maps and national descriptions of data from Norway, Sweden and Finland separately given in English and 'national languages' (Norwegian, Swedish and Finnish).

Digital versions of the maps and their derivatives are available from the geological surveys. They can be used interactively with PC:s and include an information file system by which vectors and point symbols can be displayed on or extracted from the maps. The information files distributed by the authors contain deep seismic sounding profiles, regional fractures (vectors) and ore indications (symbols) of the Mid-Norden area. New information files can also be created separately by the user from any location (x,y) data.

The data matrices of Mid-Norden area (Ruotoistenmäki et al., 1996 a, b) and the previous Nordkalott project (Korhonen et al., 1986 a, b) have been combined to a common data base. In the following a summary will be given of the existing Mid-Norden geophysical data and maps and their combinations with Nordkalott data. We also give preliminary examples of the interpretation of the data.

Other geophysical information available from the geological surveys include regional and local scale gravity and magnetic maps (paper and digital maps) and grids, low-altitude gamma radiation and electromagnetic response data and maps, as well as ground profiles for various geophysical methods. The petrophysical databases for the Mid-Norden area contain information (mainly density, magnetic susceptibility, intensity of remanence and less often electrical conductivity) obtained from about 49 454 samples in Finland, 3 800 in Norway and 16 000 in Sweden.

The data and maps of the Mid-Norden and Nordkalott areas can be ordered from the geological surveys of Norway, Sweden and Finland:

• Geological Survey of Norway
Leiv Eirikssons vei 39, BOX 3006 - Lade, N-7002 Trondheim, Norway
• Geological Survey of Sweden
Box 670, S-75128 Uppsala, Sweden
• Geological Survey of Finland
P.O.Box 96, FIN-02151 Espoo, Finland
• Geological Survey of Denmark and Greenland
Thoravej 8, DK-2400 Copenhagen NV, Denmark
Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
(Return)

It must be emphasized that all data used for map production is not readily available outside the surveys. In such cases consulting for interpretation work and producing various special maps can be ordered from the surveys.

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More Info:
Caj Kortman
Information Manager
Geological Survey of Finland
FIN-02150 ESPOO
FINLAND

Phone: +358 - 205 50 2236, fax: +358 - 205 50 16
Email: Caj.Kortman at gsf.fi

 

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Norway:
National description
Sweden:
National description
Finland:
National description
Index Map
Mid-Norden area:
Statistics
Mid-Norden + Nordkalott
Gravity Map (Gif)
(Ruotoistenmäki et al.,1997,
Appended map 1.)
Gravity Lineaments
(Mid-Norden) (Gif)

Gravity maps of Mid-Norden project;
Introduction

The gravity anomaly map of the Mid-Norden area has been prepared by the geological surveys of Finland, Norway and Sweden during the period 1989 to 1995. The distribution of observation sites is shown in the index map. A Bouguer density of 2670 kg/m3 has been used for onshore data. For correction of water depth in offshore areas, a water density of 1027 kg/m3 has been used for the Norwegian Sea, and 1000 kg/m3 for the Gulf of Bothnia. The International Gravity Standardization Net 1971 (IGSN-71) and the Gravity Formula 1980 for normal gravity have been used. The data have been interpolated to a square grid of 2.5 km by 2.5 km. Statistics relating to the data are depicted in the adjoining figure.

The enclosed figures depict the combined gravity map of Mid-Norden and Nordkalott area and the interpreted gravity lineaments of the Mid-Norden area. Anomaly gradients have been emphasized by 'illuminating' them from the NW and NE. From the lineaments it can be seen e.g. that the main gravity minimum A - A' (yellow in the figure) controlling the ore critical Ladoga-Bothnian Bay (LBZ) zone on its NE side continues northeast to Sweden where it is congruent with the Archaean paleoboundary defined by Öhlander et al. (1993) by Sm-Nd isotope analyses.

It must also be emphasized that the gravity maps do not show any evidence of the existence of a large N-S-fracture system in the Bothnian Bay (the "Baltic Bothnian megashear" suggested by Berthelsen et al., 1986). Especially, the linear continuation of LBZ-fractures A - A' - apparently even on Swedish side - is a strong argument against that.

The National descriptions below are given in English and 'national languages' (Norwegian, Swedish and Finnish).

The combined gravity map of of Mid-Norden and Nordkalott areas in scale 1:2 000 000 is available from the Surveys in digital and paper forms (see also Ruotoistenmäki et al.,1997).

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GRAVITY DATA OF NORWAY (Jan Skilbrei)

The gravity field of mainland Norway has been measured by the Geological Survey of Norway (NGU), the Norwegian Mapping Authority (Statens kartverk) and other Norwegian and foreign institutions. The original data spacing is variable, from less than 0.4 km to 10 km. The onshore Bouguer values have been terrain-corrected. The marine gravity data used in this compilation have been acquired by the Norwegian Petroleum Directory (Oljedirektoratet), NGU, Norwegian Mapping Authority, Statoil, Norsk Hydro and other Norwegian and foreign oil companies. Extensive areas are covered with a dense grid of ship tracks (spacing 0.5 km to 4 km). The varying areal distribution of the original gravity observations has been homogenized by using a minimum of 600 m separation between points.

NORGE

Tyngdekartet representerer Bougueranomalier beregnet på grunnlag av observert tyngde. Bougueranomaliene på kartet representerer hovedsakelig tetthetsvariasjoner til bergartene i jordskorpen, tykkelsen på jordskorpen, samt sedimentære strukturer fra kontinentalsokkelen (f.eks. forkastningsgrabener og begravde høyder). På land kan tyngdeanomaliene brukes til hjelp for kartleggingen av bergartene i dagen og mot dypet, for mineralleting og strukturelle studier. På sjøen blir tyngdedata brukt til studier av forkastningssoner, tykkelsen til sedimentære lagpakker og utbredelsen av vulkanske bergarter. Forskjellige sorter residualkart blir brukt til å studere alt fra lokale geologiske fenomener til geologiske strukturer med regional utbredelse. Sikkerheten til tolkningene av tyngdedata øker vesentlig når en tar i bruk magnetiske data, refleksjonsseismikk, og andre type geologiske data.

Tyngdedata er innsamlet av og for Norges Geologiske Undersøkelse (NGU), Statens Kartverk, Oljedirektoratet, Statoil, Norsk Hydro og andre norske og utenlandske institusjoner. Datasettet består av Bouguerverdier beregnet på grunnlag av observert tyngde. På land er verdiene korrigert for effekten av terrenget (topografien). En bergartstetthet på 2670 kg/m3 er brukt i beregningen av Bouguer- og terrengkorreksjoner. Den ujevne fordelingen av målepunkt er kompensert ved å ta punkter med en minimum avstand på 600 m fra det originale datasettet. Dette reduserte datasettet er så interpolert til et regulært nett bestående av 2.5 km x 2.5 km ruter.

Andre typer geofysisk informasjon som er tilgjengelig fra NGU er regionale og lokale magnetiske- og tyngdedatasett, data over radioaktiv stråling og data over elektromagnetiske anomalier. Informasjonen foreligger både i kartform og på digital form. Data fra Midt-Nordenområdet er tilgjengelige på digital form for personlige datamaskiner. De inneholder forskjellige utgaver av tyngdedata og magnetiske data. Sammen med kartene (bildene) er det vedlagt "informasjonsfiler". Disse viser malmforekomster, regionale lineamenter og grafiske framstillinger av refleksjonsseismiske snitt.

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GRAVITY DATA OF SWEDEN (Sven Aaro)

Gravity data from the Swedish Mid-Norden area have been provided by the Geological Survey of Sweden (SGU), the National Land Survey of Sweden (LMV), the Boliden Mineral Company and the University of Uppsala. Measurements made over the Gulf of Bothnia when ice-covered represent collaboration between SGU, LMV and the Finnish Geodetic Institute. Original data for the 2.5 by 2.5 km grid has a spacing of 3 - 10 km. Maps and data are available from SGU.

SVERIGE

Storleken på tyngdkraften är beroende av bl.a. latituden, höjden över havet (geoiden), geologin och av topografin. Geofysiker och geologer är i allmänhet enbart intresserade av den del av tyngdkraften som påverkas av massfördelningen i jordskorpan, dvs av geologin. Därför reduceras tyngdkraftsvärdet för en punkt med hänsyn till latitud, höjd över geoiden, massan (2670 kg/m3) mellan mätpunkten och geoiden samt med hänsyn till topografin. På detta sätt erhålls avvikelser, så kallade terrängkorrigerade Bougueranomalier, som (nästan) enbart är relaterade till geologin.

Lokalt påverkas tyngdkraften av fördelningen av tunga och lätta bergarter. Något förenklat gäller att bergarter med hög densitet, som basiska djupbergarter, ger upphov till positiva Bougueranomalier och bergarter med låg densitet, som graniter, till negativa anomalier. Med kännedom om densitetsskillnaden mellan bergarter som förekommer inom ett område kan tyngdkraftsinformationen användas för beräkning av bergarternas djupförhållanden. Likaså kan informationen användas för bedömning av lätta och tunga bergarters utbredning vid ytan i områden som är jordtäckta. Tyngdkraftsinformation utnyttjas, förutom vid geodetiska tillämpningar, främst vid berggrundskartläggning och vid prospektering efter malmer. Informationen kan också användas som komplement till seismiska undersökningar och georadarundersökningar i samband med lokalisering av större vattenreservoarer. Vid berggrundskartläggning och prospektering erhålls bästa resultat då olika geofysiska, petrofysiska och geologiska metoder kombineras.

Tyngdkraftsinformation föreligger i digital form vilket gör att data och/eller kartor i valfri skala lätt kan tillhandahållas av SGU. Tillrättalagd information från Mittnordenområdet är tillgänglig för PC. Den består av olika typer av digitala bilder (kartor) baserade på tyngdkraftsdata och magnetiska data. Tillsammans med dessa bilder finns informationsfiler som visar malmförekomster, regionala lineament och seismiska tolkningsprofiler.

Tyngdkraftsmätningarna över den svenska delen av Mittnordenområdets landområden har utförts av Sveriges geologiska undersökning (SGU), Lantmäteriverket (LMV), Boliden Mineral AB och Uppsala universitet. Mätningarna i Bottenviken och Bottenhavet har utförts i samarbete mellan SGU, LMV och Geodetiska institutet i Helsingfors. Dessa havsmätningar är utförda på is. För Mittnordenkartan har mätpunkter med ett avstånd av 3 - 10 km utnyttjats. Betydligt tätare information finns tillgänglig vid SGU.

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GRAVITY DATA OF FINLAND (Tapio Ruotoistenmäki)

The gravity data for Finland have been measured by the Finnish Geodetic Institute with an original grid spacing of about 5 km. At present about 20% of onshore Finland is also covered with a denser grid measured by the Geological Survey of Finland (GSF), the station spacing varying from 0.4 km to 0.7 km. Where possible, GSF observations were used to give an average station interval of about 2 km. Because of the generally flat topography the Finnish data have not been terrain-corrected. Updated maps and their derivatives covering the whole country are available from GSF.

SUOMI

Painovoimakartta (gravimetrinen Bouguer-anomaliakartta) esittää geologisten muodostumien aiheuttamia poikkeamia (anomalioita) maan paino-voimakentässä. Anomaliat johtuvat maan kuoren kivien rakenteen ja mineraalien vaihteluista. Kivilajien tiheysvaihtelut on määritetty mittaamalla systemaattisesti näytteitä Suomen eri kivilajeista. Hyödyntämällä tämä petrofysikaalinen tieto voidaan gravimetrista mittausaineistoa ja karttoja käyttää mm. malminetsintään, kallioperän kartoitukseen ja rakennetulkintaan. Erilaisia johdannaiskarttoja käyttämällä voidaan korostaa kallioperän kivilajien ja rakenteiden alueellisia ja paikallisia vaihteluita. Koska yhdestä mittaus-aineistosta tehdyt tulkinnat ovat harvoin yksikäsitteisiä, pitää tulkintatyössä aina hyödyntää myös kaikki muu olemassaoleva alueen geologinen ja geofysikaalinen tieto.

Geodeettinen laitos on mitannut Suomen alueen painovoima-aineiston keskimäärin 5 km pistevälillä. Koko Suomen alueen painovoimakartta ja sen johdannaiskartat ovat saatavissa Geologian tutkimuskeskuksesta (GTK). Tällä hetkellä noin 20% Suomen maa-alueesta on mitattu myös tiheämmällä, noin 0.4 - 0.7 km pistevälillä. Kopioita kartoista ja mittausaineistosta on saatavissa GTK:lta.

Mid-Norden alueelta on myös saatavissa mikrotietokoneen kuvaruuduilla katsottavia digitaalisia karttoja. Nämä kartat käsittävät eri tyyppisiä johdannaisia painovoimakartoista ja magneettisista kartoista sekä erilaisia petrofysikaalisia karttoja. Lisäksi niihin on liitetty oheistiedostoja, joissa on sijaintitiedot Mid-Norden alueen pääruhjevyöhykkeistä ja malmiesiintymistä. Oheistiedostojen sisältämä tieto voidaan esittää digitaalisilla kartoilla graafisesti symboleina tai viivoina. Vastaavia sijaintitiedostoja voi myös käyttäjä itse valmistaa. Digitaalisista kartoista voidaan edelleen tulostaa paperiversioita yleisesti käytössä olevilla piirtureilla.

Geologian tutkimuskeskuksesta voi tilata myös Suomen alueelta tehtyjä alueellisia magneettisia karttoja (paperikarttoja ja digitaalisia karttoja), magneettisia, radiometrisia ja sähkömagneettisia matalalentokarttoja sekä erilaisia maastoprofiileita. Myös vastaava mittausaineisto on tilattavissa. Suomen alueen petrofysikaalinen tietokanta käsittää tällä hetkellä tiedot (pääosin tiheys, sähkönjohtavuus ja magneettiset ominaisuudet) noin 60000 näytteestä Mid-Norden alueelta ja noin 125000 näytteestä koko Suomen alueelta.

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Norway:
National description
Sweden:
National description
Finland:
National description
Index Map
Mid-Norden area:
Statistics
Mid-Norden + Nordkalott
Magnetic Map (Gif)
(Ruotoistenmäki et al.,1997,
Appended map 2.)
Mid-Norden + Nordkalott
Magnetic Lineaments
+ Base Metals(Gif)

Magnetic maps of Mid-Norden project;
Introduction

The magnetic anomaly map of the Mid-Norden area has been prepared by the geological surveys of Finland, Norway and Sweden during the period 1989 to 1995. The distribution of survey types is shown in the index map. The data matrices have been interpolated to a common net with cell size 1 km by 1 km and the Definite International Geomagnetic Reference Field 1965.0 (DGRF-65) has been subtracted. Statistics relating to the data are given in the adjoining figure.

The enclosed figures depict the combined magnetic map of Mid-Norden and Nordkalott area and the interpreted magnetic lineaments of the Mid-Norden area connected with base metal ores. Anomaly gradients have been emphasized by 'illuminating' them from the NW and NE. The main gravity minimum A - A' described above in the gravity section has also been included in the lineament figure. From the figure it can be seen that the majority of Finnish ore showings in the Mid-Norden area are connected with the magnetic maximum zone NE of the main gravity minimum A - A'. This magnetic maximum zone is also a regional gravity maximum referring to large amounts of mafic rocks in the upper part of the crust (e.g. Elo et al., 1978; Ruotoistenmäki, 1993, 1996).

The National descriptions below are given in English and 'national languages' (Norwegian, Swedish and Finnish).

The combined magnetic map of of Mid-Norden and Nordkalott areas in scale 1:2 000 000 is available from the Surveys in digital and paper forms (see also Ruotoistenmäki et al.,1997).

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MAGNETIC DATA OF NORWAY (Jan Skilbrei)

The airborne magnetic data for mainland Norway and offshore areas were measured by the Geological Survey of Norway (NGU) between 1959 and 1976. The aeromagnetic map is based on a matrix digitized from manually drawn contour maps. The index map shows flight altitude and line spacing of the original measurements. Nearly half of central Norway (mainly the Trøndelag region) is covered by data with a line spacing of 500 m and a terrain clearance of 150 m. Remaining onshore areas mainly have a line spacing of 1000 m and a flight altitude of 300 m. In the offshore part of the map, flight altitude was 200 - 500 m with a line spacing varying from 2 km to 5 km. At present about 10% of central Norway is covered by low altitude (60 m) data in the form of paper and digital maps. Copies of maps and data can be ordered from the NGU.

NORGE

Det flymagnetiske kartet viser avvik (anomalier) fra jordens normale magnetfelt. Slike anomalier representerer variasjoner i mineralogi til bergartene og geologiske strukturer i øvre deler av jordskorpen. De magnetiske egenskapene til ulike bergarter er målt på prøver fra utvalgte deler av berggrunnen i Norge. Kombinert med slik informasjon om petrofysiske egenskaper til bergartene kan magnetiske data og kart brukes til hjelp for kartlegging av berggrunnen, mineralleting, forkastninger, tykkelse på løsmasseavsetninger, og miljøundersøkelser (f. eks. deponiundersøkelser). Fra kontinentalsokkelen blir magnetiske data brukt til å beregne tykkelsen på sedimentasjonsbasseng, kartlegging av avsetningsmønstre i sedimentene og lagrekkefølge inn mot land, kartlegging av begravde vulkanske bergarter og forkastninger.

Det flymagnetiske kartet er basert på et rutenett interpolert fra digitaliserte håndkonturerte kart. Indekskartet viser flyhøyde og profilavstand av de opprinnelige målingene. Områdene med lav flyhøyde (150 m - 300 m) ble målt mellom 1959 og 1968 med et halemontert fluxgate magnetometer. Fra 1968 ble et halemontert proton magnetometer brukt. Cellestørrelsen som er brukt for å lage kartet er 1000 m x 1000 m.

Andre typer geofysisk informasjon som er tilgjengelig fra NGU, er regionale og lokale magnetiske- og tyngdedatasett, data over radioaktiv stråling og elektromagnetiske anomalier. Informasjonen foreligger både i kartform og på digital form.

Data fra Midt-Nordenområdet er tilgjengelige på digital form for personlige datamaskiner. De inneholder forskjellige utgaver av tyngdedata og magnetiske data. Sammen med kartene (bildene) er det vedlagt "informasjonsfiler". Disse viser malmforekomster, regionale lineamenter og grafiske framstillinger av refleksjonsseismiske snitt.

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MAGNETIC DATA OF SWEDEN (Sven Aaro)

The airborne magnetic measurements in the Swedish Mid-Norden area have been carried out by the Boliden Mineral Company, by LKAB and by the Geological Survey of Sweden (SGU), the latter with partial financing by the Swedish Nuclear Fuel and Waste Management Company (SKB). Most of onshore areas are covered by low altitude (30-50 m), 200 by 40 m data and offshore areas with 600 by 80 m data. In the Caledonides, ten low altitude (c. 50 m) profiles were measured by SGU for the University of Uppsala, using a line spacing of 5 - 20 km. The aeromagnetic data sets have been compiled on a 200 by 200 m grid, which has been upward continued from 30 to 150 m and regridded to 1 by 1 km. Maps and data can be ordered from SGU.

SVERIGE

Flygmagnetisk information presenteras vanligen som avvikelser från jordens normala magnetfält. Avvikelserna beror i hög grad på skillnader i bergarters magnetiserbarhet och remanenta magnetisering. Graden av magnetiserbarhet bestäms i huvudsak av bergarternas innehåll av högmagnetiska mineral såsom magnetit och magnetkis. Genom flygmätningar, som normalt utförs på 30 meters höjd över markytan och med 200 meters linjeavstånd, erhålls en detaljerad bild av de magnetiska avvikelserna. Avvikelserna eller de så kallade magnetiska anomalierna ger information om bergarters utbredning på ytan och på djupet samt om förkastningar och sprickzoner i berggrunden. Den flygmagnetiska informationen är ett nödvändigt underlag vid prospektering efter malmer och vid berggrundskartläggning. Inom områden där berggrunden är täckt av jord eller av vatten är den flygmagnetiska informationen, liksom tyngdkraftsinformationen, mycket viktig för berggrundsgeologisk kartläggning.

I samband med den flygburna magnetiska mätningen utförs också mätningar av sekundära elektromagnetiska fält och av markens gammastrålning. Flyggeofysisk information föreligger i digital form vilket gör att data och/eller kartor i valfri skala lätt kan tillhandahållas av SGU. Tillrättalagd information från Mittnordenområdet är tillgänglig för PC. Den består av olika typer av digitala bilder (kartor) baserade på tyngdkraftsdata och magnetiska data. Tillsammans med dessa bilder finns informationsfiler som visar malmförekomster, regionala lineament och seismiska tolkningsprofiler.

De flygmagnetiska mätningarna över Mittnordenområdet har utförts av Sveriges geologiska undersökning (SGU) delvis finansierade av Svensk Kärnbränslehantering AB (SKB), samt av Boliden Mineral AB och LKAB. Huvuddelen av mätningarna har utförts under 60- och 70-talen. Flyghöjden har varit 30 - 50 meter över markytan. Inom större delen av området har mätningarna utförts med ett linjeavstånd på 200 meter och ett mätpunktsintervall på 40 meter. För havsområdet är avstånden 600 meter respektive 80 meter. Inom fjällområdet har tio profiler mätts av SGU för avdelningen för Fasta jordens fysik vid Uppsala universitet. Linjeavståndet för dessa profiler är 5 - 20 km. Vid framtagningen av ovanstående karta har den magnetiska informationen omräknats till ett 200 m x 200 m dataset vilket sedan med hjälp av så kallad analytisk fortsättning räknats upp från 30 m till 150 m. Därefter har ett 1 km x 1 km dataset framtagits.

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MAGNETIC DATA OF FINLAND (Tapio Ruotoistenmäki)

The airborne magnetic data for Finland were measured by the Geological Survey of Finland during the years 1951-1971 and 1993 (eastern border zone), with a terrain clearance of 150 m and line spacing of 400 m. The original analog format data were digitized to a 1 km by 1 km grid. At present about 75% of onshore Finland is also covered by low-altitude (30 m) data and maps with a line spacing of 200 m, and observations made every 12.5 metres. Copies of maps and grid matrices are available from the Geological Survey of Finland.

SUOMI

Suomen aeromagneettinen kartta esittää geologisten muodostumien aiheuttamia poikkeamia (anomalioita) maan magneettikentässä. Anomaliat johtuvat maan kuoren yläosan kivien rakenteen ja magneettisten mineraalien määrän vaihteluista. Kivilajien magneettisia ominaisuuksia on määritetty mittaamalla systemaattisesti näytteitä Suomen eri kivilajeista. Hyödyntämällä tämä petrofysikaalinen tieto voidaan magneettista mittausaineistoa ja karttoja käyttää mm. malminetsintään, kallioperän kartoitukseen ja rakennetulkintaan. Erilaisia johdannaiskarttoja käyttämällä voidaan korostaa kallioperän kivilajien ja rakenteiden alueellisia ja paikallisia vaihteluita. Koska yhdestä mittausaineistosta tehdyt tulkinnat ovat harvoin yksikäsitteisiä, pitää tulkintatyössä aina hyödyntää myös kaikki muu olemassaoleva alueen geologinen ja geofysikaalinen tieto.

Geologian tutkimuskeskus (GTK) mittasi Suomen aeromagneettisen aineiston vuosina 1951-1971 ja 1993 (itäraja). Mittausten lentokorkeus oli 150 metriä ja linjaväli 400 metriä. Mittausaineistosta on piirretty sama-arvokäyräkartat, joista edelleen on poimittu tässä kartassa käytetty 1 km x 1 km dataverkko. Tällä hetkellä noin 75% Suomen alueesta on mitattu myös matalalentomittauksena noin 30 metrin korkeudelta ja 200 metrin linjavälillä mittauspistetiheyden linjoilla ollessa 12.5 metriä. Kopioita kartoista ja mittausaineistosta on saatavissa GTK:lta.

Mid-Norden alueelta on myös saatavissa mikrotietokoneen kuvaruuduilla katsottavia digitaalisia karttoja. Nämä kartat käsittävät eri tyyppisiä johdannaisia magneettisista kartoista ja painovoimakartoista sekä erilaisia petrofysikaalisia karttoja. Lisäksi niihin on liitetty oheistiedostoja, joissa on sijaintitiedot Mid-Norden alueen pääruhjevyöhykkeistä ja malmiesiintymistä. Oheistiedostojen sisältämä tieto voidaan esittää digitaalisilla kartoilla graafisesti symboleina tai viivoina. Vastaavia sijaintitiedostoja voi myös käyttäjä itse valmistaa. Digitaalisista kartoista voidaan edelleen tulostaa paperiversioita yleisesti käytössä olevilla piirtureilla.

Geologian tutkimuskeskuksesta voi tilata myös Suomen alueelta tehtyjä alueellisia ja paikallisia painovoimakarttoja (paperikarttoja ja digitaalisia karttoja), radiometrisia ja sähkömagneettisia matalalentokarttoja sekä erilaisia maastoprofiileita. Myös vastaava mittausaineisto on tilattavissa. Suomen alueen petrofysikaalinen tietokanta käsittää tällä hetkellä tiedot (pääosin tiheys, sähkönjohtavuus ja magneettiset ominaisuudet) noin 60000 näytteestä Mid-Norden alueelta ja noin 125000 näytteestä koko Suomen alueelta.

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Norway:
National description
Sweden:
National description
Finland:
National description
Seismic Profiles (Gif)

Selected Seismic profiles in the Mid-Norden area

For the Mid-Norden project some examples of deep seismic profiles were digitized. Two profiles are from the Norwegian Sea and two from onshore areas in Sweden and Finland. These profiles have been included in the 'extra Info files' of the digital map browser (in CD-ROM-version).

The image shown in this page gives the location of these profiles shown with the combined gravity map of Mid-Norden and Nordkalott areas. In the "National description" pages are given a short explanation of the profiles and a close-up image of the profiles separately.

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Seismic Profiles
(Close-up; Gif)

Norway:

Explanation for the two Seismic Profiles from the Norwegian Sea

The two geoseismic profiles were digitised from Norwegian Petroleum Directorate Bulletin no. 8. (Blystad et al., 1995). Vertical scale is two-way-traveltime in seconds. The height of the edge is 12 seconds. Note, that only the parts of the original profiles that are located within the mid-Norden area are shown (western part of original profiles have bee cut).

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Fennolora Profile
(Close-up; Gif)

Sweden:

Crustal structure of the Fennoscandian Shield: A traveltime interpretation of the long-range FENNOLORA seismic refraction profile

(Guggisberg et al., 1991)

The 1979 Fennoscandian Long-Range Project (FENNOLORA) was aimed at the determination of the detailed structure in the earth's mantle down to a depth of about 400 km. Observation distances reached almost 2000 km within Scandinavia between shotpoints off the North Cape and the southern coast of Sweden. To achieve an unbiased upper mantle structure, a careful crustal survey was carried out along the entire profile at the same time. Beneath the Fennoscandian Shield, i.e. the central section of the profile. the crust is charactenzed by quite a smooth increase in P-wave velocity down to the Moho which lies at a depth of about 50 km in the southern half of the shield and at about 45 km further north. The mean crustal velocity is 6.6-6.7 km/s. At the base of the crust the velocity increases gradually from about 7 km/s to 8.0-8.4 km/s in a 5-10 km thick crust-mantle transition zone. Both in the south and in the north, the relatively homogeneous crust of the Baltic Shield borders on areas with a more differentiated velocity structure. First-order discontinuities at shallower depth characterize the crust-mantle boundary near the southeastern tip of Sweden (38km) and under the Caledonides in the north (43 km).

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Sveka Profile
(Close-up; Gif)

Finland:

Deep seismic refraction sounding profile SVEKA

The NE part of the deep seismic sounding profile SVEKA (Grad et al., 1987; Luosto et al., 1994 and Yliniemi J., 1994. Personal communication. University of Oulu, Finland) overlapping with the Mid-Norden area has been digitized along the shotpoints. In the figure the profile has been 'projected' along a straight line between the end points. The profile has been framed so that along the profile the scale is the same as that of the map. However, in vertical dimension the scale factor is 2. The height of the frame is 70 km. It must be emphasized that 'stretching' in vertical dimension causes the dips of the reflector surfaces to become steeper.

From the figure it can be seen that the ore critical area NE from the gravity lineament A - A' in fig 2 is characterized by a very thick crust, ca 60 km, possibly due to tectonic thickening (e.g. Ruotoistenmäki, 1996) and / or introduction of mafic mantle melts in the lower crust (e.g. Lahtinen, 1994; Korja, 1995).

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Density Map (Gif)
Susceptibility Map (Gif)
Remanence Map (Gif)

Example: Petrophysical maps of the Finnish Mid-Norden area

Heikki Säävuori (GSF)

The petrophysical databases for the Mid-Norden area contain information (mainly density, magnetic susceptibility, intensity of remanence and less often electrical conductivity) from about 49 000 samples in Finland, 3 800 in Norway and 16 000 in Sweden. In the following is given examples of the distribution of density, susceptibility and remanence in the Finnish Mid-Norden area.

The total number of samples in the Finnish petrophysical data base is ca. 131 000. In the Finnish Mid-Norden area the average sampling density is ca. 40 samples / 100 km2. The density and susceptibility has been defined from nearly all samples and the remanence from about 77 % of the samples. Most samples are taken from outcrops, only 4 % of samples being from drill cores or till. The average weight of the samples is ca. 0.5 kg. About 48 % of samples are from igneous rocks, 39 % are from rocks classified as 'metamorphic', 6 % are from dykes and 7% from other rock types.

The average density of all samples in the Finnish Mid-Norden area is ca. 2734 kg/m3±2 kg/m3. The amount of more strongly magnetic ferrimagnetic samples is ca. 24 %. The distribution of susceptibility has two peaks, the ferrimagnetic peak being at ca. 36500*10-6 (SI) ±5 % and paramagnetic peak at 370*10-6 (SI) ± 7 %. About 17 % of the samples, being mainly ferrimagnetic, has remanent magnetization above 100 mA/m standard error being below 10 %. The values of remanent magnetization are more uncertain for weakly magnetized samples.

The colour maps show the density, susceptibility and remanence distribution in the Finnish Mid-Norden area. The data has been grouped in 5 * 5 km 'dots' using 13 one square kilometer sub-elements the maximum distance of samples in the interpolation thus being 5 km.

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Seismic Maps
(Intro / Map)
Ore Deposits
+ Gravity map (Gif)
Gravity Lineaments
(Mid-Norden) (Gif)

Digital Maps

(The Digital Map browser will be included in the CD-ROM version)

Digital maps and their derivatives are available from the geological surveys. They include an information file system by which vectors and point symbols can be displayed on or extracted from the maps. The information files distributed by the authors contain deep seismic sounding profiles (see Seismic Maps), regional fractures (vectors) and ore indications (symbols) for the Mid-Norden area. New information files can also be created separately by the user from any location (x,y) data.

The interactive digital map browser is based on the use of various versions of gravity and magnetic maps in Tagged Image File format (TIFF). Thus, they can be viewed with other image processing programs as well. As an example of the use of the 'Extra Info Files' are shown gravity lineaments and ore deposits (slightly enlarged) connected with graytone gravity map (hillshaded from NE and NW).

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REFERENCES

Berthelsen A. and Marker M., 1986. 1.9-1.8 Ga old strike-slip megashears in the Baltic shield and their plate tectonic implications. Tectonophysics, 128, 163-181.

Blystad, P., Brekke, H., Færseth, R. B., Larsen, B. T., Skogseid, J. & Tørudbakken, B. 1995: Structural elements of the Norwegian continental shelf, Part II: The Norwegian Sea Region. NPD-Bulletin No 8, pp. 45.

Elo S., Korhonen J., and Puranen R. 1978: Geophysical studies of Ladoga-Bothnian Bay zone. In: Ladoga-Bothnian Bay ore zone. Vuorimiesyhdistys. Helsinki, Finland. (In Finnish).

Grad, M. and Luosto, U., 1987. Seismic models of the crust of the Baltic shield along the Sveka profile in Finland. Annales Geophysicae, 187, 5B, (6), 639-650.

Guggisberg B., Kaminski W. and Prodehl C. (1991). Crustal structure of the Fennoscandian Shield: A traveltime interpretation of the long-range FENNOLORA seismic refraction profile Tectonophysics, 195, 105-137

Kautsky, G. 1986. The Nordkalott Project. Abtract in: Terra Cognita 6, no. 3, p. 564.

Korhonen J., Aalstad I., Arkko V., Granar L., Henkel H., Karlemo B., Kihle O., Krook L., Lind J., Normann E., Olesen O., Puranen M., Sindre A., Thorning L., Werner S. (1986a). Magnetic Anomaly map, Northern Fennoscandia1:1 mill.. Geological Surveys of Finland, Norway and Sweden. ISBN 91-7158-375-0.

Korhonen J., Aalstad I., Elo S., Haller L-Å., Kiviniemi A., Midtsunstad Å., Nylund, B., Sindre A. (1986b). Gravity Anomaly map, Northern Fennoscandia1:1 mill. Geodetic institutes and Geological surveys of Finland, Norway and Sweden. ISBN 91-7158-374-2.

Luosto, U., Grad, M., Guterch, A., Heikkinen, P., Janik, T., Komminaho, K., Lund, C., Thybo, H. and Yliniemi, J., 1994. Crustal structure along the Sveka '91 profile (Finland). Paper sent for publication in Proceedings of XXIV General Assembly of the European Seismological Commission, Athens, 1994.

Ruotoistenmäki T., Aaro S., Elo S., Gellein J., Gustavsson N., Henkel H., Hult K., Kauniskangas E., Kero L., Kihle O., Lehtonen M., Lerssi J., Sindre A., Skilbrei J., Tervo T., Thorning L. (1996a). Gravity Anomaly map of Central Fennoscandia. Scale 1:1 000000. Geological Surveys of Finland (Espoo), Norway (Trondheim) and Sweden (Uppsala). 1995. ISBN 951-690-610-9.

Ruotoistenmäki T. 1996. A schematic model of the evolution of Finnish bedrock. Geological Survey of Finland, Report of Investigation 133, 23 pp.

Ruotoistenmäki T., Aaro S., Elo S., Gellein J., Gustavsson N., Henkel H., Hult K., Kauniskangas E., Kero L., Kihle O., Lehtonen M., Lerssi J., Sindre A., Skilbrei J., Tervo T., Thorning L. (1996b). Aeromagnetic Anomaly map of Central Fennoscandia. Scale 1:1 000000. Geological surveys of Finland (Espoo), Norway (Trondheim) and Sweden (Uppsala). 1995. ISBN 951-690-609-5.

Ruotoistenmäki T., Elo S., Aaro S., Kauniskangas E., Kortman C., Skilbrei J. and Tervo T. 1997. MID-NORDEN project, Geophysical sub-project: Introduction to combined geophysical maps of central and northern Fennoscandia. In: Autio, S. (ed.) Geological Survey of Finland, Current Research 1995 - 1996. Geological Survey of Finland, Special Paper 23, 185-191.

Tontti M., Gautneb H., Grenne T., Juve G., Kauniskangas E., Nikander J., Nilsson G. and Sandstad J. S. (1996). Map of Ore Deposits in Central Fennoscandia. Scale 1:1 000000. Geological surveys of Finland (Espoo), Norway (Trondheim) and Sweden (Uppsala). 1995. ISBN 951-690-607-9.

Öhlander B., Skiöld T., Elming S.-Å, Claesson S., Nisca D., H. and BABEL working group, 1993 Delineation and character of the Archaean-Proterozoic boundary in Northern Sweden. Precambrian Res. 64, 67-84.