Geological Model of the Olkiluoto Site

Version 2.0

Mari Lahti, Jon Engström, Jussi Mattila, Markku Paananen, Seppo Paulamäki, Seppo Gehör, Aulis Kärki, Turo Ahokas, Taija Torvela, Kai Front, Ismo Aaltonen (Editor)

Research output: Book/ReportReportProfessional

Abstract

The rocks of Olkiluoto can be divided into two major classes: 1) supracrustal high-grade metamorphic rocks including various migmatitic gneisses, tonalitic-granodioriticgranitic gneisses, mica gneisses, quartz gneisses and mafic gneisses, and 2) igneous rocks including pegmatitic granites and diabase dykes. The migmatitic gneisses can further be divided into three subgroups in terms of the type of migmatite structure: veined gneisses, stromatic gneisses and diatexitic gneisses. On the basis of refolding and crosscutting relationships, the metamorphic supracrustal rocks have been subjected to polyphased ductile deformation, consisting of five stages, the D2 being locally the most intensive phase, producing thrust-related folding, strong migmatisation and pervasive foliation. In 3D modelling of the lithological units, an assumption has been made, on the basis of measurements in the outcrops, investigation trenches and drill cores, that the pervasive, composite foliation produced as a result of polyphase ductile deformation has a rather constant attitude in the ONKALO area. Consequently, the strike and dip of the foliation has been used as a tool, through which the lithologies have been correlated between the drillholes and from the surface to the drillholes. In addition, the largest ductile deformation zones and tectonic units are described in 3D model. The bedrock at the Olkiluoto site has been subjected to extensive hydrothermal alteration, which has taken place at reasonably low temperature conditions, the estimated temperature interval being from slightly over 300°C to less than 100°C. Two types of alteration can be observed: firstly, pervasive alteration and secondly fracturecontrolled alteration. Clay mineralisation and sulphidisation are the most prominent alteration events in the site area. Sulphides are located in the uppermost part of the model volume following roughly the foliation and lithological trend. Kaolinite is also mainly located in the uppermost part, but is not controlled by lithological trend. Another member of the clay system, illitisation, consists of few distinct volumes, which are located deeper, and are spatially associated with site-scale thrust faults. The fault zones at Olkiluoto are mainly SE-dipping thrust faults formed during contraction in the last stages of the Fennian orogeny, approximately at 1800 Ma ago and were reactivated in several deformation phases, as indicated by fault-slip data and K-Ar age determinations. In addition, NE-SW striking strike-slip faults are also common. Fault zone intersections from drillholes, the ONKALO access tunnel and outcrops have been correlated by the application of slickensides orientations, mise-à-lamassemeasurements, eletctromagnetic soundings, 3D seismics and VSP-reflectors, resulting the model of 179 brittle fault zones.
Original languageEnglish
PublisherPosiva
Number of pages580
Edition2.0
Publication statusPublished - 2010
MoE publication typeD4 Published development or research report or study

Publication series

NameWorking Report
PublisherPosiva Oy
No.2010-70

Fingerprint

foliation
ductile deformation
fault zone
thrust fault
metamorphic rock
outcrop
illitization
slickenside
clay
migmatization
supracrustal rock
migmatite
fault slip
age determination
diabase
hydrothermal alteration
strike-slip fault
orogeny
mica
igneous rock

Keywords

  • lithology
  • deformation
  • hydrothermal alteration
  • geological model
  • 3D modelling
  • spent nuclear fuel disposal
  • Olkiluoto
  • Eurajaoki
  • Finland

Cite this

Lahti, M., Engström, J., Mattila, J., Paananen, M., Paulamäki, S., Gehör, S., ... Aaltonen, I. (Ed.) (2010). Geological Model of the Olkiluoto Site: Version 2.0. (2.0 ed.) Posiva . Working Report, No. 2010-70
Lahti, Mari ; Engström, Jon ; Mattila, Jussi ; Paananen, Markku ; Paulamäki, Seppo ; Gehör, Seppo ; Kärki, Aulis ; Ahokas, Turo ; Torvela, Taija ; Front, Kai ; Aaltonen, Ismo (Editor). / Geological Model of the Olkiluoto Site : Version 2.0. 2.0 ed. Posiva , 2010. 580 p. (Working Report; No. 2010-70).
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abstract = "The rocks of Olkiluoto can be divided into two major classes: 1) supracrustal high-grade metamorphic rocks including various migmatitic gneisses, tonalitic-granodioriticgranitic gneisses, mica gneisses, quartz gneisses and mafic gneisses, and 2) igneous rocks including pegmatitic granites and diabase dykes. The migmatitic gneisses can further be divided into three subgroups in terms of the type of migmatite structure: veined gneisses, stromatic gneisses and diatexitic gneisses. On the basis of refolding and crosscutting relationships, the metamorphic supracrustal rocks have been subjected to polyphased ductile deformation, consisting of five stages, the D2 being locally the most intensive phase, producing thrust-related folding, strong migmatisation and pervasive foliation. In 3D modelling of the lithological units, an assumption has been made, on the basis of measurements in the outcrops, investigation trenches and drill cores, that the pervasive, composite foliation produced as a result of polyphase ductile deformation has a rather constant attitude in the ONKALO area. Consequently, the strike and dip of the foliation has been used as a tool, through which the lithologies have been correlated between the drillholes and from the surface to the drillholes. In addition, the largest ductile deformation zones and tectonic units are described in 3D model. The bedrock at the Olkiluoto site has been subjected to extensive hydrothermal alteration, which has taken place at reasonably low temperature conditions, the estimated temperature interval being from slightly over 300°C to less than 100°C. Two types of alteration can be observed: firstly, pervasive alteration and secondly fracturecontrolled alteration. Clay mineralisation and sulphidisation are the most prominent alteration events in the site area. Sulphides are located in the uppermost part of the model volume following roughly the foliation and lithological trend. Kaolinite is also mainly located in the uppermost part, but is not controlled by lithological trend. Another member of the clay system, illitisation, consists of few distinct volumes, which are located deeper, and are spatially associated with site-scale thrust faults. The fault zones at Olkiluoto are mainly SE-dipping thrust faults formed during contraction in the last stages of the Fennian orogeny, approximately at 1800 Ma ago and were reactivated in several deformation phases, as indicated by fault-slip data and K-Ar age determinations. In addition, NE-SW striking strike-slip faults are also common. Fault zone intersections from drillholes, the ONKALO access tunnel and outcrops have been correlated by the application of slickensides orientations, mise-{\`a}-lamassemeasurements, eletctromagnetic soundings, 3D seismics and VSP-reflectors, resulting the model of 179 brittle fault zones.",
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editor = "Ismo Aaltonen",
year = "2010",
language = "English",
series = "Working Report",
publisher = "Posiva",
number = "2010-70",
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Lahti, M, Engström, J, Mattila, J, Paananen, M, Paulamäki, S, Gehör, S, Kärki, A, Ahokas, T, Torvela, T, Front, K & Aaltonen, I (ed.) 2010, Geological Model of the Olkiluoto Site: Version 2.0. Working Report, no. 2010-70, 2.0 edn, Posiva .

Geological Model of the Olkiluoto Site : Version 2.0. / Lahti, Mari; Engström, Jon; Mattila, Jussi; Paananen, Markku; Paulamäki, Seppo; Gehör, Seppo; Kärki, Aulis; Ahokas, Turo; Torvela, Taija; Front, Kai; Aaltonen, Ismo (Editor).

2.0 ed. Posiva , 2010. 580 p. (Working Report; No. 2010-70).

Research output: Book/ReportReportProfessional

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T1 - Geological Model of the Olkiluoto Site

T2 - Version 2.0

AU - Lahti, Mari

AU - Engström, Jon

AU - Mattila, Jussi

AU - Paananen, Markku

AU - Paulamäki, Seppo

AU - Gehör, Seppo

AU - Kärki, Aulis

AU - Ahokas, Turo

AU - Torvela, Taija

AU - Front, Kai

A2 - Aaltonen, Ismo

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N2 - The rocks of Olkiluoto can be divided into two major classes: 1) supracrustal high-grade metamorphic rocks including various migmatitic gneisses, tonalitic-granodioriticgranitic gneisses, mica gneisses, quartz gneisses and mafic gneisses, and 2) igneous rocks including pegmatitic granites and diabase dykes. The migmatitic gneisses can further be divided into three subgroups in terms of the type of migmatite structure: veined gneisses, stromatic gneisses and diatexitic gneisses. On the basis of refolding and crosscutting relationships, the metamorphic supracrustal rocks have been subjected to polyphased ductile deformation, consisting of five stages, the D2 being locally the most intensive phase, producing thrust-related folding, strong migmatisation and pervasive foliation. In 3D modelling of the lithological units, an assumption has been made, on the basis of measurements in the outcrops, investigation trenches and drill cores, that the pervasive, composite foliation produced as a result of polyphase ductile deformation has a rather constant attitude in the ONKALO area. Consequently, the strike and dip of the foliation has been used as a tool, through which the lithologies have been correlated between the drillholes and from the surface to the drillholes. In addition, the largest ductile deformation zones and tectonic units are described in 3D model. The bedrock at the Olkiluoto site has been subjected to extensive hydrothermal alteration, which has taken place at reasonably low temperature conditions, the estimated temperature interval being from slightly over 300°C to less than 100°C. Two types of alteration can be observed: firstly, pervasive alteration and secondly fracturecontrolled alteration. Clay mineralisation and sulphidisation are the most prominent alteration events in the site area. Sulphides are located in the uppermost part of the model volume following roughly the foliation and lithological trend. Kaolinite is also mainly located in the uppermost part, but is not controlled by lithological trend. Another member of the clay system, illitisation, consists of few distinct volumes, which are located deeper, and are spatially associated with site-scale thrust faults. The fault zones at Olkiluoto are mainly SE-dipping thrust faults formed during contraction in the last stages of the Fennian orogeny, approximately at 1800 Ma ago and were reactivated in several deformation phases, as indicated by fault-slip data and K-Ar age determinations. In addition, NE-SW striking strike-slip faults are also common. Fault zone intersections from drillholes, the ONKALO access tunnel and outcrops have been correlated by the application of slickensides orientations, mise-à-lamassemeasurements, eletctromagnetic soundings, 3D seismics and VSP-reflectors, resulting the model of 179 brittle fault zones.

AB - The rocks of Olkiluoto can be divided into two major classes: 1) supracrustal high-grade metamorphic rocks including various migmatitic gneisses, tonalitic-granodioriticgranitic gneisses, mica gneisses, quartz gneisses and mafic gneisses, and 2) igneous rocks including pegmatitic granites and diabase dykes. The migmatitic gneisses can further be divided into three subgroups in terms of the type of migmatite structure: veined gneisses, stromatic gneisses and diatexitic gneisses. On the basis of refolding and crosscutting relationships, the metamorphic supracrustal rocks have been subjected to polyphased ductile deformation, consisting of five stages, the D2 being locally the most intensive phase, producing thrust-related folding, strong migmatisation and pervasive foliation. In 3D modelling of the lithological units, an assumption has been made, on the basis of measurements in the outcrops, investigation trenches and drill cores, that the pervasive, composite foliation produced as a result of polyphase ductile deformation has a rather constant attitude in the ONKALO area. Consequently, the strike and dip of the foliation has been used as a tool, through which the lithologies have been correlated between the drillholes and from the surface to the drillholes. In addition, the largest ductile deformation zones and tectonic units are described in 3D model. The bedrock at the Olkiluoto site has been subjected to extensive hydrothermal alteration, which has taken place at reasonably low temperature conditions, the estimated temperature interval being from slightly over 300°C to less than 100°C. Two types of alteration can be observed: firstly, pervasive alteration and secondly fracturecontrolled alteration. Clay mineralisation and sulphidisation are the most prominent alteration events in the site area. Sulphides are located in the uppermost part of the model volume following roughly the foliation and lithological trend. Kaolinite is also mainly located in the uppermost part, but is not controlled by lithological trend. Another member of the clay system, illitisation, consists of few distinct volumes, which are located deeper, and are spatially associated with site-scale thrust faults. The fault zones at Olkiluoto are mainly SE-dipping thrust faults formed during contraction in the last stages of the Fennian orogeny, approximately at 1800 Ma ago and were reactivated in several deformation phases, as indicated by fault-slip data and K-Ar age determinations. In addition, NE-SW striking strike-slip faults are also common. Fault zone intersections from drillholes, the ONKALO access tunnel and outcrops have been correlated by the application of slickensides orientations, mise-à-lamassemeasurements, eletctromagnetic soundings, 3D seismics and VSP-reflectors, resulting the model of 179 brittle fault zones.

KW - lithology

KW - deformation

KW - hydrothermal alteration

KW - geological model

KW - 3D modelling

KW - spent nuclear fuel disposal

KW - Olkiluoto

KW - Eurajaoki

KW - Finland

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BT - Geological Model of the Olkiluoto Site

PB - Posiva

ER -

Lahti M, Engström J, Mattila J, Paananen M, Paulamäki S, Gehör S et al. Geological Model of the Olkiluoto Site: Version 2.0. 2.0 ed. Posiva , 2010. 580 p. (Working Report; No. 2010-70).