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C.-h. Wahlgren - One of the best experts on this subject based on the ideXlab platform.

  • Unraveling 1.5 Ga of Brittle Deformation history in the Laxemar‐Simpevarp area, southeast Sweden: A contribution to the Swedish site investigation study for the disposal of highly radioactive nuclear waste
    Tectonics, 2009
    Co-Authors: Giulio Viola, G. Venvik Ganerød, C.-h. Wahlgren
    Abstract:

    [1] The Swedish Nuclear Fuel and Waste Management Company (SKB) is undertaking site investigation at two locations in Sweden, Forsmark and Laxemar-Simpevarp, with the aim of identifying a suitable area for the construction of a deep repository for the disposal of highly radioactive nuclear waste. Fault slip data from outcrops and oriented drill cores were used to compute paleostress states and to unravel the sites' Brittle Deformation history. Results from the Laxemar-Simpevarp area show that its suggested Brittle history results from multiple reactivation of fracture and fault sets caused by the many orogenic episodes that affected the region during at least 1.5 Ga of geological evolution in the Brittle Deformational regime. Two compressional, approximately NW/NNW-SE/SSE and NNE-SSW oriented shortening events generated sets of conjugate, steep strike-slip fractures. These sets formed during the late stages of the Svecokarelian and possibly also of the Gothian orogeny, soon after the region entered the Brittle Deformation domain. The Mesoproterozoic Sveconorwegian orogeny generated fractures and faults that are assigned to a third set of conjugate strike-slip faults, which constrain an approximately E-W σ1. The Caledonian shortening, oriented approximately NW-SE to E-W, reactivated the latter but also formed a new, similarly oriented set of subvertical strike-slip fractures. Permian transtension was oriented NW-SW and caused a prominent set of moderately dipping NW-SE trending normal faults in the Precambrian basement of the study area. Two other approximately NW-SW and NW-SE oriented shortening events are recorded in Ordovician limestones and can be tentatively linked to the far-field effects of the Laramide and Alpine orogenies.

  • unraveling 1 5 ga of Brittle Deformation history in the laxemar simpevarp area southeast sweden a contribution to the swedish site investigation study for the disposal of highly radioactive nuclear waste
    Tectonics, 2009
    Co-Authors: Giulio Viola, Venvik G Ganerod, C.-h. Wahlgren
    Abstract:

    [1] The Swedish Nuclear Fuel and Waste Management Company (SKB) is undertaking site investigation at two locations in Sweden, Forsmark and Laxemar-Simpevarp, with the aim of identifying a suitable area for the construction of a deep repository for the disposal of highly radioactive nuclear waste. Fault slip data from outcrops and oriented drill cores were used to compute paleostress states and to unravel the sites' Brittle Deformation history. Results from the Laxemar-Simpevarp area show that its suggested Brittle history results from multiple reactivation of fracture and fault sets caused by the many orogenic episodes that affected the region during at least 1.5 Ga of geological evolution in the Brittle Deformational regime. Two compressional, approximately NW/NNW-SE/SSE and NNE-SSW oriented shortening events generated sets of conjugate, steep strike-slip fractures. These sets formed during the late stages of the Svecokarelian and possibly also of the Gothian orogeny, soon after the region entered the Brittle Deformation domain. The Mesoproterozoic Sveconorwegian orogeny generated fractures and faults that are assigned to a third set of conjugate strike-slip faults, which constrain an approximately E-W σ1. The Caledonian shortening, oriented approximately NW-SE to E-W, reactivated the latter but also formed a new, similarly oriented set of subvertical strike-slip fractures. Permian transtension was oriented NW-SW and caused a prominent set of moderately dipping NW-SE trending normal faults in the Precambrian basement of the study area. Two other approximately NW-SW and NW-SE oriented shortening events are recorded in Ordovician limestones and can be tentatively linked to the far-field effects of the Laramide and Alpine orogenies.

Giulio Viola - One of the best experts on this subject based on the ideXlab platform.

  • Unraveling 1.5 Ga of Brittle Deformation history in the Laxemar‐Simpevarp area, southeast Sweden: A contribution to the Swedish site investigation study for the disposal of highly radioactive nuclear waste
    Tectonics, 2009
    Co-Authors: Giulio Viola, G. Venvik Ganerød, C.-h. Wahlgren
    Abstract:

    [1] The Swedish Nuclear Fuel and Waste Management Company (SKB) is undertaking site investigation at two locations in Sweden, Forsmark and Laxemar-Simpevarp, with the aim of identifying a suitable area for the construction of a deep repository for the disposal of highly radioactive nuclear waste. Fault slip data from outcrops and oriented drill cores were used to compute paleostress states and to unravel the sites' Brittle Deformation history. Results from the Laxemar-Simpevarp area show that its suggested Brittle history results from multiple reactivation of fracture and fault sets caused by the many orogenic episodes that affected the region during at least 1.5 Ga of geological evolution in the Brittle Deformational regime. Two compressional, approximately NW/NNW-SE/SSE and NNE-SSW oriented shortening events generated sets of conjugate, steep strike-slip fractures. These sets formed during the late stages of the Svecokarelian and possibly also of the Gothian orogeny, soon after the region entered the Brittle Deformation domain. The Mesoproterozoic Sveconorwegian orogeny generated fractures and faults that are assigned to a third set of conjugate strike-slip faults, which constrain an approximately E-W σ1. The Caledonian shortening, oriented approximately NW-SE to E-W, reactivated the latter but also formed a new, similarly oriented set of subvertical strike-slip fractures. Permian transtension was oriented NW-SW and caused a prominent set of moderately dipping NW-SE trending normal faults in the Precambrian basement of the study area. Two other approximately NW-SW and NW-SE oriented shortening events are recorded in Ordovician limestones and can be tentatively linked to the far-field effects of the Laramide and Alpine orogenies.

  • unraveling 1 5 ga of Brittle Deformation history in the laxemar simpevarp area southeast sweden a contribution to the swedish site investigation study for the disposal of highly radioactive nuclear waste
    Tectonics, 2009
    Co-Authors: Giulio Viola, Venvik G Ganerod, C.-h. Wahlgren
    Abstract:

    [1] The Swedish Nuclear Fuel and Waste Management Company (SKB) is undertaking site investigation at two locations in Sweden, Forsmark and Laxemar-Simpevarp, with the aim of identifying a suitable area for the construction of a deep repository for the disposal of highly radioactive nuclear waste. Fault slip data from outcrops and oriented drill cores were used to compute paleostress states and to unravel the sites' Brittle Deformation history. Results from the Laxemar-Simpevarp area show that its suggested Brittle history results from multiple reactivation of fracture and fault sets caused by the many orogenic episodes that affected the region during at least 1.5 Ga of geological evolution in the Brittle Deformational regime. Two compressional, approximately NW/NNW-SE/SSE and NNE-SSW oriented shortening events generated sets of conjugate, steep strike-slip fractures. These sets formed during the late stages of the Svecokarelian and possibly also of the Gothian orogeny, soon after the region entered the Brittle Deformation domain. The Mesoproterozoic Sveconorwegian orogeny generated fractures and faults that are assigned to a third set of conjugate strike-slip faults, which constrain an approximately E-W σ1. The Caledonian shortening, oriented approximately NW-SE to E-W, reactivated the latter but also formed a new, similarly oriented set of subvertical strike-slip fractures. Permian transtension was oriented NW-SW and caused a prominent set of moderately dipping NW-SE trending normal faults in the Precambrian basement of the study area. Two other approximately NW-SW and NW-SE oriented shortening events are recorded in Ordovician limestones and can be tentatively linked to the far-field effects of the Laramide and Alpine orogenies.

Van Lichtervelde Marieke - One of the best experts on this subject based on the ideXlab platform.

  • Uranium mineralization associated with late magmatic ductile to Brittle Deformation and Na–Ca metasomatism of the Pan-African A-type Zabili syntectonic pluton (Mayo-Kebbi massif, SW Chad)
    Mineralium Deposita, 2020
    Co-Authors: Vanderhaeghe Olivier, Mbaguedje Diondoh, Eglinger Aurélien, Ohnenstetter Maryse, Isseini Moussa, Cuney Michel, Poujol Marc, Anne-sylvie André-mayer, Van Lichtervelde Marieke
    Abstract:

    The Mayo-Kebbi massif (Chad) exposes a Neoproterozoic juvenile crustal segment that has been tectonically accreted in the Central African Orogenic Belt and reworked during the Pan-African orogeny. It comprises a syntectonic high-K magmatic suite including the Zabili A-type granitic pluton. The Zabili pluton is made of a highly differentiated granite generated by fractional crystallization of a magma formed by partial melting of a Neoproterozoic juvenile protolith. Syn- to post-magmatic ductile to Brittle Deformation of the Zabili pluton is associated with metasomatism and deposition of uranium. Primary magmatic U-bearing minerals are zircon, monazite, and uranothorite. Late-magmatic Deformation and Na-metasomatism are marked by the development of R’ antithetic shear zones with high-temperature dynamic recrystallization of K-feldspar and Ca-plagioclase phenocrysts coeval with crystallization of albite along Deformation bands and grain boundaries, and crystallization of interstitial amphibole, calcite epidote and albite also affected by intracrystalline Deformation. At this stage, U-bearing minerals are monazite, uraninite, brannerite (pseudomorphosed in ekanite). This late-magmatic event is dated by U–Th–Pb on monazite at 599 ± 4 Ma. Brittle Deformation and Ca-metasomatism are marked by cataclastic zones and veins containing albite, epidote, calcite, chlorite, apatite, metamict zircon, pitchblende, U-silicates, and iron oxides. U-bearing minerals are altered and/or remobilized in ekanite, kasolite, and uranophane. These data suggest that the uranium mineralization hosted by the Zabili pluton records a superposition of processes and traces extreme crustal differentiation of a Neoproterozoic juvenile crustal segment reworked during the Pan-African orogeny.

  • Uranium mineralization associated with late magmatic ductile to Brittle Deformation and Na–Ca metasomatism of the Pan-African A-type Zabili syntectonic pluton (Mayo-Kebbi massif, SW Chad)
    'Springer Science and Business Media LLC', 2020
    Co-Authors: Vanderhaeghe Olivier, André-mayer Anne-sylvie, Mbaguedje Diondoh, Eglinger Aurélien, Ohnenstetter Maryse, Isseini Moussa, Cuney Michel, Poujol Marc, Van Lichtervelde Marieke
    Abstract:

    International audienceThe Mayo-Kebbi massif (Chad) exposes a Neoproterozoic juvenile crustal segment that has been tectonically accreted in the Central African Orogenic Belt and reworked during the Pan-African orogeny. It comprises a syntectonic high-K magmatic suite including the Zabili A-type granitic pluton. The Zabili pluton is made of a highly differentiated granite generated by fractional crystallization of a magma formed by partial melting of a Neoproterozoic juvenile protolith. Syn- to post-magmatic ductile to Brittle Deformation of the Zabili pluton is associated with metasomatism and deposition of uranium. Primary magmatic U-bearing minerals are zircon, monazite, and uranothorite. Late-magmatic Deformation and Na-metasomatism are marked by the development of R’ antithetic shear zones with high-temperature dynamic recrystallization of K-feldspar and Ca-plagioclase phenocrysts coeval with crystallization of albite along Deformation bands and grain boundaries, and crystallization of interstitial amphibole, calcite epidote and albite also affected by intracrystalline Deformation. At this stage, U-bearing minerals are monazite, uraninite, brannerite (pseudomorphosed in ekanite). This late-magmatic event is dated by U–Th–Pb on monazite at 599 ± 4 Ma. Brittle Deformation and Ca-metasomatism are marked by cataclastic zones and veins containing albite, epidote, calcite, chlorite, apatite, metamict zircon, pitchblende, U-silicates, and iron oxides. U-bearing minerals are altered and/or remobilized in ekanite, kasolite, and uranophane. These data suggest that the uranium mineralization hosted by the Zabili pluton records a superposition of processes and traces extreme crustal differentiation of a Neoproterozoic juvenile crustal segment reworked during the Pan-African orogeny

Marc Fournier - One of the best experts on this subject based on the ideXlab platform.

  • polyphase ductile Brittle Deformation along a major tectonic boundary in an ophiolitic nappe alpine corsica insights on subduction zone intermediate depth asperities
    Journal of Structural Geology, 2017
    Co-Authors: Remi Magott, Olivier Fabbri, Marc Fournier
    Abstract:

    In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes metagabbro over serpentinite and peridotite. Ductile and Brittle Deformation structures are observed in the fault damage zones. In the metagabbro damage zone, early Deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early Deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic Deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late Deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-metagabbro interfaces, rare or absent at serpentinite-metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-metagabbro contacts could correspond to asperities whereas low-friction serpentinite-metagabbro contacts could correspond to creeping zones.

  • Polyphase ductile/Brittle Deformation along a major tectonic boundary in an ophiolitic nappe, Alpine Corsica: Insights on subduction zone intermediate-depth asperities
    Journal of Structural Geology, 2017
    Co-Authors: Remi Magott, Olivier Fabbri, Marc Fournier
    Abstract:

    In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes metagabbro over serpentinite and peridotite. Ductile and Brittle Deformation structures are observed in the fault damage zones. In the metagabbro damage zone, early Deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early Deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic Deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late Deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-metagabbro interfaces, rare or absent at serpentinite-metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-metagabbro contacts could correspond to asperities whereas low-friction serpentinite-metagabbro contacts could correspond to creeping zones.

Riccardo Rasà - One of the best experts on this subject based on the ideXlab platform.

  • Very shallow earthquakes and Brittle Deformation in active volcanic areas: The Eatnean region as an example
    Tectonophysics, 1992
    Co-Authors: Emanuele Lo Giudice, Riccardo Rasà
    Abstract:

    Some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity (h≤1-2 km) and the Brittle Deformation pattern of the Etna volcano. The magmatic composition and structural character of Mt. Etna are described, together with its geodynamic regional context, after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity. The high level of surficial seismicity, the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of Mt. Etna is a shallow seismotectonic domain, structurally decoupled from the rest of the volcanic body.

  • Very shallow earthquakes and Brittle Deformation in active volcanic areas: The Eatnean region as an example
    Tectonophysics, 1992
    Co-Authors: Emanuele Lo Giudice, Riccardo Rasà
    Abstract:

    Abstract Some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity (h ⩽ 1–2 km) and the Brittle Deformation pattern of the Etna volcano. The magmatic composition and structural character of Mt. Etna are described, together with its geodynamic regional context, after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity. The high level of surficial seismicity, the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of Mt. Etna is a shallow seismotectonic domain, structurally decoupled from the rest of the volcanic body. This flank shows a tendency to slide in an eastern direction and is bound to the north by a left-lateral, oblique-slip, normal fault trending E-W, and in the south by an arcuate fault system with right-lateral features (right-lateral, oblique slip normal faults).