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K. Schulmann - One of the best experts on this subject based on the ideXlab platform.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2020Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:International audienceThe geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes
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An Andean type Palaeozoic convergence in the Bohemian Massif - Convergence paléozoïque de type Andin dans le Massif de Bohême
Comptes Rendus Géoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Tepla-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Tepla-Barrandian middle crust along the so-called Tepla suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Tepla-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Tepla suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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Vertical extrusion and horizontal channel flow of orogenic lower crust: key exhumation mechanisms in large hot orogens?
Journal of Metamorphic Geology, 2008Co-Authors: K. Schulmann, J. KonopÁsek, O. Lexa, J.b. Edel, P. ŠtÍpskÁ, Martin Racek, Lucie Tajčmanová, A. Peschler, Jérémie LehmannAbstract:A large database of structural, geochronological and petrological data combined with a Bouguer anomaly map is used to develop a two-stage exhumation model of deep-seated rocks in the eastern sector of the Variscan belt. An early sub-vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks. These events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18−20 kbar to depths equivalent to 8−10 kbar, and for coeval burial of upper crustal rocks to depths equivalent to 8–9 kbar. Following the folding and vertical extrusion event, sub-horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening. Fabrics that record the early vertical extrusion originated between 350 and 340 Ma, during building of an orogenic root in response to SE-directed Saxothuringian continental subduction. Fabrics that record the later sub-horizontal exhumation event relate to an eastern promontory of the Brunia continent indenting into the rheologically weaker rocks of the orogenic root. Indentation initiated thrusting or flow of the orogenic crust over the Brunia continent in a north-directed sub-horizontal channel. This sub-horizontal flow operated between 330 and 325 Ma, and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re-equilibration. The erosion depth as well as the degree of reworking decreases from south to north, pointing to an outflow of lower crustal material to the surface, which was subsequently eroded and deposited in a foreland basin. Indentation by the Brunia continental promontory was highly noncoaxial with respect to the SE-oriented Saxothuringian continental subduction in the Early Visean, suggesting a major switch of plate configuration during the Middle to Late Visean.
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Chronological constraints on the pre-orogenic history, burial and exhumation of deep-seated rocks along the eastern margin of the Variscan Orogen, Bohemian Massif, Czech Republic
American Journal of Science, 2005Co-Authors: K. Schulmann, Alfred Kröner, J. KonopÁsek, O. Lexa, Ernst Hegner, Immo Wendt, P. ŠtÍpskÁAbstract:Key lithological units of the high-grade eastern margin of the Bohemian Massif were dated using the U-Pb and Pb-Pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the Variscan orogenic root. The protolith ages for metagranitoids, orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from Cambro-Ordovician to early Devonian times, probably related to discontinuous intracontinental rifting of Neoproterozoic crust. Our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted Neoproterozoic crust, preserved farther to the east as the Brunia microcontinent. Zircon ages for felsic granulites, high-grade gneisses of the lower crust and of a syn-convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 Ma. Exhumation of the lower crust to mid-crustal levels was a localized process that occurred at ∼340 Ma and was associated with crustal-scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin. Both types of exhumation mechanisms were driven by deep-level wedging (indentation) of the easterly Brunia continent, followed by deposition of heavy minerals and pebbles derived from high-pressure rocks in the adjacent foreland basin. Final orogenic development was characterized by NE-SW dextral transpressive shearing parallel to the Brunia margin as well as dextral trans tension associated with activity along the Elbe lithospheric fault. These processes affected the marginal parts of. the orogenic root and were accompanied by 330 to 325 Ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries. Rotation of the assembled orogenic belt, accompanied by lithospheric faulting driven by westerly subduction roll-back, may be the most plausible model to explain late deformation of the orogenic root.
P. ŠtÍpskÁ - One of the best experts on this subject based on the ideXlab platform.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2020Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:International audienceThe geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes
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An Andean type Palaeozoic convergence in the Bohemian Massif - Convergence paléozoïque de type Andin dans le Massif de Bohême
Comptes Rendus Géoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Tepla-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Tepla-Barrandian middle crust along the so-called Tepla suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Tepla-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Tepla suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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Vertical extrusion and horizontal channel flow of orogenic lower crust: key exhumation mechanisms in large hot orogens?
Journal of Metamorphic Geology, 2008Co-Authors: K. Schulmann, J. KonopÁsek, O. Lexa, J.b. Edel, P. ŠtÍpskÁ, Martin Racek, Lucie Tajčmanová, A. Peschler, Jérémie LehmannAbstract:A large database of structural, geochronological and petrological data combined with a Bouguer anomaly map is used to develop a two-stage exhumation model of deep-seated rocks in the eastern sector of the Variscan belt. An early sub-vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks. These events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18−20 kbar to depths equivalent to 8−10 kbar, and for coeval burial of upper crustal rocks to depths equivalent to 8–9 kbar. Following the folding and vertical extrusion event, sub-horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening. Fabrics that record the early vertical extrusion originated between 350 and 340 Ma, during building of an orogenic root in response to SE-directed Saxothuringian continental subduction. Fabrics that record the later sub-horizontal exhumation event relate to an eastern promontory of the Brunia continent indenting into the rheologically weaker rocks of the orogenic root. Indentation initiated thrusting or flow of the orogenic crust over the Brunia continent in a north-directed sub-horizontal channel. This sub-horizontal flow operated between 330 and 325 Ma, and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re-equilibration. The erosion depth as well as the degree of reworking decreases from south to north, pointing to an outflow of lower crustal material to the surface, which was subsequently eroded and deposited in a foreland basin. Indentation by the Brunia continental promontory was highly noncoaxial with respect to the SE-oriented Saxothuringian continental subduction in the Early Visean, suggesting a major switch of plate configuration during the Middle to Late Visean.
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Chronological constraints on the pre-orogenic history, burial and exhumation of deep-seated rocks along the eastern margin of the Variscan Orogen, Bohemian Massif, Czech Republic
American Journal of Science, 2005Co-Authors: K. Schulmann, Alfred Kröner, J. KonopÁsek, O. Lexa, Ernst Hegner, Immo Wendt, P. ŠtÍpskÁAbstract:Key lithological units of the high-grade eastern margin of the Bohemian Massif were dated using the U-Pb and Pb-Pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the Variscan orogenic root. The protolith ages for metagranitoids, orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from Cambro-Ordovician to early Devonian times, probably related to discontinuous intracontinental rifting of Neoproterozoic crust. Our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted Neoproterozoic crust, preserved farther to the east as the Brunia microcontinent. Zircon ages for felsic granulites, high-grade gneisses of the lower crust and of a syn-convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 Ma. Exhumation of the lower crust to mid-crustal levels was a localized process that occurred at ∼340 Ma and was associated with crustal-scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin. Both types of exhumation mechanisms were driven by deep-level wedging (indentation) of the easterly Brunia continent, followed by deposition of heavy minerals and pebbles derived from high-pressure rocks in the adjacent foreland basin. Final orogenic development was characterized by NE-SW dextral transpressive shearing parallel to the Brunia margin as well as dextral trans tension associated with activity along the Elbe lithospheric fault. These processes affected the marginal parts of. the orogenic root and were accompanied by 330 to 325 Ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries. Rotation of the assembled orogenic belt, accompanied by lithospheric faulting driven by westerly subduction roll-back, may be the most plausible model to explain late deformation of the orogenic root.
S. Ulrich - One of the best experts on this subject based on the ideXlab platform.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2020Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:International audienceThe geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes
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An Andean type Palaeozoic convergence in the Bohemian Massif - Convergence paléozoïque de type Andin dans le Massif de Bohême
Comptes Rendus Géoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Tepla-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Tepla-Barrandian middle crust along the so-called Tepla suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Tepla-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Tepla suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
J. KonopÁsek - One of the best experts on this subject based on the ideXlab platform.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2020Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:International audienceThe geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes
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An Andean type Palaeozoic convergence in the Bohemian Massif - Convergence paléozoïque de type Andin dans le Massif de Bohême
Comptes Rendus Géoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Tepla-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Tepla-Barrandian middle crust along the so-called Tepla suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Tepla-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Tepla suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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Vertical extrusion and horizontal channel flow of orogenic lower crust: key exhumation mechanisms in large hot orogens?
Journal of Metamorphic Geology, 2008Co-Authors: K. Schulmann, J. KonopÁsek, O. Lexa, J.b. Edel, P. ŠtÍpskÁ, Martin Racek, Lucie Tajčmanová, A. Peschler, Jérémie LehmannAbstract:A large database of structural, geochronological and petrological data combined with a Bouguer anomaly map is used to develop a two-stage exhumation model of deep-seated rocks in the eastern sector of the Variscan belt. An early sub-vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks. These events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18−20 kbar to depths equivalent to 8−10 kbar, and for coeval burial of upper crustal rocks to depths equivalent to 8–9 kbar. Following the folding and vertical extrusion event, sub-horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening. Fabrics that record the early vertical extrusion originated between 350 and 340 Ma, during building of an orogenic root in response to SE-directed Saxothuringian continental subduction. Fabrics that record the later sub-horizontal exhumation event relate to an eastern promontory of the Brunia continent indenting into the rheologically weaker rocks of the orogenic root. Indentation initiated thrusting or flow of the orogenic crust over the Brunia continent in a north-directed sub-horizontal channel. This sub-horizontal flow operated between 330 and 325 Ma, and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re-equilibration. The erosion depth as well as the degree of reworking decreases from south to north, pointing to an outflow of lower crustal material to the surface, which was subsequently eroded and deposited in a foreland basin. Indentation by the Brunia continental promontory was highly noncoaxial with respect to the SE-oriented Saxothuringian continental subduction in the Early Visean, suggesting a major switch of plate configuration during the Middle to Late Visean.
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Chronological constraints on the pre-orogenic history, burial and exhumation of deep-seated rocks along the eastern margin of the Variscan Orogen, Bohemian Massif, Czech Republic
American Journal of Science, 2005Co-Authors: K. Schulmann, Alfred Kröner, J. KonopÁsek, O. Lexa, Ernst Hegner, Immo Wendt, P. ŠtÍpskÁAbstract:Key lithological units of the high-grade eastern margin of the Bohemian Massif were dated using the U-Pb and Pb-Pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the Variscan orogenic root. The protolith ages for metagranitoids, orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from Cambro-Ordovician to early Devonian times, probably related to discontinuous intracontinental rifting of Neoproterozoic crust. Our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted Neoproterozoic crust, preserved farther to the east as the Brunia microcontinent. Zircon ages for felsic granulites, high-grade gneisses of the lower crust and of a syn-convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 Ma. Exhumation of the lower crust to mid-crustal levels was a localized process that occurred at ∼340 Ma and was associated with crustal-scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin. Both types of exhumation mechanisms were driven by deep-level wedging (indentation) of the easterly Brunia continent, followed by deposition of heavy minerals and pebbles derived from high-pressure rocks in the adjacent foreland basin. Final orogenic development was characterized by NE-SW dextral transpressive shearing parallel to the Brunia margin as well as dextral trans tension associated with activity along the Elbe lithospheric fault. These processes affected the marginal parts of. the orogenic root and were accompanied by 330 to 325 Ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries. Rotation of the assembled orogenic belt, accompanied by lithospheric faulting driven by westerly subduction roll-back, may be the most plausible model to explain late deformation of the orogenic root.
O. Lexa - One of the best experts on this subject based on the ideXlab platform.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2020Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:International audienceThe geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes
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An Andean type Palaeozoic convergence in the Bohemian Massif - Convergence paléozoïque de type Andin dans le Massif de Bohême
Comptes Rendus Géoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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An Andean type Palaeozoic convergence in the Bohemian Massif
Comptes Rendus Geoscience, 2009Co-Authors: K. Schulmann, J. KonopÁsek, V. Janousek, O. Lexa, J.m. Lardeaux, J.b. Edel, P. ŠtÍpskÁ, S. UlrichAbstract:The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Tepla-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Tepla-Barrandian middle crust along the so-called Tepla suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Tepla-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Tepla suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.
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Vertical extrusion and horizontal channel flow of orogenic lower crust: key exhumation mechanisms in large hot orogens?
Journal of Metamorphic Geology, 2008Co-Authors: K. Schulmann, J. KonopÁsek, O. Lexa, J.b. Edel, P. ŠtÍpskÁ, Martin Racek, Lucie Tajčmanová, A. Peschler, Jérémie LehmannAbstract:A large database of structural, geochronological and petrological data combined with a Bouguer anomaly map is used to develop a two-stage exhumation model of deep-seated rocks in the eastern sector of the Variscan belt. An early sub-vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks. These events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18−20 kbar to depths equivalent to 8−10 kbar, and for coeval burial of upper crustal rocks to depths equivalent to 8–9 kbar. Following the folding and vertical extrusion event, sub-horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening. Fabrics that record the early vertical extrusion originated between 350 and 340 Ma, during building of an orogenic root in response to SE-directed Saxothuringian continental subduction. Fabrics that record the later sub-horizontal exhumation event relate to an eastern promontory of the Brunia continent indenting into the rheologically weaker rocks of the orogenic root. Indentation initiated thrusting or flow of the orogenic crust over the Brunia continent in a north-directed sub-horizontal channel. This sub-horizontal flow operated between 330 and 325 Ma, and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re-equilibration. The erosion depth as well as the degree of reworking decreases from south to north, pointing to an outflow of lower crustal material to the surface, which was subsequently eroded and deposited in a foreland basin. Indentation by the Brunia continental promontory was highly noncoaxial with respect to the SE-oriented Saxothuringian continental subduction in the Early Visean, suggesting a major switch of plate configuration during the Middle to Late Visean.
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Chronological constraints on the pre-orogenic history, burial and exhumation of deep-seated rocks along the eastern margin of the Variscan Orogen, Bohemian Massif, Czech Republic
American Journal of Science, 2005Co-Authors: K. Schulmann, Alfred Kröner, J. KonopÁsek, O. Lexa, Ernst Hegner, Immo Wendt, P. ŠtÍpskÁAbstract:Key lithological units of the high-grade eastern margin of the Bohemian Massif were dated using the U-Pb and Pb-Pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the Variscan orogenic root. The protolith ages for metagranitoids, orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from Cambro-Ordovician to early Devonian times, probably related to discontinuous intracontinental rifting of Neoproterozoic crust. Our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted Neoproterozoic crust, preserved farther to the east as the Brunia microcontinent. Zircon ages for felsic granulites, high-grade gneisses of the lower crust and of a syn-convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 Ma. Exhumation of the lower crust to mid-crustal levels was a localized process that occurred at ∼340 Ma and was associated with crustal-scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin. Both types of exhumation mechanisms were driven by deep-level wedging (indentation) of the easterly Brunia continent, followed by deposition of heavy minerals and pebbles derived from high-pressure rocks in the adjacent foreland basin. Final orogenic development was characterized by NE-SW dextral transpressive shearing parallel to the Brunia margin as well as dextral trans tension associated with activity along the Elbe lithospheric fault. These processes affected the marginal parts of. the orogenic root and were accompanied by 330 to 325 Ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries. Rotation of the assembled orogenic belt, accompanied by lithospheric faulting driven by westerly subduction roll-back, may be the most plausible model to explain late deformation of the orogenic root.
