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Hugues Raimbourg - One of the best experts on this subject based on the ideXlab platform.
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Large-scale strain localization induced by phase nucleation in mid-crustal granitoids of the south Armorican massif
Tectonophysics, 2018Co-Authors: Nicolas Mansard, Hugues Raimbourg, Romain Augier, Jacques Précigout, Nicole Le BretonAbstract:The reduction of grain size is believed to play a critical role in strain localization to form shear zones. Although many mechanisms have been proposed, the source of grain size reduction remains debated. The South Armorican Shear Zone (SASZ) is a crustal-scale strike-slip fault that deforms granitoids at mid-crustal conditions. The SASZ records the transition from protolith to ultramylonite, representative of increasing ductile shear strain. To investigate the evolution of strain localization, the different states of deformation were studied using a combination of detailed microstructural, chemical and electron backscatter diffraction analyzes. Increasing strain from protolith to ultramylonite resulted in (1) grain size reduction, (2) the development of interconnected monophase layers of mica and incipient mixed-phase zones composed of phengite-Quartz ± K-feldspar in protomylonite and low-strain mylonite, and (3) the formation of fine-grained mixed-phase zones composed of K-feldspar-Quartz ± phengite in high-strain mylonite and ultramylonite. We propose that the causes for interconnection of mica are the formation of cracks in the protolith combined with fluid-assisted nucleation. The latter process also plays a major role in phase mixing, as attested by the precipitation of K-feldspar at triple junctions in Quartz-rich layers and in fine-grained tails of inherited K-feldspar porphyroclasts in ultramylonite. The transition from Quartz-rich layers and mixed-phase zones is accompanied by a strong dispersion of the Quartz lattice preferred orientation. These microstructural and textural evidences suggest that phase nucleation is the major process behind phase mixing, possibly accompanied by the action of grain-boundary sliding to open cavities during deformation. Instead of a single process, we therefore highlight a succession of weakening processes in the evolution of the SASZ, starting with the crystallization of mica as a first weakening material, and then evolving with the formation of very fine-grained mixed-phase zones made principally of feldspar, Quartz and phengite.
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Deformation processes at the down-dip limit of the seismogenic zone: The example of Shimanto accretionary complex
Tectonophysics, 2016Co-Authors: Giulia Palazzin, Hugues Raimbourg, Vincent Famin, Laurent Jolivet, Y Kusaba, A YamaguchiAbstract:In order to constrain deformation processes close to the brittle-ductile transition in seismogenic zone, we have carried out a microstructural study in the Shimanto accretionary complex (Japan), the fossil equivalent of modern Nankai accretionary prisms. The Hyuga Tectonic Mélange was sheared along the plate interface at mean temperatures of 245 °C ± 30 °C, as estimated by Raman spectroscopy of carbonaceous material (RSCM). It contains strongly elongated Quartz ribbons, characterized by very high fluid inclusions density, as well as micro-veins of Quartz. Both fluid inclusion planes and micro-veins are preferentially developed orthogonal to the stretching direction. Furthermore, crystallographic preferred orientation (CPO) of Quartz c-axes in the ribbons has maxima parallel to the stretching direction. Recrystallization to a small grain size is restricted to rare deformation bands cutting across the ribbons. In such recrystallized Quartz domains, CPO of Quartz c-axes are orthogonal to foliation plane. The evolution of deformation micro-processes with increasing temperature can be further analyzed using the Foliated Morotsuka, a slightly higher-grade metamorphic unit (342 ± 30 °C by RSCM) from the Shimanto accretionary complex. In this unit, in contrast to Hyuga Tectonic Mélange, recrystallization of Quartz veins is penetrative. CPO of Quartz c-axes is concentrated perpendicularly to foliation plane. These variations in microstructures and Quartz crystallographic fabric reflect a change in the dominant deformation mechanism with increasing temperatures: above ~300 °C, dislocation creep is dominant and results in intense Quartz dynamic recrystallization. In contrast, below ~300 °C, Quartz plasticity is not totally activated and pressure solution is the major deformation process responsible for Quartz ribbons growth. In addition, the geometry of the Quartz ribbons with respect to the phyllosilicate-rich shear zones shows that bulk rheology is controlled by Quartz behavior. Consequently, below 300 °C, the application of Quartz pressure-solution laws, based on realistic geometry derived from Hyuga microstructures, results in strongly lowering the overall strength of the plate interface with respect to the classical brittle envelop.
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Fluid circulation in the depths of accretionary prisms: an example of the Shimanto Belt, Kyushu, Japan
Tectonophysics, 2015Co-Authors: Hugues Raimbourg, Romain Augier, Giulia Palazzin, Vincent Famin, Maxime Vacelet, Claire Ramboz, Asuka Yamaguchi, Gaku KimuraAbstract:Accretionary prisms constitute ideal targets to study fluid circulation and fluid-rock interactions at depths beyond the reach of active margin deep drilling. The highest-grade rocks from the Shimanto Belt on Kyushu were buried under 3-5 kbars at ~ 300°C (Toriumi and Teruya, 1988). They contain abundant Quartz veins, formed throughout burial and exhumation and variably affected by brittle and ductile deformation. Cathodoluminescence (CL) reveals the existence of two distinct types of Quartz, characterized by a blue and brown color, respectively. CL-blue Quartz fills macro-veins (width ≥ 10μm), while CL-brown Quartz is present in micro-veins (width ~ 1 − 10μm) and ductilely recrystallized domains. On the basis of microstructures, the fluids associated with the CL-blue and CL-brown Quartz are interpreted as “external” and “local”, respectively. Quartz growth rims of alternating CL colors as well as mutually cross-cutting veins show that the two fluids cyclically wetted the host rock. From fluid inclusions analysis, the fluid associated with CL-blue Quartz has a salinity similar to seawater, while the fluid associated with CL-brown Quartz is less saline. In addition, CL-blue Quartz is richer in aluminum than the CL-brown one. In contrast to the salinity/aluminum signature, the δ18O isotopic signature of both Quartz types is similar and buffered by host rock. The difference between the preservation of the salinity signature of the fluid and the loss of its δ18O signature is explained by quicker exchange kinetics and larger host rock buffering capacity for isotopic reequilibration. The “local” fluid, associated with CL-brown Quartz, reflects the dilution of pore water by the pure water produced by prograde dehydration reactions of clay minerals. The “external” fluid associated with CL-blue Quartz is interpreted as seawater or pore water from shallow (depth
Nicole Le Breton - One of the best experts on this subject based on the ideXlab platform.
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Large-scale strain localization induced by phase nucleation in mid-crustal granitoids of the south Armorican massif
Tectonophysics, 2018Co-Authors: Nicolas Mansard, Hugues Raimbourg, Romain Augier, Jacques Précigout, Nicole Le BretonAbstract:The reduction of grain size is believed to play a critical role in strain localization to form shear zones. Although many mechanisms have been proposed, the source of grain size reduction remains debated. The South Armorican Shear Zone (SASZ) is a crustal-scale strike-slip fault that deforms granitoids at mid-crustal conditions. The SASZ records the transition from protolith to ultramylonite, representative of increasing ductile shear strain. To investigate the evolution of strain localization, the different states of deformation were studied using a combination of detailed microstructural, chemical and electron backscatter diffraction analyzes. Increasing strain from protolith to ultramylonite resulted in (1) grain size reduction, (2) the development of interconnected monophase layers of mica and incipient mixed-phase zones composed of phengite-Quartz ± K-feldspar in protomylonite and low-strain mylonite, and (3) the formation of fine-grained mixed-phase zones composed of K-feldspar-Quartz ± phengite in high-strain mylonite and ultramylonite. We propose that the causes for interconnection of mica are the formation of cracks in the protolith combined with fluid-assisted nucleation. The latter process also plays a major role in phase mixing, as attested by the precipitation of K-feldspar at triple junctions in Quartz-rich layers and in fine-grained tails of inherited K-feldspar porphyroclasts in ultramylonite. The transition from Quartz-rich layers and mixed-phase zones is accompanied by a strong dispersion of the Quartz lattice preferred orientation. These microstructural and textural evidences suggest that phase nucleation is the major process behind phase mixing, possibly accompanied by the action of grain-boundary sliding to open cavities during deformation. Instead of a single process, we therefore highlight a succession of weakening processes in the evolution of the SASZ, starting with the crystallization of mica as a first weakening material, and then evolving with the formation of very fine-grained mixed-phase zones made principally of feldspar, Quartz and phengite.
Romain Augier - One of the best experts on this subject based on the ideXlab platform.
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Large-scale strain localization induced by phase nucleation in mid-crustal granitoids of the south Armorican massif
Tectonophysics, 2018Co-Authors: Nicolas Mansard, Hugues Raimbourg, Romain Augier, Jacques Précigout, Nicole Le BretonAbstract:The reduction of grain size is believed to play a critical role in strain localization to form shear zones. Although many mechanisms have been proposed, the source of grain size reduction remains debated. The South Armorican Shear Zone (SASZ) is a crustal-scale strike-slip fault that deforms granitoids at mid-crustal conditions. The SASZ records the transition from protolith to ultramylonite, representative of increasing ductile shear strain. To investigate the evolution of strain localization, the different states of deformation were studied using a combination of detailed microstructural, chemical and electron backscatter diffraction analyzes. Increasing strain from protolith to ultramylonite resulted in (1) grain size reduction, (2) the development of interconnected monophase layers of mica and incipient mixed-phase zones composed of phengite-Quartz ± K-feldspar in protomylonite and low-strain mylonite, and (3) the formation of fine-grained mixed-phase zones composed of K-feldspar-Quartz ± phengite in high-strain mylonite and ultramylonite. We propose that the causes for interconnection of mica are the formation of cracks in the protolith combined with fluid-assisted nucleation. The latter process also plays a major role in phase mixing, as attested by the precipitation of K-feldspar at triple junctions in Quartz-rich layers and in fine-grained tails of inherited K-feldspar porphyroclasts in ultramylonite. The transition from Quartz-rich layers and mixed-phase zones is accompanied by a strong dispersion of the Quartz lattice preferred orientation. These microstructural and textural evidences suggest that phase nucleation is the major process behind phase mixing, possibly accompanied by the action of grain-boundary sliding to open cavities during deformation. Instead of a single process, we therefore highlight a succession of weakening processes in the evolution of the SASZ, starting with the crystallization of mica as a first weakening material, and then evolving with the formation of very fine-grained mixed-phase zones made principally of feldspar, Quartz and phengite.
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Fluid circulation in the depths of accretionary prisms: an example of the Shimanto Belt, Kyushu, Japan
Tectonophysics, 2015Co-Authors: Hugues Raimbourg, Romain Augier, Giulia Palazzin, Vincent Famin, Maxime Vacelet, Claire Ramboz, Asuka Yamaguchi, Gaku KimuraAbstract:Accretionary prisms constitute ideal targets to study fluid circulation and fluid-rock interactions at depths beyond the reach of active margin deep drilling. The highest-grade rocks from the Shimanto Belt on Kyushu were buried under 3-5 kbars at ~ 300°C (Toriumi and Teruya, 1988). They contain abundant Quartz veins, formed throughout burial and exhumation and variably affected by brittle and ductile deformation. Cathodoluminescence (CL) reveals the existence of two distinct types of Quartz, characterized by a blue and brown color, respectively. CL-blue Quartz fills macro-veins (width ≥ 10μm), while CL-brown Quartz is present in micro-veins (width ~ 1 − 10μm) and ductilely recrystallized domains. On the basis of microstructures, the fluids associated with the CL-blue and CL-brown Quartz are interpreted as “external” and “local”, respectively. Quartz growth rims of alternating CL colors as well as mutually cross-cutting veins show that the two fluids cyclically wetted the host rock. From fluid inclusions analysis, the fluid associated with CL-blue Quartz has a salinity similar to seawater, while the fluid associated with CL-brown Quartz is less saline. In addition, CL-blue Quartz is richer in aluminum than the CL-brown one. In contrast to the salinity/aluminum signature, the δ18O isotopic signature of both Quartz types is similar and buffered by host rock. The difference between the preservation of the salinity signature of the fluid and the loss of its δ18O signature is explained by quicker exchange kinetics and larger host rock buffering capacity for isotopic reequilibration. The “local” fluid, associated with CL-brown Quartz, reflects the dilution of pore water by the pure water produced by prograde dehydration reactions of clay minerals. The “external” fluid associated with CL-blue Quartz is interpreted as seawater or pore water from shallow (depth
Giulia Palazzin - One of the best experts on this subject based on the ideXlab platform.
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Deformation processes at the down-dip limit of the seismogenic zone: The example of Shimanto accretionary complex
Tectonophysics, 2016Co-Authors: Giulia Palazzin, Hugues Raimbourg, Vincent Famin, Laurent Jolivet, Y Kusaba, A YamaguchiAbstract:In order to constrain deformation processes close to the brittle-ductile transition in seismogenic zone, we have carried out a microstructural study in the Shimanto accretionary complex (Japan), the fossil equivalent of modern Nankai accretionary prisms. The Hyuga Tectonic Mélange was sheared along the plate interface at mean temperatures of 245 °C ± 30 °C, as estimated by Raman spectroscopy of carbonaceous material (RSCM). It contains strongly elongated Quartz ribbons, characterized by very high fluid inclusions density, as well as micro-veins of Quartz. Both fluid inclusion planes and micro-veins are preferentially developed orthogonal to the stretching direction. Furthermore, crystallographic preferred orientation (CPO) of Quartz c-axes in the ribbons has maxima parallel to the stretching direction. Recrystallization to a small grain size is restricted to rare deformation bands cutting across the ribbons. In such recrystallized Quartz domains, CPO of Quartz c-axes are orthogonal to foliation plane. The evolution of deformation micro-processes with increasing temperature can be further analyzed using the Foliated Morotsuka, a slightly higher-grade metamorphic unit (342 ± 30 °C by RSCM) from the Shimanto accretionary complex. In this unit, in contrast to Hyuga Tectonic Mélange, recrystallization of Quartz veins is penetrative. CPO of Quartz c-axes is concentrated perpendicularly to foliation plane. These variations in microstructures and Quartz crystallographic fabric reflect a change in the dominant deformation mechanism with increasing temperatures: above ~300 °C, dislocation creep is dominant and results in intense Quartz dynamic recrystallization. In contrast, below ~300 °C, Quartz plasticity is not totally activated and pressure solution is the major deformation process responsible for Quartz ribbons growth. In addition, the geometry of the Quartz ribbons with respect to the phyllosilicate-rich shear zones shows that bulk rheology is controlled by Quartz behavior. Consequently, below 300 °C, the application of Quartz pressure-solution laws, based on realistic geometry derived from Hyuga microstructures, results in strongly lowering the overall strength of the plate interface with respect to the classical brittle envelop.
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Fluid circulation in the depths of accretionary prisms: an example of the Shimanto Belt, Kyushu, Japan
Tectonophysics, 2015Co-Authors: Hugues Raimbourg, Romain Augier, Giulia Palazzin, Vincent Famin, Maxime Vacelet, Claire Ramboz, Asuka Yamaguchi, Gaku KimuraAbstract:Accretionary prisms constitute ideal targets to study fluid circulation and fluid-rock interactions at depths beyond the reach of active margin deep drilling. The highest-grade rocks from the Shimanto Belt on Kyushu were buried under 3-5 kbars at ~ 300°C (Toriumi and Teruya, 1988). They contain abundant Quartz veins, formed throughout burial and exhumation and variably affected by brittle and ductile deformation. Cathodoluminescence (CL) reveals the existence of two distinct types of Quartz, characterized by a blue and brown color, respectively. CL-blue Quartz fills macro-veins (width ≥ 10μm), while CL-brown Quartz is present in micro-veins (width ~ 1 − 10μm) and ductilely recrystallized domains. On the basis of microstructures, the fluids associated with the CL-blue and CL-brown Quartz are interpreted as “external” and “local”, respectively. Quartz growth rims of alternating CL colors as well as mutually cross-cutting veins show that the two fluids cyclically wetted the host rock. From fluid inclusions analysis, the fluid associated with CL-blue Quartz has a salinity similar to seawater, while the fluid associated with CL-brown Quartz is less saline. In addition, CL-blue Quartz is richer in aluminum than the CL-brown one. In contrast to the salinity/aluminum signature, the δ18O isotopic signature of both Quartz types is similar and buffered by host rock. The difference between the preservation of the salinity signature of the fluid and the loss of its δ18O signature is explained by quicker exchange kinetics and larger host rock buffering capacity for isotopic reequilibration. The “local” fluid, associated with CL-brown Quartz, reflects the dilution of pore water by the pure water produced by prograde dehydration reactions of clay minerals. The “external” fluid associated with CL-blue Quartz is interpreted as seawater or pore water from shallow (depth
Douglas Winston Fuerstenau - One of the best experts on this subject based on the ideXlab platform.
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selective flocculation of hematite in Quartz hematite ferric ion polyacrylic acid system part 2 effect of grinding and a hydrofluoric treatment on selectivity of flocculation
International Journal of Mineral Processing, 2014Co-Authors: Jan Drzymala, Douglas Winston FuerstenauAbstract:Abstract A variety of materials and particle preparation methods were investigated to delineate their effect on the selective flocculation of Quartz and hematite suspensions with polyacrylic acid (PAA) as flocculant. Synthetic hematite particles were effectively separated by selective flocculation with PAA in the 3 to 8 pH range from a mixture of Quartz that had been ground in a Quartz mill. However, grinding the Quartz in a porcelain mill or co-grinding it with the hematite fines in a Quartz mill resulted in non-selective flocculation due to cross-contamination of the Quartz particles by coating of impurities from the porcelain or from hematite. Treatment of the ground product with hydrofluoric acid restored the purity of the Quartz particles, thereby restoring selectivity in the flocculation step. Effective selective flocculation of Tilden hematitic taconite ore was achieved by hydrofluoric acid treatment of the minus 37 μm fraction of the crushed ore.
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Selective flocculation of hematite in Quartz–hematite–ferric ion–polyacrylic acid system. Part 2. Effect of grinding and a hydrofluoric treatment on selectivity of flocculation
International Journal of Mineral Processing, 2014Co-Authors: Jan Drzymala, Douglas Winston FuerstenauAbstract:Abstract A variety of materials and particle preparation methods were investigated to delineate their effect on the selective flocculation of Quartz and hematite suspensions with polyacrylic acid (PAA) as flocculant. Synthetic hematite particles were effectively separated by selective flocculation with PAA in the 3 to 8 pH range from a mixture of Quartz that had been ground in a Quartz mill. However, grinding the Quartz in a porcelain mill or co-grinding it with the hematite fines in a Quartz mill resulted in non-selective flocculation due to cross-contamination of the Quartz particles by coating of impurities from the porcelain or from hematite. Treatment of the ground product with hydrofluoric acid restored the purity of the Quartz particles, thereby restoring selectivity in the flocculation step. Effective selective flocculation of Tilden hematitic taconite ore was achieved by hydrofluoric acid treatment of the minus 37 μm fraction of the crushed ore.