Modelling fault reactivation and fluid flow around a fault restraining step‐over structure in the L averton gold region, Y ilgarn C raton, W estern A ustralia
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Abstract Laverton is an important region in the Y ilgarn C raton for gold mineralization. Previous studies suggested that the premineralization structure was dominated by a fault restraining step‐over structure with the W allaby fault and S unrise S hear Z one as the key fault splays hosting the world‐class W allaby and S unrise D am gold deposits, respectively. Two major gold mineralization phases occurred during two of a series of tectonic events with different far‐field stress orientations. 3D coupled deformation and fluid flow modelling was used to investigate the effects of varying far‐field stress orientations on reactivation of the fault structure in the region. The results show that structural reactivation is sensitive to regional shortening directions. Two shortening directions are identified to be favourable for reactivation of the Wallaby fault and Sunrise Shear Zone: (i) NW – SE shortening and (ii) ENE – WSW to E – W shortening. The reactivated segments exhibited localization of shear strain and dilation as well as fluid focusing at locations corresponding to the W allaby and S unrise D am deposits. This is in contrast to the models with shortening direction between NNW – SSE and NE – SW , which showed little fault reactivation at both locations. These results support previous independent interpretations of the controls on gold mineralization at L averton. The two shortening directions favourable for structural reactivation inferred from the models are consistent with the kinematics of the two main gold mineralization events in the region. Our results suggest that strain localization, dilation and fluid focusing during structural reactivation could be some of the key factors governing gold mineralization at L averton.Keywords:
Dilation (metric space)
Stress field
Echelon formation
Abstract Numerous transcurrent NE-SW, mainly sinistral, and E-W dextral-trending shear zones transect Borborema Province, northeastern Brazil. The most important kinematic event involving those shear zones reflects deformation related to the Brasiliano (Pan-African) tectonic cycle. The Afogados da Ingazeira shear zone (AISZ) is probably the most important of the NE-SW-trending lineaments, having continuity for over 250 km. Field work associated with petrographic studies (including quartz c-axis patterns), conducted in an area encompassing the north-central part of this shear zone, indicate that sinistral transcurrent deformation was responsible for the main banding/foliation (C-S) observed in the rocks. Mineral assemblages and microstructural features are suggestive of a deformational history starting under low- to medium-amphibolite facies (thermal peak conditions) and decreasing until greenschist facies.
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The north–north‐east‐trending (NNE) shear zones, which are defined by the Jiekou shear zone and Huangmao shear zone, are located in the eastern Jiangnan Orogen. This article provides kinematics, geochronological data, and dynamics on the Jiekou and Huangmao shear zones and serves as a reference for understanding the tectonic evolution in the South China Block during the Early Palaeozoic orogeny. All shearing signatures show that the Huangmao shear zone is dextral, and the Jiekou shear zone is sinistral. Both shear zones have certain genetic connections. The rocks from the Jiekou and Huangmao shear zones are metamorphosed and deformed into protomylonite and mylonite. Results of the deformation fabrics of feldspar and quartz and quartz c ‐axis fabric analysis indicate that the ductile deformation temperatures of the Jiekou shear zone sinistral shearing are ~400–500°C. Dextral shearing with medium–high temperature (450–550°C) is mainly recorded in the Huangmao shear zone. In combination with the previous geochronology, NNE‐trending sinistral and dextral shearing in the eastern Jiangnan Orogen occurred at 465–430 Ma, coeval with the Early Palaeozoic orogeny. Therefore, the geodynamics of the NNE‐trending shear zones is related to a major strain transformation from NW to WNW, which is remotely affected by the intracontinental convergence of Yangtze and Cathaysia blocks during the Early Palaeozoic orogeny.
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The north-north-east-trending (NNE) shear zones, which are defined by the Jiekou shear zone and Huangmao shear zone, are located in the eastern Jiangnan Orogen. This article provides kinematics, geochronological data, and dynamics on the Jiekou and Huangmao shear zones and serves as a reference for understanding the tectonic evolution in the South China Block during the Early Palaeozoic orogeny. All shearing signatures show that the Huangmao shear zone is dextral, and the Jiekou shear zone is sinistral. Both shear zones have certain genetic connections. The rocks from the Jiekou and Huangmao shear zones are metamorphosed and deformed into protomylonite and mylonite. Results of the deformation fabrics of feldspar and quartz and quartzc-axis fabric analysis indicate that the ductile deformation temperatures of the Jiekou shear zone sinistral shearing are similar to 400-500 degrees C. Dextral shearing with medium-high temperature (450-550 degrees C) is mainly recorded in the Huangmao shear zone. In combination with the previous geochronology, NNE-trending sinistral and dextral shearing in the eastern Jiangnan Orogen occurred at 465-430 Ma, coeval with the Early Palaeozoic orogeny. Therefore, the geodynamics of the NNE-trending shear zones is related to a major strain transformation from NW to WNW, which is remotely affected by the intracontinental convergence of Yangtze and Cathaysia blocks during the Early Palaeozoic orogeny.
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The north-north-east-trending (NNE) shear zones, which are defined by the Jiekou shear zone and Huangmao shear zone, are located in the eastern Jiangnan Orogen. This article provides kinematics, geochronological data, and dynamics on the Jiekou and Huangmao shear zones and serves as a reference for understanding the tectonic evolution in the South China Block during the Early Palaeozoic orogeny. All shearing signatures show that the Huangmao shear zone is dextral, and the Jiekou shear zone is sinistral. Both shear zones have certain genetic connections. The rocks from the Jiekou and Huangmao shear zones are metamorphosed and deformed into protomylonite and mylonite. Results of the deformation fabrics of feldspar and quartz and quartzc-axis fabric analysis indicate that the ductile deformation temperatures of the Jiekou shear zone sinistral shearing are similar to 400-500 degrees C. Dextral shearing with medium-high temperature (450-550 degrees C) is mainly recorded in the Huangmao shear zone. In combination with the previous geochronology, NNE-trending sinistral and dextral shearing in the eastern Jiangnan Orogen occurred at 465-430 Ma, coeval with the Early Palaeozoic orogeny. Therefore, the geodynamics of the NNE-trending shear zones is related to a major strain transformation from NW to WNW, which is remotely affected by the intracontinental convergence of Yangtze and Cathaysia blocks during the Early Palaeozoic orogeny.
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The north-north-east-trending (NNE) shear zones, which are defined by the Jiekou shear zone and Huangmao shear zone, are located in the eastern Jiangnan Orogen. This article provides kinematics, geochronological data, and dynamics on the Jiekou and Huangmao shear zones and serves as a reference for understanding the tectonic evolution in the South China Block during the Early Palaeozoic orogeny. All shearing signatures show that the Huangmao shear zone is dextral, and the Jiekou shear zone is sinistral. Both shear zones have certain genetic connections. The rocks from the Jiekou and Huangmao shear zones are metamorphosed and deformed into protomylonite and mylonite. Results of the deformation fabrics of feldspar and quartz and quartzc-axis fabric analysis indicate that the ductile deformation temperatures of the Jiekou shear zone sinistral shearing are similar to 400-500 degrees C. Dextral shearing with medium-high temperature (450-550 degrees C) is mainly recorded in the Huangmao shear zone. In combination with the previous geochronology, NNE-trending sinistral and dextral shearing in the eastern Jiangnan Orogen occurred at 465-430 Ma, coeval with the Early Palaeozoic orogeny. Therefore, the geodynamics of the NNE-trending shear zones is related to a major strain transformation from NW to WNW, which is remotely affected by the intracontinental convergence of Yangtze and Cathaysia blocks during the Early Palaeozoic orogeny.
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Mylonite
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The north-north-east-trending (NNE) shear zones, which are defined by the Jiekou shear zone and Huangmao shear zone, are located in the eastern Jiangnan Orogen. This article provides kinematics, geochronological data, and dynamics on the Jiekou and Huangmao shear zones and serves as a reference for understanding the tectonic evolution in the South China Block during the Early Palaeozoic orogeny. All shearing signatures show that the Huangmao shear zone is dextral, and the Jiekou shear zone is sinistral. Both shear zones have certain genetic connections. The rocks from the Jiekou and Huangmao shear zones are metamorphosed and deformed into protomylonite and mylonite. Results of the deformation fabrics of feldspar and quartz and quartzc-axis fabric analysis indicate that the ductile deformation temperatures of the Jiekou shear zone sinistral shearing are similar to 400-500 degrees C. Dextral shearing with medium-high temperature (450-550 degrees C) is mainly recorded in the Huangmao shear zone. In combination with the previous geochronology, NNE-trending sinistral and dextral shearing in the eastern Jiangnan Orogen occurred at 465-430 Ma, coeval with the Early Palaeozoic orogeny. Therefore, the geodynamics of the NNE-trending shear zones is related to a major strain transformation from NW to WNW, which is remotely affected by the intracontinental convergence of Yangtze and Cathaysia blocks during the Early Palaeozoic orogeny.
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Abstract This paper contributes to the understanding of the offset on the 80 km long E-W striking Mérens fault in the central Pyrenees. Parameters such as amount and sense of offset are a prerequisite for a better understanding of the evolution of the fault, its tectonic significance and for reconstruction of the pre-existing configuration of its wall rocks. In the western Aston massif, north of the Mérens fault, an over 5 km long, N125E striking steep dextral shear zone occurs. This shear zone is characterized by medium-grade assemblages of metamorphic minerals and is considered to be of late Variscan age. The presence of such a shear zone in this area was deduced from i) published structural data on the Mérens fault, and ii) its cut off relation with an over 40 km long late Variscan shear zone to the south. In this study it is shown that the shear zones north and south of the Mérens fault initially formed a single late Variscan shear zone, cut and displaced by the younger Mérens fault. The exact geographical location of the shear zone in the Aston massif constrains the finite dextral horizontal movement on the Mérens fault to at least 10,4 ± 0,5 km. Finite uplift of the Aston massif exceeds 4 km. Extrapolation of the arguments to the eastern Aston and Hospitalet massifs indicates that the NE terminations of both gneiss cores also lined up along one single steep (W)NW striking shear zone prior to Mérens fault activity. Dextral horizontal offset is 8,5 ± 1 km in that area. Restoration of the late Variscan configuration of the Aston and Hospitalet massifs reveals an elongate WNW trending mantled gneiss antiform, bordered by steep dextral shear zones with similar trend.
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