The formation of the architecture of the main cratons of the Canadian Shield has been debated ove... more The formation of the architecture of the main cratons of the Canadian Shield has been debated over the past three decades. Understanding the role of tangential Vs. vertical tectonics in the Rae craton is of great interest as the role of inherited structure is fundamental for the subsequent drainage of fluids and the formation of high to ultra-high grade unconformity-type uranium deposits. These deposits are located in the vicinity of the intersection between the unconformity at the base of the Paleoproterozoic Athabasca sedimentary basin (1.75-1.5 Ga) and the graphite-rich metasediments of the Wollaston-Mudjatik transition zone, one of the main fault system of the Rae Craton related to the Trans-Hudson orogeny (1.82-1.78 Ga). A new tectonic model, Pop-down tectonics, was proposed as the primary driving process to concentrate supracrustal materials, strains, fluid transfers and metal transport in permeability enhanced deformation zones. The sub-vertical structural patterns with regio...
Field observations from Archean and Paleoproterozoic cratons show strain zones often marked by wi... more Field observations from Archean and Paleoproterozoic cratons show strain zones often marked by widespread sub-vertical stretching lineations throughout the crust and partial melting conditions. These regions contain deformation bands that show large strains despite a lack of metamorphic jumps and often contain economical ore deposits. But, these provinces are often interpreted under the lens of modern plate tectonics (i.e. vertical motions with a stronger localisation of strain seen in modern orogenic systems). This contrasts with ancient orogens with a consensus for gravity-driven tectonics due to an inverse density contrast that describe the structural profiles of granite-greenstone belts. However, gravity-driven tectonics could not be applied to provinces that contain a normal crustal density profile. This led to a proposal of an Archean-Proterozoic transitional tectonic style. Recent analogue modelling experiments and field observations confirm vertical tectonics is the dominant...
The occurrence of unconformity-related uranium mineralization requires the combination of three c... more The occurrence of unconformity-related uranium mineralization requires the combination of three components: fluids with the right composition, geochemical traps with the right agents that produce precipitation, and structural traps with the right geometry. In the Athabasca Basin unconformity-related uranium deposits, while basinal brines are commonly accepted as the principal mineralized fluids and graphite and gases (CH4, CO2, and H2S) are well known as the reductants, only few case studies describing structural traps are published. A number of recent works, including numerical modelling, have improved the understanding of the role of inherited shear zones on fluid flow and the development of uranium deposits at a micro- and regional-scale. Nevertheless, there is still a lack of knowledge about the meso- or deposit-scale structural controls that lead to the present (and potentially predictive) localization of uranium deposits along a given shear zone. The present work examines new ...
In the Kiggavik area (Nunavut, Canada), major fault zones along, or close to, where uranium depos... more In the Kiggavik area (Nunavut, Canada), major fault zones along, or close to, where uranium deposits are found are often associated with occurrence of thick quartz breccia (QB) bodies. These bodies formed in an early stage (~1750 Ma) of the long-lasting tectonic history of the Archean basement, and of the Proterozoic Thelon basin. The main characteristics of the QB are addressed in this study; through field work, macro and microscopic observations, cathodoluminescence microscopy, trace elements, and oxygen isotopic signatures of the quartz forming the QB. Faults formed earlier during syn- to post-orogenic rifting (1850–1750 Ma) were subsequently reactivated, and underwent cycles of cataclasis, pervasive silicification, hydraulic brecciation, and quartz recrystallization. This was synchronous with the circulation of meteoric fluids mixing with Si-rich magmatic-derived fluids at depth, and were coeval with the emplacement of the Kivalliq igneous suite at 1750 Ma. These processes led t...
Abstract: The thermal history of the Velay anatectic dome, which extends over 10 000 km in the so... more Abstract: The thermal history of the Velay anatectic dome, which extends over 10 000 km in the southern part of the French Massif Central, is still poorly constrained, especially as to its duration. We studied by U-Pb chronology the accessory minerals (zircon, monazite, ...
Understanding exhumation processes of high to ultra-high pressure (HP to UHP) terrains during pla... more Understanding exhumation processes of high to ultra-high pressure (HP to UHP) terrains during plate convergence is a major challenge for the comprehension of plate convergence processes and mountain building. Contemporaneous contraction and extension coupled with erosion are frequently proposed to drive the exhumation process. In the internal alpine belt, HP and UHP metamorphism are recorded both in the Piemont oceanic
Deep temperature estimates previously made in France show three main positive thermal anomalies, ... more Deep temperature estimates previously made in France show three main positive thermal anomalies, one of them being centred on the Provence basin (southeast France) between Marseille and Montpellier. This study presents newly corrected temperature data and improved temperature maps in order to (i) validate or to invalidate the thermal anomalies previously identified and (ii) relate deep temperatures with major geological structures of the area.Although the thermal gradient varies from place to place, it averages 31.3°C./km in the Provence basin (from 30.6 to 32.5°C/km in average for France according to the chosen database), but some locations show gradients reaching 36°C/km. To characterize thermal anomalous areas, a three-dimensional model of the temperatures was built between the surface and 6 km depth, allowing us to elaborate thermal maps and cross-sections. The identified thermal anomalies are different from those obtained by former works. New other "hot" anomalous areas (Montpellier, Lodève and Drôme areas) and cold anomalous areas (Aix-en-Provence and Cévennes areas) have been highlighted. At depth, thermal cross-sections show 50 km-scale anomalies, which are parallel with the major faults (Cévennes, Nimes, Salon-Cavaillon and Moyenne-Durance faults) whereas more elongated (roughly 100 km) anomalies are associated with perpendicular cross-sections. On these cross-sections each major fault is associated with a thermal anomaly. In addition, a cold area may overlie a warm one, and vice versa. Among different possible explanations, these thermal signatures could correspond to convective fluid circulation within the faults. Simple numerical models of hydrothermal convection within fault zones appear to reproduce similar amplitudes and vertical variations of thermal anomalies as those observed in the Provence basin.
The formation of the architecture of the main cratons of the Canadian Shield has been debated ove... more The formation of the architecture of the main cratons of the Canadian Shield has been debated over the past three decades. Understanding the role of tangential Vs. vertical tectonics in the Rae craton is of great interest as the role of inherited structure is fundamental for the subsequent drainage of fluids and the formation of high to ultra-high grade unconformity-type uranium deposits. These deposits are located in the vicinity of the intersection between the unconformity at the base of the Paleoproterozoic Athabasca sedimentary basin (1.75-1.5 Ga) and the graphite-rich metasediments of the Wollaston-Mudjatik transition zone, one of the main fault system of the Rae Craton related to the Trans-Hudson orogeny (1.82-1.78 Ga). A new tectonic model, Pop-down tectonics, was proposed as the primary driving process to concentrate supracrustal materials, strains, fluid transfers and metal transport in permeability enhanced deformation zones. The sub-vertical structural patterns with regio...
Field observations from Archean and Paleoproterozoic cratons show strain zones often marked by wi... more Field observations from Archean and Paleoproterozoic cratons show strain zones often marked by widespread sub-vertical stretching lineations throughout the crust and partial melting conditions. These regions contain deformation bands that show large strains despite a lack of metamorphic jumps and often contain economical ore deposits. But, these provinces are often interpreted under the lens of modern plate tectonics (i.e. vertical motions with a stronger localisation of strain seen in modern orogenic systems). This contrasts with ancient orogens with a consensus for gravity-driven tectonics due to an inverse density contrast that describe the structural profiles of granite-greenstone belts. However, gravity-driven tectonics could not be applied to provinces that contain a normal crustal density profile. This led to a proposal of an Archean-Proterozoic transitional tectonic style. Recent analogue modelling experiments and field observations confirm vertical tectonics is the dominant...
The occurrence of unconformity-related uranium mineralization requires the combination of three c... more The occurrence of unconformity-related uranium mineralization requires the combination of three components: fluids with the right composition, geochemical traps with the right agents that produce precipitation, and structural traps with the right geometry. In the Athabasca Basin unconformity-related uranium deposits, while basinal brines are commonly accepted as the principal mineralized fluids and graphite and gases (CH4, CO2, and H2S) are well known as the reductants, only few case studies describing structural traps are published. A number of recent works, including numerical modelling, have improved the understanding of the role of inherited shear zones on fluid flow and the development of uranium deposits at a micro- and regional-scale. Nevertheless, there is still a lack of knowledge about the meso- or deposit-scale structural controls that lead to the present (and potentially predictive) localization of uranium deposits along a given shear zone. The present work examines new ...
In the Kiggavik area (Nunavut, Canada), major fault zones along, or close to, where uranium depos... more In the Kiggavik area (Nunavut, Canada), major fault zones along, or close to, where uranium deposits are found are often associated with occurrence of thick quartz breccia (QB) bodies. These bodies formed in an early stage (~1750 Ma) of the long-lasting tectonic history of the Archean basement, and of the Proterozoic Thelon basin. The main characteristics of the QB are addressed in this study; through field work, macro and microscopic observations, cathodoluminescence microscopy, trace elements, and oxygen isotopic signatures of the quartz forming the QB. Faults formed earlier during syn- to post-orogenic rifting (1850–1750 Ma) were subsequently reactivated, and underwent cycles of cataclasis, pervasive silicification, hydraulic brecciation, and quartz recrystallization. This was synchronous with the circulation of meteoric fluids mixing with Si-rich magmatic-derived fluids at depth, and were coeval with the emplacement of the Kivalliq igneous suite at 1750 Ma. These processes led t...
Abstract: The thermal history of the Velay anatectic dome, which extends over 10 000 km in the so... more Abstract: The thermal history of the Velay anatectic dome, which extends over 10 000 km in the southern part of the French Massif Central, is still poorly constrained, especially as to its duration. We studied by U-Pb chronology the accessory minerals (zircon, monazite, ...
Understanding exhumation processes of high to ultra-high pressure (HP to UHP) terrains during pla... more Understanding exhumation processes of high to ultra-high pressure (HP to UHP) terrains during plate convergence is a major challenge for the comprehension of plate convergence processes and mountain building. Contemporaneous contraction and extension coupled with erosion are frequently proposed to drive the exhumation process. In the internal alpine belt, HP and UHP metamorphism are recorded both in the Piemont oceanic
Deep temperature estimates previously made in France show three main positive thermal anomalies, ... more Deep temperature estimates previously made in France show three main positive thermal anomalies, one of them being centred on the Provence basin (southeast France) between Marseille and Montpellier. This study presents newly corrected temperature data and improved temperature maps in order to (i) validate or to invalidate the thermal anomalies previously identified and (ii) relate deep temperatures with major geological structures of the area.Although the thermal gradient varies from place to place, it averages 31.3°C./km in the Provence basin (from 30.6 to 32.5°C/km in average for France according to the chosen database), but some locations show gradients reaching 36°C/km. To characterize thermal anomalous areas, a three-dimensional model of the temperatures was built between the surface and 6 km depth, allowing us to elaborate thermal maps and cross-sections. The identified thermal anomalies are different from those obtained by former works. New other "hot" anomalous areas (Montpellier, Lodève and Drôme areas) and cold anomalous areas (Aix-en-Provence and Cévennes areas) have been highlighted. At depth, thermal cross-sections show 50 km-scale anomalies, which are parallel with the major faults (Cévennes, Nimes, Salon-Cavaillon and Moyenne-Durance faults) whereas more elongated (roughly 100 km) anomalies are associated with perpendicular cross-sections. On these cross-sections each major fault is associated with a thermal anomaly. In addition, a cold area may overlie a warm one, and vice versa. Among different possible explanations, these thermal signatures could correspond to convective fluid circulation within the faults. Simple numerical models of hydrothermal convection within fault zones appear to reproduce similar amplitudes and vertical variations of thermal anomalies as those observed in the Provence basin.
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