Anne Verlaguet - Academia.edu (original) (raw)

Papers by Anne Verlaguet

Lithos, 2014

In the inner part of the External Alps, inherited Liassic basins were buried and inverted during ... more In the inner part of the External Alps, inherited Liassic basins were buried and inverted during the Oligo-Miocene collisional phase of the Alpine orogeny. In northern Oisans, during crustal shortening, the basement was locally sheared while the cover was disharmonically folded above the main basement shear zones that did not propagate into the cover. In this contribution, we analyze the witnesses of paleo-fluid circulations associated with these crustal deformations, focusing particularly on Bourg d'Oisans and Mizoën basins (external Western Alps). On the basis of structural and microstructural observations coupled to geochemical analyses (cathodoluminescence, O and C stable isotopes, trace elements) of vein versus host-rock minerals, we show that in the cover, fluids mainly circulated over short distances (closed-system). However, trace element data also show that percolation of small amounts of basement-derived fluids occurred over several tens of meters in cover rocks right above basement shear zones. Indeed, the three successive vein sets recognized in the field display enrichments in basementderived Ni, Co, and Cr, which indicate that fluid transfer from the basement was efficient since the beginning of basin inversion, therefore confirming the synchronous deformation of cover and basement. Fluid temperatures and pressures are estimated (microthermometry coupled to δ 18 O of vein minerals) to about 250-400°C and 2-5 kbar for veins that most likely formed at or close to metamorphic peak conditions. These results coupled to literature data are finally integrated into a model of fluid circulation evolution through progressive deformation of the whole external Western Alps.

Journal of Structural Geology, 2014

Geochimica et Cosmochimica Acta, 2006

In order to quantify Al transfer in response to fluid-mineral equilibration under evolving metamo... more In order to quantify Al transfer in response to fluid-mineral equilibration under evolving metamorphic conditions, isobaric (0.7 GPa) experiments were conducted in the 350-550°C range. Disequilibrium was induced (1) by holding initially pure water and natural minerals (kyanite + quartz ± muscovite enclosed in a perforated inner capsule) under isothermal conditions and (2) by stepwise temperature variations. In all experiments, secondary Al-bearing phases crystallized in the external tube of a ''tube-in-tube'' setup (SEM characterization); they are interpreted as witnesses of the evolution of the fluid composition (fluid reaction path). These reaction paths and the subsequent amount of secondary crystallizations were modeled using thermodynamic data from SUPCRT92 and estimates of both starting-mineral dissolution rates and elemental diffusion coefficients from the literature. A major result is that the amount of aluminum transferred to secondary phases is a thousand times larger than the calculated Al concentration in the fluid. Although the crystallization of Al-bearing phases was expected as a response to a temperature decrease, the stepwise temperature increase (20°C/day) also led to aluminum transfer towards secondary phases. In the course of re-equilibration, the fluid first becomes saturated with respect to aluminosilicates and then reaches silica saturation, due to the low solubility of Al-minerals. Consequently, aluminosilicates partly recrystallize in response to a temperature increase. Crystallization of secondary Al-phases in the external tube implies that aqueous aluminum was efficiently transported from the inner capsule, even in the pure Al 2 O 3 -SiO 2 -H 2 O system. Therefore, mass balance calculations considering a constant Al reference frame, i.e., postulating Al immobility, should be regarded with caution.

European Journal of Mineralogy, 2007

Environmental Science & Technology, 2014

Batch experiments were conducted in water at 150°C and P CO 2 = 280 bar on a Mg-rich tholeiitic b... more Batch experiments were conducted in water at 150°C and P CO 2 = 280 bar on a Mg-rich tholeiitic basalt (9.3 wt % MgO and 12.2 wt % CaO) composed of olivine, Ti-magnetite, plagioclase, and clinopyroxene. After 45 days of reaction, 56 wt % of the initial MgO had reacted with CO 2 to form Fe-bearing magnesite, (Mg 0.8 Fe 0.2 )CO 3 , along with minor calcium carbonates. The substantial decrease in olivine content upon carbonation supports the idea that ferroan magnesite formation mainly follows from olivine dissolution. In contrast, in experiments performed under similar run durations and P/T conditions with a San Carlos olivine separate (47.8 wt % MgO) of similar grain size, only 5 wt % of the initial MgO content reacted to form Fe-bearing magnesite. The overall carbonation kinetics of the basalt was enhanced by a factor of ca. 40. This could be explained by differences in the chemical and textural properties of the secondary silica layer that covers reacted olivine grains in both types of sample. Consequently, laboratory data obtained on olivine separates might yield a conservative estimate of the true carbonation potential of olivine-bearing basaltic rocks.

Lithos, 2014

In the inner part of the External Alps, inherited Liassic basins were buried and inverted during ... more In the inner part of the External Alps, inherited Liassic basins were buried and inverted during the Oligo-Miocene collisional phase of the Alpine orogeny. In northern Oisans, during crustal shortening, the basement was locally sheared while the cover was disharmonically folded above the main basement shear zones that did not propagate into the cover. In this contribution, we analyze the witnesses of paleo-fluid circulations associated with these crustal deformations, focusing particularly on Bourg d'Oisans and Mizoën basins (external Western Alps). On the basis of structural and microstructural observations coupled to geochemical analyses (cathodoluminescence, O and C stable isotopes, trace elements) of vein versus host-rock minerals, we show that in the cover, fluids mainly circulated over short distances (closed-system). However, trace element data also show that percolation of small amounts of basement-derived fluids occurred over several tens of meters in cover rocks right above basement shear zones. Indeed, the three successive vein sets recognized in the field display enrichments in basementderived Ni, Co, and Cr, which indicate that fluid transfer from the basement was efficient since the beginning of basin inversion, therefore confirming the synchronous deformation of cover and basement. Fluid temperatures and pressures are estimated (microthermometry coupled to δ 18 O of vein minerals) to about 250-400°C and 2-5 kbar for veins that most likely formed at or close to metamorphic peak conditions. These results coupled to literature data are finally integrated into a model of fluid circulation evolution through progressive deformation of the whole external Western Alps.

Journal of Structural Geology, 2014

Geochimica et Cosmochimica Acta, 2006

In order to quantify Al transfer in response to fluid-mineral equilibration under evolving metamo... more In order to quantify Al transfer in response to fluid-mineral equilibration under evolving metamorphic conditions, isobaric (0.7 GPa) experiments were conducted in the 350-550°C range. Disequilibrium was induced (1) by holding initially pure water and natural minerals (kyanite + quartz ± muscovite enclosed in a perforated inner capsule) under isothermal conditions and (2) by stepwise temperature variations. In all experiments, secondary Al-bearing phases crystallized in the external tube of a ''tube-in-tube'' setup (SEM characterization); they are interpreted as witnesses of the evolution of the fluid composition (fluid reaction path). These reaction paths and the subsequent amount of secondary crystallizations were modeled using thermodynamic data from SUPCRT92 and estimates of both starting-mineral dissolution rates and elemental diffusion coefficients from the literature. A major result is that the amount of aluminum transferred to secondary phases is a thousand times larger than the calculated Al concentration in the fluid. Although the crystallization of Al-bearing phases was expected as a response to a temperature decrease, the stepwise temperature increase (20°C/day) also led to aluminum transfer towards secondary phases. In the course of re-equilibration, the fluid first becomes saturated with respect to aluminosilicates and then reaches silica saturation, due to the low solubility of Al-minerals. Consequently, aluminosilicates partly recrystallize in response to a temperature increase. Crystallization of secondary Al-phases in the external tube implies that aqueous aluminum was efficiently transported from the inner capsule, even in the pure Al 2 O 3 -SiO 2 -H 2 O system. Therefore, mass balance calculations considering a constant Al reference frame, i.e., postulating Al immobility, should be regarded with caution.

European Journal of Mineralogy, 2007

Environmental Science & Technology, 2014

Batch experiments were conducted in water at 150°C and P CO 2 = 280 bar on a Mg-rich tholeiitic b... more Batch experiments were conducted in water at 150°C and P CO 2 = 280 bar on a Mg-rich tholeiitic basalt (9.3 wt % MgO and 12.2 wt % CaO) composed of olivine, Ti-magnetite, plagioclase, and clinopyroxene. After 45 days of reaction, 56 wt % of the initial MgO had reacted with CO 2 to form Fe-bearing magnesite, (Mg 0.8 Fe 0.2 )CO 3 , along with minor calcium carbonates. The substantial decrease in olivine content upon carbonation supports the idea that ferroan magnesite formation mainly follows from olivine dissolution. In contrast, in experiments performed under similar run durations and P/T conditions with a San Carlos olivine separate (47.8 wt % MgO) of similar grain size, only 5 wt % of the initial MgO content reacted to form Fe-bearing magnesite. The overall carbonation kinetics of the basalt was enhanced by a factor of ca. 40. This could be explained by differences in the chemical and textural properties of the secondary silica layer that covers reacted olivine grains in both types of sample. Consequently, laboratory data obtained on olivine separates might yield a conservative estimate of the true carbonation potential of olivine-bearing basaltic rocks.