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Baptiste Debret - One of the best experts on this subject based on the ideXlab platform.
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magnetic signatures of Serpentinization at ophiolite complexes
Geochemistry Geophysics Geosystems, 2016Co-Authors: D. Bonnemains, Muriel Andreani, J. Escartín, Julie Carlut, Catherine Mevel, Baptiste DebretAbstract:We compare magnetic properties of 58 variably serpentinized peridotites from three ophiolite complexes (Pindos, Greece; Oman; Chenaillet, France) and the mid-Atlantic Ridge near the Kane fracture zone (MARK). The Pindos and Oman sites show low susceptibility and remanence (K 250–3008C) occurring at the axis (i.e., Chenaillet, similar to serpentinites from magmatically poor mid-ocean ridges), from lower temperature Serpentinization (<200–2508C), likely occurring off axis and possibly during obduction (i.e., Pindos and Oman). At both settings, Serpentinization can result in significant hydrogen release.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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Trace element behavior during Serpentinization/de-Serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, < 20% Serpentinization) to the paleo-Moho, composed of massive serpentinites (MS, 80% Serpentinization), the trace elements mobility is reduced. The chemical composition of lizardite and antigorite is homogenized with the local degree of Serpentinization: in SSP, serpentine veins composition is inherited from the host mineral while, in MS, their composition is homogenous between destabilized phases at the scale of the outcrop (~ 5 m). In the shallowest part of the oceanic lithosphere, from the paleo-Moho to the oceanic paleo-seafloor, the serpentinites are foliated (FS, > 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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three steps of Serpentinization in an eclogitized oceanic Serpentinization front lanzo massif western alps
Journal of Metamorphic Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Stephane Schwartz, Muriel Andreani, Marguerite GodardAbstract:The Lanzo peridotite massif is a fragment of oceanic lithosphere generated in an ocean-continent transition context and eclogitized during alpine collision. Despite the subduction history, the massif has preserved its sedimentary oceanic cover, suggesting that it may have preserved its oceanic structure. It is an exceptional case for studying the evolution of a fragment of the lithosphere from its oceanization to its subduction and then exhumation. We present a field and petrological study retracing the different Serpentinization episodes and their impact on the massif structure. The Lanzo massif is composed of slightly serpentinized peridotites (<20% Serpentinization) surrounded by an envelope of foliated serpentinites (100% Serpentinization) bordered by oceanic metabasalts and metasedimentary rocks. The limit between peridotites and serpentinites defines the front of Serpentinization. This limit is sharp: it is marked by the presence of massive serpentinites (80% Serpentinization) and, locally, by dykes of metagabbros and mylonitic gabbros. The deformation of these gabbros is contemporaneous with the emplacement of the magma. The presence of early lizardite in the peridotites testifies that Serpentinization began during the oceanization, which is confirmed by the presence of meta-ophicarbonates bordering the foliated serpentinite envelope. Two additional generations of serpentine occur in the ultramafic rocks. The first is a prograde antigorite that partially replaced the lizardite and the relict primary minerals of the peridotite during subduction, indicating that Serpentinization is an active process at the ridge and in the subduction zone. Locally, this episode is followed by the deSerpentinization of antigorite at peak P-T (estimated in eclogitized metagabbros at 2-2.5 GPa and 550-620 °C): it is marked by the crystallization of secondary olivine associated with chlorite and/or antigorite and of clinopyroxene, amphibole and chlorite assemblages. A second antigorite formed during exhumation partially to completely obliterating previous textures in the massive and foliated serpentinites. Serpentinites are an important component of the oceanic lithosphere generated in slow to ultraslow spreading settings, and in these settings, there is a Serpentinization gradient with depth in the upper mantle. The seismic Moho limit could correspond to a Serpentinization front affecting the mantle. This partially serpentinized zone constitutes a less competent level where, during subduction and exhumation, deformation and fluid circulation are localized. In this zone, the reaction kinetics are increased and the later steps of Serpentinization obliterate the evidence of this progressive zone of Serpentinization. In the Lanzo massif, this zone fully recrystallized into serpentinite during alpine subduction and collision. Thus, the serpentinite envelope represents the oceanic crust as defined by geophysicists, and the sharp front of Serpentinization corresponds to an eclogitized seismic palaeo-Moho.
Christian Nicollet - One of the best experts on this subject based on the ideXlab platform.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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Trace element behavior during Serpentinization/de-Serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, < 20% Serpentinization) to the paleo-Moho, composed of massive serpentinites (MS, 80% Serpentinization), the trace elements mobility is reduced. The chemical composition of lizardite and antigorite is homogenized with the local degree of Serpentinization: in SSP, serpentine veins composition is inherited from the host mineral while, in MS, their composition is homogenous between destabilized phases at the scale of the outcrop (~ 5 m). In the shallowest part of the oceanic lithosphere, from the paleo-Moho to the oceanic paleo-seafloor, the serpentinites are foliated (FS, > 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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three steps of Serpentinization in an eclogitized oceanic Serpentinization front lanzo massif western alps
Journal of Metamorphic Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Stephane Schwartz, Muriel Andreani, Marguerite GodardAbstract:The Lanzo peridotite massif is a fragment of oceanic lithosphere generated in an ocean-continent transition context and eclogitized during alpine collision. Despite the subduction history, the massif has preserved its sedimentary oceanic cover, suggesting that it may have preserved its oceanic structure. It is an exceptional case for studying the evolution of a fragment of the lithosphere from its oceanization to its subduction and then exhumation. We present a field and petrological study retracing the different Serpentinization episodes and their impact on the massif structure. The Lanzo massif is composed of slightly serpentinized peridotites (<20% Serpentinization) surrounded by an envelope of foliated serpentinites (100% Serpentinization) bordered by oceanic metabasalts and metasedimentary rocks. The limit between peridotites and serpentinites defines the front of Serpentinization. This limit is sharp: it is marked by the presence of massive serpentinites (80% Serpentinization) and, locally, by dykes of metagabbros and mylonitic gabbros. The deformation of these gabbros is contemporaneous with the emplacement of the magma. The presence of early lizardite in the peridotites testifies that Serpentinization began during the oceanization, which is confirmed by the presence of meta-ophicarbonates bordering the foliated serpentinite envelope. Two additional generations of serpentine occur in the ultramafic rocks. The first is a prograde antigorite that partially replaced the lizardite and the relict primary minerals of the peridotite during subduction, indicating that Serpentinization is an active process at the ridge and in the subduction zone. Locally, this episode is followed by the deSerpentinization of antigorite at peak P-T (estimated in eclogitized metagabbros at 2-2.5 GPa and 550-620 °C): it is marked by the crystallization of secondary olivine associated with chlorite and/or antigorite and of clinopyroxene, amphibole and chlorite assemblages. A second antigorite formed during exhumation partially to completely obliterating previous textures in the massive and foliated serpentinites. Serpentinites are an important component of the oceanic lithosphere generated in slow to ultraslow spreading settings, and in these settings, there is a Serpentinization gradient with depth in the upper mantle. The seismic Moho limit could correspond to a Serpentinization front affecting the mantle. This partially serpentinized zone constitutes a less competent level where, during subduction and exhumation, deformation and fluid circulation are localized. In this zone, the reaction kinetics are increased and the later steps of Serpentinization obliterate the evidence of this progressive zone of Serpentinization. In the Lanzo massif, this zone fully recrystallized into serpentinite during alpine subduction and collision. Thus, the serpentinite envelope represents the oceanic crust as defined by geophysicists, and the sharp front of Serpentinization corresponds to an eclogitized seismic palaeo-Moho.
Marguerite Godard - One of the best experts on this subject based on the ideXlab platform.
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Experimental study of the effects of solute transport on reaction paths during incipient Serpentinization
Lithos, 2018Co-Authors: Sofia Escario Perez, Marguerite Godard, Philippe Gouze, Richard LeprovostAbstract:This paper presents the results of 4 reactive percolation experiments set up for investigating the impact of flow rate on Serpentinization reaction paths for conditions relevant of the oceanic peridotite sub-seafloor during the initial stages of its hydrothermal alteration. The experiments consisted in injecting artificial seawater into porous compressed olivine powder cores at constant flow rates Q: 0.24, 0.48, 1.14 and 5.21 mL·h−1. The experiments were conducted at constant temperature (170 °C) and pressure (25 MPa) and lasted 11 to 28 days. At the end of the experiments, the outlet fluids composition displayed similar compositions, buffered by the formation of serpentine (aMg2+/a(H+)2 = 9.7–10; aSiO2 = −3.9 to −5.2; pH in situ = 6.1). These values were achieved in a few to up to 300 h for the high flow rate experiment suggesting that they corresponded to a steady-state regime of mass transfer which depended on flow rate. Differences in the composition of fluid versus time and in the structure of reacted samples during and after the four reactive percolation experiments suggested also various incipient Serpentinization reaction paths. The low Q experiments produced SiO2(aq) enriched outlet fluids and nodular aggregates were identified covering the reacted olivine surfaces. During high Q experiments, fibrous filaments of proto-serpentine were formed on the olivine surfaces and the fluids progressively achieved steady state compositions similar to the other experiments. These results together with those of previously published reactive percolation experiments lead us to propose two end-member reaction paths for incipient Serpentinization of olivine-dominated permeable rocks infiltrated by seawater derived hydrothermal fluids: (1) a transport-controlled reaction path occurring in diffusion dominated zones is characterized by transient brucite precipitation, which produces Mg trapping and Si release in solution, followed by serpentine precipitation and (2) a kinetics-controlled reaction path occurring in advection dominated zones where transport conditions are favorable to Mg leaching and where serpentine precipitates first. The occurrence of these two end-member reaction paths is determined locally by the composition of the fluid, which varies along flow paths. Thus, both reaction paths can coexist in the sample depending on the local pore geometry. Our study shows that the interplay between fluid transport and reaction kinetics controls the chemical fluxes between the mineral surface and the bulk solution, and the incipient Serpentinization reaction paths. In natural systems, the scale and distribution of these reaction domains will depend on the complex structure of the ultramafic basement. Our results suggest that the precipitation of serpentine and silica rich phases will be favored in fluid focusing zones such as faults and fractures, whilst formation of brucite will preferentially occur as part of pervasive background Serpentinization.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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Trace element behavior during Serpentinization/de-Serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, < 20% Serpentinization) to the paleo-Moho, composed of massive serpentinites (MS, 80% Serpentinization), the trace elements mobility is reduced. The chemical composition of lizardite and antigorite is homogenized with the local degree of Serpentinization: in SSP, serpentine veins composition is inherited from the host mineral while, in MS, their composition is homogenous between destabilized phases at the scale of the outcrop (~ 5 m). In the shallowest part of the oceanic lithosphere, from the paleo-Moho to the oceanic paleo-seafloor, the serpentinites are foliated (FS, > 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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geochemistry of subduction zone serpentinites a review
Lithos, 2013Co-Authors: Fabien Deschamps, Stéphane Guillot, Marguerite Godard, Keiko HattoriAbstract:Abstract Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field observations of modern and ancient subduction zones and large amounts of geochemical database of serpentinites have been created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical data of abyssal, mantle wedge and exhumed serpentinites after subduction. The aim was to better understand the geochemical evolution of these rocks during their subduction as well as their impact in the global geochemical cycle. When studying serpentinites, it is essential to determine their protoliths and their geological history before Serpentinization. The geochemical data of serpentinites shows little mobility of compatible and rare earth elements (REE) at the scale of hand-specimen during their Serpentinization. Thus, REE abundance can be used to identify the protolith for serpentinites, as well as magmatic processes such as melt/rock interactions before Serpentinization. In the case of subducted serpentinites, the interpretation of trace element data is difficult due to the enrichments of light REE, independent of the nature of the protolith. We propose that enrichments are probably not related to Serpentinization itself, but mostly due to (sedimentary-derived) fluid/rock interactions within the subduction channel after the Serpentinization. It is also possible that the enrichment reflects the geochemical signature of the mantle protolith itself which could derive from the less refractory continental lithosphere exhumed at the ocean–continent transition. Additionally, during the last ten years, numerous analyses have been carried out, notably using in situ approaches, to better constrain the behavior of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, U, Th, Sr) incorporated in serpentine phases. The abundance of these elements provides information related to the fluid/rock interactions during Serpentinization and the behavior of FME, from their incorporation to their gradual release during subduction. Serpentinites are considered as a reservoir of the FME in subduction zones and their role, notably on arc magma composition, is underestimated presently in the global geochemical cycle.
Muriel Andreani - One of the best experts on this subject based on the ideXlab platform.
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magnetic signatures of Serpentinization at ophiolite complexes
Geochemistry Geophysics Geosystems, 2016Co-Authors: D. Bonnemains, Muriel Andreani, J. Escartín, Julie Carlut, Catherine Mevel, Baptiste DebretAbstract:We compare magnetic properties of 58 variably serpentinized peridotites from three ophiolite complexes (Pindos, Greece; Oman; Chenaillet, France) and the mid-Atlantic Ridge near the Kane fracture zone (MARK). The Pindos and Oman sites show low susceptibility and remanence (K 250–3008C) occurring at the axis (i.e., Chenaillet, similar to serpentinites from magmatically poor mid-ocean ridges), from lower temperature Serpentinization (<200–2508C), likely occurring off axis and possibly during obduction (i.e., Pindos and Oman). At both settings, Serpentinization can result in significant hydrogen release.
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Contrasted effect of aluminum on the Serpentinization rate of olivine and orthopyroxene under hydrothermal conditions
Chemical Geology, 2016Co-Authors: Maria Pens, Muriel Andreani, Isabelle Daniel, Jean-phillipe Perrillat, Hervé CardonAbstract:Olivine and pyroxene are the major minerals of ultramafic rocks. The hydrothermal alteration of these rocks leads to the Serpentinization reaction that mainly forms serpentine and variable amounts of talc, brucite and magnetite, as well as hydrogen. The Serpentinization kinetics of pyroxene under hydrothermal conditions has been very little studied in comparison with olivine, and both have been evaluated experimentally only in simple aqueous fluids. Here, we evaluate the effect of aluminum on the Serpentinization rate of olivine and orthopyroxene at 200 degrees C, 340 degrees C and 200 MPa to simulate natural hydrothermal conditions. We used low-pressure diamond-anvil cells (lp-DAC) and time-resolved X-ray diffraction to monitor in situ the progress of the Serpentinization reaction in four experiments. We also performed two long-lasting additional experiments with orthopyroxene for six days at 340 degrees C and 200 MPa, for which in situ monitoring was not possible. At 340 degrees C in presence of Al, olivine conversion into lizardite is extremely fast (half-time reaction t(1/2) = 7 h) while orthopyroxene did not react much even after 6 days (11%). In contrast to olivine, orthopyroxene conversion to serpentine was faster without Al (48% in 6 days). Magnetite was also observed in the run with olivine only at 340 degrees C. In experiments run with orthopyroxene only, we observed the exclusive formation of proto-serpentine instead of lizardite. We propose that the contrasted effect of Al on the Serpentinization rate of olivine and orthopyroxene results from the complexation of Al in the solution that reacts differently with the different mineral surfaces during their dissolution. The positively charged olivine surface allows the adsorption of the dominant negatively charged Al(OH)(4)(-) complex, while the neutral surface of orthopyroxene does not. This adsorption process could facilitate both the dissolution of olivine and the nucleation-growth of an Al-enriched lizardite. (C) 2016 Elsevier B.V. All rights reserved.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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Trace element behavior during Serpentinization/de-Serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, < 20% Serpentinization) to the paleo-Moho, composed of massive serpentinites (MS, 80% Serpentinization), the trace elements mobility is reduced. The chemical composition of lizardite and antigorite is homogenized with the local degree of Serpentinization: in SSP, serpentine veins composition is inherited from the host mineral while, in MS, their composition is homogenous between destabilized phases at the scale of the outcrop (~ 5 m). In the shallowest part of the oceanic lithosphere, from the paleo-Moho to the oceanic paleo-seafloor, the serpentinites are foliated (FS, > 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
Romain Lafay - One of the best experts on this subject based on the ideXlab platform.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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trace element behavior during Serpentinization de Serpentinization of an eclogitized oceanic lithosphere a la icpms study of the lanzo ultramafic massif western alps
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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Trace element behavior during Serpentinization/de-Serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)
Chemical Geology, 2013Co-Authors: Baptiste Debret, Christian Nicollet, Marguerite Godard, Stephane Schwartz, Muriel Andreani, Romain LafayAbstract:Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of Serpentinization/de-Serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during Serpentinization/de-Serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge. Geochemical analyses of serpentine and associated minerals show that the Serpentinization/de-Serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, < 20% Serpentinization) to the paleo-Moho, composed of massive serpentinites (MS, 80% Serpentinization), the trace elements mobility is reduced. The chemical composition of lizardite and antigorite is homogenized with the local degree of Serpentinization: in SSP, serpentine veins composition is inherited from the host mineral while, in MS, their composition is homogenous between destabilized phases at the scale of the outcrop (~ 5 m). In the shallowest part of the oceanic lithosphere, from the paleo-Moho to the oceanic paleo-seafloor, the serpentinites are foliated (FS, > 90% Serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of ~ 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction.
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Mineral replacement rate of olivine by chrysotile and brucite under high alkaline conditions
Journal of Crystal Growth, 2012Co-Authors: Romain Lafay, German Montes-hernandez, Emilie Janots, Rodica Chiriac, Nathaniel Findling, François TocheAbstract:Olivine mineral replacement by serpentine is one major alteration reaction of oceanic hydrothermalism. In the present experimental study, olivine grains were replaced by chrysotile and brucite under high alkaline conditions. In our study, olivine replacement implied a spatial and temporal coupling of dissolution and precipitation reactions at the interface between olivine and chrysotile-brucite minerals. Coupled dissolution-precipitation led to the alteration of starting olivine grains (so-called primary or parent mineral) to a porous mineral assemblage of chrysotile and brucite with preservation of the initial olivine morphology. This mineral replacement reaction of olivine (Serpentinization) has been characterized using XRD, FESEM and FTIR measurements. Moreover, a simple and novel method is here proposed to quantify the mineral replacement rate (or Serpentinization rate) of olivine by using thermogravimetric (TG) and differential TG (DTG) analyses. Serpentinization extent depends on the grain size: it is complete after 30 days of reaction for the smallest olivine grains (
