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Carlos J Garrido - One of the best experts on this subject based on the ideXlab platform.
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morphological transition during prograde olivine growth formed by high pressure dehydration of Antigorite serpentinite to chlorite harzburgite in a subduction setting
Lithos, 2021Co-Authors: Nicole Dilissen, Vicente Lopez Sanchezvizcaino, Carlos J Garrido, Karoly Hidas, Wolfachim KahlAbstract:Abstract Crystal morphologies are essential for deciphering the reaction history of igneous and metamorphic rocks because they often record the interplay between nucleation and growth rates controlled by the departure from equilibrium. Here, we report an exceptional record of the morphological transition of olivine formed during subduction metamorphism and high-pressure dehydration of Antigorite-serpentinite to prograde chlorite-harzburgite in the Almirez ultramafic massif (Nevado–Filabride Complex, Betic Cordillera, SE Spain). In this massif, rare varied-textured chlorite-harzburgite (olivine+enstantite+chlorite+oxides) —formed after high–P dehydration of Antigorite-serpentinite— exhibits large olivine porphyroblasts made up of rounded cores mantled by coronas of tabular olivine grains, similar to single tabular olivines occurring in the matrix. The correlative X-ray μ-CT and EBSD study of two varied-textured chlorite-harzburgite samples show that tabular olivine in coronas is tabular on (100)Ol with c > b >> a, and grew in nearly the same crystallographic orientation as the rounded olivine cores of the porphyroblast. Quantitative textural analysis and mass balance indicate that varied-textured chlorite-harzburgite is the result of a two-stage nucleation and growth of olivine during the progress of the high–P dehydration of Antigorite-serpentinite to chlorite-harzburgite reaction. The first stage occurred under a low affinity (ΔGr) and affinity rate (ΔGr/dt) of the Antigorite dehydration reaction that resulted in a low time-integrated nucleation rate and isotropic growth of olivine, forming rounded olivine porphyroblasts. With further progress of the dehydration reaction, a second stage of relatively higher affinity and affinity rate resulted in a higher time-integrated nucleation rate of olivine coeval with a shift from isotropic to anisotropic olivine growth, leading to tabular olivines. The two-stage evolution resulted in olivine porphyroblasts made up of rounded cores mantled by coronas of tabular olivine grains characteristic of varied-texture chlorite-harzburgite. Although a switch to anisotropic tabular olivine in the second stage is consistent with the relative increase in the affinity and affinity rate, these changes cannot solely account for the growth of Almirez olivine tabular on (100). Tabular olivines in komatiites and other igneous rocks are tabular on (010)Ol with either a > c >> b, or a ≈ c > > b, in agreement with experimentally determined growth rates of olivine phenocrysts under moderate to high undercooling and cooling rates. On the other hand, olivine tabular on (100) is expected in the presence of highly polymerized fluids where inhibited growth of the olivine (100) and (010) interfaces occurs, respectively, due to dissociative and molecular adsorption of water monolayers. Rounded and tabular olivines in Almirez varied-textured chlorite-harzburgite show differing trace element compositions that we interpret as due to the infiltration of external fluids during Antigorite dehydration. Isothermal infiltration of highly polymerized fluids would explain the shift in the affinity and affinity rate of the Antigorite dehydration reaction, as well as the olivine morphology tabular on (100) due to the inhibited growth on the (100) and, to a lesser extent, (010). Our study shows that surface-active molecules may play an essential role in shaping the morphology of growing crystals during fluid-present metamorphic crystallization.
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High-P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones
Journal of Metamorphic Geology, 2018Co-Authors: Casto Laborda-lopez, Jose Alberto Padron Navarta, Claudio Marchesi, Carlos J Garrido, Vicente López Sánchez-vizcaíno, Maria T. Gomez-pugnaire, Antonio Jabaloy-sanchez, Karoly HidasAbstract:The transition between Antigorite‐serpentinite and chlorite‐harzburgite at Cerro del Almirez (Betic Cordillera, Southern Spain) exceptionally marks in the field the front of Antigorite breakdown at high pressure (~16–19 kbar) and temperature (~650°C) in a paleosubducted serpentinite. These ultramafic lithologies enclose three types of metarodingite boudins of variable size surrounded by metasomatic reaction rims. Type 1 Grandite‐metarodingite (garnet+chlorite+diopside+titanite±magnetite±ilmenite) mainly crops out in the Antigorite‐serpentinite domain and has three generations of garnet. Grossular‐rich Grt‐1 formed during rodingitization at the seafloor (10 kbar, ~350–650°C, ~FMQ buffer) to influx events of oxidizing fluids (fO2 ~HM buffer) released by brucite breakdown in the host Antigorite‐serpentinite. Type 2 Epidote‐metarodingite (epidote+diopside+titanite±garnet) derives from Type 1 and is the most abundant metarodingite type enclosed in dehydrated chlorite‐harzburgite. Type 2 formed by increasing μSiO2 (from −884 to −860 kJ/mol) and decreasing μCaO (from −708 to −725 kJ/mol) triggered by the flux of high amounts of oxidizing fluids during the high‐P Antigorite breakdown in serpentinite. The growth of Grt‐4, with low‐grandite and high‐pyralspite components, in Type 2 metarodingite accounts for progressive reequilibration of garnet with changing intensive variables. Type 3 Pyralspite‐metarodingite (garnet+epidote+amphibole+chlorite±diopside+rutile) crops out in the chlorite‐harzburgite domain and formed at peak metamorphic conditions (16–19 kbar, 660–684°C) from Type 2 metarodingite. This transformation caused the growth of a last generation of pyralspite‐rich garnet (Grt‐5) and the recrystallization of diopside into tremolitic amphibole at decreasing fO2 and μCaO (from −726 to −735 kJ/mol) and increasing μMgO (from −630 to −626 kJ/mol) due to chemical mixing between the metarodingite and the reaction rims. The different bulk Fe3+/FeTotal ratios of Antigorite‐serpentinite and chlorite‐harzburgite, and of the three metarodingite types, reflect the highly heterogeneous oxidation state of the subducting slab and likely point to the transfer of localized oxidized reservoirs, such as metarodingites, into the deep mantle.
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On topotaxy and compaction during Antigorite and chlorite dehydration: an experimental and natural study
Contributions to Mineralogy and Petrology, 2015Co-Authors: Jose Alberto Padron Navarta, Carlos J Garrido, Andrea Tommasi, David MainpriceAbstract:Dehydration reactions result in minerals’ replacement and a transient fluid-filled porosity. These reactions involve interface-coupled dissolution–precipitation and might therefore lead to fixed crystallographic orientation relations between reactant (protolith) and product phases (i.e. topotaxy). We investigate these two phenomena in the dehydration of a foliated Antigorite (atg) serpentinite by comparing the crystallographic preferred orientation (CPO) developed by olivine (ol), orthopyroxene (opx) and chlorite (chl) during high-pressure Antigorite and chlorite dehydration in piston-cylinder experiments and in natural samples recording the dehydration of Antigorite (Cerro del Almirez, Betic Cordillera, Spain). Experiments were performed under undrained conditions resulting in fluid-filled porosity and in strong CPO of the prograde minerals, controlled by the pre-existing Antigorite CPO in the reactant foliated serpentinite. The orientation of a _ol,opx and $$c_{\text{chl}}^{ * }$$ c chl ∗ is parallel to $$c_{\text{atg}}^{ * }$$ c atg ∗ from the protolith. The Cerro del Almirez samples show similar, locally well-developed topotactic relations between orthopyroxene, chlorite and Antigorite, but the product CPOs are weaker and more complex at the thin section scale. In contrast to the experiments, olivine from natural samples shows a weak correlation between b _ol and the former $$c_{\text{atg}}^{ * }$$ c atg ∗ . We relate the strengthening of local topotactic relations and the weakening of the inherited CPO at a larger scale in natural samples to compaction and associated fluid migration. Microstructural features that might be related to compaction in the natural samples include: (1) smooth bending of the former foliation, (2) gradual crystallographic misorientation (up to 16°) of prismatic orthopyroxene due to buckling by dislocation creep, (3) inversion of enstatite to low clinoenstatite (P2_1/c) along lamellae and (4) brittle fracturing of prismatic orthopyroxene enclosed by plastically deformed chlorite. The coexistence of orthopyroxene buckling and clinoenstatite lamellae enables estimating the local strain rates and shear stresses generated during compaction. An lower bound for the strain rates in the order of 10^−12 to 10^−13 s^−1 and shear stresses of 60–70 MPa are estimated based on creep data. Lower shear stresses (20–40 MPa) are retrieved using a theoretical approach. These data point to slow compaction (and fluid extraction) in nature if the system is not perturbed by external forces, with rates only marginally higher than the viscoplastic deformation of the solid matrix.
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tschermak s substitution in Antigorite and consequences for phase relations and water liberation in high grade serpentinites
Lithos, 2013Co-Authors: Jose Alberto Padronnavarta, Vicente Lopez Sanchezvizcaino, Maria Teresa Gomezpugnaire, Carlos J Garrido, Joerg Hermann, James A D Connolly, Claudio MarchesiAbstract:Abstract A model for the incorporation of alumina in FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O (FMASH) serpentinites has been developed by considering ideal Tschermak (Al 2 Mg − 1 Si − 1 ) solid solution in Antigorite. The Antigorite model has been calibrated by fitting the experimental conditions for the decomposition of Antigorite to chlorite + olivine + orthopyroxene + fluid in the FMASH system. The Antigorite Al-contents predicted with this model are in agreement with natural observations and suggest a maximum alumina solubility in Antigorite of 3.6 wt.% Al 2 O 3 at 20 kbar–650 °C and of 4.5 wt.% Al 2 O 3 at 3 kbar–560 °C. In the assemblage Antigorite–olivine–chlorite–fluid, the Al-content of Antigorite is buffered and temperature sensitive. This temperature sensitivity is the basis for a serpentinite geothermometer at greenschist, amphibolite and eclogite facies conditions. The buffered assemblage is stable in harzburgite compositions for relatively moderate amounts of Al 2 O 3 (> 1.8 wt.%) and is widespread in lherzolites, where it occurs together with diopside or, in a narrow temperature field, with tremolite.
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Plastic deformation and development of Antigorite crystal preferred orientation in high-pressure serpentinites
Earth and Planetary Science Letters, 2012Co-Authors: Jose Alberto Padron Navarta, Carlos J Garrido, Andrea Tommasi, Vicente López Sánchez-vizcaínoAbstract:We have inferred the deformation mechanisms of Antigorite by high-resolution EBSD mapping of samples from Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain). Textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600-630 °C and 1.6-1.9 GPa. Deformation was followed by static annealing of Antigorite at ca. 680 °C. The Crystal Preferred Orientation (CPO) of Antigorite is characterised by a strong alignment of (001) poles normal to the foliation plane and a weaker, but clear, parallelism between [100] axes and the macroscopic lineation defined by the elongation of magnetite aggregates. Analysis of misorientations across subgrains shows predominance of [010] rotation axis, consistent with activation of the [100](001) slip system. However, tilt subgrain boundaries subparallel to (100), probably formed by edge dislocations of this system, are subsidiary. Most subgrain boundaries are subparallel to (001) planes. They are interpreted as (001) twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins. Modelling of the evolution of the Antigorite CPO using a lower bound approach and considering different deformation regimes and sets of basal and non-basal slip systems has shown that intensities of [100] and [010] maxima reflect the relative strength of the Antigorite [100](001) and [010](001) systems. Activation of other basal or non-basal slip systems does not change significantly the CPO patterns, but results in less concentrated CPO. 3D transpression models better reproduce the CPO of natural Antigorite serpentinites. We propose that the widespread occurrence of strong CPO in high-pressure Antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on [hk0](001), together with the activation of twinning, implying that a power law rheology would better account for the mechanical behaviour of Antigorite serpentinite deep in the subduction channel and mantle wedge.
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: Muriel Andreani, Marguerite Godard, Christian Nicollet, Stephane Schwartz, 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: Muriel Andreani, Marguerite Godard, Christian Nicollet, Stephane Schwartz, 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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pressure temperature estimates of the lizardite Antigorite transition in high pressure serpentinites
Lithos, 2013Co-Authors: Stephane Schwartz, Romain Lafay, Christian Nicollet, Bruno Reynard, Baptiste Debret, Pierre Lanari, Anne Line AuzendeAbstract:Serpentine minerals in natural samples are dominated by lizardite and Antigorite. In spite of numerous petrological experiments, the stability fields of these species remain poorly constrained. This paper presents the petrological observations and the Raman spectroscopy and XRD analyses of natural serpentinites from the Alpine paleo-accretionary wedge. Serpentine varieties are identified from a range of metamorphic pressure and temperature conditions from sub-greenschist (P 20 kbar, T > 460°C) along a subduction geothermal gradient. We used the observed mineral assemblage in natural serpentinite along with the Tmax estimated by Raman spectroscopy of the carbonaceous matter of the associated metasediments to constrain the temperature of the lizardite to Antigorite transition at high pressures. We show that below 300°C, lizardite and locally chrysotile are the dominant species in the mesh texture. Between 320 and 390°C, lizardite is progressively replaced by Antigorite at the grain boundaries through dissolution-precipitation processes in the presence of SiO2 enriched fluids and through a solid-state transition in the cores of the lizardite mesh. Above 390°C, under high-grade blueschist to eclogite facies conditions, Antigorite is the sole stable serpentine mineral until the onset of secondary olivine crystallization at 460°C.
Jose Alberto Padron Navarta - One of the best experts on this subject based on the ideXlab platform.
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High-P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones
Journal of Metamorphic Geology, 2018Co-Authors: Casto Laborda-lopez, Jose Alberto Padron Navarta, Claudio Marchesi, Carlos J Garrido, Vicente López Sánchez-vizcaíno, Maria T. Gomez-pugnaire, Antonio Jabaloy-sanchez, Karoly HidasAbstract:The transition between Antigorite‐serpentinite and chlorite‐harzburgite at Cerro del Almirez (Betic Cordillera, Southern Spain) exceptionally marks in the field the front of Antigorite breakdown at high pressure (~16–19 kbar) and temperature (~650°C) in a paleosubducted serpentinite. These ultramafic lithologies enclose three types of metarodingite boudins of variable size surrounded by metasomatic reaction rims. Type 1 Grandite‐metarodingite (garnet+chlorite+diopside+titanite±magnetite±ilmenite) mainly crops out in the Antigorite‐serpentinite domain and has three generations of garnet. Grossular‐rich Grt‐1 formed during rodingitization at the seafloor (10 kbar, ~350–650°C, ~FMQ buffer) to influx events of oxidizing fluids (fO2 ~HM buffer) released by brucite breakdown in the host Antigorite‐serpentinite. Type 2 Epidote‐metarodingite (epidote+diopside+titanite±garnet) derives from Type 1 and is the most abundant metarodingite type enclosed in dehydrated chlorite‐harzburgite. Type 2 formed by increasing μSiO2 (from −884 to −860 kJ/mol) and decreasing μCaO (from −708 to −725 kJ/mol) triggered by the flux of high amounts of oxidizing fluids during the high‐P Antigorite breakdown in serpentinite. The growth of Grt‐4, with low‐grandite and high‐pyralspite components, in Type 2 metarodingite accounts for progressive reequilibration of garnet with changing intensive variables. Type 3 Pyralspite‐metarodingite (garnet+epidote+amphibole+chlorite±diopside+rutile) crops out in the chlorite‐harzburgite domain and formed at peak metamorphic conditions (16–19 kbar, 660–684°C) from Type 2 metarodingite. This transformation caused the growth of a last generation of pyralspite‐rich garnet (Grt‐5) and the recrystallization of diopside into tremolitic amphibole at decreasing fO2 and μCaO (from −726 to −735 kJ/mol) and increasing μMgO (from −630 to −626 kJ/mol) due to chemical mixing between the metarodingite and the reaction rims. The different bulk Fe3+/FeTotal ratios of Antigorite‐serpentinite and chlorite‐harzburgite, and of the three metarodingite types, reflect the highly heterogeneous oxidation state of the subducting slab and likely point to the transfer of localized oxidized reservoirs, such as metarodingites, into the deep mantle.
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Titanian clinohumite and chondrodite in Antigorite serpentinites from Central Chile: evidence for deep and cold subduction
European Journal of Mineralogy, 2017Co-Authors: Jose M. Gonzalez-jimenez, Jose Alberto Padron Navarta, Claudio Marchesi, Gaelle Plissart, Leonardo N. Garrido, Thomas Aiglsperger, Rurik Romero, Antonio Moreno-abril, Martin Reich, Fernando BarraAbstract:Humite minerals, including Ti-rich, hydroxyl-dominant chondrodite and clinohumite, occur in Paleozoic Antigorite serpentinite in the La Cabaña area, in the Chilean Coastal Cordillera (~38° 30 ′ S–73° 15 ′ W). This may be the first report from South America. Humite minerals are intergrown with Mn-rich olivine hosting Antigorite blades in textural equilibrium, indicating a metamorphic origin. A comparison with previous results from piston-cylinder experiments and petrological studies of other high-P serpentinites constrains the formation conditions of the humite + olivine + Antigorite assemblage to ca. 2.0–2.5 GPa and 60 km, suggesting that the Paleozoic serpentinites were entrained into the mantle at higher P– T conditions than those experienced by the spatially associated olivine–lizardite metadunites and enclosing metasedimentary rocks (subducted to < 30 km). During exhumation along the subduction channel, high- P serpentinites together with metadunites underwent tectonic mingling with metasediments of the accretionary prism, preserving their signature of distinct metamorphic trajectories. This could be similar to the tectonic evolution of blueschists and high-P amphibolites found as isolated blocks in the metasediments of the Chilean Coastal Cordillera.
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On topotaxy and compaction during Antigorite and chlorite dehydration: an experimental and natural study
Contributions to Mineralogy and Petrology, 2015Co-Authors: Jose Alberto Padron Navarta, Carlos J Garrido, Andrea Tommasi, David MainpriceAbstract:Dehydration reactions result in minerals’ replacement and a transient fluid-filled porosity. These reactions involve interface-coupled dissolution–precipitation and might therefore lead to fixed crystallographic orientation relations between reactant (protolith) and product phases (i.e. topotaxy). We investigate these two phenomena in the dehydration of a foliated Antigorite (atg) serpentinite by comparing the crystallographic preferred orientation (CPO) developed by olivine (ol), orthopyroxene (opx) and chlorite (chl) during high-pressure Antigorite and chlorite dehydration in piston-cylinder experiments and in natural samples recording the dehydration of Antigorite (Cerro del Almirez, Betic Cordillera, Spain). Experiments were performed under undrained conditions resulting in fluid-filled porosity and in strong CPO of the prograde minerals, controlled by the pre-existing Antigorite CPO in the reactant foliated serpentinite. The orientation of a _ol,opx and $$c_{\text{chl}}^{ * }$$ c chl ∗ is parallel to $$c_{\text{atg}}^{ * }$$ c atg ∗ from the protolith. The Cerro del Almirez samples show similar, locally well-developed topotactic relations between orthopyroxene, chlorite and Antigorite, but the product CPOs are weaker and more complex at the thin section scale. In contrast to the experiments, olivine from natural samples shows a weak correlation between b _ol and the former $$c_{\text{atg}}^{ * }$$ c atg ∗ . We relate the strengthening of local topotactic relations and the weakening of the inherited CPO at a larger scale in natural samples to compaction and associated fluid migration. Microstructural features that might be related to compaction in the natural samples include: (1) smooth bending of the former foliation, (2) gradual crystallographic misorientation (up to 16°) of prismatic orthopyroxene due to buckling by dislocation creep, (3) inversion of enstatite to low clinoenstatite (P2_1/c) along lamellae and (4) brittle fracturing of prismatic orthopyroxene enclosed by plastically deformed chlorite. The coexistence of orthopyroxene buckling and clinoenstatite lamellae enables estimating the local strain rates and shear stresses generated during compaction. An lower bound for the strain rates in the order of 10^−12 to 10^−13 s^−1 and shear stresses of 60–70 MPa are estimated based on creep data. Lower shear stresses (20–40 MPa) are retrieved using a theoretical approach. These data point to slow compaction (and fluid extraction) in nature if the system is not perturbed by external forces, with rates only marginally higher than the viscoplastic deformation of the solid matrix.
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Plastic deformation and development of Antigorite crystal preferred orientation in high-pressure serpentinites
Earth and Planetary Science Letters, 2012Co-Authors: Jose Alberto Padron Navarta, Carlos J Garrido, Andrea Tommasi, Vicente López Sánchez-vizcaínoAbstract:We have inferred the deformation mechanisms of Antigorite by high-resolution EBSD mapping of samples from Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain). Textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600-630 °C and 1.6-1.9 GPa. Deformation was followed by static annealing of Antigorite at ca. 680 °C. The Crystal Preferred Orientation (CPO) of Antigorite is characterised by a strong alignment of (001) poles normal to the foliation plane and a weaker, but clear, parallelism between [100] axes and the macroscopic lineation defined by the elongation of magnetite aggregates. Analysis of misorientations across subgrains shows predominance of [010] rotation axis, consistent with activation of the [100](001) slip system. However, tilt subgrain boundaries subparallel to (100), probably formed by edge dislocations of this system, are subsidiary. Most subgrain boundaries are subparallel to (001) planes. They are interpreted as (001) twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins. Modelling of the evolution of the Antigorite CPO using a lower bound approach and considering different deformation regimes and sets of basal and non-basal slip systems has shown that intensities of [100] and [010] maxima reflect the relative strength of the Antigorite [100](001) and [010](001) systems. Activation of other basal or non-basal slip systems does not change significantly the CPO patterns, but results in less concentrated CPO. 3D transpression models better reproduce the CPO of natural Antigorite serpentinites. We propose that the widespread occurrence of strong CPO in high-pressure Antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on [hk0](001), together with the activation of twinning, implying that a power law rheology would better account for the mechanical behaviour of Antigorite serpentinite deep in the subduction channel and mantle wedge.
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An experimental investigation of Antigorite dehydration in natural silica-enriched serpentinite
Contributions to Mineralogy and Petrology, 2009Co-Authors: Jose Alberto Padron Navarta, Carlos J Garrido, Jörg Hermann, Vicente López Sánchez-vizcaíno, María Teresa Gómez-pugnaireAbstract:Piston cylinder experiments were performed to constrain the pressure and temperature conditions for two high-pressure Antigorite dehydration reactions found in silica-enriched serpentinites from Cerro del Almirez (Nevado–Filábride Complex, Betic Cordillera, southern Spain). At 630–660°C and pressures greater than 1.6 GPa, Antigorite first reacts with talc to form orthopyroxene ± chlorite + fluid. We show that orthopyroxene + Antigorite is restricted to high-pressure metamorphism of silica-enriched serpentinite. This uncommon assemblage is helpful in constraining metamorphic conditions in cold subduction environments, where Antigorite serpentinites have no diagnostic assemblages over a large pressure and temperature range. The second dehydration reaction leads to the breakdown of Antigorite to olivine + orthopyroxene + chlorite + fluid. The maximum stability of Antigorite is found at 680°C at 1.9 GPa, which also corresponds to the maximum pressure limit for tremolite coexisting with olivine + orthopyroxene. The high aluminium (3.70 wt% Al_2O_3) and chromium contents (0.59 wt% Cr_2O_3) of Antigorite in the investigated starting material is responsible for the expansion of the serpentinite stability to 60–70°C higher temperatures at 1.8 GPa than the Antigorite stability calculated in the Al-free system. The Antigorite from our study has the highest Al–Cr contents among all experimental studies and therefore likely constraints the maximum stability of Antigorite in natural systems. Comparison of experimental results with olivine–orthopyroxene–chlorite–tremolite assemblages outcropping in Cerro del Almirez indicates that peak metamorphic conditions were 680–710°C and 1.6–1.9 GPa.
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: Muriel Andreani, Marguerite Godard, Christian Nicollet, Stephane Schwartz, 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: Muriel Andreani, Marguerite Godard, Christian Nicollet, Stephane Schwartz, 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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pressure temperature estimates of the lizardite Antigorite transition in high pressure serpentinites
Lithos, 2013Co-Authors: Stephane Schwartz, Romain Lafay, Christian Nicollet, Bruno Reynard, Baptiste Debret, Pierre Lanari, Anne Line AuzendeAbstract:Serpentine minerals in natural samples are dominated by lizardite and Antigorite. In spite of numerous petrological experiments, the stability fields of these species remain poorly constrained. This paper presents the petrological observations and the Raman spectroscopy and XRD analyses of natural serpentinites from the Alpine paleo-accretionary wedge. Serpentine varieties are identified from a range of metamorphic pressure and temperature conditions from sub-greenschist (P 20 kbar, T > 460°C) along a subduction geothermal gradient. We used the observed mineral assemblage in natural serpentinite along with the Tmax estimated by Raman spectroscopy of the carbonaceous matter of the associated metasediments to constrain the temperature of the lizardite to Antigorite transition at high pressures. We show that below 300°C, lizardite and locally chrysotile are the dominant species in the mesh texture. Between 320 and 390°C, lizardite is progressively replaced by Antigorite at the grain boundaries through dissolution-precipitation processes in the presence of SiO2 enriched fluids and through a solid-state transition in the cores of the lizardite mesh. Above 390°C, under high-grade blueschist to eclogite facies conditions, Antigorite is the sole stable serpentine mineral until the onset of secondary olivine crystallization at 460°C.
Jose Alberto Padronnavarta - One of the best experts on this subject based on the ideXlab platform.
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changes in the cell parameters of Antigorite close to its dehydration reaction at subduction zone conditions
American Mineralogist, 2020Co-Authors: Tingting Shen, Jose Alberto Padronnavarta, Jörg Hermann, Li Chen, Cong Zhang, Jing Chen, Lifei Zhang, Jingsui YangAbstract:The unit-cell parameter a of Antigorite (usually expressed as the polysome m value) has been determined as a function of temperature (T) and pressure (P) in the range of 600–650 °C, 25–45 kbar in weeklong piston-cylinder experiments. A well-characterized natural Antigorite (with m = 16 and less abundant m = 15) was used as a starting material that coexisted with olivine, chlorite, Ti-humite, and aqueous fluid at run conditions. Transmission electron microscope (TEM) measurements on selected focused ion beam (FIB) wafers showed that Antigorite m values after the experiments varied between 14 and 22. More than 40 punctual analyses for each run condition were acquired to determine the range and the primary m value. The most frequent Antigorite m-value decreased systematically from 17–19 at 600 °C to 15–16 at 650 °C. The spacing of the m-isolines is getting narrower as the Antigorite breakdown reaction is approached. The topology of the m-isolines is similar to that previously characterized for the simple MgO-SiO2-H2O (MSH) system. However, the isolines are shifted to about 50–100 °C higher temperatures due to the incorporation of Al into Antigorite. Powder samples and FIB wafers of natural Antigorite from the Tianshan UHP belt (China) with peak metamorphic conditions of ~35 kbar, ~520 °C were also investigated with TEM. Low Al-Antigorite formed at peak metamorphic conditions displays a peak m value of 20–21, whereas high-Al Antigorite formed during isothermal decompression displays a lower m value of 19. Combination of our results with the published data of m values from metamorphic Antigorite that experienced various conditions allowed construction of a P-T-m diagram that can be used in future studies to better constrain formation conditions of serpentinites. The decrease of m values and the increase of Al in Antigorite with increasing temperature result in small, continuous dehydration whereby the H2O content of Antigorite changes from 12.4 to 12.1 wt%. Therefore, it is expected that a pore fluid is present during the prograde deformation of serpentinites. TEM observations showed that Antigorite adjusted its Al content by segregation of chlorite at the nanoscale. Together with the observation that multiple m values are always present in a single sample, this result indicates that full equilibration of Antigorite at the micrometer-scale is rare, with important implications for the interpretation of geochemical signatures obtained by in situ techniques.
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11b rich fluids in subduction zones the role of Antigorite dehydration in subducting slabs and boron isotope heterogeneity in the mantle
Chemical Geology, 2014Co-Authors: Jason Harvey, C. J. Garrido, Ivan Savov, Samuele Agostini, Claudio Marchesi, Jose Alberto Padronnavarta, Vicente Lopez Sanchezvizcaino, Maria Teresa GomezpugnaireAbstract:Serpentinites form by hydration of mantle peridotite and constitute the largest potential reservoir of fluid-mobile elements entering subduction zones. Isotope ratios of one such element, boron, distinguish fluid contributions from crustal versus serpentinite sources. Despite 85% of boron hosted within abyssal peridotite being lost at the onset of subduction at the lizardite-to-Antigorite transition, a sufficient cargo of boron to account for the composition of island arc magma is retained (c. 7 μg g− 1, with a δ11B of + 22‰) until the down-going slab reaches the Antigorite-out isograd. At this point a 11B-rich fluid, capable of providing the distinctive δ11B signature of island arc basalts, is released. Beyond the uniquely preserved Antigorite-out isograd in serpentinites from Cerro del Almirez, Betic Cordillera, Spain, the prograde lithologies (Antigorite–chlorite–orthopyroxene–olivine serpentinite, granofels-texture chlorite-harzburgite and spinifex-texture chlorite-harzburgite) have very different boron isotope signatures (δ11B = − 3 to + 6‰), but with no significant difference in boron concentration compared to the Antigorite-serpentinite on the low P–T side of the isograd. 11B-rich fluid, which at least partly equilibrated with pelagic sediments, is implicated in the composition of these prograde lithologies, which dehydrated under open-system conditions. Serpentinite-hosted boron lost during the early stages of dehydration is readily incorporated into forearc peridotite. This, in turn, may be dragged to sub-arc depths as a result of subduction erosion and incorporated in a melange comprising forearc serpentinite, altered oceanic crust and pelagic sediment. At the Antigorite-out isograd it dehydrates, thus potentially providing an additional source of 11B-rich fluids.
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tschermak s substitution in Antigorite and consequences for phase relations and water liberation in high grade serpentinites
Lithos, 2013Co-Authors: Jose Alberto Padronnavarta, Vicente Lopez Sanchezvizcaino, Maria Teresa Gomezpugnaire, Carlos J Garrido, Joerg Hermann, James A D Connolly, Claudio MarchesiAbstract:Abstract A model for the incorporation of alumina in FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O (FMASH) serpentinites has been developed by considering ideal Tschermak (Al 2 Mg − 1 Si − 1 ) solid solution in Antigorite. The Antigorite model has been calibrated by fitting the experimental conditions for the decomposition of Antigorite to chlorite + olivine + orthopyroxene + fluid in the FMASH system. The Antigorite Al-contents predicted with this model are in agreement with natural observations and suggest a maximum alumina solubility in Antigorite of 3.6 wt.% Al 2 O 3 at 20 kbar–650 °C and of 4.5 wt.% Al 2 O 3 at 3 kbar–560 °C. In the assemblage Antigorite–olivine–chlorite–fluid, the Al-content of Antigorite is buffered and temperature sensitive. This temperature sensitivity is the basis for a serpentinite geothermometer at greenschist, amphibolite and eclogite facies conditions. The buffered assemblage is stable in harzburgite compositions for relatively moderate amounts of Al 2 O 3 (> 1.8 wt.%) and is widespread in lherzolites, where it occurs together with diopside or, in a narrow temperature field, with tremolite.
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highly ordered Antigorite from cerro del almirez hp ht serpentinites se spain
Contributions to Mineralogy and Petrology, 2008Co-Authors: Jose Alberto Padronnavarta, Maria Teresa Gomezpugnaire, Lopez V Sanchezvizcaino, Carlos J Garrido, A Jabaloy, Gian Carlo Capitani, Marcello MelliniAbstract:The Cerro del Almirez ultramafic massif offers an example of high pressure and high temperature Antigorite serpentinites. A sharp Antigorite-out isograd separates them from Chl-harzburgites, consisting of olivine + enstatite + chlorite. Antigorite is characterized by aluminium contents as high as 4 wt.% Al2O3. The microstructural study shows that, prior to the transformation, Antigorite is exceptionally ordered and consists of the polysome m = 17. No polysomatic defect occurs in Antigorite forming most of the Cerro del Almirez serpentinites. Close to the Antigorite-out isograd, limited disorder features may occur, mainly as (001) twins, reaction rims and reduction of m down to 14–15. Here, local recrystallization phenomena lead to sporadic growth of large Antigorite and chlorite crystals.