Mantle Wedge Metasomatism During Subduction Initiation: Mineral Transformations and Fluid Fluxes (BOIC Ophiolite, Newfoundland)
Abstract
The soles of ophiolites preserve slices of oceanic crust metamorphosed to amphibolite‐ to granulite‐facies conditions beneath heavily deformed mantle peridotites, providing key records of fluid and mass transfer across nascent subduction interfaces. This study investigates these processes in the Bay of Islands Ophiolitic Complex (BOIC) in Newfoundland through field observations, petrology, and geochemistry. Textural and chemical analyses reveal progressive metasomatism of basal peridotites, recorded by crystallization of pargasitic amphibole and compositional changes in pyroxenes, olivine and spinel up to 2 km above the metamorphic sole. Mantle peridotites evolve from weakly deformed porphyroclastic peridotites far from the contact with the metamorphic sole to ultramylonites close to the contact, reflecting fluid‐assisted strain localization. Thermometry on the peridotites indicated syn‐kinematic cooling from approximately 1150°C–800°C. At the contact, primary mantle‐derived minerals are entirely replaced by a re‐equilibrated ultramafic assemblage of metamorphic nature. Metasomatism was dominantly triggered by aqueous fluid infiltration, as shown by trace‐element analysis. Melt percolation was spatially restricted and not voluminous. The underlying nascent slab (the future metamorphic sole) undergoing dehydration was the likely source of metasomatic fluids. Based on these observations, a petrological evolution model for a young mantle wedge is proposed through comparisons with other ophiolites, where efficient mass transfer also appears to be restricted to a few hundreds of meters above the major tectonic contact with the metamorphic sole.
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BibTeX
@article{merit2026mantle,
title = {{Mantle Wedge Metasomatism During Subduction Initiation: Mineral Transformations and Fluid Fluxes (BOIC Ophiolite, Newfoundland)}},
author = {Louise Mérit and Philippe Agard and Loïc Labrousse and Benoît Dubacq and Cécile Prigent and Carl Guilmette and Jean Bédard and François Fournier-Roy and Horst Marschall and Axel Gerdes and Benjamin Lefeuvre and Alana Hinchey},
journal = {Geochemistry, Geophysics, Geosystems},
year = {2026},
month = oct,
doi = {10.1029/2026gc013121},
url = {https://hal.science/hal-05848972v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Mantle Wedge Metasomatism During Subduction Initiation: Mineral Transformations and Fluid Fluxes (BOIC Ophiolite, Newfoundland)
AU - Louise Mérit
AU - Philippe Agard
AU - Loïc Labrousse
AU - Benoît Dubacq
AU - Cécile Prigent
AU - Carl Guilmette
AU - Jean Bédard
AU - François Fournier-Roy
AU - Horst Marschall
AU - Axel Gerdes
AU - Benjamin Lefeuvre
AU - Alana Hinchey
PY - 2026
DA - 2026/10/26
JO - Geochemistry, Geophysics, Geosystems
DO - 10.1029/2026gc013121
UR - https://hal.science/hal-05848972v1
AB - The soles of ophiolites preserve slices of oceanic crust metamorphosed to amphibolite‐ to granulite‐facies conditions beneath heavily deformed mantle peridotites, providing key records of fluid and mass transfer across nascent subduction interfaces. This study investigates these processes in the Bay of Islands Ophiolitic Complex (BOIC) in Newfoundland through field observations, petrology, and geochemistry. Textural and chemical analyses reveal progressive metasomatism of basal peridotites, recorded by crystallization of pargasitic amphibole and compositional changes in pyroxenes, olivine and spinel up to 2 km above the metamorphic sole. Mantle peridotites evolve from weakly deformed porphyroclastic peridotites far from the contact with the metamorphic sole to ultramylonites close to the contact, reflecting fluid‐assisted strain localization. Thermometry on the peridotites indicated syn‐kinematic cooling from approximately 1150°C–800°C. At the contact, primary mantle‐derived minerals are entirely replaced by a re‐equilibrated ultramafic assemblage of metamorphic nature. Metasomatism was dominantly triggered by aqueous fluid infiltration, as shown by trace‐element analysis. Melt percolation was spatially restricted and not voluminous. The underlying nascent slab (the future metamorphic sole) undergoing dehydration was the likely source of metasomatic fluids. Based on these observations, a petrological evolution model for a young mantle wedge is proposed through comparisons with other ophiolites, where efficient mass transfer also appears to be restricted to a few hundreds of meters above the major tectonic contact with the metamorphic sole.
SN - 1525-2027
ER -