1. Mantle metasomatic influence on water contents in continental lithosphere: New constraints from garnet pyroxenite xenoliths (France & Cameroon volcanic provinces)
- Author
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Samantha Azevedo-Vannson, Lydéric France, Jannick Ingrin, Gilles Chazot, Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Muséum national d'Histoire naturelle (MNHN)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de recherche pour le développement [IRD] : UR206-Centre National de la Recherche Scientifique (CNRS), Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Unité Matériaux et Transformations - UMR 8207 (UMET), Centrale Lille-Institut de Chimie du CNRS (INC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Laboratoire Géosciences Océan (LGO), Université de Bretagne Sud (UBS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Université de Lille, CNRS, INRA, ENSCL, Institut de minéralogie, de physique des matériaux et de cosmochimie [IMPMC], Centre de Recherches Pétrographiques et Géochimiques [CRPG], Unité Matériaux et Transformations - UMR 8207 [UMET], Laboratoire Géosciences Océan [LGO], Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de recherche pour le développement [IRD] : UR206-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS), Institut de Chimie du CNRS (INC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centrale Lille Institut (CLIL), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), and Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Garnet pyroxenites ,010504 meteorology & atmospheric sciences ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,[PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph] ,Pyroxene ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle (geology) ,Geochemistry and Petrology ,Lithosphere ,Xenolith ,Metasomatism ,0105 earth and related environmental sciences ,Peridotite ,Nominally anhydrous minerals ,Hydroxyl ,Mantle metasomatism ,Adamawa Volcanic Plateau ,French Massif Central ,geography ,geography.geographical_feature_category ,[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph] ,Geology ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Massif ,Geodynamics ,13. Climate action ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
Quantifying water contents in the lithospheric mantle is key to our understanding of global geodynamics, mantle composition, and related physical properties. Most mantle lithologies (peridotite) contain little water (similar to 50 ppm), but petrological heterogeneities such as pyroxenites are more hydrous (similar to 300 ppm) relative to the mantle rocks. Pyroxenites also melt at lower temperatures than peridotites and are thus important to magma genesis. Thus, quantifying pyroxenite water contents provides new information on the distribution of water in the mantle. Here, we present phase-specific FTIR measurements of the water contents in pyroxenite mantle xenoliths from two continental lithospheric domains that experienced intense metasomatism: the French Massif Central (FMC, France) and the Adamawa Volcanic Plateau (AVP, Cameroon). The AVP garnet pyroxenites are more hydrated 9[H2O](Clinopyroxene) = 386-685 ppm; [H2O](Orthopyroxene) = 124-155 ppm; [H2O](Garnet) < 0.5 ppm) than FMC ones 9[H2O](Clinopyroxene) = 112-465 ppm; [H2O](Orthopyroxene )= 61-104 ppm; [H2O](Garnet) < 0.5 ppm). These water concentrations are homogenous at the grain and correlate with equilibrated major element concentrations, indicating that they are representative of lithospheric water, although the FMC pyroxenites were dehydrated during metasomatism by a carbonatitic fluid (based on the correlation between La-N/Sm-N and Ti/Eu ratios); the water contents of AVP pymxenites were likely not affected by metasomatism. FMC pyroxenites show peculiar FTIR spectra that may reflect the preferential dehydration of specific sites in the pyroxene structure. In both regions, metasomatism modified the light rare Earth element contents (e.g., Ce) of the pyroxenites, resulting in highly variable H2O/Ce ratios. Therefore, we conclude that the utility of the H2O/Ce ratio to identify the involvement of pyroxenites in magmas genesis is limited.
- Published
- 2021
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