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Impact of metasomatism on halogen distribution in the North American sub-continental lithospheric mantle.

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Title: Impact of metasomatism on halogen distribution in the North American sub-continental lithospheric mantle.
Authors: Segee-Wright, George1,2 (AUTHOR) george.segee-wright@univ-lorraine.fr, Lassiter, John C.2 (AUTHOR), Barnes, Jaime D.2 (AUTHOR), Le Roux, Véronique1,3 (AUTHOR), Monteleone, Brian D.3 (AUTHOR), Riley, Matthew K.2,4 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. Jul2026, Vol. 425, p200-212. 13p.
Subjects: Metasomatism, Chlorine, Earth's mantle, Fluorine, Fluorination, Subduction, Lithosphere
Geographic Terms: Colorado Plateau, United States
Abstract: Fluorine (F) and chlorine (Cl) in the mantle are useful tracers of subduction processes. Recent work has suggested that F and Cl can be sequestered in the Sub-Continental Lithospheric Mantle (SCLM) through interactions with subduction- or mantle-derived fluids and melts. Yet, the distribution of metasomatic halogens in the SCLM is unclear. In this study, we examine the effects of metasomatism and melt depletion on the halogen abundances in nominally anhydrous minerals (NAMs; olivine, orthopyroxene, and clinopyroxene), as well as in hydrous minerals (antigorite, chlorite, amphibole) in variably metasomatized SCLM peridotite xenoliths from the Colorado Plateau (USA) and the southern Rio Grande Rift (USA). We find that F and Cl are dominantly hosted in hydrous minerals in modally hydrated xenoliths, but H 2 O and Cl are variably enriched in NAMs resulting from recent metasomatism via a Cl-rich fluid. Fluorine shows no such enrichment in NAMs, likely due to the F-poor nature of the fluid in this region. In modally anhydrous xenoliths, Cl hosted in NAMs show no correlations with indices of metasomatism. Instead, the majority of Cl and variable amounts of other incompatible trace elements are likely hosted along grain boundaries, resulting from metasomatic enrichment of the SCLM. Grain boundaries may be an important host of metasomatic Cl in the modally anhydrous SCLM, potentially altering the calculated quantity of Cl in global SCLM and impacting the extent of Cl released during intraplate magmatism. [ABSTRACT FROM AUTHOR]
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Abstract:Fluorine (F) and chlorine (Cl) in the mantle are useful tracers of subduction processes. Recent work has suggested that F and Cl can be sequestered in the Sub-Continental Lithospheric Mantle (SCLM) through interactions with subduction- or mantle-derived fluids and melts. Yet, the distribution of metasomatic halogens in the SCLM is unclear. In this study, we examine the effects of metasomatism and melt depletion on the halogen abundances in nominally anhydrous minerals (NAMs; olivine, orthopyroxene, and clinopyroxene), as well as in hydrous minerals (antigorite, chlorite, amphibole) in variably metasomatized SCLM peridotite xenoliths from the Colorado Plateau (USA) and the southern Rio Grande Rift (USA). We find that F and Cl are dominantly hosted in hydrous minerals in modally hydrated xenoliths, but H 2 O and Cl are variably enriched in NAMs resulting from recent metasomatism via a Cl-rich fluid. Fluorine shows no such enrichment in NAMs, likely due to the F-poor nature of the fluid in this region. In modally anhydrous xenoliths, Cl hosted in NAMs show no correlations with indices of metasomatism. Instead, the majority of Cl and variable amounts of other incompatible trace elements are likely hosted along grain boundaries, resulting from metasomatic enrichment of the SCLM. Grain boundaries may be an important host of metasomatic Cl in the modally anhydrous SCLM, potentially altering the calculated quantity of Cl in global SCLM and impacting the extent of Cl released during intraplate magmatism. [ABSTRACT FROM AUTHOR]
ISSN:00167037
DOI:10.1016/j.gca.2026.04.042