In situ quantification of the nitrogen content of olivine-hosted melt inclusions from Klyuchevskoy volcano (Kamchatka): Implications for nitrogen recycling at subduction zones

Evelyn Füri (1) , Maxim Portnyagin (2, 3) , Nikita Mironov (3) , Cécile Deligny (1) , Andrey Gurenko (1) , Roman Botcharnikov (4) , François Holtz (5)

1 CRPG - Centre de Recherches Pétrographiques et Géochimiques
2 GEOMAR - Helmholtz Centre for Ocean Research [Kiel]
3 GEOKHI - Vernadsky Institute of Geochemistry and Analytical Chemistry
4 Institut für Geowissenschaften [Mainz]
5 Institut für Mineralogie [Hannover]

Assessing the N content of arc magmas and their mantle source remains a challenge because the volatile element composition of melts and gases can be modified during magma ascent, storage, and eruption. Given that melt inclusions (MIs) in Mg-rich olivine represent the best proxies for primary arc melts, we applied, for the first time, an in situ high-resolution secondary ion mass spectrometry (SIMS) method to determine the N concentration in olivine-hosted MIs from Klyuchevskoy volcano in Kamchatka. To reverse the effects of post-entrapment modification processes (i.e., exsolution of volatiles into a fluid bubble), the MIs were partially to completely homogenized at high temperatures (1150-1400°C) and pressures ranging from 0.1 to 500 MPa under dry to H 2 O-saturated conditions at variable oxygen fugacities (CCO to QFM+3.3). After the experiments, N concentrations in water-rich MI glasses correlate positively with H 2 O and CO 2 contents as well as with N/CO 2 ratios, and negatively with the volume of the remaining fluid bubble. Glasses of completely homogenized (fluid bubble-free) MIs contain up to 25.7 ± 0.5 ppm N, whereas glasses of three unheated (natural, bubblebearing) MIs have significantly lower N concentrations of ~1 ± 0.3 ppm. The N-CO 2-Nb characteristics of completely homogenized MIs indicate that melts feeding Klyuchevskoy volcano have high absolute concentrations of both N and CO 2 , as well as large excess of these volatiles relative to Nb, compared to primary mid-ocean ridge melts. This implies that large amounts of N and CO 2 in Klyuchevskoy melts and their mantle source are derived from the subducting slab, and that these subducted volatiles are (partially) returned to the crust and atmosphere by arc-related magmatism.

Mots clés: Nitrogen; SIMS; melt inclusions; subduction; volatile recycling; Klyuchevskoy volcano

Domaines: Planète et Univers [physics]

Evelyn Füri, Maxim Portnyagin, Nikita Mironov, Cécile Deligny, Andrey Gurenko, et al.. In situ quantification of the nitrogen content of olivine-hosted melt inclusions from Klyuchevskoy volcano (Kamchatka): Implications for nitrogen recycling at subduction zones. Chemical Geology, 2021, 582, pp.120456. ⟨10.1016/j.chemgeo.2021.120456⟩. ⟨hal-03321267⟩