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

• Published in: Chemical Geology
• Main Authors: Füri, Evelyn, Portnyagin, Maxim, Mironov, Nikita, Deligny, Cécile, Gurenko, Andrey, Botcharnikov, Roman, Holtz, François
• Other Authors: 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), Helmholtz Centre for Ocean Research Kiel (GEOMAR), Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKHI), Russian Academy of Sciences Moscow (RAS), Institut für Geowissenschaften Mainz, Johannes Gutenberg - Universität Mainz = Johannes Gutenberg University (JGU), Institut für Mineralogie Hannover, Leibniz Universität Hannover=Leibniz University Hannover, European Project: 715028,VOLATILIS
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Nitrogen; SIMS; melt inclusions; subduction; volatile recycling; Klyuchevskoy volcano; [SDU]Sciences of the Universe [physics]; Kamchatka
• Online Access: https://hal.science/hal-03321267; https://hal.science/hal-03321267/document; https://hal.science/hal-03321267/file/Fueri%20et%20al%20ChemGeol_preprint.pdf; https://doi.org/10.1016/j.chemgeo.2021.120456

International audience 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.