In situ quantification of the nitrogen content of olivine-hosted melt inclusions from Klyuchevskoy volcano (Kamchatka): Implications for nitrogen recycling at subduction zones
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 prox...
Published in: | Chemical Geology |
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Main Authors: | , , , , , , |
Other Authors: | , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2021
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Subjects: | |
Online Access: | https://hal.archives-ouvertes.fr/hal-03321267 https://hal.archives-ouvertes.fr/hal-03321267/document https://hal.archives-ouvertes.fr/hal-03321267/file/Fueri%20et%20al%20ChemGeol_preprint.pdf https://doi.org/10.1016/j.chemgeo.2021.120456 |
Summary: | 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. |
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