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

Assessing the N content of arc magmas and their mantle source remains a challenge because volatile element composition melts gases can be modified during magma ascent, storage, eruption. Given that melt inclusions (MIs) in Mg-rich olivine represent best proxies for primary melts, we applied, first time, an situ high-resolution secondary ion mass spectrometry (SIMS) method to determine concentration olivine-hosted MIs from Klyuchevskoy volcano Kamchatka. To reverse effects post-entrapment modification processes (i.e., exsolution volatiles into fluid bubble), were partially completely homogenized at high temperatures (1150–1400 °C) pressures ranging 0.1 500 MPa under dry H2O-saturated conditions variable oxygen fugacities (CCO QFM + 3.3). After experiments, concentrations water-rich MI glasses correlate positively with H2O CO2 contents as well N/CO2 ratios, negatively volume remaining bubble. Glasses (fluid bubble-free) contain up 25.7 ± 0.5 ppm N, whereas three unheated (natural, bubble-bearing) have significantly lower ~1 0.3 ppm. The N-CO2-Nb characteristics indicate feeding absolute both CO2, large excess these relative Nb, compared mid-ocean ridge melts. This implies amounts are derived subducting slab, subducted (partially) returned crust atmosphere by arc-related magmatism.