The behaviour of nitrogen during subduction of oceanic crust: Insights from in situ SIMS analyses of high-pressure rocks

Understanding the Earth’s geological nitrogen (N) cycle requires an understanding of how N behaves during dehydration subducted crust. We present first in situ measurements silicate minerals by secondary ion mass spectrometry, focusing on high pressure rocks representing oceanic investigate distribution between mineral phases, and combine analyses with other trace major elements order to constrain behaviour fluid-rock interaction. The data confirm that white mica (phengite, paragonite) is primary host for N, containing up 320 μg/g, whereas including clinopyroxene, amphibole epidote contain <5 μg/g N. Chlorite can also (up 83 μg/g) may play a previously unrecognised role subduction zone cycling. Bulk rock concentrations estimated from modes are consistent measured bulk combustion, which confirms most hosted within not along grain boundaries or fluid inclusions. contents correlate K2O (N/K2O = 19.3 ± 2.0). Using N/K2O ratios average altered crust, flux upper crust be 0.6-2.4×1011g/yr, but at lower end previous estimates. were used Open system interaction modelling was model evolution B Li phengite garnet-phengite quartzite. By comparison Li, phengite-fluid partition coefficient 0.1–1.5. Separately, growth paragonite blueschist shown sequester limit loss fluid. stability therefore critical controlling Nitrogen addition sediment-derived fluids appears important process rocks. Mafic act as sink this if stable. This work provides natural constraints fluid-mineral partitioning conditions emphasises complexity mobility zones, redistribution different phases lithologies being important.