Intraslab remobilization of nitrogen during early subduction facilitates deep nitrogen recycling: Insights from the blueschists in the Heilongjiang Complex in NE China

Abstract Nitrogen (N) in subducting slab resides in both sediments and altered oceanic crust (AOC). The extent of subduction-zone metamorphic devolatilization of N in these reservoirs determines the amount of remaining N for deep recycling. However, N behavior inside the subduction zone, particularly below the forearc region, remains poorly understood so far. Here, we studied the pillow-shaped epidote-blueschist facies meta-basalts (hereafter refer to as blueschists) in the Heilongjiang Complex in Northeast China, aiming to understand the N behavior during the early subduction stage. Results show that these blueschists contain N (13.9 to 122.6 ppm; average: 51.0 ppm) up to seven times higher than the AOC (including pillow lavas) entering global trenches (N