Supplementary to: Fluid loss to the fore-arc controls the recycling efficiency of nitrogen in subduction zones
Description
Nitrogen is vital for life on Earth, but its interaction with the deeper Earth and subduction zone processes remains poorly understood. Previous studies focused on hot subduction zones and siliceous melts as nitrogen carriers. Our study investigated nitrogen partitioning in modern, cold to intermediate temperature subduction zones. We conducted 22 experiments in the subsolidus regime, revealing that nitrogen prefers the fluid phase at high pressure and low temperature. In contrast, nitrogen concentration in the melt dominates in the suprasolidus regime. Nitrogen loss to subduction fluids is higher in cold subduction zones beyond the volcanic arc front. Nitrogen retention in the residue increases under suprasolidus conditions. Nitrogen recycling to the deeper mantle is rare on the modern Earth, while it is favored in hotter subduction zones. Our findings also shed light on the nitrogen source for diamond-forming fluids, suggesting a transport pathway to lower depths through intermediate to hotter subduction zones, especially in earlier stages of Earth's history. The supplementary tables here present the compositions of the starting materials as determined by XRF and automated CHN analyzer and EPMA analyses of high-pressure experimental phases.