In the Catalina Schist subduction-zone metamorphic complex (California), metasedimentary rocks show a decrease in N concentration and an increase in delta-N-15(air) with increasing metamorphic grade. Lowest-grade lawsonite-albite rocks contain 632 +/- 18 5 ppm N with delta-N-15 = +1.9 +/- 0.6 parts per thousand, whereas high-grade amphibolite equivalents contain 138 +/- 76 ppm N with delta-N-15 = +4.3 +/- 0.8 parts per thousand. Loss of N accompanied devolatilization reactions that evolved H2O-rich C-O-H-S-N fluids through consumption of chlorite and phengitic white mica and production of mineral assemblages containing muscovite, biotite, garnet, and kyanite. Whole-rock N concentrations of up to 200 ppm in veins and pegmatites produced during high-P/T metamorphism reflect the redistribution of N during devolatilization and partial melting of the metasedimentary rocks. Bulk fluid-rock N-isotope fractionations (DELTA-N-15 = delta-N-15(fluid) - delta-N-15(rock)) of -1.5 +/- 1 parts per thousand were calculated with the Rayleigh distillation equation, taking into account variability in rock composition by comparison of samples with similar K2O concentrations. These fractionations are similar to but slightly lower than published calculated fractionations for N2-NH4+ exchange at the temperature range of 350-600-degrees-C over which most of the devolatilization occurred in the Catalina Schist (approximately -3.4 to -2.25 parts per thousand). The N systematics appear to be explained by N2-NH4+ exchange and a devolatilization process intermediate in behavior to batch volatilization and Rayleigh distillation. The observed shifts in N concentration and delta-N-15 cannot be explained by NH3-NH4+ exchange at these temperatures using the equilibrium models. The distillation devolatilization process implicated in this study may govern the behavior of other trace elements partitioned into hydrous fluids during devolatilization (e.g., B, Cs, U). Similarity of the calculated fluid delta-N-15 (is similar to -1.5 to +5.5 part per thousand) with compositions of natural gases inferred to be derived from metasedimentary sources indicates the possibility of using N as a tracer of large-scale volatile transport.
