Genesis of strongly peraluminous granites facilitates nitrogen retention in the crust

作者：Yunzhe Chen, Jian Xu, Xiaoping Xia, Long Li · 发表于：Geochimica et Cosmochimica Acta · 年份：2025 · DOI：10.1016/j.gca.2025.05.010 · 被引用次数：3 · 研究领域：Geochemistry and Elemental Analysis、Geological and Geochemical Analysis、Radioactive element chemistry and processing

Sediments/sedimentary rocks are a major sink of atmospheric N 2 , which is mainly fixed into diazotrophic biomass and recycled into other organic matters or diagenetically transferred (in the form of NH 4 + ) into the crystal structures of phyllosilicate minerals in sediments. Driven by tectonic activities, sedimentary rocks may experience various degrees of metamorphism with some eventually being melted to form S-type granitoids. The destiny of sedimentary N during these processes, i.e., retained in the crust or returned to the atmosphere, determines the long-term N evolution in the crust and the atmosphere, which profoundly impacts not only volatile properties in the lithosphere but also the surface climatic and environmental conditions. Previous studies have reported various extents of N loss (from very subtle to up to 70 %) from regional meta -sedimentary rocks. However, detailed studies on the N-losing mechanism during crustal anatexis and S-type granitoid formation are rare. Here, we examined the Permian–Triassic strongly peraluminous granites (SPGs) in the Diancangshan-Ailaoshan area in SW China, which were formed by extensional decompression melting of Precambrian pelitic sediments in the upper–middle crust within a back-arc basin triggered by slab rollback of the subducted Paleo-Tethyan oceanic crust. The results show that the SPGs have a N-content range of 6.8 ppm to 58.2 ppm (mean = 37.9 ± 11.3 ppm; 1σ; n = 19). The δ 15 N values of the samples mostly cluster betwe...