Carbon cycling during crustal magmatism: Constraints from Fe-Mg isotopes of Early Cretaceous adakitic rocks in Liaodong Peninsula, NE China

Abstract Carbon cycling mediated by magmatism is fundamental to planetary habitability, yet the role of crustal magmatism, particularly adakitic rocks, in tracing deep carbon transfer remains poorly constrained. Here, we employ coupled Fe-Mg isotopes in Early Cretaceous low-Mg (LMA) and high-Mg adakitic rocks (HMA) from northeastern China to identify the geochemical fingerprint of carbon cycling within crustal magmatism. The LMA exhibit high δ56Fe (0.14‰ to 0.23‰) and low δ26Mg (−0.40‰ to −0.28‰), whereas HMA display low δ56Fe (0.05‰ to 0.15‰) and high δ26Mg (−0.31‰ to −0.21‰). Partial melting modeling and major-element variations indicate that they originated from a carbonated eclogite source. The widespread distribution of Mesozoic adakitic rocks across northeastern China demonstrates that carbonated eclogite is a critical carbon reservoir. Temporal correlations between regional Mg isotope compilations and subducted carbon fluxes reveal that slab subduction (Paleo-Pacific plate in Mesozoic; Pacific plate in Cenozoic) facilitated carbon recycling. Our results establish adakitic rocks as robust tracers of deep carbon cycling and demonstrate that plate-tectonic processes have governed this transfer over millions of years, advancing understanding of Earth’s deep carbon cycle and its planetary habitability implications.