The India-Asia convergence generated a series of porphyry deposits formed in the post-collisional stage, yet the enrichment mechanisms of critical ore-forming elements such as chlorine (Cl) remain poorly understood. Multi-isotope systems, particularly Cl isotopes, offer a powerful tool to trace these material cycling processes. However, the limited understanding of the δ³⁷Cl values of collisional zones has hindered our understanding of Cl cycling. To address this, we systematically collected ore-forming porphyries, granitoid batholiths, a deep crustal granulite xenolith, an ultramafic cumulate, and an ultrapotassic volcanic rock from the southern Tibetan Plateau. Apatite Cl and Nd isotopes, along with whole-rock boron (B) isotopes, were analyzed to constrain the Cl isotope compositions of various endmembers and to further trace the origin of Cl for porphyry ore-forming magmas. From the Late Cretaceous to the Oligocene, the Zedong granitoid batholiths exhibit progressively enriched apatite εNd(t) and decreasing apatite δ³⁷Cl, indicating increasing involvement of a low-δ³⁷Cl enriched crustal component. Two components are therefore recognized in the collisional crust: a juvenile, depleted crust with high δ³⁷Cl (+0.62 ± 0.28 ‰), and a reworked, enriched crust with relatively low δ³⁷Cl (？0.51 ‰). The post-collisional Qulong and Jiama porphyry deposits show significantly higher apatite δ³⁷Cl values (Qulong: +0.88 ± 0.42 ‰; Jiama: +0.72 ± 0.61 ‰) compared to the Zedong granitoid batholiths (+0.11 ± 0.44 ‰), yet similar to those of ultrapotassic magmas (+0.85 ± 0.10 ‰) and the juvenile crust (+0.88 ± 0.46 ‰). Combined with Nd isotope evidence, we suggest that metasomatized lithospheric mantle (represented by the ultrapotassic magmas) and juvenile crustal components are the dominant sources of Cl in the collisional porphyry ore-forming magmas.

Article link: https://doi.org/10.1016/j.gca.2026.07.019