Tectono-magmatic–volatile coupling in postcollisional giant porphyry Cu formation: Evidence from slab tearing and mantle inputs at Qulong, Tibet

The origin of postcollisional porphyry copper deposits (PCDs) within thickened crust remains debated, particularly regarding the coupling between tectono-magmatic–volatile evolution and ore formation. At Qulong, Tibet, new geochemical and isotopic data across four Miocene intrusive phases define a magmatic transition from juvenile crustal to mantle-influenced sources. Pre-ore biotite monzogranite (17.4 ± 0.2 Ma) is derived from juvenile lower crust with depleted Sr-Nd-Hf isotopes and negative ∆199Hg. Syn-ore monzonitic granite porphyry (17.6 ± 0.3 Ma) shares crustal isotopes but shows positive ∆199Hg, implying volatile influx from metasomatized mantle. Intermediate granodiorite porphyry (15.3 ± 0.1 Ma) exhibits transitional isotopic traits and rare earth element patterns, reflecting crust–mantle hybridization. Post-ore diorite porphyry (14.6 ± 0.1 Ma and 14.7 ± 0.1 Ma) displays mantle affinities, positive ∆199Hg, and enriched Sr-Nd-Hf signatures, indicating metasomatized lithospheric mantle melting. Across the sequence toward the young rocks with mantle signatures, decreasing Sr/Y ratios and increasing zircon saturation temperatures record a shift from amphibole- to plagioclase-dominated fractionation. High magmatic oxygen fugacity (fO2) and H2O contents and near-zero ∆199Hg values in magnetite and chalcopyrite point to oxidized, H2O-rich mantle-derived magmas as key metal carriers. Geophysical and isotopic data links reveal that the locations and fertility of the Miocene porphyry deposits, including the deposit at Qulong, were controlled by focused mantle-derived inputs facilitated by tearing of the subducting Indian continental slab. This tearing, particularly along structures such as the Yadong–Gulu rift corridor, provided vertical zones of weakness for asthenospheric upwelling within the broader context of continued Indian continental subduction. This explains the northward younging of ore centers (Qulong → Jiama → Bangpu). We propose that the formation of postcollisional PCDs in this region required (1) slab tearing during the sustained subduction of the Indian continental plate-triggered mantle upwelling, which provided the necessary heat for crustal melting and the generation of crustal-derived magmas; (2) syn-mineralization interaction between crustal melts and mantle-derived volatiles and metals; (3) tectonic transition from compression to extension facilitating underplating; and (4) slab-tear-induced mantle flow sustaining high fO2 and volatile flux. This model provides a conceptual framework integrating magmatism, metal sources, and geodynamics in collisional orogens with specific relevance to settings affected by slab tearing and substantial mantle uplift, as exemplified by Tibet.