Apatite O-Sr isotopes record the mantle source characteristics of the Fe-Ti-V-rich Taihe layered intrusion, Emeishan large Igneous Province, SW China

• Decoupling of apatite O-Sr isotopes reveals recycled materials in the mantle source. • Variable δ 18 O values of apatite indicate distinct melting domains. • Hybrid mantle sources are essential for Fe-Ti enrichment in primitive magmas. The Taihe layered mafic intrusion, located in the central part of the Emeishan Large Igneous Province, hosts a giant Fe-Ti-V oxide deposit. However, the petrogenesis of the Fe-Ti-V oxide ore-bearing layered intrusion is still debated. The Taihe intrusion is classified into three lithologic zones based on mineral assemblages and textural characteristics: Lower Zone, Middle Zone, and Upper Zone. Six cyclic units (Cycles I-VI) are recognized within the Middle Zone based on the rhythmic variations of Fe-Ti oxide contents. The most economically important Fe-Ti-V oxide ore layers are concentrated in the lower sections of these cycles, where magnetite clinopyroxenites are notably enriched in 5–12 vol% apatite. Petrographic and geochemical data indicate that these apatite grains were fresh and crystallized nearly simultaneously with Fe-Ti oxides and clinopyroxene, with no evidence of hydrothermal alteration. Apatite from the apatite-olivine gabbro and apatite-magnetite clinopyroxenite of Cycle II displays mantle-like 87 Sr/ 86 Sr (i) (0.7048–0.7050; average = 0.7049) and elevated δ 18 O (6.78–8.76 ‰; average = 7.73 ‰). However, apatite separated from the apatite gabbro of Cycle IV exhibits mantle-like 87 Sr/ 86 Sr (i) ratios (0.7048–0.7052; average = 0.7049) and δ 18 O values (5.55–6.79 ‰; average = 6.09 ‰). In contrast, apatite from the apatite-magnetite clinopyroxenite of Cycle VI shows slightly higher 87 Sr/ 86 Sr (i) (0.7050–0.7055; average = 0.7052) and notably higher δ 18 O (7.99–9.38 ‰; average = 8.50 ‰). The decoupling of the apatite O-Sr isotopes in the Cycles II and VI indicates the contribution of recycled altered oceanic crust in the mantle source. The elevated δ 18 O values of the apatite suggest interactions between subduction-related materials and the Emeishan plume, which resulted in the heavy oxygen isotopic signatures in the primitive magmas of the Taihe intrusion. The variability in apatite O-Sr isotopic compositions among cyclic units of the Taihe intrusion implies that the parental magmas originated from distinct melting domains that were heterogeneous due to the variable distribution and volume of altered oceanic crust components. The interaction of an upwelling mantle plume and the subcontinental lithospheric mantle that contains ancient recycled crustal materials may be a crucial factor in the formation of the giant Fe-Ti-V oxide deposit.