Petrogenesis of highly fractionated S-type granite in the Longling area, southwest China: Implications for tectonic settings and mineralization

• The Longling granites formed from the collision of the Tengchong and Baoshan blocks. • Breakdown of rare-metal minerals and fractional crystallization enriched Sn, W, Nb, and Ta. • The Longling granites are enriched in Li, suggesting possible Li deposits in the region. • The two-mica granite underwent the most extensive fractional crystallization. • The two-mica granite is the most favorable for rare metal mineralization. A systematic study of highly fractionated S-type granites enhances our understanding of tectonic evolution and rare metal mineralization. The Longling granites are surrounded by several rare metal deposits. Zircon U-Pb ages, whole-rock geochemistry, ore-forming elements, and Sr-Nd-Pb isotopic data were obtained from Longling granites to constrain their metallogenic and tectonic significance. The zircon U-Pb dating indicates that the Longling biotite granite and two-mica granite were formed at 88 Ma and 77 Ma, respectively. They exhibit strong peraluminous features (A/CNK = 1.23–1.82), with high SiO 2 , Al 2 O 3 , volatile elements (F, B), and Rb/Sr (17.5–100.8), and low MgO (0.03–0.21 wt%), total iron (Fe 2 O 3 t = 0.62–1.31 wt%), and Nb/Ta (2.1–5.0). These geochemical features, along with enriched Nd isotopes (ε Nd (t) = − 13.6 to − 13.1) and Pb isotopic compositions (( 206 Pb/ 204 Pb) i = 18.19–18.91, ( 207 Pb/ 204 Pb) i = 15.69–15.75, ( 208 Pb/ 204 Pb) i = 39.06–39.20), suggest that they are highly fractionated S-type granites derived from muscovite-dehydration melting of ancient crustal pelite. We infer that the breakdown of rare-metal-enriched minerals (muscovite) and volatile-caused prolonged fractional crystallization caused the extraordinary enrichment of Sn, W, Nb, and Ta in the Longling Sn-W-Nb-Ta polymetallic deposit. Simulation calculations suggest that the two-mica granite underwent the most extensive fractional crystallization and is the most enriched in rare metals, making it a prime target for future exploration. Based on geological and geochemical evidence, we propose that the Longling granites formed in a syn -collision compressional tectonic setting as a result of the collision between the Tengchong and Baoshan blocks following the closure of the Meso-Tethyan Nujiang Ocean.