Petrogenesis and Tectonic Setting of the Madeng Dacite, SW Sanjiang Indosinian Orogen: Evidence from Zircon U-Pb-Hf Isotopes, and Whole-Rock Geochemistry and Sr-Nd Isotopes

The Sanjiang Indosinian orogen, located in the eastern part of Paleo-Tethys tectonic domain, is a critical region to study Paleo-Tethyan Ocean evolution. Middle Permian–Late Triassic magmatic rocks are widespread Deqin–Weixi–Madeng area southwestern (SW) yet their petrogenesis and setting remain disputed. In this study, LA-ICP-MS zircon U-Pb age Hf isotopes, whole-rock elemental Sr-Nd isotope geochemistry Madeng dacite were studied. was dated at ca. 241.7 243.4 Ma. samples had high Al2O3 (12.91 14.39 wt.%) but low MgO (0.62 1.76 contents, alkali-rich (Na2O + K2O = 6.97 8.66 with A/CNK > 1.1, strongly resembling peraluminous S-type granites. enriched Rb, K, Th, U LREE, depleted Ba, Sr, Nb, Ta, P Ti, showed obvious negative Eu anomalies, suggesting fractionation Ti-bearing minerals (e.g., rutile ilmenite) plagioclase. an initial 87Sr/86Sr value 0.705698 0.710277, εNd(t) (−11.28 −10.64) εHf(t) (−13.99 −8.60), indicating continental meta-sedimentary source. Their average Nb/Ta (12.24) Th/U (4.65) also consistent crust. According lithological assemblage geochemical features, we propose that intermediate-felsic magmatism generated subduction-related setting.