New zircon U-Pb data, along with the data reported in the literature, reveal five phases of magmatic activity in the Tengchong Terrane since the Early Paleozoic with spatial and temporal variations summarized as to the east, minor in the east and west, abundant Early Cretaceous (131-114 Ma) in the east, extensive Late Cretaceous (77-65 Ma) in the central region, and Paleocene-Eocene (65-49 Ma) in the central and western Tengchong Terrane, in which the Cretaceous-Eocene magmatism migrated from east to west. The increased zircon ε Hf (t) of the Early Cretaceous granitoids from -12.3 to -1.4 at ca. 131-122 Ma to -4.6 to +7.1 at ca. 122-114 Ma, identified for the first time in this study, and the magmatic flare-up at ca. 53 Ma in the central and western Tengchong Terrane indicate increased contributions from mantle-or juvenile crust-derived components. The spatial and temporal variations and changing magmatic compositions over time in the Tengchong Terrane closely resemble those of the Lhasa Terrane in southern Tibet. Such similarities, together with the data of stratigraphy and paleobiogeography, enable us to propose that the Tengchong Terrane in SW Yunnan is most likely linked with the Lhasa Terrane in southern Tibet, both of which experienced similar tectonomagmatic histories since the Early Paleozoic.

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Potassium-rich adakitic rocks have been used to infer high-pressure (HP) melting of thickened or foundered mafic lower crust in post-collisional settings. However, their origin remains debated because of their potassic rather than sodic nature. We address this debate by investigating the source of post-collisional Oligocene high-K adakitic granites in southern Tibet, which are widely attributed to melting of overthickened mafic lower crust. Our new data provide evidence for the generation of these high-K adakitic granites by anatexis of exposed migmatitic intermediate to felsic arc orthogneisses. These granites contain high-Th/U Oligocene magmatic zircons (30–22 Ma), and inherited zircons (66–48 Ma) with the same εHf(t) (0 to +12) as the coeval migmatites. The migmatites have in turn low-Th/U metamorphic Oligocene zircon rims around 66–48 Ma magmatic zircon cores recording the anatectic event at 29–25 Ma. Phase equilibrium modeling yields an anatectic temperature of ~740 °C and pressure (P) of ~0.9 GPa and shows that garnet is stable at P > 0.7 GPa in the melt-present field. The results indicate that high-K adakitic magmas are derived from melting of older intermediate to felsic arc rocks at intermediate pressures, in the garnet stability field, without any involvement of HP melting of metabasaltic rocks. We propose that hybridization between such purely crustal magmas and subcontinental lithospheric mantle–derived shoshonitic magmas results in the hybridized post-collisional Oligocene–Miocene mafic microgranular enclave–bearing potassic adakitic granitic rocks in southern Tibet.

Magmatism and the related mineralization have been hot topic for decades. The mineral resources are very abundant in Sanjiang region, southwestern Yunnan, with several giant ore deposits of copper, stannum, gold and lead-zinc. Magmatic activation usually accompany with metallic mineralization (Deng et al., 2009(Deng et al., , 2011Wang et al., 2010). Tectonic-magmatic-metallogenic system is essential for the magmatism associated with mineralization. Guyong granite with Sn mineralization is located in a metallogenic belt, western Yunnan, and it is also a granitoid complex. We choose the intrusive rocks to reveal both the intrusive and mineralized processes based on their geochemistry and dating data.