Petrogenesis, Tectonics, and Metallogenic Potential of Early Paleozoic S-type Granites in Pinghe, Southwestern Yunnan, China

Abstract

A systematic study of early Paleozoic S-type granites in Pinghe enhances our understanding of the tectonic evolution of proto-Tethys and provides a foundation for exploring rare metal deposits in the region. The Pinghe granites consist of monzogranite and leucogranite. Zircon U-Pb dating shows that the emplacement ages of the monzogranite and leucogranite are 502.0 Ma and 500.9 Ma, respectively. All samples have high SiO₂ content and a weakly to strongly peraluminous character (A/CNK = 1.08–1.23), consistent with S-type granites. The monzogranite has relatively high CaO, Sr, Ba, and CaO/Na₂O ratios but lower Rb. In contrast, the leucogranite has lower CaO, Sr, Ba, and CaO/Na₂O ratios but higher Rb. The similar ε_Nd(t) values (–9.3 to –8.4) and Pb isotopic compositions ((²⁰⁶Pb/²⁰⁴Pb)_t = 18.03–19.36, (²⁰⁷Pb/²⁰⁴Pb)_t = 15.66–15.76, (²⁰⁸Pb/²⁰⁴Pb)_t = 37.97–38.55) suggest that the monzogranite formed through partial melting of crustal greywacke, while the leucogranite originated from partial melting of crustal pelite. Regional geological studies suggest that these S-type granites in Pinghe were emplaced in an active continental margin setting, associated with the westward subduction of the proto-Tethys oceanic slab. The geochemical characteristics of leucogranite are consistent with those of tungsten-tin-related granites, indicating significant metallogenic potential for W and Sn deposits.