ArticleIdentification of an Early-Middle Jurassic oxidized magmatic belt, south Gangdese, Tibet, and geological implications

The south Gangdese region is the site of subduction of the Neo-Tethys and subsequent continental collision. Compared with widespread Cretaceous and Cenozoic magmatism, Early-Middle Jurassic magmatic rocks and related deposits are rarely reported. Our work identified a >200 km long felsic rock belt associated with Cu mineralization in the south Gangdese region. We report here zircon U-Pb ages, zircon Ce4+/Ce3+ values, and mineral assemblages of two Cu mineralized intrusions within the belt. A hornblende granite and a diorite porphyry were emplaced at 177.3 Ma and 166.3 Ma, respectively. Geological occurrence and magmatic hematite-magnetite-chalcopyrite intergrowths suggest that Cu mineralization formed coeval with Jurassic intrusions. Mineralized intrusions have high zircon Ce4+/Ce3+ and EuN/EuN∗ ratios, and hematite-magnetite intergrowths, suggesting their parent magmas were highly oxidized. Hornblende is common and primary fluid inclusions are found in titanite and apatite, indicating their parent magmas were water-saturated and exsolved volatile phases at early stage of magmatic evolution. Those magma characters contribute to the formation of porphyry Cu deposits. Given that majority subduction-related porphyry Cu systems have been eroded following uplift and denudation, the well-preserved Early-Middle Jurassic Cu mineralized igneous rocks in south Gangdese are favorable prospecting targets for subduction-related porphyry Cu deposits.