Zircon U–Pb ages and geochemistry of granitoids in the Truong Son terrane, Vietnam: Tectonic and metallogenic implications

Abstract

Truong Son terrane, one of the most important tectonic and metallogenic terranes in Indochina block, is composed of many volcano–plutonic complexes. Reported here is geochronological and geochemical data obtained from six different volcano–plutonic complexes. The new data reveals that the granite from the Hai Van complex is 438Ma in age, and shows collision-related geochemical characteristics; whereas another five samples from five volcano–plutonic complexes present consistent emplacement and crystallization ages ranging from 261 to 242Ma. Dien Bien granodiorite, Phia Bioc monzogranite and Dong Trau rhyolite display typical subduction-related calc-alkaline affinity (e.g., depletion in Nb–Ta and Ti and enrichment in Rb and La), while monzogranite from Song Ma complex displays collision-related shoshoniteseries and granites from Bengiang-Queson complex are related to post-collision calc-alkaline series. Based on these observations, in combination with the previous published geochronological data, we propose that at least four major stages of magmatic activities occurred during the Paleozoic and the Early Mesozoic through the Truong Son terrane: Ordovician–Silurian (420–470Ma), Late Carboniferous-Early Permian (280–300Ma), Late Permian to Mid-Triassic (245–270Ma) and Middle-Late Triassic (200–245Ma). These magmatic activities are not only attributed to the Tethyan Song Ma ocean southwestward subduction but also related to Paleo Tamky–Phuoc Son oceanic bidirectional subduction. Synthesized with regional metallogenic data, we identified three metallogenic epochs: (1) Late Carboniferous-Early Permian (280–300Ma) arc-magmatic hydrothermal Cu–Au–Fe polymetallic metallogenic system related to the Tamky–Phuoc Son ocean north-dipping subduction; (2) Late Permian-Middle Triassic (245–280Ma) arc-magmatic hydrothermal Cu–Au–Fe and orogenic W–Sn–Au polymetallic metallogenic system, which linked to both Paleo-Tethyan Song Ma ocean south-dipping subduction and Tamky–Phuoc Son ocean closure; (3) Middle to Late Triassic (200–245Ma) syn-collisional magmatic epithermal Fe–Au–W–Sn and post-collisional (or orogenic) Au system.