U-pb zircon ages of granites from the Song Chay complex, Hoang Su Phi, Ha Giang, and their geological implications

Abstract

Granitoids of the Song Chay Complex occupy nearly 89% of the study area. The lithological assemblage includes: Phase I-two-mica granite, fine-grained muscovite granite with deformation features, granitic gneiss, and porphyritic granite; Phase II—muscovite granite and massive two-mica granite; and Phase III-pegmatite and aplite granite. Zircon grains were separated from biotite granitic gneiss (HS.1168), massive muscovite granite (HS.1248), and massive two-mica granite (HS.3054), which belong to Phase I and Phase II of the Song Chay Complex in the Hoang Su Phi area. U-Pb zircon ages were determined using LA-ICP-MS, yielding weighted mean ²⁰⁶Pb/²³⁸U ages ranging from 431 to 433 Ma, corresponding to the Middle Silurian (Wenlock epoch). Combined with the oscillatory zoning characteristics observed in zircon, these ages are interpreted as the magmatic crystallization age of the granites.