Geochemistry and zircon U–Pb ages and Hf isotopic composition of Permian alkali granitoids of the Phan Si Pan zone in northwestern Vietnam

Abstract

The late Permian granitoids exposed in the Phan Si Pan zone of northwestern Vietnam consist mainly of the Ye Yen Sun metaluminous granites and the Nam Xe–Tam Duong peralkaline granites. Laser ablation inductively coupled plasma mass spectrometry U–Pb zircon analysis reveals that both the granite suites were emplaced from 253Ma to 251Ma. They have a distinctive A-type geochemistry of high 10,000×Ga/Al ratios of 3.0–5.7 and are also characterized by elevated contents of high field strength elements, A/CNK values of 0.85–1.58, negative Eu-anomalies. Magmatic zircons from the granitoids exhibit positive initial ɛHf values ranging from 6.4 to 15.9 and yield single-stage depleted mantle Hf model ages of 257–663Ma. This Hf isotopic feature implies significant contribution of juvenile mantle material to the magmas of the spatially and temporally associated Ye Yen Sun metaluminous and Nam Xe–Tam Duong peralkaline granites.