Zircon U–Pb ages and Hf isotopic compositions of alkaline silicic magmatic rocks in the Phan Si Pan-Tu Le region, northern Vietnam: Identification of a displaced western extension of the Emeishan Large Igneous Province

Abstract In-situ zircon U–Pb and Hf isotope analyses were carried out for alkaline silicic magmatic rocks from the Phan Si Pan-Tu Le region in northern Vietnam to constrain their possible sources and to determine their petrogenetic relationship with the Emeishan Large Igneous Province (ELIP), SW China. Nine granites and nine rhyolites yield zircon 206 Pb/ 238 U ages from 262 Ma to 249 Ma, coinciding with the timing of silicic magmatism in the Panxi area of the ELIP. The zircon e Hf ( t ) values (+14 to +3) of these granites and rhyolites suggest a moderately depleted mantle source and overlap with those of peralkaline and metaluminous granites in the Panxi area [i.e. e Hf ( t ) = +14 to +4]. The zircon Hf isotope ratios show that the zircons probably record the original source characteristics whereas whole-rock Nd isotope data indicate an evidence for crustal contamination that may have occurred at lower temperatures during magma emplacement. The synchroneity, coupled with petrological and geochemical similarities, indicate that silicic rocks from the Phan Si Pan-Tu Le region are cogenetic with the Panxi silicic plutonic rocks and that they are likely derived by similar petrogenetic processes (i.e. fractionation of mafic magmas or partial melting of mafic rocks). Therefore, we propose that the Phan Si Pan-Tu Le region represents a displaced portion of the ELIP inner zone.