Zircon U–Pb ages and Hf–O isotopes of Xiaomasa Miocene granite in the Ximeng area, western Yunnan, southwest China: Constraints on petrogenesis and tectonic setting

Abstract

Characteristic granites of the East Tethyan Tectonic Domain (ETTD) are primarily exposed along the Himalayan orogenic belt and Gangdese batholith in the north, extend from western Yunnan in the centre, and through the Burma batholith to Peninsular Malaysia in the south. Western Yunnan is an important part of the ETTD magmatic arc, featuring characteristic granites that mainly developed between the Jurassic and Paleogene. Nonetheless, compared to other regions of the ETTD, Miocene magmatism has been poorly documented in western Yunnan. The Xiaomasa granite occurs in the Ximeng area of western Yunnan. In this study, we present U–Pb ages, and Hf–O isotope data for zircon crystals from the Xiaomasa granite pluton. Laser Ablation–Multicollector–Inductively Coupled Plasma–Mass Spectrometry (LA–MC–ICP–MS) zircon U–Pb dating yields precise emplacement ages of 15.8–16.1 Ma for the Xiaomasa granite, indicating that Miocene granitic magmatism occurred in western Yunnan. Zircons from the Xiaomasa granite have negative εHf(t) values ranging from −6.6 to −11.6, relatively high δ18O values (6.8%–10.2‰), and two‐stage Hf isotopic model ages (1.51–1.83 Ga). Zircon Hf–O isotopic characteristics indicate that the Xiaomasa granite was mainly derived from partial melting of ancient continental crust. The Ximeng Precambrian metamorphic basement is a probable material source for the granite. The Xiaomasa granite was probably produced by partial melting of the thickened Ximeng ancient metamorphic basement under a reduced pressure environment, reflecting a cumulative effect of the escape of Sundaland caused by the dynamics of the continuous India–Asia collision.