DATING THE MENGHAI BATHOLITH, SOUTHERN CHINA

Paleogeographic reconstructions are used to determine the evolution and migration of Earth’s continents, identify important economic resources that formed during specific times in Earth’s history, and assess geological hazards that result due to reactivation of older faults or mass movement of rocks. The goal of this study is to improve our understanding of the complex tectonic history of southern China by constraining the timing of crystallization and uplift of the Menghai batholith, a suite of metaluminous and peraluminous granodiorites on the Shan Plateau. We obtained U-Pb zircon ages from 8 samples of the batholith to decipher its tectonic and magmatic history and relationship to surrounding areas. The batholith is part of the Lancangjiang belt, a principle boundary between Gondwana and Eurasia, on the eastern side of China’s Shan Plateau, and encompasses the southern extension of the Lincang Granite group. A few U-Pb zircon ages have been reported for the Lincang granite, timing emplacement during the Upper Triassic. Prior to this study, no U-Pb ages exist for the Menghai batholith. Zircon grains were separated from rock samples from the study area and have been dated using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). From LA-ICP-MS data, zircon rim ages range from 207.6±8.9 Ma to 254.1±4.7 Ma, constraining crystallization to throughout most the Triassic period, starting as early as the end of the Permian. Core ages for some zircons range from 434.8±6.0 Ma to 3187.0±23.0 Ma. Overall, reliable age data from the Menghai batholith aid in determining the tectonic and magmatic history of the region, including understanding the dynamics of ancient Tethyan ocean closure in southern China.