Integration of zircon and apatite U–Pb geochronology and geochemical mapping of the Wude basalts (Emeishan large igneous province): A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP

Abstract

Radiogenic isotopic dating and Lu–Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) of the Wude basalt in Yunnan province from the Emeishan large igneous province (ELIP) yielded timing of formation and post-eruption tectonothermal event. Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP. A zircon U–Pb age of 251.3 ​± ​2.0 ​Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251–263 ​Ma for the emplacement of the ELIP. Such zircons had εHf(t) values ranging from −7.3 to +2.2, identical to those of magmatic zircons from the intrusive rocks of the ELIP, suggesting that crust-mantle interaction occurred during magmatic emplacement, or crust-mantle mixing existed in the deep source region prior to deep melting. The apatite U–Pb age at 53.6 ​± ​3.4 ​Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event, corresponding to the Indian–Eurasian plate collision. Negative Nb, Ta, Ti and P anomalies of the Emeishan basalt may reflect crustal contamination. The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin. Therefore, the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian–Eurasian plate collision during early Eocene.