Cenozoic mantle plume activity in East Asia: Constraints from geochemistry of olivine, spinel, and melt inclusions

Abstract

It is generally believed that the Cenozoic basalts distributed across eastern China, east of the Daxinganlin-Taihangshan gravity lineament (DTGL), are related to the big mantle wedge (BMW) beneath East Asia. Basalts that are widely distributed across central and eastern Mongolia form a contemporaneous ‘diffuse’ igneous province with similar major element, trace element and Sr-Nd-Hf-Pb isotopic characteristics to those in eastern China. However, they are located to the west of the DTGL, far from the influence of the BMW system. To explain the consistency of geochemistry and eruption ages of Cenozoic basalts on both sides of the DTGL, we have analyzed the compositions of Cenozoic basalts, olivines, spinels, and olivine-hosted melt inclusions from central-eastern Mongolia. We report olivine crystallization temperatures (Tc, up to 1404 and 1343 °C in central and eastern Mongolia, respectively) and mantle potential temperatures (Tp: 1456–1519 °C in eastern Mongolia) that are much higher than those in the MORB source (Tc 1230–1300 °C and Tp ∼ 1350 °C), indicating that there are thermal anomalies in the mantle sources feeding the central-eastern Mongolia volcanism. The Pb isotope ratios of basalts and olivine-hosted melt inclusions on both sides of the gravity zone show a linear array between EM1 and FOZO mantle components, which can be explained by the mixing of ancient recycled ocean crust (EM1-like) with lower mantle peridotite (FOZO-like) in different proportions. Combined with reported high Tp, 3He/4He, and a low-velocity anomaly extending to the lower mantle in the source of the Cenozoic basalts in East Asia, we propose a branched plume model that could explain the similarity of geochemistry and eruption ages for Cenozoic basalts on both sides of the DTGL.