Exploring small-scale recycled mantle components with intraplate continental twin volcanoes

Abstract

Primitive magmas with distinct geochemical signatures that record mantle heterogeneity are obscured in continental intraplate volcanic settings owing to crustal interaction. Here, we report new geochronological and geochemical data for two adjacent Late Neogene primitive intraplate volcanoes in Northeast China: the Great and Lesser Wangqing River twin volcanoes (GWR/LWR). Our results suggest that the GWR and LWR volcanics are controlled by olivine crystal sorting and that crustal contamination is negligible, which implies these twin volcanoes provide a rare window into mantle components. The LWR tephrite is marked by moderate enrichment of light rare earth elements (REEs) with significant positive Sr anomalies. It is also enriched in radiogenic Sr-Nd-Hf-Pb isotopes but exhibits 187Os/188Os values that are comparable to those of the primitive upper mantle. The GWR volcanics (picrite, basanite and tephrite) are characterised by a steeper REE pattern and a lack of Sr anomalies, while being isotopically more radiogenic. Combined with olivine chemistry, which reveals a hybrid source lithology, we propose that the LWR and GWR sampled recycled lower and upper oceanic crust components, respectively. Both components have high 87Sr/86Sr and low 206Pb/204Pb ratios, akin to an enriched mantle I (EM1) source, indicating that the EM1 components can be formed by recycling oceanic crust with limited sediment.