Seismic and isotopic evidence for depth-dependent mantle sources of intraplate basalts from Eastern China

The origin of intraplate basalts remains controversial, despite numerous isotope and seismic studies. Here we employ thermodynamic modeling with MAGEMin to integrate the Sr-Nd-Hf isotopes of basaltic volcanics with the seismic velocities of their mantle source. The results indicate that residual garnets generate high P-wave velocity anomalies in the mantle, and impart distinctive time-integrated εNd-εHf isotope signatures to the partial melts (i.e., the erupted basaltic magmas). Since the garnet-spinel transition (~42-60 km) is always shallower than the lithosphere-asthenosphere boundary (~70-100 km), garnet effects may serve as an indicator of thermal magmatic events. These findings suggest that the widely distributed Cenozoic intraplate basalts in Eastern China originated from the lithospheric mantle (<~60 km) that didn’t retain garnet. Two notable exceptions are the Wudalianchi and Nuominhe basalts, which originate from the asthenosphere (~100-140 km) and the lithosphere-asthenosphere transition, respectively. The integrated radiogenic isotope-seismic velocity framework can be applied to intraplate basalts globally. Most Eastern China basalts originate or re-equilibrate with the lithospheric mantle, except for Wudalianchi and Nuominhe basalts, which originate from asthenospheric or lithosphere-asthenosphere transition sources, according to analysis of thermodynamic modeling, radiogenic isotopes, and seismic tomography.