Data for the research entitled " Bilateral heterogeneity in an upwelling mantle via double subduction of oceanic lithosphere" by Dao et al., 2021 published in the Journal of Geophysical Research: Solid Earth. Table S1: Locality, major- and trace-element concentrations, and Sr-Nd-Pb isotopic compositions of Vietnamese volcanic rocks (Con Co, Ly Son-Quang Ngai, Kong Plong, Pleiku, Buon Ma Thuot, Phuoc Long, Xuan Loc and Phu Quy) and seafloor basalts from the EVS/SCS. Results of replicated ICP-MS analysis of the in-house standard rock MYK-1. Table S2: CIPW normative compositions. Table S3: Results of K-Ar dating for the volcanic rocks from Vietnam. Table S4: K-Ar ages obtained for the reference standard materials. Table S5: F test statistics of the Pb isotope regression trends for Vietnamese basalts. Table S6: Trace element and isotope compositions of proposed end-member components. Table S7: a) Parental magma (PM, this study) and wallrock (WR, Owada et al., 2007; Shellnutt et al., 2013) compositions, and input parameters for the AFC model using the Magma Chamber Simulator (Borhson et al., 2014, 2020; Heinonen et al., 2020). b) Partition coefficients for trace elements used in AFC modeling (Adam & Green, 2006; Bacon & Druitt, 1988; Bea et al., 1994; Elkins et al., 2008; Klemme et al., 2006; McKenzi & Onion, 1991; Pilet et al., 2011; Ronov & Yaroshevskiy, 1976). Table S8: Major-element compositions of primary magmas of Vietnamese basalts (equilibrated with Fo90) and estimated melting pressure (P) and temperature (T) by thermobarometry. Table S9: Input parameters for REEBOX PRO model (Brown & Lesher, 2016).