Fig. 1: ¹⁴³Nd/¹⁴⁴Nd versus ⁸⁷Sr/⁸⁶Sr of new ALIA-D115-18 single clinopyroxene data and prior data on the whole rock and bulk (100s of grains of) clinopyroxene.

Fields for Samoan shield lavas (excluding lavas from Savaiʼi Island), and global OIB and mid-ocean ridge basalts, are shown in orange and gray fields, respectively. Other Samoan shield lavas from the ALIA dataset (i.e., submarine shield lavas from Savaiʼi Island) are shown for reference as well (i.e. ALIA-D114: orange triangles, ALIA-D115: red squares, ALIA-D118: orange circles, and ALIA-D128 lavas: orange diamonds, and the new clinopyroxene data, denoted as yellow crossed squares, collected in this study)⁷. The inset shows a zoomed view of the clinopyroxene data in addition to the bulk clinopyroxene analyses (representing 100s of pooled grains; gray squares with an “x”) and the ALIA-D115-18 whole rock (red square) published previously^7,8. All error bars smaller than symbols except where shown and represent 2σ standard errors. Note that only nine of the 17 clinopyroxenes analyzed for ⁸⁷Sr/⁸⁶Sr also have ¹⁴³Nd/¹⁴⁴Nd data, so not all clinopyroxenes analyzed for ⁸⁷Sr/⁸⁶Sr can be shown on this figure. However, the nine clinopyroxenes analyzed for both Sr and Nd isotopes encompass the full range of ⁸⁷Sr/⁸⁶Sr observed in this study. Samoan shield lavas, ALIA lavas, and Savai’i xenolith compositions are from elsewhere^5,6,7,69. The black dashed line is a theoretical magma mixing line derived in this study using binary mixing theory; mixing endmember compositions are provided in Supplementary Table 2, and methods for calculating endmembers are discussed in the text. Each hatch is a 10% increment except for the first two hatches, which are in 5% increments. The green star denotes the EM2-derived, high ⁸⁷Sr/⁸⁶Sr, trachytic mixing endmember calculated in this study (see Supplementary Table 2).