Fig. 3.

Variations of Mg isotopic composition with Sr, Nd, and Pb isotopic compositions of Martinique arc lavas and subducting sediments from the Lesser Antilles arc (Tables S1 and S2). A−C include data of both Martinique arc lavas and subducting sediments, and D−F focus on the range observed in the lavas. The yellow star represents the hypothesized composition of the normal mantle. The hexagon represents an estimate of the average composition of subducting sediments (Tables S1–S3). D−F show mixing curves corresponding to three different types of mixing: Source mixing (SM) is depleted mantle−sediment mixing in the subarc mantle; crust mixing (CM) is primitive magma−sediment mixing; and AFC is assimilation and fractional crystallization. The ticks on modeling curves represent 10% increments during fractional crystallization or mixing. These mixing curves clearly do not fit the data measured on the Martinique arc lavas. A and D are ⁸⁷Sr/⁸⁶Sr, B and E are ¹⁴³Nd/¹⁴⁴Nd, and C and F are ²⁰⁶Pb/²⁰⁴Pb. See Table S3 for modeling details.