Zinc isotopic systematics of the South China Sea basalts and implications for its behavior during plate subduction

Zinc isotopes is a new tracer for deep materials recycling. However, its behavior during plate subduction remains obscure. To address this issue, here we present high precision Zn isotopic compositions (δ66Zn) of basalts recovered from International Ocean Discovery Program (IODP) Expedition 349 in the South China Sea (SCS), which have been influenced by various amounts of subducted materials. Based on (La/Sm)N values, these basalts are classified into N-MORB ((La/Sm)N < 1) and E-MORB ((La/Sm)N ≥ 1) types. The results show that both of the N-MORB and E-MORB type basalts have similar and homogeneous Zn isotopic compositions with δ66Zn ranging from 0.22 to 0.28‰ and 0.24 to 0.31‰, respectively. These values are similar to that of typical MORB reported in the literature (0.28 ± 0.03‰), but are systematically higher than the estimated average value of depleted MORB-type mantle (DMM, 0.18‰).