Large zinc isotope variations in eastern Pacific seamount basalts as a result of mantle metasomatism

This dataset includes major, trace element data, Sr-Nd-Pb isotope data and Zn-Fe isotope data of near-EPR 5-15°N seamount lavas, as well as major element abundances corrected for the effect of fractional crystallization to Mg# = ~72, modeling result of the Zn isotope variation during mantle melting, and estimation result of the age of the enriched source component. In recent years, zinc (Zn) isotope systematics was proposed as a novel tracer for additions of near-surface materials to the mantle, while Zn isotope fractionation during magmatic processes was considered insignificant. Here we show that lavas from seamounts near the East Pacific Rise (5°-15°N) define the largest δ66Zn variation (from 0.19 ± 0.03‰ to 0.52‰ ± 0.02‰) observed in unaltered oceanic basalts. The high-δ66Zn lavas have low CaO contents and CaO/Al2O3 ratios, clearly arguing against an origin related to additions of recycled carbonates. Furthermore, high-δ66Zn lavas have higher abundances of highly incompatible elements (e.g., high La/Sm and Sm/Yb) as well as more enriched radiogenic Sr-Nd-Pb isotope compositions. These characteristics link their origin with a compositionally enriched mantle component of ancient low-degree melt metasomatic origin. We suggest that the low-degree melt metasomatism in the seismic low-velocity zone beneath ocean basins may cause significant chemical and isotopic (e.g., Zn and Fe) variations in the upper mantle at present and in the past. Our findings further indicate that the high-δ66Zn signatures in terrestrial basalts most likely originate from additions of low-degree metasomatic melts to their mantle sources. We also demonstrate that widespread interpretation that invokes subducted carbonates to explain mantle-derived melts with heavy Zn isotope compositions is inconsistent with multiple observations.