Large correlated zinc isotope variability in the eastern Pacific mantle as a result of low-degree melt metasomatism

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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. Recently, Zn isotope systematics has been widely used as a novel tracer for subducted carbonate sediments in mantle-derived magmas. However, the effect of magmatism in Zn isotope variations in mantle-derived magmas has been overlooked. This study reports the largest δ66Zn variation range (0.19-0.52‰) known in oceanic basalts in lavas from seamounts near the East Pacific Rise (EPR) between 5° and 15°N. The variably high δ66Zn values have a clear magmatic origin because: (1) high-δ66Zn lavas have low CaO and CaO/Al2O3, clearly arguing against an origin from recycled carbonates, and (2) high-δ66Zn lavas have higher abundances of progressively more incompatible elements with more enriched radiogenic Sr-Nd-Pb isotope compositions, which requires low-degree melting from a compositionally enriched mantle component of ancient low-degree melt metasomatic origin. We conclude that the high-δ66Zn signature in terrestrial basalts is not evidence for recycled carbonates as widely advocated but evidence for the effects of low-degree mantle melting as a way of Earth’s chemical differentiation over its histories.

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