The role of subduction recycling on the selenium isotope signature of the mantle: Constraints from Mariana arc lavas

Abstract

Investigating the isotope systematics and behavior of selenium in subduction zones provides valuable insights into mechanisms that contribute to chalcophile and moderately volatile element distribution between terrestrial reservoirs. In this study, we present high-precision Se isotope and Se–Te elemental data on subduction zone lavas from the Mariana arc system. Our results indicate that Se–Te concentrations are unaffected by submarine degassing but are affected by magmatic differentiation. In contrast, Se isotopes of submarine lavas are unaffected by both magmatic differentiation and degassing and thus may preserve their magmatic source signature. Compared to the average Se isotope composition previously obtained for mantle-derived samples (δ82/76Se = 0.23 ± 0.12‰, 2 s.d., n = 5), suitable to represent the Mariana pre-subduction wedge, Mariana lavas show a larger overall range (δ82/76Se from 0.03 to −0.33‰, n = 21) with a clear tendency towards lighter Se isotope compositions. The variable Se isotope signatures within the Mariana suite can further be attributed to different slab-derived fluid and melt-like subduction components. This provides evidence for a significant role of subduction recycling of hydrothermal sulfide-containing altered oceanic crust and pelagic sediments with possible implications for the Se isotope evolution of the crust-mantle system throughout geological time.