Across-arc variations of potassium isotope compositions in a fluid-dominated subduction zone and implications for global potassium recycling

To reveal the fluid variations in the mantle sources of arc lavas from a fluid-dominated subduction zone and to further constrain its implications for global potassium (K) recycling, we present the K isotope compositions of thirty-two arc lavas from a 220 km arc-front to back arc transect across the Kamchatka Peninsula. Our results show that arc lavas from Eastern Volcanic Front (EVF, −0.48 ± 0.02 ‰ to −0.19 ± 0.03 ‰, average at −0.37 ± 0.08 ‰, n = 15) and Central Kamchatka Depression (CKD, −0.39 ± 0.03 ‰ to −0.25 ± 0.05 ‰, average at −0.32 ± 0.05 ‰, n = 9) display slightly higher δ41K than those from Sredinny Range (SR, −0.44 ± 0.03 ‰ to −0.37 ± 0.02 ‰, average at −0.41 ± 0.03 ‰, n = 5) and the mantle value (−0.42 ± 0.08 ‰), which indicate the incorporation of slab-derived fluids within their mantle sources. Notably, the δ41K values of CKD arc lavas show positive correlations with δ18O, and fluid indices (e.g., K/Nb, Sb/Ce, Pb/Ce and As/Ce ratios), suggesting the contributions of fluids derived from the subducted Hawaii-Emperor Seamount Chain. In addition, this study reveals that arc lavas from North Central Kamchatka Depression (NCKD) have higher δ41K values (−0.32 ± 0.03 ‰ to −0.31 ± 0.02 ‰, average at −0.32 ± 0.01 ‰, n = 3) than the mantle value. Their high δ41K values were accompanied with high Sr/Y ratios, indicating that the K isotope data of NCKD arc lavas may reflect the influence of slab-derived melts. This study demonstrates that recycling of a slab-derived fluid components can modify the K isotope compositions in the mantle source of the arc magmas. Consequently, when combined with other indicators (e.g., Sb/Ce, As/Ce ratios and Pb-O isotopes), the K isotope system helps to constrain recycling of fluid-mobile elements in subduction settings and to reveal how crustal materials recycle back via dehydration fluids from the subducted slab to the Earth’s surface.