Late-stage sulfide saturation in Kaikata Seamount magmas (Izu-Bonin arc) constrained by platinum group element geochemistry

Abstract

Assessing the behavior of chalcophile elements during magma differentiation is essential for understanding sulfide saturation processes in arc systems. Kaikata Seamount, located along the modern volcanic front of the Izu-Bonin arc, exhibits vigorous hydrothermal activity but only modest reported gold grades. We present the first platinum group element (PGE) data for Kaikata Seamount volcanic rocks to evaluate their magmatic chalcophile element evolution. The basaltic andesites (~4 wt.% MgO) are characterized by high Pd/MgO, Pd/Cu, and Pd/Pt ratios close to primitive mantle values, whereas evolved andesites (<3 wt.% MgO) display marked decreases in Pd/Cu ratios and Pd, Pt, and Cu concentrations. These geochemical trends indicate that sulfide saturation was suppressed during early differentiation and initiated only at later magmatic stages. This behavior is consistent with low-pressure differentiation in a thin arc crust and oxidized conditions, both of which favor enhanced sulfur solubility and late-stage sulfide segregation.