Trace element concentrations and clumped isotope compositions of calcite veins pervading the Western Pacific Izu-Bonin forearc and rear arc crust'

International Ocean Discovery Program Expeditions 352 and 351 drilled into the Western Pacific Izu-Bonin forearc and rear arc. The drill cores revealed that the forearc is composed of forearc basalts (FAB) and boninites, and the rear arc consists of FAB-like rocks. These rocks are pervaded by calcite veins, which document extensive fluid circulation and secondary mineralization. Here we present two data sets with rare earth element and yttrium (REE+Y) concentrations and clumped isotopic (Δ47) compositions. Clumped isotopes reveal precipitation temperatures < 100 °C. REE+Y characteristics and clumped isotopic compositions indicate varying parental fluid compositions ranging from pristine seawater to variably modified seawater. The most pristine seawater signatures are recorded by FAB-hosted low-T (< 30 °C) vein calcites with seawater-like REE+Y distribution patterns and parental fluid δ18O values within the range of seawater (-2 to +2 ‰ VSMOW). As a result of weak fluid-rock interaction and precipitation from modified seawater, boninite-hosted low-T (< 30 °C) vein calcites show reduced Y/Ho ratios (< 36) and less pronounced negative Ce anomalies relative to seawater. In the rear arc, intense low-T host rock alteration produced fluids with significantly depleted δ18O compositions (up to -9.7 ‰ VSMOW) and reduced Y/Ho ratios (< 36). Vein calcites precipitated at temperatures up to 74 ± 12 °C.