Geochemical analysis of calcite veins in the Mugi Mélange, Shimanto accretionary complex: implications for fluids in a seismogenic zone

Abstract

At subduction plate boundaries, fluid supply and mineral precipitation play a key role in maintaining high fluid pressure. In this study, we analyzed calcite veins in the Mugi Mélange of the Shimanto accretionary complex using major and trace element analysis, along with elemental mapping by micro-XRF and EPMA. Systematic differences in elemental ratios among vein types, as well as the presence or absence of Mn and Fe zoning, suggest variations in fluid origin and precipitation environment. Additionally, some calcite veins exhibit extremely low Li/Ca ratios, indicating the necessity of separating trace Li from a high-Ca matrix for precise determination of Li isotope ratios.