Source Lithology Characteristics of Different Tectonic Stages of Mariana Subduction Zone: Insights From Major and Trace Element Compositions of Olivine From Basalts

ABSTRACT The mantle beneath the Mariana subduction zone is commonly described as depleted, primarily composed of peridotite. This study aims to investigate whether subduction processes influence the lithologic characteristics of the mantle source beneath the Mariana subduction zone. We conducted a comprehensive analysis of olivine elemental compositions from basalts in different subduction settings in the Mariana region, including the island arc, back‐arc and initial arc rifting stages. Analysis of major and trace elements in olivines, as well as key elemental ratios (e.g., 10,000 × Zn/Fe, Mn/Zn and 100 × Mn/Fe), reveals that olivines from different subduction settings exhibit characteristics consistent with a peridotite source. While Ca content varies significantly among samples, olivines with high Fo values (Fo > 87) and high Ca contents are consistent with peridotite characteristics. In contrast, olivines with low Fo values (Fo < 87) exhibit lower Ca contents, reflecting the characteristics of a pyroxenite mantle source. This discrepancy is attributed to slab subduction, which increases water content in the mantle wedge and facilitates greater incorporation of Ca into the melt. The compositional distributions of Mn in olivines indicate distinct partitioning behaviours under varying pressure and temperature conditions, with Mn concentrations being particularly sensitive to pressure variations. Therefore, the variation in Mn composition reflects the different pressure conditions experienced by peridotite during its evolution. In different tectonic settings, the variation in Ni contents is mainly controlled by magmatic evolution, with minimal influence from temperature and pressure. Despite the differences in elemental content, our results demonstrate that the mantle source region in the Mariana subduction zone, whether in the island arc, back‐arc basin or initial arc rifting, consistently consists of peridotite, with no different results arising from variations in the subduction processes.