Depth-dependent Variations in Elemental and Mineral Distribution in the Deep Oceanic Floor Sediments (WP21GPC04) near the Mariana Trench in the Western Pacific Ocean

This study reports depth-dependent elemental distribution and mineral abundance of the oceanic sediment sample (WP21GPC04) near the Mariana Trench collected during the WP21 expedition in 2021. The elemental distribution determined by μ-XRF shows no significant differences with varying depth, with an average SiO 2 53.91 wt%, FeO 4.48 wt%, Al 2 O 3 16.56 wt%, MgO 2.56 wt%, CaO 4.79 wt%, Na 2 O 3.52 wt%, K 2 O 5.48 wt%, similar to the average chemical composition of global subducting sediments (GLOSS). The mineral abundances analyzed using synchrotron XRD, however, vary with depth. While quartz, mica, and plagioclase were identified at all depths, chlorite was found at shallow depths, and zeolite group minerals, phillipsite and heulandite, showed a gradual change in phase fraction with depth. This suggests a change in sedimentation and alteration environments in the region, or the potential for coexistence emerges due to similar sediment stability. Overall, this study will provide a basis for the future investigations on the evolution of sedimentary environment near the Mariana Trench in the western Pacific Ocean and the phase distribution and the behavior of subducting oceanic sediments, which will affect the lithological and geochemical characteristics of the Mariana susduction system.