3:30 PM - 3:45 PM
[SGL29-06] Arsenic behavior in accretionary complex of Shikoku, Japan
Keywords:Kerogen, Organo-arsenic, diagenesis, metamorphism, deep-fluid, dehydration
Total arsenic concentration of the sedimentary rocks varies within 3 and 23 ppm. Generally, arsenic concentration was higher in the rocks of Sanbagawa belt than those of the Shimanto belt. Dark-colored mudstones and a coal-bearing sample were characterized with high arsenic content. These results are consistent with the known pattern of arsenic concentrations, which are concentrated in organic rich sediments and reinforce the importance of biogenic input of arsenic via organic matter deposition in marine sediments. The OM-associated arsenic to total arsenic was generally less than 10%, and much lower in the Sanbagawa belt samples than in the Shimanto belt samples. Thus, the arsenic mineralization likely progress in parallel with enhanced metamorphism up to the level of Sanbagawa samples, where the majority of OM-associated arsenic seem to have been released via decomposition.
Higher total arsenic concentration of the Sanbagawa samples would be attributed to either the primary arsenic concentration of the sediments or replacement of arsenic during diagenetic and metamorphic processes. The samples bearing quartz vein, which were frequently observed in Sanbgawa belt sedimentary rocks, were characterized by elevated arsenic concentrations.
The observation of this study suggests the arsenic redistributes in the accretionary complex associating with formation and migration of deep fluids through dehydration of hydrous minerals and also OM. The dehydrated water may supply deep fluid which flows through fracture and ultimately fueling mud volcano and potentially sourcing the arsenic accumulated in such settings.