Deformation-enhanced diagenesis and bacterial proliferation in the Nankai accretionary prism

Abstract. Understanding diagenetic reactions in accreted sediments is critical for establishing the balance of fluid sources and sinks accretionary prisms, which turn important assessing pressure field ability faults to host seismic slip. For this reason, we studied deformation bands (shear zones veins) within deep mud from Nankai prism (SW Japan) drilled at site C0001 during IODP Expedition 315, by means microscopic observation, X-ray diffraction, major- trace-element analyses. Deformation are not only more compacted than sediment but also enriched framboidal pyrite, as observed under microscopy confirmed chalcophile-element enrichments (Fe, S, Cu, As, Sb, Pb). In tandem, one shear zone sample displays a destabilization smectite or illite–smectite mixed layers slight crystallization illite relative its matrix, another shows correlated increases B Li veins compared sediment, both effects suggesting transformation into bands. The two sulfide precipitation smectite-to-illite explained combined action sulfate-reducing methanogen bacteria, strongly suggests an increased activity anaerobic microbial communities localized This local bacterial proliferation was possibly enhanced liberation hydrogen strained phyllosilicates. We suggest that anoxic boosted deformation, may contribute pore water freshening depth prisms. Deformation-enhanced metabolic explain illitization major Care therefore needed before interpreting illitization, other well, evidence heating, these might be biogenic instead thermogenic.