Whole-rock major element concentrations (wt.%), loss on ignition (LOI), and titrated ferrous iron (FeO) measurements were used to establish total iron oxidation states (Fe³⁺/Fe_total). Samples were collected from seafloor detachment surfaces of the Onnuri Oceanic Core Complex, Central Indian Ridge, during the 2019 and 2022 R/V ISABU dredge operations (RD1912, RD1913, RD2208). The aim was to characterize the bulk-rock geochemical transition, hydration states, and chemical redox fluctuations associated with the pervasive replacement of background serpentinites into talc-rich suites. Pulverized rock powders (400 mesh) were analyzed at Actlabs (Canada). Major oxide abundances were determined by lithium metaborate/tetraborate fusion followed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), whereas ferrous iron (FeO) contents were independently quantified using cold acid digestion (V₂O₅-HF) and subsequent potassium dichromate colorimetric titration.