This study, at the first time, presents petrology of abyssal peridotites and related fault rocks recovered from an oceanic core complex (OCC) in the southern part of the Central Indian Ridge using submersible SHINKAI 6500 of Japan Agency for Marine-Earth Science and Technology. Less deformed, statically serpentinized peridotites were recovered from the ridge-facing slope whereas highly deformed talc-chlorite-serpentine schists were recovered from sheet-like structures on the top surface of the OCC. The top surface of the OCC is interpreted to be a detachment fault. Spinel compositions in the schist are overlapped with those in the granular peridotites, indicating that spinel grains were originally derived from residual peridotites, probably footwall of the detachment fault. The schist also contains gabbroic fragments, now completely recrystallized at low temperature mineral assemblages of tremolite and chlorite, and gabbro-derived minerals (e.g., ilmenite). These indicate that deformation and alteration were locally concentrated along the long-lived detachment fault, resulting in mechanical mixing of both hydrated gabbros and serpentinized peridotites during the exhumation of the OCC along the fault. Major element compositions of the primarly mantle minerals in the serpentinized peridotites were consistent with residue after moderate degree (13-15 %) of partial melting, and were later chemically modified due to the infiltration of evolved melt during the formation of leucocratic veins. Fluid-mobile elements such as Li, Rb, Ba and Sr are higher in serpentines than their precursor mantle minerals, and were thus added in serpentine during serpentinization of peridotite. Uranium content in serpentine is variable but is likely abundant in the outermost margin of the precursor minerals. Trace element compositions of serpentine were continuously changed with changing in fluid chemistry probably due to decreasing of temperature.