Rocks of ophiolitic affinity occurring in east Arunachal Pradesh, India consist of a number of dismembered units of mantle peridotites, mafic intrusives, amphibolites, volcano-sedimentaries and meta-carbonates and are considered to be the north-eastern continuation of the Indus-Tsangpo Suture Zone. Petrographical observations of the mantle peridotites include features such as occurrence of two kinds of olivine – larger (0.25mm) showing embayed boundaries and surrounded by smaller olivines (0.12mm) which show cumulate textures, low modal abundance of clinopyroxenes, serpentinized olivine and orthopyroxene, presence of Cr-chlorite surrounding spinels and formation of tremolite at the expense of clinopyroxene. They depict highly refractory geochemical characteristics like low CaO (<0.7 wt%) and TiO₂ (<0.08 wt%) values accompanied by Fo content between 0.90 and 0.92 for the larger olivine grains. Low HREE fractionation suggests a moderate to high degree of partial melting (~21%). We also observe selective enrichment in LREEs and HFSEs, extremely high Cr content of metamorphic spinels (0.97-0.99) and high Fo content in recrystallized cumulative olivines (>96).These evidences suggest that peridotites are residual in nature and formed by moderate to high degree of partial melting. They were subjected to interactions with a percolating boninitic melt in the nascent fore-arc of an intra-oceanic subduction zone which caused their re-fertilization in terms of REEs and HFSEs. Later, the peridotites underwent low-temperature fluid-rock interactions during the mature subduction or exhumation stage which caused formation of hydrous minerals like Cr-chlorite and tremolite.