The Tuting–Tidding Suture Zone (TTSZ), exposed along Dibang and Lohit river valleys in Arunachal Himalaya, NE India, is the easternmost continuation of the Indus–Tsangpo Suture Zone (ITSZ) and consists of ophiolites associated with metabasics and carbonates. Amphibolites, existing at the base of the ophiolite complex, were studied using whole-rock, mineral chemical analyses and pressure–temperature (P-T) pseudosection modelling to understand their metamorphic and petrogenetic history, and interpret the tectonic environment of their formation. They exhibit two-stage deformation, where D₁ is depicted by polymineralic inclusion trails in former melt pools and the main foliation represents D₂. Sub-alkaline tholeiitic character, high-field-strength element (HFSE) ratios and mid-oceanic ridge basalt (MORB) -like rare earth element (REE) patterns with negative Eu anomaly indicate that the protolith of these amphibolites originated in a spreading regime by extensive partial melting of a depleted mantle source at shallow depth. Petrography, mineral chemistry and P-T modelling indicate a three-stage metamorphic history for them. M₁ is the prograde (c. 2.1 GPa, c. 450°C) defined by garnet centre compositions corresponding to the D₁ event. The existence of former melts in the samples demarcates the M₂ stage (1.4–1.8 GPa, c. 600°C). The rocks later underwent retrogression (M₃: 0.8–1.0 GPa, 480–520°C), which corresponds to the D₂ event. These observations suggest that the protolith of the TTSZ amphibolites originated in a mid-oceanic ridge setting, which accreted below a subduction zone where it underwent M₁ metamorphism followed by M₂ metamorphism, corresponding to partial melting of the rocks. Finally, the M₃ event occurred during the obduction phase of the ophiolite complex, where the amphibolites were obducted as the metamorphic sole of the TTSZ ophiolites.

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 TiO ₂ (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.