Mesozoic ophiolites crop out discontinuously in the Indo-Myanmar Ranges in NE India and Myanmar,and represent the remnants of the Neotethyan oceanic lithosphere(Sengupta et al.,1990;Mitchell,1993).These ophiolites in the Indo-Myanmar Ranges are the southern continuation of the Neotethyan ophiolites occurring along the Yarlung Zangbo Suture Zone(YZSZ)in southern Tibet farther northwest(Mitchell,1993;Fareeduddin and Dilek,2015),as indicated by their coeval crystallization ages and geochemical compositions(Yang et al.,2012;Liu et al.,2016).The Kalaymyo ophiolite is located in the central part of the eastern Indo-Myanmar Ranges(Fig.1).composition of these ophiolites from the central Tibetan Plateau(CTP)is dominated by MORBs and minor OIBs and a distinct lack of IATs and BONs,which is inconsistent with most ophiolites worldwide(Robinson and Zhou,2008;Zhang et al.,2008).But the generation and tectonic nature of these ophiolites are still controversial.*The Kalaymyo peridotites consist mainly of harzburgites,which show typical porphyroclastic or coarse-grained equigranular textures.They are composed ofolivine(Fo=89.8–90.5),orthopyroxene(En86-91Wo1-4Fs8-10;Mg#=89.6–91.9),clinopyroxene(En46-49Wo47-50Fs3-5;Mg#=90.9–93.6)and spinel(Mg#=67.1–78.9;Cr#=13.5–31.5),and have relatively homogeneous whole-rock compositions with Mg#s of90.1–90.8 and Si O2(41.5–43.65 wt.%),Al2O3(1.66–2.66wt.%)and Ca O(1.45–2.67 wt.%)contents.TheydisplayLightRareEarthElement(LREE)-depleted chondrite-normalized REE patterns with(La/Yb)CN=0.04–0.21 and(Gd/Yb)CN=0.40–0.84,and show a slight enrichment from Pr to La with(La/Pr)CN in the range of 0.98–2.36.The Kalaymyo peridotites are characterized by Pd-enriched chondrite-normalized PGE patterns with superchondritic(Pd/Ir)CN ratios(1.15–2.36).Their calculated oxygen fugacities range between QFM–0.57 and QFM+0.90.These mineralogical and geochemical features collectively suggest that the Kalaymyo peridotites represent residual upper mantle rocks after low to moderate degrees(5–15%)of partial melting at a mid-ocean-ridge(MOR)environment.The observed enrichment in LREE and Pd was a result of their reactions with enriched MORB-like melts,percolating through these already depleted,residual peridotites.The Kalaymyo and other ophiolites in the Indo-Myanmar Ranges hence represent mid-ocean ridge(MOR)–type Tethyan oceanic lithosphere derived from a downgoing plate and accreted into a westward migrating subduction–accretion system along the eastern margin of India. Mesozoic ophiolites crop out discontinuously in the Indo-Myanmar Ranges in NE India and Myanmar, and for the remnants of the Neotethyan oceanic lithosphere (Sengupta et al., 1990; Mitchell, 1993). The ophiolites in the Indo-Myanmar Ranges are the southern continuation of the Neotethyan ophiolites occurring along the Yarlung Zangbo Suture Zone (YZSZ) in southern Tibet farther northwest (Mitchell, 1993; Fareeduddin and Dilek, 2015), as indicated by their coeval crystallization ages and geochemical compositions (Yang et al., 2012; Liu et al., 2016). The Kalaymyo ophiolite is located in the central part of the eastern Indo-Myanmar Ranges (Fig.1) .composition of these ophiolites from the central Tibetan Plateau (CTP) is dominated by MORBs and minor OIBs and a distinct lack of IATs and BONs, which is inconsistent with most ophiolites worldwide (Robinson and Zhou, 2008; Zhang et al., 2008) .But the generation and tectonic nature of these ophiolites are still controversial. * The Kalaymyo peridotites consist mainly of harzburgites, which show typical porphyroclastic or coarse-grained equigranular textures. thesey are composed of olivine (Fo = 89.8-90.5), orthopyroxene (En86-91Wo1-4Fs8-10; Mg # = 89.6-91.9), clinopyroxene (En46-49Wo47- 50Fs3-5; Mg # = 90.9-93.6) and spinel (Mg # = 67.1-78.9; Cr # = 13.5-31.5), and have relatively homogeneous whole-rock compositions with Mg # s of 90.1-90.8 and Si02 ( 41.5-43.65 wt.%), Al2O3 (1.66-2.66 wt.%) And CaO (1.45-2.67 wt.%) Contents.TheydisplayLightRareEarthElement (LREE )-depleted chondrite-normalized REE patterns with (La / Yb) CN = 0.04 -0.21 and (Gd / Yb) CN = 0.40-0.84, and show a slight enrichment from Pr to La with (La / Pr) CN in the range of 0.98-2.36. The Kalaymyo peridotites are characterized by Pd-enriched chondrite-normalized Porph patterns with superchondritic (Pd / Ir) CN ratios (1.15-2.36). Their calculated oxygen fugacities range between QFM-0.57 and QFM + 0.90. These mineralogical and geochemical features collectively suggest that the Kalaymyo peridotites represent residual upper mantle rocks after low to moderate degrees (5-15%) of partial melting at a mid-ocean-ridge (MOR) environment. The observed enrichment in LREE and Pd was a result of their reactions with enriched MORB-like melts, percolating through these already depleted, residual peridotites. The Kalaymyo and other ophiolites in the Indo-Myanmar Ranges are represent mid-ocean ridge (MOR) -type Tethyan oceanic lithosphere derived from a downgoing plate and accreted into a westward migrating subduction-accretion system along the eastern margin of India.