Petrogenesis of the Kalaymyo Ophiolite: Insights into mantle-melt interaction and tectonic transition from mid-ocean ridge to supra-subduction zone setting in the eastern Neo-Tethys

The collision between the Indian plate and the West Burma Block led to the formation of Neo-Tethyan ophiolite along the Western Ophiolitic Belt (WOB). The ophiolitic rocks in the WOB exhibit geochemical characteristics of both mid-ocean ridge (MOR) and supra-subduction zone (SSZ) settings, implying a complex geodynamic evolution. However, the processes responsible for such diverse geochemistry remain a topic of debate. This study investigates the petrogenesis of podiform chromitite and associated peridotite in the Kalaymyo ophiolite, located in the central WOB, through petrography, mineral and whole-rock geochemistry, and geochemical modeling. Five groups with distinct textures and chemical compositions are noticed: Group 1, Group 2, and plagioclase spinel (Pl-Spl) peridotite, dunite, and chromitite. Group 1 peridotite represents residual mantle in MOR settings, as shown by its geochemical similarity with the modern abyssal peridotite and partial melting modeling. Pl-Spl peridotite, containing intergranular plagioclase, is characterized by elevated HREE contents in clinopyroxene and high Ti in spinel, suggesting localized MORB-like melt impregnation. Dunite and chromitite display enrichment of incompatible elements in clinopyroxene and chromite with high oxygen fugacity value, collectively suggesting their formation in SSZ environments. Clinopyroxene oikocryst in chromitite is comparable to that of modern island-arc tholeiite with relative Ba enrichment and Nb depletion, further supporting its SSZ origin. Group 2 peridotites record the intermediate stages of the melt-mantle interaction including hydrous melting and reactive melt percolation under SSZ settings, as supported by intermediate chemical composition, amphibole inclusions, and melt-mantle interaction modeling. We propose that the coexistence of MOR-type and SSZ-type lithologies in the Kalaymyo ophiolite reflects in-situ tectono-magmatic transition rather than tectonic juxtaposition via mélange formation. This interpretation is supported by transitional variations in lithology and geochemistry and the spatial association of SSZ-type rocks with dunite and podiform chromitite bodies. • Petrogenesis of chromitite and peridotite in the Kalaymyo ophiolite was investigated. • Group 1 peridotite represents a residual mantle in MOR settings. • Plagioclase-bearing spinel peridotite formed by MORB melt impregnation. • Melt-mantle interaction in SSZ settings formed Group 2 peridotite, dunite, and chromitite. • The Kalaymyo ophiolite records transition from MOR to SSZ settings.