Geochemistry of the Babu Ophiolitic Mélange in the Sanjiang Tectonic Belt: Constraints on the Tectonic Evolution of the Paleo‐Tethys Ocean

ABSTRACT The origin of the mafic–ultramafic rocks within the Babu ophiolitic mélange of southeastern Yunnan remains debated, leaving the timing and tectonic setting of mafic oceanic‐crust formation in the eastern Paleo‐Tethyan domain poorly constrained. In order to solve this issue, we present zircon LA–ICP–MS U–Pb ages and Lu–Hf isotopes, clinopyroxene major‐ and trace‐element data, whole‐rock geochemistry and Sr–Nd–Pb isotopes for meta‐gabbroic blocks from the mélange. Zircon U–Pb dating yielded a crystallisation age of 271.5 ± 1.2 Ma, indicating that the Babu gabbroic protoliths formed in the Middle Permian. The Babu meta‐gabbro exhibits tholeiitic compositions and displays MORB‐like geochemical features. Whole‐rock Nd and Pb isotopic data of the Babu meta‐gabbro reveal a DUPAL‐like affinity, characteristic of Indian Ocean‐type mantle. Positive ε Nd ( t ) values and zircon ε Hf ( t ), together with clinopyroxene compositions, suggest that the magma was derived from a depleted mantle source but was subsequently modified by slab‐derived fluids and minor sediment‐related components. Trace‐element modelling suggests 5%–10% partial melting of depleted spinel lherzolite. Considering the geological and geochemical evidence, we propose that the Babu meta‐gabbros formed in a back‐arc basin during slab rollback in the Paleo‐Tethyan subduction system.