Evolution of the Paleo–Tethyan Ocean between the South China and Indochina Blocks: Insights from the Babu Ophiolite in Southwestern China

Abstract The Paleo–Tethyan Ocean in Southeast (SE) Asia is generally considered to be primarily represented by the Jinshajiang–Ailaoshan suture between the South China and Indochina Blocks. However, the distribution of the Jinshajiang–Ailaoshan suture zone, particularly its southeastern continuation, remains poorly constrained. This study presents a comprehensive investigation into the detailed field study, new zircon U–Pb dating, and whole-rock geochemistry of the Babu ophiolite near the China–Vietnam border. Field observations and geochemical characteristics define two distinct types of basaltic rocks within the Babu ophiolite. Type 1 basaltic rocks, primarily metamorphosed basalts and diabase dykes that intrude into gabbro and serpentinite, represent the lower and central oceanic crust. These rocks were subjected to metasomatism by subduction-related fluids, leading to Zr–Hf depletion. Type 2 basaltic rocks are copper mineralized and likely represent the upper and marginal oceanic crust, which were influenced by crustal components, resulting in Zr–Hf enrichment. Both basalt types exhibit N-MORB geochemical affinities and lack characteristics associated with the Emeishan large igneous province (LIP), indicating that the Babu ophiolite is of a MORB-type origin, with its volcanic rocks derived predominantly from N-MORB tholeiitic magmas in a back-arc setting. Zircon U–Pb dating of two gabbros yields concordant ages of 272 ± 3 Ma and 264 ± 1 Ma. Integrating these results with previous data suggests that the Babu ophiolite formed during the Early Permian and was emplaced during the Late Triassic (ca. 230 Ma). The Babu ophiolite may correlate with the Cao Bang ophiolite in the Song Hien belt of Vietnam, which marks the western segment of the Dian–Qiong suture, a remnant of the Paleo–Tethys Ocean. These findings contribute to a better understanding of the spatial and temporal evolution, as well as the final closure mechanism, of the Paleo–Tethys Ocean in SE Asia.