Linking the Tectonic Evolution of Hainan Island and Borneo Since the Paleozoic: Implication for Interaction Between the Tethyan and Paleo‐Pacific Tectonic Domains in Southeast Asia

Abstract The interaction between the Tethyan and Paleo‐Pacific subduction systems in Southeast Asia since the Paleozoic is still poorly understood. Hainan Island and Borneo, located near the junction of the Tethyan and Paleo‐Pacific domains, provide the critical regions for understanding the dynamic processes and interaction between the two tectonic domains. Using new and published zircon U‐Pb‐Hf isotopes, and the detrital zircon Eu/Eu* data, we evaluate crustal evolution and the relative crustal‐thickness variations in both regions. The data sets indicate broadly synchronous intervals of reduced apparent crustal thickness inferred from Eu/Eu* at 440–410 Ma, 370–350 Ma, 270–220 Ma and 160–140 Ma, together with largely negative ε Hf ( t ) values through the Paleozoic‐Triassic, which characterized by the mixed mantle‐derived material and older crustal components, probably associated with the Paleo‐Pacific subduction. Jurassic–Cretaceous zircons from Borneo shift to mainly positive ε Hf ( t ), supporting the mantle‐derived material addition and a Tethyan–Paleo‐Pacific double‐subduction system beneath Sundaland. However, the Hainan retains mostly negative ε Hf ( t ), consistent with continued Paleo‐Pacific subduction and older crustal components. These results clarify how the Tethyan and Paleo‐Pacific systems interacted in Southeast Asia.