Age and tectonic setting of the East Taiwan Ophiolite: Implications for the growth and development of the South China Sea

The South China Sea is one of the youngest marginal seas and understanding its development is important for reconstructing the tectonic evolution of Southeast Asia. The South China Sea is thought to have been actively spreading between 32 Ma and 15.5 Ma. The East Taiwan Ophiolite (ETO) is one of the few preserved remnants of the South China Sea on land and provides an opportunity to investigate the age and the tectonic setting of the accreted easternmost portion. The age of the ETO was obtained by LA-ICP-MS in situ zircon U-Pb methods and yielded a mean ²⁰⁶Pb-²³⁸U age of 14.1±0.4 Ma, suggesting that magmatic activity in the South China Sea continued ∼1.5 million years beyond current estimates. Cr-spinel data (Cr no. = 42-54) and depleted ϵ_Nd(t) values (i.e. +9.1 to +11.4) from the serpentinized peridotites and gabbros and the light rare earth element depleted patterns (La/Yb ≤ 1) of the ETO mafic rocks are consistent with a ridge setting (i.e. N-MORB composition). Therefore, the ETO likely represents the terminal portion of the South China Sea spreading ridge that was sheared off during the northward translation of the Luzon arc.