Ages of ophiolitic rocks along plate suture in Taiwan orogen: Fate of the South China Sea from subduction to collision

Abstract

Ophiolite-bearing belts mark convergent plate suture zones and are central in reconstructing plate configuration and structures of mountain belts. The active Taiwan mountain belt, product of ongoing convergence between the Eurasian and Philippine Sea plates, has dismembered ophiolitic rocks exposed on both sides of the Longitudinal Valley suture: blueschist blocks in schistose Yuli Belt to the west, and the Eastern Taiwan Ophiolite (ETO) in the unmetamorphosed Lichi Mélange to the east. How these ophiolitic materials correlate with the consumed South China Sea and Luzon forearc oceanic lithospheres between the colliding Chinese continental margin and the Luzon Arc remained speculative. We present zircon U-Pb age results from both ophiolitic rocks in the Yuli Belt and the ETO to pinpoint the formation ages of respective oceanic crusts, and 40Ar/39Ar dates to unravel the tectonothermal history. The zircon U-Pb ages of ~15 Ma for all analyzed samples indicate a common South China Sea origin for ophiolitic materials across the plate suture, since oceanic crust of the Philippine Sea Plate near Taiwan is either Eocene or older. The 40Ar/39Ar ages of Yuli meta-ophiolitic rocks might suggest blueschist metamorphic overprint at ~9 Ma. The 40Ar/39Ar results are generally identical to zircon U-Pb ages for the ETO rocks, concurrent to their olistostromal origin in the forearc basin after being tectonically transported from the trench interface to the eastern retrowedge within the Hengchun accretionary prism. A working tectonic model for the Taiwan arc-continent collision is put forward with emphasis on the fate of the South China Sea during the mountain building processes.