The island of Taiwan has been actively uplifted since the collision of a volcanic island arc with the Eurasian continent began 5 million to 6 million years ago. This convergence has created a mountainous island with distinctive belts of north–south trending rock units, including a metamorphic complex that comprises a significant portion of the isle’s eastern Central Range.
For more than 4 decades, the eastern side of this complex, called the Yuli metamorphic belt, has been considered to be a Cretaceous age mélange, a deformed unit approximately 110–100 million years old and characterized by jumbled blocks of schist embedded in a fine-grained matrix. Here Chen et al. present new evidence that the Yuli belt is actually much younger than previous studies have indicated.
Using the uranium-lead radiometric dating method, the team dated detrital zircons separated from blocks of schist and host rock collected from the metamorphic belt as well as from potential sources of sediment in southeastern China. The results show that the parent material of the Yuli belt’s host rocks ranges from Cretaceous to Miocene and that the protolith of several embedded blueschist blocks is from the mid-Miocene, providing compelling evidence that the belt can be no older than about 15.6 million years.
Because the blueschist is indicative of high-pressure, low-temperature conditions and was not locally derived, the team argues that the Yuli belt must have formed at deep structural levels in a mid- to late Miocene accretionary wedge complex that was later rapidly uplifted. (Tectonics, https://doi.org/10.1002/2016TC004383, 2017)
—Terri Cook, Freelance Writer