A Late-Miocene Yuli Belt? New constraints on the eastern Central Range depositional ages

  • Chulai Fm. is the youngest (< 11.2 ± 0.2 Ma) metamorphosed unit in the Central Range
  • Chulai Fm. and Yuli Belt share a common sedimentary source of continental affinity
  • Deformation and metamorphism of Taiwan’s orogeny is < 11.2 ± 0.2 Ma

The eastern Central Range Mountains of Taiwan host highly deformed sediments and well-studied metamorphosed rocks. However fundamental constraints on depositional ages and the timing of deformation and metamorphism remain a problematic issue. In this contribution, we report detrital zircon U-Pb detrital ages for the Chulai Formation, the easternmost strip of metamorphic sediments depositionally overlying the metamorphic, high-pressure Yuli Belt. We demonstrate that the maximum depositional age of this unit is 11.2±0.2Ma (Upper Miocene, Tortonian), making it the youngest pervasively deformed unit of the Central Range. Detrital zircon ages suggest an almost exclusively continental origin of the sediments similar to the Yuli belt’s matrix detrital age zircon spectra. Sedimentary relationships and structural considerations indicate that the Chulai Formation underwent essentially the same deformation history as the underlying Yuli Belt, and thus the maximum depositional age of 11.2±0.2Ma is interpreted as the upper limit for the start of pervasive deformation of the eastern Central Range geological units. When considering the existing geochronological constraints on the metamorphism, we argue that the likely timing for the Cenozoic metamorphism of the Taiwan orogen is likely to be ca. 6-8Ma. 

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