Detrital zircon analysis of Miocene Series of the Hengchun Peninsula, southern Taiwan

Abstract:

The island of Taiwan is produced by the oblique collision between the Eurasian plate and the Luzon arc from north to south since about 5-6 Ma. The Hengchun Peninsula (HCP) in the southernmost Taiwan is the southern extension of the mountainous core of the orogen. Thus studying HCP could provide information of the early history of the orogeny. It is generally considered that Taiwan was located on the Eurasian continental margin before the collision, and the source of pre-collision sediments was southeastern China. However, the submarine topography shows that HCP is on the eastern side of Manila trench. Therefore, either HCP should belong to the Philippine Sea plate instead of the Eurasian continental margin, or the HCP sediments need to somehow move across the plate boundary. In order to further understand the evolution of HCP, this study aims to identify potential sediment sources of the Miocene Series in HCP.

We performed U-Pb dating of detrital zircons obtained from HCP. 7 sandstone samples were collected from the Lilongshan, Shihmen and Loshui Formations in HCP. The U-Pb dating results show that zircons in these three formations all have peaks in the range of 1840-1870 Ma and 150-250 Ma. However, in the Shihmen Formation, the ages concentrate more between 20-25 Ma than the two previously identified peaks. Such an age distribution pattern is significantly different from the other two. According to previous studies, no major magmatic events occurred during this relatively young period in southeastern China. Thus the provenance of these young sediments in HCP is still under debate. Combining with results of Hf isotopes of the zircons and comparing the detrital zircon ages of samples collected from the Luzon Island, we hope to establish alternative models for sediment sources of HCP in Miocene. Such results may provide additional information about the sediment sources and history of HCP, as well as the entire Taiwan orogen.