Sedimentary records from Hengchun accretionary prism turbidites on Taiwan Island: Implication on late Neogene migration rate of the luzon subduction system

摘要

Although plate motion models for the Philippine Sea Plate (PSP) are relatively well established, they remain to be confirmed by reliable geological records. Oblique convergence between Eurasia and the PSP has resulted in the uplift of Taiwan Island along the plate boundary. As the latest exposed portion of Taiwan, the Hengchun Peninsula features well-preserved deep-sea turbidites with rounded mafic conglomerate clasts. We apply an integrated source-to-sink analysis and broad field investigations to generate a reliable kinematic reconstruction linking the Hengchun turbidite outcrops with South China Sea (SCS) borehole sediments. Deposited in the lowermost turbidite layer, the Hengchun rounded gabbro and basalt clasts resemble the SCS oceanic crust based on our U-Pb geochronological (similar to 23.6-25.4 Ma) and elemental geochemical results (normal mid-ocean ridge basalts), along with previous magnetic anomaly constraints. The multimodal U-Pb spectra of the matrix-supported sandstones suggest a mixed provenance including central Vietnam, the Pearl River tributaries and potential intrabasinal uplifts, which have not received prior consideration. During the late Miocene, abundant terrigenous sediments from the eastward-flowing "Kontum-Ying-Qiong River" and Pearl River were transported into the submarine environment. The extensive turbidity currents scoured and eroded the SCS mid-ocean ridges, which feature numerous low-angle detachment faults. These materials of various sources were transported eastwards for thousands of kilometers prior to their incorporation into the accretionary prism adjacent to the Manila Trench. From the late Miocene to Pleistocene, the PSP moved northwestward at estimated velocities of similar to 61-65 mm/yr, facilitating the final uplift and exposure of the accretionary prism.