DETRITUS ZIRCON U-PB GEOCHRONOLOGY AND ITS GEOLOGICAL SIGNIFICANCE IN MIOCENE ACCRETIONARY PRISM OF HENGCHUN PENINSULA,SOUTHERN TAIWAN

The Miocene accretionary prism in the Hengchun Peninsula, southern Taiwan, consists of three formations. The Mutan and Loshui Formations are deposited in a middle-lower deep-water fan and the Lilungshan Formation deposited in a shallow-water environment. U-Pb age data show that the age patterns of zircon grains of the Lilungshan and Mutan Formations are similar with those of the Minjiang estuary sands, while the age pattern of the Loshui Formation is identical to the Jiulongjiang estuary sands by absence of 400~600 Ma zircon grains and less 700~1 000 Ma and 1 600~2 000 Ma zircon grains. During the Late Miocene, the global sea-level fell significantly due to a dramatic expansion of the Antarctic ice sheet. The coast line of the China continent shifted eastward and a large part of the present East China Sea-Taiwan Strait was exposed. Consequently, large rivers like the Minjiang River in SE China could transport debris flow deposits southeastward to the upper slope of the Chinese continental margin. These turbidite sequences were then deformed as the accretionary prism in the Hengchun Peninsula, while the South China Sea subducted in the Late Miocene time.