| Summary: | 碩士 === 國立中正大學 === 地震研究所暨應用地球物理研究所 === 96 === Since Palaeocene, South China provided most of the sediments to deposit in the basin located at Taiwan island. Until 3-5 Ma, the collision between Philippine Sea Plate and Eurasian Plate led to the end of sedimentation. The sedimentation of basin was deformed and subsequently uplifted. The orogeny is call Penli Movement. Many studies proposed that the orogeny gradually migrated from north to south and the southern Central Range should be lately uplifted. In this study, the zircons from five major watersheds in Taiwan were collected and analyzed with fission track age dating. Consequently, the distribution of fission track ages of strata sources can be depicted. It is much efficient to collect samples from high mountain ranges.
According to the resultant fission track ages of detrital zircons, all samples from different watersheds shows a multi-peak distribution of fission track ages. It demonstrates that five major rivers cut through strata with different thermal history, including partial anealing and total anealing.
The peak ages of Tahan Creek sample are 9.6 Ma, 28.3 and 69.5 Ma. It confirms that the Western Foothills composed of Tertiary sedimentary strata has not been affected by partial annealing. The youngest peak age are much older than that of Penli Movement. It may be caused by the retention of total anealing zircons in Shimen Reservoir. The zircons from Tatu Creek have three peaks: 3.7 Ma, 10.4 and 25.3 Ma. The youngest peak age is obviously anealed and closed to that of Penli Movement. These total anealing zircon grains may be eroded from high metamorphic rocks or strata in the foreland basin receiving the zircons from high metamorphic rocks. The samples collected from Tsengwen Creek basin shows a three-peak age distribution, which are 3.8 Ma,11.2 and 23.1 Ma. It is very similar to that of Tatu Creek.
For the samples from eastern Taiwan, the peak ages of Liwu Creek sample are 0.9 and 7.3 Ma, which should be correlated to those of Tananao Schist. The sample from Chihben Creek basin shows three major peaks: 1.5 Ma, 4.6 Ma and 11.3 Ma, respectively. The youngest peak is related to the thermochronological age of Tananao Schist. The other two peaks should represent the ages of partial anealing zircons.
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