T33A-2913
Pleistocene onset of Simultaneous and Rapid Exhumation in the Eastern Central Range of the Taiwan Orogenic Belt

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Wei-Hao Hsu, Department of Geoscience, National Taiwan University, Taipei, Taiwan, Timothy B Byrne, University of Connecticut, Groton, CT, United States, William B Ouimet, University of Connecticut, Storrs, CT, United States, Yuan-Hsi Lee, CCU National Chung Cheng University, Chiayi County, Taiwan, Yue-Gau Chen, National Taiwan University, Taipei, Taiwan, Matthijs C Van Soest, Arizona State University, School for Earth and Space Exploration, Tempe, AZ, United States and Kip V Hodges, Arizona State University, Tempe, AZ, United States
Abstract:
The Taiwan orogenic belt is often treated as a steady, southward propagating orogenic system with an erosion rate of 4–6 mm/yr for 5 My. A few recent studies of the exhumation history, however, suggest that the collision was initially simultaneous and that exhumation rates changed through time. To test this hypothesis, we constructed four new age-elevation curves that span the length of the orogen from the Central Cross-Island Hwy (CXIH) in northern Taiwan to Small Ghost Lake (XGH) in the south. The age-elevation curves are based on 10 new zircon (U-Th)/He (ZrnHe), 10 new zircon fission track (ZrnFT) ages and 82 previously published ZrnFT and ZrnHe dates. Samples used for each age-elevation analysis extended map distances, ranging from 11 to 17 km for ZrnHe and 11 to 27 Km for ZrnFT to limit the influence of topography on estimated uplift rates. Three of the sites, CXIH, XGH and the South Cross-Island Hwy, are from the eastern Central Range whereas the fourth, Mt Yu, is from western Central Range.

The results show that all four sites record similar exhumation histories from about 5 Ma to the present, except for a slight difference at Mt Yu. For example, the three eastern sites record an apparent increase in exhumation rate from < 1.2 mm/yr. to ~ 3-5 mm/yr. at about 1.5 Ma. At Mt. Yu, however, a similar increase in the rate of exhumation occurs at about 2 Ma. In addition, the zero-age intercepts of the youngest phase of uplift from the three eastern sites suggest the possibility of an additional increase in exhumation rate after ~0.4 Ma that is not recorded at Mt. Yu. Interestingly, Mt Yu is also mapped as a continuation of the Eocene rocks exposed in the Hsüehshan Range rather than part of the Central Range, consistent with the presence of a major structural boundary between Mt Yu and the three areas to the east.

These data suggest the following conclusions: 1) the Hsüehshan and Central Ranges appear to have different exhumation histories; 2) the eastern Central Range appears to have experienced two stages of accelerated exhumation cooling – the first at about 1.5 Ma and the second at about 0.4 Ma and 3) changes in exhumation cooling through time appear to have been simultaneous along strike.

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