Thermal and thermochronological constraints on the late Cenozoic metamorphic evolution and exhumation of Taiwan

HR: 15:25h
AN: T23D-08 [Abstracts]
TI: Thermal and thermochronological constraints on the late Cenozoic metamorphic evolution and exhumation of Taiwan
AU: * Beyssac, O
EM: Olivier.Beyssac@ens.fr
AF: Laboratoire de GＰlogie, Ecole Normale SupＳieure, CNRS UMR 8538, Paris, 75005 France
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: Tectonic observatory, GPS division, Caltech, Pasadena, CA 91125 United States
AU: Farley, K
EM: farley@gps.caltech.edu
AF: Tectonic observatory, GPS division, Caltech, Pasadena, CA 91125 United States
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: Dept of Geosciences, National Taiwan University, Taipei, 106 Taiwan
AU: Simoes, M
EM: simoes@gps.caltech.edu
AF: Laboratoire de GＰlogie, Ecole Normale SupＳieure, CNRS UMR 8538, Paris, 75005 France
AU: Simoes, M
EM: simoes@gps.caltech.edu
AF: Tectonic observatory, GPS division, Caltech, Pasadena, CA 91125 United States
AU: Chan, Y
EM: yuchang@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Taipei, 115 Taiwan
AU: Goffe, B
EM: goffe@geologie.ens.fr
AF: Laboratoire de GＰlogie, Ecole Normale SupＳieure, CNRS UMR 8538, Paris, 75005 France
AB: The central range (CR) of Taiwan is composed of a Cenozoic slate belt and the pre-Tertiary Tananao schists (TS). Ongoing crustal shortening has resulted from the collision between the Chinese continental margin and the Luzon volcanic arc, which started ~6.5 Ma ago. Due to the obliquity of the Luzon arc relatively to the continental margin, the collision initiated in the north and propagated southward. Key to understanding the collision and accretion processes is the knowledge of metamorphism, in terms of intensity and chronology. Because the CR is mostly composed of accreted sediments lacking metamorphic index and datable minerals, quantitative constraints on metamorphism are sparse. By contrast, these rocks are rich in carbonaceous material (CM) and therefore particularly appropriate for RSCM thermometry (Raman Spectroscopy of CM). We have therefore applied this technique in addition to (U-Th)/He thermochronology on detrital zircons to investigate the peak metamorphic temperature (T) and the low-T chronology along different transects in southern and central Taiwan. We found evidence for surprisingly high metamorphic T in the Hsuehshan Range (HR) (western slate belt) where T reached at least 340-350 C and locally as much as 475 C. Thermochonologic data also indicate relative rapid exhumation with (U-Th)/He ages on zircons in the range of 1.5 to 2 Ma. Farther east, the slates of the Backbone Range (BR) were only slightly metamorphosed (T<250 C) and zircons were not reset for (U-Th)/He. From BR to the inner TS, T gradually increases from ~350 C up to ~500 C following an inverted metamorphic gradient. Zircons yielded (U-Th)/He ages of about 0.5-1.2 Ma in both the TS and the eastern slate belt. This indicates that the HR experienced greater tectonic uplift than the BR. These data show significant departures from the prediction of critical wedge theory and shed new light on how the range has grown as a result of underplating and/or frontal accretion.
DE: 1140 Thermochronology
DE: 3651 Thermobarometry
DE: 8108 Continental tectonics: compressional
DE: 9320 Asia
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: Fall Meeting 2005