HR: 0800h
AN: T11D-1318    [Abstracts]
TI: Entrenched, Transverse Rivers as Geomorphic Strain Markers: Insights From South-Eastern Taiwan
AU: * Ramsey, L A
EM: lar26@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 1TQ United Kingdom
AU: Hovius, N
EM: nhovius@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 1TQ United Kingdom
AU: Haines, A J
EM: haines@esc.cam.ac.uk
AF: Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Hu, J C
EM: jchu@ccms.ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No. 1 Sec. 4 Roosevelt Road, Taipei, 106 Taiwan
AB: In order to unravel continental deformation through time we need to know the strain rate history of a deforming region. Techniques such as GPS, earthquake moment tensor summation and palaeomagnetism generally lack the required temporal and/or spatial resolution to fully describe the deformation. In Taiwan, we explore the use of entrenched, transverse rivers to constrain the history of crustal deformation in geological time. Taiwan is built from the oblique collision of the Luzon Arc and Chinese continental margin. The collision propagates at 60 km/Myr from north to south. This space-time relationship provides a unique opportunity to study an evolving mountain belt through time. The area of interest is a series of seven river basins spanning nearly 60 km along the south-east coast of Taiwan, equivalent to nearly 1 Myr in time. The rivers drain roughly east-west perpendicular to the ridgepole of the mountain belt. The oldest, most northerly, basins show a pronounced asymmetry in their trunk stream position and appear to be rotated anticlockwise. Both the rotation rate and asymmetry factor increase steadily from south to north. The maximum finite rotation is $\sim$ $30\deg$ for a basin $\sim$ 1 million years old. The rotation of the drainage basins may result from the indentation of the Luzon Arc into the Chinese continental platform and the position of the relatively rigid Peikang High. We compare the estimates of rotation rate determined from the river basins to GPS rotation vectors. The deformation of passive markers, in this case river basins, have the potential to provide a continuous record of strain in tectonically active regions. We also note a linear increase in mean elevation and mean local slope of the drainage basins with distance from the southern tip of Taiwan. This is equivalent to a linear increase in elevation and mean slope through time. The mean slope reaches a threshold of $\sim$ $30\deg$ at $\sim$ 0.5 Myr despite a continuing increase in mean height. The space-time relationship allows us to constrain the rate at which a mountain belt attains steady state and has important implications for the development of mean elevation and threshold slopes.
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
DE: 1824 Geomorphology (1625)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting