HR: 12:05h
AN: T32C-07    [Abstracts]
TI: Systematic variations in synorogenic fill architecture and fault offsets along strike across the Puli topographic embayment: Quaternary strain gradients in the central Western Foothills and Taiwanese foreland basin
AU: * Wilcox, T
EM: tarka.wilcox@colorado.edu
AF: Dept. of Geological Sciences, University of Colorado at Boulder, 2200 Colorado Ave, Boulder, CO 80309, United States
AU: Mueller, K
EM: karl.mueller@colorado.edu
AF: Dept. of Geological Sciences, University of Colorado at Boulder, 2200 Colorado Ave, Boulder, CO 80309, United States
AU: Chen, Y
EM: ygchen@ntu.edu.tw
AF: Dept. of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan
AB: New balanced cross sections of the Taiwanese foreland show systematic and fundamental variations in the thicknesses of synorogenic foreland basin fill that correlate with the northern and southern boundaries of the Puli topographic embayment. Transitions in structural styles across the northern and southern boundaries of the embayment are closely related to the variations in the foreland basin fill architecture. These variations provide a bounding rheological framework that has resulted in the modern reorganization of strain in and around Puli, where actively deforming terraces within that basin provide evidence that active contraction of the orogen occurs over a broader area across the Puli region than in other parts of Taiwan. The greatest observed thicknesses of Quaternary and late Pliocene synorogenic sediments within the foreland basin are located to the west of the Puli basin and thin markedly where they cross the boundaries of the embayment, especially to the south. The Oligocene and Eocene rocks of the Hsueshan range, which the the modern Puli basin sits on top of, have been translated eastward with respect to Asia by ~11.4km Since the initiation of the Chelungpu Thrust. The Puli Basin itself may have not existed at this point in time; ages of the Puli basin fill, indistinguishable from Toukushan from a physical standpoint, have been determined to be as young as 70 ka in some places. Horizontal offsets across the Chelungpu thrust increase southward from 10.5km at the Tatu river to 11.9km just north of the Choshui river. Similarly, the horizontal offsets across the Changhua thrust also vary systematically along strike within the boundaries of the Puli embayment, from 0.13km at the Tachia river to 4.0km immediately north of the Choshui river, which marks the southern boundary of the topographic embayment. Horizontal offset on the Chelungpu thrust just south of the Choshui drops to 8.8km, while the horizontal offset across the Tungshu Hu/Changhua fault immediately south of the Choshui river drops to 0.5km. This large drop in displacement across the Choshui river suggests that the location of the river itself may be controlled by the observed transition in structural style and marked strain gradient across the southern boundary of the topographic embayment.
DE: 8104 Continental margins: convergent
DE: 8107 Continental neotectonics (8002)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting