Print this pageReactivated Structures and Evolving Thrusts in Northwestern Taiwan
YANG, KENN-MING, JONG-CHANG WU, HSIN-HSIU TING, JOHN S. WICKHAM, JAR-BEN WANG, and WEN-RONG CHI
The foreland area in the northwestern Taiwan is characterized by extensional and reactivated structures. The pre-existing normal faults strike at a high angle to the general trend of the orogenic belt in Taiwan. The main purpose of this study is to investigate the effects of the pre-existing normal faults and their associated structures on the development of the structural features in the fold-and-thrust belt.
In the outer part of the foothills belt, the high angle thrusts strike parallel to the normal faults and at a high angle to the anticlines and the associated low angle thrusts that strike parallel to the general trend of the orogenic belt to the east. The two sets of thrusts are transverse to each other and form complex geometry in the fold-and-thrust belt. The complex features might be related to the preexisting normal faults and their associated transfer faults, which might have behaved in three ways during the compressive tectonics: 1, they might have become lateral ramp of low angle thrusts; 2, they were reactivated and became high angle thrusts; 3, some of them may have become tear faults and bounded the shallower low angle thrusts.
The cross-cut relationship among the various types of structures indicates that the reactivation along the pre-existing normal faults predates the development of the low angle thrusts and might have been the earlier signature responding to the westward moving orogen. The reactivation initially propagated laterally alone the normal fault planes but eventually produced curved planes deviated from the normal fault planes. The deviated planes might be important in developing the low angle thrusts in the later stage.
The reactivated normal faults are those with large throw and consistently dipping toward the southeast, indicating that reactivation is selective in altitude and mechanical property of normal fault planes in the compressive tectonics.