High strain zones in the Mesozoic metamorphic basement of Taiwan: A possible fossil transform fault during convergence between Eurasia and the Philippine Sea plate
Abstract
Detailed observations of meso- and microscopic scale structures along a more than 150-km-long strip in the Mesozoic Tailuko belt and the Miocene Yuli belt in eastern Central Range of Taiwan indicate numerous high strain zones with a consistent sinistral strike-slip motion. This pattern was observed along the Mugua, Shoufeng, Wanliqiao, and Chinshui Rivers and along the two main highways that cross the Central Range of Taiwan. In the studied sections, strain is concentrated in zones that show predominant cleavage generally dipping to NW with a penetrative lineation defined by deformed mica fibers and elongated Qtz-veins. The lineation typically plunges gently N-NE. Observations on both outcrops and thin-sections, by viewing parallel to the lineation and perpendicular to the dominate foliation asymmetric structures (e. g., folds, feldspar and quartz augen, S-C fabrics), show top-to-the south motion. These results are consistent with previous studies in the Taroko Gorge area that show well-developed sheath folds with sub-horizontal axes (Lu and Wang Lee, 1986) and left-lateral shear in the Chipan granitic gneiss (Pulver et al., 2002). In addition, the ductile shear zone can be traced southward in the Central Range where lower-grade rocks are exposed to two brittle fault zones that bound the east and west margins of the Tailuko Formation. These brittle faults offset Miocene strata with a lateral sense of slip (Usami, 1940).
We propose that the left-lateral high strain zones in the eastern Central Range and the two major brittle faults in southern Taiwan represent the predominant strike-slip characteristics that developed during highly oblique convergence between Eurasia and the Philippine Sea plate. In this interpretation, the orthogonal component is interpreted to be represented by the penetrative strain in the Slate Belt of the western Central Range which consistently records top-to-the west thrusting and down-dip stretching. This interpretation is also consistent with recent plate reconstructions that show highly oblique converge between the Philippine Sea plate and Eurasia plate from before 15 Ma to less than 2 Ma when the motion changed to the current motion that is nearly orthogonal to the plate boundary.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T21C0327H
- Keywords:
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- 1140 Thermochronology;
- GEOCHRONOLOGY;
- 8025 Mesoscopic fabrics;
- STRUCTURAL GEOLOGY;
- 8102 Continental contractional orogenic belts and inversion tectonics;
- TECTONOPHYSICS;
- 8111 Continental tectonics: strike-slip and transform;
- TECTONOPHYSICS