[SIT29-10] A high strain shear zone in the metamorphic core of Central Range, Taiwan: A possible Plio- Pleistocene transform fault
Keywords:Tananao metamorphic belt, high strain shear zone, left-lateral strike slip motion
Observations of meso- and microscopic structures along the eastern Central Range of Taiwan (a strip area of about 200-km-long, 30-km-wide) show two generations of superposed folds with type-1/type-3 interference patterns in the hinge and asymmetric folds in the limb of the metamorphic core complex, which was associated with corresponding two cleavage sets. The transition between the surrounding Slate Belt and the higher-grade metamorphic core of Tailuko Belt are marked by a well-developed, penetrative crenulation cleavage, S2, that dips moderately northwest. The stretching lineation plunges moderately south-southwest is oblique to both the gently plunging lineation in the Tailuko Belt and to the steeply plunging lineation in the Slate Belt (Pulver et al., 2002). A high-strain shear zone can be identified with the consistency of the asymmetric structures and paleotemperature in the detail-studied areas. Stereonets reveal highly concentrated shear planes and asymmetric structures in the high-strain zones suggested top-to-southwest sense of shear. The mineral grain size/boundary mobility and illite-crystallinity index suggested the metamorphic temperature has exceeded 400°C, which is higher than the closure temperature of the biotite (~350°C). Therefore, the biotite 40Ar/39Ar age in the gneiss mylonite yield well-defined plateau dates ranging from 4.1-3.0 Ma (Wang et al., 1998), suggested a syntectonic age for this high-strain zone. The results indicate systematic left-lateral kinematics from north to south in the eastern Central Range (from Hoping, Liwu, Mugua, Shoufeng, Wanrung, Hongye, Chinshui, Xinwulu, to Dalun rivers), that suggested a possible major transform fault in the Tananao metamorphic belt.