MULTI-PHASE FOLDING AND FAULTING OF METAMORPHIC COMPLEX AND ITS SIGNIFICANCE FOR THE TAIWAN OROGENY

The spatial relationships between multi-phase folding and faulting are discussed for the metamorphic basement “Tananao complex” from the Taiwan Orogeny. Tananao complex is the metamorphic core of Taiwan Orogeny. Yen (1963) divided Tananao complex into two domains, HP-LT Yuli belt at the east and LP-HT Tailuko belt at the west, which constitute the paired-metamorphic belt separated by Soufong fault. Yui, et al. (2012) points out that Tailuko belt and Yuli belt are accretion complex of different age, so the paired-metamorphic belt doesn’t exist. Recently, U/Pb ages of detrital zircon indicates that the Yuli belt has been deposited in the Tertiary of a Cenozoic mélange (Chen, et al., 2013). The tectonic significance of Soufong fault is still on debate and the field evidence was vague.

Our study in the middle domain of Tananao complex proposes a map unit named Daguan shear zone which relates to Soufong fault separated Tailuko belt and Yuli belt. Regionally at least two stages of deformation D₁ and D₂ developed and accompanied by the axial plane cleavage of minor folds S₁ and S₂ respectively. S₁ and S₂ are both defined by muscovite. S₂ cleavages crenulated S₁ cleavages, making orientations of the latter difficult to measure. S₂ strikes and dips 220° / 30° at the west of Daguan Shear zone, and 290° / 20° at the east. Pervasive S₁ cleavage has overprinted the S₀ bedding more or less. In addition, minor folds (F₃) are locally developed along fault planes. S₃ is the cleavage related to local deformation. These results indicate that the Daguan shear zone plays a role as the boundary fault of two distinct belts, in lithology, structure and geochronology, for the Taiwan Orogeny.