Abstract
The subduction and collision boundaries of the Eurasia and Philippine Sea Plates in the Taiwan mountain belt expose a NE-trending coherent crustal section in the Tananao Complex. This study investigates the structures in three dimensions in the Shoufengsi area, which is located in the middle section of the Tananao Complex to understand the Taiwan orogeny mountain building processes. Detailed geological mapping and structural analyses shows the eastward shortening associated with metamorphism indicative of three deformation events. Three sets of axial plane foliation S1, S2, and S3 can be recognized by Type-1 and Type-3 fold interference patterns. Different structural characteristics can be further revealed in five domains based on domain analysis. Each domain shows the superposed process characteristics. Synthetic structural mapping and microstructure examination analyses on the Shoufengsi area show that NE-trending isoclinal folds and axial D1 and D2 plane foliation events represent shortening deformation and NW-trending crenulation cleavage. Normal D3 event faults display the gravity collapse deformation. These observations are consistent with shortening to extension stage predictions during Eurasia and Philippine Sea Plate collisions.
Highlights
Regional structures with compositional layering are frequently used to analyze the structural style of foliations
D2 is the regional structure of the Tananao Complex and D3 reflects the local structure in the eastern Shoufengsi area
Based on domain analysis and transposition analysis in this study, mountain collapse influences the eastern slope of the Tananao Complex and its effects are widely distributed in the Domain I, IV, and V areas in the Shoufengsi area (Table 1) (Fig. 8)
Summary
Regional structures with compositional layering are frequently used to analyze the structural style of foliations. Detailed geological mapping and structural analyses shows that at least three sets of foliation have different structural styles (Wang and Yang 1979; Yang 1981; Lin 1986; Zhan 1990) and different attitudes exist (Stanley et al 1981; Chen and Yang 1985; Jiao 1991; Lo 1993) These ductile/brittle structures include the recumbent folds with vertical stress from the mountain collapse process (Lee 1997; Yeh 2004). The Tananao Complex is the oldest geological and tectonic unit in Taiwan and can be divided into two metamorphic belts using the Shoufeng Fault (Yen 1963) (Fig. 1) It consists of black schist, metasandstone, quartz schist, meta-chert, meta-conglomerate, meta-limestone, gneiss, meta-granite, green schist, glaucophane schist, amphibolite, and serpentine rock types. These mesoscopic or microscopic folds will be examined to clarify the structural history of the Shoufengsi
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