Kinematic analyses of the Hsüehshan Range, Taiwan: A large‐scale pop‐up structure

Abstract

The Hstiehshan Range, exposed in the northern and central Taiwan slate belt, is a fault-bounded structural high cored by biotite grade slates and metasandstones.Syntectonic overgrowths in pyrite pressure shadows indicate that much of the eastern Hstiehshan Range experienced coaxial strain histories and that finite strain magnitudes generally increase toward the hinterland. Near the eastern boundary of the Hstiehshan Range, however, pressure shadows record noncoaxial strain histories consistent with a top-to-theeast sense of shear along a steep NW dipping shear zone. This noncoaxiality is attributed to SE directed backthrusting on the Lishan fault, which separates the higher-grade, Eo-Oligocene rocks of the Hstiehshan Range from the lower-grade Miocene rocks of the Backbone Range. Because it is bounded to the east by the SE-vergent Lishan fault and to the west by a series of NW-vergent thrusts (e.g., the Chtichih fau10, the Hsilehshan Range is envisaged as a pop-up structure. Strain magnitudes measured from pressure shadows in the coaxial part of the range are consistently lower than those predicted by steady state wedge models that assume all deformation is accommodated by penetrative strain. Departure from the model predictions is attributed primarily to strain localization along discrete fault surfaces (e.g., the Lishan fau10. The Hstiehshan Range tapers in width to the south; thus the pop-up may be buried or die out to the south where the collision is younger. of the collision. Consequently, the Taiwan mountain belt is approximately 4 m.y. older in the north than in the south.In spite of this north to south age difference, the mountain belt has a constant width for nearly 150 km along strike, an observation which Suppe [1981] attributed to a balance between the flux of material into the wedge by accretion and the flux of material out of the wedge due to erosion (i.e., steady state geometry). Dahlen and Bart [1989] used this steady state assumption as the basis for a kinematic model in which particles enter the wedge through the toe or base by accretion and underplating, respectively, and follow hyperbolic paths through the wedge until they are removed at the surface by erosion. Velocity gradients within the wedge result in penetrative strain, where the principal incremental strain axes are fixed and always parallel to the principal stress directions (i.e., isotropic material). Particle velocities within the wedge are a function of only the wedge geometry and fluxes at the boundaries. The kinematic model proposed by Dahlen and Bart [1989] predicts (1) a steep, SE dipping cleavage, (2) an up-dip extension direction, (3) a progressive increase in strain magnitudes from foreland to hinterland across the wedge, and (4) an increase in the maximum depth of burial and therefore metamorphic grade from foreland to hinterland [Bart and Dahlen, 1989; Bart et al., 1991]. Although there have been several studies of the thermal history and structure of Taiwan using apatite and zircon fission track [Liu, 1982, 1988; Hsieh, ...

Application of titanium-in-quartz thermobarometry to greenschist facies veins and recrystallized quartzites in the Hsüehshan range, Taiwan

“…2 and 7). This fabric is indistinguishable in orientation from the collisional fabrics in neighboring slates (figure 2; Clark et al, 1993;Tillman and Byrne, 1995;Fisher et al, 2002).…”

“…Tillman and Byrne, 1995). Synkinematic fibers in pressure shadows in slates indicate that throughout most of the range compressional deformation was co-axial with a horizontal shortening direction (Clark et al, 1993;Tillman and Byrne, 1995). Internal strain generally increases from west to east across the Hsüehshan range.…”

“…Structural characteristics of the Hsüehshan range are described by Tsan (1971), Lu (1992), Lu et al (1991;, Tillman et al (1992), Clark et al (1992Clark et al ( , 1993, Byrne (1995, 1996), Fisher et al (2002), and Kidder et al (2012). Early extensional deformation is associated with minor normal faults and quartz veining (Lu et al, 1991;Tillman et al, 1992;Clark et al, 1993).…”

“…Early extensional deformation is associated with minor normal faults and quartz veining (Lu et al, 1991;Tillman et al, 1992;Clark et al, 1993). Overprinting compressional deformation features include upright folds (e.g.…”

“…We suggest that the two phases proposed by the different research groups correspond to the same two geologic phases. This constrains the timing of the upright folding, subvertical cleavage, and strain markers described by Clark et al (1993) and Tillman and Byrne (1995) to before ∼4 Ma, the timing of phase two onset in the model of . The second phase of deformation may continue to the present-day, where little or no internal shortening in the Hsüehshan range is observed (Simoes and Avouac, 2006).…”