Late Cenozoic metamorphism and mountain building in Taiwan: A review

“…South of the Choshui River, the Tili Unit appears to be offset to the west before it bends into, and terminates against, the Shuilikeng fault (Figure 2). On the basis of Raman spectroscopy of carbonaceous material, Beyssac et al [2007]estimate metamorphic temperatures in the Tili Unit to range from ∼350°C to greater than 450°C, significantly higher than the 284°C determined for the Sun‐Moon Lake Unit [ Sakaguchi et al , 2007] [see also Simoes et al , 2012].…”

Section: Structurementioning

confidence: 99%

The structure and kinematics of the central Taiwan mountain belt derived from geological and seismicity data

et al. 2012

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[1] The structure of the Taiwan mountain belt is thought to be that of an imbricate thrust and fold belt developed in a forward breaking sequence above a shallowly dipping basal detachment. In recent years, however, a growing amount of seismicity data from the internal part of the mountain belt indicates the existence of widespread fault activity in the middle and lower crust, suggesting that deeper levels of the crust must be involved in the deformation than predicted by the shallow detachment, imbricate thrust belt model. To address this issue, we present new geological mapping, together with earthquake focal mechanism and seismic energy release data from the central part of Taiwan. We concur with the interpretation that the foreland basin part of the Western Foothills comprises an imbricate thrust system that is developing as a forward breaking sequence that is structurally and kinematically linked to a basal detachment at between 7 and 10 km depth. To the east of the foreland basin, however, in the Hsuehshan and Central Ranges, our data show the presence of two fault systems. An earlier, inactive thrust system with a well-developed cleavage is cut by a system of steeply dipping active faults that penetrate to a depth of 25 to 30 km or more. In the Hsuehshan Range, the second fault system is best represented by a structural and kinematic model in which this part of the mountain belt forms a zone of transpression with a structural architecture similar to that of a crustal-scale positive flower structure. Eastward, in the Central Range, Mesozoic basement rocks are over thrusting strongly folded and cleaved deep water sediments of the first, now inactive, thrust system. The involvement of deep crustal levels and Mesozoic basement in the second fault system is suggestive of the reactivation of preexisting basin-bounding faults that were located on the Eurasian continental margin.

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“…We cannot prove that penetrative deformation occurred simultaneously throughout this zone, however microstructures indicate fairly uniform coaxial deformation due to horizontal compression [ Fisher et al , 2002; Tillman and Byrne , 1995]. To accomplish this diachronously would require a propagating wave of shortening across the zone that is not indicated by the spatial distribution of (limited) thermochronologic data [ Liu et al , 2001; Simoes et al , 2012]. …”

Section: Geologic Background and Deformation Conditionsmentioning

confidence: 99%

Constraints from rocks in the Taiwan orogen on crustal stress levels and rheology

2012

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[1] Taiwan's Hsüehshan range experienced penetrative coaxial deformation within and near the brittle-plastic transition between $6.5 and 3 Ma. This recent and short-lasting deformation in an active, well-studied orogen makes it an ideal natural laboratory for studying crustal rheology. Recrystallized grain size piezometry in quartz and Ti-in-quartz thermobarometry yield peak differential stresses of $200 MPa at 250-300 C that taper off to $80 MPa at $350 C and $14 MPa at $400-500 C. Stress results do not vary with lithology: recrystallized quartz veins in slates and metasiltstones yield equivalent stresses as recrystallized grains in quartzites. A minimum strain rate of 2.9 Â 10 À15 s À1 associated with this deformation is calculated by dividing a strain measurement (axial strain $0.3) in a strongly deformed quartzite by the available 3.5 m.y. deformation interval. We estimate a maximum strain rate of 7.0 Â 10 À14 s À1 by distributing the geodetic convergence rate throughout a region homogeneously deformed under horizontal compression. These stress, strain rate and temperature estimates are consistent with the predictions of widely applied dislocation creep flow laws for quartzite. The samples record stress levels at the brittle-plastic transition, indicating a coefficient of friction (m) of 0.37 in the upper crust consistent with results based on critical taper. Integrated crustal strength of the Hsüehshan range amounts to 1.7 Â 10 12 N/m based on our analysis, consistent with potential energy constraints based on topography. Other strength profiles are considered, however high crustal stresses (>300 MPa) conflict with our analysis. The study supports the use of the recrystallized grain size piezometer in quartz as a quick and inexpensive method for resolving stress histories in greenschist facies rocks. For consistency with the independent constraints presented here, we find it accurate to within +20%/À40%, significantly better than previously recognized.

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Late Cenozoic metamorphism and mountain building in Taiwan: A review

Cited by 42 publications

References 85 publications

The deep structure of south-central Taiwan illuminated by seismic tomography and earthquake hypocenter data

The deep structure of south-central Taiwan illuminated by seismic tomography and earthquake hypocenter data

The structure and kinematics of the central Taiwan mountain belt derived from geological and seismicity data

Constraints from rocks in the Taiwan orogen on crustal stress levels and rheology

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