Conclusions
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Evaluation of the Classic Model

Studies since 1995 have revealed some holes in older models and the critical wedge model of Taiwan orogenesis:

  1. Isotope geochemistry clearly shows the affinity of the Tananao basement complex of Taiwan with the Fujian province of coastal China. Therefore the Tananao basement complex is not an exotic block accreted to Taiwan.

  2. Interpretations of the Lishan fault and the Lichi Melange in the Longitudinal Valley have changed. Interpretations now favor processes consistent with those presently observed offshore south of Taiwan. The collapse of a forearc basin is clearly shown in this offshore area.

  3. Deep structure observed from seismic, gravity, and thermal studies contradicts that predicted by a critical wedge model in the following ways:

  4. Leveling and thermochronologic data indicate a possible acceleration uplift in the Central Ranges over the last million or so years. This result would only be reproduced by specific conditions in the critical wedge that result from weather patterns causing increasing erosion off the western slope of Taiwan over the last million years.

The Lithospheric Model of Collision

The continental subduction of Taiwan orogenesis is best illustrated in figure 9. While a wedge-shaped fold and thrust belt is part of the model, especially in western Taiwan, it differs from the critical wedge model in many ways:

  1. The buoyancy of the subducted continental crust drives the collapse of the forearc basin and the collision of the arc with the continent, rather than the arc creating a backstop against which to pile continental crustal materials.

  2. The lower lithosphere of Eurasia is coupled with the overlying upper crust and they deform, in part, as a coherent block.

  3. Decoupling of the Eurasian continental lithosphere from the down-going oceanic slab is a driving force in the uplift of the Taiwan orogeny.

The continental subduction model fits the data shown above that contradicts the classic critical wedge model:

  1. The chronology of deformation processes (buildup of wedge, then forearc collapse) matches that seen off the south shore of Taiwan.

  2. Deep structure and uplift are explained:

Further Study

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Last edited 5/3/2001 by Megan Anderson anderson@geo.arizona.edu