HIGH UPLIFT RATES COINCIDENT WITH NORMAL FAULTING, SOUTHERN CENTRAL RANGE, TAIWAN

The Taiwan orogenic belt straddles the boundary between the Philippine Sea and Eurasian plates and is the product of the collision between the north-trending Luzon volcanic arc and the northeast trending Chinese passive margin. Progressive collision has resulted in zipperlike mountain building along the oblique margin. In areas of collision it is common to see thrust faults in foreland areas and normal faults in hinterland areas. In areas of high elevation, it is also common to see normal faults play an important role in the exhumation of metamorphic rocks. Usually the normal faults appear to be post orogenic structures, and appear to result from gravitational collapse of the orogeny as far-field stress changed. Outcrop-scale normal faults documented during 2014 field work accommodate maximum principal stretching at a high angle to the topographic grain of the orogenic belt. Most of these faults dip shallowly to moderately NE. Earthquake focal mechanisms for nearby upper crustal events reveal similar strain geometries suggesting that the surface faults and earthquakes are not a result of gravitational collapse. If correct, this suggests that other processes (e.g., crustal delamination or slab tearing) may be responsible for crustal thinning occurring in the southern Central Range where uplift rates are high.