Active Mountain Building Processes in Taiwan

Prof. Kaj Johnson

Indiana University

The ongoing Taiwan orogeny is the type-example of arc-continent collision. Here the Philippine Sea plate is converging about 80 mm/yr relative to Eurasia resulting in 10 earthquakes of M > 7.0 in the last century. The mechanism of active mountain building in Taiwan has been debated for some time, with the debate centered on whether Taiwan is forming as a thin accretionary wedge over a gently dipping decollement underlying the entire island or whether the entire lithosphere is thickening and shortening. We combine geodetic (GPS, InSAR) and geologic data with models of active crustal deformation to examine how the 80 mm/yr of convergence is distributed across the island of Taiwan resulting in rapid exhumation of the mountain belt. We find that active deformation in Taiwan appears to be concentrated in two neotectonic belts including the fold and thrust belt in the west and the suture zone on the east coast. Furthermore, a significant amount of shortening appears to be accommodated offshore of the east coast of Taiwan. The core of the mountain belt may be actively exhuming by underplating deep in the range.