16:15 〜 16:30
[SCG42-03] New model of the mountain building in Taiwan
キーワード：Taiwan orogen, mountain building, thermochronology dates, thermo-mechanical wedge theory
As the northern Luzon arc moves northwestward at a ca. 8 cm/yr, it collides with the Eurasian continental margin, forming one of the planet's archetypical examples of the arc-continent collisional orogenic system. The Taiwan orogen can be separated into four tectonic units from east to west, the Coastal Range of Luzon arc, Backbone Range, Hsuehshan Range, and the fold-and-thrust belt. Many different theories have been proposed to explain the deformation mechanism, but they still have difficulty explaining the new findings and data for the Taiwan orogenic belt.
We first constrain the crustal structures and exhumation process based on low-temperature thermochronology dates, metamorphic temperature, and seismic tomography images, and then we develop a novel thermal-mechanical wedge deformation theory to reveal the mountain building process.
According to the thermochronology dates, the initial deformation process is in-sequence from 8 Ma, 6 Ma, to Quaternary from east to west. We, however, find a significant out-of-sequence Tayulin thrust fault (T-OOST) in the Backbone Range with ca. 270 km in length. The exhumation of T-OOST starts from ca. 3Ma with a nearly constant exhumation rate of 2-5 mm/yr since about 2 Ma on the hanging wall, indicating that the ductile deformation plays an important role during the crustal thickening and rapid exhumation. The Hsuehshan Range exposed a higher metamorphic anticlinorium structure associated with a high exhumation rate. The seismic tomography image shows a significant ramp structure beneath the Hsuehshan Range. Sliding along the ramp structure could be the mechanism of rapid exhumation.
Our new thermo-mechanical wedge theory is similar to a bulldozer pushing the snow including brittle and ductile deformation mechanism and erosion process related to hill slope and rock strength. We also consider the ramp and flat decollement fault geometry based on the seismic tomography images. Our preferred model agrees with the crustal structures revealed by the seismic tomography image and is also consistent with the new finding of the T-OOST in the Backbone Range, metamorphic temperature, exhumation rate, and thermochronology dates in the orogenic belt. The model suggests that ductile deformation consumes most of the shortening in the early stage, and the new model also proves that developing the Hsuehshan Range is related to the ramp structure.
We first constrain the crustal structures and exhumation process based on low-temperature thermochronology dates, metamorphic temperature, and seismic tomography images, and then we develop a novel thermal-mechanical wedge deformation theory to reveal the mountain building process.
According to the thermochronology dates, the initial deformation process is in-sequence from 8 Ma, 6 Ma, to Quaternary from east to west. We, however, find a significant out-of-sequence Tayulin thrust fault (T-OOST) in the Backbone Range with ca. 270 km in length. The exhumation of T-OOST starts from ca. 3Ma with a nearly constant exhumation rate of 2-5 mm/yr since about 2 Ma on the hanging wall, indicating that the ductile deformation plays an important role during the crustal thickening and rapid exhumation. The Hsuehshan Range exposed a higher metamorphic anticlinorium structure associated with a high exhumation rate. The seismic tomography image shows a significant ramp structure beneath the Hsuehshan Range. Sliding along the ramp structure could be the mechanism of rapid exhumation.
Our new thermo-mechanical wedge theory is similar to a bulldozer pushing the snow including brittle and ductile deformation mechanism and erosion process related to hill slope and rock strength. We also consider the ramp and flat decollement fault geometry based on the seismic tomography images. Our preferred model agrees with the crustal structures revealed by the seismic tomography image and is also consistent with the new finding of the T-OOST in the Backbone Range, metamorphic temperature, exhumation rate, and thermochronology dates in the orogenic belt. The model suggests that ductile deformation consumes most of the shortening in the early stage, and the new model also proves that developing the Hsuehshan Range is related to the ramp structure.