T021-05
Deformation, Metamorphism, and Exhumation Process of the Retro-wedge, Eastern Central Range, Taiwan

Wednesday, 9 December 2020: 17:46
Virtual
Yuan-His Lee1, Han-Chun Lin2, Lucas Mesalles3, Jian-Cheng Lee4, Wei Lo5, En-Chao Yeh6 and Gong-Ruei Ho4, (1)CCU National Chung Cheng University, Chiayi County, Taiwan, (2)National Chung Cheng University, Earth and Environmental Sciences, Chaiyi, Taiwan, (3)National Chung-Cheng University, Department of Earth and Environment Sciences, Chiayi, Taiwan, (4)Academia Sinica, Institute of Earth Sciences, Taipei, Taiwan, (5)NTUT, Institute of Mineral Resources Engineering, Taipei, Taiwan, (6)National Taiwan Normal Univ., Taipei, Taiwan
Recorded Presentation
Abstract:
Taiwan orogeny results from the subduction and collision process between the continental margin of the Philippine Sea Plate and the Philippine Sea plate since 6.5Ma. The orogeny results in the regional metamorphism strata and high-pressure terrane (Yuli belt) exposes in the retro-wedge, eastern Taiwan. We conduct the RSCM metamorphic temperature, structural analysis, and combine with thermochronology ages to reveal the process from metamorphism to exhumation of the retro-wedge.

In the retro-wedge, it is comprised of the late Miocene Chulai formation, middle Miocene Yuli belt, Mesozoic Tananao metamorphic complex, and Eocene to Miocene slate belt. The metamorphic temperature progressively increases from east (330 oC) to west, and it reaches the highest temperature (500 oC) around the Tananao metamorphic complex and then decreases toward the west. Most of the strata experience D1, D2, and D3 ductile deformation, but the high-pressure terrane has been undergone early-stage high-pressure metamorphism. Considering the metamorphic and structural characteristics are similar across the different strata units, we suggest that there are no significant vertical offset faults (such as Shaofeng fault and CHulai fault) among them.

Combing with thermochronology ages, we propose that the D1 is the highest metamorphic grade stage after 10Ma to 7Ma, which could result from the subduction process. D2 controls the regional strata distribution, which is related to horizontal shortening and is associated with tight to isoclinal folding with crenulation cleavage development. This stage shows slow exhumation from c.7Ma to c.2Ma. The D3 is related to the highest exhumation rate stage after 2Ma, which shows the maximum principal stress is vertical.

The high-pressure terrane also experiences D1 to D3 events, and we suggest the high-pressure terrane extrudes to low-pressure pelitic strata before or near the D1 stage and then exhumates to surface with surrounding strata.

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