[S-IT20] New perspectives on accretion and exhumation processes during oblique plate convergence

[SIT20-11] Study of Anisotropy of Magnetic Susceptibility across the Southern Portion of the Backbone Range, Taiwan

*Ya-Chu Tseng¹, En-Chao Yeh¹, Ning-Shan Hsu¹, Yu-Ching Chang¹, Jian-Cheng Lee², Gong-ruei Ho², Ching-Chou FU² (1.Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan, 2.Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan)

Keywords:Anisotropy of Magnetic Susceptibility, Backbone Range, Shoufeng shear zone

Mountain building process is a fascinating and intriguing topic for solid earth research. Taiwan orogen is a classical mountain belt resulted from on-going arc-continent collision between the Eurasian Plate and the Philippine Sea Plate. The Backbone Range of Taiwan is the oldest geological unit, which is formed and exhumed during subduction and collision. The eastern Backbone Range is commonly composed of the Tananao metamorphic complex and the slate. The former could further be divided into Tarako belt and Yuli belt separated by the Shoufeng shear zone due to huge age difference between each belt. Although the Tananao metamorphic complex has underwent several deformation events, the mesoscopic mylonitic schists within the Shoufeng shear zone shared the same attitude with the wall rocks of each belt. These observations make difficulty to reconstruct the structural evolution of the Tananao metamorphic complex and examine the role of Shoufeng shear zone. In order to evaluate the deformation imposed on Taiwan orogeny, we plan to explore the different deformation events by investigating the strain pattern across the eastern Backbone Range.
This study plans to shed the lights on illustrating deformation domains with the regional strain distribution across the eastern Backbone Range. Anisotropy of Magnetic Susceptibility (AMS) is an efficient tool to analyze the finite strain and characterize petrofabrics and structures. The experiment will measure the principal directions and values of magnetic susceptibility ellipsoid, and further evaluate the mean magnetic susceptibility, the degree of anisotropy, ellipsoid type and strain pattern. Based on the strain distribution inferred from AMS, the changes of deformation across the eastern Backbone Range could be inspected, and the aspects of Shoufeng shear zone can be further characterized.