MR33B-2661
Study of Magnetic Fabrics across the Central Part of the Chimei Fault, the Coastal Range of Eastern Taiwan

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Ying-Rong Chu1, En-Chao Yeh2, Yu-Min Chou3, Teh-Quei Lee4, Szu-Ting Kuo3,5 and Yuan Min Cai6, (1)NTNU National Taiwan Normal University, Taipei, Taiwan, (2)NTNU National Taiwan Normal University, Department of Earth Sciences, Taipei, Taiwan, (3)National Taiwan University, Department of Geosciences, Taipei, Taiwan, (4)Academia Sinica, Institute of Earth Sciences, Taipei, Taiwan, (5)National Taiwan University, Taipei, Taiwan, (6)Department of Geoscience, National Taiwan University, Taipei, Taiwan
Abstract:
Taiwan is an ongoing collisional mountain belt located in the conjunction of two subduction-arc systems with opposite vergences between the Philippine Sea and Eurasian plates. The Coastal Range along the eastern Taiwan is the accreted Luzon arcs and surrounding basins onto the Eurasian crust. The Chimei fault, a typical lithology-contrast fault thrusting the Miocene volcanic Tuluanshan Formation over the Pleistocene sedimentary Paliwan Formation, is the only major reverse fault across the entire Coastal Range. To investigate the deformation pattern and strain history across the Chimei fault, we analyzed oriented samples of mudstone and volcanic rocks across the fault zone, fold zone, damage zone, and wall rocks along the Hsiukuluan River via anisotropy of magnetic susceptibility (AMS).

AMS can be represented as a susceptibility ellipsoid with 3 principal directions and values (Kmax, Kint, Kmin) and therefore is well known as a tool of magnetic fabrics to study the deformation. Results of AMS across the central part of the Chimei fault show that the direction of Kmax changed from N-S orientation to sub-vertical and the orientation of Kmin switched from 270/70 to N-S orientation when samples were closed to the fault zone. At the same time, anisotropy was increasing and susceptibility ellipsoid changed from oblate to prolate in the fold zone back to oblate in the fault zone. Based on identification works of magnetic minerals, the major magnetic carrier is magnetite with pseudo-single domain. As a result, it strongly speculated when samples were approaching to the central part of Chimei fault, stress altered from sub-vertical sedimentary loading to horizontally N-S tectonic compression. Due to increasing deformation, oblate ellipsoids with strong anisotropy developed within the fault zone highlighted the strain history of the central part of the Chimei fault.