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Reactivated Timings of the Yangsan Fault in the Yeonghae area based on the Mineralogical Characteristics of Fault Clays
단층암 점토광물 특성에 기초한 영해지역 양산단층의 단층활동연대 결정
Econ. Environ. Geol. 2020 Dec;53(6):645-54
Published online December 31, 2020;  https://doi.org/10.9719/EEG.2020.53.6.645
Copyright © 2020 the Korean society of economic and environmental gelology.

Seongsik Hong1, Ho Sim1*, Sung-Ja Choi2 and Yungoo Song1
홍성식1 · 심호1* · 최성자2 · 송윤구1

1Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea
2Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Korea
1연세대학교 지구시스템과학과, 2한국지질자원연구원
Received October 28, 2020; Revised December 1, 2020; Accepted December 2, 2020.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
 Abstract
We present the K-Ar age dating results of <0.1µm fraction of the selected fault rocks from the Yangsan fault in the Yeonghae area. Based on the mineralogical characterization, the <0.1µm fractions were mostly composed of 1Md illite polytype, or I-S interstratified mineral, which should be formed by fault activation. Therefore, we determined the timings of fault activation events by analyzing K-Ar age-dating for the <0.1µm fractions. Accordingly, the activation timings of Yangsan Fault in the Yeonghae area were determined as 45.5±1.1 Ma, 50.9±1.2 Ma, 58.2±1.3 Ma, 60.8±1.4 Ma, 65.3±1.6 Ma, 66.8±1.5 Ma, 67.1±1.5 Ma, and 75.1±1.7 Ma. These results indicate that at least 5- times of major fault events occurred in the Yangsan fault from late Mesozoic to Cenozoic Era. In the outcrop, age dating results tend to be younger age from the location of the oldest sample(75.1±1.7 Ma) toward to the both sides. From the results, it suggests that the fault activation extends from the location of oldest age saple to both sides. This geochronological research of the multiple fault activation ages for the Yangsan Fault will provide crucial information for establishing the tectonic evolution model in the southeastern part of the Korean Peninsula.
Keywords : fault activation, Yangsan fault, illite polytype, K-Ar age, fault gouge

 

February 2021, 54 (1)