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Insights of fault activities through 3D shape preferred orientation and illite age analysis

Ho Sim, Yungoo Song and Seongsik Hong
Insights of fault activities through 3D shape preferred orientation and illite age analysis
Geological Society of America Bulletin (December 2024) Pre-Issue Publication

Abstract

Combining the absolute age of illite in fault rocks with microstructure analysis plays a significant role in inferring the deformation processes of fault zones that have undergone multiple complex fault activities. We aim to propose a new approach to reconstruct fault activation history by conducting systematic fabric observations, X-ray diffraction analysis, 3D shape preferred orientation (SPO) analysis, and illite age analysis (IAA) on fault gouge affected by brittle deformation in the Yeonghae area of the Yangsan fault in the southeastern part of the Korean Peninsula, where the tectonic environment has been continuously changing since the Cretaceous. We inferred the early fault activation process from large carbonate fragments, aggregates, and chlorite in the fault gouge, and the late fault activation process from the composition of matrix-filling clay minerals, the presence and foliation of clay-bearing layers, and the SPO of rigid clasts. The outcrop in the Yeonghae area of the Yangsan fault initially experienced fault activation at relatively high temperatures and depths, and finally underwent left-lateral strike-slip fault motion due to slip inferred as aseismic creep at relatively low temperatures and shallower depths. Comparing the K-Ar IAA results with previous studies analyzing paleostress fields, it is estimated that the multiple early fault activations in the Yeonghae area of the Yangsan fault occurred between 67 Ma and 38 Ma, and the late aseismic creep occurred at ca. 17-10 Ma. Integrating quantitative 3D SPO analysis and IAA with in-depth fabric observations will provide evidence to elucidate the developmental history of fault rocks based on highly reliable data.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: Pre-Issue Publication
Title: Insights of fault activities through 3D shape preferred orientation and illite age analysis
Affiliation: Yonsei University, Department of Earth System Sciences, Seoul, South Korea
Published: 20241213
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 100
Accession Number: 2025-005888
Categories: General mineralogyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., geol. sketch map
N35°00'00" - N38°00'00", E125°00'00" - E130°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2025, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 2025
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