Characterization of Pseudotachylite and Fault Gouges in Drill Cores from Andong, Korea and Its Implications for Paleo-Earthquakes

Chang Oh Choo, Su Hyeon Jo, Sang-Youl Lee, Sang-Eun Lee and Gyo-Cheol Jeong
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Chang Oh Choo: Department of Earth and Environmental Sciences, Andong National University, Andong 36729, Korea
Su Hyeon Jo: Department of Earthquake and Disaster Prevention Engineering, Andong National University, Andong 36729, Korea
Sang-Youl Lee: Department of Civil Engineering, Andong National University, Andong 36729, Korea
Sang-Eun Lee: Department of Energy and Mineral Resources Engineering, Kangwon National University, Samcheok 25913, Korea
Gyo-Cheol Jeong: Department of Earth and Environmental Sciences, Andong National University, Andong 36729, Korea

Sustainability, 2020, vol. 12, issue 24, 1-21

Abstract: Pseudotachylite and fault gouges were observed in core samples of Precambrian granitic gneiss drilled from depths as great as 1000 m in Andong, Korea. Fault gouges were found in the upper parts of the borehole, whereas pseudotachylites developed in the lower parts. Pseudotachylite with widths varying from a few mm to 10 cm sharply contacted or were interlayered with the host rock. The quartz-rich portion of the granitic gneiss remained unaffected, but the mafic portion was melted preferentially. The glassy surface of pseudotachylite is characterized by a smooth, glassy matrix with an amorphous phase and silicate beads with diameters of ~200 nm, together with slickenlines. Slickenlines composed of parallel grooves showed a wavelength of 4–7 μm and an amplitude < 1–2 μm. Residual or surviving grains have rounded corners and edges, indicating that those grains experienced abrasion, possibly from grain rotation or shear stress. Both melting and crushing contribute to the formation of pseudotachylite. Fe was always enriched in the glassy matrix, indicating that the pseudotachylite matrix originated from mafic minerals. The occurrence of pseudotachylite related to paleo-earthquake events showed that crystalline rocks in this area are unsatisfactory candidates for deep-disposal sites for high-level nuclear waste.

Keywords: pseudotachylite; fault gouges; glassy matrix; beads; slickenlines; paleo-earthquake (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2020
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