Interpretation of Geological Deformation History by Integrated Analysis of Field and Borehole Survey Around KURT Area

2019 ⦽ǎႊᔍᖒ⠱ʑྜྷ⦺⫭ ⇹ĥ⦺ᚁݡ⫭ םྙ᫵᧞Ḳ

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Interpretation of Geological Deformation History by Integrated Analysis of Field and

Borehole Survey Around KURT Area

Soolim Jung*, Kyung-Woo Park, Sung-Hoon Ji, and Kyung-Su Kim

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon, Republic of Korea *

sljung@kaeri.re.kr

1. Introduction

In order to evaluate safety of disposal facilities for radioactive waste, it is necessary to understand the long-term evolution history of the disposal site. Tectonic deformation of geological environment, especially abrupt brittle deformation such as earthquake, can cause serious disturbances to the facility. Tectonic deformation processes are often considered to be less relevant due to the enormous time scale of geological events compared with the relatively short disposal period. However, it is still important to investigate the geological deformation history as a fundamental survey in order to understand the geochemical and hydrogeological environment of the site. In this study, the deformation history was interpreted by integrated analysis of field and borehole survey of the targeted area.

2. Methods

2.1 Study Area

The regional scale area around KURT(KAERI Underground Research Tunnel) is called Yuseong area, which is located in the boundary between Okcheon Belt and Kyunggi Massif. The area is mostly composed of Mesozoic intrusive body. The major rock type consisting KURT area is two-mica granite [1].

2.2 Geological Survey

In a previous study, a regional scale field survey and geological observation were performed along outcrops, exposed in the KURT. Different types of rocks were sampled and underwent chemical and microscopic analysis to interpret the intrusive and ductile deformation history of the site. Faults and joint systems were also observed and measured to interpret the brittle deformation history [2].

In this study, borehole data was gathered to supplement the history and to verify the potential to interpolation of the history into deep underground. Sampled core rocks were observed and logging data were applied to understand the brittle structure of the site.

3. Results

The major deformation history of the area revealed by the previous study was that the Paleozoic metamorphosed basement rock was intruded by magma in the Jurassic and the magma had cooled down until the Cretaceous. During the cooling, the hardened intrusive body started to uplift and fracture, and then mafic dykes intruded along the fractures after cooling in late Cretaceous [2].

Observation of cored rock showed similar petrogenesis to that of the outcrops. The Brittle structures were recognized more clearly in core logging data. Most of distinctive joint sets were

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corresponded to approximately 6 sets of joints recognized in the outcrop of KURT, including three major sets of joints measured from the regional scale field survey. Detailed observation using relatively fresh cored rock suggested further classification of fractures with regard to fracture-filling minerals and associated evolution history.

4. Conclusion

According to the results so far, the regional area around KURT site had remained stable at least during the Quaternary period. The classification of fractures indicates that earlier hydrothermal alteration and later low temperature precipitation of calcite occurred during the uplifting and cooling of intrusive body. To clarify the alteration-related geological history, further chemical and microstructural analyses are necessary.

ACKNOWLEDGEMENT

This work was supported by the Ministry of Science, ICT and Future Planning within the framework of the national long-term nuclear R&D program (NRF- 2017M2A8A5014858)

REFERENCES

[1] H.-I. Park, J.-'/HHDQG-*-HRQJ³*HRORJLFDO map of Korea: Yuseong sheeW´.RUHD,QVWLWXWHRI Geoscience and Mineral Resources (1977). [2] S. Jung, S.-H. Ji, and K.-6 .LP ³,QWHUSUHWDWLRQ

of geological deformation history using flat-FXWWLQJVXUIDFHVRIWKHLQQHUZDOORI.857´3URF of the KRS 2018 Autumn Conference, 16(2), October 31-November 27, 2018, Jeju.