Journal of the Geological Society of Korea (지질학회지)

The Geological Society of Korea (대한지질학회)
권호 표지

Fabric development of granite mylonites in the Soonchang shear zone: 2. Fabrics

순창전단대내 화강분쇄암의 열구조 발달: 2. 열구조

Chang, Tae-Woo;Lee, Mi-Kyung
장태우;이미경

  • Published : 19961200

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Abstract

Composite planar fabrics in granite mylonites in the Soonchang shear zone consist of four types of foliations: 1) S-foliation, 2) C-foliation, 3) oblique foliation, and 4) extensional crenulation foliation. Their development is closely related to the strain intensity. At low strain, S-foliations are the most conspicuous. whereas C-foliations are weak and nonpenetrative. At intermediate strain. C-foliations become penetrative and the angle between S - and C - foliations decreases with increasing strain. At high strain, S- and C-foliations are virtually parallel: oblique foliations more conspicuous. Finally, extensional crenulation foliations superimpose on the earlier-formed foliations. Quartz c-axes progressively become concentrated in orientation with increasing strain toward the center of the shear zone and the patterns of fabric diagram gradually change as follows: point maximum around z axis ${\rightarrow}$ crossed girdle ${\rightarrow}$ single girdle ${\rightarrow}$ point maximum around Y axis. Active slip system was probably basal slip at the margin of the shear zone, and rhomb slip and prism slip at the center. Mylonitization in the Soonchang shear zone probably took place in the Late Middle Jurassic with a dextral movement under a temperature condition of $400^{\circ}{\sim}500^{\circ}C$.

순창전단대 화강분쇄암에서는 혼합 면열구조 (S엽리, C엽리, 사각엽리, 신장 파랑엽리) 4가지 형태가 발견되며 이들의 발달은 변형 증가에 밀접히 상관된다. 저변형에서 S엽리는 현저하고 균질하나 C엽리는 드물고 비관통상이다. 중변형에서는 C엽리도 관통상이 되고 S와 C사이의 각은 감소한다. 고변형에서 S엽리는 C엽리와 거의 평행하게 되고 사각엽리는 중변형에서 보다 더 뚜렷하게 관찰된다. 신장 파랑엽리는 마지막으로 발달하여 이전에 생성된 엽리들을 간섭하고 있다. 전단대의 가장자리에서 중심부를 향해 석영 c축은 배향이 점차 집중되어지고 열구조 그림의 가장자리에서 중심을 향해 이동한다. 작용한 슬립계는 전단대의 가장자리에서 저면 슬립, 중심부에서 능면 슬립과 주면 슬립이 지배적으로 일어났다. 순창전단대의 분쇄암화 작용은 $400^{\circ}{\sim}500^{\circ}C$의 온도 조건하에서 우수 운동하에 (쥬라기 중기 말엽) 일어난 것으로 추정된다.

Keywords

References

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