月岳山北側 古雲里層 方解石 雙晶을 利用한 推定差應力 分析

Inferred differential stress from twinning in calcite of Gounri formation in the northern area of Worak-san, Korea

Ogchon Supergroup directly contacts with Choseon Supergroup in the northern area of Worak-san, where evidences indicating thrust-fault formed during D₂-deformation are observed. On footwall of thrust fault, calcite veins in Gounri Formation belonging to Choson Supergroup may be deformed during thrust faulting(D₂). Calcite veins are parallel to axial plane cleavage(S₂) of F₂ fold and truncate slaty cleavage(S₁). Therefore, we can use deformation twins in calcite grains of the veins as a marker for inferred differential stress operated upon thrust faulting. The inferred differential stresses are estimated at 190 Mpa from K₁ sample. The stress from K₁ sample close to the contact between Ogchon Supergroup and Choseon Supergroup shows a higher value than K₂-K₆ samples, probably having an important influence upon thrust faulting. The differential stress reveal again high value at K₇ sample, which may suggest the presence of another thrust fault.