• The Journal of the Petrological Society of Korea
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• v.19 no.2
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• pp.123-139
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• 2010

The properties of fracture system in Precambrian Jangbong schist and Mesozoic granites from Seokmo-do, Ganghwa-gun were investigated and analyzed. Most of the fractures measured at outcrops are nearly vertical or steeply dipping. Orientations of fracture sets in terms of frequency order are as follows: Set $1:N2^{\circ}E/77^{\circ}SE$, Set $2:N17^{\circ}E/84^{\circ}NW$, Set $3:N26^{\circ}E/64^{\circ}SE$, Set $4:N86^{\circ}W/82^{\circ}SW$, Set $5:N80^{\circ}W/77^{\circ}NE$, Set $6:N60^{\circ}W/85^{\circ}SW$, Set $7:N73^{\circ}E/87^{\circ}NW$, Set $8:N82^{\circ}W/53^{\circ}NE$, Set $9:N23^{\circ}W/86^{\circ}SW$, Set 10: $N39^{\circ}W/61^{\circ}NE$. Especially, the rose diagram of fracture strikes(N:240) indicates that there are two dorminant directions of N-S~NNE and WNW. These distribution pattern of fractures from Seokmo-do correponds with those of major lineaments from South Korea suggested in previous study. Meanwhile, the scaling properties on the length distribution of fracture populations have been investigated. First, fracture sets from Precambrian Jangbong schist and Mesozoic granites(north and south rock body) has been classified into five groups(group I~V) based on strike and frequency. Then, the distribution chart generalized the individual length-cumulative frequency diagram for above five groups were made. From the related chart, five subpopulations(group I~V) that closely follow a power-law length distribution show a wide range in exponents(-0.79~-1.53). These relative differences in exponent among five groups emphasizes the importance of orientation effect. From the related chart, the diagram of group III occupies an upper region among five groups. Finally, the distribution chart showing the chracteristics of the length frequency distribution for each rock body were made. From the related chart, the diagram of each rock body shows an order of porphyritic biotite granite < hornblende granodiorite < medium-grained biotite granite(south rock body) < medium-grained biotite granite(north rock body) < Precambrian Jangbong schist. From the related chart, the diagram of more older rock body in the formation age tends to occupy an upper region. Especially, the diagram of Precambrian Jangbong schist occupies an upper region compared with the diagrams of Mesozoic granites. These distributional chracteristics suggests that coexistence of new fracture initiation and growing of existing fractures corresponding with stress field acted since the formation of rock body.

• The Journal of the Petrological Society of Korea
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• v.26 no.2
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• pp.127-141
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• 2017

Jurassic granite from Geochang was analysed with respect to the characteristics of the rock cleavage. The multicriteria evaluation for the six directions of rock cleavages was performed using the microcrack spacing-related parameters derived from the enlarged photomicrographs (${\times}6.7$) of the thin section and the spacing-cumulative frequency diagrams. The results of analysis for the representative values of these spacing parameters with respect to the rock cleavage are summarized as follows. First, the analysis for deriving the main parameter indicating the order of arrangement among six diagrams was performed. The values of five parameters with respect to six directions of the rock cleavages were arranged in increasing or decreasing order for the above analysis. The decreasing order of the values of main parameter(mean spacing-median spacing, $S_{mean}-S_{median}$) and mean spacing are consistent with the order of H1, H2, G1, G2, R1 and R2 directions. These sequential arrangements of six directions of the rock cleavages can provide a basis for those of the six diagrams related to spacing. Second, the nine correlation charts between the above main parameter and various parameters were arranged in decreasing order of correlation coefficient ($R^2$). These related charts shows a high correlation of power-law function in common. The values of mean spacing, density (${\rho}$) and length of line oa are directly proportional to the value of main parameter, while the values of constant (a), exponent (${\lambda}$), spacing frequency (N), length of line oa', slope of exponential straight line (${\theta}$) and total length ($1mm{\geq}$) are inverse proportional. Third, the results of correlation analysis between the values of parameters for three planes and those for three rock cleavages are as follows. The values of frequency, total spacing, constant, exponent, slope and length of line oa' for three planes and three rock cleavages show an order of R' < G' < H' and H < G < R, respectively. On the other hand, the values of mean spacing, (mean spacing-median spacing), density and length of line oa show an order of H' < G' < R' and R < G < H, respectively. The correlation of the mutually reverse order of the values of parameters between three planes and three rock cleavages can be drawn. This type of correlation analysis is useful for discriminating three quarrying planes.