Paleostress fields from calcite twins in the Pyeongan Supergroup, South Korea

Abstract

Paleostress fields of the Late Paleozoic to Early Mesozoic Pyeongan Supergroup that is distributed along the northeastern part of the Ogcheon Belt in South Korea were investigated using the calcite strain gauge (CSG) technique. Combining the results of this study with those of other studies investigating the relationship between twin strain, twin density and width, which are used as indicators of deformation conditions in the natural low-temperature deformation of limestone, it was estimated that calcite twins in the study area were probably formed at temperatures lower than 170 ∞ C. From two samples, two different principal paleostress directions were inferred from calcite twins, while only one direction was inferred from two other samples. This result suggests that deformation occurred during two or more different tectonic events in the Pyeongan Supergroup during the Mesozoic era. The maximum shortening axis was oriented in two directions, northeastsouthwest and northwest-southeast, respectively, which coincide well with the paleostress directions inferred from the stress inversion for many fault sets. Combining the results of the paleostress analysis from this and other studies, we hypothesize that the directions of the maximum shortening axis in the Pyeongan Supergroup changed from northeastsouthwest during the pre-Daebo orogeny period (Late Triassic period) to northwestsoutheast during the syn-Daebo orogeny period (Early Jurassic to Early Cretaceous period) in the Mesozoic era.

Mesozoic paleostress from healed microcracks and fluid inclusions in some granites of South Korea

“…These directions and ages correlate very well with Mesozoic tectonism in South Korea, which is characterized by polycyclic deformation in the eastern Asian continental margin during the Songrim orogeny, the Daebo orogeny and the Bulguksa tectonic event. That is, the paleostress direction changed from E-W during the Songrim orogeny in the Middle Triassic via NW-SE during the Daebo orogeny in the Jurassic~Early Cretaceous to N-S during the Bulguksa tectonic event in the Middle~Late Cretaceous Koh, 1995;Kim, 1996;Kihm and Kim, 2003;Kang et al, 2005;Kim et al, 2008). Kim et al (1992) established the deformational sequence in the Danyang area by analyzing paleostress tensors with a thrust zone.…”

“…This orogeny is mild and is not clear because of the modification affected by the later Daebo orogeny. The orientation of the maximum horizontal stress may be NE-SW Kihm and Kim, 2003;Kang et al, 2005;Kim et al, 2008). Jang and Kang (1998) mentioned that the maximum horizontal stress (σ H max ) direction during the Songrim orogeny was E-W.…”

“…Kim (1996) reported Mesozoic tectonics in Korea, and Kihm and Kim (2003) studied the structural evolution of the central Ogcheon Belt. Kang et al (2005) showed paleostress fields of the late Paleozoic to Early Mesozoic Pyeongan Supergroup distributed along the northeastern part of the Ogcheon Belt. Kim et al (2005) also clarified paleostress reconstructions based on calcite twins in the Joseon Supergroup, northeastern Ogcheon Belt.…”

“…Kang et al (2005) showed paleostress fields of the late Paleozoic to Early Mesozoic Pyeongan Supergroup distributed along the northeastern part of the Ogcheon Belt. Kim et al (2005) also clarified paleostress reconstructions based on calcite twins in the Joseon Supergroup, northeastern Ogcheon Belt. A comparison of the above results suggests that the Daebo orogeny would mainly affect the Jechon, Inje and Wolaksan granite, and the Bulguksa tectonic event would mainly affect the Sokrisan granite, although an effect of the Songrim orogeny and Bulguksa tectonic event remained weakly in the Jecheon and Wolaksan granites.…”

Inversion of calcite twin data, paleostress reconstruction and multiphase weak deformation in cratonic interior – Evidence from the Proterozoic Cuddapah basin, India

“…Dynamic analysis of calcite twins is a useful tool in areas where fault-slip data are sparse or altogether absent, and for an independent check on the results obtained from fault-slip analysis. The study of calcite e-twins for estimation of stress and strain has been used in many areas across the world, such as from the Sevier Laramide continental interior (van der Pluijm et al, 1997;Craddock and van der Pluijm, 1999); Southern Pyrenean foreland (Gonz alez-Casado and García-Cuevas, 1999); Paris basin (Rocher et al, 2004); Sheep Mountain, Wyoming (Amrouch et al, 2010); Ogcheon Belt, South Korea (Kang et al, 2005); Iberian Chain, Spain (Gonz alez-Casado and García-Cuevas, 2002); various fold-and-thrust belts including western foreland of Taiwan, Zagros fold belt and Northern Pyrenean foreland (Lacombe, 2010). These studies on mechanical twins in calcite are instrumental in deciphering the regional patterns of tectonic stress, and estimation of strain and differential stress.…”