• The Journal of the Petrological Society of Korea
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• v.12 no.1
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• pp.16-31
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• 2003

The granites in the southern Gimcheon area can be divided into two parts, marginal hornblende biotite granodiorite (Mgd) and central biotite granodiorite to granite (Cgd). Mgd and Cgd are gray in color and display gradational contact relations and are mainly composed of coarse-grained and medium-grained rocks, respectively. Mgd has more frequent and larger mafic enclaves than Cgd, and the two granites partly show parallel foliation at thire contact with gneisses. From representative samples of the granites, K-Ar biotite ages of 197∼207 Ma were obtained. Considering the blocking temperature of biotite, it is suggested that the emplacement age of the granitic magma was probably late Triassic. The anorthite contents of plagioclases in Mgd display less variation than those of Cgd, indicating that Mgd crystallized within a narrow range of temperatures. In the Al$\_$total/-Mg diagram, the biotites from the granites plot within the subalkaline field, and the smooth slope indicates differentiation from a single magma. All amphiboles from the granites belong to magnesio-hornblende. The linear trends of major oxides, AFM and Ba-Sr-Rb indicate that Mgd and Cgd were fractionally differentiated from a single granitic magma body crystallizing from the margin inwards. The relations of modal (Qz+Af) vs. Op, K$_2$O vs. Na$_2$O, Fe$_2$ $O_3$ vs. FeO, Fe$\^$+3/(Fe$\^$+3/+Fe$\^$+2/) and K/Rb vs. Rb/Sr show that they belong to I-type and magnetite-series granitic rocks developed by the progressive melting products of fixed sources. REE data, normalized to chondrite value, have trends of enriched LREE and depleted HREE together with weakly negative Eu anomalies.

• The Journal of the Petrological Society of Korea
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• v.27 no.4
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• pp.223-233
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• 2018

In this study, SHRIMP zircon U-Pb dating was performed on deformed granitic rocks in the Sancheong area in the northeastern part of the Jirisan area, southwest of Yeongnam Massif. Until now, these have been known as Precambrian or age-unknown old igneous rocks, but the U-Pb concordant ages obtained from two samples are $237.8{\pm}4.0Ma$ and $230.2{\pm}3.4Ma$, respectively, showing their emplacements in Early to Middle Triassic. These results indicate that the deformed granite was emplaced at about 238~230 Ma. The study area shows the characteristics of ductile deformation with prominent development of foliation, augen structure, and lineation. It is observed that the deformed granites occur as xenoliths within the syenite, indicating that the time of deformation is earlier than the intrusion of the syenite of about 220 Ma. The emplacement and deformation periods of the deformed granite is similar to that of Permo-Triassic granite gneisses distributed in the Gimcheon and Andong areas of the Yeongnam Massif. Taken together, the eastern part of the Yeongnam Massif, extending from the central part to the southwestern part, granite intrusions occurred at about 260-230 Ma, followed by metamorphism-deformation of about 230-220 Ma.

• The Journal of the Petrological Society of Korea
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• v.15 no.1 s.43
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• pp.39-48
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• 2006

U-Pb ages were determined from the granitic rocks from central and northeastern parts of Yeongnam massif. Porphyritic granite of Seosang-myeon, Hamyang-gun near the boundary with Anui-myeon shows age of $225.4{\pm}4.1Ma$. Foliated granodiorites of Anui-myeon, Hamyang-gun and Sinwon-myeon, Geochang-gun are $195.6{\pm}1.8Ma$ and $194.2{\pm}2.4Ma$ old respectively. Granites from Hari-myeon and Buksang-myeon of Geochang-gun show almost identical ages of $198.4{\pm}2.5Ma$ and $194.6{\pm}2.6Ma$ respectively, while foliated granodiorite of Yeongju shows an age ot $171.3{\pm}2.3Ma$. Combining with previously reported results, Triassic granitoids were emplaced almost identically at ca. 225 Ma throughout the areas of Hamyang and Sangju oi Yeongnam massif and Baengnok, Jeomchon and Goesan of Okcheon metamorphic belt. There were significant gap of non-magmatism before the resume of granitic activities over the large areas of Hamyang-gun, Geochang-gun, Gimcheon-si and Seongju-gun from Triassic-Jurassic boundary to early Jurassic, 200-194 Ma. Igneous activity within the Yeongnam massif of this period has not been reported from the Okcheon belt or Gyeonggi massif and may reflect distinct tectonic environment. Around 170 Ma, when Yeongju granodiorite was emplaced, there were active granitic magamtism throughout the Yeongnam massif, Okcheon belt and also Gyeonggi massif.