• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.185-209
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• 1997

Granitic rocks in the Cheongsan area cosist of three plutons-Baegrog granodiorite, Cheongsan porphyritic granite, and two mica granite. Amphilboles from the Baegrog granodiorite belong to the calcic amphilbole group and show compositional variations from magnesio-hornblende in the core to actinolitic hornblende in the rim. Biotites from the three granites represent intermediate compositions between phlogopite and annite. Muscovites from the two mica granite are considered to be primary muscovite in terms of the occurrence and mineral chemistry. Each granitic rock reveals systematic variation of major oxide contents with $SiO_2$. Major oxide variation trends of the Baegrog granodiorite are fairly different from those of Cheongsan porphyritic granite and two mica granite. The latter two granitic rocks are also different with each other in variation trends for some oxides. Thus three granitic rocks in the Cheongsan area were solidifield from the independent magmas of chemically different, heterogeneous origin. The granitic rocks in the area show calc-alkaline nature. The whole rock geochemistry shows that the Baegrog granodiorite and Cheongsan porphyritic granite belong to metaluminous, I-type granite, whereas the two mica granite to peraluminous, I/S-type granite. The opaque mineral contents and magnetic susceptibility represent that the granitic rocks in the area are ilmenite-series granite, indicating that each magma was solidified under relatively reducing environment. The tectonic environment of the granitic activity in the area seems to have been active continental margin. Alkali feldspar megacryst in the Cheongsan porphyritic granite is considered to be magmatic, judging from the crystal size, shape, arrangement, and distribution pattern of inclusions. The petro-graphical characteristics of the Cheongsan porphyritic granite can be explained by two stage crystallization. Under the smaller degree of undercooling the alkali feldspar megacrysts rapidly grew owing to slow rate of nucleation and fast growth rate. At the larger degree of undercooling the nucleation rate and density drastically increased and the small crystals of the matrix were formed.

• 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.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.37-52
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• 1998

The granites in the Jeomchon area can be divided into hornblende biotite granite (Hbgr), deformed biotite granite (Dbgr), deformed pinkish biotite granite(Dpbgr), biotite granite (Btgr), and granite porphyry(Gp). These granites show metaluminous, 1-type and calc-alkaine characteristics from their whole-rock chemistry. Hbgr and Dbgr belong to ilmenite-series granitoids, but Gp to magnetite-series. Dpbgr and Btgr show the intermediate nature between ilmenite- and magnetite-series. Tectonic discriminations indicate that Hbgr and Dbgr were formed in active continental margin environment, whereas Dpbgr, Btgr, and Gp in post-orogenic and/or anorogenic rift-related environment. From the Harker diagrams major oxide contents of Hbgr and Dbgr show a continuous variation with $SiO_2$, indicating that they are genetically correlated with each other. On the other hand, any correlation of major oxides variation cannot be recognized among Dpbgr, Btgr and Gp. It seems like that Hbgr and Dbgr were derived from a same parent granitic magma, judging from their occurrence of outcrop, mineral composition as well as whole-rock chemistry. Variation trends of major oxide contents between Hbgr and Baegnok granodiorite are very similar and continuous. If the two granites were derived from a cogenetic magma, there exists a possibility that the granitic bodies had been separated by Btgr and Gp of Cretaceous age. Three stages of the granitic intrusions are understood in the Jeomchon area. After the intrusion of Hbgr and Dbgr during middle to late Paleozoic time, Dpbgr emplaced into the area next, and finally Btgr and Gp intruded during Cretaceous time. Tectonic movement accompanying shear and/or thrust deformation seems likely to have occurred bewteen the intrusions of Dpbgr and Btgr.