• The Journal of the Petrological Society of Korea
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• v.10 no.1
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• pp.36-55
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• 2001

Hornblende geobarometry has been applied to estimate the emplacement depth of the Jurassic Yeongiu, Andong, and Gimcheon granites in the Yeongnam Massif. Geobarometry was determined from the twenty two samples of the Yeongiu granite, ten samples of the Andong granite and twelve samples of the Gimcheon granite, using the composition of hornblende rims coexisting with the mineral assemblage required for pressure determination. Amphibole compositions in the three granites vary from edenite to ferropargasite with the increase of pressure. According to the equation of Schmidt(1992), the pressures of emplacement of the Yeongiu, Andong, and Gimcheon granites are 5.6 to 7.9 kb, 5.5 to 7.5 kb, and 4.1 kb to 5.3 kb, respectively. The emplacement depth in the Yeongiu granites increase systematically from about 6 kb in the northwest to about 7.5 kb in the southeast. Andong granite shows no systematic change of the pressure estimates. The Gimcheon granite shows almost consistent pressure distribution. The pressure difference of about 1.5 kb across the Yeongiu granite may be explained by a model combining late postemplacement upsurge of a deeper part of the pluton in the south with tilting of the batholith by Yecheon shear zone.

• The Journal of the Petrological Society of Korea
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• v.7 no.2
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• pp.111-131
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• 1998

The migmatitic gneiss in the Odesan Gneiss Complex has small amount of quartzite, amphibolite and marble and the Kuryong Group which contact with migmatitic gneiss unconformitly, also contains some amphibolite. Preview studies of this area had regarded that the amphibolites contact with marble had been produced by metasomatism from the pelitic and calcareous sediments mixtures, but the amphibolite is reinterpreted as igneous origin. $SiO_2$ content of the amphibolite is 45.9~52.7 wt%, which corresponds to basaltic composition. MgO content has narrow range (4.6~6.87 wt%) and major and trace element are plotted against MgO,$TiO_2, P_2O_5$, Hf, Zr are reduced and Cr and Ni are increased their content with increasing MgO. This phenomenon indicates that the basaltic magma as the protolith of the amphibolite had frationated with the crystallization of the pyroxene and/or olivine. REE pattern has smoothly decrease from LREE to HREE. Eu/Eu(0.83~1.19) show the flat Eu anomaly, which indicate small fractional crystallization of plagioclase. HREE is enriched in the garnet-bearing amphibolites. Several discrimination diagram for the basaltic magma show that the amphibolite of the study area is originated tholeiitic basaltic magma indicating continental rift environment. Due to determine the metamorphic condition garnet-hornblende geothermometry and hornblende-plagioclase geobarometry are used. Peak metamorphic temperature range of the amphibolite $788~870^{\circ}C$ and is deduced toward the northeastern part. The calculated temperature from the amphibolite has slightly higher than the temperature of the metapelites but the trend of metamorphic grade which decrease from western to eastern part progradly is similar to each other. The metamorphic pressure calculated by garnet- hornblede-plagioclase geobarometry is 4~5kb. But ilmenite-plagioclase pair enclosed in garnet show 8 kb at $700^{\circ}C$ by garnet-ilmenite-rutile-plagioclase geobarometery. The zonal profile of garnet in sample 84 shows the bell-shape profile, which grossular content decreases whereas pyrope content increases progressively. This means that the amphibolite has undergone the clockwise P-T-t path which is shown in the migmatitic gneiss of the Odesan Gneiss Complex.

• Journal of the Mineralogical Society of Korea
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• v.17 no.4
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• pp.365-383
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• 2004

Granitic rocks in the southeastern Gyeongsang Basin can be classified into three groups. The group I contains various mafic microgranular enclave (MME) and/or mafic clot which implies magma mixing or mingling. The group II show the feature of shallow depth emplacement at low pressure, and the group III is characterized by A-type granite implying extensional tectonic environment. Mineralogical characteristics of the granitic rocks have showed systematic variations in perthite exsolution temperatures and biotite compositions according to their rock facies, although they do not show any distinctively different trend in geography and textures or rock facies. Amphiboles from Group I are calcic-amphibole and they were formed at 0.4 ～ 2.8 kb in pressure based on the amphibole geobarometry. Amphiboles from group ill are riebeckite, whileas amphiboles were not observed in Group II. The chemical composition of biotite defined in clusters showing a continuous spectrum between group I to ferric-annite of group ill. The composition of plagioclase generally plotted in albite, oligoclase, and andesine area without any distinctive differences among their geography or rock facies. The exsolution temperatures by perthite geothermometry are calculated as $300～400^{\circ}C$ in Group I, and 500～$600^{\circ}C$ in equigranular granite of group II and alkali-feldspar granite of group III.

• The Journal of the Petrological Society of Korea
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• v.3 no.1
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• pp.1-19
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• 1994

We present petrography, mode and chemistry data for Fe-Ti oxide minerals from the Mesozoic granitoids in South Korea. Magnetites from the Daebo Uurassic) granites are nearly pure $Fe_3O_4$, while those from the Bulgugsa (Cretaceous) granites contain considerable amounts of Mn and Ti. This is probably related to rapid cooling of the Bulgugsa granites compared with slow cooling of Daebo granites, which is supported by geologic relations and hornblende geobarometry results of Cho and Kwon (1994) on the emplacement depth for these granites. The composition of ilmenite does not shew appreciable difference between the Daebo and Bulgugsa granites. However, $Fe_2O_3$ contents are higher for the ilmenites coexisting with magnetite than for those without magnetite. In the temperature vs. oxygen fugacity diagram, the Bulgugsa granites plot near Ni-NiO and QFM buffer curves, although only two samples show greater than the granite solidus temperature. The mode data suggest that both magnetite- and ilmenite-series exist in Daebo and Bulgusa granites from the Kyonggi massif, Ogcheon belt and Youngnam massif, while only magnetite-series exists in Bulgugsa granites from the Kyongsang basin. Many ilmenite-series granites occur in the Ogcheon belt, which might be related to assimilation of carboniferous sediments in the belt. The proportion (44 : 56) between ilmenite- and magnetite-series for the Daebo granites is significantly different from that of Ishihara et al. (1981) who showed, using magnetic susceptibility data, predominance of ilmenite-series (more than 70%) for the Daebo granites, which can be mainly attributed to preference in sampling and to wrong assignment of age for some plutons. We also found magnetite in weakly-magnetized Kanghwa granite which was formerly classified as ilmenite-series by Ishihara et al. (1981). The proportion of ilmenite-series increases in the order of hornblende biotite granite, biotite granite and two mica granite. We conclude from these observations that the ilmeniteseries granites might have originated from contamination of carboniferous crustal material and/or such source material.