• The Journal of the Petrological Society of Korea
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• v.26 no.3
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• pp.271-280
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• 2017

The Dongcheondong granite is alkali feldspar granite in Dongcheondong, Gyeongju. The granite is coarse grained and consists of alkali feldspar, quartz, amphibole, and biotite. Alkali feldspar is perthitic orthoclase and quartz often shows undulatory extinction. Plagioclase often shows albite twins, and biotite and amphibole emplace as interstitial minerals. The Dongcheondong granite is plotted in A-type area having high ($Na_2O+K_2O)/Al_2O_3$ and low (MgO+CaO)/FeOT ratio. The Dongcheondong A-type granite has higher $SiO_2$, $Na_2O$, $K_2O$, Zr, Y, and REE contents (except for Eu) and lower $TiO_2$, $Al_2O_3$, CaO, MgO, Sr, Ba, and Eu contents than I-type granites in Gyeongsang Basin. These results show that the geochemical characteristics of the Dongcheondong A-type granite are distinguished from I-type granite in Gyeongsang Basin. A-type granite in the Dongcheondong is thought to has been generated by partial melting of I-type tonalite or granodiorite.

• Economic and Environmental Geology
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• v.27 no.4
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• pp.375-385
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• 1994

The studied area is composed of Precambrian gneiss complex, middle Jurassic biotite granite, late Cretaceour sediments, volcanics and pink feldspar granite. Characteristic minerals of the biotite granite is plagioclase and hornblende whereas the pink feldspar granite is pink feldspar (perthite) and quartz. Plagioclase compositions of the biotite granite and the pink feldspar granite are oligoclase to calcic andesine ($An_{18-44}$) and sodic albite ($An_{0.5-5.0}$), respectively. In the variation diagrams of the Harker and normative Q-Or-Pl diagram, the biotite granite belongs to the category from granodiorite to granite, the pink feldspar granite from nomal to late granite. The values of D.I. L.I. and alkalinity of the pink feldspar granite are higher than those of the biotite granite. While CaO is enriched in the biotite granite, $K_2O$ is enriched in the pink feldspar granite. The ratio of $K_2O/Na_2O$ which indicates the relative ratio of alkali is 1.06 in the pink feldspar granite, and 0.86 in the biotite granite. In A-M-F and N-C-K diagrams both these granites are plotted in peraluminus granite ($Al_2O_3$>$Na_2O+K_2O+CaO$) region, assigned to calc alkaline series and alkaline series respectively. Put into the form of A-C-F diagram, the biotite granite falls under I-type, and the pink feldspar granite S-type. On the base of whole rock ratios of $Fe^{+3}/Fe^{+2}+Fe^{+3}$ and $^{87}Sr/^{86}Sr$ for the granites in studied area, the biotite granite indicates ilmenite series (0.26) and S-type and/or contaminated I-type ($0.72020{\pm}0.00050$), the pink feldspar granite magnetite series (0.44) and I-type ($0.70826{\pm}0.00020$).

• The Journal of the Petrological Society of Korea
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• v.5 no.2
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• pp.142-160
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• 1996

Petrological and geochemical characteristics of A-type granite were studied from the Namsan and Tohamsan granites in the vicinity of Kyeongju city, southeastern Korea. The Namsan granite consists of hypersolvus alkali-feldspar granite in the northern part and subsolvus alkali-feldspar to biotite granite in the southern part. This hypersolvus granite usually has miarolitic cavities and is characteristically composed of quartz, single homogeneous one-feldspar (alkali feldspar) forming tabular microperthite crystals, or micrographic intergrowth with quartz, and interstitial biotite (Fe-rich annite), alkali amphibole (riebeckitic arfvedsonite) and fluorite. Petrographic and petrochemical characteristics indicate that the hypersolvus granite and subsolvus granite from the Namsan belogn to the A-type and I-type granitoid, respectively. The A-type granite is petrochemically distinguished from the I-type Bulgugsa granites of Late Cretaceous in South Korea, by higher abundance of $SiO_2$, $Na_2O$, $Na_2O+K_2O$, large highly charged cations such as Rb, Nb, Y, Zr, Ga, Th, Ce. U the REEs and Ga/Al ratio, and lower abundance of $TiO_2$, $Al_2O_3$, CaO, $P_2O_5$, MnO, MgO, Ba, Sr, Eu. The total abundance of REEs is 293 ppm to 466 ppm, showing extensively fractionated granitic compositon, and REEs/chondrite normalized pattern shows flat form with strong Eu '-' anomaly ($Eu/Eu^{\ast}$=0.03-0.05). A-type granite from the Namsan area is thought to have been generated late in the magmatic/orogenic cycle after the production of I-type granite and by direct, high-temperature partial melting of melt-depleted, relatively dry tonalitic/granulitic lower crustal material with underplating by mantle-derived basaltic magmas associated with subduction.

• Economic and Environmental Geology
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• v.26 no.1
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• pp.83-96
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• 1993

Kwangju granite body located in vicinity of Kwangju city consist of three rock bodies-Kwangju rock body, Jangsung rock body and Youngkwang rock body. Petrochemistry of Kwangju granite is as follows: Kwangju granite body is igneous complex which compose of a series of differential products of a magma. Kwangju granites are divided into four rock facies based on the geologic age, mineralogical and chemical constituents and texture: Triassic hornblende-biotite granodiorite and biotite granite, and Jurassic porphyritic granite and two mica granite. Harker and other variation diagrams of Kwangju granites plot on trend of calc-alkali rock series and range of peraluminous granite. Parental magma type of Kwangju granites correspond to I-type, Syn-Collision type in compressive stress field by collision movement between both rock block. In chondrite normalized REE patterns of Kwangju grnites, LREE enriched than HREE in REE amount and have more steep negative slope with slightly (-) Eu anormaly.

• Economic and Environmental Geology
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• v.34 no.1
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• pp.55-70
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• 2001

Granitoids in the Younggwang-Kimje area can be divided into two types of granite. One is foliated granite (Cheongup and Kochang foliated granites) developed along the NE-SW direction kwangju fault system and the other is undeformed granite (Kimje and Younggwang granites) developed in the western part of the area. $SiO_2$ content of study area, Younggwang granite is 62.8-74.0%, Kochang foliated granite is 64.5-74.4%, Cheongup foliated granite is 64.5-70.2%, Kimje granite is 63.4-72.0%. The result indicated that these granitoids belong to the intermediate and acidic rock. In Harker's diagram, as $SiO_2$ increases, $Al_2O_3$, $Fe_2O_3$, MgO, CaO, $TiO_2$> $P_2O_{5}$s and MnO decrease, but $K_2O$ increases. In AFM diagram, Younggwang granite, Kochang foliated granite, Cheongup foliated granite and Kimje granite belong to calk-alkaline rock series. And in triangular diagrams of normative Qz-Or-Pl and An-Ab-Or, they are located in granodiorite and granite region. On the co-variation diagrams of trace elements with silica, Ba, Co, Li, Nb, An, Rb elements show increasing patterns. The diagrams of ACF and $Na_2O$ vs. $K_2O$ ratios indicate that granitoids of the study area belong to I-type.

• The Journal of the Petrological Society of Korea
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• v.26 no.4
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• pp.327-339
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• 2017

The Cretaceous Myeongseongsan Granite in the northwestern Gyeonggi Massif consists of a major pale pink-colored biotite monzogranite and a minor white-colored biotite alkaligranite. Low Sr and high Ba concentrations, negative Eu-anomalies in REE plot, negative Sr anomalies in spider diagram, a negative correlation between Sr and Rb, and positive correlations between Sr and Ba and $Eu/Eu^*$ indicate that a fractional crystallization of both plagioclase and K-feldspar played a significant role during magma evolution. The Myeongseongsan Granite is plotted in I-& S-type granites on I, S, A-type granite classification scheme. While the biotite monzogranite is plotted in unfractionated I-& S-type granite, the biotite alkaligranite is plotted in fractionated I-& S-type granite, which indicates that the biotite alkaligranite is a more differentiated product. In order to elucidate the nature of the protoliths of the peraluminous Myeongseongsan magma, we plotted in $Al_2O_3/TiO_2$ vs. $CaO/Na_2O$ and Rb/Sr vs. Rb/Ba diagrams, and they suggest that the Myeongseongsan Granite was derived from clay-poor metagreywackes and meta-psammites or their igneous counterparts. Whole-rock zircon saturation temperature indicates that the Myeongseongsan magma was melted at $740-799^{\circ}C$.

• Economic and Environmental Geology
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• v.28 no.5
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• pp.445-454
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• 1995

The petrochemical data of the porphyritic granites of Cretaceous age in the Yonghwa-Seolcheon area show the trend of subalkaline magma, calc-alkaline magma, I-type granitoid and magnetite series. This granite is the relevant igneous rock of gold-silver mineralization in this mining district Fluid inclusions have been studied in phenocryst quartz from the Cretaceous porphyritic granite. Three main types of fluid inclusion were found : liquid-rich inclusion(I type), gas-rich inclusion(II type) and solid-bearing inclusions(III-A, III-B). The solid-bearing inclusions(III-A,B) represent the earliest trapped fluids. They have salinities between 41.0 and 67.5 wt% equivalent to NaCl. These are high saline inclusions containing NaCl and KCl daughter crystals. Homogenization temperature inferred from the fluid inclusion study ranges from 650 to $75^{\circ}C$ Type I and II inclusions were observed within the same fracture. This cause for these differences in degree of filling is evidence of boiling. Salinities of type I and II inclusions range from 9.87 wt% to 15.29 wt%, from 8.40 wt% to 14.64 wt% NaCl equivalent, respectively.

• Geomechanics and Engineering
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• v.12 no.6
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• pp.919-933
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• 2017

A series of Brazilian tests under diameter compression for disc specimens was carried out to investigate the strength and failure behavior by using acoustic emission (AE) and photography monitoring technique. On the basis of experimental results, load-displacement curves, AE counts, real-time crack evolution process, failure modes and strength property of granite specimens containing two pre-existing holes were analyzed in detail. Two typical types of load-displacement curves are identified, i.e., sudden instability (type I) and progressive failure (type II). In accordance with the two types of load-displacement curves, the AE events also have different responses. The present experiments on disc specimens containing two pre-existing holes under Brazilian test reveal four distinct failure modes, including diametrical splitting failure mode (mode I), one crack coalescence failure mode (mode II), two crack coalescences failure mode (mode III) and no crack coalescence failure mode (mode IV). Compared with intact granite specimen, the disc specimen containing two holes fails with lower strength, which is closely related to the bridge angle. The failure strength of pre-holed specimen first decreases and then increases with the bridge angle. Finally, a preliminary interpretation was proposed to explain the strength evolution law of granite specimen containing two holes based on the microscopic observation of fracture plane.

• The Journal of the Petrological Society of Korea
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• v.13 no.2
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• pp.81-102
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• 2004

The plutonic rocks in Seonsan area are divided into dioritic-syenitic rock, gneissose granite, biotite granite and fine grained biotite granite. These rocks intruded into the Pre-cambrian metamorphic complex and are all covered by the Cretaceous Nakdong formation. According to modal minerals, dioritic-syenitic rock corresponds to quartz monzonite, granodiorite, tonalite fields, whereas all the other plutonic rocks fall in granite field. Petrochemically the dioritic-syenitic rock is lower in SiO$_2$ content, differentiation index and Larsen index than all the other plutonic rocks. About the zircon morphology, dioritic-syenitic rock shows (100) dominant type but other granitic rocks exhibit mixed types between (100) and (110) type. The dioritic-syenitic rock could be crystallized in higher temperature than the other plutonic rocks. The plutonic rocks correspond to calc-alkaline rock series, and belong to I-type granite and mostly magnetite-series in magmatic origin. In plutonic processes, the dioritic-syenitic rock with 5kb vapor pressure could intrude into the metamorphic batement at 17km deep below the surface. Later the gneissose granite with lower 3kb vapor pressure could intrude at 10km deep. Sequentially the biotite granite with 0.7kb could intrude at 2km deep. Finally the fine grained biotite granite with 3kb vapor pressure could intrude at 10km deep.

• Economic and Environmental Geology
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• v.23 no.2
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• pp.233-244
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• 1990

Plutons of Damyang-Jinan area consist of gray feldspar granite gneiss, biotite granite gneiss, foliated granites, Namweon granites, gabbro, biotite granite and Ogangri granite in term of mineralogical, texture and field evidence. From Isotope data of study area, chronological order of the Plutons are the Pre-cambrian gray feldspar granite gneiss(Ar39-Ar40, hornblende, $1998.4{\pm}8.3Ma$), middle to late Triassic Daegang foliated granite(Rb/Sr, whole rock, $288{\pm}4Ma$), foliated hornblende biotite granodiorite(K/Ar, hornblende, $198.7{\pm}9.9Ma$), Sunchang foliated granodiorite(Rb/Sr, whole rock, $222{\pm}4Ma$), foliated two mica granite, Samori foliated granite and Namweon granite(Rb/Sr, whole rock, $211{\pm}3Ma$: K/Ar, hornblende, $203{\pm}10.2Ma$), middle Jurassic Gabbro(K/Ar, hornblende, $180.7{\pm}9MA$) and biotite granite, and Cretaceous Ogangri granite. According to variations diagrams of $Al_2O_3$ versus normative PI(100 An)/(Ab+An), Daegang foliated granite is plotted on tholeiitic series, and other foliated granites on calc alkaline rock series which are consider to be formed by magmatism at continental margin and island arc region. And alkalinity versus $SiO_2$ shows that Daegang folited granite and Samori foliated granite are correspond to alkaline region, foliated hornblende biotite granodiorite and Sunchang foliated granodiorite to calc alkaline region, and foliated two mica granite to both regions. According to ACF diagrams, Daegang and Samori foliated granites are plotted on S-type. Foliated hornblende biotite granodiorite and Sunchang foliated granodiorite on I-type, and foliated two mica granite on both type. Foliated granites are a series of differentiated products from cogenetic magma, and effected under ductile sheared zone. Characteristic foliation of foliated granites are considered to be generated by dextral strike slip faulting and ductile shearing.