• Analytical Science and Technology
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• v.5 no.2
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• pp.213-216
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• 1992

Semiinsulating GaAs crystals employing LPLEC technique should be grown from the Ga-rich melt due to a very low incorporation of unintentional impurities such as carbon (<$10^{15}cm^{-3}$). High resisitivity of this material can be derived from the balanced compensation among not only EL2 deep donors and carbon acceptors but also H1 double charge native acceptors(Ev + 77meV, Ev + 200 meV) and H2 native acceptors(Ev + 68 meV). Considering of the complicated compensation mechanism using statistical calculation of the electron occupancy of each level, SI GaAs crystal with low impurity contents(<$10^{15}cm^{-3}$) can be successfully obtained by maintaining the melt composition around 0.45 As mole fraction.

• 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.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.235-247
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• 2012

Peridotite xenoliths hosted by alkali basalts from South Korea occur in Baengnyeong Island, Jeju Island, Boeun, Asan, Pyeongtaek and Ganseong areas. K-Ar whole-rock ages of the basaltic rocks range from 0.1 to 18.9 Ma. The peridotites are dominantly lherzolites and magnesian harzburgites, and the constituent minerals are Fo-rich olivine ($Fo_{88.4-92.0}$), En-rich orthopyroxene, Di-rich clinopyroxene, and Cr-rich spinel (Cr# = 7.8-53.6). Hydrous minerals, such as pargasite and phlogopite, or garnet have not been reported yet. The Korean peridotites are residues after variable degree of partial melting (up to 26%) and melt extraction from fertile MORB mantle. However, some samples (usually refractory harzburgites) exhibit metasomatic enrichment of the highly incompatible elements, such as LREE. Equilibration temperatures estimated using two-pyroxene geothermometry range from ca. 850 to $1050^{\circ}C$. Sr and Nd isotopic compositions in clinopyroxene separates from the Korean peridotites show trends between depleted MORB-like mantle (DMM) and bulk silicate earth (BSE), which can be explained by secondary metasomatic overprinting of a precursor time-integrated depleted mantle. The Korean peridotite clinopyroxenes define mixing trends between DMM and EM2 end members on Sr-Pb and Nd-Pb isotopic correlation diagrams, without any corresponding changes in the basement. This is contrary to what we observe in late Cenozoic intraplate volcanism in East Asia which shows two distinct mantle sources such as a DMM-EM1 array for NE China including Baengnyeong Island and a DMM-EM2 array for Southeast Asia including Jeju Island. This observation suggests the existence of large-scale two distinct mantle domains in the shallow asthenosphere beneath East Asia. The Re-Os model ages on Korean peridotites indicate that they have been isolated from convecting mantle between ca. 1.8 and 1.9 Ga.