• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.279-292
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• 2014

Nd isotopic compositions analyzed from the Phanerozoic granitoids of Korea are integrated and discussed. Variations in Nd isotopic compositions can be explained either by temporal trend or by regional differences. Among the three active periods, first two periods during the Permian-Triassic and Jurassic seem to show variations from rather high ${\varepsilon}_{Nd}(t)$ values at the beginning to lower ${\varepsilon}_{Nd}(t)$ values during the later stages. Such trends probably reflect melting of the subducting oceanic crust and producing magma with higher proportion of depleted mantle derived materials during the early stage of subduction process, and subsequent magmas with greater proportion of old continental crust with progress of subduction. However, the Cretaceous-Paleogene period of active magmatism displays higher ${\varepsilon}_{Nd}(t)$ values during the advanced stage of the igneous activities, which is opposite to the previous active periods. The other explanation is that such differences in ${\varepsilon}_{Nd}(t)$ reflect regional differences, based on the observations that such high-${\varepsilon}_{Nd}(t)$ granitoids distribute in the northeastern Gyeongbuk Province and Gyeongsang Basin. If this is the case, the regions with highr ${\varepsilon}_{Nd}(t)$ values may have distinct crustal evolution histories, e.g. younger average age. The choice between the two hypothesis could be made through further studies.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.307-324
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• 2020

Major and trace elements, and Sr, Nd, isotopic composition analysis have been carried out on the Miocene basalt (Huangsongpu basalt, 20 Ma) 25 km to northeast from the Mt. Baekdu. The basalt has Na2O+K2O=3.5~4.7 wt.%, and MgO=9.9~11.1 wt.%, containing Mg-rich olivine (Mg#=75~86), clinopyroxene (Mg#=72~85) and Ca-rich plagioclase micro-phenocrysts. These data suggest that the basalt belongs to the alkaline magma series with a primitive nature, crystallized at a near-liquidus. The basalt is also characterized by high Cr (394~479 ppm) and Ni (389~519 ppm) contents, Nb-Ta enrichment anomalies and OIB-like trace elements patterns, displaying identical signatures to those of typical intraplate magmas. The rare earth element (REE) patterns of the basalt and high (Gd/Yb)sample/(Gd/Yb)PM ratio (=2.8~3.5) suggest the parental magma was derived from relatively low-degree (3~5%) partial melting of garnet peridotite. The 143Nd/144Nd and 87Sr/86Sr composition of the basalt are higher than those of BSE. The high 87Sr/86Sr (= ~0.7058) ratio of the basalt indicates a contribution of recycled ancient oceanic crust or continental crust on the Pacific slab suggesting that the Huangsongpu basalt was generated from metasomatized mantle.

• Economic and Environmental Geology
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• v.24 no.4
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• pp.447-463
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• 1991

Petrological and chemical studies of Precambrian dikes in the southern Lake Superior region were conducted with the objects of evaluating magma source and constraining models for the paleo-tectonic environment. Forty-six samples were analyzed for major, trace, and rare earth elements. Chemical data of the studied dikes are typical of continental tholeiites and showing iron-enrichment fractionation trend. With wallrock contamination carefully evaluated, a series of tectonic discriminating methods utilizing immobile trace elements indicate that the source magma was a high-Ti tholeiitic basalt similar to present-day T-type MORB. Effect of chemical contamination from wallrock assimilation accmulates with increasing differentiation. Evolved rocks show LREE enriched patterns and have enhanced levels of LIL elements (e.g., Rb, K, Ba, Th), but low levels of high field strength elements (e.g., Nb, P, Ti) with respect to their neighboring elements. It is suggested from this study that this enrichment possibly due to a combination of a feature inherited from the subcontinental lithosphere and crustal contamination. Geochemical signatures of these rocks are distinctively different from those of arc-related volcanics. Comparisons with chemistries of modern magmas show a pattern of overlap between Within-plate and ocean-floor characteristics, and chemical signatures of these rocks favor a model of intrusion into a crustal environment undergoing lithospheric attenuation.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.27-36
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• 1998

The volcanic piles in the northern Yucheon Minor Basin area are the Hagbong basaltic rocks, the Chaeyaksan basaltic rocks, the Jusasan andesitic rocks, the Unmunsa rhyolitic rocks, and the Tertiary voicanics. Stratigraphically, from the lowermost, (1) the Hagbong basaltic rocks are composed mainly of basaltic tuff with two olivine basalt flows intercalated, (2) the Chaeyagsan basaltic rocks are predominantly in tuffs and agglomerate with 3 basaltic flow interlayers, (3) the Jusasan andesitic rocks consist of thick piles of alternated sequences of 4 andesite flows and 5 andesitic tuffs and tuffaceous sediments and (4) the Unmunsa rhyolitic rocks which embed some rhyolite and obsidian are dominant in tuffs such as ash flow and crystal welded tuff. These volcanics reveal distinguishable characteristics in petrochemistry. In discriminating by major elements, the Hagbong and the Chaeyagsan basaltic rocks are alkaline, whereas the latter is also spilitic. In comparison, the volcanic rocks of the Jusasan andesitic rocks and the Tertiary sequences are characteristically calc-alkaline although their distribution is spatially separated. On the other hand, the variations in immobile trace elements indicate that the Hagbong basaltic rocks range from alkaline to calc-alkaline and from WPB/VAB transition to VAB, whereas the Chaeyagsan basaltic rocks are calc-alkaline WPB/VAB transition type and the two others calc-alkaline VAB. In order to show such a variety in their rock series of the volcanic rocks, the environment during their magma generation, magma rising, and post-eruption alteration could be positively considered.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.302-305
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• 2003

진안-장수지역 (이하 본 역)은 한반도를 구성하는 중요한 지괴인 영남육괴 지리산지역의 북서부와 옥천지향사대의 동남연변부에 위치한 곳으로 두 지괴의 경계면을 따라 압쇄작용으로 형성된 순창전단대가 분포하며 지질시대와 암석학적 특징이 상이한 여러 화성암체가 나타난다. 본 연구지역의 지질은 지리산 편마암복합체를 기반으로 선캠브리아기의 변성퇴적암류, 신암리섬암, 장수화강편마암, 선각산화강편마암 그리고 쥬라기의 대성리엽리상화강암, 순창엽리상화강암과 남원화강암으로 구성된다. (중략)

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.288-290
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• 2003

전북진안의 운장산일대에 분포하는 백악기 홍색 흑운모 화강암류는 연구지역의 동부와 서부에서 각각 원형 및 타원형의 독립된 암체로 발달한다. 서부 화강암체의 흑운모연령 (K/Ar 법)은 백악기초기(김옥준, 1971)로 보고된 바 있어, 같은 암석학적 특성을 가지는 동부암체도 거의 같은 시기의 것으로 해석된다. 동부와 서부 화강암체에는 공동구조(miarolitic)가 도처에서 산점상으로 발달하며, 이들은 부분적으로 다소 큰 형태를 이루기도 한다. (중략)

• Economic and Environmental Geology
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• v.32 no.4
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• pp.323-337
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• 1999

Late Cretaceous to early Tertiary volcanic rocks in the Kyongsang basin exhibit high-K calc-alkaline characteristics, and originated from the magmatism related genetically to subduction of Kula-Pacific plate. They represent HFSE depletion and LlLE enrichment characteristics as shown by magmas related to subduction. Early studies on the depth of magma generation has been estimated as 180-230 km based on K-h relation should be reevaluated, because the depth of peridotite partial melting with 0.4 wt. % water is 80-120 km at subduction zone, and subducting slab in premature arc can melted even lower than 70 km. Moreover the increase of potassium contents depends on either contamination of crustal material and fluids of subducting slab or low degree of partial melting. If the inclination of subduction zone is 30 degrees and the depth to the Benioff zone is 180-230 km, the calculated distance between the volcanic zone and trench axis would be 310-400 km. It is unlikely because the distance between the Kyongsang basin and trench during late Cretaceous to early Tertiary is closer than this value and not comparable with generally-accepted models in subduction zone magmatism. $K_{55}$ of the volcanics in the Kyongsang basin is 0.3-2.3 wt.% and the average indicate that the depth ranges between 80-170 km on the diagram of Marsh, Carmichael (1974). Fractionation from garnet lherzolite, assumed the depth of 180-230km, is not consistent with the REE patterns of the volcanoes in the Kyongsang basin. Futhermore, the range of depth suggested by many workers, who studied magmatism related to subduction, imply shallower than this depth. Crustal thickness calculated by the content of CaO and $Na_2O$ is about 30 km and about 35 km, respectively. Paleo-crustal thickness during late Cretaceous to early Tertiary times in the Kyongsang basin inferred about 30 km calculated by La/Sm versus LaJYb data, which is also supported by many previous studies.

• Journal of the Korean earth science society
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• v.22 no.5
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• pp.405-414
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• 2001

Jecheon granite can be divided into two types; porphyritic granite (K-feldspar megacryst bearing) and medium-grained biotite granite. Porphyritic granite, host body of feldspar deposits, is 8${\sim}$11 km in diameter and about 80 $km^{2}$ in area. It mainly contains K-feldspar, plagioclase, biotite and quartz, and magnetite, zircon, sphene and apatite are accessary minerals. Enclosed minerals in K-feldspar megacryst with 3${\sim}$10 cm in diameter are hornblende, plagioclase, quartz, magnetite, apatite, sphene and zircon. Mafic enclaves mainly consisting of hornblende, plagioclase and quartz are frequently observed in porphrytic granite. Medium-grained biotite granite consists of K-feldspar, plagioclase, biotite and hornblende as main, and hematite, muscovite, apatite and zircon as accessary minerals. Core and rim An contents of plagioclase from porphyritic granite, medium biotite granite, K-feldspar megacryst, and mafic enclave are 36 and 21, 40 and 32, 37 and 32, and 43 and 36, respectively. $X_{Fe}$ values of hornblende are 0.57 at biotite granite, 0.51 at K-feldspar mehacryst and 0.45 at mafic enclave. $X_{Fe}$ values of biotite and hornblende are homogeneous without chemical zonation. K-feldspar megacryst shows end member of pure composition with exsolved thin lamellar pure albites. Characteristics of mineral compositions and petrography indicate porphyritic granite is igneous origin and medium-grained biotite granite comes from the same source of magma; biotite granite is initiated to solidly and from residual melt porphyritic granite can be formed. Possibly K-feldspar megacrysts are formde under H$_{2}$O undersaturation condition and near K-feldspar solidus curve temperature; growth rate is faster than nucleation rate. Mafic enclaves are thought to be mingled mafic magma in felsic magma, which is formed from compositional stratigraphy. Estimated equilibrium temperature and pressure for medium-grained biotite granite are about $800^{\circ}C$ and 4.83${\sim}$5.27 Kb, respectively.

• The Journal of the Petrological Society of Korea
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• v.24 no.4
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• pp.337-345
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• 2015

Pumices from the summit area of the Mt. Baekdu was analysed with respect to the physical characteristics. Fallout pumice deposits around the somma of the Cheonji caldera, Mt. Baekdu consist mainly of white pumices, but black pumices and gray pumices are also displayed together. White pumices are mainly rhyolitic($SiO_2$ 71.1%) and black pumices are trachytic($SiO_2$ 64.8%) in composition, and gray pumices are intermediate composition($SiO_2$ 68.0%) between white pumices and black pumices. Average density of felsic magma formed the Mt. Baekdu pumices is $2.45g/cm^3$ in anhydrous magma and $2.33g/cm^3$ in hydrous magma, respectively. We determined the density and calculated the vesicularity of three different coloured pumices, which collected in the vicinity of the Waho-bong(2,566 m) and Gwanmyeonbong(2,526 m) of southern somma of the Cheonji caldera, Mt. Baekdu. Average density of the yellow pumices was measured as $0.74g/cm^3$, black pumices as $0.75g/cm^3$, and gray t0 white pumices as $0.73g/cm^3$. Average density regardless of the colour of pumices was nearly constant at $0.75g/cm^3$. Vesicularity of pumices is calculated to be 67.8~69.4% and these pumices can be classified as a highly vesicular according to classification of vesiculation characteristics.

• Journal of the Mineralogical Society of Korea
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• v.21 no.4
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• pp.373-382
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• 2008

First reported geochemical characteristics of mantle xneoliths (spinel peridotites) from Sunheul-ri, Jeju Island, provide important clues for understanding the lithosphere composition, equilibrium temperature, and the period of entrainment and transport of the xenoliths in the host magma. Core and rim of mineral phases in the xenoliths are constant chemical compositions as $Fo_{89-90}$ of olivines. The ranges of equilibrium temperature, obtained by two pyroxenes geothermometer, are about $951{\sim}1035^{\circ}C$ for Sunheul-ri spinel peridotite xenoliths and are similar to the range of equilibrium temperatures for the xenoliths from other sites in Jeju island. The period of entrainment and transport of the xenoliths in the host magma of Sunheul-ri mantle xenoliths is about 42 days.