• The Journal of the Petrological Society of Korea
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• v.18 no.3
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• pp.255-267
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• 2009

The intrusive rocks in the Hudongri area, Chuncheon located in central Gyeonggi Massif consist of gabbroic diorite and diorite. K-Ar age of biotite separated from diorite sample records middle Triassic age of 228 Ma. The intrusives are characterized by enrichment of MgO, Ni and Cr as well as large ion lithophile elements such as Sa and Sr, which is indicative of derivation of magma from enriched mantle. The intrusives also have enriched Sr-Nd isotopic compositions, which appear to result from a long-term incompatible element enriched mantle source with an effect of crustal contamination. Occurrence of abundant hydrous minerals such as amphiboles and biotite rather than anhydrous minerals of pyroxene and olivine in mafic intrusive as well as being plotted in volcanic arc field in tectonic environment discrimination diagram indicate the mafic-intermediate intrusives in the Hudongri area, Chuncheon were derived from mantle material enriched by subduction.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.89-107
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• 1996

Sr, Nd and Pb isotopic characteristics of alkaline lavas and tholeiites in Cheju Island show that the isotopic compositions of the former slightly overlap, but have relatively more depleted than the latter. However, in viewpoint of the two eruptional stratigraphies of tholeiites, the isotopic compositon of the older one is similar to those of alkaline rocks in Lava Plateau Stage after Lee (1982). These suggest that the parental magmas of alkaline lavas and tholeiites might have originated from the homogenous mantle sourve and that the characteristics of the mantle source to be partially melted might be different between the eruption stages. The isotopic signatures of the bolcanic rocks in Cheju Island overlap with those in Samoa Islands and South China Basin, indicating the DMM-EM IImixing trend. This is distingushed from the DMM-EM I trend of the Cenozoic volcanic rocks in Korea except for cheju Island and Northeastern China. The modelled binary mixing calculation between MM and EM IImaterials indicates that the mantle source of the volcanic rocks in Cheju Island has been mixed about less than 10% of enriched mantle material (EM II) with depleted mantle material (DMM). Concerned with the indentation model between North China Block (NCB) and South China Block (SCB) after Yin an Nie (1993), we suggest that the distinct isotopic features of DMM-EM I and DMM-EM IIof the Cenozoic volcanic rock in Korea as well as China can be explained by the difference of the nature of subcontinental lithospheric mantle as enriched mantle materials, i.e. EM I of NCB, while EM II of SCB.

• The Journal of the Petrological Society of Korea
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• v.17 no.3
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• pp.144-153
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• 2008

Sr, Nd, Pb isotopic compositions of the Cenozoic basaltic rocks distributed in Pyeongtaek-Asan area display significantly enriched values compared with mid-ocean ridge basalts just like other Cenozoic basalts of Korea. The isotopic compositions of most of the Cenozoic basaltic rocks of Korea including those from Pyeongtaek-Asan area can be explained as mixing between enriched mantle component with relatively low $^{206}Pb/^{204}Pb$ ratios and depleted mantle component. In contrast, Jejudo basalts can be explained as mixing between enriched mantle component with realtively higher $^{206}Pb/^{204}Pb$ ratios and depleted mantle componsnt. Combined with that very similar division of enriched mantle components is applied to the Cenozoic basalts of northeast China and southeast China, it is suggested that subcontinental lithospheric mantle of central and southern parts of Korea represents eastern extension of North China Block and South China Block respectively. The indentation model for the late Paleozoic to early Mesozoic continental collision of China contradicts to such an interpretation, because it cannot explain occurrence of subcontinental lithospheric mantle component of South China Block-affinity under the Jejudo area. Instead, it is more probable that suture zone of the two continental blocks crosses between central and southern Korea and its location is further south from the Pyeongtaek-Asan area. Such distinct location compared with Imjingal belt, supposedly collisional boundary suggested before, suggests that mantle boundary may not be coincide with crustal boundary for the continental collision.

• Economic and Environmental Geology
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• v.27 no.2
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• pp.171-180
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• 1994

Several ultramafic bodies and ultramafic origin talc deposits are distributed in Chungnam province near the contact zone with Ogchun fold belt They occur as discontinued belt form with northeast trending, and most of them are more or less sepentinized. Major, trace, and rare earth elements analyses were made of the ultramafics from the study area to constrain their origin and genetic relationships. Compared to the primitive mantle estimates of privious workers, the correlations defined by the studied rock samples indicate similar Ni but very lower $Al_{2}O_{3}$, CaO and $TiO_{2}$ contents. It is inferred that source material of the studied rocks might be residual mantle which had undergone a large degree of partial melting event. The REE patterns show relatively flat to enriched in LREE (chondrite normalized La/Yb and Sm/Yb ratios are 1.1-5.2 and 1.2-1.6). Several alternative explaination are possible for LREE enrichment patterns in the studied ultramafic rocks such as 1) enrichment due to late stage alteration, 2) enriched pre-melting composition, and 3) mixing of two components. Based on the result, the LREE enrichment characteristic of the studied rocks might be result from the mixture of two geochemically distinct components; one is depleted residual mantle and the other component which determine the abundances of incompatible elements and responsible for the LREE enrichment.

• 한국지구과학회:학술대회논문집
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• 2010.04a
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• pp.23-23
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• 2010

스발바드 서측에 위치하는 스피츠버겐 하부의 암석권맨틀의 분화시기를 규명하기 위하여, 두 개의 독립적인 방사성동위원소 시스템인 Lu-Hf과 Re-Os 시스템을 스피넬 페리도타이트(spinel peridotite)에 활용하였다. 전암에 대한 Re-Os 계통(Re-Os 에러크론, 알루미노크론, Re-결핍연대 등)은 연구지역의 페리도타이트가 대류하는 맨틀로부터 고기원생대/후기시생대에 분리되었음을 지시한다. 흥미롭게도 이런 연대는 페리도타이트내 단사휘석 결정들에 대하여 얻어진 Lu-Hf 에러크론 연대와 일치한다. 또한 시료 내에 지구화학적으로 기록된 현무암질 액의 결핍정도 역시 계통적으로 위의 연대를 지지한다. 위 연대는 스피츠버겐 서측부에 보고된 가장 오래된 지각의 연대와 일치한다. 따라서 연구지역의 암석권맨틀이 연약권으로부터 분리된 것은 접촉하고 있는 지각과 동시기적으로 이루어진 사건임을 알 수 있다. 연구지역은 팔레오세 이래로 복잡한 지구조적 응력장 변화(압축에서 신장환경으로의 변화)를 겪었다. 그럼에도 불구하고 지각과 커플링된 암석권맨틀이 현존한다는 것은 연구지역내 응력장변화가 대규모의 암석권 디라미네이션(delamination)을 유발하지는 않았다는 것을 의미한다. 그러므로 북극권의 화산활동을 설명하기 위하여 북극권 상부맨틀에 존재한다고 알려진 듀팔(DUPAL) 같은 부화된 물질의 성인으로 일부의 연구자들이 주장하여 온 디라미네이션된 암석권맨틀의 존재는 설득력이 없다고 판단된다.

• The Journal of the Petrological Society of Korea
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• v.25 no.3
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• pp.261-281
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• 2016

Our knowledge of the lithosphere beneath the Korean Peninsula has been improved through petrologic and geochemical studies of upper mantle xenoliths hosted by Quaternary intraplate alkali basalts from Jeju Island. The xenoliths are mostly spinel lherzolites, accompanied by subordinate harzburgite and pyroxenites. The mantle xenoliths represent residual mantle material showing textural and geochemical evidence for at least a three-stage evolution, fractional partial melting, recrystallization, and metasomatism. Their composition primarily controlled by early fractional melt extraction and porphyroclastic and mylonitic fabrics formed in a shear-dominated environment, which was subsequently modified by residual slab-derived fluids (or melts). Modal metasomatic products occur as both anhydrous phase(orthopyroxene) and hydrous phase (phlogopite). Late-stage orthopyroxene is more common than phlogopite. However, chemical equilibrium is evident between the primary and secondary orthopyroxene, implying that the duration of post-metasomatic high temperatures enabled complete resetting/reequilibration of the mineral compositions. The metasomatic enrichment pre-dates the host Jeju Quaternary magmatism, and a genetic relationship with the host magmas is considered unlikely. Following enrichment in the peridotite protolith in the mantle wedge, the upper mantle beneath proto-Jeju Island was transformed from a subarc environment to an intraplate environment. The Jeju peridotites, representing old subarc fragments, were subsequently transported to the surface, incorporated into ascending Quaternary intraplate alkali basalt. The result of this study implies that long term material transfer in the transformation of geotectonic setting from a subarc to intraplate may have played a significant role in the evolution of lithospheric mantle, resulting in the enriched mantle domains, such as EM I or EM II in the lithospheric mantle beneath East Asia.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.3
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• pp.183-197
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• 2022

Geochemical data, including Sr-Nd-Pb-Mg-Zn isotopes, reported on the late Cenozoic intraplate basaltic rocks in the Korean Peninsula (Mt. Baekdu, Jeongok, Baengnyeong Island, Pyeongtaek, Asan, Ganseong, Ulleung Island, Dok Island, and Jeju Island) are summarized to constrain their mantle source lithologies, and the nature of mantle end-members required. In the Sr-Nd isotope correlation diagram, Jeju basalts plot in the field of EM2-type oceanic island basalts (OIB), while the other basalts fall in the EM1-type OIB field. In Pb-Pb isotope space, Jeju basalts show a mixing array between Indian MORB and EM2 component, whereas the other basalts display an array with EM1 component. The Korean basalts were derived from a hybrid source of garnet lherzolite and recycled stagnant slab materials (eclogite/pyroxenite, pelagic sediments, carbonates) in the mantle transition zone. The EM1 component could be ancient (~2.0 Ga) K-hollandite-bearing pelagic sediments that were isolated for a long period in the mantle transition zone due to their neutral buoyancy. The EM2 component might have been relatively young (probably Pacific slab) and recently recycled clay-rich pelagic sediments. Eclogite and carbonates are unlikely to account for the EM components, but they are common in the mantle source of the Korean basalts.

• The Journal of the Petrological Society of Korea
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• v.20 no.1
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• pp.61-75
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• 2011

Mantle-derived xenoliths, corresponding to spinel harzburgite and lherzolite in alkali basalts from Jeju Island, are metasomatized to various extents. They contain distinctive secondary orthopyroxene, forming corona or poikilitic textures. It clearly indicate that this secondary orthopyroxene has been produced at the expense of olivine along the grain boundaries and margins, suggesting silica-enriched metasomatic melt infiltrated through grain boundaries. Based on the geotectonic characteristics of Jeju Island and textural characteristics and major elements composition of mantle xenoliths, it is suggested that the silica-enriched melt/fluid could have derived from the ancient subducted slab, possibly in the mantle wedge, implying that the high $SiO_2$ activity in the lithospheric upper mantle beneath Jeju Island at that time.

• Journal of the Mineralogical Society of Korea
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• v.18 no.1
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• pp.61-72
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• 2005

Modal and chemical compositions of clinopyroxnes in spinel peridotites from the Baegryeong Island and the Boeun, enclosed in Miocene alkali basalt, are important for understanding the pre-eruptive temperature condition and chemical processes such as mantle depletion and enrichment. All spinel peridotites show transitional texture between protogranular and porphyroclastic textures. Temperature ranges of spinel peridotites from the Baegryeong Island and the Boeun at 15 kb are 773∼1188℃ and 705∼1106℃, respectively. The spinel peridotites from the Baegryeong Island and the Boeun have undergone the 1∼10% and 1∼4% fractional melting, which were determined by using primitive mantle-normalized Y and Yb of clinopyroxenes. LREE enrichment patterns of clinopyroxene indicate that these rocks from both areas have undergone cryptic mantle metasomatism without new minerals.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.3
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• pp.173-182
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• 2022

Dongsuak crater, located in the mid-mountainous region of Jeju Island, is located at an altitude of about 700 m, and the newly discovered Dongsuak spinel peridotites was enclosed in Dongsuak alkaline basalt. The Dongsuak spinel peridotites are composed of olivine, orthopyroxene, clinopyroxene, and spinel with porphyroclastic texture under the an equilibrium state. The variations of mineral major and trace compositions indicates that the Dongsuak spinel peridotites originate at depth from 66 to 88 km under an equilibrium temperature of about 960℃~1068℃. The Dongsuak spinel peridotites have been undergone about 1~3% fractional melting. The LREE-enriched characteristics indicate that the Dongsuak spinel peridotites have been undergone cryptic metasomatism by silicate melt without new minerals.