• 한국광물학회:학술대회논문집
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• 한국광물학회.한국암석학회 2001년도 공동학술발표회 논문집
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• pp.75-75
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• 2001

We report Sr, Nd and Pb isotope data of clinopyroxene separates from ultramafic xenoliths and their host basaltic rocks in Jeju Island, Baekryeong Island, Boeun and Ganseong, Korea. The isotopic data of the xenoliths and host basalts are distinctly different from those of Korean basement rocks. Except for two xenoliths from Ganseong, all samples in this study have isotopic ratios within the combined range of MORB-OIB data. All basaltic rocks have Nd-Sr-Pb isotope compositions different from those of xenoliths, indicating that the host basaltic magma did not derive from the lithospheric mantle where the xenoliths originated. The range of isotopic composition of xenoliths is much greater than that observed in host basalts, which reflects small-scale heterogeneity of the lithospheric mantle. The greater isotopic heterogeneity of the lithospheric mantle probably reflects its long-term stability. The spinel peridotite xenolith data of Jeju Island, Baekryeong Island and Boeun display mixing hyperbolas between DMM and EM II end members. Since Jeju basalts have EM II-like isotopic signature, the mixing relationship shown by the isotopic data of the Jeju xenoliths can be interpreted as the result of infiltration of metasomatic fluid or melt derived from basaltic magma into DMM-like lithospheric mantle. In contrast to other xenolith sites, the Ganseong xenoliths are dominantly clinopyroxene megacryst and pyroxenite. Clinopyroxene megacrysts have different isotopic ratios from their host basalt, reflecting its exotic origin. Two Ganseong xenoliths (wherlite and clinopyroxenite) have much enriched Sr and Nd isotopic ratios and Nd model ages of 2.5-2.9 Ga, and plot in an array away from the MORB-OIB field. The mantle xenoliths from Korean Peninsula have similar $\^$87/Sr/$\^$86/Sr,$\^$143/Nd/$\^$144/Nd and $\^$207/Pb/$\^$204/Pb ratios to, but higher $\^$208/Pb/$\^$204/Pb ratios than, those from eastern China, indicating that Korean xenoliths are derived from the lithospheric mantle with higher Th/U ratio compared with Chinese ones. The isotopic data of xenolith-bearing basalts of Baekryeong Island and Ganseong, along with Ulreung and Dok Islands, show a mixing trend betlveen DMM and EM I in Sr-Nd-Pb isotopic correlation diagrams, which is also observed in tile northeastern Chinese basalts. However, the Jeju volcanic rocks show an EM II signature that is observed in southeastern Chinese basalts. The isotopic variations in volcanic rocks from the northern and southern portions of the East Asia reflect a large-scale isotopic heterogeneity in their source mantle.

• 자원환경지질
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• 제56권4호
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• pp.475-499
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• 2023

경상지역 제철유적의 원료산지 추정을 위해 제철시료와 주요 철광상 철광석을 대상으로 암석기재학 및 지화학적 특성을 비교 분석하였다. 각 지역에서 발굴된 제철유적 시료는 제련공정 단계에 따라 원료철광석, 괴련철, 괴련철슬래그, 선철, 선철슬래그, 단조박편, 단야철, 철정 및 화살촉으로 분류되었고 각각 상이한 구성광물과 조직을 보였다. 또한 슬래그를 구성하는 규산염광물에서의 알루미늄 및 칼슘 등의 주원소 성분의 농집과 제철유물에서 니켈 및 구리 등의 미량원소 함량이 높은 것은 원료철광석의 특성이 반영된 것으로 잠재적인 제철원료의 산지추정인자로 여겨진다. 특히 제철유적 시료의 납-스트론튬 동위원소비는 크게 1) 원료철광석과 유사한 조성을 보이는 경우, 2) 스트론튬 동위원소비가 부화된 경우, 그리고 3) 납-스트론튬 동위원소비 모두 부화된 경우로 구별되며 이러한 동위원소비 특성은 고온의 제련공정 과정에서 첨가된 특정 조재제와의 혼염 가능성을 시사한다. 이러한 결과는 첨가물이 제련과정에 미치는 잠재적인 기여 측면에서 경상지역 제철유적의 산지추정 해석에 새로운 시각을 제시한다.

• 자원환경지질
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• 제29권3호
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• pp.293-304
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• 1996

The Wolchul Mt. area is composed of a biotite granite and a pink feldspar granite. These granites are distinctly different in terms of their field occurrence, mineralogy, trace element and REE composition, as well as their isotope ages. The biotite granite has higher ferromagnesian elements and lower lithophile trace element abundances than the pink feldspar granite. The biotite granite has high Sr and Ba while the pink feldspar granite has high Rb. On the Rb-Sr-Ba diagram the biotite granite plots as a granodiorite while the pink feldspar granite belongs to a strongly differentiated granite. The ${\Sigma}$ LREE/ ${\Sigma}$ REE for the biotite granite is 0.95 and for the pink feldspar granite it is 0.88. The ratio shows a steep decrese in LREE while HREE is essentially constant. Based on the Eu/Sm, $[La/Lu]_{cN}$ and low Eu(-), the biotite granite has quartz diorite to granodiorite composition while the pink feldspar granite, with a relatively high Eu(-) anomaly, falls into the monzo- to syenogranite classification. The silica vs. trace element diagrams for the two granites indicate that the biotite granite could have formed near to a continental margin or volcanic island setting environment while the pink feldspar granite formed within a continental plate or as result of plate collision. The biotite granite has a U-Pb zircon age of 175 Ma, i.e. Middle Jurassic. The pink feldspar granite is younger, it has a K-Ar orthoclase age $93.6{\pm}1.5$ Ma which is Late Cretaceous age.

• 자원환경지질
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• 제15권3호
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• pp.123-154
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• 1982

Petrochemical, K-Ar dating, Sand Rb/Sr isotopes, metallogenic zoning, paleomagnetic and geotectonic studies of the Gyongsang basin were carried out to examine applicability of plate tectonics to the post-late Cretaceous igneous activity and metallogeny in the southeastern part of Korean Peninsula. The results obtained are as follows: 1. Bulgugsa granitic rocks range from granite to adamellite, whose Q-Ab-Or triangular diagram indicates that the depth and pressure at which the magma consolidated increase from coast to inland varying from 6 km, 0.5-3.3 kb in the coastal area to 17 km, 0.5-10 kb in the inland area. 2. The volcanic rocks in Gyongsang basin range from andesitic to basaltic rocks, and the basaltic rocks are generally tholeiitic in the coastal area and alkali basalt in the inland area. 3. The volcanic rocks of the area have the initial ratio of Sr^{87}/Sr^{86} varying from 0.706 to 0.707 which suggests a continental origin; the ratio of Rb/Sr changing from 0.079-0.157 in the coastal area to 0.021-0.034 in the inland area suggests that the volcanism is getting younger toward coastal side, which may indicate a retreat in stage of differentiation if they were derived from a same magma. The K_2O/SiO_2 (60%) increases from about 1.0 in the coastal area to about 3.0 in the inland area, which may suggest an increase indepth of the Benioff zone, if existed, toward inland side. 4. The K-Ar ages of volcanic rocks were measured to be 79.4 m.y. near Daegu, and 61.7 m.y. near Busan indicating a southeastward decrease in age. The ages of plutonic rocks also decrease toward the same direction with 73 m.y. near Daegu, and 58 m.y. near Busan, so that the volcanism predated the plutonism by 6 m.y. in the continental interior and 4 m.y. along the coast. Such igneous activities provide a positive evidence for an applicability of plate tectonics to this area. 5. Sulfur isotope analyses of sulfide minerals from 8 mines revealed that these deposits were genetically connected with the spacially associated ingeous rocks showing relatively narrow range of ${\delta}^{34}S$ values (-0.9‰ to +7.5‰ except for +13.3 from Mulgum Mine). A sequence of metallogenic zones from the coast to the inland is delineated to be in the order of Fe-Cu zone, Cu-Pb-Zn zone, and W-Mo zone. A few porphyry type copper deposits are found in the Fe-Cu zone. These two facts enable the sequence to be comparable with that of Andean type in South America. 6. The VGP's of Cretaceous and post Cretaceous rocks from Korea are located near the ones($71^{\circ}N$, $180^{\circ}E$ and $90^{\circ}N$, $110^{\circ}E$) obtained from continents of northern hemisphere. This suggests that the Korean peninsula has been stable tectonically since Cretaceous, belonging to the Eurasian continent. 7. Different polar wandering path between Korean peninsula and Japanese islands delineates that there has been some relative movement between them. 8. The variational feature of declination of NRM toward northwestern inland side from southeastern extremity of Korean peninsula suggests that the age of rocks becomes older toward inland side. 9. The geological structure(mainly faults) and trends of lineaments interpreted from the Landsat imagery reveal that NNE-, NWW- and NEE-trends are predominant in the decreasing order of intensity. 10. The NNE-trending structures were originated by tensional and/or compressional forces, the directions of which were parallel and perpendicular respectively to the subduction boundary of the Kula plate during about 90 m.y. B.P. The NWW-trending structures were originated as shear fractures by the same compressional forces. The NEE-trending structures are considered to be priginated as tension fractures parallel to the subduction boundary of the Kula plate during about 70 m.y. B.P. when Japanese islands had drifted toward southeast leaving the Sea of Japan behind. It was clearly demonstrated by many authors that the drifting of Japanese islands was accompanied with a rotational movement of a clock-wise direction, so that it is inferred that subduction boundary had changed from NNE- to NEE-direction. A number of facts and features mentioned above provide a suite of positive evidences enabling application of plate tectonics to the late Cretaceous-early Tertiary igneous activity and metallogeny in the area. Synthesizing these facts, an arc-trench system of continental margin-type is adopted by reconstructing paleogeographic models for the evolution of Korean peninsula and Japan islands. The models involve an extention mechanism behind the are(proto-Japan), by which proto-Japan as of northeastern continuation of Gyongsang zone has been drifted rotationally toward southeast. The zone of igneous activity has also been migrated from the inland in late-Cretaceous to the peninsula margin and southwestern Japan in Tertiary.