Seung-Gu Lee

An early Proterozoic leuco-granitic gneiss with the REE tetrad phenomenon

Abstract We report here the occurrence of a peculiar leuco-granitic gneiss in the Imweon area in South Korea. The chondrite-normalized rare-earth element (REE) patterns of this leuco-granitic gneiss and its constituent minerals exhibit the tetrad phenomenon which suggests a special event related to aqueous activity. In addition, the Sm/1bNd internal isochron for the whole rock and its constituent minerals gives an age of 2250 ± 4 Ma with an initial ratio of 0.50942 ± 0.00002 (ϵNd = −5.7). These facts suggest that there should be an environment to give rise to the REE tetrad phenomenon in the crust 2.25 Ga ago. Such an environment may be produced by the water phase resulting from anatexis or the fluid phase in the source material itself before anatexis, subsequent to the stage where the REE content was lowered due to prolonged fluid circulation throughout the granitic melt. The Eu depletion compared to the REE, the REE redistribution among constituent minerals and the tetrad phenomenon are considered to be cognate, even if there had been some time lags between the responsible steps.

Sorption properties of152Eu and241 Am in geological materials: Eu as an analogue for monitoring the Am behaviour in heterogeneous geological environments

In order to confirm the similar behavior of Eu and Am in heterogeneous geological materials, we carried out the batch experiments for determining the sorption property of radionuclides,152Eu and241Am. We used four different types of core rocks including biotite banded gneiss, biotite gneiss, metabasite and andestic tuff, and selected two samples per each lithology, one of which is fracture-bearing and another is fracture-free. Except for metabasites, rock samples of each type are similar in their compositions. We calculated sorption ratios of two radionuclides from the experimental results. Biotite gneiss and tuff had similar sorption trends for152Eu and241Am regardless of the existence of fractures, whereas two metabasite samples showed very different sorption properties. Such difference in the sorption trends revealed a close relationship with chemical compositions of the host rocks. Nevertheless,152Eu and241Am showed similar adsorption trends for all the samples with variable contact times regardless of petrography and pH variations, and particularly, the sorption trends of152Eu and241Am in the metabasites were similar. This observation suggests that Eu and Am have similar sorption properties on geological materials. Therefore, Eu can be used as a useful analogue of Am in all kinds of geological environments regardless of variations in lithology and pH of groundwater. In addition, sorption ratios of152Eu and241 Am are correlated with the contents of P2O5 and TiO2, suggesting that the chemical components such as P2O5 and TiO2 might be important for deciphering the interaction between the radionuclide and groundwater.

Geochemical Composition of the Continental Crust in Korean Peninsula

대륙지각의 화학조성은 지각의 형성과 진화에 대한 이해 및 대륙지각내에서 발생된 여러 과정을 정량화하는데 있어서 중요한 역할을 한다. 이 논문에서는 1990년대 이후 보고된 한반도내 화성암류와 퇴적암류의 지구화학적 자료를 토대로 한반도를 구성하고 있는 대륙지각의 화학조성을 지질시대별로 살펴보았다. 평균상부지각조성을 기준으로 한반도에서의 생성시기별 상부지각의 지구화학적 특성을 비교해보았을 때, 트라이 아스기의 화강암이 다른 시대와 비교해서 일부 원소에서 현저하게 부화되었거나 결핍된 특성을 보여주었다. 또한 선캠브리아기와 쥬라기 이후의 화강암은 매우 유사한 주성분, 미량성분, 희토류원소의 지구화학적 특성을 보여준다. 하부지각의 지구화학적 특성을 지시해주는 선캠브리아기 고변성도 편마암의 희토류원소 및 미량원소의 지구화학적 특징은 쥬라기 이후 상부지각을 형성한 화강암의 희토류원소 및 미량원소의 지구화학적 특징과 유사한 특징을 보여주는데, 이는 이들 변성암류가 중생대 쥬라기 이후 화강암질 마그마의 기원물질이 되었을 가능성을 지시해준다. 반면에 한반도내 중생대 트라이아스기의 상부지각의 기원물질은 선캠브리아기나 쥬라기 이후의 상부지각을 형성한 기원물질과는 다른 것으로 나타났다.

Effect of Zircon on Rare-Earth Element Determination of Granitoids by ICP-MS

요약: ICP-MS를 이용한 화강암질 암석내 희토류원소의 함량 분석시 저어콘이 미치는 영향과 저어콘의 산분해 정도를 미국지질조사소(USGS)의 화강섬록암 표준시료 GSP-2와 일본지질조사소(GSJ) 화강암 표준시료JG-1a를 이용하여 조사하였다. 아울러 화강암에서 분리된 저어콘 광물에 대해 일반적인 산분해법과 압력용기(bomb)을 이용한 산분해법을 적용하여 지르코늄(Zr)과 희토류원소의 함량을 측정하였다. 실험결과에 의하면,저어콘은 일반 산분해의 경우 50% 정도가 산분해된 것으로 나타났고, 압력용기를 이용한 경우에는 약 90%전후가 분해된 것으로 확인되었다. 그리고 GSP-2와 JG-1a의 경우 추천값에 비해 지르코늄의 함량이 50% 정도인 것으로 나타났다. 이는 일반적인 화강암의 산분해의 경우 저어콘의 용해도가 실제로는 50% 정도 밖에되지 않음을 지시한다. 하지만, 화강암내 희토류원소의 함량의 경우, 저어콘의 분해도와 상관없이, 추천값과거의 일치하였다. 이는 저어콘의 불완전분해가 암석시료에서의 희토류원소 분포도를 이용한 암석학적 혹은 지구화학적 해석에 큰 영향을 주지는 않는다는 것을 지시해준다.핵심어: 화강암, 희토류원소, 저어콘, ICP-MSAbstract:

Rare Earth Element, Sm-Nd and Rb-Sr Age and its Geochemical Implication of Leucogranite in the Deokgu Hot Spring Area, Yeongnam Massif, Korea

Here we report major element composition, trace and rare earth element abundance, Sm-Nd and Rb-Sr isotopic composition from Deokgu leucogranite. Chondrite-normalized REE pattern and its Eu anomaly are divided into 3 types systematically, and have close relationship with contents. Such geochemical characteristic indicates that the leucogranite was derived by feldspar fractionation from a common source magma. Sm-Nd and Rb-Sr whole rock ages are (initial

Geochemical significance of 14C, 3H, δ18O, δ2H and 87Sr/86Sr isotope data for the Dongrae and Haeundae hot spring waters, Busan, South Korea

^{143}Nd/^{144}Nd\;ratio

Geochemistry of anorthositic xenolith and host tholeiite basalt from Jeju Island, South Korea

Dongrae and Haeundae are representative hot spring areas that have been used as spas for more than 1,000 years in the southern Korean Peninsula. These hot springs have water temperatures >58 °C and are located along the southeast coastal area of the peninsula. We used 14C, 3H, δ18O, δ2H, and 87Sr/86Sr isotope data for the Dongrae and Haeundae hot spring waters collected over 2004–2014 to investigate the groundwater cycle and heat source for these hot springs. The stable isotope compositions of O and H suggested meteoric origin of the hot spring waters. The 87Sr/86Sr ratios for the Dongrae and Haeundae hot spring waters have been steady for 11 years at 0.70567 ± 0.00002 and 0.70607 ± 0.00002, respectively, suggesting that they are in a near equilibrium state. The 14C age of the Dongrae hot spring waters ranges from 1,401 to 2979 years BP, and that of the Haeundae hot spring waters from 1930 to 6687 years BP. We observed a strong correlation between 87Sr/86Sr and 14C, as well as δ18O. Therefore, the hot springs in the Busan area were supposed to be heated by a paleo-heat source, suggesting that there may be no current heat source under the present crustal conditions. This study also demonstrates that monitoring of the 87Sr/86Sr ratio and 14C in the groundwater and deep thermal water can be used as a proxy for tracing the heat source of geothermal waters such as hot springs and an indicator of groundwater mixings between upper and lower aquifers in granite area.

Ln-resin and HIBA Method for La-Ce and Sm-Nd Isotope Measurement

Volcanic rocks on Jeju Island consist mainly of intraplate alkaline lavas with subordinate intercalated tholeiite basaltic rocks. The alkaline suite can be divided into high-Al alkali (HAA) and low-Al alkali (LAA) sub-suites. We determined the 87Sr/86Sr ratios of anorthositic xenolith plagioclases and the Sr-Nd-Pb isotope compositions of the host tholeiite basalt (Taeheungri basalt). The anorthositic xenoliths are considered to represent buoyancy-induced floating cumulates from previous tholeiite magmatism on Jeju Island. The 87Sr/86Sr ratios of the xenolith plagioclases are highly elevated compared with those of the Jeju tholeiite lavas, including the host basalt. The 87Sr/86Sr ratios of the Jeju volcanic rocks increase from the LAA through the HAA to the tholeiite suite. The tholeiite suite generally exhibits less radiogenic 143Nd/144Nd ratios than the alkaline suite. In Pb-Pb space, the tholeiite suite has, in general, elevated 207Pb/204Pb ratios compared with those of the alkaline suite at a given 206Pb/204Pb ratio. In contrast to the 87Sr/86Sr ratios, the two alkaline sub-suites (HAA and LAA) display indistinguishable Nd and Pb isotope compositions. Notably, some of the tholeiite and HAA suites exhibit distinctive positive anomalies in Eu and Sr in the trace element distribution pattern and the 87Sr/86Sr ratios increase as a function of the degree of Sr or Eu enrichment. These observations, along with the relatively fractionated nature of the tholeiite and especially the HAA suites, indicate that the suites might be products of assimilation of plagioclase-rich cumulates, possibly at lower crustal depth, during parent magma evolution. Jeju volcanic rocks exhibit a mixing line between Indian mid-ocean ridge basalt-like depleted mantle and enriched mantle type 2 (EM2) components in Sr-Nd and Pb-Pb isotope correlation diagrams. The enriched component, the source of which may have been the asthenosphere, is supposed to have been higher in the Jeju tholeiite magmatism than in the alkaline magmatism.

Geochemical interpretation of magnesium and oxygen isotope systematics in granites with the REE tetrad effect

A column chemistry is the most useful tools for isolating the elements of interest in isotope geochemistry. Here we introduce the chemical experimental procedure for Sm, Nd, La and Ce separation such as Teflon powder or Ln-resin method using HDEHP of KIGAM, KBSI, KOPRI and -HIBA(-Hydroxy Isobutyric acid) method of Nagoya University, Japan. This technical report will provide an useful information in selecting the experiment method for rare earth element isotope system study such as Sm-Nd and La-Ce isotope system.

The Effect of Eluent Concentration on the Separation of Nd with Ln-resin Method

The rare earth element (REE) tetrad effect includes a large, strongly negative Eu anomaly, and appears in highly evolved, fractionated granite and/or A-type granite, which it is sometimes interpreted as evidence of fluid-rock interaction. Magnesium is a fluid-mobile element, and its isotopes show very little fractionation during igneous processes. In order to understand the formational processes that cause the REE tetrad effect in granitic magmas and the role of fluid-rock interaction in producing REE tetrad patterns, this study analyzed magnesium and oxygen isotope compositions along with REE patterns in three Cretaceous granites from the Okcheon belt, Korea. Samples exhibited a linear correlation between magnesium isotopic values (δ26Mg) and SiO2, MgO, TiO2, initial 87Sr/86Sr, 143Nd/144Nd values. Oxygen isotope values also showed some correlation with SiO2, TiO2, δ26Mg, initial 87Sr/86Sr, and 143Nd/144Nd values. Our data indicate that the three granites should be evolved from source magma derived from isotopically heterogeneous source materials within the crust. In addition, the relationship between initial 143Nd/144Nd and δ26Mg values strongly suggests that the REE tetrad effect may develop before the granitic magma evolved from crustal source material rather than during late stage of magma differentiation or hydrothermal alteration.