Youngwoo Kil

Precise determination of the lithium isotope ratio in geological samples using MC-ICP-MS with cool plasma

Lithium has two naturally occurring isotopes, 6Li and 7Li, with approximate relative abundances of 7.5% and 92.5%, respectively. Due to large Li isotope variations in nature, lithium isotopes have the potential to reveal important information relevant to nuclear technology, biomedicine, astrophysics, and geochemistry. With the advent of multi-collector inductively coupled mass spectrometry (MC-ICP-MS), studies of Li isotopes have largely focused on the analysis of geological materials, with varying degrees of accuracy. However, this technique has often been affected by either baseline interferences or isobaric interferences on mass 6 and 7 during ionization in Ar plasma, which is mainly due to the Li compound with hydrogen gas, and double-charged nitrogen and carbon ions at higher levels of RF power. In this study, we reduced baseline interferences in Ar plasma using a cool plasma (∼800 W) technique with a X-type cone. Lithium was separated using a cation exchange column (BioRad AG50W-X8, 200–400 mesh) with a mixture of 6 N HNO3 and 80% methanol at <0.2 mL min−1 elution speed. The short-term reproducibility of δ7Li values of the NASS-5 seawater standard was 30.55 ± 0.45‰ (2σ, n = 15). Measured δ7Li values of rock and seawater standards ranged from 2.48 to 30.55‰, in good agreements with reported values.

LA-ICP-MS analysis of natural rock samples using XRF glass beads

Glass beads that remain after measuring major element compositions using XRF can also be used to measure trace element compositions using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The JA-1 and JB-3 reference glass beads were used to evaluate the homogeneity of trace elements contained within them as well as the data quality of LA-ICP-MS measurements. JA-1 has a homogenous trace element composition with less than 10% relative standard deviation, and JB-3 has an average relative standard deviation and average limit of detection of the trace elements of 4% and 0.94%, respectively. The measured and reference values of JB-3 have the highest correlation (R2 = 0.996). Natural rock samples with intermediate to acidic compositions, such as Hwasun andesite, Mudeungsan dacite tuff, and Dogok rhyolite from Mudeungsan National Park, South Korea, are also used to evaluate the LA-ICP- MS data quality. Trace elements in these natural rock samples are plotted in a reasonable area of the geochemical discrimination diagram with sufficient precision. Accordingly, glass beads made from natural rock samples can be used to measure their trace element compositions using fast in situ and low-cost LA-ICP-MS analysis with similar data quality as achieved with normal solution ICP-MS analysis.

The Formation of the Cenozoic Volcanic Edifice in the Goseong-Ganseong Area, Gangwondo, Korea

In the Obongri-Goseong area of Gangwondo, South Korea, there are six densely distributed volcanic edifices i.e., Duibaejae, Oeumsan, Galmibong, 249 m height, 166 m height, and 102 m height, and two other volcanic edifices including Goseongsan and Unbongsan volcanic edifice that are separately located from a distance. A previously undiscovered 249m volcanic edifice in Obongri was found in this investigation, and the six volcanic edifices distributed in Obongri will be referred to as the Obongri volcanic edifice group. Volcanic edifices in this area were interpreted by other researchers as being volcanic plug, plug dome, and cylindrical volcanic pipe type edifices. The aim of this study is to investigate the aspect of volcanic activity in the Obongri-Goseong area and the formation of volcanic edifices by examining of the shape of volcanic edifices, stratigraphy, and characterization of volcanic products. All the volcanic edifices in the area are composed of basaltic rocks on the Mesozoic granite basement, and the prevalence of the dome shape increased towards the upper part of the mountain. Three volcanic edifices (Duibaejae, 166 m height, 102 m height) include intercalated pyroclastic deposits between the basaltic rocks and the basement. The pyroclastic deposit in the Duibaejae volcanic edifice is composed of quartz, feldspar, granite fragments originated from the basement, and scoria fragments originated from the volcanic eruption. In addition to angular olivine, plagioclase, and pyroxene xenocrysts, all the basaltic rocks contained mantle xenolith, gabbroic xenolith originated from the lower crust, and granitic xenolith originated from the basement. This fact indicates that magma rapidly rose to the surface and that the volcanic activity was explosive. It is also interpreted that, as the basaltic magma became highly viscous due to the large amount of xenocrysts, the erupted magma formed a dome structure on the surface. The original dome structure was then severely eroded out leaving a plug dome formation on the basement.

Petrochemical Characteristics of the Duibaejae Volcanic Rocks from Goseong, Gangwon-do, Korea

Duibaejae basalts from Goseong, Gangwon-do, are divided into the lower basalt and the upper basalt depending on the properties, such as occurrence, mineral compositions, and major and trace compositions of the basalts. The lower basalts have characteristics of agglomerate rocks as well as contain, crustal and mantle xenoliths, and olivine, pyroxene, and plagioclase xenocrysts. The upper basalts with columnar joints contain relatively more mantle xenolith and olivine xenocryst than the lower basalts. The major and trace element compositions suggest that the composition of the upper basalts is close to primary magma composition. Enrichment and depletion patterns of the trace and the rare-earth elements of the lower basalts are similar to those of the upper basalts, whereas the lower basalts are more LREE enriched than the upper basalts. The source magmas of the lower and upper basalts from Duibaejae volcanic edifice were generated from about 0.8-1.2% and 3.7-4.0% batch melting of garnet peridotite, respectively. The abundance of granite xenolith, and plagioclase and quartz xenocrysts with reaction rim indicates that the lower basalts, compared with upper basalts, might have been assimilated with the crustal materials during ascending to surface.

Geochemical analyses on bituminous carbonate reservoir in Alberta, Canada: focusing on the GC/GC-MS results of bitumen

The geochemical study on bituminous carbonate reservoir in Alberta has been performed to document the organic geochemical characteristics of the Grosmont Formation using two drilling cores (SAL 03-34 and SAL 08-01), especially focusing on the GC and GC-MS analyses. The results of GC and GC-MS analyses for the extracted organic matter (EOM) showed that all samples have been severely undergone a biodegradation process. However, the GC-MS data have displayed a little variation among the samples, which may be due to degree/type of biodegradation and the type of microbial activity. Triterpane biomarkers are present in low amounts, and steranes in even lesser amounts. Source and maturity assessments from both biomarkers are limited due to the lack of peaks by advanced biodegradation. The demethylated hopanes, which are typical of biodegraded oils, are not seen in these samples but they are apparently not unusual for the Athabasca tar sands, probably due to the specific type of post-emplacement microbial activity. Triterpanes biomarkers illustrate that a highly anoxic hypersaline source environment has contributed to the original oils, at the same time having anoxic marine carbonate/marl character. There is also tenuous evidence for a post-Triassic source according to the tricyclic terpane ratios. The steranes similarly indicate a marine, possibly carbonate-influenced source. Some of the aromatic compounds could also indicate a marine and anoxic hypersaline sourcing. The available peak ratios and patterns of EOM by GC-MS suggest high maturity, and aromatic parameters infer condensate window level with a vitrinite reflectance equivalent range of ∼0.9–1.2%. This could explain the remaining relatively light n-alkanes in the saturated GC chromatograms.

Origin of Sangumburi, Jeju Island

천연기념물 제63호로 지정된 산굼부리 분화구은 기존 마르형 분화구로 인식되었지만, 새로운 정밀지질도 작성과 함께 야외에서의 지질학적 특징들이 산굼부리 분화구가 두 번에 걸친 화산활동으로 형성된 함몰분화구(pit crater)임을 지시한다. Stage 1 단계에서는 비현정질휘석현무암 I와 화산재와 래필리로 구성된 화성쇄설물 I가 동시에 형성되었고, stage 2 단계에서는 침상장석감람석현무암 형성 후 비현정질휘석현무암 II와 집괴암으로 구성된 화성쇄설물 II가 동시에 형성되었다. Stage 2의 침상장석감람석현무암을 Ar-Ar 연대측정 결과 산굼부리 함몰분화구는 7만3천 년 전에 형성되었다. 산굼부리 분화구는 함몰분화구(pit crater)임에도 불구하고 현재까지는 하부로 빠져나간 마그마의 방향을 알 수 없다.

A Petrological Study of the Mudeungsan Tuff Focused on Cheonwangbong and Anyangsan

Even though Mesozoic Mudeungsan tuff, located within Neungju Basin, has been named several rock names, it should be named as Mudeungsan tuff due to several evidences, such as fiamme, welded texture and rock fragments in the Mudeungsan tuff. Volcanic eruption boundary between the Cheonwangbong and Anyangsan areas is not clear, but petrochemical and mineral chemical evidences with different ages indicate clear petrological boundary between Cheonwangbong and Anyangsan. The Mudeungsan tuffs from Cheonwangbong and Anyangsan is welded crystal tuff with dacitic composition and were generated from cogenetic calc-alkaline magma in the volcanic arc environment. Geochemical events indicate that magma beneath Cheonwangbong was seems to have been evolved from the magma beneath Anyangsan due to fractional crystallization dominated by plagioclase.

Geochemical Characteristics of Devonian Bitumen Carbonates in Alberta, Canada

The objective of this study is to investigate inorganic characteristics of Devonian bitumen carbonates in Alberta using two drilling cores, Saleski 03-34-88-20w4 and Saleski 08-01-88-20w4, taken from the Core Research Center (CRC) of Canada. The bitumen carbonates are mainly composed of less than 0.2 mm dolomites and some carbonate includes small amount of quartz and calcite. The bitumen carbonates from two cores are interpreted to have formed in similar sedimentary environments and dolomitization processes. Carbonates from Saleski 03-34-88-20w4 core were formed under higher inflow of clastic sediment than those from Saleski 08-01-88-20w4 core. Range of crystallization temperature of dolomites in the both bitumen carbonate cores is about 40~. Dolomitizing fluid of the bitumen carbonates would be Devonian seawater. Bitumen carbonates from Cairn Formation, compared with the CRC cores, have experienced a similar crystallization temperature, but dolmititizing fluid of the bitumen carbonates from Cairn Formation have been modified from the isotopic exchange with continental crust.

Biodegradation characteristics of bitumen from the Upper Devonian carbonates (Grosmont and Nisku formations) in Alberta, Canada

In this study, we investigated the biodegradation processes of bitumen from the Upper Devonian carbonates (Grosmont and Nisku formations) in Alberta using GC and GC-MS analyses of four drilling cores. The analyzed samples contain notable rich extracted bitumen, which is predominantly composed of NSO and asphaltene compounds and has lesser amounts of saturated and aromatic hydrocarbons (HCs). The GC and GC-MS results for both saturated and aromatic HCs indicate that there are considerable variations among the samples, which are primarily attributed to the differences in the degree of biodegradation involving microbial activity. The sulfur content and its isotope values for the samples also support biodegradation. Three groups can be classified based on the biomarker distributions as follows: (1) in Group 1, C19-C25 tricyclic terpanes are most abundant, particularly the C23 compounds; (2) Group 2 has no C30-C35 αβ hopanes and more abundant 25-norhopanes than the other two groups; and (3) Group 3 is similar to Group 1, but generally has less abundant C19-C25 tricyclic terpanes than Group 1. The reservoir alteration processes have notably influenced the biomarker properties of the samples. The most pronounced effects are the reduction of the amounts of C30+ hopanes and increasing demethylated hopanes, particularly in Groups 1 and 2, but not in Group 3. For Group 3, unlike Group 1, the degradation of hopanes apparently does not result in demethylated hopanes, indicating that there is another pathway to produce hopanes and/or destroy demethylated hopanes. These findings indicate that the biodegradation processes that occurred in the Grosmont and Nisku formations have been spatially and vertically varied due to the different environmental conditions and microbial processes.

Li isotopic disequilibrium of the Cenozoic subcontinental lithospheric mantle in East Asia

Mantle-derived spinel peridotite xenoliths, enclosed in alkali basalt and dating between 18.9 Ma and <1.2 Ma occur in southwestern Japan (On-yama and Arato-yama), South Korea (Baegryeong Island, Asan and Pyeongtaeg, Boeun, Jeju Island, and Goseong), and eastern China (Qixia and Nushan). Sample locations were specifically selected to evaluate spatial differences in lithium (Li) isotopes in the spinel peridotite xenoliths, which have undergone both enrichment and depletion processes under mantle conditions. Li concentrations and isotopic compositions of coexisting olivine, orthopyroxene, and clinopyroxene in the spinel peridotite xenoliths from these units reveal both elemental and isotopic disequilibrium. The observed Li isotopic disequilibrium between xenolith minerals may reflect fractional infiltration of Li isotopic compositions from the host magma by later metasomatism during transport from the mantle to the surface.