이성근 Sung Keun Lee , 김진욱 Jin-wook Kim

DOI:10.22807/KJMP.2025.38.4.239 Vol.38(No.4) 239-242, 2025

이성록 Lee Sung-rock

DOI:10.22807/KJMP.2025.38.4.243 Vol.38(No.4) 243-248, 2025

Professor Kim Soo Jin, a pioneer and eternal mentor of modern Korean mineralogy, is honored for his brilliant achievements on the occasion of the 50th anniversary of the discovery of ‘Janggunite’ in 2025. In 1975, despite challenging research conditions, through persistent inquiry and in-depth study during his time in Germany, he discovered ‘Janggunite,’ Korea’s first new mineral, and gained international recognition, thereby elevating the status of Korean mineralogy. Dedicated to research and education for 36 years, Professor Kim not only nurtured numerous students through his commitment to mineralogical studies but also expanded academic horizons into fields such as environmental mineralogy and the conservation of stone cultural heritage, contributing to the resolution of societal issues. Furthermore, he founded the Mineralogical Society of Korea and served as its first president, and also served as vice-chair of the National Academy of Sciences of the Republic of Korea, laying a solid foundation for the development of Korean mineralogy through his outstanding leadership. Professor Kim Soo Jin’s life and accomplishments, characterized by his academic passion, gentle character, and profound legacy to our society, will continue to serve as inspiration and a guiding light for many future geologists.

장군석, 신종광물, 한국광물학회, 환경광물학, 석조문화유산, 대한민국학술원, Janggunite, Mineralogical Society of Korea, Environmental mineralogy, Stone culture heritage, National Academy of Sciences

신우창 Woochang Shin , 박규승 Gyuseung Park , 이범한 Bum Han Lee

DOI:10.22807/KJMP.2025.38.4.249 Vol.38(No.4) 249-262, 2025

This study evaluates the applicability of Micro-XRF analysis for investigating magmatic nickel-sulfide mineralization in the Andong Ultramafic Complex. Multi-element maps produced by Micro-XRF were used to estimate modal mineral proportions and document the spatial distribution of sulfide phases in wehrlite, olivine clinopyroxenite, orthopyroxenite, and a net-textured sulfide sample. Chromium reverse zoning in clinopyroxene was identified, suggesting processes such as localized magma recharge, magma mixing, or fluctuations in melt composition. We estimated a nickel tenor of approximately 7.5 wt% for the network-textured sulfide sample by integrating sulfide modal proportions derived from Micro-XRF with EPMA mineral compositions. This result supports the potential presence of magmatic nickel sulfide mineralization in the deeper portions of the Andong ultramafic complex. The results of this study demonstrate that Micro-XRF is a useful supplementary analytical technique for characterizing chemical heterogeneity within ultramafic rocks, interpreting sulfide concentration processes, and constraining nickel grade.

Micro-XRF, 초염기성암, 마그마성 니켈 황화물, 모달 분석, 니켈 테너, ultramafic rocks, magmatic nickel sulfide, modal analysis, nickel tenor

정혜정 Hye Jeong Jung , 이성근 Sung Keun Lee

DOI:10.22807/KJMP.2025.38.4.263 Vol.38(No.4) 263-273, 2025

Zinc (Zn) is among the key trace elements in igneous rocks and hydrothermal fluids and thus, traces differentiation of magmas, hydrothermal alterations, and other related geochemical processes. The characteristic behavior of Zn rises from the detailed network environments around Zn in silicate melts. Nevertheless, the Zn-driven modification of network structures and cation coordination environments (e.g., Al) in silicate melts remain to be extensively explored. In this study, ²⁷Al solid-state NMR spectroscopy was employed to analyze the atomic-scale structural variations in Zn-bearing multicomponent aluminosilicate glasses. ²⁷Al NMR results indicate that atomic environments around Al are significantly influenced by the chemistry of coexisting non-network-forming cations (Na⁺, Ca²⁺, Mg²⁺). The quadrupolar coupling constant (C_q) and the proportion of [5]Al tend to increase with increasing average cation field strength of non-network formers. The results indicate that Zn acts as a network modifier, whereas coexisting Ca and Na act as a charge balancer in proximity to Al. The prominent difference in ionic radii between Zn and Na leads to an ordered Zn-Na configuration near non-bridging oxygen (NBO). This ordering is expected to enhance Zn diffusivity, leading to a lighter Zn isotopic composition. While the effect is less pronounced, Ca exhibits behavior similar to Na. Finally, while the field strengths of Mg and Zn are similar, an addition of Zn induces larger structural disorder in silicate melts, though the effect of larger composition variation needs to be considered. Such structural characteristics provide an atomic basis for the mobility, isotope concentration of Zn, and its enrichment in complex magmatic melts.

아연을 함유한 비정질규산염, 아연의 마그마 내 거동, ²⁷Al NMR, 비정질 마그마의 원자 구조, Zinc-bearing silicates melts, Zinc behavior in silicate magmas, ²⁷Al NMR, Atomic structure of magmas

권희원 Hee Won Kwon , 김영훈 Young Hun Kim , 김정진 Jeong Jin Kim

DOI:10.22807/KJMP.2025.38.4.275 Vol.38(No.4) 275-285, 2025

This study investigates the characteristics of turbidity generation associated with different rock types in the upper watershed of the Imha Dam. The study areas include the Banbyeon River basin in Yeongyang, where basalt and shale are distributed, and the Yongjeon River basin in Cheongsong, which mainly consists of granite and sandstone. Mountain and farmland soils were collected from each lithological unit and analyzed for turbidity, particle-size distribution, and clay mineral composition. X-ray diffraction (XRD) analysis revealed that chlorite and illite are the dominant clay minerals in the Banbyeon River basin samples, whereas illite and kaolinite are predominant in the Yongjeon River basin. Turbidity measurements showed that initial turbidity ranged from 6,560 to 13,680 NTU, with more than a 95% reduction observed after five days in most samples. These findings provide mineralogical insights into how variations in clay-mineral composition and particle-size characteristics, governed by rock type and weathering conditions, influence the generation and persistence of turbidity.

임하댐, 탁수, 반변천, 용전천, 밭토양, Imha Dam, turbidity, Banbyeon River, Yongjeon River, farmland soil

권기덕 Kideok D. Kwon

DOI:10.22807/KJMP.2025.38.4.287 Vol.38(No.4) 287-294, 2025

Feitknechtite (β-MnOOH) is a metastable layered manganese oxyhydroxide that commonly forms during Mn(II) oxidation in aqueous systems. Despite being frequently observed in diverse Mn redox reactions, the detailed crystal structure of feitknechtite, particularly stacking modes of Mn octahedral sheets and hydrogen atom positions, remains incompletely resolved. This study presents a structural analysis of feitknechtite using quantum mechanical density functional theory calculations. Our calculated lattice parameters for feitknechtite show excellent agreement with recent synchrotron-based experimental observations. Nudged elastic band calculations estimated an interlayer hydrogen diffusion barrier of 113 meV between Mn octahedral sheets, indicating dynamic hydrogen disorder under ambient temperature. These findings provide critical insight into the redox reactivity of feitknechtite through proton-coupled electron transfer mechanisms. The newly proposed phase, ε-MnOOH, which coprecipitates with feitknechtite, is predicted to adopt a feitknechtite-like stacking mode of Mn octahedral sheets, rather than the pyrochroite-like stacking previously suggested. Our results refine the understanding of MnOOH polymorph crystal structures and contribute to elucidating manganese redox mechanisms involved in metastable phases.

페이크네타이트, 수소 동적 무질서, rSCAN, NEB 계산, MnOOH, Feitknechtite, Hydrogen dynamic disorder, NEB calculations

정기영 Gi Young Jeong

DOI:10.22807/KJMP.2025.38.4.295 Vol.38(No.4) 295-305, 2025

Halloysite is a common kaolin mineral formed in the weathering zones of silicate rocks and sediments, but its recognition has been relatively limited compared to that of kaolinite. Based on a comprehensive review of X-ray diffraction (XRD) data and scanning and transmission electron microscopic analyses of bulk samples and thin sections from Korean weathering profiles, halloysite was confirmed as a major kaolin mineral in a wide range of geological environments. In the weathering of anorthosite, granite, gneiss, and basalt, plagioclase acts as the most important parent mineral, and halloysite aggregates develop along microfractures and cleavages, forming a characteristic porous boxwork structure following plagioclase dissolution. In porous gravel deposits, plagioclase in gravels is weathered and pore spaces between gravels are filled with halloysite. In muddy sand deposits, part of the ultra-fine illite in the matrix is transformed into halloysite. In volcanic environments, volcanic glass is altered to spherical or platy halloysite associated with amorphous materials. Halloysite occurs in various morphologies and is naturally present as the hydrated 10 A form, but its facile dehydration makes mineral identification difficult. However, when carefully distinguished from kaolinite through detailed mineralogical analyses, halloysite can provide important insights into elemental migration and phase transformations within weathering zones, which represent key boundaries in Earth’s material cycles.

할로이사이트, 카올리나이트, 사장석, 화산유리, 풍화, Halloysite, kaolinite, plagioclase, volcanic glass, weathering

Sung Pil Hyun

DOI:10.22807/KJMP.2025.38.4.307 Vol.38(No.4) 307-320, 2025

Chemical weathering of silicate minerals constitutes one of Earth's most significant long-term sinks for atmospheric CO₂. In the Hadong-Sancheong region of southern Korea, Proterozoic anorthosite bodies have undergone extensive in-situ weathering to residual kaolin deposits dominated by halloysite and kaolinite. Because the parent rock is composed almost entirely of Ca-rich plagioclase (labradorite-bytownite), these deposits provide a rare natural archive of CO₂ consumption associated with plagioclase weathering. The exceptional preservation of pseudomorphic plagioclase textures, the prevalence of halloysite in well-drained zones, and the transition to kaolinite in more equilibrated horizons collectively record the environmental mineralogical pathways by which CO₂-charged meteoric waters transformed the regolith. Integrating field observations with detailed clay mineralogy from the literature, together with mass-balance calculations based on the labradorite-to-halloysite reaction, we estimate that approximately 2.6×10⁷ to 3.7×10⁷ t CO₂ have been consumed over the lifetime of the weathering profile, with a broader plausible range of 1.4×10- to 8.4×10⁸ t CO₂. When averaged over geological timescales, the corresponding natural CO₂ uptake rates are modest - on the order of 0.3 to 17 t CO₂ yr-¹ - reflecting the inherently slow dissolution of plagioclase yet allowing exceptional preservation of the mineralogical record of weathering. These findings underscore the central role of calcic plagioclase weathering as a robust long-term carbon regulator of atmospheric CO₂ and suggest that anorthosite could be an effective candidate for enhanced weathering applications in engineered CO₂ removal.

anorthosite weathering, kaolin deposits, plagioclase, halloysite, CO₂ removal

Sang Soo Lee , Changyong Park , Paul Fenter

DOI:10.22807/KJMP.2025.38.4.321 Vol.38(No.4) 321-333, 2025

Mineral-water interfaces mediate adsorption, ion exchange, and secondary mineral formation that control elemental mobility in natural and engineered systems. Reliable prediction and control of these processes require a fundamental understanding of the interfacial structure that links adsorbed ion speciation to macroscopic sorption capacity and strength. Here, we determine atomic-scale changes in the hydration and distribution of Ni(II) at the muscovite mica (001)-water interface using in situ high-resolution X-ray reflectivity (XR) and resonant anomalous X-ray reflectivity (RAXR) in a 1 mM NiCl₂ solution at pH 5.7. XR reveals reorganization of the primary hydration structure relative to that in deionized water: the water layer adsorbed in the cavity sites at a height of ∼1.3 Å disappears, while distinct solution layers emerge at ∼2.3, ∼4.1, and ∼5.6 Å above the basal oxygen plane. RAXR resolves three interfacial Ni(II) species: a dominant outer-sphere complex at ∼3.65 Å (∼80% of the total coverage), a minor inner-sphere complex at ∼0.75 Å, and a low-coverage, more distant outer-sphere species at ∼5.63 Å. These three adsorbed Ni(II) species account for a total Ni(II) coverage of 0.54 ± 0.02 ion per unit cell area that compensates for the surface charge. These results highlight the role of interfacial hydration in controlling the speciation and stability of adsorbate cations on the negatively charged mica surface, providing quantitative insight into predicting the geochemical behavior of divalent metal cations in the aqueous environments.

Critical-element adsorption, Adsorbed cation speciation, Hydration energy, Muscovite mica

권진중 Jin Jung Kweon , 이성근 Sung Keun Lee

DOI:10.22807/KJMP.2025.38.4.335 Vol.38(No.4) 335-343, 2025

Abstract: Corundum (α-Al₂O₃) is an end-member mineral composed of aluminum and oxygen, the primary constituents of the earth’s crust and mantle. It is geologically and industrially significant and has diverse applications in catalysts, batteries, and other fields. When corundum is mechanically deformed, its atomic structure evolves and undergoes phase transitions. The structural changes enable atomic inference of diverse processes at the Earth’s surface and deep within planets. In this study, we experimentally elucidated the detailed changes in the lattice structures of corundum and those accompanying phases undergoing deformation. As the deformation duration (10 and 60 min) increases, the crystallinity of corundum gradually decreased, and noticeable amorphization was observed. Specifically, the ²⁷Al solid-state nuclear magnetic resonance (solid-state NMR) spectra of corundum undergoing such deformation show an increase in the fractions of ^[4]Al and ^[5]Al coordination environments with amorphization. We also examined the role of fluids involved during deformation and phase transitions. The presence of water tends to suppress the formation of ^[4]Al and ^[5]Al during amorphization. To further quantify the deformation-induced changes in the atomic structures, more extensive experimental results under a wider range of deformation duration and fluids contents are required. Nevertheless, current preliminary experimental results with α-Al₂O₃ contribute to establishing a simple atomistic mechanism for deformation processes of complex planetary materials.

강옥, 기계적 변형, 결정도, 강옥의 비정질화, Al 배위수, corundum, mechanical deformation, crystallinity, amorphization of corundum, Al coordination number

김용현 Yong-hyun Kim , 이성근 Sung Keun Lee

DOI:10.22807/KJMP.2025.38.4.345 Vol.38(No.4) 345-353, 2025

Amorphous oxides under extreme pressures relevant to planetary interiors are characterized by the formation of dense atomic structures, involving gradual increases in coordination numbers. Pressure-driven structural transitions for amorphous oxides control magma density, isotopic fractionation, thermal conductivity, or viscosity, thereby affecting the evolution of planetary interiors. Despite the importance, experimental probing of atomic structures of planetary magmas under extreme compression remains a challenge. X-ray Raman scattering provides a unique opportunity to access the electronic structures of amorphous oxides at high pressure. In this study, Si L_2,3-edge X-ray Raman scattering spectra reveal the electronic transitions in SiO₂ glass at high pressure. The similarities of the Si L_2,3-edge and O K-edge spectral features for SiO₂ crystals and glasses suggest a close structural resemblance. The Si L_2,3-edge spectra display peaks from the s- and d-orbitals of silicon in the conduction bands. Each spectral feature shows distinct pressure-driven changes, where the peak at∼130 eV exhibits pronounced changes in peak position and width. Notably, the spectral width initially decreases with increasing pressure, while above∼50 GPa, starts to increase with increasing pressures up to∼124 GPa. Such trends are closely related to the changes in the Si-O bond length at high pressures. Current results highlight the unique capability of X-ray Raman scattering in probing the Si coordination environments and polyhedral Si-O bond lengths of amorphous silicate networks under compression, offering valuable insights into the magma density and viscosity of planetary mantle magmas.

SiO₂ 유리, 행성 내부, 고압 환경, 전자 구조, X-선 라만 산란, SiO₂ glass, planetary interiors, high pressure, electronic structure, X-ray Raman scattering

방윤아 Yoonah Bang , Ana Maria Fernandez , 류지훈 Ji-hun Ryu

DOI:10.22807/KJMP.2025.38.4.355 Vol.38(No.4) 355-369, 2025

Bentonite, primarily consisting of montmorillonite, plays a crucial role as a key component of the engineering barrier in deep geological repositories (DGR). Bentonites take advantage of their swelling, adsorption, ion exchange, and water retention capacities, fulfilling the role of a buffer to physically and chemically isolate high-level waste disposal facilities from the surrounding environment. To ensure the long-term safety of disposal systems over hundreds of thousands of years, fundamental scientific investigation of bentonite under conditions analogous to natural environments is essential. As part of a natural analogue study, this work aims to compare and analyze the mineralogical characteristics of bentonite rock samples collected from two natural deposits: Jianping Xian, Chaoyang Shi, Liaoning Sheng, China (W-B sample), and Yeongnam, Gyeongju, Gyeongsangbuk-do, Korea (NA-B sample). In this study, we conducted X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), X-ray fluorescence (XRF), and iron oxidation state analysis. Both samples were found to contain dioctahedral montmorillonite as the major phase. Illite and carbonate minerals were additionally observed in the W-B sample. Thermal analysis showed cis-vacant structure in the NA-B sample, whereas the W-B sample exhibited additional peaks attributed to decomposition of illite/smectite mixed-layer clay and carbonate. The iron oxidation state in both samples was dominated by Fe(III), with the W-B sample exhibiting a higher total iron content. Chemical formulae derived from EDS data showed that both samples have typical smectite compositions and can be classified as montmorillonite. The findings of this study, focusing on bentonite collected from natural deposits, are expected to provide fundamental data for understanding changes in the characteristics of bentonite in DGR over geological time.

벤토나이트, 자연유사, 몬모릴로나이트, 심층처분시스템, Bentonite, Natural analogue, Montmorillonite, Deep geological repository

도진영 Jin Young Do

DOI:10.22807/KJMP.2025.38.4.371 Vol.38(No.4) 371-383, 2025

This study investigates the provenance and material characteristics of zeolite (Bulseok) Buddha statues from the late Joseon Dynasty and evaluates the applicability of conservation treatments. Field surveys and historical records indicate that the source rocks are zeolitic tuffs from the Tertiary Beomgokri Group (Waeupri and Yongdongri Tuffs) in the Gyeongju area. Geochemical and mineralogical analyses confirmed that the statues and source rocks share similar characteristics, primarily composed of clinoptilolite. Experimental results on consolidation showed that ethyl silicate-based consolidant (Silres BS OH 100) significantly improved physical properties, increasing compressive strength by 21-45 % and reducing water absorption by approximately 97 %. However, since some source rocks contain swelling clay minerals like smectite, mineralogical analysis must precede consolidation to avoid secondary damage caused by swelling. For adhesion, epoxy resin (L30) without fillers demonstrated superior bonding strength and structural stability compared to filler-mixed resins. This study suggests that while Gyeongju zeolitic tuff is a suitable replacement material for restoration, a scientific diagnostic process considering mineral composition is essential for the conservation of zeolite Buddha statues.

불석질 응회암, 불석제 불상, 산지, 에틸실리케이트 강화제, 에폭시수지, Zeolitic tuff, Buddha statue made of Bulseok, Provenance, Ethylsilicate consolidant, Epoxy resin

곽경윤 Kyeong Yoon Kwak , 강정원 Jeongwon Kang , 장석 Seok Jang , 금병철 Byung-cheol Kum , 구효진 Hyo Jin Koo

DOI:10.22807/KJMP.2025.38.4.385 Vol.38(No.4) 385-394, 2025

This study quantitatively evaluates how amorphous content and grain-size variation in marine sediments influence the X-ray diffraction (XRD) pattern of an internal standard. To achieve this, crystalline calcite (CaCO₃) and amorphous silica (SiO₂) were mixed in various proportions, and 20 wt.% corundum was added as an internal standard prior to XRD analysis. The results show that the height of the amorphous hump in the 15-30° 2θ range gradually increases with increasing amorphous content. Both the intensity and area of the corundum (104) peak increase proportionally with the amorphous fraction, and a strong correlation was observed between the hump height and the corundum (104) peak intensity (R² = 0.9738). In addition, the corundum (104) peak area and intensity exhibit an excellent linear relationship (R² = 0.9966). These findings indicate that the intensity ratio between the amorphous signal and the corundum (104) peak (Amorphous/Corundum (104) peak intensity ratio) serves as a reliable proxy for quantifying amorphous phases. Grain-size-fraction analyses of marine sediment-corundum mixtures further show that the area of the corundum (104) peak is lowest in the sand fraction and highest in the clay fraction, indicating preferential concentration of amorphous material in finer particles. However, no meaningful correlation was found between the intensity and area of the corundum (104) peak in the natural sediment mixtures. Therefore, quantitative interpretation of XRD data for marine sediments requires simultaneous consideration of both amorphous content and grain-size distribution, and the presence and abundance of amorphous phases should ideally be verified through complementary chemical analyses. Collectively, these results highlight the importance of minimizing grain-size bias in amorphous-phase assessment and improving the reliability of XRD-based quantitative mineralogical analysis of marine sediments.

X-선 회절, 비정질, 내부표준물질, 강옥, 입도, X-ray diffracton, Amorphous, Internal standard, Corundum, Grain size

박한범 Hanbeom Park , 정재우 Jaewoo Jung , 양기호 Kiho Yang

DOI:10.22807/KJMP.2025.38.4.395 Vol.38(No.4) 395-403, 2025

We investigated ferromanganese crust and ferromanganese coating formed on skeletal surfaces of Porifera from the western Pacific Magellan Seamount Cluster, using multi-technique electron microscopic analyses to characterize their micro- to nanoscale mineral structures and chemical properties. The ferromanganese crust was subdivided into a non-phosphatized upper layer and a phosphatized lower layer based on macroscopic features and the presence or absence of phosphatization reported in previous studies, and these were compared in detail. Ferromanganese coated samples were prepared as cross-section using a focused ion beam and subsequently examined to describe their fine-scale structural characteristics. Transmission electron microscopy revealed distinct differences in elemental composition, including Fe and P contents, of vernadite occurring in each crust layer depending on the degree of phosphatization, as well as contrasting distributions of Fe oxidation states within the vernadite structure through electron energy loss spectroscopy analysis. In addition, ferromanganese coatings showed a characteristic association in which spherical Fe-oxide nanoparticles, 2-4 nm in diameter, are mixed with and aggregated around flaky and hairy vernadite. This study demonstrates that combined electron microscopy analysis provides integrative interpretation of the fine mineral structures, local microenvironments, and paleoenvironmental conditions recorded in ferromanganese crusts and ferromanganese coatings, and highlights the potential and advantages of this methodology for future studies of a wide range of geological materials.

주사전자현미경, 투과전자현미경, 마젤란해저산군, 망가니즈각, 생물골격구조, SEM, TEM, Magellan Seamount Cluster, Ferromanganese Crust, Porifera

박영규 Young Kyu Park , 박성준 Seongjun Park , 정재우 Jaewoo Jung

DOI:10.22807/KJMP.2025.38.4.405 Vol.38(No.4) 405-419, 2025

Deep Learning has recently become an important tool for solving problems in geology as Artificial Intelligence (AI). Geological research typically deals with large datasets and complex patterns. Deep learning algorithms applied to these challenges have substantially improved analytical accuracy and efficiency compared to traditional methods. In this study, we introduce development process of Deep Learning algorithms that can be applied in geology (problem definition and topic selection; data collection and refinement; algorithms model design and training; algorithms model optimization; deployment and interpretation). Furthermore, we introduce Deep Learning architectures and their applications in various geological fields, including mineral exploration, satellite image analysis and seismic waveform analysis. Overall, this study highlights the potential of deep learning to serve as a robust tool for understanding and predicting geological phenomena.

딥러닝, 지질학, AI, 지질 데이터 분석, 머신러닝, Deep learning, Geology, Geological data analysis, Machine learning

엄정현 Junghyun Um , 안웅산 Ung San Ahn , 이혁준 Hyukjun Lee , 박준현 Junhyun Park , 이혜은 Hyeeun Lee , 김효임 Hyo-im Kim

DOI:10.22807/KJMP.2025.38.4.421 Vol.38(No.4) 421-439, 2025

This study investigates the petrological, geochemical, and mineralogical characteristics of the Eoseungsaeng-1 drill core (ES core, 0-238 m) from the Jeju Volcanic Field (JVF), together with revealing the details of chemical zoning patterns of basaltic phenocrysts formed during different eruption stages that reflect the pre-eruptive magmatic processes. Based on the petrological observation and whole-rock geochemical data, the core was divided into three main stages: the upper Eoseungsaengak eruption stage (0-60 m), the middle basaltic shield-forming stage (63-163 m), and the lower trachybasaltic-trachyandesitic eruption stage (164-238 m). Among these stages, the basaltic shield-forming stage is characterized by the relatively primitive and homogeneous nature with MgO contents of∼8-11.5 wt%, indicating sustained magma recharge and mixing that maintained a primitive composition throughout the sequence. Here, we subdivided this stage into four thick lava flow units (Units 1-4). The current observations of the basaltic phenocrysts (i.e., olivine and clinopyroxene) exhibit the systematic variations in the size, abundance and chemical zoning patterns among eruption units. Olivine phenocrysts from the earlier eruption units [i.e., Units 1 (154 m) and 2 (141 and 125 m)] commonly show reverse zoning, with low-Mg cores (Fo∼74-75) and more Mg-rich rims (Fo∼81-83). Clinopyroxenes from these units similarly show the reverse zoning patterns, with En values increasing from∼74 in the core to∼85 at the rim. These textural characteristics indicate that the earlier eruption units in the basaltic shield-forming stage were formed by the recharge and mixing of Mg-rich primitive magma into a more evolved magma in the chamber. On the other hand, in Unit 3 (109 m), the upper unit of the basaltic forming stage, olivine phenocrysts are dominated by normal zoning, with Fo values decreasing continuously from Fo∼81 at the cores to∼65 at the rims. In addition, the clinopyroxene at 109 m present no distinct zoning with an equilibrium composition (En∼83), suggesting the phenocrysts are crystallized under the equilibrium conditions of primitive magma without significant recharge and mixing events. This study demonstrates that a detailed knowledge of chemical textures of phenocrysts is essential for reconstructing complex volcanic eruptions, and provides valuable information for further diffusion chronometry, which will contribute to obtaining quantitative constraints on the timescales of magma evolution.

제주 화산지대, 마그마 혼합, 누대구조, 광물 반정, 현무암질 순상 화산체, Jeju volcanic field, Magma mixing, Zoning pattern, Phenocrysts, Basaltic shield