Geosciences Journal最新文献

The Nari Caldera on Ulleung Island, an oceanic intraplate volcano, is a significant repository of information on the latest volcanic activity. To interpret the characteristics of the latest volcanic activity, it is essential to understand the caldera structures formed by the most explosive eruption of the Ulleung volcanic edifice. This study presents a three-dimensional (3-D) resistivity model based on audio-magnetotelluric (AMT) data and interprets the caldera structure of Ulleung Island. New land and ocean terrain models were used for the 3-D inversion of the AMT data, and a finer, nonuniform grid was generated for the caldera area. Subsequently, 3-D inversion and imaging were conducted on the AMT data at 25 stations. In the caldera area of Ulleung Island, the 3-D resistivity model is divided into two bodies: a high resistivity body located in the south and a low resistivity body located in the north. This structure is consistent with the location of the two calderas, Seongin Caldera and Nari Caldera, as inferred from geological studies. Furthermore, the high resistivity body located in the south exhibited a bowl shape in the 3-D space. Therefore, we suggest that the high resistivity body located south of the caldera on Ulleung Island is a structure of the Seongin Caldera. The Seongin Caldera has a diameter of approximately 1.5 km and a caldera fill height of approximately 0.8 km, as measured from the resistivity model. Based on the stratigraphy of Ulleung Island and the physical properties of the rock types, the interior of the Seongin Caldera was considered to have been filled with trachytic lavas of the Seonginbong Group. From the high geothermal gradient of Ulleung Island and the stratigraphy of the GH-4 borehole, the low resistivity body extending from the shallow depths of the Nari Caldera to the lower part of the Seongin Caldera could be interpreted as trachytic rocks that underwent hydrothermal alteration. In addition, a low resistivity body contains highly porous and/or weathered rock. This study presents information on the calderas of Ulleung Island that can aid in interpreting the characteristics of the latest volcanic activity. We expect this information to contribute to the preparation for potential volcanic hazards.

The Suwolbong tuff ring is a basaltic monogenetic volcano in the Quaternary intraplate volcanic field of Jeju Island, Korea. The tuff ring was formerly interpreted to have had a congested magma plumbing system consisting of multiply-sourced dike complexes, based on stepped and mixed chemical trends of alkaline to sub-alkaline glassy pyroclasts. Microscopic observations, petrological analysis, and componentry analysis of the glassy pyroclasts reveal, however, that some of the glassy pyroclasts in the tuff ring are accidental and inappropriate for interpreting magmatic processes. Juvenile particles are vesicular, alkaline in composition, mainly contain olivine, clinopyroxene, and plagioclase phenocrysts, and comprise about 35 vol% of the deposits. In contrast, accidental particles are non-vesicular, alkaline to subalkaline in composition, less abundant (avg. 8 vol%), and show alteration rims. The accidental particles are interpreted to have been derived from the volcaniclastic layers deposited before the eruption of the Suwolbong tuff ring. When removing the effects of the accidental particles and considering only the geochemical characteristics of the newly defined juvenile particles, the Suwolbong tuff ring is interpreted to have had a rather simple, not necessarily congested, plumbing system fed by independently ascending multiple magma batches. This study shows that the interpretation of the properties of the source magma and the magma plumbing system in monogenetic volcanoes must be performed after clearly distinguishing between juvenile and accidental particles based on rigorous microscopic analysis of pyroclastic materials.

On January 7, 2022, a Mw 6.6 earthquake occurred in Menyuan County, Qinghai Province, China. To understand the coseismic deformation mechanism of this earthquake, we utilized GNSS and InSAR geodetic observations to obtain the coseismic deformation field and inverted for the slip distributions of different fault models. Through a comparative analysis of the coseismic slip distribution characteristics of different fault models and fitting degree of observations, we proposed the relatively optimal fault model. The coseismic deformation results of two types of observations consistently show a dominant horizontal strike-slip motion for this earthquake. The deformation characteristics of the coseismic LOS displacement profile model, considering the fault dip angle and slip amount, indicate that the coseismic slip is concentrated in the shallow portion, with a maximum slip of 3.29 m at a depth of 1.31 km. The inversion results of the optimal fault model proposed in this study indicate that compared to the surface trace of the Lenglongling fault, the surface trace of the eastern section of the primary fault is deflected by 9.28°, with a length of approximately 14 km, and the western section extends westward approximately 9 km along the Lenglongling fault. In the strike-change area between the Lenglongling fault and the Tuolaishan fault, the secondary fault connects the primary fault and extends westward along the Tuolaishan fault for approximately 8 km. The primary fault corresponds to the Lenglongling fault, with a maximum slip of 4.28 m, and the secondary fault corresponds to the Tuolaishan fault, with a maximum slip of 2.44 m.

Monitoring active volcanoes is necessary to analyze their current status to pose a mitigation hazard. Mount Melbourne is an active volcano that has erupted in the past, and future eruptions are possible. This condition could threaten future eruptions, particularly near scientific bases. Jang Bogo, a South Korean research station, is located only 30 km from the summit and could be affected by significant ash fallout in case of an explosive eruption. This condition leads to the necessity of observing Mount Melbourne’s activity frequently. This study used Sentinel-1 SAR data acquired from 2017 to 2024 to monitor the volcanic activity of Mount Melbourne by utilizing InSAR multitemporal time-series analysis implementing the improved combined scatterers interferometry with optimized point scatterers (ICOPS) method. The ICOPS method combined persistent scatterer (PS) and distributed scatterer (DS) with measurement point (MP) optimization based on convolutional neural network (CNN) and optimized hot spot analysis (OHSA). The ICOPS measurement results maintain reliable MP along the Mount Melbourne summit and around Jang Bogo station. The absence of GPS stations around these two areas makes it difficult to validate the result with the ground truth measurement, so the comparison with another method, small baseline (SBAS) measurement, is made to evaluate the reliability of the ICOPS measurement points. The comparison between the MP from ICOPS and the SBAS methods shows a good correlation with R² of about 0.8134 in the Melbourne area and 0.8678 in the Jang Bogo area. The selected time-series plot around the summit of Mount Melbourne and the Jang Bogo area shows a stable trend of surface deformation. Thus, a total accumulated deformation of around 0.82 cm and an average deformation of about 0.10 cm/year was found around Mount Melbourne. Meanwhile, the Jang Bogo area exhibits a total deformation of about 0.15 cm with an average deformation of about 0.02. Overall, this research is a preliminary study of the ability of the ICOPS algorithm to monitor volcanic activity in snow-covered areas.

We present the results of seismic profiling aimed to characterize the structure of shallow formation in the Geoncheon Valley (GCV), an area we interpreted as the north tip of the Miryang Fault This profile was deployed in the GCV, near the City of Gyeongju, Republic of Korea. The Miryang Fault is one of the major faults of the Yangsan Fault System in the Cretaceous Gyeongsang Basin, the southeastern Korean Peninsula. Despite local earthquake records showing scattered micro-seismicity along the trace of Miryang Fault, other geophysical and geological information is rare. The location of the GCV is tectonically critical: it is on the major stratigraphic boundary in the Cretaceous Gyeongsang Basin: the Hayang Group (dominantly sedimentary rocks) to the north and Yucheon Group (volcanic and volcanoclastic rocks) to the south. The surface expression of the Miryang Fault in this area is difficult to define by geomorphology since the surface is covered by highly altered cultivated farmlands. We tackle this problem by conducting seismic profiling. On a 1,200-m long linear profile, we deployed a dense array using 3-component seismic sensors and acquired both passive and active seismic data. The passive seismic data acquisition lasted about 12 days. At the end of the deployment period directly before withdrawing the array, an active survey using a sledgehammer source was also conducted. The integrated seismic cross-section displays significant segmentation in the texture of the seismic image, the sediment-bedrock interface is between less than 10 meters to slightly greater than 20 meters with a general trend of dipping to the southeast. The preliminary seismic results suggest that it is likely the Miryang Fault terminates inside the GCV, and the type of tip damage zone appears to be a group of horsetail splays.

CO₂ flux measurements and soil gas samples were collected to determine the origin and distribution characteristics of soil gas discharged at Andeok area, Jeju, South Korea. Additionally, this study aims to discuss agricultural activities that may contribute to increased soil CO₂ emissions. CO₂ flux was measured at 127 points, while soil gas sampling for gas components and carbon-13 (δ¹³C_CO2) analysis was performed at 56 points. The measured CO₂ fluxes in the study area ranged from 0.8 to 83.8 g/m²/d (mean: 14.3 g/m²/d), which was lower than CO₂ fluxes observed in areas with geogenic CO₂ discharge (e.g., near active volcanoes, faults, and CO₂-rich water sources). The soil gas analysis revealed that the CO₂ concentration and δ¹³C_CO2 ranged from 491 to 23,722 ppmv (mean: 3,205 ppmv) and from −25.2 to −10.7‰ (mean: −19.4‰), respectively. In the cumulative probability diagram, the threshold values for CO₂ flux and soil CO₂ concentration were 41.3 g/m²/d and 6,693 ppmv, respectively. Samples exceeding the CO₂ flux threshold were affected by urea fertilizer application based on land use nearby, and did not overlay with samples exceeding the soil CO₂ threshold, indicating different transport mechanisms. Results from a detailed survey near a soil gas sampling location close to high soil CO₂ showed that soil CO₂ concentrations increased with depth, especially during summer when atmospheric temperatures increased. Spatially, higher soil CO₂ concentrations were observed in areas with accumulated plant debris from tangerine orchards. The δ¹³C_CO2 and relationships among CO₂-O₂, N₂-CO₂, and N₂/O₂-CO₂ indicated that all collected samples had a biogenic origin. Although geogenic soil gases were not observed in this study, our findings are useful for future research on Jeju Island, as they provide baseline values for distinguishing geogenic soil gas from those with natural and agricultural origins. Moreover, this result provides insights into agricultural activities such as urea fertilization and plowing and their contribution to soil CO₂ increase, and inspires future research on negative soil CO₂ flux.

The scientific question of precisely determining the northern boundary of the Qinling Orogenic Belt (QOB) with regard to the southern segment of the North China Craton (S-NCC) has been controversial and unresolved, as it is heavily covered by loess and lacks some geological evidence. In order to identify the concrete northern boundary of the QOB, this paper first reports the metabasalt discovered in the Qianhe River Basin in Northwestern China, on the foundation of petrography, mineralogy, geochronology and geochemistry analyses. Detailed regional geological survey presents that the Qianhe metabasalt (QMB) is in unconformable contact with the Mesoproterozoic Gaoshanhe Group. Moreover, there is the new laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS) U-Pb dating for magmatic zircons that yielded a weighted mean age of 450 ± 9 Ma, revealing that the QMB occurred in the Late Ordovician rather than that in the Mesoproterozoic period as previously considered. Both major and trace elements show that the samples are characterized by the back-arc basin (BAB) basalt affinity. In addition, combined with the regional geology analysis, it stands to reason that the QMB is very similar to those of Ordovician Caotangou Group along the northern QOB (N-QOB). Accordingly, it is illuminated that the QMB belonging to the N-QOB, is more likely originated from the back-arc basin setting, and truly defines the QOB’s northern boundary in this segment, which has prominent geoscientific significance for determining the tectonic boundary in the heavily loess-covered regions.

The increasing global demand for Mn necessitates cost-effective recovery methods applicable to low- and medium-grade ores. Reductive bioleaching has emerged as a promising technique for Mn extraction from low-grade ores. This study aimed to simultaneously bioleach both Cu and Mn from low-grade ore obtained from Boleo, Mexico, using Acidithiobacillus thiooxidans. Additionally, the influence of activated coffee charcoal on the leaching process was examined. The biotic samples exhibited significantly higher Cu (70.6–71.9%) and Mn (78.8–82.2%) extraction compared to abiotic samples (41.7% Cu and 2.7% Mn). The presence of activated coffee charcoal improves the extraction rate and leaching efficiency of Mn, but it does not significantly impact Cu bioleaching from low-grade ore. Additional experiments confirmed that sulfur oxidation by A. thiooxidans played a significant role in Mn dissolution. A. thiooxidans oxidizes elemental sulfur, and during this process, Mn undergoes reduction either through enzymatic or non-enzymatic pathways. After the bioleaching process, the majority of Cu and Mn in the aqueous phase, and Cu and Mn within the residual ore can also be easily leached in a weak acid environment. This study demonstrates the applicability of simultaneous bioleaching without the necessity of an additional chemically reducing agent, effectively contributing to metal extraction practices. Further optimization of operational parameters, including sulfur concentration and operation time, is necessary to enhance leaching efficiency before the scaling-up of the approach validated in the presented study.

The Yangsan Fault, a long-lived intracontinental fault in SE Korea, exhibits various slip behaviors, including coseismic slip and aseismic creep. However, there is insufficient knowledge of deformation microstructures to reveal the deformation mechanisms operating within the fault. In this study, we present an analysis of the mechanical behaviors displayed by the Byeokgye section of the Yangsan Fault over seismic cycles. Our results are based on detailed microscopic observations of drillcore samples recovered from the Byeokgye section, using an electron backscattered diffraction (EBSD) technique. In injected calcite veins located close to the principal slip zone (PSZ) of < 2 cm in width, plastic deformation (including dynamic recrystallization by subgrain rotation and deformation twins) is concentrated in the blocky calcite grains. In a narrow microbrecciated slip zone (< 1 cm wide) within the granitic damage zone, we observed mechanical Dauphiné twins associated with fractures and microfaults in quartz, as well as intergranular pressure solution (IPS) in the quartz fragments. Given that dynamic recrystallization and IPS are indicative of mechanical behavior of aseismic creep, it is possible that aseismic creep occurs upon the fault during interseismic periods. Conversely, the presence of mechanical Dauphiné twins, coupled with the nature of the PSZ, gouge injections, and the blocky structure of calcite veins, suggests the exposure of the fault section to local seismic stresses during coseismic slip. In conclusion, various deformation processes have operated upon the Yangsan Fault at the studied section throughout multiple seismic cycles. Furthermore, our study demonstrates that EBSD analysis is an effective technique for elucidating the mechanical behavior of fault zones.

This study investigates the relationship between olivine fabric transitions and seismic anisotropy in mantle shear zones, focusing on the Yugu peridotite body in the Korean Peninsula. Olivine, a key mineral in the upper mantle, influences seismic anisotropy through deformation fabrics. The Yugu peridotite body provides insights into these processes within mantle shear zones. Based on microstructures and olivine fabric transitions, this study categorizes peridotites into three groups (PM: proto-mylonite, M: mylonite, and UM: ultra-mylonite) and explores their seismic properties. The findings highlight a direct correlation between olivine fabric strength and seismic anisotropy. Group PM peridotites exhibited higher seismic anisotropy compared to those in Group M and UM peridotites. This study emphasizes that variations in seismic anisotropy within mantle shear zones are primarily driven by the strength of olivine fabric, with additional influences from fabric type and rock composition. The calculated anisotropic layer thickness supports the observation that seismic anisotropy is significantly larger away from the UM peridotites. These insights contribute to understanding of the complex interplay among olivine fabric, seismic anisotropy, and geological processes within mantle shear zones. The implications of this study extend to the improved interpretation of seismic data related to shear localization during peridotite exhumation.