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- A comparative study of 2D numerical simulations using vector and potential
methods for extending 3D modeling of planetary evolution-
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Abstract: Abstract Numerical simulations provide an improved understanding of the evolution and core formation processes of terrestrial bodies. The differentiation of silicate and iron metal has been simulated by solving the two-dimensional Stokes equation using either the vector or potential method. To describe the realistic geometry of planetesimals and planets, the development of a 3D model is necessary. Here, we developed a vector method model implemented in FEniCS project via scripting the weak forms of governing equations. Subsequently, we compared the solutions of the vector method models with those of the benchmark potential method implemented in Python. Three cases were modeled using the two methods and confirmed for consistency to verify the feasibility of developing a 3D model for core formation. Case 1 corresponds to planetary evolution triggered by impact heating in early terrestrial bodies with a homogeneous metal fraction. The vector method developed in the current study showed the consistency with the potential methods. In Case 2, the model mimicked a scenario depicting post-evolutionary impact heating by assuming heterogeneous metal fractions. The results of Case 2 simultaneously represent the behavior of the solid mixture based on the density contrast and multiphase flow of the solid matrix and metallic pores. The checkerboard test (Case 3) used to evaluate the resolution of the numerical model as a function of the heat source size also indicated identical spatial resolutions for both methods. In all cases, two methods simulated identical physical behaviors, indicating that a three-dimensional model can be developed using the vector method. The 2D FEM vector method developed in this study was effectively utilized to simulate the advection scheme, showing the fast descent of metal phases and relatively slower silicate phases. We extended the 2D FEM vector method to calculate the velocity fields of silicate, Darcy, and iron metal in a 3D model with an impact heating case (similar to Case 1). The 3D results show that the velocity of fluid metal in 3D model is faster than that in 2D model, suggesting the difference in the resistance to viscous flow depending the dimension of model. Our 3D vector method, implemented in FEniCS, demonstrates the numerical prospect of the methods necessary to model the multiphase fluid dynamics of a 3D planetary evolution.
PubDate: 2024-08-01
- Geochronology and geochemistry of the polyphase mafic rocks in the North
Liaohe Group, Jiao-Liao-Ji Belt, North China Craton: implications for
petrogenesis and tectonic evolution-
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Abstract: Abstract The Jiao-Liao-Ji Belt (JLJB) is one of the Paleoproterozoic orogenic belts within the North China Craton (NCC), whose tectonic evolution is still controversial due to multiple magmatic/metamorphic events after its formation. To tackle this controversy, we conducted petrological, geochronological, geochemical and zircon Hf isotopic studies for the meta-mafic rocks from the North Liaohe Group (NLG) in the central JLJB. 207Pb/206Pb weighted average ages of 1849 ± 36 Ma and 1853 ± 13 Ma indicate that the protoliths of the amphibolites in the Shisixian area formed at ca. 1.85 Ga. Geochemically, the amphibolites belong to tholeiitic series; while the meta-gabbros can be divided into the low-Ti and high-Ti types: the former belongs to calc-alkaline series, whereas the latter belongs to tholeiitic series. The high-Ti rocks are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs; e.g., Ba, K and Pb), and depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs; e.g., Nb, Ta, P and Ti). These rocks display slightly positive εHf(t) values (+1.40 to +2.02). The low-Ti meta-gabbros were most likely derived from the partial melting of the enriched lithospheric mantle in the spinel stability field, which was metasomatized by subduction-related fluids and/or melts with significant contamination of crustal material, while the amphibolites and high-Ti meta-gabbros were derived from partial melting of depleted asthenospheric mantle in the spinel stability field, which was metasomatized by limited subduction-related fluids and/or melts, coupled with fractional crystallization. The lithological and geochemical characteristics show that the low-Ti meta-gabbros formed in a magmatic arc environment, the high-Ti rocks formed in the later stage of a back-arc basin; while the amphibolites formed in a post-collisional extensional environment. Combined with literature data, we suggest that the JLJB experienced a process from subduction, collision, to extension: At ca. 2.2–2.1 Ga back-arc basin opened via southward subduction of an oceanic plate followed by northward subduction at ca. 2.1–1.91 Ga, and subsequently closed to form the JLJB at ca. 1.91 Ga, which led to the Longgang-Nangrim continental collision, and post-collision extension occurred at ca. 1.85 Ga along with the collapse of the collisional orogen.
PubDate: 2024-08-01
- Simultaneously leaching of copper and manganese from low-grade ore from
Boleo Mine by bacterial sulfur oxidation-
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Abstract: Abstract 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.
PubDate: 2024-08-01
- Seismic anisotropies of the Yugu peridotites (Gyeonggi Massif, South
Korea) and their seismic implications in mantle shear zones-
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Abstract: Abstract 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.
PubDate: 2024-08-01
- Physical conditions for basaltic volcanism beneath the Jeju volcanic field
and the geodynamic implications-
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Abstract: Abstract The origin of the late Cenozoic intraplate volcanoes in the NE Asia has sparked debate, with explanations ranging from deep mantle plume to lithospheric extension and decompression melting of mantle upwelling by distal subduction tectonics. The Jeju volcanic field (JVF), being the closest late Cenozoic intraplate volcano to the subduction zone, sheds light on whether the intraplate volcanism is primarily plume-related or linked to plate tectonics. This study determined the primary magma composition for JVF basalts, using the most primitive bulk-rock samples (MgO > 8.5 wt%), by incrementally adding olivine to melt until reaching equilibrium with olivine (Mg# = 90) in the residual mantle. The estimated temperature and pressure of mantle melting are 1,466–1,587 °C and 2.1–4.1 GPa for anhydrous primary magma and 1,347–1,512 °C and 2.0–3.6 GPa for hydrous primary magma within the acceptable range of water contents (H2O = 2–4 wt%) reported from the Chinese intraplate basalts. The pressure estimates suggest that the minimal depth of the lithosphere-asthenosphere boundary is approximately ∼50–55 km. The mantle potential temperature for anhydrous primary magma is estimated to be 1,460–1,580 °C, higher than 1,300–1,400 °C of the ambient upper mantle, indicating a hot thermal regime below the JVF. Despite the absence of geophysical evidence for a mantle plume beneath the JVF, this study proposes that the hot mantle wedge is likely caused by the lateral influx or edge-driven convective upwelling of thermal plume near the leading edge of the stagnant Pacific Plate slab, contributing to the big mantle wedge. Intraplate volcanism in the JVF is proposed to be driven by lithospheric extension and decompression melting of the convective upwelling of hot sub-lithospheric mantle, influenced by distal subduction tectonics in the hot subduction zone. This model is supported by the present-day tectonics observed in the hot Ryukyu subduction zone, SW Japan.
PubDate: 2024-07-23
- Multi-archive record of late Quaternary paleoseismicity along the surface
projection of the 2017 Pohang earthquake seismogenic fault, SE Korea-
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Abstract: Abstract The 2017 Pohang earthquake (ML 5.4) ranks as the second-largest instrumental earthquake in the Korean Peninsula and the country’s most destructive seismic event. The earthquake history of the Pohang area prior to the 2017 event is unknown due to the absence of instrumental seismic activity and the lack of mapped Quaternary faults near the 2017 epicenter. The aim of the present study is to identify evidence for previous earthquake ruptures along the surface projection of the seismogenic fault and interpret their paleoseismic implications. The study involved comprehensive paleoseismological investigation, including geomorphic analysis, field-work, drillhole surveys, trench excavation, and numerical age dating. Geomorphic analysis and drillhole surveys revealed two lineaments presumed to have originated from Quaternary faulting: NNE-SSW-striking Fault-1 and NE-SW to NNE-SSW-striking Fault-2. At the excavation site of Fault-1, which is regarded as the seismogenic fault of the 2017 Pohang earthquake, stratigraphic features and numerical ages show that the penultimate event occurred between 11 ± 1 and 2.6 ± 0.1 ka and that the most recent event took place after 0.17 ± 0.01 ka. Combined results from two outcrops of Fault-2 give occurrence ages for the penultimate and most recent events of ca. 200 ka and between 148 ± 7 ka and the analytical limit of 14C dating (> 43,500 BP), respectively. Our findings reveal that at least three seismic events causing surface ruptures have occurred in the Pohang area during the late Quaternary before the 2017 Pohang earthquake.
PubDate: 2024-07-23
- Multi-scale analysis and paleoseismic investigations along the Geumwang
Fault: an example of integrated approach in paleoseismology in slow
tectonic region-
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Abstract: Abstract Paleoseismological research for a slowly deforming intraplate fault can provide essential information for understanding not only the spatiotemporal characteristics of past earthquakes but also seismic behavior in the case of long recurrence intervals. To reveal the paleoseismological properties and faulting processes of the intraplate fault, the Geumwang Fault Zone in the central Korean Peninsula, we conducted comprehensive paleoseismological investigations along the fault zone, incorporating geomorphological mapping with airborne light detection and ranging (LiDAR), electrical resistivity tomography (ERT), borehole drilling, trench excavation, optically stimulated luminescence (OSL) dating, and microstructural analysis. Along NE-SW-striking lineaments of the Geumwang Fault Zone, surface deformation is weakly recognized by LiDAR imagery in a damage zone along the northern section of the fault zone (Suha site). Results of ERT and borehole logging at the Suha site suggest a localized zone of low resistivity and unconformity level separation in sedimentary layers, respectively. A trench section excavated along the ERT traverse and borehole sites exposes a fault contact between granite and unconsolidated Quaternary strata comprising boulders (47 ± 3 ka), clayey sand (24 ± 2 ka), pebbly cobbles, coarse sand, and artificial layers from bottom to top. The < 5-cm-wide slip zone is oriented N09°E/85°NW and cuts the granite to the west and the boulder layer to the east. This slip zone that covered by the clayey sand stratum records an apparent vertical offset of ∼1.5 m and has sub-horizontal striations indicating dextral movement. Microstructures at the contact between the granite and the boulder layer support the occurrence of seismic slip propagation along the contact and include injected sedimentary materials, clay-clast aggregates, and fresh, open fractures in quartz and feldspar grains in the boulder layer. The slip zone consists of a < 4.5-cm-wide zone of cataclasite and a < 5-mm-wide principal slip zone (PSZ). Microstructures in the slip zone and sediments near the slip zone include seismic-slip indicators of pressurized gouge materials and fluid injection within PSZ, and deformed sediments. These reveal that the slip zone underwent repeated seismic slip events during uplift to the surface. Our paleoseismological analyses with microstructures show that the boulder layer was cut by strike-slip faulting with a minor vertical component between 47–24 ka, following which the overlying sediments were deposited along the exposed fault scarp as incision fill. The results show that microstructural observations can provide key information on the deformation of unconsolidated sediments and on the nature and timing of seismic faulting.
PubDate: 2024-07-18
- Morphology and development of volcanic hummock structures at the Jimibong
horseshoe scoria cone, Jeju Island, South Korea-
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Abstract: Abstract Jimibong is a north-facing horseshoe-shaped scoria cone in the northeast of Jeju Island that released lava flows to form a semicircular lava plateau. Sixty volcanic hummocks comprising scoria, spatter, and volcanic bombs are found on the lava plateau. The hummocks can be classified into Type 1 and Type 2 according to clast components, distance from the vent, and internal structure. Type 1 hummocks, distributed within approximately 1,000 m of the vent, comprise scoria deposits mixed with volcanic bombs and relatively few dykes that rise from the underlying lava. In contrast, Type 2 hummocks, distributed 1,000–1,300 m from the vent along the coast, comprise spatter/scoria and volcanic bomb deposits. The spatter/scoria of the Type 2 hummocks is highly agglutinated with abundant squeezing dykes that originated from the underlying lava and locally extruded over the hummocks. Although both the Type 1 and Type 2 hummocks comprise parts of the collapsed and rafted spatter/scoria blocks, their differences in shape, clast components, and structures are explained by changes in the eruption style (from spatter to scoria) and rheological changes in the lava with distance from the vent. Lava flows breached the cone following spatter-dominated eruptions in the early stages of Hawaiian eruption. Through this partial cone collapse, spatter blocks were transported with the lava flow away from the cone. The lava surface then cooled and hardened as the lava temperature decreased and viscosity increased. The contraction of the lava due to cooling caused the rafted cones to fragment into various sizes as they cracked, fractured, and rotated. Hot liquid lava from within the flow was squeezed-up because of the volcanic load of the rafted blocks, intruding into the fractures in the rafted blocks before locally flowing over them, creating the characteristic Type 2 hummocks. In contrast, Type 1 hummocks formed in the later stages of Strombolian activity, when scoria-dominant eruptions caused collapsed scoria blocks to be rafted with the lava flow. These scoria blocks were deposited in areas proximal to the cone and show few dyke intrusions due to the limiting effects of edifice load on dyke development. The Jimibong volcano provides an example of changing hummock structures in relation to changing eruption styles of scoria cones, deepening our understanding of the geomorphic development in volcanic regions.
PubDate: 2024-07-18
- Data and early results from temporary seismic arrays for monitoring and
investigating magmatic processes beneath Mt. Halla and Ulleung Island
volcanoes, South Korea-
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Abstract: Abstract Temporary seismic networks on Mt. Halla and Ulleung Island volcanoes were deployed, which employ broadband and geophone arrays to monitor potential volcanic activities and to estimate high-resolution magmatic structures beneath these volcanoes. The purpose of this paper is to introduce these networks and present early results through basic seismic analyses, suggesting the potential for future comprehensive seismological studies. The array in Mt. Halla volcano consists of five broadband sensors (JH array), and it has been operational around the Baengnokdam summit crater since October 2020. There was an additional linear geophone array (HL array) installed in September 2021 for detailed shallow subsurface imaging. Ulleung Island volcano had been under observation for two years since June 2021 with a network of nine broadband sensors (UL array) along its coast and in the Nari crater basin, complemented by a 52-geophone array (UG array) deployed in May 2022 for high-resolution subsurface studies. Despite the noisy environments typical of temporary setups, power spectral density analyses confirmed the quality of data as comparable to established reference noise models in permanent stations. Our study aimed to initiate studies uncovering seismic activities and structures beneath Mt. Halla and Ulleung Island volcanoes, specifically regarding volcanic activity. This approach detected no clear sign of volcanic seismicity on both islands, suggesting a period of magmatic dormancy. Seismic velocity variation (dv/v) analyses further indicated that environmental factors, rather than volcanic processes, influenced the changes in the physical properties of the underground structures. Conversely, the receiver function analysis and ambient noise data processing hinted at the presence of complex subsurface structures, potentially indicative of volcanic features, such as partial melting. Despite the lack of direct evidence for active magmatic processes, the collected seismic data provides a crucial baseline for future monitoring and a deeper understanding of the magmatic and tectonic dynamics beneath these volcanoes, offering valuable insights for ongoing volcanic research.
PubDate: 2024-07-10
- Textural and mineralogical characteristics of sediments originated from
salt domes in the northern part of the Hormuz Strait-
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Abstract: Abstract In this research, field studies, surface sediment samples, and laboratory studies were used to determine the textural and mineralogical characteristics of the sediments that originated from the salt domes of the northern coastal area of Hormuz Strait. In this way, were studied the texture and mineralogy of sediments. The main minerals of the sediments are quartz, calcite, feldspar, and clay. Pyroxene and Fe-bearing minerals are the main heavy minerals of studied sediments. The abundance of these minerals is determined by the mineralogy and creation of sediment of the source rocks. The presence of stable clay minerals indicates the re-entry into the sedimentary cycle, and unstable minerals indicate the initial diagenesis conditions of their mineralogical transformation in surface sediments. Thus, the presence of salt diapirs is the most important structural-tectonic phenomenon that has caused rock fractures and intensified the effect of weathering. On the other hand, dry weather has weakened the intensity and extent of chemical weathering processes, especially in clay minerals. However, the seasonal flooding hydrological system has caused dissolution and changes in soluble and unstable sediment components and introduced some minerals, such as illite, into the re-sedimentary cycle. In addition, the transport of sedimentary particles in waterways with the mechanism of seasonal flood waters has created a non-continuous transportation system. All these factors have caused the sediments originating from salt domes to be texturally bad sorted, platykurtic, and have to vary kurtosis affected by the presence and extent of source rock units.
PubDate: 2024-07-10
- Revisiting geochemical perspectives on degassing of the subcontinental
lithospheric mantle-
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Abstract: Abstract In general, mantle-derived volatiles are mainly released into the atmosphere through volcanoes in mid-ocean ridges and subduction zones. However, relatively little attention has been paid to the emission of volatiles from continents on the Earth’s surface. It has recently been shown that significant amounts of gases such as carbon dioxide of mantle origin are emitted from continental rifts. Continental degassing has been reported in various ways around the world, however compared to mid-ocean ridges where the depleted upper mantle contributes significantly or arc volcanoes affected by subduction slabs, geochemical generalization is still in progress. In particular, in continental environments, other volatile sources may be added due to the distribution of the subcontinental lithospheric mantle. In the previously reported mantle xenolith samples, components such as noble gases are distinct from the mid-ocean ridge gases, and volcano/fault-related gases on some continents also showed different characteristics. Here, this work proposes representative values of volatiles of the lithosphere by synthesizing the geochemical data of gases emitted from the continent that have been reported until recently. In addition, this study provides a new perspective by considering the recently reported gas results from South Korea.
PubDate: 2024-07-10
- A comparative study of different radiometric dating techniques applied to
Quaternary volcanic rocks from Jeju Island, South Korea-
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Abstract: Abstract To constrain the timing of magma emplacement and eruption of volcanic rocks at Mt. Halla, Jeju Island, South Korea, a range of dating techniques (U-Pb, U-Th disequilibrium, and (U-Th)/He dating of zircon, and 40Ar/39Ar dating of groundmass) were applied to one trachyandesite sample and one trachyte sample. Trachyandesite sample CS92-7 from north of Mt. Halla yielded a homogeneous population of zircon U-Pb crystallization ages averaging 97 ± 3 ka and U-Th disequilibrium ages averaging 96.2 + 6.2/−10.6 ka. Both groundmass 40Ar/39Ar ages and zircon (U-Th)/He ages corrected for disequilibrium record the time of sample cooling, yielding ages of 105 ± 5 ka and 105.4 ± 4.0 ka, respectively. The nearly concordant crystallization and cooling ages are interpreted to document eruption of the sample shortly after its relatively rapid crystallization in the magma reservoir. The eruption age of this sample, based on the available geo- and thermochronological results, is estimated at 100.4 ± 7.6 ka. Trachyte sample SS35-23 from south of Mt. Halla yielded an overdispersed spectrum of zircon crystallization ages, suggesting protracted crystallization in the magma reservoir over a period of at least 140 ka. Weighted mean ages of 40.0 ± 5.9 ka and 39.4 ± 3.8 ka (determined from U-Pb and U-Th disequilibrium dating of the youngest coherent subpopulation, respectively), provide a maximum limit for the eruption age. The eruption age is directly constrained in this work at 32.4 ± 8.4 ka by (U-Th)/He data. The 40Ar/39Ar age of 54 ± 7 ka is distinctly different from the zircon crystallization and eruption ages, and is considered to be inaccurate due to a possible issue with sample contamination or excess argon. The combined geochronological methods applied in this study constrain the timing of zircon crystallization, magma residence, and eruption of volcanic rocks on Jeju Island, and provide essential information further improving our understanding of the chronological history of volcanic rocks on Jeju Island.
PubDate: 2024-07-06
- Implication of Nari Caldera structure of Ulleung Island from a 3-D
resistivity model using magnetotellurics-
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Abstract: Abstract 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.
PubDate: 2024-07-01
- Reexamination of the magma plumbing system of the Suwolbong tuff ring,
Jeju Island, Korea, based on a refined componentry analysis-
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Abstract: Abstract 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.
PubDate: 2024-06-24
- Complex fault geometry and slip distribution of 2022 Mw 6.6 Menyuan,
China, earthquake from joint inversion of GNSS and InSAR observations-
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Abstract: Abstract 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.
PubDate: 2024-06-20
- Integrated passive and active seismic profiling for detection of buried
faults: a case study at the north end of the Miryang Fault in the
Geoncheon Valley, southeastern Korean Peninsula-
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Abstract: Abstract 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.
PubDate: 2024-06-20
- Monitoring activity in Mount Melbourne, Antarctica, by multi-temporal SAR
interferometry based on the ICOPS algorithm-
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Abstract: Abstract 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.
PubDate: 2024-06-20
- New evidence of late Quaternary earthquake surface rupturing along the
Gongju Fault, central Korea-
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Abstract: Abstract Advanced technologies such as light detection and ranging (LiDAR) and unmanned aerial vehicles (UAVs) have revolutionized the detection of subtle surface deformation and the generation of high-resolution digital elevation models, overcoming the challenges posed by low tectonic activity and climatic surface erosion on fault-generated landscapes. This study presents a new record of paleoearthquake surface rupture along a section of the central Gongju Fault, transecting the central part of the Korean Peninsula, by analyzing geomorphic, stratigraphic, and structural features. We identified a NE-SW-striking, prominent fault-generated landform derived from LiDAR analysis and surface ruptures showing a vertical offset of < 15 cm by trench excavation. We also constrained the depositional ages to ∼94 ka using optically stimulated luminescence (OSL). Our comprehensive findings suggest that the seismic activity along the main trace of the Gongju Fault resulted in a distributed deformation within the fault zone, likely from multiple seismic events rather than a single occurrence. Structural features of the surface ruptures exposed on the trench wall show systematic changes in slip zone geometry, influenced by the pre-existing fault geometry, the imposed regional tectonic stress, and the physical properties of unconsolidated materials. This study enhances our understanding of seismic activity and fault dynamics in the central part of the Korean Peninsula, highlighting the significant influence of geological and climatic factors over tens of thousands of years in the intraplate regions with similar tectonic and climate settings.
PubDate: 2024-06-08
DOI: 10.1007/s12303-024-0018-0
- Geochemistry and geochronology of the Ordovician Qianhe metabasalt in
Northwest China: implications for the northern boundary of Qinling
Orogenic Belt in heavily loess-covered regions-
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Abstract: Abstract 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.
PubDate: 2024-05-29
DOI: 10.1007/s12303-024-0017-1
- Spatial distribution and origin of soil CO2 in Andeok area, Jeju
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Abstract: Abstract 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 (δ13CCO2) 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 δ13CCO2 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 δ13CCO2 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.
PubDate: 2024-05-29
DOI: 10.1007/s12303-024-0015-3
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