Pub Date : 2024-04-18DOI: 10.1007/s12303-024-0008-2
Tae-Hoon Uhmb, Jin-Han Ree, Hyeong Soo Kim
The formations in the early Paleozoic Joseon Supergroup (mainly carbonates with subordinate siliciclastics) within the Taebaeksan Basin in the Danyang area, South Korea, show an apparent right-side-up homoclinal stratigraphy without repetition or omission of any formation, and it was therefore thought that the NW-dipping formation boundaries are primary depositional contacts. Our detailed examination revealed, however, that the formation boundaries are reverse-slip shear zones parallel to the second-generation foliation (S2) crenulating transposed S0//S1 foliation and that WNW-dipping bedding planes (S0) are only locally preserved. The most penetrative regional planar structure in the area is the NNW-dipping first-generation foliation (S1) that is defined by compositional layering and is parallel to the axial planes of isoclinal F1 folds. Isoclinal to close F1 folds occur on both the mesoscopic and macroscopic scale, whereas tight to close F2 folds occur locally only on the mesoscopic scale. D1 deformation presumably involved a NNW-SSE horizontal contraction and resulted in the buckle folding and transposition of S0. D2 deformation involved a NW-SE contraction, probably at a high angle to the S0//S1 transposed layers, and produced passive shear folding of S0//S1 with S2 crenulation cleavages as discrete shear surfaces. Shearing deformation was strongly localized along some S2 foliation planes, resulting in reverse shear zones that represent the current ‘pseudo’-formation boundaries. Based on zircons U-Pb ages, we suggest that the Okdong Fault was initiated from an unconformable boundary between the Precambrian basement gneiss and overlying sediments of the Paleozoic Taebaeksan Basin, probably during the Middle Jurassic.
{"title":"Deformation-induced right-side-up pseudo-stratigraphy of the early Paleozoic Joseon Supergroup in the southeastern Danyang area, South Korea","authors":"Tae-Hoon Uhmb, Jin-Han Ree, Hyeong Soo Kim","doi":"10.1007/s12303-024-0008-2","DOIUrl":"https://doi.org/10.1007/s12303-024-0008-2","url":null,"abstract":"<p>The formations in the early Paleozoic Joseon Supergroup (mainly carbonates with subordinate siliciclastics) within the Taebaeksan Basin in the Danyang area, South Korea, show an apparent right-side-up homoclinal stratigraphy without repetition or omission of any formation, and it was therefore thought that the NW-dipping formation boundaries are primary depositional contacts. Our detailed examination revealed, however, that the formation boundaries are reverse-slip shear zones parallel to the second-generation foliation (<i>S</i><sub><i>2</i></sub>) crenulating transposed <i>S</i><sub>0</sub>//<i>S</i><sub>1</sub> foliation and that WNW-dipping bedding planes (<i>S</i><sub><i>0</i></sub>) are only locally preserved. The most penetrative regional planar structure in the area is the NNW-dipping first-generation foliation (<i>S</i><sub><i>1</i></sub>) that is defined by compositional layering and is parallel to the axial planes of isoclinal <i>F</i><sub><i>1</i></sub> folds. Isoclinal to close <i>F</i><sub><i>1</i></sub> folds occur on both the mesoscopic and macroscopic scale, whereas tight to close <i>F</i><sub><i>2</i></sub> folds occur locally only on the mesoscopic scale. <i>D</i><sub><i>1</i></sub> deformation presumably involved a NNW-SSE horizontal contraction and resulted in the buckle folding and transposition of <i>S</i><sub><i>0</i></sub>. <i>D</i><sub><i>2</i></sub> deformation involved a NW-SE contraction, probably at a high angle to the <i>S</i><sub>0</sub>//<i>S</i><sub>1</sub> transposed layers, and produced passive shear folding of <i>S</i><sub>0</sub>//<i>S</i><sub>1</sub> with <i>S</i><sub><i>2</i></sub> crenulation cleavages as discrete shear surfaces. Shearing deformation was strongly localized along some <i>S</i><sub><i>2</i></sub> foliation planes, resulting in reverse shear zones that represent the current ‘pseudo’-formation boundaries. Based on zircons U-Pb ages, we suggest that the Okdong Fault was initiated from an unconformable boundary between the Precambrian basement gneiss and overlying sediments of the Paleozoic Taebaeksan Basin, probably during the Middle Jurassic.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140611847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-18DOI: 10.1007/s12303-024-0007-3
Habimana Emmanuel, Jaehyung Yu, Lei Wang, Sung Hi Choi, Gilljae Lee, Digne E. Rwabuhungu R
This study aims to develop an automated impact crater classification machine learning (ML) method based on the morphometric parameters extracted from SRTM DEM. The training and testing dataset comprises data from 52 confirmed, well preserved, and moderately eroded impact craters and a recently discovered impact crater in Korea, Jeokjung Chogye Basin (JCB). The morphometric parameters including rim diameter, floor diameter, and wall width of complex craters and simple craters were tested by Mann Whitney U test and One Sample Wilcoxon signed rank test. The tests showed that those parameters can statistically separate the two types of craters. The Random Forest model classified them with an accuracy of 88.6% and a Kappa coefficient of 0.67, where rim diameter, floor diameter, and wall width were identified as variables with the highest Gini indices. Complex craters are characterized by a large flat diameter and wide wall width compared to simple craters with parabolic bases. The difference is caused by the impact energy when the craters were formed. The study confirmed that using machine learning, the complex craters and simple craters can be separated by checking the SRTM elevation model with machine learning methods. The morphometric parameters of JCB impact crater indicated that the crater is highly a complex crater concluded by both statistical tests and machine learning algorithm.
本研究旨在开发一种基于从 SRTM DEM 提取的形态参数的自动撞击坑分类机器学习(ML)方法。训练和测试数据集包括 52 个已确认的、保存完好的和中度侵蚀的撞击坑数据,以及韩国最近发现的一个撞击坑--Jeokjung Chogye Basin(JCB)的数据。对复杂陨石坑和简单陨石坑的边缘直径、底面直径和壁宽等形态参数进行了曼-惠特尼 U 检验和单样本 Wilcoxon 符号秩检验。检验结果表明,这些参数能在统计学上将两类陨石坑区分开来。随机森林模型对它们进行分类的准确率为 88.6%,卡帕系数为 0.67,其中边缘直径、底面直径和壁宽被认为是基尼指数最高的变量。与具有抛物线基底的简单陨石坑相比,复杂陨石坑的特点是平面直径大、壁宽。造成这种差异的原因是陨石坑形成时的撞击能量。研究证实,利用机器学习方法,通过检查 SRTM 高程模型,可以将复杂陨石坑和简单陨石坑区分开来。通过统计检验和机器学习算法,JCB 撞击坑的形态参数表明该撞击坑属于高度复杂的撞击坑。
{"title":"Classification of terrestrial impact craters based on morphometric parameters using remote sensing data: a case study of Jeokjung-Chogye impact crater, South Korea","authors":"Habimana Emmanuel, Jaehyung Yu, Lei Wang, Sung Hi Choi, Gilljae Lee, Digne E. Rwabuhungu R","doi":"10.1007/s12303-024-0007-3","DOIUrl":"https://doi.org/10.1007/s12303-024-0007-3","url":null,"abstract":"<p>This study aims to develop an automated impact crater classification machine learning (ML) method based on the morphometric parameters extracted from SRTM DEM. The training and testing dataset comprises data from 52 confirmed, well preserved, and moderately eroded impact craters and a recently discovered impact crater in Korea, Jeokjung Chogye Basin (JCB). The morphometric parameters including rim diameter, floor diameter, and wall width of complex craters and simple craters were tested by Mann Whitney U test and One Sample Wilcoxon signed rank test. The tests showed that those parameters can statistically separate the two types of craters. The Random Forest model classified them with an accuracy of 88.6% and a Kappa coefficient of 0.67, where rim diameter, floor diameter, and wall width were identified as variables with the highest Gini indices. Complex craters are characterized by a large flat diameter and wide wall width compared to simple craters with parabolic bases. The difference is caused by the impact energy when the craters were formed. The study confirmed that using machine learning, the complex craters and simple craters can be separated by checking the SRTM elevation model with machine learning methods. The morphometric parameters of JCB impact crater indicated that the crater is highly a complex crater concluded by both statistical tests and machine learning algorithm.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140611881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-18DOI: 10.1007/s12303-024-0009-1
Lixiang Zhao, Minxia Ma, Ye Qian, Haoran Li, Lingyun Sun, Jinlei Sun, Yanjie Shen, Fengyue Sun
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.
焦辽冀带是华北克拉通(NCC)中的古新生代造山带之一,由于其形成后发生了多次岩浆/变质事件,其构造演化至今仍存在争议。针对这一争议,我们对金陵拗陷中部北辽河组的元杂岩进行了岩石学、地质年代学、地球化学和锆石Hf同位素研究。207Pb/206Pb加权平均年龄分别为1849±36Ma和1853±13Ma,表明石西县地区闪长岩的原岩形成于约1.85Ga。1.85 Ga。在地球化学上,闪长岩属于透辉岩系列;而元辉长岩可分为低钛和高钛类型:前者属于钙碱性系列,后者属于透辉岩系列。高钛岩石富含轻稀土元素(LREEs)和大离子亲岩元素(LILEs;如Ba、K和Pb),而贫含重稀土元素(HREEs)和高场强元素(HFSEs;如Nb、Ta、P和Ti)。这些岩石的εHf(t)值略微偏正(+1.40 至 +2.02)。低钛元辉长岩很可能来自于尖晶石稳定场中富集的岩石圈地幔的部分熔融,这些地幔在与俯冲有关的流体和/或熔体的作用下发生了变质作用,并受到大量地壳物质的污染;而闪长岩和高钛元辉长岩则来自于尖晶石稳定场中贫乏的星体层地幔的部分熔融,这些地幔在有限的与俯冲有关的流体和/或熔体的作用下发生了变质作用,再加上碎裂结晶作用。岩石学和地球化学特征表明,低钛元辉长岩形成于岩浆弧环境,高钛岩石形成于后弧盆地后期,而闪长岩则形成于碰撞后延伸环境。结合文献数据,我们认为JLJB经历了从俯冲、碰撞到延伸的过程:在约 2.2-2.1 Ga 时,通过一个大洋板块向南俯冲打开了弧后盆地,随后在约 2.1-1.91 Ga 时向北俯冲,随后在约 1.91 Ga 时闭合形成了 JLJB。约 1.91 Ga 时,龙岗-南岭大陆发生碰撞,碰撞后的延伸发生在约 1.85 Ga 时,同时发生了塌陷。随着碰撞造山带的塌陷,碰撞后的延伸发生在约1.85 Ga。
{"title":"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","authors":"Lixiang Zhao, Minxia Ma, Ye Qian, Haoran Li, Lingyun Sun, Jinlei Sun, Yanjie Shen, Fengyue Sun","doi":"10.1007/s12303-024-0009-1","DOIUrl":"https://doi.org/10.1007/s12303-024-0009-1","url":null,"abstract":"<p>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. <sup>207</sup>Pb/<sup>206</sup>Pb 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.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140612155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-27DOI: 10.1007/s12303-024-0006-4
Nhat-Phi Doan, Duy Triet Doan, Van Nam Nguyen, Sung-Sik Park
Liquefaction has been known as a phenomenon in which the shear strength and stiffness of saturated soil are reduced by the generation of pore water pressure under earthquake loading. Consequently, liquefaction-induced settlement can result in severe damage including building cracks or slope failure, which pose a threat to human lives and properties. In the current Vietnamese standard TCVN 9386:2012, liquefaction potential hazard is often evaluated using the simplified method, which solely identifies the areas with a high risk of liquefaction. Prediction of Safety Factor (FS), Settlement (S), Liquefaction Potential Index (LPI), and Liquefaction Severity Number (LSN) has not received sufficient attention to a completeness standard. This study assesses the liquefaction of the site at Ho Chi Minh City, Vietnam by using four conventional methods: the simplified procedure, linear equivalent analysis, loosely-coupled effective stress analysis, and fully-coupled effective stress analysis based on standard penetration test (SPT) data in Ho Chi Minh Metropolitan City. A class of seismic events that are compatible with the design response spectrum in the Vietnamese standard TCVN 9386:2012 is used as input ground motion at the bedrock. According to the results of different methods, maps of ground settlement, LPI, and LSN are proposed as useful references for construction works on such soils, which may have a high potential for liquefaction and subsidence.
{"title":"Liquefaction assessment using alternative approaches: a case study of Ho Chi Minh City stratigraphy","authors":"Nhat-Phi Doan, Duy Triet Doan, Van Nam Nguyen, Sung-Sik Park","doi":"10.1007/s12303-024-0006-4","DOIUrl":"https://doi.org/10.1007/s12303-024-0006-4","url":null,"abstract":"<p>Liquefaction has been known as a phenomenon in which the shear strength and stiffness of saturated soil are reduced by the generation of pore water pressure under earthquake loading. Consequently, liquefaction-induced settlement can result in severe damage including building cracks or slope failure, which pose a threat to human lives and properties. In the current Vietnamese standard TCVN 9386:2012, liquefaction potential hazard is often evaluated using the simplified method, which solely identifies the areas with a high risk of liquefaction. Prediction of Safety Factor (FS), Settlement (S), Liquefaction Potential Index (<i>LPI</i>), and Liquefaction Severity Number (<i>LSN</i>) has not received sufficient attention to a completeness standard. This study assesses the liquefaction of the site at Ho Chi Minh City, Vietnam by using four conventional methods: the simplified procedure, linear equivalent analysis, loosely-coupled effective stress analysis, and fully-coupled effective stress analysis based on standard penetration test (SPT) data in Ho Chi Minh Metropolitan City. A class of seismic events that are compatible with the design response spectrum in the Vietnamese standard TCVN 9386:2012 is used as input ground motion at the bedrock. According to the results of different methods, maps of ground settlement, <i>LPI</i>, and <i>LSN</i> are proposed as useful references for construction works on such soils, which may have a high potential for liquefaction and subsidence.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140312620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-14DOI: 10.1007/s12303-023-0046-1
Mahmoud A. Galmed, Hisham A. Gahlan, Habes A. Ghrefat, Essam A. Mohamed, Khaled M. Al Kahtany
In the central north of Saudi Arabia, outcrop samples from the Cretaceous bauxite profile deposits in the Az Zabirah area were subjected to a comprehensive evaluation aimed at investigating their petrographical and geochemical characteristics using X-ray diffraction analysis (XRD), Scanning electron microscope (SEM) coupled with Energy dispersive (EDS) analysis, and X-ray fluorescence spectrometer (XRF) analysis. These bauxite deposits in the Az Zabirah area comprises of three main zones: the South zone, the Central zone, and the North zone. Petrologically, the bauxite samples predominantly consist of oolitic to pisolitic grains that are bound together by a matrix comprising bauxitic materials, iron oxides, calcite, and/or kaolinite. Mineralogical investigations indicate that the primary mineral composition of the bauxite includes gibbsite, boehmite, diaspore (kaolinite), hematite, quartz, and calcite. XRF showed that the dominant chemical components of the bauxite samples are Al2O3, SiO2, and Fe2O3. When considering the collective data from the rare earth elements (REEs) analysis (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and chemical weathering indices such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Weathering Index of Parker (WIP), it becomes evident that the Az Zabirah South Zone bauxite laterite profile at Al Ba’itha mine was formed under the influence of significant and persistent weathering conditions. The findings and methods used in this study are considered beneficial and valuable as they support mineral exploration in arid and semi-arid environments.
对沙特阿拉伯中北部 Az Zabirah 地区白垩纪铝土剖面矿床的露头样本进行了全面评估,旨在利用 X 射线衍射分析 (XRD)、扫描电子显微镜 (SEM) 结合能量色散 (EDS) 分析以及 X 射线荧光光谱仪 (XRF) 分析,研究其岩石学和地球化学特征。Az Zabirah 地区的这些铝土矿藏包括三个主要区域:南区、中区和北区。从岩石学角度来看,铝土矿样本主要由鲕粒到鲕粒组成,这些鲕粒被由铝土矿材料、氧化铁、方解石和/或高岭石组成的基质结合在一起。矿物学研究表明,铝土矿的主要矿物成分包括辉绿岩、波长石、透辉石(高岭石)、赤铁矿、石英和方解石。XRF 显示,铝土矿样品的主要化学成分是 Al2O3、SiO2 和 Fe2O3。在考虑稀土元素(REEs)分析(La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb 和 Lu)和化学风化指数(如化学蜕变指数(CIA))的综合数据时,需要考虑以下因素:(a) 铝土矿样品的化学成分;(b) 铝土矿样品的化学成分;(c) 铝土矿样品的化学成分、根据这些指数,可以明显看出 Al Ba'itha 矿区 Az Zabirah 南区红土铝土矿剖面是在显著而持久的风化条件影响下形成的。本研究的发现和使用的方法被认为是有益和有价值的,因为它们有助于在干旱和半干旱环境中进行矿产勘探。
{"title":"Petrology and geochemistry of the Az Zabirah south zone bauxite deposit at Al Ba’itha mine, north-central Saudi Arabia","authors":"Mahmoud A. Galmed, Hisham A. Gahlan, Habes A. Ghrefat, Essam A. Mohamed, Khaled M. Al Kahtany","doi":"10.1007/s12303-023-0046-1","DOIUrl":"https://doi.org/10.1007/s12303-023-0046-1","url":null,"abstract":"<p>In the central north of Saudi Arabia, outcrop samples from the Cretaceous bauxite profile deposits in the Az Zabirah area were subjected to a comprehensive evaluation aimed at investigating their petrographical and geochemical characteristics using X-ray diffraction analysis (XRD), Scanning electron microscope (SEM) coupled with Energy dispersive (EDS) analysis, and X-ray fluorescence spectrometer (XRF) analysis. These bauxite deposits in the Az Zabirah area comprises of three main zones: the South zone, the Central zone, and the North zone. Petrologically, the bauxite samples predominantly consist of oolitic to pisolitic grains that are bound together by a matrix comprising bauxitic materials, iron oxides, calcite, and/or kaolinite. Mineralogical investigations indicate that the primary mineral composition of the bauxite includes gibbsite, boehmite, diaspore (kaolinite), hematite, quartz, and calcite. XRF showed that the dominant chemical components of the bauxite samples are Al<sub>2</sub>O<sub>3</sub>, SiO<sub>2</sub>, and Fe<sub>2</sub>O<sub>3</sub>. When considering the collective data from the rare earth elements (REEs) analysis (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and chemical weathering indices such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Weathering Index of Parker (WIP), it becomes evident that the Az Zabirah South Zone bauxite laterite profile at Al Ba’itha mine was formed under the influence of significant and persistent weathering conditions. The findings and methods used in this study are considered beneficial and valuable as they support mineral exploration in arid and semi-arid environments.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140148351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-12DOI: 10.1007/s12303-024-0004-6
Junghee Son, Soonmi Cho, In Gul Hwang
In ancient records, discrimination of specific triggering events from sediment gravity flow deposits is very difficult, due to multiple interactions between triggering events and similar sedimentary characteristics. For this study, we introduce the Hakcheon-Chogok Megaturbidite (HCM) in the Miocene Pohang-Youngduk Basin (PYB), providing an opportunity to differentiate the triggering events. This megaturbidite is over 70 m thick in the proximal part and less than 4 m thick in the distal part. The diachronous stratigraphic position and distinct coarser sediments than those of the underlying and overlying successions suggest a large-scale slope failure of the fine-grained foreset (more than 2 km3). The occurrence of exotic granitic boulders, originating from the basement rock, more than 1 km west of the present fan-apex, is indicative of extreme sea-level run-up. The dispersal pattern and paleocurrent direction suggest that the HCM flowed to the northeast, irrespective of the local depositional slope which show a radial distribution from the fan-apex. The distribution pattern almost perpendicular to the strike of the NW-SE trending transfer fault suggests that the HCM was triggered by a reflection flow of giant tsunami wave, resulting in a large-scale failure of high-gradient (> 15° in slope angle) fandelta slope.
{"title":"The Hakcheon-Chogok Megaturbidite in the Miocene Pohang-Youngduk Basin, SE Korea: high-gradient slope failure probably triggered by a giant tsunami wave","authors":"Junghee Son, Soonmi Cho, In Gul Hwang","doi":"10.1007/s12303-024-0004-6","DOIUrl":"https://doi.org/10.1007/s12303-024-0004-6","url":null,"abstract":"<p>In ancient records, discrimination of specific triggering events from sediment gravity flow deposits is very difficult, due to multiple interactions between triggering events and similar sedimentary characteristics. For this study, we introduce the Hakcheon-Chogok Megaturbidite (HCM) in the Miocene Pohang-Youngduk Basin (PYB), providing an opportunity to differentiate the triggering events. This megaturbidite is over 70 m thick in the proximal part and less than 4 m thick in the distal part. The diachronous stratigraphic position and distinct coarser sediments than those of the underlying and overlying successions suggest a large-scale slope failure of the fine-grained foreset (more than 2 km<sup>3</sup>). The occurrence of exotic granitic boulders, originating from the basement rock, more than 1 km west of the present fan-apex, is indicative of extreme sea-level run-up. The dispersal pattern and paleocurrent direction suggest that the HCM flowed to the northeast, irrespective of the local depositional slope which show a radial distribution from the fan-apex. The distribution pattern almost perpendicular to the strike of the NW-SE trending transfer fault suggests that the HCM was triggered by a reflection flow of giant tsunami wave, resulting in a large-scale failure of high-gradient (> 15° in slope angle) fandelta slope.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140126883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-12DOI: 10.1007/s12303-024-0005-5
Abstract
Lithostratigraphy of the Yongtan Group is newly established based on detailed sedimentologic and stratigraphic studies on recently exposed, less deformed, relatively continuous outcrops and comprehensive review of previous studies, mainly focusing on the Jeongseon Formation which occupies most of the group spatially and stratigraphically. The Yongtan Group is divided into the Jeongseon, Haengmae, and Hoedongri formations in ascending order, and all the units are assigned to the Ordovician. The Jeongseon Formation is divided into three members based on lithology. Eleven sedimentary facies are recognized in the Jeongseon Formation and organized into five facies associations (FAs), FA1 (tidal flat), FA2 (inner-ramp), FA3 (shoal), FA4 (mid-ramp), and FA5 (ramp-slope to outer-ramp). The formation is interpreted to have been deposited on a homoclinal ramp. The Yongtan Group is divided into two supersequences separated by type 1 sequence boundary and the lower and middle members of the Jeongseon Formation belong to Supersequence I and the Upper Member to Supersequence II which includes the Haengmae and Hoedongri formations. The relative sea-level curve inferred from sequence stratigraphic analysis suggests that the formation evolved through two depositional stages in accordance with second-order sea-level changes separated by the boundary between the Sauk and Tippecanoe sequence, and the curve is greatly similar to that of the Taebaek and Yeongwol groups. The southeastward thickening of FA3 and northwestward prevalence of shale-rich facies suggest that topographic highs and lows were present in the Taebaeksan Basin and a slope might have developed along the carbonate platform during the early stage of deposition. The correlation and lateral thickness variation of the facies associations additionally suggest that the basin was deeper toward the northwestern part of the Jeongseon area. The deepening is likely attributed to the weakening of the productivity of the carbonate factory during the early Ordovician.
{"title":"A new lithostratigraphic scheme of the Ordovician Jeongseon Formation of the Yongtan Group in the Taebaeksan Basin and sequence stratigraphic analysis with discussion on basin geometry","authors":"","doi":"10.1007/s12303-024-0005-5","DOIUrl":"https://doi.org/10.1007/s12303-024-0005-5","url":null,"abstract":"<h3>Abstract</h3> <p>Lithostratigraphy of the Yongtan Group is newly established based on detailed sedimentologic and stratigraphic studies on recently exposed, less deformed, relatively continuous outcrops and comprehensive review of previous studies, mainly focusing on the Jeongseon Formation which occupies most of the group spatially and stratigraphically. The Yongtan Group is divided into the Jeongseon, Haengmae, and Hoedongri formations in ascending order, and all the units are assigned to the Ordovician. The Jeongseon Formation is divided into three members based on lithology. Eleven sedimentary facies are recognized in the Jeongseon Formation and organized into five facies associations (FAs), FA1 (tidal flat), FA2 (inner-ramp), FA3 (shoal), FA4 (mid-ramp), and FA5 (ramp-slope to outer-ramp). The formation is interpreted to have been deposited on a homoclinal ramp. The Yongtan Group is divided into two supersequences separated by type 1 sequence boundary and the lower and middle members of the Jeongseon Formation belong to Supersequence I and the Upper Member to Supersequence II which includes the Haengmae and Hoedongri formations. The relative sea-level curve inferred from sequence stratigraphic analysis suggests that the formation evolved through two depositional stages in accordance with second-order sea-level changes separated by the boundary between the Sauk and Tippecanoe sequence, and the curve is greatly similar to that of the Taebaek and Yeongwol groups. The southeastward thickening of FA3 and northwestward prevalence of shale-rich facies suggest that topographic highs and lows were present in the Taebaeksan Basin and a slope might have developed along the carbonate platform during the early stage of deposition. The correlation and lateral thickness variation of the facies associations additionally suggest that the basin was deeper toward the northwestern part of the Jeongseon area. The deepening is likely attributed to the weakening of the productivity of the carbonate factory during the early Ordovician.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140126984","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-07DOI: 10.1007/s12303-024-0003-7
Dabeen Heo, Tae-Seob Kang, Minook Kim, Byeong Seok Ahn, Hobin Lim, Jaeseoung Han, Kwang-Hee Kim, Junkee Rhie, YoungHee Kim, Jin-Han Ree
The 2016 magnitude (MW) 5.5 Gyeongju earthquake, which occurred in Korea near assumed epicenters of several substantial historical earthquakes and Quaternary fault segments, underscores the importance of seismic hazard assessment in the region. However, uncertainties about potential seismic sources make evaluating the potential for a moderate-to-large earthquake challenging. Microearthquake monitoring through a dense seismic network can provide crucial insights into the regional seismic characteristics. An extensive temporary seismic array known as the Gyeongju Hi-density Broadband Seismic Network (GHBSN) was established to investigate microearthquake activity in the southeastern Korean Peninsula. This included the zone of aftershocks from the 2016 Gyeongju earthquake sequence. The GHBSN comprises 200 broadband stations located at approximately 4.5 km intervals in an area of approximately 60 × 60 km2 around the epicenter of the mainshock. A total of 4,773 events were detected from November 2017 to December 2021, including 3,935 events within the GHBSN. The detected events were categorized into five seismic regions excluding quarry blasting sites, that is, the 2016 Gyeongju earthquake region, eastern part of the Ulsan Fault, 2017 Pohang earthquake region, eastern offshore Gyeongju, and western part of the Miryang Fault. A local magnitude scale was developed for the southeastern Korean Peninsula using events detected through the GHBSN. This reflects the distance attenuation and site conditions of the GHBSN stations for earthquakes. An event catalog was created using two automatic detection methods based on the measurement of the energy ratio. This provided high-resolution hypocenter parameters at a completeness magnitude (MC) of 0.0 despite the seismic environment of the network being exposed to high cultural noise. The Gutenberg-Richter b-value was estimated as 0.82 ± 0.02 for all events and 1.01 ± 0.02 for those inside GHBSN. This implies that the seismicity reflects a representative intraplate seismic environment. Testing the obtainability of the focal mechanism solutions showed that the GHBSN outperformed the regional network. Depending on the relationship between the magnitude and frequency of earthquakes, a relatively large number of small earthquakes can provide detailed information on the geometric properties of the causative faults and the state of the acting stress. High-precision microearthquake observation and analysis through GHBSN could provide an unprecedented opportunity with seismic datasets to understand the seismogenesis of the southeastern Korean Peninsula, including the zone of aftershocks of the 2016 Gyeongju earthquake.
{"title":"New insights on seismic activity in the southeastern Korean Peninsula from the Gyeongju Hi-density Broadband Seismic Network (GHBSN)","authors":"Dabeen Heo, Tae-Seob Kang, Minook Kim, Byeong Seok Ahn, Hobin Lim, Jaeseoung Han, Kwang-Hee Kim, Junkee Rhie, YoungHee Kim, Jin-Han Ree","doi":"10.1007/s12303-024-0003-7","DOIUrl":"https://doi.org/10.1007/s12303-024-0003-7","url":null,"abstract":"<p>The 2016 magnitude (M<sub>W</sub>) 5.5 Gyeongju earthquake, which occurred in Korea near assumed epicenters of several substantial historical earthquakes and Quaternary fault segments, underscores the importance of seismic hazard assessment in the region. However, uncertainties about potential seismic sources make evaluating the potential for a moderate-to-large earthquake challenging. Microearthquake monitoring through a dense seismic network can provide crucial insights into the regional seismic characteristics. An extensive temporary seismic array known as the Gyeongju Hi-density Broadband Seismic Network (GHBSN) was established to investigate microearthquake activity in the southeastern Korean Peninsula. This included the zone of aftershocks from the 2016 Gyeongju earthquake sequence. The GHBSN comprises 200 broadband stations located at approximately 4.5 km intervals in an area of approximately 60 × 60 km<sup>2</sup> around the epicenter of the mainshock. A total of 4,773 events were detected from November 2017 to December 2021, including 3,935 events within the GHBSN. The detected events were categorized into five seismic regions excluding quarry blasting sites, that is, the 2016 Gyeongju earthquake region, eastern part of the Ulsan Fault, 2017 Pohang earthquake region, eastern offshore Gyeongju, and western part of the Miryang Fault. A local magnitude scale was developed for the southeastern Korean Peninsula using events detected through the GHBSN. This reflects the distance attenuation and site conditions of the GHBSN stations for earthquakes. An event catalog was created using two automatic detection methods based on the measurement of the energy ratio. This provided high-resolution hypocenter parameters at a completeness magnitude (M<sub>C</sub>) of 0.0 despite the seismic environment of the network being exposed to high cultural noise. The Gutenberg-Richter b-value was estimated as 0.82 ± 0.02 for all events and 1.01 ± 0.02 for those inside GHBSN. This implies that the seismicity reflects a representative intraplate seismic environment. Testing the obtainability of the focal mechanism solutions showed that the GHBSN outperformed the regional network. Depending on the relationship between the magnitude and frequency of earthquakes, a relatively large number of small earthquakes can provide detailed information on the geometric properties of the causative faults and the state of the acting stress. High-precision microearthquake observation and analysis through GHBSN could provide an unprecedented opportunity with seismic datasets to understand the seismogenesis of the southeastern Korean Peninsula, including the zone of aftershocks of the 2016 Gyeongju earthquake.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140075793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-29DOI: 10.1007/s12303-023-0045-2
Liadira K. Widya, Chang-Wook Lee
Wildfires have caused natural environmental damage that has contributed to deforestation, consequently demonstrating a significant influence on atmospheric emissions. Wildfires occur frequently in South Korea, especially during the spring season. This study assessed post-wildfires areas in Gangneung, South Korea, on April 11, 2023, which were generated by implementing remote sensing technology and statistical analysis. Remote sensing and classification techniques, including PlanetScope, have been developed for identifying wildfire-damaged areas. The method for classifying post-wildfire mapping estimation includes the utilization of deep learning approaches, especially using the U-Net architecture. Therefore, the assessment of wildfire severity can be conducted using Sentinel-2 and Sentinel-5P imagery in addition to an analysis of the vegetation type and air pollutant within the affected region. In the present study, Sentinel-2 imagery was to generate spectral indices, including the differenced normalized burn ratio (dNBR), differenced normalized difference moisture index (dNDMI), differenced soil adjusted vegetation index (dSAVI), and differenced normalized vegetation index (dNDVI). Sentinel-5P imagery was utilized to produce carbon monoxide (CO) column number densities. The estimation of wildfire areas was conducted using a PlanetScope classified image with the U-Net classifier, which was evaluated based on the overall accuracy value of 95% and kappa accuracy of 0.901. The wildfire severity level was shown by dNBR, which was correlated with the parameters, including RBR, dNDMI, dSAVI, dNDVI, and CO. The statistical analysis demonstrated a significant and positive correlation between the wildfire severity and the parameters. Moreover, the average of vegetation indices (NDMI, SAVI, and NDVI) before and after a wildfire were found to decrease by vegetation type, including 17.55% in mixed barren land areas, 17.49% in other grasses, 24.71% in mixed forest land, 22.48% in coniferous land, 13.48% in fields, and 4.29% in paddy fields. On the basis of the results, these estimates can be employed to identify the level of damage caused by wildfires to vegetation and air quality.
{"title":"Geospatial technologies for estimating post-wildfire severity through satellite imagery and vegetation types: a case study of the Gangneung Wildfire, South Korea","authors":"Liadira K. Widya, Chang-Wook Lee","doi":"10.1007/s12303-023-0045-2","DOIUrl":"https://doi.org/10.1007/s12303-023-0045-2","url":null,"abstract":"<p>Wildfires have caused natural environmental damage that has contributed to deforestation, consequently demonstrating a significant influence on atmospheric emissions. Wildfires occur frequently in South Korea, especially during the spring season. This study assessed post-wildfires areas in Gangneung, South Korea, on April 11, 2023, which were generated by implementing remote sensing technology and statistical analysis. Remote sensing and classification techniques, including PlanetScope, have been developed for identifying wildfire-damaged areas. The method for classifying post-wildfire mapping estimation includes the utilization of deep learning approaches, especially using the U-Net architecture. Therefore, the assessment of wildfire severity can be conducted using Sentinel-2 and Sentinel-5P imagery in addition to an analysis of the vegetation type and air pollutant within the affected region. In the present study, Sentinel-2 imagery was to generate spectral indices, including the differenced normalized burn ratio (dNBR), differenced normalized difference moisture index (dNDMI), differenced soil adjusted vegetation index (dSAVI), and differenced normalized vegetation index (dNDVI). Sentinel-5P imagery was utilized to produce carbon monoxide (CO) column number densities. The estimation of wildfire areas was conducted using a PlanetScope classified image with the U-Net classifier, which was evaluated based on the overall accuracy value of 95% and kappa accuracy of 0.901. The wildfire severity level was shown by dNBR, which was correlated with the parameters, including RBR, dNDMI, dSAVI, dNDVI, and CO. The statistical analysis demonstrated a significant and positive correlation between the wildfire severity and the parameters. Moreover, the average of vegetation indices (NDMI, SAVI, and NDVI) before and after a wildfire were found to decrease by vegetation type, including 17.55% in mixed barren land areas, 17.49% in other grasses, 24.71% in mixed forest land, 22.48% in coniferous land, 13.48% in fields, and 4.29% in paddy fields. On the basis of the results, these estimates can be employed to identify the level of damage caused by wildfires to vegetation and air quality.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140003107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-23DOI: 10.1007/s12303-024-0002-8
Abstract
Skarn and Fe-Zn-Pb mineralization at the Wondong deposit located in the Taebaeksan Basin of the central-eastern region of Korean Peninsula occurs along the contact between the Upper Cretaceous quartz-feldspar porphyry (QFP) and carbonate rocks of the Ordovician Makgol Formation. The QFP is relatively fresh and has a sharp contact with the garnet skarn. Skarn is dominant in the carbonate rocks but is rare in the QFP. It consists almost of grandite throughout the skarn but has mineralogical zonation of proximal garnet, intermediate pyroxene, and distal wollastonite with increasing distance from the contact between the QFP and garnet skarn. Garnet becomes Fe-rich, and pyroxene tends to be enriched in Fe and Mn toward the marble front. Massive Fe mineralization, replacing garnet skarn, is restricted proximal to the QFP. In contrast, although the Zn-Pb mineralization is found in all areas it mostly occurs in the carbonate rocks beyond the skarn. Zinc-Pb mineralization occurred as stockwork and vein in the QFP and the garnet skarn consists of sphalerite, galena, Al-rich garnet, and calcite with a minor quantity of arsenopyrite. In contrast, the carbonate replacement of the Zn-Pb mineralization beyond skarn consists of sphalerite, pyrrhotite, galena, diopsidic pyroxene, and calcite with minor minerals such as arsenopyrite, löellingite, and chalcopyrite. Sphalerite, principal ore mineral, becomes darker and Fe- (up to 34.4 mol% FeS) and Mn-rich (up to 1.5 mol% MnS) with increasing distance from the QFP. Arsenopyrite is closely associated with sphalerite tends to be decreased in As away from the QFP. All sulfide minerals from Zn-Pb mineralization in the Wondong deposit have δ34S values ranging from 2.9 to 5.9‰, which are attributed to the magmatic source. In addition, the narrow range and subtle variation of the δ34S values for all sulfides throughout the Wondong deposits are not interpreted to be involved in the mixing of multiple sulfur sources. Geological, petrographic, mineralogical, and isotopic geochemical investigations show that the early skarn was formed in an environment of high fluid: rock ratios at the contact between the QFP and Makgol Formation and it was dominated by grandite, indicating the oxidizing nature of the skarn-forming fluids. The ore deposition began after the formation of the main garnet dominated skarn. The ore-forming fluids responsible for Zn-Pb mineralization are characterized by a less oxidizing nature, as defined by comparatively Al-enriched garnet in vein type mineralization in and around the QFP. Farther, the fluids producing the carbonate replacement of the Zn-Pb mineralization are unlikely to be engaged in external effects such as mixing with multiple sulfur sources even though it travels over long distance.
{"title":"Skarn alteration and Fe-Zn-Pb mineralization at the Wondong deposit in the Taebaeksan Basin, South Korea","authors":"","doi":"10.1007/s12303-024-0002-8","DOIUrl":"https://doi.org/10.1007/s12303-024-0002-8","url":null,"abstract":"<h3>Abstract</h3> <p>Skarn and Fe-Zn-Pb mineralization at the Wondong deposit located in the Taebaeksan Basin of the central-eastern region of Korean Peninsula occurs along the contact between the Upper Cretaceous quartz-feldspar porphyry (QFP) and carbonate rocks of the Ordovician Makgol Formation. The QFP is relatively fresh and has a sharp contact with the garnet skarn. Skarn is dominant in the carbonate rocks but is rare in the QFP. It consists almost of grandite throughout the skarn but has mineralogical zonation of proximal garnet, intermediate pyroxene, and distal wollastonite with increasing distance from the contact between the QFP and garnet skarn. Garnet becomes Fe-rich, and pyroxene tends to be enriched in Fe and Mn toward the marble front. Massive Fe mineralization, replacing garnet skarn, is restricted proximal to the QFP. In contrast, although the Zn-Pb mineralization is found in all areas it mostly occurs in the carbonate rocks beyond the skarn. Zinc-Pb mineralization occurred as stockwork and vein in the QFP and the garnet skarn consists of sphalerite, galena, Al-rich garnet, and calcite with a minor quantity of arsenopyrite. In contrast, the carbonate replacement of the Zn-Pb mineralization beyond skarn consists of sphalerite, pyrrhotite, galena, diopsidic pyroxene, and calcite with minor minerals such as arsenopyrite, löellingite, and chalcopyrite. Sphalerite, principal ore mineral, becomes darker and Fe- (up to 34.4 mol% FeS) and Mn-rich (up to 1.5 mol% MnS) with increasing distance from the QFP. Arsenopyrite is closely associated with sphalerite tends to be decreased in As away from the QFP. All sulfide minerals from Zn-Pb mineralization in the Wondong deposit have <em>δ</em><sup>34</sup>S values ranging from 2.9 to 5.9‰, which are attributed to the magmatic source. In addition, the narrow range and subtle variation of the <em>δ</em><sup>34</sup>S values for all sulfides throughout the Wondong deposits are not interpreted to be involved in the mixing of multiple sulfur sources. Geological, petrographic, mineralogical, and isotopic geochemical investigations show that the early skarn was formed in an environment of high fluid: rock ratios at the contact between the QFP and Makgol Formation and it was dominated by grandite, indicating the oxidizing nature of the skarn-forming fluids. The ore deposition began after the formation of the main garnet dominated skarn. The ore-forming fluids responsible for Zn-Pb mineralization are characterized by a less oxidizing nature, as defined by comparatively Al-enriched garnet in vein type mineralization in and around the QFP. Farther, the fluids producing the carbonate replacement of the Zn-Pb mineralization are unlikely to be engaged in external effects such as mixing with multiple sulfur sources even though it travels over long distance.</p>","PeriodicalId":12659,"journal":{"name":"Geosciences Journal","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139953769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}