L. Medaris, B. Jicha, B. Singer, B. Wathen, Youjuan Li, S. Driese
Six Proterozoic, two Cambrian, and two Cretaceous paleosols in the Lake Superior region of midcontinental Laurentia were investigated in detail. All but the Cretaceous paleosols experienced potassium metasomatism, which resulted in the precipitation of muscovite in Proterozoic paleosols or illite and microcline in Cambrian paleosols. A comparison of the magnitude of potassium metasomatism among the paleosols is provided by depth-normalized mass flux (DNMF), where DNMF=1000×[(mass flux)/(depth of weathering)], which normalizes for different thicknesses of weathering profiles. Average DNMF values for the total addition of K2O are 0.98 ± 0.19 mol cm−3 for the Proterozoic paleosols and 1.27 ± 0.06 mol cm−3 for the Cambrian paleosols. The ages of potassium metasomatism were determined by 40Ar/39Ar isotopic dating of metasomatic muscovite in the Proterozoic McGrath, Ville Marie, and Baraboo paleosols, which yielded ages of 1742 ± 3, 1589 ± 3, and 1467 ± 11 Ma, respectively, the former being coeval with the Yavapai orogeny and the latter with the Baraboo orogeny. Metasomatic microcline in the Cambrian Trempealeau paleosol yielded a plateau age of 488.0 ± 1.0 Ma, which corresponds to the age of the Cambrian-Ordovician boundary. SiO2, CaO, and Na2O were substantially removed from the paleosols by weathering, as was K2O (before metasomatism). The average total amount of SiO2, CaO, Na2O, and K2O removed was 17.6% ± 1.9% from six Proterozoic paleosols, 28.5% ± 4.2% from two Cambrian paleosols, 36.5% ± 8.6% from two Cretaceous paleosols, and 34.2% ± 2.7% from five modern soils. The greater magnitude of weathering in the Phanerozoic weathering profiles compared with the Proterozoic ones, despite lower levels of CO2 in the Phanerozoic atmosphere, may reflect the emergence of land plants at ∼500 Ma and their profound effects on weathering.
{"title":"Evaluating the Magnitudes of Weathering and Potassium Metasomatism in Paleosols: Examples from Proterozoic, Cambrian, and Cretaceous Paleosols in Midcontinental Laurentia","authors":"L. Medaris, B. Jicha, B. Singer, B. Wathen, Youjuan Li, S. Driese","doi":"10.1086/724252","DOIUrl":"https://doi.org/10.1086/724252","url":null,"abstract":"Six Proterozoic, two Cambrian, and two Cretaceous paleosols in the Lake Superior region of midcontinental Laurentia were investigated in detail. All but the Cretaceous paleosols experienced potassium metasomatism, which resulted in the precipitation of muscovite in Proterozoic paleosols or illite and microcline in Cambrian paleosols. A comparison of the magnitude of potassium metasomatism among the paleosols is provided by depth-normalized mass flux (DNMF), where DNMF=1000×[(mass flux)/(depth of weathering)], which normalizes for different thicknesses of weathering profiles. Average DNMF values for the total addition of K2O are 0.98 ± 0.19 mol cm−3 for the Proterozoic paleosols and 1.27 ± 0.06 mol cm−3 for the Cambrian paleosols. The ages of potassium metasomatism were determined by 40Ar/39Ar isotopic dating of metasomatic muscovite in the Proterozoic McGrath, Ville Marie, and Baraboo paleosols, which yielded ages of 1742 ± 3, 1589 ± 3, and 1467 ± 11 Ma, respectively, the former being coeval with the Yavapai orogeny and the latter with the Baraboo orogeny. Metasomatic microcline in the Cambrian Trempealeau paleosol yielded a plateau age of 488.0 ± 1.0 Ma, which corresponds to the age of the Cambrian-Ordovician boundary. SiO2, CaO, and Na2O were substantially removed from the paleosols by weathering, as was K2O (before metasomatism). The average total amount of SiO2, CaO, Na2O, and K2O removed was 17.6% ± 1.9% from six Proterozoic paleosols, 28.5% ± 4.2% from two Cambrian paleosols, 36.5% ± 8.6% from two Cretaceous paleosols, and 34.2% ± 2.7% from five modern soils. The greater magnitude of weathering in the Phanerozoic weathering profiles compared with the Proterozoic ones, despite lower levels of CO2 in the Phanerozoic atmosphere, may reflect the emergence of land plants at ∼500 Ma and their profound effects on weathering.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"447 - 464"},"PeriodicalIF":1.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49295705","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}
To better understand Early Cretaceous climate variation in inland East Asia, the temporal variation in the chemical index of alteration (CIA) was reconstructed in black shale from an outcrop of the Fajiaying Formation in the Lower Cretaceous Laiyang Group at Lingshan Island, East China. As the formation height increased, the corresponding CIA increased. The obtained index of compositional variability values and an (Al2O3)–(CaO* + Na2O)–K2O ternary diagram demonstrate that the gathered samples had not evolved into K-metasomatism during diagenesis. Moreover, low Zr concentrations parallel to the magmatic trend in the Th/Sc-versus-Zr/Sc diagram reveal that the sediment sorting and recycling did not affect the paleoweathering proxies. The lack of correlation between the CIA and Al/Si or K/Si further suggests that the paleoweathering proxies were not affected by the sediment sorting. Accordingly, as the CIA and the chemical index of weathering increased, the corresponding chemical weathering increased slightly. This is consistent with the transition from a dry-hot climate to a warm-humid one proposed by paleoclimatic proxies such as Rb/Sr, Sr/Cu, Al2O3/MgO, and clay minerals. In this study, a near-ubiquitous correlation is proposed between the variations of paleoclimate and the CIA of shale, in which a rise in humidity significantly increased the chemical weathering. Meanwhile, it was found that under the dry-hot conditions of the Early Cretaceous, chemical weathering in inland areas far from the ocean was relatively weak and dependent on atmospheric humidity. This analysis validates the CIA, as part of the stratigraphic record, to be a robust proxy for terrestrial paleoclimatic variation during the Early Cretaceous.
{"title":"Temporal Variation in the Chemical Index of Alteration in Early Cretaceous Black Shale as a Proxy for Paleoclimate","authors":"Wenxia Wang, Zuobin Gan, Xiang Zhang, Shoujun Li, Yanming Xu","doi":"10.1086/722337","DOIUrl":"https://doi.org/10.1086/722337","url":null,"abstract":"To better understand Early Cretaceous climate variation in inland East Asia, the temporal variation in the chemical index of alteration (CIA) was reconstructed in black shale from an outcrop of the Fajiaying Formation in the Lower Cretaceous Laiyang Group at Lingshan Island, East China. As the formation height increased, the corresponding CIA increased. The obtained index of compositional variability values and an (Al2O3)–(CaO* + Na2O)–K2O ternary diagram demonstrate that the gathered samples had not evolved into K-metasomatism during diagenesis. Moreover, low Zr concentrations parallel to the magmatic trend in the Th/Sc-versus-Zr/Sc diagram reveal that the sediment sorting and recycling did not affect the paleoweathering proxies. The lack of correlation between the CIA and Al/Si or K/Si further suggests that the paleoweathering proxies were not affected by the sediment sorting. Accordingly, as the CIA and the chemical index of weathering increased, the corresponding chemical weathering increased slightly. This is consistent with the transition from a dry-hot climate to a warm-humid one proposed by paleoclimatic proxies such as Rb/Sr, Sr/Cu, Al2O3/MgO, and clay minerals. In this study, a near-ubiquitous correlation is proposed between the variations of paleoclimate and the CIA of shale, in which a rise in humidity significantly increased the chemical weathering. Meanwhile, it was found that under the dry-hot conditions of the Early Cretaceous, chemical weathering in inland areas far from the ocean was relatively weak and dependent on atmospheric humidity. This analysis validates the CIA, as part of the stratigraphic record, to be a robust proxy for terrestrial paleoclimatic variation during the Early Cretaceous.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"393 - 411"},"PeriodicalIF":1.8,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42287457","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}
How voluminous granite magmas are emplaced in congested convergent regimes is still debated. The space problem is significant for voluminous batholiths, such as Cordilleran batholiths, because granite magmas cannot create their own way into the crust, and the regional tectonic circumstances are contractional. Both regional and local models have been suggested to solve this problem, but these awkward models are limited in space-time framework without any possibility for generalization to repeated pulses within large Mesozoic batholiths. To investigate the Sierra Nevada batholith (SNB) incremental emplacement at different levels, potential field data were integrated with the age database. Three pulses emplaced incrementally during the Mesozoic era contemporaneously with regional events, suggesting a synkinematic origin and implying the same structural framework. The potential field data reveal that the presence of a synorogenic fault zone accommodates the westward migration of the feeder zone. These feeder zones passed underneath the main batholithic body obliquely from northwest to southeast in the Triassic and Jurassic, before the cessation of magmatism within the SNB underneath the Sierra crest shear zone and Kern Canyon fault zone in the Cretaceous. The structurally controlled feeder zones accommodate the spatiotemporal distribution of the SNB Mesozoic flare-ups magmatism, which is disturbed by small feeder dikes underneath the rising plutons. The rising plutons dissected the western part of the Sierra Nevada during the Mesozoic and extended to the Salinas Valley region to the west of the SNB. In conclusion, bends on thrusts are proposed as an alternative model for the space problem; the higher the orogenic stress, the greater the space available for granite magma.
{"title":"Incremental Emplacement of the Sierra Nevada Batholith Constrained by U-Pb Ages and Potential Field Data","authors":"H. Sehsah, Ahmed M. Eldosouky, L. Pham","doi":"10.1086/722724","DOIUrl":"https://doi.org/10.1086/722724","url":null,"abstract":"How voluminous granite magmas are emplaced in congested convergent regimes is still debated. The space problem is significant for voluminous batholiths, such as Cordilleran batholiths, because granite magmas cannot create their own way into the crust, and the regional tectonic circumstances are contractional. Both regional and local models have been suggested to solve this problem, but these awkward models are limited in space-time framework without any possibility for generalization to repeated pulses within large Mesozoic batholiths. To investigate the Sierra Nevada batholith (SNB) incremental emplacement at different levels, potential field data were integrated with the age database. Three pulses emplaced incrementally during the Mesozoic era contemporaneously with regional events, suggesting a synkinematic origin and implying the same structural framework. The potential field data reveal that the presence of a synorogenic fault zone accommodates the westward migration of the feeder zone. These feeder zones passed underneath the main batholithic body obliquely from northwest to southeast in the Triassic and Jurassic, before the cessation of magmatism within the SNB underneath the Sierra crest shear zone and Kern Canyon fault zone in the Cretaceous. The structurally controlled feeder zones accommodate the spatiotemporal distribution of the SNB Mesozoic flare-ups magmatism, which is disturbed by small feeder dikes underneath the rising plutons. The rising plutons dissected the western part of the Sierra Nevada during the Mesozoic and extended to the Salinas Valley region to the west of the SNB. In conclusion, bends on thrusts are proposed as an alternative model for the space problem; the higher the orogenic stress, the greater the space available for granite magma.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"381 - 391"},"PeriodicalIF":1.8,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47757032","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}
Jingbo Sun, Wen Chen, K. Qin, Ze Shen, Shuangfeng Zhao, Wen Zhang, Jiyuan Yin
The southern Great Xing’an Range in southeastern Inner Mongolia, north of the North China Craton, is a region influenced by different tectonic regimes. The Mesozoic–Cenozoic geological and topographic evolution remains controversial. In this study, we decipher the thermal evolution of the southern Great Xing’an Range by applying zircon and apatite (U-Th)/He and apatite fission-track thermochronology to granitoids to constrain the history of exhumation induced by the superposition of different tectonic activities and the history of geomorphological evolution. Zircon (U-Th)/He dating yields Early Cretaceous ages (109.1–134.9 Ma) and one early Permian age (292.0 Ma). Apatite (U-Th)/He dating and fission-track dating yield Early Cretaceous to early Late Cretaceous ages of 89.8–117.6 and 97.8–99.9 Ma, respectively. Combining these ages with previously published zircon U-Pb data and thermal history modeling, we suggest that the southern Great Xing’an Range experienced rapid cooling and exhumation during the Early Cretaceous. This cooling stage coincided with widespread extensional tectonics in northeastern China, which are thought to have been induced by the postorogenic collapse of thickened crust associated with the Mongol-Okhotsk Ocean and backarc extension associated with subduction of the Paleo-Pacific plate. This study implies that the southern Great Xing’an Range does not record significant exhumation during the Cenozoic.
{"title":"Early Cretaceous Exhumation of the Southern Great Xing’an Range, Northeastern China: Evidence from (U-Th)/He and Fission-Track Thermochronology","authors":"Jingbo Sun, Wen Chen, K. Qin, Ze Shen, Shuangfeng Zhao, Wen Zhang, Jiyuan Yin","doi":"10.1086/722958","DOIUrl":"https://doi.org/10.1086/722958","url":null,"abstract":"The southern Great Xing’an Range in southeastern Inner Mongolia, north of the North China Craton, is a region influenced by different tectonic regimes. The Mesozoic–Cenozoic geological and topographic evolution remains controversial. In this study, we decipher the thermal evolution of the southern Great Xing’an Range by applying zircon and apatite (U-Th)/He and apatite fission-track thermochronology to granitoids to constrain the history of exhumation induced by the superposition of different tectonic activities and the history of geomorphological evolution. Zircon (U-Th)/He dating yields Early Cretaceous ages (109.1–134.9 Ma) and one early Permian age (292.0 Ma). Apatite (U-Th)/He dating and fission-track dating yield Early Cretaceous to early Late Cretaceous ages of 89.8–117.6 and 97.8–99.9 Ma, respectively. Combining these ages with previously published zircon U-Pb data and thermal history modeling, we suggest that the southern Great Xing’an Range experienced rapid cooling and exhumation during the Early Cretaceous. This cooling stage coincided with widespread extensional tectonics in northeastern China, which are thought to have been induced by the postorogenic collapse of thickened crust associated with the Mongol-Okhotsk Ocean and backarc extension associated with subduction of the Paleo-Pacific plate. This study implies that the southern Great Xing’an Range does not record significant exhumation during the Cenozoic.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"413 - 428"},"PeriodicalIF":1.8,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47246393","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}
Jared T. Freiburg, M. Peltz, D. Willette, G. Grathoff
At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.
{"title":"High-Resolution Pore Space Imaging, Mineralogical Characterization, and Sealing Capacity Estimates of Confining Units at a Geologic Carbon Storage Demonstration: The Illinois Basin–Decatur Project, USA","authors":"Jared T. Freiburg, M. Peltz, D. Willette, G. Grathoff","doi":"10.1086/722563","DOIUrl":"https://doi.org/10.1086/722563","url":null,"abstract":"At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"335 - 355"},"PeriodicalIF":1.8,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49573787","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}
The final closure time of the Paleozoic ocean in the Eastern Tianshan is debated, and the geotectonics are still poorly constrained; hence, research on late Paleozoic igneous rocks has important implications for the evolutionary processes involved in this area’s tectonic history. However, limited attention has been given to the volcanic rocks in the late Paleozoic strata across the Eastern Tianshan because of their rarity and identification difficulty. This article focuses on the key site of an accretionary orogen in Central Asia, the Kalatage (Shaerhu)-Dananhu–Lop Nur area, to promote the study of tectonomagmatic evolution. The interbedded volcanic rock layers in late Paleozoic strata, including volcanic edifice deposits, are mainly rhyolitic volcanic, andesitic/dacitic, and basaltic rocks. These felsic, intermediate, and mafic rocks have zircon laser ablation ICP-MS U-Pb ages of 362.5–303 Ma. Geochemically, all samples have similar primitive mantle–normalized trace-element spider diagrams and chondrite-normalized rare earth element plots. The felsic and intermediate volcanic rocks are classified as I-type rocks and formed in a volcanic arc, and the mafic rocks belong to the tholeiite series and formed in island arc (earlier) and intraplate (later) settings. By the time the mafic rocks with intraplate basalt characteristics formed at 303±13 Ma, the Paleo-Asian Ocean had completely closed, and the region had entered the intraplate evolution stage. On the basis of other findings regarding the ages of igneous rocks and synthetic analysis, the northward subduction of the Paleo-Asian oceanic slab can preferably explain the relationship between the distinctive tectonic environment and the age variation trend in the study area. The process generated subduction-, collision- and postcollision-related magmatism from the Devonian to the late Carboniferous, and after 310 Ma, the Kalatage-Dananhu–Lop Nur area synchronously underwent a tectonic transition from subduction and collision to an intracontinental environment.
{"title":"Late Paleozoic Tectonomagmatic Evolution of the Eastern Tianshan, Northwest China: Insights from Geochronology and Geochemistry of Volcanic Rocks from the Dananhu–Lop Nur Area","authors":"Xinqi Yu, Xiu Liu, Jun Hu, Wei Li, Zongxiu Wang, Weifeng Xiao","doi":"10.1086/722751","DOIUrl":"https://doi.org/10.1086/722751","url":null,"abstract":"The final closure time of the Paleozoic ocean in the Eastern Tianshan is debated, and the geotectonics are still poorly constrained; hence, research on late Paleozoic igneous rocks has important implications for the evolutionary processes involved in this area’s tectonic history. However, limited attention has been given to the volcanic rocks in the late Paleozoic strata across the Eastern Tianshan because of their rarity and identification difficulty. This article focuses on the key site of an accretionary orogen in Central Asia, the Kalatage (Shaerhu)-Dananhu–Lop Nur area, to promote the study of tectonomagmatic evolution. The interbedded volcanic rock layers in late Paleozoic strata, including volcanic edifice deposits, are mainly rhyolitic volcanic, andesitic/dacitic, and basaltic rocks. These felsic, intermediate, and mafic rocks have zircon laser ablation ICP-MS U-Pb ages of 362.5–303 Ma. Geochemically, all samples have similar primitive mantle–normalized trace-element spider diagrams and chondrite-normalized rare earth element plots. The felsic and intermediate volcanic rocks are classified as I-type rocks and formed in a volcanic arc, and the mafic rocks belong to the tholeiite series and formed in island arc (earlier) and intraplate (later) settings. By the time the mafic rocks with intraplate basalt characteristics formed at 303±13 Ma, the Paleo-Asian Ocean had completely closed, and the region had entered the intraplate evolution stage. On the basis of other findings regarding the ages of igneous rocks and synthetic analysis, the northward subduction of the Paleo-Asian oceanic slab can preferably explain the relationship between the distinctive tectonic environment and the age variation trend in the study area. The process generated subduction-, collision- and postcollision-related magmatism from the Devonian to the late Carboniferous, and after 310 Ma, the Kalatage-Dananhu–Lop Nur area synchronously underwent a tectonic transition from subduction and collision to an intracontinental environment.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"357 - 380"},"PeriodicalIF":1.8,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48160727","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}
In 2008, Pogue and Katz reported that on granitic exposures in the Cassia City of Rocks, Idaho, the larger pans (shallow flat-floored gnammas or rock basins with overhanging sidewalls) are developed and preserved high in the local relief. They related this aspect of pan distribution to duration of exposure. This working hypothesis is tested by examining pan distribution on granitic inselbergs located on northwestern Eyre Peninsula, in semiarid southern South Australia. Pans in numbers have developed on sensibly level surfaces and have been shaped by pools of standing water. The larger—and more complex—forms are situated high in the local relief, as concluded by Pogue and Katz, but where water supply is limited to direct precipitation, by contrast with lower sites, where rainfall is augmented by runoff.
2008年，Pogue和Katz报告说，在爱达荷州Cassia City of Rocks的花岗岩暴露中，较大的平底锅(浅层平坦的岩浆或具有突出侧壁的岩石盆地)在当地的浮雕中发育并保存得很高。他们将这方面的泛分布与暴露时间联系起来。通过对位于半干旱的南澳大利亚南部艾尔半岛西北部的花岗岩inselberg上的泛盆分布进行研究，验证了这一工作假设。大量的平底锅在相当平坦的表面上形成，并由静水池形成。根据Pogue和Katz的结论，更大、更复杂的形式位于当地地势较高的地方，但那里的供水仅限于直接降水，而在较低的地方，降雨由径流增加。
{"title":"Distribution and Morphology of the Bedrock Basins Known as Pans in a Granitic Inselberg Landscape","authors":"C. Twidale","doi":"10.1086/722288","DOIUrl":"https://doi.org/10.1086/722288","url":null,"abstract":"In 2008, Pogue and Katz reported that on granitic exposures in the Cassia City of Rocks, Idaho, the larger pans (shallow flat-floored gnammas or rock basins with overhanging sidewalls) are developed and preserved high in the local relief. They related this aspect of pan distribution to duration of exposure. This working hypothesis is tested by examining pan distribution on granitic inselbergs located on northwestern Eyre Peninsula, in semiarid southern South Australia. Pans in numbers have developed on sensibly level surfaces and have been shaped by pools of standing water. The larger—and more complex—forms are situated high in the local relief, as concluded by Pogue and Katz, but where water supply is limited to direct precipitation, by contrast with lower sites, where rainfall is augmented by runoff.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"311 - 324"},"PeriodicalIF":1.8,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44427713","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}
Yihong Tian, L. Zeng, Li-E. Gao, Yaying Wang, K. Hou, Suo‐han Tang, Chunli Guo
An Early Jurassic (∼196 Ma, laser ablation multiple-collector ICP-MS zircon U-Pb ages) suite of diabase dikes and sills has been identified within the Late Triassic Langjiexue Group, part of the Tethyan sedimentary sequence that is composed of shale and fine-grained sandstone. More primitive rocks (MgO>8.0 wt%) from this suite are characterized by mid-ocean ridge basalt–like rare earth element distribution patterns and isotope (Sr and Nd) compositions, as well as relatively high contents of mantle-compatible elements (e.g., Cr, Ni, and Co), which indicates that they were derived from partial melting of depleted mantle. Younger (∼140 Ma) mafic magmatism in the region has been proposed to represent the initial breakup of the eastern Gondwana continent and the opening of the Indian Ocean. We propose that the ∼196 Ma diabases developed in a continental extension setting and represent the products of melting of depleted mantle within or on the margin of the Neo-Tethyan Ocean.
{"title":"Early Jurassic Mafic Magmatism in the Eastern Tethyan Himalaya, Southern Tibet","authors":"Yihong Tian, L. Zeng, Li-E. Gao, Yaying Wang, K. Hou, Suo‐han Tang, Chunli Guo","doi":"10.1086/721486","DOIUrl":"https://doi.org/10.1086/721486","url":null,"abstract":"An Early Jurassic (∼196 Ma, laser ablation multiple-collector ICP-MS zircon U-Pb ages) suite of diabase dikes and sills has been identified within the Late Triassic Langjiexue Group, part of the Tethyan sedimentary sequence that is composed of shale and fine-grained sandstone. More primitive rocks (MgO>8.0 wt%) from this suite are characterized by mid-ocean ridge basalt–like rare earth element distribution patterns and isotope (Sr and Nd) compositions, as well as relatively high contents of mantle-compatible elements (e.g., Cr, Ni, and Co), which indicates that they were derived from partial melting of depleted mantle. Younger (∼140 Ma) mafic magmatism in the region has been proposed to represent the initial breakup of the eastern Gondwana continent and the opening of the Indian Ocean. We propose that the ∼196 Ma diabases developed in a continental extension setting and represent the products of melting of depleted mantle within or on the margin of the Neo-Tethyan Ocean.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"283 - 296"},"PeriodicalIF":1.8,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45396496","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}
Here we report geochronological, geochemical, and Sr-Nd-Hf isotopic data of a basic intrusion exposed in the Jiacha area within the Tethyan Himalaya, southern Tibet. The Jiacha dikes are composed mainly of mafic rocks (gabbros). In zircon U-Pb dating of Jiacha dikes samples, the weighted mean ages of magma emplacement were determined to be 241.5±4.2 to 245.5±3.3 Ma, showing a Middle Triassic magmatic event in the eastern part of the Tethyan Himalaya. The Jiacha dikes have relatively low MgO and total alkali (K2O+Na2O) contents but high TiO2 contents, exhibit weakly fractionated rare earth element (REE) patterns with slight depletions in light REEs and no obvious Eu anomalies, and show enrichment in high field strength elements and depletion in large-ion lithophile elements. Their initial 87Sr/86Sr ratios vary in the range 0.704250–0.704321, with a positive εNd(t = 243 Ma) of +3.07 to +3.67, and their initial 176Hf/177Hf ratios vary in the range 0.282872–0.283044, with a positive εHf(t = 243 Ma) of +8.53 to +14.45. We propose that the Jiacha dikes were derived from spinel lherzolites in the mantle with no crustal contamination and underwent fractional crystallization of clinopyroxene. Considering previous studies, we propose that Jiacha dikes represent oceanic crustal products of the early evolution of the Neo-Tethys, indicating that the ocean had already begun to open in the Middle Triassic.
{"title":"Late Paleozoic to Early Mesozoic Evolution of Neo-Tethys: Geochemical Evidence from Early Triassic Mafic Intrusive Rocks in the Tethyan Himalaya","authors":"Tong Zhou, Z. Kang, Ji‐Feng Xu, Feng Yang, Rui Wang, chun-xi Shan","doi":"10.1086/722390","DOIUrl":"https://doi.org/10.1086/722390","url":null,"abstract":"Here we report geochronological, geochemical, and Sr-Nd-Hf isotopic data of a basic intrusion exposed in the Jiacha area within the Tethyan Himalaya, southern Tibet. The Jiacha dikes are composed mainly of mafic rocks (gabbros). In zircon U-Pb dating of Jiacha dikes samples, the weighted mean ages of magma emplacement were determined to be 241.5±4.2 to 245.5±3.3 Ma, showing a Middle Triassic magmatic event in the eastern part of the Tethyan Himalaya. The Jiacha dikes have relatively low MgO and total alkali (K2O+Na2O) contents but high TiO2 contents, exhibit weakly fractionated rare earth element (REE) patterns with slight depletions in light REEs and no obvious Eu anomalies, and show enrichment in high field strength elements and depletion in large-ion lithophile elements. Their initial 87Sr/86Sr ratios vary in the range 0.704250–0.704321, with a positive εNd(t = 243 Ma) of +3.07 to +3.67, and their initial 176Hf/177Hf ratios vary in the range 0.282872–0.283044, with a positive εHf(t = 243 Ma) of +8.53 to +14.45. We propose that the Jiacha dikes were derived from spinel lherzolites in the mantle with no crustal contamination and underwent fractional crystallization of clinopyroxene. Considering previous studies, we propose that Jiacha dikes represent oceanic crustal products of the early evolution of the Neo-Tethys, indicating that the ocean had already begun to open in the Middle Triassic.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"130 1","pages":"297 - 310"},"PeriodicalIF":1.8,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46668337","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}
Matthias Schmidt, Peter Bartenstein, Jan Bucerius, Markus Dietlein, Alexander Drzezga, Ken Herrmann, Constantin Lapa, Kerstin Lorenz, Thomas J Musholt, James Nagarajah, Christoph Reiners, Carsten O Sahlmann, Michael C Kreissl
{"title":"Correction: Individualized treatment of differentiated thyroid cancer: The value of surgery in combination with radioiodine imaging and therapy - A German position paper from Surgery and Nuclear Medicine.","authors":"Matthias Schmidt, Peter Bartenstein, Jan Bucerius, Markus Dietlein, Alexander Drzezga, Ken Herrmann, Constantin Lapa, Kerstin Lorenz, Thomas J Musholt, James Nagarajah, Christoph Reiners, Carsten O Sahlmann, Michael C Kreissl","doi":"10.1055/a-1824-1280","DOIUrl":"10.1055/a-1824-1280","url":null,"abstract":"","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"103 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82735575","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}
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