Isabel C. Zutterkirch, M. Barham, C. Kirkland, C. Elders
{"title":"Contrasting detrital feldspar Pb isotope ratios and zircon geochronology to distinguish proximal vs. distal transport","authors":"Isabel C. Zutterkirch, M. Barham, C. Kirkland, C. Elders","doi":"10.1086/726757","DOIUrl":"https://doi.org/10.1086/726757","url":null,"abstract":"","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2023-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41396593","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}
{"title":"Eocene Andesitic Adakite from Lone Mountain, Southwestern Montana","authors":"F. Dudás, N. Chatterjee, M. Krol","doi":"10.1086/726207","DOIUrl":"https://doi.org/10.1086/726207","url":null,"abstract":"","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2023-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45083691","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}
This study presents the restored Pliocene topography along northerly trending profiles in Manitoba, northwestern Ontario, eastern North Dakota, Minnesota, and western Wisconsin. A top-of-bedrock slope profile of the Red River/Lake Winnipeg/Nelson River and 19 south-trending landscape topographic and top-of-bedrock slope profiles of the region were made from published elevation data. These profiles reveal a clear change in slope and slope direction (flexure) in the top-of-bedrock elevation. The flexure axis trends southeasterly across Manitoba into northwestern Ontario. The profiles were then tilted southerly by lifting the profiles along the southern margin of Hudson Bay to restore remaining glacial isostatic rebound. When imposing a minimum 80 m of isostatic rebound to the Nelson River/Lake Winnipeg/Red River profile, the northern portion of the profile slopes north but the southern portion of the profile slopes south at 0.01%. When imposing a minimum 60 m of isostatic rebound to all 19 top-of-bedrock profiles, the bedrock slopes north to Hudson Bay northeast of the flexure; however, southwest of the flexure, the southern portions of the 19 top-of-bedrock profiles slope south. We interpret the flexure axis to have been the northern divide of the Pliocene Mississippi River basin in Manitoba and northwestern Ontario and the divide that will lie between the north-flowing Nelson River and south-flowing Red River with future glacial isostatic adjustment.
{"title":"Pliocene Drainage in Manitoba and Northwestern Ontario, Canada","authors":"R. V. Van Arsdale, Youngsang Kwon","doi":"10.1086/722972","DOIUrl":"https://doi.org/10.1086/722972","url":null,"abstract":"This study presents the restored Pliocene topography along northerly trending profiles in Manitoba, northwestern Ontario, eastern North Dakota, Minnesota, and western Wisconsin. A top-of-bedrock slope profile of the Red River/Lake Winnipeg/Nelson River and 19 south-trending landscape topographic and top-of-bedrock slope profiles of the region were made from published elevation data. These profiles reveal a clear change in slope and slope direction (flexure) in the top-of-bedrock elevation. The flexure axis trends southeasterly across Manitoba into northwestern Ontario. The profiles were then tilted southerly by lifting the profiles along the southern margin of Hudson Bay to restore remaining glacial isostatic rebound. When imposing a minimum 80 m of isostatic rebound to the Nelson River/Lake Winnipeg/Red River profile, the northern portion of the profile slopes north but the southern portion of the profile slopes south at 0.01%. When imposing a minimum 60 m of isostatic rebound to all 19 top-of-bedrock profiles, the bedrock slopes north to Hudson Bay northeast of the flexure; however, southwest of the flexure, the southern portions of the 19 top-of-bedrock profiles slope south. We interpret the flexure axis to have been the northern divide of the Pliocene Mississippi River basin in Manitoba and northwestern Ontario and the divide that will lie between the north-flowing Nelson River and south-flowing Red River with future glacial isostatic adjustment.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49623834","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 common-Pb isotope composition (207Pb/204Pb vs. 206Pb/204Pb) of detrital K-feldspar was measured on the same clastic units from southeastern Laurentia that were previously characterized by detrital zircon and detrital monazite geochronology for provenance analysis. The purpose is to test a model that invokes late Paleozoic recycling of sediment initially sourced from erosion of exhuming Grenvillian basement in the Neoproterozoic. The approach takes advantage of the difference in Pb isotope compositions between Laurentian and Amazonian cratonic sources documented by previous workers. Neoproterozoic samples sourced from southern Amazonia and central Laurentian basement that serve as controls on methodology plot within Pb isotope space characteristic of their respective sources. K-feldspar in the Cryogenian Ocoee Supergroup in the southern Appalachian orogen falls within the field of Pb isotope compositions defined by south-central Appalachian basement (SCAB). The latter, in turn, exhibits Pb isotope compositions characteristic of Amazonia, because SCAB was transferred to Laurentia from Amazonia during Rodinian assembly. In contrast, K-feldspar in early Cambrian arenite falls within the Laurentian field, indicating a shift in the early Paleozoic to a sediment source from the Laurentian Craton. K-feldspar in Lower Pennsylvanian lithic arenites of the Central Appalachian Basin exhibit Pb isotope compositions that fall within the SCAB field but at higher Pb isotope ratios than in the inferred Ocoee sources. Incorporation of all provenance constraints requires an immediate source that is isotopically more radiogenic than the Ocoee but similar in all other petrologic and geochronologic characteristics, for example, other Cryogenian to Ediacaran units along strike in the Appalachian orogen. The results further demonstrate the importance of having multiple detrital mineral proxies for accurate provenance analysis rather than using detrital zircon geochronology alone.
{"title":"Beyond Zircon: Incorporating Detrital Feldspar Pb Isotope Analysis into the Multiproxy Toolbox for Sedimentary Provenance Analysis—an Example from a Long-Lived Eastern Laurentian Clastic System","authors":"D. Moecher, E. Badenszki, J. Daly, D. Chew","doi":"10.1086/724287","DOIUrl":"https://doi.org/10.1086/724287","url":null,"abstract":"The common-Pb isotope composition (207Pb/204Pb vs. 206Pb/204Pb) of detrital K-feldspar was measured on the same clastic units from southeastern Laurentia that were previously characterized by detrital zircon and detrital monazite geochronology for provenance analysis. The purpose is to test a model that invokes late Paleozoic recycling of sediment initially sourced from erosion of exhuming Grenvillian basement in the Neoproterozoic. The approach takes advantage of the difference in Pb isotope compositions between Laurentian and Amazonian cratonic sources documented by previous workers. Neoproterozoic samples sourced from southern Amazonia and central Laurentian basement that serve as controls on methodology plot within Pb isotope space characteristic of their respective sources. K-feldspar in the Cryogenian Ocoee Supergroup in the southern Appalachian orogen falls within the field of Pb isotope compositions defined by south-central Appalachian basement (SCAB). The latter, in turn, exhibits Pb isotope compositions characteristic of Amazonia, because SCAB was transferred to Laurentia from Amazonia during Rodinian assembly. In contrast, K-feldspar in early Cambrian arenite falls within the Laurentian field, indicating a shift in the early Paleozoic to a sediment source from the Laurentian Craton. K-feldspar in Lower Pennsylvanian lithic arenites of the Central Appalachian Basin exhibit Pb isotope compositions that fall within the SCAB field but at higher Pb isotope ratios than in the inferred Ocoee sources. Incorporation of all provenance constraints requires an immediate source that is isotopically more radiogenic than the Ocoee but similar in all other petrologic and geochronologic characteristics, for example, other Cryogenian to Ediacaran units along strike in the Appalachian orogen. The results further demonstrate the importance of having multiple detrital mineral proxies for accurate provenance analysis rather than using detrital zircon geochronology alone.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49076081","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 Ediacaran (607–593 Ma) Ferani volcanic rocks are exposed in South Sinai, at the extreme northern tip of the Arabian-Nubian Shield (ANS). The studied volcanics constitute a cogenetic continuous intermediate (andesite to dacite) to acid (rhyodacite to rhyolite) lava sequence with a high-K calc-alkaline metaluminous to slightly peraluminous nature. They contain a high concentration of large-ion lithophile elements (i.e., Ba, Rb, Pb, and Th), but lower contents of Nb, P, Ti, and Sr. They also have a general enrichment in light rare earth elements ((La/Sm)N=2.66–4.92), compared to heavy rare earth elements ((Gd/Yb)N=1.10–2.29), with a slightly negative Eu anomaly (Eu/Eu*=0.35–0.94). The cooling of the Ferani magma began at ∼1000°–1100°C and went to ∼700°C at low pressure (<5.1 kbar) and shallow crustal levels (<17 km), according to thermobarometric modeling. The low degree of partial melting of the mafic lower-crustal rocks could have produced the andesitic-dacitic magmas that ascended through the crust and fractionated, leading to the production of the early intermediate Ferani lavas. Progressive fractional crystallization of the intermediate melts could consequently have formed the rhyodacite and rhyolite melts, which were later erupted to form the upper acidic Ferani volcanic sequence. Petrological and geochemical features support a postcollisional setting of the Ferani volcanics. Lithospheric delamination is the main geodynamic process responsible for the formation of the Ferani volcanics during the postcollisional extensional stage in the northern ANS crust.
{"title":"Postcollisional Ferani Volcanics from North Arabian–Nubian Shield (South Sinai, Egypt): Petrogenesis and Implication for Ediacaran (607–593 Ma) Geodynamic Evolution","authors":"Mabrouk Sami, M. Azer, A. Abdel-Karim","doi":"10.1086/724335","DOIUrl":"https://doi.org/10.1086/724335","url":null,"abstract":"The Ediacaran (607–593 Ma) Ferani volcanic rocks are exposed in South Sinai, at the extreme northern tip of the Arabian-Nubian Shield (ANS). The studied volcanics constitute a cogenetic continuous intermediate (andesite to dacite) to acid (rhyodacite to rhyolite) lava sequence with a high-K calc-alkaline metaluminous to slightly peraluminous nature. They contain a high concentration of large-ion lithophile elements (i.e., Ba, Rb, Pb, and Th), but lower contents of Nb, P, Ti, and Sr. They also have a general enrichment in light rare earth elements ((La/Sm)N=2.66–4.92), compared to heavy rare earth elements ((Gd/Yb)N=1.10–2.29), with a slightly negative Eu anomaly (Eu/Eu*=0.35–0.94). The cooling of the Ferani magma began at ∼1000°–1100°C and went to ∼700°C at low pressure (<5.1 kbar) and shallow crustal levels (<17 km), according to thermobarometric modeling. The low degree of partial melting of the mafic lower-crustal rocks could have produced the andesitic-dacitic magmas that ascended through the crust and fractionated, leading to the production of the early intermediate Ferani lavas. Progressive fractional crystallization of the intermediate melts could consequently have formed the rhyodacite and rhyolite melts, which were later erupted to form the upper acidic Ferani volcanic sequence. Petrological and geochemical features support a postcollisional setting of the Ferani volcanics. Lithospheric delamination is the main geodynamic process responsible for the formation of the Ferani volcanics during the postcollisional extensional stage in the northern ANS crust.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48977751","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}
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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}
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