Mathilde Mercuzot, Camille Rossignol, Sylvie Bourquin, Jahandar Ramezani, Céline Ducassou, Marc Poujol, Laurent Beccaletto, Pierre Pellenard
Intramontane late Carboniferous–Permian basins of western Europe developed during the latest orogenic stages of the Variscan Mountain Belt in eastern Pangaea, at equatorial palaeolatitudes. Their stratigraphic framework is mainly based on continental subdivisions (e.g. Stephanian and Autunian continental stages), which can be contentious owing to biostratigraphic biases, resulting in long-distance diachronous subdivisions. To provide precise inter-basinal and global correlations to the internationally recognized chronostratigraphic marine stages, this study reports new U–Pb geochronology from the Aumance and Decize–La Machine basins, located in the northern French Massif Central. Zircon grains extracted from three volcanic ash-fall layers give weighted mean 206 Pb/ 238 U ages of 299.11 ± 0.35, 298.73 ± 0.36 and 298.59 ± 0.35 Ma (2 σ total propagated uncertainty) by the chemical abrasion isotope dilution thermal ionization mass spectrometry method, coinciding with the Carboniferous–Permian transition (Gzhelian and Asselian stages). These ages imply that the northern Massif Central basins developed synchronously in relatively short periods of time (<10 myr), reflecting substantial sedimentation rates. Finally, the new chronology of infilling of these basins confirms that they were connected during the late Carboniferous and early Permian periods, improving the knowledge on the late orogenic Variscan geodynamic setting in this area. Supplementary material: Operating conditions and complete analytical results are available at https://doi.org/10.6084/m9.figshare.c.6805228
西欧晚石炭世—二叠纪山内盆地发育于泛古大陆东部瓦里斯坎山带的最新造山带阶段，位于赤道古纬度。它们的地层格架主要基于大陆细分(如斯蒂芬期和奥图尼期大陆阶段)，但由于生物地层偏差，这种划分可能存在争议，导致了长距离的历时细分。为了提供国际公认的海相地层年代学阶段的精确的盆地间和全球相关性，本研究报告了位于法国中部地块北部的Aumance和Decize-La Machine盆地的新的U-Pb地质年代学。利用化学磨损同位素稀释热电离质谱法，从3个火山灰落层中提取的锆石颗粒加权平均206pb / 238 U年龄分别为299.11±0.35、298.73±0.36和298.59±0.35 Ma (2 σ总传播不确定度)，符合石炭-二叠纪过渡时期(Gzhelian和Asselian阶段)。这些年龄表明，北部地块中央盆地在相对较短的时间内(约10myr)同步发育，反映了可观的沉积速率。最后，新的盆地充填年代学证实了这些盆地在晚石炭世和早二叠世之间的连接，提高了对本区晚造山期Variscan地球动力学背景的认识。补充资料:操作条件和完整的分析结果可在https://doi.org/10.6084/m9.figshare.c.6805228上获得
{"title":"U–Pb age constraints on the Carboniferous–Permian transition in continental basins of eastern equatorial Pangaea (France): implications for the depositional history and correlations across the late Variscan Belt","authors":"Mathilde Mercuzot, Camille Rossignol, Sylvie Bourquin, Jahandar Ramezani, Céline Ducassou, Marc Poujol, Laurent Beccaletto, Pierre Pellenard","doi":"10.1144/jgs2023-075","DOIUrl":"https://doi.org/10.1144/jgs2023-075","url":null,"abstract":"Intramontane late Carboniferous–Permian basins of western Europe developed during the latest orogenic stages of the Variscan Mountain Belt in eastern Pangaea, at equatorial palaeolatitudes. Their stratigraphic framework is mainly based on continental subdivisions (e.g. Stephanian and Autunian continental stages), which can be contentious owing to biostratigraphic biases, resulting in long-distance diachronous subdivisions. To provide precise inter-basinal and global correlations to the internationally recognized chronostratigraphic marine stages, this study reports new U–Pb geochronology from the Aumance and Decize–La Machine basins, located in the northern French Massif Central. Zircon grains extracted from three volcanic ash-fall layers give weighted mean 206 Pb/ 238 U ages of 299.11 ± 0.35, 298.73 ± 0.36 and 298.59 ± 0.35 Ma (2 <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\"> <mml:mi>σ</mml:mi> </mml:math> total propagated uncertainty) by the chemical abrasion isotope dilution thermal ionization mass spectrometry method, coinciding with the Carboniferous–Permian transition (Gzhelian and Asselian stages). These ages imply that the northern Massif Central basins developed synchronously in relatively short periods of time (<10 myr), reflecting substantial sedimentation rates. Finally, the new chronology of infilling of these basins confirms that they were connected during the late Carboniferous and early Permian periods, improving the knowledge on the late orogenic Variscan geodynamic setting in this area. Supplementary material: Operating conditions and complete analytical results are available at https://doi.org/10.6084/m9.figshare.c.6805228","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135923906","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wei Li, Xinqi Yu, Jun Hu, Yichao Zhang, Teng Peng, Nianwei Liu
Understanding the tectonic evolution of the Proto-Tethys Ocean is important for exploring the initial assembly of the Gondwana supercontinent. The closure of the Proto-Tethys Ocean represents the end of convergence along the northern edge of Eastern Gondwana. However, the timing and processes of the closing of the ocean have different interpretations. This work focuses on the early Paleozoic granitic rocks in the Baoshan Block (BSB), SW China, to constrain the tectonic evolution of the Proto-Tethys Ocean. Zircons from the Pinghe and Zhen'an granitic plutons yield concordant U–Pb ages from 489.8 Ma to 467.7 Ma. The bulk-rock geochemical features suggest that these samples are high-K, calc-alkaline, S-type granites enriched in LREEs and depleted in HREEs. With obvious negative Eu-anomalies and high K 2 O/Na 2 O ratios (1.01–2.57), they are enriched in LILEs and depleted in HFSEs. Thus, these rocks were derived from partial crustal melting associated with subduction of the converging plate. Previous studies on the Changning–Menglian suture zone suggested that the Early Paleozoic magmatic activity in the BSB was related to the westward subduction of the Proto-Tethys Ocean, combining the Early Paleozoic subduction-related magmatic activity to the east, it is suggested that the Changning–Menglian Ocean experienced bidirectional subduction.
{"title":"Bidirectional subduction of the Proto-Tethys Ocean: Constraints from geochronology and geochemistry of S-type granites from Baoshan Block in western Yunnan (SW China)","authors":"Wei Li, Xinqi Yu, Jun Hu, Yichao Zhang, Teng Peng, Nianwei Liu","doi":"10.1144/jgs2022-188","DOIUrl":"https://doi.org/10.1144/jgs2022-188","url":null,"abstract":"Understanding the tectonic evolution of the Proto-Tethys Ocean is important for exploring the initial assembly of the Gondwana supercontinent. The closure of the Proto-Tethys Ocean represents the end of convergence along the northern edge of Eastern Gondwana. However, the timing and processes of the closing of the ocean have different interpretations. This work focuses on the early Paleozoic granitic rocks in the Baoshan Block (BSB), SW China, to constrain the tectonic evolution of the Proto-Tethys Ocean. Zircons from the Pinghe and Zhen'an granitic plutons yield concordant U–Pb ages from 489.8 Ma to 467.7 Ma. The bulk-rock geochemical features suggest that these samples are high-K, calc-alkaline, S-type granites enriched in LREEs and depleted in HREEs. With obvious negative Eu-anomalies and high K 2 O/Na 2 O ratios (1.01–2.57), they are enriched in LILEs and depleted in HFSEs. Thus, these rocks were derived from partial crustal melting associated with subduction of the converging plate. Previous studies on the Changning–Menglian suture zone suggested that the Early Paleozoic magmatic activity in the BSB was related to the westward subduction of the Proto-Tethys Ocean, combining the Early Paleozoic subduction-related magmatic activity to the east, it is suggested that the Changning–Menglian Ocean experienced bidirectional subduction.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136295397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Sukhothai Terrane in northern Thailand comprises a continental basement and a Permo-Triassic magmatic arc related to the subduction of the main Paleo-Tethys Ocean. The Donchai Group represents the oldest sedimentary sequence of the Sukhothai Terrane and consists mainly of meta-sandstone, quartzo-feldspathic schist, phyllite and silty slate. This paper presents new detrital zircon U–Pb geochronology and Lu–Hf isotope data, and geochemical results for the sedimentary rocks of the Donchai Group to elucidate the depositional age, provenance and nature of the group. The youngest detrital zircon ages (433–403 Ma) suggest that the Donchai Group was accumulated between 433 Ma and 368 Ma, revealing Silurian–Devonian arc magmatic rocks on the western margin of the Sukhothai Terrane. Sediments of the Donchai Group were sourced from both the continental basement and a Silurian–Early Devonian magmatic arc, suggesting a depositional setting on the continental slope of a back-arc basin along the western flank of the Sukhothai Terrane. The Silurian–Devonian arc belt in SW China likely extend to the Chiang Rai region, to the west of the Sukhothai Terrane, northern Thailand, revealing the northward subduction of the Proto-Tethys Ocean along the western Simao and Sukhothai margin during the middle Paleozoic. The inferred arc and back-arc configuration of the Proto-Tethys in northern Thailand is comparable with that recently established in Yunnan, SW China. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6858373
{"title":"Detrital zircon U–Pb and Hf analyses of Silurian–Devonian sediments in the Sukhothai Terrane, northern Thailand: Implications for the middle Paleozoic arc belt","authors":"Xiaomei Nie, Qinglai Feng, Jianwei Zi, Zhengqin Gan, Ian Metcalfe, Chongpan Chonglakmani, Denchok Monjai, Tianyu Zhao, Jianye Ren, Jongkonnee Khanmanee, Pradit Nulay","doi":"10.1144/jgs2023-049","DOIUrl":"https://doi.org/10.1144/jgs2023-049","url":null,"abstract":"The Sukhothai Terrane in northern Thailand comprises a continental basement and a Permo-Triassic magmatic arc related to the subduction of the main Paleo-Tethys Ocean. The Donchai Group represents the oldest sedimentary sequence of the Sukhothai Terrane and consists mainly of meta-sandstone, quartzo-feldspathic schist, phyllite and silty slate. This paper presents new detrital zircon U–Pb geochronology and Lu–Hf isotope data, and geochemical results for the sedimentary rocks of the Donchai Group to elucidate the depositional age, provenance and nature of the group. The youngest detrital zircon ages (433–403 Ma) suggest that the Donchai Group was accumulated between 433 Ma and 368 Ma, revealing Silurian–Devonian arc magmatic rocks on the western margin of the Sukhothai Terrane. Sediments of the Donchai Group were sourced from both the continental basement and a Silurian–Early Devonian magmatic arc, suggesting a depositional setting on the continental slope of a back-arc basin along the western flank of the Sukhothai Terrane. The Silurian–Devonian arc belt in SW China likely extend to the Chiang Rai region, to the west of the Sukhothai Terrane, northern Thailand, revealing the northward subduction of the Proto-Tethys Ocean along the western Simao and Sukhothai margin during the middle Paleozoic. The inferred arc and back-arc configuration of the Proto-Tethys in northern Thailand is comparable with that recently established in Yunnan, SW China. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6858373","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136294929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The collage of the Indochina Block to the Eurasian continent during the Mesozoic resulted in major changes in source-to-sink systems of East Asia, whilst the sedimentation in the Khorat-Simao Basin of the Indochina Block transited from marine to continental environments. Previous studies conducted the existence of transcontinental river systems in the East Asia mainland during the Cretaceous to early Cenozoic with few studies on pre-Cretaceous drainage systems. To determine the impact on the evolution of paleo-drainage systems triggered by tectonic movement of the Indochina Block, we performed paleomagnetic and U-Pb geochronologic analyses on the Late Triassic to Early Cretaceous sedimentary rocks in the Simao Basin. Paleomagnetic data indicate stable Jurassic tectonic environments between the Indochina and Songpan Ganzi-South China blocks, following their Late Triassic collision. Based on detrital zircon U-Pb dating, the Late Triassic age spectra consist of mainly Phanerozoic components, while the Jurassic to Cretaceous age spectra displayed more Precambrian age peaks. The contribution of potential provenance to the Simao Basin changed during the Early Cretaceous, suggesting several sedimentary provenance transitions. Also, we believe that large continental-scale drainage systems sourced from the Songpan-Ganzi Block flowing through North Qiangtang, Sichuan, Simao, and Khorat basins since after the Late Jurassic. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.6862918
{"title":"Mesozoic evolution of large-scale drainage systems in the Indochina Block: evidence from paleomagnetic and U-Pb geochronological constraints","authors":"Zhenyang Lai, Qian Zhao, Yonggang Yan, Danxin Li, Bingxu Liu, Kang Liu, Baochun Huang, Peizhen Zhang","doi":"10.1144/jgs2023-084","DOIUrl":"https://doi.org/10.1144/jgs2023-084","url":null,"abstract":"The collage of the Indochina Block to the Eurasian continent during the Mesozoic resulted in major changes in source-to-sink systems of East Asia, whilst the sedimentation in the Khorat-Simao Basin of the Indochina Block transited from marine to continental environments. Previous studies conducted the existence of transcontinental river systems in the East Asia mainland during the Cretaceous to early Cenozoic with few studies on pre-Cretaceous drainage systems. To determine the impact on the evolution of paleo-drainage systems triggered by tectonic movement of the Indochina Block, we performed paleomagnetic and U-Pb geochronologic analyses on the Late Triassic to Early Cretaceous sedimentary rocks in the Simao Basin. Paleomagnetic data indicate stable Jurassic tectonic environments between the Indochina and Songpan Ganzi-South China blocks, following their Late Triassic collision. Based on detrital zircon U-Pb dating, the Late Triassic age spectra consist of mainly Phanerozoic components, while the Jurassic to Cretaceous age spectra displayed more Precambrian age peaks. The contribution of potential provenance to the Simao Basin changed during the Early Cretaceous, suggesting several sedimentary provenance transitions. Also, we believe that large continental-scale drainage systems sourced from the Songpan-Ganzi Block flowing through North Qiangtang, Sichuan, Simao, and Khorat basins since after the Late Jurassic. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.6862918","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134975059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jialun Huang, Xiubin Lin, Kaixuan An, Yang Qu, Li Li, Lin Jiang, Zhuxin Chen, Hanlin Chen, Xiaogan Cheng, Lining Wang, Cai Chen, Liang Zhang, Wei Liu, Xianzhang Yang, Yong Li, Yuqing Zhang, Nan Su
The Tian Shan is one of the world's largest intracontinental orogens and provides an excellent example for deciphering the intracontinental responses to the tectonics of plate boundaries. Despite its significance, the timing and driving mechanism of the Cenozoic mountain building of the Tian Shan in the context of the India-Eurasia collision remain controversial. In this study, Cenozoic stratigraphy of the Tiereke section along the western Kuqa Depression of the northern Tarim Basin on the south foreland of Eastern Tian Shan (east of 80°E) has been investigated. The results indicated that the Cenozoic deposition of the Tiereke region sequentially experienced a transgression from the Kumugeliemu Group to the Suweiyi Formation and a regression from the Suweiyi to the Kuqa Formations. Based on the contact relationships and conglomerate textures, three stages of high-energy alluvial deposition have been identified in the lower Kumugeliemu Group, upper Jidike, and Kangcun-Kuqa Formations, respectively. These sedimentary events were interpreted to represent phases of Eastern Tian Shan mountain building at ca. 54 Ma, ca. 27 Ma and since ca. 9.7 Ma according to previous magnetostratigraphic results, which were possibly related to the initial India-Eurasia collision, the collision between the India and Tarim lithospheric mantles, and the basinward propagation of deformation, respectively. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change
{"title":"Cenozoic sedimentary evolution of the Tiereke section on the northern Tarim Basin: implications for the intracontinental mountain building of the Eastern Tian Shan","authors":"Jialun Huang, Xiubin Lin, Kaixuan An, Yang Qu, Li Li, Lin Jiang, Zhuxin Chen, Hanlin Chen, Xiaogan Cheng, Lining Wang, Cai Chen, Liang Zhang, Wei Liu, Xianzhang Yang, Yong Li, Yuqing Zhang, Nan Su","doi":"10.1144/jgs2023-114","DOIUrl":"https://doi.org/10.1144/jgs2023-114","url":null,"abstract":"The Tian Shan is one of the world's largest intracontinental orogens and provides an excellent example for deciphering the intracontinental responses to the tectonics of plate boundaries. Despite its significance, the timing and driving mechanism of the Cenozoic mountain building of the Tian Shan in the context of the India-Eurasia collision remain controversial. In this study, Cenozoic stratigraphy of the Tiereke section along the western Kuqa Depression of the northern Tarim Basin on the south foreland of Eastern Tian Shan (east of 80°E) has been investigated. The results indicated that the Cenozoic deposition of the Tiereke region sequentially experienced a transgression from the Kumugeliemu Group to the Suweiyi Formation and a regression from the Suweiyi to the Kuqa Formations. Based on the contact relationships and conglomerate textures, three stages of high-energy alluvial deposition have been identified in the lower Kumugeliemu Group, upper Jidike, and Kangcun-Kuqa Formations, respectively. These sedimentary events were interpreted to represent phases of Eastern Tian Shan mountain building at ca. 54 Ma, ca. 27 Ma and since ca. 9.7 Ma according to previous magnetostratigraphic results, which were possibly related to the initial India-Eurasia collision, the collision between the India and Tarim lithospheric mantles, and the basinward propagation of deformation, respectively. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135548078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Increasing mineralogical and textural evidence from podiform chromitites in ophiolites show their ultra–high pressure origin (>150 km), challenging the conventional models for their formation under low pressure conditions (< 60 km) in the upper mantle. However, this challenge remains controversial due to the lack of in-situ mineralogical evidence. Here, we report new data and observations from the Skenderbeu massif in Mirdita ophiolite, Albania. Transmission electron microscopy (TEM) analysis reveal for the first time that these chromitites (Cr#= 41.8-43.2) have numerous exsolution lamellae of diopsidic clinopyroxene and orthoenstatite. TEM analysis also show that these lamellae have a crystallographic topotaxy relationship with the host chromite, i.e., (020) Cpx ∥︀ (22(—)0) Chr , (2(—)00) Cpx ∥︀ (111) Chr , and (010) Opx ∥︀ (22(—)0) Chr , (200) Opx ∥︀ (22(—)0) Chr , indicating an exsolution origin. The abundant presence of pyroxene exsolution lamellae in center of the host chromites implies the incorporation of Si 4+ and Ca 2+ cations in the precursor chromite, a CaFe 2 O 4 -structured high-pressure polymorph, which was stable >12.5 GPa (i.e., 380 km deep). These in-situ, nano-scale observations, and geological occurrence, together with previously discovered ophiolitic diamonds in the Mirdita ophiolite, suggest a much deeper origin for ophiolitic chromitites than conventional interpretations, and provide a valuable opportunity to understand the composition of the deep mantle. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists
{"title":"Two-pyroxene, intergrowth exsolution textures in ophiolitic chromites: implications for the deep mantle origin of the Mirdita Ophiolite, Albania","authors":"Weiwei Wu, Jingsui Yang, Yildirim Dilek, Souvik Das, Dongyang Lian, Pengjie Cai, Yun Wang, Yu Yang, Yuanyun Wen","doi":"10.1144/jgs2023-128","DOIUrl":"https://doi.org/10.1144/jgs2023-128","url":null,"abstract":"Increasing mineralogical and textural evidence from podiform chromitites in ophiolites show their ultra–high pressure origin (>150 km), challenging the conventional models for their formation under low pressure conditions (< 60 km) in the upper mantle. However, this challenge remains controversial due to the lack of in-situ mineralogical evidence. Here, we report new data and observations from the Skenderbeu massif in Mirdita ophiolite, Albania. Transmission electron microscopy (TEM) analysis reveal for the first time that these chromitites (Cr#= 41.8-43.2) have numerous exsolution lamellae of diopsidic clinopyroxene and orthoenstatite. TEM analysis also show that these lamellae have a crystallographic topotaxy relationship with the host chromite, i.e., (020) Cpx ∥︀ (22(—)0) Chr , (2(—)00) Cpx ∥︀ (111) Chr , and (010) Opx ∥︀ (22(—)0) Chr , (200) Opx ∥︀ (22(—)0) Chr , indicating an exsolution origin. The abundant presence of pyroxene exsolution lamellae in center of the host chromites implies the incorporation of Si 4+ and Ca 2+ cations in the precursor chromite, a CaFe 2 O 4 -structured high-pressure polymorph, which was stable >12.5 GPa (i.e., 380 km deep). These in-situ, nano-scale observations, and geological occurrence, together with previously discovered ophiolitic diamonds in the Mirdita ophiolite, suggest a much deeper origin for ophiolitic chromitites than conventional interpretations, and provide a valuable opportunity to understand the composition of the deep mantle. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135592407","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jean-Bernard Caron, Mark Webster, Derek E.G. Briggs, Giovanni Pari, Guy Santucci, M. Gabriela Mángano, Alejandro Izquierdo-López, Michael Streng, Robert R. Gaines
Discovered over a century ago, the lower Cambrian (Series 2, Stage 4) Cranbrook Lagerstätte of southeastern British Columbia's Eager Formation is one of the oldest Burgess Shale-type deposits in North America. This Konservat-Lagerstätte is rich in olenelloid trilobites, but also yields a very low-diversity soft-bodied fossil assemblage including Tuzoia and Anomalocaris , and a low-diversity ichnofauna. Its scientific study, however, remains limited. A 2015 field-based investigation by the Royal Ontario Museum has revealed new information about the site's biota, depositional environment, and taphonomic conditions. Not only is the Cranbrook Lagerstätte significant for early Cambrian biostratigraphy and comparisons with other Burgess Shale-type deposits, it also reveals some of the little-known diversity of life along a distal outer shelf environment during the Cambrian period. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850810
{"title":"The lower Cambrian Cranbrook Lagerstätte of British Columbia","authors":"Jean-Bernard Caron, Mark Webster, Derek E.G. Briggs, Giovanni Pari, Guy Santucci, M. Gabriela Mángano, Alejandro Izquierdo-López, Michael Streng, Robert R. Gaines","doi":"10.1144/jgs2023-106","DOIUrl":"https://doi.org/10.1144/jgs2023-106","url":null,"abstract":"Discovered over a century ago, the lower Cambrian (Series 2, Stage 4) Cranbrook Lagerstätte of southeastern British Columbia's Eager Formation is one of the oldest Burgess Shale-type deposits in North America. This Konservat-Lagerstätte is rich in olenelloid trilobites, but also yields a very low-diversity soft-bodied fossil assemblage including Tuzoia and Anomalocaris , and a low-diversity ichnofauna. Its scientific study, however, remains limited. A 2015 field-based investigation by the Royal Ontario Museum has revealed new information about the site's biota, depositional environment, and taphonomic conditions. Not only is the Cranbrook Lagerstätte significant for early Cambrian biostratigraphy and comparisons with other Burgess Shale-type deposits, it also reveals some of the little-known diversity of life along a distal outer shelf environment during the Cambrian period. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850810","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135387223","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jose Nano, David W. Haig, Edwin Ornai Fraga, Moises Soares, Isaias Santos Barros, Eujay McCartain, Peter Baillie
Timor lies at the centre of a rapidly evolving orogenic belt. Matebian Range, one of its largest mountains, was previously mapped as Lower Miocene neritic Cablac Limestone and regarded as allochthonous (viz. Banda Terrane). New analyses have demonstrated a disjunct stratigraphy, extending from the Lower Jurassic to lowest Miocene and encompassing neritic to abyssal strata. Positioning each stratigraphic unit (six new) on a time vs. bathymetry plot and identifying clast types in conglomerates and turbidites allows reconstruction of changes in provenance to depo-centres through time. Terrane progression from the northern margin of Gondwana to the southern Sundaland margin (Asia) and then back to the northwest margin of the Australian continent is indicated involving progressive amalgamation and rifting and substantial episodes of uplift, particularly during the Middle Eocene and the Late Oligocene. The youngest unit (Late Oligocene–earliest Miocene) was deposited adjacent a rapidly rising hinterland (southern Sundaland) very different from that on the coeval Australian margin. The study provides a model for the tectonostratigraphic reconstruction of limestone-dominated mountains in young orogenic belts and demonstrates the importance of using sedimentary clasts in mass-flow deposits to interpret ages and depositional environments of reworked material and to stitch together tectonostratigraphic pathways through time. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6852387
{"title":"Debris-slides, olistoliths and turbidites: keys to understanding the tectonostratigraphic affinities of a terrane block in a young orogenic belt, Timor-Leste","authors":"Jose Nano, David W. Haig, Edwin Ornai Fraga, Moises Soares, Isaias Santos Barros, Eujay McCartain, Peter Baillie","doi":"10.1144/jgs2023-079","DOIUrl":"https://doi.org/10.1144/jgs2023-079","url":null,"abstract":"Timor lies at the centre of a rapidly evolving orogenic belt. Matebian Range, one of its largest mountains, was previously mapped as Lower Miocene neritic Cablac Limestone and regarded as allochthonous (viz. Banda Terrane). New analyses have demonstrated a disjunct stratigraphy, extending from the Lower Jurassic to lowest Miocene and encompassing neritic to abyssal strata. Positioning each stratigraphic unit (six new) on a time vs. bathymetry plot and identifying clast types in conglomerates and turbidites allows reconstruction of changes in provenance to depo-centres through time. Terrane progression from the northern margin of Gondwana to the southern Sundaland margin (Asia) and then back to the northwest margin of the Australian continent is indicated involving progressive amalgamation and rifting and substantial episodes of uplift, particularly during the Middle Eocene and the Late Oligocene. The youngest unit (Late Oligocene–earliest Miocene) was deposited adjacent a rapidly rising hinterland (southern Sundaland) very different from that on the coeval Australian margin. The study provides a model for the tectonostratigraphic reconstruction of limestone-dominated mountains in young orogenic belts and demonstrates the importance of using sedimentary clasts in mass-flow deposits to interpret ages and depositional environments of reworked material and to stitch together tectonostratigraphic pathways through time. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6852387","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135387362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The mechanisms of the upward and outwards growth of the Tibetan Plateau are crucial for understanding the geodynamic significance of Cenozoic continental collisions. Northeastern Tibet has been suggested as one of the youngest deforming and uplifting margins surrounding the plateau. The existence of fluvial knickpoints and low-relief topographic surfaces along the Yellow River and its tributaries indicate the transience of the landscape in response to active tectonic uplift. Therefore, the uplift history of the North Eastern Tibetan Plateau (NETP) can be potentially inverted from the disequilibrium channel profiles of the Yellow River and its tributaries. The West Qinling Fault (WQF) is part of the geomorphological and topographic boundaries of the NETP. Its uplift history helps explore the deformation history of the Tibetan Plateau. In this study, the focus was on the Daxia River (one of the Yellow River tributary) in order to identify the distribution of peneplain surfaces and knickpoints, and present a linear inversion on the fluvial longitudinal profiles for the relative uplift history of the West Qinling. We obtained a relative uplift history with two pulses of change in the uplift rates at ∼5 Ma and ∼2 Ma. Rates of relative uplift maintained low values during the Late Miocene, then slowly increased from 0.1 mm/a to 0.2 mm/a since ∼5 Ma and suddenly jumped to 0.3 mm/a at ∼2 Ma, consistent with recent findings on the deformation records in the NE Tibetan Plateau. We suggest that 1) the Late Miocene-Pliocene landscape evolution was driven by both tectonics and climate change and 2) inversion of the transient longitudinal channel profiles, if applied, may provide broader insights into the upward and outwards growth patterns of the NE Tibetan Plateau. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change
{"title":"Inversion of Late Miocene uplift history from the transient Daxia River landscape, NE Tibetan Plateau","authors":"Yihui Zhang, Huiping Zhang, Zifa Ma, Yizhou Wang, Xudong Zhao","doi":"10.1144/jgs2023-030","DOIUrl":"https://doi.org/10.1144/jgs2023-030","url":null,"abstract":"The mechanisms of the upward and outwards growth of the Tibetan Plateau are crucial for understanding the geodynamic significance of Cenozoic continental collisions. Northeastern Tibet has been suggested as one of the youngest deforming and uplifting margins surrounding the plateau. The existence of fluvial knickpoints and low-relief topographic surfaces along the Yellow River and its tributaries indicate the transience of the landscape in response to active tectonic uplift. Therefore, the uplift history of the North Eastern Tibetan Plateau (NETP) can be potentially inverted from the disequilibrium channel profiles of the Yellow River and its tributaries. The West Qinling Fault (WQF) is part of the geomorphological and topographic boundaries of the NETP. Its uplift history helps explore the deformation history of the Tibetan Plateau. In this study, the focus was on the Daxia River (one of the Yellow River tributary) in order to identify the distribution of peneplain surfaces and knickpoints, and present a linear inversion on the fluvial longitudinal profiles for the relative uplift history of the West Qinling. We obtained a relative uplift history with two pulses of change in the uplift rates at ∼5 Ma and ∼2 Ma. Rates of relative uplift maintained low values during the Late Miocene, then slowly increased from 0.1 mm/a to 0.2 mm/a since ∼5 Ma and suddenly jumped to 0.3 mm/a at ∼2 Ma, consistent with recent findings on the deformation records in the NE Tibetan Plateau. We suggest that 1) the Late Miocene-Pliocene landscape evolution was driven by both tectonics and climate change and 2) inversion of the transient longitudinal channel profiles, if applied, may provide broader insights into the upward and outwards growth patterns of the NE Tibetan Plateau. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135536642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dongping Shi, Hongbing Tan, Yu Zhang, Peixin Cong, Yucheng Cao
The Yarlungzngbo River (YR) is the largest river system draining the northern slopes of the Himalayan ranges on the southern Tibetan Plateau and is critical to the water supply of the people downstream. In this paper the chemical composition of the YR and its major tributaries (Nianchu River and Lhasa River) are studied. Water samples (n=165) were collected and analyzed for major ions and trace elements. Multivariable analysis shows that geology and climate are the major explanatory variables for the spatio-temporal variation in water chemistry in this river system. Water chemistry is mainly controlled by carbonate weathering, with Ca 2+ and HCO 3 - being the dominant ions. Furthermore, hot spring discharge rich in Na + , Cl - , SO 4 2- and Li is another potential ion source affecting river water chemistry, resulting in higher solute concentrations in the source region and upstream, TDS reached 176.9 mg/L. Levels of most trace elements were generally found to be low. However, elevated As (16.6 μg/L) and Sb concentration (2.08 μg/L) in the headwaters and additions from untreated wastewater were evident, which exceeded the national standard of China (GB) and the World Health Organization (WHO) drinking water guide, posing a risk to human livelihood in the local and surrounding areas. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850720
{"title":"Water quality of the southern Tibetan Plateau: hydrogeochemistry assessment of the Yarlungzangbo River","authors":"Dongping Shi, Hongbing Tan, Yu Zhang, Peixin Cong, Yucheng Cao","doi":"10.1144/jgs2023-040","DOIUrl":"https://doi.org/10.1144/jgs2023-040","url":null,"abstract":"The Yarlungzngbo River (YR) is the largest river system draining the northern slopes of the Himalayan ranges on the southern Tibetan Plateau and is critical to the water supply of the people downstream. In this paper the chemical composition of the YR and its major tributaries (Nianchu River and Lhasa River) are studied. Water samples (n=165) were collected and analyzed for major ions and trace elements. Multivariable analysis shows that geology and climate are the major explanatory variables for the spatio-temporal variation in water chemistry in this river system. Water chemistry is mainly controlled by carbonate weathering, with Ca\u0000 2+\u0000 and HCO\u0000 3\u0000 -\u0000 being the dominant ions. Furthermore, hot spring discharge rich in Na\u0000 +\u0000 , Cl\u0000 -\u0000 , SO\u0000 4\u0000 2-\u0000 and Li is another potential ion source affecting river water chemistry, resulting in higher solute concentrations in the source region and upstream, TDS reached 176.9 mg/L. Levels of most trace elements were generally found to be low. However, elevated As (16.6 μg/L) and Sb concentration (2.08 μg/L) in the headwaters and additions from untreated wastewater were evident, which exceeded the national standard of China (GB) and the World Health Organization (WHO) drinking water guide, posing a risk to human livelihood in the local and surrounding areas.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6850720","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135538435","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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