The Late Triassic Carnian pluvial event (CPE) was an interval marked by global climatic and environmental changes that occurred simultaneously with enhancement of the hydrological cycle. This event is characterized by multiple negative carbon isotope excursions (NCIEs). However, the driving mechanism behind these multiple NCIEs remains elusive because each of the NCIEs had different magnitudes in different geological settings. In this study, we present a high-resolution record of carbonate carbon isotope ( δ 13 C carb ) and major and trace element data from Well QZ-8 in the Qiangtang Basin, eastern Tethys. The carbon isotope profile from this well displays a similar trend to those for contemporaneous strata in the NW Tethys and South China. This trend is characterized by a distinct negative excursion during the CPE, supporting a global event. Interestingly, our results reveal five NCIEs for the first time in the marine sedimentary succession. Furthermore, each of these NCIEs corresponds well to changes in Ti/Al, Sr/Al and Sr/Ba, suggesting a regional effect of the hydrological cycle on carbon isotope excursions. This study emphasizes that each of the NCIEs was influenced by regional hydrological cycles although the long carbon isotope excursion during the CPE was driven by the global carbon cycle. Supplementary material: Tables showing major element, isotope and trace element data and element ratios, and a supplementary figure are available at https://doi.org/10.6084/m9.figshare.c.6805266
{"title":"Multiple carbon isotope excursions during the Carnian (Late Triassic) pluvial event: Implications for global and regional perturbation","authors":"Puyang Ke, Xiugen Fu, Qinghua Peng, Hengye Wei, Yuhong Zeng, Qian Zhang, Jinxian Deng","doi":"10.1144/jgs2022-168","DOIUrl":"https://doi.org/10.1144/jgs2022-168","url":null,"abstract":"The Late Triassic Carnian pluvial event (CPE) was an interval marked by global climatic and environmental changes that occurred simultaneously with enhancement of the hydrological cycle. This event is characterized by multiple negative carbon isotope excursions (NCIEs). However, the driving mechanism behind these multiple NCIEs remains elusive because each of the NCIEs had different magnitudes in different geological settings. In this study, we present a high-resolution record of carbonate carbon isotope ( <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\"> <mml:mi>δ</mml:mi> </mml:math> 13 C carb ) and major and trace element data from Well QZ-8 in the Qiangtang Basin, eastern Tethys. The carbon isotope profile from this well displays a similar trend to those for contemporaneous strata in the NW Tethys and South China. This trend is characterized by a distinct negative excursion during the CPE, supporting a global event. Interestingly, our results reveal five NCIEs for the first time in the marine sedimentary succession. Furthermore, each of these NCIEs corresponds well to changes in Ti/Al, Sr/Al and Sr/Ba, suggesting a regional effect of the hydrological cycle on carbon isotope excursions. This study emphasizes that each of the NCIEs was influenced by regional hydrological cycles although the long carbon isotope excursion during the CPE was driven by the global carbon cycle. Supplementary material: Tables showing major element, isotope and trace element data and element ratios, and a supplementary figure are available at https://doi.org/10.6084/m9.figshare.c.6805266","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"186 1‐6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135775905","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}
T.C. Pharaoh, D. Beamish, J.D.O. Williams, J.N. Carney, P.R.W. Wilby
We based an integrated petrological and petrophysical model for the Ediacaran crust of southern Britain on a review of the c. 570–550 Ma Charnian volcano-sedimentary complex. The latter was emplaced in a magmatic rift wedge within the juvenile continental crust of the c. 720–600 Ma Marches Terrane, a subduction magmatic domain formed at the margin of the Gondwana palaeocontinent. The Charnian magmatic arc is characterized by primitive island arc tholeiite to more evolved calc-alkaline compositions. The inversion of aeromagnetic potential field data and petrophysical modelling reveals details of the internal structure of the Charnian Domain, including a median rift, superimposed annular structures and partitioning lineaments. The modelling suggests that the arc foundation could incorporate magnetite-rich cumulates, which may explain the anomalous geophysical properties, including crustal thickness, rigidity and buoyancy. There is no evidence for significant tectonic displacement between the Charnian Domain and its Marches Terrane host. Instead, the domain likely occupies a wedge-shaped arc/marginal rift basin complex, propagated from a neighbouring ocean into the Gondwana margin. Contemporaneous volcanic rift successions in the Welsh Borderland and Wales of the 570–550 Ma Charnian magmatic phase developed in coeval ensialic rifts within less strongly extended Marches Terrane lithosphere. A comparable diversity of subduction-related magmatism is found in the Neogene–recent Hikurangi destructive margin of New Zealand, providing a plausible analogue for Charnian magmatism. Supplementary material: Supplementary Publication 1 (borehole geophysical log correlation; petrophysical data table; unannotated geophysical maps and sections) and Supplementary Publication 2 (geochemistry analytical conditions and data table) are available at https://doi.org/10.6084/m9.figshare.c.6805248
通过对c. 570-550 Ma charian火山-沉积杂岩的研究，建立了英国南部埃迪卡拉系地壳的岩石学和岩石物理综合模型。后者位于c. 720-600 Ma marchane幼年大陆地壳内的岩浆裂谷楔中，Ma marchane是在冈瓦纳古大陆边缘形成的俯冲岩浆域。夏期岩浆弧以原始岛弧拉斑岩为主要特征，演化为钙碱性成分。航磁位场数据反演和岩石物理模拟揭示了查尔年域内部构造的细节，包括中间裂谷、叠加环形构造和分区构造。该模型表明，弧底可能含有富含磁铁矿的堆积物，这可能解释了异常的地球物理性质，包括地壳厚度、刚度和浮力。没有证据表明在恰尔年构造域和它的马奇地体之间有明显的构造位移。相反，该区域可能占据了一个楔形弧/边缘裂谷盆地复合体，从邻近的海洋传播到冈瓦纳边缘。570-550 Ma charian岩浆期威尔士边地和威尔士的同时期火山裂谷序列是在扩张不太强烈的marchane岩石圈内的同时期裂谷中发育起来的。在新西兰新近纪-新近纪的Hikurangi破坏性边缘发现了与俯冲相关的岩浆活动的类似多样性，为恰尔期岩浆活动提供了一个合理的类比。补充资料:补充出版物1(钻孔地球物理测井对比;岩石物理数据表;未注释的地球物理图和剖面)和补充出版物2(地球化学分析条件和数据表)可在https://doi.org/10.6084/m9.figshare.c.6805248上获得
{"title":"The Charnwood Terrane revisited: an integrated petrogenetic and petrophysical model for crustal structure in S Britain","authors":"T.C. Pharaoh, D. Beamish, J.D.O. Williams, J.N. Carney, P.R.W. Wilby","doi":"10.1144/jgs2023-001","DOIUrl":"https://doi.org/10.1144/jgs2023-001","url":null,"abstract":"We based an integrated petrological and petrophysical model for the Ediacaran crust of southern Britain on a review of the c. 570–550 Ma Charnian volcano-sedimentary complex. The latter was emplaced in a magmatic rift wedge within the juvenile continental crust of the c. 720–600 Ma Marches Terrane, a subduction magmatic domain formed at the margin of the Gondwana palaeocontinent. The Charnian magmatic arc is characterized by primitive island arc tholeiite to more evolved calc-alkaline compositions. The inversion of aeromagnetic potential field data and petrophysical modelling reveals details of the internal structure of the Charnian Domain, including a median rift, superimposed annular structures and partitioning lineaments. The modelling suggests that the arc foundation could incorporate magnetite-rich cumulates, which may explain the anomalous geophysical properties, including crustal thickness, rigidity and buoyancy. There is no evidence for significant tectonic displacement between the Charnian Domain and its Marches Terrane host. Instead, the domain likely occupies a wedge-shaped arc/marginal rift basin complex, propagated from a neighbouring ocean into the Gondwana margin. Contemporaneous volcanic rift successions in the Welsh Borderland and Wales of the 570–550 Ma Charnian magmatic phase developed in coeval ensialic rifts within less strongly extended Marches Terrane lithosphere. A comparable diversity of subduction-related magmatism is found in the Neogene–recent Hikurangi destructive margin of New Zealand, providing a plausible analogue for Charnian magmatism. Supplementary material: Supplementary Publication 1 (borehole geophysical log correlation; petrophysical data table; unannotated geophysical maps and sections) and Supplementary Publication 2 (geochemistry analytical conditions and data table) are available at https://doi.org/10.6084/m9.figshare.c.6805248","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"185 S500","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135775906","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}
Accurate estimates of past topography are required to reliably reconstruct past ice sheets to infer paleoclimate. For this reason, understanding erosion rates across East Greenland is crucial to constrain landscape evolution driven by tectonics and climate-dependent erosion rates. Here we analyse published apatite fission track (AFT) data to constrain the spatial pattern of AFT bedrock ages across the landscape. We compare these bedrock ages with published detrital distribution to highlight ambiguity in the pattern of erosion. In contrast to earlier work, we regress a simple model of exhumation pace through the bedrock ages such that age can vary both as a function of elevation and position. The resulting iso-age surfaces enable us to determine potential source areas for detrital AFT ages distributions. We find that old ages observed in detrital distributions are just as likely to be sourced from low-elevation locations that are far from the coast, as high elevation locations close to the coast. Additional data from lower temperature systems are thus required to make firm conclusions on landscape evolution in the region and distinguish between the two landscape-forming scenarios.
{"title":"Old detrital AFT ages from E. Greenland do not require plateau erosion","authors":"Matthew Fox, Vivi Pedersen","doi":"10.1144/jgs2023-103","DOIUrl":"https://doi.org/10.1144/jgs2023-103","url":null,"abstract":"Accurate estimates of past topography are required to reliably reconstruct past ice sheets to infer paleoclimate. For this reason, understanding erosion rates across East Greenland is crucial to constrain landscape evolution driven by tectonics and climate-dependent erosion rates. Here we analyse published apatite fission track (AFT) data to constrain the spatial pattern of AFT bedrock ages across the landscape. We compare these bedrock ages with published detrital distribution to highlight ambiguity in the pattern of erosion. In contrast to earlier work, we regress a simple model of exhumation pace through the bedrock ages such that age can vary both as a function of elevation and position. The resulting iso-age surfaces enable us to determine potential source areas for detrital AFT ages distributions. We find that old ages observed in detrital distributions are just as likely to be sourced from low-elevation locations that are far from the coast, as high elevation locations close to the coast. Additional data from lower temperature systems are thus required to make firm conclusions on landscape evolution in the region and distinguish between the two landscape-forming scenarios.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"56 1-2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135222008","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}
Boran Wang, Zhilong Huang, Tianjun Li, Guobin Fu, Jingyi Yan
Lacustrine organic-rich shales in the second member of the Jurassic Qiketai Formation (J 2 q 2 ) in the Shengbei Sub-sag, Turpan-Hami basin, northwest China exhibit strong heterogeneity due to frequent alternations of sedimentary environments. The distinct shale environments present in both upper and lower units of J 2 q 2 provide an ideal example for studying the enrichment mechanism of organic matter (OM) under a complex sedimentary background. In this study, petrological, mineralogical, major/trace element, and isotopic analyses were used to reconstruct the paleo-environment and reveal the mechanisms of OM enrichment. The results indicate that the J 2 q 2 shale was deposited in a lacustrine mixed carbonate-siliciclastic environment and the paleo-environment indicators suggesting an oxic-dysoxic, mildly brackish water condition. Based on a comprehensive comparison of both members of J 2 q 2 , an OM enrichment model was established and the main controlling factor of the formation of the organic-rich shale is elucidated. Under the background of a warm-humid climate, the lower unit of J 2 q 2 was deposited in a deeper and more restricted water body with stronger chemical weathering, resulting in limited terrestrial input compared to that of the upper unit. The inorganic geochemical analysis indicates a higher primary productivity in the lower unit of J 2 q 2 with local fluctuations. High primary productivity and favorable preservation conditions domain the OM enrichment in the study area. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6901480
{"title":"Organic matter enrichment and paleo-sedimentary environment reconstruction of lacustrine shale in the second member of the Middle Jurassic Qiketai Formation in Shengbei Sub-sag, Turpan-Hami Basin, northwest China","authors":"Boran Wang, Zhilong Huang, Tianjun Li, Guobin Fu, Jingyi Yan","doi":"10.1144/jgs2023-093","DOIUrl":"https://doi.org/10.1144/jgs2023-093","url":null,"abstract":"Lacustrine organic-rich shales in the second member of the Jurassic Qiketai Formation (J 2 q 2 ) in the Shengbei Sub-sag, Turpan-Hami basin, northwest China exhibit strong heterogeneity due to frequent alternations of sedimentary environments. The distinct shale environments present in both upper and lower units of J 2 q 2 provide an ideal example for studying the enrichment mechanism of organic matter (OM) under a complex sedimentary background. In this study, petrological, mineralogical, major/trace element, and isotopic analyses were used to reconstruct the paleo-environment and reveal the mechanisms of OM enrichment. The results indicate that the J 2 q 2 shale was deposited in a lacustrine mixed carbonate-siliciclastic environment and the paleo-environment indicators suggesting an oxic-dysoxic, mildly brackish water condition. Based on a comprehensive comparison of both members of J 2 q 2 , an OM enrichment model was established and the main controlling factor of the formation of the organic-rich shale is elucidated. Under the background of a warm-humid climate, the lower unit of J 2 q 2 was deposited in a deeper and more restricted water body with stronger chemical weathering, resulting in limited terrestrial input compared to that of the upper unit. The inorganic geochemical analysis indicates a higher primary productivity in the lower unit of J 2 q 2 with local fluctuations. High primary productivity and favorable preservation conditions domain the OM enrichment in the study area. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6901480","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"326 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135863189","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}
Tectonic mélanges are crucial for deciphering collision processes in orogenic belts. This study investigates the nature of metamorphosed mélange in the Milin area of the eastern Himalayan syntaxis to shed light on the India-Asia collision in the region. The mélange exhibits a “block-in-matrix” fabric in the lower and upper parts and a “lenticular-thrust-slices” fabric in the middle. Quartzite blocks in the lower part are proposed to be the Silurian or younger quartz arenites with a Tethyan affinity. Metacherts and amphibolites in the middle and upper parts may have originated from hydrothermal or terrestrial cherts and Nb-enriched basalts in the Asian forearc or syncollisional basin at ∼48-45 Ma. The diverse blocks/slices of the mélange, sourced from both the subducting and overriding plates, are suggested to be formed during Indian plate subduction. The protoliths of the amphibolite-metachert slice (∼45 Ma) in the mélange are distinctly different from the contemporary shallow sea (post-collisional) deposits but similar to the deep-water (initial collisional or pre-collisional) sediments in other parts of the suture zone. This implies that the amphibolite-metachert slice may represent the product of the initial India-Asia collision or even pre-collision and that (hard) collision likely lagged by ∼10-Myr in the eastern Himalaya syntaxis. 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 Supplementary material: https://doi.org/10.6084/m9.figshare.c.6896942
{"title":"Metamorphosed mélange in eastern Himalayan syntaxis: constraint for the India-Asia collision in Eocene","authors":"Zhen Wei, Xianghui Li, Minjia Sun, Xiaolong Fan, Jingyu Wang, Juanjuan Zhou, Shoucai Wei","doi":"10.1144/jgs2023-067","DOIUrl":"https://doi.org/10.1144/jgs2023-067","url":null,"abstract":"Tectonic mélanges are crucial for deciphering collision processes in orogenic belts. This study investigates the nature of metamorphosed mélange in the Milin area of the eastern Himalayan syntaxis to shed light on the India-Asia collision in the region. The mélange exhibits a “block-in-matrix” fabric in the lower and upper parts and a “lenticular-thrust-slices” fabric in the middle. Quartzite blocks in the lower part are proposed to be the Silurian or younger quartz arenites with a Tethyan affinity. Metacherts and amphibolites in the middle and upper parts may have originated from hydrothermal or terrestrial cherts and Nb-enriched basalts in the Asian forearc or syncollisional basin at ∼48-45 Ma. The diverse blocks/slices of the mélange, sourced from both the subducting and overriding plates, are suggested to be formed during Indian plate subduction. The protoliths of the amphibolite-metachert slice (∼45 Ma) in the mélange are distinctly different from the contemporary shallow sea (post-collisional) deposits but similar to the deep-water (initial collisional or pre-collisional) sediments in other parts of the suture zone. This implies that the amphibolite-metachert slice may represent the product of the initial India-Asia collision or even pre-collision and that (hard) collision likely lagged by ∼10-Myr in the eastern Himalaya syntaxis. 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 Supplementary material: https://doi.org/10.6084/m9.figshare.c.6896942","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136261722","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}
Hadi Shafaii Moghadam, Yildirim Dilek, Harald Furnes, Osamu Ishizuka, Massimo Chiaradia, Qiu-li Li, Orhan Karsli, Federico Lucci, Ali Asadi
Chemostratigraphy of lavas in extrusive sequences of modern and ancient forearc environments provides significant information on oceanic crust formation through progressive stages of melt evolution from subduction initiation magmatism (SIM) to arc infancy, and arc maturation-related magmatism. We present here new trace element and radiogenic Sr–Nd–Pb isotopic data from a Late Cretaceous ophiolite in the Outer Zagros Belt of southern Iran and discuss its magmatic development through SIM in a Neotethyan forearc setting. Initial volcanism produced the stratigraphically oldest boninitic (BON) lavas in the Haji-Abad ophiolite whose trace element ratios as well as Pb isotopic signatures indicate a refractory mantle source, which was contaminated by subducting slab-derived fluids. The BON lavas change structurally upwards into island-arc tholeiitic (IAT) lavas and their fractionated felsic derivatives that display isotopic evidence for the contribution of sediment-derived melts in their magmatic source(s). This melt evolution pattern of the Haji-Abad ophiolite marks a major difference from the progressive melt evolution trends reported from the Izu–Bonin–Mariana (IBM) forearc lava sequence, which starts at the bottom with forearc basalts (FAB) phasing up-section into BON and IAT affinity lavas. IAT lavas in the IBM are in turn overlain by calc-alkaline (CAL) lavas. Our geochemical modelling points to a probable existence of a less depleted, pre-subduction mantle whose partial melting probably generated primary magmas before the eruption of boninitic lavas, although the record of such magmas is missing in the Haji-Abad ophiolite. Our comparison of the chemostratigraphy of the Outer Zagros ophiolites with the documented record of subduction initiation generated volcanic rocks in the other Neotethyan ophiolites in the region and the IBM forearc setting strongly suggests that there is no single rule or template for SIM. Supplementary material: Details of analytical procedures and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6837597 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":"Chemostratigraphy of the extrusive sequence of a Late Cretaceous Neotethyan ophiolite in Southern Iran and its significance for the mode and tempo of subduction initiation magmatism and melt evolution in forearc tectonic settings","authors":"Hadi Shafaii Moghadam, Yildirim Dilek, Harald Furnes, Osamu Ishizuka, Massimo Chiaradia, Qiu-li Li, Orhan Karsli, Federico Lucci, Ali Asadi","doi":"10.1144/jgs2023-080","DOIUrl":"https://doi.org/10.1144/jgs2023-080","url":null,"abstract":"Chemostratigraphy of lavas in extrusive sequences of modern and ancient forearc environments provides significant information on oceanic crust formation through progressive stages of melt evolution from subduction initiation magmatism (SIM) to arc infancy, and arc maturation-related magmatism. We present here new trace element and radiogenic Sr–Nd–Pb isotopic data from a Late Cretaceous ophiolite in the Outer Zagros Belt of southern Iran and discuss its magmatic development through SIM in a Neotethyan forearc setting. Initial volcanism produced the stratigraphically oldest boninitic (BON) lavas in the Haji-Abad ophiolite whose trace element ratios as well as Pb isotopic signatures indicate a refractory mantle source, which was contaminated by subducting slab-derived fluids. The BON lavas change structurally upwards into island-arc tholeiitic (IAT) lavas and their fractionated felsic derivatives that display isotopic evidence for the contribution of sediment-derived melts in their magmatic source(s). This melt evolution pattern of the Haji-Abad ophiolite marks a major difference from the progressive melt evolution trends reported from the Izu–Bonin–Mariana (IBM) forearc lava sequence, which starts at the bottom with forearc basalts (FAB) phasing up-section into BON and IAT affinity lavas. IAT lavas in the IBM are in turn overlain by calc-alkaline (CAL) lavas. Our geochemical modelling points to a probable existence of a less depleted, pre-subduction mantle whose partial melting probably generated primary magmas before the eruption of boninitic lavas, although the record of such magmas is missing in the Haji-Abad ophiolite. Our comparison of the chemostratigraphy of the Outer Zagros ophiolites with the documented record of subduction initiation generated volcanic rocks in the other Neotethyan ophiolites in the region and the IBM forearc setting strongly suggests that there is no single rule or template for SIM. Supplementary material: Details of analytical procedures and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6837597 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":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136376537","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}
A complex and chaotic assemblage of the north Croatian inselbergs, considered as a real geologic conundrum, is marked by omnipresent ophiolite mélange. This is a vestige of the unbroken formation of the lithosphere in the northwestern segment of Neotethys during the Mesozoic, spanning from the late Anisian to the late Tithonian. In this contribution, we present detailed mineralogical, petrological, geochemical, and isotopic data on the mélange collected from 1991 to 2023. These data include the entire normal ophiolite sequence, from mantle tectonites and cumulate ultramafic rocks through cumulate and isotropic gabbro and sheeted dyke complex to massive and pillow lavas with interbedded radiolarian cherts. We found that the continuous development of oceanic lithosphere during the Mesozoic has been evidenced by seven geochemical groups of ophiolitic rocks, each representing a distinct basalt-gabbro suite. Based on their geochemical and isotopic characteristics, a sequence of petrogenetic processes and tectono-magmatic events has been reconstructed. Proposed geodynamic models which shed light on the Mesozoic evolution of the northwestern segment of Neotethys are consistent with the current geodynamic understanding of the broader Mediterranean region. The similarities in the tectono-magmatic and geodynamic history of NW Neotethyan ophiolites and ophiolites from the Dinaridic-Albanide-Hellenide belts suggest that they evolved together, likely within a single branch of the Neotethys Ocean during Triassic to Jurassic time. 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":"The evolution of the Mesozoic lithosphere of northwestern Neotethys: A petrogenetic and geodynamic perspective","authors":"Damir Slovenec, Branimir Šegvić","doi":"10.1144/jgs2023-132","DOIUrl":"https://doi.org/10.1144/jgs2023-132","url":null,"abstract":"A complex and chaotic assemblage of the north Croatian inselbergs, considered as a real geologic conundrum, is marked by omnipresent ophiolite mélange. This is a vestige of the unbroken formation of the lithosphere in the northwestern segment of Neotethys during the Mesozoic, spanning from the late Anisian to the late Tithonian. In this contribution, we present detailed mineralogical, petrological, geochemical, and isotopic data on the mélange collected from 1991 to 2023. These data include the entire normal ophiolite sequence, from mantle tectonites and cumulate ultramafic rocks through cumulate and isotropic gabbro and sheeted dyke complex to massive and pillow lavas with interbedded radiolarian cherts. We found that the continuous development of oceanic lithosphere during the Mesozoic has been evidenced by seven geochemical groups of ophiolitic rocks, each representing a distinct basalt-gabbro suite. Based on their geochemical and isotopic characteristics, a sequence of petrogenetic processes and tectono-magmatic events has been reconstructed. Proposed geodynamic models which shed light on the Mesozoic evolution of the northwestern segment of Neotethys are consistent with the current geodynamic understanding of the broader Mediterranean region. The similarities in the tectono-magmatic and geodynamic history of NW Neotethyan ophiolites and ophiolites from the Dinaridic-Albanide-Hellenide belts suggest that they evolved together, likely within a single branch of the Neotethys Ocean during Triassic to Jurassic time. 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":"39 9","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135273112","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}
Charles H. Wellman, Gilda Lopes, Zoë McKellar, Adrian Hartley
The basal upper Silurian-Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Midland Valley of Scotland contain several important fossil biotas, including that from the Cowie Harbour Fish Bed. This biota is of great significance because it represents one of the oldest known examples of a fossilised terrestrial ecosystem and includes the oldest reported air-breathing land animal (the myriapod Pneumodesmus newmani Wilson & Anderson 2004). Based on biostratigraphical evidence from dispersed spores this biota is dated as late Wenlock (late Silurian) in age. Recently, however, this age constraint was challenged, based on 238 U- 296 Pb radiometric analysis of zircons, and it was proposed that these deposits are much younger (Early Devonian: Lochkovian). This proposal has serious implications regarding: (i) the composition and nature of early terrestrial ecosystems; (ii) the geological setting with respect to the timing of terrane accretion and the onset of ‘Lower Old Red Sandstone’ sedimentation. We report on newly discovered dispersed spore assemblages and additional zircon data that confirm a late Wenlock (late Silurian) age. This age designation establishes the importance of the biota of the Cowie Harbour Fish Bed and is more compatible with both its biotic composition and the regional geological setting.
苏格兰米德兰河谷的基础上志留统-下泥盆统“下老红砂岩”沉积物包含了几种重要的生物化石，包括来自考伊港鱼床的化石。这个生物群意义重大，因为它代表了已知最古老的陆地生态系统化石之一，包括报道的最古老的呼吸空气的陆地动物(多足动物纽马尼肺desmus newmani Wilson & &;安德森2004年)。根据分散孢子的生物地层证据，该生物群的年龄为晚文洛克(晚志留纪)。然而，根据对锆石的238 U- 296 Pb放射性分析，最近对这一年龄限制提出了挑战，并提出这些矿床要年轻得多(早泥盆世:Lochkovian)。这一建议对以下方面有严重影响:(i)早期陆地生态系统的组成和性质;(ii)有关地体增生的时间和“下古红砂岩”沉积开始的地质背景。我们报告了新发现的分散孢子组合和额外的锆石数据，证实了晚温洛克(晚志留纪)时代。这一年龄划分确立了考伊港鱼床生物群的重要性，并更符合其生物组成和区域地质环境。
{"title":"Age of the basal ‘Lower Old Red Sandstone’ Stonehaven Group of Scotland: The oldest reported air-breathing land animal is Silurian (late Wenlock) in age","authors":"Charles H. Wellman, Gilda Lopes, Zoë McKellar, Adrian Hartley","doi":"10.1144/jgs2023-138","DOIUrl":"https://doi.org/10.1144/jgs2023-138","url":null,"abstract":"The basal upper Silurian-Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Midland Valley of Scotland contain several important fossil biotas, including that from the Cowie Harbour Fish Bed. This biota is of great significance because it represents one of the oldest known examples of a fossilised terrestrial ecosystem and includes the oldest reported air-breathing land animal (the myriapod Pneumodesmus newmani Wilson & Anderson 2004). Based on biostratigraphical evidence from dispersed spores this biota is dated as late Wenlock (late Silurian) in age. Recently, however, this age constraint was challenged, based on 238 U- 296 Pb radiometric analysis of zircons, and it was proposed that these deposits are much younger (Early Devonian: Lochkovian). This proposal has serious implications regarding: (i) the composition and nature of early terrestrial ecosystems; (ii) the geological setting with respect to the timing of terrane accretion and the onset of ‘Lower Old Red Sandstone’ sedimentation. We report on newly discovered dispersed spore assemblages and additional zircon data that confirm a late Wenlock (late Silurian) age. This age designation establishes the importance of the biota of the Cowie Harbour Fish Bed and is more compatible with both its biotic composition and the regional geological setting.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"6 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135266817","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}
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":"1 1","pages":"0"},"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":"38 1","pages":"0"},"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}
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