Multiple magnetic fabrics, referred to as F1–F5, were revealed through the anisotropy of magnetic susceptibility (AMS) in an Ocean Plate Stratigraphy (OPS) mélange of the Neoproterozoic–Cambrian Blovice accretionary complex, Bohemian Massif. The fabrics postdate the mélange formation and rotation of basalt blocks within the matrix and are interpreted in terms of a complex structural history of the mélange. Excluding local fabrics, the F1 fabric formed earlier along the mélange belt, recording shortening of the accretionary wedge front, whereas the higher-grade F4 fabric pervasively overprinted both blocks and matrix in the SW part of the belt, recording shearing and vertical shortening at deeper structural levels closer to a megathrust surface. The preservation of angular relationships between the F1 and F4 fabrics across different parts of mélange suggests that blocks were only strained and not rotated during deformation, exemplifying the notion that the OPS mélanges may be a product of deformation at very shallow levels. Finally, the F1–F5 fabrics may be viewed as snapshots in a protracted evolution of OPS mélanges, where earlier fabrics in basalt blocks may record the travel path of an oceanic plate from mid-ocean ridge towards the trench, before being overprinted in the accretionary wedge. 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.7008173
{"title":"Magnetic fabric of OPS mélanges: a tool for unravelling protracted histories of oceanic plates from sea-floor spreading to tectonic emplacement into accretionary wedges","authors":"Lucia Pellerey, J. Žák, F. Tomek, Andrea Festa","doi":"10.1144/jgs2023-141","DOIUrl":"https://doi.org/10.1144/jgs2023-141","url":null,"abstract":"Multiple magnetic fabrics, referred to as F1–F5, were revealed through the anisotropy of magnetic susceptibility (AMS) in an Ocean Plate Stratigraphy (OPS) mélange of the Neoproterozoic–Cambrian Blovice accretionary complex, Bohemian Massif. The fabrics postdate the mélange formation and rotation of basalt blocks within the matrix and are interpreted in terms of a complex structural history of the mélange. Excluding local fabrics, the F1 fabric formed earlier along the mélange belt, recording shortening of the accretionary wedge front, whereas the higher-grade F4 fabric pervasively overprinted both blocks and matrix in the SW part of the belt, recording shearing and vertical shortening at deeper structural levels closer to a megathrust surface. The preservation of angular relationships between the F1 and F4 fabrics across different parts of mélange suggests that blocks were only strained and not rotated during deformation, exemplifying the notion that the OPS mélanges may be a product of deformation at very shallow levels. Finally, the F1–F5 fabrics may be viewed as snapshots in a protracted evolution of OPS mélanges, where earlier fabrics in basalt blocks may record the travel path of an oceanic plate from mid-ocean ridge towards the trench, before being overprinted in the accretionary wedge.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Ophiolites, melanges and blueschists collection available at:\u0000 https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7008173\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"28 12","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139445122","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}
Guangwei Li, Haibin Yang, M. Sandiford, Barry P. Kohn, Zhiqin Xu, Hanwen Dong, Dongxu Cai
The syntaxes at the eastern and western ends of the Himalaya located at the Tsangpo and Indus gorge regions provide examples of the interplay between tectonics and erosion. A previous borehole study along the Yarlung River in the Eastern Himalayan Syntaxis (EHS) reveals a ∼1 km thick sedimentary wedge upstream of the Tsangpo gorge with a >2.5 Ma depositional age. However, mechanism of formation of this sedimentary wedge remains under debate. Here, we combine low-temperature thermochronology data and thermo-mechanical modelling to discuss how a sedimentary wedge formed at the highly eroded EHS. Our low-temperature thermochronology results show late Miocene fast cooling episodes focused at the Gyaca and Tsangpo gorges, which are interpreted to be related to coeval rifting at the former and rapid erosion and hot-crust upwelling at the latter. Constrained by the geological and geophysical observations, we apply thermo-mechanical models to illustrate the mechanism of formation of the sedimentary wedge and present high relief of the EHS. The numerical geodynamic model shows that localised erosion triggers middle ‘crust extrusion’ and regional topographic adjustment at the EHS. 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.7008098
{"title":"Interaction of surface processes and crustal flow in the Eastern Himalayan Syntaxis","authors":"Guangwei Li, Haibin Yang, M. Sandiford, Barry P. Kohn, Zhiqin Xu, Hanwen Dong, Dongxu Cai","doi":"10.1144/jgs2023-041","DOIUrl":"https://doi.org/10.1144/jgs2023-041","url":null,"abstract":"The syntaxes at the eastern and western ends of the Himalaya located at the Tsangpo and Indus gorge regions provide examples of the interplay between tectonics and erosion. A previous borehole study along the Yarlung River in the Eastern Himalayan Syntaxis (EHS) reveals a ∼1 km thick sedimentary wedge upstream of the Tsangpo gorge with a >2.5 Ma depositional age. However, mechanism of formation of this sedimentary wedge remains under debate. Here, we combine low-temperature thermochronology data and thermo-mechanical modelling to discuss how a sedimentary wedge formed at the highly eroded EHS. Our low-temperature thermochronology results show late Miocene fast cooling episodes focused at the Gyaca and Tsangpo gorges, which are interpreted to be related to coeval rifting at the former and rapid erosion and hot-crust upwelling at the latter. Constrained by the geological and geophysical observations, we apply thermo-mechanical models to illustrate the mechanism of formation of the sedimentary wedge and present high relief of the EHS. The numerical geodynamic model shows that localised erosion triggers middle ‘crust extrusion’ and regional topographic adjustment at the EHS.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at:\u0000 https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7008098\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"54 7","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139446024","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}
Studies of high pressure-low temperature (HP-LT) metamorphic complexes are critical for advancing our understanding of subduction processes, such as underplating, metamorphism, and exhumation. Detailed new U-Pb zircon data of blueschist-facies metasedimentary units at Pelion indicate two distinct, stratigraphically upright, and coherent structural slices, with (1) the South Pelion slice consisting of strata with Permian-Late Cretaceous zircon maximum depositional ages (MDAs) and (2) the North Pelion slice comprising strata with Triassic-Late Cretaceous zircon MDAs. Both slices have Late Cretaceous strata at the top of the section with cosmopolitan detrital zircon (DZ) signatures. Ages from zircon U-Pb rim overgrowths correlate with existing constraints from subduction-metamorphism during the Paleocene-Eocene, with a possible second stage recorded during Basal underplating in the Late Eocene-Oligocene. DZ provenance data and multi-dimensional scaling (MDS) comparisons demonstrate a tectono-metamorphic linkage between the Pelion rocks and the Cycladic Blueschist Unit (CBU), and between the southern Pelion Basement and the Cycladic Basement (CB). Protolith deposition for Pelion blueschist-facies rocks occurred during Permo-Carboniferous intra-arc extension and Adria-Pindos rifting. Our results show that the Pelion blueschist-facies rocks, representing lateral equivalents of the CBU, are comprised of two separate, coherent upper-crustal slivers that were underplated and metamorphosed during Hellenic subduction beneath the Pelagonian margin. 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.7008123
{"title":"Coherent underplating of HP-LT blueschist packages and basement during Hellenic subduction recorded by zircon U-Pb data, Pelion, Greece","authors":"Emily R. Hinshaw, D. Stockli, Kostantinos Soukis","doi":"10.1144/jgs2023-147","DOIUrl":"https://doi.org/10.1144/jgs2023-147","url":null,"abstract":"Studies of high pressure-low temperature (HP-LT) metamorphic complexes are critical for advancing our understanding of subduction processes, such as underplating, metamorphism, and exhumation. Detailed new U-Pb zircon data of blueschist-facies metasedimentary units at Pelion indicate two distinct, stratigraphically upright, and coherent structural slices, with (1) the South Pelion slice consisting of strata with Permian-Late Cretaceous zircon maximum depositional ages (MDAs) and (2) the North Pelion slice comprising strata with Triassic-Late Cretaceous zircon MDAs. Both slices have Late Cretaceous strata at the top of the section with cosmopolitan detrital zircon (DZ) signatures. Ages from zircon U-Pb rim overgrowths correlate with existing constraints from subduction-metamorphism during the Paleocene-Eocene, with a possible second stage recorded during Basal underplating in the Late Eocene-Oligocene. DZ provenance data and multi-dimensional scaling (MDS) comparisons demonstrate a tectono-metamorphic linkage between the Pelion rocks and the Cycladic Blueschist Unit (CBU), and between the southern Pelion Basement and the Cycladic Basement (CB). Protolith deposition for Pelion blueschist-facies rocks occurred during Permo-Carboniferous intra-arc extension and Adria-Pindos rifting. Our results show that the Pelion blueschist-facies rocks, representing lateral equivalents of the CBU, are comprised of two separate, coherent upper-crustal slivers that were underplated and metamorphosed during Hellenic subduction beneath the Pelagonian margin.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Ophiolites, melanges and blueschists collection available at:\u0000 https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7008123\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"42 10","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139448088","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 Morello Tectonic Unit in the Tuscan Apennines (Italy) represents the result of tectono-sedimentary deformation, occurring in the frontal part of the non-metamorphosed Ligurian Accretionary Wedge, which consists of ophiolitic slices imbricated with a sedimentary succession containing ophiolite-bearing sedimentary mélanges. Geological mapping, structural and stratigraphic observations, allow us to document that (i) the ophiolite-bearing sedimentary mélanges formed by gravitational reworking of material sourced from intrabasinal structural highs facing the oceanic basin environment from Jurassic to lower Eocene, before the middle Eocene accretion stage, and (ii) the ophiolitic tectonic slices represent the scraping off at shallow structural levels of part of these crustal oceanic highs sequence. The final internal architecture of the shallow frontal portion of the Ligurian Accretionary Wedge does not differ from those observed in metamorphosed orogenic belts and exhumed accretionary complexes throughout the world (e.g., blueschist and eclogite units of Western Alps). This suggests that to the classical model of subduction and metamorphism followed by accretion and mélange formation (i.e., underplating), a model in which frontal accretion and ophiolite mélange formation at a shallow level are followed by underthrusting and subduction can be added, providing additional constraints to a better reconstruction of orogenic belts and accretionary complexes evolution. 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":"Offscraping and shallow ophiolite accretion in the Ligurian Accretionary Wedge (Tuscan Apennines): role of seafloor structural inheritance","authors":"G. Nirta, F. Remitti, Edoardo Barbero, A. Festa","doi":"10.1144/jgs2023-189","DOIUrl":"https://doi.org/10.1144/jgs2023-189","url":null,"abstract":"The Morello Tectonic Unit in the Tuscan Apennines (Italy) represents the result of tectono-sedimentary deformation, occurring in the frontal part of the non-metamorphosed Ligurian Accretionary Wedge, which consists of ophiolitic slices imbricated with a sedimentary succession containing ophiolite-bearing sedimentary mélanges. Geological mapping, structural and stratigraphic observations, allow us to document that (i) the ophiolite-bearing sedimentary mélanges formed by gravitational reworking of material sourced from intrabasinal structural highs facing the oceanic basin environment from Jurassic to lower Eocene, before the middle Eocene accretion stage, and (ii) the ophiolitic tectonic slices represent the scraping off at shallow structural levels of part of these crustal oceanic highs sequence. The final internal architecture of the shallow frontal portion of the Ligurian Accretionary Wedge does not differ from those observed in metamorphosed orogenic belts and exhumed accretionary complexes throughout the world (e.g., blueschist and eclogite units of Western Alps). This suggests that to the classical model of subduction and metamorphism followed by accretion and mélange formation (i.e., underplating), a model in which frontal accretion and ophiolite mélange formation at a shallow level are followed by underthrusting and subduction can be added, providing additional constraints to a better reconstruction of orogenic belts and accretionary complexes evolution.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Ophiolites, melanges and blueschists collection available at:\u0000 https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"7 9","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139382806","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}
We have investigated the geology, geochemistry, and geochronology of various plagiogranite intrusions that are spatially associated with ophiolitic subunits in a mélange terrain exposed within the Nain–Baft fault zone along the western boundary of the Central–East Iranian Microcontinent (CEIM). One group of plagiogranites is intrusive into foliated amphibolites, whereas the plagiogranites of the other group are intrusive into gabbros, dike swarms, and pillow lavas that are tectonically juxtaposed. U–Pb zircon dating of the first group of plagiogranites has revealed near concordant crystallization ages of 176.94±0.71, 179.84±0.92, and 190.40±2.1 Ma, indicating the early Jurassic timing of their emplacement. U–Pb zircon dating of the second group of plagiogranites has revealed a weighted average age of 92.34±0.38 Ma, indicating that they were emplaced in the early Late Cretaceous. The Early Jurassic plagiogranites are low–K, sub–alkaline rocks with negative Eu anomalies, low Ti and high La and Ce contents. They display elevated LILE/HFSE ratios. They were part of a magmatic system which facilitated the earliest rift–drift stages of a Neotethyan seaway development, and their magmas were produced by fractional crystallization of a mafic melt associated with asthenospheric upwelling beneath a rift system. The Late Cretaceous plagiogranites are low–K, sub–alkaline rocks with negative Eu anomalies, high Y and low Ta contents. They show LREE depletion relative to flat HREE patterns, and high Ba/Th ratios. Magmas of these plagiogranites were the products of partial melting of amphibolites in the subducting oceanic lithosphere in the same Neotethyan seaway. Thus, we posit that plagiogranite rocks in suture zones can be excellent trackers of geochemical, geochronological, and magmatic evolution of various types of oceanic crust through rift–drift, seafloor spreading, and subduction initiation stages within the same ocean basins in the past. 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
我们对伊朗中部-东部微大陆（CEIM）西部边界纳因-巴夫特断裂带内出露的在空间上与蛇绿岩亚单位相关的各种长花岗岩侵入体的地质、地球化学和地质年代进行了研究。其中一组斜长花岗岩侵入到叶状闪长岩中，而另一组斜长花岗岩则侵入到构造并列的辉长岩、梭状岩群和枕状熔岩中。第一组斜长花岗岩的铀-铅锆石年代测定显示了近乎一致的结晶年龄，分别为 176.94±0.71、179.84±0.92 和 190.40±2.1Ma，表明它们的成岩时间为侏罗纪早期。第二组长花岗岩的U-Pb锆石年代测定显示其加权平均年龄为（92.34±0.38）Ma，表明其成岩时间为晚白垩世早期。早侏罗世长花岗岩是低 K、亚碱性岩石，具有负 Eu 异常、低 Ti 以及高 La 和 Ce 含量。它们显示出较高的 LILE/HFSE 比率。它们是岩浆系统的一部分，该岩浆系统促进了新近纪海道发展的最早裂谷-漂移阶段，其岩浆是由裂谷系统下与星体层上升流有关的黑云母熔体分块结晶产生的。晚白垩世长花岗岩是低K、亚碱性岩石，具有负Eu异常、高Y和低Ta含量。相对于平坦的 HREE 模式，它们显示出 LREE 贫化以及高 Ba/Th 比率。这些斜长花岗岩的岩浆是同一新特提安海道中俯冲洋岩石圈中的闪长岩部分熔融的产物。因此，我们认为缝合带中的长花岗岩可以很好地追踪过去同一大洋盆地内各类大洋地壳在经历裂谷-漂移、海底扩张和俯冲起始阶段的地球化学、地质年代和岩浆演化过程。 专题集：本文是蛇绿岩、熔岩和蓝晶岩文集的一部分，可在以下网址查阅：https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists。
{"title":"Early Jurassic and Late Cretaceous plagiogranites in Nain-Baft ophiolitic mélange zone in Iran: remnants of rift–drift and SSZ evolution of a Neotethyan seaway","authors":"N. Shirdashtzadeh, Y. Dilek, H. Furnes, E. Dantas","doi":"10.1144/jgs2023-181","DOIUrl":"https://doi.org/10.1144/jgs2023-181","url":null,"abstract":"We have investigated the geology, geochemistry, and geochronology of various plagiogranite intrusions that are spatially associated with ophiolitic subunits in a mélange terrain exposed within the Nain–Baft fault zone along the western boundary of the Central–East Iranian Microcontinent (CEIM). One group of plagiogranites is intrusive into foliated amphibolites, whereas the plagiogranites of the other group are intrusive into gabbros, dike swarms, and pillow lavas that are tectonically juxtaposed. U–Pb zircon dating of the first group of plagiogranites has revealed near concordant crystallization ages of 176.94±0.71, 179.84±0.92, and 190.40±2.1 Ma, indicating the early Jurassic timing of their emplacement. U–Pb zircon dating of the second group of plagiogranites has revealed a weighted average age of 92.34±0.38 Ma, indicating that they were emplaced in the early Late Cretaceous. The Early Jurassic plagiogranites are low–K, sub–alkaline rocks with negative Eu anomalies, low Ti and high La and Ce contents. They display elevated LILE/HFSE ratios. They were part of a magmatic system which facilitated the earliest rift–drift stages of a Neotethyan seaway development, and their magmas were produced by fractional crystallization of a mafic melt associated with asthenospheric upwelling beneath a rift system. The Late Cretaceous plagiogranites are low–K, sub–alkaline rocks with negative Eu anomalies, high Y and low Ta contents. They show LREE depletion relative to flat HREE patterns, and high Ba/Th ratios. Magmas of these plagiogranites were the products of partial melting of amphibolites in the subducting oceanic lithosphere in the same Neotethyan seaway. Thus, we posit that plagiogranite rocks in suture zones can be excellent trackers of geochemical, geochronological, and magmatic evolution of various types of oceanic crust through rift–drift, seafloor spreading, and subduction initiation stages within the same ocean basins in the past.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Ophiolites, melanges and blueschists collection available at:\u0000 https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"59 39","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139381878","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}
Í. F. Dias da Silva, Manuel Francisco Pereira, E. G. Clavijo, José Brandão Silva
A review of the synorogenic basins formed on the Gondwana side of the Variscan orogen of Iberia is presented, highlighting the widespread ocurrence of calciturbiditic formations and olistostromes containing reef-limestone olistoliths in Iberia's Variscan basins. Using key-examples from the Variscan orogen for comparison (Azrou-Khenifra and Rhenohercynian basins), the significance of these olistostromes and flyschoid deposits is discussed. Our tectonic models of the Variscan belt in Iberia propose possible drivers of synorogenic carbonate platform/reef destruction responsible for the origin of calciturbidites and olistostromes. One model proposes the formation of an orogenic plateau by lateral flow of partially molten orogenic roots in the context of Laurussia-Gondwana convergence, following the destruction of the Rheic Ocean and Gondwana (lower) plate slab retreat. An alternative model invokes subduction of Paleotethys oceanic lithosphere beneath the Gondwana (upper) plate. Both emphasize the Mississippian occurrence of a significant thermal anomaly beneath Gondwana that favored strong lithosphere thinning, creating ideal conditions for synorogenic carbonate platform/reef destruction, and for the formation of calciturbidite deposits and olistostromes in Iberia. Variscan paleotopography would look alike in both situations. Thus, distinguishing these models is not straightforward, with differences in the kinematics of the regional tectonic transport in the superstructure of Mississippian gneiss domes. 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":"Mississippian olistostromes of Iberia revisited: Tectonic drivers of synorogenic carbonate platform/reef destruction","authors":"Í. F. Dias da Silva, Manuel Francisco Pereira, E. G. Clavijo, José Brandão Silva","doi":"10.1144/jgs2023-187","DOIUrl":"https://doi.org/10.1144/jgs2023-187","url":null,"abstract":"A review of the synorogenic basins formed on the Gondwana side of the Variscan orogen of Iberia is presented, highlighting the widespread ocurrence of calciturbiditic formations and olistostromes containing reef-limestone olistoliths in Iberia's Variscan basins. Using key-examples from the Variscan orogen for comparison (Azrou-Khenifra and Rhenohercynian basins), the significance of these olistostromes and flyschoid deposits is discussed. Our tectonic models of the Variscan belt in Iberia propose possible drivers of synorogenic carbonate platform/reef destruction responsible for the origin of calciturbidites and olistostromes. One model proposes the formation of an orogenic plateau by lateral flow of partially molten orogenic roots in the context of Laurussia-Gondwana convergence, following the destruction of the Rheic Ocean and Gondwana (lower) plate slab retreat. An alternative model invokes subduction of Paleotethys oceanic lithosphere beneath the Gondwana (upper) plate. Both emphasize the Mississippian occurrence of a significant thermal anomaly beneath Gondwana that favored strong lithosphere thinning, creating ideal conditions for synorogenic carbonate platform/reef destruction, and for the formation of calciturbidite deposits and olistostromes in Iberia. Variscan paleotopography would look alike in both situations. Thus, distinguishing these models is not straightforward, with differences in the kinematics of the regional tectonic transport in the superstructure of Mississippian gneiss domes.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Ophiolites, melanges and blueschists collection available at:\u0000 https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"20 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139383904","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}
Meng Ning, Yao Wang, Judith A. McKenzie, C. Vasconcelos, Chenqing Li, Anjiang Shen, Feng Liang, Bing Shen
Early lithification of carbonate mud during the subaerial exposure stage, under semiarid conditions, has been proposed to facilitate dolomite formation. However, how the biogeochemical processes during subaerial diagenesis promote dolomite formation remains unclear. Here, we employ a multiproxy approach to investigate the process of dolomite formation by analyzing modern dolomite crusts forming in lagoon Brejo do Espinho (LBE). Petrological analysis reveals that the crusts comprise coexisting high-Mg calcite (HMC) and dolomite. Low Fe and Mn concentrations indicate the formation of dolomite under oxic conditions, while a higher Sr concentration in well-lithified crust suggests primary bacterial-induced dolomite precipitation. The Mg isotopic composition of the crusts exhibits a lighter value compared to that of modern sabkha dolomite, suggesting different dolomitization processes and Mg sources. More negative δ ¹³C values of the crusts than unlithified carbonate mud in LBE, indicating the incorporation of 13 C depleted organic carbon. The biogeochemical processes related to decaying organic matter during subaerial diagenesis generate partially oxidized organic matter that promotes Mg 2+ dehydration and enhances the dissolution of primary HMC, ultimately triggering the transition of HMC to dolomite or/and direct dolomite precipitation. The ancient "dolomite factory" operated through cyclic deposition of carbonate sediments and penecontemporaneous subaerial diagenesis. Thematic collection: This article is part of the Towards unravelling the ‘Dolomite Problem’: new approaches and novel perspectives collection available at: https://www.lyellcollection.org/topic/collections/towards-unravelling-the-dolomite-problem
{"title":"Dolomite formation during penecontemporaneous subaerial diagenesis: Evidence from modern dolomite crusts forming in lagoon Brejo do Espinho, Brazil","authors":"Meng Ning, Yao Wang, Judith A. McKenzie, C. Vasconcelos, Chenqing Li, Anjiang Shen, Feng Liang, Bing Shen","doi":"10.1144/jgs2023-159","DOIUrl":"https://doi.org/10.1144/jgs2023-159","url":null,"abstract":"\u0000 Early lithification of carbonate mud during the subaerial exposure stage, under semiarid conditions, has been proposed to facilitate dolomite formation. However, how the biogeochemical processes during subaerial diagenesis promote dolomite formation remains unclear. Here, we employ a multiproxy approach to investigate the process of dolomite formation by analyzing modern dolomite crusts forming in lagoon Brejo do Espinho (LBE). Petrological analysis reveals that the crusts comprise coexisting high-Mg calcite (HMC) and dolomite. Low Fe and Mn concentrations indicate the formation of dolomite under oxic conditions, while a higher Sr concentration in well-lithified crust suggests primary bacterial-induced dolomite precipitation. The Mg isotopic composition of the crusts exhibits a lighter value compared to that of modern sabkha dolomite, suggesting different dolomitization processes and Mg sources. More negative\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 ¹³C values of the crusts than unlithified carbonate mud in LBE, indicating the incorporation of\u0000 13\u0000 C depleted organic carbon. The biogeochemical processes related to decaying organic matter during subaerial diagenesis generate partially oxidized organic matter that promotes Mg\u0000 2+\u0000 dehydration and enhances the dissolution of primary HMC, ultimately triggering the transition of HMC to dolomite or/and direct dolomite precipitation. The ancient \"dolomite factory\" operated through cyclic deposition of carbonate sediments and penecontemporaneous subaerial diagenesis.\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Towards unravelling the ‘Dolomite Problem’: new approaches and novel perspectives collection available at:\u0000 https://www.lyellcollection.org/topic/collections/towards-unravelling-the-dolomite-problem\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"113 4","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139383440","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}
C. Rapela, M. García, F. Hervé, R. Pankhurst, M. Calderon, C. Fanning, S. Verdecchia
Remnants of coeval Devonian oceanic and continental foreland rocks are preserved in the basement of the North Patagonian Andes. Our previous studies of igneous rocks have shown the primitive oceanic and continental igneous rocks are coeval, and belong to a marginal basin that opened and closed over 50 Myr. A structural study and four new U-Pb SHRIMP ages and zircon Hf-O determinations allow identification of three metamorphic episodes, the first one M 1 (D 1 -S 1 ) coeval with Andean type granite intrusion in the foreland (405–380 Ma). This activity was simultaneous with development of an oceanic ridge and a marginal basin, at the outer edge of which a primitive granitic oceanic arc formed (380–385 Ma; zircon δ 18 O 3.6–5.2 δ 18 ‰). Ridge extinction initiated under-thrusting of the oceanic crust below the continent and an important mid-to-high grade metamorphic event M 2 (D 2 -S 2; 375–360 Ma), its peak dated by metamorphic zircon rims in migmatite at 365 ± 3 Ma. Basin closure occurred after intrusion of S-type granites (357 ± 2 Ma; zircon δ 18 O 7.4–10.4‰) in the foreland, and accretion of gabbros, cumulate gabbros and trondhjemites at the proto-Pacific margin. Compression prevailed for 20 Myr in the foreland, causing a mylonitic medium-grade M 3 (D 3 -S 3 ) event. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6989873
{"title":"Late Paleozoic magmatism and foreland deformation associated with opening and closing of marginal basins in the North Patagonian Andes","authors":"C. Rapela, M. García, F. Hervé, R. Pankhurst, M. Calderon, C. Fanning, S. Verdecchia","doi":"10.1144/jgs2023-171","DOIUrl":"https://doi.org/10.1144/jgs2023-171","url":null,"abstract":"\u0000 Remnants of coeval Devonian oceanic and continental foreland rocks are preserved in the basement of the North Patagonian Andes. Our previous studies of igneous rocks have shown the primitive oceanic and continental igneous rocks are coeval, and belong to a marginal basin that opened and closed over 50 Myr. A structural study and four new U-Pb SHRIMP ages and zircon Hf-O determinations allow identification of three metamorphic episodes, the first one M\u0000 1\u0000 (D\u0000 1\u0000 -S\u0000 1\u0000 ) coeval with Andean type granite intrusion in the foreland (405–380 Ma). This activity was simultaneous with development of an oceanic ridge and a marginal basin, at the outer edge of which a primitive granitic oceanic arc formed (380–385 Ma; zircon δ\u0000 18\u0000 O 3.6–5.2 δ\u0000 18\u0000 ‰). Ridge extinction initiated under-thrusting of the oceanic crust below the continent and an important mid-to-high grade metamorphic event M\u0000 2\u0000 (D\u0000 2\u0000 -S\u0000 2;\u0000 375–360 Ma), its peak dated by metamorphic zircon rims in migmatite at 365 ± 3 Ma. Basin closure occurred after intrusion of S-type granites (357 ± 2 Ma; zircon δ\u0000 18\u0000 O 7.4–10.4‰) in the foreland, and accretion of gabbros, cumulate gabbros and trondhjemites at the proto-Pacific margin. Compression prevailed for 20 Myr in the foreland, causing a mylonitic medium-grade M\u0000 3\u0000 (D\u0000 3\u0000 -S\u0000 3\u0000 ) event.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6989873\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"65 25","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139385447","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}
In Serbia ophiolitic mélanges occur widespread below ophiolites. These ophiolites are interpreted to derive from different oceanic domains and are therefore attributed to different tectonic units. We revisited all existing data from matrix ages and blocks in the mélanges, studied the relictic sedimentological features and dated new sections and blocks from various ophiolitic mélanges. On base of these results we can distinguish three different ophiolitic mélanges: 1. Intra-oceanic ophiolitic mélanges (OM1); 2. Ophiolitic mélanges formed during ophiolite obduction with continental blocks (OM2), and 3. Ophiolitic mélanges with fluviatile transported sedimentary rocks or tectonically incorporated much younger blocks at the base (OM3). These three types of ophiolitic mélanges resemble the polyphase history of shortening and ophiolite emplacement on the wider Adria plate of Serbia. All ophiolitic mélanges contain the same Triassic component spectrum of oceanic sedimentary cover rocks and have similar matrix ages. It can be concluded that all different ophiolites/ophiolitic mélanges derive from the same Triassic-Jurassic oceanic domain, the Neotethys Ocean which western part obducted during Middle-Late Jurassic times on wider Adria. 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 Jurassic ophiolitic mélanges in Serbia - a review and new insights","authors":"N. Djerić, H. Gawlick, M. Sudar","doi":"10.1144/jgs2023-165","DOIUrl":"https://doi.org/10.1144/jgs2023-165","url":null,"abstract":"In Serbia ophiolitic mélanges occur widespread below ophiolites. These ophiolites are interpreted to derive from different oceanic domains and are therefore attributed to different tectonic units. We revisited all existing data from matrix ages and blocks in the mélanges, studied the relictic sedimentological features and dated new sections and blocks from various ophiolitic mélanges. On base of these results we can distinguish three different ophiolitic mélanges: 1. Intra-oceanic ophiolitic mélanges (OM1); 2. Ophiolitic mélanges formed during ophiolite obduction with continental blocks (OM2), and 3. Ophiolitic mélanges with fluviatile transported sedimentary rocks or tectonically incorporated much younger blocks at the base (OM3). These three types of ophiolitic mélanges resemble the polyphase history of shortening and ophiolite emplacement on the wider Adria plate of Serbia. All ophiolitic mélanges contain the same Triassic component spectrum of oceanic sedimentary cover rocks and have similar matrix ages. It can be concluded that all different ophiolites/ophiolitic mélanges derive from the same Triassic-Jurassic oceanic domain, the Neotethys Ocean which western part obducted during Middle-Late Jurassic times on wider Adria.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Ophiolites, melanges and blueschists collection available at:\u0000 https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"44 22","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139451989","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}
Active submarine channel bases are marked by large erosional features, such as knickpoints and plunge pools. Their presence in ancient channel-fills has rarely been documented, meaning their importance in submarine channel morphodynamics requires investigation. Using seismic reflection data calibrated by wells from a buried submarine channel-fill, we document erosional features 100s m long and 10s m deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record for the first time. Channel incision patterns are interpreted to record a transient uplift in an otherwise subsiding depocentre. Local structural complexities in the channel slope formed zones of preferential scouring. A switch to a depositional regime preserved the irregular channel base inhibiting their upstream migration and smoothing of the channel base. Their formation and preservation record responses to salt tectonics and provide a unique snapshot of the formative processes of an ancient submarine channel. The presence of these exceptional basal scours indicates that headward erosion processes did not operate rapidly, challenging the paradigm that knickpoint migration controls channel evolution. Our results show that the primary erosion of the main channel surface, and long-term channel evolution, are dominated by far more gradual processes.
{"title":"A salty snapshot: extreme variations in basal erosion patterns preserved in a submarine channel","authors":"J. Casagrande, David M. Hodgson, Jeffrey Peakall","doi":"10.1144/jgs2023-006","DOIUrl":"https://doi.org/10.1144/jgs2023-006","url":null,"abstract":"Active submarine channel bases are marked by large erosional features, such as knickpoints and plunge pools. Their presence in ancient channel-fills has rarely been documented, meaning their importance in submarine channel morphodynamics requires investigation. Using seismic reflection data calibrated by wells from a buried submarine channel-fill, we document erosional features 100s m long and 10s m deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record for the first time. Channel incision patterns are interpreted to record a transient uplift in an otherwise subsiding depocentre. Local structural complexities in the channel slope formed zones of preferential scouring. A switch to a depositional regime preserved the irregular channel base inhibiting their upstream migration and smoothing of the channel base. Their formation and preservation record responses to salt tectonics and provide a unique snapshot of the formative processes of an ancient submarine channel. The presence of these exceptional basal scours indicates that headward erosion processes did not operate rapidly, challenging the paradigm that knickpoint migration controls channel evolution. Our results show that the primary erosion of the main channel surface, and long-term channel evolution, are dominated by far more gradual processes.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"7 8","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139450842","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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