A. M. S. Nugraha, Juliane Hennig-Breitfeld, Riska Puspita, Adam D. Switzer, Robert Hall
The Palu Formation, previously known as the Celebes Molasse in the Palu area, is understudied and was previously considered to be associated with the Pliocene collision between an Australian-derived micro-continent – Banggai Sula– and the eastern margin of Sundaland (West Sulawesi). Here, we present sedimentological, heavy mineral, and zircon geochronological data to provide insights into sediment provenance and to elucidate Neogene tectonic activity in Sulawesi. These analyses suggest that the Pleistocene Palu Formation comprises syn-orogenic alluvial fan to braided river deposits that record the rapid uplift of metamorphic and granitoid rocks in the Neck and west Central Sulawesi. The Palu Formation is characterised by predominant granitoid and metamorphic clasts and heavy mineral assemblages dominated by pyroxene, amphibole, and garnet. Detrital zircons record youngest grain ages of ca. 2.5 and 3.0 Ma with a significant Pliocene age population and subsidiary Eocene, Cretaceous, Jurassic, and Late Triassic age peaks. Rapid uplift and erosion associated with mountain building shaped the topography and influenced the evolution of Palu River networks. 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.7033388
{"title":"Detrital zircon and heavy mineral provenance from the Palu Formation, Sulawesi, Indonesia: constraints on exhumation of the Palu Metamorphic Complex and drainage evolution","authors":"A. M. S. Nugraha, Juliane Hennig-Breitfeld, Riska Puspita, Adam D. Switzer, Robert Hall","doi":"10.1144/jgs2023-118","DOIUrl":"https://doi.org/10.1144/jgs2023-118","url":null,"abstract":"The Palu Formation, previously known as the Celebes Molasse in the Palu area, is understudied and was previously considered to be associated with the Pliocene collision between an Australian-derived micro-continent – Banggai Sula– and the eastern margin of Sundaland (West Sulawesi). Here, we present sedimentological, heavy mineral, and zircon geochronological data to provide insights into sediment provenance and to elucidate Neogene tectonic activity in Sulawesi. These analyses suggest that the Pleistocene Palu Formation comprises syn-orogenic alluvial fan to braided river deposits that record the rapid uplift of metamorphic and granitoid rocks in the Neck and west Central Sulawesi. The Palu Formation is characterised by predominant granitoid and metamorphic clasts and heavy mineral assemblages dominated by pyroxene, amphibole, and garnet. Detrital zircons record youngest grain ages of ca. 2.5 and 3.0 Ma with a significant Pliocene age population and subsidiary Eocene, Cretaceous, Jurassic, and Late Triassic age peaks. Rapid uplift and erosion associated with mountain building shaped the topography and influenced the evolution of Palu River networks.\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.7033388\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"15 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139600084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To understand breakup styles and syn-rifting magmatism in the northern South China Sea (SCS), we analyze how the continent-ocean transition zone (COT) varies along strike in its potential field and deep structures. High free-air gravity anomaly and accompanied basement structures evidence significant mantle upwelling and serpentinization in the northeastern COT. The top basement of the COT is uplifted and rough, but gradually retrogrades into a relatively flat and low relief towards the mid-northern margin, where reduced gravity anomaly reflects subdued mantle upwelling but perhaps stronger syn-rifting magmatism. In the northwestern margin, low gravity anomaly suggests fairly limited mantle upwelling, but more syn-rifting magmatic intrusions in the crust, and the top basement of the COT is smooth and slightly deepened. The COT widths are mostly less than 30 km, and within the COT the oldest legible magnetic anomaly C11r is related to the final continental breakup. The seaward limit of the COT should be relocated further south beyond anomaly C11r, pointing to a very narrow zone of true oceanic lithosphere in the Northwest Subbasin. The coexistence of mantle upwelling/serpentinization, magmatic underplating, and volcanisms atop the COT during continental breakup characterizes a typical intermediate rifted margin that shows, nonetheless, significant along-strike variations. Thematic collection: This article is part of the Emerging knowledge on the tectonics of the South China Sea collection available at: https://www.lyellcollection.org/topic/collections/south-china-sea
{"title":"Along-strike breakup variations of the continent-ocean transition zone in the northern South China Sea","authors":"Xi Peng, Chun-Feng Li","doi":"10.1144/jgs2023-134","DOIUrl":"https://doi.org/10.1144/jgs2023-134","url":null,"abstract":"To understand breakup styles and syn-rifting magmatism in the northern South China Sea (SCS), we analyze how the continent-ocean transition zone (COT) varies along strike in its potential field and deep structures. High free-air gravity anomaly and accompanied basement structures evidence significant mantle upwelling and serpentinization in the northeastern COT. The top basement of the COT is uplifted and rough, but gradually retrogrades into a relatively flat and low relief towards the mid-northern margin, where reduced gravity anomaly reflects subdued mantle upwelling but perhaps stronger syn-rifting magmatism. In the northwestern margin, low gravity anomaly suggests fairly limited mantle upwelling, but more syn-rifting magmatic intrusions in the crust, and the top basement of the COT is smooth and slightly deepened. The COT widths are mostly less than 30 km, and within the COT the oldest legible magnetic anomaly C11r is related to the final continental breakup. The seaward limit of the COT should be relocated further south beyond anomaly C11r, pointing to a very narrow zone of true oceanic lithosphere in the Northwest Subbasin. The coexistence of mantle upwelling/serpentinization, magmatic underplating, and volcanisms atop the COT during continental breakup characterizes a typical intermediate rifted margin that shows, nonetheless, significant along-strike variations.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Emerging knowledge on the tectonics of the South China Sea collection available at:\u0000 https://www.lyellcollection.org/topic/collections/south-china-sea\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"118 45","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139605518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ailin M. Lopasso, Felipe Tapia, Román Feal, R. Ondrak, Jiří Sláma, Julio Hlebszevitsch, L. Giambiagi, M. Ghiglione
We report uplift and shortening rates from a late Neogene–Pleistocene deformation stage of the frontal fold-thrust belt and adjacent wedge-top in the Principal Cordillera of the southern Central Andes (33-39° SL). A structural model is presented based on integration of surface field data and subsurface 2D seismic sections. Shortening, uplift, and sedimentation rates were calculated from different steps of kinematic modelling. Our structural interpretations and modelling are integrated with new detrital zircon U-Pb geochronology to define a previously overlooked Pleistocene period of orogenic shortening and syntectonic sedimentation in the Malargüe basin. This task was possible due to the dating of three samples yielding between ∼12 and 1 Ma obtained from a 900 m deep well located in the foreland. From stratigraphic correlations, our data records an active Plio-Pleistocene wedge-top depozone coeval with retreat of the volcanism, and the emplacement of retroarc basalts. Structural modelling, together with detrital zircon U-Pb provenance data register shortening producing a foredeep to wedge-top Plio-Pleistocene transition, adjusting and completing the knowledge of the frontal fold-thrust belt and foreland basin in the southern Central Andes. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7033425
{"title":"Pleistocene deformation of the Malargüe fold-thrust belt from structural modelling and geochronology of syntectonic sedimentation","authors":"Ailin M. Lopasso, Felipe Tapia, Román Feal, R. Ondrak, Jiří Sláma, Julio Hlebszevitsch, L. Giambiagi, M. Ghiglione","doi":"10.1144/jgs2023-065","DOIUrl":"https://doi.org/10.1144/jgs2023-065","url":null,"abstract":"We report uplift and shortening rates from a late Neogene–Pleistocene deformation stage of the frontal fold-thrust belt and adjacent wedge-top in the Principal Cordillera of the southern Central Andes (33-39° SL). A structural model is presented based on integration of surface field data and subsurface 2D seismic sections. Shortening, uplift, and sedimentation rates were calculated from different steps of kinematic modelling. Our structural interpretations and modelling are integrated with new detrital zircon U-Pb geochronology to define a previously overlooked Pleistocene period of orogenic shortening and syntectonic sedimentation in the Malargüe basin. This task was possible due to the dating of three samples yielding between ∼12 and 1 Ma obtained from a 900 m deep well located in the foreland. From stratigraphic correlations, our data records an active Plio-Pleistocene wedge-top depozone coeval with retreat of the volcanism, and the emplacement of retroarc basalts. Structural modelling, together with detrital zircon U-Pb provenance data register shortening producing a foredeep to wedge-top Plio-Pleistocene transition, adjusting and completing the knowledge of the frontal fold-thrust belt and foreland basin in the southern Central Andes.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7033425\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"15 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139603077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The concept of the Akiyoshi Orogeny emerged from the geological study of the overturned Akiyoshi Limestone. However, our understanding of the stratigraphy and geological structure of the siliceous-clastic rocks surrounding the Akiyoshi Limestone remains incomplete. In this study, we conducted a geological survey within the Beppu unit, distributed on the north of the Akiyoshi Limestone, revealing substantial-scale strata overturning even within the siliceous-clastic rocks, which formed as the upper section of the ocean plate stratigraphy within the accretionary complex. Additionally, the Tsunemori Formation, which is regarded as sediments of forearc or trench-slope basin, has also undergone overturning. Consequently, extensive overturned structures exist throughout the entire accretionary complex of the Mine-Akiyoshidai Area. To understand the mechanism behind these overturned structures within the accretionary complex, we focused on the collision and deformation resulting from the interaction between the accretionary wedge and a massive seamount along with the backstop. The overturning of the forearc or slope basin sediments suggested that post-accretion deformation along the large lateral fault may have occurred during the time of the collision between the South China and North China blocks. These tectonic events during and after accretion may represent the true nature of the Akiyoshi Orogeny. 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":"Beyond the Akiyoshi Orogeny: unravelling overturned structures and tectonic processes in the Permian accretionary complex of the Mine-Akiyoshidai Area, Yamaguchi, western Japan","authors":"Koji Wakita, Masao Kametaka","doi":"10.1144/jgs2023-170","DOIUrl":"https://doi.org/10.1144/jgs2023-170","url":null,"abstract":"The concept of the Akiyoshi Orogeny emerged from the geological study of the overturned Akiyoshi Limestone. However, our understanding of the stratigraphy and geological structure of the siliceous-clastic rocks surrounding the Akiyoshi Limestone remains incomplete. In this study, we conducted a geological survey within the Beppu unit, distributed on the north of the Akiyoshi Limestone, revealing substantial-scale strata overturning even within the siliceous-clastic rocks, which formed as the upper section of the ocean plate stratigraphy within the accretionary complex. Additionally, the Tsunemori Formation, which is regarded as sediments of forearc or trench-slope basin, has also undergone overturning. Consequently, extensive overturned structures exist throughout the entire accretionary complex of the Mine-Akiyoshidai Area. To understand the mechanism behind these overturned structures within the accretionary complex, we focused on the collision and deformation resulting from the interaction between the accretionary wedge and a massive seamount along with the backstop. The overturning of the forearc or slope basin sediments suggested that post-accretion deformation along the large lateral fault may have occurred during the time of the collision between the South China and North China blocks. These tectonic events during and after accretion may represent the true nature of the Akiyoshi Orogeny.\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":507891,"journal":{"name":"Journal of the Geological Society","volume":"31 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139612006","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jiachen Cai, Haoran Sun, Wenjin Zhao, Jianhua Wang, Min Zhu
The Early Devonian Xitun Vertebrate Fauna, represented by early members of crown sarcopterygians such as Youngolepis , Diabolepis , Psarolepis , Achoania , and Styloichthys , is mainly hosted in the Xitun Formation in Qujing area, East Yunnan of China. Despite numerous research articles describing taxa from this famous Lochkovian fauna and its sedimentary and tectonic environments, there is no objective and coherent interpretation of the palaeoenvironment in which these early vertebrates lived. Based on detailed field geological investigation in recent years in the surrounding areas of Qujing City and measurements from the Xitun Formation section, this paper focuses on the analysis of some geochemistry indices of major, trace, and rare earth elements to accurately elucidate the sedimentary environment of the Xitun Formation and deepen our understanding on the relationship between Early Devonian fishes and the environment. The analyses of the sensitive geochemistry indices of depositional and tectonic settings, sedimentary provenance, weathering, palaeoclimate, palaeosalinity, and palaeoredox conditions indicate that the Lower Devonian Xitun Formation in East Yunnan was mainly deposited in a shallow marine setting with three phases of seawater-freshwater influx under a warm and humid climate, and a stable, oxygen-rich condition, which promoted the flourishing of Early Devonian marine fishes . Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system Supplementary material: https://doi.org/10.6084/m9.figshare.c.7020642
{"title":"The Early Devonian Xitun Vertebrate Fauna in South China inhabited a shallow marine environment with changing salinity","authors":"Jiachen Cai, Haoran Sun, Wenjin Zhao, Jianhua Wang, Min Zhu","doi":"10.1144/jgs2023-146","DOIUrl":"https://doi.org/10.1144/jgs2023-146","url":null,"abstract":"\u0000 The Early Devonian Xitun Vertebrate Fauna, represented by early members of crown sarcopterygians such as\u0000 Youngolepis\u0000 ,\u0000 Diabolepis\u0000 ,\u0000 Psarolepis\u0000 ,\u0000 Achoania\u0000 , and\u0000 Styloichthys\u0000 , is mainly hosted in the Xitun Formation in Qujing area, East Yunnan of China. Despite numerous research articles describing taxa from this famous Lochkovian fauna and its sedimentary and tectonic environments, there is no objective and coherent interpretation of the palaeoenvironment in which these early vertebrates lived. Based on detailed field geological investigation in recent years in the surrounding areas of Qujing City and measurements from the Xitun Formation section, this paper focuses on the analysis of some geochemistry indices of major, trace, and rare earth elements to accurately elucidate the sedimentary environment of the Xitun Formation and deepen our understanding on the relationship between Early Devonian fishes and the environment. The analyses of the sensitive geochemistry indices of depositional and tectonic settings, sedimentary provenance, weathering, palaeoclimate, palaeosalinity, and palaeoredox conditions indicate that the Lower Devonian Xitun Formation in East Yunnan was mainly deposited in a shallow marine setting with three phases of seawater-freshwater influx under a warm and humid climate, and a stable, oxygen-rich condition, which promoted the flourishing of Early Devonian marine fishes\u0000 .\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at:\u0000 https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7020642\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"95 19","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139612463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kang Liu, Weitao Wang, Ruizhi Jin, Hulu Jing, Renjie Zhou
The Tibetan Plateau, which is deformed by the collision between the Indian and Eurasian plates, is a natural laboratory to study intracontinental deformation related to northeastward growth of the Plateau. However, how and when the Tibetan Plateau propagated to its present-day margins remain unclear. The Qilian Shan and Haiyuan fault, which serve as the topographic and geological boundaries of high Plateau, are key to revealing the uplift and expansion of the Tibetan Plateau. Here, we present detrital apatite (U-Th)/He and reverse modelling results from the Laolongwan basin, which is interpreted as a pull-apart basin controlled by activity of the Haiyuan fault in the east portion of the Qilian Shan region. Our results reveal three stage tectono-thermal evolution of Qilian Shan: (a) late Jurassic to Cretaceous rapid exhumation; (b) late Cretaceous to middle Miocene tectonic quiescence period and (c) exhumation after middle Miocene. We suggest that the Jurassic to Cretaceous rapid exhumation might be related to the convergence of the Lhasa block with the Eurasian plate or regional extension during the Mesozoic closure of the Meso-Tethys, and the mid-Miocene accelerated exhumation was driven by Haiyuan fault activation related to the growth of the Tibetan Plateau to its northeastern margin. 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.7018149
{"title":"Exhumation of the Qilian Shan and Miocene activity of the Haiyuan Fault: Insights from apatite (U-Th)/He thermochronology in the Laolongwan basin, northeastern Tibetan Plateau","authors":"Kang Liu, Weitao Wang, Ruizhi Jin, Hulu Jing, Renjie Zhou","doi":"10.1144/jgs2023-111","DOIUrl":"https://doi.org/10.1144/jgs2023-111","url":null,"abstract":"The Tibetan Plateau, which is deformed by the collision between the Indian and Eurasian plates, is a natural laboratory to study intracontinental deformation related to northeastward growth of the Plateau. However, how and when the Tibetan Plateau propagated to its present-day margins remain unclear. The Qilian Shan and Haiyuan fault, which serve as the topographic and geological boundaries of high Plateau, are key to revealing the uplift and expansion of the Tibetan Plateau. Here, we present detrital apatite (U-Th)/He and reverse modelling results from the Laolongwan basin, which is interpreted as a pull-apart basin controlled by activity of the Haiyuan fault in the east portion of the Qilian Shan region. Our results reveal three stage tectono-thermal evolution of Qilian Shan: (a) late Jurassic to Cretaceous rapid exhumation; (b) late Cretaceous to middle Miocene tectonic quiescence period and (c) exhumation after middle Miocene. We suggest that the Jurassic to Cretaceous rapid exhumation might be related to the convergence of the Lhasa block with the Eurasian plate or regional extension during the Mesozoic closure of the Meso-Tethys, and the mid-Miocene accelerated exhumation was driven by Haiyuan fault activation related to the growth of the Tibetan Plateau to its northeastern margin.\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.7018149\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"6 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139613947","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We use ground-penetrating radar (GPR) to investigate the geometry, inland extent, and continuity of sand layers interpreted as tsunami deposits in the Shetland Islands, UK. Four sites where sand layers within peat deposits are recorded in previous studies provide ground-truth. In addition, we describe survey results from one site where deposits are not exposed, to test the potential of GPR to identify candidate tsunami deposits in areas that are not well documented. Sand layers can be clearly imaged at all five locations because they are interbedded with peat and the contrast in lithology gives a good reflection on GPR profiles, even very thin sand layers, less than 1 cm in thickness, that are beneath the theoretical resolution of the GPR. 2-D and 3-D surveys show that tsunami deposits appear to drape a buried topography. Most sand layers form continuous reflections although some gaps are attributed to later erosion, most likely by streams. Sand layers have been traced up to 150 m inland and 10 m above the present shoreline which is consistent with data from boreholes. If a similar sized event occurred today it would have a devastating impact on the Shetland Islands.
{"title":"Using ground-penetrating radar (GPR) to investigate deposits from the Storegga Slide Tsunami and other sand-sheets in the Shetland Islands, UK","authors":"L. Buck, C. S. Bristow","doi":"10.1144/jgs2023-042","DOIUrl":"https://doi.org/10.1144/jgs2023-042","url":null,"abstract":"We use ground-penetrating radar (GPR) to investigate the geometry, inland extent, and continuity of sand layers interpreted as tsunami deposits in the Shetland Islands, UK. Four sites where sand layers within peat deposits are recorded in previous studies provide ground-truth. In addition, we describe survey results from one site where deposits are not exposed, to test the potential of GPR to identify candidate tsunami deposits in areas that are not well documented. Sand layers can be clearly imaged at all five locations because they are interbedded with peat and the contrast in lithology gives a good reflection on GPR profiles, even very thin sand layers, less than 1 cm in thickness, that are beneath the theoretical resolution of the GPR. 2-D and 3-D surveys show that tsunami deposits appear to drape a buried topography. Most sand layers form continuous reflections although some gaps are attributed to later erosion, most likely by streams. Sand layers have been traced up to 150 m inland and 10 m above the present shoreline which is consistent with data from boreholes. If a similar sized event occurred today it would have a devastating impact on the Shetland Islands.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"64 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139244823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ophiolite obduction, the process by which part of the oceanic crust overlaps the continental margin, is challenging when it comes to the geodynamic reconstruction of lithospheric processes. This buoyancy difference between dense oceanic crust and the relatively buoyant continental crust makes the obduction of the oceanic crust difficult, if not impossible, when only buoyancy forces are considered. To overcome the difficulties posed by the negative buoyancy, the initial configuration of the oceanic basins must have specific thermal and geometric constraints. Here we present a systematic investigation of the geometrical and the geodynamical parameters which control the ophiolite emplacement process. Our study reveals which parameters are the most important during ophiolite emplacement and which are the most optimal geometries that favour ophiolite emplacement. We focus on “Tethyan” ophiolites which are characterized by relatively small inferred basin size and are commonly found in Mediterranean region. Based on a combination of various parameters, we identified the most susceptible configurations for ophiolite obduction. Our models demonstrate, in agreement to geological data, that the obducted lithosphere must be young and the length of the Ocean-Continent-Transition zone must be relatively sharp in order to achieve ophiolite obduction. 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.6922526
{"title":"The role of continental-margin architecture on models of ophiolite emplacement","authors":"Iskander Ibragimov, E. Moulas","doi":"10.1144/jgs2023-063","DOIUrl":"https://doi.org/10.1144/jgs2023-063","url":null,"abstract":"Ophiolite obduction, the process by which part of the oceanic crust overlaps the continental margin, is challenging when it comes to the geodynamic reconstruction of lithospheric processes. This buoyancy difference between dense oceanic crust and the relatively buoyant continental crust makes the obduction of the oceanic crust difficult, if not impossible, when only buoyancy forces are considered. To overcome the difficulties posed by the negative buoyancy, the initial configuration of the oceanic basins must have specific thermal and geometric constraints. Here we present a systematic investigation of the geometrical and the geodynamical parameters which control the ophiolite emplacement process. Our study reveals which parameters are the most important during ophiolite emplacement and which are the most optimal geometries that favour ophiolite emplacement. We focus on “Tethyan” ophiolites which are characterized by relatively small inferred basin size and are commonly found in Mediterranean region. Based on a combination of various parameters, we identified the most susceptible configurations for ophiolite obduction. Our models demonstrate, in agreement to geological data, that the obducted lithosphere must be young and the length of the Ocean-Continent-Transition zone must be relatively sharp in order to achieve ophiolite obduction. 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.6922526","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"3 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139268836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Di Rosa, Federico Farina, M. Marroni, Heejin Jeon, L. Pandolfi
The External Ligurian Units are regarded as representative of the ocean continent transition between the Ligure-Piemontese oceanic basin and the hyperextended Adria continental margin. The remnants of this transition are preserved as slide blocks embedded in a sedimentary mélange. This mélange sedimented during the Santonian to Campanian in the rear of the accretionary wedge that developed during the east-dipping subduction of the oceanic lithosphere below Adria. The main characteristic of this mélange is the occurrence of slide blocks of subcontinental mantle, lower continental crust, granitoids, gabbro, basalt, and sedimentary rocks in a sedimentary matrix. In this paper, we provide petrographic observations coupled with U‒Pb zircon ages and δ 18 O zircon isotopes of the slide blocks of felsic granulites and granitoids. U‒Pb data indicate ages ranging from Neoproterozoic to Late Triassic. δ 18 O isotopes help to define the source of the magma of granitoids and felsic granulites, which was the continental crust. Overall, the collected data indicate that the slide blocks from sedimentary mélanges can be regarded as true archives that are able to provide useful constraints about the geodynamic history of the source area of these deposits. 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.6922535
{"title":"U–PB ages from felsic rocks of the External Ligurian sedimentary mélange (Northern Apennine, Italy): tracing the pre-Jurassic history of the hyperextended Adria continental margin","authors":"M. Di Rosa, Federico Farina, M. Marroni, Heejin Jeon, L. Pandolfi","doi":"10.1144/jgs2023-121","DOIUrl":"https://doi.org/10.1144/jgs2023-121","url":null,"abstract":"The External Ligurian Units are regarded as representative of the ocean continent transition between the Ligure-Piemontese oceanic basin and the hyperextended Adria continental margin. The remnants of this transition are preserved as slide blocks embedded in a sedimentary mélange. This mélange sedimented during the Santonian to Campanian in the rear of the accretionary wedge that developed during the east-dipping subduction of the oceanic lithosphere below Adria. The main characteristic of this mélange is the occurrence of slide blocks of subcontinental mantle, lower continental crust, granitoids, gabbro, basalt, and sedimentary rocks in a sedimentary matrix. In this paper, we provide petrographic observations coupled with U‒Pb zircon ages and δ 18 O zircon isotopes of the slide blocks of felsic granulites and granitoids. U‒Pb data indicate ages ranging from Neoproterozoic to Late Triassic. δ 18 O isotopes help to define the source of the magma of granitoids and felsic granulites, which was the continental crust. Overall, the collected data indicate that the slide blocks from sedimentary mélanges can be regarded as true archives that are able to provide useful constraints about the geodynamic history of the source area of these deposits. 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.6922535","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"7 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139268083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Zermatt-Saas Zone is an eclogite-facies metaophiolite unit representing the fossil oceanic lithosphere of the Jurassic Tethys. In the Italian Northwestern Alps, the Zermatt-Saas Zone includes a chaotic rock unit, or mélange, ca. 40 m thick, interposed between serpentinites and calcschists. The mélange consists of decimetric ultramafic layers and boudins embedded in a serpentine + carbonate-rich matrix showing a block-in-matrix fabric. The mélange shares the same Alpine tectono-metamorphic evolution with the surrounding rocks, starting with a prograde path developed under high-pressure (HP) conditions followed by a retrograde path during exhumation. The kinematic and metamorphic relations between inside- and outside-boudin foliations attests that boudinage and shearing developed during the prograde HP path. Fluid-rock interaction enhanced shearing and focused ductile and brittle/ductile deformation along lithological contacts between rigid blocks and boudins and flowing carbonaceous matrix. Despite a pervasive orogenic evolution, the primary tectono-sedimentary features of the mélange are still recognizable in some outcrops and attributed to an intraoceanic (Jurassic) setting characterized by mass transport processes. The present-day fabric of the studied mélange unit thus results from the superposition of the Alpine processes, responsible for fluid-assisted stratal disruption and mixing in the subduction channel, on the original stratigraphy formed during intraoceanic gravitational processes. Supplementary material Figures S1 to S6 and Tables S1 and S2 are available at https://doi.org/10.6084/m9.figshare.c.6924080 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 effect of tectonic boudinage and folding in a subducted mélange of the Alpine orogenic belt (Zermatt-Saas Zone, Italian Western Alps)","authors":"S. Guerini, P. Tartarotti","doi":"10.1144/jgs2023-142","DOIUrl":"https://doi.org/10.1144/jgs2023-142","url":null,"abstract":"The Zermatt-Saas Zone is an eclogite-facies metaophiolite unit representing the fossil oceanic lithosphere of the Jurassic Tethys. In the Italian Northwestern Alps, the Zermatt-Saas Zone includes a chaotic rock unit, or mélange, ca. 40 m thick, interposed between serpentinites and calcschists. The mélange consists of decimetric ultramafic layers and boudins embedded in a serpentine + carbonate-rich matrix showing a block-in-matrix fabric. The mélange shares the same Alpine tectono-metamorphic evolution with the surrounding rocks, starting with a prograde path developed under high-pressure (HP) conditions followed by a retrograde path during exhumation. The kinematic and metamorphic relations between inside- and outside-boudin foliations attests that boudinage and shearing developed during the prograde HP path. Fluid-rock interaction enhanced shearing and focused ductile and brittle/ductile deformation along lithological contacts between rigid blocks and boudins and flowing carbonaceous matrix. Despite a pervasive orogenic evolution, the primary tectono-sedimentary features of the mélange are still recognizable in some outcrops and attributed to an intraoceanic (Jurassic) setting characterized by mass transport processes. The present-day fabric of the studied mélange unit thus results from the superposition of the Alpine processes, responsible for fluid-assisted stratal disruption and mixing in the subduction channel, on the original stratigraphy formed during intraoceanic gravitational processes. Supplementary material Figures S1 to S6 and Tables S1 and S2 are available at https://doi.org/10.6084/m9.figshare.c.6924080 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":507891,"journal":{"name":"Journal of the Geological Society","volume":"18 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139267263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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