W. Bian, Tianshui Yang, Suo Wang, Wenxiao Peng, Xianwei Jiao, Shihong Zhang, Huaichun Wu, Haiyan Li, Pan Zhao
Understanding the northern extension of Greater India is vital for modeling the India-Asia collision process and the formation of the Tibetan Plateau. We present new palaeomagnetic data from the mid-Cretaceous (ca. 106 Ma) Gyabula Formation red beds in the Tethyan Himalaya. Well-defined high laboratory unblocking temperature component magnetizations were isolated from 19 sites and pass the fold tests, indicating that they are pre-folding magnetizations. The tilt-corrected site-mean direction is D s = 222.9°, I s = +39.4° with α 95 = 4.2°. The site-mean inclination increases from 39.4° to 45.8° after anisotropy-based inclination shallowing correction. The declination and inclination differ considerably from those of neighboring sections. This directional discrepancy of the red beds may be attributed to the fact that the sampled section (sites ZB1–11, 40–52) is overturned and local vertical axis rotation. The combination of our new and previously published palaeomagnetic data shows that the Tethyan Himalaya was located at 27.5° ± 2.4°S for the sampled area. Our new results, together with the reliable Cretaceous palaeomagnetic data obtained from the Tethyan Himalaya as well as coeval palaeolatitudes expected from the Indian craton, support a smaller Greater India and that the Tethyan Himalaya did not rift from the Indian craton during the mid-Cretaceous. 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.6795683
了解大印度的北部延伸对于模拟印度-亚洲碰撞过程和青藏高原的形成至关重要。本文介绍了特提斯喜马拉雅地区中白垩世(约106 Ma)嘉布拉组红层的新古地磁资料。从19个位点分离出明确的高实验室解封温度组分磁化，并通过了折叠测试，表明它们是预折叠磁化。倾斜校正后的位置-平均方向为D s = 222.9°，I s = +39.4°，α 95 = 4.2°。经各向异性倾角浅化校正后，井位平均倾角由39.4°增加到45.8°。赤纬和倾角与邻近的剖面有很大的不同。这种红色层的方向性差异可能是由于采样剖面(zb1 - 11,40 - 52)被翻转和局部垂直轴旋转所致。结合新的古地磁资料和已有的古地磁资料，特提斯喜马拉雅位于27.5°±2.4°S。我们的新结果，结合从特提斯喜马拉雅地区获得的可靠的白垩纪古地磁数据，以及从印度克拉通获得的同时期古纬度，支持了一个较小的大印度，并且特提斯喜马拉雅地区在白垩纪中期没有从印度克拉通断裂。专题文集:本文是中生代和新生代构造、景观和气候变化文集的一部分，可在:https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change获取补充资料:https://doi.org/10.6084/m9.figshare.c.6795683
{"title":"Palaeomagnetism of the mid-Cretaceous red beds from the Tethyan Himalaya: direction discrepancy and tectonic implications","authors":"W. Bian, Tianshui Yang, Suo Wang, Wenxiao Peng, Xianwei Jiao, Shihong Zhang, Huaichun Wu, Haiyan Li, Pan Zhao","doi":"10.1144/jgs2023-029","DOIUrl":"https://doi.org/10.1144/jgs2023-029","url":null,"abstract":"\u0000 Understanding the northern extension of Greater India is vital for modeling the India-Asia collision process and the formation of the Tibetan Plateau. We present new palaeomagnetic data from the mid-Cretaceous (ca. 106 Ma) Gyabula Formation red beds in the Tethyan Himalaya. Well-defined high laboratory unblocking temperature component magnetizations were isolated from 19 sites and pass the fold tests, indicating that they are pre-folding magnetizations. The tilt-corrected site-mean direction is D\u0000 s\u0000 = 222.9°, I\u0000 s\u0000 = +39.4° with\u0000 \u0000 \u0000 α\u0000 \u0000 \u0000 95\u0000 = 4.2°. The site-mean inclination increases from 39.4° to 45.8° after anisotropy-based inclination shallowing correction. The declination and inclination differ considerably from those of neighboring sections. This directional discrepancy of the red beds may be attributed to the fact that the sampled section (sites ZB1–11, 40–52) is overturned and local vertical axis rotation. The combination of our new and previously published palaeomagnetic data shows that the Tethyan Himalaya was located at 27.5° ± 2.4°S for the sampled area. Our new results, together with the reliable Cretaceous palaeomagnetic data obtained from the Tethyan Himalaya as well as coeval palaeolatitudes expected from the Indian craton, support a smaller Greater India and that the Tethyan Himalaya did not rift from the Indian craton during the mid-Cretaceous.\u0000 \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.6795683\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42028035","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}
Fault locations and orientation of the Zabargad Transform Fault Zone, also called the Zabargad Fracture Zone (ZFZ) have, so far, only been delineated by satellite-based geophysical data, causing intense debate over the last decades. Newly recognized geomorphological features identified in bathymetry and lidar data from the NE Red Sea margin present the first ground evidence for the northern extent of the ZFZ. The features are aligned over 84 km starting from the Mabahiss Deep, near the spreading axis, and continue to the shallow Saudi Arabian shelf, along the northern termination of the Al Wajh carbonate platform. Analysis of the seafloor morphology revealed three geomorphic terrains: (1) a deep incised canyon feeding into the Mabahiss Deep, which is characterized by dozens of amphitheatre-shaped scarps, (2) a 22 km-wide head-scarp that follows the Al Wajh platform edge, (3) and multiple fault scars and graben-like structures on the shallow shelf. We interpret these morphological features as deformation indicators in association with the deformation processes in the ZFZ, and postulate that they represent the northern end of the ZFZ. In addition, the fault zone delineates the northwest margin of the Al Wajh carbonate platform, and most likely continues to shape it. This paper gives new insights in the interaction between fracture zones and continental margins and their role in the seafloor morphogenesis.
{"title":"Morphological evidence of the extension of the Zabargad Transform Fault Zone to the Saudi Arabian Red Sea margin","authors":"A. Petrovic, Y. Panara, V. Vahrenkamp","doi":"10.1144/jgs2023-009","DOIUrl":"https://doi.org/10.1144/jgs2023-009","url":null,"abstract":"Fault locations and orientation of the Zabargad Transform Fault Zone, also called the Zabargad Fracture Zone (ZFZ) have, so far, only been delineated by satellite-based geophysical data, causing intense debate over the last decades. Newly recognized geomorphological features identified in bathymetry and lidar data from the NE Red Sea margin present the first ground evidence for the northern extent of the ZFZ. The features are aligned over 84 km starting from the Mabahiss Deep, near the spreading axis, and continue to the shallow Saudi Arabian shelf, along the northern termination of the Al Wajh carbonate platform. Analysis of the seafloor morphology revealed three geomorphic terrains: (1) a deep incised canyon feeding into the Mabahiss Deep, which is characterized by dozens of amphitheatre-shaped scarps, (2) a 22 km-wide head-scarp that follows the Al Wajh platform edge, (3) and multiple fault scars and graben-like structures on the shallow shelf. We interpret these morphological features as deformation indicators in association with the deformation processes in the ZFZ, and postulate that they represent the northern end of the ZFZ. In addition, the fault zone delineates the northwest margin of the Al Wajh carbonate platform, and most likely continues to shape it. This paper gives new insights in the interaction between fracture zones and continental margins and their role in the seafloor morphogenesis.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46522083","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 end-Triassic mass extinction (ETME) is one of the five catastrophic extinction events. However, the driving mechanisms of biodiversity loss during this interval remain controversial. In this study, we investigate the marine sediment geochemistry and fauna across the Triassic-Jurassic boundary in the Wenquan section of Qiangtang Basin, and the triggering mechanism of the Late Triassic extinction in the eastern Tethys Ocean. Our study shows that the main pulse of the ETME occurred in Bed 8, manifesting as the disappearance of four brachiopod species, a significant decrease of other faunas, and the “Lilliput Effect” on bivalves. Analyses of pyrite framboids and redox-sensitive trace elements, suggest the development of photic zone anoxia near the T/J boundary and coincident with the Late Triassic extinction. Thus, the development of abrupt and intense photic-zone anoxia could play an important role in the end-Triassic extinction. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6771606
{"title":"Biological extinction and photic-zone anoxia across the Triassic-Jurassic transition: Insights from the Qiangtang Basin, eastern Tethys","authors":"Fangzhi Hu, X. Fu, Jian Wang, Hengye Wei, Ying Nie, Jian Zhang, Kangzhi Tian","doi":"10.1144/jgs2022-108","DOIUrl":"https://doi.org/10.1144/jgs2022-108","url":null,"abstract":"The end-Triassic mass extinction (ETME) is one of the five catastrophic extinction events. However, the driving mechanisms of biodiversity loss during this interval remain controversial. In this study, we investigate the marine sediment geochemistry and fauna across the Triassic-Jurassic boundary in the Wenquan section of Qiangtang Basin, and the triggering mechanism of the Late Triassic extinction in the eastern Tethys Ocean. Our study shows that the main pulse of the ETME occurred in Bed 8, manifesting as the disappearance of four brachiopod species, a significant decrease of other faunas, and the “Lilliput Effect” on bivalves. Analyses of pyrite framboids and redox-sensitive trace elements, suggest the development of photic zone anoxia near the T/J boundary and coincident with the Late Triassic extinction. Thus, the development of abrupt and intense photic-zone anoxia could play an important role in the end-Triassic extinction.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6771606\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42698851","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}
L. Tao, Hongfei Zhang, Zhongning Gao, Zhuo Lu, He Yang, Liqi Zhang
Dissection of relicts of Ocean Plate Stratigraphy (OPS) at orogens could provide important insights into oceanic evolution, orogenic formation, and continental growth. Here we put forward a study of petrology, geochronology, geochemistry, and Sr–Nd isotopes for OPS at the South Qilian Accretionary Belt (SQAB) with aim to provide new constraints on evolution of the Proto-Tethys Ocean (PTO). Three types of OPS units were recognized by their discrepant petrological, geochemical, and isotopic features. Type 1 OPS as relicts of ocean islands/seamounts comprises OIB-type basalt and gabbro (t = 525 ± 4 Ma, ( 87 Sr/ 86 Sr) i = 0.7035–0.7039, and ε Nd ( t ) = +3.63 to +4.16) and (siliceous) carbonate rocks. Type 2 OPS, representing fragments of normal oceanic crusts, consists of N-MORB-like basalt and basaltic andesite (( 87 Sr/ 86 Sr) i = 0.7059–0.7063, and ε Nd ( t ) = +6.33 to +7.44), chert, and siliceous mudstone. Type 3 OPS could be oceanic plateau-derived and comprises E-MORB-like basalt and dolerite (( 87 Sr/ 86 Sr) i = 0.7051–0.7064 and ε Nd ( t ) = +4.81 to +6.24), carbonate-siliceous mudstone, and carbonate rock. These OPS witnessed evolution of the PTO. By available studies on regional arc-type magmatism and U-Pb geochronological data of detrital zircon in this study, a model of “trench jam accompanying with subduction flip induced by accretion of the OPS” is put forward. 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.6764637
{"title":"Recognizing different types of Ocean Plate Stratigraphy at the southeastern South Qilian Accretionary Belt, northeastern Tibet Plateau","authors":"L. Tao, Hongfei Zhang, Zhongning Gao, Zhuo Lu, He Yang, Liqi Zhang","doi":"10.1144/jgs2023-035","DOIUrl":"https://doi.org/10.1144/jgs2023-035","url":null,"abstract":"\u0000 Dissection of relicts of Ocean Plate Stratigraphy (OPS) at orogens could provide important insights into oceanic evolution, orogenic formation, and continental growth. Here we put forward a study of petrology, geochronology, geochemistry, and Sr–Nd isotopes for OPS at the South Qilian Accretionary Belt (SQAB) with aim to provide new constraints on evolution of the Proto-Tethys Ocean (PTO). Three types of OPS units were recognized by their discrepant petrological, geochemical, and isotopic features. Type 1 OPS as relicts of ocean islands/seamounts comprises OIB-type basalt and gabbro (t = 525 ± 4 Ma, (\u0000 87\u0000 Sr/\u0000 86\u0000 Sr)\u0000 i\u0000 = 0.7035–0.7039, and ε\u0000 Nd\u0000 (\u0000 t\u0000 ) = +3.63 to +4.16) and (siliceous) carbonate rocks. Type 2 OPS, representing fragments of normal oceanic crusts, consists of N-MORB-like basalt and basaltic andesite ((\u0000 87\u0000 Sr/\u0000 86\u0000 Sr)\u0000 i\u0000 = 0.7059–0.7063, and ε\u0000 Nd\u0000 (\u0000 t\u0000 ) = +6.33 to +7.44), chert, and siliceous mudstone. Type 3 OPS could be oceanic plateau-derived and comprises E-MORB-like basalt and dolerite ((\u0000 87\u0000 Sr/\u0000 86\u0000 Sr)\u0000 i\u0000 = 0.7051–0.7064 and ε\u0000 Nd\u0000 (\u0000 t\u0000 ) = +4.81 to +6.24), carbonate-siliceous mudstone, and carbonate rock. These OPS witnessed evolution of the PTO. By available studies on regional arc-type magmatism and U-Pb geochronological data of detrital zircon in this study, a model of “trench jam accompanying with subduction flip induced by accretion of the OPS” is put forward.\u0000 \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.6764637\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44590852","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}
M. Sephton, Jonathan S W Tan, J. Watson, K. Hickman‐Lewis, J. M. Madariaga
A high priority goal for past, present and future missions to Mars is the search for evidence of past or present life. Some of the most information-rich signals are those represented by organic biomarkers. Thermal extraction has historically been the most popular in situ analysis technique employed on Mars owing to its elegance and ability to liberate both small compounds and large macromolecular networks. The geological record of Mars contains a variety of minerals, some of which can interact with organic matter when subjected to thermal extraction. Here we discuss the organic records that may be associated with these mineral hosts and the problems encountered when mineral-organic mixtures are analysed by thermal-based methods. We also suggest potential mitigations for future experiments of a similar nature and note that these mitigating steps can be applied not only in situ on Mars but also after samples are returned to Earth as part of Mars Sample Return where more resources and time for sample preparation are available. Thematic collection: This article is part of the Astrobiology: Perspectives from the Geology of Earth and the Solar System collection available at: https://www.lyellcollection.org/topic/collections/astrobiology
{"title":"Organic geochemistry of in situ thermal-based analyses on Mars: the importance and influence of minerals","authors":"M. Sephton, Jonathan S W Tan, J. Watson, K. Hickman‐Lewis, J. M. Madariaga","doi":"10.1144/jgs2022-152","DOIUrl":"https://doi.org/10.1144/jgs2022-152","url":null,"abstract":"A high priority goal for past, present and future missions to Mars is the search for evidence of past or present life. Some of the most information-rich signals are those represented by organic biomarkers. Thermal extraction has historically been the most popular in situ analysis technique employed on Mars owing to its elegance and ability to liberate both small compounds and large macromolecular networks. The geological record of Mars contains a variety of minerals, some of which can interact with organic matter when subjected to thermal extraction. Here we discuss the organic records that may be associated with these mineral hosts and the problems encountered when mineral-organic mixtures are analysed by thermal-based methods. We also suggest potential mitigations for future experiments of a similar nature and note that these mitigating steps can be applied not only in situ on Mars but also after samples are returned to Earth as part of Mars Sample Return where more resources and time for sample preparation are available.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Astrobiology: Perspectives from the Geology of Earth and the Solar System collection available at:\u0000 https://www.lyellcollection.org/topic/collections/astrobiology\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44329216","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 Sommerodde positive organic carbon isotope excursion (SOCIE), within the Oktavites spiralis graptolite Biozone (Telychian, Silurian), was first identified in the Sommerodde-1 core, Bornholm, Denmark, where it is the largest positive excursion within the Upper Ordovician–lower Silurian part of the core. Other published occurrences of the SOCIE are discussed here, together with new δ 13 C org data from the Jabalón River section, Corral de Calatrava, central Spain where the SOCIE is only a very minor positive excursion. Very unusually, the SOCIE is best developed in deeper water settings, contrary to the typical pattern of declining excursion magnitude offshore. In the Sommerodde-1 core (Bornholm), and where it has been tentatively identified in the Vežaičiai-2 core (Lithuania), the SOCIE is developed in pale, organic-poor mudstones. It is considered likely that the SOCIE's magnitude has been enhanced in the Sommerodde-1 core record by a change in organic matter composition in the deep marine environment that did not affect shallower marine environments so significantly. 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: A table of organic carbon isotope data from the Jabalón River section, Corral de Calatrava, central Spain is available at https://doi.org/10.6084/m9.figshare.c.6769514
在丹麦Bornholm的Sommerodde-1岩心中，首次发现了位于Oktavites spiralis笔石生物带(Telychian，志留纪)内的Sommerodde阳性有机碳同位素偏移(SOCIE)，这是岩心上奥陶统-下志留统部分最大的阳性偏移。本文讨论了其他已发表的SOCIE事件，以及来自西班牙中部Corral de Calatrava Jabalón河段的新δ 13c org数据，其中SOCIE只是一个非常小的正偏移。非常不寻常的是，与海上偏移幅度下降的典型模式相反，深水环境中SOCIE发育最好。在Sommerodde-1岩心(Bornholm)中，以及在Vežaičiai-2岩心(立陶宛)中初步确定的地方，SOCIE发育在苍白的、缺乏有机物的泥岩中。人们认为，在Sommerodde-1岩心记录中，由于深海环境中有机质组成的变化对浅层海洋环境的影响没有那么大，因此很可能增强了SOCIE的强度。专题收集:本文是《中古生代地球系统的化学演化和生物反应》收集的一部分，可在:https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system。补充材料:来自西班牙中部卡拉特拉瓦河(Corral de Calatrava) Jabalón河段的有机碳同位素数据表，可在https://doi.org/10.6084/m9.figshare.c.6769514上获得
{"title":"The Sommerodde (Telychian, Silurian) positive carbon isotope excursion: why is its magnitude so variable?","authors":"D. Loydell, J. C. Gutiérrez-Marco, P. Štorch","doi":"10.1144/jgs2023-037","DOIUrl":"https://doi.org/10.1144/jgs2023-037","url":null,"abstract":"\u0000 The Sommerodde positive organic carbon isotope excursion (SOCIE), within the\u0000 Oktavites spiralis\u0000 graptolite Biozone (Telychian, Silurian), was first identified in the Sommerodde-1 core, Bornholm, Denmark, where it is the largest positive excursion within the Upper Ordovician–lower Silurian part of the core. Other published occurrences of the SOCIE are discussed here, together with new δ\u0000 13\u0000 C\u0000 org\u0000 data from the Jabalón River section, Corral de Calatrava, central Spain where the SOCIE is only a very minor positive excursion. Very unusually, the SOCIE is best developed in deeper water settings, contrary to the typical pattern of declining excursion magnitude offshore. In the Sommerodde-1 core (Bornholm), and where it has been tentatively identified in the Vežaičiai-2 core (Lithuania), the SOCIE is developed in pale, organic-poor mudstones. It is considered likely that the SOCIE's magnitude has been enhanced in the Sommerodde-1 core record by a change in organic matter composition in the deep marine environment that did not affect shallower marine environments so significantly.\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 A table of organic carbon isotope data from the Jabalón River section, Corral de Calatrava, central Spain is available at\u0000 https://doi.org/10.6084/m9.figshare.c.6769514\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44997090","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}
Alteration of serpentinised peridotites of Highland Border Complex in Scotland took place in two steps. Listvenite-like dolomite-quartz rocks formed by addition of CaO, Sr and CO 2 at constant MgO and SiO 2 involving a mass increase of ca. 140 %. Stage-two involved the dissolution of dolomite evinced by the abundant pores and rhombohedral-shaped grains of quartz to form Cr- and Ni-rich jasper and quartzites. Formation of the jasper-quartzites involve a mass reduction of ca. 80%. The listvenite-like and jasper-quartzite rocks have enrichment in the fluid mobile elements Ba, Sr, Cs, As and Sb. The As is present in the Aluminium-Phosphate-Sulphate group of minerals formed during alteration of Cr-spinel. Cr-spinel also alters to porous hematite and ferrihydrite with patches containing up to 5.5 wt% As 2 O 3 . Enrichment of As, related to alteration of chromite, is previously unknown from natural rocks, but strongly resembles efficient methods used for remediation of this toxic element. Formation of quartzite and jasper from peridotite and their common presence as pebbles both in the Devonian Old Red conglomerates, in the Highland Border Complex and in Devonian Basins in the Scandinavian Caledonides, highlights their importance and potential for provenance- and tectono-stratigraphic correlations. 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.6764598
{"title":"Extreme enrichment of Arsenic and Antimony during alteration of serpentinised peridotites to form listvenite-like dolomite-quartz rocks and Ni-Cr-rich jasper and quartzites in the Highland Border Complex of Scotland","authors":"H. Austrheim, Torgeir B. Andresen","doi":"10.1144/jgs2023-054","DOIUrl":"https://doi.org/10.1144/jgs2023-054","url":null,"abstract":"\u0000 Alteration of serpentinised peridotites of Highland Border Complex in Scotland took place in two steps. Listvenite-like dolomite-quartz rocks formed by addition of CaO, Sr and CO\u0000 2\u0000 at constant MgO and SiO\u0000 2\u0000 involving a mass increase of ca. 140 %. Stage-two involved the dissolution of dolomite evinced by the abundant pores and rhombohedral-shaped grains of quartz to form Cr- and Ni-rich jasper and quartzites. Formation of the jasper-quartzites involve a mass reduction of ca. 80%. The listvenite-like and jasper-quartzite rocks have enrichment in the fluid mobile elements Ba, Sr, Cs, As and Sb. The As is present in the Aluminium-Phosphate-Sulphate group of minerals formed during alteration of Cr-spinel. Cr-spinel also alters to porous hematite and ferrihydrite with patches containing up to 5.5 wt% As\u0000 2\u0000 O\u0000 3\u0000 . Enrichment of As, related to alteration of chromite, is previously unknown from natural rocks, but strongly resembles efficient methods used for remediation of this toxic element. Formation of quartzite and jasper from peridotite and their common presence as pebbles both in the Devonian Old Red conglomerates, in the Highland Border Complex and in Devonian Basins in the Scandinavian Caledonides, highlights their importance and potential for provenance- and tectono-stratigraphic correlations.\u0000 \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.6764598\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44554546","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}
F. Tomek, Irena Olšanská, J. Trubač, J. Černý, Jan Rejšek, L. Ackerman
The evolution of eruptive vents related to calderas is not fully understood. We focus on a structural, rock-magnetic, and geochemical investigation of a ∼314 Ma rhyolite dyke swarm associated with the late-orogenic Altenberg–Teplice Caldera, Bohemian Massif, eastern Variscan belt. The whole-rock major element, trace element, and Nd–Pb isotope geochemistry along with the published U-Pb zircon geochronology link the extra-caldera dyke swarm with intra-caldera ignimbrites. The magnetic fabrics determined using the anisotropy of magnetic susceptibility are interpreted to record a continuum from magma ascent, emplacement, and eruption during sinistral shearing. The latter evidences an interplay with regional tectonics associated with the activity of crustal-scale shear zones. The sinistral kinematics and strike of the dyke swarm, the elongation of caldera intrusive units, and the kinematics of major caldera faults are consistent with the dextral Riedel shear system, where the dykes correspond to antithetic Ŕ/X-shears. Such a kinematic configuration implies that the maximum and minimum principal stresses were oriented roughly north-south and east-west, respectively. The relation between the stress field with respect to the caldera elongation and orientation is not typical. We suggest that a pre-existing mutually perpendicular set of cross-cutting structural lineaments largely controlled the magma chamber and caldera formation. Supplementary material: The whole-rock major, trace element and isotope geochemical tables, magnetic fabrics source data, and methodology details are available at https://doi.org/10.6084/m9.figshare.c.6715893 .
{"title":"On the anatomy and structural control of a dyke swarm that fed caldera-forming ignimbrite eruptions","authors":"F. Tomek, Irena Olšanská, J. Trubač, J. Černý, Jan Rejšek, L. Ackerman","doi":"10.1144/jgs2022-119","DOIUrl":"https://doi.org/10.1144/jgs2022-119","url":null,"abstract":"The evolution of eruptive vents related to calderas is not fully understood. We focus on a structural, rock-magnetic, and geochemical investigation of a ∼314 Ma rhyolite dyke swarm associated with the late-orogenic Altenberg–Teplice Caldera, Bohemian Massif, eastern Variscan belt. The whole-rock major element, trace element, and Nd–Pb isotope geochemistry along with the published U-Pb zircon geochronology link the extra-caldera dyke swarm with intra-caldera ignimbrites. The magnetic fabrics determined using the anisotropy of magnetic susceptibility are interpreted to record a continuum from magma ascent, emplacement, and eruption during sinistral shearing. The latter evidences an interplay with regional tectonics associated with the activity of crustal-scale shear zones. The sinistral kinematics and strike of the dyke swarm, the elongation of caldera intrusive units, and the kinematics of major caldera faults are consistent with the dextral Riedel shear system, where the dykes correspond to antithetic Ŕ/X-shears. Such a kinematic configuration implies that the maximum and minimum principal stresses were oriented roughly north-south and east-west, respectively. The relation between the stress field with respect to the caldera elongation and orientation is not typical. We suggest that a pre-existing mutually perpendicular set of cross-cutting structural lineaments largely controlled the magma chamber and caldera formation.\u0000 \u0000 Supplementary material:\u0000 The whole-rock major, trace element and isotope geochemical tables, magnetic fabrics source data, and methodology details are available at\u0000 https://doi.org/10.6084/m9.figshare.c.6715893\u0000 .\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43204038","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}
L. Du, Yunying Zhang, Hongli Zhu, Zhao-Yu Zhang, Y. An, C. Yuan, Zongying Huang, Xu-Ping Li, X. Long
Fluids are important media for elemental cycling in subduction zones, but the compositions of such fluids remain obscure, especially those derived from dehydration of serpentinite. To better understand the role of subduction zone fluids in arc magmatism from the Chinese Eastern Tianshan (CET), we present Mg and B isotopic data for the arc diorites (e.g., Kalatage and Nanshankou). Our results show that the Kalatage diorites have higher δ 26 Mg (−0.23 to −0.13‰) and δ 11 B (−0.04 to +1.08‰) values than the corresponding mantle values, while the Nanshankou diorites display relatively lower δ 26 Mg (−0.26 to −0.19‰) and δ 11 B (−10.7 to −2.97‰) values. Since high-temperature magmatic and post-magmatic processes have limited effects on Mg and B isotope fractionation of our samples, their distinct Mg–B isotopic signatures inherited from the mantle sources should be caused by subduction-related metasomatism. Because neither altered oceanic crust (AOC) directly melting nor the incorporation of subducted sediments could induce significant Mg–B isotope fractionation in these rocks, we infer that their variable δ 26 Mg and δ 11 B values were probably associated with subduction fluids that were derived from different sources. Specifically, dehydrated fluids from serpentinites possess both high δ 26 Mg and δ 11 B values, which resulted in the heavy Mg–B isotopic compositions of the Kalatage diorites, whereas mantle metasomatized by fluids from AOC and subducted sediments were responsible for the Nanshankou rocks with relatively low δ 26 Mg and δ 11 B values. Taking into account the different effects of serpentinite-derived and slab-derived fluids in the formation of arc magmatism, subduction zone fluids can be probably an important process in changing the Mg–B isotope composition of mantle sources. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6702686
{"title":"Different effects of serpentinite-derived and slab-derived fluids on arc magmatism in the Chinese Eastern Tianshan: Evidence from Mg–B isotopic systematics","authors":"L. Du, Yunying Zhang, Hongli Zhu, Zhao-Yu Zhang, Y. An, C. Yuan, Zongying Huang, Xu-Ping Li, X. Long","doi":"10.1144/jgs2023-011","DOIUrl":"https://doi.org/10.1144/jgs2023-011","url":null,"abstract":"\u0000 Fluids are important media for elemental cycling in subduction zones, but the compositions of such fluids remain obscure, especially those derived from dehydration of serpentinite. To better understand the role of subduction zone fluids in arc magmatism from the Chinese Eastern Tianshan (CET), we present Mg and B isotopic data for the arc diorites (e.g., Kalatage and Nanshankou). Our results show that the Kalatage diorites have higher\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg (−0.23 to −0.13‰) and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B (−0.04 to +1.08‰) values than the corresponding mantle values, while the Nanshankou diorites display relatively lower\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg (−0.26 to −0.19‰) and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B (−10.7 to −2.97‰) values. Since high-temperature magmatic and post-magmatic processes have limited effects on Mg and B isotope fractionation of our samples, their distinct Mg–B isotopic signatures inherited from the mantle sources should be caused by subduction-related metasomatism. Because neither altered oceanic crust (AOC) directly melting nor the incorporation of subducted sediments could induce significant Mg–B isotope fractionation in these rocks, we infer that their variable\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B values were probably associated with subduction fluids that were derived from different sources. Specifically, dehydrated fluids from serpentinites possess both high\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B values, which resulted in the heavy Mg–B isotopic compositions of the Kalatage diorites, whereas mantle metasomatized by fluids from AOC and subducted sediments were responsible for the Nanshankou rocks with relatively low\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B values. Taking into account the different effects of serpentinite-derived and slab-derived fluids in the formation of arc magmatism, subduction zone fluids can be probably an important process in changing the Mg–B isotope composition of mantle sources.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6702686\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47136360","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. Tămaș, R. Holdsworth, D. M. Tămaș, E. Dempsey, K. Hardman, A. Bird, N. Roberts, J. Lee, J. Underhill, D. McCarthy, K. McCaffrey, D. Selby
Like many rift basins worldwide, the Inner Moray Firth Basin (IMFB) is bounded by major reactivated fault zones including the Helmsdale and Great Glen faults (HF, GGF). The Jurassic successions exposed onshore close to these faults at Helmsdale and Shandwick preserve folding, calcite veining and minor faulting consistent with sinistral (HF) and dextral (GGF) transtensional movements, respectively. This deformation has widely been attributed to Cenozoic post-rift fault reactivation. Onshore fieldwork and U-Pb calcite geochronology of five vein samples associated with transtensional movements along the HF and a splay of the GGF show that faulting occurred during the Early Cretaceous (c. 128-115 Ma, Barremian-Aptian), whilst the HF preserves evidence for earlier Late Jurassic sinistral movements (c. 159 Ma, Oxfordian). This demonstrates that both basin-bounding faults were substantially reactivated during the episodic NW-SE-directed Mesozoic rifting that formed the IMFB. Whilst there is good evidence for Cenozoic reactivation of the GGF offshore, the extent of such deformation along the north coast of the IMFB remains uncertain. Our findings also illustrate the importance of oblique slip reactivation processes in shaping the evolution of continental rift basins given that this deformation style may not be immediately obvious in interpretations of offshore seismic reflection data. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6708518
{"title":"Older than you think: Using U-Pb calcite geochronology to better constrain basin-bounding fault reactivation, Inner Moray Firth Basin, W North Sea","authors":"A. Tămaș, R. Holdsworth, D. M. Tămaș, E. Dempsey, K. Hardman, A. Bird, N. Roberts, J. Lee, J. Underhill, D. McCarthy, K. McCaffrey, D. Selby","doi":"10.1144/jgs2022-166","DOIUrl":"https://doi.org/10.1144/jgs2022-166","url":null,"abstract":"Like many rift basins worldwide, the Inner Moray Firth Basin (IMFB) is bounded by major reactivated fault zones including the Helmsdale and Great Glen faults (HF, GGF). The Jurassic successions exposed onshore close to these faults at Helmsdale and Shandwick preserve folding, calcite veining and minor faulting consistent with sinistral (HF) and dextral (GGF) transtensional movements, respectively. This deformation has widely been attributed to Cenozoic post-rift fault reactivation.\u0000 Onshore fieldwork and U-Pb calcite geochronology of five vein samples associated with transtensional movements along the HF and a splay of the GGF show that faulting occurred during the Early Cretaceous (c. 128-115 Ma, Barremian-Aptian), whilst the HF preserves evidence for earlier Late Jurassic sinistral movements (c. 159 Ma, Oxfordian). This demonstrates that both basin-bounding faults were substantially reactivated during the episodic NW-SE-directed Mesozoic rifting that formed the IMFB. Whilst there is good evidence for Cenozoic reactivation of the GGF offshore, the extent of such deformation along the north coast of the IMFB remains uncertain. Our findings also illustrate the importance of oblique slip reactivation processes in shaping the evolution of continental rift basins given that this deformation style may not be immediately obvious in interpretations of offshore seismic reflection data.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6708518\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47961492","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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