Aleksandra Milyukova, Anfisa Skoblenko, Yildirim Dilek, Kuo-Lung Wang, Valentina Batanova, Kirill E. Degtyarev
In this study we report on the petrography, major, trace element and mineral chemistry, platinum group elements (PGE), and Re–Os isotope systematics of depleted ultramafic rock suites from the Itmurundy Block in the North Balkhash ophiolite zone (NBOZ) in Kazakhstan. Represented mainly by variably serpentinized harzburgites and dunites, our samples are characterized by low whole-rock Al2O3 (0.33–0.86 wt.%), CaO (0.51–0.86 wt%), and Na2O (0.07–0.25 wt.%) concentrations, and high-Mg olivine (Fo = 91–92) and orthopyroxene (Mg# = 92–93) contents, together with moderately high-Cr spinel numbers (Cr# = 63–68). They are depleted in incompatible elements (ΣREE, Nb, Sc) and enriched in compatible elements, such as Cr (up to 2817 ppm) and Ni (up to 2327 ppm), representing highly refractory mantle residues derived from a forearc mantle wedge. They underwent 19–23% hydrous partial melting to produce boninitic melts. 187Os/188Os values vary from 0.1202 to 0.12599, and 187Re/188Os ratios from 0.230 to 0.316. The Re–Os model ages (TMA) and maximum Re depletion model age (TRD) were calculated based on the obtained data. Re–Os isotope systematics suggest that the analysed peridotites formed in two stages: first stage around 1.5 Ga, and a later stage around 668 to 589 Ma. 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.6845683
{"title":"Geochemistry, mineral chemistry and Re–Os isotopes of refractory peridotites of the North Balkhash ophiolite zone in the West Central Asian Orogenic Belt (Central Kazakhstan): multi–stage melt evolution of a Late Precambrian forearc mantle","authors":"Aleksandra Milyukova, Anfisa Skoblenko, Yildirim Dilek, Kuo-Lung Wang, Valentina Batanova, Kirill E. Degtyarev","doi":"10.1144/jgs2023-091","DOIUrl":"https://doi.org/10.1144/jgs2023-091","url":null,"abstract":"In this study we report on the petrography, major, trace element and mineral chemistry, platinum group elements (PGE), and Re–Os isotope systematics of depleted ultramafic rock suites from the Itmurundy Block in the North Balkhash ophiolite zone (NBOZ) in Kazakhstan. Represented mainly by variably serpentinized harzburgites and dunites, our samples are characterized by low whole-rock Al2O3 (0.33–0.86 wt.%), CaO (0.51–0.86 wt%), and Na2O (0.07–0.25 wt.%) concentrations, and high-Mg olivine (Fo = 91–92) and orthopyroxene (Mg# = 92–93) contents, together with moderately high-Cr spinel numbers (Cr# = 63–68). They are depleted in incompatible elements (ΣREE, Nb, Sc) and enriched in compatible elements, such as Cr (up to 2817 ppm) and Ni (up to 2327 ppm), representing highly refractory mantle residues derived from a forearc mantle wedge. They underwent 19–23% hydrous partial melting to produce boninitic melts. 187Os/188Os values vary from 0.1202 to 0.12599, and 187Re/188Os ratios from 0.230 to 0.316. The Re–Os model ages (TMA) and maximum Re depletion model age (TRD) were calculated based on the obtained data. Re–Os isotope systematics suggest that the analysed peridotites formed in two stages: first stage around 1.5 Ga, and a later stage around 668 to 589 Ma. 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.6845683","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135536644","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}
Malcolm S.W. Hodgskiss, Nick M.W Roberts, Päärn Päiste, Niels Rameil, Erik Hammer, Harald Brunstad, Aivo Lepland
Many fossil-barren or poorly fossiliferous red bed units are found in the North, Norwegian, and Barents seas. Due to the near-absence of biostratigraphic markers in these units, and the possibility of unconformities at their upper and lower boundaries, determining their depositional ages and stratigraphic assignment can be challenging. We apply in-situ U-Pb carbonate dating on North Sea samples, including plant-root related carbonates (rhizoliths) from paleosols and calcite veins crosscutting clasts in a conglomeratic red bed unit, to constrain their respective ages. Our data indicate that one of the studied units was deposited ca. 260 to 250 Ma (Ma – millions of years ago) and may represent an early development of the Skagerrak Formation. The second unit yielded an oldest age of 180.2 ± 9.7 Ma, interpreted to represent a late diagenetic event rather than deposition. High Mn/Sr and low δ 13 C values in many cements dated between ca. 180 to 100 Ma are interpreted to represent precipitation of diagenetic carbonates and reprecipitation of root carbonates, potentially related to Jurassic-Cretaceous volcanism and uplift during rifting of the North Sea. These new data point to U-Pb carbonate geochronology as an effective tool for directly dating red bed units and subsequent diagenetic events. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850741
在北海、挪威海和巴伦支海发现了许多化石贫瘠或化石含量低的红层单元。由于这些单元几乎没有生物地层标志，而且它们的上下边界可能存在不整合面，因此确定它们的沉积年龄和地层分配可能具有挑战性。我们对北海样品进行了原位U-Pb碳酸盐岩测年，包括古土壤中与植物根相关的碳酸盐(根茎岩)和红层砾岩单元中方解石脉横切碎屑，以限制它们各自的年龄。我们的数据表明，其中一个研究单元大约沉积于260至250 Ma (Ma -百万年前)，可能代表了Skagerrak组的早期发展。第二个单元的最古老年龄为180.2±9.7 Ma，被解释为晚期成岩事件，而不是沉积。在180 ~ 100 Ma之间的许多胶结物中，高Mn/Sr值和低δ 13c值被解释为成岩碳酸盐的沉淀和根碳酸盐的再沉淀，可能与侏罗纪-白垩纪的火山作用和北海裂谷期的隆升有关。这些新数据表明，U-Pb碳酸盐岩地质年代学可以作为红层单元和后续成岩事件直接测年的有效工具。补充资料:https://doi.org/10.6084/m9.figshare.c.6850741
{"title":"Direct dating of deposition and rift-related alteration of fossil barren red bed units in the North Sea","authors":"Malcolm S.W. Hodgskiss, Nick M.W Roberts, Päärn Päiste, Niels Rameil, Erik Hammer, Harald Brunstad, Aivo Lepland","doi":"10.1144/jgs2023-052","DOIUrl":"https://doi.org/10.1144/jgs2023-052","url":null,"abstract":"Many fossil-barren or poorly fossiliferous red bed units are found in the North, Norwegian, and Barents seas. Due to the near-absence of biostratigraphic markers in these units, and the possibility of unconformities at their upper and lower boundaries, determining their depositional ages and stratigraphic assignment can be challenging. We apply in-situ U-Pb carbonate dating on North Sea samples, including plant-root related carbonates (rhizoliths) from paleosols and calcite veins crosscutting clasts in a conglomeratic red bed unit, to constrain their respective ages. Our data indicate that one of the studied units was deposited ca. 260 to 250 Ma (Ma – millions of years ago) and may represent an early development of the Skagerrak Formation. The second unit yielded an oldest age of 180.2 ± 9.7 Ma, interpreted to represent a late diagenetic event rather than deposition. High Mn/Sr and low δ 13 C values in many cements dated between ca. 180 to 100 Ma are interpreted to represent precipitation of diagenetic carbonates and reprecipitation of root carbonates, potentially related to Jurassic-Cretaceous volcanism and uplift during rifting of the North Sea. These new data point to U-Pb carbonate geochronology as an effective tool for directly dating red bed units and subsequent diagenetic events. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850741","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"728 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135538076","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}
Detailed mapping, structural analysis and cross-section constructions yield new data on the geometry and chronology of Variscan and Alpine deformations in the central Pyrenees of southern Andorra. The studied area is characterized by polyphase deformation and strain partitioning due to the presence of an efficient décollement level within Silurian black shales. Variscan macrostructures gave rise to a minimum shortening of ca. 22% for Cambrian-Ordovician and Upper Ordovician units below the décollement level and of ca. 35% for Silurian and Devonian units above it. Variscan structures are cut by out-of-sequence thrusts, presumably developed after late Variscan igneous intrusions, and extensional faulting. Those thrusts cut previous Variscan D 2 (main-phase) folds and originate additive and subtractive contacts. We propose an Alpine age for most of these thrusts which, together with the Variscan structures, are affected by subsequent Alpine deformation, which causes changes in their orientation around the intrusions, and a progressive steepening of the cleavage from south to north. We discuss the usefulness and limitations of balanced cross-sections in polydeformed areas and propose that the technique is valid to construct regional sections and to obtain geologically reasonable pre-deformational configurations.
{"title":"Superposed Variscan and Alpine deformation in the basement rocks of southern Andorra, Central Pyrenees","authors":"A. Margalef, P. Granado, J.M. Casas","doi":"10.1144/jgs2023-099","DOIUrl":"https://doi.org/10.1144/jgs2023-099","url":null,"abstract":"Detailed mapping, structural analysis and cross-section constructions yield new data on the geometry and chronology of Variscan and Alpine deformations in the central Pyrenees of southern Andorra. The studied area is characterized by polyphase deformation and strain partitioning due to the presence of an efficient décollement level within Silurian black shales. Variscan macrostructures gave rise to a minimum shortening of ca. 22% for Cambrian-Ordovician and Upper Ordovician units below the décollement level and of ca. 35% for Silurian and Devonian units above it. Variscan structures are cut by out-of-sequence thrusts, presumably developed after late Variscan igneous intrusions, and extensional faulting. Those thrusts cut previous Variscan D 2 (main-phase) folds and originate additive and subtractive contacts. We propose an Alpine age for most of these thrusts which, together with the Variscan structures, are affected by subsequent Alpine deformation, which causes changes in their orientation around the intrusions, and a progressive steepening of the cleavage from south to north. We discuss the usefulness and limitations of balanced cross-sections in polydeformed areas and propose that the technique is valid to construct regional sections and to obtain geologically reasonable pre-deformational configurations.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135536786","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 investigate the paleo earthquakes and slip-rate on the Pazarcık segment of East Anatolian Fault which has involved surface rupture of 6 February 2023 Pazarcık-Kahramanmaraş earthquake (Mw:7.7) and provided insights of the long-term behavior of this major continental fault. Paleoseismologic data from two trench sites, reveal evidence for at least five surface ruptures in the Holocene Period. The historical earthquake of 1114AD is verified at both trench sites but the following event of 1513AD is only identified at one site. In addition, the age difference of the older events shows historical activity are separated by much longer periods of relative quiescence that range from 500 years to 1000 years which suggest quasiperiodic earthquake occurrence on sub-segments of the Pazarcık segment. Our fault parallel trenches revealed 101±5 m offset in the last 18 ka and 51±1 m offset in the last 9 ka on a buried stream channel and the actual channel of the same stream respectively. The correlation of the maximum and abandonment age of the channel with measured offsets revealed 5.6 mm a -1 long-term slip rate of the fault. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850786
我们研究了东安纳托利亚断层Pazarcık段的古地震和滑动速率，该段涉及2023年2月6日Pazarcık-Kahramanmaraş地震(Mw:7.7)的地表破裂，并提供了这一主要大陆断层的长期行为的见解。来自两个海沟遗址的古地震数据，揭示了全新世时期至少五个地表破裂的证据。公元1114年的历史地震在两个海沟地点都得到了证实，但公元1513年的地震只在一个地点得到了证实。此外，较老事件的年龄差异表明，历史活动被500年至1000年的较长相对静止期隔开，这表明Pazarcık段的子段发生了准周期性地震。断层平行沟在近18 ka和近9 ka分别在隐蔽河道和实际河道上显示了101±5 m的偏移。通道的最大和废弃年龄与测量的偏移量的相关性揭示了断层的长期滑动率为5.6 mm a -1。补充资料:https://doi.org/10.6084/m9.figshare.c.6850786
{"title":"Surface rupture history and 18-ka-long slip rate along the Pazarcık segment of the East Anatolian Fault","authors":"Önder Yönlü, Volkan Karabacak","doi":"10.1144/jgs2023-056","DOIUrl":"https://doi.org/10.1144/jgs2023-056","url":null,"abstract":"We investigate the paleo earthquakes and slip-rate on the Pazarcık segment of East Anatolian Fault which has involved surface rupture of 6 February 2023 Pazarcık-Kahramanmaraş earthquake (Mw:7.7) and provided insights of the long-term behavior of this major continental fault. Paleoseismologic data from two trench sites, reveal evidence for at least five surface ruptures in the Holocene Period. The historical earthquake of 1114AD is verified at both trench sites but the following event of 1513AD is only identified at one site. In addition, the age difference of the older events shows historical activity are separated by much longer periods of relative quiescence that range from 500 years to 1000 years which suggest quasiperiodic earthquake occurrence on sub-segments of the Pazarcık segment. Our fault parallel trenches revealed 101±5 m offset in the last 18 ka and 51±1 m offset in the last 9 ka on a buried stream channel and the actual channel of the same stream respectively. The correlation of the maximum and abandonment age of the channel with measured offsets revealed 5.6 mm a -1 long-term slip rate of the fault. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850786","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"300 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135472716","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}
Three parallel east–west (E–W)-trending shear zones are components of the polyphase shear zones in the eastern Jiangnan belt. The meso- and microstructural characteristics and the estimates of deformation temperatures, vorticities, and geochronology of these shear zones provide significant information regarding the tectonic evolution of the South China Block (SCB) during the early Paleozoic. Most shear sense indicators (e.g., asymmetric folds, S-C fabrics, and rotating porphyroclasts) reveal that the kinematics were characterized by E–W dextral shear. Finite strain measurements indicate an oblate strain ellipsoid shape with S-type and SL-type tectonites. The rotated rigid porphyroclasts and Mohr circle methods yield vorticity (Wk) values of 0.58–0.80 and 0.66–0.89, respectively, indicating that the flow was generally shear-dominated with almost equal proportions of simple and pure shear. Both mineral deformation thermometers and quartz c-axis fabrics indicate that the deformation occurred at medium temperature conditions of 400–550℃. Combined with our new age and regional geological data, the E–W-trending shear zones might represent an increment of deformation during the last period of the early Paleozoic orogeny in the SCB.
{"title":"Early Paleozoic ductile deformation of the South China Block: the polyphase shear zones in the Eastern Jiangnan Belt","authors":"Jun Hu, Xinqi Yu, Wei Li, Nianwei Liu","doi":"10.1144/jgs2023-062","DOIUrl":"https://doi.org/10.1144/jgs2023-062","url":null,"abstract":"Three parallel east–west (E–W)-trending shear zones are components of the polyphase shear zones in the eastern Jiangnan belt. The meso- and microstructural characteristics and the estimates of deformation temperatures, vorticities, and geochronology of these shear zones provide significant information regarding the tectonic evolution of the South China Block (SCB) during the early Paleozoic. Most shear sense indicators (e.g., asymmetric folds, S-C fabrics, and rotating porphyroclasts) reveal that the kinematics were characterized by E–W dextral shear. Finite strain measurements indicate an oblate strain ellipsoid shape with S-type and SL-type tectonites. The rotated rigid porphyroclasts and Mohr circle methods yield vorticity (Wk) values of 0.58–0.80 and 0.66–0.89, respectively, indicating that the flow was generally shear-dominated with almost equal proportions of simple and pure shear. Both mineral deformation thermometers and quartz c-axis fabrics indicate that the deformation occurred at medium temperature conditions of 400–550℃. Combined with our new age and regional geological data, the E–W-trending shear zones might represent an increment of deformation during the last period of the early Paleozoic orogeny in the SCB.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135718742","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. Costa, C. Invernizzi, G. Penza, S. Teloni, P.P. Pierantoni
The seismotectonic setting of external Marche Apennines (Central Italy) was defined integrating geomorphological, structural, and seismological data. Strong historical earthquakes characterized the area, but geometries and kinematics of the seismogenic sources are not well defined. Plio-Quaternary Apennine compressional NW-SE structures are segmented by NE-SW oriented transversal faults, whose origin and role are still debated. We characterize the geometry, kinematics, and activity of four main transversal faults to better define their seismogenic potential. These high-angle and deeply rooted transversal fault systems have been mapped; they separate the external Apennine sector into blocks and sub-blocks with different structural and evolutionary features. The integrated dataset revealed that some inherited fault segments have recently been reactivated displacing Quaternary deposits. Spatial distribution of seismicity indicates that some clusters of hypocentres are located within the basement. Stress field analysis using available focal mechanism solutions confirms the prevalence of left-lateral kinematics on roughly SW–NE oriented structures. The transversal structures thus contribute to the longitudinal segmentation of the Apennine structures and, more in general, they are involved in the northern part of Adria plate kinematics toward N and NNW. Assessing seismic hazard and planning to mitigate risk in populated areas close to the Adriatic coast should consider these potentially active faults evidenced by the instrumental seismicity and important historical earthquakes.
{"title":"The seismotectonic role of transversal structures in the Plio-Quaternary evolution of the External Marche Apennines (Italy)","authors":"M. Costa, C. Invernizzi, G. Penza, S. Teloni, P.P. Pierantoni","doi":"10.1144/jgs2023-002","DOIUrl":"https://doi.org/10.1144/jgs2023-002","url":null,"abstract":"The seismotectonic setting of external Marche Apennines (Central Italy) was defined integrating geomorphological, structural, and seismological data. Strong historical earthquakes characterized the area, but geometries and kinematics of the seismogenic sources are not well defined. Plio-Quaternary Apennine compressional NW-SE structures are segmented by NE-SW oriented transversal faults, whose origin and role are still debated. We characterize the geometry, kinematics, and activity of four main transversal faults to better define their seismogenic potential. These high-angle and deeply rooted transversal fault systems have been mapped; they separate the external Apennine sector into blocks and sub-blocks with different structural and evolutionary features. The integrated dataset revealed that some inherited fault segments have recently been reactivated displacing Quaternary deposits. Spatial distribution of seismicity indicates that some clusters of hypocentres are located within the basement. Stress field analysis using available focal mechanism solutions confirms the prevalence of left-lateral kinematics on roughly SW–NE oriented structures. The transversal structures thus contribute to the longitudinal segmentation of the Apennine structures and, more in general, they are involved in the northern part of Adria plate kinematics toward N and NNW. Assessing seismic hazard and planning to mitigate risk in populated areas close to the Adriatic coast should consider these potentially active faults evidenced by the instrumental seismicity and important historical earthquakes.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135152932","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. Carver, J. Cartwright, A. Mcgrandle, C. Kirkham, Evan Pryce
We present new geophysical observations of the Mull Dyke Swarm in the Southern North Sea. 2D and 3D reflection seismic and aeromagnetic data were used to map the dykes. The three main dyke groups recognised onshore (Cleveland, Blyth and Hawick-Acklington) are found to extend to varying distances into the North Sea, crossing a number of major crustal-scale fault zones and domain boundaries, with almost no re-orientation. The Blyth Dyke Group extends furthest, for a distance of 672km from the source on Mull. The seismic data shows extensive development of pit chain craters above the upper tips of these dykes, which can be approximately dated to the late Palaeocene from the ages of crater fills. Volumetric estimates are made of the intrusive volumes associated with each group, ranging from 90km 3 to 202km 3 . These three main axes of intrusion probably formed in different intrusive events within a c. 1 million year period, from 59 to 58Ma, during magnetic chron C26R.
我们对北海南部的Mull堤坝群进行了新的地球物理观测。利用二维和三维反射地震和航磁数据绘制堤坝地图。陆上公认的三个主要岩脉群（Cleveland、Blyth和Hawick Acklington）被发现延伸到北海不同的距离，穿过许多主要的地壳规模断层带和域边界，几乎没有重新定向。Blyth堤坝群延伸最远，距离Mull源头672公里。地震数据显示，在这些堤坝的上端上方，坑链坑广泛发育，从坑填充的年代来看，这些坑链坑的年代大约可以追溯到古新世晚期。体积估计是根据与每组相关的侵入体积进行的，范围从90 km 3到202 km 3。这三条侵入主轴可能是在大约100万年的时间段内，从59到58Ma，在磁时C26R期间，在不同的侵入事件中形成的。
{"title":"The continuation of the Mull Dyke Swarm into the Southern North Sea","authors":"F. Carver, J. Cartwright, A. Mcgrandle, C. Kirkham, Evan Pryce","doi":"10.1144/jgs2023-039","DOIUrl":"https://doi.org/10.1144/jgs2023-039","url":null,"abstract":"\u0000 We present new geophysical observations of the Mull Dyke Swarm in the Southern North Sea. 2D and 3D reflection seismic and aeromagnetic data were used to map the dykes. The three main dyke groups recognised onshore (Cleveland, Blyth and Hawick-Acklington) are found to extend to varying distances into the North Sea, crossing a number of major crustal-scale fault zones and domain boundaries, with almost no re-orientation. The Blyth Dyke Group extends furthest, for a distance of 672km from the source on Mull. The seismic data shows extensive development of pit chain craters above the upper tips of these dykes, which can be approximately dated to the late Palaeocene from the ages of crater fills. Volumetric estimates are made of the intrusive volumes associated with each group, ranging from 90km\u0000 3 \u0000 to 202km\u0000 3\u0000 . These three main axes of intrusion probably formed in different intrusive events within a c. 1 million year period, from 59 to 58Ma, during magnetic chron C26R.\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46375802","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}
Inayat Ullah, Chuandong Xue, Tiannan Yang, H. Furnes, Y. Dilek, Wen Wang, Abdul Ghaffar
Our recent field investigations in western Pakistan have revealed that serpentinized peridotites here are crosscut by numerous intrusions of gabbro and tonalite. New zircon U–Pb dating of these plutons indicates Late Cretaceous–Early Eocene ages of their crystallization. They have arc-like geochemical signatures and constitute the middle crust of an island arc complex. Together with their extrusive counterparts they form the RasKoh island arc (RIA), defined for the first time in this study. The RIA and the Chaiga continental arc to the north represent the manifestations of two separate subduction zone systems within Neotethys, developed between India and Eurasia. We posit that this Neotethyan domain contained two oceanic plates. Subduction of the leading plate beneath Eurasia generated the Jurassic–Late Oligocene Chaiga continental arc, and the northward subduction of the trailing plate resulted in the development of the Late Cretaceous–Oligocene, ensimatic RasKoh arc. Arrival of the Indian subcontinent at the latitude of the RasKoh arc in the earliest Miocene caused the emplacement of the RasKoh arc onto India via oblique arc–continent collision. The subsequent collision of this composite Indian plate with Eurasia resulted in extensive deformation of Late Cretaceous flysch deposits and the ophiolitic arc basement. 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.6795686
{"title":"Double arc–continent collision record in the Latest Mesozoic–Cenozoic tectonic history of the Himalayan–Tibetan orogenic belt in Western Pakistan","authors":"Inayat Ullah, Chuandong Xue, Tiannan Yang, H. Furnes, Y. Dilek, Wen Wang, Abdul Ghaffar","doi":"10.1144/jgs2023-076","DOIUrl":"https://doi.org/10.1144/jgs2023-076","url":null,"abstract":"Our recent field investigations in western Pakistan have revealed that serpentinized peridotites here are crosscut by numerous intrusions of gabbro and tonalite. New zircon U–Pb dating of these plutons indicates Late Cretaceous–Early Eocene ages of their crystallization. They have arc-like geochemical signatures and constitute the middle crust of an island arc complex. Together with their extrusive counterparts they form the RasKoh island arc (RIA), defined for the first time in this study. The RIA and the Chaiga continental arc to the north represent the manifestations of two separate subduction zone systems within Neotethys, developed between India and Eurasia. We posit that this Neotethyan domain contained two oceanic plates. Subduction of the leading plate beneath Eurasia generated the Jurassic–Late Oligocene Chaiga continental arc, and the northward subduction of the trailing plate resulted in the development of the Late Cretaceous–Oligocene, ensimatic RasKoh arc. Arrival of the Indian subcontinent at the latitude of the RasKoh arc in the earliest Miocene caused the emplacement of the RasKoh arc onto India via oblique arc–continent collision. The subsequent collision of this composite Indian plate with Eurasia resulted in extensive deformation of Late Cretaceous flysch deposits and the ophiolitic arc basement.\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.6795686\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41901921","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}
Pub Date : 2023-08-25eCollection Date: 2023-01-01DOI: 10.11604/pamj.2023.45.183.38569
Ndubueze Ezemba, Augustine Chukwudi Onuh, Uchenna Simon Onoh
Anomalies of the arterial branches of the arch of the aorta are rare, with the aberrant right subclavian artery being the most common of this anomaly. Majority of the anomalies are asymptomatic and often discovered as incidental findings. In the great majority of the symptomatic cases, the presentation may be either with breathlessness or dysphagia or both. This is in addition to the nature of the intrinsic arterial disease of the aberrant vessel, especially in adult patients; and unless borne in mind, the diagnosis is often missed leading to delays and wrong treatment. In this report we present a case of dysphagia in an adult male Nigerian initially diagnosed as œsophageal stricture from herbal potion ingestion but review of his imaging investigations gave a final diagnosis of dysphagia lusoria from an aberrant right subclavian artery. The difficulty in making a diagnosis and the need for a multidisciplinary review of the imaging investigations are highlighted. The patient was successfully treated by a combined trans-thoracic and cervical approach with division and re-implantation of the aberrant vessel unto the right common carotid artery. He has remained symptom-free for 2 years after surgery. Although the great majority of these anomalies are often asymptomatic, it is important they are borne in mind both in imaging investigations as well as in procedures involving structures in the upper visceral mediastinum. Various surgical approaches have been documented in the management of symptomatic ones; it is however recommended that options that ensure revascularization of the affected limb be selected.
{"title":"Incomplete vascular ring of the aortic arch presenting with dysphagia in an adult: case report.","authors":"Ndubueze Ezemba, Augustine Chukwudi Onuh, Uchenna Simon Onoh","doi":"10.11604/pamj.2023.45.183.38569","DOIUrl":"10.11604/pamj.2023.45.183.38569","url":null,"abstract":"<p><p>Anomalies of the arterial branches of the arch of the aorta are rare, with the aberrant right subclavian artery being the most common of this anomaly. Majority of the anomalies are asymptomatic and often discovered as incidental findings. In the great majority of the symptomatic cases, the presentation may be either with breathlessness or dysphagia or both. This is in addition to the nature of the intrinsic arterial disease of the aberrant vessel, especially in adult patients; and unless borne in mind, the diagnosis is often missed leading to delays and wrong treatment. In this report we present a case of dysphagia in an adult male Nigerian initially diagnosed as œsophageal stricture from herbal potion ingestion but review of his imaging investigations gave a final diagnosis of dysphagia lusoria from an aberrant right subclavian artery. The difficulty in making a diagnosis and the need for a multidisciplinary review of the imaging investigations are highlighted. The patient was successfully treated by a combined trans-thoracic and cervical approach with division and re-implantation of the aberrant vessel unto the right common carotid artery. He has remained symptom-free for 2 years after surgery. Although the great majority of these anomalies are often asymptomatic, it is important they are borne in mind both in imaging investigations as well as in procedures involving structures in the upper visceral mediastinum. Various surgical approaches have been documented in the management of symptomatic ones; it is however recommended that options that ensure revascularization of the affected limb be selected.</p>","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"164 1","pages":"183"},"PeriodicalIF":1.2,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10656587/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85978356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ronge Bo, Y. Dilek, S. Nasir, Weiwei Wu, Peng-Jie Cai, Yu-Xiao Lu, D. Lian, Jing S. Yang
The Oman ophiolite is one of the largest and best-exposed ophiolites in the world with >450 chromitite deposits. We report here a newly identified chromitite deposit in the Wadi Rajmi in Oman. This deposit occurs within a dunitic envelope, which is surrounded by harzburgite, and consists of massive and disseminated chromitite types. The Rajmi peridotites represent depleted upper mantle rocks, which underwent >20% of partial melting and which experienced metasomatism by melts and fluids derived from a subducting slab. They demonstrate geochemical affinities similar to those of the Izu-Bonin-Mariana forearc peridotites, supporting their formation in a forearc environment. The Rajmi chromitites have low Cr# values and are classified as high-Al type. They have geochemical compositions comparable to those of chromitites crystallized from mid-ocean ridge basalt (MORB)-type melts. However, the chromites in these high-Al chromitites contain various silicate inclusions (i.e. amphibole, mica), indicating a hydrous and atypical MORB nature of their parental magmas. Combined with the mineralogical and geochemical characteristics of the country rocks, we posit that the parental melts of the Rajmi high-Al chromitites had a MORB-like affinity, derived from partial melting of a nascent forearc mantle. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: https://doi.org/10.6084/m9.figshare.c.6795689
{"title":"Mineral & whole–rock geochemistry of high-Al podiform chromitites in the Fizh Massif of the Cretaceous Oman ophiolite: Origin of hydrous, N–MORB melts in a nascent forearc setting","authors":"Ronge Bo, Y. Dilek, S. Nasir, Weiwei Wu, Peng-Jie Cai, Yu-Xiao Lu, D. Lian, Jing S. Yang","doi":"10.1144/jgs2023-047","DOIUrl":"https://doi.org/10.1144/jgs2023-047","url":null,"abstract":"The Oman ophiolite is one of the largest and best-exposed ophiolites in the world with >450 chromitite deposits. We report here a newly identified chromitite deposit in the Wadi Rajmi in Oman. This deposit occurs within a dunitic envelope, which is surrounded by harzburgite, and consists of massive and disseminated chromitite types. The Rajmi peridotites represent depleted upper mantle rocks, which underwent >20% of partial melting and which experienced metasomatism by melts and fluids derived from a subducting slab. They demonstrate geochemical affinities similar to those of the Izu-Bonin-Mariana forearc peridotites, supporting their formation in a forearc environment. The Rajmi chromitites have low Cr# values and are classified as high-Al type. They have geochemical compositions comparable to those of chromitites crystallized from mid-ocean ridge basalt (MORB)-type melts. However, the chromites in these high-Al chromitites contain various silicate inclusions (i.e. amphibole, mica), indicating a hydrous and atypical MORB nature of their parental magmas. Combined with the mineralogical and geochemical characteristics of the country rocks, we posit that the parental melts of the Rajmi high-Al chromitites had a MORB-like affinity, derived from partial melting of a nascent forearc mantle.\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.6795689\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":"43015083","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：