Using pattern classification algorithms can help recognise and predict patterns in large and complex multivariate datasets. Utilising competitive learning, self-organising maps (SOMs) are known unsupervised classification tools that are considered very useful in pattern classification and recognition. This technique is based on the principles of vector quantification of similarities and clustering in a high-dimensional space, where the method can handle the analysis and visualization of high-dimensional data. The tool is ideal for analysing a complex combination of categorical and continuous spatial variables, with particular applications to geological features. In this paper, we employ the tool to predict geological features based on airborne geophysical data acquired through the Tellus project in Northern Ireland. SOMs are applied through 8 experiments (iterations), incorporating the radiometric data in combination with geological features, including elevation, slope angle, terrain ruggedness (TRI), and geochronology. The SOMs proved successful in differentiating contrasting bedrock geology, such as acidic versus mafic igneous rocks, while data clustering over intermediate rocks was not as apparent. The presence of a thick cover of glacial deposits in most of the study area presented a challenge in the data clustering, particularly over the intermediate igneous and sedimentary bedrock types. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6603098
{"title":"Unsupervised classification applications in enhancing lithological mapping and geological understanding – A case study from Northern Ireland","authors":"Z. Smillie, V. Demyanov, J. McKinley, M. Cooper","doi":"10.1144/jgs2022-136","DOIUrl":"https://doi.org/10.1144/jgs2022-136","url":null,"abstract":"Using pattern classification algorithms can help recognise and predict patterns in large and complex multivariate datasets. Utilising competitive learning, self-organising maps (SOMs) are known unsupervised classification tools that are considered very useful in pattern classification and recognition. This technique is based on the principles of vector quantification of similarities and clustering in a high-dimensional space, where the method can handle the analysis and visualization of high-dimensional data. The tool is ideal for analysing a complex combination of categorical and continuous spatial variables, with particular applications to geological features.\u0000 In this paper, we employ the tool to predict geological features based on airborne geophysical data acquired through the Tellus project in Northern Ireland. SOMs are applied through 8 experiments (iterations), incorporating the radiometric data in combination with geological features, including elevation, slope angle, terrain ruggedness (TRI), and geochronology. The SOMs proved successful in differentiating contrasting bedrock geology, such as acidic versus mafic igneous rocks, while data clustering over intermediate rocks was not as apparent. The presence of a thick cover of glacial deposits in most of the study area presented a challenge in the data clustering, particularly over the intermediate igneous and sedimentary bedrock types.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6603098\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44780356","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}
Global synchronisation of environmental change in terrestrial successions in deep-time is challenging due to the paucity of dating methods, a case also applicable to the Middle to Upper Triassic Mercia Mudstone Group in Britain. Using coastal cliff sections, magnetostratigraphy was evaluated at 263 horizons, defining 53 magnetozones. Magnetozones from the lower 140 m of the group demonstrate correspondence to those from the mid Ladinian to early Carnian polarity timescale, dating which is compatible with magnetostratigraphy from the underlying Sherwood Sandstone Group. Magnetostratigraphy of the Dunscombe Mudstone Formation, and associated palynological data, suggest a late Carnian to earliest Norian age, and a dramatically lower accumulation rate than adjacent formations. The polarity record demonstrates coeval flooding events, evaporite deposits and intervals of sand supply between the Wessex Basin and the Central European Basin in the Carnian. This is the result of linked climatic and eustatic changes between these separate basins, related to aeolian dust supply and the shrinkage of hyper-arid source regions for the fines. Magnetostratigraphy from the Branscombe Mudstone and Blue Anchor formations demonstrates their Norian and early Rhaetian age. These and other data suggest an alternative synchronization of marine and non-marine polarity records for the Norian polarity timescale. 198 words Supplementary material: Section details and detailed logs of the sampled sections and inferred sequence boundaries, magnetic mineralogy data, demagnetisation behaviour and mean directions, summary of virtual geomagnetic pole data and a comparison to other European poles, construction of other composite reference sections and revised polarity scales. Excel sheet of magnetic data statistically evaluated correlation models, and age models. https://doi.org/10.6084/m9.figshare.c.6613788
{"title":"Magnetostratigraphy of the Mercia Mudstone Group (Devon, UK): implications for regional relationships and chronostratigraphy in the Middle to Late Triassic of western Europe","authors":"M. Hounslow, R. Gallois","doi":"10.1144/jgs2022-173","DOIUrl":"https://doi.org/10.1144/jgs2022-173","url":null,"abstract":"Global synchronisation of environmental change in terrestrial successions in deep-time is challenging due to the paucity of dating methods, a case also applicable to the Middle to Upper Triassic Mercia Mudstone Group in Britain. Using coastal cliff sections, magnetostratigraphy was evaluated at 263 horizons, defining 53 magnetozones. Magnetozones from the lower 140 m of the group demonstrate correspondence to those from the mid Ladinian to early Carnian polarity timescale, dating which is compatible with magnetostratigraphy from the underlying Sherwood Sandstone Group. Magnetostratigraphy of the Dunscombe Mudstone Formation, and associated palynological data, suggest a late Carnian to earliest Norian age, and a dramatically lower accumulation rate than adjacent formations. The polarity record demonstrates coeval flooding events, evaporite deposits and intervals of sand supply between the Wessex Basin and the Central European Basin in the Carnian. This is the result of linked climatic and eustatic changes between these separate basins, related to aeolian dust supply and the shrinkage of hyper-arid source regions for the fines. Magnetostratigraphy from the Branscombe Mudstone and Blue Anchor formations demonstrates their Norian and early Rhaetian age. These and other data suggest an alternative synchronization of marine and non-marine polarity records for the Norian polarity timescale. 198 words\u0000 \u0000 Supplementary material:\u0000 Section details and detailed logs of the sampled sections and inferred sequence boundaries, magnetic mineralogy data, demagnetisation behaviour and mean directions, summary of virtual geomagnetic pole data and a comparison to other European poles, construction of other composite reference sections and revised polarity scales. Excel sheet of magnetic data statistically evaluated correlation models, and age models.\u0000 \u0000 \u0000 https://doi.org/10.6084/m9.figshare.c.6613788\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49256591","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}
While the Flemish Cap played a pivotal role in the opening of the North Atlantic, the tectonic history of this continental ribbon has been poorly constrained due to insufficient seismic coverage. In this study, we present thirteen newly acquired seismic reflection profiles over the Flemish Cap, on which seismic reflectors show highly variable seismic facies both on and beneath the top acoustic basement, with exceptional imaging of layered crustal structure. The upper crust is primarily characterized by transparent, chaotic amplitude reflectivity. The lower crust, particularly on the flanks of the cap, exhibits relatively bright and coherent reflection packages interpreted as Appalachian orogenic fabrics based on onshore-offshore correlations from pre-rift plate reconstructions. Extensional systems within the continental crust of the Flemish Cap record a transitional stage between Paleozoic orogenic collapse and pre-Jurassic rifting. The crustal architecture associated with Mesozoic rifting of the Flemish Cap is also mapped and the interpreted distinct rift domains display along-strike variations. Overall, the complex tectonic history of the Flemish Cap involved dominantly ductile deformation during the Paleozoic orogenic stage, multiple deformation styles (primarily ductile and brittle-ductile) during the orogen-to-rift transitional stage, and brittle deformation during the major Jurassic-Cretaceous rifting stage.
{"title":"Structural configuration and tectonics of the Flemish Cap, offshore Newfoundland, from newly acquired seismic reflection data","authors":"P. Yang, J. Welford","doi":"10.1144/jgs2022-115","DOIUrl":"https://doi.org/10.1144/jgs2022-115","url":null,"abstract":"While the Flemish Cap played a pivotal role in the opening of the North Atlantic, the tectonic history of this continental ribbon has been poorly constrained due to insufficient seismic coverage. In this study, we present thirteen newly acquired seismic reflection profiles over the Flemish Cap, on which seismic reflectors show highly variable seismic facies both on and beneath the top acoustic basement, with exceptional imaging of layered crustal structure. The upper crust is primarily characterized by transparent, chaotic amplitude reflectivity. The lower crust, particularly on the flanks of the cap, exhibits relatively bright and coherent reflection packages interpreted as Appalachian orogenic fabrics based on onshore-offshore correlations from pre-rift plate reconstructions. Extensional systems within the continental crust of the Flemish Cap record a transitional stage between Paleozoic orogenic collapse and pre-Jurassic rifting. The crustal architecture associated with Mesozoic rifting of the Flemish Cap is also mapped and the interpreted distinct rift domains display along-strike variations. Overall, the complex tectonic history of the Flemish Cap involved dominantly ductile deformation during the Paleozoic orogenic stage, multiple deformation styles (primarily ductile and brittle-ductile) during the orogen-to-rift transitional stage, and brittle deformation during the major Jurassic-Cretaceous rifting stage.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"321 ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41274427","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}
D. Phillips, E. Matchan, A. Gleadow, F. Brown, I. Mcdougall, T. Cerling, M. Leakey, J. Hergt, Louise N. Leakey
The Turkana Basin in Kenya/Ethiopia hosts remarkable fossil-rich sediments that are central to our understanding of early hominin evolution, with interbedded volcanic tuffs providing critical time markers. However, the resolution of existing Early Pleistocene/Pliocene ages is limited to ∼20-60 kyr, inhibiting evaluation of climatic/environmental drivers of evolution. Here, we present high precision, single-feldspar 40 Ar/ 39 Ar age and elemental data for four stratigraphically significant tuffs. These samples exhibit variably dispersed age distributions correlated with feldspar compositional trends, interpreted to indicate partial retention of inherited argon, related to crustal ‘cold storage’ and rapid melt infiltration preceding eruption. We evaluated various statistical methods and calculate astronomically calibrated, Bayesian age estimates of 1879.1 ± 0.6 ka (± 2.4 ka including external errors) for the KBS/H2 Tuff, 1837.4 ± 0.9 ka (± 2.4 ka) for the Malbe/H4 Tuff, 1357.5 ± 1.8 ka (± 2.5 ka) for the Chari/L Tuff and 1315.4 ± 1.9 ka (± 2.5 ka) for the Gele Tuff. Our results permit refined age constraints for important early Homo fossils, including the cranium KNM-ER1813 ( Homo habilis ) and various Homo erectus fossils. The KBS Tuff age also provides an important calibration locus for orbital tuning of paleoclimate proxy records, revealing complex interplay between paleoclimate and geological drivers of sedimentation. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6602994
{"title":"40\u0000 Ar/\u0000 39\u0000 Ar eruption ages of Turkana Basin tuffs: millennial scale resolution constrains paleoclimate proxy tuning models and hominin fossil ages","authors":"D. Phillips, E. Matchan, A. Gleadow, F. Brown, I. Mcdougall, T. Cerling, M. Leakey, J. Hergt, Louise N. Leakey","doi":"10.1144/jgs2022-171","DOIUrl":"https://doi.org/10.1144/jgs2022-171","url":null,"abstract":"\u0000 The Turkana Basin in Kenya/Ethiopia hosts remarkable fossil-rich sediments that are central to our understanding of early hominin evolution, with interbedded volcanic tuffs providing critical time markers. However, the resolution of existing Early Pleistocene/Pliocene ages is limited to ∼20-60 kyr, inhibiting evaluation of climatic/environmental drivers of evolution. Here, we present high precision, single-feldspar\u0000 40\u0000 Ar/\u0000 39\u0000 Ar age and elemental data for four stratigraphically significant tuffs. These samples exhibit variably dispersed age distributions correlated with feldspar compositional trends, interpreted to indicate partial retention of inherited argon, related to crustal ‘cold storage’ and rapid melt infiltration preceding eruption. We evaluated various statistical methods and calculate astronomically calibrated, Bayesian age estimates of 1879.1 ± 0.6 ka (± 2.4 ka including external errors) for the KBS/H2 Tuff, 1837.4 ± 0.9 ka (± 2.4 ka) for the Malbe/H4 Tuff, 1357.5 ± 1.8 ka (± 2.5 ka) for the Chari/L Tuff and 1315.4 ± 1.9 ka (± 2.5 ka) for the Gele Tuff. Our results permit refined age constraints for important early\u0000 Homo\u0000 fossils, including the cranium KNM-ER1813 (\u0000 Homo habilis\u0000 ) and various\u0000 Homo erectus\u0000 fossils. The KBS Tuff age also provides an important calibration locus for orbital tuning of paleoclimate proxy records, revealing complex interplay between paleoclimate and geological drivers of sedimentation.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6602994\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45014060","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}
H. Karabulut, S. E. Güvercin, J. Hollingsworth, A. Konca
On the 06th February 2023, an earthquake with magnitude ∼Mw7.0 on the Narlı Fault, a fault subparallel to the East Anatolian Fault Zone (EAFZ), initiated a chain of large earthquakes on the EAFZ. The earthquakes occurred in a seismic gap with low geodetic strain rates, low background seismicity, where deformation is distributed across a wide fault zone and long recurrence time of historical earthquakes. The ∼50 km long rupture of the Narlı Fault towards Pazarcık, led to Mw7.8 left-lateral strike-slip earthquake breaking ∼300 km section of the ∼600 km long EAFZ bilaterally with a total duration of more than 80 s. Toward the southwest, the rupture propagated on ∼100 km long Amanos segment with a peak surface offset of 5 m, before diminishing toward the Hatay graben. In the northeast direction, the rupture reached a peak surface offset of 7 m before sharply declining at the termination of the 2020, Mw6.8 Sivrice earthquake rupture. A second large earthquake with Mw7.6 occurred 9 hours later on the Çardak Fault, located at the western margin of (and sub-parallel to) the EAFZ breaking the surface with almost 9 m left-lateral slip (average of ∼4 m). Following these large earthquakes, the increase in the regional stress led to a rapid seismic activation in a broad region from central to eastern Anatolia loading the faults at various scales and increasing seismic hazard. Two weeks after the initiation of the seismic crisis, a third earthquake with Mw6.4 occurred at the southern boundary of the Hatay graben, near the southwestern termination of the Amanos rupture. The earthquakes caused significant loss of human life, devastating 12 cities. We evaluate the observations prior to the ruptures, present preliminary seismological results with surface displacements from sub-pixel correlation of optical satellite images and the stress perturbations computed on the nearby faults based on preliminary slip models. The reevaluation of the seismic potential in light of the recent and historical earthquakes provides some new insight on seismic hazard assessment. The recent series of events on the EAFZ is an important reminder that large faults can generate very large earthquakes of multiple segments. The seismic potential of large earthquakes on these fault zones can only be estimated by considering multiple seismic cycles, and moment deficits from very large earthquakes. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6567094
{"title":"Long silence on the East Anatolian Fault Zone (Southern Turkey) ends with devastating double earthquakes (6 February 2023) over a seismic gap: Implications for the seismic potential in the Eastern Mediterranean region","authors":"H. Karabulut, S. E. Güvercin, J. Hollingsworth, A. Konca","doi":"10.1144/jgs2023-021","DOIUrl":"https://doi.org/10.1144/jgs2023-021","url":null,"abstract":"On the 06th February 2023, an earthquake with magnitude ∼Mw7.0 on the Narlı Fault, a fault subparallel to the East Anatolian Fault Zone (EAFZ), initiated a chain of large earthquakes on the EAFZ. The earthquakes occurred in a seismic gap with low geodetic strain rates, low background seismicity, where deformation is distributed across a wide fault zone and long recurrence time of historical earthquakes. The ∼50 km long rupture of the Narlı Fault towards Pazarcık, led to Mw7.8 left-lateral strike-slip earthquake breaking ∼300 km section of the ∼600 km long EAFZ bilaterally with a total duration of more than 80 s. Toward the southwest, the rupture propagated on ∼100 km long Amanos segment with a peak surface offset of 5 m, before diminishing toward the Hatay graben. In the northeast direction, the rupture reached a peak surface offset of 7 m before sharply declining at the termination of the 2020, Mw6.8 Sivrice earthquake rupture. A second large earthquake with Mw7.6 occurred 9 hours later on the Çardak Fault, located at the western margin of (and sub-parallel to) the EAFZ breaking the surface with almost 9 m left-lateral slip (average of ∼4 m). Following these large earthquakes, the increase in the regional stress led to a rapid seismic activation in a broad region from central to eastern Anatolia loading the faults at various scales and increasing seismic hazard. Two weeks after the initiation of the seismic crisis, a third earthquake with Mw6.4 occurred at the southern boundary of the Hatay graben, near the southwestern termination of the Amanos rupture. The earthquakes caused significant loss of human life, devastating 12 cities. We evaluate the observations prior to the ruptures, present preliminary seismological results with surface displacements from sub-pixel correlation of optical satellite images and the stress perturbations computed on the nearby faults based on preliminary slip models. The reevaluation of the seismic potential in light of the recent and historical earthquakes provides some new insight on seismic hazard assessment. The recent series of events on the EAFZ is an important reminder that large faults can generate very large earthquakes of multiple segments. The seismic potential of large earthquakes on these fault zones can only be estimated by considering multiple seismic cycles, and moment deficits from very large earthquakes.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6567094\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45921256","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}
H. Maher, A. Braathen, M. Ganerød, P. Myhre, P. Osmundsen, T. Redfield
Koglin et al. (2022) present valuable new isotopic and field data regarding northwest Spitsbergen's tectonic history, and propose the existence of the Germaniahalvøya terrane with Scandian (Late Caledonian) igneous activity and deformation. Within this terrane, the Lerner Deformation zone (LDZ), is cast as an east-directed thrust, with the Liefdefjorden Migmatite Complex in the footwall and Lenerøyane Group meta-sediments above. The LDZ occurs on the west limb of the major, shallowly north plunging, Bockfjorden anticline. We suggest their data supports the unmentioned and discussed idea (Dallmann & Piepjohn 2018, Braathen et al. 2018) that a Scandian metamorphic core complex exists here and that the LDZ is part of the Keisarhjelmen extensional detachment (Braathen et al. 2017, Maher et. al. 2022). The detachment consists of ductile to brittle, retrogressive, fault rocks up to several hundred meters thick along the contact between metamorphic basement and overlying Devonian basin strata. In addition, we note that Koglin et al's (2022) evidence for Scandian activity is consistent with core complex dynamics.
Koglin et al.(2022)提出了有关斯匹次卑尔根西北构造史的有价值的新同位素和野外资料，并提出了具有加拿大(晚加里东)火成岩活动和变形的germanmaniahalv øya地体的存在。在该地块内，勒纳变形带(LDZ)是一个向东的逆冲构造，下盘为Liefdefjorden杂岩杂岩杂岩，上部为勒纳岩群变质沉积物。低密度区位于主要的、浅北倾的Bockfjorden背斜的西翼。我们认为他们的数据支持未被提及和讨论过的观点(Dallmann & Piepjohn 2018, Braathen et al. 2018)，即这里存在加拿大变质核杂岩，LDZ是Keisarhjelmen张拉拆离的一部分(Braathen et al. 2017, Maher et al. 2022)。沿变质基底与上覆泥盆纪盆地地层的接触，滑脱由厚达数百米的韧性至脆性退退断裂岩组成。此外，我们注意到Koglin等人(2022)关于加拿大活动的证据与核心复杂动力学一致。
{"title":"Discussion on Koglin et al. (2022): The Lerner Deformation Zone as part of a Scandian core complex","authors":"H. Maher, A. Braathen, M. Ganerød, P. Myhre, P. Osmundsen, T. Redfield","doi":"10.1144/jgs2022-179","DOIUrl":"https://doi.org/10.1144/jgs2022-179","url":null,"abstract":"Koglin et al. (2022) present valuable new isotopic and field data regarding northwest Spitsbergen's tectonic history, and propose the existence of the Germaniahalvøya terrane with Scandian (Late Caledonian) igneous activity and deformation. Within this terrane, the Lerner Deformation zone (LDZ), is cast as an east-directed thrust, with the Liefdefjorden Migmatite Complex in the footwall and Lenerøyane Group meta-sediments above. The LDZ occurs on the west limb of the major, shallowly north plunging, Bockfjorden anticline. We suggest their data supports the unmentioned and discussed idea (Dallmann & Piepjohn 2018, Braathen et al. 2018) that a Scandian metamorphic core complex exists here and that the LDZ is part of the Keisarhjelmen extensional detachment (Braathen et al. 2017, Maher et. al. 2022). The detachment consists of ductile to brittle, retrogressive, fault rocks up to several hundred meters thick along the contact between metamorphic basement and overlying Devonian basin strata. In addition, we note that Koglin et al's (2022) evidence for Scandian activity is consistent with core complex dynamics.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41762940","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 Johnston Complex represents a rare inlier of the Neoproterozoic basement of southern Britain and offers a window into the tectonomagmatic regime of East Avalonia during the assembly of Gondwana. This work presents in-situ zircon (U-Pb, Lu-Hf), apatite (U-Pb), and trace element chemistry for both minerals from the Complex. Zircon and apatite yield a coeval crystallisation age of 570 ± 3 Ma, and a minor antecrystic zircon core component is identified at 615 ± 11 Ma. Zircon Lu-Hf data imply a broadly chondritic source, comparable to Nd data from East Avalonia, and T DM 2 model ages of ca. 1.5 Ga indicate source extraction during the Mesoproterozoic. Zircon trace element chemistry is consistent with an ensialic calc-alkaline continental arc setting and demonstrates that magmatism was ongoing prior to terrane dispersal at 570 Ma. Apatite trace element chemistry implies a sedimentary component within the melt consistent with voluminous S-type granite production during the formation of Gondwana. The similarity of ɛHf and geochemistry between both zircon age populations suggest derivation from a uniform source that did not undergo significant modification between 615 – 570 Ma. Time-constrained apatite-zircon chemistry addresses complexities in dating S-type granitoids (zircon inheritance) and permits inferences on post-magmatic thermal histories. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6484464
{"title":"A detective duo of apatite and zircon geochronology for East Avalonia, Johnston Complex, Wales","authors":"Anthony J.I. Clarke, C. Kirkland, S. Glorie","doi":"10.1144/jgs2022-178","DOIUrl":"https://doi.org/10.1144/jgs2022-178","url":null,"abstract":"\u0000 The Johnston Complex represents a rare inlier of the Neoproterozoic basement of southern Britain and offers a window into the tectonomagmatic regime of East Avalonia during the assembly of Gondwana. This work presents\u0000 in-situ\u0000 zircon (U-Pb, Lu-Hf), apatite (U-Pb), and trace element chemistry for both minerals from the Complex. Zircon and apatite yield a coeval crystallisation age of 570 ± 3 Ma, and a minor antecrystic zircon core component is identified at 615 ± 11 Ma. Zircon Lu-Hf data imply a broadly chondritic source, comparable to Nd data from East Avalonia, and T\u0000 DM\u0000 2\u0000 model ages of ca. 1.5 Ga indicate source extraction during the Mesoproterozoic. Zircon trace element chemistry is consistent with an ensialic calc-alkaline continental arc setting and demonstrates that magmatism was ongoing prior to terrane dispersal at 570 Ma. Apatite trace element chemistry implies a sedimentary component within the melt consistent with voluminous S-type granite production during the formation of Gondwana. The similarity of ɛHf and geochemistry between both zircon age populations suggest derivation from a uniform source that did not undergo significant modification between 615 – 570 Ma. Time-constrained apatite-zircon chemistry addresses complexities in dating S-type granitoids (zircon inheritance) and permits inferences on post-magmatic thermal histories.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6484464\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42842314","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}
S. Oriolo, P. González, Pablo Alegre, K. Wemmer, R. Varela, M. Basei
New geological, structural, microstructural, and K-Ar biotite and illite geochronological data of igneous-metamorphic rocks exposed in the Cuesta de Rahue Basement Inlier are presented to reconstruct the Late Palaeozoic to Mesozoic tectonometamorphic and magmatic history of northwestern Patagonia. This block comprises a medium-grade metasedimentary sequence (Cuesta de Rahue Metamorphic Complex), Late Carboniferous granitoids and a low-grade metavolcano-sedimentary unit (Arroyo Coloco Metamorphic Complex). The Cuesta de Rahue Metamorphic Complex was deposited during the middle Palaeozoic and underwent Devonian low-pressure regional metamorphism, succeeded by the intrusion of granitoids at ca. 300 Ma. On the other hand, the Arroyo Coloco Metamorphic Complex record deformation and metamorphism at epizonal conditions (> 300 °C), constrained at ca. 232-199 Ma by K-Ar and XRD illite data. The Cuesta de Rahue Basement Inlier thus records a protracted orogenic evolution, recording Devonian metamorphism, Late Carboniferous-Permian Gondwanide tectonomagmatic processes, and Late Triassic deformation and metamorphism. Afterwards, this block was also affected by Mesozoic normal faulting and, finally, by Miocene-Pliocene Andean deformation. The latter was intimately related to reactivation of inherited basement fabrics, favouring a transpressional deformation regime. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6484467
提供了Cuesta de Rahue基底Inlier中暴露的火成变质岩的新的地质、结构、微观结构和K-Ar黑云母和伊利石地质年代数据，以重建巴塔哥尼亚西北部晚古生代至中生代的构造变质和岩浆史。该区块包括一个中等级别的变质沉积序列（Cuesta de Rahue变质杂岩）、晚石炭世花岗质岩石和一个低级别的变质火山沉积单元（Arroyo Coloco变质杂岩体）。Cuesta de Rahue变质杂岩沉积于古生代中期，经历了泥盆纪低压区域变质作用，随后在约300 Ma发生了花岗岩类侵入。另一方面，Arroyo Coloco变质杂岩记录了表带条件（>300°C）下的变形和变质作用，受K-Ar和XRD伊利石数据的限制，在约232-199 Ma。因此，Cuesta de Rahue基底Inlier记录了漫长的造山演化，记录了泥盆纪变质作用、晚石炭世-二叠纪冈瓦纳构造岩浆作用以及晚三叠纪变形和变质作用。之后，该地块还受到中生代正断层的影响，最后受到中新世-上新世-安第斯变形的影响。后者与继承基底构造的再活化密切相关，有利于转换挤压变形机制。补充材料：https://doi.org/10.6084/m9.figshare.c.6484467
{"title":"The Cuesta de Rahue Basement Inlier (Southern Neuquén Precordillera, Argentina): A Devonian to Triassic polyphase orogenic record in northern Patagonia","authors":"S. Oriolo, P. González, Pablo Alegre, K. Wemmer, R. Varela, M. Basei","doi":"10.1144/jgs2022-143","DOIUrl":"https://doi.org/10.1144/jgs2022-143","url":null,"abstract":"New geological, structural, microstructural, and K-Ar biotite and illite geochronological data of igneous-metamorphic rocks exposed in the Cuesta de Rahue Basement Inlier are presented to reconstruct the Late Palaeozoic to Mesozoic tectonometamorphic and magmatic history of northwestern Patagonia. This block comprises a medium-grade metasedimentary sequence (Cuesta de Rahue Metamorphic Complex), Late Carboniferous granitoids and a low-grade metavolcano-sedimentary unit (Arroyo Coloco Metamorphic Complex). The Cuesta de Rahue Metamorphic Complex was deposited during the middle Palaeozoic and underwent Devonian low-pressure regional metamorphism, succeeded by the intrusion of granitoids at ca. 300 Ma. On the other hand, the Arroyo Coloco Metamorphic Complex record deformation and metamorphism at epizonal conditions (> 300 °C), constrained at ca. 232-199 Ma by K-Ar and XRD illite data. The Cuesta de Rahue Basement Inlier thus records a protracted orogenic evolution, recording Devonian metamorphism, Late Carboniferous-Permian Gondwanide tectonomagmatic processes, and Late Triassic deformation and metamorphism. Afterwards, this block was also affected by Mesozoic normal faulting and, finally, by Miocene-Pliocene Andean deformation. The latter was intimately related to reactivation of inherited basement fabrics, favouring a transpressional deformation regime.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6484467\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48698650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Naing, S. Robinson, M. Searle, C. Morley, I. Millar, O. Green, P. Bown, T. Danelian, M. Petrizzo, G. Henderson
The Indo-Myanmar Ranges (IMR) are an enigmatic mountain belt that occupy a complex tectonic zone in western Myanmar extending from the northern continuation of the active Sunda-Andaman arc into the eastern Himalayan syntaxis. The IMR are part of an accretionary fore-arc basin-arc complex that includes the Central Myanmar Basin and the Wuntho-Popa Arc to the east. New biostratigraphic, petrologic, and detrital zircon U-Pb age data are presented that are used to test and refine the divergent tectonic models that have been proposed for western Myanmar. These data suggest: 1) that the Upper Triassic Pane Chaung Formation was originally deposited adjacent to the NE Indian continental margin within northern Gondwana during the Late Triassic, and 2) that the Upper Cretaceous – Paleogene rocks of the IBR were mainly derived from the Wuntho-Popa Arc and Inner Belt, with a subordinate input from a crustal source, potentially from the Naga metamorphic-type Paleozoic basement. The Kalemyo ophiolite has an Early Cretaceous age similar to ages of ophiolites in the Indus Yarlung-Tsangpo suture zone, south Tibet and Nagaland, reinforcing the hypothesis that they were once part of the same Neo-Tethyan ocean floor. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6487105
{"title":"Age, depositional history and tectonics of the Indo-Myanmar Ranges, Myanmar","authors":"T. Naing, S. Robinson, M. Searle, C. Morley, I. Millar, O. Green, P. Bown, T. Danelian, M. Petrizzo, G. Henderson","doi":"10.1144/jgs2022-091","DOIUrl":"https://doi.org/10.1144/jgs2022-091","url":null,"abstract":"The Indo-Myanmar Ranges (IMR) are an enigmatic mountain belt that occupy a complex tectonic zone in western Myanmar extending from the northern continuation of the active Sunda-Andaman arc into the eastern Himalayan syntaxis. The IMR are part of an accretionary fore-arc basin-arc complex that includes the Central Myanmar Basin and the Wuntho-Popa Arc to the east. New biostratigraphic, petrologic, and detrital zircon U-Pb age data are presented that are used to test and refine the divergent tectonic models that have been proposed for western Myanmar. These data suggest: 1) that the Upper Triassic Pane Chaung Formation was originally deposited adjacent to the NE Indian continental margin within northern Gondwana during the Late Triassic, and 2) that the Upper Cretaceous – Paleogene rocks of the IBR were mainly derived from the Wuntho-Popa Arc and Inner Belt, with a subordinate input from a crustal source, potentially from the Naga metamorphic-type Paleozoic basement. The Kalemyo ophiolite has an Early Cretaceous age similar to ages of ophiolites in the Indus Yarlung-Tsangpo suture zone, south Tibet and Nagaland, reinforcing the hypothesis that they were once part of the same Neo-Tethyan ocean floor.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6487105\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46546298","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}
Volkan Karabacak, Ç. Özkaymak, H. Sözbilir, O. Tatar, B. Aktuğ, Ö. Özdağ, R. Çakır, E. Aksoy, Fikret Koçbulut, Mustafa Softa, Elif Akgün, Ahmet Demir, Gökhan Arslan
Southern Türkiye faced widespread catastrophic destruction by two devastating earthquakes on the same day. As the earthquakes occurred at 04:17 (Mw=7.7, Pazarcık, Kahramanmaraş) and 12:30 (Mw=7.6, Elbistan, Kahramanmaraş) on February 6, 2023, neighboring active fault systems were broken in succession between the Hatay and Malatya Provinces in the region. The first earthquake, one of the largest earthquakes in this region during the last century, caused widespread damage to infrastructure and buildings, and produced large scale seismo-gravitational surface deformation such as landslides, lateral spreading, liquefaction and also extensional cracks. Here, we present the surface rupture geometry and coseismic displacement characteristics of the fault systems, determined with field observations immediately after the February 6, 2023 Pazarcık (Kahramanmaraş, Türkiye) earthquake (Mw=7.7). Preliminary results show that the total rupture length (L max ) is 270±10 km on the Karasu, Pazarcık and Erkenek segments of the East Anatolia Fault Zone. Left-lateral strike-slip faulting is developed with a maximum horizontal displacement (D max ) of 7.30 m and an average displacement (D avg ) of 3.00 m. Although the surface rupture generally exhibits a narrow deformation zone width of 2-5 m, it expands up to 50 m in some sections of the faults. Our implications for rupture dynamics suggest that fracture development started on a secondary fault (Narlı Fault), transferred to the main fault and triggered the breaking of asperities on Pazarcık segment which exhibits a long period accumulation of stress to initiate the major rupturing. Supplementary material: Figures S1 – S12 with details on coseismic displacement are available at: https://doi.org/10.6084/m9.figshare.c.6487245
{"title":"The 2023 Pazarcık (Kahramanmaraş, Türkiye) Earthquake (Mw: 7.7): Implications for surface rupture dynamics along the East Anatolian Fault Zone","authors":"Volkan Karabacak, Ç. Özkaymak, H. Sözbilir, O. Tatar, B. Aktuğ, Ö. Özdağ, R. Çakır, E. Aksoy, Fikret Koçbulut, Mustafa Softa, Elif Akgün, Ahmet Demir, Gökhan Arslan","doi":"10.1144/jgs2023-020","DOIUrl":"https://doi.org/10.1144/jgs2023-020","url":null,"abstract":"\u0000 Southern Türkiye faced widespread catastrophic destruction by two devastating earthquakes on the same day. As the earthquakes occurred at 04:17 (Mw=7.7, Pazarcık, Kahramanmaraş) and 12:30 (Mw=7.6, Elbistan, Kahramanmaraş) on February 6, 2023, neighboring active fault systems were broken in succession between the Hatay and Malatya Provinces in the region. The first earthquake, one of the largest earthquakes in this region during the last century, caused widespread damage to infrastructure and buildings, and produced large scale seismo-gravitational surface deformation such as landslides, lateral spreading, liquefaction and also extensional cracks. Here, we present the surface rupture geometry and coseismic displacement characteristics of the fault systems, determined with field observations immediately after the February 6, 2023 Pazarcık (Kahramanmaraş, Türkiye) earthquake (Mw=7.7). Preliminary results show that the total rupture length (L\u0000 max\u0000 ) is 270±10 km on the Karasu, Pazarcık and Erkenek segments of the East Anatolia Fault Zone. Left-lateral strike-slip faulting is developed with a maximum horizontal displacement (D\u0000 max\u0000 ) of 7.30 m and an average displacement (D\u0000 avg\u0000 ) of 3.00 m. Although the surface rupture generally exhibits a narrow deformation zone width of 2-5 m, it expands up to 50 m in some sections of the faults. Our implications for rupture dynamics suggest that fracture development started on a secondary fault (Narlı Fault), transferred to the main fault and triggered the breaking of asperities on Pazarcık segment which exhibits a long period accumulation of stress to initiate the major rupturing.\u0000 \u0000 \u0000 Supplementary material:\u0000 Figures S1 – S12 with details on coseismic displacement are available at:\u0000 https://doi.org/10.6084/m9.figshare.c.6487245\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47086340","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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