Active submarine channel bases are marked by large erosional features, such as knickpoints and plunge pools. Their presence in ancient channel-fills has rarely been documented, meaning their importance in submarine channel morphodynamics requires investigation. Using seismic reflection data calibrated by wells from a buried submarine channel-fill, we document erosional features 100s m long and 10s m deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record for the first time. Channel incision patterns are interpreted to record a transient uplift in an otherwise subsiding depocentre. Local structural complexities in the channel slope formed zones of preferential scouring. A switch to a depositional regime preserved the irregular channel base inhibiting their upstream migration and smoothing of the channel base. Their formation and preservation record responses to salt tectonics and provide a unique snapshot of the formative processes of an ancient submarine channel. The presence of these exceptional basal scours indicates that headward erosion processes did not operate rapidly, challenging the paradigm that knickpoint migration controls channel evolution. Our results show that the primary erosion of the main channel surface, and long-term channel evolution, are dominated by far more gradual processes.
{"title":"A salty snapshot: extreme variations in basal erosion patterns preserved in a submarine channel","authors":"J. Casagrande, David M. Hodgson, Jeffrey Peakall","doi":"10.1144/jgs2023-006","DOIUrl":"https://doi.org/10.1144/jgs2023-006","url":null,"abstract":"Active submarine channel bases are marked by large erosional features, such as knickpoints and plunge pools. Their presence in ancient channel-fills has rarely been documented, meaning their importance in submarine channel morphodynamics requires investigation. Using seismic reflection data calibrated by wells from a buried submarine channel-fill, we document erosional features 100s m long and 10s m deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record for the first time. Channel incision patterns are interpreted to record a transient uplift in an otherwise subsiding depocentre. Local structural complexities in the channel slope formed zones of preferential scouring. A switch to a depositional regime preserved the irregular channel base inhibiting their upstream migration and smoothing of the channel base. Their formation and preservation record responses to salt tectonics and provide a unique snapshot of the formative processes of an ancient submarine channel. The presence of these exceptional basal scours indicates that headward erosion processes did not operate rapidly, challenging the paradigm that knickpoint migration controls channel evolution. Our results show that the primary erosion of the main channel surface, and long-term channel evolution, are dominated by far more gradual processes.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139450842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Anthony J. I. Clarke, C. L. Kirkland, Latha R. Menon, Daniel J. Condon, John C. W. Cope, R. Bevins, S. Glorie
The Llangynog Inlier of south Wales contains an assemblage of Ediacaran macrofossils from a shallow-marine environment, including discoidal morphs of Aspidella and rare examples of Hiemalora , Palaeopascichnus and Yelovichnus . These are taxa found at other sites in the Avalonian microcontinent (e.g. Charnwood Forest and eastern Newfoundland) and in the younger White Sea Ediacaran assemblages. As the Charnwood fossils reflect a deep-water environment, and no macrofossils have been found in the Ediacaran rocks of the Long Mynd, the fossils of the Llangynog Inlier represent a unique glimpse of shallow-marine life in southern Britain (East Avalonia). However, the lack of absolute age constraints has hampered direct comparison with other assemblages. Here, we report in situ zircon and rutile U–Pb dates from a rhyolitic ash-flow layer of the Coed Cochion Volcaniclastic Member, Llangynog Inlier, which constrains the age of the fossiliferous strata. A weighted mean single grain zircon isotope dilution thermal ionization mass spectrometry U–Pb age of 564.09 ± 0.70 Ma is interpreted as the rhyolite's crystallization age. This age is consistent with in situ laser ablation inductively coupled plasma mass spectrometry zircon and rutile U–Pb dating. The Llangynog age temporally correlates these fossils to dated horizons within East Avalonia at the Beacon Hill Formation, Charnwood (565.22 ± 0.89 Ma) and the Stretton Shale Formation, Long Mynd (566.6 ± 2.9 Ma). Correlations to West Avalonia include the time-equivalent Fermeuse Formation, St John's Group, eastern Newfoundland (564.13 ± 0.65 Ma). The data presented here establish the biota of the Llangynog Inlier as a lateral equivalent to the similarly shallow-marine, tidally influenced ecosystem of the upper Fermeuse Formation. Intra-terrane depositional environmental variability also affects what is preserved in Avalonian fossil sites. Further, time-constrained geochemical data reinforce the Llangynog Inlier's classification within the Wrekin Terrane. Supplementary material : U–Pb data, reference material and figures showing sedimentary structures are available at https://doi.org/10.6084/m9.figshare.c.6965642
{"title":"U–Pb zircon–rutile dating of the Llangynog Inlier, Wales: constraints on an Ediacaran shallow-marine fossil assemblage from East Avalonia","authors":"Anthony J. I. Clarke, C. L. Kirkland, Latha R. Menon, Daniel J. Condon, John C. W. Cope, R. Bevins, S. Glorie","doi":"10.1144/jgs2023-081","DOIUrl":"https://doi.org/10.1144/jgs2023-081","url":null,"abstract":"\u0000 The Llangynog Inlier of south Wales contains an assemblage of Ediacaran macrofossils from a shallow-marine environment, including discoidal morphs of\u0000 Aspidella\u0000 and rare examples of\u0000 Hiemalora\u0000 ,\u0000 Palaeopascichnus\u0000 and\u0000 Yelovichnus\u0000 . These are taxa found at other sites in the Avalonian microcontinent (e.g. Charnwood Forest and eastern Newfoundland) and in the younger White Sea Ediacaran assemblages. As the Charnwood fossils reflect a deep-water environment, and no macrofossils have been found in the Ediacaran rocks of the Long Mynd, the fossils of the Llangynog Inlier represent a unique glimpse of shallow-marine life in southern Britain (East Avalonia). However, the lack of absolute age constraints has hampered direct comparison with other assemblages. Here, we report\u0000 in situ\u0000 zircon and rutile U–Pb dates from a rhyolitic ash-flow layer of the Coed Cochion Volcaniclastic Member, Llangynog Inlier, which constrains the age of the fossiliferous strata. A weighted mean single grain zircon isotope dilution thermal ionization mass spectrometry U–Pb age of 564.09 ± 0.70 Ma is interpreted as the rhyolite's crystallization age. This age is consistent with\u0000 in situ\u0000 laser ablation inductively coupled plasma mass spectrometry zircon and rutile U–Pb dating. The Llangynog age temporally correlates these fossils to dated horizons within East Avalonia at the Beacon Hill Formation, Charnwood (565.22 ± 0.89 Ma) and the Stretton Shale Formation, Long Mynd (566.6 ± 2.9 Ma). Correlations to West Avalonia include the time-equivalent Fermeuse Formation, St John's Group, eastern Newfoundland (564.13 ± 0.65 Ma). The data presented here establish the biota of the Llangynog Inlier as a lateral equivalent to the similarly shallow-marine, tidally influenced ecosystem of the upper Fermeuse Formation. Intra-terrane depositional environmental variability also affects what is preserved in Avalonian fossil sites. Further, time-constrained geochemical data reinforce the Llangynog Inlier's classification within the Wrekin Terrane.\u0000 \u0000 \u0000 Supplementary material\u0000 : U–Pb data, reference material and figures showing sedimentary structures are available at\u0000 https://doi.org/10.6084/m9.figshare.c.6965642\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139540502","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}
Alexandra E. Pye, K. Hodges, Todd A. Ehlers, M. V. van Soest, Christopher S. McDonald, Basant Bhandari
Understanding how the South Tibetan Detachment System (STDS) evolved through time and space is necessary for understanding the evolution of the Himalayan orogen. We present new (with previously published) thermochronologic results from a transect in the footwall and ductile shear zone of the basal structure of the STDS in the Kali Gandaki region: the Annapurna detachment. The exhumation history is interpreted from observations using 1D thermal-kinematic models that invert for the exhumation rate of samples. Recently published data suggested that high-temperature slip on the detachment persisted until at least ca. 12 Ma, more recently than is commonly assumed for STDS deformation. Our new data and modelling support those findings and suggest that the cessation of slip coincided with a dramatic, > 50% decrease in the exhumation rate of the shear zone and its footwall at ca. 12-10 Ma. Exhumation rates remained low until ca. 3 Ma, after which they increased to levels comparable with those that characterised STDS activity. Plausible causes of this late pulse of exhumation include an intensification of the Asian Winter monsoon and establishment of today's Indian Summer Monsoon, glaciation, and/or an internal structural reorganisation of the Himalayan orogenic wedge driving localised rock uplift in the hinterland. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6949467
{"title":"Constraining the exhumation history of the Greater Himalayan sequence, Kali Gandaki, Central Nepal","authors":"Alexandra E. Pye, K. Hodges, Todd A. Ehlers, M. V. van Soest, Christopher S. McDonald, Basant Bhandari","doi":"10.1144/jgs2023-100","DOIUrl":"https://doi.org/10.1144/jgs2023-100","url":null,"abstract":"Understanding how the South Tibetan Detachment System (STDS) evolved through time and space is necessary for understanding the evolution of the Himalayan orogen. We present new (with previously published) thermochronologic results from a transect in the footwall and ductile shear zone of the basal structure of the STDS in the Kali Gandaki region: the Annapurna detachment. The exhumation history is interpreted from observations using 1D thermal-kinematic models that invert for the exhumation rate of samples. Recently published data suggested that high-temperature slip on the detachment persisted until at least ca. 12 Ma, more recently than is commonly assumed for STDS deformation. Our new data and modelling support those findings and suggest that the cessation of slip coincided with a dramatic, > 50% decrease in the exhumation rate of the shear zone and its footwall at ca. 12-10 Ma. Exhumation rates remained low until ca. 3 Ma, after which they increased to levels comparable with those that characterised STDS activity. Plausible causes of this late pulse of exhumation include an intensification of the Asian Winter monsoon and establishment of today's Indian Summer Monsoon, glaciation, and/or an internal structural reorganisation of the Himalayan orogenic wedge driving localised rock uplift in the hinterland.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6949467\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138977160","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}
R. Lu, Cuiping Zhao, Jinyu Zhang, Qincai Wang, Xiao Sun, Fang Xu, Haoyue Sun
Area of active tectonics hosts many active faults and frequently experiences moderate to large earthquakes. The possibility of devastating earthquakes makes the development of major infrastructure projects in these areas risky. World-class large-scale step hydroelectric projects were built along the Jinsha River, such as the Xiangjiaba, Xiluodu, Baihetan, and Wudongde reservoirs in the Daliang Mountains of the southeastern Tibetan Plateau. Using the SKUA-GoCAD modeling platform, we created a thorough three-dimensional (3D) model of the active faults. Regional geological information, historical strong earthquake catalogs, small earthquakes with fine displacement, and 3D seismic tomography are all integrated in this model. The Mabian-Yanjin fault belt consists of a number of discontinuous faults that are either exposed on the surface or concealed, according to the 3D fault model. Some destructive earthquakes, including two enormous M 7 and many moderate earthquakes, have occurred along this fault belt. Some pre-existing thrust faults, together with numerous immature faults in specific areas, may have been reactivated and changed into strike-slip faults. The Jinsha River basin's seismic and geological concerns must be carefully considered given the existence of such intricate fault networks and seismic activity. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6949201
{"title":"3D fault model and seismotectonics indicate the potential seismic risk in the Daliang Mountains, southeastern Tibetan Plateau","authors":"R. Lu, Cuiping Zhao, Jinyu Zhang, Qincai Wang, Xiao Sun, Fang Xu, Haoyue Sun","doi":"10.1144/jgs2023-136","DOIUrl":"https://doi.org/10.1144/jgs2023-136","url":null,"abstract":"\u0000 Area of active tectonics hosts many active faults and frequently experiences moderate to large earthquakes. The possibility of devastating earthquakes makes the development of major infrastructure projects in these areas risky. World-class large-scale step hydroelectric projects were built along the Jinsha River, such as the Xiangjiaba, Xiluodu, Baihetan, and Wudongde reservoirs in the Daliang Mountains of the southeastern Tibetan Plateau. Using the SKUA-GoCAD modeling platform, we created a thorough three-dimensional (3D) model of the active faults. Regional geological information, historical strong earthquake catalogs, small earthquakes with fine displacement, and 3D seismic tomography are all integrated in this model. The Mabian-Yanjin fault belt consists of a number of discontinuous faults that are either exposed on the surface or concealed, according to the 3D fault model. Some destructive earthquakes, including two enormous\u0000 M\u0000 7 and many moderate earthquakes, have occurred along this fault belt. Some pre-existing thrust faults, together with numerous immature faults in specific areas, may have been reactivated and changed into strike-slip faults. The Jinsha River basin's seismic and geological concerns must be carefully considered given the existence of such intricate fault networks and seismic activity.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6949201\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139007126","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}
Dominique Cluzel, A. Montanini, A. Secchiari, E. Ferrari, M. Heizler, F. Jourdan, S. Meffre, R. Zhou, C. Teyssier
New Caledonia Ophiolite is crosscut by coarse to medium grained pyroxenites and hornblende gabbros/diorites dykes intruded between 55.5Ma and 50Ma (U-Pb zircon and 40 Ar/ 39 Ar hornblende), while finer-grained dolerites of tholeiitic affinity are younger (50-47 Ma). Production of hornblende-gabbros/diorites was modelled by moderate degree (20-40%) of partial melting of the HT amphibolites of the metamorphic sole. End-member compositions, hornblendites and anorthosites, resulted from solid-state phase segregation of crystal mushes within tectonically active magmatic conduits. Cascade reactions of slab melts with mantle wedge peridotites successively formed clinoenstatite-boninite magmas, which fed gabbronorite cumulate lenses at the mantle-crust transition, in turn clinoenstatite-boninite melts reacted with peridotites to form websterites. The youngest magmas of tholeiitic affinity, appeared about 6 Ma after subduction inception when the cooler subducting slab plunged more steeply. Incipient slab retreat allowed corner flow, triggering low pressure hydrous melting of the uplifted asthenosphere . The early stages of forearc magmatism were closely associated with transcurrent shear zones, which recorded oblique subduction inception. The lower Eocene tectonic and magmatic features of the New Caledonia ophiolite witness the existence of a north- or northeast-dipping hot (forced) subduction zone in the Southwest Pacific, which appears notably distinct from the slightly younger west-dipping Izu-Bonin-Marianna cold (spontaneous) subduction system. 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.6949265
{"title":"New geochemical and age constraints (\u0000 40\u0000 Ar/\u0000 39\u0000 Ar and U-Pb) on forearc intrusive rocks from New Caledonia Ophiolite (SW Pacific): diversity of melts generated at hot subduction inception","authors":"Dominique Cluzel, A. Montanini, A. Secchiari, E. Ferrari, M. Heizler, F. Jourdan, S. Meffre, R. Zhou, C. Teyssier","doi":"10.1144/jgs2023-145","DOIUrl":"https://doi.org/10.1144/jgs2023-145","url":null,"abstract":"\u0000 New Caledonia Ophiolite is crosscut by coarse to medium grained pyroxenites and hornblende gabbros/diorites dykes intruded between 55.5Ma and 50Ma (U-Pb zircon and\u0000 40\u0000 Ar/\u0000 39\u0000 Ar hornblende), while finer-grained dolerites of tholeiitic affinity are younger (50-47 Ma). Production of hornblende-gabbros/diorites was modelled by moderate degree (20-40%) of partial melting of the HT amphibolites of the metamorphic sole. End-member compositions, hornblendites and anorthosites, resulted from solid-state phase segregation of crystal mushes within tectonically active magmatic conduits. Cascade reactions of slab melts with mantle wedge peridotites successively formed clinoenstatite-boninite magmas, which fed gabbronorite cumulate lenses at the mantle-crust transition, in turn clinoenstatite-boninite melts reacted with peridotites to form websterites. The youngest magmas of tholeiitic affinity, appeared about 6 Ma after subduction inception when the cooler subducting slab plunged more steeply. Incipient slab retreat allowed corner flow, triggering low pressure hydrous melting of the uplifted asthenosphere . The early stages of forearc magmatism were closely associated with transcurrent shear zones, which recorded oblique subduction inception. The lower Eocene tectonic and magmatic features of the New Caledonia ophiolite witness the existence of a north- or northeast-dipping hot (forced) subduction zone in the Southwest Pacific, which appears notably distinct from the slightly younger west-dipping Izu-Bonin-Marianna cold (spontaneous) subduction system.\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.6949265\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139007694","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}
R. Stern, M. Khedr, M. Whitehouse, Rolf L. Romer, Saif M. Abo Khashaba, N. H. El-Shibiny
Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian-Nubian Shield (ANS), six samples from five rare metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U-Pb ages and O isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb- isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies . Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96 ‰ and yielded ages of 628-633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7 - 678.9 Ma with δ 18 O V-SMOW ∼5.95 ‰ . All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared to unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and un-mineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6949402
稀有金属（Nb、Ta、Y、Zr、Sn、U、W 和 REE）具有重要的经济价值，需要找到新的供应来源。为了了解阿拉伯-努比亚地盾（ANS）新元古代稀有金属花岗岩的情况，对埃及中部和东南部沙漠的五个稀有金属成矿碱长岩花岗岩、正长岩和花岗闪长岩的六个样本进行了研究，以了解锆石U-Pb年龄和O同位素组成，以及全岩Sr-、Nd-和碱长岩Pb-同位素组成。这些花岗岩介于 I 型和 A 型之间，大多为高 K 钙碱性过铝花岗岩，具有鸥翼形 REE 模式和强烈的负 Eu 异常。 四块花岗岩的锆石δ 18 O V-SMOW介于4.2和5.96 ‰之间，年龄为628-633 Ma。这大约是与俯冲有关的岩浆活动开始被与碰撞有关的岩浆活动所取代的时间。Igla Ahmr 花岗岩的形成年代更早，为 691.7 - 678.9 Ma，δ 18 O V-SMOW ∼ 5.95 ‰。所有地幔和幼壳的初始ε钕值均为正值（+3.3 至 +6.9）。与未矿化的ANS花岗岩相比，Pb同位素组成具有异常的放射性。这些数据表明，ANS成矿花岗岩和未成矿花岗岩的岩浆来源相似。对ANS地区其他稀有金属矿化花岗岩的勘探应集中在具有类似特征的岩体上。 补充材料：https://doi.org/10.6084/m9.figshare.c.6949402
{"title":"Late Cryogenian and Early Ediacaran rare metal-rich granites in the Eastern Desert of Egypt: constraints from zircon ages and whole-rock Sr- and Nd- and feldspar Pb- isotopic compositions","authors":"R. Stern, M. Khedr, M. Whitehouse, Rolf L. Romer, Saif M. Abo Khashaba, N. H. El-Shibiny","doi":"10.1144/jgs2023-068","DOIUrl":"https://doi.org/10.1144/jgs2023-068","url":null,"abstract":"\u0000 Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian-Nubian Shield (ANS), six samples from five rare metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U-Pb ages and O isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb- isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies\u0000 . \u0000 Four granites gave mantle-like zircon\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 18\u0000 O\u0000 V-SMOW\u0000 between 4.2 and 5.96 ‰ and yielded ages of 628-633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7 - 678.9 Ma with\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 18\u0000 O\u0000 V-SMOW\u0000 ∼5.95 ‰\u0000 .\u0000 All have positive initial\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Nd\u0000 values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared to unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and un-mineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6949402\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139007322","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}
V.V. Ene, S. Tapster, D.J. Smith, C. Panaiotu, E. Roşu, J. Naden, M. Munteanu
Magmatism with arc-like features, formed in extensional settings, was active in the South Apuseni Mountains, Romania, during the Neogene and Quaternary periods. To date the chronological framework is primarily restricted to K-Ar dates. We present newly determined LA-ICP-MS U-Pb zircon age data for subvolcanic and volcanic rocks (N=20) from 8 different Cenozoic volcanic-intrusive complexes and from Jurassic and Cretaceous lava flows. Our results support magmatic ages between c. 14 to c. 7 Ma, with Uroi, an alkaline intrusion, occurring significantly later at c. 1.5 Ma. Revising the timeline for the South Apuseni Mountains paleomagnetic rotations shows that most of the vertical-axis clockwise rotation of the Apuseni Mountains (54.4° ± 10.7°) took place between approximately 14 and 11 Ma, the age interval when the majority of magmas were emplaced. Xenocrystic zircon dates exhibit differences in age populations between individual volcanic-intrusive complexes. A Permo-Triassic population is almost ubiquitous, indicating that basement Permo-Triassic igneous rocks are more widespread than previously thought or that they were significantly involved in the generation of Neogene magmas. However, other observed age populations, such as Triassic or Paleogene have no clear correspondence in the known geological record, indicating the presence of a cryptic component interacting with Neogene magmas. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6951429
{"title":"Spatio-temporal distribution of magmatism and crustal inheritance within an extensional-rotational environment: An updated geochronology of the Miocene & Quaternary magmatism of the South Apuseni Mountains","authors":"V.V. Ene, S. Tapster, D.J. Smith, C. Panaiotu, E. Roşu, J. Naden, M. Munteanu","doi":"10.1144/jgs2023-048","DOIUrl":"https://doi.org/10.1144/jgs2023-048","url":null,"abstract":"Magmatism with arc-like features, formed in extensional settings, was active in the South Apuseni Mountains, Romania, during the Neogene and Quaternary periods. To date the chronological framework is primarily restricted to K-Ar dates. We present newly determined LA-ICP-MS U-Pb zircon age data for subvolcanic and volcanic rocks (N=20) from 8 different Cenozoic volcanic-intrusive complexes and from Jurassic and Cretaceous lava flows. Our results support magmatic ages between c. 14 to c. 7 Ma, with Uroi, an alkaline intrusion, occurring significantly later at c. 1.5 Ma. Revising the timeline for the South Apuseni Mountains paleomagnetic rotations shows that most of the vertical-axis clockwise rotation of the Apuseni Mountains (54.4° ± 10.7°) took place between approximately 14 and 11 Ma, the age interval when the majority of magmas were emplaced. Xenocrystic zircon dates exhibit differences in age populations between individual volcanic-intrusive complexes. A Permo-Triassic population is almost ubiquitous, indicating that basement Permo-Triassic igneous rocks are more widespread than previously thought or that they were significantly involved in the generation of Neogene magmas. However, other observed age populations, such as Triassic or Paleogene have no clear correspondence in the known geological record, indicating the presence of a cryptic component interacting with Neogene magmas.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6951429\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139009728","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}
Microfacies analysis and conodont dating on carbonates associated with the Vourinos-Pindos ophiolite emplacement on the Pelagonian unit in northern Greece, combined with structural analysis, enhance our understanding of the palaeogeography and geotectonic evolution of the Hellenides. We focus on a dismembered Triassic Hallstatt Limestone succession incorporated as blocks in the Middle-Late Jurassic Avdella ophiolitic mélange, which is identical to a Triassic succession in the western Pindos (Hallstatt/Pindos succession). Initially, the Hallstatt/Pindos succession was deposited on the outer shelf along the eastern Pelagonian margin and later incorporated into the mélange during west-directed obduction processes. During the Middle to early Late Jurassic, ophiolites obducted on the eastern Pelagonian margin, resulting in a nappe stack in front of the ophiolites in the lower plate position. Newly formed trench-like basins in front of the advancing nappe stack became filled with sedimentary mélanges, consisting of ophiolitic material mixed with blocks from the Hallstatt/Pindos succession, deposited in an outer shelf position. Subsequently, the Pindos ophiolites overthrust their foreland basin, forming a typical ophiolitic mélange (Avdella mélange). Consequently, the Triassic-Middle Jurassic Hallstatt/Pindos succession represents a far-traveled Middle-Late Jurassic nappe deriving east of the Pelagonian unit, which was bulldozed westward in front of the west-directed obducting Neotethys ophiolites. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists
{"title":"New stratigraphic and paleontological data from carbonates related to the Vourinos-Pindos ophiolite emplacement: Implications for the provenance of the ophiolites (Hellenides)","authors":"Georgia Kostaki, Hans-Jürgen Gawlick, Sigrid Missoni, Adamantios Kilias, Emmanouil Katrivanos","doi":"10.1144/jgs2023-127","DOIUrl":"https://doi.org/10.1144/jgs2023-127","url":null,"abstract":"Microfacies analysis and conodont dating on carbonates associated with the Vourinos-Pindos ophiolite emplacement on the Pelagonian unit in northern Greece, combined with structural analysis, enhance our understanding of the palaeogeography and geotectonic evolution of the Hellenides. We focus on a dismembered Triassic Hallstatt Limestone succession incorporated as blocks in the Middle-Late Jurassic Avdella ophiolitic mélange, which is identical to a Triassic succession in the western Pindos (Hallstatt/Pindos succession). Initially, the Hallstatt/Pindos succession was deposited on the outer shelf along the eastern Pelagonian margin and later incorporated into the mélange during west-directed obduction processes. During the Middle to early Late Jurassic, ophiolites obducted on the eastern Pelagonian margin, resulting in a nappe stack in front of the ophiolites in the lower plate position. Newly formed trench-like basins in front of the advancing nappe stack became filled with sedimentary mélanges, consisting of ophiolitic material mixed with blocks from the Hallstatt/Pindos succession, deposited in an outer shelf position. Subsequently, the Pindos ophiolites overthrust their foreland basin, forming a typical ophiolitic mélange (Avdella mélange). Consequently, the Triassic-Middle Jurassic Hallstatt/Pindos succession represents a far-traveled Middle-Late Jurassic nappe deriving east of the Pelagonian unit, which was bulldozed westward in front of the west-directed obducting Neotethys ophiolites. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136281717","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}
Duje Kukoč, Damir Slovenec, Branimir Šegvić, Matija Vukovski, Mirko Belak, Tonći Grgasović, Marija Horvat, Duje Smirčić
Ophiolite exposures in NW Croatia have been attributed to the Western Vardar Ophiolitic Unit and interpreted as derived from the Meliata-Maliac-Vardar branch of the Neotethys. Blocks within the ophiolitic mélange on Mt. Ivanščica were investigated for petrological and geochemical characteristics of effusive rocks and radiolarian dating of associated pelagic sedimentary rocks. Analysed effusive basic rocks represent chemographically uniform sub-alkaline high-Ti massive tholeiitic basalts characterized by an enriched composition typical of E-MORB. These basalts are compatible with approximately 9 to 11% of partial melting of an enriched mantle source transitional between primitive and depleted MORB-type mantle and are formed in the non-subduction geotectonic setting of E-MORB-type. This reflects an initial succession of oceanic protocrust formation and the onset of ocean spreading. Radiolarians from chert and shale succession associated with basalts indicate a Late Anisian to Early Ladinian age of the initial ocean floor spreading, which continued into the Langobardian. Obtained data are correlative with reported blocks interpreted as remnants of the Triassic Neotethys crust from the ophiolitic mélange of the Western Vardar Ophiolitic Unit and further reaffirm common origin from a single ocean basin located east of the Adria microplate. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists
{"title":"The early history of the Neotethys archived in the ophiolitic mélange of northwestern Croatia","authors":"Duje Kukoč, Damir Slovenec, Branimir Šegvić, Matija Vukovski, Mirko Belak, Tonći Grgasović, Marija Horvat, Duje Smirčić","doi":"10.1144/jgs2023-143","DOIUrl":"https://doi.org/10.1144/jgs2023-143","url":null,"abstract":"Ophiolite exposures in NW Croatia have been attributed to the Western Vardar Ophiolitic Unit and interpreted as derived from the Meliata-Maliac-Vardar branch of the Neotethys. Blocks within the ophiolitic mélange on Mt. Ivanščica were investigated for petrological and geochemical characteristics of effusive rocks and radiolarian dating of associated pelagic sedimentary rocks. Analysed effusive basic rocks represent chemographically uniform sub-alkaline high-Ti massive tholeiitic basalts characterized by an enriched composition typical of E-MORB. These basalts are compatible with approximately 9 to 11% of partial melting of an enriched mantle source transitional between primitive and depleted MORB-type mantle and are formed in the non-subduction geotectonic setting of E-MORB-type. This reflects an initial succession of oceanic protocrust formation and the onset of ocean spreading. Radiolarians from chert and shale succession associated with basalts indicate a Late Anisian to Early Ladinian age of the initial ocean floor spreading, which continued into the Langobardian. Obtained data are correlative with reported blocks interpreted as remnants of the Triassic Neotethys crust from the ophiolitic mélange of the Western Vardar Ophiolitic Unit and further reaffirm common origin from a single ocean basin located east of the Adria microplate. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136346847","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}
Urbez Majarena, José Julián Estéban, Carlos Galé, Andrés Gil-Imaz, Marceliano Lago
The Herrera Unit of the Iberian Chain (Cantabrian Zone, Iberian Massif) exhibits hundreds of outcrops of calc-alkaline igneous rocks that have been classically attributed to the Upper Carboniferous and the Lower Permian, although only two absolute radiometric ages have been reported. This work, with six new zircon laser ablation inductively coupled plasma mass spectrometry ages obtained from some of the most representative outcrops, provides the most complete age repository for the calc-alkaline magmatism of the prolongation of the Cantabrian Zone within the Iberian Chain. The obtained ages range between 294 and 288 Ma (Cisuralian Epoch) and show a well-defined peak at 290 Ma, which can be attributed to a main magmatic activity stage. This result allows us to correlate and integrate this magmatism within the widespread SW European calc-alkaline magmatism province developed under strike-slip tectonics. Therefore, the Iberian Chain magmatism and its age can be considered as a good temporal marker for the upper limit of the compressive tectonics associated with the Variscan Orogeny and the onset of the extensional tectonics linked to Permo-Triassic rifting. Supplementary material: Analytical settings (1) and analytical data from: the standard zircons (2) and the zircons from the samples of this work (3) are available at https://doi.org/10.6084/m9.figshare.c.6843778
{"title":"Cisuralian calc-alkaline magmatism in the Herrera Unit of the Iberian Chain (Cantabrian Zone of the Iberian Massif, Spain): Age and geodynamic constraints from U-Pb LA-ICP-MS zircon analysis","authors":"Urbez Majarena, José Julián Estéban, Carlos Galé, Andrés Gil-Imaz, Marceliano Lago","doi":"10.1144/jgs2022-102","DOIUrl":"https://doi.org/10.1144/jgs2022-102","url":null,"abstract":"The Herrera Unit of the Iberian Chain (Cantabrian Zone, Iberian Massif) exhibits hundreds of outcrops of calc-alkaline igneous rocks that have been classically attributed to the Upper Carboniferous and the Lower Permian, although only two absolute radiometric ages have been reported. This work, with six new zircon laser ablation inductively coupled plasma mass spectrometry ages obtained from some of the most representative outcrops, provides the most complete age repository for the calc-alkaline magmatism of the prolongation of the Cantabrian Zone within the Iberian Chain. The obtained ages range between 294 and 288 Ma (Cisuralian Epoch) and show a well-defined peak at 290 Ma, which can be attributed to a main magmatic activity stage. This result allows us to correlate and integrate this magmatism within the widespread SW European calc-alkaline magmatism province developed under strike-slip tectonics. Therefore, the Iberian Chain magmatism and its age can be considered as a good temporal marker for the upper limit of the compressive tectonics associated with the Variscan Orogeny and the onset of the extensional tectonics linked to Permo-Triassic rifting. Supplementary material: Analytical settings (1) and analytical data from: the standard zircons (2) and the zircons from the samples of this work (3) are available at https://doi.org/10.6084/m9.figshare.c.6843778","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135775741","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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