Bing Pan, Malik Muhammad Saud Sajid Khan, Guoxiang Li, Shehryar Ahmed, M. Qasim, Z. Yin, I. A. Jadoon, Maoyan Zhu
The tommotiids are an important group of Cambrian small shelly fossils, primarily retrieved from the carbonate rock by acid process. Herein, the abundant isolated sclerites of Tannuolina are recovered from the siltstone-dominated upper part of the Hazira Formation in the eastern Hazara Basin, North Pakistan. This discovery of tommotiids preserved in the siltstones not only suggests their occurrences in a variety of sedimentary lithofacies, but also provides the opportunity to look for the sclerites or scleritomes (even soft-tissue) of tommotiids in much wider taphonomic windows. The sclerites include two morphs, i.e. mitral and sellate types. Through morphological comparison, they can be identified as Tannuolina zhangwentangi Qian & Bengtson, 1989. The large mitral and sellate sclerites (about 1 cm) illustrated herein manifest a relatively consistent morphology during the size increasement. The sellate sclerites may contain two sub-types, the larger sellate sclerite with sella on the sellate side and the smaller convex sellate side without sella on either sides. In the original scleritome, the two sub-types of sellate sclerites probably combine as a composite with the duplicatural side of the smaller one attached on the sella area of the large one. For the first time, T. zhangwentangi has been recovered from the Indian subcontinent, previously unknown outside South China. The middle and upper part of the Hazira Formation exclusively bearing T. zhangwentangi can directly invite correlation with the S. flabelliformis – T. zhangwentangi Assemblage Zone of South China representing the uppermost Cambrian Stage 2. This new palaeontological finds not only signifies the utility of T. zhangwentangi for intercontinental biostratigraphical correlation, but also suggests that the Terreneuvian SSF biostratigraphy between the Indian subcontinent and South China are quite consistent, comprising of three (at least two) correlative SSF Assemblage Zone (Zone Ⅰ, possible Ⅲ, and Ⅳ of South China). Additionally, our result may also support a relatively close palaeogeographical linkage between these two regions in early Cambrian. Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/topic/collections/advances-in-the-cambrian-explosion
{"title":"Occurrence of\u0000 Tannuolina\u0000 in the early Cambrian siltstones of Hazara Basin, North Pakistan and its biostratigraphical significance","authors":"Bing Pan, Malik Muhammad Saud Sajid Khan, Guoxiang Li, Shehryar Ahmed, M. Qasim, Z. Yin, I. A. Jadoon, Maoyan Zhu","doi":"10.1144/jgs2021-149","DOIUrl":"https://doi.org/10.1144/jgs2021-149","url":null,"abstract":"\u0000 The tommotiids are an important group of Cambrian small shelly fossils, primarily retrieved from the carbonate rock by acid process. Herein, the abundant isolated sclerites of\u0000 Tannuolina\u0000 are recovered from the siltstone-dominated upper part of the Hazira Formation in the eastern Hazara Basin, North Pakistan. This discovery of tommotiids preserved in the siltstones not only suggests their occurrences in a variety of sedimentary lithofacies, but also provides the opportunity to look for the sclerites or scleritomes (even soft-tissue) of tommotiids in much wider taphonomic windows. The sclerites include two morphs, i.e. mitral and sellate types. Through morphological comparison, they can be identified as\u0000 Tannuolina zhangwentangi\u0000 Qian & Bengtson, 1989. The large mitral and sellate sclerites (about 1 cm) illustrated herein manifest a relatively consistent morphology during the size increasement. The sellate sclerites may contain two sub-types, the larger sellate sclerite with sella on the sellate side and the smaller convex sellate side without sella on either sides. In the original scleritome, the two sub-types of sellate sclerites probably combine as a composite with the duplicatural side of the smaller one attached on the sella area of the large one. For the first time,\u0000 T. zhangwentangi\u0000 has been recovered from the Indian subcontinent, previously unknown outside South China. The middle and upper part of the Hazira Formation exclusively bearing\u0000 T. zhangwentangi\u0000 can directly invite correlation with the\u0000 S. flabelliformis\u0000 –\u0000 T. zhangwentangi\u0000 Assemblage Zone of South China representing the uppermost Cambrian Stage 2. This new palaeontological finds not only signifies the utility of\u0000 T. zhangwentangi\u0000 for intercontinental biostratigraphical correlation, but also suggests that the Terreneuvian SSF biostratigraphy between the Indian subcontinent and South China are quite consistent, comprising of three (at least two) correlative SSF Assemblage Zone (Zone Ⅰ, possible Ⅲ, and Ⅳ of South China). Additionally, our result may also support a relatively close palaeogeographical linkage between these two regions in early Cambrian.\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Advances in the Cambrian Explosion collection available at:\u0000 https://www.lyellcollection.org/topic/collections/advances-in-the-cambrian-explosion\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42217934","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. Paxton, J. Andrews, P. Dennis, A. Marca, C. Holmden
This study focusses on new clumped isotope data from concretionary calcite cements in the Middle Jurassic Valtos Sandstone Formation (Great Estuarine Group) of the Inner Hebrides. Clumped isotopes show that concretion cementation began at 45±6 °C increasing to temperatures in excess of 70 °C before cooling slightly to 57 ± 7 °C at the concretion margin. In the early stages of cementation, calculated δ 18 O FLUID values were ∼ –12‰ VSMOW, identical to an estimate of Paleocene Hebridean meteoric water based on hydrothermal reactions close to Paleocene Igneous Centres. These δ 18 O FLUID values imply that concretion cementation started in the Paleocene probably during the earliest stages of phreato-magmatic effusive igneous activity. As the concretion grew, temperature changes were accompanied by progressively evolving δ 18 O FLUID compositions up to +2.1 ± 1.1‰ VMOW. These evolving δ 18 O FLUID compositions were caused by isotope exchange reactions between 18 O-rich lithologies and hot basinal fluids migrating upward along faults. This fluid flow was driven by progressive crustal loading from the thickening Paleocene lava pile which also caused sandstone compaction. Published radiometric dates that constrain the emplacement time of the Skye Lava Group, and its subsequent rapid erosion, suggest that concretion formation and final compaction was completed in no more than 2.6 myr, far more rapidly than modelled previously. Initial concretion growth that pre-dates development of volcanic topography shows that the strongly negative compositions of Hebridean Paleocene meteoric water are mainly of latitudinal rather than orographic origin. Supplementary material: Clumped isotope data correction and uncertainties, sample details and additional figures is available at https://doi.org/10.6084/m9.figshare.c.6459860
{"title":"Concretionary cementation of a Scottish Middle Jurassic sandstone by hot, Paleocene fluids: a clumped isotope study","authors":"R. Paxton, J. Andrews, P. Dennis, A. Marca, C. Holmden","doi":"10.1144/jgs2022-175","DOIUrl":"https://doi.org/10.1144/jgs2022-175","url":null,"abstract":"\u0000 This study focusses on new clumped isotope data from concretionary calcite cements in the Middle Jurassic Valtos Sandstone Formation (Great Estuarine Group) of the Inner Hebrides. Clumped isotopes show that concretion cementation began at 45±6 °C increasing to temperatures in excess of 70 °C before cooling slightly to 57 ± 7 °C at the concretion margin. In the early stages of cementation, calculated δ\u0000 18\u0000 O\u0000 FLUID\u0000 values were ∼ –12‰ VSMOW, identical to an estimate of Paleocene Hebridean meteoric water based on hydrothermal reactions close to Paleocene Igneous Centres. These δ\u0000 18\u0000 O\u0000 FLUID\u0000 values imply that concretion cementation started in the Paleocene probably during the earliest stages of phreato-magmatic effusive igneous activity. As the concretion grew, temperature changes were accompanied by progressively evolving δ\u0000 18\u0000 O\u0000 FLUID\u0000 compositions up to +2.1 ± 1.1‰ VMOW. These evolving δ\u0000 18\u0000 O\u0000 FLUID\u0000 compositions were caused by isotope exchange reactions between\u0000 18\u0000 O-rich lithologies and hot basinal fluids migrating upward along faults. This fluid flow was driven by progressive crustal loading from the thickening Paleocene lava pile which also caused sandstone compaction. Published radiometric dates that constrain the emplacement time of the Skye Lava Group, and its subsequent rapid erosion, suggest that concretion formation and final compaction was completed in no more than 2.6 myr, far more rapidly than modelled previously. Initial concretion growth that pre-dates development of volcanic topography shows that the strongly negative compositions of Hebridean Paleocene meteoric water are mainly of latitudinal rather than orographic origin.\u0000 \u0000 \u0000 Supplementary material:\u0000 Clumped isotope data correction and uncertainties, sample details and additional figures is available at\u0000 https://doi.org/10.6084/m9.figshare.c.6459860\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49296645","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}
J. Hovikoski, M. Olivarius, J. Bojesen‐Koefoed, S. Piasecki, P. Alsen, M. Fyhn, I. Sharp, M. Bjerager, H. Vosgerau, S. Lindström, C. Bjerrum, J. Ineson
The Upper Jurassic – Lower Cretaceous interval represents a prolonged marine deoxygenation period particularly in the Boreal–Arctic basins, the controlling factors of which remain poorly understood. Two drill cores totaling >450 m cover the Kimmeridgian–Barremian succession in contrasting locations in an evolving half-graben system (basin center and near the footwall crest) in Wollaston Forland, NE Greenland; they provide an exceptional ∼20 myr long window into paleoenvironmental development and changes in redox conditions within a detailed tectonostratigraphic framework. Synthesis of a multidisciplinary dataset including sedimentology, inorganic and previously published organic geochemistry indicates that, despite continuous black mudstone accumulation from the Kimmeridgian to the Ryazanian, sea floor anoxia was intermittent in the Kimmeridgian, whereas more sustained anoxia/euxinia occurred in the middle Volgian – early Ryazanian. Correlation to reported contemporaneous successions along the Greenland margin, indicate that protracted rifting and generation of localized sea-floor topography were among the major drivers both of sea-floor deoxygenation and current funneling and amplification during the Jurassic–Cretaceous transition. Consequently, distribution of seaway current activity and dysoxia, anoxia and euxinia varied spatially, allowing fully oxygenated and anoxic pockets to coexist. Supplementary material: [S1: Facies table, S2: Summary of geochemistry data, S3: Geochemistry raw data, S4: Sedimentological log from Store Koldewey] is available at https://doi.org/10.6084/m9.figshare.c.6442539
{"title":"Late Jurassic – Early Cretaceous marine deoxygenation in Northeast Greenland","authors":"J. Hovikoski, M. Olivarius, J. Bojesen‐Koefoed, S. Piasecki, P. Alsen, M. Fyhn, I. Sharp, M. Bjerager, H. Vosgerau, S. Lindström, C. Bjerrum, J. Ineson","doi":"10.1144/jgs2022-058","DOIUrl":"https://doi.org/10.1144/jgs2022-058","url":null,"abstract":"The Upper Jurassic – Lower Cretaceous interval represents a prolonged marine deoxygenation period particularly in the Boreal–Arctic basins, the controlling factors of which remain poorly understood. Two drill cores totaling >450 m cover the Kimmeridgian–Barremian succession in contrasting locations in an evolving half-graben system (basin center and near the footwall crest) in Wollaston Forland, NE Greenland; they provide an exceptional ∼20 myr long window into paleoenvironmental development and changes in redox conditions within a detailed tectonostratigraphic framework. Synthesis of a multidisciplinary dataset including sedimentology, inorganic and previously published organic geochemistry indicates that, despite continuous black mudstone accumulation from the Kimmeridgian to the Ryazanian, sea floor anoxia was intermittent in the Kimmeridgian, whereas more sustained anoxia/euxinia occurred in the middle Volgian – early Ryazanian. Correlation to reported contemporaneous successions along the Greenland margin, indicate that protracted rifting and generation of localized sea-floor topography were among the major drivers both of sea-floor deoxygenation and current funneling and amplification during the Jurassic–Cretaceous transition. Consequently, distribution of seaway current activity and dysoxia, anoxia and euxinia varied spatially, allowing fully oxygenated and anoxic pockets to coexist.\u0000 \u0000 Supplementary material:\u0000 [S1: Facies table, S2: Summary of geochemistry data, S3: Geochemistry raw data, S4: Sedimentological log from Store Koldewey] is available at\u0000 https://doi.org/10.6084/m9.figshare.c.6442539\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49089935","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.A.G. Utley, R. Holdsworth, G. Blackbourn, E. Dempsey, R. Strachan, K. McCaffrey, A. Morton, A. Bird, R. R. Jones, A. Saßnowski, R. J. Walker
The island of Foula located 25 km SW of Shetland preserves a gently folded, 1.6 km thick sequence of Middle Devonian sandstones spectacularly exposed in kilometre-long cliff sections over 350 m high. These rocks unconformably overlie likely Precambrian-age amphibolite facies basement rocks, intruded by sheeted granites. The onshore succession is similar in age to the nearby Lower Clair Group offshore to the west. New mapping which incorporates use of drone imagery in inaccessible cliff sections uses down-plunge projections to show that growth folding and faulting on Foula were contemporaneous with sedimentation during basin filling. The large-scale structural geometry is consistent with regional constrictional strain due to sinistral transtension associated with movements along the Walls Boundary - Great Glen Fault Zone system during the Middle Devonian. Detrital zircon provenance studies indicate that the Devonian sequences of Foula - and nearby Melby in western Shetland - show similarities with the Clair Group and Orkney successions. We suggest that NE-SW transtensional fold development contemporaneous with regional subsidence may be more widespread than previously realised in the Devonian basins of Scotland. Large, kilometre-scale folds previously interpreted to be related to Permo-Carboniferous inversion may therefore have initiated earlier in the basin evolution than previously realised. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6442552
{"title":"The strike-slip influenced stratigraphic and structural development of the Foula Sandstone Group, Shetland: implications for offshore Devonian basin development in the northern UKCS","authors":"T.A.G. Utley, R. Holdsworth, G. Blackbourn, E. Dempsey, R. Strachan, K. McCaffrey, A. Morton, A. Bird, R. R. Jones, A. Saßnowski, R. J. Walker","doi":"10.1144/jgs2022-148","DOIUrl":"https://doi.org/10.1144/jgs2022-148","url":null,"abstract":"The island of Foula located 25 km SW of Shetland preserves a gently folded, 1.6 km thick sequence of Middle Devonian sandstones spectacularly exposed in kilometre-long cliff sections over 350 m high. These rocks unconformably overlie likely Precambrian-age amphibolite facies basement rocks, intruded by sheeted granites. The onshore succession is similar in age to the nearby Lower Clair Group offshore to the west. New mapping which incorporates use of drone imagery in inaccessible cliff sections uses down-plunge projections to show that growth folding and faulting on Foula were contemporaneous with sedimentation during basin filling. The large-scale structural geometry is consistent with regional constrictional strain due to sinistral transtension associated with movements along the Walls Boundary - Great Glen Fault Zone system during the Middle Devonian. Detrital zircon provenance studies indicate that the Devonian sequences of Foula - and nearby Melby in western Shetland - show similarities with the Clair Group and Orkney successions. We suggest that NE-SW transtensional fold development contemporaneous with regional subsidence may be more widespread than previously realised in the Devonian basins of Scotland. Large, kilometre-scale folds previously interpreted to be related to Permo-Carboniferous inversion may therefore have initiated earlier in the basin evolution than previously realised.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6442552\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47220567","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}
Kai Weng, Yunpeng Dong, Liuqing Jiang, Zhongping Ma, Shuangshuang Wang, Bo Chen
The Chinese Altai features abundant granitoids, which can be used to reconstruct the tectonic evolution of the orogen. Here, petrological, geochronological, geochemical and isotopic analyses have been conducted on several representative granitoids from the Altai region. U‒Pb dating revealed ages of 444±3 Ma for gneissic granites, 406±8 Ma for syenogranites, 280±6 Ma for diorites, 278±3 Ma for two-mica monzonitic granites, and 269±3 Ma for muscovite granites. Ordovician gneissic granites have I-type arc-related element characteristics and are derived from volcanic magmas extracted from the mantle wedge metasomatized by subducted sediment in a continental arc. Devonian syenogranites show I-type arc and within-plate granite dual geochemical signatures, suggesting derivation from volcanic magmas extracted from the lithospheric mantle metasomatized by subducted fluid/melt in a back-arc basin. Permian diorites are Mg-diorites derived from a mixed magma source involving residual subducted basaltic oceanic crust and lithospheric mantle; two-mica monzonitic granites are S-type granites originating from crustal recycling of sedimentary rocks; muscovite granites are leucogranites resulting from the anatexis of ancient metasedimentary rocks. Their tectonic setting is syn/postcollision. Combining with previous data, we propose that the Chinese Altai experienced middle–late Ordovician continental arc magmatism, early–middle Devonian back-arc extension, and early–middle Permian arc–arc syn/postcollision. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6420236
{"title":"Geochemistry, geochronology and Sr–Nd–Hf isotopes of Paleozoic granitoids in the Chinese Altai, NW China: Constraints on the conversion from subduction–accretion to syn/post-collision","authors":"Kai Weng, Yunpeng Dong, Liuqing Jiang, Zhongping Ma, Shuangshuang Wang, Bo Chen","doi":"10.1144/jgs2022-150","DOIUrl":"https://doi.org/10.1144/jgs2022-150","url":null,"abstract":"The Chinese Altai features abundant granitoids, which can be used to reconstruct the tectonic evolution of the orogen. Here, petrological, geochronological, geochemical and isotopic analyses have been conducted on several representative granitoids from the Altai region. U‒Pb dating revealed ages of 444±3 Ma for gneissic granites, 406±8 Ma for syenogranites, 280±6 Ma for diorites, 278±3 Ma for two-mica monzonitic granites, and 269±3 Ma for muscovite granites. Ordovician gneissic granites have I-type arc-related element characteristics and are derived from volcanic magmas extracted from the mantle wedge metasomatized by subducted sediment in a continental arc. Devonian syenogranites show I-type arc and within-plate granite dual geochemical signatures, suggesting derivation from volcanic magmas extracted from the lithospheric mantle metasomatized by subducted fluid/melt in a back-arc basin. Permian diorites are Mg-diorites derived from a mixed magma source involving residual subducted basaltic oceanic crust and lithospheric mantle; two-mica monzonitic granites are S-type granites originating from crustal recycling of sedimentary rocks; muscovite granites are leucogranites resulting from the anatexis of ancient metasedimentary rocks. Their tectonic setting is syn/postcollision. Combining with previous data, we propose that the Chinese Altai experienced middle–late Ordovician continental arc magmatism, early–middle Devonian back-arc extension, and early–middle Permian arc–arc syn/postcollision.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6420236\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49377983","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 metamorphic core of the Himalayan orogen, once viewed as a structurally contiguous unit, is now known to be divided into multiple packages by a series of structural discontinuities. While these structures have been identified based on distinct metamorphic and kinematic histories of the bounding packages, the number of structures identified across the exhumed former midcrustal core varies throughout the Himalaya. The scarcity of field evidence for these structures not only impedes their identification, but also hinders our understanding of their role in the development of the Himalaya. This study characterizes the metamorphic and geochronological history of garnet, sillimanite, and kyanite bearing gneisses in Makalu-Arun region, Nepal. Phase equilibria modelling coupled with monazite U/Th-Pb petrochronology delineates four rock packages with distinct metamorphic histories separated by at least three thrust-sense structures. The earliest thrust activity and subsequent in-sequence thrusting lasted from ca. 23-14 Ma, with initiation of late out-of-sequence thrust after ca.14 Ma. These results are consistent with foreland thrust migration and juxtaposition consistent with models that incorporate underplating, metamorphism and exhumation of midcrustal rocks during orogenesis. Moreover, the demonstrated complex evolution of the metamorphic core in Makalu region is inconsistent with models that incorporate singular, orogenic-wide structures in the Himalaya. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6420244
{"title":"Tectonometamorphic evolution of the Himalayan metamorphic core in the Makalu-Arun region, eastern Nepal","authors":"Iva Lihter, K. Larson, S. Shrestha, J. Cottle","doi":"10.1144/jgs2022-056","DOIUrl":"https://doi.org/10.1144/jgs2022-056","url":null,"abstract":"The metamorphic core of the Himalayan orogen, once viewed as a structurally contiguous unit, is now known to be divided into multiple packages by a series of structural discontinuities. While these structures have been identified based on distinct metamorphic and kinematic histories of the bounding packages, the number of structures identified across the exhumed former midcrustal core varies throughout the Himalaya. The scarcity of field evidence for these structures not only impedes their identification, but also hinders our understanding of their role in the development of the Himalaya. This study characterizes the metamorphic and geochronological history of garnet, sillimanite, and kyanite bearing gneisses in Makalu-Arun region, Nepal. Phase equilibria modelling coupled with monazite U/Th-Pb petrochronology delineates four rock packages with distinct metamorphic histories separated by at least three thrust-sense structures. The earliest thrust activity and subsequent in-sequence thrusting lasted from ca. 23-14 Ma, with initiation of late out-of-sequence thrust after ca.14 Ma. These results are consistent with foreland thrust migration and juxtaposition consistent with models that incorporate underplating, metamorphism and exhumation of midcrustal rocks during orogenesis. Moreover, the demonstrated complex evolution of the metamorphic core in Makalu region is inconsistent with models that incorporate singular, orogenic-wide structures in the Himalaya.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6420244\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44902133","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}
B. Solís-Alulima, J. Abati, A. López-Carmona, G. Gutiérrez-Alonso, J. Fernández-Suárez, D. Stockli
This study presents Lu–Hf data on detrital zircon grains from the Lower Paleozoic metasedimentary successions of the Sierra Albarrana Domain (SW Iberian Massif). We provide new information about their origin, record of continental crustal evolution, and geological affinity. Previous detrital zircon U–Pb data in this terrane reveal two main age populations, with age peaks at c. 595 Ma and c. 1.90 Ga. The Ediacaran events are interpreted to represent a magmatic arc with input of juvenile magmas intruding into the Eburnean basement of Gondwana, and probably mixing with it. The different evolutionary stages of the arc were probably linked to the Cadomian Orogeny during Neoproterozoic-earliest Cambrian times. The Paleoproterozoic zircon population corresponds to the Eburnean orogeny. The magmas derived from an Eburnean depleted mantle partly intruded an older basement, leading to an incipient mixing process. εHf isotopic compositions indicate a possible affinity with the Central Iberian Zone suggesting a common geological setting during Ediacaran-Cambrian times, but different during the Paleoproterozoic. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6420215
{"title":"Hf isotopes in detrital zircon grains of the Sierra Albarrana Domain (SW Iberian Massif): Eburnean vs. Archaean basement signatures","authors":"B. Solís-Alulima, J. Abati, A. López-Carmona, G. Gutiérrez-Alonso, J. Fernández-Suárez, D. Stockli","doi":"10.1144/jgs2022-151","DOIUrl":"https://doi.org/10.1144/jgs2022-151","url":null,"abstract":"This study presents Lu–Hf data on detrital zircon grains from the Lower Paleozoic metasedimentary successions of the Sierra Albarrana Domain (SW Iberian Massif). We provide new information about their origin, record of continental crustal evolution, and geological affinity. Previous detrital zircon U–Pb data in this terrane reveal two main age populations, with age peaks at c. 595 Ma and c. 1.90 Ga. The Ediacaran events are interpreted to represent a magmatic arc with input of juvenile magmas intruding into the Eburnean basement of Gondwana, and probably mixing with it. The different evolutionary stages of the arc were probably linked to the Cadomian Orogeny during Neoproterozoic-earliest Cambrian times. The Paleoproterozoic zircon population corresponds to the Eburnean orogeny. The magmas derived from an Eburnean depleted mantle partly intruded an older basement, leading to an incipient mixing process. εHf isotopic compositions indicate a possible affinity with the Central Iberian Zone suggesting a common geological setting during Ediacaran-Cambrian times, but different during the Paleoproterozoic.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6420215\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42639546","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}
J. Greenman, Angelo dos Santos, M. Patzke, T. Gibson, A. Ielpi, G. Halverson
The Bylot basins of northeastern Canada and northwestern Greenland comprise the Borden, Aston-Hunting, Fury and Hecla, and Thule basins. This system of late Mesoproterozoic (ca. 1.27– 1.0 Ga) sedimentary basins preserves an important record of present-day northeastern Laurentia coincident with the emplacement of the Mackenzie Large Igneous Province, the Shawinigan and Ottawan phases of the Grenville orogeny, and the development of the Midcontinent Rift. However, establishing correlations between the sedimentary successions of the Bylot basins has been hindered by the absence of robust chronostratigraphic constraints. As a result, the degree to which these basins were interconnected, whether they share a common tectonostratigraphic history, and how their sedimentary patterns relate to regional tectonic events remain open questions. Recent Re-Os geochronology from organic-rich strata has yielded depositional ages from the Borden (1048 Ma and 1046 Ma) and Fury and Hecla (1087 Ma) basins, which we integrate with existing models for the depositional history of these basins to derive three tectonostratigraphic assemblages from the Bylot basins. We project our refined tectonostratigraphic framework for the Borden and Fury and Hecla successions to Greenland in order to establish a testable hypothesis for how the Thule Supergroup fits into this tectonostratigraphic picture.
{"title":"A tectonostratigraphic framework for the late Mesoproterozoic Bylot basins of Laurentia","authors":"J. Greenman, Angelo dos Santos, M. Patzke, T. Gibson, A. Ielpi, G. Halverson","doi":"10.1144/jgs2022-174","DOIUrl":"https://doi.org/10.1144/jgs2022-174","url":null,"abstract":"The Bylot basins of northeastern Canada and northwestern Greenland comprise the Borden, Aston-Hunting, Fury and Hecla, and Thule basins. This system of late Mesoproterozoic (ca. 1.27– 1.0 Ga) sedimentary basins preserves an important record of present-day northeastern Laurentia coincident with the emplacement of the Mackenzie Large Igneous Province, the Shawinigan and Ottawan phases of the Grenville orogeny, and the development of the Midcontinent Rift. However, establishing correlations between the sedimentary successions of the Bylot basins has been hindered by the absence of robust chronostratigraphic constraints. As a result, the degree to which these basins were interconnected, whether they share a common tectonostratigraphic history, and how their sedimentary patterns relate to regional tectonic events remain open questions. Recent Re-Os geochronology from organic-rich strata has yielded depositional ages from the Borden (1048 Ma and 1046 Ma) and Fury and Hecla (1087 Ma) basins, which we integrate with existing models for the depositional history of these basins to derive three tectonostratigraphic assemblages from the Bylot basins. We project our refined tectonostratigraphic framework for the Borden and Fury and Hecla successions to Greenland in order to establish a testable hypothesis for how the Thule Supergroup fits into this tectonostratigraphic picture.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49486182","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}
N. D'Mello, G. Zellmer, G. Kereszturi, T. Ubide, J. Procter, R. Stewart
The prevalence of antecrysts in arc volcanic rocks is widely accepted, yet the origin of their carrier melts remains debated. Crystal cargo in lava flows from Taranaki volcano, New Zealand, is dominated by plagioclase, clinopyroxene, and amphibole. Except for some crystal rims, mineral phases are in disequilibrium with the melt they are entrained in. Major element chemistry reveals an almost complete compositional overlap between the crystals in the lava and those in xenoliths. The large volume fraction of crystals (35–55 vol%) exerts a strong control on whole-rock compositions, reducing silica by 5–11 wt% compared to the carrier melt. Yet there is no clear relationship between mineral proportion and bulk rock compositions. Our data are inconsistent with extensive fractional crystallization, commonly invoked as a driver of magma evolution towards silica-rich compositions. Instead, high-temperature, aphyric carrier melts with varied compositions (55–68 SiO 2 wt%) entrain crystal cargo while ascending through colder, low-silica rocks. Thus, some primary melts at Taranaki volcano are significantly more silica-rich than arc basalts commonly invoked as parental magmas. Further, thermometric and hygrometric constraints preclude a deep crustal hot zone for the source of these melts, which we argue are of subcrustal origin. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6406813
{"title":"Crystal entrainment from cool, low-silica rocks into hot, high-silica melts: diverse primary melt compositions at Taranaki volcano, New Zealand","authors":"N. D'Mello, G. Zellmer, G. Kereszturi, T. Ubide, J. Procter, R. Stewart","doi":"10.1144/jgs2022-036","DOIUrl":"https://doi.org/10.1144/jgs2022-036","url":null,"abstract":"\u0000 The prevalence of antecrysts in arc volcanic rocks is widely accepted, yet the origin of their carrier melts remains debated. Crystal cargo in lava flows from Taranaki volcano, New Zealand, is dominated by plagioclase, clinopyroxene, and amphibole. Except for some crystal rims, mineral phases are in disequilibrium with the melt they are entrained in. Major element chemistry reveals an almost complete compositional overlap between the crystals in the lava and those in xenoliths. The large volume fraction of crystals (35–55 vol%) exerts a strong control on whole-rock compositions, reducing silica by 5–11 wt% compared to the carrier melt. Yet there is no clear relationship between mineral proportion and bulk rock compositions. Our data are inconsistent with extensive fractional crystallization, commonly invoked as a driver of magma evolution towards silica-rich compositions. Instead, high-temperature, aphyric carrier melts with varied compositions (55–68 SiO\u0000 2\u0000 wt%) entrain crystal cargo while ascending through colder, low-silica rocks. Thus, some primary melts at Taranaki volcano are significantly more silica-rich than arc basalts commonly invoked as parental magmas. Further, thermometric and hygrometric constraints preclude a deep crustal hot zone for the source of these melts, which we argue are of subcrustal origin.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6406813\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42732052","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. Grenne, D. Gasser, R. Bøe, F. Corfu, Ø. Skår, T. Slagstad
The Hølonda area of the central Scandinavian Caledonides is a key for models of the Caledonian orogen due to its Ordovician fauna of Laurentian affinity, now stranded on the Baltic side during opening of the North Atlantic. Here, we present a revised stratigraphic and tectonomagmatic model based on remapping, sedimentology, igneous geochemistry, Nd and Sr isotopes, and geochronology. The Hølonda Group (c. 470–461 Ma) reflects a transition from subaerial and shallow-marine deposition on a continental shelf, to deeper-water sedimentation along a subsiding slope. Adakitic and MORB-type magmatism at c. 468 Ma was succeeded by benmoreitic–rhyolitic, shoshonitic, calc-alkaline, and ultra-alkaline volcanism at c. 467–465 Ma. The complex magmatism followed arc–continent collision along a microcontinent outboard of Laurentia, associated with subduction polarity flip and slab rollback. This led to rifting and opening of a wide basin and its adjoining shelf on thickened orogenic lithosphere. Associated mantle upwelling and partial melting of depleted and variably metasomatized mantle occurred in a tectonomagmatic setting comparable to that of the central Mediterranean. The Hølonda–Ilfjellet setting is unique along the Caledonian–Appalachian orogen, possibly reflecting interaction with Laurentia-derived continental terranes at the northeastern end of the Taconian–Grampian orogenic tract. Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle Supplementary material: https://doi.org/10.6084/m9.figshare.c.6368922
{"title":"Mid-Ordovician stratigraphy and volcanism in the Hølonda area, Scandinavian Caledonides: complex tectonomagmatic development following arc–continent collision near the Laurentian margin of Iapetus","authors":"T. Grenne, D. Gasser, R. Bøe, F. Corfu, Ø. Skår, T. Slagstad","doi":"10.1144/jgs2022-133","DOIUrl":"https://doi.org/10.1144/jgs2022-133","url":null,"abstract":"The Hølonda area of the central Scandinavian Caledonides is a key for models of the Caledonian orogen due to its Ordovician fauna of Laurentian affinity, now stranded on the Baltic side during opening of the North Atlantic. Here, we present a revised stratigraphic and tectonomagmatic model based on remapping, sedimentology, igneous geochemistry, Nd and Sr isotopes, and geochronology. The Hølonda Group (c. 470–461 Ma) reflects a transition from subaerial and shallow-marine deposition on a continental shelf, to deeper-water sedimentation along a subsiding slope. Adakitic and MORB-type magmatism at c. 468 Ma was succeeded by benmoreitic–rhyolitic, shoshonitic, calc-alkaline, and ultra-alkaline volcanism at c. 467–465 Ma. The complex magmatism followed arc–continent collision along a microcontinent outboard of Laurentia, associated with subduction polarity flip and slab rollback. This led to rifting and opening of a wide basin and its adjoining shelf on thickened orogenic lithosphere. Associated mantle upwelling and partial melting of depleted and variably metasomatized mantle occurred in a tectonomagmatic setting comparable to that of the central Mediterranean. The Hølonda–Ilfjellet setting is unique along the Caledonian–Appalachian orogen, possibly reflecting interaction with Laurentia-derived continental terranes at the northeastern end of the Taconian–Grampian orogenic tract.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Caledonian Wilson cycle collection available at:\u0000 https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6368922\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49188377","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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