Journal of the Geological Society最新文献

{"title":"On the anatomy and structural control of a dyke swarm that fed caldera-forming ignimbrite eruptions","authors":"F. Tomek, Irena Olšanská, J. Trubač, J. Černý, Jan Rejšek, L. Ackerman","doi":"10.1144/jgs2022-119","DOIUrl":"https://doi.org/10.1144/jgs2022-119","url":null,"abstract":"The evolution of eruptive vents related to calderas is not fully understood. We focus on a structural, rock-magnetic, and geochemical investigation of a ∼314 Ma rhyolite dyke swarm associated with the late-orogenic Altenberg–Teplice Caldera, Bohemian Massif, eastern Variscan belt. The whole-rock major element, trace element, and Nd–Pb isotope geochemistry along with the published U-Pb zircon geochronology link the extra-caldera dyke swarm with intra-caldera ignimbrites. The magnetic fabrics determined using the anisotropy of magnetic susceptibility are interpreted to record a continuum from magma ascent, emplacement, and eruption during sinistral shearing. The latter evidences an interplay with regional tectonics associated with the activity of crustal-scale shear zones. The sinistral kinematics and strike of the dyke swarm, the elongation of caldera intrusive units, and the kinematics of major caldera faults are consistent with the dextral Riedel shear system, where the dykes correspond to antithetic Ŕ/X-shears. Such a kinematic configuration implies that the maximum and minimum principal stresses were oriented roughly north-south and east-west, respectively. The relation between the stress field with respect to the caldera elongation and orientation is not typical. We suggest that a pre-existing mutually perpendicular set of cross-cutting structural lineaments largely controlled the magma chamber and caldera formation.\u0000 \u0000 Supplementary material:\u0000 The whole-rock major, trace element and isotope geochemical tables, magnetic fabrics source data, and methodology details are available at\u0000 https://doi.org/10.6084/m9.figshare.c.6715893\u0000 .\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43204038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Different effects of serpentinite-derived and slab-derived fluids on arc magmatism in the Chinese Eastern Tianshan: Evidence from Mg–B isotopic systematics","authors":"L. Du, Yunying Zhang, Hongli Zhu, Zhao-Yu Zhang, Y. An, C. Yuan, Zongying Huang, Xu-Ping Li, X. Long","doi":"10.1144/jgs2023-011","DOIUrl":"https://doi.org/10.1144/jgs2023-011","url":null,"abstract":"\u0000 Fluids are important media for elemental cycling in subduction zones, but the compositions of such fluids remain obscure, especially those derived from dehydration of serpentinite. To better understand the role of subduction zone fluids in arc magmatism from the Chinese Eastern Tianshan (CET), we present Mg and B isotopic data for the arc diorites (e.g., Kalatage and Nanshankou). Our results show that the Kalatage diorites have higher\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg (−0.23 to −0.13‰) and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B (−0.04 to +1.08‰) values than the corresponding mantle values, while the Nanshankou diorites display relatively lower\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg (−0.26 to −0.19‰) and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B (−10.7 to −2.97‰) values. Since high-temperature magmatic and post-magmatic processes have limited effects on Mg and B isotope fractionation of our samples, their distinct Mg–B isotopic signatures inherited from the mantle sources should be caused by subduction-related metasomatism. Because neither altered oceanic crust (AOC) directly melting nor the incorporation of subducted sediments could induce significant Mg–B isotope fractionation in these rocks, we infer that their variable\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B values were probably associated with subduction fluids that were derived from different sources. Specifically, dehydrated fluids from serpentinites possess both high\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B values, which resulted in the heavy Mg–B isotopic compositions of the Kalatage diorites, whereas mantle metasomatized by fluids from AOC and subducted sediments were responsible for the Nanshankou rocks with relatively low\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 26\u0000 Mg and\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 11\u0000 B values. Taking into account the different effects of serpentinite-derived and slab-derived fluids in the formation of arc magmatism, subduction zone fluids can be probably an important process in changing the Mg–B isotope composition of mantle sources.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6702686\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47136360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Older than you think: Using U-Pb calcite geochronology to better constrain basin-bounding fault reactivation, Inner Moray Firth Basin, W North Sea","authors":"A. Tămaș, R. Holdsworth, D. M. Tămaș, E. Dempsey, K. Hardman, A. Bird, N. Roberts, J. Lee, J. Underhill, D. McCarthy, K. McCaffrey, D. Selby","doi":"10.1144/jgs2022-166","DOIUrl":"https://doi.org/10.1144/jgs2022-166","url":null,"abstract":"Like many rift basins worldwide, the Inner Moray Firth Basin (IMFB) is bounded by major reactivated fault zones including the Helmsdale and Great Glen faults (HF, GGF). The Jurassic successions exposed onshore close to these faults at Helmsdale and Shandwick preserve folding, calcite veining and minor faulting consistent with sinistral (HF) and dextral (GGF) transtensional movements, respectively. This deformation has widely been attributed to Cenozoic post-rift fault reactivation.\u0000 Onshore fieldwork and U-Pb calcite geochronology of five vein samples associated with transtensional movements along the HF and a splay of the GGF show that faulting occurred during the Early Cretaceous (c. 128-115 Ma, Barremian-Aptian), whilst the HF preserves evidence for earlier Late Jurassic sinistral movements (c. 159 Ma, Oxfordian). This demonstrates that both basin-bounding faults were substantially reactivated during the episodic NW-SE-directed Mesozoic rifting that formed the IMFB. Whilst there is good evidence for Cenozoic reactivation of the GGF offshore, the extent of such deformation along the north coast of the IMFB remains uncertain. Our findings also illustrate the importance of oblique slip reactivation processes in shaping the evolution of continental rift basins given that this deformation style may not be immediately obvious in interpretations of offshore seismic reflection data.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6708518\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47961492","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Xenotime reveals Caledonian hydrothermal overprint on Neoproterozoic Cu mineralization, East Greenland","authors":"H. Olierook, Kelsey Crook, Penelope Sinclair, D. Fougerouse, Cilva Joseph, C. Kirkland, A. Kennedy, Hao Gao, N. Evans, B. McDonald, Raiza R. Quintero, Anusha Shantha Kumara, Graeme Cameron, Ben Walsh, M. Roberts, B. McInnes","doi":"10.1144/jgs2022-141","DOIUrl":"https://doi.org/10.1144/jgs2022-141","url":null,"abstract":"Constraining the age of many types of ore deposits remains challenging due to the lack of radiogenic isotopes incorporated into common ore-forming minerals. The timing of pre-Caledonian-hosted Cu mineralization along the entire ∼1200 km-long East Greenland Caledonides remains virtually unknown, hampering our knowledge of ore deposit timing and genesis in a frontier exploration region. Here, automated mineral analysis of a series of nodular, disseminated and vein-hosted Cu- ± Pb-mineralized metasedimentary rocks in central East Greenland reveals detrital zircon and hydrothermal xenotime, both amenable to U-Pb geochronology. Detrital zircon geochronology of a co-deposited quartzite reveals an age distribution highly similar to the Cryogenian (∼700 Ma) upper Eleanore Bay Supergroup. Hydrothermal xenotime U-Pb analyses adjacent to nodular and disseminated chalcocite across three proximal samples have variable amounts of common Pb that together yield a well-defined single discordia with a lower concordia intercept of 438 ± 13 Ma (2σ). This age is within uncertainty of the onset of Caledonian regional metamorphism and granitoid production and clearly post-dates deposition of the upper Eleanore Bay Supergroup by several hundred Myr. Considering a published chalcocite Pb-Pb isochron age of 680 ± 65 Ma, the hydrothermal xenotime U-Pb ages imply that Caledonian-driven fluid activity, sourced from metamorphic reactions or from granitoids, remobilized diagenetic Cu and Pb mineralization. Chalcocite Pb-Pb isotopes show that dissolved and reprecipitated portions are volumetrically minor, radiogenic and Pb-poor, implying that fluids stripped most of the Pb from the system. Thus, it is likely that remobilization was localized on the grain scale, although some Cu and Pb was transported away from diagenetic sites, perhaps into veins. Whilst Caledonian metamorphism and granitoid emplacement is widespread in central East Greenland, the full extent of their roles in upgrading Cu mineralization remains to be ascertained.\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.6675384\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42581185","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}

{"title":"3D seismic reflection evidence for lower crustal intrusions beneath the Faroe-Shetland Basin, NE Atlantic Margin","authors":"Lucinda K. Layfield, N. Schofield, D. Watson, S. Holford, D. Jolley, Ben A. Kilhams, D. Muirhead, A. Roberts, A. Alvey, Alex Ellwood, M. Widdowson","doi":"10.1144/jgs2022-172","DOIUrl":"https://doi.org/10.1144/jgs2022-172","url":null,"abstract":"\u0000 Lower crustal intrusion is considered a common process along volcanic or magma-rich passive margins, including the NE Atlantic Margin, where it is considered to have occurred during phases of Paleogene magmatism, prior to and during continental break-up between NW Europe and Greenland. Evidence of Paleogene magmatism is prevalent throughout the sub-basins of the Faroe-Shetland Basin (FSB) as extensive lava flows and pervasive suites of igneous intrusions. However, in contrast to other areas located along the NE Atlantic Margin, no lower crustal reflectivity indicative of lower crustal intrusions has been documented beneath the FSB. The nearest documentation of lower crustal reflectivity and interpretation of lower crustal intrusions to the FSB is NW of the Fugloy Ridge, beneath the Norwegian Basin of the Faroese sector. Despite this, the addition of magma within the lower crust and/or at the Mohorovičić discontinuity is thought to have played a role regarding Paleogene uplift and the subsequent deposition of Paleocene-Eocene sequences. Advances in sub-basalt seismic acquisition and processing have made significant improvements in facilitating the imaging of deep crustal structures along the NE Atlantic Margin. This study uses broadband 3D seismic reflection data to map a series of deep (\u0000 c.\u0000 14 to 20 km depth) high-amplitude reflections which may represent igneous intrusions within the lower crust beneath the central-northern Corona Ridge. We estimate that the cumulative thicknesses of the reflections may be over 5 km in places, which is consistent with published values of magmatic underplating within the region based on geochemical and petrological data. We also estimate that the total volume of lower crustal high-amplitude reflections within the 3D dataset may be over 2000 km\u0000 3\u0000 . 2D gravity modelling of a seismic line located along the central-northern Corona Ridge supports the interpretation of lower crustal intrusions beneath the central-northern Corona Ridge. This study provides evidence of a potential mechanism for Paleogene uplift within the region. If uplift occurred as a result of lower crustal intrusions emplaced within the crust during the Paleogene, based on previous work, we estimate that around 300 m of uplift may have been generated within the Corona Ridge area.\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44812735","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}

{"title":"Multiple stages of continental rifting in Eastern Peninsular Malaysia: New insights from Jurassic–Cretaceous granitoids","authors":"Xin Qian, Tianxing Bai, Yongqi Yu, K. A. Mustapha, Thomas C. Sheldrick, Chengshi Gan, Yuejun Wang","doi":"10.1144/jgs2023-025","DOIUrl":"https://doi.org/10.1144/jgs2023-025","url":null,"abstract":"\u0000 Mesozoic granitoids in Peninsular Malaysia provide crucial information on the temporal-spatial relationship between the Tethyan and Paleo-Pacific domains. This paper presents new ages and geochemical data for the newly identified Jurassic–Cretaceous granites and meta-granites in East Malaya. These granitoids can be divided into three groups. Group 1 high-K calc-alkaline granites and granodiorites (171–162 Ma) have variable\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Nd\u0000 (t) values of −7.4–+0.5, zircon\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Hf\u0000 (t) values of −7.4–+8.6, and high initial ratios for\u0000 206\u0000 Pb/\u0000 204\u0000 Pb (20.04–20.65),\u0000 207\u0000 Pb/\u0000 204\u0000 Pb (15.73–15.7) and\u0000 208\u0000 Pb/\u0000 204\u0000 Pb (39.80–40.20). These samples were probably derived from the metasedimentary rocks with a juvenile mafic component. Despite Group 2 granite porphyries (∼131 Ma) with A-type affinities and Group 3 granitic gneisses (∼130 Ma) with I-type affinities share similar\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Nd\u0000 (t) values (−5.5–−7.2), zircon\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Hf\u0000 (t) values (−10.1–+6.5), and initial ratios for\u0000 206\u0000 Pb/\u0000 204\u0000 Pb (18.81–19.02),\u0000 207\u0000 Pb/\u0000 204\u0000 Pb (15.71–15.77) and\u0000 208\u0000 Pb/\u0000 204\u0000 Pb (38.95–39.95). Although Group 2 and 3 samples were derived from an “ancient” meta-mafic source region, Group 2 has evidence for the involvement of a juvenile mafic component. All these granitoids are akin to the Permian–Triassic igneous rocks in East Malaya. The Jurassic–Cretaceous igneous rocks in Eastern Peninsular Malaysia were formed during multiple stages of continental rifting in response to pulses of the Paleo-Pacific slab rollback rather than from Tethyan evolutionary processes.\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at:\u0000 https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6689085\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49299512","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}

{"title":"Silurian to Early Devonian tectonic evolution of the southeastern Qilian Orogen inferred from zircon U–Pb dating and geochemistry of intrusive rocks","authors":"Xiyao Li, San-zhong Li, Sheng‐yao Yu, Yong‐jiang Liu, Zhen Qin, Zeng-Bao Huang, Qing Lu","doi":"10.1144/jgs2022-162","DOIUrl":"https://doi.org/10.1144/jgs2022-162","url":null,"abstract":"\u0000 Early to mid-Paleozoic tectono-thermal events in the Qilian Orogen developed during the closure of the Proto-Tethys Ocean and the convergence of microcontinents in the periphery of East Gondwana. In this paper, we present geochronological, geochemical, and Sr-Nd-Hf isotopic data for the granitoid rocks and mafic dykes in southeastern Qilian Orogen. The Liwan (440 Ma), Shixia (434 Ma), and Huchuan (429 Ma) granitoid rocks have metaluminous to weakly peraluminous features, with whole-rock\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Nd\u0000 (t) values of 1.1 to 1.6, -4.2 to -4.4, and -2.6 to 1.1, and zircon\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Hf\u0000 (t) values of 0 to 8.9, -6.6 to 1.6, and -4.6 to 2.2, respectively. Geochemical data suggest that the Liwan, Shixia, and Huchuan granitoids are derived from partial melting of the Proterozoic basement with an addition of juvenile material, a felsic crustal basement, and a mafic crustal material, respectively. The Zhangjiayuan mafic dykes (403 Ma) are high-K to shoshonitic with whole-rock\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Nd\u0000 (t) (-1.1 to -0.9) and zircon\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Hf\u0000 (t) values (-0.9 to 13.3), derived from an enriched lithospheric mantle. We suggest that these Silurian–Early Devonian intrusive rocks were formed via a complex series of events involving arc-related subduction followed by slab-tearing to post-collisional processes during the Silurian and subsequent lithospheric extension in the Early Devonian.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6693575\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46515078","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}

{"title":"Magmatic arc evolution during the tectonic closure of the Rocas Verdes basin: insights from Cretaceous-earliest Paleocene intrusive rocks of Navarino Island (55°S), Fuegian Andes","authors":"R. Velásquez, J. Bastías, E. Salazar, F. Poblete, M. G. Guillot, D. Chew, M. Peña, Felipe Tapia, Adán Ramirez, Foteini Drakou","doi":"10.1144/jgs2022-163","DOIUrl":"https://doi.org/10.1144/jgs2022-163","url":null,"abstract":"\u0000 Navarino Island is located in the southernmost part of the Fuegian Andes, south of the Beagle Channel. It geological record documents the complex tectonic history of Tierra del Fuego that includes the opening and closure of the Rocas Verdes basin, Cordillera arc collision and subsequent subduction processes. The geology of the island is mostly comprised of the Cretaceous Yahgán Formation, a marine meta-sedimentary sequence, which is intruded by diverse plutons that are mostly exposed on the northwestern tip of the island. We herein present a new dataset that shows the presence of three Cretaceous-earliest Paleocene magmatic suites of active margin magmatism emplaced during the early stage of the Fuegian Andes, which are referred to as (i) the Dientes de Navarino Microdioritic Sills, a suite of pre-tectonic microdioritic sills that formed during ∼101-97 Ma; (ii) the Castores Plutonic Complex, a series of pre- to syn-tectonic gabbroic to tonalitic plutons emplaced during ∼90-87 Ma and (iii) the Samantha Monzonites, a suite of isolated monzonitic to monzodioritic post-tectonic plutons that formed at ∼66-65 Ma. These distinct magmatic episodes are recognised by field observations, geological mapping, petrography and whole-rock geochemistry integrated with amphibole and biotite\u0000 40\u0000 Ar/\u0000 39\u0000 Ar and U-Pb zircon LA-ICP-MS geochronology. The geochemical compositions of these rocks are consistent with a continental arc setting that formed during the interval ∼101-65 Ma. While the three pulses spatially overlap in Navarino Island, the arc magmatism shows a migration (or expansion) throughout the Late Cretaceous. The locus of the arc then migrates at ∼68-66 Ma towards the southwest. We suggest that this trench-ward migration at ∼68-66 Ma may be associated with a change in the subduction angle. The three Cretaceous- earliest Paleocene plutonic pulses recorded in Navarino Island formed during the early stages of development of the Fuegian Andes, and are pre-, syn-and post-tectonic with respect to a major compressional event caused by the collision and obduction of the back-arc Rocas Verdes oceanic floor.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6675416\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43946679","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}

{"title":"Early Neoproterozoic magmatism and Caledonian metamorphism recorded by the Mårma Terrane, Seve Nappe Complex, northern Swedish Caledonides","authors":"R. Callegari, K. Kośmińska, C. Barnes, I. Klonowska, A. Barker, S. Rousku, E. Nääs, E. Kooijman, P. Witt-Nilsson, J. Majka","doi":"10.1144/jgs2022-092","DOIUrl":"https://doi.org/10.1144/jgs2022-092","url":null,"abstract":"Petrology, geochronology, and bulk rock chemistry are combined to investigate the early Neoproterozoic magmatism and Cambrian-Ordovician metamorphism in the northern Swedish Caledonides. This includes several lithologies of the Mårma terrane in the Seve Nappe Complex exposed in the Kebnekaise region. U–Pb zircon geochronology yielded crystallization ages of 835 ± 8 Ma for a mylonitic orthogneiss, 864 ± 3 Ma for the Vistas Granite and 840 ± 7 Ma for a related granitic dyke. While a gabbro and granodiorite intrusions gave U–Pb zircon crystallization ages of 856 ± 3 Ma and 850 ± 1 Ma, respectively. U–Pb monazite dating of the mylonitic orthogneiss gave an upper intercept age of 841 ± 7 Ma and a lower intercept age of 443 ± 20 Ma. Pressure-temperature estimates derived for the mylonitic orthogneiss reveal metamorphic peak-pressure and peak-temperature of 10.5–11.75 kbar and 550–610 °C and 7.4–8.1 kbar at 615–675 ℃, respectively. Metamorphic pressure-temperature estimates for the Vistas Granite yield 6.5–7.5 kbar at 600–625 ℃. Whole rock chemistry coupled with U–Pb geochronology indicate that bimodal magmatism was related to attempted rifting of Rodinia between 870-840 Ma.\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.6675075\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45747730","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}

{"title":"Tectonic evolution of a Palaeoproterozoic diffuse cryptic suture zone in northern Fennoscandia and the correlation of northern Fennoscandia and southern Greenland","authors":"R. Lahtinen, J. Köykkä, M. Kurhila","doi":"10.1144/jgs2023-007","DOIUrl":"https://doi.org/10.1144/jgs2023-007","url":null,"abstract":"\u0000 The boundary between the Karelia and Norrbotten continental blocks in Fennoscandia is a diffuse cryptic suture zone recording ca. 200 Ma of tectono-metamorphic evolution between 1.92 and 1.72 Ga. Syn-collisional deposition at 1.92–1.91 Ga was followed by post-collisional deposition at 1.88–1.87 Ga and 1.85–1.84 Ga. The post-collision structural overprint in the suture starts with sinistral movements due to aulacogen inversion (D2), east of the suture. Late-D2 and D\u0000 orocline\u0000 extensional stages are followed by NE-vergent basin inversion (D3) of <1.88 Ga rocks and transpressional dextral shear in the suture zone. Nearly orthogonal D4 and D5 deformation events overprint earlier fabrics at ca. 1.83 Ga and ca. 1.78 Ga, respectively. The youngest (D6, ca. 1.73 Ga) structures include sinistral brittle-ductile movements. Northern Fennoscandia and southern Greenland are linked by coeval continent–continent collisions (D1, 1.92–1.89 Ga). The D\u0000 orocline\u0000 stage (ca. 1.87 Ga), responsible for oroclinal buckling in central Fennoscandia, is conceivably related to W-directed subduction and subsequent regional shortening in western Greenland. The D3–D4 events in Fennoscandia are comparable to and D5–D6 correlate well with tectonic events in the suture zone in the eastern Nagssugtoqidian orogen in Greenland.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6675191\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46282932","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}