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
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. 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. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6708518
{"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":null,"pages":null},"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}
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
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. 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.6675384
{"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":null,"pages":null},"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}
Lucinda K. Layfield, N. Schofield, D. Watson, S. Holford, D. Jolley, Ben A. Kilhams, D. Muirhead, A. Roberts, A. Alvey, Alex Ellwood, M. Widdowson
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 ( c. 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 3 . 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.
下地壳侵入被认为是沿火山或富含岩浆的被动边缘的一个常见过程，包括东北大西洋边缘，在那里，它被认为发生在古近纪岩浆活动阶段，在欧洲西北部和格陵兰岛之间的大陆破裂之前和期间。古近系岩浆作用的证据在整个法罗-设得兰盆地（FSB）的子盆地中普遍存在，表现为广泛的熔岩流和普遍的火成岩侵入岩。然而，与位于东北大西洋边缘的其他地区相比，FSB下方没有记录到表明下部地壳侵入的较低地壳反射率。与FSB最近的低地壳反射率和低地壳侵入体解释文件是位于法罗群岛地区挪威盆地下方的Fugloy山脊西北部。尽管如此，下地壳和/或Mohorovičić不连续面内的岩浆添加被认为在古近系隆起和随后的古新世-始新世序列沉积方面发挥了作用。亚玄武岩地震采集和处理的进展在促进东北大西洋边缘地壳深部结构成像方面取得了重大进展。这项研究使用宽带3D地震反射数据绘制了一系列深（约14至20公里深）高振幅反射图，这些反射图可能代表科罗纳山脊中北部下地壳内的火成侵入体。我们估计，反射的累积厚度在某些地方可能超过5公里，这与根据地球化学和岩石学数据公布的该地区岩浆底侵值一致。我们还估计，3D数据集中的低地壳高振幅反射的总体积可能超过2000 km 3。位于中北部科罗纳山脊沿线的地震线的2D重力建模支持对中北部科罗纳山脊下的下地壳侵入体的解释。这项研究为该地区古近系隆起的潜在机制提供了证据。根据先前的工作，如果隆起是由于古近纪地壳内侵位的下地壳侵入而发生的，我们估计科罗纳山脊地区可能产生了约300米的隆起。
{"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":null,"pages":null},"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}
Xin Qian, Tianxing Bai, Yongqi Yu, K. A. Mustapha, Thomas C. Sheldrick, Chengshi Gan, Yuejun Wang
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 ε Nd (t) values of −7.4–+0.5, zircon ε Hf (t) values of −7.4–+8.6, and high initial ratios for 206 Pb/ 204 Pb (20.04–20.65), 207 Pb/ 204 Pb (15.73–15.7) and 208 Pb/ 204 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 ε Nd (t) values (−5.5–−7.2), zircon ε Hf (t) values (−10.1–+6.5), and initial ratios for 206 Pb/ 204 Pb (18.81–19.02), 207 Pb/ 204 Pb (15.71–15.77) and 208 Pb/ 204 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. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.6689085
{"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":null,"pages":null},"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}
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 ε Nd (t) values of 1.1 to 1.6, -4.2 to -4.4, and -2.6 to 1.1, and zircon ε Hf (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 ε Nd (t) (-1.1 to -0.9) and zircon ε Hf (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. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6693575
{"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":null,"pages":null},"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}
R. Velásquez, J. Bastías, E. Salazar, F. Poblete, M. G. Guillot, D. Chew, M. Peña, Felipe Tapia, Adán Ramirez, Foteini Drakou
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 40 Ar/ 39 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. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6675416
{"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":null,"pages":null},"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}
R. Callegari, K. Kośmińska, C. Barnes, I. Klonowska, A. Barker, S. Rousku, E. Nääs, E. Kooijman, P. Witt-Nilsson, J. Majka
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. 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.6675075
{"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":null,"pages":null},"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}
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 orocline 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 orocline 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. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6675191
{"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":null,"pages":null},"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}
Although prey selection has been commonly documented in extant animals, evidence of prey selection in deep time is rare by comparison. Here, we collected 147 broken sclerites of trilobites, almost of which caused by lethal predation, from the Upper Ordovician in NW China. The damages were mainly distributed in three larger trilobites ( Platyptychopyge , Birmanites and Ordosaspis ), and larger-bodied trilobites were more vulnerable to predation. One plausible explanation is that Late Ordovician predators in this area preferred larger trilobites, because the greater nutrients and energy provided by larger prey, and larger prey require less effort to capture because they are less capable of escaping from predation compared with smaller prey, which can more easily hide or escape. Another lower possibility is survivor bias due to smaller prey being completely eaten up. Moreover, the large-eyed trilobite Nileus , which has a similar size and morphology to Ordosaspis , had a theoretical preying rate less than 1/20 of that of Ordosaspis , indicating that the eye is an important sensory organ in trilobites. The increased predation pressure may have also contributed to the increased eye diversity and visual system resolution of trilobites since the Ordovician. Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system Supplementary material: https://doi.org/10.6084/m9.figshare.c.6670609
{"title":"Predation Bias of Ordovician Predators on Trilobites","authors":"Ruiwen Zong, Ruoying Fan, Y. Gong","doi":"10.1144/jgs2023-019","DOIUrl":"https://doi.org/10.1144/jgs2023-019","url":null,"abstract":"\u0000 Although prey selection has been commonly documented in extant animals, evidence of prey selection in deep time is rare by comparison. Here, we collected 147 broken sclerites of trilobites, almost of which caused by lethal predation, from the Upper Ordovician in NW China. The damages were mainly distributed in three larger trilobites (\u0000 Platyptychopyge\u0000 ,\u0000 Birmanites\u0000 and\u0000 Ordosaspis\u0000 ), and larger-bodied trilobites were more vulnerable to predation. One plausible explanation is that Late Ordovician predators in this area preferred larger trilobites, because the greater nutrients and energy provided by larger prey, and larger prey require less effort to capture because they are less capable of escaping from predation compared with smaller prey, which can more easily hide or escape. Another lower possibility is survivor bias due to smaller prey being completely eaten up. Moreover, the large-eyed trilobite\u0000 Nileus\u0000 , which has a similar size and morphology to\u0000 Ordosaspis\u0000 , had a theoretical preying rate less than 1/20 of that of\u0000 Ordosaspis\u0000 , indicating that the eye is an important sensory organ in trilobites. The increased predation pressure may have also contributed to the increased eye diversity and visual system resolution of trilobites since the Ordovician.\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at:\u0000 https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6670609\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2023-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44569390","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}
Aggressive ground conditions and physical deterioration of ground and engineering materials are attributed to a wide range of factors but in the UK a high proportion of occurrences in the engineering environment result from the presence of sulfur minerals, particularly pyrite which is unstable in oxidising and damp atmospheric weathering conditions. The oxidation reactions are complex in that the rate - and the products - depend on the crystalline form and grain size of the pyrite as well as the host mineralogy, rock fabric and environmental conditions, including exposure to weathering action brought about by engineering works. Therefore, to prevent any negative impacts on engineering design and construction, the possibility of changes in the potential for pyrite oxidation during and after construction need to be considered. The aim of this paper is to review the implications of sulfur minerals, especially of pyrite oxidation, with reference to engineering situations in which pyrite oxidation may have a significant negative impact. Changes in the potential for oxidation because of ground engineering works and strategies for avoiding problems are also considered. Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/topic/collections/sulfur-in-the-earth-system
{"title":"Implications of sulfur mineralogy and consequences of pyrite oxidation for ground engineering","authors":"M. A. Czerewko, J. Cripps","doi":"10.1144/jgs2022-101","DOIUrl":"https://doi.org/10.1144/jgs2022-101","url":null,"abstract":"Aggressive ground conditions and physical deterioration of ground and engineering materials are attributed to a wide range of factors but in the UK a high proportion of occurrences in the engineering environment result from the presence of sulfur minerals, particularly pyrite which is unstable in oxidising and damp atmospheric weathering conditions.\u0000 The oxidation reactions are complex in that the rate - and the products - depend on the crystalline form and grain size of the pyrite as well as the host mineralogy, rock fabric and environmental conditions, including exposure to weathering action brought about by engineering works. Therefore, to prevent any negative impacts on engineering design and construction, the possibility of changes in the potential for pyrite oxidation during and after construction need to be considered.\u0000 The aim of this paper is to review the implications of sulfur minerals, especially of pyrite oxidation, with reference to engineering situations in which pyrite oxidation may have a significant negative impact. Changes in the potential for oxidation because of ground engineering works and strategies for avoiding problems are also considered.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Sulfur in the Earth system collection available at:\u0000 https://www.lyellcollection.org/topic/collections/sulfur-in-the-earth-system\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2023-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48072059","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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