A. Bustard, David R. Lentz, James A Walker, Chris R. M. McFarlane
Dykes intruding along the Melanson Brook Fault record two magmatic episodes in northern New Brunswick. Dykes at the South Gold Zone of the Elmtree gold deposit are aphanitic and magnesian-calcic, whereas those at Ellis Brook (2.5 km to the west) are ilmenite-series and weakly peraluminous with hornblende- and plagioclase-porphyritic phases. Elevated 147Sm/44Nd generated by partial melting, titanium depletion, absence of rare earth element fractionation, and trondhjemite-like compositions indicate the South Gold Zone dykes were sourced from low-volume fluid fluxed melting of gabbroic crust. A Sm-Nd depleted model mantle age of 1.1 Ga for the Ellis Brook dykes suggests that they were sourced from melting of Ganderian crustal rocks rather than the sinking Acadian slab. 143Nd/144Nd evolution curves for the South Gold Zone dykes intersect that of the Ellis Brook dykes at 432 Ma and 427 Ma. This suggests that the magma from which the South Gold Zone dykes crystallized was extracted from a similar source area as the magma that generated the Ellis Brook dykes. Evidence of fluid exsolution in the Ellis Brook dykes indicates they could be a potential source for reduced intrusion-related gold mineralization. The Ellis Brook dykes yielded a U-Pb zircon age of 391 ± 5 Ma, which is consistent with the timing of oceanic slab break-off at the end of the Acadian orogenic cycle. Extraction of South Gold Zone magma occurred up to 40 Myr earlier, likely during the Salinic orogenic cycle.
{"title":"Crustal Melting Recorded by Dykes along the Gold-bearing Melanson Brook Fault, Northern New Brunswick Appalachians","authors":"A. Bustard, David R. Lentz, James A Walker, Chris R. M. McFarlane","doi":"10.1139/cjes-2024-0034","DOIUrl":"https://doi.org/10.1139/cjes-2024-0034","url":null,"abstract":"Dykes intruding along the Melanson Brook Fault record two magmatic episodes in northern New Brunswick. Dykes at the South Gold Zone of the Elmtree gold deposit are aphanitic and magnesian-calcic, whereas those at Ellis Brook (2.5 km to the west) are ilmenite-series and weakly peraluminous with hornblende- and plagioclase-porphyritic phases. Elevated 147Sm/44Nd generated by partial melting, titanium depletion, absence of rare earth element fractionation, and trondhjemite-like compositions indicate the South Gold Zone dykes were sourced from low-volume fluid fluxed melting of gabbroic crust. A Sm-Nd depleted model mantle age of 1.1 Ga for the Ellis Brook dykes suggests that they were sourced from melting of Ganderian crustal rocks rather than the sinking Acadian slab. 143Nd/144Nd evolution curves for the South Gold Zone dykes intersect that of the Ellis Brook dykes at 432 Ma and 427 Ma. This suggests that the magma from which the South Gold Zone dykes crystallized was extracted from a similar source area as the magma that generated the Ellis Brook dykes. Evidence of fluid exsolution in the Ellis Brook dykes indicates they could be a potential source for reduced intrusion-related gold mineralization. The Ellis Brook dykes yielded a U-Pb zircon age of 391 ± 5 Ma, which is consistent with the timing of oceanic slab break-off at the end of the Acadian orogenic cycle. Extraction of South Gold Zone magma occurred up to 40 Myr earlier, likely during the Salinic orogenic cycle.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"107 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141926856","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Mount Grace metamorphosed carbonatites (Late Devonian) outcrop as thin (0.5 to 4 m), laterally discontinuous, strata-bound mappable lenses within the Monashee complex of the southeastern Canadian Cordillera. The host stratigraphic sequence (Monashee cover gneiss) was metamorphosed and deformed in the Late Cretaceous to early Eocene followed immediately by exhumation of the Frenchman Cap and Thor Odin domes. We present seven stratigraphic logs for Mount Grace carbonatites including new and previously described outcroppings spanning ~30 km. The Mount Grace carbonatite units were deposited regionally within or near the top of a shallow marine sedimentary sequence within miogeoclinal strata of the western margin of paleo North America (Laurentia). The distribution of the Mount Grace carbonatite lithofacies and the preserved depositional structures and textures suggest these are pyroclastic deposits resulting from phreatomagmatic eruptions. Our new data enhance the volcanological story with an eruption scenario involving phreatomagmatic reactions and deposition from pyroclastic density currents, sourced from multiple centres within a field of monogenetic maar volcanoes. The distribution of the Mount Grace carbonatites parallel to the western margin of the paleo-North American continent correlates well with regional Late Devonian alkaline magmatism associated with development of an extensional back-arc basin.
{"title":"The volcanic architecture and tectono-magmatic framework of the Mount Grace carbonatites, southeastern Canadian Cordillera","authors":"Lindsey Abdale, James Kelly Russell, Lee A. Groat","doi":"10.1139/cjes-2024-0001","DOIUrl":"https://doi.org/10.1139/cjes-2024-0001","url":null,"abstract":"The Mount Grace metamorphosed carbonatites (Late Devonian) outcrop as thin (0.5 to 4 m), laterally discontinuous, strata-bound mappable lenses within the Monashee complex of the southeastern Canadian Cordillera. The host stratigraphic sequence (Monashee cover gneiss) was metamorphosed and deformed in the Late Cretaceous to early Eocene followed immediately by exhumation of the Frenchman Cap and Thor Odin domes. We present seven stratigraphic logs for Mount Grace carbonatites including new and previously described outcroppings spanning ~30 km. The Mount Grace carbonatite units were deposited regionally within or near the top of a shallow marine sedimentary sequence within miogeoclinal strata of the western margin of paleo North America (Laurentia). The distribution of the Mount Grace carbonatite lithofacies and the preserved depositional structures and textures suggest these are pyroclastic deposits resulting from phreatomagmatic eruptions. Our new data enhance the volcanological story with an eruption scenario involving phreatomagmatic reactions and deposition from pyroclastic density currents, sourced from multiple centres within a field of monogenetic maar volcanoes. The distribution of the Mount Grace carbonatites parallel to the western margin of the paleo-North American continent correlates well with regional Late Devonian alkaline magmatism associated with development of an extensional back-arc basin.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"58 24","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141651929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. L. La Croix, S. Dashtgard, PR Hill, K. Ayranci, John J. Clague
The Fraser River Delta (FRD) is a large sedimentary system and home to Metro Vancouver, situated within the unceded territories of several First Nations. This review provides an overview of the geological evolution of the FRD, connecting hydrodynamic processes with sedimentary deposits across its diverse environments, from the river to the delta slope. The study emphasizes the implications of sedimentation and delta evolution for natural hazards and coastal/delta management, pinpointing knowledge gaps. Comprising four main zones – river, delta plain, tidal flats, and delta slope – the FRD is subject to several natural hazards including subsidence, flooding, earthquakes, liquefaction, and tsunamis. The delta plain, bordering the Fraser River’s distributary channels, hosts tidal marshes and flats, including both active and abandoned areas. Active tidal flats like Roberts Bank and Sturgeon Bank receive sediment directly from the Fraser River, while abandoned tidal flats, like those at Boundary Bay and Mud Bay, no longer receive sediment. The tidal flats transition into the delta slope, characterized by sand in the south and mud in the north of the Main Channel. The FRD's susceptibility to hazards necessitates protective measures, with approximately 250 km of dykes shielding the delta plain from river floods and storm surges. Subsidence amplifies the impact of rising sea levels. Earthquakes in the region can induce tsunamis, submarine slope failures, and liquefaction of delta sediments, emphasizing the importance of incorporating sedimentation patterns and delta evolution into management strategies for sustainable urban development, habitat restoration, and coastal defence initiatives.
菲沙河三角洲（Fraser River Delta，FRD）是一个大型沉积系统，也是大温哥华地区的所在地，位于几个原住民的未受保护领地内。本综述概述了菲沙河三角洲的地质演变，将从河流到三角洲斜坡等不同环境中的水动力过程与沉积物联系起来。研究强调了沉积和三角洲演变对自然灾害和沿海/三角洲管理的影响，并指出了知识空白。三角洲地区由河流、三角洲平原、滩涂和三角洲斜坡四个主要区域组成，受到多种自然灾害的影响，包括沉降、洪水、地震、液化和海啸。三角洲平原毗邻菲沙河的支流河道，拥有潮汐沼泽和滩涂，包括活跃和废弃的区域。活跃的潮汐滩涂（如罗伯茨滩和鲟鱼滩）直接接收来自菲沙河的沉积物，而废弃的潮汐滩涂（如边界湾和泥浆湾）则不再接收沉积物。潮滩过渡到三角洲斜坡，主航道南部为沙，北部为泥。由于 FRD 易受灾害影响，因此必须采取保护措施，约 250 公里长的堤坝保护三角洲平原免受河流洪水和风暴潮的侵袭。地表下沉加剧了海平面上升的影响。该地区的地震会引发海啸、海底斜坡坍塌和三角洲沉积物液化，因此将沉积模式和三角洲演变纳入可持续城市发展、生境恢复和海岸防御措施的管理战略非常重要。
{"title":"The Holocene to Modern Fraser River Delta, Canada: Geological History, Processes, Deposits, Natural Hazards, and Coastal Management","authors":"A. L. La Croix, S. Dashtgard, PR Hill, K. Ayranci, John J. Clague","doi":"10.1139/cjes-2024-0041","DOIUrl":"https://doi.org/10.1139/cjes-2024-0041","url":null,"abstract":"The Fraser River Delta (FRD) is a large sedimentary system and home to Metro Vancouver, situated within the unceded territories of several First Nations. This review provides an overview of the geological evolution of the FRD, connecting hydrodynamic processes with sedimentary deposits across its diverse environments, from the river to the delta slope. The study emphasizes the implications of sedimentation and delta evolution for natural hazards and coastal/delta management, pinpointing knowledge gaps. Comprising four main zones – river, delta plain, tidal flats, and delta slope – the FRD is subject to several natural hazards including subsidence, flooding, earthquakes, liquefaction, and tsunamis. The delta plain, bordering the Fraser River’s distributary channels, hosts tidal marshes and flats, including both active and abandoned areas. Active tidal flats like Roberts Bank and Sturgeon Bank receive sediment directly from the Fraser River, while abandoned tidal flats, like those at Boundary Bay and Mud Bay, no longer receive sediment. The tidal flats transition into the delta slope, characterized by sand in the south and mud in the north of the Main Channel. The FRD's susceptibility to hazards necessitates protective measures, with approximately 250 km of dykes shielding the delta plain from river floods and storm surges. Subsidence amplifies the impact of rising sea levels. Earthquakes in the region can induce tsunamis, submarine slope failures, and liquefaction of delta sediments, emphasizing the importance of incorporating sedimentation patterns and delta evolution into management strategies for sustainable urban development, habitat restoration, and coastal defence initiatives.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":" 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141668997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Archibald, S. Barr, C. White, Shae J. Nickerson, R. Stern, Yan Luo, Graham D. Pearson
Abundant granitic plutons intruded the eastern Meguma terrane of Nova Scotia in the middle- to late Devonian. Less voluminous diorite-tonalite and gabbro intrusions are associated with the granitic plutons along the northern margin of the terrane adjacent to the Cobequid-Chedabucto fault zone. All plutons contain metasedimentary xenoliths, and the mafic plutons show magma mingling textures with their adjacent granitic plutons. New U-Pb zircon data from autocrystic zircon in 13 samples indicate coeval emplacement of mafic and granitic plutons between ca. 382 and 368 Ma. However, the zircon grains contain numerous inherited domains that range in age from Palaeoproterozoic to Devonian. These inherited ages correspond to detrital zircon U-Pb dates from the Cambrian to Ordovician metasedimentary host rocks. Zircon oxygen isotopic data (δ18O) are between +7.4 ± 0.2 ‰ and +9.3 ± 0.3 ‰ indicating significant involvement of the crust as the magma source or contaminant. If the high δ18Ozrc values are a result of contamination, the contaminant was likely the metasedimentary rocks of the Meguma terrane. Hafnium isotopic data from autocrystic zircon have εHf(t) between -6.0 ± 1.5 and +2.1 ± 2.5. The new zircon U-Pb, O and Hf isotopic data from plutons in the eastern Meguma terrane are indistinguishable from published data from the South Mountain Batholith. These data suggest that Devonian magmatism in the Meguma terrane post-dated or was coeval with the orogenic event that caused folding and regional metamorphism, involved the same magma source and/or contaminants throughout the terrane, and did not involve Avalonian crust.
{"title":"Devonian plutons in the eastern Meguma terrane, Nova Scotia, Canada: zircon U-Pb, Lu-Hf and O isotopic compositions, age, and petrogenetic implications","authors":"D. Archibald, S. Barr, C. White, Shae J. Nickerson, R. Stern, Yan Luo, Graham D. Pearson","doi":"10.1139/cjes-2024-0023","DOIUrl":"https://doi.org/10.1139/cjes-2024-0023","url":null,"abstract":"Abundant granitic plutons intruded the eastern Meguma terrane of Nova Scotia in the middle- to late Devonian. Less voluminous diorite-tonalite and gabbro intrusions are associated with the granitic plutons along the northern margin of the terrane adjacent to the Cobequid-Chedabucto fault zone. All plutons contain metasedimentary xenoliths, and the mafic plutons show magma mingling textures with their adjacent granitic plutons. New U-Pb zircon data from autocrystic zircon in 13 samples indicate coeval emplacement of mafic and granitic plutons between ca. 382 and 368 Ma. However, the zircon grains contain numerous inherited domains that range in age from Palaeoproterozoic to Devonian. These inherited ages correspond to detrital zircon U-Pb dates from the Cambrian to Ordovician metasedimentary host rocks. Zircon oxygen isotopic data (δ18O) are between +7.4 ± 0.2 ‰ and +9.3 ± 0.3 ‰ indicating significant involvement of the crust as the magma source or contaminant. If the high δ18Ozrc values are a result of contamination, the contaminant was likely the metasedimentary rocks of the Meguma terrane. Hafnium isotopic data from autocrystic zircon have εHf(t) between -6.0 ± 1.5 and +2.1 ± 2.5. The new zircon U-Pb, O and Hf isotopic data from plutons in the eastern Meguma terrane are indistinguishable from published data from the South Mountain Batholith. These data suggest that Devonian magmatism in the Meguma terrane post-dated or was coeval with the orogenic event that caused folding and regional metamorphism, involved the same magma source and/or contaminants throughout the terrane, and did not involve Avalonian crust.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":" 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141673857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Travis Hudson, Frederic H. Wilson, Paul B. O'Sullivan
New U-Pb zircon geochronology identifies a latest Triassic (ca 214-201 Ma) igneous suite of tuff, hypabyssal dikes, and a pluton on the southern Kenai Peninsula, Alaska. The igneous suite was emplaced within Upper Triassic sedimentary rocks along the southern margin of Western Wrangellia, the western-most fragment of the Wrangellia composite terrane. The igneous rocks range from mafic (50.6% SiO2) to felsic (78.3% SiO2), characteristically have less than 1.55% K2O, and generally have low trace element abundances. The tonalitic and trondhjemitic magmas were largely sourced in mafic-rich lower crust and incompletely assimilated quartz and other mineral xenocrysts are common. Fractionation involving plagioclase and amphibole is indicated for some magmas and composite intrusions and igneous xenoliths indicate magma mixing was possible. Paleozoic and Precambrian inherited zircons and initial 87Sr/86Sr (0.704103-0.705609) and 143Nd/144Nd (0.512396-0.512777) ratios indicate that the Western Wrangellia crustal sources are heterogeneous and contain sialic components. The latest Triassic magmatism reflects processes that preceded Early Jurassic subduction along the Wrangellia composite terrane and Pacific Ocean plate boundary. These processes involved heating and melting of mantle lithosphere and lower crust as mantle instabilities accompanied the breaking of the plate boundary linkages. The Late Triassic transition to subduction along the Wrangellia composite terrane margin coincided with the transition to subduction cessation in the Late Triassic arcs of the western Intermontane terranes of Canada. The shift to subduction along the outboard Wrangellia composite terrane margin marks the beginning of the Pacific Ocean-Cordillera plate interactions that came to dominate the tectonic evolution of the northern Cordillera from the Early Jurassic to today.
{"title":"Upper Triassic igneous rocks of the southern Kenai Peninsula, Alaska – prelude to Early Jurassic subduction along the western Wrangellia composite terrane margin","authors":"Travis Hudson, Frederic H. Wilson, Paul B. O'Sullivan","doi":"10.1139/cjes-2024-0009","DOIUrl":"https://doi.org/10.1139/cjes-2024-0009","url":null,"abstract":"New U-Pb zircon geochronology identifies a latest Triassic (ca 214-201 Ma) igneous suite of tuff, hypabyssal dikes, and a pluton on the southern Kenai Peninsula, Alaska. The igneous suite was emplaced within Upper Triassic sedimentary rocks along the southern margin of Western Wrangellia, the western-most fragment of the Wrangellia composite terrane. The igneous rocks range from mafic (50.6% SiO2) to felsic (78.3% SiO2), characteristically have less than 1.55% K2O, and generally have low trace element abundances. The tonalitic and trondhjemitic magmas were largely sourced in mafic-rich lower crust and incompletely assimilated quartz and other mineral xenocrysts are common. Fractionation involving plagioclase and amphibole is indicated for some magmas and composite intrusions and igneous xenoliths indicate magma mixing was possible. Paleozoic and Precambrian inherited zircons and initial 87Sr/86Sr (0.704103-0.705609) and 143Nd/144Nd (0.512396-0.512777) ratios indicate that the Western Wrangellia crustal sources are heterogeneous and contain sialic components. The latest Triassic magmatism reflects processes that preceded Early Jurassic subduction along the Wrangellia composite terrane and Pacific Ocean plate boundary. These processes involved heating and melting of mantle lithosphere and lower crust as mantle instabilities accompanied the breaking of the plate boundary linkages. The Late Triassic transition to subduction along the Wrangellia composite terrane margin coincided with the transition to subduction cessation in the Late Triassic arcs of the western Intermontane terranes of Canada. The shift to subduction along the outboard Wrangellia composite terrane margin marks the beginning of the Pacific Ocean-Cordillera plate interactions that came to dominate the tectonic evolution of the northern Cordillera from the Early Jurassic to today.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"6 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141344553","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
He Feng, C. Gerbi, Scott E Johnson, A. Cruz‐Uribe, Martin G. Yates
Strain localization occurs across the crust in both brittle and viscous regimes, but the exact causes remain debated. Natural rock observations suggest that changes in phase properties (such as physical properties, phase distribution, and grain geometry) are more influential in weakening than variations in stress and temperature. Investigating the early stages of strain accumulation in various pressure-temperature conditions leads to a better understanding of these causes. Our study focuses on three weakly deformed rocks showing zones of localization on a millimeter or smaller scale, which we term “bridge zones”. These localized zones appear to mechanically connect weak domains and typically exhibit finer grain sizes within a narrow band. Importantly, these zones occur in less deformed rocks from the margins of shear zones. They result from both in-situ grain size reduction and chemical processes leading to phase mixing or element mobility on a limited spatial scale. Numerical modeling aligns high-stress areas with these zones, supporting their impact on reducing rock strength. We propose a conceptual model linking far-field loading to microscale changes in developing these zones. Characterization of bridge zones aids in elucidating the microstructural processes driving deformation localization, which is fundamental for plate tectonics, metamorphism, seismicity, and other lithospheric processes. This research reveals microscale mechanisms driving weak domain development, improving our knowledge of rheological changes and laying the groundwork for predictive models regarding strength evolution in the lithosphere.
{"title":"Rheological Bridge Zones: The Initialization of Strain Localization","authors":"He Feng, C. Gerbi, Scott E Johnson, A. Cruz‐Uribe, Martin G. Yates","doi":"10.1139/cjes-2023-0132","DOIUrl":"https://doi.org/10.1139/cjes-2023-0132","url":null,"abstract":"Strain localization occurs across the crust in both brittle and viscous regimes, but the exact causes remain debated. Natural rock observations suggest that changes in phase properties (such as physical properties, phase distribution, and grain geometry) are more influential in weakening than variations in stress and temperature. Investigating the early stages of strain accumulation in various pressure-temperature conditions leads to a better understanding of these causes. Our study focuses on three weakly deformed rocks showing zones of localization on a millimeter or smaller scale, which we term “bridge zones”. These localized zones appear to mechanically connect weak domains and typically exhibit finer grain sizes within a narrow band. Importantly, these zones occur in less deformed rocks from the margins of shear zones. They result from both in-situ grain size reduction and chemical processes leading to phase mixing or element mobility on a limited spatial scale. Numerical modeling aligns high-stress areas with these zones, supporting their impact on reducing rock strength. We propose a conceptual model linking far-field loading to microscale changes in developing these zones. Characterization of bridge zones aids in elucidating the microstructural processes driving deformation localization, which is fundamental for plate tectonics, metamorphism, seismicity, and other lithospheric processes. This research reveals microscale mechanisms driving weak domain development, improving our knowledge of rheological changes and laying the groundwork for predictive models regarding strength evolution in the lithosphere.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"17 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141354132","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Using new and published data, we synthesize the tectonic evolution of the Ottawa River Gneiss Complex (ORGC), the metamorphic core and detachment zone of a large mid- to late-Ottawan metamorphic core complex in the western Grenville Province. Field and petrologic data indicative of retrogression and exhumation, combined with maps and schematic crustal-scale sections, are used to document spatial and temporal relationships of multi-scale structures developed during its formation, of which the largest, termed mega-cross-folds and megaboudins, occur within and define the detachment zone. Mega-cross-folds, orogen-normal structures up to 70 km in length with coaxial constrictional fabrics in their hinge-lines, formed in a single phase of deformation during retrogression and exhumation. A cluster of asymmetric megaboudins, individually from 10-50 km long with granulite-facies cores and high-strain amphibolite-facies rims, similarly formed during syntectonic retrogression and exhumation of granulite-facies precursors. We argue the mega-cross-folds developed in a regime of regional transtension, whereas the megaboudin cluster formed by extensional inversion of an anastomosing early-Ottawan thrust system, with the strain patterns of both suggesting the detachment zone was the site of intense ductile flow between the stronger metamorphic core and cover. Comparison of these results with generic numerical models of extensional collapse of overthickened continental crust suggests the first-order tectonometamorphic features of the ORGC developed during necking of the upper crust and associated large-scale extensional flow of the mid and lower crust into the domiform necked region during collapse of the overthickened early-Ottawan thrust stack.
{"title":"The Ottawa River Gneiss Complex revisited: definition of the metamorphic core and detachment zone of a large Grenvillian metamorphic core complex","authors":"T. Rivers, W. M. Schwerdtner","doi":"10.1139/cjes-2023-0060","DOIUrl":"https://doi.org/10.1139/cjes-2023-0060","url":null,"abstract":"Using new and published data, we synthesize the tectonic evolution of the Ottawa River Gneiss Complex (ORGC), the metamorphic core and detachment zone of a large mid- to late-Ottawan metamorphic core complex in the western Grenville Province. Field and petrologic data indicative of retrogression and exhumation, combined with maps and schematic crustal-scale sections, are used to document spatial and temporal relationships of multi-scale structures developed during its formation, of which the largest, termed mega-cross-folds and megaboudins, occur within and define the detachment zone. Mega-cross-folds, orogen-normal structures up to 70 km in length with coaxial constrictional fabrics in their hinge-lines, formed in a single phase of deformation during retrogression and exhumation. A cluster of asymmetric megaboudins, individually from 10-50 km long with granulite-facies cores and high-strain amphibolite-facies rims, similarly formed during syntectonic retrogression and exhumation of granulite-facies precursors. We argue the mega-cross-folds developed in a regime of regional transtension, whereas the megaboudin cluster formed by extensional inversion of an anastomosing early-Ottawan thrust system, with the strain patterns of both suggesting the detachment zone was the site of intense ductile flow between the stronger metamorphic core and cover. Comparison of these results with generic numerical models of extensional collapse of overthickened continental crust suggests the first-order tectonometamorphic features of the ORGC developed during necking of the upper crust and associated large-scale extensional flow of the mid and lower crust into the domiform necked region during collapse of the overthickened early-Ottawan thrust stack.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"47 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141355294","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Susan Strowbridge, G. Dunning, A. Indares, G. Jenner
Basement rocks in the Humber terrane of the Appalachian Orogen record the last stages in the history of the Mesoproterozoic Laurentian margin in Canada. These stages were revealed by recent work in the East Pond Metamorphic Suite on the western Baie Verte Peninsula, Newfoundland, where two Tonian bimodal volcaniclastic-sedimentary successions were recognized (Pine Pond successions). The older, ca. 980 Ma succession contains detrital igneous zircon and titanite (ca. 1160‒1057 Ma) presumably derived from the Mesoproterozoic Laurentian margin, while the younger, ca. 950 Ma succession, contains 980 Ma detrital igneous zircon and titanite. Although metamorphosed to eclogite facies during the assembly of the Appalachian Orogen, the successions preserve protolith features and geochemical data that indicate melt likely originated in an extensional setting. The new ages, integrated with geochemical and Sm–Nd isotopic data suggest that the felsic volcaniclastic units of the Pine Pond successions are related to 975–950 Ma granitic plutons in the Pinware terrane of the eastern Grenville Province, in southeastern Labrador. These new data solidify a previous interpretation that the Pine Pond successions were deposited at the continental apex of the Asgard Sea and that the Pinware terrane intrusions are a part of this event. Furthermore, these new Tonian ages for rift-related strata call into question the interpretation of Ediacaran depositional ages for clastic sequences in the northern Appalachian Orogen, with youngest detrital zircons that are Tonian, and show that the tectonic evolution of the Mesoproterozoic Laurentian margin in Canada is more complex than previously known.
阿巴拉契亚造山带亨伯阶地的基底岩石记录了加拿大中新生代劳伦大陆边缘历史的最后阶段。纽芬兰省 Baie Verte 半岛西部的东池塘变质岩组最近的研究揭示了这些阶段，在那里发现了两个托尼双峰火山碎屑沉积演替（松树池塘演替）。较早的，约 980 Ma 的演替包含可能来自中新生代劳伦伦边缘的锆英石和榍石（约 1160-1057 Ma），而较年轻的，约 950 Ma 的演替包含 980 Ma 的锆英石和榍石。虽然在阿巴拉契亚造山带的组装过程中变质成了夕闪岩面，但这些演替保留了原岩特征和地球化学数据，表明熔体很可能起源于伸展环境。新的年龄与地球化学和 Sm-Nd 同位素数据相结合，表明松树池岩层的长岩火山碎屑岩单元与拉布拉多东南部格勒维尔省东部 Pinware 陆相中的 975-950 Ma 花岗质岩块有关。这些新数据巩固了之前的解释，即松树塘演替沉积于阿斯加德海的大陆顶点，Pinware 陆相侵入体是这一事件的一部分。此外，这些与断裂有关的地层的新托尼世年龄对阿巴拉契亚造山带北部碎屑岩序列的埃迪卡拉纪沉积年龄的解释提出了质疑，这些碎屑岩最年轻的锆石是托尼世的，这也表明加拿大中新生代劳伦大陆边缘的构造演化比以前所知的更为复杂。
{"title":"Tonian rift successions in Newfoundland, Canada: A window to late tectonic events in the Mesoproterozoic Laurentian margin","authors":"Susan Strowbridge, G. Dunning, A. Indares, G. Jenner","doi":"10.1139/cjes-2024-0007","DOIUrl":"https://doi.org/10.1139/cjes-2024-0007","url":null,"abstract":"Basement rocks in the Humber terrane of the Appalachian Orogen record the last stages in the history of the Mesoproterozoic Laurentian margin in Canada. These stages were revealed by recent work in the East Pond Metamorphic Suite on the western Baie Verte Peninsula, Newfoundland, where two Tonian bimodal volcaniclastic-sedimentary successions were recognized (Pine Pond successions). The older, ca. 980 Ma succession contains detrital igneous zircon and titanite (ca. 1160‒1057 Ma) presumably derived from the Mesoproterozoic Laurentian margin, while the younger, ca. 950 Ma succession, contains 980 Ma detrital igneous zircon and titanite. Although metamorphosed to eclogite facies during the assembly of the Appalachian Orogen, the successions preserve protolith features and geochemical data that indicate melt likely originated in an extensional setting. The new ages, integrated with geochemical and Sm–Nd isotopic data suggest that the felsic volcaniclastic units of the Pine Pond successions are related to 975–950 Ma granitic plutons in the Pinware terrane of the eastern Grenville Province, in southeastern Labrador. These new data solidify a previous interpretation that the Pine Pond successions were deposited at the continental apex of the Asgard Sea and that the Pinware terrane intrusions are a part of this event. Furthermore, these new Tonian ages for rift-related strata call into question the interpretation of Ediacaran depositional ages for clastic sequences in the northern Appalachian Orogen, with youngest detrital zircons that are Tonian, and show that the tectonic evolution of the Mesoproterozoic Laurentian margin in Canada is more complex than previously known.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"90 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141384956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mitch Marcelissen, P. Hollings, David R. Cooke, Michael J. Baker, Ivan Belousov, Evan Orovan, Richard M. Friedman
The Mines Gaspé area hosts multiple Cu-Mo skarn and porphyry orebodies near the town of Murdochville in the northeastern part of the Gaspé Peninsula, Québec. The orebodies occur within overlapping alteration aureoles in calcareous Lower Devonian sedimentary rocks. The strata are intruded by numerous multiphase porphyry sills, dykes, and plugs of Devonian age. The Porphyry Mountain intrusion and a sill in the Copper Mountain pit have been dated at 378.80 ± 0.37 Ma and 377.60 ± 0.45 Ma, respectively, refining the results of previous studies, and demonstrating Porphyry Mountain intrusion emplacement at least 0.38 m.y. before Copper Mountain. Circa 392 Ma inherited zircon grains at Mines Gaspé suggest an early phase of magmatism that produced the extensive skarn alteration aureoles throughout the Gaspé Peninsula at sites like Mines Gaspé and the nearby McGerrigle Complex, followed by significantly later ( > 10 m.y.) porphyritic intrusions and associated mineralization that added to existing skarn resources. Epidote at both Mines Gaspé and Sullipek occur as disseminated/granular crystals within the host groundmass and as larger crystals within veinlets or veinlet halos in metasomatised sedimentary rocks. Epidote ages suggest that there are several different propylitic hydrothermal events within the region at Mines Gaspé and Sullipek, which combined with new zircon U-Pb ages implies a prolonged and complex history of propylitic alteration within Gaspésie.
{"title":"Geochronology of the Mines Gaspé porphyry deposit, Québec, Canada","authors":"Mitch Marcelissen, P. Hollings, David R. Cooke, Michael J. Baker, Ivan Belousov, Evan Orovan, Richard M. Friedman","doi":"10.1139/cjes-2024-0013","DOIUrl":"https://doi.org/10.1139/cjes-2024-0013","url":null,"abstract":"The Mines Gaspé area hosts multiple Cu-Mo skarn and porphyry orebodies near the town of Murdochville in the northeastern part of the Gaspé Peninsula, Québec. The orebodies occur within overlapping alteration aureoles in calcareous Lower Devonian sedimentary rocks. The strata are intruded by numerous multiphase porphyry sills, dykes, and plugs of Devonian age. The Porphyry Mountain intrusion and a sill in the Copper Mountain pit have been dated at 378.80 ± 0.37 Ma and 377.60 ± 0.45 Ma, respectively, refining the results of previous studies, and demonstrating Porphyry Mountain intrusion emplacement at least 0.38 m.y. before Copper Mountain. Circa 392 Ma inherited zircon grains at Mines Gaspé suggest an early phase of magmatism that produced the extensive skarn alteration aureoles throughout the Gaspé Peninsula at sites like Mines Gaspé and the nearby McGerrigle Complex, followed by significantly later ( > 10 m.y.) porphyritic intrusions and associated mineralization that added to existing skarn resources. Epidote at both Mines Gaspé and Sullipek occur as disseminated/granular crystals within the host groundmass and as larger crystals within veinlets or veinlet halos in metasomatised sedimentary rocks. Epidote ages suggest that there are several different propylitic hydrothermal events within the region at Mines Gaspé and Sullipek, which combined with new zircon U-Pb ages implies a prolonged and complex history of propylitic alteration within Gaspésie.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"32 24","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141273022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Three new fossil mayfly (Ephemeroptera) larvae from the Redmond Formation (Cenomanian) of Newfoundland and Labrador, Canada, are described: Alatuscapillus icarus gen. et sp. nov. (family Oligoneuriidae), Cruscolli sheppardae gen. et sp. nov. (family Heptageniidae), and Protoligoneuria borealis sp. nov. (family Hexagenitidae). This discovery marks the first juvenile insect nymphs to be described from this formation and helps fill gaps in our understanding of the global and temporal distribution of mayflies during the Cretaceous period. Of these, C. sheppardae marks the oldest occurrence of the family Heptageniidae in the fossil record, while A. icarus and P. borealis mark the first fossil occurrences of the families Oligoneuriidae and Hexagenitidae in North America. The anatomy, preservation, and behaviour of these new mayfly species inferred from modern taxa consolidate the hypothesis that the Redmond Formation’s palaeoenvironment was lacustrine in nature.
{"title":"New Late Cretaceous (Cenomanian) fossil mayfly nymphs (Oligoneuriidae, Heptageniidae, Hexagenitidae) from the Redmond Formation, Labrador, Canada","authors":"André S. Mueller, Alexandre V. Demers‐Potvin","doi":"10.1139/cjes-2023-0133","DOIUrl":"https://doi.org/10.1139/cjes-2023-0133","url":null,"abstract":"Three new fossil mayfly (Ephemeroptera) larvae from the Redmond Formation (Cenomanian) of Newfoundland and Labrador, Canada, are described: Alatuscapillus icarus gen. et sp. nov. (family Oligoneuriidae), Cruscolli sheppardae gen. et sp. nov. (family Heptageniidae), and Protoligoneuria borealis sp. nov. (family Hexagenitidae). This discovery marks the first juvenile insect nymphs to be described from this formation and helps fill gaps in our understanding of the global and temporal distribution of mayflies during the Cretaceous period. Of these, C. sheppardae marks the oldest occurrence of the family Heptageniidae in the fossil record, while A. icarus and P. borealis mark the first fossil occurrences of the families Oligoneuriidae and Hexagenitidae in North America. The anatomy, preservation, and behaviour of these new mayfly species inferred from modern taxa consolidate the hypothesis that the Redmond Formation’s palaeoenvironment was lacustrine in nature.","PeriodicalId":503418,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"19 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141409004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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