In the Coast Mountains of western British Columbia, an anomalous seismicity concentration exists near the intersection of the Coast Shear Zone, a major NW-SE trending Eocene-age shear zone that accommodated deformation between the Pacific and North America plates, with the Anahim Volcanic Belt, an ENE-WSW trending zone of volcanic features that decrease in age to the east. To better characterize seismicity in the Coast Mountains, we augment the existing Natural Resources Canada seismicity catalog by applying an automatic detection and location algorithm to both permanent Canadian National Seismic Network stations and temporary stations from the 2005-2006 BATHOLITHS deployment, resulting in 837 relocated events with at least 3 paired P and S phase picks. Double-difference relocation reveals several small-scale linear strands subparallel to the Coast Shear Zone and within the Anahim Volcanic Belt, and three clusters of events striking at a high angle to the Coast Shear Zone that occurred as swarms in 2015 and 2017. First-motion focal mechanisms exhibit extensional and strike-slip faulting. Our observations indicate that most of these events are not associated with surficial processes such as landslides, but rather, we hypothesize that interaction of the Anahim Volcanic Belt and Coast Shear Zone has weakened the lithosphere in this region leading to current-day strain localization and high heat flow that manifest seismicity including swarm-like activity.
{"title":"Seismicity at the Intersection of the Coast Shear Zone and Anahim Volcanic Belt near Bella Coola, British Columbia, Canada","authors":"G. Littel, M. Bostock","doi":"10.1139/cjes-2023-0057","DOIUrl":"https://doi.org/10.1139/cjes-2023-0057","url":null,"abstract":"In the Coast Mountains of western British Columbia, an anomalous seismicity concentration exists near the intersection of the Coast Shear Zone, a major NW-SE trending Eocene-age shear zone that accommodated deformation between the Pacific and North America plates, with the Anahim Volcanic Belt, an ENE-WSW trending zone of volcanic features that decrease in age to the east. To better characterize seismicity in the Coast Mountains, we augment the existing Natural Resources Canada seismicity catalog by applying an automatic detection and location algorithm to both permanent Canadian National Seismic Network stations and temporary stations from the 2005-2006 BATHOLITHS deployment, resulting in 837 relocated events with at least 3 paired P and S phase picks. Double-difference relocation reveals several small-scale linear strands subparallel to the Coast Shear Zone and within the Anahim Volcanic Belt, and three clusters of events striking at a high angle to the Coast Shear Zone that occurred as swarms in 2015 and 2017. First-motion focal mechanisms exhibit extensional and strike-slip faulting. Our observations indicate that most of these events are not associated with surficial processes such as landslides, but rather, we hypothesize that interaction of the Anahim Volcanic Belt and Coast Shear Zone has weakened the lithosphere in this region leading to current-day strain localization and high heat flow that manifest seismicity including swarm-like activity.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84585808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
He Jiao, Haifeng Lu, Guo-Biao Huang, Qiang-Qiang Cui, Q. Ding, Xuan Zhou, Ruiing Wu
The Yama fluorite deposit in the Qilian Orogen in NW China is characterized by predominant granitic magmatism and fluorite mineralization. The wall rocks hosting the fluorite–quartz veins in the Yama area consist of the Yama porphyritic syenogranite and the Wulandawu syenogranite. In this study, the major and trace element compositions, zircon U–Pb ages, and zircon Hf isotopes and trace element compositions were investigated. Two samples for the Yama porphyritic syenogranite yielded weighted mean 206Pb/238U zircon ages of 440.7±4.8 Ma and 447.9±6.0 Ma, and one sample for the Wulandawu syenogranite yielded a weighted mean 206Pb/238U zircon age of 441.2±5.0 Ma, all of which indicate a Late Ordovician to Early Silurian crystallization age. Geochemically, both syenogranites are peraluminous, with high alkali contents, low Zr+Nb+Ce+Y contents, relatively low (K2O+Na2O)/CaO ratios, and high Rb/Sr and Rb/Ba ratios, suggesting that they are fractionated S-type granites. They have zircon εHf(t) values of –14.9 to –4.4 and −12.2 to −4.5, respectively, suggesting that they were derived from the partial melting of pelitic-rich sources within the relatively shallow Paleoproterozoic reworked crust. The detailed geochronological and geochemical data suggest that the studied syenogranites were emplaced in a post-collisional setting related to the closure of the South Qilian Ocean. Finally, they have relatively low quantitative oxygen fugacity (fO2) values, indicating relatively reduced redox states, but their very low zircon Ce4+/Ce3+ ratios, low whole-rock K/Rb ratios, relatively high Nb/Ta ratios, and low Zr/Hf ratios suggest that they are not likely to form important W-Sn deposits and related fluorite deposits.
{"title":"Geochronology, petrogenesis, and mineralization potential of the syenogranites in the Yama fluorite deposit, Tataleng granitic batholith, Qilian Orogen, NW China","authors":"He Jiao, Haifeng Lu, Guo-Biao Huang, Qiang-Qiang Cui, Q. Ding, Xuan Zhou, Ruiing Wu","doi":"10.1139/cjes-2023-0044","DOIUrl":"https://doi.org/10.1139/cjes-2023-0044","url":null,"abstract":"The Yama fluorite deposit in the Qilian Orogen in NW China is characterized by predominant granitic magmatism and fluorite mineralization. The wall rocks hosting the fluorite–quartz veins in the Yama area consist of the Yama porphyritic syenogranite and the Wulandawu syenogranite. In this study, the major and trace element compositions, zircon U–Pb ages, and zircon Hf isotopes and trace element compositions were investigated. Two samples for the Yama porphyritic syenogranite yielded weighted mean 206Pb/238U zircon ages of 440.7±4.8 Ma and 447.9±6.0 Ma, and one sample for the Wulandawu syenogranite yielded a weighted mean 206Pb/238U zircon age of 441.2±5.0 Ma, all of which indicate a Late Ordovician to Early Silurian crystallization age. Geochemically, both syenogranites are peraluminous, with high alkali contents, low Zr+Nb+Ce+Y contents, relatively low (K2O+Na2O)/CaO ratios, and high Rb/Sr and Rb/Ba ratios, suggesting that they are fractionated S-type granites. They have zircon εHf(t) values of –14.9 to –4.4 and −12.2 to −4.5, respectively, suggesting that they were derived from the partial melting of pelitic-rich sources within the relatively shallow Paleoproterozoic reworked crust. The detailed geochronological and geochemical data suggest that the studied syenogranites were emplaced in a post-collisional setting related to the closure of the South Qilian Ocean. Finally, they have relatively low quantitative oxygen fugacity (fO2) values, indicating relatively reduced redox states, but their very low zircon Ce4+/Ce3+ ratios, low whole-rock K/Rb ratios, relatively high Nb/Ta ratios, and low Zr/Hf ratios suggest that they are not likely to form important W-Sn deposits and related fluorite deposits.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81297691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Rimando, A. Peace, K. Goda, Navid Sirous, P. Rosset, L. Chouinard
There is currently no active fault map for the intraplate western Quebec seismic zone (WQSZ) in eastern Canada, and consequently, no detailed finite-fault source models which are critical for seismic hazard assessments in this region with a rapidly growing population. While previous numerical stress modelling studies have shown that mostly NNW-SSE to NW-SE-striking faults exhibit the highest potential for reactivation under the present-day tectonic stress field, such modelling is unable to take into account the interaction of faults and earthquakes. This study attempts to identify possible future rupture zones using Coulomb stress analysis. We explore the static stress transfer caused by the 1935 M_W 6.1 Témiscaming, 1944 M_W 5.8 Cornwall-Massena, and the 2013 M_W 4.7 Ladysmith earthquakes, which are proximal to faults in the WQSZ that exhibit a relatively high reactivation potential, to determine if they have an increased potential for failure. The significance of Coulomb stress changes (ΔCFS) observed on the nearby ‘receiver’ faults varied widely. Among the events analyzed in this study, only the 1935 M_W 6.1 Témiscaming earthquake caused extensively positive ΔCFS (≥ 0.1 Bar) on its receiver fault. The areal extent of the receiver fault that has been promoted to failure suggests that earthquakes with a comparable magnitude to the 1935 event can be triggered. This work is the first attempt to provide a physical basis for seismic hazard assessment input parameters in the WQSZ based on the results of numerical stress modelling.
目前，加拿大东部魁北克西部板内地震带(WQSZ)没有活动断层图，因此，没有详细的有限断层源模型，而这些模型对该地区人口快速增长的地震危险性评估至关重要。以往的数值应力模拟研究表明，在现今的构造应力场下，大部分NNW-SSE至nw - se走向的断层表现出最高的再激活潜力，但这种模拟无法考虑断层与地震的相互作用。本研究试图利用库仑应力分析来确定未来可能的破裂带。我们研究了1935年m_w6.1 t miscaming地震、1944年m_w5.8 Cornwall-Massena地震和2013年m_w4.7 Ladysmith地震引起的静态应力传递，这些地震位于WQSZ断层附近，表现出相对较高的再激活潜力，以确定它们是否有增加的失败潜力。在附近的“接收断层”上观测到的库仑应力变化(ΔCFS)的意义差别很大。在本研究分析的事件中，只有1935年m_w6.1 tsammiscaming地震在其接收断层上引起了广泛的正ΔCFS(≥0.1 Bar)。接收断层被提升为失效的面积范围表明，可以触发与1935年事件相当震级的地震。本文首次尝试以数值应力模拟结果为基础，为该区地震危险性评价输入参数提供物理依据。
{"title":"Coseismic Coulomb Stress Changes on Intraplate Faults in the Western Quebec Seismic Zone Following Three Major Earthquakes in the Past Century","authors":"J. Rimando, A. Peace, K. Goda, Navid Sirous, P. Rosset, L. Chouinard","doi":"10.1139/cjes-2023-0025","DOIUrl":"https://doi.org/10.1139/cjes-2023-0025","url":null,"abstract":"There is currently no active fault map for the intraplate western Quebec seismic zone (WQSZ) in eastern Canada, and consequently, no detailed finite-fault source models which are critical for seismic hazard assessments in this region with a rapidly growing population. While previous numerical stress modelling studies have shown that mostly NNW-SSE to NW-SE-striking faults exhibit the highest potential for reactivation under the present-day tectonic stress field, such modelling is unable to take into account the interaction of faults and earthquakes. This study attempts to identify possible future rupture zones using Coulomb stress analysis. We explore the static stress transfer caused by the 1935 M_W 6.1 Témiscaming, 1944 M_W 5.8 Cornwall-Massena, and the 2013 M_W 4.7 Ladysmith earthquakes, which are proximal to faults in the WQSZ that exhibit a relatively high reactivation potential, to determine if they have an increased potential for failure. The significance of Coulomb stress changes (ΔCFS) observed on the nearby ‘receiver’ faults varied widely. Among the events analyzed in this study, only the 1935 M_W 6.1 Témiscaming earthquake caused extensively positive ΔCFS (≥ 0.1 Bar) on its receiver fault. The areal extent of the receiver fault that has been promoted to failure suggests that earthquakes with a comparable magnitude to the 1935 event can be triggered. This work is the first attempt to provide a physical basis for seismic hazard assessment input parameters in the WQSZ based on the results of numerical stress modelling.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78751154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hypersaline spring water (TDS ∼ 85 g/L) and gas are escaping from the top of a calcite travertine mound on Anticosti Island. This mound is located in the Chaloupe River area above the Jupiter Fault which cuts through the Ordovician formations in the subsurface, including the oil and gas-rich Macasty Shale Formation. The Cl content is approximately 3 times that of seawater, but the geochemical profile indicates it to be a Paleozoic basin brine (geogenic He = 2E–7 cc/cc) evaporatively enriched beyond halite saturation (Br:Cl molar ratio = 0.0022 ± 0.00013) that has been diluted by some 73 ± 6% with meteoric waters. Measurable tritium (3.4 TU) indicates this to be a mixture of modern and Holocene recharge. The radioiodine (129I < 10 million atoms/L) is a three-component mixture of geogenic and post-nuclear contributions with low levels in pre-nuclear Holocene recharge. Degassing at the vent (1% to 2% CO2, PCO2 = 0.02 atm, >90% CH4) provokes calcite precipitation and travertine mound formation. Methane comprises a thermo-catalytic component and a biogenic component produced at depth in the organic-rich Macasty Formation by reduction of surface-derived dissolved inorganic carbon (DIC; a14C = 3.5 pMC), producing enriched δ13CDIC values recorded in the travertine. The occurrence of basin-derived brine and gas discharging in association with the surface expression of the Jupiter fault implies that this fault provides a pathway for deep circulation of meteoric waters, likely driven by the relief on the island.
{"title":"Origin of gases and waters from a hypersaline, carbonate spring on Anticosti Island, Québec, Canada","authors":"P. Daoust, I. Clark, A. Desrochers","doi":"10.1139/cjes-2023-0019","DOIUrl":"https://doi.org/10.1139/cjes-2023-0019","url":null,"abstract":"Hypersaline spring water (TDS ∼ 85 g/L) and gas are escaping from the top of a calcite travertine mound on Anticosti Island. This mound is located in the Chaloupe River area above the Jupiter Fault which cuts through the Ordovician formations in the subsurface, including the oil and gas-rich Macasty Shale Formation. The Cl content is approximately 3 times that of seawater, but the geochemical profile indicates it to be a Paleozoic basin brine (geogenic He = 2E–7 cc/cc) evaporatively enriched beyond halite saturation (Br:Cl molar ratio = 0.0022 ± 0.00013) that has been diluted by some 73 ± 6% with meteoric waters. Measurable tritium (3.4 TU) indicates this to be a mixture of modern and Holocene recharge. The radioiodine (129I < 10 million atoms/L) is a three-component mixture of geogenic and post-nuclear contributions with low levels in pre-nuclear Holocene recharge. Degassing at the vent (1% to 2% CO2, PCO2 = 0.02 atm, >90% CH4) provokes calcite precipitation and travertine mound formation. Methane comprises a thermo-catalytic component and a biogenic component produced at depth in the organic-rich Macasty Formation by reduction of surface-derived dissolved inorganic carbon (DIC; a14C = 3.5 pMC), producing enriched δ13CDIC values recorded in the travertine. The occurrence of basin-derived brine and gas discharging in association with the surface expression of the Jupiter fault implies that this fault provides a pathway for deep circulation of meteoric waters, likely driven by the relief on the island.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84066636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Eberth, David C Evans, J. Ramezani, S. Kamo, Caleb M. Brown, P. Currie, D. R. Braman
The 100 m thick stratigraphic section exposed at Dinosaur Provincial Park (DPP, southern Alberta) contains bentonites that have been used for more than 30 years to date DPP's rocks and fossils using the K-Ar decay scheme. Limited reproducibility among different vintages of K-Ar and 40Ar/39Ar ages inhibited the development of a high resolution chronostratigraphy. Here we employ and further test a recently completed CA-ID-TIMS U–Pb geochronology and associated age-stratigraphy model to update temporal constraints on the Park’s bentonites, formational contacts, and other markers. In turn, we document rock accumulation rates, and calibrate ages and durations of informal megaherbivore dinosaur assemblage zones and other biozones. Weighted mean 206Pb/238U ages from five bentonites range from 76.718 ± 0.020 Ma to 74.289 ± 0.014 Ma (2σ internal uncertainties) through an interval of 88.75 m, indicating a duration of ~2.43 Myr and an overall rock accumulation rate of 3.65 ± 0.04 cm/ka. An increase in rate above the Oldman-Dinosaur Park formational contact conforms to a regionally expressed pattern of increased accommodation at ~76.3 Ma across Alberta and Montana. Palynological biozone data suggest a condensed section/hiatus in the uppermost portion of the Oldman Formation. Dinosaur assemblage zones exhibit durations of ~600–700 kyr and are significantly shorter than those in the overlying Horseshoe Canyon Formation. A decreased rate in dinosaur-assemblage turnovers in the last eight million years of the Mesozoic in western Canada may be explained by withdrawal of the Western Interior Seaway and the expansion of ecologically homogenous lowlands in its wake.
在阿尔伯塔省南部的恐龙省立公园(DPP)出土的100米厚的地层剖面中含有膨润土，使用K-Ar衰变方案对DPP的岩石和化石进行了30多年的测定。不同年份K-Ar和40Ar/39Ar年龄的可重复性有限，抑制了高分辨率年代学的发展。在这里，我们采用并进一步测试了最近完成的CA-ID-TIMS U-Pb地质年代学和相关的年龄-地层学模型，以更新公园膨润土、地层接触和其他标志的时间限制。反过来，我们记录了岩石堆积速率，并校准了非正式的巨型食草恐龙组合带和其他生物带的年龄和持续时间。5个膨润土的加权平均206Pb/238U年龄范围为76.718±0.020 Ma ~ 74.289±0.014 Ma (2σ内部不确定度)，间隔为88.75 m，持续时间为~2.43 Myr，总体堆积速率为3.65±0.04 cm/ka。在奥德曼-恐龙公园地层接触面以上的增加速率符合阿尔伯塔和蒙大拿州~76.3 Ma增加可容纳性的区域表达模式。孢粉生物带资料显示，在Oldman组的最上部有一个浓缩剖面/裂孔。恐龙组合带的持续时间约为600-700 kyr，明显短于其上的马蹄峡谷组。在加拿大西部中生代的最后800万年里，恐龙组合的更替率下降，这可能是由于西部内陆海道的退缩和其后生态上同质的低地的扩张。
{"title":"Calibrating geologic strata, dinosaurs, and other fossils at Dinosaur Provincial Park (Alberta, Canada) using a new CA-ID-TIMS U–Pb geochronology","authors":"D. Eberth, David C Evans, J. Ramezani, S. Kamo, Caleb M. Brown, P. Currie, D. R. Braman","doi":"10.1139/cjes-2023-0037","DOIUrl":"https://doi.org/10.1139/cjes-2023-0037","url":null,"abstract":"The 100 m thick stratigraphic section exposed at Dinosaur Provincial Park (DPP, southern Alberta) contains bentonites that have been used for more than 30 years to date DPP's rocks and fossils using the K-Ar decay scheme. Limited reproducibility among different vintages of K-Ar and 40Ar/39Ar ages inhibited the development of a high resolution chronostratigraphy. Here we employ and further test a recently completed CA-ID-TIMS U–Pb geochronology and associated age-stratigraphy model to update temporal constraints on the Park’s bentonites, formational contacts, and other markers. In turn, we document rock accumulation rates, and calibrate ages and durations of informal megaherbivore dinosaur assemblage zones and other biozones. Weighted mean 206Pb/238U ages from five bentonites range from 76.718 ± 0.020 Ma to 74.289 ± 0.014 Ma (2σ internal uncertainties) through an interval of 88.75 m, indicating a duration of ~2.43 Myr and an overall rock accumulation rate of 3.65 ± 0.04 cm/ka. An increase in rate above the Oldman-Dinosaur Park formational contact conforms to a regionally expressed pattern of increased accommodation at ~76.3 Ma across Alberta and Montana. Palynological biozone data suggest a condensed section/hiatus in the uppermost portion of the Oldman Formation. Dinosaur assemblage zones exhibit durations of ~600–700 kyr and are significantly shorter than those in the overlying Horseshoe Canyon Formation. A decreased rate in dinosaur-assemblage turnovers in the last eight million years of the Mesozoic in western Canada may be explained by withdrawal of the Western Interior Seaway and the expansion of ecologically homogenous lowlands in its wake.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72562048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The structural geology of the northeastern Paleoproterozoic Amer belt, central Nunavut, has been evaluated in light of new field mapping combined with legacy data and independently acquired subsurface geophysics data. Proterozoic sequences Ps1–Ps4 of the Amer supergroup unconformably overlie Archean basement. Of these sequences, Ps1–Ps3 have been intensely deformed (D1) in association with the Snowbird Orogeny (2.05–1.865 Ga). Ps4 was deposited unconformably on the first three sequences and exhibits none of the D1 effects. Deformation within Ps4 is slight compared to the underlying sequences and is restricted to D2 folding that occurred in the 1.84–1.81 Ga Hudsonian Orogeny. Deformation of sequences Ps1–Ps3 forms the core of this study. D1 comprises imbricate thrusting, intersequence detachment, and three generations of isoclinal folding and transposition. The stratigraphic order is maintained in many areas by decoupling of sequence packages along incompetent units so as not to “mix” lithologies; there is a fundamental mechanical stratigraphy. Within sequences, transposition can be otherwise intense. The resultant architecture is a shallowly southwest-dipping sequence of tectonically rotated and transposed layering (primary and tectonic) similar in many ways in orientation regardless of whether preserved with original bedding features or completely transposed. D1 folding is characterized by recumbent folds, noncylindrical folds that are sometimes rooted in detachments, verging to the northeast. D2 folding is controlled by the pre-existing large-scale D1 fabric, resulting in the overturned synforms that parallel the belt. Post-D2 fault modification of northern side of the belt along northwest-trending faults is interpreted to relate to extension and exhumation.
{"title":"Paradoxical mid-crustal displacements and stratigraphic continuity: structural evolution of the northeastern Paleoproterozoic Amer belt, Nunavut, Canada","authors":"J. White, Lydia Calhoun, C. Jefferson","doi":"10.1139/cjes-2022-0083","DOIUrl":"https://doi.org/10.1139/cjes-2022-0083","url":null,"abstract":"The structural geology of the northeastern Paleoproterozoic Amer belt, central Nunavut, has been evaluated in light of new field mapping combined with legacy data and independently acquired subsurface geophysics data. Proterozoic sequences Ps1–Ps4 of the Amer supergroup unconformably overlie Archean basement. Of these sequences, Ps1–Ps3 have been intensely deformed (D1) in association with the Snowbird Orogeny (2.05–1.865 Ga). Ps4 was deposited unconformably on the first three sequences and exhibits none of the D1 effects. Deformation within Ps4 is slight compared to the underlying sequences and is restricted to D2 folding that occurred in the 1.84–1.81 Ga Hudsonian Orogeny. Deformation of sequences Ps1–Ps3 forms the core of this study. D1 comprises imbricate thrusting, intersequence detachment, and three generations of isoclinal folding and transposition. The stratigraphic order is maintained in many areas by decoupling of sequence packages along incompetent units so as not to “mix” lithologies; there is a fundamental mechanical stratigraphy. Within sequences, transposition can be otherwise intense. The resultant architecture is a shallowly southwest-dipping sequence of tectonically rotated and transposed layering (primary and tectonic) similar in many ways in orientation regardless of whether preserved with original bedding features or completely transposed. D1 folding is characterized by recumbent folds, noncylindrical folds that are sometimes rooted in detachments, verging to the northeast. D2 folding is controlled by the pre-existing large-scale D1 fabric, resulting in the overturned synforms that parallel the belt. Post-D2 fault modification of northern side of the belt along northwest-trending faults is interpreted to relate to extension and exhumation.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87652044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Long, C. Jefferson, R. Rainbird, Patricia Corcoran
{"title":"Understanding the Precambrian: a collection of papers in celebration of the life and work of Grant McAdam Young (1937–2020)","authors":"D. Long, C. Jefferson, R. Rainbird, Patricia Corcoran","doi":"10.1139/cjes-2022-0111","DOIUrl":"https://doi.org/10.1139/cjes-2022-0111","url":null,"abstract":"","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90781941","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Cheakamus basalts are voluminous (1.65 km3) Late Pleistocene, valley-filling lavas erupted from a vent situated near Conflict Lake, in the alpine Callaghan Valley near Whistler, British Columbia. Geochemical and petrographic properties suggest these olivine-plagioclase porphyritic basalts derive from a single magma batch affected by minor sorting of phenocrysts and xenocrystic plagioclase. Thirty-four sites sampled for paleomagnetic direction measurement record a mean pole direction of 345.2 ̊ / 73.0 ̊ (α95 = 1.3°), showing no statistical variation nor drift with stratigraphic position. These data suggest the lavas were emplaced in a single paleomagnetic moment – a period of time significantly less than 2,000 years. 40Ar/39Ar geochronometry on three samples return a weighted mean age estimate of 15.95 ± 7.9 ka (2s) and field evidence, including till-covered, well-glaciated lava flow surfaces, indicate the eruption coincided with the early stages of the Fraser glaciation (~18-20 ka). The lavas preserve features indicative of a landscape hosting diverse and dynamic paleoenvironments. Subaerial eruption of basalt filled an ice-free Callaghan Creek drainage before inundating and damming the paleo-Cheakamus River, creating an upstream rising body of water. Periodic lava-dam overtopping resulted in syn-eruptive intermittent flooding of lava surfaces, expressed by discontinuous interflow sediment lenses. Rare instances of enigmatic cooling columns may also indicate localized ice-contact with glaciers that partially filled the Cheakamus Valley. The displacement of the modern Cheakamus River and the formation of Callaghan and Conflict Lakes via long-term lava-damming remain direct indicators of the impact basaltic eruptions have on the geomorphology of valley systems.
Cheakamus玄武岩是巨大的(1.65 km3)晚更新世，山谷填充熔岩喷发自位于冲突湖附近的一个喷口，位于不列颠哥伦比亚省惠斯勒附近的高山卡拉汉山谷。地球化学和岩石学特征表明，这些橄榄石-斜长石斑状玄武岩来自单一岩浆批，受斑晶和异晶斜长石的轻微分选影响。34个古地磁测向点的平均极向为345.2℃/ 73.0℃(α95 = 1.3℃)，与地层位置无统计学差异和漂移。这些数据表明，熔岩是在一个单一的古磁极时刻形成的——一个明显不到2000年的时期。3个样品的40Ar/39Ar年代学的加权平均年龄估计为15.95±7.9 ka (2s)，而现场证据(包括未被覆盖且冰川覆盖良好的熔岩流表面)表明，火山喷发与弗雷泽冰川的早期阶段(~18-20 ka)一致。熔岩保存的特征表明，这里的景观具有多样性和动态的古环境。玄武岩的地面喷发填满了无冰的卡拉汉河流域，然后淹没并阻塞了古切卡穆斯河，形成了上游上升的水体。周期性的熔岩坝溢流导致岩浆面同步喷发的间歇洪水，表现为不连续的互流沉积物透镜体。罕见的神秘的冷却柱也可能表明，切卡穆斯山谷与冰川局部接触。现代切卡穆斯河(Cheakamus River)的位移，以及长期熔岩淤积形成的卡拉汉湖(Callaghan)和冲突湖(Conflict Lakes)，仍然是玄武岩喷发对山谷系统地貌影响的直接指标。
{"title":"Cheakamus Basalt Lavas, British Columbia: A Pleistocene record of rapid, continuous eruption within a mountainous drainage system","authors":"A. Borch, J. Russell, R. Barendregt","doi":"10.1139/cjes-2023-0004","DOIUrl":"https://doi.org/10.1139/cjes-2023-0004","url":null,"abstract":"The Cheakamus basalts are voluminous (1.65 km3) Late Pleistocene, valley-filling lavas erupted from a vent situated near Conflict Lake, in the alpine Callaghan Valley near Whistler, British Columbia. Geochemical and petrographic properties suggest these olivine-plagioclase porphyritic basalts derive from a single magma batch affected by minor sorting of phenocrysts and xenocrystic plagioclase. Thirty-four sites sampled for paleomagnetic direction measurement record a mean pole direction of 345.2 ̊ / 73.0 ̊ (α95 = 1.3°), showing no statistical variation nor drift with stratigraphic position. These data suggest the lavas were emplaced in a single paleomagnetic moment – a period of time significantly less than 2,000 years. 40Ar/39Ar geochronometry on three samples return a weighted mean age estimate of 15.95 ± 7.9 ka (2s) and field evidence, including till-covered, well-glaciated lava flow surfaces, indicate the eruption coincided with the early stages of the Fraser glaciation (~18-20 ka). The lavas preserve features indicative of a landscape hosting diverse and dynamic paleoenvironments. Subaerial eruption of basalt filled an ice-free Callaghan Creek drainage before inundating and damming the paleo-Cheakamus River, creating an upstream rising body of water. Periodic lava-dam overtopping resulted in syn-eruptive intermittent flooding of lava surfaces, expressed by discontinuous interflow sediment lenses. Rare instances of enigmatic cooling columns may also indicate localized ice-contact with glaciers that partially filled the Cheakamus Valley. The displacement of the modern Cheakamus River and the formation of Callaghan and Conflict Lakes via long-term lava-damming remain direct indicators of the impact basaltic eruptions have on the geomorphology of valley systems.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87569185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Geodynamic models allow insights into the processes that control lithosphere structure and evolution. Here, we highlight geodynamic studies along a profile through southwestern Canada, from the Cascadia subduction zone into the Laurentian craton. Geophysical and geological observations show distinct changes in thermal structure along this profile. One major change is between the cool forearc and hot volcanic arc. This marks the transition from (1) a stagnant forearc mantle that is cooled by the subducting Juan de Fuca Plate to (2) an advection-dominated arc region, where high temperatures arise from mantle flow driven by the subducting plate (corner flow). High temperatures occur for 400-500 km east of the arc to the Rocky Mountain Trench (RMT), where lithosphere thickness increases from 60-70 km below the Cordillera to >200 km below the craton. The timing of Cordillera lithosphere thinning is debated. A long-lived (>100 Ma) thin lithosphere inherited from earlier tectonics requires vigorous convection of a weak, hydrated mantle. Conversely, thinning may have occurred through gravitational removal of the lower lithosphere in the Eocene. Models show that a removal event only allows for a short-lived thin lithosphere (~25 Myr), owing to conductive cooling. Even if there was Eocene delamination, the present-day thin lithosphere requires small-scale convection in the Cordillera mantle. The thermal contrast across the RMT is enhanced by edge-driven convection at the Cordillera-craton lithosphere step. The step itself is an enigmatic feature, and its long-term preservation requires that the craton mantle lithosphere is strong (dry) with moderate chemical depletion.
{"title":"Geodynamic studies of southwestern Canada: Subduction zone processes and backarc mantle dynamics","authors":"C. Currie, Tai‐Chieh Yu","doi":"10.1139/cjes-2022-0140","DOIUrl":"https://doi.org/10.1139/cjes-2022-0140","url":null,"abstract":"Geodynamic models allow insights into the processes that control lithosphere structure and evolution. Here, we highlight geodynamic studies along a profile through southwestern Canada, from the Cascadia subduction zone into the Laurentian craton. Geophysical and geological observations show distinct changes in thermal structure along this profile. One major change is between the cool forearc and hot volcanic arc. This marks the transition from (1) a stagnant forearc mantle that is cooled by the subducting Juan de Fuca Plate to (2) an advection-dominated arc region, where high temperatures arise from mantle flow driven by the subducting plate (corner flow). High temperatures occur for 400-500 km east of the arc to the Rocky Mountain Trench (RMT), where lithosphere thickness increases from 60-70 km below the Cordillera to >200 km below the craton. The timing of Cordillera lithosphere thinning is debated. A long-lived (>100 Ma) thin lithosphere inherited from earlier tectonics requires vigorous convection of a weak, hydrated mantle. Conversely, thinning may have occurred through gravitational removal of the lower lithosphere in the Eocene. Models show that a removal event only allows for a short-lived thin lithosphere (~25 Myr), owing to conductive cooling. Even if there was Eocene delamination, the present-day thin lithosphere requires small-scale convection in the Cordillera mantle. The thermal contrast across the RMT is enhanced by edge-driven convection at the Cordillera-craton lithosphere step. The step itself is an enigmatic feature, and its long-term preservation requires that the craton mantle lithosphere is strong (dry) with moderate chemical depletion.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80753857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lac Simard is a glaciated Shield basin situated in the Western Quebec Seismic Zone, an area of recurrent intraplate seismicity encompassing several densely populated areas. Previous works nearby have demonstrated that sediments preserved in lake basins hold the potential to serve as valuable archives of paleoseismicity. Correspondingly, a high-resolution chirp seismic reflection survey was conducted in Lac Simard, with results showing four acoustic facies (Af-1 to Af-4) within two stratigraphic successions (SS-1 and SS-2). The lowermost SS-1 is dominated by high-amplitude, laminated Af-2, interpreted as lateglacial varves deposited by suspension from primarily overflows and interflows during glacial lake ponding following deglaciation. Suspension deposition of Af-2 was episodically interrupted by stacked, chaotically bedded, weakly graded to opaque, channelled Af-3 interpreted as either debris flows or high-density turbidity currents. Presence of silt-clast breccias in Af-3 also suggests downslope collapse and reworking of varves from basin sidewalls. The overlying SS-2 is dominated by weakly reflective, laminated, high-frequency varved Af-4, suggesting a continuing seasonal control on postglacial sedimentation but with relative sediment starvation. A basin-wide erosional unconformity separating SS-1 and postglacial SS-2 records the abrupt drainage of glacial Lake Barlow-Ojibway around 8 000 years ago. Considering the history of lake floor disturbance in the region, mass flow facies Af-3 may be seismogenic, and thus, have regional tectonic significance. However, we cannot rule out the possibility of mass flows triggered by abrupt inflows of meltwater and sediment from a highly dynamic retreating Laurentide Ice Sheet prone to surging.
{"title":"Seismic reflection stratigraphy of Lac Simard, Quebec, Canada: mass flow sedimentation in glacial Lake Barlow-Ojibway","authors":"A.J. Yu, N. Eyles, M. Doughty, S. Bukhari","doi":"10.1139/cjes-2023-0027","DOIUrl":"https://doi.org/10.1139/cjes-2023-0027","url":null,"abstract":"Lac Simard is a glaciated Shield basin situated in the Western Quebec Seismic Zone, an area of recurrent intraplate seismicity encompassing several densely populated areas. Previous works nearby have demonstrated that sediments preserved in lake basins hold the potential to serve as valuable archives of paleoseismicity. Correspondingly, a high-resolution chirp seismic reflection survey was conducted in Lac Simard, with results showing four acoustic facies (Af-1 to Af-4) within two stratigraphic successions (SS-1 and SS-2). The lowermost SS-1 is dominated by high-amplitude, laminated Af-2, interpreted as lateglacial varves deposited by suspension from primarily overflows and interflows during glacial lake ponding following deglaciation. Suspension deposition of Af-2 was episodically interrupted by stacked, chaotically bedded, weakly graded to opaque, channelled Af-3 interpreted as either debris flows or high-density turbidity currents. Presence of silt-clast breccias in Af-3 also suggests downslope collapse and reworking of varves from basin sidewalls. The overlying SS-2 is dominated by weakly reflective, laminated, high-frequency varved Af-4, suggesting a continuing seasonal control on postglacial sedimentation but with relative sediment starvation. A basin-wide erosional unconformity separating SS-1 and postglacial SS-2 records the abrupt drainage of glacial Lake Barlow-Ojibway around 8 000 years ago. Considering the history of lake floor disturbance in the region, mass flow facies Af-3 may be seismogenic, and thus, have regional tectonic significance. However, we cannot rule out the possibility of mass flows triggered by abrupt inflows of meltwater and sediment from a highly dynamic retreating Laurentide Ice Sheet prone to surging.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78400587","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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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