2023

Permanent URI for this collectionhttps://hdl.handle.net/1807/126406

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Changing your perspective: the impact of different visualisation methods on seismic hazard maps
(Canadian Science Publishing, 2024-09-16) Yin, Yue; Crameri, Fabio; Shephard, Grace; Heron, Philip J
A number of widely used colour palettes applied to display critical scientific results not only distort data but are also inaccessible to a proportion of the population. An issue with the rainbow palette (and variants such as ‘jet’) is that the gradients between the colours are not even. The impact of an uneven colour gradient is that certain colours are highlighted over others, distorting the underlying data. Furthermore, an uneven colour palette like rainbow may be inaccessible for people with colour vision deficiencies or colour blindness. When communicating scientific results, data should always be presented without distortion and be universally accessible. This is particularly important when communicating public-facing and time-critical information such as hazards. Here, we show the impact of changing the visualisation profile of seismic hazard maps on the perception of risk, as well as qualifying the public accessibility of this information. Using Canadian seismic hazard as an example, our results reveal that an uneven colour map applied to seismic hazard data can exaggerate lower hazard values and reduce the perception of extremely high hazard values. Applying an even colour gradient to our sample data not only allows this essential public resource to be universally accessible but was found to lead to the greatest visual change in regions with the most populated cities. The choice of colour map and subsequent data interpretations also holds relevance for considerations such as insurance. We highlight potential next steps to promote inclusiveness in data visualisation and welcome discussion on science communication best practices.
The Ottawa River Gneiss Complex revisited: definition of the metamorphic core and detachment zone of a large Grenvillian metamorphic core complex
(Canadian Science Publishing, 2023-10-10) Rivers, Toby; Schwerdtner, Walfried M.
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.
Petrology and lithogeochemistry of Paleozoic alkalic magmatism in the Selwyn Basin, Yukon, Canada
(Canadian Science Publishing, 2023-12-18) Scanlan, Emma J; LEYBOURNE, Matthew; Layton-Matthews, Dan; Van Wagoner, Nancy; Paradis, Suzanne; Piercey, Stephen J.; Crowley, James L.
Alkalic magmatism occurred in the Selwyn Basin, Yukon, Canada throughout the Paleozoic, concurrent with extension during passive margin sedimentation. To examine magmatism associated with this extension, geochemical data were obtained from several locations in the Selwyn Basin (MacMillan Pass, Anvil District, Keno Hill, and the Misty Creek Embayment). Volcanic rocks from the Anvil District and the Misty Creek Embayment are dominated by alkalic basalts with LREE-enriched geochemical signatures whereas metavolcanic and dike samples from Keno Hill comprise subalkaline basalts with E-MORB signatures. The Early Ordovician Menzie Creek volcanic rocks of the Anvil District display trace element geochemical signatures intermediate between OIB and E-MORB, whereas the Middle-Late Ordovician volcanic rocks from the Misty Creek Embayment have OIB signatures. Differences in the trace element geochemistry of the sample suites are attributed to the degree of partial melting. The Menzie Creek volcanic rocks formed from large volume melts of enriched mantle that diluted incompatible element signatures in the Early Ordovician. Late Ordovician magmatism produced the Misty Creek Embayment samples, where restricted melt volumes of an enriched mantle source resulted in the most enriched samples geochemically. The Keno Hill samples represent the shallowest melting of the analysed samples and may have resulted from melting of heterogenous subcontinental lithospheric mantle. Magmatic zircons from a Keno Hill metavolcanic sample analysed by CA-TIMS resulted in a primary deposition age of c. 296 ± 0.36 Ma (Early Permian), during a period with little magmatism in the Selwyn Basin and representing a previously unknown unit in the area.
Calibrating geologic strata, dinosaurs, and other fossils at Dinosaur Provincial Park (Alberta, Canada) using a new CA-ID-TIMS U–Pb geochronology
(Canadian Science Publishing, 2023-06-12) Eberth, David Anthony; Evans, David C.; Ramezani, Jahandar; Kamo, Sandra L.; Brown, Caleb Marshall; Currie, Philip J.; Braman, Dennis R.
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.
Seismicity and Seismic Monitoring of Canada's Volcanic Zones
(Canadian Science Publishing, 2023-08-31) Cassidy, John F.; Mulder, Taimi L.
Canada’s recently active volcanic zones (e.g., eruptions during the past 10,000 years) are all located along the tectonic plate boundary region of western Canada, extending for more than 2000 km from southern British Columbia to the Yukon/Alaska border. In this article, we describe the history of seismic monitoring in and near these volcanic zones and the past and current seismicity detection thresholds. The most recently active volcanoes in Canada are Tseax Cone (~1700) and Lava Forks (1800’s), both in northwestern British Columbia. However, no eruptions have occurred in Canada since the deployment of the earliest seismographs in 1898 (Victoria, BC) and 1904 (Sitka, Alaska). Seismic detection levels have decreased from M~7 in 1900 to M~0-1 (in many regions) today, with more than 120 seismic stations currently operating in British Columbia and the Yukon, including ~20 seismic stations within the volcanic zones. The most recent significant seismic activity attributed to volcanic zones in Canada is the 2007 Nazko Cone earthquake swarm when nearly 1000 tiny (M
Net evolution of subglacial sediment transport in the Quebec-Labrador sector of the Laurentide Ice Sheet
(Canadian Science Publishing, 2023-12-04) Rice, Jessey; Ross, Martin; Campbell, Heather; Paulen, Roger C.; McClenaghan, M. Beth
The Laurentide Ice Sheet's (LIS) interior had a dynamic polythermal base, but the spatiotemporal variations of subglacial processes related to ice-divide migration and other transient changes remain largely unknown, limiting our understanding of regional glacial dynamics. Previous studies focused on the regional glacial landform record, while ice sheet models lacked detailed parameterization within these regions, leading to an overestimation of cold-based subglacial conditions' extent and duration. In this study, glacial sediment dispersal patterns as identified by heavy minerals, clasts, and multivariate statistics of till matrix geochemistry were used to assess ice-sheet dynamics within the Quebec-Labrador sector of the LIS. The earliest ice-flow phase produced and transported till across the study area (> 175 km). However, major oxide data from till matrix geochemistry shows a correlation with underlying bedrock and this relationship is relatively common in areas of thin till cover and resistant bedrock lithologies. These results suggest a switch from an early phase of widespread erosion and long, sustained sediment transport to one of more limited erosion, perhaps abrasion dominant, and shorter transport. Till compositional data and related dispersal patterns add supporting evidence to earlier ice sheet reconstructions based on ice-flow indicators and 10Be data together suggesting a transition from widespread uniform warm-based conditions during the earliest ice-flow followed by the development of an ice divide, its migration, and more sporadic warm-based conditions. Consequently, a thorough understanding of ice-flow history is essential for ice sheet modelling and future mineral exploration programs in inner ice sheet regions of the LIS.
Structural Geology of the Mount Meager Volcanic Complex, BC, Canada: Implications for geothermal energy and geohazards
(Canadian Science Publishing, 2023-10-04) Muhammad, Mahmud; Williams-Jones, Glyn; Barendregt, René W.
The Mount Meager Volcanic Complex (Qwe̓lqwe̓lústen or Mt. Meager) coincides tectonically with the intra-arc to back-arc transition zone and exhibits the loci of strain partitioning in response to a rapid change in orientation of the Pemberton and Garibaldi Arc segments which are coeval with a shift in Pacific plate motion after 5 Ma. This strain partition is manifested through development of a transpressional deformation from 5 Ma to 1.9 Ma at the latitude of Mt. Meager. Mt. Meager is an active volcanic system with at least two explosive eruptions in the last 25,000 years, the most recent occurring around 2360 BP. Additionally, it is the site of the largest landslide in Canadian history, which occurred during the summer of 2010, originating from the southeastern side the massif. During early exploration at Mt. Meager, geothermal boreholes drilled to 3 km reached 270°C but did not find sufficient permeability to sustain self-flowing conditions. To understand the geological challenges in Mt. Meager's geothermal exploration, we analyzed outcrop-scale faults and folds, incorporating structural mapping, volcanic rock paleomagnetism, and radiometric dating to establish kinematic history and kinematic compatibility of structural geology features including faults and folds. Our findings suggest that stress partitioning during the last 5 Ma resulted in formation of a transpressional structure exhibited as an elongate and rhomboidal structure at Mt. Meager with anomalously high topographic elevations which led to ENE-WSW crustal shortening and exhumation of crystalline basement. This new structural geology model improves our understanding of the geothermal reservoir and potentially significant geohazards.
Analysis of the late Hirnantian and early Rhuddanian Unconformities of Southern Ontario: Evidence for Far Field Glacioeustatic Effects
(Canadian Science Publishing, 2023-12-08) Farnam, Cole Austin; Brett, Carlton
Several unconformities have been previously recognized in the Late Ordovician and early Silurian strata of southern Ontario. We examined the Georgian Bay, Queenston, Whirlpool, Manitoulin, Power Glen, Cabot Head formations and associated unconformities. Detailed sequence stratigraphic and chemostratigraphic analysis of Late Ordovician and early Silurian outcrops between Niagara, New York and Manitoulin Island, Ontario reveals new insights on the timing of the erosional unconformities and the Ordovician–Silurian boundary. We recognize three significant lowstand unconformities in this interval, which are referred to as the Cherokee, S1B and S2 unconformities. Additional small-scale surfaces are present but do not reflect any major change in sea level or pause in sedimentation. Using δ13Ccarb chemostratigraphy, biostratigraphy and sequence stratigraphy we tentatively correlate units and the mentioned unconformities from southern Ontario to other eastern North American sections of comparable age, showing how glacioeustasy had a widespread effect on the deposition and removal of strata in far-field, subtropical basins. The Cherokee Unconformity appears to be a composite erosion surface found across eastern North America that formed during the two or more episodes of glacioeustatic sea level fall in the early to middle Hirnantian. The overlying S1B and S2 unconformities can also be found across eastern North America and appear to be the result of glacioeustatic sea level fall occurring during the early Silurian. Additionally, these new insights on the timing of these erosional unconformities help better constrain the placement of the Ordovician/Silurian Boundary in Ontario.
LA–ICP–MS zircon U–Pb age, geochemistry, and genesis of Paleozoic granite in Biezhentao Mountain, Western Tianshan, Xinjiang
(Canadian Science Publishing, 2023-11-15) Li, Xiang; Xia, Fang; Gao, Ling-Ling; Chen, Chuan; Du, Xiao-Fei; Li, Shunda
The geologic history of the Western Tianshan region is important for understanding the evolution of the Central Asian Orogenic Belt and accretionary orogenesis. Paleozoic and Mesozoic igneous rocks are present along the northern margin of the Yili Block; however, studies of Paleozoic subduction and collisional events have been relatively limited. Published geochronologies of Middle Devonian magmatic rocks in this region are also lacking. Therefore, this study analyzed the zircon U-Pb ages and major and trace elemental compositions of three granite types collected from Biezhentao Mountain (Wenquan County, Western Tianshan). The medium-grained diorite (384.1 ± 3.6 Ma) and diorite-porphyrite (382 ± 3.2 Ma) are silica-rich, weakly peraluminous, alkali-rich, enriched in large ion lithophile elements, depleted in high field strength elements, and belong to the calc-alkaline series, with A-type granite characteristics. The monzogranite (423.3 ± 9.4 Ma) exhibits A-type granite characteristics and belongs to the peraluminous calc-alkaline series. The findings suggest that the granitoids recorded two stages of tectonomagmatism during the Middle Devonian–Late Silurian. The Middle Devonian medium-grained diorite and diorite-porphyrite formed in a back-arc extensional setting, whereas the Late Silurian monzogranite formed in an active continental margin setting during the subduction of the North Tianshan Ocean. These results provide insights into the tectonic and magmatic processes that occurred during the evolution of the Western Tianshan region and the formation and evolution of the Central Asian Orogenic Belt.
Late history of glacial Lake Agassiz in northwestern Ontario, Canada: A case study in the Sandy Lake basin
(Canadian Science Publishing, 2023-11-20) Gao, Cunhai
The Sandy Lake basin in northwestern Ontario is a potentially important area for insights into the late history of glacial Lake Agassiz because of its extensive glaciolacustrine deposits and well-preserved shoreline features of this geological episode. However, little information is available on its deglaciation history. Recent mapping shows the withdrawal of the ice from the basin center and subsequent deposition of extensive varved clay in the lake with an OSL-dated maximum age at 11.4 ± 0.9 ka. With its further recession, the ice constructed the Opasquia moraine on the northern rim of the basin sometime before the development on the moraine of the first major shoreline of the lake (The The Pas, inferred at 10.1 ka). Lowering of the lake level formed many strandlines on the moraine and elsewhere in the basin, which can be correlated with those in the main Agassiz basin based on projected water planes (The The Pas to Ponton). Radiocarbon dating on basal wood remains of surface peat in a former strait defined by the Ponton shoreline and a nearby site on the former lake floor indicates the abandonment of this shoreline and hence the withdrawal of Lake Agassiz from the Sandy Lake basin by 8.3 ± 0.1 cal ka (UOC-7883). The date although a minimum-limiting age provides the hitherto best possible age constraint for the Ponton-Kinojévis shorelines which many hypothesize represent one of the major lake levels during the final drainage of Lake Agassiz into Hudson Bay but have never been adequately dated before.
Evaluation of Carbon Dioxide Sequestration via Interaction with Peridotite and Peridotite Hosted Groundwaters. An Experimental Case Study with Bay of Islands Ophiolite Rocks, Western Newfoundland, Canada.
(Canadian Science Publishing, 2023-10-10) Gill, Matthew James; Poduska, Kristin M.; Morrill, Penny
This study measured the CO2 gas flux into various aqueous media (i.e., simulated ultra-basic and basic groundwater, and deionized water) containing ultramafic rock. Basic and ultra-basic waters simulated the aqueous chemistry and ion concentrations of distinct groundwaters found within terrestrial ultramafic bodies. Experiments were performed in a closed chamber in line with a CO2 analyzer, which measured the gaseous CO2 concentration in the chamber every second. Total inorganic carbon, as well as aqueous species Ca, Mg, and Si were monitored in the reaction fluids. All three fluid types sequestered CO2. The addition of crushed peridotite to deionized water reduced the CO2 concentration in the headspace by 70 ppm (± 9 ppm, 1σ, n=3) and had a calculated CO2 flux of -2.5 x 104 mol/m
The Empress Group in Alberta, Canada
(Canadian Science Publishing, 2023-07-24) Hartman, Gregory Michael Douglas; Pawley, Steven M.; Utting, Daniel J; Atkinson, Nigel; Liggett, Jessica E.
Basal gravel and sand mantling the bedrock floors of buried valleys throughout the Canadian Interior Plains, and conformably overlying proglacial lacustrine sediment, comprise the Empress Group. While previously conceptualized as stratigraphically equivalent deposits of preglacial rivers prior to the first and most extensive continental and montane glaciations, subsequent stratigraphic studies indicated that buried valley basal gravel must have been deposited between, or during, progressively more extensive continental glaciations and could not be stratigraphically equivalent throughout the buried valley network. However, in the general absence of formation-rank stratigraphic description of basal gravel units that might better inform the geologic history of the deposits, most workers simply consider Empress Group sediments time-transgressive. In this paper we examine basal gravel at provincial and regional scales to understand its genesis and geologic history. At the provincial scale we map basal gravel in three dimensions using a novel machine learning approach. At the regional scale we formally define basal gravel formations at either end of the largest buried valley system in Alberta, which informs its glacial history and physiographic development, and shows the importance of formation-rank stratigraphic description. Our results indicate that the buried valley network across Alberta is palimpsest in genesis and basal gravel units within it are chronostratigraphically intercalated between tills. We advocate that the Empress Group definition be extended across Alberta with modifications to improve its clarity and utility, and formally define the Old Fort, Unchaga, Ipiatik, and Winefred formations as part of the Empress Group.
PbIso: an R package and web app for calculating and plotting Pb isotope data
(Canadian Science Publishing, 2023-07-05) Armistead, Sheree; Eglington, Bruce; Pehrsson, Sally J.
The package PbIso is a free and open R toolbox for commonly used calculations and plots of Pb-Pb isotope data and for generating Pb evolution models. In this paper, we review Pb isotope systematics and the calculations that are commonly used, such as model age, model source (238U/204Pb), time-integrated (232Th/238U), and initial Pb isotope ratios. These equations are implemented into R functions in the package PbIso. In addition, functions are provided for generating Pb evolution models, paleoisochrons, and isochrons. This allows users to apply calculations to their data in a straightforward way, while providing transparency and flexibility of the calculations used. We have implemented some basic features of the PbIso package into an online shiny R application (see https://shereearmistead.github.io/software/pbiso), which makes it easy for users without any R experience to use these calculations with their own data and to generate plots. We have provided a case study from the Superior Province in Canada, showing how different Pb evolution models can be generated in PbIso and compared to Pb isotope data.
Where Ice Gave Way to Fire: Deglacial Volcanic Activity at the Edge of the Coast Mountains in Milbanke Sound, B.C.
(Canadian Science Publishing, 2023-08-11) Hamilton, Tark; Enkin, Randy J.; Li, Zhen; Bednarski, Jan M.; Stacey, D. Cooper; McGann, Mary L.; Jensen, Britta J. L.
Kitasu Hill and MacGregor Cone formed along the Principe Laredo Fault on British Columbia’s central coast as the Wisconsinan ice sheet withdrew from the Coast Mountains. These small-volume Milbanke Sound Volcanoes (MSV) provide remarkable evidence for the intimate relationship between volcanic and glacial facies. The lavas are within-plate, differentiated (low MgO
A record of the Steptoean Positive Carbon Isotope Excursion (SPICE; Cambrian, Paibian) from the Cow Head Group, western Newfoundland
(Canadian Science Publishing, 2023-09-14) Westrop, Stephen R.; Engel, Michael
Analysis of biostratigraphically-dated boulders demonstrates that the Steptoean Positive Carbon Isotope Excursion (SPICE) is recorded in debris flow conglomerates of the Downes Point Member of the Shallow Bay Formation in western Newfoundland. Fifteen boulders composed of bioclastic carbonates were assigned to five faunas based on assemblages of agnostids and trilobites. The Glyptagnostus reticulatus and "Innitagnostus" inexpectans faunas correlate into strata that record the rising limb of the SPICE in its type area of Nevada and Utah, whereas equivalents of the Acmarhachis kindlei Fauna lie in the interval that records peak δ13C values. The Crepicephalus and Triorygma burkhalteri faunas correlate into pre- and post-SPICE strata, respectively. δ13C values for boulders from the three faunas correlative with the SPICE are significantly higher than "background" levels of the pre- and post-SPICE boulders, but the maximum value in the Acmarhachis kindlei Fauna (1.5‰) is less than half of the peak values recorded in Nevada and Utah. The values are, however, in line with those reported from the Port au Port Peninsula of Newfoundland, which reach 2.2‰. The differences in magnitude between Newfoundland and Nevada-Utah hint at differences in the expression of the SPICE in different geographic regions of the Laurentian continent that might reflect oceanographic conditions.
Tithonian mafic intrusions in north-central Newfoundland: link to Atlantic rifting?
(Canadian Science Publishing, 2023-08-31) Peace, Alexander L; Sandeman, Hamish A.; Welford, J Kim Kim; Dunning, Greg R.; Camacho, Alfredo
The small volume, Mesozoic alkali gabbro intrusions of the Budgell Harbour and Dildo Pond stocks and associated alkaline lamprophyre dykes in Notre Dame Bay in Newfoundland are an example of onshore magmatism which may be associated with North Atlantic Ocean opening. Chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb dating of zircon from Budgell Harbour Stock drill core samples yielded a weighted average 206Pb/238U age of 147.9 ± 0.5 Ma (95% CI, MSWD = 0.10). Five 40Ar/39Ar laser step-heating, single phlogopite grain analyses from the Budgell Harbour and Dildo Pond stocks, plus a lamprophyre dyke, yielded ages ranging from 146.3 ± 0.2 to 149.5 ± 0.5 Ma. The data demonstrate a ca. 148 Ma (Jurassic, Tithonian) alkaline magmatic event in Newfoundland, contemporaneous with rifting and offshore basin formation. These new age data and published determinations from magmatic rocks on conjugate margins and adjacent regions reveal long-lived episodic magmatism in the embryonic North Atlantic rift environment. We propose a new model whereby magmatism occurred in Notre Dame Bay at the convergence of older crustal-scale faults and localized Moho depth variations which may have triggered lithospheric mantle melting through isothermal, distal, edge-driven upwelling related to regional extension.
Pleistocene to Holocene Volcanism in the Canadian Cordillera
(Canadian Science Publishing, 2023-07-13) Russell, James Kelly; Edwards, Benjamin R.; Williams-Jones, Glyn; Hickson, Catherine
The Canadian Cordillera hosts numerous Pleistocene and Holocene volcanoes and volcanic deposits, including a number that have erupted within the last several hundred years. The nature and composition of volcanic edifices and deposits are diverse and dictated by the complex configuration of tectonic plates along the western margin of British Columbia and the thermal structure of the underlying mantle. Our modern knowledge of these is built upon more than a century of field- and increasingly, laboratory-based studies. We recognize five distinct volcanic domains within the Cordillera that are distributed across British Columbia, the Yukon Territory, and easternmost Alaska. These include: the Wrangell Volcanic Belt (WVB), the Northern Cordilleran Volcanic Province (NCVP), the Anahim Volcanic Belt (AVB), the Wells Grey - Clearwater Volcanic Field (WGCVF) and the Garibaldi Volcanic Belt (GVB) representing the northern extension of the Cascade Volcanic Arc. Volcanism in the Canadian Cordillera spans the full range of explosive to effusive behaviours, encompasses the suite of common volcanic chemical compositions (alkaline to calc-alkaline, nephelinite to peralkaline rhyolite), and is expressed by long-lived stratovolcanoes, shield volcanoes, and calderas, as well as shorter-lived tephra cones and associated lava flows. The range in tectonic settings (subduction to extension), eruption environments (subaerial-subaqueous-cryospheric), and topographic variability make volcanism within the Canadian Cordillera as diverse as anywhere on Earth, yet it is also the least studied. Here, we summarize the current state-of-knowledge concerning volcanism within the Canadian Cordillera and conclude with thoughts on research areas that merit further effort, namely glaciovolcanism and volcanic hazards.
Seismicity at the Intersection of the Coast Shear Zone and Anahim Volcanic Belt near Bella Coola, British Columbia, Canada
(Canadian Science Publishing, 2023-06-30) Littel, Geena; Bostock, Michael G.
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.
Coseismic Coulomb Stress Changes on Intraplate Faults in the Western Quebec Seismic Zone Following Three Major Earthquakes in the Past Century
(Canadian Science Publishing, 2023-06-30) Rimando, Jeremy; Peace, Alexander L; Goda, Katsuichiro; Sirous, Navid; Rosset, Philippe; Chouinard, Luc
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 MW 6.1 Témiscaming, 1944 MW 5.8 Cornwall-Massena, and the 2013 MW 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 MW 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.
Geodynamic studies of southwestern Canada: Subduction zone processes and backarc mantle dynamics
(Canadian Science Publishing, 2023-06-06) Currie, Claire A; Yu, Tai-Chieh
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.

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