2024 Onward

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Relative timing and controls on advanced argillic and conventional alteration of the Neoarchean Onaman volcanogenic massive sulfide deposit, Ontario, Canada
(Canadian Science Publishing, 2024-09-14) Strongman, Keaton Reid; Gibson, Harold L.; Howard, Avrom E.; Lafrance, Bruno; Hamilton, Michael A.
Volcanogenic massive sulfide (VMS) deposits with advanced argillic alteration display characteristics typical of conventional VMS and high-sulfidation epithermal deposits. Unlike conventional VMS deposits, these “hybrid” VMS are interpreted to have formed through a magmatic fluid contribution to an evolved, seawater-dominated, hydrothermal system. The close spatial association of advanced argillic alteration assemblages with more typical chlorite-sericite assemblages in the same VMS deposit has implications for the controls on magmatic versus seawater convective systems that have not been previously addressed in the literature. The Neoarchean Onaman assemblage (ca. 2780-2769 Ma) in northwestern Ontario hosts a conventional base-metal VMS system with chlorite-sericite alteration that is overprinted by argillic and advanced argillic alteration, now manifested as a metamorphosed zone of kyanite-chloritoid-calcite- Fe-chlorite, that is associated with a barren, pyritic VMS deposit. The change from typical to advanced argillic alteration occurred during, or immediately following, the deposition of a tonalite clast-bearing heterolithic breccia, which recorded the uplift and subaerial exposure of the larger volcanic edifice. We postulate that the reactivation of synvolcanic structures during uplift, concomitant localized subsidence, and magmatism enhanced cross-stratal permeability and allowed for a direct magmatic volatile input into, or overprint on, an evolved seawater dominated hydrothermal system. Our results suggest that geodynamic regimes exert a strong local, and possibly regional, control on the style, timing, and fluid characteristics of VMS hydrothermal systems. The association of advanced argillic alteration with barren pyritic massive sulfide also suggests that magmatic volatile input alone is not sufficient to enrich VMS systems in gold. This interpretation is consistent with observations from other magmatic-hydrothermal systems such as porphyry and epithermal deposits.
Petrochemistry, mineralogy and Nd isotopic analyses of Tithonian alkaline lamprophyric intrusions, north-central Newfoundland, Canada
(Canadian Science Publishing, 2024-08-09) Sandeman, Hamish A.; Peace, Alexander L.
The Newfoundland Atlantic margin in Eastern Canada formed through protracted lithospheric extension, subsequent rifting, and ultimately, breakup. Mesozoic-Cenozoic magmatism on and offshore Newfoundland coincided with, and potentially resulted from, the concurrent rifting and breakup. In north-central Newfoundland, the alkali monzogabbroic Budgell Harbour and Dildo Pond stocks, an accompanying lamprophyre dyke swarm, and a peridotite sill of the Notre Dame Bay Magmatic Province are products of a punctuated alkaline magmatic pulse on the Newfoundland margin at ca. 148 Ma (Jurassic, Tithonian) with contemporaneous with rifting and the formation of offshore petroliferous basins. The stocks comprise coarsely modally layered phlogopite-ilmenite-magnetite-kaersutite olivine gabbro or essexite. The radially disposed lamprophyre dykes are aphyric to ilmenite-magnetite-diopside±olivine±kaersutite±phlogopite porphyritic camptonites containing common feldspathic- and/or carbonate-dominant ocelli. Silica-undersaturated (kirschsteinite), oxidized (esseneite, calderite) and incompatible-element-bearing minerals (barite, kainosite) form paragenetically late, small grains in the groundmass mantling other phases. Mineral chemistry, lithogeochemistry and Nd isotopic data indicate the rocks are similar to ocean island basalt and alkaline lamprophyres and were generated via low degrees of partial melting of a Neoproterozoic, weakly garnetiferous lithospheric mantle source. The intrusions occur along the intersections of broadly northeast-trending, inherited, Appalachian-cycle lithospheric scale faults with a prominent east-west step in the northeast Newfoundland MOHO along the northeast Newfoundland coast. The convergence of inherited structures with the topographic variation of the lithosphere-asthenosphere boundary likely focused decompression melting of the lithospheric mantle driven through distal, edge-driven upwelling associated with continued extension in the northwest Atlantic.
Serpentinization of the forearc mantle wedge in subduction zones: Revisiting Roy D. Hyndman’s seminal contributions 25 years later
(Canadian Science Publishing, 2024-07-30) Peacock, Simon; Bostock, Michael G
In this paper we focus on the serpentinization of the forearc mantle wedge, just one of Roy Hyndman’s many contributions to our understanding of subduction zones. Over the past 25 years, numerous advances in geophysics, petrology, and geology clearly document that H2O-rich fluids, derived from the subducting plate, hydrate portions of the overlying mantle to form serpentinite. The extent of mantle-wedge serpentinization depends, to first approximation, on the thermal evolution of the subducting plate. Dehydration reactions in warm subducting slabs occur at shallow (
Coesite-bearing garnet xenocrysts from diatexite in the Nordøyane domain, Western Gneiss Region, Norway: Implications for eclogite-melt interaction at ultra-high pressure
(Canadian Science Publishing, 2024-07-18) Jamieson, Rebecca; Hilchie, Luke M; Myrer, Benjamin
Ultra-high-pressure (UHP) metamorphic rocks in the Western Gneiss Region (WGR) of Norway formed in subducted Baltican crust during the Scandian phase of the Caledonian orogeny. In the Nordøyane UHP domain, eclogites locally preserve coesite and microdiamond. Along the north coasts of Haramsøya and Flemsøya, in situ orthopyroxene-eclogite bodies are surrounded by dioritic "diatexite selvages" containing abundant eclogitic enclaves and xenocrysts. In one location eclogite and diatexite are associated with a quartz diorite dyke that is highly contaminated with eclogitic material. The diatexite matrix and dyke have similar plagioclase + quartz + biotite assemblages with abundant embayed and fragmented garnet and clinopyroxene xenocrysts. Coesite is present in some garnet xenocrysts but has not been found in the adjacent eclogite bodies. Pressure-temperature (P-T) estimates from in situ eclogites range from 2.2-3.2 GPa and 810-840 °C, spanning the quartz-coesite transition, with P-T estimates from xenocrysts spanning a wider range. Diorites and retrogressed eclogites record amphibolite-facies conditions, ca. 1.0-1.5 GPa and 700-800 °C. The wide range and large uncertainties in P-T estimates reflect high-temperature re-equilibration and a relative lack of P-sensitive assemblages. Differences in texture, composition, and included assemblages indicate that the xenocrysts were not derived from the nearby eclogite bodies. By implication, their dioritic hosts were not locally derived but must have originated from a different, probably deeper, source. The results are integrated with a numerical model for WGR tectonic evolution to assess the sources of the melts and their possible effects on the exhumation of UHP rocks in western Norway.
The structural setting and evolution of the Upper Beaver Gold-Copper deposit, Ontario, Canada
(Canadian Science Publishing, 2024-06-20) Orlóci-Goodison, Ruth Anne; Lafrance, Bruno; Beaudoin, Georges; Côté-Mantha, Olivier
The ca. 2680 Ma Upper Beaver deposit is an Archean intrusion-related gold-copper deposit located in the Abitibi greenstone belt, Ontario. The deposit is associated with the Upper Beaver Intrusive Complex, which was emplaced in the hanging wall of an extensional listric fault rooted in metavolcanic rocks of the ca. 2704-2695 Ma Blake River assemblage. The fault formed during the development of an overlying basin of fluvial metasedimentary and alkalic metavolcanic rocks of the ca. 2679-2669 Ma Timiskaming assemblage. The Upper Beaver deposit was subsequently rotated to its current position during the formation of a post-Timiskaming fold, the Spectacle Lakes Anticline, associated with the development of the Larder Lake-Cadillac deformation zone, located 7 km south of the deposit. The Upper Beaver deposit is overprinted by the axial planar cleavage of the anticline but is less deformed than other gold deposits located along the deformation zone. Alteration and other preexisting planar anisotropies enhanced strain partitioning and the development of folds and fabrics in strained mineralized zones of the deposit. Steeply-dipping, sericite-altered mineralized zones developed a continuous foliation surrounding boudinaged and recrystallized quartz-calcite-anhydrite veins, whereas strong, shallowly-dipping, stratiform, skarnoid mineralized zones developed a wavy disjunctive cleavage and deformed mainly by folding. The mineralized zones acted as pre-existing anisotropies during deformation and their orientation and composition were key factors in the development of structures at the Upper Beaver deposit, which can be used as a guide for interpreting the development of structures in similar but more complexly deformed deposits along major deformation zones.
Crustal Melting Recorded by Dykes along the Gold-bearing Melanson Brook Fault, Northern New Brunswick Appalachians
(Canadian Science Publishing, 2024-07-26) Bustard, Aaron Leigh; Lentz, David; Walker, James A; McFarlane, Christopher R.M.
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
Classifying Intrusive and Strongly Metamorphosed Rock Units: CLASS – A Cooperative Lithodemic and Stratigraphic System
(Canadian Science Publishing, 2024-05-27) Maxeiner, Ralf O.; Bosman, Sean A.; Card, Colin D.; Marsh, Arden; Morelli, Ryan M.; Coueslan, Chris; Martins, Tania; Reid, Kyle; Easton, Michael R.M.; Knox, Bernadette; Mihalynuk, Mitchell G.; Ootes, Luke; Cui, Yao; Grobe, Matthias; Guemache, Mehdi; Lawley, Chris; Böhm, Chris; Ashton, Ken E.
We review currently available Canadian and international lithostratigraphic and lithodemic schemes and find most of them inadequate for classifying intrusive and strongly metamorphosed rocks of Canada and beyond. A new system is proposed, one that unifies, complements and extends components of the revised North American Stratigraphic Code, the British Geological Survey Rock Unit Classification System of 2021, and the International Stratigraphic Guide of 1999. This new Cooperative Lithodemic and Stratigraphic System (CLASS) is intended to serve as a practical guide to geoscientists who need to classify and report on lithodemic units in North America and has broad applicability to other jurisdictions. It is built with database management practices in mind and employs the concept of inheritance of root characteristics between seven formal rock unit ranks, which will allow incorporation of the scheme into compact object-oriented and relational databases designed for purpose. Broad application of CLASS, especially to historically problematic lithodemic units, should help to foster jurisdictional interoperability, data sharing, global compilations and thematic studies. At the heart of this proposed system is a subdivision and accompanying nomenclature that allows classification of rocks into seven formal ranks. Following the well-established lithostratigraphic supergroup, group, subgroup, formation, member, submember and bed approach, CLASS proposes three classes of lithodemic subdivisions for formally naming lithodemic rock units.
Ages and structural relationships in the Ganderian central Cape Breton Highlands, Nova Scotia, Canada
(Canadian Science Publishing, 2024-07-28) van Rooyen, Deanne; White, Chris E; Barr, Sandra M.; Sunatori, Évelyne; Grant, Caleb J.; Kucker, Kyle J.
Structural complexity of the Cape Breton Highlands is a key problem in reconstructing tectonic events in the northern Appalachian orogen. A new U-Pb TIMS age of 428.53 ± 0.16 Ma for metarhyolite in the Calumruadh Brook Formation shows that volcanic and sedimentary rocks were deposited before collision of the Aspy and Bras d’Or terranes along the Eastern Highlands shear zone. A new U-Pb laser ablation zircon age of 394 +6/-4 Ma confirms that peak metamorphism in the Middle River complex continued during convergence linked to late stages of the Acadian orogeny. The compressive tectonic environment evolved into a transpressional system after initial collision in the late Silurian and caused a repeated pattern of imbrication of units in the Aspy terrane in the hanging wall in the collision. The shear zones bounding the geological units are curvilinear and have south-directed kinematics, imbricating units and transporting higher-grade rocks over lower-grade rocks, and moving plutons upward relative to their host rocks during and shortly after intrusion. The vergence of imbrication is parallel to the direction of transpressional movement on the main Eastern Highlands shear zone. This geometry is present in Ordovician-Silurian rocks and repeated in Devonian plutonic rocks, indicating that the overall transpressional tectonic setting was a long-lived feature of the orogen. The shear zones localized late syn- to post-deformational plutons that intruded at ca. 375-370 Ma. By the latest Devonian, emplacement of the ca. 363 Ma Margaree and related plutons marked the beginning of extension in the central Cape Breton Highlands.
Devonian plutons in the eastern Meguma terrane, Nova Scotia, Canada: zircon U-Pb, Lu-Hf and O isotopic compositions, age, and petrogenetic implications
(Canadian Science Publishing, 2024-05-08) Archibald, Donnelly; Barr, Sandra M.; White, Chris E.; Nickerson, Shae J.; Stern, Richard A.; Luo, Yan; Pearson, Graham D.
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 (δ
Tonian rift successions in Newfoundland, Canada: A window to late tectonic events in the Mesoproterozoic Laurentian margin
(Canadian Science Publishing, 2024-05-30) Strowbridge, Susan; Dunning, Greg R.; Indares, Aphrodite; Jenner, George A.
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.
The Holocene to Modern Fraser River Delta, Canada: Geological History, Processes, Deposits, Natural Hazards, and Coastal Management
(Canadian Science Publishing, 2024-05-31) La Croix, Andrew D; Dashtgard, Shahin; Hill, PR; Ayranci, Korhan; Clague, John J
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.
Paleoenvironmental and chemostratigraphic implications of variations in geochemical proxies across the Upper Jurassic–Lower Cretaceous boundary: a case study from the Flemish Pass Basin
(Canadian Science Publishing, 2024-05-03) Bingham-Koslowski, Nikole; Azmy, Karem; Layton-Matthews, Dan
The Jurassic–Cretaceous boundary is the only Phanerozoic period-level boundary that lacks a golden spike on the geological timescale despite significant global geological and environmental change during this time related to the opening of the Atlantic Ocean. Paleoenvironmental proxy profiles (TOC, δ34S, δ15N, Fe, Mn, Ce/Ce*, Th/U, δ13Corg, P, Ni, Zn, Cu, and B/Ga) for core 3 of the Baccalieu I-78 well in the Flemish Pass Basin, offshore eastern Canada, exhibit a geochemical anomaly between 3288.5 m and 3289 m, overlapping with the biostratigraphic placement of the Jurassic–Cretaceous boundary. Collectively the geochemical analyses are interpreted to indicate that the anomaly is associated with a fall in relative sea level, followed by a rise, which led to restricted circulation, stratification, and widespread anoxia. This anoxia, coupled with an arid climate, further resulted in reduced weathering, limited nutrient supply, and an overall reduction in primary productivity. The results of this study, in conjunction with previous biostratigraphic studies on core 3, suggest that the Jurassic–Cretaceous boundary in Baccalieu I-78 likely falls within the geochemical anomaly, specifically between 3228.5 m and 3288.85 m. Furthermore, the paleoenvironmental interpretations derived in this study agree with published reports on global sea level and climate trends around the Jurassic–Cretaceous boundary, implying the influence of global, rather than regional, factors on deposition. This suggests that geochemical proxies may be useful in providing additional paleoenvironmental insights and helping to constrain stratigraphic boundaries, particularly in intervals that lack significant lithological or biological change.
The Yellowknife greenstone belt and underlying Central Slave Cover Group, Slave craton, Canada: constraints and questions arising from a U-Pb dating study
(Canadian Science Publishing, 2024-05-13) Ketchum, John W.F.; Bleeker, Wouter; Falck, Hendrik; Jackson, Valerie A
Legacy U-Pb isotopic data are reported for the Mesoarchean Central Slave Cover Group and Neoarchean Yellowknife greenstone belt, Slave craton, Northwest Territories, Canada. In two locations north of the City of Yellowknife, exposures of cover group rocks occur beneath mafic volcanic and subvolcanic units traditionally assigned to the basal Chan Formation of the Kam Group. Both cover group occurrences contain felsic volcanic tuff units that yield eruption ages of 2853 +2/-1.5 Ma and 2826 ± 1.5 Ma. The younger tuff is underlain by felsic volcaniclastic schist with a dominant, basement-aged detrital zircon population that was deposited after 2840 ± 6 Ma. Near the south end of the exposed greenstone belt, a felsic tuff within the Octopus Formation provides an age of 2699 ± 3 Ma, confirming that this formation is not part of the Central Slave Cover Group. A pillowed basalt flow within the Chan Formation is cut by a composite gabbro dyke dated as 2738 +3.5/-3 Ma. However, a more general ca. 2730-2740 Ma age interpretation for this dyke may be appropriate due to the potential for complex lead loss behaviour in the dated baddeleyite fractions. Younger U-Pb zircon and monazite ages reported herein (2710-2706 Ma) contribute to our understanding of felsic magmatic and gold-mineralizing events that influenced later development of the Yellowknife greenstone belt. Although the depositional history of the autochthonous Central Slave Cover Group is becoming better known, questions remain regarding the age and tectonomagmatic affinity of adjacent mafic volcanic rocks traditionally assigned to the Kam Group and correlative assemblages. Are some of these rocks actually part of the Central Slave Cover Group?
Laurentide Ice Sheet configuration in southern Ontario, Canada during the last glaciation (MIS 4 to 2) from stratigraphic drilling and LIDAR-based surficial mapping
(Canadian Science Publishing, 2024-01-15) Bukhari, Syed; Eyles, Nicholas; Mulligan, Riley P.M.; Burt, Abigail K.; Eyles, Carolyn H.; Paulen, Roger C.; Ross, Martin; Putkinen, Nico
Regional subsurface mapping of glacial depositional systems preserved in buried bedrock paleovalleys, and quantitative analysis of new LiDAR imagery of surface glacial landforms using machine learning techniques, when combined, are powerful tools for assessing the dynamics of the Laurentide Ice Sheet (LIS) during the last (Wisconsinan) glaciation in southern Ontario. While age dating of deposits preserved below Last Glacial Maximum tills (LGM: MIS 2
A primary evaporite weld revealed in the late Paleozoic Antigonish sub-basin of Nova Scotia
(Canadian Science Publishing, 2024-04-15) Thomas, Alison K.; Waldron, John W.F.
The Antigonish sub-basin lies within the late Paleozoic Maritimes Basin of Atlantic Canada. Late Devonian to early Carboniferous basin development resulted in a basin-and-range topography, within which the clastic Horton Group was deposited in grabens and half-grabens. The overlying Visean Windsor Group contains substantial evaporite units; later basin development was accompanied by expulsion of these evaporites. In the Antigonish sub-basin a significant stratigraphic omission surface initially described as a thrust was subsequently reinterpreted as the extensional Ainslie Detachment. This surface can be examined in drill-core, where the halite-bearing interval is reduced to 3.8 m of halite-cemented breccia of sedimentary rock fragments. The halite cement is sub-horizontally foliated and lineated. At Lakevale an outcrop section of the Windsor Group is reduced in thickness to tens of metres. Above a basal limestone unit containing pseudomorphs of gypsum, most of the Windsor Group is represented by sedimentary-clast breccias which resemble those seen in core, but with the halite removed by solution in the near-surface environment. The stratigraphic record within the sub-basin implies that expulsion of lower Windsor salt was initially toward the edges of the basin where rising diapirs blocked the deposition of Middle Windsor group, but in the basin centre a second salt unit was deposited. Subsequently, during contractional inversion of basin-bounding faults, the middle Windsor salt was expelled into diapirs near the centre of the basin. The Ainslie Detachment is reinterpreted as a primary salt weld: a boundary between units formerly above and below expelled lower Windsor evaporites. The resulting stratigraphic omissions and structures match those seen above expelled evaporite layers on continental margins.
Conjugate shear model for emplacement of midcrustal plutons during dextral transpression, southern Nova Scotia, Canada: tectonic and petrological consequences
(Canadian Science Publishing, 2024-04-15) Collins, William J.; Murphy, J. Brendan
The South Mountain Batholith (SMB) is a syntectonic composite batholith emplaced in the upper crust within the Meguma terrane between 380 Ma and 370 Ma during the later stages of the Neoacadian orogeny. Coeval plutons in southern Nova Scotia are surrounded by mid-crustal (~4 kbar) andalusite-staurolite aureoles and are discordant to NE-trending, regional Neoacadian folds. Detailed field studies, combined with published results, indicate emplacement within a dextral transpressional regime during the transition from distributed (D1) to focused heterogeneous strain (D2), which provided vertical conduits that facilitated magma ascent. The Port Mouton Pluton (PMP) intruded along P-orientated crustal-scale fractures as a series of subvertical granitic sheets, which were progressively rotated and folded with ongoing dextral shearing. By contrast, the Barrington Passage pluton (BPP) intruded between crustal-scale, antithetic (sinistral) P-shear fractures and spread laterally between them as pulsed increments to form a layered, subhorizontal, sill-like complex resembling the laccolithic structure of the SMB. The SMB was emplaced below the Meguma Supergroup, with magma derived from underthrust Avalon terrane and Silurian Rockville Notch Group. The lack of mantle components in the SMB suggests transpressional orogenesis facilitated conductive crustal heating without significant mantle addition, consistent with low p-wave velocities of Meguma lower crust. 400-355 Ma zircons, recorded either as inherited grains in granites or in felsic granulite xenoliths, imply the Neoacadian thermal anomaly extended for 45 Ma, but magmatism represented only ~40% of that perturbation.
The volcanic architecture and tectono-magmatic framework of the Mount Grace carbonatites, southeastern Canadian Cordillera
(Canadian Science Publishing, 2024-07-04) Abdale, Lindsey; Russell, James Kelly; Groat, Lee Andrew
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.
The Grenville Province: revisiting the orogenic framework and integrating recent findings
(Canadian Science Publishing, 2024-05-16) Indares, Aphrodite
The Grenville Province holds record of Mesoproterozoic orogenic processes at the Laurentian margin during the assembly of Rodinia. This contribution reviews key characteristics of the Province, integrates recently published data, and questions some earlier interpretations. Despite crustal reworking during the Grenvillian orogeny (1.09–0.98 Ga), contrasts between crustal-age domains across the Allochthon Boundary largely reflect differences between internal and external Laurentia, and allochthonous units were far-travelled in the west but not in the east. In addition, there is growing evidence towards a continuum between the Ottawan and Rigolet orogenic phases. Based on ages of metamorphism, the High-Pressure segments of the hinterland reflect localized thickening at the front of the Ottawan orogen and evidence for an orogenic plateau is limited to the western Grenville. Peak-metamorphic conditions in the Mid-P orogenic core, mostly within the confines of biotite dehydration melting (max ~900oC) for aluminous rocks, culminated in early Ottawan and were followed by protracted extension. In addition, high-temperature granitoid magmatism was active throughout the duration of the orogeny and localized in formerly pericratonic terranes accreted at ~1.4 Ga and 1.2–1.1 Ga, indicating an influence of inherited lithospheric structures on Grenvillian mantle dynamics. The overall orogenic pattern reveals considerable lateral variations in the hinterland potentially linked to the earlier configuration of external Lautentia and is consistent with weak lithosphere supporting a broad, hot, but not necessarily high-standing orogen for most of the Ottawan, in contrast to the Rigolet phase that marks the propagation of the orogen against Archean lithosphere of internal Laurentia.
Polyphase formation of a Neoarchean auriferous fault zone network in the Michipicoten greenstone belt, southern Superior craton
(Canadian Science Publishing, 2024-05-13) Ma, Chong; Lafrance, Bruno; Montreuil, Jean-François
Correlating structurally distinctive fault zones for understanding an unknown deformation system at the regional scale remains a challenge for understanding orogenic evolution and gold endowment. The current study deals with this challenge in the southern Michipicoten greenstone belt (MGB) of the Superior craton focusing on a Neoarchean auriferous fault zone network. Three deformation events associated with episodic gold mineralization are revealed in the ca. 2745 Ma host granitoid: (1) NW‒SE shortening recorded by the subvertical Grace and Minto B fault zones and locally the inclined Jubilee and Hornblende fault zones; (2) top-to-NNE strike-slip to oblique faulting indicated primarily by the dominant structures of the Jubilee and Hornblende fault zones; and (3) top-to-NE extension demonstrated by the northeast-dipping Parkhill #4 and Cooper fault zones. Fault zone lithologies and mineral assemblages suggest that the localization of deformation for the formation of these fault zones was controlled by rheological heterogeneities and syn-deformation fluids. The first and second events are correlated with two shortening events in a gold-endowed, structurally and kinematically distinctive deformation zone of the northern MGB. This correlation based on deformation processes suggests a larger footprint of gold mineralization associated with a regional deformation in the MGB and has implications for investigating structural evolution of orogens and orogenic gold mineralization in general.
Geochronology of the Mines Gaspé porphyry deposit, Québec, Canada
(Canadian Science Publishing, 2024-05-15) Marcelissen, Mitch; Hollings, Pete; Cooke, David; Baker, Michael J.; Belousov, Ivan; Orovan, Evan; Friedman, Richard M
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.

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