Spherulitic microfabrics of calcareous deposits along the Dewar Creek geothermal spring in the Canadian Cordillera: case study for Sr2+ controls on amorphous calcium carbonate-vaterite-calcite phase transformation

Strong lateral strength contrasts in the mantle lithosphere of continents: A case study from the hot SW Canadian Cordillera

Bulk compositional controls on the preservation of age domains within metamorphic monazite: A case study from quartzite and garnet–cordierite–gedrite gneiss of Thor-Odin dome, Monashee complex, Canadian Cordillera

The influence of water–rock interaction on the chemistry of thermal springs in western Canada

Refinement of Eocene lapse rates, fossil-leaf altimetry, and North American Cordilleran surface elevation estimates

SUMMARYSubduction zones are recognized as an important class of plate boundaries and are the location of a number of important geological processes. They are also important because of the mineral and geothermal energy resources formed by plate convergence. While subduction zones around the world have a number of common features, there are also significant differences among them. The Cascadia subduction zone in southern British Columbia is characterized by a relatively hot subducting plate, and a broad backarc region that is believed to exhibit a shallow, convecting asthenosphere. The magnetotelluric (MT) method is a useful tool to study subduction zones and backarc regions because measurements of subsurface resistivity are sensitive to the presence of fluids. A number of previous MT studies have taken place in this region, but they were limited to a 2-D approach to data analysis. As the MT method has developed, it has become clear that there is a significant advantage to using a 3-D approach to data analysis. This paper presents the first regional-scale 3-D resistivity model of the southern Canadian Cordillera and provides new insights into the lithospheric structure and the distribution of fluids. The southeastern Canadian Cordillera has high heat flow and numerous thermal springs, the locations of which are often controlled by faults. However, the deeper thermal structure and origin of the fluids are poorly understood. To develop an improved understanding of the structure of this area, MT data measured at 331 locations were used to create a 3-D model of subsurface electrical resistivity. This study is primarily focused on the Omineca and Foreland morphogeological belts in southeastern British Columbia, which are separated by the southern Rocky Mountain Trench. The resistivity model is presented to a depth of 100 km and a number of conductive features are observed in the crust and uppermost mantle of the southeastern Cordillera. The locations of these conductors broadly matched previously reported conductors, but the 3-D inversion revealed new details of their geometry. The previously reported Canadian Cordilleran Regional conductor was modelled as a number of discrete conductors in the depth range 15–55 km beneath the Omineca belt. Temperatures approximately in the range 400–700 °C are expected at depths of 15–26 km and saline aqueous fluids are likely the cause of the low resistivity. Temperatures approximately in the range 700–1300 °C are expected at depths of 26–55 km and small volumes of partial melt may explain the low resistivity. The Southern Alberta–British Columbia conductor, Red Deer conductor and Loverna conductor were imaged as a single connected conductor, whose low resistivity is likely caused by sulphide mineralization. A group of conductors was imaged near the southern Rocky Mountain Trench in the depth range 10–70 km and their low resistivity is likely caused by interconnected saline fluids and possibly interconnected graphite films. To understand if the distribution of thermal springs was correlated with the 3-D resistivity model, a statistical study was undertaken. This showed no clear correlation between crustal conductance and the distribution of thermal springs.

Terrestrial sedimentary archives record critical information about environment and climate of the past, as well as provide insights into the style, timing, and magnitude of structural deformation in a region. The Cretaceous Newark Canyon Formation, located in central Nevada, USA, was deposited in the hinterland of the Sevier fold–thrust belt during the North American Cordilleran orogeny. While previous research has focused on the coarser-grained, fluvial components of the Newark Canyon Formation, the carbonate and finer-grained facies of this formation remain comparatively understudied. A more complete understanding of the Newark Canyon Formation provides insights into Cretaceous syndeformational deposition in the Central Nevada thrust belt, serves as a useful case study for deconvolving the influence of tectonic and climatic forces on sedimentation in both the North American Cordillera and other contractional orogens, and will provide a critical foundation upon which to build future paleoclimate and paleoaltimetry studies. We combine facies descriptions, stratigraphic measurements, and optical and cathodoluminescence petrography to develop a comprehensive depositional model for the Newark Canyon Formation. We identify six distinct facies that show that the Newark Canyon Formation evolved through four stages of deposition: 1) an anastomosing river system with palustrine interchannel areas, 2) a braided river system, 3) a balance-filled, carbonate-bearing lacustrine system, and 4) a second braided river system. Although climate undoubtedly played a role, we suggest that the deposition and coeval deformation of the synorogenic Newark Canyon Formation was in direct response to the construction of east-vergent contractional structures proximal to the type section. Comparison to other contemporary terrestrial sedimentary basins deposited in a variety of tectonic settings provides helpful insights into the influences of regional tectonics, regional and global climate, catchment characteristics, underlying lithologies, and subcrop geology in the preserved sedimentary record.

Quantification of the crustal thickening processes that construct orogenic plateaus is essential for interpreting their genesis. In the North American Cordillera, a 2.75–3.5-km-elevation, 200–250-km-wide plateau was constructed to the west of the Cretaceous–Paleogene Sevier fold-and-thrust belt (SFTB). The SFTB deformed a Mesoproterozoic to Mesozoic sedimentary package that thickened westward from a 2–3-km-thick platform section that was deposited above the ~40-km-thick craton to a 15–25-km-thick continental margin section that was deposited above middle to lower crust that had been significantly thinned during Neoproterozoic rifting. Shortening in the SFTB translated this thick sedimentary package as much as 265 km eastward, which resulted in the relative westward underthrusting of an equivalent length of thick cratonic basement beneath the hinterland region. Measurement of components of thickening with respect to the initial and final crustal thickness above and below the basal thrust décollement demonstrates that thickening accommodated by underthrusting outweighed thickening in the overlying SFTB by a factor of 1.5–3 and was likely the dominant thickening mechanism that constructed the broad hinterland plateau. In eastern Nevada, the reconstructed western edge of the underthrusted craton underlies the western limit of 2.75–3.5 km paleoelevations, which supports this interpretation. This analysis provides an important case study for underthrusting as a first-order thickening process in fold-and-thrust systems that deform sedimentary packages with a high pre-orogenic taper.

<p>Crustal extension is a fundamental process in plate tectonics, and understanding its driving mechanisms is critical to our understanding the role of extensional deformation in the evolution of the Earth’s continents. How and why extension localizes into narrow belts versus being distributed across wide orogens remains enigmatic. Here we investigate extensional strain localization in the North American Cordillera (NAC) and Basin and Range province, where early phases of high magnitude strain (>100%) were fairly localized along a ~2500-km long belt of metamorphic core complexes, and subsequent late-stage low-magnitude strain appears to be fairly distributed across the 500-600-km width of the Great Basin. Various forces compete to drive intracontinental extension in the western United States, and we present field-based case studies of the Central NAC core complexes—the Ruby-East Humboldt, Snake Range, and Albion-Raft River-Grouse Creek—to explore strain localization due to plate-boundary stresses, internal body forces (GPE), and/or crustal rheology including thermal weakening from pervasive magmatism. The studied core complexes consist of significant syn-kinematic intrusions, and we demonstrate how the composition, volume and age (i.e., duration and relative timing) of these intrusions affected strain rates. Through a combination of new and synthesized U-Pb geochronology, <sup>40</sup>Ar/<sup>39</sup>Ar thermochronology and electron backscatter diffraction (EBSD) analysis we link transient thermal and rheological evolution of the crust with deformation mechanisms from grain to outcrop to regional scales.  More broadly, we discuss the mechanisms and modes of crustal extension during orogenesis, and whether extension in active orogens is a transient response to modulate GPE gradients, or a precursor to orogenic collapse.</p>

Integrated structural-petrographic-magnetic-basin modeling case studies in numerous foreland fold-and-thrust belts provided key information on the critical parameters and processes controlling reservoir evolution from the end of the passive margin phase to the post-orogenic collapse of the tectonic pile. Fluid-rock interactions in reservoir rocks are intensified during tectonic events, as tectonic compaction in the foreland and development and re-opening of fracture systems in the allochthon help remobilizing basinal fluids, to squeeze-out host-rock buffered fluids as well as to reinject exotic fluids in reservoir sandstone or carbonate layers. For instance, quartz cementation in Sub-Andean foothills is dominantly controlled by Layer Parallel Shortening (LPS/tectonic compaction) in the footwall of frontal thrusts. LPS can also be inferred to cause in situ recrystallisation of mesodolomite in the Canadian Cordilleran Foreland Belt. In contrast, secondary hydrothermal dolomitization of limestone strata usually accounts for lateral migration in stratigraphic conduits in the foreland and for vertical migration of mineralizing fluids in open fractures in the allochthon, respectively. Alternatively, vuggy porosity observed in allochthonous carbonate strata in the North American Cordillera can also be interpreted to result from reservoir cooling operating in a dominantly closed fluid system during tectonic uplift and coeval erosion. Basin models can provide realistic estimates of burial-temperature history that can be compared to paleo-thermometers, such as fluid inclusions or stable isotopes, and thus provide a means to determine the relative age of cementation or dissolution episodes. Basin models can also provide fluid velocities, that can be subsequently used as critical constraints on diagenetic models at reservoir scale. Natural fluid-rock interactions induced by exotic tectonic fluids are short, no longer than one million years. As such, they constitute very good models of the long term effects of CO2 and H2 S injection and storage in natural reservoirs. The integrated quantitative appraisal approach proposed here for petroleum evaluation and reservoir prediction, also provides useful information on the overall changes in fluid flow regime and fluid velocities trough time in natural open systems, that should be used as regional boundary conditions for future reservoir storage and monitoring of acid gases in natural reservoirs.

Tomotectonics hindcasts paleo-trenches, through the spatiotemporal superposition of subducted lithosphere (slabs imaged in the earth’s mantle) with plate reconstructions (constrained by seafloor isochrons). The two geophysical datasets are linked through the tomotectonic null hypothesis, that oceanic lithosphere sinks vertically down after entering in the mantle. This linkage permits simple and testable predictions about the location and lifespan of volcanic arcs, and specifically about arc-continent collisions, switches in subduction polarity, and switches from consuming to transform plate boundaries. In a second stage, tomotectonics uses land geological observations from the accretionary orogen in order to test predictions arising from the geophysical data sets.We have applied the tomotectonic method to the North American Cordillera, where lower-mantle slab geometries indicate the nearly simultaneous initiation (~200-180 Ma) of three intra-oceanic archipelagos in the northeastern proto-Pacific (figure: MEZ, ANG, and CR slabs). Westward subduction beneath 10,000 km-long MEZ and ANG pulled North America from Pangaea, opening the Central Atlantic. Coeval eastward convergence of Farallon plate beneath intra-oceanic CR is predicted from Pacific seafloor isochrons. This configuration of subduction zones facing each other across an archipelago is analogous to today’s southwest Pacific, where Australia, embedded in Indian/Tethys Ocean floor, and the Pacific Ocean are drawn in by double-sided subduction.Each slab must be associated with a paleo-arc. Central and controversial in formation accounts of the Cordilleran has been the Insular microcontinent (INS, comprising Peninsular, Alexander, Wrangellia superterranes of Alaska and B.C.) and its southward extension of Guerrero superterrane (GUE) of Mexico. When, where and in what style did MEZ accrete to North America? Did INS subsequently translate thousands of kilometres along the margin (the “Baja-BC” debate between geology and paleomagnetism)? How did INS unite with the remainder of accretionary terranes that form Alaska?We demonstrate how tomotectonics hindcasts the INS journey. Massive MEZ slab wall fixes INS-GUE’s initial, stationary, offshore position – in an accretionary regime. Full consumption of North American oceanic lithosphere, pulled beneath INS-GUE arcs, caused diachronous collision from ~155 Ma to ~90 Ma (Nevadan-Sevier deformation), leaving a trail of collapsed basins. Subduction was gradually forced outboard of MEZ: flip to Farallon subduction, eastward beneath INS-GUE (now attached to North America), brought another accretionary episode of Franciscan and Chugach subduction complexes, linked to Sierra Nevada and Coast Mountain batholith arcs.Northward translation of INS by ~2000 km between 90-50 Ma (the “BajaBC” regime) corresponds with a lack of subduction (slab) beneath the paleo-margin. A key result is that both tomotectonics and paleomagnetic observations, which are completely independent, support large-scale translation.Simultaneously, INS and North Americal collided obliquely with Central Alaska and Farallon arcs in a second collisional phase ~100-50 Ma, again in double-sided subduction. Since 170 Ma, Insular micro-continent experienced all regimes of modern double-sided archipelagos: subduction accretion, collision, subduction flip, and transform.  Reference: Sigloch, K. & Mihalynuk, M.G. (2025), Tomotectonics of Cordilleran North America since Jurassic times: double-sided subduction, archipelago collisions, and Baja-BC translation. In review (revision) with GSA Books. Preprint: https://eartharxiv.org/repository/view/7460/

Isotopic chemostratigraphy has proven successful in the correlation of carbonate-rich Neoproterozoic successions. In successions dominated by siliciclastic rocks, chemostratigraphy can be problematic, but if thin carbonates punctuate siliciclastic strata, useful isotopic data may be obtained. The upper Pocatello Formation and lower Brigham Group of southeastern Idaho provide an opportunity to assess the potential and limitations of isotopic chemostratigraphy in overwhelmingly siliciclastic successions. The 5000 m thick succession consists predominantly of siliciclastic lithologies, with only three intervals that contain thin intercalated carbonates. Its depositional age is only broadly constrained by existing biostratigraphic, sequence stratigraphic and geochronometric data. The lowermost carbonates include a cap dolomite atop diamictites and volcanic rocks of the Pocatello Formation. The delta 13C values of these carbonates are distintly negative (-5 to -3), similar to carbonates that overlie Neoproterozoic glaciogenic rocks worldwide. Stratigraphically higher carbonates record a major positive delta 13C excursion to values as high as +8.8 within the carbonate member of the Caddy Canyon Quartzite. The magnitude of this excusion is consistent with post-Sturtian secular variation recorded elsewhere in the North American Cordillera, Australia, Svalbard, Brazil and Nambia, and exceeds the magnitude of any post-Varanger delta 13C excursion documented to date. In most samples, Sr-isotopic abundances have been altered by diagenesis and greenschist facies metamorphism, but a least-altered value of approximately 0.7076 supports a post-Sturtian and pre-Marinoan/Varanger age for upper Pocatello and lower Brigham rocks that lie above the Pocatello diamictite. Thus, even though available chemostratigraphic data are limited, they corroborate correlations of Pocatello Formation diamictites and overlying units with Sturtian glaciogenic rocks and immediately post-Sturtian successions in western North America and elsewhere.

The Cordilleria model for Mesozoic plate tectonics in the northern part of the American cordillera can make a useful case study in the teaching of plate tectonics. Published geologic field evidence, together with published geophysical, geochemical, paleontological, paleomagnetic, sedimentological and structural details can be used by the student to reconstruct the most likely sequence of events. This involves the student in a study of relative plate motions between the North American Plate and a more westerly lithospheric plate on which Cordilleria, a Mesozoic microcontinent, was riding. The student can also discover the effects of continent-continent collision on plate motions, plate boundaries, foreland sedimentary basins and crust-mantle relationships.

Thrust Tectonics and Hydrocarbon Systems resulted from an international conference at Royal Holloway University in London. The volume contains 33 chapters divided into four sections:Geodynamics of Thrust Systems, Analog Modeling of Thrust Systems, Fault-Related Folds in Thrust Systems,and Case Studies. These papers summarize recent advances in thrust studies and their application to hydrocarbon exploration and production.Key topics addressed include the application of the critically tapered Coulomb wedge model to thrust systems both in nature and in experiments, the interaction of surface proceses with thrust systems, basement-involved thrust systems and inversion, fault-related folds in thrust belts, and growth stratal development in thrust belts. Fold-and thrust belts described and discussed in this volume include the Alps, the Andes, the Apennines, the Appalacians, the Alice Springs Orogen in Australia, the Albanides, the Atlas in Morocco, the Canadian Cordillera and the Canadian Rocky Mountains, Kutei Basin, Kalimantan, the Himalayas, the New England Orogen, Papua New Guinea, and the Spanish Pyrenees, as well as depwater fold and thrust belts such as the Niger Delta and the Gulf of Mexico. Memoir 82 provides an in-depth look at thrust tectonics and hydrocarbon systems, and is a milestone publication as a major new examination of thrust fault systems.

Book Reviewed in this article: Huronia: A History and Geography of the Huron Indians, 1600–1650. Conrad Heidenreich. The Pennsylvania German Family Farm Amos Long, Jr. The Kingdom of Madison: A Southern Mountain Fastness and Its People. Manly Wade Wellman Rural Poverty and the Urban Crisis: A Strategy for Regional Development. N. M. Hansen Intermediate-Size Cities as Growth Centers: Applications for Kentucky, the Piedmont Crescent, the Ozarks, and Texas. N. M. Hansen Location Preferences, Migration, and Regional Growth: A Study of the South and Southwest United States. N. M. Hansen Residence, Employment and Mobility of Puerto Ricans in New York City. Terry J. Rosenberg Health Care Delivery: Spatial Perspectives. G. W. Shannon and G. E. A. Dever. Urban Land Use Analysis: A Case Study on Hong Kong. Chi-sen Liang Mental Maps. Peter Gould and Rodney White Mental Maps Peter Gould and Rodney White Mountain Geomorphology: Geomorphological Processes in the Canadian Cordillera. Edited by H. Olav Slaymaker and H. J. McPherson The History of Malindi: A Geographical Analysis of an East African Coastal Town from the Portuguese Period to the Present. William Bradley Martin La Vigencia del Mar; Una investigación acerca de la Soberanía Marítima y la Plataforma Continental de Venezuela dentro del marco internacional del Derecho del Mar. Kaldone G. Nweihed The Indian Hill Station: Kodaikanal. Nora Mitchell T'ai-Chung, T'ai-Wan: Structure and Function. Clifton W. Pannell The Idea of Culture in the Social Sciences. Edited by Louis Schneider and Charles M. Bonjean Modern Chinese Society: An Analytical Bibliography. Volume I, Publications in Western Languages. Edited by G. William Skinner

Human activities and global factors have caused imbalances in mountain regions, leading to significant changes in these environments. One of the most visible impacts of rising temperatures is the melting of glaciers, which causes changes in the pressure on adjacent slopes and increases their instability, leading to mass movements (Chiarle et al., 2021). Other notable effects include the degradation of permafrost and increased erosion in previously glaciated areas (Savi et al., 2021). These changes affect the prevalence of natural hazards and result in the loss of geodiversity and ecosystem services, making it necessary to develop new conservation strategies to protect mountain regions and their geoheritage.To understand the impact of climate change and human activity on geoheritage and on the benefits that geodiversity provides to society, we conducted a study in the Alagna Valsesia municipality, a high-elevation mountain area in the Sesia Val Grande UGGp. We mapped geodiversity in that area using GIS data following a quali-quantitative approach. Then we identified geosites and evaluated their value to show their potential. We also assessed various abiotic ecosystem services, including regulating, provisioning, knowledge, cultural, and supporting services, and mapped them analysing the evolutionary relationship between humans and nature. By evaluating global drivers of change, we were able to understand the impact of these changes on identified services and to highlight the need for strong planning and management strategies for the Sesia Val Grande UGGp and for the sustainable development of vulnerable mountain regions.This approach helps us to understand the natural and human-induced threats to geodiversity and enables us to understand the importance of considering geoheritage in planning and management to promote sustainable development actions.ReferencesChiarle M, Geertsema M, Mortara G, Clague JJ. 2021. Relations between climate change and mass movement: Perspectives from the Canadian Cordillera and the European Alps. Global and Planetary Change 202: 103499;Savi S, Comiti F, Strecker MR. 2021. Pronounced increase in slope instability linked to global warming: A case study from the eastern European Alps. Earth Surface Processes and Landforms 46 : 1328–1347. DOI: 10.1002/ESP.5