Stephen T. Johnston

University of Alberta | UAlberta · Department of Earth and Atmospheric Sciences

Thermal springs in the southeastern Canadian Cordillera occur in association with several major fault zones, which may permit deep circulation of fluid through fractured reservoirs to depths greater than 2 km. Both the current stress field and the most recent kinematics of these faults likely play a significant role in localizing hydrothermal upwel...

Oriented carbonate (calcite twinning strains; n=78 with 2414 twin measurements) and quartzites (finite strains, n=15) were collected around Gondwana to study the deformational history associated with the amalgamation of the supercontinent. The Buzios orogen (545-500 Ma), within interior Gondwana, records the high-grade collisional orogen between Sã...

The Palaeozoic Variscan orogen in Europe has a markedly circuitous trace for which several different origins have been postulated, including deformation around promontories on the colliding continental margins, extrusion within the collision zone, folding of a ribbon continent, and collision with a substantial dextral component. Adopting the latter...

The Isortoq Shear Zone (ISZ), a 100km-scale structure in northern Baffin Island, was originally identified through the interpretation of regional geophysical surveys. In the field the ISZ is cryptic, and its significance ambiguous with respect to the regional structural framework of northern Baffin Island. Mapping along the ISZ and within the spati...

The Paleoproterozoic oroclines of Fennoscandia played a vital role in the making of continental equidimensional crust during the Svecofennian orogeny. We propose that the 1.90–1.88 Ga arc rocks in south-central Finland originally formed a single linear arc system that is now represented by the coupled Bothnian oroclines and their southern continuat...

A concentration of thermal springs with outlet temperatures ranging from ~20-80˚C occurs in the southeastern corner of British Columbia, Canada, and is an attractive target for geothermal energy exploration. There is no active or young volcanism in the immediate vicinity (within 100s of km), and yet the crustal heat flow in this region is relativel...

This volume honors Eldridge Moores, one of the most accomplished geologists of his generation. The volume starts with a summary of Moores’ achievements, along with personal dedications and memories from people who knew him. Leading off the volume’s 12 chapters of original scientific contributions is Moores’ last published paper that presents an exa...

Geological and geophysical data coupled with numerical simulations have shown that lithospheric extension at passive margins may be classified into three end-member scenarios of pure shear, simple shear, and depth-dependent deformation. However, how lithospheric extension evolves in an intraplate setting remains enigmatic due to lack of reliable co...

This study aims to understand the influences of argillaceous content on carbonate rocks’ mechanical parameters in the Hetianhe gas field. Through core observation, thin section study and log identification, we characterized the argillaceous content and tectonic fractures in the carbonate rock. We then determined the fracture generation mechanism an...

Regional metamorphism provides critical constraints for unravelling lithosphere evolution and geodynamic settings, especially in an orogenic system. Recently, there has been a debate on the Rodinia-forming Tarimian orogeny within the Greater Tarim block in NW China. The North Wulan terrane, involved in the Paleozoic Qilian orogen, was once part of...

Paleogeographic maps are essential tools for understanding Earth system dynamics. They provide boundary conditions for climate and geodynamic modelling, for analysing surface processes and biotic interactions. However, the temporal and spatial distribution of key features such as seaways and mountain belts that govern climate changes and biotic int...

The tectonic significance and age of carbonatite intrusions in the central Foreland Belt of the Canadian Cordillera are poorly constrained. Recent work has demonstrated that one of these carbonatite intrusions, the Aley carbonatite, was emplaced as a syn-kinematic sill, coeval with a major nappe-forming tectonic event. Determining the age of the Al...

Density, aperture and developmental position are key parameters of tectonic fractures in carbonate reservoirs for oil and gas exploration and development. The analysis of fracture development and distribution in interbedded bioclastic and biological limestone and mudstone of Carboniferous and Ordovician age in the Hetianhe area of the Bachu uplift,...

Clarifying the contributions of pre‐Cenozoic and especially the Mesozoic tectonism to build crustal architecture of the Tibetan plateau is important, especially for evaluating the role of Cenozoic Indo‐Asian collision in creating the present‐day plateau. However, how the Mesozoic tectonism evolved and its influence on the Cenozoic strain distributi...

Raw data for the manuscript "Contributions of Triassic tectonism to build the northern Tibetan plateau"

Plate reconstructions since the breakup of Pangaea are mostly based on the preserved spreading history of ocean basins, within absolute reference frames that are constrained by a combination of age‐progressive hotspot tracks and palaeomagnetic data. The evolution of destructive plate margins is difficult to constrain from surface observations as mu...

This map presents the field observations and initial geological interpretations for the Angijurjuk–Mary River area (NTS 37-G west), Baffin Island, Nunavut. The regional bedrock geology depicted on CGM maps 402 to 406 comprises Archean tonalitic to monzogranitic gneiss that includes mafic to intermediate components, and relatively homogeneous monzog...

This map presents the field observations and initial geological interpretations for the Barnes Ice Cap northwest area (NTS 37-E west), Baffin Island, Nunavut. The regional bedrock geology depicted on CGM maps 402 to 406 comprises Archean tonalitic to monzogranitic gneiss that includes mafic to intermediate components, and relatively homogeneous mon...

This map presents the field observations and initial geological interpretations for the Nina Bang Lake area (NTS 37-F west and part of 37-C west), Baffin Island, Nunavut. The regional bedrock geology depicted on CGM maps 402 to 406 comprises Archean tonalitic to monzogranitic gneiss that includes mafic to intermediate components, and relatively hom...

This map presents the field observations and initial geological interpretations for the Rowley River–Isortoq River area (NTS 37-F east) Baffin Island, Nunavut. The regional bedrock geology depicted on CGM maps 402 to 406 comprises Archean tonalitic to monzogranitic gneiss that includes mafic to intermediate components, and relatively homogeneous mo...

Hydrothermal systems (i.e., thermal springs) in the Canadian Cordillera are broadly associated with major fault zones (Grasby and Hutcheon, 2001). However, detailed investigations of the significant hydrogeological properties of many of these faults have not previously been conducted. The research presented in this paper focuses on hydrothermal sys...

The Paleozoic geology of Iberia is dominated by the tectonics of the Variscan orogeny and its aftermath. This defining geologic event was the result of large-scale collision that involved amalgamation of multiple continents and micro-continents, the closure of oceanic basins and eventual orogenic collapse, and finally modification and oroclinal ben...

The origin of the North American Cordillera and its affinity with the bounding craton are subjects of contentious debate. The mechanisms of orogenesis are rooted in two competing hypotheses known as the accretionary and collisional models. The former model attributes the Cordillera to an archetypal accretionary orogen comprising a collage of exotic...

Deducing mechanisms for advance and retreat of magmatic arcs is fundamental to understanding accretionary tectonics and the evolution of continents. However, first-order explanations of large spatial and long temporal changes in magmatic arcs remain elusive. We present isotopic evidence that Cordilleran magmatic arc systems were controlled by spher...

The Qilian block, one of the Precambrian terranes in the Qinling-Qilian-Kunlun orogenic system, is a critical region for reconstruction of the overall architecture and tectonic evolution of NW China. This investigation of zircon U-Pb and Lu-Hf isotopes and whole-rock geochemistry of a metasupracrustal sequence in the North Wulan terrane provides ne...

Kimberlite magmas are volatile-rich, potassic, and ultramafic, and they are host to most of the world's diamond deposits. A continental-scale kimberlite magmatic belt (the central Cretaceous kimberlite corridor [CCKC]) is found in the interior of the North American continent. Parallel to and coeval with the CCKC, the Cretaceous Omineca magmatic bel...

We examine the partial melting and the cooling history of a ~5 km section of mantle lithosphere preserved in the Donjek massif, part of a Permian ophiolite in the northern Cordillera of Yukon, Canada. The mantle rocks are depleted spinel harzburgite containing <3% clinopyroxene displaying steep rare-earth element (REE) chondrite-normalized profiles...

The concave-inboard (concave toward the overriding plate) geometry of most convergent margins is considered a natural consequence of the depression of the edge of a thin spherical cap, whereas concave-outboard margin segments commonly form around indenters on the subducting plate. At the Cascadia subduction zone, the apex of a > 500-km-long concave...

The Geological Survey of Canada conducted two seasons of 1:100 000 scale bedrock mapping on northern Baffin Island, as part of the Geo-Mapping for Energy and Minerals (GEM-2) Program. The new mapping will contribute to modernizing the geoscience knowledge base of this part of Nunavut, as well as further characterizing poorly understood Archean and...

In the Mesozoic, South China was situated along the convergent margin between the Asian and Pacific plates, providing an excellent laboratory to understand the interactions between deformation, sedimentation and magmatism in a retroarc environment. The crustal architecture of northwest South China is displayed along the ∼600-km-long SINOPROBE deep...

Three-dimensional analogue models are employed to investigate whether oroclines may develop by horizontal buckling. A first series of experiments demonstrates that a crustal ribbon carried by a subducting plate cannot buckle and detach from its mantle root because it weakens and deforms when entering the subduction zone, such that little compressiv...

This paper presents the field observations and initial interpretations stemming from six weeks of regional bedrock mapping during the summer of 2017 in the Pond Inlet–Mary River area (NTS 37G, 38B) of northern Baffin Island, Nunavut. This area, which is notable for the world-class Mary River Fe-deposit, was targeted under the second phase of the Ge...

Detailed bedrock mapping was completed in the Tuktuliarvik study area (part of NTS 37G) 100 km south of the hamlet of Pond Inlet, northern Baffin Island, Nunavut. In this study, field observations collected along four east–west transects on the western side of the largest lake (Long Lake) in the eastern Tuktuliarvik study area and from a north–sout...

We conducted field mapping coupled with radiometric dating across the Shiwandashan and Youjiang structural belts (SWSB and YJSB), to investigate how southwest South China evolved and to better understand its links to plate boundary dynamics during the Late Permian to Middle Triassic. Our results reveal an episodic tectono-magmatic evolutionary hist...

The Proterozoic Grenville orogeny (~ 1300–980 Ma) reactivated the Archean-hosted Kapuskasing suture in Laurentia which then propagated west and south initiating the Keweenaw rift (1141–1085 Ma) which closed by thrust shortening at 1060 Ma. Late Proterozoic-Paleozoic sediments were then deformed in association with the amalgamation of Pangea in the...

The northeast Cathaysia area is characterized by an archetypical, transpressional system with widespread strike-slip shear zones whose geometries, kinematics and ages are critical for deciphering the Phanerozoic tectonic evolution of South China. We present new structural, geochronological and thermochronological data from the shear zones in the ea...

The origin of the Cantabrian orocline of the Variscan orogen in NW Iberia remains a topic of debate. We present a structural study of the Ponga Unit, a Cambrian to Carboniferous tectonostratigraphic package within the West European Variscan belt foreland fold-and-thrust belt that lies within the core region of the orocline. Our primary goal was to...

The coupled Iberian oroclines of the western European Variscan orogen accommodated > 1100 km of post-Variscan orogen-parallel shortening at translation rates in excess of 5 cm·yr⁻¹. Palinspastic restoration of the Iberian coupled oroclines reveals a north-south-trending 2300-kmlong Variscan ribbon bound by ophiolite-bearing allochthons. The require...

The Leech River Complex (LRC) on southern Vancouver Island is part of the Pacific Rim Terrane of the North American Cordillera. In the Port Renfrew area it comprises mylonitic tightly folded black schists and meta-sandstones of the Leech River Schist (LRS), which underthrust meta-mudstones, ribbon cherts, and meta-volcanics of the Pandora Peak Unit...

The central Jiangnan Orogen, genetically formed by the Proterozoic Yangtze-Cathaysia collision, presents as a composite structural feature in the Phanerozoic with multiple ductile and brittle fabrics whose geometries, kinematics, and ages are crucial to decipher the tectonic evolution of south China. New structural observations coupled with thermoc...

Three major orogenic belts that are host to coupled oroclines (terrane wrecks) are likewise characterized by or directly associated with paleomagnetic inclination anomalies: (1) the North American Cordillera, (2) the Western European Variscan belt, and (3) the Eastern European Alpine system. Implied paleolatitudinal discrepancies in each orogen are...

International Association for Gondwana Research (IAGR) 2015 Annual Convention and 12th International Symposium on Gondwana to Asia were held at the University of Tsukuba, Japan, during October 21–23, 2015.

The Cantabrian orocline of NW Iberia is interpreted as a secondary orocline formed by vertical-axis rotation of an originally linear, N-S trending segment of the Western European Variscan belt (WEVB). We present a local-scale structural study of the Ponga Unit, a Cambrian to Carboniferous tectonostratigraphic package within the WEVB foreland fold a...

The Variscan orogen provides the European record of the late Paleozoic continental collisions that culminated with formation of the super-continent Pangea. An S-shaped pair of isoclinal coupled oroclines characterizes the Variscan orogen of the Iberian Massif. Though oroclines are common features of the world's orogenic belts, the mechanisms that d...

An ‘orocline’ is an orogen that expresses plan view curvature either developed over the course of orogen formation (progressive orocline) or subsequent to orogen formation (secondary orocline) by vertical axis buckling in response to a reorientation of regional compressive stress from orogen perpendicular to orogen parallel. An sshaped pair of coup...

Mafic and ultramafic rocks crop out as decimetre- to centimetre-sized bodies of talc–antigorite–olivine (±orthopyroxene) and chlorite–amphibole schists interleaved in the pelitic Kluane Schist of southwestern Yukon. The metamorphic assemblages in ultramafic rocks exposed at Doghead Point overprint two generations of cleavage and are consistent with...

The Leech River Complex on southern Vancouver Island is a part of the Pacific Rim Terrane of the North American Cordillera and comprises a series of fault-bounded slices of mainly meta-sedimentary and meta-igneous rocks of Triassic to Cretaceous age. The tectono-metamorphic history of this unit provides important constraints on the history of terra...

The Cantabrian orocline of NW Iberia is interpreted to be a secondary orocline that was formed by the vertical axis rotation caused by N­S shortening of an originally linear, N­S trending Western European Variscan Belt (WEVB). Here we report on a structural study of the WEVB foreland fold and thrust belt from the core region of the Cantabrian orocl...

Seven samples of Siluro-Devonian sedimentary rocks from the Cantabrian and Central Iberian zones of the Iberian Variscan belt have been investigated for provenance and contain four main age populations in variable relative proportion: Ediacaran–Cryogenian (c. 0.55–0.8 Ga), Tonian–Stenian (0.85–1.2 Ga), Palaeoproterozoic (c. 1.8–2.2 Ga) and Archaean...

Orogenic curvature is a ubiquitous feature of mountain belts, and the plate tectonic and geodynamic setting responsible for the development of curved orogens is a subject of debate. In order to distinguish between different models of orocline formation it is necessary to tightly constrain the absolute timing of oroclinal development. However, deter...

We use scaled 3-D thermo-mechanical analogue models to investigate the formation mechanism of oroclines, originally linear thrust belts or orogens that have been curved in map-view due to bending or buckling about a vertical axis of rotation. Several ideas have been proposed for the formation of oroclines. The common view is that oroclines develop...

The Cretaceous tectonic evolution of South China is characterized by widespread extensional basin and dome generation, voluminous magma intrusion/eruption and associated polymetallic mineralization, all of which are of world-wide interests that have stimulated the attention of geologists for more than half a century. Due to the lack of a comprehens...

Though oroclines are common features of the world’s orogenic belts, the mechanisms that drive oroclinal formation, and the manner in which these lithospheric-scale vertical-axis folds of orogens are accommodated at different structural levels, are poorly understood. An s-shaped pair of isoclinal coupled oroclines characterizes the Variscan orogen o...

Seven Silurian and Devonian samples from the Cantabrian and Central Iberian zones of the Variscan belt have been investigated for paleogeographic purposes using detrital zircon U-Pb ages. A total of 764 analyses were performed. All samples contain four main age populations in variable relative proportions: Ediacaran–Cryogenian (ca. 0.55–0.8 Ga), To...

The Western European Variscan shows a lithospheric-scale “S”-shaped map pattern and has been interpreted as two coupled oroclines; a northern Cantabrian orocline and southern Central Iberian orocline. The northern Cantabrian orocline shows a striking 180°curvature that is concave towards the east. The orocline model for this relies on a wealth of p...

Understanding the causes of the opening and closure of oceanic tracts is a major ongoing endeavour in contemporary Earth Science. Ancient oceans are an important part of this process because they preserve a record of the different processes involved and so shed light on the causes of ocean opening and widening, and the subsequent dynamic flip towar...

Numerous plate kinematic models for the North Pacific realm have been developed since the advent of plate tectonics in the early seventies (Atwater (1970), and others). Although published kinematic models are consistent with the broad scale features of the North Pacific, the link between plate motions and the evolution of the North American Cordill...

The accretion of magmatic arcs gives rise to elongate, linear orogens and is a key process in forming new continental crust. Many Precambrian continents are, however, presently equidimensional or have large areas without any clear linearity, such as the central part of the Paleoproterozoic Svecofennian Orogen (1.92-1.77 Ga). One way of forming an e...