Stephen T. Johnston
Research Publications Students Teaching Gallery

 

MAIN ACHIEVMENTS – (1) Developed the concept of ribbon continents; (2) Introduced “oroclinal orogeny” as a process explaining bends of mountain belts; (3) Provided the first comprehensive tectonic model of the Cordillera of North America explaining geological and paleomagnetic data; (4) Originated Velocity Net Plots as a means of constraining paleogeographic reconstructions


RESEARCH STATEMENT - The Paleogeographic evolution of Earth through deep time provides a first order constraint for understanding Plate Tectonics and the role played by tectonics in the evolution of the Earth’s atmosphere, biosphere and continental lithosphere and deep mantle. Unfortunately, the oldest intact oceanic lithosphere, which provides the only direct record of plate motions, formed as recently as 180 Ma; the bulk of Earth’s oceanic lithosphere formed more recently than 100 Ma. Hence reconstructing Earth’s paleogeography requires that we make use of the highly imperfect continental record of plate motion.

Orogenic belts develop at and record interactions along continental plate margins. It has, therefore, been in modern mountain systems and the eroded roots of ancient orogens that most of the constraints on Earth paleogeography have been and continue to be mined. But while we generally agree on the geological and geophysical data generated in the study of orogens, the same cannot be said regarding interpretations of such data. It is in the disparate readings of the continental record of plate motions and interactions that most all current controversies and conundrums in geodynamics and geology lay, and it is along these fault lines that I have focused my research.

My research is rooted in field-based geological mapping of key parts of mountain belts, both modern and ancient. Multidisciplinary studies, including geophyscial investigations (paleomagnetism, geodetic surveys and reflection seismic studies), and geochemical and geochronological analyses are utilized to further constrain the geometry and evolution of mountain belts. Models of development and evolution of ancient orogens are tested against (1) tectonically active modern analogues, including the Apennines of southern Italy, and the Melanesian region of the southwest Pacific, and (2) geodynamic, geometric, climate and thermal models. It is through this two-pronged approach field- and laboratory-based approach that I have addressed questions such as: (1) How do map-view bends of mountain belts originate, and are they important? (they are!!) (2) To what extent does paleogeography control climate, and was it responsible for Earth having descended into a Snowball state in the Neoproterozoic? and (3) Why is it that in numerous orogenic belts, ranging from the modern day Melanesian region, through the Neogene of southern Europe, the Mesozoic Cordillera of western North America, and the Paleozoic Appalachian-Variscan orogen that lay at the heart of Pangea, that paleomagnetic data is commonly held to be irreconcilable with abundant geological data? My hope is that in asking and answering these questions, we will improve our understanding of Earth history, and in doing so, help insure our continued evolution as part of the Earth system.

See me interviewed by David Suzuki here.

Go on a Geologic Journey through the Rocky Mountains.

Listen to Quirks and Quarks interviews about my research: 1 or 2.

In addition to my own research, I also edit the journal GSA Today and am the secretary and director of the Canadian Geological Foundation.

Key Words: Plate Tectonics, Structural Geology, Orogenesis, Convergent Margin Orogens, Oroclines, Paleomagnetism.