116. Cordilleran Terranes (1972)
Geological Survey of Canada scientists began using plate tectonics to unravel the complex geology of the Cordillera in the early 1970s. They recognized that the older sedimentary rocks of the eastern Cordillera were originally deposited along the non-active margin of the Precambrian core of North America. By contrast, the rocks of the western Cordillera were produced at active, convergent, plate margins elsewhere on the globe.
It became clear that these rocks were formed in settings like the present western Pacific basin where ocean trenches and volcanic island arcs are associated with relatively young mountain systems. However, as the Pacific Plate moved slowly eastwards, North America collided obliquely with these island arc systems and the results of the collisions slid northwards along long fault systems.
The present distribution of these rocks within the Cordillera presented a geological jigsaw puzzle of narrow slivers of rocks called “terranes.” Each terrane had a common geological record, and its original location relative to North America could be established by its paleomagnetism and/or fossil content.
The whole process started in the Jurassic as the future North American Plate drifted westward. Something like driftwood arriving on the shore, the terranes were swept up and incorporated in its western margin, eventually building today’s geologically complex Cordillera.
Category: Science Advances
Monger, J.W.H., Price, R.A., and Tempelman-Kluit, D.J., 1982. Tectonic accretion and the origin of two major metamorphic and plutonic welts in the Canadian Cordillera; Geology, v. 10, p. 70–75. doi:10.1130/0091-7613(1982)10<70:TAATOO>2.0.CO;2
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