37 



IGNEOUS AND 

 TECTONIC PROVINCES 

 OF WESTERN CANADA 



region subsided and great thicknesses of sedimentary and volcanic mate- 

 rial accumulated. 



Large areas in the Yukon and Interior plateaus are underlain by 

 Triassic, Jurassic, and Lower Cretaceous formations made up of inter- 

 bedded limestone, argillite, graywacke, conglomerate, tuff, breccia, and 

 andesite flows. They have been invaded widely by great batholiths. Their 

 original extent may have been approximately that of the batholithic belt 

 of the map, Fig. 37.1, plus the areas shown as eugeosyncline. See also 

 Fig. 17.13. 



Miogeosyncline 



The position of the Paleozoic miogeosyncline was that of the eastern 

 Cordillera or more commonly referred to as the Canadian Rockies, east of 

 the Rocky Mountain trench. The Cambrian and Ordovician strata are here 

 particularly thick. The transition from the miogeosyncline to the Alberta 

 shelf is probably a gradual one and lies under the Alberta basin. The 

 miogeosyncline apparently dies out at about the Yukon Territory bound- 

 ary on the north, and thence northwestward the eugeosyncline is transi- 

 tional to the shelf. Thickness and lithologies in the Mackenzie and Selwyn 

 Mountains are very poorly known, and therefore, also geosynclinal and 

 shelf conditions cannot be very well discerned. 



GEOSYNCLINE 



Eugeosyncline 



The eugeosynclinal division of the Cordilleran geosyncline of western 

 Canada and southeastern Alaska has been described in Chapter 6. Suffice 

 it to say here that sediments of the eugeosynclinal type occur west of the 

 Beltian geanticline of British Columbia. In southeastern Alaska strata of 

 Ordovician, Silurian, Devonian, Permian, and Triassic age are laden with 

 volcanics, whereas the lower and middle Paleozoic systems are not repre- 

 sented as far as known in the interior east of the Coast Range batholith. 

 During the Carboniferous and Permian periods, however, the interior 



OROGENIES 



The eugeosynclinal complex attests crustal unrest almost constantly 

 In places it was intense (see Chapter 5). Isoclinal folding with attendant 

 low-grade metamorphism occurred in late Jurassic or early Cretaceous 

 time to precede immediately the invasions of the numerous and large 

 batholiths. 



The Laramide belt embraces the eastern Cordillera, and possibly a wide 

 region in Yukon Territory and in the western part of the Northwest 

 Territories, including the Franklin, Mackenzie, Selwyn, and Richardson 

 Mountains. The Mackenzie and Selwyn region is described as one of 

 broad folds and a subordinate amount of faulting (Lord et a!., 1947). 

 The folds are commonly arcuate and arranged en echelon. The Franklin 



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