The Yukon Crystalline Terrane: Enigma in the Canadian Cordillera

Abstract

The Yukon Crystalline Terrane, an area of Proterozoic and Paleozoic metamorphic rocks intruded by Mesozoic and Tertiary plutons and covered by Tertiary volcanic strata, has been one of the least understood tectonic elements in the Canadian Cordillera. It incorporates characteristics of the Omineca Crystalline Belt, Intermontane Belt, and Coast Plutonic Complex. The metamorphic rocks are not part of a single time-stratigraphic assemblage as the term “Yukon Group” has implied. They can be divided into gross lithologic assemblages which are correlated with Proterozoic and Paleozoic strata of the Omineca Crystalline Belt, and the metamorphic rocks of the Yukon Crystalline Terrane are therefore the continuation of the Omineca Crystalline Belt. Four plutonic suites are recognized in the Yukon Crystalline Terrane. The two oldest (Late Triassic and mid-Jurassic) are related to similar plutons in the Intermontane Belt and mark its continuation through the central part of the Yukon Crystalline Terrane. The mid-Cretaceous suite in the northern part of the Yukon Crystalline Terrane is a westward continuation of plutonic rocks of the Omineca Crystalline Belt. Early Eocene alaskite marks the superposition of Coast Plutonic Complex igneous rocks on the southern part of the Yukon Crystalline Terrane. Tertiary tholeiitic basalts, which cover part of the Yukon Crystalline Terrane, lie on an eroded plateau whose relief and physiography approximate the present terrane.