Yukon is located in the northern part of the North American Cordillera, the mountainous backbone of the western part of the continent. Like most of the Cordillera, Yukon is composed of rocks that record more than a billion years of Earth history. These document the evolution of the western margin of Ancestral North America (Laurentia) and of the various displaced terranes that were accreted to it since late Paleozoic.

The northwest-striking Tintina fault is one of the most prominent physiographic and geologic features in the Yukon. It is a dextral strike-slip fault with about 430 km of Paleogene displacement. It generally separates rocks of Ancestral North American affinity to the northeast from those of the allochthonous Intermontane terranes to the southwest; except in southeast Yukon, where the Tintina fault has shuffled this order and the allochthonous Yukon-Tanana and Slide Mountain terranes lie northeast of the fault, and parautochthonous rocks of Cassiar terrane underlie the Pelly Mountains to the southwest.

The Intermontane terranes are mainly comprised of magmatic arc rocks and related sedimentary deposits that fringed western Laurentia between mid-Paleozoic and early Mesozoic. They envelop more exotic oceanic rocks of Cache Creek terrane in south-central Yukon, which includes elements of Tethyan affinity. The Intermontane terranes are bounded to the southwest by the northwest-striking Denali fault, an active dextral strike-slip fault with more than 400 km of displacement, that separates them from the Insular terranes. The Insular terranes consist of continental fragments and volcanic arc rocks that contain exotic elements of Baltican and Siberian affinities.

In northern Yukon, structures along the northeast-striking Porcupine lineament juxtapose rocks of the Ancestral North American margin with those of the Arctic-Alaska terrane to the northwest. Arctic Alaska is a composite terrane which includes Neoproterozoic and Paleozoic elements of Baltican-Siberian affinities, as well as less exotic northern Laurentian rocks.

Cretaceous and younger, mainly post-accretionary plutonic suites intrude part of the Laurentian margin strata and the Intermontane and Insular terranes in southern Yukon. These represent a succession of continental magmatic arcs and related back-arc environments that record the Cretaceous-Paleogene convergence of the various terranes.

The various terranes and plutonic suites that make up Yukon geology are host to a wide range of base and precious metal deposits. Successor basins that developed during Jurassic to Paleogene terrane convergence in the northern Cordillera have hydrocarbon potential.

Adapted From

Overview of Yukon Geology

By: Steve Israel, Maurice Colpron, Charlie Roots and Tiffany Fraser

© Government of Yukon 2018