ACCOMMODATION OF MESOZOIC ROTATIONAL OPENING OF CANADA BASIN: THE ROLE OF THE RUBY TERRANE

Widely accepted models for opening of the Canada basin involve rotation of the Arctic Alaska terrane away from the Canadian Arctic into its present position by a windshield-wiper style of movement, much of which occurred during the Early Cretaceous. These models predict the existence of Early Cretaceous structures in the hinge that accommodated basin opening. Identification of these structures in the eastern Brooks Range and northern Yukon is difficult; the area has been tectonically active since rotation occurred. Reconstruction of post-rotation deformational events requires restoring significant amounts of Tertiary deformation in the Brooks Range and Yukon Flats basin as well as >400 km of movement on the Tintina Fault.

We propose that a pre-Albian dextral strike-slip fault at least 400 km long nucleated near the hinge of rotation and propagated across the continental margin of the Arctic Alaska terrane as rotation progressed. The fault translated the Ruby terrane, which is cored by Paleozoic and Proterozoic(?) continental rocks which have affinities with both Arctic Alaska and North America, into the oceanic realm during the Early Cretaceous, starting around 140 Ma.

We suggest that the current high-angle fault that traces the western boundary of the Ruby terrane and separates relatively mafic crust on the west from thinned continental crust on the east is a remnant of this Early Cretaceous dextral fault system. It is truncated on its northern end, along the southern flank of the Brooks Range, by the Tertiary Kobuk-Malamute fault system.

Remnants of the pre-Albian strike-slip fault are difficult to identify north of the Kobuk-Malamute system. However, major Mesozoic contractional structures in the Brooks Range that involved hinterland metamorphic rocks and shallowly-deformed rocks of the fold and thrust belt are truncated in the eastern part of the range. Little evidence exists for significant Mesozoic crustal thickening in the Brooks Range east of the truncation. The proposed pre-Albian dextral strike-slip fault was the eastern boundary of Early Cretaceous shortening in the Brooks Range. Restoration of 400-km of offset along the fault places the Ruby terrane adjacent to Paleozoic and older rocks that have affinities with Arctic Alaska and North America that are now exposed north and east of the Yukon Flats basin.