ESCAPE OF THE RUBY TERRANE FROM ARCTIC ALASKA DURING MESOZOIC ROTATIONAL OPENING OF CANADA BASIN

Prevalent models for opening of the Canada basin involve rotation of the Arctic Alaska terrane into its present position by a windshield-wiper or saloon-door style of movement. One means of testing these models is to search for structures near the hinge of rotation that accommodated shortening coeval with basin opening. However, the area near the accepted hinge, the eastern Brooks Range and northernmost Yukon, has been tectonically active since the rotation event. The accumulated effects of post-rotation deformation must be reconstructed before any hinge-related structures might be confidently identified. This exercise involves: (1) restoring Tertiary shortening in the eastern Brooks Range; (2) removing Tertiary dextral slip on the Kobuk-Malamute fault system; (3) closing the Tertiary Yukon Flats basin; and (4) removing >400 km of Tertiary 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 southern boundary of the Arctic Alaska terrane as rotation progressed. Remnants of this fault are difficult to identify near the hinge. However, several factors support the existence of a significant strike-slip structure in the eastern Brooks Range: (1) anomalously broad exposures of the Lisburne carbonate platform, which may have resulted from structural duplication along the strike-slip fault; (2) truncation of E–W-trending structures by NE-trending structures; and (3) little evidence for significant Mesozoic crustal thickening in the Brooks Range hinterland east of the truncation. At the southern boundary of the Brooks Range, the Kobuk fault cuts the likely trace of the pre-Albian structure. South of the Kobuk, the extension of the pre-Albian fault corresponds to the western side of the Ruby terrane. That boundary is a high-angle fault separating relatively mafic crust on the west from thinned continental crust on the east. Voluminous granitic plutons intruded Ruby terrane schist at ~112 Ma; strike-slip movement along the west side of the Ruby was waning or complete by that time.

Escape of the Ruby terrane on the postulated dextral strike-slip fault likely commenced around 140 Ma, coincident with timing estimates for seafloor spreading in the Canada basin.